Rapid Removal of Organic Pollutants from Aqueous Systems under Solar Irradiation Using ZrO2/Fe3O4 Nanoparticles.

Pure water scarcity is an emerging, all-around problem that globally affects both the life quality and the world's economy. Heterogeneous photocatalysis under solar irradiation is a promising technique for the organic pollutants (e.g., pesticides, drugs) removal from an aqueous environment. Furthermore, the drawbacks of commercially available photocatalysts can be successfully overcome by using innovative nanoparticles, such as ZrO2/Fe3O4. Four ZrO2/Fe3O4 nanopowders with a different mass ratio of ZrO2 and Fe3O4 were synthesized using the chemical co-precipitation method. XRD analysis showed the presence of magnetite and hematite Fe-oxide phases in all samples. The content of the magnetite phase increased with the addition of 19% ZrO2. The efficiency of the newly synthesized ZrO2/Fe3O4 nanoparticles was investigated in the rapid removal of selected pollutants under various experimental conditions. Nevertheless, the influence of the water matrix on photocatalytic degradation was also examined. The obtained data showed that using ZrO2/Fe3O4 nanosystems, an appropriate removal rate of the selected pesticides and pharmaceuticals can be reached after 120 min of solar irradiation. Further, the total organic carbon measurements proved the mineralization of the target emerging pollutants. ZrO2/Fe3O4 nanoparticles are economically feasible, as their removal from the suspension can be easily achieved using affordable, environmentally-friendly magnetic separation.

Reusable Fe2O3/TiO2/PVC Photocatalysts for the Removal of Methylene Blue in the Presence of Simulated Solar Radiation.

Currently, environmental pollution by various organic pollutants (e.g., organic dyes) is a serious, emerging global issue. The aqueous environment is highly exposed to the harmful effects of these organic compounds. Furthermore, the commonly applied conventional purification techniques are not sufficient enough. Heterogeneous photocatalysis and the photo-Fenton process are effective, low-cost and green alternatives for the removal of organic pollutants. In this study, different iron(III) oxide/titanium(IV) oxide/polyvinyl chloride (Fe2O3/TiO2/PVC) nanocomposites in tablet form were investigated in the photodegradation of methylene blue (MB) under simulated sunlight, and their possible antibacterial effects were examined. The newly synthesized nanocomposites were characterized by scanning electron microscope, X-ray diffraction, UV-Vis diffuse reflectance spectroscopy, and Raman spectroscopy. The results showed a hematite crystal form in the case of Fe2O3(2) and Fe2O3 samples, while the Fe2O3(1) sample showed a combination of hematite and synthetic mineral akaganeite. The highest photocatalytic efficiency was achieved in the presence of Fe2O3/TiO2/PVC, when 70.6% of MB was removed. In addition, the possible photo-cleaning and reuse of the mentioned photocatalyst was also examined. Based on the results, it can be seen that the activity did not decrease after five successive runs. Nanocomposites also exhibited mild antibacterial effects against the two tested Gram-positive bacteria (S. aureus and B. cereus).

Removal of methyl orange using combined ZnO/Fe2O3/ZnO-Zn composite coated to the aluminium foil in the presence of simulated solar radiation.

In this paper, the optimal preparative conditions (current density, deposition temperature, calcination temperature) for the original electrochemical synthesis of ZnO-Zn coating on aluminum foil support (ZnAF) were examined and determined the application for the removal of methyl orange (MO). Optimal application conditions for removing MO (volume and concentration of a treated solution) were also determined. In the following, four immobilized ZnO/Fe2O3 photocatalysts with different molar ratios of Zn to Fe (0.42, 0.84, 1.68, and 3.36) were synthesized via the chemical precipitation method on optimized electrochemically synthesized ZnAF support. Characterization studies of synthesized materials included SEM-EDS and Raman scattering analyses. The efficiency of these catalysts for MO removal in the presence/absence of simulated solar radiation (SSR) was investigated. The adsorption isotherms were investigated, and the results show that the adsorption data were best fitted with the Freundlich adsorption isotherm model. Assessment of the thermodynamic parameters showed that although the adsorption process was weakly endothermic over the range of temperatures studied, the relatively high entropy change gave an overall negative change in Gibbs free energy making the processes spontaneous. In the presence of SSR, the optimal molar ratio of Zn to Fe was determined to be 1.68. The possibility of potential reusing the catalyst was examined six times in a row. The possibility for multiple uses of suspension, which is used for immobilization, was also examined. It was also determined that the application of the 1.68Zn/Fe/ZnAF/H2O2/SSR system after the dye removal generates hydrogen at a rate of 186.5 µmol g-1 after 6 h. Furthermore, in the presence of SSR and using a suspended form of catalyst, the removal efficiency was 1.6 times higher than the efficiency achieved with immobilized ZnO/Fe2O3 catalyst. Using the HPLC method for 1.68Zn/Fe/ZnAF/SSR system, five primary intermediates were found to be formed. The applicability of ZnO/Fe2O3/ZnAF for removal of other dyes was also examined.

Environmental Photocatalytic Degradation of Antidepressants with Solar Radiation: Kinetics, Mineralization, and Toxicity.

This work is focused on the kinetics, mineralization, and toxicological assessments of the antidepressant drug amitriptyline hydrochloride (AMI) in UV or solar illuminated aqueous suspensions of ZnO, TiO2 Degussa P25, and TiO2 Hombikat. ZnO was proven to be the most effective photocatalyst, and it was used for all further experiments under solar irradiation. The highest reaction rate was observed at 1.0 mg/mL of catalyst loading. In the investigated initial concentration range (0.0075-0.3000 mmol/L), the degradation rate of AMI increased with the increase of initial concentration in the investigated range. The effects of H2O2, (NH4)2S2O8, and KBrO3, acting as electron acceptors, along with molecular oxygen were also studied. By studying the effects of ethanol and NaI as a hydroxyl radical and hole scavenger, respectively, it was shown that the heterogeneous catalysis takes place mainly via free hydroxyl radicals. In the mineralization study, AMI photocatalytic degradation resulted in ~30% of total organic carbon (TOC) decrease after 240 min of irradiation; acetate and formate were produced as the organic intermediates; NH4+, NO3-, NO2- ions were detected as nitrogen byproducts. Toxicity assessment using different mammalian cell lines, showed that H-4-II-E was the most sensitive one.

Photocatalytic decomposition of selected biologically active compounds in environmental waters using TiO2/polyaniline nanocomposites: Kinetics, toxicity and intermediates assessment.

A comprehensive study of the removal of selected biologically active compounds (pharmaceuticals and pesticides) from different water types was conducted using bare TiO2 nanoparticles and TiO2/polyaniline (TP-50, TP-100, and TP-150) nanocomposite powders. In order to investigate how molecular structure of the substrate influences the rate of its removal, we compared degradation efficiency of the initial substrates and degree of mineralization for the active components of pharmaceuticals (propranolol, and amitriptyline) and pesticides (sulcotrione, and clomazone) in double distilled (DDW) and environmental waters. The results indicate that the efficiency of photocatalytic degradation of propranolol and amitriptyline was higher in environmental waters: rivers (Danube, Tisa, and Begej) and lakes (Moharac, and Sot) in comparison with DDW. On the contrary, degradation efficacy of sulcotrione and clomazone was lower in environmental waters. Further, of the all catalysts applied, bare TiO2 and TP-100 were found to be most effective in the mineralization of propranolol and amitriptyline, respectively, while TP-150 appeared to be the most efficient in terms of sulcotrione and clomazone mineralization. Also, there was no significant toxicity observed after the irradiation of pharmaceuticals or pesticides solutions using appropriate catalysts on rat hepatoma (H-4-II-E), mouse neuroblastoma (Neuro-2a), human colon adenocarcinoma (HT-29), and human fetal lung (MRC-5) cell lines. Subsequently, detection and identification of the formed intermediates in the case of sulcotrione photocatalytic degradation using bare TiO2 and TP-150 showed slightly different pathways of degradation. Furthermore, tentative pathways of sulcotrione photocatalytic degradation were proposed and discussed.

Efficient removal of sulcotrione and its formulated compound Tangenta® in aqueous TiO2 suspension: Stability, photoproducts assessment and toxicity.

The photocatalytic degradation of the herbicide sulcotrione (0.05 mM) and its formulated compound Tangenta® in aqueous suspensions of TiO2 Degussa P25 was examined as a function of the different operational parameters. The optimum of the catalyst loading was found to be 2.0 mg mL(-1) under UVA light. In the first stage of the reaction, the photocatalytic degradation of sulcotrione alone and in Tangenta® followed the pseudo-first order kinetics, in which the heterogeneous catalysis proceeds via OH and holes. Further, it can be concluded that degradation rate of sulcotrione alone is about two times higher compared to formulated compound. The results showed that the disappearance of sulcotrione led to the formation of three organic intermediates and ionic byproducts (Cl(-), SO4(2-), acetate and formate), whereas their mineralization was about 90% after 4 h. Tentative photodegradation pathways were proposed and discussed. Also, there was no significant toxicity observed after the irradiation of sulcotrione solution and Tangenta® formulation using TiO2 catalyst on three mammalian cell lines.

Thermochromism, stability and thermodynamics of cobalt(II) complexes in newly synthesized nitrate based ionic liquid and its photostability.

In this work a 1-(2-hydroxyethyl)-3-methylimidazolium nitrate ionic liquid, [HO(CH2)2mim]NO3, has been synthesized in order to serve as a new thermochromic material upon addition of cobalt(II) ions. Spectrophotometric measurements of a series of cobalt(II) nitrate and cobalt(II) chloride solutions in [HO(CH2)2mim]NO3 at 298.15, 308.15, 318.15, 328.15, and 338.15 K, were performed. Based on the recorded spectra, the overall stability constants and thermodynamic parameters for the cobalt(II) associations with chloride and nitrate ions were calculated. The thermodynamic calculations suggest that thermochromism is not observed in the ionic medium due to a small entropy change during the replacement of nitrate with chloride ions in the co-ordination sphere of cobalt(II). The absence of the molecular solvent was also the reason for the lack of thermochromism. Thus, cobalt(II) solutions in [HO(CH2)2mim]NO3 and water mixtures were studied as a new and green medium that can be used for the auto-regulation of the light intensity and shade protection. The investigated system with water upon addition of cobalt(II) was found to be a far more efficient and responsive thermochromic medium for all of the studied systems up until now. The structure of [HO(CH2)2mim]NO3 was confirmed by both (1)H NMR and IR spectroscopy. Also, the efficiency of different advanced oxidation processes (UV-induced photolysis, UV/H2O2 photolysis, heterogeneous photocatalysis using TiO2 Degussa P25 and TiO2 with 7.24%, w/w Fe catalysts) for [HO(CH2)2mim]NO3 degradation were investigated. The reaction intermediates formed during the photo-oxidation process were identified using LC-ESI-MS/MS and (1)H NMR techniques.

Degradation of thiacloprid in aqueous solution by UV and UV/H2O2 treatments.

Although some studies concerning flash photolysis and photocatalytic ozonation of thiacloprid have already been published, no complete investigation and explanation of the effects of thiacloprid photodegradation under the conditions of UV and UV/H(2)O(2) (high-pressure mercury lamp and H(2)O(2)) have been reported yet. The photochemical degradation of thiacloprid (0.32 mM) was studied under a variety of solution conditions, by varying the initial concentrations of H(2)O(2) from 0 to 162 mM and the pH from 2.8 to 9. In the UV/H(2)O(2) system, thiacloprid reacted rapidly, the maximum first-order rate constant (2.7 x 10(-2)min(-1), r=0.9996) being observed at the H(2)O(2)/thiacloprid molar ratio of 220 and pH 2.8. Under these conditions, 97% of the thiacloprid was removed in about 120 min. The thiacloprid degradation is accompanied by the formation of a number of ionic byproducts (Cl(-), acetate, formate, SO(4)(2-), and NH(4)(+)) and organic intermediates, so that after 35 h of irradiation, 17% of organic carbon remained non-degraded. The application of UV radiation, or H(2)O(2) alone, yielded no significant thiacloprid degradation. The study of the rate of removal of thiacloprid from natural water showed that it is dominantly influenced by the presence of HCO(3)(-).