Silver nanoparticles deposited multiwalled carbon nanotubes for removal of Cu(II) and Cd(II) from water: Surface, kinetic, equilibrium, and thermal adsorption properties

We prepared Ag-MWCNTs by simple chemical reduction method. Ag nanoparticles were well dispersed on the surface of Ag-MWCNTs. The Ag-MWCNTs were used for removal of Cu(II) and Cd(II) from aqueous solutions. Adsorption isothermal data could be well interpreted by the Langmuir isotherm model. Thermodynamic studies indicate that the adsorption process was spontaneous and endothermic. A novel composite based on functionalized multiwalled carbon nanotubes (FMWCNTs) reduced with N,N-dimethylformamide and cross-linked with silver nitrate, i.e., Ag-MWCNTs, was fabricated for effective removal of Cu(II) and Cd(II) ions. The performance of Ag-MWCNTs was characterized by Fourier transform infrared, Raman spectroscopy, thermal gravimetric analysis, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The adsorption characteristics were explored using well-established and effective parameters including pH, contact time, adsorbent dosage, initial metal ion concentration, and temperature. Optimum adsorption of Cu(II) and Cd(II) was observed at pH 6.0 and 7.0, respectively. Kinetic studies revealed that the adsorption data fitted well to the pseudo-second-order kinetic model and Langmuir model gave a better fit than the other models. Thermodynamic properties, i.e., δG^o, δH^o, and δS^o, showed that adsorption of Cu(II) and Cd(II) onto Ag-MWCNTs was endothermic, spontaneous and feasible in the temperature range of 293-313K.