Enhanced visible-light-driven photocatalytic activity of bi-phase titanium dioxide @ covalent organic framework Z-scheme system for photocatalytic removal of Cr (VI)

The discharge of industrial heavy metal wastewater not only leads to environmental pollution, but also harms human health, so it is imperative to control heavy metal pollution. In the current work, a sequence of anatase/ brookite TiO2@COF with different mass ratios, bi-phase TiO2 and bare COF were successfully synthesized by simple hydrothermal synthesis. The photocatalytic activity of the prepared catalysts was assessed by reducing Cr (VI) in model pollutant (K2Cr2O7). Under the condition of pH = 3, the Cr(VI) reduction rate of TiO2@COF-4 was as high as 99.19% in 30 min. The photocatalytic activity of TiO2@COF-4 remained stable in four consecutive cycles, suggesting that it has a potential application prospect for the removal of Cr(VI) in the actual environment. The morphology and structure of photocatalysts were observed by different techniques (SEM/EDS, HRTEM, BET analysis, XRD, FTIR and XPS). The specific reasons for the enhancement of photocatalytic performance of materials were explored by different methods (PL, UV-vis DRS, Mott-Schottky plots, I-T curves and EIS). Finally, we concluded that the photocatalytic system of TiO2@COF-4 may follow the typical direct Z- scheme mechanism. This work provides an effective solution for the water treatment of heavy metal pollution.

Automated summary

In this study, a series of catalysts were successfully synthesized and their photocatalytic activity towards the model pollutant Cr(VI) was evaluated. Among them, TiO2@COF-4 showed high efficiency in removing Cr(VI) within 30 minutes and remained stable in consecutive cycles. The morphology and structure of the catalysts were observed using various techniques, and the reasons for the enhancement in photocatalytic performance were analyzed. The experimental results suggested that the photocatalytic system of TiO2@COF-4 may follow a typical direct Z-scheme mechanism. These findings provide an effective solution for water treatment of heavy metal pollution.