Search

Browse

• Communities
• Authors
• Year
• Titles
• Subjects

My Space

• Login

Photocatalyst synthesis and photochemical processes for the removal of organic pollutants in aqueous phase

Drosou Aikaterini

Full record

---

Summary

In our days, emerging organic contaminants (EOCs) are released into aquatic environments mainly due to their incomplete removal in wastewater treatment plants.The present thesis focuses on the removal and degradation of organic pollutants of emerging concern - specifically widely prescribed pharmaceuticals- in aqueous solutions. This is achieved through the application of advanced oxidation methods and adsorption processes using innovative adsorbent materials.Initially, we investigated the photochemical degradation of commonly prescribed pharmaceuticals, the antidepressant namely sertraline and the antiviral, namely acyclovir, in aqueous matrices, under UVC irradiation. The molar absorption coefficient of sertraline and acyclovir at 254 nm and various pH values in the range from 4.0 to 9.0 was 444±65 L‧mol–1‧cm–1 and (1.36±0.02) ×104 L‧mol–1‧cm–1, respectively. Next, we investigated the photochemical degradation of sertraline and acyclovir under UVC radiation in the presence of hydrogen peroxide, H2O2 (i.e., UVC/H2O2) or persulfate ions, S2O82− (i.e., UVC/PS). Several parameters were studied, such as the initial oxidants concentration, the solution pH, and the composition of the aqueous matrices (experiments were carried out in ultrapure water, in aqueous phosphate buffers, in synthetic wastewater, as well as in synthetic fresh and hydrolyzed human urine). In the case of sertraline, it was observed that its photochemical degradation in all aqueous matrices followed pseudo-first-order kinetics. Additionally, the pseudo-first-order rate constants observed in the UVC/H2O2 and UVC/PS processes were found to be one to three orders of magnitude higher than the corresponding rate constant in the UVC process. In the photochemical degradation of acyclovir, in the presence of hydrogen peroxide (H₂O₂), the kinetics varied from pseudo-zero-order kinetics when the initial concentration was below 5.0 mM, to pseudo-first-order kinetics when the initial concentration of H₂O₂ was between 7.5 mM and 50 mM. In contrast, in the presence of PS, the photochemical degradation of antiviral exhibited pseudo-zero-order kinetics. For both substances, the UVC/PS process was more efficient than the UVC/H2O2 process, either in aqueous phosphate buffer solutions or in wastewater, despite the comparable reactivity of sertraline and acyclovir towards hydroxyl and sulfate radicals. However, both processes resulted in partial mineralization of the compounds after prolonged irradiation. Moreover, in the UVC/H2O2 process, there was an optimal concentration of H2O2 beyond which no additional improvement in process performance was observed. In contrast, the UVC/PS process demonstrated a nearly linear increase in treatment efficiency as the concentration of PS increased, at least within the range of PS concentrations examined in the present study. Solution pH (in the range from 6.0 to 9.0 for sertraline, and in the range of 4.0 to 9.0 for acyclovir) had a relatively negligible effect on treatment performance for both processes. In synthetic urine matrices, although the reaction rate decreased, the photochemical degradation of sertraline and acyclovir occurred to a satisfactory extent. Furthermore, the calculations of electrical energy per order and the associated costs indicated that both the UVC/H2O2 and UVC/PS processes were cost-effective and suitable for large-scale applications.A relatively novel material, graphite oxide, was prepared using a modified Hummers method for the removal of the antidepressant sertraline and citalopram from aqueous solutions. Various characterization techniques, including BET, XRD, XPS, Raman spectroscopy, FTIR, and elemental analysis, were employed to achieve the physicochemical and structural characterization of the composite material. Graphite oxide demonstrated a high adsorption capacity compared to commercially available activated carbon, achieving adsorption values of 245.1 μmol·g-1 for sertraline and 206.9 μmol·g-1 for citalopram, at 25 ° C after 6 hours of contact time. Equilibrium experiments were conducted to study the effects of various parameters, such as the solution's pH, the water matrix's composition, and ionic strength. The kinetic study indicated that the non-linear form of the pseudo-second-order model best described the adsorption of sertraline and citalopram on graphite oxide. The adsorption isotherms were analyzed using both the Langmuir and Freundlich models, in both linear and non-linear forms, at temperatures of 10, 25, and 40°C. It was found that the non-linear form of the Langmuir model effectively describes the adsorption isotherms for both substances. Additionally, a thermodynamic study was conducted to calculate the parameters of free energy, enthalpy, and entropy (ΔG°, ΔH°, and ΔS°). The thermodynamic parameters indicated that the adsorption process of antidepressants was spontaneous and endothermic within the temperature range of 10-40°C.

Available Files

Services