Prof. Hoffmann’s primary interest during his early professional years was explore the advantages of using hydrogen peroxide and related peroxides (peroxymonosulfate, peroxydisulfate, and peroxyacetic acid) for pollution control applications. For example, H2O2 is now commonly used to control hydrogen sulfide generation and emissions in sanitary sewer systems, wastewater pumping basins, and wastewater treatment plants. His early work paved the way for the current widespread use of hydrogen peroxide in a variety of pollution control applications such as hazardous waste treatment using Fenton’s reagent and peroxone (hydrogen peroxide combined ozone) and for the remediation of MTBE contaminated groundwater. Representative research publications1-17 related to this early area of Hoffmann’s work are listed in the cited references section and the end of this report.
Based on an early interest in sulfur pollution control, Prof. Hoffmann initiated a new area of pollution control research in 1980 that was focused on using semiconductor photocatalysis for the control of reduced sulfur compounds18,19. Research in the Hoffmann Lab was focused on the synthesis and characterization of metal oxide semiconductors that could be activated with solar light. This research focused on the use of simple earth-abundant metal oxides such as Fe2O3, TiO2, and ZnO. During this period of time, a major challenge was the development of self-stabilizing colloid suspensions of nanometer-sized semiconductors for practical applications. Several novel synthetic methods for the production of semiconductor quantum-dots in the particle size range of 1 to 4 nm were developed in the Hoffmann lab. Prof. Hoffmann’s research group20,21 was the first to develop novel sol-gel synthetic methods for the production of TiO2 and ZnO quantum dots (also called quantum-sized semiconductors) without the use of stabilizing organic surfactants. Hoffmann’s research group took advantage of a detailed knowledge of the surface chemistry of metal oxide and metal sulfide materials in order to synthesize stable suspensions of quantum-dots in water and other polar solvents. This particular sol-gel synthetic approach is now widely used by variety of industries to coat glass and other surfaces such as ceramic roofing tiles with transparent nano-particulate titanium dioxide to produce light-activated self-cleaning surfaces. Major companies that employ transparent nanoparticulate colloidal suspensions of TiO2 and other metal oxides include Toto, St. Gobain, Dow-Corning, PPG, Pilkington and many other industries.
Hoffmann and colleagues published an review of his group’s research activities in the area of the environmental applications of semiconductor photocatalysis in 199522. This single research publication has been cited to date more than 4000 times. His earlier publication23 on the metal-ion doping of quantum-sized TiO2 has garnered more than 1000 citations in the primary literature. Semiconductor photocatalysis is still one of the principal research are of the Hoffmann research group. For example, a current research within the Hoffmann group is focused on the use of earth-abundant semiconducting materials for solar fuels production24-28 via artificial photosynthesis and for water treatment applications29.
Hoffmann and his group have worked together with several major companies to translate their laboratory-scale research into commercially-viable processes. Major companies that have supported Hoffmann’s research include DuPont30,31, Chevron32,33, the Eaton Corporation34-37, Northrop-Grumman and Bell Helmets38-40, 3M41-47, and Falcon Water-Free Technologies (http://www.falconwaterfree.com/about/hoffman.htm ). Some of the practical engineering objectives of the various research projects included the application of quantum-dots in photo-resist polymerization, the retardation of wax deposition in producing oil wells, for the control of anti-oxidant wastes in metals manufacturing, for the development of self-cleaning surfaces for military aircraft and vehicles, for the development of future generations of self-cleaning gas-masks and protective coatings for soldiers and first-responders, and for the development of water-free urinals (http://www.falconwaterfree.com/home/flash_v4.html).
Hoffmann has been listed by ISI Web of Knowledge as one of the most highly-cited researcher in engineering in the world with over 19000 total citations, while his work on groundwater remediation48-50 relevant to MTBE contamination at the JFK International Airport done in conjunction with Brown and Caldwell and American Airlines was recognized by the award of Jack G. McKee Medal by the Water Environment Federation in 2003. In 1991, Hoffmann was awarded the Alexander von Humboldt Prize for his scientific contributions in the field of environmental chemistry and in 2001, Hoffmann was presented with the Creative Advances in Environmental Science and Technology Award by the ACS.