Group-III-nitrides have been intensively investigated for optoelectronics and power electronics and are uniquely suitable for energy-related applications, such as solar hydrogen generation and nanogenerators. Compared to planar group-III-nitrides, their nanostructures offer a high surface-to-volume ratio, increased light absorption cross-section, and improved carrier transportation behavior. This thesis focuses on molecular-beam-epitaxy-grown group-III-nitrides, specifically nanowires and membranes, and applications in renewable energy harvesting and conversion. A Mo2C-decorated (In,Ga)N nanowire-based photocathode was demonstrated for nitrogen fixation. The conventional Haber-Bosch method demands high reaction pressure and temperature while releasing a considerable amount of greenhouse gas. The proposed photoelectrocatalytic method can utilize solar energy to generate ammonia without carbon emissions. The proposed photocathodes can achieve maximum faradaic efficiency of 12 %, ammonia yield of 8.9 µg/h/cm2, and excellent stability for over 12 hrs. Moreover, group-III-nitrides were fabricated into a freestanding membrane through a novel method combining electrochemical porosification and controlled spalling. The novel method is reproducible and scalable, which can significantly reduce the consumption of sacrificial substrates compared to existing nitride membrane exfoliation techniques, thus promising a scalable platform. The as-fabricated GaN membranes were demonstrated for photoelectrocatalytic methylene blue degradation. Through laboratory tests and rooftop field tests, we proved the feasibility of our wafer-scale GaN membranes in achieving a dye degradation efficiency of 92%, a total organic carbon removal rate of 50.2%, and extraordinary stability for ~ 50 hours under solar illumination. The membrane can also degrade ~87% of MB under visible-light illumination. Furthermore, the (Al,Ga)N membranes were fabricated into flexible transparent piezoelectric devices. The devices can sense compression pressure and bending strain while giving a comparable compression sensitivity to other thin film piezotronics devices of ~ 2.41 mV/kPa and 42.36 pA/kPa, a maximum bending gauge factor of ~ 1271, and an output power density of ~ 5.38 nW/cm2. The sensors can withstand over 35000 cycles of operation and can be utilized for sensing and harvesting mechanical energies from human motions and environmental signals. This research utilized nanowires and membrane-based group-III-nitrides for different photoelectrocatalytic reactions and piezotronics devices, from material preparation and characterizations, and demonstrated practical devices for clean energy-related applications.

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The preparation of visible light driven photocatalysts for photocatalytic water splitting has been achieved by a CO₂ free, low cost and simple novel method. Combination of peroxide based route with organic free solvent and titanium nitride, carbon free precursor and air and moisture stable, would be useful. Clear red-brown solution of titanium peroxo species was obtained by dissolution of TiN in H₂O₂ and HNO₃ acid at room temperature without stirring. The resultant red brown solution is then used as a titanium solution precursor for yellow amorphous and yellow crystalline TiO₂ synthesis. Visible light photoactivity of the samples was evaluated by photooxidation of methylene blue and photoreduction producing hydrogen from water splitting. The high surface area of yellow amorphous TiO₂ exhibits an interesting property of being both surface adsorbent and photoactive under visible light for photodecolourisation of aqueous solution of methylene blue. However, it might not appropriate for hydrogen production. Nanoparticulate yellow crystalline TiO₂ with defect disorder of Ti³⁺ and oxygen vacancies depending upon synthesis conditions has been characterised by ESR, XPS, CHN analysis and SQUID. Single phase rutile can be produced at low temperature. It is stable at high temperature and the red shift of absorption edge increases with the treatment temperature. Yellow crystalline TiO₂ exhibits an interesting property of being photoactive under visible light. The best photocatalytic performance was observed for 600°C calcination, probably reflecting a compromise between red shift and surface area with changing temperature. Moreover, overall water splitting into hydrogen and oxygen might be obtained by using this material even in air atmosphere. Photoactivity can be improved by testing under anaerobic atmosphere and/or adding sacrificial agent. Quantum efficiency under visible light is still low but comparable to other reports. The maximum efficiency varies from 0.03 % to 0.37 % for hydrogen production and from 0.03 % to 0.12 % for oxygen production, depending on photon energy and sacrificial agents.

Thesis advisor: Dunwei Wang / Semiconductor devices offer promise for efficient conversion of sunlight into other useful forms of energy, in either photovoltaic or photoelectrochemical cell configurations to produce electrical power or chemical energy, respectively. This dissertation examines ionic and electronic phenomena in some candidate semiconductors and seeks to understand their implications toward solar energy conversion applications. First, copper sulfide (Cu₂S) was examined as a candidate photovoltaic material. It was discovered that its unique property of cation diffusion allows the room-temperature synthesis of vertically-aligned nanowire arrays, a morphology which facilitates study of the diffusion processes. This diffusivity was found to induce hysteresis in the electronic behavior, leading to the phenomena of resistive switching and negative differential resistance. The Cu₂S were then demonstrated as morphological templates for solid-state conversion into different types of heterostructures, including segmented and rod-in-tube morphologies. Near-complete conversion to ZnS, enabled by the out-diffusion of Cu back into the substrate, was also achieved. While the ion diffusion property likely hinders the reliability of Cu₂S in photovoltaic applications, it was shown to enable useful electronic and ionic behaviors. Secondly, iron oxide (Fe₂O₃, hematite) was examined as a photoanode for photoelectrochemical water splitting. Its energetic limitations toward the water electrolysis reactions were addressed using two approaches aimed at achieving greater photovoltages and thereby improved water splitting efficiencies. In the first, a built-in n-p junction produced an internal field to drive charge separation and generate photovoltage. In the second, Fe₂O₃ was deposited onto a smaller band gap material, silicon, to form a device capable of producing enhanced total photovoltage by a dual-absorber Z-scheme mechanism. Both approaches resulted in a cathodic shift of the photocurrent onset potential, signifying enhanced power output and progress toward the unassisted photoelectrolysis of water. / Thesis (PhD) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Controlling the electronic structure and requisite charge transfer at and across interfaces is a grand challenge of materials science. Despite decades of research and numerous successes in the fields microelectronics and photovoltaics much work remains to be done. In many applications, whether they be in microelectronics, photovoltaics or display technology there is a demand for multiple functions at a single interface. Historically, existent materials were either discarded as an option due to known properties or tested with some application based figure of merit in mind. Following this, the quality of the material and/or the preparation of the surface/interface to which the material would be deposited was optimized. As the microelectronics and photovoltaics industries have matured, continued progress (faster, lower power transistors and more efficient, cheaper, abundant solar cells) will require new materials (possibly not previously existent) that are fundamentally better for their application than their highly optimized existent counter parts. The manifestation of this has been seen in the microelectronics field with introduction of hafnium silicates to replace silica (which had previously been monumentally successful) as the gate dielectrics for the most advanced transistors. Continued progress in efficient, cheap, abundant photovoltaics will require similar advances. Advances will be needed in the area of new abundant absorbers that can be deposited cheaply which result in materials with high efficiencies. In addition, selective contacts capable of extracting charge from efficient absorbers with low ohmic losses and low recombination rates will be needed. Presented here are two approaches to the multifunctional interface problem, first the use of amorphous alloys that open up the accessible composition space of thin films significantly and second the use of bilayers that loosen the requirements of a single film at an interface.

Thesis (Ph. D.)--University of Oregon, 2000. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 122-126). Also available for download via the World Wide Web; free to University of Oregon users.

Thesis (Ph. D. in Chemical Engineering)--Vanderbilt University, May 2006. / Title from title screen. Includes bibliographical references.

Orientador: Regina Maura Bueno Franco / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-09T07:00:20Z (GMT). No. of bitstreams: 1 Franca_RitaBorges_M.pdf: 4952448 bytes, checksum: 49473f55f00ae94646a96bb8c6672aac (MD5) Previous issue date: 2007 / Resumo: O efluente hospitalar apresenta, dentre seus componentes, organismos como vírus, bactérias, protozoários e helmintos, que ocasionam muitas doenças com implicações em saúde pública. Cryptosporidium spp. e Giardia spp. são protozoários parasitos com grande importância por sua veiculação hídrica e cujas formas infectantes são resistentes aos processos rotineiramente usados no tratamento de água e esgoto. A transmissão destes pode ocorrer com a ingestão dos oocistos e cistos eventualmente presentes na água e nos alimentos contaminados, por contato direto (pessoa a pessoa), por contato indireto (objetos contaminados), pelo contato sexual ou pode ser zoonótica. Os métodos mais utilizados para desinfecção em estações de tratamento são a aeração, cloração e irradiação por UV, mas a cloração, não é suficiente para eliminar oocistos de Cryptosporidium spp e cistos de Giardia spp. A tecnologia eletroquímica oferece um meio de tratamento eficiente para a oxidação. da carga orgânica e microbiológica degradando-as ou mineralizando-as. O presente trabalho teve por objetivos: (1) verificar a ocorrência natural de Cryptosporidium spp. e Giardia spp. em amostras de esgoto do Hospital de Clínicas de Campinas, utilizando o método, de centrífugo-concentração seguido de clarificação com éter e visualização por, imunofluorescência direta, durante o período de um ano; (2) verificar a presença de ovos e larvas de helmintos no esgoto hospitalar empregando a técnica da NOM (Norma Oficial Mexicana) e (3) avaliar a taxa de destruição e o dano estrutural causado em cistos e oocistos após o tratamento fotoeletroquímico. No esgoto hospitalar bruto 4,1 % e 58,3 % das amostras foram positivas para Cryptosporidium spp. e Giardia spp., respectivamente, sendo observada a concentração média de 2,7 x 103 oocistos/L e 3,8 x 105 cistos/L. Foi possível verificar a elevada presença de helmintos, com 90 % das amostras apresentando positividade e concentração de 5,8 x 104 ovos/L e 4,0 x 105 larvas/L. Os protozoários e helmintos presentes em altas concentrações no esgoto hospitalar representam uma séria ameaça à saúde humana. Para os ensaios com o tratamento fotoeletroquímico, amostras de 1 L de esgoto hospitalar foram artificialmente contaminadas com cistos e oocistos e, posteriormente, submetidas a esse tratamento em um reator de bancada, com tempos de exposição de 0,30, 60 e 90 minutos. Por meio das técnicas de imunofluorescência direta, microscopia de contraste de fase e microscopia eletrônica de varredura verificou-se o dano estrutural causado pela ação dos radicais hidroxila nesses protozoários patogênicos e a destruição dos mesmos. O tratamento fotoeletroquímico mostrou uma redução na concentração dos protozoários nos tempos de 30 e 60 minutos e após 90 minutos, nenhum cisto ou oocisto foi detectado. A presença do cloreto no efluente bruto (média de 45 mg/l) desencadeou uma potencializaçáo da ação de mecanismo do reator, gerando efeito associado com a eletrólise, dos radicais hidroxila com a formação de hipoclorito / Abstract: Hospital effluent presents organisms as virus, bacteria, protozoan and helminthes, that cause many iIInesses with implications in public health. Cryptosporidium spp. and Giardia spp. are parasites with waterborne importance and its cysts and oocysts are resistant to the routinely processes used in water treatment. Their transmission can occur by oocysts and cysts ingestion in the water and contaminated foods, by direct contact (person the person), by indirect contact (contaminated objects), by sexual contact or zoonotic. The methods used for disinfection and treatment of sewage are aeration, chlorination and irradiation of ultraviolet light, but the treatment by chlorination is not enough to inactivate Cryptosporidium spp. oocyst and Giardia spp. cysts. The electrochemical technology offers an efficient treatment for the oxidation of organic and microbiological load, degrading and mineralizing them. The present work had as objectives: (1) to verify the natural occurrence of Cryptosporidium spp. and Giardia spp. in samples of Clinical Hospital sewage from Unicamp using centrifugal concentration followed by clarification with ether method and visualization by immunoflourescence assay, during one year, (2) to verify the presence of eggs and larvae of helminthes in the hospital sewage by NOM (Mexican Official Norm) technique and (3) to evaluate the destruction rate and the structural damage caused in cysts and oocysts by photoelectrochemical treatment. In raw hospital sewage 4.1 % and 58.3% of the samples were positive for Cryptosporidium spp. and Giardia spp., respectively, with concentrations of 2.7 x 103 oocysts/L and 3.8 x 105 cysts/L. The high presence of helminthes, 90% positive, with 5.8 x 104 eggs/L and 4.0 x 105 larvae/L and protozoan in hospital sewage represent a serious threat to human being health. For the assays with the photoelectrochemical treatment, samples of 1 L of hospital sewage artificially contaminated with cysts and oocysts ! were submitted to this treatment in a bench reactor, with times of exposition of 0, 30, 60 and 90 minutes. By the techniques of immunofluorescence assays, microscopy of phase contrast and scanning electronic microscopy, the structural damage and destruction were observed, caused by hydroxyl radicals in these pathogenic protozoans. The photoelectrochemical treatment showed a concentration reduction of the protozoan in 30 and 60 minutes, and after 90 minutes no cyst or oocysts were detected. The chloride present in raw effluent (average of 45 rng/L) unchained a potential action of the reactor mechanism, generating an effect associated with electrolysis of the hydroxyl radicals with production of hypochlorite / Mestrado / Parasitologia / Mestre em Parasitologia

Ph.D. (Chemistry) / In this study, carbon based electrode materials such as glassy carbon, graphene, diamond and exfoliated graphite were explored as suitable electrode materials for electrochemical detection, electrochemical and photoelectrochemical degradation of organic water pollutants. Graphene modified glassy carbon electrode sensor was developed for bisphenol A. Cyclic voltammetry was used to study the electrochemical properties of the prepared graphene- modified glassy carbon electrode using potassium ferricyanide as a redox probe. The prepared graphene- modified glassy carbon electrode exhibited more facile electron kinetics and enhanced current of about 75% when compared to the unmodified glassy carbon electrode...