ARTICLE | doi:10.20944/preprints201806.0094.v1
Subject: Engineering, Biomedical & Chemical Engineering Keywords: TiO2; AOP; photodegradation; semiconductor based photocatalysis; reaction kinetics
Online: 6 June 2018 (12:56:35 CEST)
Some contaminants of emerging concern (CECs) are known to survive conventional wastewater treatment plants, which introduce them back to the environment and can potentially cycle up in drinking water supplies. This is especially concerning because of the inherent ability of some CECs to induce physiological effects in humans at very low doses. Advanced oxidation processes (AOPs) such as TiO2 based photocatalysis are of prominent interest for addressing CECs in aqueous environments. Natural water resources often contain dissolved metal cations concentrations in excess of targeted CEC concentrations. These cations may significantly, adversely impact degradation of CECs by scavenging TiO2 surface generated electrons. Consequently, simple pseudo first order or Langmuir-Hinshelwood kinetics are not sufficient for reactor design and process analysis in some scenarios. Rhodamine B dye and dissolved copper cations were studied as reaction surrogates to demonstrate that TiO2 catalyzed degradation for very dilute solutions is very nearly completely due to homogeneous reaction with hydroxyl radicals and that in this scenario the hole trapping pathway has negligible impact. Chemical reaction kinetic studies were then carried out to develop a robust model for RB/metal reactions that is exact in the electron pathways for hydroxyl radical production and metal scavenging.
ARTICLE | doi:10.20944/preprints201710.0159.v1
Subject: Engineering, Biomedical & Chemical Engineering Keywords: photodegradation; TiO2; ionic liquids; activated carbon; synergistic effect
Online: 24 October 2017 (11:32:13 CEST)
Ionic liquids (ILs) have gained interest among researchers due to its tunable properties that can be used in wide applications. However, toxicity and bio-degradation studies of ILs proved that most of the aromatic ILs, such as imidazolium is highly toxic and non-biodegradable. Several advance oxidation processes (AOPs) have been investigated by researchers to evaluate the efficiency of the systems for the removal of ILs from wastewater. However, the issue on relative high cost and environmental concern has limited the application of these AOPs in industry. In this research, photocatalytic study using hybrid nano-materials was conducted to evaluate the efficiency of this system as an alternative AOP system for removal of ILs from wastewater. The synergistic effect of adsorption-photodegradation was introduced by depositing Fe-TiO2 onto the functionalized activated carbon (AC). Nano-TiO2 was synthesized using micromulsion method before modification with transition metal and deposited onto the oxidized AC. Photodegradation reaction of 1-butyl-3-methylimidazolium chloride [bmim]Cl was investigated under simulated visible light irradiation. It was observed that the overall efficiency of the system was increased with the increasing amount of Fe dopant. Investigation on the extrinsic factors such as solution pH, initial concentration of ILs and photocatalyst dosage showed to significantly affect the overall efficiency of the systems where the optimum condition for the system was observed at pH 10, with initial ILs at 1mM at 1 g/L of photocatalyst. The best performance photocatalyst was 0.2Fe-TiO2/AC.
ARTICLE | doi:10.20944/preprints202103.0123.v1
Subject: Materials Science, Biomaterials Keywords: fly ash waste; platinum nanoparticles; industrial dyes; adsorption; photodegradation
Online: 3 March 2021 (10:03:12 CET)
New materials are obtained by transforming fly ash wastes into a valuable composite, with tandem adsorption and photodegradation properties. Mild hydrothermal synthesis, from titanium dioxide, Platinum nanoparticles and zeolite materials obtained from a waste, fly ash, as support, was involved in the composite preparation. The Platinum nanoparticles extended the photocatalytic activity of the composite in Visible range (Eg = 2.1 eV). The efficiency of tandem adsorption and photocatalytic activity of the new composite were evaluated to 80.70% for Bemacid Blau and 93.89% for Bemacid Rot, after 360 min, the irradiation time, with H2O2 addition.
ARTICLE | doi:10.20944/preprints202206.0379.v1
Subject: Chemistry, Inorganic & Nuclear Chemistry Keywords: porous TiO2; hybrid TiO2/CDs; photocatalysts; photodegradation; large surface areas
Online: 28 June 2022 (06:02:11 CEST)
Electron-hole recombination and narrow range utilization of sunlight limit the photocatalytic efficiency of TiO2. We synthesized a carbon dots (CDs) modified TiO2 nanoparticles (NPs) with flower-like mesoporous structure, i.e., porous TiO2/CDs nanoflowers. Among such hybrid parti-cles, CDs worked as photosensitizers for the mesoporous TiO2 and enabled the resultant TiO2/CDs nanoflowers with a wide-range light absorption. Rhodamine B (Rh-B) was employed as a model organic pollutant to investigate the photocatalytic activity of the TiO2/CDs nanoflowers. The results demonstrated that the decoration of CDs on both TiO2 nanoflowers and P25 NPs enabled a significant improvement of the photocatalytic degradation efficiency compared with the pristine TiO2. TiO2/CDs nanoflowers with porous structure and larger surface areas than P25 showed a higher efficiency owing to prevent local aggregation of carbon materials. All the results revealed that the introduced CDs and the unique mesoporous structure, large surface areas and loads of pore channels of the prepared TiO2 NPs played important roles in the enhancement of the photocatalytic efficiency of the TiO2/CDs hybrid nanoflowers. Such TiO2/CDs composite NPs also opens a door for photodegradation, photocatalytic water splitting and enhanced solar sun-light as light source.
ARTICLE | doi:10.20944/preprints201806.0199.v1
Subject: Chemistry, Applied Chemistry Keywords: needle-like BiVO4, photodegradation of Rhodamine B, monoclinic-scheelite type BiVO4
Online: 12 June 2018 (15:19:49 CEST)
A highly crystallized monoclinic-scheelite type BiVO4 powders were successfully synthesized by solvothermal method. The as-synthesized BiVO4 powders were characterized by XRD, FE-SEM, Raman spectroscopy, UV-vis DRS spectroscopy and TA-PL. From the XRD data and Raman spectra, the monoclinic-scheelite phase BiVO4 sample can be obtained at higher solvothermal synthesis temperature more than 140 oC. The preparation conditions such as, the Bi/V molar ratio and synthesis temperature, have significantly effects on the morphologies of the BiVO4 samples. BVO2 sample shows the highest PL peak, which has the highest formation rate of OH radicals and the highest photocatalytic activity. This result suggests that the formation rate of OH radicals shows a good correlation with the photocatalytic activity.
ARTICLE | doi:10.20944/preprints201805.0062.v1
Subject: Medicine & Pharmacology, Pharmacology & Toxicology Keywords: hair; solar light; photodegradation; amphetamines; MDMA; ketamine; photoproduct; photostability; solar simulator
Online: 3 May 2018 (09:11:57 CEST)
Background: Drug incorporated in hair are exposed to the environment and to cosmetic and chemical treatments, with possible decrease of their content. Knowledge concerning the effect of sun light on drug content in hair can be helpful to the forensic toxicologist, in particular when investigating on drug concentrations above or below pre-determined cut-offs. Materials and Methods: Twenty authentic positive hair samples were selected that had previously tested positive for amphetamines and/or ketamine. Washed hairs were divided into two identical strands: the former was exposed at 765 W/m2 (310–800 nm spectrum of irradiance) for 48 hours in a solar simulator, the latter was kept in the dark. Hair samples were extracted and analyzed by LC-HRMS detection. The percent photodegradation was calculated for each analyte (amphetamine, methamphetamine, methylendioxyamphetamine methylendioxymethamphetamine, ketamine, norketamine). In parallel, photodegradation processes of standard molecules dissolved in aqueous and organic solutions were studied. Results: In 20 hair samples positive for the targeted analytes, exposure to artificial sun light induced an appreciable decrease of drug concentrations. The concentration ranges in the non-irradiated hair samples were 0.01–24 ng/mg; 65% of samples exhibited a decrease in post-irradiation samples, with reduction from 3% to 100%. When more drugs were present in the same hair sample (e.g, MDMA and ketamine) the degradation yields were compound dependent. A degradation product induced by irradiation of ketamine in aqueous and methanol solutions was identified; it was also found to be present in a true positive hair sample after irradiation. Conclusions: Ketamine, amphetamines and their metabolites incorporated in hair of drug users undergo degradation when irradiated by artificial sunlight. Only for ketamine a photoproduct was identified in irradiated standard solutions and in true positive irradiated hair. When decisional cut-offs are applied to hair analysis, photodegradation must be taken into account since sunlight may produce false negative results. Moreover, new markers could be investigated as evidence of illicit drug use.
ARTICLE | doi:10.20944/preprints202104.0038.v1
Subject: Chemistry, Analytical Chemistry Keywords: dye; ZnO; NPs; leaf extract; Rosmarinus officinalis; photodegradation; methylene bleu; crystal violet
Online: 2 April 2021 (08:11:51 CEST)
Zinc oxide (ZnO) nanoparticles (NPs) were synthesized using Rosmarinus officinalis leaf extract at 80 ° C (ZnO-80) and 180 ° C (ZnO-180). The biosynthesized ZnO NPs were characterized and their photocatalytic activity was evaluated for the degradation of methylene blue (MB) and crystal violet (CV) under sunlight irradiation. The results of the characterizations by XRD, TEM and SEM showed that the size of the NPs of ZnO-80 was smaller than that of ZnO-180 which exhibited flakier agglomerated spherical structures. Photocatalytic tests showed ZnO-80 which was prepared by a cheap and easy procedure compared to ZnO-180 effectively degrades MB and CV dyes under sunlight. The superior performance of ZnO-80 over ZnO-180 can be explained by the differences in their textural properties. This is because ZnO-80 has a smaller crystallite size, a specific surface area and a higher pore volume than ZnO-180. Fourier-transform infrared spectroscopy (FTIR) analyzes revealed that both samples contained an adsorbed carboxylate group (COO-), and accordingly a mechanism was proposed for the formation of ZnO NPs that include the carboxyl group.
ARTICLE | doi:10.20944/preprints202111.0573.v2
Subject: Chemistry, Other Keywords: ofloxacin; rate-law; pseudo-order; half-life time; homogeneous catalysis; heterogeneous catalysis; photodegradation
Online: 15 December 2021 (08:24:46 CET)
Ofloxacin is a highly efficient and widely used antibiotic drug. It is classified as a refractory pollutant due to its poor biodegradability. Consequently, it is commonly found in water sources, requiring efficient methods for its removal. Advanced Oxidation Processes (AOPs) offer efficient alternatives since those yield complete degradation not achieved in adsorption or membrane processes. Previous studies suggest ofloxacin degradation follows a pseudo-first or -second order processes, whereas for full removal of refractory pollutants – lower pseudo-orders are required. Monitoring the actual “pseudo-order” degradation kinetics of ofloxacin is needed to evaluate any proposed AOP process. This study presents a simple procedure to evaluate pseudo-orders of AOPs. Photolysis of 20 mM ofloxacin solutions follow pseudo-zero order kinetics, with half-life times (t1/2) of approx. 60 min. TiO2 heterogenous catalyst show to have no influence at low concentration (0.2 mg L-1) but a significant reduction of half-life time (t1/2 = 20 min) and increase in pseudo-order (0.8) is measured at 2.0 mg L-1. Similar results are obtained with homogenous catalysis by 2.0 mg L-1 H2O2. The combination of H2O2 and TiO2 catalysts shows additional reduction in half-time life with increase in the pseudo-order to 1.2. The conclusions are (1) heterogenous and homogenous photocatalysis can effectively degrade ofloxacin, (2) combined photocatalysis yields higher pseudo-order, being less prone to achieve full removal, (3) analysis of specific pseudo-orders in AOPs of refractory pollutants helps to further elucidate the efficiency of the processes.
ARTICLE | doi:10.20944/preprints202112.0228.v1
Subject: Life Sciences, Biophysics Keywords: lipofuscin; retina; retinal pigment epithelium; docosahexaenoate; docosahexaenoic acid; fluorescence; photodegradation; photobleaching; cell viability; endocytic activity
Online: 14 December 2021 (11:41:14 CET)
Retinal lipofuscin accumulates with age in the retinal pigment epithelium (RPE) where its fluorescence properties are used to assess the retinal health. It was observed that there is a decrease in lipofuscin fluorescence above the age of 75 years and in early stages of age-related macular degeneration (AMD). The purpose of this study was to investigate the response of lipofuscin isolated from human RPE, and lipofuscin-laden-cells to visible light, and determine whether an abundant component of lipofuscin, docosahexaenoate (DHA) can contribute to lipofuscin fluorescence upon oxidation. Exposure of lipofuscin to visible leads to a decrease of its long-wavelength fluorescence at about 610 nm with concomitant growth of the short-wavelength fluorescence. The emission spectrum of photodegraded lipofuscin exhibits similarity with that of oxidized DHA. Exposure to light of lipofuscin-laden cells leads to loss of lipofuscin granules from cells, while retaining cell viability. The spectral changes of fluorescence in lipofuscin-laden cells resemble those seen during photodegradation of isolated lipofuscin. Our results demonstrate that fluorescence emission spectra together with quantitation of intensity of long-wavelength fluorescence can serve as a marker useful for lipofuscin quantification and for monitoring its oxidation, thereby useful for screening the retina for increased oxidative damage and early AMD-related changes.