Mesoporous and nanostructured metal oxides for adsorptive water treatment
Authors:   , Al-Salihi Sara 
Published: September 2022

[EMBARGOED UNTIL 6/1/2023] Sewage containing a certain amount of dyes, when discharged into the environment, will cause serious problems and diseases to the human body and pose a threat to the ecosystem. In addition, waste from large animal farms, antibiotics used in aquaculture, and wastewater from hospitals and manufacturers are the main sources of antibiotic pollution in the environment, leading to antibiotic resistance genes. Therefore, this dissertation research was focused on materials that are easily available, environmentally friendly and low cost in removing dyes and antibiotics from the wastewater streams. The condensed layer deposition technique (CLD) was used to make novel mesoporous metal oxides to achieve nanoscale structures with high surface areas for adsorptive water treatment. The potential of mesoporous Al2O3 nanoshells, mesoporous TiO2 coatings on Fe3O4 nanoparticles, and aluminosilicate zeolite as adsorbents in water treatment was evaluated for the removal of Congo red (CR), sulfamethazine (SMZ) and tetracycline (TC) from aqueous solutions, respectively. Experimental parameters such as contact time, temperature, ionic strength and pH value were investigated in each study. The kinetics and thermodynamic equilibrium of those adsorption processes were modeled based on the experiments. For alumina nanoshells, carbon black (CB) was first successfully coated with alumina using the CLD process, followed by removing the CB, leading to porous Al2O3 nanoshells, with a high specific surface area (217.7 m2 g-1) The adsorption rate of CR on the Al2O3 nanoshells was fast, with 68.5 [percent] achieved in the first 5 min and 94.5 [percent] within 30 min. The strong adsorptive affinity of Al2O3 nanoshells for CR is attributed to the hydrogen bonding and electrostatic attraction. The activation energy studies indicated that the binding process occurs through chemisorption. Mesoporous TiO2 coatings on Fe3O4 nanoparticles (m-TiO2/Fe3O4) were prepared with a high specific surface area of 291.42 m2 g-1 and used to remove SMZ. The m-TiO2/Fe3O4 achieved a high adsorption capacity of 270.3 mg g-1 toward SMZ at 25 [degrees] C and pH 7.01, with a fast equilibrium time of 40 min. The adsorption process was exothermic and spontaneous. The hydrogen bonding and hydrophobic interactions between the SMZ and m-TiO2/Fe3O4 played a vital role in the adsorption process. Reusability experiments on this magnetic nanocomposite adsorbent showed only a 5.2 [percent] decrease in activity after 5 cycles, demonstrating a great reusability of the adsorbent. It can reduce both cost and material waste in water treatment. Aluminosilicate zeolite in the form of nanoparticles were synthesized in heptane with condensed water and aluminum and silicon precursors. The TC removal efficiency on this adsorbent is above 97 [percent] in a wide pH range from 4.70 to 7.17 within only 20 min. The high adsorption affinity is attributed to the hydrogen bonding between TC and the hydroxyl groups in the aluminosilicate zeolite and the outer-sphere complexation. The thermodynamic studies revealed that the adsorption process is spontaneous and exothermic. Finally, the kinetic studies have shown that the adsorption processes of the three organic pollutants follow a pseudo-second-order model. In addition, the Langmuir isotherm adsorption model is in good agreement with the experimental data. Overall, these studies suggest that, due to their fast kinetics and high adsorption capacity, the low-cost mesoporous materials are highly effective as adsorbents for separating dyes and antibiotics from contaminated water.