An overview and recent progress in photocatalytic Cr(VI) reduction and hydrogen evolution

The problems of environmental pollution caused by Cr(VI) wastewater and energy crisis have received intensive attention because of the rapid development of industrialization process. Semiconductor-based photocatalysis was deemed as an idea strategy to solve these issues. Regarding this, photocatalytic mechanisms of Cr(VI) reduction and hydrogen evolution were first introduced. Then this study first reviewed the recent research progress in photocatalytic reduction of Cr(VI) based on various semiconductor materials such as pristine and doped photocatalysts, metal organic frameworks (MOFs) photocatalysts, heterojunction photocatalysts (type-II heterojunction, direct and indirect Z-scheme heterojunctions and S-scheme heterojunction). We concluded that a broad scope of photocatalytic materials was available and deserve in-depth investigation for promising applications. Converting Cr(VI) wastewater to hydrogen energy before being discarded into the environment may be a novel idea for future research. Hence we also summarized the recent advancements in hydrogen generation from Cr(VI) wastewater based various heterojunctions. Finally, further challenges and developments were proposed. Photocatalytic technique offers a sustainable and efficient and strategy for addressing environmental and energy problems.