Immobilization of ZnIn₂S₄ on sodium alginate foam for efficient hexavalent chromium removal

Photocatalytic technology has been extensively studied in the removal of toxic Cr(VI) from wastewater. However, common powdery photocatalysts suffer from poor recyclability and secondly pollution. Herein, the zinc indium sulfide (ZnIn₂S₄) particles were integrated onto the sodium alginate foam(SA) matrix through a facile way to obtain foam-shape catalyst. Diverse characterization techniques including X-ray diffraction(XRD), Fourier transform infrared(FT-IR), scanning electron microscope(SEM) and X-ray photoelectron spectroscopy(XPS) were employed to reveal the composite compositions, organic-inorganic interface interactions, mechanical property, and pore morphology of the foams. Results demonstrated that the ZnIn₂S₄ crystals wrapped on SA skeleton tightly and constructed a flower-like structure. As-prepared hybrid foam with lamellar structure showed great potential in Cr(VI) treatment due to the presence of macropores and highly available active sites. A maximum Cr(VI) photoreduction efficiency of 93 % were observed over the optimal sample of ZS-1 (with a ZnIn₂S₄:SA mass ratio of 1:1) under visible irradiation. When tested with mixed pollutants (Cr(VI)/dyes), the ZS-1 sample displayed an enhanced removal efficiency of 98 % for Cr(VI) and 100 % for Rhodamine B(RhB). Moreover, the composite maintained prominent photocatalytic performance and a relatively integral 3D structure scaffold after continuous six runs, revealing its superior reusability and durability.