| Phosphorus is one of the crucial elements making up majority of biomass of organisms in nature, in addition to carbon, oxygen, nitrogen and hydrogen. However, the accumulation of phosphorus in aquatic environment induces eutrophication. Therefore, it is of importance to prevent the excessive presence of phosphorus in natural bodies, e.g. lakes, rivers, and estuaries. One of the solutions is to limit or reduce the phosphorus level in the discharge after various human activities. So far, a number of methods have been developed to achieve that, including biological treatment, membrane separation and chemical coagulation/ precipitation. Because of operation simplicity, low operation cost, and insensitivity to toxic pollutants, adsorption has been recommended as one of the most effective and economic technologies in the field of phosphorus removal. The key issue regarding to the widespread application of adsorption in phosphate removal is to select a suitable adsorbent with superior adsorption performances, including high adsorption capacity and fast removal rate. Considering the above demands, the thesis is conducted based on the following three areas: 1) electrodeposition synthesis of porous Pr(OH)3 nanowires and study of their adsorption capacities; 2) electrodeposition synthesis of porous La(OH)3 with tailorable nanostructures for enhanced phosphate removal; 3) electrodeposition synthesis of porous Nd(OH)3 nanowires and study of their adsorption capacities; 4) electrodeposition synthesis of porous Ce O2 nanowires and study of their adsorption capacities; 5) electrodeposition synthesis of porous Ce O2 nanowire arrays and study of their adsorption capacitiesPorous Pr(OH)3 nanowires(NWs), which were synthesized via an electrodeposition approach, were utilized in phosphate removal for the first time. The as-prepared porous Pr(OH)3 NWs exhibited superior phosphate removal performances, due to their large surface area, unique porous structure, and abundant hydroxyl groups as active sites. Their phosphate adsorption equilibrium data were well described by utilizing the Langmuir isotherm model(R2 ≥ 0.962), with a maximum phosphate adsorption capacity of 129.0 mg P/g at 25 °C. The thermodynamic study showed that the phosphate adsorption of Pr(OH)3 NWs was a spontaneous and exothermic process. On the other hand, the phosphate adsorption kinetics was well described with the use of the pseudo-second-order model, suggesting the adsorption process be chemisorption. In the p H range of 3.0 – 10.0, the high adsorption capacities of Pr(OH)3 NWs were observed; whilst, the presenceof Cl-, HCO3-, or NO3- did not dramatically affect the phosphate uptake. Our experimental results strongly suggest that the use of porous Pr(OH)3 NWs hold a great potential in achieving highly efficient phosphate removal in practical water treatment.Porous La(OH)3 nanobelt arrays(NBAs), nanowire arrays(NWAs), nanowire bundles(NWBs), nanowires(NWs), nanonets(NNs), which were synthesized by a facile electrochemical deposition method, were used to remove phosphate from solution.In particular, La(OH)3NWs featured a unique porous structure, large surface area, and abundant hydroxyl groups as active sites. They exhibited superior phosphate removal performances, with a maximum adsorption capacity of 131.3 mg P/g at 25 °C estimated by using the Langmuir model. The thermodynamic study showed that the phosphate adsorption onto La(OH)3 NWs was a spontaneous and exothermic process. Meanwhile, the pseudo-second-order model could well describe the phosphate adsorption kinetics, suggesting it be controlled by chemisorption. High adsorption capacities of La(OH)3 NWs were observed in the p H range of 3.0–10.0 and in the presence of coexisting ions, e.g.Cl-, HCO3-, or NO3-. The use of La(OH)3 NWs could reduce the phosphate concentration of the synthetic secondary treated wastewater to <50 μg P/L. Our experimental results reveal that La(OH)3 NWs hold agreat potential for use as a highly efficient phosphate adsorbent in removing phosphate fromaqueous solution.Porous Nd(OH)3 nanostructures synthesized via an electrodeposition approach with different ammonium salts, were utilized in phosphate removal for the first time. The as-prepared porous Nd(OH)3 NWs exhibited superior phosphate removal performances, due to their large surface area, unique porous structure, and abundant hydroxyl groups as active sites. Their phosphate adsorption equilibrium data were well described by utilizing the Langmuir isotherm model(R2 ≥ 0.999), with a maximum phosphate adsorption capacity of 131.6 mg P/g at 25 °C. The thermodynamic study showed that the phosphate adsorption of Nd(OH)3 NWs was a spontaneous and exothermic process. On the other hand, the phosphate adsorption kinetics was well described with the use of the pseudo-second-order model, indicating the adsorption process be chemisorption. In the p H range of 3.0 – 10.0, the high adsorption capacities of Nd(OH)3 NWs were observed; whilst, the presence of Cl-, HCO3-, or NO3- did not dramatically affect the phosphate uptake. In the reusability study, the adsorbent showed no significant loss in their adsorption performance after three adsorption-desorption cycles, showing that Nd(OH)3 NWs were able to be utilized as apotential cost-effective phosphate adsorbent for practical applications.Porous Ce O2 nanowires(NWs) and Ce O2 nanowire arrays(NWAs) synthesized via an electrodeposition approach with different current and potential, respectively,were utilized in phosphate removal. The as-prepared porous Ce O2 NWs and Ce O2 NWAs exhibited superior phosphate removal performances, due to their large surface area, unique porous structure, and abundant hydroxyl groups as active sites. Their phosphate adsorption equilibrium data were well described by utilizing the Langmuir isotherm model(R2 ≥ 0.999), with a maximum phosphate adsorption capacity of 136.6 mg P/g and 139.1 mg P/g at 45 °C. The thermodynamic study showed that the phosphate adsorption of Ce O2 NWs and Ce O2 NWAs was a spontaneous and endothermic process. On the other hand, the phosphate adsorption kinetics was well described with the use of the pseudo-second-order model, indicating the adsorption process be chemisorption. In the p H range of 3.0 – 10.0, the high adsorption capacities of Ce O2 NWs and Ce O2 NWAs were observed; whilst, the presence of Cl-, SO42-, or NO3- did not dramatically affect the phosphate uptake. In the reusability study, the adsorbent showed no significant loss in their adsorption performance after three adsorption-desorption cycles, showing that Ce O2 nanostructures were able to be utilized as a potential cost-effective phosphate adsorbent for practical applications. |
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