“One-pot” synthesis of Au–ZnO–SiO2 nanostructures for sunlight photodegradation

•Low cost photoactive materials (∼90% efficiency) under sunlight irradiation.•One-step synthesis of Au–ZnO–SiO2 synergistic couple for VIS dye degradation (73%).•Au–ZnO–SiO2 for tandem adsorption–photodegradation of cationic dyes (0–60 mg L−1).•Effective dye removal at low content of ZnO (0.13%) and Au (0.02%) components.•Band gap energy (2.25 eV) and surface area, parameters that controls dye removal.

Effective low cost photoactive adsorbent materials (∼90% efficiency, 0–60 mg L−1 dye loading), under sunlight irradiation, at a very low content of functional components (0.13% ZnO and 0.02% Au), were designed by incorporating ZnO and Au nanoparticles as synergistic couple in silica matrix. The tandem Au/ZnO dispersed into silica matrix formed a Schottky barrier in this type of structure and thus the band gap energy was reduced to 2.25 eV and the photocatalytic activity under visible light irradiation was increased. Highly homogeneous distribution of ZnO quantum dots (4 nm) and gold plasmons (7 nm) into the silica matrix, by a convenient “one-pot” synthesis way, namely microemulsion assisted sol–gel procedure was reported. The study of how the Au/ZnO ratio (0.01/1, 0.1/1 and 1/1) affects the silica based materials activity was evaluated and the optimal Au/ZnO ratio (0.1/1) was established. The silica network formed around the Au and ZnO nanoparticles which were confined within the microemulsions colloidal aggregates, improved the stability of the final materials in different environments and the direct contact between dye and Au–ZnO couple. Tandem adsorption and photodegradation processes, following a first order kinetics, described the path ways and mechanism of interaction between dye molecules and materials surface.

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