Study on the Enhanced Remediation of Petroleum-Contaminated Soil by Biochar/g-C₃N₄ Composites

This work developed an environmentally-friendly soil remediation method based on BC and g-C₃N₄, and demonstrated the technical feasibility of remediating petroleum-contaminated soil with biochar/graphite carbon nitride (BC/g-C₃N₄). The synthesis of BC/g-C₃N₄ composites was used for the removal of TPH in soil via adsorption and photocatalysis. BC, g-C₃N₄, and BC/g-C₃N₄ have been characterized by scanning electron microscopy (SEM), Brunauer-Emmett-Teller surface area analyzer (BET), FT-IR, and X-ray diffraction (XRD). BC/g-C₃N₄ facilitates the degradation due to reducing recombination and better electron-hole pair separation. BC, g-C₃N₄, and BC/g-C₃N₄ were tested for their adsorption and photocatalytic degradation capacities. Excellent and promising results are brought out by an apparent synergism between adsorption and photocatalysis. The optimum doping ratio of 1:3 between BC and g-C₃N₄ was determined by single-factor experiments. The removal rate of total petroleum hydrocarbons (TPH) by BC/g-C₃N₄ reached 54.5% by adding BC/g-C₃N₄ at a dosing rate of 0.08 g/g in a neutral soil with 10% moisture content, which was 2.12 and 1.95 times of BC and g-C₃N₄, respectively. The removal process of TPH by BC/g-C₃N₄ conformed to the pseudo-second-order kinetic model. In addition, the removal rates of different petroleum components in soil were analyzed in terms of gas chromatography-mass spectrometry (GC-MS), and the removal rates of nC₁₃-nC₃₅ were above 90% with the contaminated soil treated by BC/g-C₃N₄. The radical scavenger experiments indicated that superoxide radical played the major role in the photocatalytic degradation of TPH. This work definitely demonstrates that the BC/g-C₃N₄ composites have great potential for application in the remediation of organic pollutant contaminated soil.