Materials Science Forum Vol. 764

Abstract: Carbonate is a common pollutant in water and wastewater. A study to understand its influence on the photodegradation rates is necessary especially when TiO₂/UV technique is emerging as an advanced technology for pollution abatement. In the present investigation, we report surface modification of titanium dioxide using carbonate ions, characterization of carbonate modified titanium dioxide (CMT) and photocatalytic application of carbonate modified TiO₂. Titanium dioxide from two different sources namely BDH, Mumbai and Degussa AG, Germany was used as photocatalyst. The CMT catalysts were characterized using potentiometry, FT-IR and XPS. Approximately, 18.9 mg CO₃/g CMT(BDH) and 8.13 mg CO₃/g CMT(Degussa) was found loaded as determined by potentiometry. The C 1s and O 1s binding energies observed at 289.2 and 531.3 eV, respectively were attributed to surface carbonate species. The adsorption and photodegradation of Acid Blue I dye examined using neat TiO₂ as well as CMT catalysts revealed that carbonate inhibits catalytic activity for color and Chemical Oxygen Demand (COD) removal. The photo degradation rate constant (k, s^-1) decreases gradually with increasing concentration of carbonate. Thus, in the absence of carbonate k_dye is 5.45 × 10^-4 s^-1 (R² = 0.97) and k_COD is 3.50 × 10^-5 s^-1 (R² = 0.97). At 100 mg/L CO₃^2-, k_dye is 0.16 × 10^-4 s^-1 (R² = 0.96) and k_COD is 2.66 × 10^-5 s^-1 (R² = 0.98). In addition, the carbonate spiking studies revealed the onset of inhibition soon after the addition of carbonate into reacting suspensions of TiO₂. The results suggest that carbonate inhibits catalytic activity through formation of strong surface complex under suitable pH by displacing OH₂⁺ and OH groups from TiO₂ surface. This results not only in fewer (OH)_surface groups available for h⁺ trapping for oxidation into OH radicals but also in non-availability of adsorption sites for the dye molecules. A pretreatment to remove carbonate from (waste) water appears necessary prior to application of TiO₂/UV technique

Abstract: Water is one of the most essential commodity for mankind, but we know that only 1% of available water on earth may be used for human consumption. However, due to increasing anthropogenic activities the water is getting polluted. Scientists all over the world are looking for ecofriendly methods to treat polluted water for its reuse. One technique that has been gaining popularity in recent years and it is quite promising also for the treatment of resilient pollutants is the photocatalysis. Numerous studies have been reported in the last decade on the photocatalytic degradation of organic pollutants using semiconductor materials as photocatalysts, but the limited optical absorption due to the relatively wide band gap energies and recombination of photogenerated electron-hole pair results in low activity of photocatalysts. Therefore, improvement of charge separation as well as enhancement of visible light absorption is highly important for the efficient photocatalytic reactions. In this context, doping of semiconductor by non-metals seems a promising strategy to enhance the activity of a photocatalyst. In this chapter; preparation, characterization, mechanism and various applications of non-metal doped semiconductors has been reported and the applications of semiconductors have been focused on waste water treatment. Some other applications include generation of hydrogen by photocatalytic splitting of water, antimicrobial activity etc.

Abstract: The TiO₂-ZnO nanocomposite materials ((TiO₂-ZnO)_NCM) with different molar ratios (Ti:Zn) was synthesized by chemical route and dispersed in functionalized silicate sol-gel matrix (Silicate/(TiO₂-ZnO)_NCM)). The as prepared Silicate/(TiO₂-ZnO)_NCM were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. The dispersion of the small amount of (TiO₂-ZnO)_NCM in silicate sol-gel matrix paves the way for the preparation of solid-state thin film photocatalyst which is advantageous for the separation of the catalyst from solution, the substrates and the reaction products. The simultaneous photoinduced oxidation of methylene blue (MB) dye and reduction of Cr (VI) to Cr (III) was examined at different amine functionalized silicate sol-gel embedded (TiO₂-ZnO)_NCM films. The (TiO₂-ZnO)_NCM dispersed into the amine functionalized silicate sol-gel matrix (TPDT) exhibited enhanced photocatalytic activity when compared to the (TiO₂-ZnO)_NCM without the silicate sol-gel. The functionalized silicate sol-gel supported (TiO₂-ZnO)_NCM is a potential candidate for energy conversion and environment remediation and cleaning applications.

Abstract: Different amounts of Fe, Co, Ni and Cu-doped TiO₂ thin films were prepared on fluorine doped tin oxide (FTO) coated soda-lime glass substrates by following a conventional sol-gel dip-coating technique followed by heat treatment at 550 and 600°C for 30 min. These thin films were characterized for photo-current, chronoamperometry and band-gap energy values. The chemical compositions of metals-doped TiO₂ thin films on FTO glass substrates were confirmed by XPS spectroscopic study. The metal-ions doped TiO₂ thin films had a thickness of <200 nm="" optical="" transparency="" of="">80%, band-gap energy of >3.6 eV, and a direct band-to-band energy transition. The photoelectrochemical (PEC) studies revealed that all the metal-ions doped TiO₂ thin films exhibit n-type semi-conducting behavior with a quite stable chronoamperometry and photo-currents that increase with the increase of applied voltage but decrease with the dopant metal-ion concentration in the thin film. Furthermore, these thin films exhibited flat-band potentials amenable to water oxidation reaction in a PEC cell. The 0.5 wt.% Cu-doped TiO₂ thin film electrode exhibited an highest incident photon-to-current conversion efficiency (IPCE) of about 21%.

Abstract: The photocatalytic degradation (PCD) of three commercially textile dyes, namely Alizarin Cyanine Green G (ACG), Reactive Red 195 (RR195) and Reactive Black 5 (RB5) has been investigated using TiO₂ (Degussa P25) photocatalyst in aqueous solution under UV light. Experiments were conducted to optimize various parameters viz. amount of catalyst, initial concentration of dye and solution pH. Degradation of all the dyes was examined by using UV spectrophotometer. Photocatalytic degradation increased with increasing TiO₂ loading (in the range 0.51.5 g/L) and decreasing with increasing dye concentration (in the range 20-100 mg/L) and solution pH (in the range 4-10). Result demonstrated that the reactivity of the three dyes for TiO₂ catalyzed PCD was as follows: Reactive Red 195 > Reactive Black 5 > Alizarin cyanine Green G, respectively.

Abstract: Optimum composition of Cd_1xPb_xSe thin films (0.1 x 0.9) were deposited using single precursor bath containing cadmium sulfate octahydrate, lead nitrate, tartaric acid, potassium hydroxide, ammonia and sodium selenosulfate onto fluorinedoped tin oxide (FTO) glass substrates. The photoelectrochemical (PEC) cells were fabricated using Cd_1xPb_xSe as an active photoelectrode with sulphide/polysulphide redox couple as an electrolyte and sensitized graphite rod as a counter electrode. The various characteristics of the cells namely currentvoltage (IV), capacitancevoltage (CV) in dark, power output, builtinpotential, photoresponse, spectral response measurements were investigated. The cell performance parameters such as opencircuit voltage (V_oc), shortcircuit current (I_sc), series resistance (R_s), shunt resistance (R_sh), conversion efficiency (η), fill factor (FF), junction ideality factor (n_d), builtinpotential (Φ_B), flatband potential (V_fb) were evaluated. PEC characteristics reveal ntype semiconducting nature for Cd_1xPb_xSe thin films with lead composition x < 0.5, while ptype nature for remaining Cd_1xPb_xSe thin films. Among the various cells, the maximum PEC efficiency (η = 1.401 %) was found to Cd_0.7Pb_0.3Se thin films; due to its increase in opencircuit voltage (225 mV) as well as shortcircuit current (3.983 mA/cm²)_, decrease in resistance (R_s = 0.75 kΩ and R_sh = 331 Ω), and increase in photoelectrode absorption as compared to other thin film materials.