Comparison of TiO2 and ZnO for Heterogeneous Photocatalytic Activation of the Peroxydisulfate Ion in Trimethoprim Degradation

The persulfate-based advanced oxidation process is a promising method for degrading organic pollutants. Herein, TiO2 and ZnO photocatalysts were combined with the peroxydisulfate ion (PDS) to enhance the efficiency. ZnO was significantly more efficient in PDS conversion and SO4•- generation than TiO2. For ZnO, the PDS increased the transformation rate of the trimethoprim antibiotic from 1.58 × 10-7 M s-1 to 6.83 × 10-7 M s-1. However, in the case of TiO2, the moderated positive effect was manifested mainly in O2-free suspensions. The impact of dissolved O2 and trimethoprim on PDS transformation was also studied. The results reflected that the interaction of O2, PDS, and TRIM with the surface of the photocatalyst and their competition for photogenerated charges must be considered. The effect of radical scavengers confirmed that in addition to SO4•-, •OH plays an essential role even in O2-free suspensions, and the contribution of SO4•- to the transformation is much more significant for ZnO than for TiO2. The negative impact of biologically treated domestic wastewater as a matrix was manifested, most probably because of the radical scavenging capacity of Cl- and HCO3-. Nevertheless, in the case of ZnO, the positive effect of PDS successfully overcompensates that, due to the efficient SO4•- generation. Reusability tests were performed in Milli-Q water and biologically treated domestic wastewater, and only a slight decrease in the reactivity of ZnO photocatalysts was observed.

A comparative study of femtosecond pulsed laser ablation of meloxicam in distilled water and in air

The increasing prevalence of water insoluble or poorly soluble drugs calls for the development of new formulation methods. Common approaches include the reduction of particle size and degree of crystallinity. Pulsed laser ablation is a clean technique for producing sub-micrometre sized drug particles and has the potential to induce amorphization. We studied the effect of femtosecond pulsed laser ablation (ELI ALPS THz pump laser system: λ_c = 781 nm, τ = 135 fs) on meloxicam in distilled water and in air. The ablated particles were characterized chemically, morphologically and in terms of crystallinity. We demonstrated that femtosecond laser ablation can induce partial amorphization of the particles in addition to a reduction in particle size. In the case of femtosecond pulsed laser ablation in air, the formation of pure meloxicam spheres showed that this technique can produce amorphous meloxicam without the use of excipients, which is a unique result. We also aimed to describe the ablation processes in both investigated media.

Wavelength Dependence of the Transformation Mechanism of Sulfonamides Using Different LED Light Sources and TiO2 and ZnO Photocatalysts

The comparison of the efficiency of the commercially available photocatalysts, TiO2 and ZnO, irradiated with 365 nm and 398 nm light, is presented for the removal of two antibiotics, sulfamethazine (SMT) and sulfamethoxypyridazine (SMP). The •OH formation rate was compared using coumarin, and higher efficiency was proved for TiO2 than ZnO, while for 1,4-benzoquinone in O2-free suspensions, the higher contribution of the photogenerated electrons to the conversion was observed for ZnO than TiO2, especially at 398 nm irradiation. An extremely fast transformation and high quantum yield of SMP in the TiO2/LED398nm process were observed. The transformation was fast in both O2 containing and O2-free suspensions and takes place via desulfonation, while in other cases, mainly hydroxylated products form. The effect of reaction parameters (methanol, dissolved O2 content, HCO3- and Cl-) confirmed that a quite rarely observed energy transfer between the excited state P25 and SMP might be responsible for this unique behavior. In our opinion, these results highlight that "non-conventional" mechanisms could occur even in the case of the well-known TiO2 photocatalyst, and the effect of wavelength is also worth investigating.

Impact of Reaction Parameters and Water Matrices on the Removal of Organic Pollutants by TiO2/LED and ZnO/LED Heterogeneous Photocatalysis Using 365 and 398 nm Radiation

In this work, the application of high-power LED_365nm and commercial, low-price LED_398nm for heterogeneous photocatalysis with TiO₂ and ZnO photocatalysts are studied and compared, focusing on the effect of light intensity, photon energy, quantum yield, electrical energy consumption, and effect of matrices and inorganic components on radical formation. Coumarin (COU) and its hydroxylated product (7-HC) were used to investigate operating parameters on the ^•OH formation rate. In addition to COU, two neonicotinoids, imidacloprid and thiacloprid, were also used to study the effect of various LEDs, matrices, and inorganic ions. The transformation of COU was slower for LED_398nm than for LED_365nm, but r₀^7-HC/r₀^COU ratio was significantly higher for LED_398nm. The COU mineralization rate was the same for both photocatalysts using LED_365nm, but a significant difference was observed using LED_398nm. The impact of matrices and their main inorganic components Cl^- and HCO₃^- were significantly different for ZnO and TiO₂. The negative effect of HCO₃^- was evident, however, in the case of high-power LED_365nm and TiO₂, and the formation of CO₃^•- almost doubled the r₀^7-HC and contributes to the conversion of neonicotinoids by altering the product distribution and mineralization rate.

Investigation of the efficiency of BiOI/BiOCl composite photocatalysts using UV, cool and warm white LED light sources - Photon efficiency, toxicity, reusability, matrix effect, and energy consumption

BiOI, BiOCl, and their composites (BiOI:BiOCl) with molar ratios from 95:5 to 5:95 were synthesized and tested in the transformation of methyl orange (MO) and sulfamethoxypyridazine (SMP) antibiotic, using three various LED light sources: UV LEDs (398 nm), cool and warm white LEDs (400-700 nm). The 80:20 BiOI:BiOCl photocatalyst showed the best adsorption capacity for MO and enhanced activity compared to BiOI and BiOCl. The apparent quantum yield (Φ_app) of the MO and SMP transformation for cool and warm white light was slightly lower than for 398 nm UV radiation. The effect of methanol and 1,4-benzoquinone proved that the transformation is initiated mainly via direct charge transfer, resulting in the demethylation of MO and SO₂ extrusion from SMP. The change of photocatalytic efficiency was followed during three cycles. After the first one, the transformation rates decreased, but there was no significant difference between the second and third cycles. The decreased efficiency is most probably caused by the intermediates, whose continuous accumulation was observed during the cycles. Ecotoxicity measurements confirmed that no toxic substances were leached from the catalyst, but the transformation of both MO and SMP results in toxic intermediates. Using 80:20 BiOI:BiOCl and LED light source, the energy requirement of the removal is about half of the value determined using TiO₂ and a mercury vapor lamp. The effect of some components of wastewater (Cl^-, HCO₃^- and humic acids), pH, and two matrices on the composite photocatalysts' efficiency and stability were also investigated.

Potential of TiO2 with Various Au Nanoparticles for Catalyzing Mesotrione Removal from Wastewaters under Sunlight

Nowadays, great focus is given to the contamination of surface and groundwater because of the extensive usage of pesticides in agriculture. The improvements of commercial catalyst TiO₂ activity using different Au nanoparticles were investigated for mesotrione photocatalytic degradation under simulated sunlight. The selected system was 2.43 × 10⁻³% Au–S–CH₂–CH₂–OH/TiO₂ (0.5 g/L) that was studied by transmission electron microscopy and ultraviolet-visible (UV-Vis) spectroscopy. It was found that TiO₂ particles size was ~20 nm and ~50 nm, respectively. The Au nanoparticles were below 10 nm and were well distributed within the framework of TiO₂. For 2.43 × 10⁻³% Au–S–CH₂–CH₂–OH/TiO₂ (0.5 g/L), band gap energy was 2.45 eV. In comparison to the pure TiO₂, addition of Au nanoparticles generally enhanced photocatalytic removal of mesotrione. By examining the degree of mineralization, it was found that 2.43 × 10⁻³% Au–S–CH₂–CH₂–OH/TiO₂ (0.5 g/L) system was the most efficient for the removal of the mesotrione and intermediates. The effect of tert-butanol, NaF and ethylenediaminetetraacetic acid disodium salt on the transformation rate suggested that the relative contribution of various reactive species changed in following order: h⁺ > ^●OH_ads > ^●OH_bulk. Finally, several intermediates that were formed during the photocatalytic treatment of mesotrione were identified.

Transformation of atrazine by photolysis and radiolysis: kinetic parameters, intermediates and economic consideration

Four techniques, UV_{254 nm} photolysis, vacuum ultraviolet (VUV_{172 nm}) photolysis, combined UV_{254 nm}/VUV_{185 nm} photolysis and gamma (γ) radiolysis were used to induce the transformation of atrazine in aqueous solution. The effects of dissolved oxygen (atrazine concentration 1 × 10^-4 mol L^-1 and 4.6 × 10^-7 mol L^-1) and matrix (high purity water/purified wastewater, atrazine concentration 4.6 × 10^-7 mol L^-1) and the electric energy requirements were investigated. The calculation of the energy input in cases of the photolyses was based on the lamp's power. In radiolysis, the absorbed dose (J kg^-1) was the basis. In UV photolysis, atrazine transforms to atrazine-2-hydroxy; this product practically does not degrade during UV photolysis; due to this reason, the mineralisation is very slow. This and some other products of atrazine decomposition degrade only in radical reactions. Dissolved oxygen usually slightly enhances the degradation rate. At 10^-7 mol L^-1 concentration level, the matrix, high purity water/purified wastewater, has not much influence on the degradation rates in UV photolysis and radiolysis. In the VUV and UV/VUV systems, considerable matrix effects were observed. Comparing the electric energy requirements of the four degradation processes, radiolysis was found to be the economically most feasible method, requiring 1-2 orders of magnitude less electric energy than UV/VUV, VUV and UV photolysis.

Interaction Studies Between Levodopa and Different Excipients to Develop Coground Binary Mixtures for Intranasal Application

Levodopa (LEVO) as the gold standard in the treatment of Parkinson's disease is usually administrated per os but its bioavailability is low. The intranasal administration is a potential alternative route to increase bioavailability of the drug and treat the off period. Our aim was to develop LEVO-containing binary nasal powders with different excipients by dry cogrinding process. The interactions between the components were examined. The optimized cogrinding process parameters (LEVO:excipient ratio and grinding time) resulted in the desired particle size range (5-40 μm). The α-cyclodextrin and poly(vinylpyrrolidone) (PVP) had an intensive crystallinity degree reducing effect on LEVO measured by XRPD, and they functioned as cogrinding agents. Hydroxypropyl methylcellulose, poly (vinyl alcohol) (PVA), and D-mannitol associate around the LEVO crystals preventing its crystalline structure. Hydrogen bonding was detected only for LEVO-PVP and LEVO-D-mannitol used Fourier-transformed infrared spectroscopy. Chemical degradation of LEVO in the products was not detected even after the accelerated stability test. The dissolution profile of the products can be characterized by the first-order kinetic model with different dissolution rate. The dissolution rate of LEVO was increased with α-cyclodextrin and PVP, and the drug release decreased in the case of hydroxypropyl methylcellulose, PVA, and D-mannitol compared to the LEVO powder.

Study of the Potential Endocrine-Disrupting Effects of Phenylurea Compounds on Neurohypophysis Cells In Vitro

Homeostatic disruptor agents, and endocrine disruptor compounds (EDC) specifically, can originate from agricultural and industrial chemicals. If they modify the adaptation of living organisms as direct (e.g., by altering hormone regulation, membrane functions) and/or indirect (e.g., cell transformation mechanisms) factors, they are classified as EDC. We aimed to examine the potential endocrine-disrupting effects of phenylurea herbicides (phenuron, monuron, and diuron) on the oxytocin (OT) and arginine-vasopressin (AVP) release of neurohypophysis cell cultures (NH). In our experiments, monoamine-activated receptor functions of neurohypophyseal cells were used as a model. In vitro NH were prepared by enzymatic (trypsin, collagenase) and mechanical dissociation. In the experimental protocol, the basal levels of OT and AVP were determined as controls. Later, monoamine (epinephrine, norepinephrine, serotonin, histamine, and dopamine) activation (10^-6 M, 30 min) and the effects of phenylurea (10^-6 M, 60 min) alone and in combination (monoamines 10^-6 M, 30 min + phenylureas 10^-6 M, 60 min) with monoamine were studied. OT and AVP hormone contents in the supernatant media were measured by radioimmunoassay. The monoamine-activated receptor functions of neurohypophyseal cells were modified by the applied doses of phenuron, monuron, and diuron. It is concluded that the applied phenylurea herbicides are endocrine disruptor agents, at least in vitro for neurohypophysis function.

Comparison of various advanced oxidation processes for the degradation of phenylurea herbicides

Various types of advanced oxidation processes (AOPs), such as UV photolysis, ozonation, heterogeneous photocatalysis and their combinations were comparatively examined at the same energy input in a home-made reactor. The oxidative transformations of the phenylurea herbicides fenuron, monuron and diuron were investigated. The initial rates of transformation demonstrated that UV photolysis was highly efficient in the cases of diuron and monuron. Ozonation proved to be much more effective in the transformation of fenuron than in those of the chlorine containing monuron and diuron. In heterogeneous photocatalysis, the rate of decomposition decreased with increase of the number of chlorine atoms in the target molecule. Addition of ozone to UV-irradiated solutions and/or TiO2-containing suspensions markedly increased the initial rates of degradation. Dehalogenation of monuron and diuron showed that each of these procedures is suitable for the simultaneous removal of chlorinated pesticides and their chlorinated intermediates. Heterogeneous photocatalysis was found to be effective in the mineralization.

Toxicology Aspects of the Decomposition of Diuron by advanced Oxidation Processes

Diuron is a phenylurea-based residual herbicide with toxic and endocrine disrupting effects. The aims of the present work were the comparison of the efficiency of various advanced oxidation processes, such as direct ultraviolet photolysis, ozonation, their combination, and heterogeneous photocatalysis from the point of view of the transformation rate of diuron, rate of mineralisation and dehalogenation, formation of aromatic intermediates, and ecotoxicological effects of the formed multicomponent solutions during the treatments. The initial rates of transformation of diuron are in the order of ozonation < heterogeneous photocatalysis < UV photolysis < combination of UV photolysis and ozonation. Each method provided similar tendencies in the decrease of the concentration of organically bound chlorines (AOX) since, until the diuron was completely degraded, the concentration of AOX decreased almost to zero in each case. However, only heterogeneous photocatalysis was found to be effective in terms of mineralisation. Ecotoxicological results showed that in each case, except for ozonation, the toxicity of the treated solutions changed through a maximum during the transformation of diuron. The maximum value was found to be lower in the case of heterogeneous photocatalysis. Thus, the formation and decomposition of by-products of relatively higher toxicity than diuron can be supposed. Our results confirmed that the amount of the formed (aromatic) intermediates, their quality and specific toxicity strongly depend on the applied processes.

Vacuum ultraviolet photolysis of diclofenac and the effects of its treated aqueous solutions on the proliferation and migratory responses of Tetrahymena pyriformis

The effects of dissolved O2, phosphate buffer and the initial concentration of diclofenac on the vacuum ultraviolet photolysis of this contaminant molecule were studied. Besides kinetic measurements, the irradiated, multicomponent samples were characterized via the proliferation and migratory responses (in sublethal concentrations) of the bioindicator eukaryotic ciliate Tetrahymena pyriformis. The results suggest that hydroxyl radicals, hydrogen atoms and hydroperoxyl radicals may all contribute to the degradation of diclofenac. The aromatic by-products of diclofenac were presumed to include a hydroxylated derivative, 1-(8-chlorocarbazolyl)acetic acid and 1-(8-hydroxycarbazolyl)acetic acid. The biological activity of photoexposed samples reflected the chemical transformation of diclofenac and was also dependent on the level of dissolved O2. The increase in toxicity of samples taken after different irradiation times did not exceed a factor of two. Our results suggest that the combination of vacuum ultraviolet photolysis with toxicity and chemotactic measurements can be a valuable method for the investigation of the elimination of micropollutants.

Degradation of naproxen by UV, VUV photolysis and their combination

Naproxen is a widely used nonsteroidal anti-inflammatory drug. Recently, this medicine was detected both in natural waters (up to 1.5 μg L(-1)) and in sewage treatment plant effluents (up to 5.2 μg L(-1)). Moreover, naproxen is only partly eliminated by classical processes used in sewage treatment plants. Therefore, its degradation is of utmost interest. Advanced oxidation processes proved to be the most suitable methods for the elimination of persistent organic contaminants. In this work ultraviolet (UV, 254 nm), vacuum ultraviolet photolysis (VUV, 172 nm) and their combination (UV/VUV, 254/185 nm) were investigated. The efficiency of the methods increased in the following order: UV < VUV < UV/VUV photolysis. However, VUV irradiation was found to mineralize the contaminant molecule most effectively. The chemical structures of three out of four aromatic by-products and of some aliphatic carboxylic acids were presumed. The effects of dissolved O2 and the initial concentration of naproxen on the degradation were also investigated.

Direct VUV photolysis of chlorinated methanes and their mixtures in an oxygen stream using an ozone producing low-pressure mercury vapour lamp

The gas-phase photooxidations of CCl(4), CHCl(3), CH(2)Cl(2) and their binary mixtures in an O(2) stream were studied in a flow reactor under various experimental conditions using a low-pressure mercury lamp as light source covered with a high-purity silica sleeve being used. The 184.9 nm VUV irradiation emitted is responsible for the Cl-C bond rupture in the chlorinated methanes and for the formation of O(3) from O(2). The rate of degradation of H-containing chlorinated methanes increased sharply on increase of their initial concentrations, most probably of a (*)Cl chain reaction, as indicated by the increase in the molar ratio of the amount of HCl formed to the amount of H-containing target substance decomposed. The experimental results suggested that the further transformations of the radicals and products formed play an important role as (*)Cl sources, causing a considerably higher rate of decomposition of the H-containing target substances. In a humidified O(2) stream, the (*)OH formed opens up another route for oxidation of the target substances. Thus, the rates of degradation of CH(2)Cl(2) and CHCl(3) increased on increase of the relative humidity, whereas the water vapour had no effect at all on the decomposition of CCl(4). At the same time, competition occurs between (*)Cl or (*)OH for reactions with the target substance. The photooxidation of binary mixtures was investigated too. The addition of CCl(4) or CHCl(3) to CH(2)Cl(2) strongly increased its degradation rate. The addition of CH(2)Cl(2) did not have a considerable effect on the rate of degradation of CHCl(3).

Direct VUV photolysis of chlorinated methanes and their mixtures in a nitrogen stream

The gas-phase decomposition of CCl(4), CHCl(3) and CH(2)Cl(2) and their binary mixtures was studied in a flow-type reactor in a nitrogen gas stream, using a low-pressure mercury vapour lamp covered with a high-purity silica quartz sleeve. The 184.9 nm vacuum-ultraviolet (VUV) light emitted is able to rupture the C-Cl bond in these target substances. For H-containing compounds, the decomposition takes place not only by direct photolysis, but also by H abstraction by .Cl formed during the direct photolysis of the target substances. The relative contributions of direct photolysis and .Cl-sensitized reactions to the decomposition were estimated at different initial concentrations. The addition of CCl(4) to CHCl(3) or CH(2)Cl(2) increased their decomposition rates via increase of the .Cl concentration, whereas the addition of CH(2)Cl(2) to CHCl(3) decreased its degradation rate, suggesting that CH(2)Cl(2) acts as a .Cl radical scavenger. The variation of the product distribution confirms the effect of the composition of the irradiated gas mixtures on the relative contributions of .Cl-sensitized reactions and direct photolysis.