Removal efficiency of Pb(ii) by coal fly ash cenospheres@carbon nanotubes

Abstract

Industrial waste cenospheres (CSs) were used as raw materials to obtain cenospheres@carbon nanotubes (CSs@CNTs) by chemical vapor deposition (CVD) and used as adsorbents for Pb(II) ions. The fluffy 3D spherical network structure of CSs@CNTs avoided the aggregation of CNTs and ensured sufficient contact area. CNTs with a high density of surface defects provide abundant adsorption sites for Pb(II) ions. To study the adsorption process, the effect of pH on the effective removal of Pb(II) ions was investigated. In addition, the adsorption isotherm, adsorption kinetics, and adsorption thermodynamics were fitted and analyzed. The experimental results showed that the adsorption capacity at equilibrium was 36.01 mg g⁻¹ when the adsorbent dosage was 0.05 g, the Pb(II) ion concentration was 60 mg L⁻¹, the optimal pH 6, and the adsorption contact time was 180 min. At 298 K, the adsorption isotherm fitted is consistent with the Freundlich equation. The adsorption kinetics were consistent with the quasi-secondary kinetic equation. Thermodynamic studies showed that the adsorption of Pb(II) ions is a spontaneous and heat-absorbing process. The adsorbed Pb(II) ions were completely eluted with 0.10 mol L⁻¹ HCl, and the adsorption stability was good after five adsorption–desorption cycles. CSs@CNTs as Pb(II) ion adsorbents not only have great market potential in wastewater treatment but also realize high value-added utilization of solid waste.