Composite ZIF-8 with CQDs for boosting visible-light-driven photocatalytic removal of NO

Metal–organic frameworks (MOFs) with the advantage of high surface area are attracting growing concern in photocatalysis, but the limitations of no visible light response and low carrier migration efficiency also exist in MOFs materials. Carbon quantum dots (CQDs) with unique optical properties are a novel class of carbon nanomaterials, which have attracted extensive attention in the field of photocatalysis. In this work, compositing with CQDs for realizing MOFs visible-light photocatalytic NO performance was elucidated. We synthesized CQDs/ZIF-8 composite via a simple surface soaking approach, and the 0.5-CQDs/ZIF-8 composite showed the best removal performance of NO, which was ∼43%. The effect of CQDs on boosting visible-light photocatalytic activity of ZIF-8 was explored based on the photocurrent test, electrochemical impedance spectra, activity tests and radical trapping experiment under different monochromatic light irradiation, up-conversion photoluminescence spectra of CQDs, and electron spin resonance spectroscopy measurement. These results demonstrated compositing with CQDs is an effective way to boost the visible-light photocatalytic activity of ZIF-8, in which CQDs improves the visible light utilization and carrier separation efficiency. Apart of that, the results fully proved that the up-conversion effect indeed played a role in driving ZIF-8 into visible light response owing to the still working holes (h+) under 500 nm of monochromatic light irradiation. The possible NOx removal mechanism over CQDs/ZIF-8 composite was then proposed in the work.