Synthesis of N doped-CQDs/Ni doped-ZnO nanocomposites for visible light photodegradation of organic pollutants

Abstract

Nowadays, visible light-driven nanophotocatalysts are being developed for high-efficiency removal of organic pollutants. Carbon quantum dots (CQDs) have been widely investigated as a superior candidate for improving the photocatalytic activity of various nanocomposites. In this paper, a nickel-doped ZnO photocatalyst was surface-modified using hydrothermally prepared nitrogen-doped carbon quantum dots for the first time. The synthesized nanocomposite (N-CQDs/Ni-ZnO) was then characterized using SEM, EDX, XRD, FT-IR, PL, and DRS analyses. The presence of Ni and N-CQDs and their effects on the band gap reduction of the ZnO and improvement of electron/hole pairs separation were confirmed with XRD, EDX, PL and DRS tests. The photocatalytic activity of the N-CQDs/Ni-ZnO was tested for methylene blue dye removal from aqueous solution under visible light irradiation. After 120 min of irradiation, the optimum photocatalyst could degrade about 87 % of the MB under the visible light irradiation. The kinetics of the MB dye degradation was modeled according to Langmuir–Hinshelwood model and k was 0.015. Also, the effects of pH and photocatalyst dosage were examined for optimizing the photocatalytic activity of the N-CQDs/Ni-ZnO. According to the results, the optimum pH was approximated at 11 (alkaline) and the best results were obtained with 0.05 g of the photocatalyst per 50 ml of a 50 ppm MB dye solution for the top synthesized nanophotocatalyst (1.5 N-CQDs/6 wt.% Ni-ZnO). The reusability experiments for the prepared nanophotocatalyst showed that the prepared N-CQDs/Ni-ZnO possessed excellent stability after four reaction cycles. The findings of this study can be used in industrial applications.