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This research was undertaken to optimize the Se(IV) adsorption from aqueous solutions by Cyperus laevigatus biomass and green-synthesized nanosilver (AgNPs). A full 24 factorial experimental design was utilized to distinguish the effects of pH, initial metal concentration (Co), adsorbent dose concentration (C. laevigatus biomass, X1 & AgNPs, X2) and contact time (t). Response surface methodology (RSM) was also applied to assess the factors interactions. The influence of selected variables on Se(IV) uptake capacity was studied and a factorial model was designed to detect the variables’ effects and their interactions. The range of pH was 2–8, Co was 100–400 mg L−1, X1 was 1–5 g L−1, X2 was 0.025–0.1 g L−1 and t was 1–8 h. The significant effects for Se(IV) adsorption on C. laevigatus biomass were ascribed to pH, Co, pH.X, and pH.Co.X, while in case of AgNPs, Co and X2 were detected. Normal distribution was noted between the model values (predicted) and the observed (experimental). RSM design revealed the same results obtained from factorial design. The characterization of both sorbents by TEM revealed that the granulated texture of AgNPs possesses high porosity and clear surface that precedes the high sorption capacity of Se(IV).