A hybrid hollow spheres Cu2O@TiO2-g-ZnTAPc with spatially separated structure as an efficient and energy-saving day-night photocatalyst for Cr(VI) reduction and organic pollutants removal

Abstract A novel hybrid Cu2O@TiO2-g-zinc-tetraamino-phthalocyanine (CT-g-ZnTAPc) hollow sphere as “day-night” photocatalyst with spatially separated structures was prepared successfully. Firstly, three layers SiO2@Cu2O@TiO2 (SCT) was synthesized with core–shell structure. Then zinc-tetraamino-phthalocyanine (ZnTAPc) immobilized on the surface of maleic anhydride (MAH) modified SCT with amide linkages. Finally, hollow CT-g-ZnTAPc spheres were obtained by NaOH etching. In this structure, ZnTAPc was grafted on the outer surface of TiO2 as the main visible light absorber, while the inner surface was adhered with Cu2O as a secondary absorption of the scattered light. Both of Cu2O and ZnTAPc sensitized TiO2 synergistically to broaden light response from ultraviolet to visible region and enhance photocatalytic activity. Meanwhile, TiO2-g-ZnTAPc and Cu2O@TiO2 p–n heterojunctions based on the close match band structures, so they were expected to facilitate electron-hole separation more effectively. Moreover, TiO2 would capture electrons from Cu2O and ZnTAPc under visible light and delayed releasing electrons without illumination to perform photocatalyzing in dark as “day-night” photocatalysts. K2Cr2O7 (Cr (VI)), Rhodamine B (RhB) and tetracycline hydrochloride (TC•HCl) were employed as model pollutants as well as Cr (VI)-RhB coexistence system. Almost 95.2% of Cr (VI) could be reduced by CT-g-ZnTAPc, which was about 1.57 times of Cu2O@TiO2 and 1.64 times of TiO2-g-ZnTAPc. Furthermore, CT-g-ZnTAPc had a high specific surface area (219.3 m2/g) as an efficient pollutant adsorbent, and was investigated by Langmuir, Freundlich and Temkin isotherm models. The maximum quantity of Cr (VI) adsorbed by CT-g-ZnTAPc was 48.8 mg/g. As a result, CT-g-ZnTAPc would be a potential effective and energy-saving multifunctional photocatalyst.