Enhanced Absorption Metal Oxides for Photocatalytic Applications

Environmental pollution and industrialization on a global scale has drawn attention to the vital need for developing new hygienic and environmentally friendly purification technologies. The most common indoor and outdoor purification process have their corresponding limitations of electricity and/or other energy sources. To address such enormous tasks, advance oxidation technology like heterogeneous photocatalytic systems via metal oxide semiconductors such as TiO2, ZnO, that are capable to operate effectively and efficiently under UV and visible light must be established. Due to the wide band gap of semiconductors, they are unable to absorb visible light. Hence, numerous research efforts have been done to increase the photocatalytic activity and optical absorption of semiconductors by various methods. This thesis presents the study of enhanced absorption capability of metal modified, especially silver modified, Ti02 and ZnO and silver-ceria co-doping on Ti02. All the experiments carried out and characterization techniques used were explained in detail. The present work deals with the synthesis of unmodified and with various mol% of metal modified Ti02, and ZnO. Photocatalytic activity is analysed using a model dye, rhodamine 6G (R6G). A noble metal such as silver is used as the metal modifier and optimised the concentration of silver giving the highest photocatalytic activity in both cases. The synthesis of Ti02 through a modified sol-gel route and effect of silver modification to enhance the photocatalytic activity of Ti02 is explored. In the case of Ti02, two methods are adopted to introduce silver, such as the light irradiation method and the direct calcination method. Of the two methods, the latter is found to produce a more effective photocatalytic material (6-50% improvement in catalytic efficiency), which is attributed to the fact that the silver is homogeneously dispersed throughout the material. 5 mol% is found as the optimum giving the highest rate of photocatalytic activity. Results demonstrate that silver modification retains the anatase phase stability up to 700°C. In addition, adsorption experiments on Ti02 which undergo further degradation. Photocatalytic activity tests of various % of urea modified Ti02 indicate urea modification can extend the anatase phase stability for higher temperatures and 1:1 TTIP:Urea modified sample at 900°C show high photocatalytic activity among other samples. Analysis on the effect of silver modification on ZnO and mechanism of photocatalytic enhancement is illustrated. In the case of Zn0, a wet chemistry approach is used for the silver modification. Materials are synthesized at various temperatures ranging from 300 to 1000°C. It is observed from the characterization that 3 mol % silver-modified ZnO at 400 °C shows approximately a four time higher rate of degradation than that of unmodified ZnO and a three times higher rate of degradation than that of unmodified ZnO and a three times higher rate of degradation than that of unmodified ZnO and a three times higher rate than that of commercial Ti02, photocatalyst standard, Degussa P-25. A possible mechanism of photocatalytic activity in presence of sensitising dye is also discussed in light of photoemission studies. It is reasoned that the presence of silver facilitates the interfacial charge transfer processes in such a way to utilise the CB electrons for enhancing the photocatalytic activity. Investigated the visible light absorption capability of Ti02, as a result of novel silverceria co-doping. The effect in structural and optical properties associated with co-doping is demonstrated. Analysis on results shows silver-ceria co-doping results in a large shift in absorption towards visible wavelength resulting in visible light active materials. Furthermore, the structural analysis clearly proves the high temperature stability of the anatase phase and it is believed that there is a silver-ceria interaction at low temperature on the Ti02 surface. In overview, the work produced and results derived form the current study have different potential applications in the field of semiconductor photocatalysis in the near future

Acculturation Stress, Covid-19 Outbreak, and Academic Burnout on the Psychological Well-being of Asian Students

The Coronavirus (Covid-19) endemic is growing exponentially in the whole world. SARS-CoV-2 is the virus responsible for causing COVID-19 disease, which is highly infectious and lethal. Acculturation stress originates from attempts by individuals to resolve the differences between their culture of origin and the dominant culture. In addition, the process of acculturation often is accompanied by several stressful psycho-social experiences, personal and institutional discrimination, leaving family and friends behind in the country of origin, and the stressor of learning a new language. Moreover, with the soaring trends in globalization, people ought to seek a highly competitive and world-class education to excel in combat. As a result, academic or student burnout, a state of emotional, mental, and physical exhaustion caused by prolonged or repeated stress in school, is a common issue among international students. During this Covid-19 pandemic, concerns on acculturation stress and academic burnout are widely discussed with a mental health issue in various spheres of contemporary society as these affect people in multiple settings

A Highly Efficient Ag-ZnO Photocatalyst: Synthesis, Properties, and Mechanism

Highly photocatalytically active silver-modified ZnO has been prepared and the effect of silver modification was studied. The structural and optical properties were characterized by X-ray diffraction, Fourier transform IR, differential scanning calorimetry, BET surface area, Raman, UV-vis, and photoluminescence spectroscopy. The photocatalytic activity of these materials was studied by analyzing the degradation of an organic dye, rhodamine 6G (R6G), and it is found that 3 mol % silver-modified ZnO at 400°C shows approximately four times higher rate of degradation than that of unmodified ZnO and a three times higher rate than that of commercial TiO 2 photocatalyst Degussa P-25. It was also noted that the photocatalytic activity for the modified ZnO sample was five times higher than the unmodified sample using sunlight. The effect of silver in enhancing the photocatalytic activity has been studied by analyzing the emission properties of both ZnO and silvermodified ZnO in the presence (emission increases) and absence (emission decreases) of R6G. We attribute these observations to the extent of valence band hole production and the role of silver in trapping the conduction band (CB) electrons in the absence of R6G. In the presence of R6G, the dye preserves the CB electron population in the metal oxide, thus preserving and enhancing emission intensity. The sensitizing property of the dye and electron scavenging ability of silver together constitute to the interfacial charge transfer process in such a way to utilize the photoexcited electrons

Equipment concept design and development plans for microgravity science and applications research on space station: Combustion tunnel, laser diagnostic system, advanced modular furnace, integrated electronics laboratory

Taking advantage of the microgravity environment of space NASA has initiated the preliminary design of a permanently manned space station that will support technological advances in process science and stimulate the development of new and improved materials having applications across the commercial spectrum. Previous studies have been performed to define from the researcher's perspective, the requirements for laboratory equipment to accommodate microgravity experiments on the space station. Functional requirements for the identified experimental apparatus and support equipment were determined. From these hardware requirements, several items were selected for concept designs and subsequent formulation of development plans. This report documents the concept designs and development plans for two items of experiment apparatus - the Combustion Tunnel and the Advanced Modular Furnace, and two items of support equipment the Laser Diagnostic System and the Integrated Electronics Laboratory. For each concept design, key technology developments were identified that are required to enable or enhance the development of the respective hardware

India's Nonalignment Policy and the American Response, 1947-1960

India's nonalignment policy attracted the attention of many newly independent countries for it provided an alternative to the existing American and Russian views of the world. This dissertation is an examination of both India's nonalignment policy and the official American reaction to it during the Truman-Eisenhower years. Indian nonalignment should be defined as a policy of noncommitment towards rival power blocs adopted with a view of retaining freedom of action in international affairs and thereby influencing the issue of war and peace to India's advantage. India maintained that the Cold War was essentially a European problem. Adherence to military allliances , it believed, would increase domestic tensions and add to chances of involvement in international war, thus destroying hopes of socio-economic reconstruction of India. The official American reaction was not consistent. It varied from president to president, from issue to issue, and from time to time. India's stand on various issues of international import and interest to the United States such as recognition of the People's Republic of China, the Korean War, the Japanese peace treaty of 1951, and the Hungarian revolt of 1956, increased American concern about and dislike of nonalignment. Many Americans in high places regraded India's nonalignment policy as pro-Communist and as one that sought to undermine Western collective security measures. Consequently, during the Truman and Eisenhower presidencies the United States took a series of diplomatic, military, and economic measures to counter India's neutralism. America refused to treat India as a major power and attempted to contain its influence on the international plane by excluding it from international conferences and from assuming international responsibilities. The Russian efforts to woo India and other nonaligned countries with trade and aid softened America's open resistance to India's nonalignment. As a result, although tactical, a new trend in America's dealings with India was visible during the closing years of Eisenhower's presidency. Therefore, America sought to keep nonaligned India at least nonaligned by extending economic aid

A Highly Efficient Ag-ZnO Photocatalyst: Synthesis, Properties, and Mechanism

Highly photocatalytically active silver-modified ZnO has been prepared and the effect of silver modification was studied. The structural and optical properties were characterized by X-ray diffraction, Fourier transform IR, differential scanning calorimetry, BET surface area, Raman, UV-vis, and photoluminescence spectroscopy. The photocatalytic activity of these materials was studied by analyzing the degradation of an organic dye, rhodamine 6G (R6G), and it is found that 3 mol % silver-modified ZnO at 400°C shows approximately four times higher rate of degradation than that of unmodified ZnO and a three times higher rate than that of commercial TiO 2 photocatalyst Degussa P-25. It was also noted that the photocatalytic activity for the modified ZnO sample was five times higher than the unmodified sample using sunlight. The effect of silver in enhancing the photocatalytic activity has been studied by analyzing the emission properties of both ZnO and silvermodified ZnO in the presence (emission increases) and absence (emission decreases) of R6G. We attribute these observations to the extent of valence band hole production and the role of silver in trapping the conduction band (CB) electrons in the absence of R6G. In the presence of R6G, the dye preserves the CB electron population in the metal oxide, thus preserving and enhancing emission intensity. The sensitizing property of the dye and electron scavenging ability of silver together constitute to the interfacial charge transfer process in such a way to utilize the photoexcited electrons