PdCl2/Bi2WO6 and Pd/Bi2WO6 composite photocatalysts were synthesized via a template free hydrothermal process and the respective photocatalytic activities were investigated by degradation of Rhodamine B. The new catalyst composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and ultraviolet visible (UV-vis) light diffuse reflectance spectra, respectively. By XRD, it was found that the loaded Pd species did not alter the crystal lattice of Bi2WO6 photocatalyst. Through the XPS spectra, it was found that the PdCl2/Bi2WO6 was successfully reduced by chemical reducing agents CH2O and N2H4, respectively, and palladium was present in the form of both metallic Pd and Pd ion spe-cies (Pd0 and Pd2+), while the Pd species in a NaBH4-reduced composite exhibited only metallic Pd species (Pd0). For the SEM images, it was observed that both classes of composites were constructed from plenty of nanoplates, which were closed packed with hierarchical structures. Furthermore, the removal efficiency of Rhodamine B was found to be influenced by parameters such as catalyst dosage, pollutant concentration and solution pH.

Orientador: Pedro Luiz Onofrio Volpe / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-06T03:53:24Z (GMT). No. of bitstreams: 1 Perles_CarlosEduardo_M.pdf: 705638 bytes, checksum: a455cca3305019a9dcda448dae6c69f3 (MD5) Previous issue date: 2006 / Mestrado / Físico-Química / Mestre em Ciências

PdCl2/Bi2WO6 and Pd/Bi2WO6 composite photocatalysts were synthesized via a template free hydrothermal process and the respective photocatalytic activities were investigated by degradation of Rhodamine B. The new catalyst composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and ultraviolet visible (UV-vis) light diffuse reflectance spectra, respectively. By XRD, it was found that the loaded Pd species did not alter the crystal lattice of Bi2WO6 photocatalyst. Through the XPS spectra, it was found that the PdCl2/Bi2WO6 was successfully reduced by chemical reducing agents CH2O and N2H4, respectively, and palladium was present in the form of both metallic Pd and Pd ion spe-cies (Pd0 and Pd2+), while the Pd species in a NaBH4-reduced composite exhibited only metallic Pd species (Pd0). For the SEM images, it was observed that both classes of composites were constructed from plenty of nanoplates, which were closed packed with hierarchical structures. Furthermore, the removal efficiency of Rhodamine B was found to be influenced by parameters such as catalyst dosage, pollutant concentration and solution pH.

Please read the abstract in the section 00front of this document / Dissertation (M Eng (Industrial Engineering))--University of Pretoria, 2006. / Industrial and Systems Engineering / unrestricted

Equilibrium exchange constants were calculated for exchange of sulphite with other sulphur compounds. The equilibrium constant for sulphur Isotope exchange between sulphate in solution and solid calcium sulphate was calcu­lated and measured experimentally. In the chemical reduc­tion of sulphate to sulphide S^32O-4 reacted 2.5% faster than S340-4 , in agreement with the calculated kinetic isotope effect for the step sulphate to sulphite. The isotope effect in the reduction of sulphate by Desulphovibrio desulphuricans was found to vary from 0.0 to 2.5% The results were inter­preted on the basis of a mechanism involving two consecutive steps, pick-up of sulphate and reduction of sulphate to sul-phite, competing for control of the rate. The isotope effect in bacterial reduction of sulphite was studied briefly. / Thesis / Doctor of Philosophy (PhD)

Reducing equivalents were extracted from in vitro photosynthesis and used to drive cell-free and enzyme-free biochemical reduction reactions in this research. To investigate photosynthetic electron flow, an algal extract dense in chloroplasts was made from the microalga Scenedesmus sp. A6. The algal extract was subjugated to a variety of environmental parameters and exogenous quinones in order to optimize electron extraction. To monitor electron extraction and donation to metabolites, a novel assay was created that monitored the chemiluminescence (CL) produced by superoxide radicals formed during the process. In particular, these formed when a reduced exogenous quinone oxidized spontaneously. Our studies found that calcium chloride improved the reduction of low redox potential mediators along with prolonged exposure to red light. Other salts and environmental conditions examined had diverse effects on the quinones based on structure, redox potential, and site of electron extraction. We next applied our assay for monitoring the reduction of different metabolites. The CL recorded for different metabolites was compared to the Gibbs free energy of reduction and a highly correlated relationship was found. The assay was then applied to the reduction of metabolites via the oxidation of glucose in an alkaline environment. To exhibit the diverse application of the CL assay, urine of healthy individuals, patients with chronic kidney disease (CKD), and patients with bladder cancer (BCa) were characterized through their interactions with different quinones. The CL output was compared to that of SurineTM and urea followed by ANOVA analysis. Statistically significant differences were found for all quinones with 1,2-napthoquinone-4-sulfonate (NQS) producing significant differences between all groups examined. Monitoring algal phenotypes for biofuels or photosynthetic output requires arduous protocols and advanced instrumentation. Both of these energy producing options were explored along with rapid, high-throughput protocols for measuring reduction reactions. To monitor the phenotypes and health of our microalgae, Raman microscopy was applied to algal cultures of Scenedesmus sp. A6 grown under stress. Statistically unique phenotypes were found based on environmental factors during cell growth. ANOVA analysis determined the effect of stressors that caused significant change to algal phenotypes related to photosynthesis and lipids. / Doctor of Philosophy / Photosynthesis is the process by which plants and algae harness sunlight to convert CO2 to plant mass. Photosynthesis is performed in the chloroplast which can excite electrons and use them to generate energy. Detecting how much energy a chloroplast can produce and what chemicals effect the chloroplast requires complex procedures with complicated instruments. In this thesis the chloroplast from the microalgae Scenedesmus sp. A6 were isolated to evaluate how they are affected by different chemicals in the environment using a new, rapid and robust assay. Then, a group of chemicals called quinones were used to steal electrons (plant energy), and this process was optimized in this research. The purpose of stealing this plant energy from photosynthesis was so it could be re-directed into synthesizing valuable chemicals that are normally produced from fossil fuels. A new sensor was also developed in this research that would "light-up" the environment whenever this plant energy (electron) stealing process was successful allowing us to measure the efficiency of this energy transfer. Once a quinone stole an electron, it would spontaneously give up the electron to oxygen, creating an unstable molecule that could then react with the chemical luminol, forming a strong luminescence (light) signal. We found that calcium chloride greatly enhanced a quinone's ability to harvest electrons from the chloroplast. We also reported unique effects caused by salt, magnesium, phosphate, a mild detergent, and changing the amount of light the chloroplast would receive. This information was then used to transfer electrons from the chloroplast to make new valuable chemicals. We found that electrons could be donated to multiple chemicals using a quinone, chloroplasts, and light. We were also able to take electrons from glucose with our quinones when glucose was in an environment with a high pH. Electrons from glucose could also be donated to chemicals of interest using quinones. In addition, Quinones were used once more to find differences in the urine composition of healthy individuals and those with chronic kidney disease or bladder cancer. The urine from healthy individuals produced a unique luminescence signal when interacting with the quinones. Thus, quinones could be used for rapidly detecting changes in a patient's kidney and bladder function. We also developed a new method for detecting changes in the health of an algal culture. Algal cultures are used for producing biofuel, food, and pharmaceuticals, therefore it is imperative to track the growth of a culture to avoid contamination and algal death. Scenedesmus sp. A6 was exposed to chemicals harmful to algal health to see how these chemicals caused the algae to grow differently. Raman spectroscopy was used to collect data on algae grown under different conditions. The Raman spectra obtained then underwent statistical analysis to determine the chemicals that had the greatest impact on algal function. Methyl viologen, nickel sulfate, salt, and light exposure had the greatest impact on the algae.

Research on metal nanoparticles (MNPs) synthesis and their applications for optoelectronic devices has been a recent interest in the fields of nanoscience and nanotechnology Photovoltaics are one of such systems in which MNPs have shown to be quite useful, due to unique physical, optical, magnetic, and electronic properties, including the metal nanoparticles synthesized in this research. Owing to the challenges with the most common physical and chemical methods of preparing MNPs, including the use of high temperatures, toxic reducing agents, and environmentally hazardous organic solvents, there is a critical need for a benign synthesis procedure for MNPs. In this work, a simple, versatile, and environmentally and economically responsible synthesis method for making iron, nickel, zinc, and bimetallic alloy nanoparticles (ANPs) has been developed and functionalization with organic capping agents were performed to form metal-organic hybrid nanocomposites with tunable properties. The size, shape, elemental composition, photophysical properties, and crystallinity of particles and their hybrids have been evaluated. Monometallic nanostructures of iron, nickel, and zinc oxide were synthesized via aqueous-phase reduction of metal(II) chloride salts with sodium borohydride. Upon optimization of the standard method described here, reaction parameters like reaction time, reagent molar ratios, and capping-agent molar ratio were evaluated. Characterization techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive x-ray (EDS), IR, and UV-visible spectroscopies, selected area electron diffraction (SAED), and power x-ray diffraction (XRD) were performed as necessary. Well-defined, reproducible nickel and iron nanoparticles were produced with average diameters of 26±4 nm and 50±26 nm, respectively, arranged into chain-like structures. Much smaller (6-9 nm) zinc oxide particles that self-assembled into single-particle thick, hexagonal hierarchical microstructures were formed from a modified standard method. Similarly, iron-nickel ANPs with the average size of 20.9±3.3 nm were also synthesized and successful grafting with the polymer capping agent, polyvinylpyrrolidone was confirmed. Because of size, ordered self-assembly, and benign synthesis procedure, the nanoparticles described here are ideal candidates for photovoltaic and thermoelectric device applications. Moreover, these particles have shown to disperse well in various organic and inorganic media, and therefore have wide versatility in thin-film deposition methods.

Various synthetic methods have been developed to produce metal nanostructures including copper and iron nanostructures. Modification of nanoparticle surface to enhance their characteristic properties through surface functionalization with organic ligands ranging from small molecules to polymeric materials including organic semiconducting polymers is a key interest in nanoscience. However, most of the synthetic methods developed in the past depend widely on non-aqueous solvents, toxic reducing agents, and high temperature and high-pressure conditions. Therefore, to produce metal nanostructures and their nanocomposites with a simpler and greener method is indeed necessary and desirable for their nano-scale applications. Hence the objective of this thesis work is to develop an environmentally friendly synthesis method to make welldefined copper and iron nanostructures on a large-scale. The size and shape-dependent optical properties, solid-state crystal packing, and morphologies of nanostructures have been evaluated with respect to various experimental parameters. Nanostructures of copper and iron were prepared by developing an aqueous phase chemical reduction method from copper(II) chloride and Fe(III) chloride hexahydrate upon reduction using a mild reducing agent, sodium borohydride, under an inert atmosphere at room temperature. Well-defined copper nanocubes with an average edge length of 100±35 nm and iron nanochains with an average chain length up to 1.70 μm were prepared. The effect of the molar ratios of each precursor to the reducing agent, reaction time, and addition rate of the reducing agent were also evaluated in order to develop an optimized synthesis method for synthesis of these nanostructures. UV-visible spectral traces and X-ray powder diffraction traces were obtained to confirm the successful preparation of both nanostructrues. The synthesis method developed here was further modified to make poly(3-hexylthiophene) coated iron nanocomposites by surface functionalization with poly(3-hexylthiophene) carboxylate anion. Since these nanostructrues and nanocomposites have the ability to disperse in both aqueous-based solvents and organic solvents, the synthesis method provides opportunities to apply these metal nanostructures on a variety of surfaces using solution based fabrication techniques such as spin coating and spray coating methods.

abstract: Mineral weathering and industrial activities cause elevated concentration of hexavalent chromium (Cr(VI)) in groundwater, and this poses potential health concern (>10 ppb) to southwestern USA. The conversion of Cr(VI) to Cr(III) – a fairly soluble and non-toxic form at typical pH of groundwater is an effective method to control the mobility and carcinogenic effects of Cr(VI). In-situ chemical reduction using SnCl2 was investigated to initiate this redox process using jar testing with buffered ultrapure water and native Arizona groundwater spiked with varying Cr(VI) concentrations. Cr(VI) transformation by SnCl2 is super rapid (<60 seconds) and depends upon the molar dosage of Sn(II) to Cr(VI). Cr(VI) removal improved significantly at higher pH while was independent on Cr(VI) initial concentration and dissolved oxygen (DO) level. Co-existing oxyanions (As and W) competed with Cr(VI) for SnCl2 oxidation and adsorption sites of formed precipitates, thus resulted in lower Cr(VI) removal in the challenge water. SnCl2 reagent grade and commercial grade behaved similarly when freshly prepared, but the reducing strength of the commercial product decreased by 50% over a week after exposing to atmosphere. Equilibrium modeling with Visual MINTEQ suggested redox potential < 400 mV to reach Cr(VI) treatment goal of 10 ppb. Kinetics of Cr(VI) reduction was simulated via the rate expression: r=-k[H+]-0.25[Sn2+]0.5[Cr2O72-]3 with k = 0.146 uM-2.25s-1, which correlated consistently with experimental data under different pH and SnCl2 doses. These results proved SnCl2 reductive treatment is a simple and highly effective method to treat Cr(VI) in groundwater. / Dissertation/Thesis / Masters Thesis Civil, Environmental and Sustainable Engineering 2019

M.Tech. / The removal and recovery of heavy metals from effluents has been a subject of significant importance due the negative impact these toxic metals have on human health and the environment as a result of water and soil pollution. Precipitation is the mostly widely used wastewater treatment method because it is the most economical and easier to implement and operate on a large scale. However, traditional precipitation methods using lime, sulfides or hydroxides recover metals in the form of a sludge which is not reusable and has to be disposed in landfills creating a potential environmental hazard and resulting in loss of valuable minerals. The current focus in effluent treatment is now on the recovery and re-use of these heavy metals rather than removal and disposal. This study investigated the use of hydrazine as a reducing agent to remove and recover Ni2+, Cu2+, Co2+ and Fe2+ from effluent by reduction crystallization. In this process chemically reduced aqueous metal ions were plated on to a base substrate (nickel powder) with no electrical current required for deposition. A feasibility study was carried out to test the efficiency and find the optimum operating conditions for this method and generate an understanding of the chemical and particulate process occurring. The results obtained indicate that hydrazine is an effective reducing agent for removal and crystallization of Ni2+, Cu2+, Co2+ and Fe2+/ Fe3+ into their elemental states with nickel powder as a seeding material. Over 99 % of metals were removed from the effluent in all the systems (Ni-only, Ni-Cu, Ni-Fe and Ni-Fe). Breakage, aggregation and molecular growth were identified as the predominant mechanisms occurring during the reduction crystallization process in Ni-only, Ni-Cu, Ni- Co systems and there was evidence of nucleation in Ni-Fe solution. These finding were confirmed by analysing the scanning electron micrographs of the powder obtained. A nearly spherical structure powder with wide distribution in particle size and evidence of fragmentation was obtained in all the experimental runs. vii The residual concentrations obtained were far below the required limit for effluent discharge into sewer where 20 mg/L Ni, 20 mg/L Cu and 20 mg/L Fe and the total metal concentration of 50 mg/L for Fe, Cr, Cu, Ni, Zn and Cd is stipulated. Reduction crystallization using hydrazine as a reducing agent can be utilized for controlling environmental pollution and eliminating hazardous metals from the environment.