Silver nanoparticles immobilised on the activated carbon as efficient adsorbent for removal of crystal violet dye from aqueous solutions. A kinetic study

The focus of the present work is on exploiting the excellent structural properties of the nanomaterials. More specifically, it is demonstrated that Ag nanoparticles (AgNPLs) chemically immobilised onto activated carbon (AC-AgNPLs) can act as an effective solid sorbent for removal and/or minimisation of selected crystal violet (CV) dye from aqueous solutions by conducting experiments on water samples. Spectroscopic tools such as FTIR, SEM, TEM and XRD were used in the characterisation of the adsorbent before and after adsorption. The adsorbent dose, pH, contact time, rotation velocity, initial concentration of adsorbate and the temperature effects were examined to evaluate their role in the percentage elimination of crystal violet. Crystal violet uptake was favourable in alkaline media at pH > 7.0, while the Langmuir model revealed CV monolayer adsorption capacity of 87.2 mg/g. The pseudo second-order model fitted the data well and the thermodynamic parameters (ΔH, ΔS, and ΔG) of CV retention revealed that the uptake is endothermic and spontaneous in nature. When AC-AgNPLs was utilised, it removed a greater CV percentage from aqueous solution relative to AC. The mechanism of adsorption was explored using the intra-particle diffusion model and the liquid-film model. Desorption studies were made to elucidate recovery of the adsorbate and adsorbent for the economic competitiveness of the removal system. The AC-AgNPLs was successfully recycled for seven successive adsorption-desorption cycles indicating its high reusability.