A visible light-driven photocatalysis process by alginate beads coupled with in-situ cadmium sulfide prepared for decontamination in aqueous solutions with treatment of chromium as an example

Abstract

An innovative photocatalysis process with alginate beads coupled with cadmium sulfide was developed for decontamination in waters via visible light. As hexavalent chromium is highly toxic and carcinogenic to humans, it was selected as a model contaminant to study the efficiency of process. A cadmium sulfide (CdS) incorporated sodium alginate (SA) bead was first synthesized by the in-situ encapsulation method that was utilized to ensure an even distribution of CdS within the beads. 1% SA and 1-mM CdS were selected for the synthesis of bead that was effective in the photocatalysis. pH 5 was the optimal condition for the reduction of Cr(VI) with the minimal Cd leakage. Such sacrificial agents as lactic and formic acids accelerated the Cr(VI) reduction, achieving a nearly complete transformation while fulfilling the water discharge requirement at a contact time of 3 h. It is suggested to further improve the reusability of the beads by increasing the cross-linking between carboxylic group and Cd. The CdS-SA bead was stable during the process, as proven by the characterization studies. Cr(VI) ion was removed slightly by adsorption mechanism while mainly by photocatalytic reduction mechanism. This study provides a stable CdS-SA bead for an effective and efficient photocatalytic reduction of Cr(VI) in the water under the visible light.