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.