Application of graphene aerogels in oil spill recovery: A review

Facile and green fabrication of biodegradable aerogel from chitosan derivatives/modified gelatin as absorbent for oil removal

Frequent oil spills have caused increasingly severe pollution of marine water bodies. As a result, exploring green and efficient aerogels to tackles oil pollution is in high demand. In this work, a unique strategy for preparing all-biomass aerogel was innovatively proposed. A series of all-biomass CW&BW@DCGA aerogels were successfully prepared by multiple dynamic covalent bonding, in which carboxymethyl chitosan (CMCS) as the substrate material, modified gelatin (Gel-ADH) as a reinforcing agent, and dialdehyde β-cyclodextrin (Da-β-CD) as a non-toxic cross-linking agent. The resulting aerogels were further hydrophobically modified with a green and natural wax blend consisting of carnauba wax (CW) and beeswax (BW). The experimental results demonstrated that incorporating Gel-ADH significantly improved the elastic properties of the materials. Specifically, when m(CMCS):m(Gel-ADH) = 7:3, the aerogel exhibited outstanding resilience, with 60 % compressive strain. In addition, CW&BW@DCGA displayed excellent hydrophobicity, boasting a water contact angle as high as 148.6°, and impressive absorption capacities ranging from 31.7 to 62.5 g/g towards different oils. Its adsorption capacity remained close to 70 % after 10 cycles, indicating favorable reusability. The dynamic absorption processes towards gasoline, diesel, and soybean oil were also well fitted with the pseudo-second-order kinetic model, suggesting that the process is primarily governed by chemisorption.

Hydrophobic dual-polymer-reinforced graphene composite aerogel for efficient water-oil separation

Addressing the environmental challenges posed by oil spills and industrial wastewater is critical for sustainable development. Graphene aerogels demonstrate significant potential as highly efficient adsorbents due to their high specific surface area, excellent structural tunability and outstanding chemical stability. Among available fabrication methods, the hydrothermal self-assembly technique stands out for its low cost, high tunability and good scalability. However, brittleness caused by stacking and agglomeration of graphene layers during self-assembly remains a significant challenge. In this study, we present a green and efficient self-assembly strategy combining a one-step hydrothermal process with a solution immersion method to fabricate a PDMS-coated epoxidized natural rubber-graphene composite aerogel (P@EGA). The resulting aerogel exhibits a high specific surface area (482.362 m2 g-1), hierarchical pore distribution from microporous to macroporous, ultra-low density (0.0104 g cm-3) and excellent hydrophobicity (contact angle = 147.6°). Remarkably, it retains 97.54% of its compressive stress after 50 compression-release cycles at 80% strain and quickly recovers its shape under a 500 g load. The P@EGA aerogel demonstrates outstanding adsorption capacities (65.37-132.75 g g-1) for various oils and organic solvents, complete oil absorption in 0.4 seconds, and effortless regeneration through simple squeezing. Furthermore, its dual functionality in gravity-driven and powered water-oil separation systems underscores its broad application potential in environmental remediation.

Comprehensive insights into the application of graphene-based aerogels for metals removal from aqueous media: Surface chemistry, mechanisms, and key features

Efficient removal of heavy metals and other toxic metal pollutants from wastewater is essential to protect human health and the surrounding vulnerable ecosystems. Therefore, significant efforts have been invested in developing practical and sustainable tools to address this issue, including high-performance adsorbents. In this respect, within the last few years, graphene-based aerogels/xerogels/cryogels (GBAs) have emerged and drawn significant attention as excellent materials for removing and recovering harmful and valuable metals from different aqueous media. Such an upward trend is mainly due to the features of the aerogel materials combined with the properties of the graphene derivatives within the aerogel's network, including the GBAs' unique three-dimensional (3D) porous structure, high porosity, low density, large specific surface area, exceptional electron mobility, adjustable and rich surface chemistry, remarkable mechanical features, and tremendous stability. This review offers a comprehensive analysis of the fundamental and practical aspects and phenomena related to the application of GBAs for metals removal. Herein, we cover all types of (bottom-up) synthesized GBAs, including true microporous graphene-based aerogels as well as other 3D graphene-based open-cell interconnected mesoporous and macroporous aerogels, foams, and sponges. Indeed, we provide insights into the fundamental understanding of the GBAs' suitability for such an important application by revealing the mechanisms involved in metals removal and the factors inducing and controlling the highly selective behavior of these distinctive adsorbents. Besides conventional adsorptive pathways, we critically analyzed the ability of GBAs to electrochemically capture metal pollutants (i.e., electrosorption) as well as their efficiency in metals detoxification through reductive mechanisms (i.e., adsorption-reduction-readsorption). We also covered the reusability aspect of graphene aerogels (GAs)-based adsorbents, which is strongly linked to the GBAs' outstanding stability and efficient desorption of captured metals. Furthermore, in view of their numerous practical and environmental benefits, the development and application of magnetically recoverable GAs for metals removal is also highlighted. Moreover, we shed light on the potential practical and scalable implementation of GBAs by evaluating their performance in continuous metals removal processes while highlighting the GBAs' versatility demonstrated by their ability to remove multiple contaminants along with metal pollutants from wastewater media. Finally, this review provides readers with an accessible overview and critical discussion of major recent achievements regarding the development and applications of GAs-based adsorbents for metal ions removal. Along with our recommendations and suggestions for potential future work and new research directions and opportunities, this review aims to serve as a valuable resource for researchers in the field of wastewater treatment and inspire further progress towards developing next-generation high-performance GBAs and expanding their application.

The role of graphene aerogels in rechargeable batteries

Energy storage systems, particularly rechargeable batteries, play a crucial role in establishing a sustainable energy infrastructure. Today, researchers focus on improving battery energy density, cycling stability, and rate performance. This involves enhancing existing materials or creating new ones with advanced properties for cathodes and anodes to achieve peak battery performance. Graphene aerogels (GAs) possess extraordinary attributes, including a hierarchical porous and lightweight structure, high electrical conductivity, and robust mechanical stability. These qualities facilitate the uniform distribution of active sites within electrodes, mitigate volume changes during repeated cycling, and enhance overall conductivity. When integrated into batteries, GAs expedite electron/ion transport, offer exceptional structural stability, and deliver outstanding cycling performance. This review offers a comprehensive survey of the advancements in the preparation, functionalization, and modification of GAs in the context of battery research. It explores their application as electrodes and hosts for the dispersion of active material nanoparticles, resulting in the creation of hybrid electrodes for a wide range of rechargeable batteries including lithium-ion batteries (LIBs), Li-metal-air batteries, sodium-ion batteries (SIBs), zinc-ion batteries (AZIBs) and zinc-air batteries (ZABs), aluminum-ion batteries (AIBs) and aluminum-air batteries and other.

Recent advances in functional micro/nanomaterials for removal of crude oil via thermal effects

Crude oil is one of the most widely used energy and industrial raw materials that is crucial to the world economy, and is used to produce various petroleum products. However, crude oil often spills during extraction, transportation and use, causing negative impacts on the environment. Thus, there is a high demand for products to remediate leaked crude oil. Among them, oleophilic and hydrophobic adsorbents can absorb crude oil through thermal effects and are research hotspots. In this review, we first present an overview of wettability theory, the heating principles of various thermal effects, and the theory of reducing crude oil viscosity by heating. Then we discuss adsorbents based on different heating methods including the photothermal effect, Joule heating effect, alternating magnetic field heating effect, and composite heating effect. Preparation methods and oil adsorption performance of adsorbents are summarized. Finally, the advantages and disadvantages of various heating methods are briefly summarized, as well as the prospects for future research.

Fabrication of a poly(N-isopropylacrylamide)-grafted alginate composite aerogel for efficient treatment of emulsified oily wastewater

The treatment of emulsion wastewater poses significant challenges. In this study, a novel porous material, namely esterified bagasse/poly(N, N-dimethylacrylamide)/sodium alginate (SBS/PDMAA/Alg) aerogel, was developed for efficient demulsification and oil recovery. By grafting a poly(N-isopropylacrylamide) (PNIPAM) brush onto the SBS/PDMAA/Alg skeleton through free radical polymerization, the resulting aerogel exhibits both surface charge and a molecular brush structure. The aerogel demonstrates remarkable demulsification efficiency for cationic surfactant-stabilized emulsions at various concentrations, achieving a demulsification efficiency of 95.6% even at an oil content of 100 g L-1. Furthermore, the molecular brush structure extends the application range of the aerogel, enabling a demulsification efficiency of 98.3% for anionic and non-ionic surfactant-stabilized emulsions. The interpenetrating polymer network (IPN) structure formed by SBS, PDMAA, and alginate enhances the mechanical stability of the aerogel, enabling a demulsification efficiency of 91.3% even after 20 repeated cycles. The demulsification ability of the composite aerogel is attributed to its surface charge, high interfacial activity, and unique brush-like structure. A demulsification mechanism based on the synergistic effect of surface charge and molecular brush is proposed to elucidate the efficient demulsification process.

Sodium Alginate Aerogel as a Carrier of Organogelators for Effective Oil Spill Solidification and Recovery

Marine oil spills pose a serious threat to the marine ecological environment. Phase-selective organogelators (PSOGs) are ideal candidates for oil spill gelation when used in combination with a mechanical recovery method. However, the toxicity of an organic solvent carrier has become a key problem when it is applied in the remediation of marine oil pollution. In this study, through an inexpensive and nontoxic ionic cross-linking and freeze-drying method, we successfully developed composite oil gelling agents that used a biomass sodium alginate aerogel as the carrier of 12-hydroxystearic acid (12-HSA). Simultaneously, carboxylated cellulose nanofibers (CNF-C) with large specific surface area and graphene oxide (GO) with excellent mechanical properties as reinforcing fillers were combined with an alginate matrix. 12-HSA, as a green and inexpensive organic gelator, was uniformly loaded on the aerogels by vacuum impregnation. The sodium alginate aerogel was capable of absorbing and storing oil due to its three-dimensional network skeleton and high porosity. Rheological studies have demonstrated that the organic gelator 12-HSA can be released from the aerogel substrate and self-assemble to form an oleogel with the absorbed oil quickly. The synergistic effect between absorption and congelation endows the composite oil gelling agent with efficient oil spill recovery capability. Based on eco-friendly, biodegradable, and simple synthesis methods, this composite oil gelling agent shows great potential for application in marine oil spill recovery.

TDA/rGO@WS with Joule heat and photothermal synergistic effect: A promising adsorption material for all-weather recovery of viscous oil spills at sea

Oil spills are a global environmental protection challenge, and traditional adsorption materials have poor effect on low temperature and high viscosity marine oil spills. This article reports composite adsorption materials TDA/rGO@WS for viscous oil spills: loaded with rGO/TDA coating on a commercial biomass wood pulp sponge (WS), achieving Joule heating, photothermal effect and hydrophobic modification. The results showed that the TDA/rGO@WS has good photothermal conversion ability and Joule heating ability, and the temperature increased to 83.7 °C and 148 °C, respectively, under simulated solar irradiation and additional voltage at room temperature. The efficiency of adsorption at a low temperature of 5 °C increased by 22.41% at 1 sun and by 51.53% at 10 V. Temperature effectively reduced the viscosity of the offshore oil spill and ensures the efficient adsorption of oil spills at low temperatures promoted. The TDA/rGO@WS also showed good hydrophobicity (WCA=129°), excellent efficiency of water-oil separation (99.53%) and good adsorption capacity (9.4-13.68 g/g) for marine fuel oils. TDA/rGO@WS effectively solves the problem of cleaning up high-viscosity oil spills from ships in winter and polar waters, and proposes a new strategy for all-weather efficient treatment of oil spills at sea.

Influence of boron doping level and calcination temperature on hydrogen evolution reaction in acid medium of metal-free graphene aerogels

In this work, metal-free boron-doped graphene-based aerogels were successfully synthesized via a one-step autoclave assembly followed by freeze-drying and used as electrocatalysts for the hydrogen evolution reaction (HER) in acidic media. The synthesized reduced graphene oxide aerogels (rGOA) showed improved electrocatalytic activity by introducing boron and structural defects. The amount of boric acid used both as a dopant and reducing agent in the synthesis was optimized (boric acid/GO mass ratio = 17.5) to practically reach the crystallization limit of boric acid (boric acid/GO mass ratio = 20). It was observed that the higher the amount of boric acid added, the more boron was incorporated into the carbonaceous structure, improving the electrocatalytic activity of the final aerogel. Furthermore, calcination of the boron-doped electrocatalyst at 600 °C resulted in final aerogels with low oxygen content, moderate surface area, bimodal pore size distribution, and a high electrochemical active surface area. The final 3D graphene aerogel developed in this work, showed such outstanding electrocatalytic activity in HER as to replace noble metal-based electrocatalysts in the future.

Tunable optical and semiconducting properties of eco-friendly-prepared reduced graphene oxide

Wide bandgap oxidized graphenes have garnered particular interest among the materials explored for these applications because of their exceptional semiconducting and optical properties. This study aims to investigate the tunability of the related properties in reduced graphene oxide (rGO) for potential use in energy conversion, storage, and optoelectronic devices. To accomplish this, we scrutinized crucial parameters of the synthesis process such as reduction time and temperature. Our findings demonstrate that controlling these parameters makes it possible to customize the optical bandgap of reduced graphene oxide within a range of roughly 2.2 eV-1.6 eV. Additionally, we observed that reduced graphene oxide has strong and superior absorption in the visible region, which is attributable to the existence of OFGs and defects. Notably, our results indicate that the absorption coefficients of reduced graphene oxide are up to almost three times higher (7426 ml mg-1 m-1) than those observed in dispersions of exfoliated graphene and graphene oxide (GO). To complement our findings, we employed several spectroscopic and morphological characterizations, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and electrical measurements. The implications of our results are significant for the development and design of future semiconductors for energy conversion and optoelectronic applications.

Temperature-Dependent Optical Properties of Oxidized Graphenes

In this study, we investigate how changing important synthesis-related parameters can affect and control the optical characteristics of graphene oxide (GO) and reduced graphene oxide (rGO). These parameters include drying time and reduction time at two different temperatures. We obtain an understanding of their impact on optical transitions, optical bandgap, absorption coefficient, and absorbance spectrum width by analyzing these factors. Accordingly, GO has an optical bandgap of about 4 eV, which is decreased by the reduction process to 1.9 eV. Both GO and rGO display greater absorption in the visible spectrum, which improves photon capture and boosts efficiency in energy conversion applications. Additionally, our results show that GO and rGO have higher absorption coefficients than those previously reported for dispersions of exfoliated graphene. Defects in GO and rGO, as well as the presence of functional oxygen groups, are the main contributors to this increased absorption. Several measurements are carried out, including spectroscopic and morphological studies, to further support our findings.

Sustainable Solution for Plastic Pollution: Upcycling Waste Polypropylene Masks for Effective Oil-Spill Management

The use of Polypropylene PP in disposable items such as face masks, gloves, and personal protective equipment has increased exponentially during and after the COVID-19 pandemic, contributing significantly to microplastics and nanoplastics in the environment. Upcycling of waste PP provides a useful alternative to traditional thermal and mechanical recycling techniques. It transforms waste PP into useful products, minimizing its impact on the environment. Herein, we synthesized an oil-sorbent pouch using waste PP, which comprises superposed microporous and fibrous thin films of PP using spin coating. The pouch exhibited super-fast uptake kinetics and reached its saturation in fewer than five minutes with a high oil uptake value of 85 g/g. Moreover, it displayed high reusability and was found to be effective in absorbing oil up to seven times when mechanically squeezed between each cycle, demonstrating robust oil-sorption capabilities. This approach offers a potential solution for managing plastic waste while promoting a circular economy.

Marine oil spill remediation by Candelilla wax modified coal fly ash cenospheres

Biodegradable candelilla wax (CW) was creatively used for hydrophobic modification of coal fly ash cenospheres (FACs), a waste product from thermal power plants, and a new spherical hollow particulate adsorbent with fast oil adsorption rate and easy agglomeration was prepared. CW was confirmed to physically coat FACs and the optimum mass of wax added to 3 g of FACs was 0.05 g. From a series of batch scale experiments, CW-FACs were found to adsorb oil, reaching adsorption efficiency of 80.6% within 10 s, and aggregate into floating clumps which were easily removed from the water's surface. The oil adsorption efficiency was highly dependent on hydrophobicity of the used adsorbent, the adsorption of Venezuela oil onto CW-FACs was found to be a homogenous monolayer, and the capacity and intensity of the adsorption decreased as temperature increased from 10 to 40 °C. The Langmuir isotherm model was the best fit, with the maximum adsorption capacity achieved at 649.38 mg/g. CW-FACs were also found to be highly stable in concentrated acid, alkaline and salt solutions, as well as for spills of different oil products. Furthermore, the retention rate of the oil adsorption capacity of the CW-FACs after 6 cycles of adsorption-extraction was as high as 93.2%. Therefore, CW-FACs can be widely used, easily recycled, and reused for marine oil spill remediation, which is also a good alternative disposal solution for FACs.

Ultralight and highly efficient oil-water selective aerogel from carboxymethyl chitosan and oxidized β-cyclodextrin for marine oil spill cleanup

Biomass-based aerogels for oil spill cleanup have attracted tremendous research interests due to their feasibility in oil-water separation. However, the cumbersome preparation process and toxic cross-linking agents hinder their application. In this work, a facile and novel method to prepare hydrophobic aerogels is reported for the first time. Da-β-CD/CMCS aerogel (DCA), Da-β-CD/CMCS/PVA aerogel (DCPA), and hydrophobic Da-β-CD/CMCS/PVA aerogel (HDCPA) were successfully synthesized via the Schiff base reaction between carboxymethyl chitosan (CMCS) and dialdehyde β-cyclodextrin (Da-β-CD). Meanwhile, polyvinyl alcohol (PVA) acted as reinforcement and hydrophobic modification was conducted via chemical vapor deposition (CVD). The structure, mechanical properties, hydrophobic behaviors and absorption performance of aerogels were comprehensively characterized. The results indicated that the DCPA containing 7 % PVA exhibited excellent compressibility and elasticity even at a compressive strain of ε = 60 %, however, the DCA without PVA showed incompressibility, suggesting that the important role played by PVA in improving compressibility. Moreover, HDCPA possessed excellent hydrophobicity (water contact angle up to 148.4°), which could be well maintained after experiencing wear and corrosion in harsh environments. HDCPA also possesses high absorption capacities (24.4-56.5 g/g) towards different oils with satisfied recyclability. These advantages endow HDCPA with great potential and application prospects in offshore oil spill cleanup.