UV-Vis Activated Cu 2 O/SnO 2 /WO 3 Heterostructure for Photocatalytic Removal of Pesticides.

A three-steps sol-gel method was used to obtain a Cu 2 O/SnO 2 /WO 3 heterostructure powder, deposited as film by spray pyrolysis. The porous morphology of the final heterostructure was constructed starting with fiber-like WO 3 acting as substrate for SnO 2 development. The SnO 2 /WO 3 sample provide nucleation and grew sites for Cu 2 O formation. Diffraction evaluation indicated that all samples contained crystalline structures with crystallite size varying from 42.4 Å (Cu 2 O) to 81.8 Å (WO 3 ). Elemental analysis confirmed that the samples were homogeneous in composition and had an oxygen excess due to the annealing treatments. Photocatalytic properties were tested in the presence of three pesticides-pirimicarb, S-metolachlor (S-MCh), and metalaxyl (MET)-chosen based on their resilience and toxicity. The photocatalytic activity of the Cu 2 O/SnO 2 /WO 3 heterostructure was compared with WO 3 , SnO 2 , Cu 2 O, Cu 2 O/SnO 2 , Cu 2 O/WO 3 , and SnO 2 /WO 3 samples. The results indicated that the three-component heterostructure had the highest photocatalytic efficiency toward all pesticides. The highest photocatalytic efficiency was obtained toward S-MCh (86%) using a Cu 2 O/SnO 2 /WO 3 sample and the lowest correspond to MET (8.2%) removal using a Cu 2 O monocomponent sample. TOC analysis indicated that not all the removal efficiency could be attributed to mineralization, and by-product formation is possible. Cu 2 O/SnO 2 /WO 3 is able to induce 81.3% mineralization of S-MCh, while Cu 2 O exhibited 5.7% mineralization of S-MCh. The three-run cyclic tests showed that Cu 2 O/SnO 2 /WO 3 , WO 3 , and SnO 2 /WO 3 exhibited good photocatalytic stability without requiring additional procedures. The photocatalytic mechanism corresponds to a Z-scheme charge transfer based on a three-component structure, where Cu 2 O exhibits reduction potential responsible for O 2 production and WO 3 has oxidation potential responsible for HO· generation.