Hydrothermal synthesis of Mo,N-CQDs Co-modified BiVO4 for enhanced photocatalytic degradation of methylene blue under visible light

In response to the need for efficient elimination of methylene blue (MB) from dye-containing wastewater, a Mo, N-co-doped carbon quantum dot-modified BiVO 4 (5% Mo, N-CQDs/BiVO 4 ) composite photocatalyst was developed. Pristine BiVO 4 suffers from rapid charge carrier recombination and limited visible-light utilization. Introduction of Mo, N-CQDs establishes a synergistic enhancement mechanism: (1) Mo, N-CQDs act as electron mediators, improving interfacial charge separation and migration, as evidenced by reduced charge transfer resistance. Mo doping introduces impurity energy levels that trap electrons and retard recombination, while nitrogen doping enhances electron tunneling and reduces interfacial resistance. (2) UV-Vis DRS confirms bandgap narrowing and enhanced visible-light absorption. (3) Photoelectrochemical analysis reveals significantly enhanced photocurrent response and reduced charge transfer resistance, confirming improved charge separation efficiency. Under visible light, the composite achieved a degradation rate constant of 0.04089 min −1 toward MB, a 3.31-fold enhancement over pure BiVO 4 , with >95% removal within 80 min. Radical trapping identified superoxide radicals (·O 2 − ) and holes (h + ) as the predominant active species, with h + contributing ∼62% of the activity. The catalyst retained 88.65% of its initial efficiency after four cycles, demonstrating good stability. This study provides a viable charge-regulation strategy using multi-element co-doped carbon quantum dots for semiconductor modification, highlighting its potential in dye wastewater treatment.