Self-Standing Adsorbent Composites of Waste-Derived Biochar and Reduced Graphene Oxide for Water Decontamination

Adsorption is one of the simplest and most cost-effective techniques for water decontamination. In this field, biochar has recently emerged as a promising alternative to traditional adsorbents, exhibiting a high surface area and affinity to metal ions, as well as often being waste-derived. Similarly, reduced graphene oxide (rGO) shows an excellent adsorption capacity. Having self-assembling properties, it has already been employed to obtain self-standing heavy-metal-adsorbing membranes. In this research, a novel self-standing membrane of biochar and rGO is presented. It was obtained through an eco-friendly method, consisting of the simple mechanical mixing of the two components, followed by vacuum filtration and mild drying. Vine pruning biochar (VBC) was employed in different rGO/biochar mass ratios, ranging from 1/1 to 1/9. The best compromise between membrane integrity and biochar content was achieved with a 4/6 proportion. This sample was also replicated using chestnut-shell-derived biochar. The composite rGO-biochar membranes were characterized through XRD, FTIR-ATR, TG-DTG, SEM-EDX, BET, ZP, particle dimension, and EPR analyses. Then, they were tested for metal ion adsorption with 10 mM Cu²⁺ and 100 mM Zn²⁺ aqueous solutions. The adsorption capacity of copper and zinc was found to be in the range of 1.51-4.03 mmol_Cu g^-1 and 18.16-21.99 mmol_Zn g^-1, respectively, at an acidic pH, room temperature, and contact time of 10 min. Interestingly, the composite rGO-biochar membranes exhibited a capture behavior between that of pure rGO and VBC.