Although　adsorption　is　regarded　as　a　facile　and　efficient　method　to　remove　heavy　metals　from　polluted　water,　the　disposal　of　the　spent　adsorbents　remains　a　great　challenge.　Here,　an　＇adsorbent-to-photocatalyst＇　conversion　strategy　is　reported.　One-unit-cell　calcium　silicate　hydrate　(CSH)　nanosheets　(~2.8　nm)　are　used　as　an　ideal　adsorbent,　and　four　typical　heavy　metals　including　Cu2+,　Zn2+,　Co2+,　and　Cd2+　ions　are　selected　for　studies.　CSH　nanosheets　show　superiority　in　the　ultrahigh　specific　surface　area　(577.8　m2　g−1)　and　chemical　stability.　After　the　heavy　metal　removal,　the　CSH　nanosheets　containing　heavy　metal　ions　are　transformed　into　metal　sulfides　through　in　situ　sulfurization　treatment.　Interestingly,　in　the　case　of　Cd2+　ions,　CdS　nanoparticles　are　produced　and　well　dispersed　on　the　surface　of　CSH　nanosheets.　CSH-CdS　has　a　narrow　bandgap　of　2.34　eV　and　shows　the　photoabsorption　edge　up　to　visible　light　(550　nm).　Besides,　CSH-CdS　also　possesses　a　suitable　energy　band　structure,　making　itself　an　ideal　photocatalyst　for　CO2　reduction　under　visible　light　(λ　＞　420　nm).　The　＇adsorbent-to-photocatalyst＇　conversion　strategy　demonstrated　here　not　only　ameliorates　the　water　and　air　pollution　but　also　produces　the　valuable　chemical　feedstock　(CO　and　H2).　©　2021　Elsevier　B.V.