Synthesis, characterization, and photocatalytic activity of a carboxymethyl cellulose sodium-based hybrid material for efficient degradation of hexavalent chromium.

Conventional water treatment technologies often struggle to eliminate Cr(VI) effectively. Consequently, developing efficient and cost-effective photocatalysts for degrading Cr(VI) has emerged as a promising approach to environmental remediation. In this study, two novel cellulose-based photocatalytic hydrogel materials, designated CF and CFS, were synthesized by cross-linking varying concentrations of Fe(III) and Fe(III) + sodium citrate (SC) with sodium carboxymethyl cellulose (CMC), marking their first application in the photocatalytic reduction of Cr(VI) in aquatic environments. Photocatalytic degradation experiments revealed that the Fe(III) concentration was 0.3 M with a Fe(III): SC molar ratio of 2:1, 150 mg/L Cr(VI) could be 100 % degraded within 90 min. The microscopic structure and chemical properties of photocatalysts were thoroughly characterized, and the results confirmed the successful cross-linking of CMC with Fe(III) and Fe(III) + SC. Optical and electrochemical tests indicated that CFS exhibited a broader visible-light absorption range, a narrower band gap, and significantly improved separation and transfer of photogenerated carriers. Furthermore, CFS had a highly photochemically active Fe(III)-SC complex, which established a Fe(III)/Fe(II) cycling process via the metal-ligand-charge transfer (MLCT) pathway, leading to the rapid degradation of Cr(VI). CF and CFS still had good stability and reusability after five cycles. Therefore, this study provides an approach for removing Cr(VI) contaminants.