key: cord-0781363-ygscb1og
authors: Kadam, Vinod; Truong, Yen Bach; Schutz, Jurg; Kyratzis, Ilias Louis; Padhye, Rajiv; Wang, Lijing
title: Gelatin/β–Cyclodextrin Bio–Nanofibers as Respiratory Filter Media for Filtration of Aerosols and Volatile Organic Compounds at Low Air Resistance
date: 2020-09-03
journal: J Hazard Mater
DOI: 10.1016/j.jhazmat.2020.123841
sha: 2a7f9c421a08309fa99461b06bd62873228411de
doc_id: 781363
cord_uid: ygscb1og

Air pollution is a universal concern. The suspended solid/liquid particles in the air and volatile organic compounds (VOCs) are ubiquitous. Synthetic polymer-based air filter media not only has disposal issues but also is a source of air and water pollution at the end of the life cycle. It has been a challenge to filter both particulate matter and VOC pollutants by a common biodegradable filter media having low air resistance. This study reports gelatin/β–cyclodextrin composite nanofiber mats with dual function air filtration ability at reduced air resistance (148 Pa) and low basis weight (1 g/m²). Gelatin/β–cyclodextrin nanofibers captured aerosols (0.3–5 μm) with < 95% filtration efficiency at 0.029/Pa quality factor. They adsorbed great amount of xylene (287 mg/g), benzene (242 mg/g), and formaldehyde (0.75 mg/g) VOCs. VOC adsorption of gelatin/β–cyclodextrin nanofibers is found several times higher than a commercial face mask and pristine powder samples. This study provides a solution for a ‘green’ dual function respiratory air filtration at low resistance. Gelatin/β–cyclodextrin nanofibers also have the potential to filter the nano-sized pandemic virus.

The ubiquitous presence of air pollutants is taxing human health and hampering eco-system all over the globe [1, 2] . Airborne solid/liquid droplets or aerosols, also known as particulate matter (PM), can cause respiratory and cardiovascular diseases leading to cancer and death [3, 4] . The severity of the hazard mainly depends on the aerodynamic diameter of the PM. The particles having aerodynamic diameter ≤ 2.5 μm are defined as PM2.5 while PM10 indicates aerosols of size 2.5-10 μm [5] . Smaller size particles cause higher risk to human health since they can be easily inhaled and penetrate the lungs without any resistance.

Volatile organic compounds (VOCs) represent another type of air pollutants, perhaps more harmful than the visible aerosols [6, 7] . They can be carcinogenic, toxic and hazardous [8] [9] [10] .

Formaldehyde, for instance, is one of the carcinogenic VOCs commonly found indoors and very hazardous even at lower concentrations. NIOSH recommended indoor exposure limit of formaldehyde is 0.019 mg/m 3 for 15 min [11] while it is alarming in US, China and Australia J o u r n a l P r e -p r o o f (>0.1 mg/m 3 ) [12, 13] . Formaldehyde exposures can mainly cause pulmonary function damage and reproduction impairment [14, 15] . Benzene and xylene are commonly used industrial chemicals and their prolonged exposure is hazardous. NIOSH recommended threshold limiting value is 31 mg/m 3 and 434 mg/m 3 for benzene and xylene, respectively [6] . Immediately dangerous to life or health (IDLH) values for formaldehyde, benzene and xylene are 20 ppm, 500 ppm and 900 ppm, respectively [16] . It is believed that the human body will be more susceptible to air pollutants due to unknown bio-physiochemical interactions with the increasing complexity of air pollutants, rapid industrialization and more urbanized lifestyle. Therefore, a dual-function air filter is a critical need for human health.

Multifunctional air filter refers to simultaneous filtration of solid/liquid droplets of various size as well as gaseous VOCs. However, designing multifunctional filters has been challenging since the filtration mechanism of PM and VOCs is entirely different. PM and VOCs vary in size and chemical composition [5, 7] . PM filtration depends on fiber diameter and pore size. The diffusion, interception, straining, electrostatic attraction and gravitational forces are the principles of PM capture [5, 6, 17] . VOC filtration depends on physical and chemical adsorption which requires functional polymer surface [5] .

Air filtration is the first commercially successful application of electrospun nanofibers [5, 6] . Electrospinning is an application of high electrical voltage to a polymer fluid to produce 1D nanosized fibers [5, 18, 19] . It has been a widely accepted technique for producing polymeric nanofibers due to its tuneable fiber morphology, versatility [19] , high specific surface area, compactness and excellent mechanical properties [20] . The synthetic polymers such as polyacrylonitrile, polyamide, polysulfone have been electrospun for air filtration due to their excellent strength and environment stability [5, 21, 22] . However, to use them as an advanced J o u r n a l P r e -p r o o f dual-function air filter, there are limitations like poor surface functionality of synthetic polymers necessary for VOC adsorption. Besides, synthetic polymer degradability after disposal is a serious environmental concern [23] [24] [25] . Synthetic polymers continue to release harmful VOCs even after disposal [26] and recycling [27] . The synthetic polymer also has lethal effects on aquatic and terrestrial ecosystem [28] . Hence, biodegradable and functional polymers can be the better choice for multifunctional air filters.

Gelatin is a low cost and abundantly available protein biopolymer obtained from partial hydrolysis of collagen found in various biomaterials [29] . It has been widely explored in biomedical applications such as tissue engineering, drug delivery and wound healing [30] [31] [32] .

Recently, gelatin nanofiber studied for air filtration where environmental susceptibility of gelatin has been addressed by carbodiimide cross-linking [33, 34] . The cross-linked gelatin nanofibers showed environmental stability, better mechanical properties and comparable filtration performance without significant difference in fiber diameter [35] . Gelatin nanofibers also showed anti-bacterial efficacy [36] . Gelatin can absorb gas pollutants due to its surface functionality. However, VOC adsorption performance of gelatin electrospun nanofibers is not known.

β-Cyclodextrin (β-CD) is a commercially available, low priced cyclic oligosaccharide [37, 38] . It is a non-hygroscopic, torus-shaped crystalline substance isolated from starch digestion [39, 40] . β-CD has seven repeating glucose units linked via α-1,4-glucosidic bonds in a coneshaped structure [41] [42] [43] [44] . It is a non-toxic and biodegradable material [45] . β-CD has been studied for water filtration [46] , air filtration [47, 48] and drug delivery applications [49, 50] due to its reactive nature and a typical cone-shaped cavity structure. Our previous work [47] did show that β-CD and polyacrylonitrile nanofibers improved VOC adsorption. β-CD combination J o u r n a l P r e -p r o o f with gelatin can offer further reactivity [51] [52] [53] along with resolving sustainability and biodegradability issues.

In this paper, gelatin/β-cyclodextrin composite nanofiber mat was prepared using electrospinning for multifunctional air filtration. The effect of various concentrations of β-CD on composite nanofibers was studied using SEM, capillary flow porometry, surface area analyser and FTIR. Air filtration was evaluated for KCl aerosols of size 0.3-5 μm. VOC adsorption was studied for three models VOCs namely formaldehyde, xylene and benzene. The adsorption performance was compared with a commercial face mask.

Gelatin (from porcine skin, Type A) and β-cyclodextrin powder were obtained from Sigma Aldrich, Australia. The solvents, formic acid (98-100%) and ethanol (99.5%) were obtained from Merck, Australia. Xylene (Merck, Australia), benzene (Merck, Australia) and formaldehyde (37% formalin, Chem-supply, Australia) solutions were used to generate respective VOC vapours under controlled conditions (Temperature 20 ± 3°C; humidity 50 ± 2%). All the chemicals were employed as received without any further purification. The control nonwoven fabric (polyester viscose (50:50)) was kindly supplied by Textor Ltd. Australia. The control fabric had a basis weight of 45 g/m², thickness 0.16 mm and pore size 12 μm. The commercial P2 type masks were purchased from the local market in Melbourne, Australia.

Gelatin powder (16% w/w) was dissolved in the formic acid at room temperature. β-CD powder was added in different proportions (10%, 20% and 30% w/w) to the gelatin solution and stirred J o u r n a l P r e -p r o o f until a homogenous solution was obtained. The terminology used to describe the various solutions was G, GC1, GC2 and GC3. G represented only gelatin while GC1, GC2 and GC3

represented the addition of 10%, 20% and 30% β-CD over the weight of gelatin, respectively.

Before electrospinning, the composite solution was centrifuged using a rotor (JA 25.50) at 9000 rpm for 15 min to remove any undissolved particles. The viscosity of solutions was measured using a viscometer (Brookfield DV-II+ Pro) with a spindle number of SC4-21.

The solution was electrospun using a laboratory electrospinning setup [6, 47, 54] . In brief, the installation consists of a rack-mounted DC voltage supply (Spellman SL150), a syringe pump (NE1000 New Era Pump Systems, Inc.) and a metal surfaced drum collector. The electrospinning parameters employed were: 22 kV applied voltage, 0.15 mL/h flow rate and 20 cm distance from the needle (23 gauge) tip to drum surface. The nanofibers were deposited on the collector covered with the control nonwoven fabric. The surface density of gelatin nanoweb (1 g/m 2 ) was obtained using Eqn.1.

(1)

Where, m is basis weight of nanoweb, cp is polymer concentration, ρs is the solution density, rf is feed rate, ts is electrospinning time and ac is collector area (19 cm x 34 cm). After electrospinning, nanofibers were dried overnight at room temperature followed by drying in a vacuum oven for 4 h at 50°C. The electrospinning experiments were conducted at room temperature (23±2°C) and relative humidity of 50±2%.

Nanofibers were sputter-coated with iridium for morphology analysis. The morphology of nanofibers was studied using a field emission scanning electron microscope (FE-SEM) (Zeiss, J o u r n a l P r e -p r o o f Gemini 2 Merlin) at 3 kV acceleration voltage. From FE-SEM images, the fiber diameter was measured using ImageJ software. The pore size of nanofibers was measured using the capillary flow porometer (Porous Materials Inc) by measuring the pressure gradient (Eqn. 2) needed to displace Galwick liquid (Surface tension 15.9 mN.m -1 ) through pore capillaries of nanofiber structure. The average of three nanofiber samples of 13 mm diameter was used to measure pore size and its distribution over the pressure range of 0-30 PSI.

where σ is the surface tension of the wetting liquid (N/m), θ is the contact angle that the wetting liquid forms with the filter and ∆P is the differential pressure (Pa) applied across the filter.

The specific surface area of nanofiber samples was determined using BET surface area analyser (Nova 1200e, Quantachrome Instruments). The values were determined from their adsorption and desorption isotherms of nitrogen at -196°C using a Quantachrome Autosorb-1

volumetric adsorption system. The samples were degassed under vacuum at 40°C for 22 h before analysis. The nanofiber membranes were also characterised using Fourier transform infrared (FTIR) spectroscopy (Thermo Nicolet 6700) in the range of 4000-800 cm -1 . Total 64 number of scans were performed for each sample to generate FTIR spectra. Energy dispersive X-ray (EDX) spectroscopy was done by analysing SEM images with the help of Xmax80 detector and Aztec software platform for determination of elemental composition. Five different areas were averaged to determine the elemental analysis.

The air filtration of nanofiber mats was measured using the experimental set up reported elsewhere [6, 47] . In short, the aerosols of average sizes of 0. (3)

where: n1: Upstream aerosol particle concentration (number); n2: Downstream aerosol particle concentration (number); P1: Upstream absolute air pressure (Pa); P2: Downstream absolute air pressure (Pa).

VOC adsorption performance was measured using a simple laboratory setup reported elsewhere in detail [6, 47, 55] . Briefly, a known quantity of xylene or benzene analyte was injected into a plastic jar (4.5 L) with a specially designed lid. The lid had rubber septa at the top, steel wire with a hook, and a mesh to hold the sample. The analyte was exposed to the sample for 4 h in the airtight jar kept in the conditioned room (20 ± 2°C and 50±3% RH). The sample was then immersed in 15 mL ethanol for 24 h to extract the VOC (xylene or benzene) analyte completely. The concentration of xylene and benzene was determined using UV-Vis spectroscopy at the characteristic absorbance of 268 nm and 255 nm, respectively. Standard calibration curves were obtained for different concentrations of xylene and benzene [6, 47, 55] .

Three readings of VOC adsorption were averaged. For HCHO, UV spectroscopy did not show any unique peak. The residual HCHO was determined using a formaldehydmeter™ (PPM J o u r n a l P r e -p r o o f Technology) and subtracted from the plain reading (empty jar without any sample) to evaluate adsorption performance.

Solution properties Table 1 shows the viscosity of the pure gelatin solution (16% w/w) and the solutions prepared Unlike viscosity, the conductivity results in Table 1 did not show a linear trend. The highest conductivity recorded for GC1 (844 μS/cm). The increase in conductivity can be due to the presence of hydroxyl group of β-CD in GC1 solution with that of G. However, further increasing the concentration β-CD as in case of GC2 and GC3, the conductivity decreased (698 μS/cm and 549 μS/cm, respectively). This result is in line with our previous study [47] where the reduction of conductivity was noticed at higher concentrations of β-CD. The reduction is due to the restricted ionic mobility caused by the high viscosity of the solution containing a high amount of β-CD.

J o u r n a l P r e -p r o o f 

Electrospinning of gelatin (16% w/w) (G) resulted in the average fiber diameter of 130 nm (Fig. 1a) . FE-SEM images in Fig.1b- [56, 57] . Although the viscosity found to dominate over conductivity, the decreased conductivity contributes to the increase of the fiber diameter. Low conductivity reduces the bending instability in the jet which cause to increase the fiber diameter [58] . The nanofiber diameter is found in normal frequency distribution ( Fig. 1 ) in all the combinations from G to GC3. It indicates homogeneity of gelatin solutions after addition of β-CD in different proportions consequently resulting in symmetry around the mean fiber diameters in each case.

Besides fluid characteristics, optimizing the electrospinning parameters has a paramount impact on defect-free composite nanofibers production and its homogenous distribution [59] .

Herein, the optimized parameters (as mentioned in methods) resulted in uniform composite nanofibers of gelatin/β-CD and no phase separation was observed upon storage for several weeks after electrospinning, despite low areal density (1g/m 2 ). Nanofibers are difficult to maintain structural integrity due to their delicacy [60] . Nonwoven porous support preserved the structural integrity of gelatin/β-CD nanofibers during handling, storage, characterisation, and filtration performance measurement. Another interesting observation in FE-SEM images of electrospun gelatin is the frequent occurrence of "web" structures ( Fig. 2) . Web in this context may be referred to densely superimposed and interconnected fibers which are much smaller dimension than nanofibers. The interconnected tiny fibers in the webs were not used for fiber diameter measurement. These webs look like cobwebs but the web fiber diameter is much smaller (< 50 nm) as compared to the nanofiber diameter. Such webs could be useful for air filtration to capture PM2.5 as well as tiny sized virus including coronavirus [61] . Maze et.al [62] simulated that nanofibers made of nm showed the most penetrating particle size of 100-200 nm. Thus, gelatin nanofiber mat is a potential candidate in the preparation of biomaterial based nanofiber mats for air filtration and respiratory protection. However, the frequency of the webs disappeared in GC2 and GC3 which is probably due to the increase in solution viscosity after incorporation of higher amounts of β-CD. Table 2 shows the EDX elemental analysis of gelatin/β-CD composite nanofibers. It can be seen that gelatine nanofiber is composed of 69% carbon (C), 21.7% nitrogen (N) and 8.9%

oxygen (O). The addition of β-CD greatly reduced nitrogen and increased oxygen. The N/C ratio was highly reduced from 0.31 to 0.12 during the conversion of G into GC1. However, the N/C ratio is found comparable for GC1 to GC3, unlike the O/C ratio, which is increased with the β-CD concentration due to the oxygen-rich structure of β-CD [55] . Pore size is an important parameter for air filtration applications. Through pores of small size are desirable for maximum filtration efficiency [5] . Table 3 describes the pore size dimensions of gelatin/β-CD nanofiber mat. The pore size is in the range of 0.97-1.43 µm despite the fiber diameter was much smaller (130-247 nm). This is because small areal density of the nanofiber meshes (1 g/m²) which results in more inter-fiber spaces. The average pore size increases as the β-CD concentration increases. An increase in gelatin nanofiber diameter subsequently leads to an increase in the pore size [63] .

Pore size distribution can influence filtration efficiency and pressure drop [64] . The pore size distribution was found to be normally distributed and shifted towards right from G to GC3 (Fig. 3) . This shift indicates an increase in pore size which is the result of an increase in fiber diameter from G to GC3. The specific surface area depends on fiber diameter. The smaller fiber diameter of G (130 nm) showed the highest surface area (124 m²/g) ( Table 3) . GC3 (247 nm J o u r n a l P r e -p r o o f mean fiber diameter) resulted in the lowest specific surface area (37 m²/g) because the increase in fiber diameter greatly reduces the specific surface area. This reduction can influence the air filtration performance which is discussed in the later section. I, Amide II and Amide III, respectively [65, 66] . Amide A refers to gelatin specific N-H stretching [67] . Amide-I is associated with C=O stretching, Amide II is due to C-N stretch and

Amide III is related to in-plane N-H deformation [68] . Also, small peaks at 1446 cm -¹, 1337 cm -¹ and 1085 cm -¹ were due to symmetric and asymmetric -CH3 bending vibrations [69] and -C-C stretching, respectively [70] . The characteristic peaks for β-CD (Fig. 4b) 

Fig . 5 shows the air filtration performance of gelatin/β-CD nanofiber mats for particle sizes ranging from 0.3 µm to 5 µm at 0.06 m/s face velocity. The filtration efficiency of G, GC1 and GC2 was found to be comparable for 0.3 µm and 5 µm particles (around 97% and 99%, respectively). While GC3 reduced the filtration efficiency (88%) due to the coarse fiber diameter (247 nm) and low surface area (37 m 2 /g) as compared to that of G (nanofiber diameter 130 nm;

surface area 124 m 2 /g). The results infer that β-CD addition up to 20% produces comparable air filtration performance to that of only gelatin nanofibers. The efficiency (97%) of gelatin/β-CD for 0.3 µm particles is slightly lower than the recent report (98%) [36] possibly due to the J o u r n a l P r e -p r o o f smaller basis weight (1 g/m 2 ) and higher average fiber diameter (130 nm) compared to the reported one (2 g/m 2 and 87 nm, respectively). However, the efficiency of gelatin/β-CD nanofibers (97%) is better than a P2 type mask (94%). For particles ≥ 0.7 µm the efficiency is beyond 99%. The high filtration efficiency is due to the effective diffusion and interception mechanism of nanofibers [54, 71] . The quality factor is an overall representation of air filtration performance where the outcome of filtration efficiency and pressure drop combined [5] . It is noteworthy that the quality factor of gelatin-based nanofiber mats is being reported for the first time. It can be seen in [54] . It this work, the maximum quality factor of 0.029/Pa was achieved for GC2 at 1 g/m 2 , which is better than 0.024/Pa as reported earlier [72] and at par (0.028/Pa) as reported recently [47] on polyacrylonitrile nanofiber mats at a similar basis weight of 1 g/m².

Commercial N95 type mask has the filtration efficiency of >95% [73] and pressure drop of 11 mm (108 Pa) [74] . However, the basis weight of these masks is more than 500 g/m 2 which induces thermal stress to wearer [75, 76] . Herein, gelatin/β-CD nanofiber media achieved >95% filtration efficiency at 1 g/m 2 basis weight. The filtration efficiency is comparable to that of the conventional facemask. Moreover, this mat is environmentally friendly and comfortable regarding the weight lightness.

Activated carbon is preferably used in filter media for VOC adsorption due to high surface area (higher than nanofibers) and porous structure [77] . However, it is not effective for solid/liquid aerosols, has poor chemical functionality and short service life [6] . Activated carbon has practical limitations concerning handling and reusability [78] . Since the particles of activated carbon are easily inhalable, proper care, maintenance and training is required while using respirators enabled with activated carbon. No such drawbacks are associated with nanofibers.

The xylene adsorption by a commercial facemask and individual powder samples of gelatin and β-CD was studied for comparison. The powder sample was wrapped in the porous nonwoven fabric which was used to deposit nanofiber mats during electrospinning. As shown in 

Gelatin nanofiber mat showed the highest xylene adsorption (311 mg/g) which is 150 times of the commercial face mask (2 mg/g) and 13 times of gelatin powder form (23 mg/g) (Fig. 7a) .

With increasing levels of β-CD addition GC1 to GC3, xylene adsorption reduced (287-250 mg/g). The results can be linked with the increase in fiber diameter from 130 nm to 247 nm, as the xylene VOC adsorption is influenced by the fiber diameter. The xylene adsorption of gelatin was found much higher than our previous works on PAN/β-CD composite nanofiber mat (201 mg/g) [47] and β-CD cross-linked fabric (11 mg/g) [55] . It is mainly due to gelatin and a multifold increase in the specific surface area of gelatin nanofiber mat. This performance was found much better than adsorbing only 0.04 mg/g xylene by polyurethane/fly ash composite nanofibers reported previously [79] .

Benzene adsorption (Fig. 7b) is found in line with xylene adsorption since they have a similar chemical structure. Gelatin nanofiber mat showed the highest benzene adsorption (279 mg/g) which again can be explained by the smallest fiber diameter (130 nm) and highest surface area. The benzene adsorption of GC1 and GC2 found comparable (around 242 mg/g) since their fiber diameter range is also comparable. GC3 displayed the lowest benzene adsorption (176 mg/g) explained by the larger fiber diameter (247 nm). The adsorption performance of β-CD powder (12.49 mg/g) was slightly higher than the gelatin powder (11.58 mg/g) due to cavities in the structure β-CD. P2 type mask has least benzene adsorption (5.27 mg/g).

Although β-CD can form complex with aromatic xylene and benzene, no significant increase in xylene and benzene adsorption by the composite gelatin/β-CD nanofibers mats (GC1, GC2 and GC3) was observed. The adsorption was found more dependent on fiber diameter and specific surface area than the use of β-CD used in electrospinning. The adsorption of xylene and benzene VOCs was not found material-specific/adsorbent specific, unlike formaldehyde which J o u r n a l P r e -p r o o f may be due to the relative inertness of xylene and benzene. Hence, any nanoscale materials having high surface area would physically adsorb these VOCs. Fig. 7c shows HCHO adsorption performance. It can be seen that the commercial mask has negligible HCHO adsorption (0.002 mg/g) while the nonwoven fabric without nanofibers showed only little (0.02 mg/g) adsorption [55] . β-CD powder has relatively higher HCHO adsorption (0.07 mg/g) than the gelatin powder (0.04 mg/g). When gelatin converted into nanofibers the adsorption increased by ten times (0.38 mg/g). This rise is attributed to the smallest diameter (130 nm), higher surface area (124 m 2 /g) and protein structure of electrospun gelatin fiber. HCHO, being a reactive electrophilic species, reacts with functional groups of gelatin by cross-linking with N-terminal amino acid residue and the side chains of arginine, cysteine, histidine and lysine residues [80] . The cross-linking is induced by primary amines (lysine) forming a stable methylene bridge [81] .

The composite gelatin/β-CD mats (GC1-GC3) further improved the HCHO adsorption (0.75 mg/g), unlike xylene and benzene VOCs. Although GC1, GC2 and GC3 showed comparable HCHO adsorption, there is a clear advantage of using β-CD for better HCHO adsorption than the gelatin only. The increase in HCHO adsorption can be due to host-guest complex formation and weak physical interactions induced by β-CD.

The HCHO adsorption by composite gelatin/β-CD nanofibers mats (0.75 mg/g) is better that by polyacrylonitrile/β-CD nanofibers (0.07 mg/g) [47] and β-CD cross-linked textiles (0.06 mg/g) [55] . The HCHO adsorption values of this work (0.75 mg/g) also higher than the 0.12 mg/mg of the previous report of PAN/β-CD nanofibers [82] . However, it was much less than that of activated carbon fiber (roughly 24 mg/g) [83] . Recently, around 70% HCHO removal efficiency was reported using PVA/soy protein nanofibers [84] and gelatin nanofibers [36] of 4.5 J o u r n a l P r e -p r o o f g/m 2 basis weight. Although a direct comparison cannot be made, relative advantage of lightness can help in designing better multifunctional respiratory filter media.

Gelatin/β-CD composite solutions have been successfully electrospun to produce nanofiber mats with a fiber diameter ranging 130-247 nm. It is found that β-CD addition (10% and 20%) in gelatin electrospinning yielded comparable filtration efficiency (97% for 0.3 μm and ˃ 99% for particles ≥ 0.7 μm), lower pressure drop (148 Pa) and improved quality factor (0.029/Pa) at 1 g/m² basis weight. Gelatin/β-CD composite nanofibers showed excellent adsorption of xylene (287 mg/g), benzene (242 mg/g) and formaldehyde (0.75 mg/g). β-CD is found most beneficial in formaldehyde adsorption while xylene and benzene adsorption is observed to be influenced by the fiber diameter and the specific surface area of nanofibers. The gelatin/β-CD biomaterialbased nanofibers filtered solid/liquid aerosols and gaseous pollutants simultaneously at lower basis weight with low air resistance. The combination of gelatin/β-CD nanofibers with their green nature, excellent dual function filtration, less air resistance and potential to capture tiny viruses make them suitable for respiratory filtration. 

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Identification of formaldehyde-induced modifications in proteins reactions with model peptides

Chemical and physical basics of routine formaldehyde fixation

Functionalization of polyacrylonitrile nanofibers with βcyclodextrin for the capture of formaldehyde

Influence of heat treatment of rayon-based activated carbon fibers on the adsorption of formaldehyde

Soy-protein-based nanofabrics for highly efficient and multifunctional air filtration

No conflict of interest to declare.Declaration of interest: None. All authors state no conflict of interest.