Nanocellulose-Based Materials for Water Treatment: Adsorption, Photocatalytic Degradation, Disinfection, Antifouling, and Nanofiltration

Abstract

Nanocelluloses are promising bio-nano-materials for use as water treatment materials in environmental protection and remediation. Over the past decades, they have been integrated via novel nanoengineering approaches for water treatment processes. This review aims at giving an overview of nanocellulose requirements concerning emerging nanotechnologies of waster treatments and purification, i.e., adsorption, absorption, flocculation, photocatalytic degradation, disinfection, antifouling, ultrafiltration, nanofiltration, and reverse osmosis. Firstly, the nanocellulose synthesis methods (mechanical, physical, chemical, and biological), unique properties (sizes, geometries, and surface chemistry) were presented and their use for capturing and removal of wastewater pollutants was explained. Secondly, different chemical modification approaches surface functionalization (with functional groups, polymers, and nanoparticles) for enhancing the surface chemistry of the nanocellulose for enabling the effective removal of specific pollutants (suspended particles, microorganisms, hazardous metals ions, organic dyes, drugs, pesticides fertilizers, and oils) were highlighted. Thirdly, new fabrication approaches (solution casting, thermal treatment, electrospinning, 3D printing) that integrated nanocelluloses (spherical nanoparticles, nanowhiskers, nanofibers) to produce water treatment materials (individual composite nanoparticles, hydrogels, aerogels, sponges, membranes, and nanopapers) were covered. Finally, the major challenges and future perspectives concerning the applications of nanocellulose based materials in water treatment and purification were highlighted.

Keywords: bacterial cellulose; hydrogels; membranes filtration; nanocrystals; nanofibers; nanoparticles; nanowhiskers; surface functionalization.

Figure 1

Electron microscope micrographs of different types of cellulose nanomaterials: (a) cellulose microfibers (CMFs) [21], © Springer Nature, 2021; (b) Cellulose fibers (CNFs) [22], © Hindawi, 2017; (c) Spherical cellulose nanoparticles (SCNPs) [23], © Elsevier, 2007; (d) Cellulose nanocrystals (CNCs) [24], © MDPI, 2008; (e) cellulose nanofibers (CNFs) [25], © Royal Society of Chemistry, 2009; (f) bacterial cellulose (BC); (g) cellulose nanofibers assembled into a material stronger than spider silk [26], © American Chemical Society, 2018; (h) Electrospun cellulose nanofibers (CNFs) [27], © Elsevier, 2014; (i) Cellulose aerogels [28], © MDPI, 2018.

Figure 2

Heavy metal removal mechanism from water system using nanocelluloses: (a) Ion exchange mechanism which involves the adsorption of hazardous metal ions (Mⁿ⁺) takes the place of other ions (K⁺, Na⁺, H⁺) already associated with the nanocellulose surface; (b) chemical complexation mechanism in which the carboxyl (-COO⁻) and hydroxyl (-OH) groups of the nanocelluloses have specific site interactions with particular hazardous metal ions.

Figure 3

Fabrication of a template structure for carboxymethylated (CM) cellulose nanofibers (CNF) with polyurethane (PU) foam with controlled pore structure, for use as a modular adsorbent of heavy metals (Cd²⁺, Cu²⁺, Pd²⁺) in contaminated water [94], ©Elsevier, 2018.

Figure 4

Highly efficient and selective removal of anionic dyes from water using a composite membrane of cellulose nanofibril (CNF)/chitosan (CS) prepared by de-hydrothermal treatment [125], © Elsevier, 2021.

Figure 5

Cellulose nanofibers (CNF) and carbon nanotubes (CNT) or graphene nanoplate (GnP) hybrid aerogels for the adsorption and removal of cationic and anionic organic dyes [126], ©MDPI, 2020.

Figure 6

Formation of dual super-amphiphilic modified cellulose acetate nanofiber membranes by electrospinning, with highly efficient oil/water separation and excellent antifouling properties, (a) Electrospinning process to prepare cellulose acetate nanofiber membrane; (b) Deacetylation process to form d-CA; (c) Prewetted process to form amphiphilic structure; and (d) super-amphiphilic structure to separate water and oil [163]. ©Elsevier, 2020. CA, cellulose acetate nanofiber; d-CA, dual super-amphiphilic modified cellulose acetate nanofiber.

Figure 7

Surface hydrophobization of bacterial cellulose acetate membranes with trimethylchlorosilane for the efficient removal of plant oil from water [169], ©American Chemical Society (2015). BCA—bacterial cellulose acetate; TMCS—trimethylchlorosilane; HBCA—hydrophobic BCA.

Figure 8

Flocculation mechanism of anionic nanocellulose to remove pollutants from water. (A) Binding and flocculation of cationic pollutants, and (B) visual observation of flocculation efficiency [10], ©Springer, 2017.

Figure 9

(a) Mechanism for photocatalytic treatment and degradation of an organic pollutant (methylene blue) in wastewater using graphene oxide (GO)/cellulose/TiO₂ nanocomposites [190], ©Royal Society of Chemistry, 2020. (b) Deposition of TiO₂ nanotubes and AgO_x nanoparticles (NPs) onto cellulose nanofibers (CNFs) for improved photocatalytic cleaning of wastewater [191], ©Springer, 2019.

Figure 10

Enhanced performance of nanocellulose filter membranes for forwarding osmosis through modification of the nanocellulose material surface by coating with a polymer (e.g., polyamide active layer), and by nanoparticle (NP) deposition (e.g., Ag, Pt) [220], ©American Chemical Society, 2017. TOC, total organic carbon.

Figure 11

Electrospinning with suitable solvent systems was used to fabricate hybrid nanocellulose fibers with solid or hollow core and deposition of Fe(OH)₃/cellulose nanoparticles: (a) Schematic representation of the electrospinning process for nanofiber fabrication; (b,c) Schematic representation of the hollow fibers as membranes for diffusion and regeneration, respectively; (d–f) Photographs of the Fe(OH)₃@Cellulose HNFs membranes and the dead-end filtration device, [223] ©American Chemical Society, 2017.

Figure 12

Control of the cellulose nanofibrous composite membrane structure by in-situ synthesis of zeolitic imidazolate framework-8 (ZIF-8) at cellulose nanofibers (CNF) for the selective removal of cationic dyes [235], © Elsevier, 2019.

Figure 13

Schematic description of (A) anisotropic carboxylated cellulose nanofiber (CCNF)-dopamine (DA)/silver nanoparticle (Ag NPs) composite formation using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS); and (B) antibacterial activity of the CCNF-DA/Ag NP composite [258]. Reproduced with permission from Nguyen et al. (2016) © MDPI [Open access].