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

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

Enhanced photocatalytic activity of transition metal ions Mn2+, Ni2+ and Zn2+ doped polycrystalline titania for the degradation of Aniline Blue under UV/solar light

Anatase TiO2 was doped with divalent transition metal ions like Mn2+, Ni2+ and Zn2+ and characterized by various analytical techniques. Powder X-ray diffraction revealed stabilization of anatase phase for Ni2+ and Zn2+ doped samples, while phase transformation from anatase to rutile was promoted due to Mn2+ inclusion. The rutile fraction increased with Mn2+ concentration due to the creation of surface oxygen vacancies. All the doped catalysts showed red shift in the band gap absorption to the visible region. The photocatalytic activities of these catalysts were evaluated in the degradation of Aniline Blue (AB) under UV/solar light. Among the photocatalysts, Mn2+ (0.06 at.)-TiO2 showed enhanced activity, which is attributed to the synergistic effect in the bicrystalline framework of anatase and rutile. Further the unique half filled electronic structure of Mn2+ serves as a shallow trap for the charge carriers to enhance the photocatalytic activity. An insight to the mechanism of interfacial charge transfer in the mixed phase of anatase and rutile is explored, taking into consideration the theories of previous models. © 2010 Elsevier B.V

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

Collective quadrupole excitations in the 50<Z,N<82 nuclei with the generalized Bohr Hamiltonian

The generalized Bohr Hamiltonian is applied to a description of low-lying collective excitations in even-even isotopes of Te, Xe, Ba, Ce, Nd and Sm. The collective potential and inertial functions are determined by means of the Strutinsky method and the cranking model, respectively. A shell-dependent parametrization of the Nilsson potential is used. An approximate particle-number projection is performed in treatment of pairing correlations. The effect of coupling with the pairing vibrations is taken into account approximately when determining the inertial functions. The calculation does not contain any free parameter.Comment: Latex2e source, 20 pages, 14 figures in EPS format, tar gzipped fil

Review on modified TiO2 photocatalysis under UV/visible light: Selected results and related mechanisms on interfacial charge carrier transfer dynamics

Titania is one of the most widely used benchmark standard photocatalysts in the field of environmental applications. However, the large band gap of titania and massive recombination of photogenerated charge carriers limit its overall photocatalytic efficiency. The former can be overcome by modifying the electronic band structure of titania including various strategies like coupling with a narrow band gap semiconductor, metal ion/nonmetal ion doping, codoping with two or more foreign ions, surface sensitization by organic dyes or metal complexes, and noble metal deposition. The latter can be corrected by changing the surface properties of titania by fluorination or sulfation or by the addition of suitable electron acceptors besides molecular oxygen in the reaction medium. This review encompasses several advancements made in these aspects, and also some of the new physical insights related to the charge transfer events like charge carrier generation, trapping, detrapping, and their transfer to surface are discussed for each strategy of the modified titania to support the conclusions derived. The synergistic effects in the mixed polymorphs of titania and also the theories proposed for their enhanced activity are reported. A recent venture on the synthesis and applications of anatase titania with a large percentage of reactive 001 facets and their band gap extension to the visible region via nonmetal ion doping which is a current hot topic is briefly outlined. © 2011 American Chemical Society

Preparation and characterization of Mn-doped titanates with a bicrystalline framework: Correlation of the crystallite size with the synergistic effect on the photocatalytic activity

Mn2+ ion was doped into the sol-gel anatase TiO2 in the concentration range of 0.02-0.1. Powder X-ray diffraction results revealed that the phase transformation from anatase to rutile proceeds at a slower rate up to an intermediate dopant concentration of 0.06 and accelerates for a higher dopant concentration of 0.1. In comparison with the previous studies, the phase transition temperature was reduced by 100 °C for the intermediate dopant concentration. The photocatalytic activity of Mn2+ (0.06)-TiO2 for the degradation of an oxo-fused polycyclic aromatic dye, Indanthrane BR Violet, was almost equal to that of Degussa P-25 under UV light, but under solar light its efficiency was nearly 4 times higher. This enhanced activity can be attributed to the (i) synergistic effect in the bicrystalline framework of anatase and rutile, (ii) small crystallite size, and (iii) high intimate contact between both the phases. The correlation of the crystallite size with the synergistic effect on the photocatalytic activity is studied in detail. © 2009 American Chemical Society