ZnO Nanoparticles Modified by Carbon Quantum Dots for the Photocatalytic Removal of Synthetic Pigment Pollutants

Abstract

Synthetic pigment pollutants caused by the rapid development of the modern food industry have become a serious threat to people's health and quality of life. Environmentally friendly ZnO-based photocatalytic degradation exhibits satisfactory efficiency, but some shortcomings of large band gap and rapid charge recombination reduce the removal of synthetic pigment pollutants. Here, carbon quantum dots (CQDs) with unique up-conversion luminescence were applied to decorate ZnO nanoparticles to effectively construct the CQDs/ ZnO composites via a facile and efficient route. The ZnO nanoparticles with a spherical-like shape obtained from a zinc-based metal organic framework (zeolitic imidazolate framework-8, ZIF-8) were coated by uniformly dispersive quantum dots. Compared with single ZnO particles, the obtained CQDs/ZnO composites exhibit enhanced light absorption capacity, decreased photoluminescence (PL) intensity, and improved visible-light degradation for rhodamine B (RhB) with the large apparent rate constant (k app ). The largest k app value in the CQDs/ZnO composite obtained from 75 mg of ZnO nanoparticles and 12.5 mL of the CQDs solution (∼1 mg•mL −1 ) was 2.6 times that in ZnO nanoparticles. This phenomenon may be attributed to the introduction of CQDs, leading to the narrowed band gap, an extended lifetime, and the charge separation. This work provides an economical and clean strategy to design visible-light-responsive ZnObased photocatalysts, which is expected to be used for the removal of synthetic pigment pollutants in food industry.