Surface modification of bacterial cellulose aerogels' web-like skeleton for oil/water separation

Porous Aerogels and Adsorption of Pollutants from Water and Air: A Review

Aerogels are open, three-dimensional, porous materials characterized by outstanding properties, such as low density, high porosity, and high surface area. They have been used in various fields as adsorbents, catalysts, materials for thermal insulation, or matrices for drug delivery. Aerogels have been successfully used for environmental applications to eliminate toxic and harmful substances-such as metal ions or organic dyes-contained in wastewater, and pollutants-including aromatic or oxygenated volatile organic compounds (VOCs)-contained in the air. This updated review on the use of different aerogels-for instance, graphene oxide-, cellulose-, chitosan-, and silica-based aerogels-provides information on their various applications in removing pollutants, the results obtained, and potential future developments.

Study on the Adsorption Properties of Graphene Oxide/Laponite RD/Chitosan Composites

A novel Graphene oxide/Laponite RD/Chitosan ternary composite was synthesized by sol-gel method and freeze-drying method. The Laponite RD was silanized by 3-aminopropyltriethoxysilane (APTES). Graphene oxide (GO) was prepared by an improved Hummers method. Under the acidic conditions, self-assembly recombination was realized by electrostatic interaction between modified Laponite RD and GO. The results from Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy confirmed that the modified Laponite RD was successfully compounded with GO, and the composite is laminated and stacked. The results from BET (Brunauer-Emmett-Teller) methods found that the BET-specific surface area of the hybrid aerogel significantly increased with the increase of the doping content of the composite, and the specific surface area of the aerogel composite with 20% doping content reached 81 m²/g. The structure of aerogel is porous, and there are numerous holes in the interior, which is closely related to adsorption properties. Thermogravimetric analysis (TG) test was used to explore the change of thermal properties of hybrid aerogel materials, and it was found that the addition of composite increased the initial decomposition temperature and thermal stability of hybrid aerogel. Finally, the potential applications of aerogel were tested, such as methylene blue adsorption and CO₂ adsorption.

Facile and sustainable fabrication of high-performance cellulose sponge from cotton for oil-in-water emulsion separation

Given complexity and diversity of oily wastewater, developing highly efficient separation materials through green and facile strategy are urgently needed. Herein, a smart strategy is demonstrated to transform raw cotton into uniform cellulose sponge for separation oil-in-water emulsion. The raw cotton is directly treated in zinc chloride aqueous solutions through a controllable dissolution process. After regeneration without any further chemical modification and freeze drying, the evolved cellulose sponge, which is composed of partially dissolved cotton fiber and exfoliated regenerated cellulose, exhibits interesting three-dimensional (3D) interconnected hierarchical porous network structure and stable wettability of superoleophobicity (θ_oil>150º) under water. Cellulose sponge has excellent underwater superoleophobicity and antifouling property due to the natural hydrophilicity of cellulose. Based on the beneficial 3D hierarchical structure and superwettability, the cellulose sponge can separate highly emulsified oil-in-water emulsions with efficiency up to 99.2% solely under the driving of gravity. Our strategy provides a generic way to convert cellulose-based materials into cellulose porous materials with excellent permeability, separation efficiency, antifouling, and reusability property for oil/water emulsions separation. This economical, environmentally friendly and functional cellulose sponge not only allows natural cotton resources to be used rationally with high value-added, but also effectively solves the problems of oily wastewater.

Electrospun stereocomplex polylactide porous fibers toward highly efficient oil/water separation

The urgent needs for water protection are not only developing the highly efficient wastewater treatment technologies but also designing the eco-friendly materials. In this work, the eco-friendly composite fibers composed of poly(L-lactide) (PLLA), poly(D-lactide) (PDLA) and maghemite nanoparticles γ-Fe₂O₃ nanoparticles were fabricated through electrospinning technology. Through regulating the processing parameters and introducing additional annealing treatment, nanoscale porous structure and the stereocomplex crystallites (SCs) are simultaneously constructed in the composite electrospun fibers. Physicochemical performances measurements exhibited that the fiber membranes had excellent lipophilicity, good mechanical performances, and high hydrolysis resistance, and all of which endowed the fiber membranes with high oil adsorption capacities, and the maximum oil adsorption capacities achieved 148.9 g/g at 23 °C and 114.8 g/g at 60 °C. Further results showed that the fiber membranes had good oil/water separation ability. The gravity-driven oil flux was 6824.4 L/m²h², and the water rejection ratio was nearly 100% during separating oil/water mixture. Specifically, the fiber membranes showed good stability during the cycling measurements. It is evidently confirmed that the composite PLLA-based fiber membranes with porous structure and SCs can be used in wastewater treatment, especially in some rigorous circumstances.

Bacterial Superoleophobic Fibrous Matrices: A Naturally Occurring Liquid-Infused System for Oil-Water Separation

Nanocellulose fibers bioengineered by bacteria are a high-performance three-dimensional cross-linked network which can confine a dispersed liquid medium such as water. The strong chemical and physical interactions of dispersed water molecules with the entangled cellulosic network allow these materials to be ideal substrates for effective liquid separation. This type of phenomenon can be characterized as green with no equivalent precedent; its performance and sustainability relative to other cellulose-based or synthetic membranes are shown herein to be superior. In this work, we demonstrated that the renewable bacterial nanocellulosic membrane can be used as a stable liquid-infused system for the development of soft surfaces with superwettability and special adhesion properties and thus address intractable issues normally encountered by solid surfaces.

pH-Sensitive W/O Pickering High Internal Phase Emulsions and W/O/W High Internal Water-Phase Double Emulsions with Tailored Microstructures Costabilized by Lecithin and Silica Inorganic Particles

Synergistic stabilization of Pickering emulsions by a mixture of surfactants and colloidal particles has received increasing interest in recent years but only a few of them can produce high internal phase double emulsions (HIPDEs) with good stability. In this study, we present a feasible and common method of preparing Pickering high internal phase emulsions (HIPEs) with tunable inner morphology costabilized by a biosurfactant lecithin and silica nanoparticles. We investigate the influence of the pH value on the interfacial behavior of lecithin and elucidate the synergistic mechanism between lecithin and silica nanoparticles in different conditions in the stability of as-prepared emulsions. Specifically, water-in-oil (W/O) Pickering HIPEs can be successfully stabilized by lecithin and hydrophobic silica nanoparticles in a wide pH range (pH 1-10), while catastrophic phase inversion occurred at high pH values (pH ≥ 11). Interestingly, stable water-in-oil-in-water (W/O/W) high internal phase double emulsions (HIPDEs) can also be prepared via a two-step method by the cooperation of lecithin and silica nanoparticles. Moreover, functional interconnected porous monoliths and microspheres are facilely fabricated by emulsion templates and their potential applications are explored.

Recent Progress on Nanocellulose Aerogels: Preparation, Modification, Composite Fabrication, Applications

The rapid development of modern industry and excessive consumption of petroleum-based polymers have triggered a double crisis presenting a shortage of nonrenewable resources and environmental pollution. However, this has provided an opportunity to stimulate researchers to harness native biobased materials for novel advanced materials and applications. Nanocellulose-based aerogels, using abundant and sustainable cellulose as raw material, present a third-generation of aerogels that combine traditional aerogels with high porosity and large specific surface area, as well as the excellent properties of cellulose itself. Currently, nanocellulose aerogels provide a highly attention-catching platform for a wide range of functional applications in various fields, e.g., adsorption, separation, energy storage, thermal insulation, electromagnetic interference shielding, and biomedical applications. Here, the preparation methods, modification strategies, composite fabrications, and further applications of nanocellulose aerogels are summarized, with additional discussions regarding the prospects and potential challenges in future development.

Nanocellulose-based lightweight porous materials: A review

Nanocellulose has been widely concerned and applied in recent years. Because of its high aspect ratio, large specific surface area, good modifiability, high mechanical strength, renewability and biodegradability, nanocellulose is particularly suitable as a base for constructing lightweight porous materials. This review summarizes the preparation methods and applications of nanocellulose-based lightweight porous materials including aerogels, cryogels, xerogels, foams and sponges. The preparation of nanocellulose-based lightweight porous materials usually involves gelation and drying processes. The characteristics and influencing factors of three main drying methods including freeze, supercritical and evaporation drying are reviewed. In addition, the mechanism of physical and chemical crosslinking during gelation and the effect on the structure and properties of the porous materials in different drying methods are especially focused on. This contribution also introduces the application of nanocellulose-based lightweight porous materials in the fields of adsorption, biomedicine, energy storage, thermal insulation and sound absorption, flame retardancy and catalysis.

Superhydrophobic metal organic framework doped polycarbonate porous monolith for efficient selective removal oil from water

A series of superhydrophobic polycarbonate porous monoliths modified with metal organic framework (Z8/PC) were firstly fabricated through a facile thermally impacted non-solvent induced phase separation method for efficient selective oil/water separation. The performance of the monoliths on oil/water separation was evaluated in terms of selectivity, equilibrium adsorption capacity, corrosion resistance, kinetics, and circulation. The results showed that the use of ZIF-8 significantly compensated for the shortage of pure monolith. Compared with pure PC monolith, the hydrophobic angle of the Z8/PC-2 monolith promoted from 136.18° to 154.25° due to the micro-nano flower surface. Meanwhile, the Z8/PC-2 monolith displayed a more intricate and continuous interconnected 3D hierarchical micro-nano structure, which possessed the monolith a higher specific surface area of 146.84 m² g^-1 and porosity of 89.5%. What's more, more superior oil/water separation abilities of Z8/PC-2 monolith were manifested by the selective removal of oil or organic solvent from water within 30s, high equilibrium adsorption capacity, and excellent corrosion resistance. In addition, the ten-cycle regeneration of porous monoliths via centrifugation or evaporation displayed additional attractiveness. Therefore, porous Z8/PC monolith will be a promising candidate for the efficient selective oil/water separation of oil spills and organic solvents.

Scalable and Robust Bacterial Cellulose Carbon Aerogels as Reusable Absorbents for High-Efficiency Oil/Water Separation

Efficient selective separation of oils or organic pollutants from water is important for ecological, environmental conservation and sustainable development. Various absorption methods have emerged; the majority of them still suffer from defects including low removal efficiency, a complicated preparation process, and high cost. Herein, we present a highly porous and mechanical resilient bacterial cellulose (BC) carbon aerogel directly from BC hydrogel via facile directional freeze-drying and high-temperature carbonization. The resultant BC carbon aerogel showed excellent mechanical compressibility (maximal height compression ∼99.5%) and elastic recovery due to the porous structure. Taking advantages of the high thermal stability and superhydrophobicity, the BC carbon aerogel was directly used as a versatile adsorbent for oil/water separation. The result demonstrated that the BC carbon aerogel showed super oil/water separation selectivity with the oil absorption capacity as high as 132-274 g g^-1. More importantly, the BC carbon aerogel adsorbent can be reused by a simple absorption/combustion method and still keep high-efficiency oil absorption capacity and excellent superhydrophobicity after 20 absorption/combustion cycles, displaying recyclability and robust stability. In sum, the BC carbon aerogel introduced here is easy to fabricate, ecofriendly, highly scalable, low cost, mechanically robust, and reusable; all of these features make it highly attractive for oil/water separation application.

Hydrophobization of Cellulose Sheets by Gas Grafting of Palmitoyl Chloride by Using Hot Press

The purpose of this study was to investigate the improvement in the hydrophobicity of cellulose through gas grafting treatment with long chain fatty acid chloride using high pressure during pressing at high temperature. To do this, the gas grafting treatment was performed on the cellulose sheet using a hot pressing method, and then the hydrophobization effect was analyzed. It was found that the gas grafting treatment by hot pressing using high pressure during pressing at high temperature produced cellulose sheets of high hydrophobicity. Especially, it was notable that the hydrophobization efficiency enhanced with an increase of the pressing pressure. In addition, the gas grafting efficiency was improved when polyvinyl alcohol (PVA) was coated to obtain high resistance to air permeability. These results indicate that protecting the loss of fatty acid gas by coating of polyvinyl alcohol (PVA) on the cellulose sheet surface contributed to the improvement of gas grafting efficiency.

High-Capacity Reusable Chitosan Absorbent with a Hydrogel-Coated/Aerogel-Core Structure and Superhydrophilicity under Oil for Water Removal from Oil

In this work, inspired by the self-cleaning surfaces of fish scales, we prepared a porous chitosan aerogel (CSA) through a simple freeze-drying process. With the three-dimensional interconnected microstructure, the aerogel was highly porous (porosity > 98.16%) and ultralight with a density ranging from 10.19 to 36.05 mg/cm³. The core/shell structure of the CS-hydrogel-coated/CS-aerogel core (CSHA) was fabricated through a simple spray process. The aerogel with low-adhesion CS-hydrogel-coating exhibited superoleophobicity (θ_oil ∼ 162°) under water and superhydrophilicity (θ_water ∼ 0°) in oil. The hydrogel coating as a switch of the absorbent resists the oil phase and induces permeation of the water phase into the aerogel easily and quickly. The dry aerogel core with a porous structure has become a huge storage space. Taking advantage of this structure, an absorption capacity of 147 times could be obtained for water. The unique water absorption process along with switching between the aerogel and hydrogel gives the CSHA incredible potential for oil purification applications on site. Using the CSHA for oil purification, the purity of the obtained oil can be as high as 99.8%. Importantly, two facile approaches, including redissolving and drying, were applied to recycle the aerogels. The natural hydrophilic aerogels are made from dissolution and regeneration of chitosan powder, which is green, low-cost, simple and easy to scale-up. Using the as-obtained high-capacity recyclable CSA for oil/water separation, the mixture can be separated with high efficiency, making it a favorable candidate for applications in large-scale separation of oil-water mixtures in the future.

Atomic Layer Deposition onto Thermoplastic Polymeric Nanofibrous Aerogel Templates for Tailored Surface Properties

Poly(vinyl alcohol-co-ethylene) (EVOH) nanofibrous aerogel (NFA) templates were fabricated through vacuum freeze-drying from EVOH nanofibrous suspensions. Aluminum oxide (Al₂O₃) layers were deposited onto highly porous templates to form organic-inorganic hybrid aerogels by the atomic layer deposition (ALD) technique. Chemical and physical measurements showed that mechanical properties were improved through ALD. In addition, the surface chemistry of ALD modified aerogels showed a fascinating cyclic change based on the number of ALD deposition cycles. A transition from hydrophilicity to hydrophobicity was observed after a few cycles of ALD coating; however, additional deposition cycles changed the wettability characteristics back to hydrophilicity. This hydrophilic-hydrophobic-hydrophilic variation is shown to be governed by a combination of geometrical and chemical surface properties. Furthermore, the deposited Al₂O₃ could substantially improve aerogels strength and reduce permanent deformation after cyclic compression. The Young's modulus of aerogels increased from 5.54 to 33.27 kPa, and the maximum stress at 80% strain went up from 31.13 to 176.11 kPa, after 100 cycles of trimethyl-aluminum (TMA)/water ALD. Thermogravimetric analysis (TGA) results confirm that ALD can effectively improve the heat resistance characteristics of polymeric aerogel. The onset temperature and the residual mass increased with increasing numbers of ALD cycles. During pyrolysis, the nanofiber cores were decomposed, and the brittle pure Al₂O₃ self-supporting nanotube aerogels with the continuous hollow nanotubular network were formed. A coating of continuous thickness Al₂O₃ layer on individual nanofiber was achieved after 100 ALD cycles. In additional to mechanical strength and physical property changes, the ALD modified aerogel also shows a superhydrophobic and oleophilic surface chemistry, which could potentially be used to remove oils/organic solvents from water. The resultant aerogels exhibit excellent absorption capacity (31-73 g/g) for various liquids, and the material could be reused after distillation or squeezing. A successful scale-up of such materials could provide some insights into the design and development of thermoplastic polymeric NFAs with substantial industrial applications.

Cellulose II Aerogel-Based Triboelectric Nanogenerator

Cellulose-based triboelectric nanogenerators (TENGs) have gained increasing attention. In this study, a novel method is demonstrated to synthesize cellulose-based aerogels and such aerogels are used to fabricate TENGs that can serve as mechanical energy harvesters and self-powered sensors. The cellulose II aerogel is fabricated via a dissolution-regeneration process in a green inorganic molten salt hydrate solvent (lithium bromide trihydrate), where. The as-fabricated cellulose II aerogel exhibits an interconnected open-pore 3D network structure, higher degree of flexibility, high porosity, and a high surface area of 221.3 m2 g-1. Given its architectural merits, the cellulose II aerogel-based TENG presents an excellent mechanical response sensitivity and high electrical output performance. By blending with other natural polysaccharides, i.e., chitosan and alginic acid, electron-donating and electron-withdrawing groups are introduced into the composite cellulose II aerogels, which significantly improves the triboelectric performance of the TENG. The cellulose II aerogel-based TENG is demonstrated to light up light-emitting diodes, charge commercial capacitors, power a calculator, and monitor human motions. This study demonstrates the facile fabrication of cellulose II aerogel and its application in TENG, which leads to a high-performance and eco-friendly energy harvesting and self-powered system.

Eco-friendly and durable PCPS nanoparticles for the effective separation of oil-water emulsions

Oil pollution is one of the main environmental problems that is attracting increasing attention from people. In this study, a new composite, namely a PNIPAm-Clay-γPGA-SiO₂ (PCPS) nanomaterial, was prepared through chemical modification. The material exhibited excellent separation efficiencies for both oil-in-water (O/W) and water-in-oil (W/O) emulsions. The maximum separation efficiency of the W/O emulsion reached 98.70%, while that of the O/W emulsion was 99.23%, and the average separation fluxes were 107.44 L m^-2 h^-1 and 1529.34 L m^-2 h^-1, respectively. The superhydrophobicity of the PCPS nanoparticles could be maintained under strong acid/alkali conditions for over 30 days. The high separation efficiency could be maintained even after 7 cycles, indicating the long-term availability of the material. Furthermore, the PCPS nanoparticles showed excellent biocompatibility due to the presence of γ-polyglutamic acid (γPGA) and poly(N-isopropylacrylamide) (PNIPAm). The properties of strong acid/alkali and thermal stabilities, recyclability, and biocompatibility gave the material great potential for applications.

Crystal and Supramolecular Structure of Bacterial Cellulose Hydrolyzed by Cellobiohydrolase from Scytalidium Candidum 3C: A Basis for Development of Biodegradable Wound Dressings

The crystal and supramolecular structure of the bacterial cellulose (BC) has been studied at different stages of cellobiohydrolase hydrolysis using various physical and microscopic methods. Enzymatic hydrolysis significantly affected the crystal and supramolecular structure of native BC, in which the 3D polymer network consisted of nanoribbons with a thickness T ≈ 8 nm and a width W ≈ 50 nm, and with a developed specific surface S_BET ≈ 260 m²·g⁻¹. Biodegradation for 24 h led to a ten percent decrease in the mean crystal size D_hkl of BC, to two-fold increase in the sizes of nanoribbons, and in the specific surface area S_BET up to ≈ 100 m²·g⁻¹. Atomic force and scanning electron microscopy images showed BC microstructure “loosening“after enzymatic treatment, as well as the formation and accumulation of submicron particles in the cells of the 3D polymer network. Experiments in vitro and in vivo did not reveal cytotoxic effect by the enzyme addition to BC dressings and showed a generally positive influence on the treatment of extensive III-degree burns, significantly accelerating wound healing in rats. Thus, in our opinion, the results obtained can serve as a basis for further development of effective biodegradable dressings for wound healing.

Flexible Underwater Oleophobic Cellulose Aerogels for Efficient Oil/Water Separation

Hybrid cellulose/N,N'-methylene bisacrylamide/graphene oxide (GO) aerogels with high flexibility and underwater oleophobicity were fabricated via the NaOH/urea solvent system. The as-prepared aerogels demonstrated low density, high porosity, and good flexibility. Underwater oleophobicity is attributed to the abundant hydrophilic groups in the aerogel skeleton, rough surface, and homogeneous distribution of GO. The samples were shaped into the membrane and filtered for oil/water separation by gravity. The separation efficiency over membrane-shaped CG₁ was 99.8% with a permeate flux of 22,900 L/(m²·h). Moreover, excellent reusability and durability were observed under long-term tests and corrosive conditions.

A Convenient and Versatile Strategy for the Functionalization of Silica Foams Using High Internal Phase Emulsion Templates as Microreactors

Functional porous materials show extensive applications in the environment, biology, aerospace, and so on. In this work, the generation of silica foams and functionalization of pore surface were simultaneously realized through an interfacial sol-gel reaction within high internal phase emulsion (HIPE) microreactors, where a hyperbranched polyethoxysiloxane (PEOS) was used as the sole stabilizer for the HIPEs. With various functional substances containing amino, epoxy, and carboxyl groups initially dissolved in the aqueous phase of HIPEs, these functional groups could be grafted onto the pore surface in the process of forming silica foams. Amino-functionalized silica foam showed fast adsorption of sunset yellow, and the adsorption capacity could reach as high as 1213.13 mg/g. Sodium polyacrylate-modified silica foam exhibited good adsorption capacity of cationic dyes and metal ions, e.g., 280.11 mg/g to methylene and 226.24 mg/g to Cu(II). Epoxy-functionalized silica foam particles were confirmed with a pronounced activity at the oil/water interface due to their Janus-like surface, which could be used as Pickering stabilizer. This HIPE-based synthesis strategy for silica foams shows promising future in adsorption, emulsion stabilization, and compatibilization.

Superhydrophobic Polypyrrole-Coated Cigarette Filters for Effective Oil/Water Separation

To facilitate the recycling and reuse of cigarette filters and oil/water separation, a superhydrophobic cigarette filter was made by coating with dodecanethiol-modified polypyrrole (Ppy) particles by a dip-coating method. SEM, FTIR, and XPS were used to analyze the surface morphology and chemical compositions. The as-prepared superhydrophobic cigarette filter can realize wettability alteration via changing the ammonium persulfate (APS) concentration from 0.15 mol/L to 3 mol/L, and the contact angle increased from 0° on the original cigarette filter to 155° with a sliding angle of 5°. The superhydrophobic cigarette filter could effectively separate various oils and organic solvents. The separation efficiency was 98.8% and the separation stability was good. Furthermore, the as-prepared superhydrophobic cigarette filter had a large oil absorption range and could absorb different oils and organic solvents, including petroleum ether, engine oil, vegetable oil, n-hexane, and chloroform, with maximum absorption capacities ranging from 9.4 g/g to 22.7 g/g. According to the above results, we believe that the as-prepared superhydrophobic cigarette filter should have great potential in the recovery of solid waste and high-efficiency oil/water separation.

Substantial Improvement of the Dielectric Strength of Cellulose-Liquid Composites: Effects of Traps at the Nanoscale Interface

The dielectric strength of cellulose-liquid composites is always about several times higher than that of the cellulose paper and insulating liquids. However, this experimental phenomenon has not yet been demonstrated theoretically. Herein, the spectra characterization, molecular simulation, and wave function analysis method provide a new insight that the role of nanoscale interfacial adsorption of cellulose-liquid is exclusive for composites affecting the charge separation and producing the deep-level traps to seriously hinder electromigration under an electric field, which is responsible for the difference in dielectric strength. Meanwhile, the π conjugation and σ-π hyperconjugation effects enhance the electrical stability of aromatic hydrocarbon insulating liquids. In conclusion, interfacial trap theory can be used to explain the correlation of dielectric strength between cellulose-liquid composites and cellulose paper or dielectric liquids. It can be expected that materials with high dielectric strength can be manufactured according to the fundamental study of interfacial trap theory.

Ultralight Programmable Bioinspired Aerogels with an Integrated Multifunctional Surface for Self-Cleaning, Oil Absorption, and Thermal Insulation via Coassembly

Creating a configurable and controllable surface for structure-integrated multifunctionality of ultralight aerogels is of significance but remains a huge challenge because of the critical limitations of mechanical vulnerability and structural processability. Herein, inspired by Salvinia minima, the facile and one-step coassembly approach is developed to allow the structured aerogels to spontaneously replicate Salvinia-like textures for function-adaptable surfaces morphologically. The in situ superimposed construction of bioinspired topography and intrinsic topology is for the first time performed for programmable binary architectures with multifunctionality without engendering structural vulnerability and functional disruption. By introducing the binding groups for hydrophobicity tailoring, functionalized nanocellulose (f-NC) is prepared via mechanochemistry as a structural, functional, and topographical modifier for a multitasking role. The self-generated bioinspired surface with f-NC greatly maintains the structural unity and mechanical robustness, which enable self-adaptability and self-supporting of surface configurations. With fine-tuning of nucleation-driving, the binary microstructures can be controllably diversified for structure-adaptable multifunctionalities. The resulting ultralight S. minima-inspired aerogels (e.g., 0.054 g cm^-3) presented outstanding temperature-endured elasticity (e.g., 90.7% high-temperature compress-recovery after multiple cycles), durable superhydrophobicity, anti-icing properties, oil absorbency efficiency (e.g., 60.2 g g^-1), and thermal insulating (e.g., 0.075 W mK^-1), which are superior to these reported on the overall performance. This coassembly strategy offers the opportunities for the design of ultralight materials with topography- and function-tailorable features to meet the increasing demands in many fields such as smart surfaces and self-cleaning coatings.

Valorizing kitchen waste through bacterial cellulose production towards a more sustainable biorefinery

In this work, water washing pretreatment was employed on kitchen waste (KW) to integrate a multi-product biorefinery process for producing biogas, biodiesel, bacterial cellulose (BC) and biofertilizer. As a crucial stream in this biorefinery process, BC production were investigated to clarify the effects of residual salt and cooked oil. Meanwhile, glycerol, a by-product in biodiesel stream, as carbon source was attempted to produce BC. Results indicated that BC yield was significantly promoted from 0.11 g L^-1 to 2.07 g L^-1 as NaCl content decreased from 0.44% to 0.04%. Correspondingly, the BC crystallinity increased from 30.1% to 57.4% and the tensile strength increased from 3.30 MPa to 21.64 MPa. In addition, the residual cooked oil didn't affect the BC yield significantly, however, the crystallinity was greatly decreased from 57.4% to 34.5% as more cooked oil was remained in the medium of KW, and the tensile strength was decreased from 21.64 MPa to 4.30 MPa, correspondingly. Obviously, reducing the salt and cooked oil content in the starch fraction of KW by intensifying the water washing pretreatment will greatly benefit the BC yield and qualities. When the glycerol from biodiesel stream was employed for BC production with content of 10 g L^-1-25 g L^-1, 34.2%-44.0% increase on BC yield can be achieved. By contrast, extra higher glycerol content (50 g L^-1) reduced the BC yield by 41%. However, the crystallinity and the tensile strength were increased by 18% and 2.2-folds, respectively. Therefore, the biodiesel stream can be well integrated in the process via producing BC with by-product of glycerol as a replaceable carbon source. Based on the results above, a more sustainable biorefinery process of KW via BC production can be achieved, which will potentially offer a new path to valorize the daily-released KW.

Synthesis of a Superhydrophobic Polyvinyl Alcohol Sponge Using Water as the Only Solvent for Continuous Oil-Water Separation

Few cases of hydrophobic materials synthesized in water have been reported. In this work, water, as the only solvent, is used to prepare a superhydrophobic sponge via a facile and environment-friendly route. The as-prepared sponge, namely silylated polyvinyl alcohol (PVA) sponge, exhibits superhydrophobic and superoleophilic characters. It has the static water contact angle (WCA) of 152 ± 1 and the static oil contact angle (OCA) of 0°, which can lead to excellent selectivity for oil-water separation. Besides, the methyltriethoxysilane (MTES) can form a stable mixed structure with the PVA skeleton, resulting in the rare shedding of polymethylsiloxane nanoparticles and the long-term stability for oil-water separation. Furthermore, the silylated sponge shows a high separation efficiency (>99.6%), removing oil up to 6200∼14000 times of its own mass. The findings demonstrated that the silylated superhydrophobic sponge can be a promising candidate in water treatment application.

Complex Aerogels Generated from Nano-Polysaccharides and Its Derivatives for Oil-Water Separation

The complex aerogel generated from nano-polysaccharides, chitin nanocrystals (ChiNC) and TEMPO-oxidized cellulose nanofibers (TCNF), and its derivative cationic guar gum (CGG) is successfully prepared via a facile freeze-drying method with glutaraldehyde (GA) as cross-linkers. The complexation of ChiNC, TCNF, and CGG is shown to be helpful in creating a porous structure in the three-dimensional aerogel, which creates within the aerogel with large pore volume and excellent compressive properties. The ChiNC/TCNF/CGG aerogel is then modified with methyltrichlorosilane (MTCS) to obtain superhydrophobicity/superoleophilicity and used for oil–water separation. The successful modification is demonstrated through FTIR, XPS, and surface wettability studies. A water contact angle of 155° on the aerogel surface and 150° on the surface of the inside part of aerogel are obtained for the MTCS-modified ChiNC/TCNF/CGG aerogel, resulting in its effective absorption of corn oil and organic solvents (toluene, n-hexane, and trichloromethane) from both beneath and at the surface of water with excellent absorption capacity (i.e., 21.9 g/g for trichloromethane). More importantly, the modified aerogel can be used to continuously separate oil from water with the assistance of a vacuum setup and maintains a high absorption capacity after being used for 10 cycles. The as-prepared superhydrophobic/superoleophilic ChiNC/TCNF/CGG aerogel can be used as a promising absorbent material for the removal of oil from aqueous media.

Preparation and characterisation of CNF/MWCNT carbon aerogel as efficient adsorbents

In recent years, carbon aerogels have attracted much attention in basic research and as potential applications in many fields. Herein, the authors report a novel approach using bamboo powder as raw material to fabricate cellulose nanofibers (CNFs)/multi-walled carbon nanotubes (MWCNTs) carbon aerogels by a simple dipping and carbonisation process. The developed material exhibits many exciting properties including low density (0.056 g cm^-3), high porosity (95%), efficient capability for separation of oily droplets from water, and high adsorption capacity for a variety of oils and organic solvents by up to 110 times its own weight. Furthermore, the CNF/MWCNT carbon aerogels (CMCA) can be recycled many times by distillation and combustion, satisfying the requirements of practical oil-water separation. Taken together with its economical, environmentally benign manufacturing process, sustainability of the precursor and versatility of material, the CMCA developed in this study will be a promising candidate for addressing the problems arising from the spills of oily compounds.

Paraffin Oil Based Soft-Template Approach to Fabricate Reusable Porous PDMS Sponge for Effective Oil/Water Separation

Three-dimensional porous material holds enormous potential in the field of life science and environmental protection. In this work, we proposed a facile route for the large-scale synthesis of porous poly(dimethylsiloxane) (PDMS) sponge via paraffin oil based emulsion technique. A stable emulsion could be formed by emulsifying water in the PDMS solution with the aid of paraffin oil. Moreover, the amount of emulsified water in 5 g of PDMS solution is as high as 35 g, and the skeleton of the prepared PDMS sponge is still in intact. This method is cost-effective, rapid, and easily scaled up. The water contact angle of the obtained PDMS sponge is 141.9 ± 1°, and the absorption capacities of the sponges are 13.5-33.3 g g^-1 for various organic solvents. The PDMS sponge only needed 0.069 MPa force to realize the compression ratio of 90%, which it still maintained after over 50 cycles of compression. In addition, the porous PDMS sponge exhibited an excellent oil absorption and an outstanding reusability, which were potentially useful in water purification.

Fast Approach to the Hydrophobization of Bacterial Cellulose via the Direct Polymerization of Ethyl 2-Cyanoacrylate

Bacterial cellulose (BC) has a broad range of applications in biomedical fields and cosmetics. Applied as wound dressing, BC tends to stick to the sore especially upon drying, and hydrophobization improves its performance in this regard. This article reports a facile and rapid yet a highly efficient approach for BC hydrophobization through direct polymerization of ethyl 2-cyanoacrylate on the BC fibers. The modified material preserves the favorable porous structure of the matrix material while displaying significantly higher hydrophobicity and significantly decreased stickiness to the wound. The BC surface can be modified in 15 min. Overall, this can be considered a ready-to-apply approach for the fabrication of BC wound dressings with enhanced performance. The modification was demonstrated to improve the material's biocompatibility and to introduce antimicrobial activity (immortalized human fibroblast assay).

Ultra-Porous Nanocellulose Foams: A Facile and Scalable Fabrication Approach

Cellulose nanofibril foams are cellulose-based porous materials with outstanding mechanical properties, resulting from the high strength-to-weight ratio of nanofibrils. Here we report the development of an optimized fabrication process for highly porous cellulose foams, based on a well-controlled freeze-thawing-drying (FTD) process at ambient pressure. This process enables the fabrication of foams with ultra-high porosity, up to 99.4%, density of 10 mg/cm³, and liquid (such as oil) absorption capacity of 100 L/kg. The proposed approach is based on the ice-templating of nanocellulose suspension in water, followed by thawing in ethanol and drying at environmental pressures. As such, the proposed fabrication route overcomes one of the major bottle-necks of the classical freeze-drying approach, by eliminating the energy-demanding vacuum drying step required to avoid wet foam collapse upon drying. As a result, the process is simple, environmentally friendly, and easily scalable. Details of the foam development fabrication process and functionalization are thoroughly discussed, highlighting the main parameters affecting the process, e.g., the concentration of nanocellulose and additives used to control the ice nucleation. The foams are also characterized by mechanical tests and oil absorption measurements, which are used to assess the foam absorption capability as well as the foam porosity. Compound water-in-oil drop impact experiments are used to demonstrate the potential of immiscible liquid separation using cellulose foams.

Transparent Poly(methyl methacrylate) Composites Based on Bacterial Cellulose Nanofiber Networks with Improved Fracture Resistance and Impact Strength

Cellulose nanofibers are often explored as biobased reinforcement for the production of high-performance composite materials. In this work, we fabricated transparent poly(methyl methacrylate) (PMMA) composites consisting of two-dimensional and three-dimensional bacterial cellulose (BC) nanofiber networks. Three different composite designs consisting of 1 vol % BC loading were fabricated and studied: (i) composites with a three-dimensional BC nanofiber network embedded uniformly throughout the PMMA matrix; (ii) sandwich-structured construction consisting of three-dimensional BC-PMMA sandwiched between two neat PMMA sheets; and (iii) dried and well-consolidated two-dimensional BC nanofiber network embedded in a PMMA matrix. All fabricated model BC-PMMA composites were found to be optically transparent, but PMMA composites consisting of the two-dimensional BC nanofiber network possessed higher light transmittance (73% @550 nm) compared to the three-dimensional BC nanofiber network counterparts (63% @550 nm). This is due to the higher specific surface area of the three-dimensional BC nanofiber network, which led to more light scattering. Nevertheless, it was found that both two-dimensional and three-dimensional BC nanofiber networks serve as excellent stiffening agents for PMMA matrix, improving the tensile modulus of the resulting composites by up to 30%. However, no improvement in tensile strength was observed. The use of three-dimensional BC nanofiber network led to matrix embrittlement, reducing the tensile strain-at-failure, fracture resistance, and Charpy impact strength of the resulting BC-PMMA composites. When the BC nanofiber network was used as two-dimensional reinforcement, cracks were observed to propagate through the debonding of BC nanofiber network, leading to higher fracture toughness and Charpy impact strength. These novel findings could open up further opportunities in the design of novel optically transparent polymeric composite laminates based on the two-dimensional BC nanofiber network for impact protection.