Tuning the Photocatalytic and Adsorption Properties of Biopolymer-Layered Double Hydroxide Composites

Abstract

This study reports the successful synthesis of layered double hydroxides (LDHs) containing various combinations of divalent and trivalent metal cations, such as Ni-Fe LDH, Mg-Al LDH, Cu-Al LDH, and Zn-Al LDH, prepared using diverse synthetic methods. Comprehensive characterization of these LDHs was performed to analyze their structural, morphological, chemical, optical, and textural properties. The efficacy of the fabricated composites was further explored through adsorptive and photodegradation studies targeting hazardous pharmaceutical contaminants and textile dyes under UV and LED-light exposure. Biopolymers, including starch, cellulose, chitosan, and sodium alginate, were highlighted as sustainable, renewable, non-toxic, cost-effective, and carbon-neutral materials with significant potential in adsorption and photocatalysis. The integration of biopolymers with LDHs proved to be an effective approach for enhancing the adsorption and photocatalytic properties of these composites. The observed improvements were attributed to several factors: (i) optimized morphologies, (ii) increased specific surface areas, providing more active sites for photocatalysis, (iii) enhanced separation of photoexcited charges, and (iv) a narrower bandgap, broadening the range of photo-absorption. Studies on the recyclability of the photocatalysts demonstrated their stability and reusability, with excellent performance retained over multiple cycles. The active species involved in the degradation process were identified through scavenger experiments, while HR-MS analysis provided insights into the photocatalytic degradation pathways. The results revealed that biopolymer-LDH composites effectively broke down pollutant molecules into smaller, less harmful compounds. Based on the HR-MS data, band energy calculations, and scavenger studies, a detailed photocatalytic mechanism was proposed to explain the enhanced activity of the synthesized composites. This research not only presents a robust strategy for improving the photocatalytic and adsorption performance of biopolymer-LDH composites but also highlights their potential application in environmental remediation, offering a sustainable solution to pollution challenges.