Cellulose for the Production of Air-Filtering Systems: A Critical Review

Abstract

The control of airborne contaminants is of great interest in improving air quality, which has deteriorated more and more in recent years due to strong industrial growth. In the last decades, cellulose has been largely proposed as suitable feedstock to build up eco-friendly materials for a wide range of applications. Herein, the issue regarding the use of cellulose to develop air-filtering systems is addressed. The review covers different cellulose-based solutions, ranging from aerogels and foams to membranes and films, and to composites, considering either particulate filtration (PM10, PM2.5, and PM0.3) or gas and water permeation. The proposed solutions were evaluated on the bases of their quality factor (QF), whose high value (at least of 0.01 Pa−1 referred to commercial HEPA (high-efficiency particulate air) filters) guarantees the best compromise between high filtration efficiency (>99%) and low pressure drop (<1 kPa/g). To face this aspect, we first analyzed the different morphological aspects which can improve the final filtration performance, outlining the importance on using nanofibers not only to increase surface area and to modulate porosity in final solutions, but also as reinforcement of filters made of different materials. Besides the description of technological approaches to improve the mechanical filtration, selected examples show the importance of the chemical interaction, promoted by the introduction of active functional groups on cellulose (nano)fibers backbone, to improve filtration efficiency without reducing filter porosity.

Natural Polymers and Their Nanocomposites Used for Environmental Applications

“…They are characterized by nontoxicity, high chemical stability, high adsorption capacity, large porosity, high inner surface area, and ultrahigh thermal and chemical stabilities [ 69 ]. Nanocellulose-based filtering materials were developed by the incorporation of ZIF nanocrystals in the cellulose microfiber network, as a subclass of MOF HKUST-1 [ 9 ]— Figure 3 .…”

“…The addition of ZIF-8 nanocrystals to cellulose microfibers led to an improved surface area, proved by an excellence enhancement in the BET surface area from 6.66 up to 620.80 m 2 /g, compared with the unmodified surface, which led to an increase in the filtration efficiency from 99.5 to 99.9% against PM 0.3 particles [ 9 ]. ZIF-8 crystal was found to coat the surface of the chitosan/polyvinyl alcohol electrospun nanofiber (CS/PVA-ENF) for dye removal from wastewater treatments [ 71 ].…”

“…According to the literature research, the most promising and commonly reported natural polymers, as single materials or in combination with other advanced materials, are chitosan, alginate, cellulose, lignocellulose, starch, and PVA. The main properties of biopolymers to be used as filter membranes or adsorbents for environmental applications are related to their high permeability for capturing airborne or water contaminants [ 9 ], the outstanding mechanical and thermal properties [ 9 ], better resistance to diverse pH conditions [ 10 ], biodegradability, swelling capacity, the slight modification needed to increase the adsorption, and last but not last, the low cost [ 11 ]. For the processing of fibers by electrospinning technology, the specific features of biopolymers are needed for the adequate solubility and compatibility in aqueous solvents, a certain molecular weight, and a desired surface topography to attract positive or negative ions.…”

A new laser device for ultra-rapid and sustainable aerosol sterilization

“…Existing technologies to prevent transmission of respiratory human pathogens such as SARS-CoV-2, can be generally classified into four main categories. The most common category consists of high efficiency particulate air (HEPA) filters, which mechanically remove > 99% of dust, pollen, mold, bacteria, and any airborne particles larger than 0.3 µm ( Lippi et al, 2022 ). Despite this high efficiency in air cleaning, filters require periodic replacement in order to function properly.…”

“…In addition, filters themselves can shelter viable microbes and support their growth, particularly under high humidity ( Pasanen et al, 1993 ). In addition, used filters requires specific disposal, with associated costs and risk of environmental contamination ( Lippi et al, 2022 ). Another limitation of these filters is that they can only purify the air when it is introduced into a closed space and not after the entrance of infected individuals.…”