Commercial Photocatalyst Research Articles

Palladium and silver nanoparticles embedded on zinc oxide nanostars for photocatalytic degradation of pesticides and herbicides

In this study, we demonstrated the efficient charge separation and migration at zinc oxide nanostars (ZnONSt) via conjugation with noble metal nanoparticle (MNP = Ag, Pd) and its application in degradation of carcinogenic pesticide [methyl parathion (MP)] and herbicides [pendimethalin (PDM), trifluralin (TFL)]. A well dispersed noble MNP incorporation on ZnONSt surface has been carried out by microwave-hydrothermal (MW-HT) method. The related phase constitution, the presence of functional groups, optical properties, elemental composition, surface area, and surface morphology were evaluated using various analytical techniques. The XRD patterns and FE-SEM/TEM micrographs revealed the ZnONSt had hexagonal wurtzite phase with a star-like morphology. The Ag@ZnONSt and Pd@ZnONSt exhibited excellent photocatalytic activity towards the photodegradation of pesticide, and herbicides under irradiation of visible light (VL). Pd and Ag nanoparticles act as electron sink and thus facilitate the interfacial charge transfer process by suppression of charge recombination rate. In particular, Pd@ZnONSt nanocomposite showed the better performance than the ZnONSt with different morphology and other commercial photocatalysts. A plausible mechanism for the enhanced photocatalytic activity by Pd@ZnONSt was proposed. Our results might open up a promising way to develop novel and highly efficient photocatalysts based on ZnONSt-related heterostructure.

Influence of the type of photocatalyst on photocatalytic oxidation of triclosan in the aquatic environment

A comparative assessment of triclosan removal (an antibacterial compound) in aqueous solutions at a concentration of 1.0 mg/dm3 during an advanced oxidation process in the presence of commercial titanium dioxide (TiO2) and photocatalysts modified with the powdered activated carbon and ultrasounds was studied. Photocatalytic processes were examined using a photocatalyst at the dose concentration of 100 mg/dm3. The influence of photocatalysts modification on triclosan sorption process and its decomposition was found. Triclosan was adsorbed in the range of 69% to 96%. After 20 minutes of the photocatalysis, triclosan decomposition was set to 91% in the presence of pure TiO2. For the modified photocatalysts, the removal degree exceeded 99% after 10 minutes of irradiation. The Langmuir-Hinshelwood model was used to describe the kinetics of triclosan degradation. Reaction kinetics showed a two-stage oxidation process in the presence of a photocatalyst modified with activated carbon and ultrasounds.

Fabrication, characterization and high photocatalytic activity of Ag-ZnO heterojunctions under UV-visible light.

Pure ZnO and Ag–ZnO nanocomposites were fabricated via a sol–gel route, and the obtained photocatalysts were characterized by XRD, SEM, TEM, BET, XPS, PL and DRS. The results showed that Ag0 nanoparticles deposit on the ZnO surface and Ag modification has negligible impact on the crystal structure, surface hydroxyl group content and surface area of ZnO. However, the recombination of photogenerated electrons and holes was suppressed effectively by Ag loading. The photocatalytic activity was investigated by evaluating the degradation of MB under xenon lamp irradiation as the UV-visible light source, and the results show that the photocatalytic activity of ZnO significantly improved after Ag modification. Ag–ZnO photocatalysts exhibit higher photocatalytic activity than commercial photocatalyst P25. The degradation degree of MB for 1%Ag–ZnO was 97.1% after 15 min. ˙O2− radicals are the main active species responsible for the photodegradation process, and Ag–ZnO heterojunctions generate more ˙O2− radicals, which is the primary reason for the improved photocatalytic performance.

Photocatalytic performance mesoporous Nd2O3 modified ZnO nanoparticles with enhanced degradation of tetracycline

This contribution reports the synthesis of mesoporous X% Nd2O3 modified ZnO (X = 1, 2, 3 and 4) during sol-gel process in existence of Pluronic F-108 for the first time. XRD indicated the construction of hexagonal ZnO nanocrystals and the isotherms exhibited of type IV with a type H2 hysteresis loop, indicating the existence of mesostructures. The synthesized samples were evaluated by photodegradation of tetracycline (TC) in visible light exposure compared to pure mesoporous ZnO nanoparticles (NPs) and commercial photocatalyst P-25. The photocatalytic efficiency mesoporous 3%Nd2O3/ZnO for degradation TC reached up to 100 % for 2 h compared to pure mesoporous ZnO and P-25 with 4 and 10 %, respectively. The mesoporous 3%Nd2O3/ZnO photocatalysts showed promoted photocatalytic performance, resulting in an improved photodegradation rate value up to 8.8 and 16.3 times that of compared to pure ZnO and P-25, which was explained by better photogenerated charge carriers separation as a result of heterojunction construction between Nd2O3 and ZnO interfaces. In addition, the 3%Nd2O3/ZnO photocatalysts showed sufficient stability for five repeated runs and created its potential utility for mitigation of organic pollutants in comparison to pure ZnO and commercial P-25.

Influence of Water on the Oxidation of NO on Pd/TiO2 Photocatalysts.

Two series of new photocatalysts were synthesized based on modification with Pd of the commercial P25 photocatalyst (EVONIK®). Two techniques were employed to incorporate Pd nanoparticles on the P25 surface: photodeposition (series Pd-P) and impregnation (series Pd-I). Both series were characterized in depth using a variety of instrumental techniques: BET, DRS, XRD, XPS, TEM, FTIR and FESEM. The modified series exhibited a significant change in pore size distribution, but no differences compared to the original P25 with respect to crystalline phase ratio or particle size were observed. The Pd0 oxidation state was predominant in the Pd-P series, while the presence of the Pd2+ oxidation state was additionally observed in the Pd-I series. The photoactivity tests were performed in a continuous photoreactor with the photocatalysts deposited, by dip-coating, on borosilicate glass plates. A total of 500 ppb of NO was used as input flow at a volumetric flow rate of 1.2 L·min−1, and different relative humidities from 0 to 65% were tested. The results obtained show that under UV-vis or Vis radiation, the presence of Pd nanoparticles favors NO removal independently of the Pd incorporation method employed and independently of the tested relative humidity conditions. This improvement seems to be related to the different interaction of the water with the surface of the photocatalysts in the presence or absence of Pd. It was found in the catalyst without Pd that disproportionation of NO2 is favored through its reaction with water, with faster surface saturation. In contrast, in the catalysts with Pd, disproportionation took place through nitro-chelates and adsorbed NO2 formed from the photocatalytic oxidation of the NO. This different mechanism explains the greater efficiency in NOx removal in the catalysts with Pd. Comparing the two series of catalysts with Pd, Pd-P and Pd-I, greater activity of the Pd-P series was observed under both UV-vis and Vis radiation. It was shown that the Pd0 oxidation state is responsible for this greater activity as the Pd-I series improves its activity in successive cycles due to a reduction in Pd2+ species during the photoactivity tests.

Theoretical calculation of a TiO2-based photocatalyst in the field of water splitting: A review

AbstractCurrently, energy and environmental problems are becoming more serious. The use of solar energy to split water and produce clean, renewable hydrogen as an energy source is a feasible and effective approach to solve these problems. As the most promising semiconductor material for photocatalytic water splitting, TiO2-based nanomaterials have received increasing attention from researchers in academia and industry in recent years. This review describes the research progress in the theoretical calculations of TiO2-based photocatalysts in water splitting. First, it briefly introduces some commonly used theoretical calculation methods, the crystal structure of TiO2and its photocatalytic mechanism, and the principle of doping and heterojunction modification to improve the photocatalytic performance of TiO2. Subsequently, the adsorption state of water molecules with different coverages on the surface of TiO2, the rate-limiting steps of the splitting of water molecules on the surface of TiO2, and the transfer process of photogenerated current carriers at the interface between water molecules and TiO2are analyzed. In addition, a brief review of research into the theoretical calculations of TiO2-based commercial photocatalysts in the field of water splitting is also provided. Finally, the calculation of TiO2-based photocatalytic water-splitting simulations is summarized, and possible future research and development directions are discussed.

TiO2 coated fiber cement composites: Effect of the load of TiO2 particles on photocatalytic degradation of H2S

This paper evaluated the effect of the amount of mass of the commercial photocatalyst Fotosan® (PC) based on TiO2 in the modification of the textural and morphological characteristics of the coatings formed in fiber cement supports (FB). The effect of mass addition on photocatalytic activity was also evaluated using the hydrogen sulfide degradation reaction (H2S) as a parameter. For this, five treatments conducted by different amounts of PC mass per area of FB in the range of 5.3 to 14.4 mg cm−2 were evaluated. The surfaces formed by these photocatalytic coatings (PCFB) were characterized by scanning electron microscopy with X-ray energy dispersive spectroscopy (SEM-EDS), X-ray diffractometry (XRD), nitrogen adsorption–desorption (BET) isotherms and infrared spectroscopy with total attenuated reflection (ATR-FTIR).The results of nitrogen isotherms confirmed that the coatings formed have a large specific pore volume (3.6×10-2 to 5.6×10-2 cm3 g−1) and a high specific surface area (18.9 to 29.9 m2 g−1). It was verified that the variation of PC mass over FB significantly affected the textural characteristics and the morphological structure of PCFB when comparing means between treatments (Tukey test; α = 5%), and probably these characteristics correlate with the respective photocatalytic activity. The modification of the structural properties produced by the accumulation of PC mass was more beneficial when the coatings were formed with a dosage of 7.3 mg cm−2, because it corresponded to the treatment where photocatalytic activity showed maximum intensity in the reaction of H2S degradation (72%) and a minimum amount of PC used in comparison to other treatments.

Antibacterial and Biofilm-Preventive Photocatalytic Activity and Mechanisms on P/F-Modified TiO2 Coatings

Photocatalytic antibacterial and biofilm-preventive activity in liquid of heavy-metal-free coatings based on a phosphorus (P)- and fluorine (F)-modified TiO2 photocatalyst has been investigated. They reveal significantly higher immediate and longer-term (biofilm-preventive) inactivation capacity than a reference coating made of the commercial photocatalyst TiO2 P25 on three bacterial species differing in cell wall type and ability to resist oxidative stress (Escherichia coli, Staphylococcus epidermidis, Pseudomonas fluorescens) (up to more than 99% reduction of colonization on P/F-modified TiO2 coating compared to about 50% on P25 TiO2 coating for 10 min UV-A illumination). This results from the P- and F-induced improvement of photocatalyst properties and from the smoother surface topography, which shortens reactive oxygen species (ROS) diffusion to the outer membrane of the targeted adhered bacteria. Decrease in ROS-related impairment of cell wall, respiratory, and enzymatic activities confirms the loss of ROS throughout the bacterial cell degradation. Staphylococcus epidermidis and Pseudomonas fluorescens are less sensitive than Escherichia coli, with a probable relation to the bacterial oxygen stress defense mechanism. The coating antibacterial efficacy was highly affected by phosphate ions and the richness in dissolved oxygen of the reaction medium.

Synthesis of TiO2/reduced graphene oxide–Al2O3 composites and their advanced properties for photocatalysis

The TiO2/reduced graphene oxide (RGO)-Al2O3 composites were synthesized by dispersing TiO2 on RGO-modified Al2O3 by impregnation method. The surface properties of TiO2/RGO–Al2O3 were systematically studied. It was found that the TiO2 particle size was about 15 nm, and the particles were relatively uniform in the loading range of 20–40 wt% compared with that of Al2O3. The surface area increased obviously as RGO was added to Al2O3. The chemical structures of the TiO2/RGO–Al2O3 composites were characterized by diffuse reflectance UV–Visible spectroscopy and X-ray photoelectron spectroscopy. Results revealed the presence of an intense interaction between TiO2 and RGO–Al2O3. The dark adsorption results showed that the TiO2/RGO–Al2O3 had a higher adsorption ability for methyl orange (MO), which was mainly due to the π-π conjugation between MO and RGO. The liquid-phase photocatalytic oxidation of MO was adopted to evaluate the efficiency of the obtained materials. TiO2/RGO–Al2O3 showed higher catalytic efficiency over the TiO2/Al2O3 or the commercial P25 photocatalyst. Recycling tests showed excellent stability of TiO2/RGO–Al2O3. The TiO2/RGO–Al2O3 was easier to separate by filtration method than TiO2 due to its high anti-hydration dispersion ability. The studies indicated their good prospects for large-scale application.

Strong effect of light scattering by distribution of TiO2 particle aggregates on photocatalytic efficiency in aqueous suspensions

This work examines the important role of light power absorbed by TiO2 on the photocatalytic degradation of dichloroacetic acid (DCA) in a semi-continuous slurry photoreactor with UV–Vis radiation. This system is an excellent model for understanding the light matter interaction, because DCA is transparent and the acid pH of the solution prevents the formation of large TiO2 aggregates. Under these conditions, the light power absorbed by four different commercial Titania photocatalysts, along the whole volume of the reactor, has been quantitatively calculated by assuming a Mie scattering model on a distribution of different particle sizes. Although the different chemical nature of the four considered samples (three of them provided by the Evonik Company, P25, P25/20 and P90, together with Hombikat UV 100), and the different catalytic efficiency based on weight, we have found that all the catalytic responses are fundamentally controlled by the absorbed radiation in the four samples. Therefore, in the studied samples, any difference in the catalytic behavior is only due to the light-matter interaction being of lesser importance other mechanisms, as space-charge blocking.

Hierarchical Bi2O2CO3 wrapped with modified graphene oxide for adsorption-enhanced photocatalytic inactivation of antibiotic resistant bacteria and resistance genes

There is growing pressure for wastewater treatment plants to mitigate the discharge of antibiotic resistant bacteria (ARB) and extracellular resistance genes (eARGs), which requires technological innovation. Here, hierarchical Bi2O2CO3 microspheres were wrapped with nitrogen-doped, reduced graphene oxide (NRGO) for enhanced inactivation of multidrug-resistant E. coli NDM-1 and degradation of the plasmid-encoded ARG (blaNDM-1) in secondary effluent. The NRGO shell enhanced reactive oxygen species (ROS) generation (•OH and H2O2) by about three-fold, which was ascribed to broadened light absorption region (red-shifted up to 459 nm) and decreased electron-transfer time (from 55.3 to 19.8 ns). Wrapping enhanced E. coli adsorption near photocatalytic sites to minimize ROS scavenging by background constituents, which contributed to the NRGO-wrapped microspheres significantly outperforming commercial TiO2 photocatalyst. ROS scavenger tests indicated that wrapping also changed the primary inactivation pathway, with photogenerated electron holes and surface-attached hydroxyl radicals becoming the predominant oxidizing species with wrapped microspheres, versus free ROS (e.g., •OH, H2O2 and •O2−) for bare microspheres. Formation of resistance plasmid-composited microsphere complexes, primary due to the π-π stacking and hydrogen bonding between the shell and nucleotides, also minimized ROS scavenging and kept free plasmid concentrations below 102 copies/mL. As proof-of-concept, this work offers promising insight into the utilization of NRGO-wrapped microspheres for mitigating antibiotic resistance propagation in the environment.

Charge Carriers in Commercial Photocatalysts: Fractal Kinetics and Effect of \u201cInert\u201d Additives

High photon conversion efficiencies and low-cost materials are crucial for implementing photocatalytic solutions in large scale applications. To improve the conversion efficiencies, knowledge on the lifetime and dynamics of photogenerated charge carriers is fundamental, for which transient absorption spectroscopy has provided important insights. Regarding the cost of the materials, one approach to decrease it is mixing the photocatalyst with cheaper additives while avoiding a significant loss in its activity. In this short review we summarize the findings of our group dealing with both aspects. A new model to fit transient absorption decays, based on fractal kinetics, is discussed. The model has been applied to the transient decays of TiO2 mixtures with binary particle size distributions and of TiO2 mixtures with a priori inert additives. In both cases, the insights obtained from the model were crucial to explain the photocatalytic activities of the mixtures.

Treatment of real artificial leather manufacturing wastewater containing Dimethylamine (DMA) by photocatalytic method

In this research, the treatment of real artificial leather manufacturing wastewater by two commercial photocatalysts as a branch of advanced oxidation processes has been investigated. A batch slurry reactor was employed in the presence of two types of catalysts, namely TiO2 and ZnO, along with UV irradiation. The experiments were performed on Box–Behnken design method considering the three effective parameters such as pH, the concentration of catalyst, and hydrogen peroxide as a co-oxidant. Results showed that the most important parameter in chemical oxygen demand (COD) reduction was pH. Additionally, some other parameters, such as the interaction between pH and co-oxidant as well as catalyst and co-oxidant concentration, are effective. At optimum condition [pHint = 3, catalyst concentration = 0.7 g/l and H2O2/COD = 4.00 (H2O2 concentration = 10 g/l)], the predicted and actual COD reduction was 52.54 and 56.87%, respectively, representing a good agreement between posed model and performed experiments. According to pH changes during the process and its influence on the removal of COD, more experiments were done by fixing pH at constant level, and the COD reduction reached 92.66% at 9 h. The kinetic studies in terms of COD removal showed that the reaction followed the first-order model.

H2Ti3O7 nanowires as a high-performance photocatalytic and surface-enhanced Raman scattering substrate

In the present work, we reported one kind of photocatalytic and surface-enhanced Raman scattering substrate, H2Ti3O7 nanowires, which prepared on the Ti foil by the hydrothermal and ion‐exchange methods. The morphologies, crystal structures, chemical compositions, optical properties of the as-prepared substrates investigated via the different kinds of characterization techniques. H2Ti3O7 nanowires revealed remarkably enhanced visible-light photocatalytic activity for the degradation of rhodamine 6 G solution compared to Na2Ti3O7 nanowires, TiO2 nanowires, and commercial photocatalysts (TiO2 and ZnO nanoparticles). These results attributed to the H2Ti3O7 nanowires with a higher concentration of oxygen vacancies can enhance the visible-light absorbance, resulting in the higher photocatalytic activity under the visible-light irradiation. The radical-trapping test shows that holes and hydroxyl radicals played central roles in rhodamine 6 G photodegradation. The deposition of Ag nanoparticles on the H2Ti3O7 nanowires can also use as a highly sensitive surface-enhanced Raman scattering substrate for detecting rhodamine 6 G solution with a concentration as low as 10−9 M by the ion-sputtering system.

Efficient N, Fe Co-Doped TiO2 Active under Cost-Effective Visible LED Light: From Powders to Films

An eco-friendly photocatalytic coating, active under a cost-effective near-visible LED system, was synthesized without any calcination step for the removal of organic pollutants. Three types of doping (Fe, N and Fe + N), with different dopant/Ti molar ratios, were investigated and compared with undoped TiO2 and the commercial P25 photocatalyst. Nano-crystalline anatase-brookite particles were successfully produced with the aqueous sol-gel process, also at a larger scale. All samples displayed a higher visible absorption and specific surface area than P25. Photoactivity of the catalyst powders was evaluated through the degradation of p-nitrophenol in water under visible light (>400 nm). As intended, all samples were more performant than P25. The N-doping, the Fe-doping and their combination promoted the activity under visible light. Films, coated on three different substrates, were then compared. Finally, the photoactivity of a film, produced from the optimal N-Fe co-doped colloid, was evaluated on the degradation of (i) p-nitrophenol under UV-A light (365 nm) and (ii) rhodamine B under LED visible light (395 nm), and compared to undoped TiO2 film. The higher enhancement is obtained under the longer wavelength (395 nm). The possibility of producing photocatalytic films without any calcination step and active under low-energy LED light constitutes a step forward for an industrial development.

Biomorphic Fibrous TiO2 Photocatalyst Obtained by Hydrothermal Impregnation of Short Flax Fibers with Titanium Polyhydroxocomplexes

A biomimetic solution technology for producing a photocatalytic material in the form of biomorphic titanium oxide fibers with a hierarchical structure using short flax fiber as a biotemplate is proposed. The impregnation of flax fibers intensified under hydrothermal conditions with a precursor was performed in an autoclave to activate the nucleation of the photoactive TiO2 phases. The interaction between precursor and flax fibers was studied by using infrared spectroscopy (IR) and differential scanning calorimetry/thermogravimetry analysis (DSC/TG). The morphology, structure, and textural properties of the TiO2 fibers obtained at annealing temperatures of 500–700 °C were determined by X-ray diffraction analysis, scanning electron microscopy, and nitrogen adsorption/desorption. It is shown that the annealing temperature of the impregnated biotemplates significantly affects the phase composition, crystallite size, and porous structure of TiO2 fiber samples. The photocatalytic activity of the obtained fibrous TiO2 materials was evaluated by using the decomposition of the cationic dye Rhodamine B in an aqueous solution (concentration 12 mg/L) under the influence of ultraviolet radiation (UV). The maximum photodegradation efficiency of the Rhodamine B was observed for TiO2 fibers annealed at 600 °C and containing 40% anatase and 60% rutile. This sample ensured 100% degradation of the dye in 20 min, and this amount significantly exceeds the photocatalytic activity of the commercial Degussa P25 photocatalyst and TiO2 samples obtained previously under hydrothermal conditions by the sol-gel method.

Photocatalytic Properties of Commercially Available TiO2: Study of Fotosan® and InterBrasil® FA-101 for H2S Degradation Using UV and Solar Radiation

This paper proposes the study and comparison of two commercial photocatalysts of TiO2 when applied as coating on a fibrocement roof tile. Are reported their respective photocatalytic activities, chemical, morphological, and textural characteristics. For that, commercial photocatalysts InterBrasil® FA-101 and Fotosan® were deposited on fibrocement support to perform photocatalytic activity tests and characterization analyses. The measurement of the photocatalytic activity of each sample was carried out through the efficiency of H2S degradation, using artificial (UV lamp) and natural (solar lighting) radiation. The surfaces formed with this photocatalyst coating were characterized by scanning electron microscopy, with energy-dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms, diffuse reflectance spectroscopy (DRS), and Fourier infrared transformation using attenuated total reflection (ATR-FTIR). The volumetric flow rate and saturation time (deactivation) were evaluated as operational performance parameters of the degradation reaction. The X-ray diffraction shows that TiO2 formed in the coatings correspond to the anatase phase. In addition, the pore volume of the coatings was from 4.9 to 9.0 × 10−3 g cm−3 and the superficial area was from 19.6 to 30.5 m2 g−1 that is considered relatively high. The results showed that, unlike the Fotosan®, the type of radiation used had a greater influence on the InterBrasil® FA-101, since there was a reduction of the photocatalytic activity when the solar radiation was used. The H2S degradation efficiency of 80% was obtained for a residence time (RT) of 115 s using Fotosan®, whereas that for InterBrasil® FA-101 was reached 45% for the same RT. Lower on the photocatalytic activity was observed after 30 min and 390 min of reaction for the InterBrasil® FA-101 and Fotosan®, respectively. The sample containing Fotosan® was the most effective photocatalyst in comparison with InterBrasil® FA-101.

Synthesis and Visible-Light Photocatalytic Activity of Graphite-like Carbon Nitride Nanopowders

Graphite-like carbon nitride (g-C3N4) nanopowders were synthesized by heat treatment of urea in air at a temperature of 450–550°С for 30 min and studied by X-ray diffraction and infrared spectroscopy. The main processes resulting in the formation of g-C3N4 from urea under the above conditions was established using the method of simultaneous thermal analysis. It was found that with an increase in the processing temperature of urea from 450 to 550°C, a rise in the specific surface of the powders occurs from 43.3 to 58.6 m2 g–1, as well as an increase in the crystallite sizes of graphite-like carbon nitride in the crystallographic direction (002) from 2.8 to 4.1 nm. According to the results of scanning electron microscopy and low-temperature nitrogen adsorption, the obtained graphite-like carbon nitride powders have a mesoporous structure and are characterized by an average pore size of 6.6–13.8 nm and porosity of 0.07–0.20 cm3 g–1. According to the results of diffuse reflectance spectroscopy, it was found that g-C3N4 nanopowders absorb radiation in the visible region and have a band gap of 2.9 eV. The photocatalytic activity of the obtained graphite-like carbon nitride during the oxidation of an aqueous murexide solution under the influence of visible light was analyzed and it was shown that the obtained g-C3N4 nanopowders have activity close to that of the commercial TiO2 photocatalyst (AEROXIDE P25). In view of the high activity and low cost, the obtained powders of graphite-like carbon nitride can be used as the substrate for new photocatalytic materials.

Photocatalytic Properties and Preparation of Nano-ZnO by Thermal Decomposition Based on ZIF-8

Using Zn(NO3)2·2H2O, 2-methylimidazole and CH3COONa·3H2O as main raw materials and methanol as solvent, ZIF-8 samples were prepared by hydrothermal reaction at 120 °C. And ZnO was obtained by calcination ZIF-8 in muffle furnace at 600 °C. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS) and thermos gravimetry-differential scanning calorimetry (TG-DSC). The photocatalytic activity of ZnO was investigated by methyl orange which was used as simulated sewage. The results show that the prepared ZnO is irregular, average grain size is about 80 nm, and the band gap width is 3.12 eV. Under UV-light, the degradation rate of 10 mg/L methyl orange is more than 70% in the presence of ZnO, while the degradation rate of methyl orange by commercial P25 is only 40%. The photocatalytic experiments show that the as-prepared ZnO has much higher photocatalytic activity than the commercial P25 photocatalyst. The ZnO is a kind of green photocatalyst which has a wide application prospect in the field of photocatalysis.

Kinetics, mechanism and toxicity of intermediates of solar light induced photocatalytic degradation of pindolol: Experimental and computational modeling approach

In this work, we have investigated the stability of pindolol (PIN), a non-selective β1-blocker detected in the river and wastewater of hospitals, in water solution under solar irradiation. Further, detailed insights into the stability of PIN were obtained by the density functional theory (DFT) calculations and molecular dynamics simulations. The kinetics of PIN photocatalytic degradation and mineralization has been studied using four commercial photocatalysts ZnO and TiO2 (P25, Hombikat, and Wackherr). It was found that the major role in degradation of PIN play the reactive hydroxyl radicals. The structures of degradation intermediates were suggested by LC–ESI–MS/MS and DFT calculations. Also, DFT calculations were used to refine molecular structures of intermediates and obtain their geometries. Toxicity of PIN and its mixtures formed during photocatalytic degradation were investigated using mammalian cell lines (H-4-II-E, HT-29, and MRC-5). The H-4-II-E cell line was the most sensitive to PIN and its photodegradation mixtures. The computational results were combined with the experimental data on the amounts of degradation intermediates for determination of the intermediates that were principally responsible for the toxicity. Intermediate with two hydroxyl groups, positioned on indole ring in meta and para positions, was proposed as the one with the highest contribution to toxicity.