Efficient degradation of dye wastewater with a novel tribocatalytic process initiated by CQDs-Bi2MoO6 catalyst: Preparation, degradation, kinetics, DFT calculations and mechanism

Tribocatalysis is becoming a novel method to decompose organic pollutants. In this work, an efficient tribocatalyst CQDs-Bi2MoO6 was prepared and evaluated by structural characterizations (SEM, TEM, XRD, BET, XPS, UV-vis DRS and PL) and electrical analysis (EIS, LSV, Mott-Schottky), and results displayed that the optimal dosage of CQDs was 5 wt% (namely CQDs(5 wt%)-Bi2MoO6). Then, CQDs-Bi2MoO6 tribocatalytic degradation of RhB was investigated detailedly, and results showed that almost 100% RhB was degraded within 5 h under the optimum. Intermediates were detected via LC-MS/MS and their toxicity was evaluated with T.E.S.T software. Major active free radicals were detected with ESR and scavengers' test. Both of them proved the presence of h(+), center dot O-2(-) and center dot OH during tribocatalytic degradation and meanwhile the contribution order of the above-mentioned radicals was as follows: h(+) > center dot O-2(-) > center dot OH. DFT calculations and tribocatalytic degradation kinetics were also investigated, as well. DFT calculations not only provided the orbit structure of CQDs(5 wt%)-Bi2MoO6, but also deduced the probable attack position of RhB molecule. And based on it, tribocatalytic mechanism involved in friction -> electrons' transition and transfer -> forming h(+), center dot O-2(-) and center dot OH -> decomposing RhB were proposed, providing some valuable insights for the application of tribocatalytic process to wastewater treatment.