Optimal Design, Development, and Characterization of Photocatalytic Composite Particles and Technology for Advanced Oxidation Process Applications

EPA Grant Number: FP917095
Title: Optimal Design, Development, and Characterization of Photocatalytic Composite Particles and Technology for Advanced Oxidation Process Applications
Investigators: Follansbee, David M.
Institution: Rensselaer Polytechnic Institute
EPA Project Officer: Lee, Sonja
Project Period: September 1, 2010 through August 31, 2013
Project Amount: $111,000
RFA: STAR Graduate Fellowships (2010) RFA Text |  Recipients Lists
Research Category: Fellowship - Drinking Water , Academic Fellowships

Objective:

Increasing demands for potable drinking water, increasingly stringent water quality standards, and the seemingly perpetual discovery of new biological and chemical contaminants all provide an impetus to develop novel, high-throughput material processing (e.g., purification and disinfection) technologies. Several studies have shown that when excited, photoactive materials (such as titanium dioxide) generate oxidizing chemical species that can destroy organic compounds (mineralization) and pathogens in aqueous media. The use of this technology has received considerable attention as a viable treatment strategy for water contaminated with organic compounds, specifically pharmaceuticals. This technology is very attractive due to its low-cost operation and ability to oxidize a wide variety of organic compounds; however much effort is needed to fundamentally understand the optimal particle properties and how to optimally design a system that will be able to efficiently treat a high-throughput of contaminated water. To this end, the focus of this research will include three specific aims: (1) to improve quantum efficiencies of photocatalytic technologies by fundamentally understanding the kinetics of photo-active materials; (2) to maximize adsorptive mass transfer rates of species to the catalyst surface under various flow conditions and develop associated Langmuir isotherms; and (3) to identify key design characteristics that facilitate the transport of composite particles within a continuous system.

Synopsis:

Increasing demands for potable drinking water, along with increasingly stringent water quality standards, provide an impetus to develop novel, high-throughput material processing. One such technology is the use of photoactive material to decompose organic material. This project will focus on improving the efficiency of photocatalytic technologies, analyze the desired optimal particle properties, and identify key design characteristics for a continuous photocatalytic water treatment system.

Approach:

The approach of this research entails three aspects that directly correspond to the specific aims (i) determine reaction rate and reactivation rate, (ii) determine mass transfer rates and isotherms for composite particles, and (iii) test mechanical durability of recirculating particles. Each one of these deals with some characteristic or aspect of design of the composite particle; however, each property can be studied independently from the others. The reactivation rate can be determined on a bench scale by activating a light source for a given length of time and then removing the light source and introducing a dye. This experiment gives insight into the rate at which the photons are absorbed by the photocatalyst and the possible mechanism associated with this process. The desire is to understand if the absorption of the photons is rate limiting and needs to be accounted for in the reaction rate. The reaction rate can be determined through similar experiments by measuring the conversion rate of a chemical process (e.g., oxidation of nitrite to nitrate) through the photon chamber while using the reactivation unit to reactivate the catalyst and comparing this to the amount of energy spent on reactivation. The mass transfer of contaminant to the surface of the catalyst can be determined by sampling the rich phase as a function of annular bed height and testing its concentration. This will be done for various influent flow rates and concentrations to provide information for the mass transfer rate and saturation of the adsorbent respectively. This equilibrium data will be used to formulate isotherms in order to characterize the particles. The mechanical durability of the particles can be tested by running the system in fluidization, hydraulic transport, and re-circulating modes. This will provide information for the force at which these particles are coming into contact with the walls and neighboring particles. The frictional and inertial effects will also be studied by the pressure drop exerted by particles of various sizes and densities within the riser section compared to the energy spent to transport them.

Expected Results:

These results will provide insight into the surface reaction kinetics and mechanism of a photocatalytic process based on light intensity, residence time, and loading of adsorbent. It will allow for the understanding of how the effective surface area of a particle can increase its adsorptive potential without hindering its photo-oxidative potential and what the pore size constraints (i.e., mesoporous or nanoporous) allow for effective adsorption and regeneration. They also will provide an understanding of the ease of transportation and operating costs associated with this system. This information will be used to construct a model-based framework that when accurate will be able to determine optimal particle properties by identifying the loading of a given adsorbent for a particular photocatalyst, the appropriate substrate to use that facilitates transportation and mechanical durability, and the optimal operating conditions for this catalyst testing system.

Potential to Further Environmental/Human Health Protection:

The impact that the proposed research will have on human society is the fundamental advancement of a low-cost technology that has the ability to completely oxidize chemical and biological contaminants in aqueous media. Photocatalytic technology takes advantage of the energy emitted from light and produces no disinfection byproducts such as those identified in drinking water (trihalomethanes, haloacetic acids, bromate, and chlorite). To date, all advanced oxidation processes (including photocatalysis) have only been performed on primarily bench scale applications. This is partially due to the bottlenecks associated with the fundamental understanding of this technology. The advancement lies with the ability to independently study the mass transfer limitations of contaminant to the surface of the particle and the efficient use of photons (quantum efficiency) that is posed by photocatalysis. With the proposed research, the intent is to move past these bottlenecks and provide a means to allow photocatalytic technologies to progress beyond the bench scale to industrial applications. This proposed research also will provide an apparatus that can be utilized to test the effectiveness of composite photocatalytic particles as well as be applied to the treatment of contaminated water prior to discharge or within drinking water plants. Although this research focuses on remediating pollution after it has been introduced, it is important to try to stop pollution at its source. This is done by developing an outreach program called “Pollution Prevention Day” at local elementary schools and addressing these issues to children. The purpose of this event would be to actively teach children of various age levels about the importance of clean drinking water, the water cycle, water sources, pollution prevention, and traditional treatment techniques. Many of these lesson plans and activities are outlined on the EPA Web Site. This outreach program will help children to take an active role for reducing pollution at its source in their own lives and make them aware that this is a growing concern.

Supplemental Keywords:

photocatalysis, fluidization, adsorption, water treatment,

Progress and Final Reports:

  • 2011
  • 2012
  • Final