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: λc = 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.

A comprehensive analysis of meloxicam particles produced by nanosecond laser ablation as a wet milling technique.

Recently, the number of water insoluble and poorly soluble drug compounds has increased significantly. Therefore, growing interest has been witnessed in different particle size reduction techniques to improve the dissolution rates, transport characteristics and bioavailability of drugs. Laser ablation has proven to be an alternative method to the production of nano- and micrometre-sized drug particles without considerable chemical damage. We present the nanosecond laser ablation of drug pastilles in distilled water, targeting meloxicam, a poorly water soluble nonsteroidal anti-inflammatory drug, at different laser wavelengths (248 nm, 532 nm and 1064 nm). Besides chemical characterization, crystallinity, morphology and particle size studies, the mechanism of the particle generation process was examined. The applicability of ablated particles in drug formulation was investigated by solubility, cytotoxicity and anti-inflammatory effect measurements. We showed that laser ablation is a clean, efficient and chemically non-damaging method to reduce the size of meloxicam particles to the sub-micrometre-few micrometre size range, which is optimal for pulmonary drug delivery. Complemented by the excellent solubility (four to nine times higher) and anti-inflammatory (four to five times better) properties of the particles compared to the initial drug, laser ablation is predicted to have wider applications in the development of drug formulations.

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 (Φapp) 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.

Removal of Emerging Pollutants from Water Using Environmentally Friendly Processes: Photocatalysts Preparation, Characterization, Intermediates Identification and Toxicity Assessment.

Pharmaceuticals and pesticides are emerging contaminants problematic in the aquatic environment because of their adverse effects on aquatic life and humans. In order to remove them from water, photocatalysis is one of the most modern technologies to be used. First, newly synthesized photocatalysts were successfully prepared using a sol-gel method and characterized by different techniques (XRD, FTIR, UV/Vis, BET and SEM/EDX). The photocatalytic properties of TiO2, ZnO and MgO nanoparticles were examined according to their removal from water for two antibiotics (ciprofloxacin and ceftriaxone) and two herbicides (tembotrione and fluroxypyr) exposed to UV/simulated sunlight (SS). TiO2 proved to be the most efficient nanopowder under UV and SS. Addition of (NH4)2S2O8 led to the faster removal of both antibiotics and herbicide fluroxypyr. The main intermediates were separated and identified for the herbicides and antibiotic ciprofloxacin. Finally, the toxicity of each emerging pollutant mixture and formed intermediates was assessed on wheat germination and biomass production.

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 LED365nm and commercial, low-price LED398nm 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 LED398nm than for LED365nm, but r07-HC/r0COU ratio was significantly higher for LED398nm. The COU mineralization rate was the same for both photocatalysts using LED365nm, but a significant difference was observed using LED398nm. 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 LED365nm and TiO2, and the formation of CO3•- almost doubled the r07-HC and contributes to the conversion of neonicotinoids by altering the product distribution and mineralization rate.

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+ > ●OHads > ●OHbulk. 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, UV254 nm photolysis, vacuum ultraviolet (VUV172 nm) photolysis, combined UV254 nm/VUV185 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.