Preparation of N-I co-doped TiO2 supported on activated carbon photocatalyst for efficient photocatalytic reduction of Cr(VI) ions

Photocatalytic reduction of Cr(VI) is a safe, economical and clean method. In this study, a series of photocatalysts based on N-I co-doped TiO2 supported on activated carbon (denoted as x/yNIT@AC-z, N-I/Ti = x/y, calcination temperature = z degrees C) were synthesized, characterized and utilized for Cr(VI) photocatalytic reduction. Results of characterization revealed that all the prepared TiO2 existed in the form of monocrystalline tetragonal anatase phase with the particle size of 20 nm. Among them, 1/2NIT@AC-350 exhibited the highest photocatalytic performance. 1/2NIT@AC-350 showed a narrow band gap of 2.77 eV, which was chiefly because of the role of defect levels caused by pentavalent iodine, interstitial and substitutional nitrogen. 1/2NIT@AC-350/UV light/citric acid system exhibited the complete removal of 50 mg/L Cr(VI), over four successive reuse cycles without any obvious decrease in its photocatalytic reduction capability. In addition, the activated carbon in 1/2NIT@AC-350 provided a high concentration reaction environment for TiO2 via electrostatic attraction, which makes the photocatalyst possess a strong photocatalytic reaction driving force even at low concentration. Cr(VI) was also successfully removed in an actual water matrix (Yangtze river). This study provides a promising demonstration for the treatment of environmental pollutants, especially for Cr(VI) in wastewater effluents.

Automated summary

The study successfully synthesized a series of N-I co-doped TiO2 catalysts, among which 1/2NIT@AC-350 showed the best photocatalytic reduction performance for Cr(VI). This catalyst has a narrow band gap and stable photocatalytic capability, allowing for complete removal of Cr(VI) in water systems.