# Combating Pathogens Using Carbon-Fiber Ionizers (CFIs) for Air Purification: A Narrative Review
## 4 Discussion
### Carbon-fiber Ionizers: The Pros and Cons
In a study by [PERSON] and colleagues [3], the investigators did not use live microorganisms _per se_ but utilized particles of approximately corresponding diameters as surrogates; subsequently, this particulate matter was subjected to different types of ions (bipolar or negative ionization). The authors reported on unipolar ions being much more efficient in increasing deposition rates for the size range up to 1 \(\upmu\)m. Figure 2 represents the relationship between deposition increase and particle size, with a comparison of the effects of negative and positive ions. The increase in the deposition coefficient (i.e., the deposition of particles itself) under the influence of small ions in the air is most pronounced for particle sizes within the middle range of the size spectrum (100-1000 nm) and is particularly significant for SARS-CoV-2, _Haemophilus influenzae_, cytomegalovirusovirus, _Staphylococcus aureus_, and _Mycoplasma pneumoniae_. It may be concluded that the action of small ions provides an efficient mechanism for reducing the concentration of infectious particles in the air, including some that would otherwise Niger for quite a long time as bioaerosols. Figure 2: Assessed efficiency in increasing particle deposition rates, according to [PERSON] et al. [3]. [PERSON] et al. tested the effectiveness of a bipolar ionization system using carbon fiber brushes to control airborne particles, especially ultrafine particles [99]. The study evaluated the impact of ionization technology on particle sizes from ultrafine to fine, with a particular focus on particles from 49.6 nm to 201.7 nm, further demonstrating broader effectiveness against pathogens in the air. [PERSON] et al. explored carbon fiber ionization technology to control pathogens in indoor environments and demonstrated the effectiveness of an electrostatic precipitator (ESP) that uses a carbon fiber ionizer to charge and remove pathogens [62]. This technology demonstrates the high efficiency of an ESP equipped with copper (Cu) collector plates in removing airborne pathogens. [PERSON] et al. [20] explained the rationale for applying carbon fiber ionization technology in healthcare and other environments to prevent or control infections. Their experiments showed strong antibacterial effects of PAIs and NAIs on Gram-positive and Gram-negative bacteria grown in Petri dishes and soaked on filters. Variation in bacterial viability is attributed to differences in their outer layers, with Gram-negative bacteria being less affected by ionization than Gram-positive bacteria. [PERSON] et al. demonstrated the potential of bipolar ionization using a carbon fiber ionizer as an effective complementary technology in healthcare facilities to reduce the burden of hospital-acquired infections (HAIs) [23]. The experiment was performed in an acrylic chamber, and significant reductions were demonstrated for both bacterial and viral pathogens, while ozone levels were monitored and maintained at low levels (mostly below the detection limit) to distinguish the effects of ionization from potential ozone-induced deactivation of pathogens. However, this study showed no significant inactivation of fungi. [PERSON] et al. developed a carbon fiber-based ionizer that produces low amounts of ozone and effectively kills Gram-positive and Gram-negative bacteria [18]. The study was conducted in a controlled environment in a sealed plastic chamber, where air was circulated by a fan and bacteria were grown on a 0.45 \(\upmu\)m filter. The study also found that the bactericidal effect was due to oxidative stress caused by negative and positive ions on the bacteria, rather than from the produced ozone. This finding contrasts with that of [PERSON] et al. [37], who attributed the bactericidal effect mainly to ozone. The study by [PERSON] et al.