# Innovative Antibacterial Air Filters Impregnated with Photocatalytic MgFe2O4 Nanoparticles for Improved Microbiological Air Quality

Abdelwahab Rai, Sara Oumenoune Tebbi, Chaima Ben Mahfoud, Maroua Bourbala, Reguia Boudraa, Abdeltif Amrane, Najeh Maaloul, Manuel Rendueles, Paula Oulego, Maymounah N. Alharthi, et al.

<figure><img src="image_1.png" /></figure>

## ► To cite this version:

Abdelwahab Rai, Sara Oumenoune Tebbi, Chaima Ben Mahfoud, Maroua Bourbala, Reguia Boudraa, et al. Innovative Antibacterial Air Filters Impregnated with Photocatalytic MgFe2O4 Nanoparticles for Improved Microbiological Air Quality. Catalysts, 2025, 15 (4), pp.365-365. 10.3390/catal15040365. hal-05049639

HAL Id: hal-05049639

https://hal.science/hal-05049639v1

Submitted on 28 Apr 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_3.png" /></figure>

Article

# Innovative Antibacterial Air Filters Impregnated with Photocatalytic MgFe₂O₄ Nanoparticles for Improved Microbiological Air Quality

Abdelwahab Rai<fnref n="1" />,*, Sara Oumenoune Tebbi<fnref n="2" />, Chaima Ben Mahfoud<fnref n="3" />, Maroua Bourbala<fnref n="3" />, Reguia Boudraa<fnref n="1" />, Abdelatif Amrane<fnref n="2" />,*, Najeh Maaloul<fnref n="2" />, Manuel Rendueles<fnref n="4" />,*, Paula Oulego<fnref n="4" />,*, Maymounah N. Alharthi<fnref n="5" /> and Lotfi Mouni<fnref n="1" />,*,

<figure><img src="image_4.png" /></figure>

check for
updates

Academic Editors: John T. Kiwi and
Ewa Kowalska

Received: 26 February 2025

Revised: 26 March 2025

Accepted: 4 April 2025

Published: 8 April 2025

**Citation:** Rai, A.; Tebbi, S.O.; Ben Mahfoud, C.; Bourbala, M.; Boudraa, R.; Amrane, A.; Maaloul, N.; Rendueles, M.; Oulego, P.; Alharthi, M.N.; et al. Innovative Antibacterial Air Filters Impregnated with Photocatalytic MgFe₂O₄ Nanoparticles for Improved Microbiological Air Quality. *Catalysts* **2025**, *15*, 365. https://doi.org/10.3390/catal15040365

**Copyright:** © 2025 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license
(https://creativecommons.org/licenses/by/4.0/).

**Abstract:** Over time, nanoparticles' chemistry has shown exceptional ability to solve a wide range of problems in various fields, including the control of microbiological air quality in buildings. Herein, magnesium ferrite (MgFe₂O₄) was synthesized using coprecipitation, then characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM) and photoelectron spectroscopy (XPS). MgFe₂O₄ nanoparticles were then assessed for their ability to inhibit *Escherichia coli* ATCC 8739 growth and airborne bacterial viability in a laboratory atmosphere through a direct air filtration system. The material showed strong inhibitory activity against *E. coli* by eliminating practically all viable cells in the tested suspensions after 1 h contact time in the presence of light. Finally, the prepared air filtration setup revealed that passing air bacteria through non-woven fabric filters impregnated with MgFe₂O₄ effectively eliminates them. Thus, only 1 colony-forming unit (CFU) was obtained from 36 L of filtered air, while a control filter (without MgFe₂O₄) allowed the passage of 2.6 × 10⁵ CFU to the liquid medium. The obtained results initiate potential applications of MgFe₂O₄ nanoparticles in controlling microbiological indoor air quality (IAQ), especially in healthcare facilities where microbial resistance to antibiotics is the most notable, individuals are the most exposed, and contamination risks are the highest.

**Keywords:** antibacterial activity; contamination; magnesium ferrite; nosocomial infections; photocatalysis; microbial safety

## 1. Introduction

Since the beginning of the 21st century, concerns about environmental pollution have acquired a central place in scientific and political agendas [1,2]. The accelerated growth of the human population, together with the industrial and technological development, has led to a significant increase in environmental contaminants [3,4]. Moreover, the rapid

<footnote n="1">¹ Laboratoire de Gestion et Valorisation des Ressources Naturelles et Assurance Qualité, MicroSOS, Faculté SNVST, Université de Bouira, Bouira 10000, Algeria; a.rai@univ-bouira.dz (A.R.); r.boudraa@univ-bouira.dz (R.B.)</footnote>

<footnote n="2">² University Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS, ISCR, UMR6226, F-35000 Rennes, France; sara-oumenoune.tebbi@univ-rennes.fr (S.O.T.); maaloul.najeh@hotmail.fr (N.M.)</footnote>

<footnote n="3">³ Faculté SNVST, Département de Biologie, Université de Bouira, Bouira 10000, Algeria; usmista144@gmail.com (C.B.M.); bourbalamarwa3@gmail.com (M.B.)</footnote>

<footnote n="4">⁴ Department of Chemical and Environmental Engineering, University of Oviedo, C/Julián Clavería 8, 33006 Oviedo, Spain; mrenduel@uniovi.es (M.R.); oulegopaula@uniovi.es (P.O.)</footnote>

<footnote n="5">⁵ Department of Chemistry, College of Science, Princess Nourah Bint Abdulrahman University, P.O. Box 84428, Riyadh 11671, Saudi Arabia; mnaalharthi@pnu.edu.sa</footnote>

<footnote>* Correspondence: abdeltif.amrane@univ-rennes.fr (A.A.); l.mouni@univ-bouira.dz (L.M.)</footnote>
development of medicinal, chemical, pharmaceutical, agricultural and textile industries has released a multitude of toxic substances, including heavy metals, phosphate and nitrogen, solvents, organic dyes, drugs such as antibiotics and various harmful chemicals such as pesticides and fertilizers [5]. These substances, when released into air, water and soil, pose serious risks to human health and natural ecosystems. For example, the excessive use of antibiotics has resulted in the spread of resistant germs, posing serious problems for health systems worldwide [6,7]. In addition, indoor air quality (IAQ) has become a major problem, especially with the acceleration of the global warming consequences on our lifestyle and the emergence of new microbial epidemics such as COVID-19 [8–10]. In this context, bacterial air contamination has emerged as a significant concern, further intensified by rising urban density and climate change factors that create favorable conditions for bacterial proliferation [11].

Bacteria in the air can be responsible for a wide variety of illnesses, including upper and lower respiratory infections, skin infections, allergies, gastrointestinal illnesses and other health problems [12–14]. Moreover, certain bacteria can release toxins that exacerbate symptoms such as asthma or chronic obstructive pulmonary disease (COPD), leading to increased health risks and complications [15]. In addition, airborne microorganisms in closed environments (domestic habitations, schools, hospitals, etc.) often released through air ducts constitute the main cause of surface, space and equipment contamination and, therefore, human and animal infection and/or reinfection in these settings [16]. Relying on traditional strategies, mainly antibiotics, to tackle harmful microorganisms has led to natural pressure, causing the appearance of new resistant strains in the environment [7,17]. In addition to antibiotics, conventional methods for controlling airborne bacterial contamination include chemical disinfection, thermal sterilization, irradiation and physical filtration. However, these methods come with notable limitations, such as variable effectiveness, high operational costs and concerns over long-term environmental sustainability [18].

Over time, several studies have demonstrated the remarkable potential of nanomaterials in environmental remediation, particularly for photocatalytic degradation of organic pollutants. For example, TiO₂-based composites, combined with metal oxides such as CuO, La₂O₃, and Bi₂O₃, have shown enhanced optical and photocatalytic properties with improved efficiency under visible light irradiation. Furthermore, the incorporation of porous supports like zeolites and hydroxyapatite enhances adsorption-photodegradation synergy, facilitating the complete removal of contaminants and highlighting the engineered nanomaterials' versatility in addressing environmental challenges, reinforcing the relevance of developing innovative photocatalysts for air and water purification applications [19–23].

Recently, the use of nanotechnology to manage IAQ has led to innovative solutions to mitigate the harmful effects of pollution in aerial ecosystems [9,24,25]. Thus, integrating bioactive nanocomposites in air filters to capture, inactivate and/or kill bacteria present in ambient air is being considered [26,27]. Over the last decade, there has been growing interest in studying the antimicrobial properties of nanoparticles such as MgFe₂O₄ [28], TiO₂, MgO, TiO₂/MgO [29] and NiO₂ [30], mainly due to the ineffectiveness of certain antibiotics against resistant bacteria. In this context, MgFe₂O₄ magnetic nanoparticles, among others, have emerged as a promising candidate due to their unique properties and potential mechanisms of action against microorganisms. In the same context, El-Khawaga et al. investigated the use of MgFe₂O₄ nanoparticles showing significant efficacy in eliminating Gram-positive and Gram-negative bacterial strains [28]. Sajid et al. showed that the highest inhibition rates (‰) are 85.4% for TiO₂/MgO, 82.8% for TiO₂ and 65.14% for MgO at a concentration of 50 mg/2 mL and a contact time of 2 h [29].

MFe₂O₄ nanocomposites are materials made of transition metal ferrite (MFe₂O₄) nanoparticles [31], where M generally represents a transition metal such as iron (Fe), cobalt
(Co), zinc (Zn), copper (Cu), nickel (Ni), manganese (Mn), etc. These nanoparticles are generally integrated into a host matrix, which can be a polymer, a metal oxide, a ceramic or another material [32,33]. $MFe_2O_4$ nanocomposites are widely used as photocatalysts to degrade organic pollutants present in water, such as dyes, pesticides, pharmaceuticals, heavy metals, etc. Their ability to adsorb and degrade pollutants makes them effective for water and wastewater treatment [34,35]. Additionally, $MFe_2O_4$ nanocomposites can be used to reduce volatile organic compounds (VOCs) in the air by acting as photocatalysts to oxidize them to harmless products, such as carbon dioxide and water. This approach is particularly useful for purifying indoor and outdoor air [36]. Under sunlight or artificial light sources, ferrite nanoparticles can generate electron-hole pairs, which can initiate oxidation and degradation reactions of pollutants [37]. Their nanometric size and large specific surface area enhance their efficiency in removing air contaminants, allowing for more effective interaction and capture of pollutants [38,39]. It is important to note that air is a dynamic and living environment. Microorganisms present in air, known as bioaerosols, encompass a great diversity and richness, including bacteria, fungi, viruses, algae, and protozoa [40]. Bacteria, for example, represent a major component of bioaerosols. Common genera include *Bacillus*, *Staphylococcus*, *Micrococcus*, and *Pseudomonas*. Some of these bacteria can be pathogenic to humans, animals, or plants, while others play beneficial roles in the biogeochemical cycles [41–43].

In this context, nanoparticles with antibacterial activity are emerging as an innovative and promising solution to combat the spread of harmful microorganisms. Due to their unique physicochemical properties, they offer new perspectives for combating bacterial infections and the spread of harmful microorganisms in the environment [44]. In fact, nanoparticles’ antibacterial mechanisms are not well defined, and some of them include damage to the cell wall, plasma membrane, cytosolic proteins, enzymes, and the production of reactive oxygen species (ROS) [45].

Metal nanoparticles are among the most studied for their antibacterial properties. Some metals have been known for their antimicrobial capabilities and nanoparticles made from these metals maximize this effectiveness, thanks to their large specific surface area, allowing increased interaction with bacterial constituents [46–48]. For example, $MgFe_2O_4$ nanoparticles exhibit important antibacterial activity, particularly under light exposure, due to their ability to generate reactive oxygen species (ROS), which cause oxidative damage to bacterial membranes, proteins, and DNA. Additionally, these nanoparticles can disrupt bacterial antioxidant defenses, release metal ions ($Mg^{2+}$ and $Fe^{2+}/Fe^{3+}$) that interfere with vital enzymes, and compromise membrane integrity. Their effectiveness is influenced by factors such as size, shape, and concentration, making them promising candidates for antimicrobial applications, especially in light-activated environments [49–55].

In general, nanoparticles have demonstrated a great capacity to interfere with the cellular components of bacteria, leading to their inactivation or total degradation [56]. Their large specific surface area promotes an effective adsorption of bacteria, allowing their antibacterial properties to eliminate the captured microorganisms. Such properties can be harnessed to manufacture air filters capable of capturing and neutralizing harmful microorganisms, making them ideal for environments where strict microbiological air quality control is essential [38]. Herein, magnesium ferrite ($MgFe_2O_4$) was used to fabricate a new air filtration system capable of eliminating airborne bacteria from the atmosphere.
## 2. Results

### 2.1. *Material Characterization*

#### 2.1.1. X-Ray Diffraction

In order to identify the crystalline phase and the average crystallite size of the synthesized samples of MgFe₂O₄ (15%, 20% and 25%), XRD measurements were carried out as shown in Figure 1. Structural phase identification showed the presence of the Fe₂O₃ hematite phase (JCPDS No. 01-073-0603) characterized by peaks at 2θ = 35.5°, 43.2, 47.7°, and 57.3° attributed to the hkl, 110, 202, 024, and 122 planes, respectively. In addition, other peaks confirmed the formation of the cubic MgFe₂O₄ phase (JCPDS No. 01-073-1960) as shown in Figure 1. An overlap between the peaks of the two phases was also observed. A prior work by [57] found that increasing the amount of magnesium increased the lattice spacing due to a bigger incorporation of the ion (Mg²⁺), which in turn reduced the diffraction angles, and also discovered that magnesium ferrite had better diffraction angles and less magnesium than MgFe₂O₄.

<figure><img src="image_5.png" /><figcaption>**Figure 1.** XRD diagram of MgFe₂O₄ nanoparticles with different Mg ratios (15%, 20%, and 25%).</figcaption></figure>

#### 2.1.2. Fourier Transform Infrared Spectroscopy (FTIR)

Using synthesized nanoparticles, the powder and both supported and non-supported tissue were analyzed using infrared spectroscopy by measuring the transmittance (%) as a function of frequency (cm⁻¹) at room temperature. Fourier transformation equipment of the JASCO FT/IR-4200® type was used in the spectral range of 400–4000 cm⁻¹. The FTIR spectra of MgFe₂O₄ powders with varying percentages in Mg ranging from 15% to 25% are displayed in Figure 2. The metal-oxygen-metal (M-O-M) links (where M = Fe, Mg) vibrated, resulting in the observed 420 and 510 cm⁻¹ absorption bands. This confirms that the metal oxide was created. Furthermore, Fe-O stretching modes were responsible for the peaks at 1072 and 1253 cm⁻¹. Moreover, the C-H vibrational modes were responsible for the peaks observed at 1442 and 1250 cm⁻¹ [58]. Generally, the carbon-hydrogen vibrational bond is a result of the absorption of 2900–3000 cm⁻¹, and the recorded peak at 3625 cm⁻¹ is attributed to the (O-H), isolated OH in Mg(OH)₂ [59].
<figure><img src="image_6.png" /><figcaption>**Figure 2.** FTIR spectra of MgFe₂O₄ powders with varying Mg percentages (15%, 20%, and 25%).</figcaption></figure>

### 2.1.3. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM)

Scanning electron microscope and transmission electron microscope analyses of the prepared MgFe₂O₄ were carried out to assess their surface morphology at the micron and submicron levels. It was observed that the particles varied in size. SEM and TEM images show aggregated particles, probably due to the change in [Mg(NO₃)₂] concentration.

The SEM micrograph of the MgFe₂O₄ samples (Figure 3a–c) showed an irregular structure of MgFe₂O₄ (15%, 20% and 25%). The SEM images showed that the particle size of the calcined material became more significant with increasing [Mg(NO₃)₂] concentration. As synthesized, MgFe₂O₄ shows an agglomeration of particles resembling flattened flakes on a generally smooth surface (Figure 3a–c). Transmission electron microscopy (TEM) was used to obtain further information on the morphology and concentration distribution of [Mg(NO₃)₂] on the surface of MgFe₂O₄. The TEM images in Figure 3d–f show spherical particles and the presence of agglomerates resulting from intra-particle interactions due to van der Waals attractive forces.

These images also show a spherical morphology of the particles, with a lower proportion of nanoparticle agglomerates (15%) in MgFe₂O₄. After change in [Mg(NO₃)₂] concentration, the dispersion of the particles decreased, as mentioned previously in SEM, due to the agglomeration of MgFe₂O₄ particles. This process provides a basis for the nucleation of MgFe₂O₄ particles, therefore weakening their tendency to aggregate. The annealed samples demonstrated a notable decrease in nanoparticle size for the calcined MgFe₂O₄. The size of primary (non-agglomerated) nanoparticles was obtained from TEM images using imageJ software (v.1.53), with an average size of 19.34 ± 0.1 nm, 9.01 ± 0.1 nm, and 8.51 ± 0.1 nm for MgFe₂O₄ (15%), MgFe₂O₄ (20%), and MgFe₂O₄ (25%), respectively. Moreover, distinct size categories of MgFe₂O₄ particles (aggregated particles) were between 44.08 nm and 65.5 nm. This finding is consistent with prior studies suggesting that the increase in concentration enhanced the aggregated particles [60,61]. A size distribution histogram (Figure 3d–f) revealed a moderate size distribution. In contrast, SEM analysis showed the formation of larger aggregates, with sizes up to 109, 261, and 400 µm, probably due to agglomeration of the nanoparticles during the coprecipitation process (drying, calcination). High-resolution TEM images (Figure 3d–f) confirmed the crystallinity of individual nanoparticles, while SEM images (Figure 3a–c) illustrated the overall morphology and aggregation behavior.
<figure><img src="image_7.png" /><figcaption>**Figure 3.** SEM image (magnitude 5000×) of (a) 15% MgFe₂O₄; (b) 20% MgFe₂O₄; (c) 25% MgFe₂O₄; and TEM image and particle size distribution of (d) 15% MgFe₂O₄; (e) 20% MgFe₂O₄; (f) 25% MgFe₂O₄ at the magnification of 10 nm.</figcaption></figure>

### 2.1.4. BET Analysis

The nitrogen adsorption-desorption isotherms for all the catalysts are of type IV according to the IUPAC classification, indicating the presence of mesoporous materials. Moreover, the H1 type hysteresis observed is typical of cylindrical pores formed by the agglomeration of spherical particles of similar size arranged in a uniform packing pattern (Figure 4). The increase in specific surface area of MgFe₂O₄ (15% MgFe₂O₄-Sarea = 62.74 ± 0.1235 m²/g; 20% MgFe₂O₄-Sarea = 71.17 ± 0.1118 m²/g; 25% MgFe₂O₄-Sarea = 73.92 ± 0.1129 m²/g) with increasing Mg content can be attributed to several factors. As Mg ions may replace Fe in the Fe₂O₃ lattice, the crystal structure is perturbed, leading to the formation of surface defects and vacancies that expose
more surface area. This substitution can also promote the formation of smaller particles or nanostructures, increasing the surface area to volume ratio. In addition, the incorporation of Mg can increase the porosity of the material, creating more mesopores that contribute to the overall surface area.

<figure><img src="image_8.png" /><figcaption>**Figure 4.** Nitrogen adsorption/desorption isotherm and distribution of nanoparticles: (a) 15% MgFe₂O₄; (b) 20% MgFe₂O₄; (c) 25% MgFe₂O₄.</figcaption></figure>

### 2.1.5. X-Ray Photoelectron Spectroscopy (XPS) Analysis

XPS analysis was carried out to determine the surface chemical composition and the oxidation states of elements in MgFe₂O₄ samples (Figure 5). Survey spectra confirmed the presence of Mg, Fe, and O elements in all samples. High-resolution spectra of Mg 1s exhibited two peaks centered at ~1303.9 eV and ~1302.9 eV, which are characteristic of Mg²⁺ in both tetrahedral and octahedral sublattices [62,63]. With the increase in Mg content during synthesis, a slight increase in the relative intensity of the peak at ~1302.9 eV was observed, from 67.6% in the 15% MgFe₂O₄ sample to 71.2% in the 25% MgFe₂O₄ sample, suggesting a higher occupancy of octahedral sites.

In the Fe 2p high-resolution spectra, two main peaks were observed at 711.0 and 724.8 eV, corresponding to Fe 2p₃/₂ and Fe 2p₁/₂, respectively. The deconvolution of Fe 2p₃/₂ revealed two peaks at ~711 eV and ~713 eV, indicating the presence of Fe²⁺ and Fe³⁺ oxidation states, respectively [64,65]. Similarly, Fe 2p₁/₂ showed peaks at ~724.5 and ~727 eV, corresponding to Fe²⁺ and Fe³⁺, respectively [65]. Additionally, satellite peaks attributed to shake-up processes were detected at 719.29 eV and 732.82 eV [66]. The analysis of the Fe²⁺/Fe³⁺ ratios revealed a progressive increase in Fe³⁺ content with increasing Mg(NO₃)₂ precursors: from 59.7% (Fe³⁺) in the 15% sample to 64.6% in the 25% sample. This trend suggests that Mg incorporation promotes a higher oxidation state of iron, possibly due to charge compensation effects within the spinel structure. For the O 1s spectra, the peak centered at 530 eV was deconvoluted into two components, reflecting different chemical environments. The peak at ~529.9 eV was assigned to lattice oxygen (metal-oxygen bonds), while the peak at ~531.1 eV was attributed to surface-adsorbed oxygen species and oxygen vacancies [67–69]. The relative contribution of surface oxygen
increased with Mg content (from 50.1% in the 15% MgFe₂O₄ sample to 53.3% in the 25% MgFe₂O₄ sample), possibly due to increased defect formation or surface reactivity.

<figure><img src="image_9.png" /><figcaption>**Figure 5.** XPS survey and high-resolution spectra corresponding to Mg 1s, O 1s, and Fe 2p regions for (a) 15% MgFe₂O₄; (b) 20% MgFe₂O₄; (c) 25% MgFe₂O₄.</figcaption></figure>
## 2.2. Photocatalytic Degradation of Crystal Violet (CV)

The efficiency of crystal violet (CV) degradation was assessed spectrophotometrically by tracking absorbance at its maximum wavelength, λmax = 591 nm. Figure 6 shows the degradation yield after 360 min of visible light irradiation, revealing almost complete elimination of CV, with an efficiency close to 100% for an initial concentration of 20 mg/L. This significant performance clearly shows that the photocatalytic activity of the synthesized MgFe₂O₄ nanoparticles under visible light is very high.

<figure><img src="image_10.png" /><figcaption>**Figure 6.** Effect of Mg proportions on crystal violet removal yield after 2 h contact time, T = 25 °C, m = 0.08 g, v = 200 mL.</figcaption></figure>

As shown in the histogram (Figure 5), the degradation rates for MgFe₂O₄ materials at 15%, 20%, and 25% were 97.6%, 99.4%, and 98.9%, respectively. The 20% MgFe₂O₄ nanoparticles showed the best performance and were selected for further work, including the study of antibacterial activity and the preparation of air filters. The photocatalytic activity of MgFe₂O₄ is based on the generation of electron-hole pairs upon light exposure, followed by the formation of reactive oxygen species (O₂\* and \*OH) that are responsible for degrading organic pollutants. Increasing the Mg content reduces the band gap, leading to improved absorption of visible light [70]. In addition, the incorporation of Mg generates defect states that act as traps for charge carriers, reducing the hole-electron recombination time and improving charge separation efficiency. The higher specific surface area observed for Mg-rich samples further enhances photocatalytic activity by providing more active sites for pollutant adsorption and ROS generation.

## 2.3. Antibacterial Activity Against Escherichia coli ATCC 8739

*Escherichia coli* ATCC 8739 was tested for its sensitivity to MgFe₂O₄ (20%) in the presence and absence of visible light. The obtained results clearly showed that light significantly promotes the activity of the tested material. Indeed, concerning the 10⁻¹ bacterial dilution, the number of colonies obtained after a bacteria-MgFe₂O₄ contact time of 1 h, in absence of exposure to light, surpassed 300 colonies (uncountable plates), results comparable to those of the untreated control. However, the T3 treatment (1 h bacteria-MgFe₂O₄ contact in the presence of light) resulted in only one colony obtained in the three replicates (Table 1, Figure 7).

<table><caption>**Table 1.** ATCC 8739 numbering (CFU) from the 10⁻¹ and 10⁻² dilutions after incubation.</caption><thead><tr><th></th><th>T1 * (10<sup>-1</sup>)</th><th>T1 (10<sup>-2</sup>)</th><th>T2 ** (10<sup>-1</sup>)</th><th>T2 (10<sup>-2</sup>)</th><th>T3 *** (10<sup>-1</sup>)</th><th>T3 (10<sup>-2</sup>)</th></tr></thead><tbody><tr><td>Bacterial count (CFU)</td><td>>300</td><td>64 ± 32.741</td><td>>300</td><td>112.33 ± 49.702</td><td>0.33 ± 0.577</td><td>0.00</td></tr></tbody></table>

<footnote>*: Spreading after 1 h ATCC 8739-physiological water contact, **: Spreading after 1 h ATCC 8739-MgFe₂O₄ contact in absence of light, ***: Spreading after 1 h ATCC 8739-MgFe₂O₄ contact under light exposure.</footnote>
<figure><img src="image_11.png" /><figcaption>**Figure 7.** ATCC 8739 numbering (CFU) from the $10^{-1}$ and $10^{-2}$ dilutions after incubation. T1: spreading after 1 h ATCC 8739-physiological water contact; T2: spreading after 1 h ATCC 8739-MgFe$_2$O$_4$ contact in absence of light; T3: spreading after 1 h ATCC 8739-MgFe$_2$O$_4$ contact under light exposure.</figcaption></figure>

The results obtained with the $10^{-2}$ bacterial dilution confirm those of the previous one. Thus, 64 CFU were obtained with the untreated control (1 h bacteria-physiological water contact), 112 CFU with the T2 treatment (1 h bacteria-MgFe$_2$O$_4$ contact in absence of light), and 0 CFU were obtained with the T3 treatment (1 h bacteria-MgFe$_2$O$_4$ contact in the presence of light) (Table 1, Figure 7).

Similar results were obtained by spreading the three treatments on the liquid LB medium. Table 2 shows the average absorbance values obtained by spectrophotometer (600 nm) after incubation for 24 h. Thus, significant differences, translated by a visible difference in the media turbidity from one treatment to another, were observed (Figure 8). Overall, no bacterial viability was obtained from the T3, indicating that light excitation of the MgFe$_2$O$_4$ particles leads to complete elimination of viable bacteria after one hour contact in a liquid solution (Table 2).

<table><caption>**Table 2.** ATCC 8739 absorbance (600 nm) after 24 h incubation from each treatment.</caption><thead><tr><th></th><th>T1 * (10<sup>-1</sup>)</th><th>T1 (10<sup>-2</sup>)</th><th>T2 ** (10<sup>-1</sup>)</th><th>T2 (10<sup>-2</sup>)</th><th>T3 *** (10<sup>-1</sup>)</th><th>T3 (10<sup>-2</sup>)</th></tr></thead><tbody><tr><td>Optical density (600 nm)</td><td>0.2781 ± 0.0437</td><td>0.2449 ± 0.0412</td><td>0.261 ± 0.0115</td><td>0.2695 ± 0.0167</td><td>0.00</td><td>0.00</td></tr></tbody></table>

## 2.4. Antibacterial Activity of Air Filters in the Air Circulation System

### 2.4.1. LB Solid Medium

As shown in Figure 9, only one colony was obtained on the LB solid medium that was deposited in the inoculation chamber that receives air from the treated air filters (impregnated with 20% MgFe$_2$O$_4$). However, the number of colonies obtained on the solid LB medium in the inoculation chamber that received air from the untreated air filters was uncountable (>300 CFU).

<footnote>*: Spreading after 1 h ATCC 8739-physiological water contact, **: Spreading after 1 h ATCC 8739-MgFe$_2$O$_4$ contact in absence of light, ***: Spreading after 1 h ATCC 8739-MgFe$_2$O$_4$ contact under light exposure.</footnote>
<figure><img src="image_12.png" /><figcaption>**Figure 8.** Bacterial load (turbidity) after 24 h incubation of the 3 treatments on a liquid LB medium. T1: spreading after 1 h ATCC 8739-physiological water contact; T2: spreading after 1 h ATCC 8739-MgFe₂O₄ contact in absence of light; T3: spreading after 1 h ATCC 8739-MgFe₂O₄ contact under light exposure.</figcaption></figure>

<figure><img src="image_13.png" /><figcaption>**Figure 9.** UFCs obtained on the solid LB medium from both untreated and MgFe₂O₄ air filtration chambers.</figcaption></figure>

### 2.4.2. LB Liquid Medium

#### a. Direct measurement of the optical density of the LB liquid media

The direct reading of optical density (OD) of the Erlenmeyer deposited in both untreated and MgFe₂O₄ treated air filtration chambers then incubated for 48 h confirmed the results obtained on the solid LB medium. Indeed, a highly significant difference was observed, translated by naked eye-visible difference in the turbidites of the media belonging to the two treatments (control filters: DO = 0.15; MgFe₂O₄-treated filters: DO = 0.0163) (Figures 10 and 11).

<figure><img src="image_14.png" /><figcaption>**Figure 10.** Optical density (OD: 600 nm) after incubation of the LB liquid media after incubation: control (inoculation chamber receiving air from the untreated air filtration chamber); MgFe₂O₄ (inoculation chamber receiving air from the MgFe₂O₄-treated air filtration chamber). Statistical analysis carried out using GraphPad Prism V 9.3.1 software through the unpaired t-test for comparison between two means. *: significant difference ($p \le 0.05$).</figcaption></figure>
<figure><img src="image_15.png" /><figcaption>**Figure 11.** Visible turbidity of the liquid LB media after 48 h incubation. (A): Erlenmeyer that received air from the untreated air filtration chamber. (B): Erlenmeyer that receives air from the MgFe₂O₄-treated air filtration chamber.</figcaption></figure>

b. Colony-forming Units (UFCs) numbering from the liquid LB media

A total of 26 × 10⁴ CFUs were obtained from the Erlenmeyer exposed to air coming from the untreated air filtration chamber. However, no viable bacteria were obtained from the MgFe₂O₄-treated air filtration chamber (Figure 12), revealing a complete inhibition of bacterial viability through the use of air filters impregnated with MgFe₂O₄ and exposed to light.

<figure><img src="image_16.png" /><figcaption>**Figure 12.** Viable bacteria numbering (CFUs) from Erlenmeyer deposited in both the untreated air filtration chamber (Control) and the MgFe₂O₄-treated air filtration chamber (MgFe₂O₄). Statistical analysis carried out using GraphPad Prism V 9.3.1 software through the unpaired t-test for comparison between two means. *: significant difference (p ≤ 0.05).</figcaption></figure>

In this work, magnesium ferrite (MgFe₂O₄) nanoparticles showed strong antibacterial activity. This activity must be expanded to ensure its use in the fight against pathogenic microorganisms, particularly those resistant to conventional antimicrobials. Magnesium ferrite nanoparticles are a class of nanomaterials that have attracted increasing interest due to their potential applications in various fields, including medical and environmental applications [71,72]. However, their antibacterial activity is a growing research topic [28].
The bacterial strain, *Escherichia coli* ATCC 8739 (American Type Culture Collection) was used to evaluate MgFe₂O₄ antibacterial activity. The entire strain's genome is already sequenced. It is widely used as a quality control strain in antimicrobial formulation testing, culture media testing, efficacy testing and bioresistance testing [73]. Like all other bacteria, this species is affected by its environment. Its cytoplasmic membrane is permeable to water, but rarely to other metabolites. Nanoparticles, especially metallic ones, can interact directly with the cell membrane of bacteria, causing structural disturbances that lead to increased permeability or complete destruction of the membrane [49], which could explain the complete inhibition of *E. coli* ATCC 8739 by the synthesized magnesium ferrite (MgFe₂O₄) nanoparticles.

Our results clearly show that MgFe₂O₄ nanoparticles have significant antibacterial activity against *E. coli* ATCC 8739 strains when exposed to light, but they are less effective in the absence of light. This could be due to the ability of light-excited MgFe₂O₄ to activate reactive oxygen species (ROS) generation. In fact, ROS are known to cause oxidative damage to bacterial cell membranes, proteins, and DNA, leading to bacterial death [50]. Some nanoparticles can also induce indirect oxidative stress by disrupting the natural antioxidant mechanisms of microorganisms by interfering with the antioxidant enzyme systems of microbial cells, such as superoxide dismutase and catalase, thus increasing their vulnerability to reactive oxygen species [51,52].

Nanoparticles can also disrupt the structure and function of bacterial cell lipid membranes. This disruption can lead to altered membrane permeability, ion leakage, and membrane disorganization, compromising cell stability and survival. For example, silver nanoparticles have been observed to induce significant changes in the lipid composition of bacterial membranes, leading to disruptions in membrane function and increased cytotoxicity [53].

When cells are exposed to metal nanoparticles, they can also partially dissolve, releasing metal ions (such as Mg⁺ in the case of magnesium nanoparticles). These ions can interfere with bacterial metabolic processes and bind to enzymes and proteins, inhibiting their vital functions [54]. Nanoparticles can also penetrate bacterial cells and interfere with various metabolic processes such as DNA and protein synthesis or inhibit enzymes critical for cell survival [55].

The fine mechanisms of action of nanoparticles are poorly explored. They vary depending on their composition, size, and shape. Small nanoparticles tend to have a large specific surface area, improving their interaction with bacterial membranes. Similarly, higher concentrations of nanoparticles generally increase the antibacterial effect [74].

To our knowledge, the use of magnesium ferrite nanoparticles for microbiological air filtration is carried out for the first time in this study. Very little work has been conducted on the antibacterial activity of magnesium-based nanoparticles. Indeed, the maximum activity, observed in the presence of visible light, is probably due to the photocatalytic effects of our material. Some metallic nanoparticles, such as those based on titanium dioxide (TiO₂) or zinc (ZnO), have already demonstrated photocatalytic properties that activate the generation of ROS upon exposure to light [75].

Lagashetty et al. [76] conducted a study on the antibacterial activity of (Ag-MgFe₂O₄) nanocomposites against various bacteria. The results showed that silver-doped magnesium ferrites (Ag-MgFe₂O₄) exhibit moderate activity against bacteria. The addition of silver is known for its antimicrobial properties, which can improve the effectiveness of magnesium ferrites. However, the results of this work clearly show that MgFe₂O₄ nanoparticles possess strong antibacterial activity once excited by visible light, which can significantly reduce the viability of airborne bacteria upon simple contact.

Ehi-Eromosele et al. [77] reported the synthesis and antibacterial activity of magnesium ferrite (MgFe₂O₄) and cobalt-doped magnesium ferrite (Co0.8Mg0.2Fe₂O₄) nanoparticles. The
synthesized nanoparticles were tested for their antibacterial activity against several bacterial
strains (*Pseudomonas aeruginosa*, *Escherichia coli*, *Staphylococcus aureus*, and *Serratia marcescens*).
Their results showed that the tested nanoparticles, especially cobalt-doped magnesium ferrite
(Co0.8Mg0.2Fe2O4), had good antibacterial properties against these bacteria.

In our study, the constructed device demonstrates the high microbial load of the
filtered air volume (control filter: viable bacteria count >300 CFU); it also demonstrates
the effectiveness of the studied nanoparticles in the elimination of bacteria from the same
sample of tested air (1 CFU). Recently, the application of nanoparticles in air filtration
systems seems to have attracted great interest due to their potential to improve air quality
by eliminating microorganisms and harmful particles.

Mekapothula et al. [78] conducted a study exploring the use of copper nanoparticles coated on polymeric fibers for air filtration, particularly in healthcare environments. Copper oxide nanoparticles were synthesized and coated on polyethylene and polypropylene fibers. These nanoparticle-coated materials showed high efficiency in reducing various pathogens, including SARS-CoV-2 and bacterial strains such as Pseudomonas aeruginosa and *Escherichia coli*. The authors considered that this coating not only provides antiviral and antibacterial properties but also prevents biofouling, making it a promising solution for air conditioning systems and medical masks.

In another approach, adopted by Bonfim et al. [79] and discussed by De Riccardis [80], the use of electrospun nanofibrous membranes for air filtration seems a promising alternative. These membranes are created by electrospinning polymers into fibers with diameters in the nanometer range, resulting in a large specific surface area. According to the authors, this structure is very effective in trapping fine particles and microorganisms. The flexibility of electrospinning allows the use of various polymers and the incorporation of inorganic nanoparticles to improve antimicrobial properties.

Similarly, Bortolassi et al. [52] developed membranes based on polyacrylonitrile (PAN) nanofibers incorporating titanium dioxide (TiO₂), zinc oxide (ZnO), and silver (Ag) nanoparticles. These membranes showed high filtration efficiency, with near-total efficiency (≈100%) for sodium chloride (NaCl) particles of 9–300 nm diameter. The silver-containing nanofibers also demonstrated significant antibacterial activity against *Escherichia coli* bacteria.

Regarding the dispersion of nanoparticles on filtration media, Vilar et al. [81] used well-dispersed silver nanoparticles on cellulose filter paper. These filters showed substantial bacterial reduction (up to 99%) under gravity filtration. The combination of polydopamine (PDA) and polyethyleneimine (PEI) allowed homogeneous distribution of silver nanoparticles, increasing their efficacy against *Staphylococcus aureus* and *Escherichia coli*.

It should be noted that nanoparticles may pose potential risks to human health due to their nanometric size and potential for interaction with biological systems. Studies have shown that some nanoparticles such as ZnFe₂O₄ and CoFe₂O₄, can be toxic to human cells, affecting their viability and function [82]. Similarly, nanocomposites that integrate nanoparticles in a polymer or ceramic matrix may pose risks to human health. Studies have shown that nanocomposites containing titanium dioxide (TiO₂) or zinc oxide (ZnO) nanoparticles can have toxic effects on human cells and living organisms [83]. These potential risks arise from exposure to the nanoparticles themselves as well as the chemicals used in their manufacture. A thorough assessment of the safety and risks associated with these materials to ensure their safety in various applications seems necessary [84]. In our study, MgFe₂O₄ nanoparticles were used to impregnate air filters that are not in intimate contact with humans, reducing the risk of exposure to such materials and their negative impact on human health.

This work opens a wide field of perspectives to demonstrate the effect of nanoparticles
on the antibacterial effect of molecules used in therapy. By exploring the synergy between
nanoparticles and antibiotics, developing targeted nanoparticles, assessing their safety, innovating in their design, and addressing chronic infections, research can pave the way for more effective and specific antibacterial therapies, addressing the challenges posed by bacterial resistance and difficult-to-treat infections.

# 3. Materials and Methods

## 3.1. *Chemicals*

Magnesium (II) nitrate $Mg(NO_3)_2$, crystal violet $C_{25}H_{30}ClN_3$, iron (III) chloride $FeCl_3$, sodium hydroxide $NaOH$, and silver nitrate ($AgNO_3$) were all acquired from Sigma Aldrich. All reagents were used without further purification. Locally sourced deionized (DI) water was used for experimental procedures.

## 3.2. *Biological Material*

The bacterial strain, *Escherichia coli* ATCC 8739 (American Type Culture Collection), was used to evaluate $MgFe_2O_4$ antibacterial activity. It is widely used as a quality control strain in antimicrobial formulation testing, culture media testing, efficacy testing, and bioresistance testing.

## 3.3. $MgFe_2O_4$ Synthesis

The $MgFe_2O_4$ nanoparticles were synthesized using the coprecipitation method. Three $MgFe_2O_4$ spinel solutions were prepared using 4.59, 6.12, and 7.65 g of magnesium nitrate [$Mg(NO_3)_2$], corresponding to 15, 20, and 25% Mg, respectively. Thus, each of the three $Mg(NO_3)_2$ concentrations was dissolved in 30 mL deionized water, and then, 2.9 g iron chloride ($FeCl_3$) was added to each mixture. The solutions were kept under stirring for 1 h 30 min at 50 °C to ensure complete dissolution of the powders. A solution of $NaOH$ was then added dropwise to the mixture to adjust the pH to 12, resulting in the formation of a precipitate.

The obtained solutions were sonicated for 20 min, kept under stirring for 30 min, then subjected to a washing process that involved alternating rinses with ethanol and deionized water. Ethanol helped to break down any organic residues and promote effective removal of contaminants, while deionized water removed water-soluble impurities. A few drops of silver nitrate ($AgNO_3$) solution were added to a small sample of the wash solution to ensure the absence of chloride ions (no white precipitate of silver chloride ($AgCl$) are formed), indicating that chloride ions were successfully removed.

The samples were dried in the oven for 10 h at 80 °C to remove the adsorbed organic products and ensure complete dryness. At the end, the powders were collected, grounded, and placed in crucibles for calcination at 500 °C for 2 h.

## 3.4. $MgFe_2O_4$ Characterization

X-ray diffraction (XRD) was carried out to determine the structural characteristics, including crystallite size, phase identification, and crystallinity of the synthesized $MgFe_2O_4$ spine. XRD measurements of powdered $MgFe_2O_4$ spinel were performed using a model Empyrean Panalytical diffractometer at 40 kV using Cu K radiation ($\lambda = 1.54178$ Å), with scans lasting 15 min over a range of angles from 20° to 80°. The functional groups were identified using a Nicolet 8700® Fourier transform infrared spectrometer (Tokyo, Japan), at wavelengths of 400–4000 cm⁻¹. Surface morphology of the prepared samples was observed using SEM (JEOL ISM 6610) (Tokyo, Japan) operating at an accelerating voltage of 20 kV to examine the synthesized material and to elucidate the morphology. A transmission electron microscope (JEOL 2000 EX II) operating at an accelerating voltage of 120 kV and equipped with ultra-high-resolution images was used to determine particle size of the nanoparticles.
The Brunauer–Emmett–Teller (BET) surface areas of the synthesized samples were recorded by nitrogen (N2) physisorption at –196 °C using a Micromeritics (Norcross, GA, USA) ASAP-2020. The XPS analysis of MgFe₂O₄ (15%), MgFe₂O₄ (20%) and MgFe₂O₄ (25%) was conducted using a SPECS (Berlin, Germany) spectrometer equipped with a Phoibos 100 MCD analyzer and a monochromatized X-ray Al Kα (1486.6 eV). High-resolution spectra of Mg, O, and Fe elements were taken with 30 eV of energy pass and 0.1 eV of energy step.

### 3.5. *Photocatalytic Activity of MgFe₂O₄*

The photocatalytic activity of the synthesized MgFe₂O₄ nanoparticles was evaluated using crystal violet dye as a model pollutant. In the experiment, 0.08 g of MgFe₂O₄ nanoparticles with different compositions (15%, 20% and 25%) was dispersed in 50 mL of crystal violet dye solution. The mixture was stirred continuously for 30 min in the absence of irradiated light to achieve adsorption equilibrium and uniform dispersion of the MgFe₂O₄ nanoparticles. The solution was then exposed to light irradiation, using three xenon lamps BEETRO® (75 W, wavelength = 400 nm). The degradation of the crystal violet dye was monitored over a period of 360 min. After exposure, a 20 mL aliquot of the solution was centrifuged at 8000 rpm for 5 min to separate the MgFe₂O₄ nanoparticles. The supernatant was then analyzed using UV-visible spectroscopy to measure absorbance and determine the rate of dye degradation [1–3].

### 3.6. *Results of the Antibacterial Activity Against Escherichia coli*

The antibacterial activity of magnesium ferrite (MgFe₂O₄) at a 20% concentration was assessed against the reference strain *Escherichia coli* ATCC 8739. Pure colonies from a fresh culture of *E. coli* were suspended in sterile physiological water, with the bacterial suspension adjusted to match a McFarland 0.5 standard, resulting in an initial bacterial concentration of approximately 10⁸ CFU/mL (CFU: colony-forming units). Two serial dilutions (10⁻¹ and 10⁻²) were prepared by diluting 1 mL of the stock suspension into 9 mL of sterile physiological water.

Each dilution (1 mL) was then incubated with 3 mL of sterile physiological water containing/or not MgFe₂O₄ (20%) for 1 hour. Three different treatments were conducted: T1 (control) involved bacterial suspension in sterile physiological water (9 g/L NaCl) exposed to light during the contact time (Philips® (Eindhoven, The Netherlands) Lamp: 50 w, 400 nm); T2 included bacterial suspension with 2 mg of MgFe₂O₄ (20%) in the dark; and T3 included bacterial suspension with 2 mg MgFe₂O₄ (20%) exposed to light during the contact time (Philips® Lamp: 50 w, 400 nm).

Following a 60 min contact time, bacterial samples from each treatment were inoculated onto two types of media to determine bacterial viability. The first inoculation was on Luria–Bertani (LB) agar plates (tryptone 10 g/L, yeast extract 5 g/L, NaCl 5 g/L, agar 20 g/L, pH 7), where 100 µL of each treated suspension was spread and incubated for 24 h at 37 °C. Bacterial viability was determined by CFU counts at the end of the incubation period. The second inoculation was carried by transferring 50 µL of treated suspension into test tubes containing 9 mL of LB broth (without agar). The tubes were incubated under the same conditions, and bacterial charge was estimated via optical density measurements at 600 nm.

### 3.7. *Air Pollution Control*

#### 3.7.1. Air Filter Fabrication

The air filters were fabricated using Vlieseline. Vlieseline is a non-woven textile made from synthetic fibers, typically polyester or polypropylene, bonded through thermal fusion
or chemical binding. This type of fabric is lightweight, breathable, durable, and relatively
inexpensive, making it a popular material for a wide range of applications [85].

Vlieseline fabric's impregnation with MgFe₂O₄ (20%) nanoparticles was performed in a series of structured steps to ensure proper adhesion and preservation of nanoparticles functionality. First, the fabric was prepared through a cleaning process that involved washing to remove any impurities, grease, or residual finishing agents that could hinder nanoparticle binding. Following cleaning, the fabric surface was activated by abrasion with a hard brush, creating a rougher texture to enhance nanoparticles' adhesion.

Once prepared, the fabric underwent nanoparticle deposition. Three pieces of the fabric were immersed in a beaker containing pure water and placed on a magnetic stirrer. Gradually, 0.5 g of MgFe₂O₄ (20%) nanoparticles was added to the beaker, with continuous stirring for 10 h, allowing sufficient contact time for nanoparticles' adhesion onto the fabric surface. The impregnated fabrics were placed in an oven and dried at 80 °C overnight, ensuring that the nanoparticles were firmly attached to the fabric and ready for use.

3.7.2. Construction of the Air Circulation System

The setup consisted of a closed system with four chambers connected by transparent
tubing, and ending in an air pump. The air pump drew air from the outside (the non-
sterile lab atmosphere) at a flow rate of 600 mL/min and directed it evenly into two
small filtration chambers. Each filtration chamber measured 12.5 cm × 5.8 cm × 5 cm,
and contained a filtration system made from Vlieseline layers impregnated (or not) with
MgFe₂O₄ (20%). The filtration system was composed of 7 parallelly overlapping layers
(5 cm² each). The layers were spaced approximately 1.5 cm apart. They were either
impregnated with MgFe₂O₄ (treated filtration chamber) or left untreated as a control
(un-treated filtration chamber).

The air from each filtration chamber was then conducted to its corresponding inocula-
tion chamber (Figure 13). Each inoculation chamber (15.5 cm × 15 cm × 15 cm) contained
both liquid and solid LB media in open Petri dishes and open Erlenmeyer, respectively.
Bacteria that pass through the filtration systems should settle onto the open culture media
inside the inoculation chambers (Figure 6).

<figure><img src="image_17.png" /><figcaption>**Figure 13.** The air filtration system. (A): Entire setup without the pump. (B): filtration chamber, (C): inoculation chamber.</figcaption></figure>

The entire system was sterilized before use, and the filtration chambers were exposed
to light (Philips® Lamp 50 w, 400 nm) during air aspiration to activate the MgFe₂O₄. After
60 min of air circulation (36 L of air), the culture media were aseptically recovered and
incubated at 25 °C for 48 h. Microbial growth was measured by direct CFU count on the
solid LB medium, and estimated by measuring absorbance at λ = 600 nm of the liquid LB
medium. Finally, a CFU count of the liquid medium was realized according to [86].
### 3.8. Statistical Analysis

The air filtering activity results were compared using GraphPad Prism V 9.3.1 software, using the unpaired *t*-test for comparison between two means.

## 4. Conclusions

This work explored the antibacterial activity of magnesium ferrite ($MgFe_2O_4$) nanoparticles, aiming to develop innovative air filters capable of inhibiting bacterial propagation in the air, thus improving its quality and health safety in various closed environments. $MgFe_2O_4$ nanoparticles were successfully synthesized using the coprecipitation method. They were evaluated for their antibacterial activity against the reference strain *Escherichia coli* ATCC 8739, then integrated into Vlieseline matrices using an impregnation-deposition method. The fabrics were used as bacterial air filters through a lab setup for air circulation. The results showed significant reduction in the viable bacterial load that crosses the enlightened $MgFe_2O_4$-treated filters compared to the untreated ones, confirming the effectiveness of $MgFe_2O_4$ antibacterial activity in the presence of visible light. Consequently, the $MgFe_2O_4$-based air filters have significant potential to improve indoor air quality by providing additional protection against bacterial pathogens. The air filters made with $MgFe_2O_4$ show a good stability over time (several uses), due to its chemical, thermal, and mechanical robustness, as well as its long-lasting antibacterial and catalytic activity. Another property of $MgFe_2O_4$ that makes it easy to recycle is its magnetic property.

Advances in the synthesis and incorporation of $MgFe_2O_4$ nanoparticles in conventional air filtration systems would open the way to potential commercialization of these filters in various sectors, including healthcare facilities, industrial environments, and public spaces. It is also important to evaluate $MgFe_2O_4$ antimicrobial activity against a broader range of microorganisms, including viruses and fungi. It would also be relevant to study the long-term effect of $MgFe_2O_4$ nanoparticles on human health and the microbial ecosystem to assess any potential side effects.

**Author Contributions:** A.R., C.B.M., M.B. and L.M.: investigation, original draft writing, formal analysis, methodology; A.A., L.M. and N.M.: project administration, validation, supervision; R.B., S.O.T. and L.M.: writing, methodology; M.R., L.M. and A.R.: supervision, validation, reviewing, editing; L.M., M.N.A., A.A. and P.O.: reviewing, editing; M.B, C.B.M. and M.N.A.: data curation, methodology; A.R. and M.N.A.: software, data curation; P.O., M.R., R.B. and M.N.A.: funding, resources; L.M., N.M., A.R. and S.O.T.: conceptualization, writing, validation, project administration, supervision. All authors have read and agreed to the published version of the manuscript.

**Funding:** This project was funded by the Researchers Supporting Project number (PNURSP2025R481), Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia.

**Data Availability Statement:** Data sharing is not applicable to this article as no new data were created or analyzed in this study.

**Acknowledgments:** The authors are grateful to Princess Nourah bint Abdulrahman University Researchers Supporting Project number (PNURSP2025R481), Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia. The authors are grateful to the Algerian direction of research and technology (DGRSDT). MN and PO thank the support from the Employment, Industry, and Tourism Office of the Principality of Asturias (Spain) for the project SEK-25-GRU-GIC-24-010.

**Conflicts of Interest:** The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
## References

1. Lascoumes, P. Les instruments d'action publique, traceurs de changement: L'exemple des transformations de la politique française de lutte contre la pollution atmosphérique (1961-2006). *Polit. Soc.* **2007**, *26*, 73-89. [CrossRef]

2. Voronina, Y.; Lopushynskyi, I.; Grechanyk, B.; Vahonova, O.; Kondur, A.; Akimov, O. Economic and environmental component in the field of sustainable development management. *Calitatea* **2024**, *25*, 7-14.

3. Schwarzenbach, R.P.; Egli, T.; Hofstetter, T.B.; Von Gunten, U.; Wehrli, B. Global water pollution and human health. *Annu. Rev. Environ. Resour.* **2010**, *35*, 109-136. [CrossRef]

4. Chaitanya, M.V.N.L.; Arora, S.; Pal, R.S.; Ali, H.S.; El Haj, B.M.; Logesh, R. Assessment of environmental pollutants for their toxicological effects on human and animal health. In *Organic Micropollutants in Aquatic and Terrestrial Environments*; Springer: Cham, Switzerland, 2024; pp. 67-85.

5. Sharma, G.; Verma, A.; Wang, T.; Naushad, M.; Kumar, A.; Dhiman, P. Remediation of antibiotics using coordination polymers. *Coord. Chem. Rev.* **2024**, *519*, 216120. [CrossRef]

6. World Health Organization. *Antimicrobial Resistance: Global Report on Surveillance*; World Health Organization: Geneva, Switzerland, 2014; Available online: https://apps.who.int/iris/handle/10665/112642 (accessed on 22 February 2025).

7. Halawa, E.M.; Fadel, M.; Al-Rabia, M.W.; Behairy, A.; Nouh, N.A.; Abdo, M.; Abdeen, A. Antibiotic action and resistance: Updated review of mechanisms, spread, influencing factors, and alternative approaches for combating resistance. *Front. Pharmacol.* **2024**, *14*, 1305294. [CrossRef]

8. Mata, T.M.; Martins, A.A.; Calheiros, C.S.C.; Villanueva, F.; Alonso-Cuevilla, N.P.; Gabriel, M.F.; Silva, G.V. Indoor air quality: A review of cleaning technologies. *Environments* **2022**, *9*, 118. [CrossRef]

9. Nguyen, M.; Burciaga, B.; Ghosh, N. *History of Implementation of Nanotechnology in Novel Air Purifiers with Special Reference to Reduction of Pollen, Mold Spores, and PM2.5 Indices*; West Texas A&M University: Canyon, TX, USA, 2024; Available online: https://wtamu-ir.tdl.org/items/0c9854cf-7203-4616-849f-6a9fcf546055 (accessed on 22 February 2025).

10. Rodríguez, M.; Seseña, S.; Valiente, N.; Palop, L.; Rodríguez, A. Indoor air quality in elderly care centers: A multidisciplinary approach. *Build. Environ.* **2024**, *262*, 111832. [CrossRef]

11. Donnet, M.; Mensi, M.; Lussi, A. La contamination bactérienne de l'air ambiant lors d'un traitement AIRFLOW®. *Swiss Dent. J. SSO* **2020**, *130*, 913-916.

12. Morawska, L.; Johnson, G.R.; Ristovski, Z.D.; Hargreaves, M.; Mengersen, K.; Corbett, S.; Chao, C.Y.H.; Li, Y.; Katoshevski, D. Size distribution and sites of origin of droplets expelled from the human respiratory tract during expiratory activities. *J. Aerosol Sci.* **2009**, *40*, 256-269. [CrossRef]

13. Gupta, J.K.; Lin, C.-H.; Chen, Q. Characterizing exhaled airflow from breathing and talking. *Indoor Air* **2010**, *20*, 31-39. [CrossRef]

14. Matys, J.; Kensy, J.; Gedrange, T.; Zawiślak, I.; Grzech-Leśniak, K.; Dobrzyński, M. A molecular approach for detecting bacteria and fungi in healthcare environment aerosols: A systematic review. *Int. J. Mol. Sci.* **2024**, *25*, 4154. [CrossRef] [PubMed]

15. World Health Organization. *Air Pollution and Child Health: Prescribing Clean Air: Summary*; World Health Organization: Geneva, Switzerland, 2018; WHO/CED/PHE/18.01; Available online: https://iris.who.int/handle/10665/275545 (accessed on 22 February 2025).

16. Baranovsky, S. Circulation et Persistance de Pathogènes Nosocomiaux Multirésistants et Hautement Résistants Émergents dans l'environnement Hospitalier: Complexité des Unités de Transmission. Ph.D. Thesis, University of Montpellier, Montpellier, France, 2020. Available online: https://theses.hal.science/tel-03118483 (accessed on 22 February 2025).

17. Gattinger, D.; Schlenz, V.; Weil, T.; Sattler, B. From remote to urbanized: Dispersal of antibiotic-resistant bacteria under the aspect of anthropogenic influence. *Sci. Total Environ.* **2024**, *924*, 171532. [CrossRef] [PubMed]

18. Jann, J. Développement d'une Technologie de Surface Bactéricide à Base d'aluminium. Ph.D. Thesis, University of Sherbrooke, Sherbrooke, QC, Canada, 2023. Available online: https://savoirs.usherbrooke.ca/bitstream/11143/20032/18/jann_jessica_PhD_2023.pdf (accessed on 22 February 2025).

19. Boudraa, R.; Talantikite-Touati, D.; Souici, A.; Djermoune, A.; Saidani, A.; Fendi, K.; Amrane, A.; Bollinger, J.C.; Tran, H.N.; Hadadi, A.; et al. Optical and photocatalytic properties of TiO₂-Bi₂O₃-CuO supported on natural zeolite for removing Safranin-O dye from water and wastewater. *J. Photochem. Photobiol. A Chem.* **2023**, *443*, 114845. [CrossRef]

20. Cheikh, S.; Imessaoudene, A.; Bollinger, J.-C.; Hadadi, A.; Manseri, A.; Bouzaza, A.; Assadi, A.; Amrane, A.; Zamouche, M.; El Jery, A.; et al. Complete Elimination of the Ciprofloxacin Antibiotic from Water by the Combination of Adsorption-Photocatalysis Process Using Natural Hydroxyapatite and TiO₂. *Catalysts* **2023**, *13*, 336. [CrossRef]

21. Imessaoudene, A.; Mechraoui, O.; Aberkane, B.; Benabbas, A.; Manseri, A.; Moussaoui, Y.; Bollinger, J.C.; Amrane, A.; Zoukel, A.; Mouni, L. Synthesis of a TiO₂/zeolite composite: Evaluation of adsorption-photodegradation synergy for the removal of Malachite Green. *Nano-Struct. Nano-Objects* **2024**, *38*, 101191. [CrossRef]

22. Boudraa, R.; Talantikite-Touati, D.; Souici, A.; Djermoune, A.; Saidani, A.; Fendi, K.; Amrane, A.; Bollinger, J.C.; Tran, H.N.; Mouni, L. Breaking new grounds: Solid-state synthesis of TiO₂-La₂O₃-CuO nanocomposites for degrading brilliant green dye under visible light. *J. Clean. Prod.* **2024**, *481*, 144126. [CrossRef]
23. Boudraa, R.; Talantikite-Touati, D.; Djermoune, A.; Souici, A.; Kebir, M.; Ait Merzeg, F.; Amrane, A.; Bollinger, J.C.; Mouni, L. Comprehensive characterization and unprecedented photocatalytic efficacy of TiO₂-CuO-La₂O₃ and TiO₂-CuO-Bi₂O₃ nanocomposites: A novel approach to environmental remediation. *Mater. Sci. Eng. B* **2025**, *312*, 117863. [CrossRef]

24. Sánchez-Bayo, F. Impacts of agricultural pesticides on terrestrial ecosystems. In *Ecological Impacts of Toxic Chemicals*; Sánchez-Bayo, F., van den Brink, P.J., Mann, R.M., Eds.; Bentham Science Publishers: Sharjah, United Arab Emirates, 2011; pp. 63–87. [CrossRef]

25. Arain, M.F. Nanotools for air remediation: An introduction. In *Nanotechnology to Monitor, Remedy, and Prevent Pollution*; Arain, M.F., Ed.; Elsevier: Amsterdam, The Netherlands, 2024; pp. 125–140. [CrossRef]

26. Rai, M.; Yadav, A.; Gade, A. Silver nanoparticles as a new generation of antimicrobials. *Biotechnol. Adv.* **2009**, *27*, 76–83. [CrossRef]

27. Fatolahi, L. Evaluation of photocatalysis inactivation in indoor air purification of pathogenic microbes by using the different nanomaterials based on TiO₂ nanomaterials. *J. Environ. Sci. Health A* **2024**, *59*, 213–222. [CrossRef]

28. El-Khawaga, A.M.; Ayman, M.; Hafez, O.; Shalaby, R.E. Photocatalytic, Antimicrobial and Antibiofilm Activities of MgFe₂O₄ Magnetic Nanoparticles. *Sci. Rep.* **2024**, *14*, 12877. [CrossRef]

29. Sajid, S.; Kodape, S.M.; Kurhade, P. A study on bacterial inactivation using green synthesized photocatalytically active TiO₂, MgO, TiO₂/MgO nanoparticles. *J. Indian Chem. Soc.* **2024**, *101*, 101425. [CrossRef]

30. Beena, V.; Parvathiraja, C.; Paulkumar, K.; Gupta, J.K.; Almutairi, T.M.; Mouni, L. Bio-engineered NiO nanoparticles for photocatalytic and antibacterial treatments. *J. Dispers. Sci. Technol.* **2025**, 1–13. [CrossRef]

31. Sun, S.; Zeng, H. Size-controlled synthesis of magnetite nanoparticles. *J. Am. Chem. Soc.* **2002**, *124*, 8204–8205. [CrossRef]

32. Laurent, S.; Forge, D.; Port, M.; Roch, A.; Robic, C.; Vander Elst, L.; Muller, R.N. Magnetic iron oxide nanoparticles: Synthesis, stabilization, vectorization, physicochemical characterizations, and biological applications. *Chem. Rev.* **2008**, *108*, 2064–2110. [CrossRef]

33. Manohar, A.; Suvarna, T.; Vattikuti, S.V.P.; Manivasagan, P.; Jang, E.S.; Sudhani, H.P.; Kim, K.H. Structural, morphological, magnetic, electrochemical and biocompatible properties of ZnFe₂O₄/MgFe₂O₄/NiFe₂O₄/CeO₂ nanocomposites. *Colloids Surf. A Physicochem. Eng. Asp.* **2024**, *705*, 135667. [CrossRef]

34. Choi, W.; Termin, A.; Hoffmann, M.R. The role of metal ion dopants in quantum-sized TiO₂: Correlation between photoreactivity and charge carrier recombination dynamics. *J. Phys. Chem.* **1994**, *98*, 13669–13679. [CrossRef]

35. Guo, X.; Yang, Z.; Dong, H.; Guan, X.; Ren, Q.; Lv, X.; Jin, X. Simple combination of oxidants with zero-valent iron (ZVI) achieved very rapid and highly efficient removal of heavy metals from water. *Water Res.* **2016**, *88*, 671–680. [CrossRef]

36. Huang, Y.; Ho, S.S.H.; Lu, Y.; Niu, R.; Xu, L.; Cao, J.; Lee, S. Removal of Indoor Volatile Organic Compounds via Photocatalytic Oxidation: A Short Review and Prospect. *Molecules* **2016**, *21*, 56. [CrossRef]

37. Laouici, R. Élaboration des Matériaux Semi-Conducteurs et Étude de Leurs Applications Environnementales. Ph.D. Thesis, University of Jijel, Jijel, Algeria, 2023.

38. Simon-Deckers, A. Biological Effects of Manufactured Nanoparticles: Influence of Their Characteristics. Ph.D. Thesis, AgroParis-Tech, Paris, France, 2008.

39. Salih, S.J.; Mahmood, W.M. Review on magnetic spinel ferrite (MFe₂O₄) nanoparticles: From synthesis to application. *Heliyon* **2023**, *9*, e16601. [CrossRef]

40. Nie, C.; Qiu, Y.; Pei, T.; Qin, Y. Specific Sources Exert Influence on the Community Structures of Bioaerosols. *Aerobiology* **2024**, *2*, 72–84. [CrossRef]

41. Hart, D. Pathogenic Bacteria in the Air of Operating Rooms: Their Widespread Distribution and the Methods of Control. *Arch. Surg.* **1938**, *37*, 521–530. [CrossRef]

42. Stryjakowska-Sekulska, M.; Piotraszewska-Pajak, A.; Szyszka, A.; Nowicki, M.; Filipiak, M. Microbiological Quality of Indoor Air in University Rooms. *Pol. J. Environ. Stud.* **2007**, *16*, 623.

43. Bragoszewska, E.; Biedroń, I. Indoor Air Quality and Potential Health Risk Impacts of Exposure to Antibiotic-Resistant Bacteria in Office Rooms in Southern Poland. *Int. J. Environ. Res. Public Health* **2018**, *15*, 2604. [CrossRef] [PubMed]

44. Jonidi Jafari, A.; Moslemzadeh, M. The Effect of TiO₂ Nanoparticles on Bacterial Growth: The Effect of Particle Size and Their Structure—A Systematic Review. *Int. J. Environ. Health Res.* **2024**, *34*, 697–707. [CrossRef]

45. Salas-Orozco, M.F.; Lorenzo-Leal, A.C.; de Alba Montero, I.; Marín, N.P.; Santana, M.A.C.; Bach, H. Mechanism of Escape from the Antibacterial Activity of Metal-Based Nanoparticles in Clinically Relevant Bacteria: A Systematic Review. *Nanomedicine* **2024**, *55*, 102715. [CrossRef]

46. Le Ouay, B.; Stellacci, F. Antibacterial Activity of Silver Nanoparticles: A Surface Science Insight. *Nano Today* **2015**, *10*, 339–354. [CrossRef]

47. Dutta, S.; Erchinger, J.E.; Strieth-Kalthoff, F.; Kleinmans, R.; Glorius, F. Energy Transfer Photocatalysis: Exciting Modes of Reactivity. *Chem. Soc. Rev.* **2024**, *53*, 1068–1089. [CrossRef]

48. Tessema, B.; Gonfa, G.; Hailegiorgis, S.M.; Workneh, G.A.; Tadesse, T.G. Synthesis and Evaluation of the Anti-Bacterial Effect of Modified Silica Gel Supported Silver Nanoparticles on *E. coli* and *S. aureus*. *Results Chem.* **2024**, *7*, 101471. [CrossRef]
49. Morones, J.R.; Elechiguerra, J.L.; Camacho, A.; Holt, K.; Kouri, J.B.; Ramírez, J.T.; Yacaman, M.J. The Bactericidal Effect of Silver Nanoparticles. *Nanotechnology* **2005**, *16*, 2346–2353. [CrossRef]

50. Rai, M.; Kon, K.; Ingle, A.; Duran, N.; Galdiero, S.; Galdiero, M. Broad-Spectrum Bioactivities of Silver Nanoparticles: The Emerging Trends and Future Prospects. *Appl. Microbiol. Biotechnol.* **2014**, *98*, 1951–1961. [CrossRef]

51. Ivask, A.; Juganson, K.; Bondarenko, O.; Mortimer, M.; Aruoja, V.; Kasemets, K.; Blinova, I.; Heinlaan, M.; Slaveykova, V.; Kahru, A. Mechanisms of Toxic Action of Ag, ZnO and CuO Nanoparticles to Selected Ecotoxicological Test Organisms and Mammalian Cells In Vitro: A Comparative Review. *Nanotoxicology* **2014**, *8* (Suppl. S1), 57–71. [CrossRef] [PubMed]

52. Bortolassi, A.C.C.; Nagarajan, S.; de Araújo Lima, B.; Guerra, V.G.; Aguiar, M.L.; Huon, V.; Soussan, L.; Cornu, D.; Miele, P.; Bechelany, M. Efficient Nanoparticles Removal and Bactericidal Action of Electrospun Nanofibers Membranes for Air Filtration. *Mater. Sci. Eng. C* **2019**, *102*, 718–729. [CrossRef] [PubMed]

53. Fayez, K.A.; El-Deeb, B.A.; Mostafa, N.Y. Toxicity of Biosynthetic Silver Nanoparticles on the Growth, Cell Ultrastructure and Physiological Activities of Barley Plant. *Acta Physiol. Plant.* **2017**, *39*, 155. [CrossRef]

54. Xiu, Z.M.; Zhang, Q.B.; Puppala, H.L.; Colvin, V.L.; Alvarez, P.J.J. Negligible Particle-Specific Antibacterial Activity of Silver Nanoparticles. *Nano Lett.* **2012**, *12*, 4271–4275. [CrossRef]

55. Da Costa, D. Développement D'une Thérapie Combinatoire à Base D'agents Anti-Biofilms et de Particules D'acide Poly-Lactique Pour la Délivrance D'antibiotiques Contre des Biofilms Bactériens. Ph.D. Thesis, University of Lyon, Lyon, France, 2020. Available online: https://theses.hal.science/tel-03612040 (accessed on 22 February 2025).

56. Jomini, S. Effets des Nanoparticules de Dioxide de Titane Sur Les Bactéries: De la Cellule à la Communauté. Ph.D. Thesis, University of Lorraine, Nancy, France, 2014. Available online: https://hal.univ-lorraine.fr/tel-01750816 (accessed on 22 February 2025).

57. Uddin, M.J.; Jeong, Y.K. Application of Magnesium Ferrite Nanomaterials for Adsorptive Removal of Arsenic from Water: Effects of Mg and Fe Ratio. *Chemosphere* **2022**, *307*, 135817. [CrossRef]

58. Manohar, A.; Vijayakanth, V.; Reddy Pallavolu, M.; Hyeon Kim, K. Effects of Ni-Substitution on Structural, Magnetic Hyperthermia, Photocatalytic, and Cytotoxicity Study of MgFe₂O₄ Nanoparticles. *J. Alloys Compd.* **2021**, *868*, 160515. [CrossRef]

59. Ilhan, S.; Izotova, S.G.; Komlev, A.A. Synthesis and Characterization of MgFe₂O₄ Nanoparticles Prepared by Hydrothermal Decomposition of Co-Precipitated Magnesium and Iron Hydroxides. *Ceram. Int.* **2015**, *41*, 577–585. [CrossRef]

60. Phenrat, T.; Saleh, N.; Sirk, K.; Tilton, R.D.; Lowry, G.V. Aggregation and Sedimentation of Aqueous Nanoscale Zerovalent Iron Dispersions. *Environ. Sci. Technol.* **2007**, *41*, 284–290. [CrossRef]

61. de Hoyos-Sifuentes, D.H.; Reséndiz-Hernández, P.J.; Díaz-Guillén, J.A.; Ochoa-Palacios, R.M.; Altamirano-Guerrero, G. Synthesis and Characterization of MgFe₂O₄ Nanoparticles and PEG-Coated MgFe₂O₄ Nanocomposite. *J. Mater. Res. Technol.* **2022**, *18*, 3130–3142. [CrossRef]

62. Uma, S.; Vignesh, D.; Shobana, M.K. Synthesis of heterostructured nanocomposite MgFe₂O₄/MoO₃ for H₂S sensing: Experimental and theoretical approach by DFT. *Sens. Actuators B Chem.* **2025**, *425*, 136950. [CrossRef]

63. Padhan, A.M.; Nayak, S.; Sahu, M.; Jagličić, Z.; Koželj, P.; Kim, H.J. Cationic redistribution induced magnetic properties of Zn²⁺ substituted MgFe₂O₄ spinel ferrite. *Phys. B Condens. Matter* **2023**, *668*, 415245. [CrossRef]

64. Zhao, L.; Li, X.; Zhao, Q.; Qu, Z.; Yuan, D.; Liu, S.; Hu, X.; Chen, G. Synthesis, characterization and adsorptive performance of MgFe₂O₄ nanospheres for SO₂ removal. *J. Hazard. Mater.* **2010**, *184*, 704–709. [CrossRef] [PubMed]

65. Taha, T.A.; Fayed, M.G.; Mohamed, S.G. Enhanced electrochemical performance of MgFe₂O₄/SrTiO₃ and MgFe₂O₄/SiO₂ nanocomposite structures. *J. Alloys Compd.* **2022**, *925*, 166660. [CrossRef]

66. Kaur Ubhi, M.; Kaur, M.; Singh, D.; Javed, M.; Oliveira, A.C.; Kumar Garg, V.; Sharma, V.K. Hierarchical Nanoflowers of MgFe₂O₄, Bentonite and B-,P- Co-Doped Graphene Oxide as Adsorbent and Photocatalyst: Optimization of Parameters by Box-Behnken Methodology. *Int. J. Mol. Sci.* **2022**, *23*, 9678. [CrossRef]

67. Heiba, Z.K.; Sanad, M.M.S.; Mohamed, M.B. Influence of Mg-deficiency on the functional properties of magnesium ferrite anode material. *Solid State Ion.* **2019**, *341*, 115042. [CrossRef]

68. Yan, Z.; Gao, J.; Li, Y.; Zhang, M.; Guo, M. Hydrothermal synthesis and structure evolution of metal-doped magnesium ferrite from saprolite laterite. *RSC Adv.* **2015**, *5*, 92778–92787. [CrossRef]

69. Kim, J.H.; Jang, Y.J.; Kim, J.H.; Jang, J.W.; Choi, S.H.; Lee, J.S. Defective ZnFe₂O₄ nanorods with oxygen vacancy for photoelectrochemical water splitting. *Nanoscale* **2015**, *7*, 19144–19151. [CrossRef]

70. Soukeur, A.; Kaci, M.; Omeiri, S.; Bellal, B.; Amara, M.; Trari, M. Photocatalytic degradation of bromothymol blue over MgFe₂O₄ under sunlight exposure. *Opt. Mater.* **2023**, *142*, 114108. [CrossRef]

71. Rajadurai, L.; Dash, C.S.; Revathi, S.; Dhiwahar, A.T.; Sundararajan, M.; Ravisankar, P.; Alagarasan, J.K.; Mohandoss, S.; Sambasivam, R. Photocatalytic Degradation of Tetracycline Hydrochloride Using Pure and Copper-Doped Magnesium Ferrite Nanoparticles: Efficiency, Kinetics, and Mechanism. *Inorg. Chem. Commun.* **2024**, *162*, 112197. [CrossRef]
72. Salama, R.S.; Gouda, M.S.; Aboud, M.F.A.; Alshorifi, F.T.; El-Hallag, A.A.; Badawi, A.K. Synthesis and Characterization of Magnesium Ferrite-Activated Carbon Composites Derived from Orange Peels for Enhanced Supercapacitor Performance. *Sci. Rep.* **2024**, *14*, 8223. [CrossRef]

73. Dadi, R. Synthèse de Nanoparticules D'oxydes Métalliques et Leur Activité Antibactérienne. Ph.D. Thesis, Université Paris-Nord-Paris XIII, Villetaneuse, France, 2019. Available online: https://theses.hal.science/tel-03119316 (accessed on 22 February 2025).

74. Sirelkhatim, A.; Mahmud, S.; Seeni, A.; Kaus, N.H.M.; Ann, L.C.; Bakhori, S.K.M.; Hasan, H.; Mohamad, D. Review on Zinc Oxide Nanoparticles: Antibacterial Activity and Toxicity Mechanism. *Nano-Micro Lett.* **2015**, *7*, 219–242. [CrossRef] [PubMed]

75. Ryu, S.; Kim, D.; Lee, H.; Kim, Y.; Lee, Y.; Kim, M.; Kim, H.; Lee, H. Biodegradable Nanofiber/Metal–Organic Framework/Cotton Air Filtration Membranes Enabling Simultaneous Removal of Toxic Gases and Particulate Matter. *Polymers* **2023**, *15*, 3965. [CrossRef] [PubMed]

76. Lagashetty, A.; Pattar, A.; Ganiger, S.K. Synthesis, Characterization and Antibacterial Study of Ag-Doped Magnesium Ferrite Nanocomposite. *Heliyon* **2019**, *5*, e01760. [CrossRef]

77. Ehi-Eromosele, C.O.; Olugbuyiro, J.A.O.; Taiwo, O.S.; Bamgboye, O.A.; Ango, C.E. Synthesis and Evaluation of the Antimicrobial Potentials of Cobalt-Doped and Magnesium Ferrite Spinel Nanoparticles. *Bull. Chem. Soc. Ethiop.* **2018**, *32*, 451–458. [CrossRef]

78. Kim, K.H.; Kabir, E.; Jahan, S.A. Airborne Bioaerosols and Their Impact on Human Health. *J. Environ. Sci.* **2018**, *67*, 23–35. [CrossRef]

79. Bonfim, D.P.; Cruz, F.G.; Guerra, V.G.; Aguiar, M.L. Development of Filter Media by Electrospinning for Air Filtration of Nanoparticles from PET Bottles. *Membranes* **2021**, *11*, 293. [CrossRef]

80. De Riccardis, M.F. Electrospun Nanofibrous Membranes for Air Filtration: A Critical Review. *Compounds* **2023**, *3*, 390–410. [CrossRef]

81. Vilar, M.R.; Ferraria, A.M.; do Rego, A.M.B.; Boufi, S. Cellulose: De Nouvelles Perspectives pour un Matériau Millénaire. *L'Actualité Chim.* **2015**, *393–394*, 102.

82. Zaich, Y.; Lourghi, A.; Rouibah, K.E.; Akika, F.Z. Adsorption et Photo-Dégradation sous Irradiation Solaire de Quelques Polluants Organiques Contenus dans les Effluents Liquides. Ph.D. Thesis, Université de Jijel, Jijel, Algeria, 2022.

83. Rossano, M. Utilisation des Nanoparticules de Dioxyde de Titane dans les Émulsions Cosmétiques: Impact sur la Santé Humaine et l'Environnement. Ph.D. Thesis, Université Le Havre, Le Havre, France, 2014. Available online: https://theses.fr/2014LEHA0003 (accessed on 22 February 2025).

84. Wolfram, J.; Zhu, M.; Yang, Y.; Shen, J.; Gentile, E.; Paolino, D.; Zhao, Y. Safety of Nanoparticles in Medicine. *Curr. Drug Targets* **2015**, *16*, 1671–1681. [CrossRef]

85. Mao, N.; Russell, S.J.; Pourdeyhimi, B. Characterisation, Testing, and Modelling of Nonwoven Fabrics. In *Handbook of Nonwovens*; Woodhead Publishing: Sawston, UK, 2022; pp. 509–626. [CrossRef]

86. Brugger, S.D.; Baumberger, C.; Jost, M.; Jenni, W.; Brugger, U.; Mühlemann, K. Automated Counting of Bacterial Colony Forming Units on Agar Plates. *PLoS ONE* **2012**, *7*, e33695. [CrossRef]

**Disclaimer/Publisher's Note:** The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.