Silver Metalized Mixed Phase Manganese-Doped Titania: Variation of Electric Field and Band Bending within the Space Charge Region with Respect to the Silver Content

Silver was deposited on manganese-doped titanates (Mn–TiO2) by photoinduced deposition method. The catalyst shows enhanced photocatalytic activity due to the synergistic effect of bicrystalline framework of anatase and rutile structures with high intimate contact due to the similarity in their crystallite sizes. The deposited metal nanostructures help in the formation of resonant surface plasmons in response to a photon flux, localizing the electromagnetic energy close to their surfaces. Better charge separation is achieved near the semiconductor surface due to the localized field. Silver deposition was varied from 0.1 to 1.5% on the surface of Mn–TiO2. The mechanism of interfacial electron transfer at heterojunctions in mixed phase induced by the plasmonic catalysis is explained. The extent of band bending, the variation of potential field in the space charge region with respect to the size of the deposited Ag metal particles is discussed. The photocatalytic activity of silver deposited Mn–TiO2 was evaluated by taking resorcinol (Rs) as the model compound along with oxidants such as hydrogen peroxide (H2O2) and ammonium per sulfate (APS) under UV/solar light illumination. The electronic level of the dopant, high intimate contact between the anatase and rutile phases along with efficient electron trapping by silver particles, plays a significant role in the photocatalytic process

TiO2- and BaTiO3-Assisted Photocatalytic Degradation of Selected Chloroorganic Compounds in Aqueous Medium: Correlation of Reactivity/Orientation Effects of Substituent Groups of the Pollutant Molecule on the Degradation Rate

Investigation of the photocatalytic activity of BaTiO3, a perovskite wideband gap semiconductor has been done in comparison with a widely used photocatalyst TiO2 for the degradation of 4-chlorophenol (4-CP), 4-chloroaniline (4-CA), 3,4-dichloronitrobenzene (3,4-DCNB), and 2,4,5-trichlorophenol (2,4,5-TCP). BaTiO3/TiO2 nanoparticles were prepared by gel-to-crystalline conversion method. BaTiO3 has exhibited better catalytic efficiency and process efficiency compared with TiO2 in most of the cases. The present research focuses mainly on two aspects: first the photocatalytic activity of BaTiO3, as there are very few reports in the literature, and second the reactivity/orientation effects of substituent groups of the pollutant molecules on the degradation rate. The above chloroorganic compounds have at least one chlorine substituent in common, along with other functional groups such as −OH, −NH2, and −NO2. Furthermore, the effect of electron acceptors and pH on the rate of degradation is presented. The reactions follow first-order kinetics. The degradation reaction was followed by UV−vis, IR, and GC-MS spectroscopic techniques. On the basis of the identification of the intermediates, a probable degradation reaction mechanism has been proposed for each compoun

Photocatalytic degradation of p-amino-azo-benzene and p-hydroxy-azo-benzene using various heat treated TiO2 as the photocatalyst

The photocatalytic degradation of azo dyes in aqueous suspensions of TiO2 is comparatively a good method for the removal of these impurities. The extent of degradation is followed by UV-visible and IR spectroscopy. The degradation process is performed with various heat treated TiO2, in which anatase form of TiO2 exhibited marked photocatalytic activity

New Insights into the Origin of the Visible Light Photocatalytic Activity of Fe(iii) Porphyrin Surface Anchored TiO2

In order to utilize visible light more effectively in photocatalytic reactions, the surfaces of TiO2 nanoparticles are sensitized by Hemin molecules (H-TiO2) and the catalyst is characterized by various analytical techniques like powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), UV-Visible absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) with an energy-dispersive X-ray (EDX) technique, BET surface area measurements and thermogravimetric analysis (TGA). The results strongly confirm the chemisorption of Hemin molecules on the TiO2 surface through O&z.dbd;C-O-Ti bonds. The photocatalytic activity of H-TiO2 was investigated by the degradation of 4-nitrophenol as a model compound in an aqueous solution under solar light irradiation with the assistance of an appropriate amount of a sacrificial electron donor. The enhanced activity of H-TiO2 confirms the sensitization process. Intermediate products were identified by HPLC analysis and a possible degradation reaction mechanism was proposed. The development of this porphyrin-based photocatalyst provides an alternative approach in harnessing visible solar light and shows promise for waste water treatment in future industrial applications

Hydrothermal synthesis of reduced graphene oxide-CoFe2O4 heteroarchitecture for high visible light photocatalytic activity: Exploration of efficiency, stability and mechanistic pathways

RGO-CoFe2O4 heterostructure nanocomposite was prepared by hydrothermal method and was characterized by various analytical techniques such as Powder X-ray Diffraction method (PXRD), UV-vis absorbance, Photoluminescence (PL), Fourier Transform Infra Red (FTIR) spectroscopic techniques, BET surface area measurements, Field Emission Scanning Electron Microscopy (FESEM), Raman Spectroscopy and Vibrating Sample Magnetometer (VSM). The results confirmed the formation of hybrid structure with CoFe2O4 particles embedded in RGO sheets. Photocatalytic activity of the nanocomposites was probed for the degradation of 4-Chlorophenol (4-CP) as the model compound under the visible light illumination. The photocatalytic activity decreases in the following order RGO-CoFe2O4 > CoFe2O4 > RGO. Further the activity of RGO-CoFe2O4 composite was explored in the presence of peroxymonosulfate (PMS) as an oxidant. LUMO of PMS can accommodate photogenerated electrons, thereby suppresses the recombination process. The enhanced activity of RGO-CoFe2O4 hybrid is compared to its individual counterparts and the higher activity is accounted to its unique electronic structure. RGO serves as electron acceptor from CoFe2O4 and electron donor to the oxygen molecule. During the photocatalysis, transformation of the native structure from normal spinel to inverse spinel and vice versa may take place continuously from the process of electron trapping and detrapping by Fe3+ and Co2+ions. The observed continuous absorption for RGO-CoFe2O4 composite in the UV-vis spectra implies active d-d transitions involving transition metals present in the nanocomposite. © 2017 Elsevier Ltd. All rights reserved

Synergistic Effect between Carbon Dopant in Titania Lattice and Surface Carbonaceous Species for Enhancing the Visible Light Photocatalysis

Visible light-sensitive carbon doped titanium dioxide (C-TiO2) was prepared by grinding anatase TiO2 with anhydrous D-glucose solution as carbon source followed by calcination. The catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), BET surface area measurements, scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), FTIR analysis and photoluminescence (PL) techniques. The results confirmed the interstitial incorporation of carbon atoms in the TiO2 lattice via Osingle bondTisingle bondC and Tisingle bondOsingle bondC surface states. The calculation of valence band (VB) edge position of C-TiO2 by using electronegativity values shows cathodic shift with increase in the carbon concentration and this renders high oxidative power for photogenerated holes. The observed new electronic state above the VB edge was responsible for the electronic origin of band gap narrowing and visible light photoactivity of C-TiO2. The carbon atom was also present as carbonaceous species on the surface which acts as sensitizer. The photocatalytic activity of C-TiO2 was evaluated for the degradation of 4-chlorophenol under both UV and solar irradiation. The undoped TiO2 showed better activity under UV light whereas C-TiO2 showed higher photocatalytic activity under visible light. The pretreatment of C-TiO2 with UV light reduced the visible light activity due to the removal of surface carbonaceous species. The synergistic effect of surface carbonaceous species along with interstitial carbon is discussed in detail and accounted for visible light activity

Photocatalytic performance of silver TiO2: Role of electronic energy levels

Nano-sized silver deposits on the surface of Degussa P25 TiO2 (Ag-DP25) particles act as sites of electron accumulation where the reduction of adsorbed species takes place. Electrons can be transferred from Degussa P25 TiO2 (DP25) to Ag particles because of the difference in the work functions of the two materials. The efficiency of the electron transfer depends on the size and the distribution of metal deposits. A significant photocatalytic oxidation enhancement by metal deposit will only be observed if the metal deposits play a more dominant role than just increasing the life time of charge carriers. The properties of metal deposits like, loaded amount, oxidation state of the deposit and its size will influence the performance. Further, a decrease in band-gap in DP25 and Ag-DP25 was observed due to the carbide ion substitution for the oxide ion in TiO2. Such unintentional carbon incorporation is expected mostly in combustion synthesized materials. Silver metal deposits and unintentional incorporation of the carbon shows the beneficial effect by specific mechanism in the photocatalytic degradation of Congo Red (CR). © 2011 Elsevier B.V. 2011 Elsevier B.V. All rights reserved

Kinetic Model Based on non-linear Regression Analysis is Proposed for the Degradation of Phenol under UV/solar Light Using Nitrogen Doped TiO2

Nitrogen was doped into the TiO2 matrix in the concentration range of 0.05-0.20 at.% and the photocatalytic activities were tested for the degradation of phenol (Ph) under UV/solar light using hydrogen peroxide (HP) and ammonium persulfate (APS) as electron acceptors. The prepared photocatalysts characterized by various analytical techniques confirm the incorporation of nitrogen in the TiO2 lattice. The 0.15 at.% dopant concentration shows higher photocatalytic activity compared with sol-gel TiO2 (SG) and Degauss P25 TiO2 (P25) for the degradation process. Photoluminescence technique was used for studying the extent of hydroxyl radicals produced on TiO2 and TiO2−xNx (NT) surface in the presence of oxidants under UV/solar light irradiation. The kinetic rate equation obtained for the best system TiO2−xNx (x = 0.15 at.%)/APS/under solar irradiation is found to be: rap,solar = 0.0041[NT]0.54[APS]0.71[Ph]−0.70. A kinetic/mathematical model was developed based on the nonlinear regression analysis for the various processes and the validity of the model was tested by comparing the experimental values with the theoretically calculated data as a function of variable parameters like catalyst dosage, concentration of electron acceptors and initial concentration of Ph

Enhanced photocatalytic activity of silver metallized TiO2 particles in the degradation of an azo dye methyl orange: Characterization and activity at different pH values

The photocatalytic activity of silver deposited Degussa P25 titanium dioxide (Ag-DP25) in the photodegradation of methyl orange (MO) was investigated. The photocatalysts were characterized using PXRD, SEM, EDX, FTIR and UV-vis spectrophotometer. The obtained results show that the silver (Ag0) deposited TiO2 exhibited visible light plasmon absorption band. The degradation experiment reveals that the catalytic property of Ag-DP25 in the degradation of MO is more efficient than that of commercially available Degussa P25 TiO2 (DP25) samples. The improvement of Ag-DP25 catalyst efficiency strongly depends on the content of silver (Ag) deposits. The present study shows that the degradation process is dominated by Ag-TiO2 photocatalytic system, complying with pseudo-first order rate law. The higher rate of photodegradation observed on Ag-DP25 at pH 6.6 can be correlated to the ratios of the concentrations of the ionized to the neutral dye molecules and also to the higher concentration of hydroxylated surface, which are able to effectively scavenge photogenerated valence band holes. Accumulation of the holes in the semiconductor particles increases the probability of formation of excited oxygen atom which is a reactive species readily oxidizing the organic dye molecule. The reduction of pH during the course of the reaction is attributed to the complete mineralization of the dye. © 2009 Elsevier B.V. All rights reserved

Strategies developed on the modification of titania for visible light response with enhanced interfacial charge transfer process: An overview

The modification of titania by metal / non metal ion doping, coupling with narrow band gap sensitizer, surface flourination, metal deposition, and together with recent ventures on application of 001 facets of anatase titania for visible light response with enhanced charge carrier separation are briefly overviewed. © Versita Sp. z o.o