Adsorption studies of methylene blue and lead ions from aqueous solution by using mesoporous coral limestones

摘要

In this work low cost and readily available Mauritius coral limestones (MCLS) were used as adsorbents for the removal of methylene blue (MB) and lead (Pb(II)) ions from aqueous solution. The adsorption studies were conducted under varying parameters such as contact time, temperature, concentration, and pH. The MCLS was characterized by SEM, FTIR, BET and XRF. The SEM images revealed that MCLS surface structure had interconnected pores which could easily trap the pollutants. BET analysis established the pores and surface area to be 4.04 nm and 20.45 m2/g respectively. FTIR spectrum affirmed the presence of (CO) and (CO) groups assigned to the asymmetric stretch, in and out of plane bend vibrations in (CO32?). XRF analysis revealed that the main constituent of the material was calcium oxide at 91.76 %. The recorded maximum experimental adsorption capacities were 37.24 and 39.26 mg/g for MB and Pb(II) respectively. This is the highest for any coral limestone previously reported. The adsorption processes had a good fit for kinetic PFOM and suggests that the removal mechanism(s) was controlled by physical adsorption. MB and Pb(II) equilibrium data had a good fit for Freundlich isotherm, suggesting that adsorption processes occurred on heterogeneous surface with a multilayer formation on MCLS at equilibrium. The free standard energy change (ΔGo) were spontaneous and feasible at all studied temperatures. The enthalpy change (ΔHo) values were negative indicating that the reaction between MB/Pb(II) and MCLS was endothermic in nature. The material was also tested for photo-degradation of MB.