Bibliography of Work on the Heterogeneous Photocatalytic Removal of Hazardous Compounds from Water and Air Update Number 3 To January 1999 Daniel M. Blake Summary The subject of this report is chemistry and engineering for the application of heterogeneous photocataly- sis. The state of the art in catalysts are forms of titanium dioxide or modifications thereof, but work on other heterogeneous catalysts is included in this compilation. This report is a continuation the bibliographies of work on the photocatalytic oxidation of organic or inorganic compounds in air or water and on the photocatalytic reduction of inorganic compounds in water that were published in May 1994, October 1995, and January 1997. The previous reports included 663, 574, and 518 citations, respectively. This update contains 1,517 new references. These were published between October 1996 and January 1999, or are references from prior years that were not included in the previous reports. The general focus of the work is removing hazardous chemical or biological contaminants from air, water, and surfaces. This report also references work on properties of semiconductor photocatalysts and the application of photocatalytic chemistry in organic synthesis. The organization is the same as in the previous reports in this series except that patents are included as a separate list because of the large number that have appeared since the last report. The first part of the report gives citations for work done in a few broad categories that are generic to the process. Three tables provide references to work on specific substances. The first covers organic compounds that are included in various lists of hazardous substances identified by the U.S. Environmental Protection Agency (EPA). The second lists compounds not included in that table, but that have been treated in a photocatalytic process. The third covers inorganic compounds that have been treated by a photocatalytic process. iii Table of Contents Page 1.0 Introduction..................................................................................................................................... 2.0 Generic Information........................................................................................................................ 2.1 Review Articles................................................................................................................. 2.2 Photocatalysts ................................................................................................................... 2.2.1 Modified Titanium Dioxide.................................................................................... 2.2.2 Hydrophobic Surface Treatment ............................................................................ 2.2.3 Dye Sensitized Titanium Dioxide........................................................................... 2.2.4 Metal Ion Doping of Titanium Dioxide.................................................................. 2.2.5 Metallized Titanium Dioxide.................................................................................. 2.2.6 Other Semiconductors ............................................................................................ 2.2.7 Immobilized Photocatalysts.................................................................................... 2.3 Hydrogen Peroxide and Related Oxidants........................................................................ 2.4 Engineering Issues ............................................................................................................ 2.4.1 Reactor and System Design.................................................................................... 2.4.2 Systems Analysis.................................................................................................... 2.5 Miscellaneous Topics.............................................................................................................. 2.6 Patents ..................................................................................................................................... 2.7 Companies Active in the Field ................................................................................................ 3.0 Compounds Studied........................................................................................................................ 4.0 Conclusions..................................................................................................................................... 5.0 Bibliography ................................................................................................................................... 5.1 Published Material.............................................................................................................. 5.2 Patents................................................................................................................................. 5.3 Address for Sending Corrections or Additions to the Bibliography .................................. 6.0 Distribution List ............................................................................................................................. iv 1.0 Introduction This update in combination with the previous reports1,2,3 provides a comprehensive bibliography of the work on photocatalytic chemistry and processes that are available in the open literature. It will be of most use to scientists and engineers interested in the use of heterogeneous photocatalytic oxidation or reduction processes in environmental remediation, process emission control, indoor air quality, or other applications in which oxidation or reduction chemistry on illuminated semiconductor surfaces can occur. Because of the large number of documents, no attempt has been made to critically assess the information in the cited literature. The combined reports include more than 3,300 citations to work published between 1970 and the beginning of 1999. The literature cited includes U.S. and foreign patents. Information was compiled by manually scanning the literature and by searching commercial databases. This update includes about 100 citations to work done before 1996 that were not included in the previous reports. Some citations have doubtless been missed and topics covered in some papers may not have been identified and covered in every appropriate category. The author is grateful to the many people who sent references and reprints of their work. Coverage is limited to heterogeneous processes, except in a few cases where review material for homogeneous processes is relevant to heterogeneous photocatalytic chemistry. The author invites readers to send references to relevant work that appeared before 1999 that has been missed to the mailing or e-mail address included in Section 5.3. The number of new publications, including patents, continues to grow each year, as shown in the plot in the figure. The growth in patents is primarily due to the high level of commercial interest in applications being developed in Japan. The number of papers, reports, and conference proceedings has leveled off at about 300 per year, with an increasing fraction coming from outside the United States. 1Blake, Daniel M. (1994). Bibliography of Work on the Photocatalytic Removal of Hazardous Compounds from Water and Air. NREL/TP-430-6084. Golden, CO: National Renewable Energy Laboratory. 75 pp. [DE94006906]. Available from the National Technical Information Service, Springfield, VA 22161. 2Blake, Daniel M. (1995). Bibliography of Work on the Photocatalytic Removal of Hazardous Compounds from Water and Air. Update Number 1, to June 1995. NREL/TP-473-20300. Golden, CO: National Renewable Energy Laboratory. 102 pp. Available from the National Technical Information Service, Springfield, VA 22161. 3Blake, Daniel M. (1997). Bibliography of Work on the Photocatalytic Removal of Hazardous Compounds from Water and Air. Update Number 2, to October 1996. NREL/TP-430-22197. Golden, CO: National Renewable Energy Laboratory. 88 pp. Available from the National Technical Information Service, Springfield, VA 22161. 1 Figure. Total Citations and Patents Related to Photocatalytic Chemistry by Year 800 600 Total Citations 400 Patents Number 200 0 70 74 78 82 86 90 94 98 Year The photocatalytic oxidation of organic compounds in water has received the most attention, but there is a rapidly increasing amount of work on the oxidation of volatile organic or inorganic compounds in the gas phase. Photocatalytic reduction of organic compounds and metal-containing ions has also received increasing attention. Studies of cell killing and disinfection by illuminated titanium dioxide (TiO2) have also been increasing in number. Nearly 1,000 substances have been tested to date. Intermediates and by-products have been widely observed to form and persist in the treated medium. These can include a variety of mineral acids, oxygenated organic compounds, and carbon monoxide. The nature of the intermediates can be used as a tool for revealing details of the chemical mechanism for the photocatalytic process. The net process involves oxidizing the organic compound to an intermediate stage of oxygen content or to carbon dioxide, water, and a mineral acid (if a heteroatom such as nitrogen or chlorine is present). Other oxidizing agents may be substituted for oxygen. Certain metal ions from water can be modified or removed when the ions replace oxygen as the electron acceptor in the process and are deposited as lower oxidation state oxides or metals