Promoting the Photo-Fenton catalytic activity with carbon dots: Broadening light absorption, higher applicable pH and better reuse performance

A new visible and near-infrared light-responsive heterogeneous Photo-Fenton catalyst, Fe 3 O 4 @Cu 2 O/carbon quantum dots (CQDs)/nitrogen-doped carbon quantum dots (N-CQDs) (FCCN) was prepared under mild conditions with the structure of double quantum dots growing on the surface of Fe 3 O 4 @Cu 2 O nanoparticles. The prepared FCCN could be used for the degradation of azo compounds, such as methyl orange, acid orange II and mordant yellow 10, even at neutral and alkaline pH (pH: 7–12) with a shortest complete degradation time of 15 min. During the Photo-Fenton process, CQDs and N-CQDs acting as up-converting photo-sensitizers improved the utilization of the light, in which the contribution of N-CQDs was greater than that of CQDs. Besides, CQDs and N-CQDs could transfer photo-generated charges between Cu 2 O and Fe 3 O 4 for the rapid decomposition of H 2 O 2 to OH. CQDs as solid light-sensitive acid sites could consume OH − and enable the efficient decomposition of H 2 O 2 under alkaline conditions. The magnetism of Fe 3 O 4 made this catalyst easily separated and the insoluble layers of CQDs and N-CQDs allowed it to be repeatedly used without activity change even after 10 cycles. The degradation constant of methyl orange in FCCN/H 2 O 2 /light system is 5.4 times higher than that of the Fe 3 O 4 @Cu 2 O/H 2 O 2 /light system, indicating that the loaded quantum dots greatly enhanced the photocatalytic activity. The degradation constant in FCCN/H 2 O 2 /light system was 2.5 times higher than that of the simple mixture (Fe 3 O 4 @Cu 2 O + CQDs + N-CQDs)/H 2 O 2 /light system, which indicated these excellent catalytic performances should come from the synergism effect of all components in FCCN.