The ability to use light and more preferably sunlight to affect chemical change is growing in importance as green chemistry and energy conservation become critical. The various polymorphs of titanium oxide (TiO2) are probably the most widely studied materials for photocatalysts. Titanium oxide nanotubes (TNT) provide the unique opportunity to combine the high aspect ratio, high surface area and mesoporosity in the design of next generation photocatalysts. The band gap for bulk TiO2 (3.2 eV for anatase) lies in the ultraviolet such that only about 10% of the sun's energy could be used in a photocatalytic process. Metal and non-metal doping as well as surface modification define the current strategy for enhancing the properties of TiO2 based photocatalysts and photovoltaic devices. Thus, in addition to controlling morphology, doping and surface modification of the TNTs is an important aspect of catalyst development. A unique feature of the TNTs is the outside and inside surfaces that can be functionalized separately. These are unprecedented composite nanostructures and potentially could lead to ground breaking photocatalysis. The proposed research below will address the synthesis and characterization of TiO2 nanotubes decorated with semiconductor nanoparticles and films as well as the evaluation of photocatalytic activity relevant to environmental pollution and energy conservation.
Intellectual Merit of the proposed activity It is clear that researchers are starting to think more of composite nanoscale materials and structures as attractive catalysts. The exciting aspect of TNTs is the ability to separately modify the inside and outside surface which may impart unprecedented catalytic activity. Thus there is the opportunity to prepare unique hybrid composites not possible with nanorods or mesoporous particles. Preliminary results show that semiconductor quantum dots and films can be exclusively encapsulated in the mesopores or coated on just the outer surface. The proposed research will describe the strategies for decorating the surfaces of TiO2 nanotubes with various semiconductor quantum dots, nanorods and films. Preliminary results for the photodegradation of organic dyes indicate dramatic improvements in activity relative to benchmark catalysts. Progress on the proposed research could also result in deployment of our new technology in areas such as photovoltaics. The results from the proposed activity may serve to define new directions in photocatalysis and water splitting.
The broader Impacts of the proposed activity The broader impacts of this project include numerous tasks that will lead to the integration of research and multilevel education in the area of catalysis and novel nanomaterials. If the proposed effort to develop TiO2 nanotube composite photocatalysts for the conversion of organic pollutants and water is successful, then we anticipate that the near term impact on society will be significant. Probable areas that will benefit from the proposed activity include ground water detoxification and homeland security as well as nanocatalysis, smart textiles, sensors, filtration and energy conservation. Additionally, a strong educational component will coincide with the research activities. The proposed research addresses contemporary topics in nanoscience and the skills acquired by students during this project will enhance their preparation for careers in nanotechnology, chemical engineering and materials chemistry. In addition to seminars and course development on nanomaterials and their applications in environment and energy, we seek to engage students at all levels in the study of nanomaterials and their many exciting applications in environment and energy. We will participate in the NanoExplorers program where students participate in discussions, workshops, and experiments/research. We are also committed to other high school student research experiences as part of the Welch and Clark Foundations summer programs as well as ACS Project SEED for disadvantaged high school students. It is anticipated that a high school teacher may be involved in this project as well. As such we anticipate that this project in catalysis and nanotechnology will also impact the community at large by educating our high school teachers and students.
Normal 0 false false false false EN-US X-NONE X-NONE This project involved the development of novel photocatalysts. Figure 1 illustrates some of the key challenges in the design of effective photocatalysts. The surface reactions involved in photocatalysis relies on the adsorption of substrates and high surface areas to optimize conversions. The various forms of titanium oxide (TiO2) are probably the most widely studied materials for photocatalysis. High surface to volume nanostructures such as titanium oxide nanotubes (TNT) may possess the optimal catalytic properties. However, the band gap for bulk TiO2 (3.2 eV for anatase) lies in the ultraviolet such that only about 10% of the sunâ€™s energy could be used in a photocatalytic process. The next generation photocatalysts will rely on surface modification and doping to access a greater portion of the solar spectrum. The titanium dioxide (TiO2) nanotubes have proven to be an excellent platform for designing new catalysts, not only because of the high surface area but also the ease of functionalization. During this project the technology to decorate TiO2 nanotubes with semiconductor quantum dots (QD) with control over the size was developed. We then demonstrated that using TNTs modified with quantum dots one could use visible light to achieve electron transfer and the effective photocatalytic degradation of organics. Several different types of QDs were supported on TNTs and shown to be effective catalysts. The QD/TNT photocatalysts were also used to trigger the photorelease of nitric oxide and the generation of singlet oxygen using visible light. This has implications for photodynamic therapy. The separation of charge is the key to improving the efficiency of photocatalysts. The approach in this project semiconductor heterojunction catalysts where, co-catalysts such as metals or carbon are added to the semiconductor surface to promote charge separation. During this project we prepared composites of TNTs with various forms of carbon including graphene and nanodiamonds. We also extended this work to include the synthesis of metal nanoparticles on the TNTs. Figure 1. Multiple challenges in the design of effective photocatalysts The broader impacts of this project included numerous tasks that resulted in the integration of research and multilevel education in the area of novel nanoscale materials. The synthesis methods, nanotechnology and catalysis impact on the advancement of basic science. The effort to develop novel composite photocatalysts could have a near term impact on society in areas such as ground water detoxification and homeland security as well as nanocatalysis, smart textiles, sensors, filtration and energy conservation. Additionally, there was a strong educational component that engaged students at both the graduate and undergraduate levels as well as students from underrepresented groups and women. The research addressed contemporary topics in catalysis/nanoscience and the skills acquired by students during this project should enhance their preparation for careers in chemical engineering, materials chemistry, and nanotechnology. Highlights include, the PI conducted demos and presentations to K-12 students on topics related to the research. The PI also taught the Chemistry merit badge several times during the funding period. Several high school students participated in this project including Amy Chyao pictured below with President Obama after winning the Intel ISEF competition. A poster based on this project can be seen in the background. The PI is also the faculty advisor to the award winning ACS affiliate Chemistry Student Association at UTD and is actively involved in their outreach activities.