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

A novel hybrid Cu 2 O@TiO 2 - g -zinc-tetraamino-phthalocyanine (CT- g -ZnTAPc) hollow sphere as “ day-night ” photocatalyst with spatially separated structures was prepared successfully. Firstly, three layers SiO 2 @Cu 2 O@TiO 2   (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 TiO 2 as the main visible light absorber, while the inner surface was adhered with Cu 2 O as a secondary absorption of the scattered light. Both of Cu 2 O and ZnTAPc sensitized TiO 2 synergistically to broaden light response from ultraviolet to visible region and enhance photocatalytic activity. Meanwhile, TiO 2 - g -ZnTAPc and Cu 2 O@TiO 2 p–n heterojunctions based on the close match band structures, so they were expected to facilitate electron-hole separation more effectively. Moreover, TiO 2 would capture electrons from Cu 2 O and ZnTAPc under visible light and delayed releasing electrons without illumination to perform photocatalyzing in dark as “ day-night ” photocatalysts. K 2 Cr 2 O 7   (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 Cu 2 O@TiO 2 and 1.64 times of TiO 2 - g -ZnTAPc. Furthermore, CT- g -ZnTAPc had a high specific surface area   (219.3 m 2 /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.