Synthesis of biochar/clay mineral nanocomposites using oil shale semi-coke waste for removal of organic pollutants

Due to the poor surface/interfacial interaction and the large gaps in the size and microstructure between biomass and clay mineral, it was difficult to adjust the structure and performance of biochar/clay mineral composites at the molecular level. Herein, oil shale semi-coke composed of multi-minerals and organic matters was used as a promising precursor to prepare biochar/clay mineral nanocomposites via phosphoric acid-assisted hydrothermal treatment followed by KOH activation for removal of organic pollutants from aqueous solution. The results revealed that the nanocomposites presented well-defined sheet-like morphology, and the carbon species uniformly anchored on the surface of clay minerals. With the changes in the pore structure, surface charge and functional groups after two-step modification, the nanocomposites exhibited much better adsorption property toward organic pollutants than the raw oil shale semi-coke, and the maximum adsorption capacities of methylene blue, methyl violet, tetracycline, and malachite green were 165.30 mg g(-1), 159.02 mg g(-1), 145.89 mg g(-1), and 2137.36 mg g(-1), respectively. The adsorption mechanisms involved electrostatic attraction, pi-pi stacking and hydrogen bonds. After five consecutive adsorption-desorption, there was no obvious decrease in the adsorption capacity of malachite green, exhibiting good cyclic regeneration performance. It is expected to provide a feasible strategy for the preparation of biochar/clay mineral nanocomposites with the excellent adsorption performances for removal of organic pollutants based on full-component resource utilization of oil shale semi-coke. [GRAPHICS]