Membranes and filters are essential devices, both in the laboratory for separation of media, solvent recovery, organic solvent and water filtration purposes, and in industrial scale applications, such as the removal of industrial pollutants, e.g. heavy metal ions, from water.
Carbohydrate Polymers 253 (2021) 117273 Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol Fungal chitin-glucan nanopapers with heavy metal adsorption properties for ultrafiltration of organic solvents and water Neptun Yousefi a, Mitchell Jones a, b, Alexander Bismarck a, c, d, Andreas Mautner a, * a Institute of Materials Chemistry and Research, Polymer and Composite Engineering (PaCE) Group, Faculty of Chemistry, University of Vienna, Wă ahringer Straòe 42, 1090 Vienna, Austria b School of Engineering, RMIT University, Bundoora East Campus, PO Box 71, Bundoora 3083, VIC, Australia c Department of Mechanical Engineering, Faculty of Engineering and the Built Environment, University of Johannesburg, South Africa d Department of Chemical Engineering, Imperial College London, South Kensington Campus, London, SW7 2AZ, UK A R T I C L E I N F O A B S T R A C T Keywords: Fungal chitin Organic solvent filtration Water treatment Copper Cellulose Membranes and filters are essential devices, both in the laboratory for separation of media, solvent recovery, organic solvent and water filtration purposes, and in industrial scale applications, such as the removal of in dustrial pollutants, e.g heavy metal ions, from water Due to their solvent stability, biologically sourced and renewable membrane or filter materials, such as cellulose or chitin, provide a low-cost, sustainable alternative to synthetic materials for organic solvent filtration and water treatment Here, we investigated the potential of fungal chitin nanopapers derived from A bisporus (common white-button mushrooms) as ultrafiltration mem branes for organic solvents and aqueous solutions and hybrid chitin-cellulose microfibril papers as high per meance adsorptive filters Fungal chitin constitutes a renewable, easily isolated, and abundant alternative to crustacean chitin It can be fashioned into solvent stable nanopapers with pore sizes of 10− 12 nm, as determined by molecular weight cut-off and rejection of gold nanoparticles, that exhibit high organic solvent permeance, making them a valuable material for organic solvent filtration applications Addition of cellulose fibres to pro duce chitin-cellulose hybrid papers extended membrane functionality to water treatment applications, with considerable static and dynamic copper ion adsorption capacities and high permeances that outperformed other biologically derived membranes, while being simpler to produce, naturally porous, and not requiring cross linking The simple nanopaper production process coupled with the remarkable filtration properties of the papers for both organic solvent filtration and water treatment applications designates them an environmentally benign alternative to traditional membrane and filter materials Introduction Filtration membranes and adsorbent filters play a vital role across a range of filtration applications, from ultrafiltration (UF), nanofiltration (NF), and solvent recovery to the removal of heavy metals from water, making it safe to drink (Mautner et al., 2014; Ng, Mohammad, Leo, & Hilal, 2013) Traditional synthetic membranes are frequently used in academic or commercial organic solvent or aqueous UF and NF, rejecting pollutants in the nm scale, or see service in removing harmful industrial effluents, e.g heavy metal ions, from waste and fresh water sources in industrialised regions (Marchetti, Jimenez Solomon, Szekely, & Livingston, 2014; Mohammad et al., 2015; Vandezande, Gevers, & Vankelecom, 2008) However, despite their efficiency in these processes, synthetic membranes, most frequently produced from poly mers, such as polysulfone, polyethylene, polytetrafluoroethylene, or polypropylene, commonly experience problems related to their hydro phobicity, resulting in biofouling (Baker & Dudley, 1998; Mansouri, Harrisson, & Chen, 2010) Additionally, synthetic membranes manu factured for applications such as organic solvent filtration typically require complex polymeric structures exhibiting solvent stability Consequently, these membranes are usually expensive and often suffer from low permeance (Marchetti et al., 2014) Tackling the disadvantages associated with these synthetic materials, biologically derived membranes and filters based on cellulose, chitosan, or chitin have experienced increased academic interest due to their low costs, and utilisation of abundant, sustainable resources (Shaheen, Eissa, * Corresponding author E-mail address: andreas.mautner@univie.ac.at (A Mautner) https://doi.org/10.1016/j.carbpol.2020.117273 Received 17 February 2020; Received in revised form 14 October 2020; Accepted 15 October 2020 Available online 27 October 2020 0144-8617/© 2020 The Author(s) Published by Elsevier Ltd This is an open (http://creativecommons.org/licenses/by-nc-nd/4.0/) access article under the CC BY-NC-ND license N Yousefi et al Carbohydrate Polymers 253 (2021) 117273 Ghanem, El-Din, & Al Anany, 2013) In particular nano-sized fibres of these biopolymers constitute a promising approach to size-exclusion filtration in both the NF and UF range (Gustafsson et al., 2019; Janesch et al., 2020; Liu, Zhu, & Mathew, 2019; Manukyan, Padova, & Mihranyan, 2019; Mautner, 2020; Metreveli et al., 2014), coupled with excellent solvent stability for organic solvent filtration in the case of nanocellulose (Mautner et al., 2014) Furthermore, chitin, and its deacetylated derivative chitosan, have received significant attention due to their high affinity toward metal ions, resulting from their many free hydroxyl and acetamide groups (chitin) or amine groups (chitosan), making these renewable sorbents particularly effective for water treat ment (Dragan & Dinu, 2020; Ghaee, Shariaty-Niassar, Barzin, & Mat suura, 2010; Khalil, Elhusseiny, El-dissouky, & Ibrahim, 2020; Preethi, Prabhu, & Meenakshi, 2017; Rostamian, Firouzzare, & Irandoust, 2019; Shaheen et al., 2013; Vold, Vårum, Guibal, & Smidsrød, 2003) Chitin can be readily sourced from the environment, where it occurs as an abundant linear macromolecule in the exoskeleton of arthropods (Pau lino, Santos, & Nozaki, 2008; Rostamian et al., 2019) and fungal cell walls, in which it occurs as native nano-sized material, well suited to nanopaper preparation with no requirement for high-energy mechanical disintegration (Nawawi, Lee, Kontturi, Bismarck, & Mautner, 2020; Zhang, Zeng, & Cheng, 2016) These natural materials are ecologically beneficial compared with traditional membrane manufacturing pro cesses, in particular for organic solvent filtration (Honda, Miyata, & Iwahori, 2002), while also offering adsorption capacities competitive with or even higher than traditional (synthetic) sorbent materials Chitin and chitosan are, by definition, distinguished from each other only by solubility differences in various media (Pillai, Paul, & Sharma, 2009) Solvent stable filtration membranes are subsequently preferen tially manufactured using chitin rather than chitosan The use of chitin as opposed to chitosan also accelerates nanopaper production since time-consuming deacetylation procedures are not required Membranes from animal-derived chitin are usually prepared by film casting methods, since simple papermaking utilising chitin fibrils extracted from this source results in papers with poor mechanical properties (Nawawi, Jones et al., 2019) due to the lack of glucan covalently bound to chitin macromolecules, which would otherwise act as a matrix and facilitate film formation properties (King & Watling, 1997; Nawawi, Lee, Kontturi, Murphy, & Bismarck, 2019, 2020) Crustacean chitin is also dependent on seasonal and regional variation and requires harsh acid and alkaline treatments for purification and demineralisation, as well as high-energy defibrillation in case that nanofibrils are desired (Di Mario, Rapana, Tomati, & Galli, 2008; Hassainia, Satha, & Boufi, 2018) In contrast, chitin derived from fungal cell walls constitutes a native ar chitecture of nanofibrils that are easily isolated using low-energy me chanical disintegration (Nawawi, Jones et al., 2019) In this natural composite, glucan acts as a flexible matrix with chitin fibrils responsible for strength This enables the preparation of strong and stiff nanopapers from fungal chitin nanofibrils (FChNF) FChNF nanopapers should subsequently be ideal candidates for membrane and filtration applica tions in both organic and aqueous environments due to their native nanoscale structure, lacking in crustacean chitin, and their higher sol vent stability compared to chitosan Agaricus bisporus (white button mushroom) is an edible mushroom that is not only nutritious but also a functional food due to its free radical scavenging and antioxidant activities (Guan, Fan, & Yan, 2013; Lin et al., 2017; Lindequist, Niedermeyer, & Jülich, 2005) It primarily comprises a chitin, glucan, and protein-based cell wall, non-structural polysaccharides, and soluble proteins (Hammond, 1979) with a distinct odour that is ascribed to flavour volatiles such as 8-carbon atom compounds (Noble, Dobrovin-Pennington, Hobbs, Pederby, & Rodger, 2009), e.g 1-octen-3-ol (Dong, Zhang, Lu, Sun, & Xu, 2012) Additional secondary compounds also have the potential to promote human health, with cytostatic, antimutagenic, and genoprotective activity reported for A bisporus, resulting from the presence of compounds such as lectins and the enzyme tyrosinase (Lindequist et al., 2005; Shi, James, Benzie, & Buswell, 2004; Yu, Fernig, Smith, Milton, & Rhodes, 1993) Large-scale production of A bisporus also makes it abundant and relatively stable in composition and properties and subsequently an ideal model system for investigation of fungal chitin-glucan nanofibrils and products We utilised native nano-sized chitin-glucan fibrils and investigated the potential of FChNF nanopapers derived from A bisporus for ultra filtration of organic solvents, e.g ethanol and tetrahydrofuran, and water with additional investigation into the removal of heavy metal ions, such as copper, from aqueous solution also performed A mild alkaline treatment was utilised for extraction of FChNF Nanopapers of various grammages were then prepared from this FChNF extract The physico-chemical properties of these nanopapers were characterised in addition to the permeance of both organic solvents and water and the nanopaper pore size was characterised by the molecular weight cut-off Hybrid papers comprising varying quantities of cellulose sludge fibres and FChNF were also trialled in order to increase the porosity and thus permeance of the filters Materials and methods 2.1 Materials Common white button mushrooms were purchased from a local su permarket (origin: B Fungi Kft., Ocsa, Hungary) Shrimp shell chitin flakes (Sigma-Aldrich, C9213, practical grade) were used for reference purposes NaOH (Sigma), NH3 solution (25 %, analytical grade, SigmaAldrich), ethylenediaminetetraacetic acid disodium salt dihydrate (EDTA) (0.1 M, analytical grade, Roth), murexide (Fluka), NH4Cl (Roth), and Cu(NO3)2⋅6 H2O (Honeywell Fluka) were used for the extraction of FChNF and complexometric titration of copper ions For carbohydrate analysis, Sugar Recovery Standards (SRS) were prepared from D-(+)-xylose (Merck 108689), D-(+)-glucosamine hydrochloride (Sigma-Aldrich G4875), L-(+)-rhamnose (Merck R3875), L-(+)-arabi nose (Merck 101492), D-(+)-mannose (Merck 4440), D-(+)-galactose (Merck 3455), and D-(+)-glucose (VWR 10117 HV) Deionised water, ethanol (Sigma-Aldrich), and tetrahydrofuran (THF, 98 %, Fisher Chemicals) were used for permeance and solvent stability tests Acetone (Sigma-Aldrich) was used to test solvent stability Polyethylene glycol (PEG) standards with molecular weights (Mw) of 2, 20, and 50 kDa (Polymer Laboratories) and polystyrene (PS) standards with 2.5, 20, and 50 kDa (Fluka) were used to determine the molecular weight cut-off (MWCO) Cellulose sludge microfibres, with a cellulose and hemicellu lose content of 95 % and 4.75 %, respectively, a charge content of approx 0.04 mmol g− 1, and diameters of 5–20 μm (Mautner et al., ă, Sweden) 10 nm 2015) were kindly provided by Processum AB (Domsjo gold nanoparticles (OD 1, stabilised suspension in citrate puffer) were purchased from Sigma-Aldrich All chemicals were used as received Deionised water was used for all experiments except for adsorption ex periments for which Type Milli-Q® ultrapure water was used 2.2 FChNF extraction and nanopaper preparation The extraction of fungal chitin nanofibrils (FChNF) and preparation of FChNF nanopapers followed the protocol described earlier by Nawawi, Lee et al (2019, 2020) Briefly, A bisporus mushrooms were soaked and washed in water to remove dirt and other impurities and blended (JB 3060, Braun) The slurry (1 % w/v) thus prepared was then heated to 85 ◦ C for 30 min, cooled, and centrifuged at 7000 rpm for 15 The supernatant was discarded, and the precipitate resuspended in aqueous NaOH solution (1 mol L− 1) at 65 ◦ C for h The suspension was cooled and neutralised (pH 7) by repeated centrifugation and re-dispersion of the precipitate in water, yielding FChNF extract Nanopapers were produced from FChNF extract by suspending pre-determined amounts of FChNF extract in water followed by me chanical blending (JB 3060, Braun) These suspensions were then vac uum filtered, and the filter cakes cold pressed for between blotting N Yousefi et al Carbohydrate Polymers 253 (2021) 117273 papers to remove excess water Two blotting paper lined metal plates and a kg mass were then utilised to press this sandwich, which was oven dried for h at 120 ◦ C Nanopaper grammages ranged from 10 to 110 g m− mM KCl electrolyte solution was pumped through the cell at pressures steadily increased to 300 mbar and the pH controlled by titrating 0.05 mol L− KOH and 0.05 mol L− HCl, respectively, into the elec trolyte solution The ζ-potential was determined from the streaming current 2.3 FChNF + cellulose hybrid filter preparation 2.7 Water permeance, pore size, and solvent stability of nanopapers Hybrid filters comprising FChNF and cellulose microfibres were produced as has been described earlier by Janesch et al (2020) Briefly, 50 g m− (gsm) nanopapers in weight ratios of 80:20, 60:40, 50:50, 40:60, and 20:80 were prepared using a 0.1 wt.% dispersion of cellulose microfibres (0.08 %) formed by mixing 1.0 g of cellulose sludge microfibres (water content 50 %) with 270 mL of water This dispersion was blended to achieve a homogenous suspension before the FChNF extract was added, the desired consistency set, and blending continued for an additional The FChNF + cellulose hybrid papers were then pressed and oven dried as previously described The permeance of the nanopapers was determined in analogy to the procedure described earlier by Mautner et al (2014) by passing water, ethanol, and tetrahydrofuran, respectively, through the samples in a dead-end cell with an effective filtration diameter of 43 mm (Sterlitech HP4750) Nanopaper discs (49 mm diameter) were placed on a sintered stainless-steel support structure and water or organic solvents, respec tively, passed through them using a nitrogen head pressure of bar and bar for hybrid papers, respectively The permeance was in turn calculated from the volume of liquid passed through the nanopaper per unit time, unit area, and unit pressure (L h− m− MPa− 1) The molecular weight cut-off (MWCO) (See Toh, Loh, Li, Bismarck, & Livingston, 2007) of the nanopapers was determined using three PEG standards (2, 20, 50 kDa) dissolved in ultrapure water in equal con centrations, with a total concentration of g L− Three PS standards (2.5, 20, 50 kDa) were also used, dissolved in tetrahydrofuran with a total concentration of 1.5 g L− Permeance tests were initially per formed as described above and the permeate fractions analysed by gel permeation chromatography for PS in THF (Waters 515 HPLC pump, Waters 2410 RI detector) and PEG in aqueous solution (Viscotek GPCmax VE2001, VE3580 RI detector) Similarly, 20 mL of a suspension (diluted with deionized water in a ratio of 1:10) of 10 nm gold nano particles was passed through CG nanopaper and the reduction in the intensity of the red colour analysed by UV–vis spectroscopy (Agilent 8453) with relative concentrations calculated from the absorbance at a wavelength of 520 nm (Janesch et al., 2020) The solvent stability of the nanopapers was tested in acetone, deionised water, ethanol, and tetrahydrofuran Nanopaper specimens, ~16 mg in mass, were placed in a small glass flask and submerged in 50 mL of each respective solvent The flask was then sealed with par afilm and left for weeks, after which time the solvent was removed and the nanopapers weighed again Solvent stability was assessed as weight loss (WL) based on the mass difference (Δm) between the initial mass (m0) and the final mass after weeks soaking in the respective solvent (m5w) 2.4 Analysis of the molecular structure of the FChNF extracts The molecular structure of dried extracts was assessed by Attenuated Total Reflection-Fourier-transform-infrared (ATR-FT-IR) spectroscopy across the full accessible range from 4000 to 400 cm− (Carry 630 FT-IR, Agilent) with a single reflection diamond ATR-module and KBr optics (beam splitter) Three spectra from different regions of each sample were recorded to verify homogeneity Carbon, hydrogen, nitrogen, and oxygen elemental analysis was performed with mg samples in dupli cate using an elemental analyser (EA 1108 CHNS-O, Carlo Erba) High performance anion exchange chromatography (HPAEC) was performed to analyse the sugar composition of the carbohydrates as described earlier by Janesch et al (2020) Briefly, freeze-dried samples and SRS were dispersed in conc H2SO4, subsequently diluted with water and placed in an autoclave The acid hydrolysate was analysed using HPAEC on a Dionex ICS3000 chromatograph equipped with a CarboPac PA20 column 2.5 Morphology and physical properties of the nanopapers Nanopaper surface morphology was examined by Scanning Electron Microscopy (SEM) using a Zeiss Supra 55 V P Scanning Electron Mi croscope Nanopapers were initially coated (Leica EM SCD 050) with 10 nm of gold before being imaged at an accelerating voltage of kV Fibril diameters were analysed for 10 replicate measurements using the Fiji distribution of ImageJ (version 1.51a) The nanopaper skeletal density ρskeletal was determined by helium gas displacement pycnometry (Micromeritics AccuPyc II 1340) with a chamber volume of cm3 The nanopaper grammage G (Eq 1), mass m, thickness d, envelope density ρenvelope (Eq 2), and porosity Φ (Eq 3) of the nanopapers were determined following the procedure established earlier by Janesch et al (2020) G (g m− ) = m (g) ( Φ (%) = G (kg m− ) d (m) (2) ρenvelope (kg m− ) ∙100 ρskeletal (kg m− ) (4) Static adsorption of Cu2+ ions on FChNF was analysed with Cu(NO3)2 solutions as earlier described by Janesch et al (2020) Suspensions of the FChNF extracts (50 mg aliquots) were allowed various periods of interaction (1, 3, 20, 30, and 60 min) with several concentrations of Cu2+ ions (0.2, 0.5, 1.0, 5.0, and 10.0 mM) before being filtered The concentration of copper in the filtrate (c) was determined by com plexometric titration with EDTA Briefly, mg of NH4Cl and 12 drops (~0.6 mL) of NH3 (25 %) were added to the test samples to attain a pH of 10 Titrations were completed with mM (molar concentration) EDTA (cEDTA) and mg of murexide used as an indicator of the transition point, a colour change of yellow-orange to pink Concentrations of the filtrate were then related to those of a reference sample that had not been exposed to FChNF This relation enabled calculation of the quantity of Cu2+ ions adsorbed on FChNF (q) c was plotted with respect to q and the Freundlich (1906) and Langmuir (1918) equations (Eqs and 6) applied to model static adsorption isotherms for each contact time ) 1− Δm (g) m0 (g) − m5w (g) ∙100 = ∙100 m0 (g) m0 (g) 2.8 Adsorption properties of FChNF and papers (1) π∙r2 (m2 ) ρenvelope (kg m− ) = WL (wt%) = (3) 2.6 Surface properties of the nanopapers The surface charge as expressed by the ζ-potential of the nanopapers was analysed with an electrokinetic analyser (Anton Paar SurPASS, Graz, Austria) as a function of pH in an adjustable gap cell (100 μm) N Yousefi et al q= Carbohydrate Polymers 253 (2021) 117273 qm c KL + c influence of inherent biological variation during growth as commonly found in natural products (Nawawi, Jones et al., 2019) The N content in fungal biomass corresponds with the secondary amide group of chitin, located in the fungal cell wall, with a lower N content indicating a smaller chitin fraction in the sample (Jones et al., 2019; Nawawi, Lee et al., 2019) The lower N content of FChNF compared to crustacean chitin was primarily the result of the significant glucan fraction present, which is covalently bonded to the chitin and was not removed during the mild alkaline extraction treatment (Nawawi, Jones et al., 2019) However, the A bisporus mushrooms did have significantly higher N contents than is typical for mycelial biomass, making them a better source of fungal chitin than mycelium (0.3–1.9 wt %) (Jones et al., 2019) From the N content the ratio between chitin and glucan could be calculated to be 59:41, which is in good agreement with previous studies (Liu et al., 2013; Nawawi, Lee et al., 2019) This was also confirmed by sugar analysis, which gave a glucosamine to glucose ratio of 57:43 The presence of chitin in FChNF extracted from A bisporus mush room was also evident in ATR-FT-IR spectra (Fig 1); the -NH stretching band was present at 3276 cm− and an − OH band at 3434 cm− in addition to − CH bands at 2911 cm− and 2841 cm− as well as a C–O–C band at 1029 cm− provided evidence of a carbohydrate backbone attributable to both the glucan and chitin polymer structure The chitin structure itself was verified by an amide I band associated – O stretching at 1628 cm− in addition to amide II and III bands with C– resulting from -NH deformation at 1560 cm− and 1315 cm− 1, respec tively (Janesch et al., 2020; Nawawi, Lee et al., 2019, 2020) The amide III band confirmed the presence of a secondary amide, indicating that the extracted FChNF primarily contained chitin as opposed to chitosan, which has a primary amine group resulting from the deacetylation of chitin in harsh alkaline conditions (Sikorski, Hori, & Wada, 2009) Compared to shrimp shell chitin, FChNF exhibited higher relative absorbance of the carbohydrate backbone in relation to the amide peaks supporting the presence of glucan No significant differences were visible in the spectra of the FChNF extracts based on the mushroom constituents analysed (cap, stalk, or whole mushroom) Subsequently, mushroom components were not separated and the FChNF gels pro duced from whole mushrooms (5) with qm being the maximum adsorption amount per unit mass of adsorbent in order to form a complete monolayer coverage on the sur face and KL the Langmuir constant (6) q = KF cn KF is the adsorption coefficient and n the Freundlich parameter The Gibbs Free Energy of adsorption (ΔG0) was calculated according to Eq (7) ΔG0 = − RT ln(KL ) Dynamic adsorption experiments for hybrid papers were performed using discs (diameter =49 mm) in a dead-end cell (Sterlitech HP4750) A total of L of a mM copper solution was deposited onto the disc and a nitrogen head pressure of bar applied An aliquot of each permeate fraction (Vfraction) was diluted with 50 mL ultrapure water and the concentration of each permeate fraction analysed by complexometric titration as described above The final concentration of Cu2+ ions was then calculated using Eq 8, based on the titration (VEDTA) and aliquot (Valiquot) volumes and assuming that one single Cu2+ ion is complexed by one EDTA molecule The mass of adsorbed Cu2+ ions was in turn calculated based on the atomic weight (M) of copper (63.546 g mol− 1, Eq 9) and the adsorption as a function of mass per unit area (qA, mg m− 2) for the effective filtration area of 1460 mm2 (Eq 10) The adsorption capacity (q, mg g− 1) of Cu2+ was finally calculated from qA and G (Eq 11) c(Cu2+ ) (mmol L-1 ) = cEDTA (mmol L-1 )∙VEDTA (L) Valiquote (L) (8) (9) m (mg) = c (mmol L-1 )∙M (mg mmol-1 )∙Vfraction (L) qA (mg m-2 ) = m (mg) A (m2 ) (10) q (mg m-2 ) q (mg g-1 ) = A G (g m-2 ) (11) Results and discussion 3.2 Physical properties of the FChNF and FChNF-cellulose hybrid papers 3.1 Chemical and elemental analysis of FChNF Nanopapers prepared from FChNF had similar envelope densities (940− 1140 kg m− 3) irrespective of grammage and were similar in density (1090− 1210 kg m− 3) to commercial crustacean chitin (Mushi, Elemental analysis (Table 1) of FChNF extracted from whole A bisporus mushrooms (yield 12 g kg− 1) resulted in a nitrogen content of 3.8 wt.%, which is significantly lower than that of commercial chitin derived from crustaceans (6.5 wt.%) but slightly higher than previously published data for A bisporus mushrooms (3.0–3.4 wt.% (Janesch et al., 2020; Nawawi, Lee et al., 2019)) The lower N content of FChNF compared to crustacean chitin indicates the presence of a second phase within the nanofibres, glucan Slightly higher N contents of about 4.5 wt.% were determined for FChNF extracted from cap and stalk constituent alone, prepared from different batches of mushrooms These minor variations in elemental composition were likely due to the Table C, H, N, O, and S elemental composition (wt.% of total mass) of alkaline treated FChNF derived from whole A bisporus mushrooms compared to commercial chitin Sample A bisporus mushroom Commercial chitin* * Elemental composition (wt.% of total mass) C H N O S 43.32 44.64 6.58 7.29 3.84 6.49 46.07 39.61 100 The average pore size of FChNF nanopapers was determined using PEG of various molecular weights dissolved in water (Fig 5) (See Toh h− 3.4 Adsorption of copper ions on FChNF and papers Heavy metal ions, such as copper (Cu2+), readily adsorb on chitin ´lez-D´ (Gonza avila & Millero, 1990) making it a useful natural material N Yousefi et al Carbohydrate Polymers 253 (2021) 117273 Fig (left) Water, ethanol, and tetrahydrofuran (THF) permeance at various grammages for FChNF nanopapers and (right) water permeance of 50 g m− papers comprising cellulose microfibres and FChNF at various ratios The error (< 2%) is too small to be visible in the graphs hybrid Fig Molecular weight cut-off (MWCO) of FChNF nanopapers for (a) PEG in aqueous solution and (b) PS in THF MWCO relates to the molecular weight of a solute which is 90 % retained by a membrane Fig Langmuir and Freundlich isotherms for copper ion (Cu2+) adsorption on FChNF after for water treatment Static adsorption tests were performed to determine the effectiveness of FChNF in removing copper ions from water, with Langmuir and Freundlich isotherms used to model adsorption behaviour (Fig 6, Table 3) The Langmuir isotherm proved a more accurate sorp tion model than the Freundlich isotherm with R2 values of 0.983− 0.997 compared to 0.70− 0.84, respectively The suitability of this monolayer sorption model for heavy metal adsorption on FChNF has also been supported by several other studies (Cao, Pan, Shi, & Yu, 2018; Liu et al., 2013; Tang et al., 2011), with the Langmuir constants calculated similar in value to those of literature in which chitin was utilised as a natural absorbent The maximum adsorption capacity (qm) of the FChNF ranged from 20.1–43.4 mg g− 1, with a maximum value reached after 20 exposure The dynamic adsorption capacities of hybrid papers, comprising FChNF and cellulose microfibres, were assessed by filtration tests Hybrid papers comprising 20 wt.% FChNF and 80 wt.% cellulose exhibited considerable dynamic adsorption properties, with an Table Langmuir and Freundlich isotherm parameters for copper ion (Cu2+) adsorption on FChNF over a period of up to 60 Langmuir Freundlich Sample KL (L mg− 1) qm (mg g− 1) ΔG0 (kJ mol− 1) Cu1min Cu3min Cu20min Cu30min Cu60min 0.16 0.11 0.02 0.05 0.21 20.1 24.1 43.4 35.1 33.1 − − − − − 12.5 11.7 7.7 9.6 13.3 R2 KF (mg g− 1) nF R2 0.983 0.997 0.986 0.989 0.988 7.9 8.9 5.4 7.1 8.0 0.16 0.17 0.34 0.27 0.26 0.79 0.82 0.84 0.70 0.68 adsorption per unit area of 805 mg m− and overall dynamic adsorption capacity of 81 mg g− Adsorption levelled off at a filtration volume of 400 mL and the nanopaper reached saturation at a filtration volume of 700 mL (Fig 7), with these volumes resulting from the low membrane N Yousefi et al Carbohydrate Polymers 253 (2021) 117273 FChNF nanopapers had molecular weight cut-offs associated with a pore size of 10− 12 nm, as also confirmed by rejection of 10 nm diameter gold nanoparticles This characterises them as tight ultrafiltration mem branes, which when coupled with their high organic solvent permeance and stability makes them a valuable alternative to traditional mem branes, particularly for organic solvent filtration FChNF/cellulose hybrid papers exhibited significant dynamic Cu2+ adsorption capacities, outperforming membranes produced by solution casting and crosslinked chitosan beads, while being simpler to produce, naturally porous, and not requiring crosslinking The remarkable filtration properties of these low-cost and sustainable filters across both organic solvent filtration and water treatment applications, coupled with their simple manufacturing process enables their use as renewable alternatives to synthetic filters, which could help to reduce the ecological impact associated with traditional membranes and their manufacturing processes Fig Copper ion (Cu2+) adsorption capacity (mg m− 2) with respect to filtration volume (V, mL) for FChNF and hybrid papers comprising 80 wt.% cellulose and 20 wt.% FChNF CRediT authorship contribution statement Neptun Yousefi: Conceptualization, Methodology, Investigation, Validation, Writing - review & editing Mitchell Jones: Conceptuali zation, Visualization, Writing - original draft, Funding acquisition Alexander Bismarck: Conceptualization, Methodology, Validation, Writing - review & editing, Supervision, Project administration, Funding acquisition Andreas Mautner: Conceptualization, Methodology, Investigation, Visualization, Validation, Writing - review & editing, Supervision area (0.0014 m ) used in these tests and scaling with membrane area The overall dynamic adsorption capacities of the FChNF-cellulose hybrid papers outperformed other renewable heavy metal adsorption membranes coated with an active layer of cellulose nanocrystals, which had adsorption capacities of 33 mg g− (Karim, Claudpierre, Grahn, Oksman, & Mathew, 2016) but were lower than TEMPO-oxidised cel lulose membranes (300 mg g− 1) (Karim, Hakalahti, Tammelin, & Mathew, 2017) It should, however, be noted that the TEMPO-oxidised membranes only utilised a very shallow surface cellulose modification resulting in their high adsorption capacity per unit mass of the thin top layer adsorption agent The FChNF-cellulose hybrids also performed remarkably better than chitosan (films), which are also used for water treatment due to their high affinity for heavy metal ions, such as copper (Cu2+) (Babel & Kurniawan, 2003; Crini & Badot, 2008; Guibal, 2004; Kumar, 2000; Varma, Deshpande, & Kennedy, 2004) Examples of comparable chitosan membranes include membranes produced by so lution casting of chitosan from acetic acid followed by crosslinking with glutaraldehyde to enhance their stability (47 mg g− 1) (Ghaee et al., 2010), formaldehyde crosslinked modified chitosan–thioglyceraldehyde Schiff’s base (76 mg g− 1) (Monier, 2012), and crosslinked chitosan beads (46− 81 mg g− 1) (Ngah, Endud, & Mayanar, 2002), although chitosan membranes produced via thermally induced phase separation did exhibit a higher dynamic adsorption capacity (163 mg g− 1) (Qin et al., 2017) This demonstrated the suitability of FChNF hybrid papers for water treatment applications without resorting to the use of chitosan and thus constitutes a simpler, cheaper manufacturing process Both the FChNF nanopapers and FChNF-cellulose hybrid papers produced in this study also have several advantages over other natural and traditional membranes, such as simple production, not requiring cross-linking (Marques, Chagas, Fonseca, & Pereira, 2016), or modification (Saheb jamee, Soltanieh, Mousavi, & Heydarinasab, 2019), and being inher ently nanofibrillated, facilitating preparation of porous networks with nm pores Acknowledgements The authors acknowledge Johannes Theiner (Mikroanalytisches Laboratorium, Faculty of Chemistry, University of Vienna) for elemental analysis as well as Beatrice Giaier for support with adsorption studies We also thank Prof Eero Kontturi (Aalto University) for carbohydrate analysis University of Vienna is acknowledged for 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organic solvent and water filtration... production of A bisporus also makes it abundant and relatively stable in composition and properties and subsequently an ideal model system for investigation of fungal chitin-glucan nanofibrils and products