Studies of Photocatalytic Processes at Nanoporous TiO2 Film Electrodes by Photoelectrochemical Techniques and Development of a Novel Methodology for Rapid Determination of Chemical Oxygen Dphotocatalemand (original) (raw)
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Environmental Science & Technology, 2007
Nanoporous TiO 2 film electrodes with a mixed anatase/ rutile phase were prepared by dip-coating TiO 2 nanoparticle colloid onto Indium Tin Oxide (ITO) conducting glass substrates and a subsequent calcination process at 700°C for 16 h. The photocatalytic oxidation of a wide range of organic compounds has been studied using the photoelectrochemical method under the conditions that the photohole capturing step controls the overall photocatalytic processes. The characteristics of the mixed anatase/ rutile phase TiO 2 film electrodes were compared with pure anatase phase TiO 2 film electrodes to identify the key differences between them. The results revealed that different organic compounds, despite their difference in chemical entities, can be stoichiometrically mineralized at the mixedphase TiO 2 electrode under diffusion-controlled conditions, which is in great contrast to the situation at the pure anatase phase TiO 2 electrode. The exceptional ability of the mixed-phase TiO 2 electrodes for mineralization of organic compounds and their remarkable resistance to the inhibition by aromatic compounds at higher concentration has been explained by the synergetic effect of the rutile and anatase phases. For this type of mixed phase electrodes, upon absorption of UV light, the electron-transfer pathway from anatase phase to rutile phase facilitates the separation of photoelectron and photohole, extending the lifetime of the photoelectron and photohole.
Catalysts, 2021
The size of TiO2 can significantly affect both its photocatalytic and photo-electrochemical properties, thus altering the photooxidation of organic pollutants in air or water. In this work, we give an account of the photo-electrochemical and photocatalytic features of some nanosized TiO2 commercial powders towards a model reaction, the photooxidation of acetone. Cyclic voltammograms (CV) of TiO2 particulate electrodes under UV illumination experiments were carried out in either saturated O2 or N2 solutions for a direct correlation with the photocatalytic process. In addition, the effect of different reaction conditions on the photocatalytic efficiency under UV light in both aqueous and gaseous phases was also investigated. CV curves with the addition of acetone under UV light showed a negative shift of the photocurrent onset, confirming the efficient transfer of photoproduced reactive oxygen species (ROSs), e.g., hydroxyl radicals or holes to acetone molecules. The photocatalytic ex...
Oriental Journal of Chemistry, 2017
The present study addresses a tailored preparation method of different structures of TiO 2 nanoparticles over narrow ranges of varying parameters. In this work, titanium-n-butoxide was used to prepare TiO 2 nanoparticles via sol gel method. The influence of the experimental preparation conditions: pH, drying and calcination temperatures were studied at ranges 5-9, 70-110°C, and 450-650 o C, respectively. Slight changes through these mentioned ranges lead to drastically change in the phase transformation, degrees of crystallinity and crystal systems of the prepared TiO 2. Pure anatase and rutile forms as well as different ratios of mixed phases were obtained. X-ray diffraction and transmitting electron microscope TEM techniques were used for the characterization of the prepared samples. The photocatalytic performance of TiO 2 samples were evaluated according to their abilities toward the generation of the highly active hydroxyl radicals. Results indicate that the photocatalytic activities of TiO 2 samples are dependent on their preparation experimental conditions. The maximal photocatalytic activities were noticed at high pH and drying temperature values.
2020
The size of TiO2 (either nanometric or micrometric) can significantly affect both its photocatalytic and photoelectrochemical properties, thus altering the photooxidation of organic pollutants in air or water. The purpose of this work is to give an account of the photoelectrochemical and photocatalytic features of some nano- and micro-sized TiO2 commercial powders towards a model reaction, the photooxidation of acetone. Cyclic voltammograms (CV) of TiO2 particulated electrodes under UV illumination experiments were carried out in either saturated O2 or N2 solutions for a direct correlation with the photocatalytic process. In addition, the effect of different reaction conditions on the photocatalytic efficiency under UV light in both aqueous and gaseous phases was also investigated. CV curves with the addition of acetone under UV light showed a negative shift of the photocurrent onset, confirming the efficient transfer of photoproduced reactive oxygen species (ROSs), e.g., hydroxyl r...
Photocatalytic activity and formation of oxygen vacancies in cation doped anatase TiO2 nanoparticles
Ceramics International, 2014
We report the influence of iron doping on structure, stoichiometry, and photocatalytic efficiency of single phase anatase TiO 2 nanoparticles which were synthesized via the sol gel technique. The XPS and FTIR results reveal the formation of oxygen vacancies and Ti 3 þ defects following doping with iron which was further confirmed by PL studies. XRD and TEM investigations indicate that the phase structure of TiO 2 nanoparticles is preserved after incorporation of iron to the crystallographic lattice. XRD peak shift and broadening, observed in the doped nanoparticles, were attributed to the formation of point defects and the resulted strains. Photocatalytic activity of the samples was examined through measuring the decomposition rate of rhodamine B under ultraviolet illumination. It was found that Fe-doping significantly improves the photocatalytic activity of anatase TiO 2. We envisage that a more effective use of the UV photon energy, higher charge carrier mobility, and suppressed charge recombination due to the point defects are the primary reasons behind the enhanced photocatalytic activity.
Materials Today: Proceedings, 2019
The application of heterogeneous photocatalysis is described as an advanced oxidation process (AOP) for the degradation of the diazo reactive dye using immobilized TiO 2 as a photocatalyst. Starting TiO 2 solutions were prepared with and without the addition of polyethylene glycol (PEG) and TiO 2 films were directly deposited on a borosilicate glass substrate using the sol-gel dip-coating method. The surface morphology and the nanoscale roughness of TiO 2 films were studied by means of atomic force microscopy (AFM). Structural properties of TiO 2 were identified by Xray diffraction (XRD). The decomposition behaviour of organic compounds from the gels was investigated using thermal gravimetry (TG) and differential scanning calorimetry (DSC). Photocatalytic activities of TiO 2 films in the process of degradation of the commercial diazo textile dye Congo red (CR), used as a model pollutant, were monitored by means of UV/vis spectrophotometry. The kinetics of the degradation of the CR dye was described with the Langmuir-Hinshelwood (L-H) kinetic model. The addition of PEG to the TiO 2 solution resulted in the changes in the film surface morphology, and affected the ratio of anatase-rutile crystal phases and the photocatalytic activity of TiO 2. The TiO 2 film prepared with PEG is characterized by higher roughness parameters (R a , R max , R q , R z and Z max), a lower amount of the rutile phase of TiO 2 , a higher amount of the anatase phase of TiO 2 and a better photocatalytic activity compared to the TiO 2 film without the addition of PEG.
Solar Energy
Nanocrystalline anatase TiO 2 was prepared through modified non-hydrolitic sol-gel method by reacting TiCl 4 with benzyl alcohol at room temperature. The as synthesized anatase TiO 2 was calcined at 450°C for 5 h. The size and morphology of the as synthesized and calcined TiO 2 nanoparticles were characterized using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM) and BET surface area analysis. The band gap energy was measured using Kulbeka-Munk function and the electronic state of the prepared TiO 2 was determined by X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the prepared samples was investigated by degrading 50 mg/L of 2,4-dichlorophenol (2,4-DCP) under natural sunlight as a source of irradiation. The obtained XRD patterns of both as synthesized and calcined TiO 2 matches completely with the tetragonal anatase phase of TiO 2 . The as synthesized sample showed higher surface area (147.34 m 2 /g) with particles size ranging between 3 and 6 nm than the calcined titania (64.92 m 2 /g) of prarticle size ranging between 11 and 15 nm. Both the TiO 2 samples showed excellent photocatalytic activity for the degradation of 2,4-DCP under natural sunlight irradiation. The complete removal of 2,4-DCP is obtained after 2.5 h for calcined TiO 2 and 3.5 h for as synthesized TiO 2 suggests that the prepared photocatalysts have the potential to degrade the organic pollutants. The degradation of 2,4-DCP followed first order kinetics.
Materials Research Bulletin, 2004
TiO 2 thin-film photocatalysts coated onto glass were prepared either by plasma enhanced chemical vapour deposition (PECVD) deposition or by a dip-coating process using sol-gel solutions. The influence of the addition of a polymer and of a highly viscous solvent on physical properties (thickness, crystallite size and porosity) of TiO 2 thin films and on their photocatalytic efficiency was evaluated.
Preparation and characterization of photocatalytic TiO2 films
2005
In the present research, Titanium dioxide (TiO 2) has been synthesized by sol-gel spin coating technique on Corning glass substrates. The sol-gel process can be easily controlled and reproduced. Titanium tetraisopropoxide, isopropanol and deionized water were used as starting materials. This precursor solution was deposited onto Corning glass substrates by spin coating and annealed at 400 and 500 C. Their photocatalytic activity was investigated by examining the degradation (oxidation) of Diuron ® , under UV and solar radiation. In order to compare the photocatalytic activity of TiO 2 and to establish possible correlations between the physicochemical properties of the prepared coatings, these were characterized by UV-Vis spectroscopy and X-ray diffraction (XRD) techniques. X-ray diffraction patterns confirmed TiO 2 anatase phase formation.
International Journal of Environmental Science and Technology, 2016
Evaluation of the photocatalytic activities of TiO 2 nanomaterials based on the chemical oxygen demand (COD) analyses under identical experimental conditions was not previously reported. In this work, COD has been selected as an adequate industrial water quality measure toward the establishment of a representative standard test method. The initial COD values of six organic pollutants representing dye, surfactants, phenols and alcohol were set at 30 ± 2 mg/L. Ten of different commercial and synthesized TiO 2 samples representing anatase, rutile and mixed phases were used and characterized. The data of photocatalytic processes were compared to that obtained using the commonly widespread Degussa-P25 TiO 2 (TD). The COD of all pollutants was completely removed by TD at UV exposure dose B9.36 mWh/cm 2. Consequently, the maximum irradiation dose was set at this value in all experiments. The percentages of COD removal as well as the values of the accumulated UV doses required for complete removal of pollutants were measured using the different TiO 2 samples. TiO 2 samples show different performance abilities toward the various pollutants compared to TD. Based on the obtained data, TiO 2 photocatalysts were divided into two categories according to the hydroxyl radical formation rates. Comparison with previous studies reveals that the photocatalytic efficiency evaluation depends on the method of measurement. COD is recommended to be used as an adequate technique of analysis that meets the purpose of water treatment applications. Keywords Photocatalytic activity Á Nanosized TiO 2 Á Organic pollutants Á Water treatment Á Chemical oxygen demand (COD) Á Standard test method