Date of Award
Doctor of Philosophy
Environmental Science and Engineering
Geoffrey B. Saupe
Water pollution is major environmental problem worldwide. Many common industrial organic compounds that make their way into water systems can be carcinogenic at trace levels and are difficult and costly to remove completely with conventional technologies. Because of this, authorities and researchers are trying to improve current water cleanup techniques.
Heterogeneous photocatalysts that accelerate the photocatalytic destruction of organic contaminants in water are a potentially inexpensive and highly effective way to remove both trace-level and saturated harmful compounds from industrial waste streams and drinking water. Titanium dioxide has the potential to completely mineralize organic compounds in water under ultraviolet light. However, the best catalysts are high surface area nanopowders, which are very difficult to remove from product streams, especially on large scale systems. Porous photocatalytic materials can have the combined qualities of high surface area and easy to handle large particles, as compared with nanoparticulate catalyst powders.
In this research, high surface area semiconductor porous materials made up of titanium-niobium mixed oxide and niobium oxide nanocomposites were developed for their utility as photocatalysts in the decontamination of water at different pHs (pH= 2, 3.6, 7, and 9). The new porous catalysts retain high catalytic activity while being easy to handle and filter out of product streams. New synthetic methods were developed to optimize physical properties and the catalyst's ability to photo-degrade organic and inorganic contaminants in water at all pHs. The porous materials were characterized with a variety of analytical techniques, including transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction, Brunauer-Emmett-Teller surface area analysis (BET), CHN elemental analysis, inductively coupled plasma/optical emission spectrophotometer (ICP-OES), flame and graphite furnace atomic absorption spectroscopy (FAAS and GFAAS), and UV-Vis spectrophotometry. The whole process of preparing and characterizing unique and stable porous titanium and niobium metal oxides is described in chapter 2.
This study was performed in three phases. In the first two phases, the nanocomposites titanoniobate and triniobate porous metal oxides derived from KTiNbO5 and KNb3O8 were prepared. The preparation involved a series of reactions that started with the solid-state synthesis of the parent compounds followed by cation exchange, exfoliation, condensation, and a supercritical point drying process of the porous metal aggregates. These materials were then treated by a thermo-dehydration step to obtain the non-topo and topo porous oxide, respectively. The products were then characterized using XRD, BET, UV-Vis, SEM, CHN elemental analysis, ICP-OES, and TEM. XRD results showed that the new materials were crystalline in structure. BET results indicated that these materials had high surface areas with large pores, especially when they were treated by thermo-dehydration. These materials were used for photocatalytic degradation of a model contamination, bromocresol green dye (BG). The results demonstrated that materials based on the titanoniobate and the triniobate had good photocatalytic activity. The pH profile studies performed on the parent, the non-topo and topo materials showed that the catalysts have the ability to effectively degrade BG in acidic media. Significant photoactivity was observed for all samples at pH 2 and 3.6. At pH 3.6, topo porous materials performed better in comparison with the other samples. Because the non-topo and topo materials had porous structures, the catalyst's surface area, increased in comparison to the parent material. Therefore, the higher activity of the porous materials was related to the greater surface area observed by SEM and BET. The catalytic stability test results also showed that the topo porous material had high and stable performance over time.
The catalytic adsorption of non-topo titanoniobate for toxic and precious metals is described in Chapter 4. The results in this phase of study showed that the porous HTiNbO5 was able to reduce Pb2+ to Pb and Cr6+ to Cr in the presence of UV-light but reduction and deposition of Cd2+ to Cd was not evident. The catalyst also reduced precious metals such as Au3+ to Au and Pt2+ to Pt in the presence of UV-light.
The photocatalytic treatment of the waste materials has proven to be an effective method for the treatment of a varied range of organic pollutants as found in colored waste waters. It appears that photoactive metal oxides is the only sub-discipline of heterogeneous catalysis able to convert organic pollutants to CO2 and water without heating, using high pressure of oxygen, or requiring any chemical reactants or additives.
Results indicate that the new porous catalysts appear to be good choices for water decontamination compared to efficient and well-known commercial TiO2 powders, and they have larger mean particle sizes, which can be exploited to help solve catalyst retrieval and filtration problems after decontamination has taken place. The reactivity of the porous catalyst was comparable to that of the TiO2 nanopowder, P25 by Degussa (Germany), one of the best commercial catalysts.
Received from ProQuest
Maryam Zarei Chaleshtori
Zarei Chaleshtori, Maryam, "Titanium Niobium Nano Porous Materials: New Photocatalysts for Water Decontamination" (2010). Open Access Theses & Dissertations. 2816.