Adsorption-Induced In-Situ Construction of TiO2 Hollow Sphere/UiO-66-NH2 Heterostructures with Boosted Photocatalytic Activity toward Cr(VI) Reduction

Water contamination caused by highly toxic Cr(VI) should be resolved imminently with a more efficient photocatalytic approach. The interaction between photocatalyst heterostructure is critical for charge separation which largely affects the photocatalytic efficiency. Herein, TiO2 hollow sphere/UiO-66-NH2 (TiO2/UiO-66-NH2) heterostructures were successfully synthesized by an adsorption-induced in-situ solvothermal growth strategy. The UiO-66-NH2 particles were well dispersed on TiO2 hollow spheres by solvothermal treatment of Zr4+ adsorbed TiO2 hollow spheres with NH2-BDC ligand. The photocatalytic activities of TiO2/UiO-66-NH2 heterostructures were investigated by reduction of Cr(VI) with visible light irradiation. With the introduction of UiO-66-NH2, the reduction efficiency toward Cr(VI) by TiO2/UiO-66-NH2 heterostructures reached 89% after 180 min of irradiation, which is much higher than those of TiO2 hollow spheres (10%) and UiO-66-NH2 crystals (29%). Moreover, the TiO2/UiO-66-NH2 heterostructures display good regeneration ability and can still maintain 70% of Cr(VI) removal ability after four cycles. The integration of TiO2 and UiO-66-NH2 could construct a type-II heterojunction to broaden the absorption range of light and suppress the recombination of photoproduced electrons and holes. As a result, such unique composite structure significantly enhance the photocatalytic performance towards Cr(VI) reduction. This work not only inspires a new approach for in-situ solvothermal synthesis of semiconductor@MOFs composites, but provides a novel photocatalyst for highly efficient removal of Cr(VI) from wastewater.

Automated summary

Water contamination by toxic Cr(VI) can be solved effectively using a more efficient photocatalytic approach. The interaction between photocatalyst heterostructure is crucial for charge separation, which greatly impacts the photocatalytic efficiency. TiO2 hollow sphere/UiO-66-NH2 (TiO2/UiO-66-NH2) heterostructures were successfully synthesized through an adsorption-induced in-situ solvothermal growth method. The introduction of UiO-66-NH2 significantly enhanced the reduction efficiency of Cr(VI) by TiO2/UiO-66-NH2 heterostructures, reaching 89% after 180 minutes of irradiation, much higher than TiO2 hollow spheres (10%) and UiO-66-NH2 crystals (29%). The TiO2/UiO-66-NH2 heterostructures also displayed good regeneration ability and maintained 70% of Cr(VI) removal capacity after four cycles. The integration of TiO2 and UiO-66-NH2 could form a type-II heterojunction, expanding the absorption range of light and suppressing recombination of photogenerated electrons and holes. This research not only provides a new approach for in-situ solvothermal synthesis of semiconductor@MOFs composites, but also offers a novel photocatalyst for highly efficient removal of Cr(VI) from wastewater.