A heterogeneous nanocomposite catalyst constructed by the Co 3 O 4 nanorods decorated with the Cu 2 O quantum dots (QDs) were successfully synthesized via a simple hydrothermal method followed by an oxidation-reduction processing. The fabricated Cu 2 O/Co 3 O 4 nanocomposite was characterized by the SEM, TEM, XPS, XRD, UV–vis and PL, and the (2 2 0) and (3 1 1) facets of the Co 3 O 4 were exposed. Compared with the original Co 3 O 4 nanorods with an average diameter of 350 nm, a substantial decrease in the band gap was observed after doping the nanorods with the Cu 2 O QDs (average diameter of 5 nm). Such a dramatic decrease in the band gap indicated a significant enhancement of the photocatalytic activities under visible light. The methylene blue (MB) dye and the phenol were used as model organic pollutants, and the Cu 2 O/Co 3 O 4 nanocomposite catalyst exhibited both high catalytic activity and good recycling stability. The catalytic activities of the Cu 2 O/Co 3 O 4 /potassium monopersulfate triple salt (PMS) system for cleaving the MB and the phenol were dependent on the dosages of the Cu 2 O QDs, and the calculated degradation rates achieved by 7.0 wt% Cu 2 O/Co 3 O 4 nanocomposite catalyst were about 11.3 and 1.8 times than that of the pristine Co 3 O 4 nanorod catalyst for the MB and the phenol, respectively. The reactive species of O 2 − and the holes were determined to be the main active species for the phenol photocatalytic degradation by the 7 wt% Cu 2 O/Co 3 O 4 /PMS system and the 7 wt% Cu 2 O/Co 3 O 4 /H 2 O 2 system, respectively.
Herein, H + in oxalic acid is used instead of Na + to obtain titanate nanosheets through P200 hydrolysis, which further curls to form a multilayer TiO 2 nanotubes (NTs) structure. Then, Cu 2 O quantum dots (QDs) are successfully loaded on TiO 2 NTs via a hydrothermal method using fructose as a reducing agent. The optical, impedance, and photocurrent tests indicate that the composite structure improves its optoelectronic performance. The photocatalytic H 2 production and CO 2 reduction efficiency of Cu 2 O QDs/TiO 2 NTs are lower than those of TiO 2 NTs. However, the molar ratio of CH 4 to CO produced by CO 2 reduction of Cu 2 O QDs/TiO 2 NTs composite catalyst is greater than that of pure TiO 2 NTs. The CH 4 production accounts for 97%, indicating that the composite catalyst has a high CH 4 selectivity. The experimental and density functional theory calculation results prove that the Z-scheme heterojunction accelerates the separation and transfer of photogenerated carriers, and broadens the absorption range of visible light.