Preparation of high elastic bacterial cellulose aerogel through thermochemical vapor deposition catalyzed by solid acid for oil-water separation

Synthesis strategies, regeneration, cost analysis, challenges and future prospects of bacterial cellulose-based aerogels for water treatment: A review

Clean water is an integral part of industries, agricultural activities and human life, but water contamination by toxic dyes, heavy metals, and oil spills is increasingly serious in the world. Aerogels with unique properties such as highly porous and extremely low density, tunable surface modification, excellent reusability, and thermal stability can contribute to addressing these issues. Thanks to high purity, biocompatibility and biodegradability, bacterial cellulose can be an ideal precursor source to produce aerogels. Here, we review the modification, regeneration, and applications of bacterial cellulose-based aerogels for water treatment. The modification of bacterial cellulose-based aerogels undergoes coating of hydrophobic agents, carbonization, and incorporation with other materials, e.g., ZIF-67, graphene oxide, nanoparticles, polyaniline. We emphasized features of modified aerogels on porosity, hydrophobicity, density, surface chemistry, and regeneration. Although major limits are relevant to the use of toxic coating agents, difficulty in bacterial culture, and production cost, the bacterial cellulose aerogels can obtain high performance for water treatment, particularly, catastrophic oil spills.

Magnetic Hyperporous Elastic Material with Excellent Fatigue Resistance and Oil Retention for Oil-Water Separation

Oily wastewater has caused serious threats to the environment; thus, high-performance absorbing materials for effective oil-water separation technology have attracted increasing attention. Herein, we develop a magnetic, hydrophobic, and lipophilic hyperporous elastic material (HEM) templated by high internal phase emulsions (HIPE), in which free-radical polymerization of butyl acrylate (BA) and divinylbenzene (DVB) is employed in the presence of poly(dimethylsiloxane) (PDMS), lecithin surfactant, and modified Fe3O4 nanoparticles. The adoption of the emulsion template with nanoparticles as both stabilizers and cross-linkers endows the HEM with biomimetic hierarchical open-cell micropores and elastic cross-linked networks, generating an oil absorbent with outstanding mechanical stability. Compressive fatigue resistance of the HEM is demonstrated to endure 2000 mechanical cycles without plastic deformation or strength degradation. By exploiting the synergistic effect of hierarchical structures and low-surface-energy components, the resulting HEM also possesses excellent and robust hydrophobicity (water contact angle of 164°) and good oil absorption capacity, in which Fe3O4 nanoparticles lead to convenient magnetically controlled oil recyclability as well. Notably, the unique biomimetic microporous structure demonstrates superior oil retention capacity (>95% at 1000 rpm and >60% at 10,000 rpm) over the state-of-the-art porous materials for a diverse variety of oils to reduce the risk of secondary oil leakage, along with good recoverability by squeezing owing to the excellent compression resilience. These excellent performances of our HEM provide broad prospects for practical applications in oil-water separation, energy conversion, and smart soft robotics.

Robust nanoparticles growth in the interior of porous sponges for efficient dye adsorption and emulsion separation

Emulsified oils and dye contaminants already pose a huge threat to global ecosystems and human health. It is a significant research topic to develop efficient, rapid, versatile methods for emulsion separation and dye adsorption. The membrane material modified with common methods only modified the outer surface of the membrane, while the interior is hardly fully decorated. In this investigation, a solvent exchange method was used to in situ grow nanoparticles in the interior of a porous sponge. These nanoparticles were obtained with polyethyleneimine, gallic acid, and tannic acid via Michael addition and Schiff base reaction. The prepared nanoparticle-coated sponges provided efficient separation of dyes, emulsions, and complex contaminants. The separation efficiency of the dye reached 99.49%, and the separation efficiency of the emulsion was as high as 99.87% with a flux of 11140.3 L m-2 h-1. Furthermore, the maximum adsorption capacity reached 486.8 mg g-1 for cationic dyes and 182.1 mg g-1 for anionic dyes. More importantly, the nanoparticles were highly robust on the surface of the porous sponge, and the modified sponge could have long-term applications in hazardous environments. Overall, it is envisioned that the nanoparticles-modified porous sponge exhibited considerable potential for emulsion and dye wastewater treatment.

Superelastic and superflexible cellulose aerogels for thermal insulation and oil/water separation

Aerogels with low thermal conductivity and high adsorption capacity present a promising solution to curb water pollution caused by organic reagents as well as mitigate heat loss. Although aerogels exhibiting good adsorption capacity and thermal insulation have been reported, materials with mechanical integrity, high flexibility and shear resistance still pose a formidable task. Here, we produced bacterial cellulose-based ultralight multifunctional hybrid aerogels by using freeze-drying followed by chemical vapor deposition silylation method. The hybrid aerogels displayed a low density of 10-15 mg/cm3, high porosity exceeding 99.1 %, low thermal conductivity (27.3-29.2 mW/m.K) and superior hydrophobicity (water contact angle>120o). They also exhibited excellent mechanical properties including superelasticity, high flexibility and shear resistance. The hybrid aerogels demonstrated high heat shielding efficiency when used as an insulating material. As a selective oil absorbent, the hybrid aerogels exhibit a maximum adsorption capacity of up to approximately 156 times its own weight and excellent recoverability. Especially, the aerogel's highly accessible porous microstructure results in an impressive flux rate of up to 162 L/h.g when used as a filter in a continuous oil-water separator to isolate n-hexane-water mixtures. This work presents a novel endeavor to create high-performance, sustainable, reusable, and adaptable multifunctional aerogels.

Recent advances in hydrophobic nanocellulose aerogels for oil spill applications: A review

In a rapidly growing world, petroleum is used extensively in various industries, and the extraction, processing, and transportation of petroleum generates large amounts of petroleum-containing wastewater. Conventional oil/water separation methodologies are often ineffective and costly. Nanocellulose-based aerogels (NA) have emerged as a possible solution to this problem. However, hydrophobic modification is required for effective use in oil/water separation. This review on materials commonly used in these processes and outlines the requirements for adsorbent materials and methods for creating unique lipophilic surfaces. New trends in hydrophobization methods for NA are also discussed. Additionally, it includes the development of composite nanocellulose aerogels (CNAs) and cellulose based membrane specially developed for oil/water (o/w) separation considering different separation requirements. This analysis also examines how CNAs have evolved by introducing special properties that facilitate oil collection or make the adsorbent recyclable. We also discuss the difficulties in creating effective NAs for these important applications in a changing society, as well as the difficulties in creating oil recovery equipment for oil spill cleanup.

Comparison of hydrophobic cellulose nanofibrils modified with different diisocyanates for circulating oil absorption

A large number of polluting substances, including chlorinated organic substances that were highly stable and hazardous, has been emitted due to the rapidly developing chemical industry, which will affect the ecological environment. Nanocellulose aerogels are effective carriers for adsorption of oil substances and organic solvents, however, the extremely strong hydrophilicity and poor mechanical properties limited their widespread applications. In this study, TEMPO-oxidized cellulose nanofibrils was modified with 2, 4-toluene diisocyanate (TDI) and 4,4'-diphenylmethane diisocyanate (MDI) to prepare strong and hydrophobic aerogels for oil adsorption. The main purpose was to evaluate and compare the effects of two diisocyanates on various properties of modified aerogels. It was found that the modified aerogel had better hydrophobic properties, mechanical properties and adsorption properties. In particular, the modified aerogel with TDI as crosslinker showed a better performance, with a maximum chloroform adsorption capacity of 99.3 g/g, a maximum water contact angle of 131.3°, and a maximum compression stress of 36.3 kPa. This study provides further evidence of the potential of functional nanocellulose aerogel in addressing environmental pollution caused by industrial emissions.

Highly elastic photothermal nanofibrillated cellulose aerogels for solar-assisted efficient cleanup of viscous oil spill

Frequent oil spills and illegal industrial pollutant discharge cause ecological and resource damages, so it is necessary to establish efficient adsorption and recovery strategies for oils in wastewater. Herein, inspired by solar-driven viscosity-breaking, we propose a facile approach to fabricate multifunctional nanofibrillated cellulose-based aerogel with high elasticity, excellent photothermal conversion, efficient selective oil adsorption and antibacterial properties. Firstly, copper sulfide (CuS) nanoparticles were in situ deposited on the template of oxidative nanofibrillated cellulose (ONC), aiming at achieving efficient photothermal effect and antibacterial properties. Ethylene glycol diglycidyl ether (EGDE) was employed to establish multiple crosslinking network between CuS@ONC and polyethyleneimine (PEI). A thin hydrophobic PMTS layer deposited on the surface of aerogel via a facile gas-solid reaction ensured stable oil selectivity. The resulting composite aerogel can rapidly adsorb oil under solar self-heating, significantly reducing the adsorption time from 25 to 5 min. Furthermore, it exhibits excellent adsorption capacities for various oils, retaining over 92 % of its initial capacity even after 20 adsorption-desorption cycles, and the antibacterial properties extend its lifespan. This work offers a promising method for constructing multifunctional aerogels for efficient oil-water separation, especially beneficial for high-viscosity and high-melting-point oil cleanup.

Superhydrophilic and Underwater Superoleophobic Copper Mesh Coated with Bamboo Cellulose Hydrogel for Efficient Oil/Water Separation

Super-wetting interface materials have shown great potential for applications in oil-water separation. Hydrogel-based materials, in particular, have been extensively studied for separating water from oily wastewater due to their unique hydrophilicity and excellent anti-oil effect. In this study, a superhydrophilic and underwater superoleophobic bamboo cellulose hydrogel-coated mesh was fabricated using a feasible and eco-friendly dip-coating method. The process involved dissolving bamboo cellulose in a green alkaline/urea aqueous solvent system, followed by regeneration in ethanol solvent, without the addition of surface modifiers. The resulting membrane exhibited excellent special wettability, with superhydrophilicity and underwater superoleophobicity, enabling oil-water separation through a gravity-driven "water-removing" mode. The super-wetting composite membrane demonstrated a high separation efficiency of higher than 98% and a permeate flux of up to 9168 L·m-2·h-1 for numerous oil/water mixtures. It also maintained a separation efficiency of >95% even after 10 cycles of separation, indicating its long-term stability. This study presents a green, simple, cost-effective, and environmentally friendly approach for fabricating superhydrophilic surfaces to achieve oil-water separation. It also highlights the potential of bamboo-based materials in the field of oil-water separation.

Superelastic Cellulose Sub-Micron Fibers/Carbon Black Aerogel for Highly Sensitive Pressure Sensing

Superelastic aerogels with rapid response and recovery times, as well as exceptional shape recovery performance even from large deformation, are in high demand for wearable sensor applications. In this study, a novel conductive and superelastic cellulose-based aerogel is successfully developed. The aerogel incorporates networks of cellulose sub-micron fibers and carbon black (SMF/CB) nanoparticles, achieved through a combination of dual ice templating assembly and electrostatic assembly methods. The incorporation of assembled cellulose sub-micron fibers imparts remarkable superelasticity to the aerogel, enabling it to retain 94.6% of its original height even after undergoing 10 000 compression/recovery cycles. Furthermore, the electrostatically assembled CB nanoparticles contribute to exceptional electrical conductivity in the cellulose-based aerogel. This combination of electrical conductivity and superelasticity results in an impressive response time of 7.7 ms and a recovery time of 12.8 ms for the SMF/CB aerogel, surpassing many of the aerogel sensors reported in previous studies. As a proof of concept, the SMF/CB aerogel is utilized to construct a pressure sensor and a sensing array, which exhibit exceptional responsiveness to both minor and substantial human motions, indicating its significant potential for applications in human health monitoring and human-machine interaction.

Super-amphiphobic arabic gum-based coatings on textile for on-demand oily and dye wastewater treatment

Different membrane materials have broadly been constructed for oil-containing water separation, but most of preparation routes involve corrosive or toxic chemicals and especially many materials have only single superwetting property. Herein, a novel and eco-friendly cellulose-based textile membrane is developed by incorporating the composite coating consisting of arabic gum (AG), attapulgite (APT), and iron (Fe) onto cellulose textiles. The functionalized textile is superoleophobic underwater and superhydrophobic underoil. As a result, the textile prewetted with water or oil can be employed to separate light oil layer/water and heavy oil layer/water mixtures, respectively, and the separation efficiency to the two types of mixtures is larger than 98.3 %. Results also reveal that the decorated textile possesses superior stability and recyclability in purifying oily wastewater. More importantly, such coated textile is capable of filtrating water-soluble contaminants (dyes) from polluted water. Due to the versatility and environmental compatibility of product as well as the accessibility as agricultural and forestry product as raw materials, the advanced textiles may offer effective solutions to oily wastewater purification and water-soluble contaminant removal.

Highly compressible and hydrophobic nanofibrillated cellulose aerogels for cyclic oil/water separation

Nanofibrillated cellulose (NFC)-based aerogels are ideal oil-sorbent materials, but the poor structural stability and hydrophilicity restrain their practical applications in the fields of oil/water separation. In the present work, we report a facile strategy for constructing a hydrophobic nanofibrillated cellulose aerogel for cyclic oil/water separation. Briefly, an aerogel matrix of C-g-PEI with multiple cross-linked network structures was constructed via the combined use of oxidized-NFC (ONC), polyethyleneimine (PEI), and ethylene glycol diglycidyl ether (EGDE), followed by rapid in situ deposition of poly(methyl trichlorosilane) (PMTS) through a low-temperature gas-solid reaction. The resulting ONC-based aerogel (C-g-PEI-PMTS) exhibits the advantages of ultralight (53.80 mg/cm³), high porosity (95.73 %), hydrophobicity (contact angle of 130.0°) and remarkable elasticity (95.86 %). Meanwhile, the composite aerogel of C-g-PEI-PMTS is extremely suitable for oil sorption-desorption by a simple mechanical squeezing method. After 10 cycles of sorption-desorption, the sorption capacity of the aerogel towards various oils reached almost the same level as in the first cycle. The filtration separation efficiency for the trichloromethane-water mixtures remained at 99 % after 50 cycles, demonstrating encouraging reusability. In summary, an efficient strategy to prepare NFC-based aerogel with highly compressible and hydrophobic properties is developed, which expands the applications of NFC in the fields of oil/water separation.

Biomass Chitosan-Based Tubular/Sheet Superhydrophobic Aerogels Enable Efficient Oil/Water Separation

Water pollution, which is caused by leakage of oily substances, has been recognized as one of the most serious global environmental pollutions endangering the ecosystem. High-quality porous materials with superwettability, which are typically constructed in the form of aerogels, hold huge potential in the field of adsorption and removal of oily substances form water. Herein, we developed a facile strategy to fabricate a novel biomass absorbent with a layered tubular/sheet structure for efficient oil/water separation. The aerogels were fabricated by assembling hollow poplar catkin fiber into chitosan sheets using a directional freeze-drying method. The obtained aerogels were further wrapped with -CH₃-ended siloxane structures using CH₃SiCl₃. This superhydrophobic aerogel (CA ≈ 154 ± 0.4°) could rapidly trap and remove oils from water with a large sorption range of 33.06-73.22 g/g. The aerogel facilitated stable oil recovery (90.07-92.34%) by squeezing after 10 sorption-desorption cycles because of its mechanical robustness (91.76% strain remaining after 50 compress-release cycles). The novel design, low cost, and sustainability of the aerogel provide an efficient and environmentally friendly solution for handling oil spills.