Synthesis of MoO3/polypyrrole nanocomposite and its adsorptive properties toward cadmium(II) and nile blue from aqueous solution: Equilibrium isotherm and kinetics modeling

Molybdenum trioxide/polypyrrole (MoO3/Ppy) nanocomposite was prepared via oxidative polymerization of pyrrole monomer with MoO3 nanoparticles. The adsorption of Cd+2 and nile blue (NB) onto the nanocomposite was investigated in terms of various process parameters. The characterization of MoO3/Ppy nanocomposite was carried out by Fourier transform-infrared spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy. Higher R-2 (0.992-0.997 for Cd+2 and 0.997-0.998 for NB) and lower standard error of estimation values (1.04-1.82 for Cd+2 and 0.87-1.07 for NB) for Freundlich isotherm highlighted the multilayer adsorption onto heterogeneous nanocomposite surface. The higher Q(m) values at 323 K for Cd+2 (181 mg/g) and NB (189 mg/g) compared to many reported adsorbents proved the adsorptive superiority of MoO3/Ppy. The energy of adsorption (E) values from Dubinin-Radushkevich model was 1.26-1.38 and 1.36-1.44 kJ/mol for Cd+2 and NB, respectively, suggesting physical adsorption. Pseudo-second order kinetic model governed the adsorption of Cd+2 and NB with intraparticle and liquid film diffusion controlling the mechanism. The negative Delta G values (8.4-9.4 kJ/mol) and positive Delta H values (2.5-6.1 kJ/mol) implied spontaneous and endothermic adsorption process. The positive Delta S values (0.036-0.048 kJ/mol/K) indicated increased randomness at MoO3/Ppy-Cd+2 or NB interface. The MoO3/Ppy nanocomposite proved to be suitable and efficient adsorbent for sequestering of Cd+2 and NB from aqueous solution.