Biosorbent silver nanoparticles decorated coffee-ground waste composite for cleaning water and antimicrobial applications

A sustainable biosorbent, silver nanoparticles-decorated coffee-ground waste (CWAg), was synthesized through a simple in-situ reduction method. CWAg is extensively characterized via SEM–EDX, PZC, FTIR, XRD, HR-TEM, and XPS analyses. The biosorbent was tested to remove chromium (Cr(VI)) and methylene blue (MB) from wastewater, and its antibacterial properties was evaluated. CWAg demonstrated efficient sorption efficiencies, achieving ⁓149.9 mg/g at 323 K and pH: 2.0 for Cr(VI) and ⁓113.4 mg/g at 293 K and pH: 6.0 for MB, at a biosorbent dose of 1 g/L. The equilibration times were 90 and 120 min for Cr(VI) and MB, with half-sorption times (t_HST) of 9.2 and 13.9 min, respectively. The sorption mechanisms were successfully fitted with Sips isotherm and Pseudo-second-order models. Simultaneous sorption of MB and Cr(VI) at pH 2.0 exhibited antagonism, while a synergistic effect was observed at pH 6.0. Desorption and regeneration were achieved using NaOH and HCl solutions for Cr(VI) and MB, respectively. The efficiencies were just reduced by 9–13%. Finally, CWAg exhibited remarkable effectiveness for removing Cr(VI) from complex tannery effluent. Moreover, CWAg demonstrated positive antibacterial effects against both Gram-positive and Gram-negative bacteria, surpassing raw coffee-ground waste, underscoring the significant role of silver nanoparticles in enhancing bacterial inhibition.