This study presents a systematic optimization of zinc-copper sulfide (ZnS:CuS) nanocomposites aimed at achieving smaller
hydrodynamic size, improved polydispersity, and enhanced colloidal stability for efficient adsorption of Reactive Black 5
(RB5) dye from aqueous solutions. The effects of key synthesis parameters, including pH, temperature, reagent addition
rate, and stabilizer concentration, were comprehensively investigated. Under optimized conditions of pH 5, 80 °C, 5-min
reagent addition, and 1% polyvinyl alcohol (PVA) stabilizer, the nanocomposite achieved a minimum hydrodynamic size
of 190 nm, a polydispersity index (PDI) of 0.37, and a zeta potential of − 29.7 mV, confirming high stability. Batch adsorption
experiments demonstrated a maximum RB5 removal efficiency of 96% at pH 3, with adsorption equilibrium reached in
70 min. The adsorption process followed the Langmuir isotherm model (
R2 = 0.9996) with a maximum adsorption capacity
(
qmax) of 153 mg/g, and kinetics were best described by the pseudo-second-order model (
R2 = 0.96), indicating chemisorption.
These findings highlight the potential of optimized ZnS:CuS nanocomposites as effective adsorbents for dye-laden
wastewater treatment applications.