Rapid Microwave-Assisted Synthesis of N/TiO2/rGO Nanoparticles for the Photocatalytic Degradation of Pharmaceuticals.

Nanocomposites comprising nitrogen-doped TiO2 and reduced graphene oxide (N/TiO2/rGO), with different rGO loading qualities, were prepared by a cost-effective microwave-assisted synthesis method. The synthesized materials were broadly characterized by Raman spectroscopy, X-ray diffraction (XRD), infrared spectroscopy (FTIR), photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), electron microscopy (SEM-EDS), and nitrogen adsorption/desorption isotherms. Anatase was the only crystalline phase observed for all synthesized materials. The rGO loading did not affect the morphological properties, but it positively influenced the photocatalytic activity of the nanocomposite materials, especially at low rGO loading. Photocatalysts were evaluated via the degradation of specific organic micropollutant (OMP) pharmaceuticals: ciprofloxacin (CIP), diclofenac (DCF), and salicylic acid (SA), under different radiation sources: ultraviolet A (UVA), solar light simulator (SLS), blue visible light (BVL) and cold visible light (CVL). CIP and SA were removed effectively via the synergy of adsorption and photocatalysis, while DCF degradation was achieved solely by photocatalysis. After implementing scavenger agents, photocatalytic degradation processes mainly depended on the specific pollutant type, while irradiation sources barely defined the photocatalytic mechanism. On the other hand, changes in irradiation intensity significantly influenced the photolysis process, while photocatalysis was slightly affected, indicating that irradiation spectra are more relevant than intensity.

Microwave-Assisted Synthesis of N/TiO2 Nanoparticles for Photocatalysis under Different Irradiation Spectra.

Nitrogen-doped TiO2 (N/TiO2) photocatalyst nanoparticles were derived by the environmentally friendly and cost-effective microwave-assisted synthesis method. The samples were prepared at different reaction parameters (temperature and time) and precursor ratio (amount of nitrogen source; urea). The obtained materials were characterized by X-ray diffraction (XRD), photoelectron spectroscopy (XPS), Raman spectroscopy (RS), infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS), electron microscopy (SEM-EDS), and nitrogen adsorption/desorption isotherms. Two cycles of optimizations were conducted to determine the best reaction temperature and time, as well as N content. The phase composition for all N/TiO2 nanomaterials was identified as photoactive anatase. The reaction temperature was found to be the most relevant parameter for the course of the structural evolution of the samples. The nitrogen content was the least relevant for the development of the particle morphology, but it was important for photocatalytic performance. The photocatalytic activity of N/TiO2 nanoparticle aqueous suspensions was evaluated by the degradation of antibiotic ciprofloxacin (CIP) under different irradiation spectra: ultraviolet A light (UVA), simulated solar light, and visible light. As expected, all prepared samples demonstrated efficient CIP degradation. For all irradiation sources, increasing synthesis temperature and increasing nitrogen content further improved the degradation efficiencies.

Is a Proactive Approach to Controlling Legionella in the Environment Justified?

RESEARCH BACKGROUND: Legionella are Gram-negative bacteria that are ubiquitous in the natural environment. Contaminated water in man-made water systems is a potential source of transmission of legionnaires' disease. The aim of this study is to explore the prevalence of Legionella pneumophila in the drinking water distribution system (DWDS) of Primorje-Gorski Kotar (PGK) County, Croatia, for the period 2013-2019, coupled with the incidence of legionnaires' disease. A number of L. pneumophila-positive samples (>100 CFU/L), serogroup distribution and the degree of contamination of specific facilities (health and aged care, tourism, and sports) were assessed. Based on the obtained results, the reasoning for the implementation of a mandatory Legionella environmental surveillance program was assessed. EXPERIMENTAL APPROACH: Sample testing for Legionella was carried out according to the standard method for enumeration of this bacterium. A heterotrophic plate count (HPC) and Pseudomonas aeruginosa number were analysed along with the basic physicochemical indicators of drinking water quality. The research period was divided into two parts, namely, the 2013-2018 period (before implementation of the prevention program, after the outbreak of legionnaires' disease), and the year 2019 (proactive approach, no disease cases recorded). RESULTS AND CONCLUSION: During the 7-year observation period in PGK County, an increase in the number of samples tested for Legionella was found. An increase in Legionella-positive samples (particularly pronounced during the warmer part of the year) was recorded, along with a growing trend in the number of reported legionnaires' disease cases. In addition to hot water systems, the risk of Legionella colonisation also applies to cold water systems. Health and aged care facilities appear to be at highest risk. In addition to the higher proportion of positive samples and a higher degree of microbiological load in these facilities, the highest proportion of L. pneumophila SGs 2-14 was identified. Due to the diagnostic limitations of the applied tests, the number of legionnaires' disease cases is underdiagnosed. NOVELTY AND SCIENTIFIC CONTRIBUTION: The introduction of a mandatory preventive approach to monitoring Legionella in DWDS water samples, along with the definition of national criteria for the interpretation of the results will create the preconditions for diagnosis and adequate treatment of larger numbers of legionnaires' disease cases.

UV filters as a driver of the antibiotic pollution in different water matrices.

Antibiotic pollution is frequently detected in fresh waters and wastewaters where they represent an environmental risk for the development of global antibiotic resistance. Due to their excessive use in personal care products, UV filters have also been found to be pseudo-persistent in the aquatic environment. In contrast to antibiotics, which can undergo photodegradation, UV filters are compounds designed to stably absorb UV radiation. This study explored the light based remediation of representative antibiotics from seven classes of antibiotics (fluoroquinolones, tetracyclines, penicillins, macrolide, glycolpeptide, sulphonamides and trimethoprim) in order to assess whether antibiotic pollution persists longer in the presence of organic UV filters. We show that the presence of UV filters either completely supresses or significantly alters the photodegradation of antibiotics in water. Advanced technologies in wastewater treatment, such as the use of UV C radiation, both effectively minimise the effect of UV filters and degrade most of the tested antibiotics proving to be effective management strategy. However, the half-life of erythromycin and amoxicillin, widely used antibiotics from macrolide- and penicillin-like classes, is extended in the presence of UV filters, even during UV C irradiation. Overall, the UV filters present within environmental mixtures are identified as important drivers of mixture toxicity, as they prolong antibiotic contamination of aquatic and engineered environments. The ramification of such finding is that inadequate consideration of UV filters may result in an imperfect prediction of the solar and UV light-based remediation of antibiotics, lead to improper classification of antibiotics persistence in the environment and cause non-optimal chemical fate and transport model performance. Use of the more benign compounds and assessment of the UV filters were identified as feasible management options in minimizing the influence of UV filters onto the remediation of antibiotics in aquatic environments.

Photocatalytic Degradation of Azithromycin by Nanostructured TiO2 Film: Kinetics, Degradation Products, and Toxicity.

In this paper, nanostructured TiO2 film was prepared by the by sol-gel process and dip-coating technique with titanium tetraisopropoxide as a precursor. After heat treatment at 550 °C, the deposited film was characterized by means of micro-Raman spectroscopy and atomic force microscopy (AFM). It was found that the TiO2 film consisted of only the TiO2 anatase phase and showed a granular microstructure. Photocatalytic degradation of azithromycin by using sol-gel nanostructured TiO2 film was studied to define the most effective degradation process for potential use in wastewater treatment. Different factors were evaluated during photocatalysis, such as pH (3, 7, and 10), water matrix (ultrapure water and synthetic municipal waste water effluent), influence of another pharmaceutically active compound (sulfamethoxazole, one of the most often detected pharmaceutic compounds in waste waters), and radiation sources (low pressure ultraviolet (UV) mercury lamps with a UV-A and UV-C range; a light-emitting diode (LED) lamp with a radiation peak at 365 nm). The most effective degradation process was achieved with the UV-C irradiation source in matrices at pH 10. The water matrix had little effect on the photocatalytic degradation rates of azithromycin. The presence of sulfamethoxazole in the water matrix decreased the degradation rate of azithromycin, however, only in matrices with a pH level adjusted to 10. During the experiments, five azithromycin degradation products were identified and none of them showed toxic properties, suggesting effective removal of azithromycin. LED 365 nm as the irradiation source was not as effective as the UV-C lamp. Nevertheless, considering the cost, energy efficiency, and environmental aspects of the irradiation source, the LED lamp could be a "real-life" alternative.

Kinetics and degradation pathways of photolytic and photocatalytic oxidation of the anthelmintic drug praziquantel.

In this study, an anthelmintic drug, praziquantel(PZQ), was degraded using the direct photolysis, photocatalysis, and oxidation processes including UV radiation, TiO2 film, and hydrogen peroxide. The photolytic degradation with predominant wavelengths of 185/254nm (UV-C) proved to be more efficient with a half-life of 3.13min compared to the radiation of 365nm (UV-A) where the degradation did not occur. In order to enhance the rate of PZQ photolytic degradation, H2O2 was added, which resulted in two to three times higher degradation rates. In the photocatalytic degradation, TiO2 film was used as catalyst. The degradation was ten times faster in the photocatalytic experiments where UV-C light (k=0.2390min-1) was used than in those with UV-A (k=0.0201min-1). Comparing the results from all performed experiments it can be concluded that the UV-C/TiO2/H2O2 process yielded the highest degradation rate and complete degradation of PZQ was obtained in less than 7min. The degradation of PZQ followed the first order kinetics in all the experiments. The photo degradation was inhibited in the presence of methanol. The degradation pathways and the structural formulae of five degradation products (m/z 273, 269, 189, 147, 132) were proposed based on the liquid chromatography tandem mass spectrometry analysis.

Degradation of Methyl Orange and Congo Red dyes by using TiO2 nanoparticles activated by the solar and the solar-like radiation.

In this study we used TiO2 nanoparticles as semiconductor photocatalysts for the degradation of Methyl Orange (MO) and Congo Red (CR) dyes in an aqueous solution. Since TiO2 particles become photocatalytically active by UV radiation, two sources of UV-A radiation were used - natural solar radiation which contains 3-5% UV-A and artificial, solar-like radiation, created by using a lamp. The optimal doses of TiO2 of 500 mg/L for the CR and 1500 mg/L for the MO degradation were determined in experiments with the lamp and were also used in degradation experiments with natural solar light. The efficiency of each process was determined by measuring the absorbance at two visible wavelengths, 466 nm for MO and 498 nm for CR, and the total organic carbon (TOC), i.e. decolorization and mineralization, respectively. In both cases, considerable potential for the degradation of CR and MO was observed - total decolorization of the solution was achieved within 30-60 min, while the TOC removal was in the range 60-90%. CR and MO solutions irradiated without TiO2 nanoparticles showed no observable changes in either decolorization or mineralization. Three different commercially available TiO2 nanoparticles were used: pure-phase anatase, pure-phase rutile, and mixed-phase preparation named Degussa P25. In terms of degradation kinetics, P25 TiO2 exhibited a photocatalytic activity superior to that of pure-phase anatase or rutile. The electric energy consumption per gram of removed TOC was determined. For nearly the same degradation effect, the consumption in the natural solar radiation experiment was more than 60 times lower than in the artificial solar-like radiation experiment.

Photolytic and thin TiO2 film assisted photocatalytic degradation of sulfamethazine in aqueous solution.

This paper deals with the photolytic and the photocatalytic degradation of sulfonamide antibiotic sulfamethazine (SMT) dissolved in Milli-Q water and in synthetic wastewater. Besides the direct photolysis, oxidation processes including UV/H2O2, UV/TiO2, and UV/TiO2/H2O2 using UV-A and UV-C radiation were investigated. Pseudo-first-order kinetics was observed for the degradation of SMT in all investigated processes. Additions of an electron acceptor (H2O2) and a catalyst (TiO2 film) accelerated the photolytic degradation of SMT for both the UV-A- and the UV-C-based processes. The most efficient process was UV-C/TiO2/H2O2 with complete degradation of SMT obtained in 10 min. The UV-A-based processes have been less efficient in terms of irradiation time required to totally degrade SMT than the UV-C-based processes. It was also confirmed that different wastewater components can significantly reduce the degradation rate of SMT. An almost ninefold reduction in the rate constant of SMT was observed for the specific synthetic wastewater. Although UV-A radiation experiments need more time and energy (2.7 times more electrical energy was consumed per gram of demineralized SMT) than UV-C experiments, they have a potential for practical use since natural UV-A solar radiation could be used here, which lowers the overall cost of the treatment. Five degradation products were detected during the degradation processes, and their structural formulae are presented. The structural formulae were elucidated based on mass spectra fragmentation pattern obtained using the tandem mass spectrometry (MS/MS) and NMR analysis.