Novel biomass carbon dots/chitosan hydrogel-modified TiO2: An effective reduction of Cr(VI) in various wastewater under sunlight

• TiO 2 was modified by the novel biomass CDs and CS hydrogel. • P-CDs/TiO 2 @CS shows the remarkable reduction of Cr(VI) under natural sunlight. • P-CDs/TiO 2 @CS demonstrates outstanding recyclability and antibacterial properties. • P-CDs/TiO 2 @CS has excellent performance in Cr(VI) wastewater treatment . Hexavalent chromium (Cr(VI)) poses a serious threat to the environment and human health owing to its inherent toxicity. Photocatalysis technology has garnered widespread attention owing to its efficiency and environmental friendliness. However, existing photocatalysts are constrained by light conditions, low reduction rates, and lack of studies in real wastewater. In this study, biomass carbon dots (P-CDs) were synthesized from peanut shell powder, then combined with chitosan (CS) and TiO 2 to create a novel photocatalyst (9:1 1 % P-CDs/TiO 2 @CS). The photocatalyst exhibited a smaller band gap and a broader light absorption range than TiO 2 , while the porous structure of the hydrogel increased the contact area between P-CDs/TiO 2 @CS and Cr(VI), thereby enhancing its photocatalytic performance. Our study demonstrates that under simulated sunlight using a xenon lamp, 0.2 g of 9:1 1 % P-CDs/TiO 2 @CS reduced 50 mg/L Cr(VI) at a rate of 99.64 % in 30 min (pH 7). The photocatalyst also exhibited excellent reduction capabilities for Cr(VI) across a pH range (pH 2–9), at different concentrations (10, 20, 30, 40, 50, and 60 mg/L), and in various real wastewater samples (influent, effluent, and electroplating wastewater). After five cycles, the reduction rate was still maintained at 90.38 %. Experiments conducted under natural sunlight and ion interference further confirmed its outstanding photocatalytic performance and stability in real-world applications. Free radical trapping experiments indicated that electrons (e - ) and holes (h + ) were the primary active species. Additionally, antibacterial experiments showed that the reactive oxygen species generated by the photocatalyst under light irradiation effectively inhibited the proliferation of Escherichia coli. Thus, P-CDs/TiO 2 @CS holds significant potential for practical application in environmental wastewater treatment .