Synergistic adsorptive and photocatalytic removal of diazinon using CdS-modified guar gum/chitosan nanofibers

Diazinon (DZ) poses a significant environmental threat due to its toxicity to humans and animals, especially given its widespread and continuous use in agriculture. In this study, cadmium sulfide-decorated electrospun guar gum/chitosan nanofibers (CGCS) were successfully synthesized and utilized for both batch adsorption and photocatalytic degradation of DZ. For comparison, other solid adsorbents, cadmium sulfide (C), chitosan (CS), and guar gum/chitosan (GCS) nanofibers, were also fabricated. Characterization results revealed that CGCS possessed a surface area of 92.2 m 2 /g, an average pore size of 3.64 nm, a point of zero charge at pH 7.1, and an energy band gap of 2.28 eV. Adsorption experiments were conducted under various conditions and analyzed using different kinetic and isothermal models. The CGCS nanofibers demonstrated the highest Langmuir adsorption capacity of 99.49 mg/g under optimal conditions: pH 7, nanofiber dosage of 3.0 g/L, equilibrium time of 4 h, and a temperature of 25°C. Photocatalytic degradation of DZ was also assessed using C and CGCS as photocatalysts. The degradation efficiency reached 81% with C and increased to 100% with CGCS after 100 min of irradiation, especially when the temperature was increased from 25 to 40°C. The photocatalytic process was further analyzed using kinetic and thermodynamic models such as Langmuir-Hinshelwood, Arrhenius, and Eyring-Polanyi to understand the degradation mechanism. The CGCS catalyst exhibited exceptional reusability, with only an 8% reduction in efficiency after seven consecutive photocatalytic cycles.