Renewable and robust biomass carbon aerogel derived from deep eutectic solvents modified cellulose nanofiber under a low carbonization temperature for oil-water separation

Biowaste-Derived Triboelectric Nanogenerators for Emerging Bioelectronics

Triboelectric nanogenerators (TENGs) combine contact electrification and electrostatic induction effects to convert waste mechanical energy into electrical energy. As conventional devices contribute to electronic waste, TENGs based on ecofriendly and biocompatible materials have been developed for various energy applications. Owing to the abundance, accessibility, low cost, and biodegradability of biowaste (BW), recycling these materials has gained considerable attention as a green approach for fabricating TENGs. This review provides a detailed overview of BW materials, processing techniques for BW-based TENGs (BW-TENGs), and potential applications of BW-TENGs in emerging bioelectronics. In particular, recent progress in material design, fabrication methods, and biomechanical and environmental energy-harvesting performance is discussed. This review is aimed at promoting the continued development of BW-TENGs and their adoption for sustainable energy-harvesting applications in the field of bioelectronics.

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.

Superhydrophobic Co-MOF-based sponge for efficient oil-water separation utilizing photothermal effect

Effectively addressing crude oil spills remains a global challenge due to its high viscosity and limited flow characteristics. In this study, we successfully prepared a modified sponge (PCP@MS) by embedding the photothermal material of Co-HHTP and coating the melamine sponge (MS) with low-surface-energy polydimethylsiloxane (PDMS). The PCP@MS exhibited outstanding hydrophobicity with WCA of 160.2° and high oil absorption capacity of 59-107 g/g. The PCP@MS showed high separation efficiency of 99.2% for various oil-water mixtures, along with notable self-cleaning properties and mechanical stability. The internal micro-nano hierarchical structure on the sponge surface significantly enhanced light absorption, synergizing with the photo-thermal conversion properties of Co-HHTP, enabled PCP@MS to achieve a surface temperature of 109.2 °C under 1.0 solar light within 300 s. With the aid of solar radiation, PCP@MS is able to heat up quickly and successfully lowering the viscosity of the surrounding crude oil, resulting in an oil recovery rate of 8.76 g/min. Density functional theory (DFT) calculation results revealed that Co-HHTP featured a zero-gap band structure, rendering advantageous electronic properties for full-wavelength light absorption. This in situ solar-heated absorbent design is poised to advance the practical application of viscous oil spill cleanup and recovery.

Starch-based carbon aerogels prepared by an innovative KOH activation method for supercapacitors

Biomass-based carbon aerogels hold promising application prospect in the field of supercapacitors. In this research, starch was selected as a raw material for preparing carbon aerogels. The preparation process of starch hydrogels was simplified by using KOH, which can change starch suspension into hydrogels at room temperature. Moreover, the molecular mixing of KOH and starch was realized, so that KOH can be fully utilized in the activation process. The specific surface area of the starch-based carbon aerogels prepared by this method was 1349 m2/g, and the proportion of micropores was 43.7 %. Remarkably, as electrode materials for supercapacitors, the starch-based carbon aerogels exhibited outstanding electrochemical performance. In a three-electrode system, the carbon aerogels exhibited specific capacitance of 211.5 F/g at 0.5 A/g and 138.5 F/g at 10 A/g, suggesting their suitability for high-current applications. In a symmetrical supercapacitor configuration, the materials exhibited an energy density of 11.3 Wh/kg at a power density of 0.5 kW/kg and the specific capacitance can maintain 98.91 % after 10,000 cycles. Overall, this work provides a new method for mixing activators, which will foster potential advances in starch based carbon aerogels.

Bio-Based Aerogels for the Removal of Heavy Metal Ions and Oils from Water: Novel Solutions for Environmental Remediation

Contamination of the aqueous environment caused by the presence of heavy metal ions and oils is a growing concern that must be addressed to reduce their detrimental impact on living organisms and safeguard the environment. Recent efficient and environmentally friendly remediation methods for the treatment of water are based on third-generation bioaerogels as emerging applications for the removal of heavy metal ions and oils from aqueous systems. The peculiarities of these materials are various, considering their high specific surface area and low density, together with a highly porous three-dimensional structure and tunable surface chemistry. This review illustrates the recent progress in aerogels developed from cellulose and chitosan as emerging materials in water treatment. The potential of aerogel-based adsorbents for wastewater treatment is reported in terms of adsorption efficacy and reusability. Despite various gaps affecting the manufacturing and production costs of aerogels that actually limit their successful implementation in the market, the research progress suggests that bio-based aerogels are ready to be used in water-treatment applications in the near future.

Ultra-sensitive detection and scavenging of arsenic ions and ciprofloxacin using 3D multipurpose hemicellulose based aerogel: Adsorption mechanism and RSM optimization

Trace level detection and efficient removal of arsenite ions (As (III)) and ciprofloxacin (CPR) antibiotic was achieved using hemicellulose based ratiometric fluorescent aerogel. Hemicellulose derived from rice straw was oxidised to dialdehyde hemicellulose followed by crosslinking using chitosan via a Schiff base reaction (C = N) yielding a highly porous 3D fluorescent aerogel (CS@DAHCA). Various factors governing adsorption were analyzed by applying response surface methodology (RSM) approach. CS@DAHCA exhibited ultra-trace level monitoring with the limit of detection of 3.529 pM and 55.2 nM for As (III) and CPR, respectively. The CS@DAHCA showed maximum adsorption capacity of 185 μg g-1 and 454 mg g-1 for As (III) and CPR, respectively. Finally, the feasibility of CS@DAHCA was ascertained for real water samples confirming it as promising candidate for remediation of As (III) and CPR.

The effect of synthesis conditions and process parameters on aerogel properties

Aerogels are remarkable nanoporous materials with unique properties such as low density, high porosity, high specific surface area, and interconnected pore networks. In addition, their ability to be synthesized from various precursors such as inorganics, organics, or hybrid, and the tunability of their properties make them very attractive for many applications such as adsorption, thermal insulation, catalysts, tissue engineering, and drug delivery. The physical and chemical properties and pore structure of aerogels are crucial in determining their application areas. Moreover, it is possible to tailor the aerogel properties to meet the specific requirements of each application. This review presents a comprehensive review of synthesis conditions and process parameters in tailoring aerogel properties. The effective parameters from the dissolution of the precursor step to the supercritical drying step, including the carbonization process for carbon aerogels, are investigated from the studies reported in the literature.

Enhanced oil-water emulsion separation through coalescence filtration utilizing milkweed fiber: a sustainable paradigm

Over the past few years, the environment and public safety have suffered due to the detrimental effects of oily industrial effluents. Natural fibers have gained popularity for their affordability, reusability, and effectiveness in separating oil from oily wastewater. Milkweed fibers were characterized using FTIR (Fourier transform infrared spectroscopy), SEM (scanning electron microscopy), and contact angle techniques. With four porosities (0.90, 0.92, 0.95, and 0.98), deep bed coalescence filters were built at three different filter bed heights (10 mm, 20 mm, and 30 mm). Using milkweed coalescence filtering technology, a novel oil separation method is described along with a method to calculate oil film thickness following emulsified oily water saturation. By combining a bed height of 30 mm and a porosity of 0.98, a maximum oil separation of 99.73% and an optimized D50 droplet ratio were achieved. Throughout a prolonged operational period lasting 250 min, the filter bed, possessing a depth of 30 mm and a porosity of 98%, exhibited no discernible fouling indications. Following five cycles, the milkweed filter bed measuring 30 mm in depth and featuring a porosity of 98% displayed an impressive oil separation efficiency of 91.5%. This study found that using a milkweed deep bed filter, coalescence filtering effectively removes oil from oily effluent. Furthermore, milkweed is a natural and biodegradable fiber that is easy to dispose of after use and does not harm the environment.

Natural microfibrils/regenerated cellulose-based carbon aerogel for highly efficient oil/water separation

Cellulose-based carbon aerogels as biodegradable and renewable biomass materials have presented potential applications in oil/water separation. Herein, a novel carbon aerogel composed of natural microfibrils/regenerated cellulose (NM/RCA) was directly prepared by economical hardwood pulp as raw material using a novel co-solvent composed of deep eutectic solvent (DES) and N-methyl morpholine-N-oxide monohydrate (NMMO·H₂O). In addition, the morphology and structure of the filiform natural microfibers could be remained after carbonized at 400 ℃, which resulted in a low density (8-10 mg cm^-3), high specific surface area (768.89 m² g^-1) and high sorption capability. In addition, the aerogel exhibited high compressibility, outstanding elasticity, excellent fatigue resistance, and recyclability (80.5% height recovery after repeating 100 cycles at the strain of 80%). Due to the morphology and composition of the carbonized microfiber surface, the superhydrophobic materials with a water contact angle of 151.5°, could sorb various oils and organic solvents with 65-133 times its own weight and maintain 91.9% sorption capacity after 25 cycles. In addition, the aerogels could achieve the continuous separation of carbon tetrachloride (CCl₄) from water with a high flux rate of 11,718.8 L m^-2 h^-1. Therefore, our prepared NM/RCA aerogels are anticipated to have broad potential applications in oil purification and contaminant remediation.

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.

Cleanup of oils and organic solvents from contaminated water by biomass-based aerogel with adjustable compression elasticity

Leakage of oils and organic solvents poses a significant threat to aquatic environments. Here, low-temperature carbonized aerogels with highly porous and anisotropic structures obtained only from biomass-derived materials were proposed to absorb polymorphic oils from contaminated water. Specifically, carbonized aerogels prepared at temperatures of 300 °C and 350 °C exhibited ultra-high absorption capacities (40‒125 g g^-1) and oil-water separation efficiencies (> 99%) even in harsh environments, which were attributed to their exceptional properties, including high porosity, abundant macropores, excellent thermal stability, and hydrophobicity. Through citric acid crosslinking and low-temperature carbonization, the aerogels exhibited superior compression elasticity and could be cyclically utilized through simple extrusion while realizing the recovery of oils. Moreover, the outstanding photothermal conversion properties obtained through carbonization contributed to the high temperature and fluidity of the oils surrounding the aerogels, which is crucial for improving the absorption performance of high-viscosity oils. Such absorbent materials are used to separate crude oil from oil-water mixtures, which can achieve maximum absorption of 56 g g^-1 and increase the absorption rate (from several days to 10 min) in a low-temperature (4 °C) seawater environment.

Composite nanofiber formation using a mixture of cellulose acetate and activated carbon for oil spill treatment

Oil and organic pollutants are significant disasters affecting the aquatic ecosystem and human health. A novel nanofiber composite from cellulose acetate/activated carbon (CA/AC) was successfully fabricated by the electrospinning technique. CA/AC nanofiber composites were prepared from 10% (w/v) polymer solutions dissolving in DMA/acetone ratio 1:3 (v/v) with adding three different percentages of AC (3.7, 5.5, and 6.7%) to the total weight of CA. The prepared CA/AC nanofiber composite morphology reveals randomly oriented bead-free fibers with submicron fiber diameter. CA/AC nanofiber composites were further characterized by TGA, DSC, and surface area analysis. Water uptake was investigated for fabricated fibers at different pH. Oil adsorption was conducted in both static (oil only) and dynamic (oil/water) systems to estimate the adsorption capacity of prepared composites to treat heavy and light machine oils. The results showed increased oil adsorption capacity incorporating activated carbon into CA nanofiber mats. The maximum sorption capacity reached 8.3 and 5.5 g/g for heavy and light machine oils obtained by CA/AC5.5 (AC, 5.5%). A higher oil uptake was reported for the CA/AC composite nanofibers and showed a constant sorption capacity after the second recycles in the reusability test. Of isotherm models, the most applicable model was the Freundlich isotherm model. The result of kinetic models proved the fit of the pseudo-second-order kinetic model to the adsorption system.

Fabrication of Large Aerogel-Like Carbon/Carbon Composites with Excellent Load-Bearing Capacity and Thermal-Insulating Performance at 1800 °C

Carbon aerogels (CAs) are attractive candidates for the thermal protection of aerospace vehicles due to their excellent thermostability and thermal insulation. However, the brittleness and low mechanical strength severely limits their practical applications, and no significant breakthroughs in large CAs with a high strength have been made. We report a high-pressure-assisted polymerization method combined with ambient pressure drying to fabricate large, strong, crack-free carbon/carbon (C/C) composites with an excellent load-bearing capacity, thermal stability, and thermal insulation. The composites are comprised of an aerogel-like carbon matrix and a low carbon crystallinity fiber reinforcement, featuring overlapping nanoparticles, macro-mesopores, large particle contact necks, and strong fiber/matrix interfacial bonding. The resulting C/C composites with a medium density of 0.6 g cm^-3 have a very high compressive strength (80 MPa), in-plane shear strength (20 MPa), and specific strength (133 MPa g^-1 cm³). Moreover, the C/C composites of 7.5-12.0 mm in thickness exposed to an oxyacetylene flame at 1800 °C for 900 s display very low back-side temperatures of 778-685 °C and even better mechanical properties after the heating. This performance makes the composites ideal for the ultrahigh temperature thermal protection of aerospace vehicles where both excellent thermal-insulating and load-bearing capacities are required.

Construction of a carbon nanosphere aerogel with magnetic response for efficient oil/water separation

A magnetic carbon nanosphere aerogel with high adsorption capacity was synthesized, which could realize positioning adsorption and rapid recovery.

Strengthening Cellulose Nanopaper via Deep Eutectic Solvent and Ultrasound-Induced Surface Disordering of Nanofibers

The route for the preparation of cellulose nanofiber dispersions from bacterial cellulose using ethylene glycol- or glycerol-based deep eutectic solvents (DES) is demonstrated. Choline chloride was used as a hydrogen bond acceptor and the effect of the combined influence of DES treatment and ultrasound on the thermal and mechanical properties of bacterial cellulose nanofibers (BC-NFs) is demonstrated. It was found that the maximal Young’s modulus (9.2 GPa) is achieved for samples prepared using a combination of ethylene glycol-based DES and ultrasound treatment. Samples prepared with glycerol-based DES combined with ultrasound exhibit the maximal strength (132 MPa). Results on the mechanical properties are discussed based on the structural investigations that were performed using FTIR, Raman, WAXD, SEM and AFM measurements, as well as the determination of the degree of polymerization and the density of BC-NF packing during drying with the formation of paper. We propose that the disordering of the BC-NF surface structure along with the preservation of high crystallinity bulk are the key factors leading to the improved mechanical and thermal characteristics of prepared BC-NF-based papers.

Current Status of Cellulosic and Nanocellulosic Materials for Oil Spill Cleanup

Recent developments in the application of lignocellulosic materials for oil spill removal are discussed in this review article. The types of lignocellulosic substrate material and their different chemical and physical modification strategies and basic preparation techniques are presented. The morphological features and the related separation mechanisms of the materials are summarized. The material types were classified into 3D-materials such as hydrophobic and oleophobic sponges and aerogels, or 2D-materials such as membranes, fabrics, films, and meshes. It was found that, particularly for 3D-materials, there is a clear correlation between the material properties, mainly porosity and density, and their absorption performance. Furthermore, it was shown that nanocellulosic precursors are not exclusively suitable to achieve competitive porosity and therefore absorption performance, but also bulk cellulose materials. This finding could lead to developments in cost- and energy-efficient production processes of future lignocellulosic oil spillage removal materials.

Advanced super-hydrophobic polymer-based porous absorbents for the treatment of oil-polluted water

The threat of environmental pollution caused by spilled oil is rapidly increasing along with the expansion of oil exploration, the development of maritime activities and industrial growth. Oil spill incidents usually affect seriously the ecosystem and human life. Therefore, the treatment and recovery of the oil spill have been considered as an ultra-important issue to protect the environment and to minimize its negative impacts on socio-economic activities. Among methods of oil spill recovery, porous materials have emerged as potential absorbents possessing the capacity of absorbing spilled oil at a fast rate, high adsorption capacity, good selectivity, and high reusability. In this review paper, two types of polymer-based porous absorbents modified surface and structure were introduced for the treatment strategy of the oil-polluted water. In addition, the absorption mechanism and factors affecting the adsorption capacity for oils and organic solvents were thoroughly analyzed. More importantly, characteristics of polymer-based porous materials were discussed in detail based on microstructure analysis, absorption efficiency, and reusability. In general, this paper has provided an overview and a comprehensive assessment of the use of advanced polymer-based porous materials for the treatment of oil-polluted water, although the impacts of environmental factors such as wind, wave, and temperature should be further investigated in the future.

Cellulose-based special wetting materials for oil/water separation: A review

Oil spill accidents and oily wastewater discharged by petrochemical industries have severely wasted water resources and damaged the environment. The use of special wetting materials to separate oil and water is efficient and environment-friendly. Cellulose is the most abundant renewable resource and has natural advantages in removing pollutants from oily wastewater. The application and modification of cellulose as special wetting materials have attracted considerable research attention. Therefore, we summarized cellulose-based superlipophilic/superhydrophobic and superhydrophilic/superoleophobic materials exhibiting special wetting properties for oil/water separation. The treatment mechanism, preparation technology, treatment effect, and representative projects of oil-bearing wastewater are discussed. Moreover, cellulose-based intelligent-responsive materials for application to oil/water separation and the removal of other pollutants from oily wastewater have also been summarized. The prospects and potential challenges of all the materials have been highlighted.

Solar-Assisted, Fast, and In Situ Recovery of Crude Oil Spill by a Superhydrophobic and Photothermal Sponge

Development of a functional sorbent for effective crude oil absorption is essential to address large-scale spilling incidents. Herein, we demonstrate a facile method for preparing a superhydrophobic and photothermal PDMS/CuS/PDA@MF sponge through sequential depositions of PDA, CuS nanoparticles, and a PDMS layer onto a melamine sponge. The optimized composite sponge exhibits a superhydrophobic surface property, high absorption capacity for oils, robust recycling, and excellent photothermal conversion performance. Under sunlight irradiation, the sponge can be rapidly heat up for effectively reducing the viscosity of the surrounding crude oil in order to enhance its fluidity. As a result, uptake of crude oil can be achieved continuously at approximately 5.3 g/min using a peristaltic pump. Overall, we believe that a simple fabrication method from low-cost reagents and excellent crude oil remediation performance render the PDMS/CuS/PDA@MF sponge as an excellent sorbent candidate for remediating crude oil spill.

Facile Fabrication of Superhydrophobic Cross-Linked Nanocellulose Aerogels for Oil-Water Separation

A facile and environmental-friendly approach was developed for the preparation of the cross-linked nanocellulose aerogel through the freeze-drying process and subsequent esterification. The as-prepared aerogel had a three-dimensional cellular microstructure with ultra-low density of 6.05 mg·cm^-3 and high porosity (99.61%). After modifying by chemical vapor deposition (CVD) with hexadecyltrimethoxysilane (HTMS), the nanocellulose aerogel displayed stable super-hydrophobicity and super-oleophilicity with water contact angle of 151°, and had excellent adsorption performance for various oil and organic solvents with the adsorption capacity of 77~226 g/g. Even after 30 cycles, the adsorption capacity of the nanocellulose aerogel for chloroform was as high as 170 g/g, indicating its outstanding reusability. Therefore, the superhydrophobic cross-linked nanocellulose aerogel is a promising oil adsorbent for wastewater treatment.

Construction of a Superhydrophobic Sodium Alginate Aerogel for Efficient Oil Absorption and Emulsion Separation

Bio-based aerogels serve as potential materials in separation of oil/water mixtures. Nevertheless, there remain some key challenges, including expensive/toxic organic cross-linkers, unpromising reusability, and poor performance in emulsion separation. Hereby, a novel, robust, and superhydrophobic sodium alginate/graphene oxide/silicon oxide aerogel (SA/GO/SiO₂-M) was fabricated by simple calcium ion cross-linking self-assembly, freeze-drying, and chemical vapor deposition methods based on the renewable and abundant raw materials. The as-prepared SA-based aerogel possesses high absorbency for varieties of organic solvents and oils. Importantly, it shows high efficiency in the separation of surfactant-stabilized water-in-oil emulsions. SA/GO/SiO₂-M aerogels display excellent reusability in both absorption and separation because of their good mechanical properties in the air and oil phase, and the mechanism in emulsion separation is discussed. This study shows that SA/GO/SiO₂-M aerogels are a promising material in treating oil contaminants from different fields.