International Graduate Conference on Science, Humanities and Engineering 2011 (IGCSHE2011)

Electrochromic films of NiO & NiO-TiO2 (with Ti concentrations 5, 10, 15, 20, 25 & 30%) have been prepared bythe sol-gel route using dip coating technique onto fluorine-doped tin oxide-coated glass substrates (FTO/glass).Ethanolic sols from nickel acetate tetrahydrate (Ni(CH3COO)2•4H2O) and titanium isopropoxide precursors wereused in the preparationsd. The nano-sized films were sintered in air between 250 and 300°C. Characteristics ofdifferent films were studied in a comparative manner. Photoluminescence spectra, UV/Visible spectra,electrochromic behavior, cyclic voltammetry, XRD and SEM have been investigated.Typically, as the TiO2 content was increased, film characteristics were enhanced. Then mechanisms of colorationand morphology transformation of the layer during cycling in 0.05 M KOH electrolyte are discussed in terms of anactivation and degradation period. Finally, a used type of electrolyte based on KOH mixed with starch has been alsotested with complete windows.

The photocatalytic degradation of organic contaminants (such as industrial dyes, insecticides, pesticides, … etc) in water, using TiO2 under UV are commonly used procedures. Modifying TiO2 with CdS is also a common technique used for water purification under visible light. In this work both commercial and prepared TiO2 were used for photo-degradation of two model contaminants, methyl orange (MO) and phenazpyridine (PhPy). In order to sensitize TiO2 to visible light, a chemical pathdeposition method (CBD) was used to precipitate non-scale (~20 nm) CdS particles on TiO2 particle surfaces. Sand was used as a supporting surface for the TiO2/CdS catalyst. UV-visible spectra, photoluminescence emission spectra, XRD and SEM imaging were measured to characterize the prepared catalyst systems. Effects of catalyst concentration, initial contaminant concentration and pH on photo-degradation rate were studied. Turnover number and quantum yield were also calculated for comparison study. Despite the high efficiency of TiO2/CdS catalyst system in degrading water contaminants, voltametric analysis confirmed complete CdS decomposition during the photo-degradation process. Due to hazardous nature of resultingCd2+ in the treated water, an alternative sensitizer has been suggested based on natural nontoxic dyes. Anthocyanin was used here for the first time as a sensitizer for the rutile TiO2 system. Activated Carbon (AC) was also used as supporting substrate. Electronic absorption spectra, FT-IR spectra, and TGA analysis were used to characterize the prepared TiO2/Anthocyanine catalyst systems. The efficiency of the new catalyst system, in photo-degradation ofMO and PhPY was assessed. An observable efficiency was noted specially when using AC/TiO2/Anthocyanin atlow pH in photo-degradation of MO.Details of results, discussions and suggested mechanisms will be presented in this presentation

In this study, we intend to introduce a new technique to prepare nano-sized films of CdS for the purpose of light-to electricity conversion processes. In order to assess the new systems, their photoelectrochemical (PEC)characteristics have been compared with conventional counterparts. The nano-sized films were prepared by different techniques, namely: electrochemical(EC), chemical bath (CB), and electrochemical followed by chemical bath (EC/CB) techniques. The latter technique describes the preparation ofour new film. All films were deposited onto fluorine-doped tin oxide-coated glass substrates (FTO/glass). Thedifferent types of films were compared with each other by monitoring different parameters, such as: open-ciruitvoltage (Voc), short-circuit current density (Jsc), dark current-density-potential (J-V) plots, photo (J-V) plots, conversion efficiency (ɳ) and stability. Enhancement of deposited CdS thin film characteristics in light-to-electricity conversion was investigated. The characteristics of different films were also studied before and after annealing treatment. The films were annealed to 250oC under N2. Cooling of pre-heated films to room temperature was performed by slow cooling and quenching. The effect of each treatment on the film characteristics was measured by monitoring Voc, Jsc, dark J-Vplots, photo J-V plots and (ɳ). The characteristics of CdS thin films in PEC systems were enhanced by annealing and slow cooling in each preparation. On the other hand, slow cooling showed higher conversion efficiency than quenching, in each preparation.CdS thin films prepared by EC/CB technique, before annealing, have higher efficiency than films prepared by EC,but lower than CB systems. After annealing, EC/CB prepared systems showed higher efficiency than either EC or CB prepared counterparts.

Several procedures are commonly used for water purification, such as adding chlorine containing substances,peroxide, bromine, silver-copper, ozone and UV. Photodegradation of microorganisms has also been examined inwater disinfection. TiO2 and ZnO were examined by researchers for inactivation of Escherichia coli andLactobacillus helveticus using photo-degradation techniques.Although ZnO is a wide band gap (3.2 ev) semiconductor, with limited photo-catalytic applications to shorterwavelengths only, and demands UV region for excitation; it has attracted attention as an interesting alternative toTiO2 in dye sensitized solar cells. Both TiO2 and ZnO have similar band gaps (3.2 ev) and similar electron injectionefficiencies from excited dyes. Moreover, ZnO exhibits analogous transport properties as TiO2. ZnO has otheradvantages such as improved performance with cheap organic dyes (it absorbs larger fraction of solar UV light thanTiO2 does).Because only about 4% of the solar spectrum falls in the UV region, ZnO semiconductor is sensitized by dyemolecules. Sensitized ZnO catalysts have been investigated for organic pollutant degradation in a safe and simplemanner.In this work, ZnO semiconductor nano-particles, combined with safe low cost sensitizer (the natural dyeanthocyanin) was used to disinfect water from bacteria by photodegrading it with solar light .The natural dyesensitizes ZnO to the visible light, the dye has lower band gap and absorbs in the visible region.Illumination has been constructed by a solar simulator lamp. A pre-contaminated water sample with e-coli bacteriawas treated with the catalyst (ZnO/anthocyanin) under halogen spot lamp. A noticeable decline in bacteriaconcentration was observed. Contaminated samples treated with naked ZnO, anthocyanin dye, and light source(without any additions) separately in control experiments.Up to 90% degradation was achieved by the ZnO/anthocyanin catalyst system under solar light in 90 minutes.Effect of different parameters on reaction rate and efficiency, such as temperature, pH, concentration and otherswill be presented.