Final Report: Titanium Dioxide and Ultra-violet Light: A Sustainable and Inexpensive Solution for Addressing Drinking Water Quality Issues in the Developing Countries

EPA Grant Number: SU831833
Title: Titanium Dioxide and Ultra-violet Light: A Sustainable and Inexpensive Solution for Addressing Drinking Water Quality Issues in the Developing Countries
Investigators: Desu, S. , Reckhow, David A. , Long, S.
Institution: University of Massachusetts - Amherst
EPA Project Officer: Page, Angela
Phase: I
Project Period: October 1, 2004 through May 30, 2005
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2004) RFA Text |  Recipients Lists
Research Category: P3 Challenge Area - Water , Pollution Prevention/Sustainable Development , P3 Awards , Sustainability

Objective:

The objective of this research is to develop oxide semiconductor based photo-catalysis system with a view to provide a self-sustaining and inexpensive reactor that would detoxify the naturally available water by removing a wile variety of contaminants and pathogens and rendering it suitable for the human consumption. The oxide semiconductors photo-catalysis might prove to be a useful component in removing the disinfecting contaminants from naturally available water supplies and provide inexpensive drinking water solutions for the third world nations where the drinking water problem is acute and present day solutions are expensive. This research is focused on the application of semiconductor oxide; TiO2 based water purification process and aims to design, develop and test contamination-testing methods, implementing TiO2 as a catalyst in combination with UV-A radiation. In recent years, semiconductor photo-catalysis has received an increasing attention for water purification. In this process, low-energy ultraviolet light is used to generate holes and electrons, which oxidizes toxic organic pollutants and/or reduces toxic metal ions. Simultaneous removal of organic compounds and metal ions makes this process unique over other process. Application of semiconducting oxides like ZrO2 or ZnO is also promising in terms of increasing the efficiency of solar disinfection process. These photo catalysts are also capable of generating strong oxidant radicals that can neutralize several aqueous organic pollutants, including textile dyes and phenols, as well as other impurities. Application of semiconductor photo-catalysis based on appropriate technology design of the reactor will be ideal for water purification. It would require no special training methodology, and will be user friendly in any language or skill level to the citizen of the world. Moreover, such water purification technique will be more beneficial to the health of the environment than the traditional process as it will not add any chemical pollutants into the environment or waste energy resources.

Summary/Accomplishments (Outputs/Outcomes):

The Ti02 based purification system reactor was built and tested by various diagnostic techniques for its efficacy in detoxification of water against organic and biological matter. Initial experiments were done with ultraviolet lamp as excitation source for photo-catalysis. Substrate immobilized nano-porous TiO coated over glass and ceramic tiles were developed as catalysts. Various compositions of binders and TiO2 loading were tried and evaluated for optimized performance. This mitigates the problem of removing ultra fine semiconductor particle suspension from the purified water. To develop self purifying storage vessels for water, we developed and tested TiO2 sputter processed coatings, which can be embedded over vessel surface. This approach has potential to realize stand-alone reactors that would require nb electricity or chemical additives and provide clean water on demand at any location. In various tests we have conducted clean water was spiked with varying concentrations of methyl blue dye.
Various TiO2 embedded discs were suspended for varying periods in a reactor filled with spiked water. The TiO2 catalyst was very successful in speeding up the oxidation process of methyl blue and this was verified visually and more quantitatively by using spectrometric determinations. The microbial tests were performed on heterotropic bacteria that are naturally present in stagnant water such as po4ds. Utilizing Ti02 catalyst plates, water samples drawn from the reactor at various times showed remarkable decrease in the concentration of bacterial colonies. In about 4 hours of photo-catalysis, complete eradication of microbial matter from the water was realized.

We have looked into scientific concepts governing the use of oxide semiconductors for toxic water remediation. More important of these is inefficient separation of the charges generated by the UV light irradiation which translates into low quantum efficiency of the process. Therefore mechanistic aspects of photo-catalytic oxidation property of wide band gap semiconductor materials such as TiO2 and ZnO to degrade organic wastes in the water was investigated to find ways to improve the catalyzing efficiency and to develop novel materials for optimum results. The mechanism we visualize is the two-step electron reduction process. The conduction electron first produces 0H radical, which injects hole in the semiconductor valence band enhancing the luminescence. 0H radicals are produced by oxidation of 4iethanol and water. These data are suggestive of alternative charge exchange processes at the semiconductor interface with the toxic substances. More investigations are however needed to establish the processes. Such knowledge is relevant for improving the quantum efficiency of the photo-catalytic process.

Conclusions:

In order to develop inexpensive drinking water systems for the third world nations, titanium dioxide (TiO2) has been found to be a useful component in removing the disinfecting contaminants from naturally available water supplies. TiO2 based water purification process focus of this research project is designed to develop and test contamination testing methods, implementing TiO2 as a catalyst in combination with UV-A radiation. Evaluation methods used in this project show affectivity of immobilized nano-porous TiO2 substrates to perform photo-catalysis and in eliminating water pollutants such as harmful pathogens, organic and inorganic compounds.

The challenge for future research is to discontinue use of electrically operated UV source and utilize available solar radiation on the earth surface. This requires innovative approaches for developing new materials and structures that not only absorb visible solar radiation but also have energy for holes and electrons to dive the catalysis process. Shifting the absorbance of TiO2 by suitable doping is an area of future work. Enhancing the photo-catalytic ability of oxide semiconductors using innovative concepts such as solar cells to drive photoeoelectrochemical process and develc4 multi-layer structures to carryout electron and hole processes in different regions of the semiconductor have considerable technology potential.

Supplemental Keywords:

RFA, Scientific Discipline, Water, TREATMENT/CONTROL, POLLUTANTS/TOXICS, Sustainable Industry/Business, Chemical Engineering, Environmental Chemistry, Sustainable Environment, Arsenic, Technology, Technology for Sustainable Environment, New/Innovative technologies, Water Pollutants, Drinking Water, clean technologies, detoxification, titanium dioxide photo catalyast, environmental sustainability, green engineering, other - risk assessment, adsorption, arsenic removal, treatment, drinking water distribution system, activated carbons, drinking water contaminants, drinking water treatment, UV light emitting diodes, drinking water system, green chemistry