2.3. Adsorption study

All batch adsorption experiments were conducted by mixing an sufficient amount of adsorbents (silver nanoparticles (AgNPs), quartz (Q) and silver-quartz composite nanoparticles (Ag/Q)NPs)) with a known volume of Hg²⁺ at varoius initial concentrations (5, 10, 50 and 100 mg/l) with shaking (150 r/min). Then, the supernatants were separated from the mixture solution by filtration with PTEF syringe filter. The influence of contact time was assessed at different time intervals by agitation (5–150 min). In order to optimize the adsorption process, other factors such as initial pH, adsorbent dose (0.05–1 g) and temperature were also examined.

Based on the following equations, the equilibrium adsorption capacity, qe (mg/g) and the removal efficiency of metal ions were estimated:

Where V: sample volume (L), m: mass of the adsorbents (g), C_o: initial metal ion concentration (mg/L), and C_e: equilibrium concentration of metal ion in the solution (mg/L).