The removal of phosphate from aqueous solutions using two nano-structures: copper oxide and carbon tubes

The removal of phosphate from water is vital in controlling eutrophication. Adsorption is one of the most popular technologies for removing phosphate. In this study, two types of nanoparticles (NPs), namely carbon nanotubes (CNTs) and copper oxide (CuO), were used and their phosphate removal potential was investigated. The physical and chemical properties of the two NPs were systematically studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), FTIR, energy-dispersive X-ray (EDX), and BET methods. The image analyses of SEM indicated that CuO NPs and CNTs were nano-structured aggregates with mean diameters of about 85.0 and 22.2 nm, respectively. The sorption kinetic data were better described by the pseudo-second-order equation indicating its chemisorption nature. The equilibrium sorption data were well fitted into the Freundlich model for CNTs but for CuO, sorption data were better fitted into Langmuir isotherm model. The phosphate sorption capacities without the presence of competing anions were 15.4 and 23.9 mg/g (PO4 (3-)-P) for CNTs and CuO, respectively. Besides, the competing anions (Cl-, NO3 (-), and humic acid) decreased the phosphate removal of CNTs and CuO. The negative values of the Gibbs' free energy change (Delta GA degrees) demonstrated the spontaneous nature of the sorption process in both sorbents, while the positive values of the enthalpy change (Delta HA degrees) indicated that the sorption process was endothermic in nature. Overall, the results of this study suggest that CuO NPs and CNTs in a single solution have the potential to act as effective sorbents of phosphate under optimum conditions, respectively.