# Exploring the Synthesis of Novel Sillenite Bi12SnO20: Effect of Calcination Temperature on the Phase Formation and Catalytic Performance

Oussama Baaloudj, Hamza Kenfoud, M Brienza, Atef El Jery, Moutaz Aldrdery, Aymen Amine Assadi

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Oussama Baaloudj, Hamza Kenfoud, M Brienza, Atef El Jery, Moutaz Aldrdery, et al. Exploring the Synthesis of Novel Sillenite Bi12SnO20: Effect of Calcination Temperature on the Phase Formation and Catalytic Performance. Catalysts, 2024, 14 (9), pp.650. 10.3390/catal14090650. [hal-04718635](https://hal.science/hal-04718635v1)

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# Exploring the Synthesis of Novel Sillenite Bi₁₂SnO₂₀: Effect of Calcination Temperature on the Phase Formation and Catalytic Performance

Oussama Baaloudj <fnref n="1" />,<fnref n="2" />,* ID, Hamza Kenfoud <fnref n="3" />, Monica Brienza <fnref n="1" />, Atef El Jery <fnref n="4" /> ID, Moutaz Aldrdery <fnref n="4" /> and Aymen Amin Assadi <fnref n="5" />,<fnref n="6" /> ID

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**Citation:** Baaloudj, O.; Kenfoud, H.; Brienza, M.; El Jery, A.; Aldrdery, M.; Assadi, A.A. Exploring the Synthesis of Novel Sillenite Bi₁₂SnO₂₀: Effect of Calcination Temperature on the Phase Formation and Catalytic Performance.
*Catalysts* **2024**, *14*, 650. https://doi.org/10.3390/catal14090650

Academic Editors: Yongjun Ji, Yuxi Liu and Shaomian Liu

Received: 26 August 2024

Revised: 16 September 2024

Accepted: 20 September 2024

Published: 23 September 2024

<figure><img src="image_3.png" /></figure>

**Copyright:** © 2024 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:** Sillenite materials have been the focus of intense research in recent years due to their unique properties and distinct structure with the I23 space group. This electronic structure has reflected high-quality applications and results for some environmental processes such as photocatalysis. This paper investigates the synthesis of a new sillenite, Bi₁₂SnO₂₀, and its characteristics, emphasizing its potential for photocatalytic applications. The sillenite Bi₁₂SnO₂₀ has been synthesized through the co-precipitation method by mixing the appropriate ratio of Bi and Sn ions. The obtained particles after precipitation and drying were characterized by thermogravimetric analysis (TGA) and then calcined at different temperatures based on this analysis. The phase has been identified by structural analysis using X-ray diffraction (XRD), and its morphology after identification was carried out by scanning electron microscopy (SEM). The calcination temperature has been found to have a critical role in obtaining the phase, where the phase was found to be formed at temperatures between 310 and 400 °C and changed to other phases within higher temperatures. The physicochemical properties of this sillenite were also studied by Fourier-transform infrared spectroscopy (FTIR) and UV Visible Spectrometer (UV-Vis). To study the obtained phases at different calcination temperatures, performance testing was performed under visible light to remove different contaminants, which are Tetracycline, Bisphenol A, and Rhodamine B. The phase Bi₁₂SnO₂₀ obtained at 350 °C with a catalyst dose of 1 g/L showed the highest performance for removing these pollutants with concentrations of 20 mg/L, with an efficiency of almost 100% within 2 h. This work will be useful as an important resource and strategy for the development of this sillenite material in its pure phase.

**Keywords:** sillenite; synthesis; calcination temperature; characterization; photocatalysis

## 1. Introduction

The catalysts' core metal ion is one of the most important components in the creation of effective photocatalysts [1,2]. As the metal core of catalysts, bismuth ions have attracted a lot of attention recently because of their many unique characteristics, including their high chemical stability, strong light absorption, low rate of pair recombination, and small

<footnote n="1">¹ Department of Science, University of Basilicata, Viale dell'Ateneo Lucano, 10, 85100 Potenza, Italy; monica.brienza@unibas.it</footnote>

<footnote n="2">² Laboratory of Advanced Materials for Energy and Environment, Université du Québec à Trois-Rivières (UQTR), 3351 Boulevard des Forges, Trois-Rivières, QC G8Z 4M3, Canada</footnote>

<footnote n="3">³ Laboratory of Reaction Engineering, Faculty of Mechanical Engineering and Process Engineering, University of Science and Technology Houari Boumediene, BP 32, Algiers 16111, Algeria; hkenfoud@usthb.dz</footnote>

<footnote n="4">⁴ Department of Chemical Engineering, College of Engineering, King Khalid University, Abha 61411, Saudi Arabia; ajery@kku.edu.sa (A.E.J.); maldrdery@kku.edu.sa (M.A.)</footnote>

<footnote n="5">5 College of Engineering, Imam Mohammad Ibn Saud Islamic University, Riyadh 11432, Saudi Arabia; aaassadi@imamu.edu.sa</footnote>

<footnote n="6">⁶ Univ Rennes, ENSCR-équipe Chimie et Ingénierie des Procédés, URM 6226 CNRS, ENSCR-11, allee de Beaulieu, CS 508307, 35708 Rennes, France</footnote>

<footnote>* Correspondence: oussama.baaloudj@unibas.it or oussama.baaloudj@uqtr.ca</footnote>
band gap [3]. Currently, bismuth sillenites, with the chemical formula Bi<sub>x</sub>[M]O<sub>y</sub> (M is the core metal), have been identified as materials with high photocatalytic potential [4]. Among them, ideal sillenite, Bi<sub>12</sub>[M]O<sub>20</sub>, has been studied the most [5,6]. Researchers have recently become interested in ideal sillenite materials because of their optical properties and photocatalytic potential [3,7], and they are considered desirable materials for a range of potentially beneficial applications, such as photocatalysis and other photonic domains [8,9].

Although numerous recent studies conducted by researchers have synthesized and examined bismuth sillenites as catalysts, the sillenite composed of bismuth (Bi) and tin (Sn), two of the most preferred ions for producing catalysts [10,11], has not yet been studied due to the challenges associated with its synthesis, including perceived difficulties in preparation and instability. In a study by Rafael et al., they found Bi<sub>1</sub>nO<sub>20</sub> as an impurity during the synthesis of Bi<sub>2</sub>Sn<sub>2</sub>O<sub>7</sub> [12]. It was also claimed that Bi<sub>12</sub>SnO<sub>20</sub> demonstrates instability and is difficult to synthesize, requiring quenching, which would limit its widespread investigation and application. In another study by Aming Lin et al. [13], it is stated that Bi<sub>12</sub>SnO<sub>20</sub> has not been studied in terms of its properties, except for sporadic reports on its possible existence. By theoretical analysis, they explained the lack of comprehensive research on this sillenite can be attributed to its high formation energy, as indicated by its high ΔG value (Gibbs free energy). This formation energy can be influenced by the stability of the binary oxide SnO<sub>2</sub>, since SnO<sub>2</sub> is highly stable, which makes the formation of Bi<sub>12</sub>SnO<sub>20</sub> energetically unfavorable. Other studies have reported the presence of sillenite Bi<sub>12</sub>SnO<sub>20</sub> as an unintended byproduct during the synthesis of other materials [14–16]. However, these studies did not delve into a dedicated investigation or understand its characteristics.

In the context of synthesizing the novel sillenite Bi<sub>12</sub>SnO<sub>20</sub> and investigating its activity, the co-precipitation method was used. Thermogravimetric analysis (TGA) was utilized to analyze the powder that was obtained after the coprecipitation in order to determine the phases that had formed. X-ray diffraction analysis (XRD) was then employed to determine the phase. Further characterization techniques were employed to examine its optical characteristics, composition, and features. To comprehend the phase formation, the photocatalytic performance of this material was assessed using three distinct pollutants: Tetracycline, Bisphenol A, and Rhodamine B, with the sillenite at varying calcination temperatures. Finally, this investigation ended with perspectives that offered broad recommendations. To our knowledge, no study has been carried out yet concerning the synthesis of the sillenite Bi<sub>12</sub>SnO<sub>20</sub> and its use for photocatalysis applications.

## 2. Materials and Methods

### 2.1. *Chemicals*

The chemicals used in the synthesis of sillenite were Bi(NO<sub>3</sub>)<sub>3</sub>·5H<sub>2</sub>O (Chem-Lab, Zedelgem, Belgium, 98%), SnCl<sub>4</sub> (Sigma Aldrich, Saint Louis, MO, USA, 98%), nitric acid HNO<sub>3</sub> (Sigma Aldrich, 60%) and NaOH (Fluka, Buchs, Switzerland, ≥97%). Tetracycline, Bisphenol A, and Rhodamine B were sourced from a pharmaceutical company in Canada. Distilled water was used as a solvent.

### 2.2. Preparation of the Sillenite Bi<sub>12</sub>SnO<sub>20</sub>

In order to create the sillenite, bismuth nitrate [Bi(NO<sub>3</sub>)<sub>3</sub>·5H<sub>2</sub>O] and Tin(IV) chloride SnCl<sub>4</sub> were combined in stoichiometric proportions and dissolved while being stirred in 10% nitric acid. The solutions were then heated to 50 °C for an hour on a hot plate. Then, the mixture was mixed with the NaOH (6 M) solution to bring the pH for precipitation to levels between 9 and 10. Once the pH was reached, white precipitation was observed. Following that, the precipitate was removed and repeatedly cleaned with distilled water before being dried in an autoclave for twenty-four hours at 120 °C. After this procedure, an amorphous powder was produced. After being ground in an agate mortar to a homogeneous powder, the mixture was calcined for 6 h at various temperatures. The final product after calcination, which had a whitish-yellow color, was passed on for optical and structural characterization
and phase identification. The preparation process to obtain Bi₁₂SnO₂₀ sillenite is shown in Figure 1.

<figure><img src="image_4.png" /><figcaption>Figure 1. Co-precipitation synthesis of sillenite-type Bi₁₂SnO₂₀.</figcaption></figure>

## 2.3. Characterization

Thermogravimetric analysis (TGA) was performed using a PerkinElmer Diamond TGA/DSC apparatus, the sample weight was 12.232 mg, and it was held at 50.00 °C for 1 min, then heated from 50.00 °C to 800.00 °C at a rate of 10.00 °C/min. After reaching 800.00 °C, the sample was cooled back to 50.00 °C at a rate of 20.00 °C/min. X-ray diffraction (XRD) analysis was performed using a Rigaku MiniFlexTM 600 diffractometer using filtered Cu Ka radiation (1.540593 Å) at an accelerating voltage of 40 kV. Fourier Transformed InfraRed Spectrometer (FTIR) analysis was performed using Cary 630 Agilent. The morphology of the samples, along with energy dispersive X-ray (EDX) analysis and mapping, was characterized using a Scanning Electron Microscope (SEM, Hitachi SU3500, Tokyo, Japan). UV-Vis diffuse reflectance spectra were recorded on a SHIMADZU (Tokyo, Japan) UV-2550 spectrophotometer with an integrating sphere.

## 2.4. Photocatalytic Application

To evaluate the photocatalytic performance of the materials at each calcination temperature, three hazardous and non-biodegradable pollutants, i.e., Rhodamine B, Bisphenol A, and Tetracycline, were examined. The photocatalytic removal tests were conducted using a photoreactor equipped with 60 W high-intensity 5000K LEDs that were purchased from a local store. An amount of 5.0 mg of the catalyst powder (1 g/L) was mixed with 5.0 mL of the pollutants (20 mg/L as inlet concentration) to investigate the photocatalytic efficiency of the materials. After that, the mixture was continuously stirred at a speed of 300 rpm. Before starting the photocatalytic process and irradiation, it was crucial to examine the catalyst's adsorption of the materials by mixing the pollutant samples with it in a dark environment for two hours to preserve the equilibrium between adsorption and desorption [17]. An air-cooling system was used to maintain a nearly constant temperature at 25 °C throughout the photocatalytic process. The photoreaction was carried out for 2 h. A Cary 60 UV-Vis Spectrophotometer was used to monitor the pollution concentrations. Using Equation (1), the removal efficiency both in the dark and under irradiation was assessed, and Equation (2) was used to study the kinetics using the pseudo-first-order kinetic model.

$$ \text{Removal efficiency (\%)} = \frac{(C_0 - C_t)}{C_0} \times 100\% \quad (1) $$
$$ \ln \frac{C_0}{C_t} = k_{app}(t) \qquad (2) $$

$C_0$ is the initial concentration of the pollutants, and $C_t$ is the concentration on the time (t), $k_{app}$ is the apparent pseudo-first-order rate constant represented in $min^{-1}$.

# 3. Results and Discussion

## 3.1. Characterization of the Materials

### 3.1.1. Phase Identification and Structural Investigation

The thermogravimetric analysis (TGA) and derivative curve (DTG) shown in Figure 2 have been used to study the thermal transitions and phase changes in the materials. The peak at 100.15 °C in the derivative curve is attributed to the evaporation of water in an endothermic reaction, which is accompanied by weight loss at this stage. The peaks at 212.83 °C and 307.55 °C can be associated with denitrification and nitrate decomposition as exothermic reactions [18,19], whereas the significant peak at 307.55 °C accompanied by the mass loss and significant exothermic effect can be due to the decomposition of hydroxide of bismuth tin mixture ($Bi_1 n(OH)_{20}$) into oxide ($Bi_{12}SnO_{20}$) where the material started to crystallize [20,21]. It can be observed that a phase has been reached after a temperature of 310 °C. A chemical reaction occurs with a significant downward peak at 481 °C accompanied by significant weight loss, which is associated with an endothermic melting reaction. Within this temperature, the obtained phase has been transformed into other phases stable across higher temperatures. Based on the derivative curve results, the $Bi_{12}SnO_{20}$ phase can be obtained at temperatures between 310 and 400 °C in air and this is in line with the literature [22]. To maintain a sufficient temperature and prevent phase loss, a calcination temperature of 350 °C was selected to be investigated.

<figure><img src="image_5.png" /><figcaption>Figure 2. Thermogravimetric analysis and derivative curve of the amorphous powder before calcination.</figcaption></figure>

X-ray diffractometry (XRD) was used to study the development of the sillenite phase. The nature of the phases generated after a calcination temperature of 310 °C has been further investigated. Figure 3 displays the usual XRD patterns of Bi-Sn powder that has been calcined at 350 °C and 600 °C. In the sample that calcined at 350 °C, crystalline sillenite nanoparticles of $Bi_{12}SnO_{20}$ were identified by comparing them to the calculated sillenite phase XRD generated by Vista software (ver. 3.5.8), and the results were in good agreement with the international card ASTM 054-1004 [14]. However, the phase was not pure, and some impurities such as $Bi_{64}SnO_{98}$ were also observed. In this calcination temperature, there is the possibility of the formation of $Bi_{12}Sn(OH)_{20}$ as another impurity due to the presence of the undecomposed hydroxyl group product -OH at low temperatures. The XRD pattern
of the sample calcinated at 600 °C shows sharper and narrower diffraction lines, a mixed phase of SnO₂ (JCPDS No. 41-1445 [23]), tetragonal Bi₂O₃ (JCPDS No. 78-1793 [24]), Bi₂O₃ doped Sn, and other new phases such as Bi₂Sn₃O₉ and Bi₂Sn₂O₇ [12,15,16]. The material calcinated at this temperature was not identical to the calculated XRD of the sillenite Bi₁₂SnO₂₀. According to the TGA/DTG and XRD analysis, it can be concluded that the sillenite phase formed between the temperatures 310 and 400 °C, and it is unstable, whereby increasing the temperature causes the decomposition and melting of the phase and leads to the formation of other stable compounds such as SnO₂, which is stable at high calcination temperatures. Based on the strongest diffraction lines in the XRD at 350 °C, the average size of the nanocrystals in the obtained phase was determined to be D = 34.215 nm. This was calculated using the full width at half maximum (β, in radians) and the Debye–Scherrer equation.

<figure><img src="image_6.png" /><figcaption>**Figure 3.** XRD analysis of Bi-Sn powder calcinated at 350 °C and 600 °C.</figcaption></figure>

In order to investigate if the temperature of the calcination 350 °C is sufficient for the development of sillenite catalysts, Fourier Transform Infrared (FT-IR) has been integrated [23]. This temperature was selected based on XRD where the appropriate calcination temperature at which the sillenite crystalline nanoparticles were detected. The spectra illustrated in Figure 4 show the contents of the sample after 350 °C calcination over the range of 700–3600 cm⁻¹, and the focus was on this area in order to investigate the remaining impurities such as nitrates in the phase post-calcination. In general, the metal oxide bonds Sn–O and Bi–O are frequently detected by absorption peaks in the 500–700 cm⁻¹ region, as already demonstrated in the literature [25,26]. The stretching vibration of hydroxyl groups and the deformation vibration of adsorbed water molecules, respectively, are responsible for the absorption peaks around 3400 cm⁻¹ and 1600 cm⁻¹, respectively [27]. The remaining nitrates in the sample were responsible for the broadband absorption peaks at 1300–1400 cm⁻¹ (N–O asymmetric stretching) [28], 1040 cm⁻¹ (N–O symmetric stretching) [26], and 840 cm⁻¹ (N–O bending vibrations) [29]. The presence of nitrates in the sample was expected since the remaining nitrogen after thermal treatment cannot be completely removed by calcination at 350 °C, and if higher heat is used during calcination, the sillenite phase may be lost, which is a limitation in obtaining this phase.
<figure><img src="image_7.png" /><figcaption>**Figure 4.** FTIR spectra of the sillenite $Bi_{12}SnO_{20}$ calcinated at 350 °C.</figcaption></figure>

### 3.1.2. Morphology Investigation

The morphology of the particles calcined at 350 °C is depicted in the scanning electron microscope (SEM) image in Figure 5a. The figure shows that the powder consists of irregular sub-micron aggregate grains, dispersed throughout the agglomerate in a nearly orderly manner, often forming a sphere-like geometry. The particles forming the agglomeration are less than 1 µm and are confirmed to be nanoparticles, which aligns with the XRD-calculated crystallite size. It is also evident from the morphology that the sample is porous, which promotes both photocatalysis and adsorption. Additionally, the EDX spectra were used to examine the elemental composition. The representative EDX spectrum of the nanoparticles is shown in Figure 5b. Several distinct lines detected the elements O, Sn, and Bi. The measured average content ratios of O/Sn and Bi/Sn were 8.45 and 15.55, respectively, which is close to the theoretical value found in the $Bi_{12}SnO_{20}$ formulas.

<figure><img src="image_8.png" /><figcaption>**Figure 5.** (a) SEM images and (b) EDX analysis of $Bi_{12}SnO_{20}$ calcinated at 350 °C.</figcaption></figure>

The mapping analysis depicted in the images in Figure 6 demonstrates a homogenous distribution of the elements throughout the sample. This finding confirms the successful formation of homogeneous phases within the material. Additionally, this homogeneous distribution demonstrates that the Sn and Bi oxides have not significantly existed in the sample; instead, they have formed the sillenite phase. This uniformity ensures predictable and reliable performance in the application of this material.
<figure><img src="image_9.png" /><figcaption>Figure 6. Mapping analysis of the elements (a) Sn, (b) Bi, and (c) O for the sillenite Bi₁₂SnO₂₀.</figcaption></figure>

### 3.1.3. Optical Study

The optical characteristics of photocatalyst materials are important information for their application, and the band gap energy is one of the parameters controlling the photocatalytic activity [30]. UV-Vis diffuse reflectance spectra of Bi₁₂SnO₂₀ at room temperature are shown in Figure 7a. The reflectance spectrum of Bi₁₂SnO₂₀ exhibits a sharp increase before 470 nm. This falls higher than the ultraviolet (UV) region (>400 nm), which suggests that this catalyst can also absorb visible spectrum rather than only the UV region. Tauc’s formula (Equation (3)) can be used to determine the energy bandgap (E_g)—a significant parameter that can be used to describe the optical properties of photocatalysts. The E_g value can be calculated by the intercept of the linear plots of direct transition (αhν)² with the hv-axis (Figure 7b).

$$ (\alpha h\nu)^2 = K(h\nu - E_g) \quad (3) $$

where hν is the photon energy, α is the absorption coefficient and K is the constant relative to the material type.

<figure><img src="image_10.png" /><figcaption>Figure 7. (a) Diffuse reflectance spectrum, (b) Tauc plot for measurement of the band gap of Bi₁₂SnO₂₀.</figcaption></figure>

The slope of the linear part suggests the band gap energy of Bi₁₂SnO₂₀ powder is 2.86 eV, which matches previous reports [11,31]. This value of E_g can be favorable for photo generation upon photoexcitation, even with visible light (E_g < 3). Therefore, the Bi₁₂SnO₂₀ catalyst has the ability of photocatalytic degradation with both visible light and UV light irradiation.

### 3.2. Material Performance Tests

Following the examination of the characteristics of the Bi-Sn materials after their calcination at varying temperatures, a sequence of experiments was conducted to assess
their effectiveness and potential applications for treating various contaminants. Before performing the photocatalytic degradation tests under irradiation, these experiments involved assessing the materials under dark adsorption tests at different temperatures. Figure 8 presents the efficiency of removal under irradiation as well as the adsorption efficiency after 1 h for the material Bi-Sn calcinated at 300, 350, 400, 500, and 600 °C for 6 h. The experiments were performed with an initial concentration of 20 mg/L with the materials added to the solution with a catalyst dose of 1 g/L and a reaction time of 1 h in the dark and under irradiation. These experiments showed that Tetracycline and Bisphenol A had slightly high adsorption efficiencies in dark conditions under different calcination temperatures, but Rhodamine B had low adsorption efficiency. In contrast, when exposed to radiation, the materials underwent considerable increases in the removal of all contaminants under certain conditions, albeit with variations across different temperatures. With all studied pollutants, almost the same behavior was recorded, where the photocatalytic activity of the Bi-Sn material increased with the calcination temperature, peaking at 350 °C, and then decreased with further temperature increases. The removal efficiency after 1 h of reaction for the Bi-Sn sample calcined at 350 °C for Rhodamine B, Bisphenol A, and Tetracycline were 98.92, 95.04 and 76.97% respectively. These results suggest that at 350 °C, there is a phase that can be activated by light to generate radicals, and that phase, as XRD showed, is the sillenite $Bi_{12}SnO_{20}$. Samples that are calcined above 350 °C exhibit lower photocatalytic activity as a result of the loss of this phase. The XRD analysis indicates that the phase has nearly completely disappeared after calcining at 600 °C, which likely contributed to the decreased photocatalytic efficiency. The enhanced efficiency of phase $Bi_{12}SnO_{20}$, which was detected at 350 °C, was higher than that of $SnO_{2}$ and $Bi_{2}O_{3}$, which were detected at 600 °C. This may be because $Bi_{12}SnO_{20}$ has a greater absorption of incident visible light, which results in the generation of more photogenerated electrons to improve the efficiency of charge separation. This, in turn, enhances the photocatalytic activity, as demonstrated by UV-Vis diffuse reflectance spectra. The improvement in removal performance can also be attributed to several factors such as particle size, morphology, porosity, crystallinity, and surface area [32–35]. However, in this material, the difference is mainly due to phase transformation as it is a total phase change, and for that, the calcination temperature played a crucial role in determining the efficiency of the samples. The results obtained from this application were in line with previous reports about similar materials [36–38]. From the data and results shown in Figure 8, we can conclude that the calcination at 350 °C is identified as the optimum temperature for sillenite $Bi_{12}SnO_{20}$, where the catalyst exhibited the highest catalytic activity, avoiding the phase transformation that reduces photocatalytic efficiency, and the enhanced photocatalytic activity could be attributed to the presence of the $Bi_{12}SnO_{20}$ phase within this temperature.

<figure><img src="image_11.png" /><figcaption>**Figure 8.** Adsorption and removal efficiency of the system Bi-Sn as a function of the calcination temperature for (a) Rhodamine B (b) Bisphenol A (c) Tetracycline, $[Pollutants]_{0}$ = 20 mg/L, catalyst dose 1 g/L, Reaction time 1 h.</figcaption></figure>
Bi-Sn material calcined at 350 °C, which exhibits the dominant phase sillenite Bi₁₂SnO₂₀, has demonstrated an effective removal for the removal of Tetracycline, Bisphenol A, and Rhodamine B. Thus, a kinetic study has been conducted using this material for the removal of these pollutants. The kinetics of photodegradation of these pollutants on the sillenite can be described by a pseudo-first-order reaction model (PFO). Figure 9 shows the kinetic data of the removal of the three pollutants that were fitted with the first-order model, and as can be seen, the sillenite Bi₁₂SnO₂₀ calcined at 350 °C demonstrated a strong photodegradation rate and nearly a total removal of the three pollutants within two hours.

<figure><img src="image_12.png" /><figcaption>**Figure 9.** Removal kinetics of the pollutants using sillenite Bi₁₂SnO₂₀, [concentration]₀ = 20 mg/L and catalyst dose 1 g/L.</figcaption></figure>

From the fitting with the PFO model, the reaction rate constant (k) and correlation coefficient (R²) were calculated and are summarized in Table 1. The slight differences in reaction rate constants between the three pollutants may be attributed to factors such as chemical structure, stability, and adsorption affinity on the photocatalyst surface. Specifically, Tetracycline's complex structure and large molecular size likely contribute to its lower reaction rate constant compared to other pollutants.

<table><caption>**Table 1.** Kinetic parameters of the pseudo-first-order model for the removal of pollutants using the sillenite Bi₁₂SnO₂₀.</caption><thead><tr><td>Pollutant</td><td>k<sub>app</sub> (min<sup>-1</sup>)</td><td>R<sup>2</sup></td></tr></thead><tbody><tr><td>Rhodamine B</td><td>0.042</td><td>0.99</td></tr><tr><td>Bisphenol A</td><td>0.04</td><td>0.99</td></tr><tr><td>Tetracycline</td><td>0.026</td><td>0.99</td></tr></tbody></table>

## 4. Conclusions

This study successfully obtained the challenging sillenite material Bi₁₂SnO₂₀ via a co-precipitation method. Thermogravimetric analysis (TGA) guided the selection of appropriate calcination temperatures, followed by X-ray diffraction (XRD) for phase identification and scanning electron microscopy (SEM) for morphological characterization. The results revealed that Bi₁₂SnO₂₀ formation occurs between 300 °C and 400 °C, transforming to other phases at higher temperatures. Fourier-transform infrared spectroscopy (FTIR) and UV-Vis spectroscopy provided further insights into the material's physicochemical properties, where the sillenite was found to have a bandgap of 2.8 eV. Performance testing under visible light for contaminant removal on the Bi-Sn material calcined in different temperatures demonstrated a high efficiency with the Bi-Sn material in which the Bi₁₂SnO₂₀ phase was identified. The efficiency has achieved a nearly total removal of Tetracycline, Bisphenol A, and Rhodamine B (20 mg/L each) within 2 h with a catalyst dose of 1 g/L. This research paves the way for further exploration of Bi₁₂SnO₂₀ as a novel sillenite photocatalyst,
but more efforts are needed to refine the synthesis method to obtain a pure Bi₁₂SnO₂₀ phase. This sillenite has demonstrated exceptional performance, achieving nearly 100% removal of various pollutants within a short timeframe. This merits further exploration and development to unlock its full potential for environmental remediation applications.

**Author Contributions:** Conceptualization, O.B.; methodology, O.B. and A.A.A.; software, O.B.; validation, O.B. and H.K.; formal analysis, H.K. and A.E.J.; investigation, O.B. H.K., A.E.J. and M.A.; resources, A.A.A., M.A. and A.E.J.; data curation, O.B.; writing—original draft preparation, O.B.; writing—review and editing, M.B. and A.A.A.; visualization, O.B.; supervision, A.A.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Data Availability Statement:** Data supporting reported results are available.

**Acknowledgments:** The authors extend their appreciation to the Deanship of Research and Graduate Studies at King Khalid University for funding this work through the Large Research Project under grant number RGP2/248/45. The authors are also grateful to the University of Quebec in Trois-Rivières (UQTR), Università degli studi della basilicata (UniBas) and IMAM University for scientific collaboration.

**Conflicts of Interest:** The authors declare no conflicts of interest.

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