Herein, an adsorption study of congo red (CR) dye onto ZnO and Al2O3/ZnO  is reported. ZnO was prepared using conventional chemicals by co-precipitation method and Al2O3 used in the composite was prepared through recycling of aluminium waste. Information about the materials was obtained through spectroscopic techniques. A batch adsorption method was used to obtain the adsorption data from which isotherm, kinetic and thermodynamic parameters were obtained. The result of the adsorbents characterisation revealed the expected properties of the prepared materials. The adsorption capacities at 250 mg/L of CR dye were 24.33 mg/g and 24.57 mg/g for ZnO and Al2O3/ZnO respectively. The isotherm study of the adsorption process revealed that Langmuir model fitted best the adsorption data with monolayer adsorption capacities (qm) of 27.67 mg/g and 33.39 mg/g for ZnO and Al2O3/ZnO respectively. The adsorption was rapid within the first 15 min and the equilibrium was reached at 45 min. The kinetic study followed a pseudo-second-order model with the rate constant of 0.049 and 0.093 g.mg-1.min-1 for ZnO and Al2O3/ZnO  respectively. Experimentally, the process was endothermic and was supported by the positive values of enthalpy (ΔH) with positive values of entropy (ΔS). The change in free energy (ΔG) is negative at all temperatures studied, indicating spontaneity but more spontaneous for Al2O3/ZnO than ZnO. The adsorption of CR dye from an aqueous solution onto ZnO as an adsorbent can be slightly improved upon by the introduction of Al2O3 to form Al2O3/ZnO composite.

The negative impact of high concentrations of lead in the analytical environment on humans and aquatic plants prompted this research. The adsorption of hazardous lead from an aqueous medium using a Modified Doum Palm (MDP) shell was investigated. The modification of the Doum palm shell was supported via 2 M 1: 2 ZnCl2 as activating agent. The batch equilibrium technique was employed to study the effect of initial concentration (800 mg/L), contact time (90 min) and temperature (313 K) on the adsorption capacity of the prepared adsorbent. Experimental data were analyzed using four kinetic models: pseudo-first-order, pseudo-secondorder, intra-particle diffusion and Elovich models and it was found that the pseudo-second-order model fitted the adsorption data most with the highest correlation (R2 = 0.9875). The studies of thermodynamic behaviour revealed negative values for ∆Go (-26.7036 to -28.1252 kJ/mol), and negative values for ∆Ho (-15.5796 kJ/mol) and ∆So (0.03554 kJ/mol/k) respectively. These indicated the adsorption process was exothermic, feasible and spontaneous in the removal of the Pb (II) ion. The findings demonstrated that the adsorbent could be exploited in the removal of Pb (II) ion from an aqueous solution.