3D graphene-based adsorbents: Synthesis, proportional analysis and potential applications in oil elimination

The effect of chemical bond and solvent solubility parameter on stability and absorption value of functionalized PU sponge

Seawater pollution from various sources such as industrial effluents, ship washing at sea, and oil spills harm humans and the marine environment. Therefore, finding ways to eliminate this pollution is crucial. This study successfully modified a polyurethane sponge through a simple dip-coating method with functionalized graphene oxide incorporating octadecylamine and oleic acid, resulting in a hydrophobic sponge capable of absorbing crude oil and various organic solvents. Characterization analyses confirmed the synthesis. The absorption capacity of the modified sponges was examined, for example, the PU sponge has absorbed 4 g/g engine oil, while the modified GO-ODA-PU sponge has increased its absorption to 36 g/g. The GO-ODA-PU sponge demonstrated great reusability compared to the GO-OA-PU sponge owing to the strong covalent bond formed between GO and ODA, which is superior to the weak hydrogen bond formed between GO and OA. The absorption capacity of the GO-OA-PU sponge decreased by 30%. The contact angle test showed that GO-ODA-PU and GO-OA-PU sponges had contact angles of 131° and 115°, respectively. Additionally, the GO-ODA-PU sponge performed optimally for semi-polar solvents in the solubility parameter range of 18-19, with its absorption capacity reaching its maximum value. The amount of oil recycling is even possible up to 98%.

SiO2/Zn0.4Co0.6Fe2O4 aerogel: an efficient and reusable superparamagnetic adsorbent for oily water remediation

Magnetic SiO2/Zn0.4Co0.6Fe2O4 aerogels were successfully prepared by sol-gel method with two different drying steps: ambient pressure drying (APD) and freeze-drying (FD). The surface chemistry of silica was modified to be hydrophobic by oleic acid. The prepared materials were fully characterized, displaying superparamagnetic behavior with saturation magnetizations of 10.2 and 15.1 emu g-1, and contact angles of ∼130° and ∼140° for the materials prepared by the APD and FD methods, respectively, indicating the hydrophobic surfaces of the prepared materials. This hydrophobicity allows the efficient separation of oil. Specifically, as high as 1.7 and 2 g g-1 adsorption capacities were obtained when using APD-dried and FD-dried silica aerogels, respectively, suggesting the preference for the FD method. Additionally, magnetic recovery and reuse of the adsorbents were successfully implemented in an attempt to reduce the overall practical application costs. To sum up, the prepared materials are good candidates for oil removal from wastewater and the protection of the environment.

Large-flake graphene-modified biochar for the removal of bisphenol S from water: rapid oxygen escape mechanism for synthesis and improved adsorption performance

The combined effects of graphene and biochar for enhanced adsorption of organic pollutants have not been demonstrated yet. Therefore, the mechanisms of graphene-modified biochar synthesis and its application to adsorption of contaminants remain unclear. In this study, the effect of flake-size graphene on biochar modification and its bisphenol S (BPS) adsorption performance was explored for the first time. Three sizes of graphene oxide were used as the precursor to prepare graphene/biochar composites using pyrolysis. It was found that the graphene with a small flake size was interspersed in the macropores of biochar, while the biochar was completely or mostly wrapped by the large-sized graphene sheet, which effectively prevented the agglomeration and pore blockage of biochar. Large-flake graphene oxide modified biochar (LGB) showed the highest adsorption capacity towards BPS, exhibiting 2.8 times higher adsorption than pristine biochar. Density functional theory (DFT) calculation suggested that the maximum diffusion barrier of O atoms in graphene coated cellulose (most frequently used biochar representative) could be reduced significantly (∼46%) at pyrolysis temperature of 873 K. Taking the advantage of small amount of graphene and enhanced adsorption performance, LGB could be a promising adsorbent for the removal of certain organic pollutants from wastewater and is conducive for the development of high-valued biochar modification.

One-Step Synthesis of 3D Pore-Structured Adsorbent by Cross-Linked PEI and Graphene Oxide Sheets and Its Application in CO2 Adsorption

In this study, a one-step method of polyethylenimine (PEI) cross-linking graphene oxide (GO) was used to prepare a 3D pore-structured adsorbent with abundant amine groups for chemisorption of CO₂. The cross-linking of PEI with GO sheets and the vacuum freeze-drying step are the keys to the formation of the 3D pore structure. The results of characterization analysis revealed that the as-prepared adsorbent had a 3D porous structure rich in amine groups. Besides, the adsorption/desorption test showed that the prepared adsorbent has excellent and stable adsorption performance, and the maximum CO₂ adsorption capacity is 2.18 mmol/g at 343 K and 10 vol % CO₂. Moreover, the adsorption kinetics analysis indicated that the adsorption process was dominated by homogeneous adsorption, and the adsorbent had a strong affinity with CO₂. Finally, the correlation analysis shows that the kinetic constants obtained by the Avrami model simulation can be effectively used for the actual CO₂ adsorption process design.