Enhanced photocatalytic performance of Hemin (chloro(protoporhyinato) iron(III)) anchored TiO2 photocatalyst for methyl orange degradation: A surface modification method

TiO2 was prepared by sol-gel method through the hydrolysis of TiCl4 and its surface derivatization was carried out with molecular catalyst like Hemin (chloro(protoporhyinato)iron(III)). Catalyst was characterized by various analytical techniques like UV-vis spectroscopy, FT-IR, FE-SEM and XRD. The anchoring of Hemin on titania surface is confirmed by FT-IR spectra through the linkage of OCOTi bond and also by TGA-DSC and elemental analysis. The photocatalytic activity of the surface modified catalyst is tested for the degradation of methyl orange (MO) as a model compound under UV light. The Hemin impregnated TiO2 (H-TiO2) in presence of H 2O2 shows an excellent photocatalytic activity compared to pristine TiO2, Hemin, H2O2, TiO 2/H2O2, and Hemin/H2O2 systems. The enhancement in the photocatalytic activity is attributed to the presence of iron (III) porphyrin ring on the TiO2 surface, which reduces the electron-hole recombination rate and also by acting as a mediator for continuous production of enriched concentration of hydroxyl radicals along with various other reactive free radicals. © 2013 Elsevier B.V. All rights reserved

Synergistic effect between orthorhombic α-Sulfur and TiO2 as co-photocatalysts for efficient degradation of methylene blue: A mechanistic approach

The synergistic effects between α-Sulfur (α-S) and TiO 2 photocatalysts is studied under UV/solar light. An enhancement in photocatalytic activity was observed under UV light, due to formation of sulfate anions in the reaction mixture and these ions get adsorbed on TiO2 surface by electrostatic force of attraction or it may react with holes/hydroxyl radicals to generate sulfate radical anion. An increase in quantum efficiency is observed with sulfated TiO2 due to reduction in electron-hole recombination rate. The extended response of α-S under visible region is due to non-vertical absorption process, which paved a new way for elemental photocatalysis. © 2014 Elsevier B.V

Exploring the critical dependence of adsorption of various dyes on the degradation rate using Ln 3+-TiO 2 surface under UV/solar light

The degradation of structurally different anionic dyes like Alizarin Red S (ARS) Amaranth (AR), Brilliant Yellow (BY), Congo Red (CR), Fast Red (FR), Methyl Orange (MO), and Methyl Red (MR) were carried out using Ln 3+ (Ln 3+ = La 3+, Ce 3+ and Gd 3+) doped TiO 2 at different pH conditions under UV/solar light. All the anionic dyes underwent rapid degradation at acidic pH, while resisted at alkaline conditions due to the adsorptive tendency of these dyes on the catalyst surface at different pH conditions. Gd 3+ (0.15 mol)-TiO 2 exhibited better activity compared to other photocatalyst ascribed to half filled electronic configuration of Gd 3+ ions. It is proposed that Ln 3+ serves only as charge carrier traps under UV light, while it also act as visible light sensitizers under solar light. Irrespective of the catalyst and excitation source, the dye degradation followed the order: AR > FR > MO > MR > ARS > BY > CR. The results suggest that pre-adsorption of the pollutant is vital for efficient photocatalysis which is dependent on the nature of the substituent's group attached to the dye molecule. © 2012 Elsevier B.V. All rights reserved

A review on plasmonic metal-TiO2 composite for generation, trapping, storing and dynamic vectorial transfer of photogenerated electrons across the Schottky junction in a photocatalytic system

The titania based nanomaterials are an attractive candidates for energy and environmental applications. TiO2 is one of the most important photocatalyst for its special multiple characteristics like high reactivity, low toxicity, low cost, high flexibility, long term stability especially in aqueous medium, shows relatively high energy conversion efficiency, easy to prepare several modifications with various morphologies, with good recycle ability, favorable band edge positions and superior physicochemical and optoelectronic properties. However, large band gap of titania and massive charge carrier recombination impairs its wide photocatalytic applications. As an alternative to various strategies reported extensively in literature, noble metal deposition on the titania surface seems to be effective and reliable method for increasing the life time of excitonic pairs and to extend the band gap absorption to visible range of the solar spectrum. In this focused review, we discuss the fundamental and critical issues in the photocatalytic activity of metal deposited titania taking into consideration the influence of various parameters like preparation methods, metal dispersion on titania, formation of heterojunctions and optimum metal loadings on the interfacial charge carrier dynamics. The metal deposition onto the varied hierarchical morphology, crystal structure, defective surface of titania along with extended modification like simultaneous doping and heterostructure coupling with other semiconductors is also highlighted. It was revealed that deposited metal is involved in multiple crucial roles like; (i) it serves as passive electron sink with high capacity to store electrons to suppress photogenerated charge carrier recombination; (ii) it facilitates rapid dioxygen reduction to generate reactive free radicals; (iii) visible light response for titania can be achieved through surface plasmon resonance effect; (iv) direct excitation of metal nanoparticles especially under visible light and vectorial electron transfer to the TiO2 CB. This review attempts to provide a comprehensive update of design and fabrication of metallization on the surface of TiO2 semiconductor particles highlighting some of the advancements made in the energy and environment applications. © 2015 Elsevier B.V. All rights reserved

Polymorphic phase transformation of Degussa P25 TiO2 by the chelation of diaminopyridine on TiO6 2- 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 TiO6 2- 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. © 2013 Elsevier B.V. © 2013 Elsevier B.V. All rights reserved

Photocatalytic activity of TiO2 doped with Zn2+ and V5+ transition metal ions: Influence of crystallite size and dopant electronic configuration on photocatalytic activity

Anatase TiO2 was prepared by sol-gel method through the hydrolysis of titanium tetrachloride and doped with transition metal ions like V5+ and Zn2+. The photocatalysts were characterized by various analytical techniques. Powder X-ray diffraction studies revealed only anatase phase for the doped samples. The band gap absorption for the doped samples showed red shift to the visible region (â¼456 nm) as confirmed by UV-vis absorption spectroscopy and diffuse reflectance spectral studies. The surface area of the Zn2+ doped samples were higher than the V5+ doped samples as observed by BET surface area measurements due to their smaller crystallite size. Scanning electron microscopy showed almost similar morphology, while energy dispersive X-ray analysis confirmed the presence of dopant in the TiO2 matrix. The photocatalytic activities of these catalysts were tested for the degradation of Congo Red under solar light. Although both the doped samples showed similar red shift in the band gap, Zn2+ (0.06 at.) doped TiO2 showed enhanced activity and its efficiency was five fold higher compared to Degussa P-25 TiO2. This enhanced activity was attributed to smaller crystallite size and larger surface area. Further completely filled stable electronic configuration (d10) of Zn2+ shallowly traps the charge carriers and detraps the same to the surface adsorbed species thereby accelerating the interfacial charge transfer process. © 2009 Elsevier B.V. All rights reserved

Photo fenton like process Fe3+/(NH4)2 S2O8/UV for the degradation of Di azo dye congo red using low iron concentration

Degradation of Congo Red (CR) a di azo dye in aqueous solution is investigated by a Photo Fenton like process using Fe3+ ions as the catalyst and peroxy disulfate as the oxidant. The influence of various reaction parameters like, concentration of Fe3+ ions, concentration of the dye, concentration of ammonium persulfate, pH of the solution and the presence of hydroxyl radical scavenger are studied and optimal conditions are reported. The degradation rate decreased at higher dye concentration and at higher pH. The rate constant (k), catalytic efficiency (kc) and process efficiency (Φ) are evaluated for different concentration of Fe3+ ions. The degradation of CR by the photo Fenton like process leads to the formation of 4-Amino, 3-azo naphthalene sulphonic acid, dihydroxy substituted naphthalene, dihydroxy substituted biphenyl, phenol, quinol etc., as intermediates, based on which probable degradation mechanism is proposed. These results show that a photo Fenton like process could be useful technology for the mineralization of di azo dyes under lower concentration of iron in acidic conditions. The present process is advantageous as it lowers the sludge production resulting from the iron compl

Photocatalytic activity of V5+, Mo6+ and Th4+ doped polycrystalline TiO2 for the degradation of chlorpyrifos under UV/solar light

TiO2 photocatalysts were prepared by doping transition metal ions like V5+, Mo6+and an inner transition metal Th4+ in the concentration range of 0.02-0.1 and were characterized by various analytical techniques. The photocatalytic activities of these catalysts were studied for the mineralization of chlorpyrifos (CP) as a probe molecule. X-ray diffraction results showed only anatase phase irrespective of nature, oxidation state and concentration of these dopants. The photocatalytic activity of undoped TiO2 showed a better activity under UV light compared to doped catalysts. Under solar light illumination, the Th4+ (0.06)-TiO2 showed highest activity for the mineralization of CP. This was attributed to the prolonged separation of photogenerated electron-hole pairs, high specific surface area of the catalyst and high concentration of surface adsorbed water/hydroxyl groups. Further large shift in the absorption band (460 and 482 nm) due to the creation of mid band gap states by Th4+ dopant and also by its small crystallite size additionally contributes to the enhancement of the degradation process. The degradation pathway was followed by UV-vis spectroscopic and GC-MS analysis. © 2009 Elsevier B.V. All rights reserved

Preparation, characterization and enhanced photocatalytic activity of Ni2+ doped titania under solar light

Anatase TiO2 was prepared by sol-gel method through the hydrolysis of TiCl4. Ni2+ was doped into the TiO2 matrix in the concentration range of 0.02 to 0.1 at. and characterized by various analytical techniques. Powder X-ray diffraction revealed only anatase phase for all the samples, while diffuse reflectance spectral studies indicated a red shift in the band gap absorption to the visible region. The photocatalytic activities of these photocatalysts were probed for the degradation of methyl orange under natural solar light. The photocatalyst with optimum doping of 0.08 at. Ni2+, showed enhanced activity, which is attributed to: (i) effective separation of charge carriers and (ii) large red shift in the band gap to visible region. The influence of crystallite size and dopant concentration on the charge carrier trapping - recombination dynamics is investigated. © Versita Warsaw and Springer-Verlag Berlin Heidelberg

Kinetic modeling based on the non-linear regression analysis for the degradation of Alizarin Red S by advanced photo Fenton process using zero valent metallic iron as the catalyst

The degradation of Alizarin Red S (ARS), an anthraquinone dye was investigated by advanced photo Fenton process using zero valent metallic iron (ZVMI) powder as the catalyst with symmetrical peroxides like hydrogen peroxide (HP)/ammonium persulfate (APS) as the oxidants. APS is proved to be a better oxidant compared to HP as it provides efficient acidic medium which is critical for Fenton process. A kinetic/mathematical model was developed based on the non-linear regression analysis and the validity of the model was tested by comparing the observed experimental values with the theoretically calculated data. The rate equation obtained was found to be a function of iron dosage, oxidant and dye concentration at pH 3.k = 0.2456 Fe 0.21 APS 0.15 ARS - 0.76k = 0.58 Fe 0.12 HP 0.10 ARS - 0.86. The degradation pathway was followed by UV-vis spectroscopy and GC-MS techniques. Based on the intermediates analyzed, a probable degradation mechanism has been proposed. © 2009 Elsevier B.V. All rights reserved