Carbon quantum dots (CQDs)/noble metal co-decorated MIL-53(Fe) as difunctional photocatalysts for the simultaneous removal of Cr(VI) and dyes

Industrial sewage often contain metal ions and dyes, and it is difficult to efficiently remove them simultaneously. In this work, novel ternary MIL-53(Fe)/carbon quantum dots/noble metal (MIL-53(Fe)/CQDs/MNPs, MNPs = Ag, Pd, Au) nanocomposites have been rationally constructed and successfully fabricated by a facile two-step strategy with self-assembling and in-situ photoreduction. The resulting MIL-53(Fe)/CQDs/2%Au composite exhibits excellent photoactivity for the Cr(VI) reduction, the reduction ratio is nearly 100% after 20 min of visible light illumination. The rate constant of MIL-53(Fe)/CQDs/2%Au is calculated to be 0.1820 min(-1), which is around 7.4, 2.76, 1.77 and 1.47 times higher than that of as-prepared MIL-53(Fe), MIL-53(Fe)/CQDs, MIL-53 (Fe)/CQDs/2%Ag and MIL-53(Fe)/CQDs/2%Pd, respectively. More significantly, MIL-53(Fe)/CQDs/2%Au nanocomposite has been proven to serve as bifunctional photocatalyst for simultaneously removing Cr(VI)/dye mixed system pollutants. The superior photoactivity may be due to the enhanced light absorption intensity, the superior electrical conductivity of Au and CQDs, as well as surface plasmon resonance (SPR) effect of Au. In particular, the possible photocatalytic reaction mechanism has been carefully investigated and proposed.