Harnessing the Synergistic Potential of ZnS Nanoparticle-Interfacing Chitosan for Enhanced Photocatalytic Degradation in Aqueous Media and Textile Wastewater

Abstract

This study explores the photocatalytic performance of ZnS nanoparticle-integrated chitosan nanocomposite for degrading organic dyes in water and textile wastewater. ZnS nanoparticles with a cubic sphalerite crystal structure were uniformly distributed in a chitosan matrix, as confirmed by FT-IR, Raman, and XRD analyses. The FT-IR spectrum of ZnS displayed peaks at 410 and 490 cm^‒1 (symmetric and asymmetric Zn‒S stretching vibrations) and a peak at 640 cm^‒1 (asymmetric Zn‒S stretching). Chitosan exhibited bands at 893 and 1156 cm^‒1 (C‒H and C‒O‒C bending modes) and a peak at 1412 cm^‒1 (C‒H bending vibrations). The FT-IR spectrum of the ZnS-chitosan nanocomposite showed Zn‒S stretching modes at 619 and 670 cm^‒1, along with peaks in the 1000–1117 cm^‒1 range attributed to ZnS vibrations. Amide groups were represented by bands at 1588 cm^‒1, while chitosan contributed peaks at 1399 and 2924 cm^‒1 (C‒H bending and stretching vibrations). A broad band at 3374 cm^‒1 indicated O‒H and N‒H stretching of chitosan. Peak shifts indicated interactions between ZnS and chitosan functional groups, confirming the formation of the nanocomposite. Raman analysis revealed peak broadening due to ZnS-chitosan interactions. XRD patterns exhibited intense diffraction peaks at 2θ values of 28.6, 47.5, and 56.4°, corresponding to the cubic ZnS sphalerite phase, and a broad chitosan peak at 2θ = 20°, confirming the presence of amorphous chitosan phases. SEM images depicted spherical or near-spherical ZnS nanoparticles (30–70 nm) within the porous chitosan network, confirmed by EDX mapping. TGA/DSC indicated chitosan degradation around 250–500 °C. The residual weight% at 600 °C directly represents the content of ZnS nanoparticles. Optical studies demonstrated a reduced band gap of 2.6 eV compared to 4.25 eV for ZnS. The optimized ZnS-chitosan nanocomposite achieved up to 100% and 97.99% removal efficiency for Brilliant Blue FCF and Acid Orange 2 dyes, respectively, following pseudo-second-order kinetics. It also demonstrated 90% dye removal from textile wastewater, surpassing ZnS alone due to the high surface area, favorable adsorption, and efficient charge transfer facilitated by the ZnS-chitosan nanostructure. The excellent reusability of the nanocomposite highlights its potential for sustainable wastewater treatment.