Photocatalytic Activity Of Powders Research Articles

Photocatalytic Degradation of Paracetamol under Simulated Sunlight by Four TiO2 Commercial Powders: An Insight into the Performance of Two Sub-Micrometric Anatase and Rutile Powders and a Nanometric Brookite Powder

The photocatalytic degradation of the emerging contaminant paracetamol in aqueous solution has been studied under 1 SUN (~1000 W m−2) in the presence of four commercial TiO2 powders, namely sub-micrometric anatase and rutile, and nanometric brookite and P25 (the popular anatase/rutile mixture used as a benchmark in most papers). The rutile powder showed low activity, whereas, interestingly, the anatase and the brookite powders outperformed P25 in terms of total paracetamol conversion to carboxylic acids, which, according to the literature, are the final products of its degradation. To explain such results, the physicochemical properties of the powders were studied by applying a multi-technique approach. Among the physicochemical properties usually affecting the photocatalytic performance of TiO2, the presence of some surface impurities likely deriving from K3PO4 (used as crystallization agent) was found to significantly affect the percentage of paracetamol degradation obtained with the sub-micrometric anatase powder. To confirm the role of phosphate, a sample of anatase, obtained by a lab synthesis procedure and having a “clean” surface, was used as a control, though characterized by nanometric particles and higher surface area. The sample was less active than the commercial anatase, but it was more active after impregnation with K3PO4. Conversely, the presence of Cl at the surface of the rutile did not sizably affect the (overall poor) photocatalytic activity of the powder. The remarkable photocatalytic activity of the brookite nanometric powder was ascribed to a combination of several physicochemical properties, including its band structure and nanoparticles size.

Photocatalytic Activity of the Modified Coupled Semiconductors and Its Relationship with Surface Properties

Background: In photocatalysis and surface chemistry, charge trapping extends the lifetime of photogenerated electrons and holes and decreases their recombination rate. The stable surface of crystals with lowest energy is (110) for rutile and (101), (010) or (100) for anatase. When these surfaces are exposed to simple molecules such as water, oxygen or methane, different reactions can occur. In this paper, the activity and mechanism of dye adsorption were studied and demonstrated significant increase in the resulting photo-catalysis with optimizing surface properties for the first time. Methods: Degussa P25 (Aldrich) was used a based materials. The mixtures of ethanol (C2H5OH) and triethanolamine (TEA, C6H15NO3) and 1 M HNO3 solution were prepared and applied to chemical etching of anatase/rutile mixture. The nano composites with (0.5 % Pt) prepared by wet impregnation methods used as photo catalysts in water splitting reaction. The metallurgical and photo catalytical properties were characterized with standard methods. Results: The X-ray diffraction (XRD) Results of the samples were shown that the chemical process affected the phases and molar ratios. The photo-catalytic properties of these powders were measured with phase ratios, crystalline size, and reaction time as parameters. TEM images of powders chemically etched at different conditions are shown that the average surface area increased. The TiO2powders consist of spherical particles, that modified to cubic like structure with etching but core of the powders seems to have similar microstructures and shapes. The photo reactivity clearly shows that with adjusting phase ratios, the microstructure, surface and photo-catalytic activity of powders are adjusted. Conclusion: In this study, new method to preparation of core shell structure of anatase and rutile with using of etching developed and photo-catalytic activity of anatase and rutile hetro structure has been investigated using two systems. The reaction rate was related to the surface area, phase's ratio, particle and pore size, adsorption mechanism of reactants, concentration of dye and catalyst. The surface reaction sites and photo reactivity are higher in composite powders with similar particle size and band gap. The concentration of reactants (dye or water, H2, O2) is important because they react in suitable surface sites. The suitable sites are determined by size of compounds and surface charges. Additional to the surface properties, effectively charge separation was increasing the photo reactivity of composites.

Microwave-assisted synthesis of TiO2 nanoparticles: photocatalytic activity of powders and thin films

A simple, rapid, and effective synthesis methodology for the preparation of high-performance TiO2 nanoparticles and thin films by combining colloidal sol-gel and microwave-assisted hydrothermal synthesis was developed. The obtained results indicate that the heating with microwaves at 180 °C for 20 min was enough to synthesize crystalline TiO2 nanoparticles, presenting anatase as a major phase with a crystal size of ~ 7 nm and a specific surface area of 220 m2 g−1. A secondary thermal treatment improved the crystallinity and induced the anatase-to-rutile transformation. The highest photocatalytic activity was found for the as-synthesized powder without any additional thermal treatment. Thin films were also prepared by dip-coating and its high photocatalytic activity showed a kinetic curve comparable to that of a thin film of commercial TiO2 powder prepared under similar conditions.

Microwave-assisted combustion synthesis of ZnAl2O4 and ZnO nanostructure particles for photocatalytic wastewater treatment

ABSTRACTZnAl2O4 and ZnO nanostructure particles and in situ crystallization of zinc aluminate and zinc oxide coating layers on sintered α-Al2O3 and γ-Al2O3 granules by the microwave-assisted combustion method were investigated. For powders, the effects of solution pH value and for coated samples the influence of support type on the structure, microstructure, and photocatalytic activity of powders were studied. Results showed that variation of synthesis pH value caused to considerable change in agglomeration, specific surface area, obtaining up to 88 and 92% yields for zinc aluminate and zinc oxide nanoparticles, respectively. γ-alumina granules were more appropriate supports than the α-alumina ones because of the better photocatalytic activities and lower extent of the attritions for both zinc aluminate and zinc oxide coating layers.

Synthesis and physico-chemical studies of vanadium doped zinc oxide nanoparticles and its photocatalysis

In this work we report the synthesis of vanadium doped zinc oxide nanoparticles by a sol–gel processing technique, and the vanadium concentrations in zinc oxide varied from 1 to 5 at.%. In our approach, the water for hydrolysis was slowly released by esterification reaction followed by a supercritical drying in ethyl alcohol. All synthesized samples were annealed in air at 500 °C for 2 h. The obtained catalysts were characterized by fluorescence X, X-ray diffraction, transition electron microscopy and UV measurements. The structural properties showed that the obtained nanoparticles are single phase wurtzite structure and no secondary phases were detected which indicated that V ions substituted for Zn ions. The energy gap decreased gradually by increasing the doping concentration of V. The photocatalytic activities of powders were evaluated by the photocatalytic degradation of methylene blue (MB) under visible light irradiation. Compared with undoped ZnO and TiO2 P25 Degussa, it was found that the incorporation of vanadium in ZnO enhances the photocatalytic degradation, and ZnO:V3% is most active photocatalyst for MB degradation than the other V-doped samples.

Aluminum-doped zinc oxide powders: synthesis, properties and application

Aluminum-doped zinc oxide (AZO) powder was successfully synthesized by coprecipitation. In comparison with other methods, coprecipitation method provides advantages such as facile, economic and environmental-benign. The effects of Al-doping concentration and post-sintering treatment on electrical conductivity of AZO were investigated. Moreover, we also studied the influences of Al-doping concentration, pH, and type of dye on the photocatalytic activity of AZO powders. The objective of this study is to obtain a set of optimum parameters that will allow for improving electrical conductivity and photocatalytic activity of the powders. Additionally, the synthesized AZO powders which had high performance were modified by silane coupling agent KH-550 and then reinforced into polypropylene (PP) matrix. In order to improve the electrical conductivity of AZO/PP composites, the effect of modified-AZO filler content on electrical conductivity of AZO/PP composites was investigated. In the vicinity of the percolation threshold (around 3 wt%), the AZO/PP composite’s resistivity decreased dramatically by several orders of magnitude.

Phase Transformations and Photocatalytic Activity of TiO<sub>2</sub> Powders Preparation via Microwave-Assisted Sol-Gel Method

The purpose of this research was to study phase transformation and photocatalytic properties of TiO2powders. TiO2powders were prepared by microwave-assisted sol-gel method. The prepared powders were refluxed at 18 W to 450 W for 1 h and dried at 180 W for 1 h by a conventional microwave oven. The phase transformations of powders were characterized by XRD and photocatalytic activities of powders were evaluated by UV-Vis spectrophotometer. The results show all samples reveal that only the anatase phase and has the crystallite size is 13.8, 10.3 and 9.2 nm when the refluxed at 180, 300 and 450 W. It was found that TiO2powders refluxed at 450 W were found to give the highest photocatalytic efficiency is about 90.06% under UV irradiation for 6 h.

Preparation and Photocatalytic Activity of Yellow Titania

Titania powder was prepared by a sol-gel method and heat-treatment (HT). The morphology and structure of the titania powder were characterized by X-ray diffraction (XRD), differential thermal analysis, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of powder was investigated using methyl orange as target compound. Colour changing of powder was due to colour centers form. Under visible light, yellow powder showed the better photocatalytic activity than P25 powder and its visible light response was expanded. Preparation of yellow powder lowered conventional calcinations temperature obviously.

Photoluminescence and photocatalytic activity of zinc tungstate powders

Abstract ZnWO4 powders with grain size in range 20 nm–10 µm have been synthesized by a simple combustion method and subsequent calcinations. The photocatalytic activities of powders were tested by degradation of methylene blue solution under UV light. The luminescence spectra and luminescence decay kinetics were studied and luminescence decay time dependence on average powder-grain size was obtained. The correlation between self-trapped exciton luminescence decay time and photocatalytic activity of ZnWO4 powders was shown. A model explaining the excitonic luminescence decay time correlation with photocatalytic activity was proposed.

Thermostable photocatalytically active TiO2 anatase nanoparticles

Anatase is the low-temperature (300–550 °C) crystalline polymorph of TiO2 and it transforms to rutile upon heating. For applications utilizing the photocatalytic properties of nanoscale anatase at elevated temperatures (over 600 °C) the issue of phase stabilisation is of major interest. In this study, binary TiO2/SiO2 particles were synthesized by a flame aerosol process with TiCl4 and SiCl4 as precursors. The theoretical Si/Ti ratio was varied in the range of 0.7–1.3 mol/mol. The synthesized TiO2/SiO2 samples were heat treated at 900 and 1,000 °C for 3 h to determine the thermostability of anatase. Pyrogenic TiO2 P25 (from Evonik/Degussa, Germany) widely applied as photocatalyst was used as non-thermostabilized reference material for comparison of photocatalytic activity of powders. Both the non-calcinated and calcinated powders were characterized by means of XRD, TEM and BET. Photocatalytic activity was examined with dichloroacetic acid (DCA) chosen as a model compound. It was found that SiO2 stabilized the material retarding the collapse of catalyst surface area during calcination. The weighted anatase content of 85% remains completely unchanged even after calcination at 1,000 °C. The presence of SiO2 layer/bridge as spacer between TiO2 particles freezes the grain growth: the average crystallite size increased negligibly from 17 to 18 nm even during the calcination at 1,000 °C. Due to the stabilizing effect of SiO2 the titania nanoparticles calcinated at 900 and 1,000 °C show significant photocatalytic activity. Furthermore, the increase in photocatalytic activity with calcination temperature indicates that the titania surface becomes more accessible either due to intensified cracking of the SiO2 layer or due to enhanced transport of SiO2 into the necks thus releasing additional titania surface.

Preparation, characterization and photocatalytic activity of Co-doped ZnO powders

ZnO powders with different Co 2+ doping concentrations (0, 0.5, 1, 3 and 5 mol%) were prepared by the hydrothermal method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectrometer, and photochemical reaction instrument. The results show that the ZnO powders are hexagonal wurtzite structures and their crystallization decrease with the increase of Co 2+ doping concentration. The products are spherical which have diameter of about 200 nm, and their absorption edge shift to longer wavelength with the increase of the Co 2+ concentration. The photocatalytic activities of the powders are evaluated using a basic organic dye, methyl orange (MO). Compared with undoped ZnO, it is found that the photocatalytic properties of the Co-doped ZnO have been improved greatly. When the doping concentration is 3 mol%, the degradation ratio of MO can reach 78% after reacting for 240 min.