Biogenic synthesis of amorphous bio-capped Co-Cu-Zn layered hydroxide using Citrus maxima leaf extract: effect of zinc content on the structural and photocatalytic degradation of organic pollutants.

The escalating discharge of recalcitrant organic dyes from industrial and agricultural sectors represents a critical threat to global aquatic ecosystems and human health. In response, heterogeneous photocatalysis has emerged as a sustainable and cost-effective strategy for environmental remediation. Thus, this study was planned for the eco-friendly synthesis of amorphous, bio-capped, tri-metal (Co-Cu-Zn) layered hydroxides using phytochemicals from Citrus maxima leaf extract as reducing and capping agents. The influence of the Zn content on the structure, morphology, and composition was systematically investigated. The predominant amorphous phase is revealed by the XRD pattern and the featureless Raman profile for samples with less Zn content (S1-LH and S2-LH), further corroborating the disordered state. The higher Zn content sample (S3-LH) manifested a distinct sharp peak at 917 cm-1, confirming the local atomic order and structural stabilization within the amorphous matrix. The elemental composition and % purity are validated via EDX, and the EDS mapping confirmed the homogeneous distribution of the counterparts throughout the sample. The SEM images showed a dramatic morphological transition from dense, plate-like aggregates to highly porous, fluffy architectures with increasing Zn content, which increases the interfacial active sites. Multi-edge UV-vis DRS and Tauc analyses revealed a complex composition-dependent electronic structure, with characteristic optical transitions at approximately 1.6, 2.3, and 5.4 eV, attributed to low-energy transition-metal-derived states, visible-region d-d/charge-transfer excitations, and high-energy ligand-to-metal charge-transfer transitions, respectively; progressive Zn incorporation modulated these electronic states and the overall light-harvesting behavior of the tri-metal LHs. The photocatalytic potential of the samples was evaluated during the degradation of methyl orange (MO) dye under UV irradiation, and the results demonstrate a clear composition-dependent catalytic performance. The degradation percentages increase from 65.31% to 81.74% and reach 92.98% for the sample with optimal Zn content.