Development of photocatalytic reduction system for Cr(Ⅵ) in solution with modified g-C₃N₄

Heavy metal pollution, particularly Cr(VI) contamination, has recently garnered significant attention. Cr(VI), which is commonly discharged in industrial wastewater, is a serious environmental and health threat due to its carcinogenic and mutagenic properties. Developing effective methods to reduce Cr(VI) to Cr(III)—a less toxic form—is therefore highly desirable. In this study, we developed an environmentally friendly and highly efficient photocatalytic method for Cr(VI) reduction. The reduction efficiency was enhanced by using modified carbon nitride under visible-light irradiation. For catalyst preparation, urea was dissolved in pure water and heated in an electric furnace at a rate of 2 °C/min to 600 °C, and this temperature was held for 2 hours. A modified version, g-C3N4 (HB), was synthesized by adding 5 mg of 1,3,5-HB before calcination. For the reduction experiments, the reaction solution was prepared with 30 ppm of Cr(VI), 100 ppm of EDTA, and 15 mg of photocatalyst. The mixture was stirred in the dark for 30 minutes to achieve adsorption/desorption equilibrium, followed by 90 minutes of irradiation with blue light (450 nm). The Cr(VI) concentration was analyzed using the diphenylcarbazide method, with the absorbance measured by a UV–visible spectrophotometer. The incorporation of 1,3,5-HB into carbon nitride increased the reduction rate by 40%, likely due to the introduction of hydroxyl groups into the carbon nitride framework. Additionally, calcination at 550 °C yielded higher reduction rates after 90 minutes compared to 600 °C, possibly because the lower temperature minimized catalyst loss during calcination. In future studies, we plan to confirm the structural changes using techniques such as SEM and TEM and evaluate the catalytic performance through electrochemical measurements.