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Water contamination by hexavalent chromium (Cr(VI)) poses a significant threat to human health, necessitating innovative and environmentally friendly solutions. One promising method involves using biochar loaded with green-synthesized nanoscale zero-valent iron (nZVI). This study successfully prepared an efficient green-modified biochar material, TP-nZVI/BC, by combining tea polyphenol (TP) and sludge biochar (BC) through a low-cost green synthesis method.

The research optimized the preparation conditions of TP-nZVI/BC using response surface methodology (RSM). It was found that the dosage of tea polyphenols is critical to the material’s performance, followed by reaction time and temperature. The optimal conditions for maximum Cr(VI) removal were determined to be a TP dosage of 48 g/L, a reaction temperature of 75℃, and a reaction time of 3 hours. Under these conditions, TP-nZVI/BC removed Cr(VI) at a rate 7.6 times higher than BC alone.

The study revealed that the pseudo-second-order kinetic model accurately describes the adsorption process, indicating that chemical adsorption primarily controls the removal of Cr(VI). Additionally, the Langmuir model effectively described the adsorption behavior, with TP-nZVI/BC achieving a maximum adsorption capacity of 105.65 mg/g. Analytical techniques, such as FTIR and XPS, confirmed the crucial role of nZVI in the reduction process of Cr(VI) and highlighted the synergistic effects of surface adsorption, reduction, and co-precipitation in enhancing Cr(VI) removal.

In conclusion, green-modified biochar represents a feasible and promising method for Cr(VI) removal from water, offering significant environmental benefits and potential for widespread application.