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

Polymorphic Phase Transformation of Degussa P25 TiO2 by the Chelation of Diaminopyridine on TiO62- Octahedron: Correlation of Anatase to Rutile Phase Ratio on the Photocatalytic Activity

A series of nitrogen-doped Degussa P25 photocatalysts were synthesized successfully by grinding and calcination method using 2,6-diaminopyridine (DAP) as a nitrogen precursor. The prepared samples were characterized by various analytical methods. The phase contents of anatase and rutile in the Degussa P25 powders have been altered by simply changing the proportion of DAP. A mechanism involving chelated DAP molecule on TiO62- octahedron is discussed. The enhanced activity is attributed to synergistic effect in the two phase solid material. Due to the low activation barrier, the effective inter particle electron transfer between the two polymorphs is quite efficient only when they are in close proximity with similar crystallite sizes. The transfer of electrons from the rutile phase to lattice/electron trapping sites of anatase and also to the Ti3+-Vo defect level created by the dopant favors effective charge separation and enhance the photocatalytic activity under solar illumination

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

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

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

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

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

Bulk and surface modification of TiO2 with sulfur and silver: Synergetic effects of dual surface modification in the enhancement of photocatalytic activity

Sulfur ion (S6+) was incorporated into the TiO2 lattice (Ti0.85S0.15O2) using sulfur powder as precursor. 0.05​% of silver was deposited on the surface of Ti0.85S0.15O2 by photoinduced deposition method. The photocatalytic reactivity of TiO2, Ag-​TiO2, Ti0.85S0.15O2 and Ag-​Ti0.85S0.15O2 photocatalysts were probed for the degrdn. of a model compd. congo red (CR) dye under UV​/solar light illumination. FTIR and XPS results suggested that the dopant sulfur ion (S6+) was incorporated into the TiO2 crystal lattice at Ti4+ lattice site and the sulfur ions on the surface were modified as SO42-​ active sites serving as electron withdrawing group. TEM and XPS anal. of Ag-​Ti0.85S0.15O2 has confirmed the deposition of silver in the Ag0 state. Ag-​Ti0.85S0.15O2 shows better photoactivty under solar light irradn. when compared to all the other photocatalysts. The enhanced photocatalytic activity of this catalyst is attributed to the synergetic effects of the incorporated dopant electronic energy level with the dual surface modifications of the type SO42-​ active centers and Schottky junctions created by metallic Ag0. Further the deposited Ag particles plays a dual role one as a sensitizer due to the Surface Plasmon Resonance (SPR) effect and also acts as an electron trapper under solar light illumination reducing the recombination of photogenerated charge carriers

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