Photocatalytic Characteristics Research Articles

ZnO nanorods surface-decorated by WO3 nanoparticles for photocatalytic degradation of endocrine disruptors under a compact fluorescent lamp

Nanoscaled tungsten oxide (WO3) particles coated on ZnO nanorods (ZNRs) were newly synthesized by combining a hydrothermal technique with a chemical solution process. The structure, morphologies and compositions of the as-prepared WO3–ZNR nanocomposites were characterized through XRD, FESEM, TEM and Raman measurements. The results revealed that pure monoclinic WO3 nanoparticles with an average size range of 18–26nm were distributed on the surfaces of ZNRs and attached strongly. Particularly, the optical properties as well as photocatalytic characteristics of pure ZNRs and WO3–ZNR nanocomposites with different loadings of WO3 were also examined. The absorption of WO3–ZNR nanocomposites was redshifted due to effective immobilization of WO3 on ZNRs. Under irradiation of a 55W compact fluorescence lamp, the photocatalytic activities of the WO3–ZNR nanocomposites were superior to those of pure ZNRs and P25 in the degradation of resorcinol (ReOH). Furthermore, WO3–ZNR nanocomposites showed very favorable recycle use potential and high sedimentation rate. Other endocrine disrupting chemicals (EDCs) such as phenol, bisphenol A (BPA) and methylparaben were also successfully photodegraded under identical conditions. These characteristics showed the practical applications of the WO3–ZNR nanocomposites in indoor environmental remediation.

Preparation of TiO2 thin films on glass surfaces with self-cleaning characteristics for solar concentrators

High concentration photovoltaic (HCPV) systems improve their long-term stability in terms of sunlight concentration by using silicone-on-glass (SOG) composite optic lenses with glasses. Due to dust pollution, reflectance of the concentrator glasses significantly decreases the output power efficiency of a solar power system. Titanium dioxide (TiO2) films are known for their hydrophilic and photocatalytic characteristics. This study investigates the effects of introducing third elements in a-TiO2 films by implantation, to enhance the photocatalytic and hydrophilicity properties, as well as widen the wavelength sensitization range. TiO2-based hydrophilic and photocatalytic films on glass for self-cleaning purposes were prepared. The implant elements are Fe, Cr, and V. The samples are prepared by a hybrid system consisting of physical vapor deposition (PVD) and metal plasma ion implantation (MPII). High quality TiO2 films are first fabricated by r.f. magnetron sputtering system, followed by metal plasma ion implantation of Fe. Experimental results indicate that the hybrid processing method significantly increases the activation and sunlight absorption rate of TiO2 thin films with the addition of third elements. Moreover, the proposed TiO2–Fe thin film exhibits superior hydrophilicity properties with a contact angle of 9.95° and reduces the optical bandgap to 3.33eV.

Photocatalytic characteristics of TiO2 films deposited by magnetron sputtering on polycarbonate at room temperature

Anatase TiO2 thin films were successfully grown at room temperature on polycarbonate substrates, using RF magnetron sputtering under various conditions. The deposition parameters used to examine the photocatalytic activity of TiO2 films included RF power, sputtering pressure, argon/oxygen ratio (O2/(Ar+O2)) and deposition time. An orthogonal array and analysis of variance (ANOVA) were used to determine the performance of the deposition process. The effects of the deposition parameters on the structure, morphology and photocatalytic performance of TiO2 films were analyzed using scanning electron microscopy (SEM), X-ray diffraction, a contact angle meter and UV/vis/NIR spectroscopy. The RF power was found to be the factor that most affected the water droplet contact angle and the sputtering pressure was found to be the second ranking factor. The results indicate that the photocatalytic performance is improved by increasing RF power, but an increase in sputtering pressure has an adverse effect. Higher photocatalytic activity is achieved for TiO2 films using an RF power of 210W, sputtering pressure of 0.93Pa, argon/oxygen ratio of 30% and a deposition time of 2h.

Electrochemical deposition of flower-like ZnO nanoparticles on a silver-modified carbon nanotube/polyimide membrane to improve its photoelectric activity and photocatalytic performance

ZnO nanoparticles have been synthesized on a silver-modified carbon nanotube/polyimide (Ag-CNT/PI) membrane by electrochemical deposition. For comparison, a CNT/PI membrane was also obtained. The effect of the improved substrate on the structural, optical, photoelectric and photocatalytic characteristics of ZnO was examined. The flower-like ZnO nanoparticles was formed by the aggregation of nanosheets. The characterization of X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectra verified that the silver nanoparticles were distributed onto the nanotube. The absorption spectrum provided a band gap of 3.29eV, which was confirmed by the band gap measurement. The photoelectric property of ZnO was investigated by current–voltage and open circuit potential measurements. The results demonstrated that the photoelectric activity and photocatalytic performance of ZnO were improved by the deposition.

Electrophotocatalysis of aqueous methyl tert-butyl ether on a titanium dioxide coated electrode

In this study, TiO2 was immobilized onto a titanium electrode for conducting MTBE degradation in aqueous solution. The TiO2 coated electrode could possess photocatalytic characteristics, and thus the application of the TiO2 coated electrode is able to perform photocatalysis and/or electrolysis under various controls. A bench-scale reactor system consisting of an electrolytic cell, an electrochemical analyzer, an electrical multimeter, and a UV-light source was employed to perform electrochemical experiments and electrophotocatalytic experiments.The results of electrochemical experiments showed that an optimum electrolytic condition was operated at 3.00V in a 1M Na2SO4 electrolyte solution, and the initial 20mg/L MTBE was reduced by 67% within 180min. Comparatively, the photocatalytic removal of MTBE was only 52% within 180min. The electrophotocatalytic experiments have demonstrated that the photocatalytic removal of MTBE was raised to 65% as applying a potential at −0.25V. The recombination of photoinduced electrons and holes could be significantly suppressed because the generated electrons by TiO2 excitation were taken away from the electrode as applying a negative potential. On the contrary, the improvement on MTBE removal is not obvious with the assistance of a positive electrical potential. Even though the mechanisms of electrochemical oxidation and electrochemically assisted photocatalysis to produce radicals for the breakdown of MTBE might be different, both processes followed the identical degradation pathway of forming acetate and CO2 based on the identification of GC/MS. According to the comparison of coulometric efficiency, photocatalysis with the assistance of a slight negative potential is the most effective and efficient approach to treat MTBE contaminated water.

Effect of heterojunction on photocatalytic properties of multilayered ZnO-based thin films

In the present study, the effects of the heterojunctions on the optical and structural characteristics and the resulting photocatalytic properties of multilayered ZnO-based thin films were investigated. The junctions were composed of semiconducting ZnO nano-porous films coated on the In2O3 and SnO2 counterpart layers. The multilayered ZnO films based on the triple-layered Ag-doped indium oxide (AIO)/tin oxide (TO)/zinc oxide (ZnO), indium oxide (IO)/Ag-doped tin oxide (ATO)/zinc oxide (ZnO), indium oxide (IO)/tin oxide (TO)/zinc oxide (ZnO) and tin oxide (TO)/indium oxide (IO)/zinc oxide (ZnO) have been fabricated by subsequent sol–gel dip coating. Their structural and optical properties combined with photocatalytic characteristics were examined toward degradation of Solantine Brown BRL (C.I. Direct Brown), an azo dye using in Iran textile industries as organic model under UV light irradiation. Effects of operational parameters such as initial concentration of azo dye, irradiation time, solution pH, absence and presence of Ag doping and consequent of sublayers on the photodegradation efficiencies of ZnO nultilayered thin films were also investigated and optimum conditions were established. It was found that the photocatalytic degradation of azo dye on the composite films followed pseudo-first order kinetics. Photocatalytic activity of AIO/TO/ZnO interface composite film was higher compared with other films and the following order was observed for films activities: AIO/TO/ZnO>IO/TO/ZnO>ATO/IO/ZnO>TO/IO/ZnO. Differences in the film efficiencies can be attributed to differences in crystallinity, interfacial lattice mismatch, and surface morphology. Besides, the presence of Ag doping between layers that may act as trap for electrons generated in the ZnO over layer thus preventing electron–hole recombination.

PLD and RF discharge combination used for preparation of photocatalytic TiO2 layers

Utilizing pulsed laser deposition technique combined with the radio-frequency discharge (between the target and the substrate), we were able to grow polycrystalline titanium dioxide layers (anatase, rutile) at substrate temperatures 85°C and 150°C. Besides the discharge no additional substrate heating was applied. The layers were prepared from pure titanium and titanium dioxide targets. To optimize deposition conditions, the oxygen background pressure, fluence (from 2Jcm−2 to 9Jcm−2), and discharge power were varied. Silicon wafers (111), fused silica, and polyethylene tubes were used as substrates. The layers’ crystalline structure was determined by X-ray diffraction. Atomic force microscopy was used to characterize the surface properties. Two methods were implemented to determine TiO2 photocatalytic characteristics: 4-chlorphenol solution degradation evaluated by pH measurement and the decomposition of Oleic acid evaluated by the change of the water contact angle on the surface layer. Both methods indicated similar results: the highest photoactivity was observed on the layers consisting from anatase phase and mixture of anatase and rutile.

Photocatalytic characteristics of immobilized SrBi2Nb2O9 film for degradation of organic pollutants

The use of semiconducting oxide photocatalyst in contaminant purification has recently drawn significant attention in both materials and environmental science. In this study, the compound SrBi2Nb2O9 with layered perovskite-type structure was synthesized by solid state reaction, and the network microstructure film was fabricated by the aerosol deposition method. The compound powder and aerosol-deposited film with SrBi2Nb2O9 were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Ultra violet–visible (UV–vis) spectrophotometry. The photocatalytic activity of the aerosol-deposited film with SrBi2Nb2O9 was evaluated by photo-induced destruction of Rhodamine B under the irradiation of UV and visible light. The aerosol-deposited film with SrBi2Nb2O9 exhibited higher photocatalytic activity than that of SrBi2Nb2O9 powders. This result is attributed not only to the small sized grain, but also to the existence of a network microstructure capable of supporting the enhanced loading of organic contaminants on the aerosol-deposited film.

Enhancement of Photocatalytic Activity of TiO<sub>2</sub> Thin Film Using Diethanolamine and MCM-41

TiO2thin film enhanced by diethanolamine (DEA) and MCM-41 (D-TiO2/MCM-41) was successfully synthesized by sol-gel dip coating technique on glass slides. The roles of DEA and MCM-41 on physical and photocatalytic characteristics of the films were studied using various techniques such as x-ray defraction (XRD), fourier transform infrared spectroscopy (FTIR), ultra violet-visible (UV-Vis) spectrometry, Brunauer, Emmett and Teller (BET) surface area analysis and field emission scanning electron microscope (FESEM). The XRD results showed that the thin film contained almost 100% anatase phase and the crystal size of TiO2was in the range of 4-8 nm. The FTIR spectra indicated the formation of Ti-O-Si and Si-O-Si linkages due to interaction of TiO2and MCM-41. The surface area of TiO2was increased significantly when MCM-41 was added. The use DEA and MCM-41 caused slight increase in visible light absorption but UV absorption was decreased. The photocatalytic reactivity of the thin film was tested by photocatalytic degradation of methylene blue under visible light. The addition of DEA as a nitrogen source was beneficial not only for obtaining stable/smooth surface of the thin film but also for enhancing photocatalysis of methylene blue by preventing charge carrier recombination. While MCM-41 played important functions in improving porosity and hydrophilicity of the film. The photodegradation of methylene blue was obtained up to 35% of its original concentration when 1M DEA and 0.3M MCM-41 were incorporated in TiO2thin film. The overall enhancement of photocatalytic activity of the film was a result of nitrogen doping, increased surface area as well as increased hydrophilicity provided by MCM-41.

Visible-light photocatalytic activity of TiO2−x by heat treatment and plasma-heat treatment

The partial reduction of TiO2 was attempted by heat treatment and plasma-heat treatment and it was carried out to investigate the photocatalytic characteristics of partially reduced TiO2 (TiO2−x) in the visible-light region. As a result, the plasma-heat treatment shows significantly stronger than the heat treatment for the visible-light photocatalytic activity of TiO2. The red-shifted absorption bands in the visible-light region of TiO2−x by plasma-heat treatment gave broader than one by heat treatment. The TiO2−x by heat treatment and plasma-heat treatment was changed white to beige color, and white to navy, respectively.

Tunable TiO2 (anatase and rutile) materials manufactured by mechanical means

Anatase and rutile are two naturally found titanium dioxide phases with attractive dielectric, catalytic, and photo-catalytic characteristics. Anatase and rutile are photo-catalytically active in the UV region, since their band gaps are 3.2eV and 3.75eV, respectively. In this work is proposed a cost-effective, easy to launch methodology for modification of the TiO2 bandgap. Such modifications will make the oxides photo-catalytically active in a wider optical range from the visible wavelengths to an extended UV spectrum. The proposed methodology is based on mechanical means such as mixing and milling. Various ratios of anatase:rutile were investigated and milled from 0 (mixing only) to 50h using high energy mills. The results on mixing and milling show that it is possible to modify the bandgap of the TiO2 from 2.53eV to 4.04eV. The characterization was conducted by means of X-ray diffraction, Raman spectroscopy, Scanning electron microscopy, and optical spectroscopy.

Novel solution routes of synthesis of metal oxide and hybrid metal oxide nanocrystals

Novel solution routes covering a wide range of processes like hydrothermal, solvothermal and supercritical techniques have been described in detail with reference to the processing of a wide range of advanced inorganic nanocrystalline materials and organic-inorganic hybrid nanocrystalline materials. The significance of the thermochemical calculations, in situ surface modification and the experimental parameters has been discussed. One step in situ fabrication of advanced functional nanocrystalline materials by soft solution processing has also been discussed briefly. Synthesis of nanocrystals of metal oxides and hybrid nanocrystals and also processing several nanocomposites like carbon nanotubes: metal oxide, activated carbon: metal oxide, etc. has been reviewed in relation to various process parameters. The effect of doping, size, shape and quality on the properties of nanocrystalline materials has been discussed in relation to the photoluminescence and photocatalytic characteristics.

Room-temperature synthesis and photocatalytic properties of lepidocrocite by monowavelength visible light irradiation

Lepidocrocite was synthesized by aerial oxidation using an Fe IIEDTA solution. The synthesis was performed under irradiation from different monowavelength light emitting diode (LED) lamps at room temperature. X-ray diffraction results showed the formation of differently crystallized lepidocrocite. The indirect bandgap values of the lepidocrocite samples were about 2.34, 2.36, and 2.31 eV for red, green, and blue light, respectively. The kinetics of the photo-decolorization of crystal violet (CV) was investigated in a system composed of lepidocrocite, H 2O 2, and visible light. H 2O 2 concentration, light irradiation, and catalyst concentration were also investigated. The rate of CV decolorization was found to fit pseudo-first-order kinetics. The results show that different as-prepared lepidocrocite have different adsorption and photocatalytic characteristics. A possible mechanism was also suggested for the dye degradation.

Synthesis, structural and photocatalytic characteristics of nano-Cu2−x Se

Large-scale synthesis of Cu 2−x Se nanocrystals (nano-Cu 2−x Se) with uniform size was performed via a facile hydrothermal method at room temperature and at 120 °C. Nano-Cu 2−x Se with different structures could be synthesized by changing the reaction/growth time, the Cu:Se molar ratios, and the initial concentration of the precursors. The synthesized nano-Cu 2-x Se was characterized using various techniques, including x-ray powder diffraction, scanning electron microscopy and photocatalytic activity. Systematic studies showed that the reaction time played a key role in controlling the morphology and structure leading to significant influence on the photocatalytic activity of nano-Cu 2−x Se. With increasing reaction/growth time, Cu 2−x Se could transform gradually from a cubic to hexagonal structure and from nanoparticles to nanoplate/nanorod shapes. The photocatalytic characteristics were evaluated by the photo-decoloration of Rhodamine B (RhB) in aqueous solution under visible light irradiation. As-prepared nano-Cu 2−x Se showed good photocatalytic activity under visible light irradiation, indicating potential applications in depollution technologies.

A comparative study of the effects of In 2O 3 and SnO 2 modification on the photocatalytic activity and characteristics of TiO 2

In this study, we investigated the photocatalytic activities of In 2O 3-, SnO 2-, and In 2O 3/SnO 2-doped titanium dioxide (ITO–TiO 2) samples prepared through a sol–gel approach from InCl 3, SnCl 4, and titanium tetraisopropoxide (TTIP) precursors, respectively. These ITO–TiO 2 samples were characterized using X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, UV–vis spectroscopy, photoluminescence, and Brunauer–Emmett–Teller techniques. Herein, we compare the physical properties and photocatalytic activities of ITO–TiO 2 samples having different In/Sn ratios. After calcination at 500 °C, In 2O 3 and SnO 2 were present as either minor phases or In 2 x Sn y O 3 x+2 y structures, or they were incorporated into the TiO 2 network. The ITO–TiO 2 samples exhibited multimodal mesopores, whereas the undoped TiO 2 displayed a monomodal pore size distribution. The ITO–TiO 2 sample calcined at 500 °C and featuring an In/Sn molar ratio of 1:19 at a doping level of approximately 15% exhibited the highest activity for the photodegradation of phenol under simulated solar light illumination. We ascribe this superior photocatalytic activity to the simultaneous influence of (i) the presence of the rutile phase in an appropriate quantity, (ii) the high specific surface area, (iii) the enhanced hydrophilicity, and (iv) the high driving force for the photoexcited electrons to be transferred from TiO 2 to ITO.

Trace elements distribution in Cu–Si alloys

The trace elements distribution in Cu–Si alloys is analyzed after mixing Si with Cu. The mass balance and atomic distribution showed that the highest concentration of trace elements was at the phase boundaries between Si and Cu–Si intermetallic. The concentrations of 21 trace elements in the refined Si were below detection limit of the ICP technique where 11 elements were below 1ppm at and another 7 elements were below 2ppm at. The amount of other elements decreased several times in the refined Si, compared to that in initial metallurgical grade silicon. The level of trace elements in refined Si allows utilization of the Si photo-catalytic characteristics for solar energy generation.

Influence of pH Value and Precipitant on Zn<sub>2</sub>SnO<sub>4</sub> Formation via Co-Precipitation Method

Nanorod-shaped zinc stannate Zn2SnO4 (ZTO) with great photocatalytic activity was successfully synthesized via a co-precipitation method. In this paper, a strong base (NaOH) and a weak base (Na2CO3) are adopted as precipitants in order to form the precursor precipitate. The titration endpoints are fixed at pH6, pH8, and pH10 in order to adjust the solution precipitant quantity. Dependent variables above were not seen in other research before. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results show that the powders synthesized were ZTO nano-particles. Photocatalytic activity of the powders was measured utilizing a photocatalytic degradation reaction with methylene blue (MB) solution. The smallest particles were obtained by utilizing NaOH as a precipitant and adjusting pH to 6. Based on TEM images, the ZTO had nano-rod particle morphology. However, when precipitant Na2CO3 was utilized, particles agglomerated together, reducing specific surface area. Hence, the former sample shows better photocatalytic activity than the latter one. Consequently, powders titrated to pH6 by precipitant NaOH and calcined for 1 hour will form partly nano-rod particles with slight agglomeration, increasing the specific surface area of ZTO and bringing about the best photocatalytic characteristics.

Graphene oxide as a photocatalytic material

The photocatalytic characteristics of graphene oxide (GO) nanostructures synthesized by modified Hummer’s method were investigated by measuring reduction rate of resazurin (RZ) into resorufin (RF) as a function of UV irradiation time. The progress of the photocatalytic reaction was monitored by change in color from blue (RZ) into pink (RF) followed by absorption spectra. It exhibited excellent photocatalytic activity, leading to the reduction of RZ in UV irradiation. The fitting of absorbance maximum versus time suggests that the reduction of RZ follow the pseudo first-order reaction kinetics. These results indicate that GO have great potential for use as a photocatalyst.

A review of TiO2 nanoparticles

Climate change and the consumption of non-renewable resources are considered as the greatest problems facing humankind. Because of this, photocatalysis research has been rapidly expanding. TiO2 nanoparticles have been extensively investigated for photocatalytic applications including the decomposition of organic compounds and production of H2 as a fuel using solar energy. This article reviews the structure and electronic properties of TiO2, compares TiO2 with other common semiconductors used for photocatalytic applications and clarifies the advantages of using TiO2 nanoparticles. TiO2 is considered close to an ideal semiconductor for photocatalysis but possesses certain limitations such as poor absorption of visible radiation and rapid recombination of photogenerated electron/hole pairs. In this review article, various methods used to enhance the photocatalytic characteristics of TiO2 including dye sensitization, doping, coupling and capping are discussed. Environmental and energy applications of TiO2, including photocatalytic treatment of wastewater, pesticide degradation and water splitting to produce hydrogen have been summarized.

Direct growth of ultra-long platinum nanolawns on a semiconductor photocatalyst

A template- and surfactant-free process, thermally assisted photoreduction, is developed to prepare vertically grown ultra-long Pt nanowires (NWs) (about 30-40 nm in diameter, 5-6 μm in length, and up to 80 NWs/100 μm2 in the wire density) on TiO2 coated substrates, including Si wafers and carbon fibers, with the assistance of the photocatalytic ability and semiconductor characteristics of TiO2. A remarkable aspect ratio of up to 200 can be achieved. TEM analytical results suggest that the Pt NWs are single-crystalline with a preferred 〈111〉 growth direction. The precursor adopted and the heat treatment conditions are crucial for the yield of NWs. The photoelectrons supplied by TiO2 gives rise to the formation of nano-sized Pt nuclei from salt melt or solution. The subsequent growth of NWs is supported by the thermal electrons which also generated from TiO2 during the post thermal treatment. The interactions between the ions and the electrons in the Pt/TiO2 junction are discussed in this study.