Biochar is a stabilized carbon-rich product, and has drawn scientists’ interest because of its specific properties and potential use in many environmental areas. It is emphasized that innovative technologies comprised of engineered nanoparticles in conventional biochar systems could ameliorate the functions of biochar to some extent, such as carbon sequestration, soil fertility and wastewater treatment. As a result, it enables an enhanced sorption of both inorganic and organic pollutants to their surfaces, reducing environmental fate and mobility. In this study, biochar and graphene-coated biochars were prepared by dip-coating of biomass by slow pyrolysis. Batch sorption experiments were performed on the resultant biochars to evaluate sorption ability. The graphene covering on biochar surface changes to increase the surface properties of the biochars, exhibiting the greatest surface area, pore volume and carbon content. Graphene-coated biochars had the ultimate sorption ability compared to their corresponding chars. The sorption data indicated that electrostatic attraction, π-π interaction between graphene sheets on the char surface and aromatic domain, was the controlling mechanism for the sorption of organic chemicals onto the chars. Graphene-coated biochars can thus be used as a stable, cheap sorbent, biomaterial for the removal of organic pollutants from aqueous media.

Graphene oxide (GO) membranes (GOMs) are robust and demonstrate excellent rejection of ions and are promising for use in water treatment. However, maintaining the stability of GOMs during processing and scale-up is difficult in practice and is somewhat counterintuitive. Herein, we report the synthesis of GOM by the blade casting technique, followed by cation (K⁺, Na⁺, Li⁺, Mg²⁺, Ca²⁺, and Ba²⁺) intercalation, leading to membranes that possess different thicknesses and interlayer spacings. The thickness and interlayer spacing as controlled by different cations were crosschecked after immersion in water and the changes were examined by SEM and XRD. The thickness and interlayer spacing was ultimately dependent on the hydrated radius of the cations and only K⁺, Mg²⁺, Ca²⁺, and Ba²⁺ were able to effectively stabilize GOM. Moreover, GOM with Ca²⁺ (GOM-Ca²⁺), and after reduction (GOM-Ca²⁺-R), was further examined in water, acidic and alkaline solutions to check the stability. The water flux of GOM-K⁺, GOM-Ba²⁺, GOM-Ca²⁺ and GOM-Mg²⁺ was decreased relative to membrane thickness, whereas the rejection % of different ions (Na⁺, Cu²⁺, Ni²⁺, Pb²⁺ and Mg²⁺) was based on the interlayer spacing. Based on these findings, we demonstrate a simple and scalable method to obtain graphene-based membranes with good stability, adjustable thickness and tunable interlayer spacing, thereby eliminating the problems caused by aggregation and functional moieties.

Accidental oil spills during oil exploration, production and transportation constitute a significant environmental threat, and thus remain a major challenge. Given that, common polymeric membranes often exhibit surface fouling, which limits their long term practical applications and makes it hard to recycle them with efficient flux stability and separation efficiency. Herein, we report a versatile porous structured polyvinyl alcohol (PVA) based nanofibrous membrane (NFM) with graphene oxide (GO), prepared by simple and straightforward electrospinning, to remediate oily water. The PVA–GO NFM was prepared keeping in view an effective pore geometry and selective wettability to facilitate oily water emulsion separation entirely under gravitational force, with a controlled GO ratio and compatibility to avoid aggregation, allowing easy spin ability. The morphology of the PVA NFM was completely changed in the presence of GO due to homogenous distribution with robust mechanical strength and outstanding thermal stability. As a result, the as-prepared PVA–GO NFM achieves a separation efficiency of above 99% for surfactant-free and surfactant-stabilized oily water emulsions with a water flux of approximately 45 and 30 L m⁻² h⁻¹, entirely under gravitational force due to the presence of GO. Furthermore, the PVA–GO NFM maintains its actual selectivity and surface wettability even after recycling, thereby allowing long term applications with almost the same separation efficiency and water flux. The present methodology for membrane fabrication is believed to be an effective energy saving filtration approach, with anti-oil property and reusability, and thus is promising for practical use in water purification and treatment processes, specifically for oily water remediation.