In-situ upcycling of cadmium from wastewater into core–shell ZnS@Zn0.58Cd0.42S heterojunction photocatalyst for environmental purification and H2 evolution

•Microalgae-derived yolk-shell microspheres were prepared to achieve Cd2+ upcycling.•Cd2+ from wastewater was directly in-site converted into photocatalyst (ZSC)•ZSC was demonstrated to have core–shell ZnS@Zn0.58Cd0.42S heterostructure.•ZSC shows excellent performance for H2 evolution and organic pollutant degradation.•Photocatalytic activity of ZSC was enhanced due to heterojunction.