Enhanced adsorption and visible-light photocatalytic degradation of toluene by CQDs/UiO-66 MOG with hierarchical pores

The development of photocatalytic materials with both promising adsorption capacity and high visible-light activity is essential for the highly-efficient and stable photocatalytic degradation of toluene. In this work, a series of carbon quantum dots (CQDs) decorated UiO-66 metal–organic-frameworks gel (MOG) composites (CQDs/UiO-66 MOG) with hierarchical pore structures were prepared. The introduction of CQDs effectively improved the light utilization and promoted the separation of photo-induced electrons and holes, which were beneficial for the generation of active free radicals. Besides, benefiting from the hierarchical pore structure of UiO-66 MOG and the new adsorption sites provided by CQDs, 0.5 wt% CQDs/UiO-66 MOG showed a high toluene adsorption capacity (29.06 μmol/g) and its enhanced degradation efficiency for toluene was 4.4 times higher than that of pristine UiO-66 MOG. Both in-situ Fourier transform infrared (FTIR) and Gas Chromatography–Mass Spectrometer (GC–MS) were conducted to give the possible degradation pathways. Toluene was firstly converted into xylene and benzene, and then degraded into acids, aldehydes, alcohols before fully mineralized into carbon dioxide. A relatively high CO2 conversion ratio (85%) of toluene was obtained when applying 0.5 wt% CQDs/UiO-66 MOG as the photocatalyst, together with less intermediates detected, confirming the positive role of CQDs decoration in the effective mineralization of toluene. This work sheds new light on MOG material optimization and degradation of low-concentration flowing toluene.