T. Pradeep, Department of Chemistry and Sophisticated Analytical Instrument Facility, Indian Institute of Technology Madras, India
Water is one of the essential enablers of life on earth. But pure water is not available to a large fraction of the population of the planet. While availability is an issue, contamination is another major concern which threatens the survival of many. Intensive farming, rapid industrialization and increasingly sophisticated lifestyles have added artificial chemicals into the water bodies. While pesticide residues in ground waters were unexpected years ago as soil was thought to act as a filter, it is an established fact that even drinking water is contaminated with them in many parts of the world. Pesticide residues measured in drinking water and soft drinks in India far exceed the acceptable limits. Although these levels are significant vis-à-vis the permissible limits, the concentrations are low in comparison to those of commonly encountered chemicals and the purification technologies have to be efficient for them to be removed at affordable cost. In addition, the kinetics of the processes has to be such that a single encounter event with the filter medium must remove them effectively. As the affected populations may be at remote locations, inaccessible to piped supply, such methodologies have to be used also for point-of-use water purification applications. Significant progress has been made to utilize the chemistry of nanomaterials for water purification.
This talk outlines the recent efforts in the use of nanotechnology for providing clean water at affordable cost. This author has used noble metal nanoparticle based chemistry extensively for drinking water purification for three major types of contaminants: halogenated organics including pesticides, heavy metals and microorganisms. Recent efforts for the removal, as well as ultralow concentration detection of such species, using noble metal nanoparticles are summarized.
Important challenges during the commercialization of nano-based products are highlighted through a case study of pesticide removal using noble metal nanoparticles. Recent efforts in drinking water purification using other forms of nanomaterials are also summarized. The talk will touch upon recent investigations on the issue of nanotoxicity and its implications for the future. Our efforts to commercialize such technologies and the need to develop partnerships will be mentioned.
1. T. Pradeep and Anshup, Noble metal nanoparticles for water purification: A critical review, Thin Solid Films (2009) ASAP.
2. T. Pradeep and Anshup, Detection and extraction of pesticides from drinking water using nanotechnologies, in Nanotechnology Applications for Clean Water, N. Savage, M. Diallo, J. Duncan, A. Street and R. Sustich (Ed.) William Adrew, Norwich, New York, 2009.
Ralf Dillert, Institut für Technische Chemie, Leibniz Universität Hannover, Germany
Photocatalysis using semiconductor particles has found increasing interest to solve global pollution problems. Compared to other semiconductor photocatalysts, TiO2 has so far been shown to be the most promising material used for both fundamental research and practical applications because it is highly photoreactive, cheap, non-toxic, chemically and biologically inert, and photostable. The artificial generation of photons required for the detoxification of polluted water is the most important source of costs during the operation of photocatalytic water or air treatment plants. This suggests using the sun as an economically and ecologically sensible light source. Thus Solar Photocatalysis has become an important issue of research and development during the past 20 years. With a typical UV-flux near the surface of the earth of 20 to 30 Wm-2 the sun puts 0.2 to 0.3 mol photons m-2h-1 in the 300 to 400 nm range at the process disposal. Principally, these photons are suitable for destroying pollutants present in water, air, or on photocatalytically coated surfaces. The present lecture will present an overview of the authors’ laboratory activities in Solar Photocatalytic Wastewater Treatment.
The properties and requirements for efficient photocatalyst materials will be discussed. A few representative model compounds have been selected to illustrate the major reaction pathways in photocatalytic degradation processes. Crucial reaction parameters such as pH, temperature, solute concentration and light intensity, are given together with current theoretical models to explain their effects on the overall process efficiency.
In recent years several reactors for the solar photocatalytic water treatment have been developed and tested. The four most frequently used reactor concepts are presented and several examples for the treatment of real wastewater are shown together with some initial economic considerations. In particular, the Thin Film Fixed Bed Reactor (TFFBR), the Double Skin Sheet Reactor (DSSR), the Compound Parabolic Concentrating Reactor (CPCR), and the Aerated Cascade Photoreactor (ACP) will be described in detail. Pilot Plants employing these reactor concepts have meanwhile been built and tested by various research teams, hence, a brief overview concerning the first experiences with these installations will be given.
1. R. Dillert, A. E. Cassano, R. Goslich, D. Bahnemann, “Large Scale Studies in Solar Catalytic Wastewater Treatment”, Catalysis Today 54 (1999) 267-282
2. D. Bahnemann, “Photocatalytic Water Treatment: Solar Energy Applications”, Solar Energy 77 (2004) 445-459
Pilar Fernández Ibáñez, Plataforma Solar de Almería, CIEMAT, Spain
During the past years there has been tremendous research and development in the area of photocatalysis. One of the major applications of this technology is the degradation of organic pollutants in water by what are then called Advanced Oxidation Processes (AOP). This conference reviews the use of sunlight to produce the •OH radicals. The systems necessary for performing solar photocatalysis will be described. Most of the research related to solar photocatalytic degradation of water contaminants carried out during recent years in Plataforma Solar de Almería facilities, and how it could significantly contribute to the treatment of very persistent toxic compounds will be summarised. Various solar reactors for photocatalytic water treatment based mainly on non-concentrating collectors erected during the last few years will be also described in detail. The use of the solar photocatalytic processes (TiO2) to inactivate microorganisms present in water will be reviewed, placing special emphasis on some experimental systems erected to optimize this disinfecting technique. Recent experiences on solar photocatalytic and solar-only disinfection of water done in Plataforma Solar de Almería will be shown in this speech.
Alexander Orlov, Materials Science and Engineering, State University of New York at Stony Brook, USA
Combining solar light with photocatalysts can destroy a variety of dangerous pollutants in air and water. Depositing the known photocatalytic materials on nanostructured support, using nanoparticles to modify the activity of semiconductors, doping and changing the particle size of the catalysts are the strategies we have employed to enhance the activity of photocatalysts. Modifying the traditional catalysts with metal nanoparticles can lead to unprecedented increase in activity. We have deposited the noble metal nanoparticles on conventional TiO2 based photocatalyts. The optimum metal loading corresponded to a mean particle size of ≤ 3 nm at which point it may no longer be metallic. Such catalysts have exhibited a threefold rate enhancement of MTBE degradation compared to unmodified TiO2. These materials have also been very active towards a degradation of 4-chlorophenol, exhibiting twofold rate enhancement.
We have also explored the unusual properties of high surface area materials, such as mesoporous molecular sieves, for environmental degradation of 4-chlorophenol. We have used several methods of post-synthesis modification of the mesoporous molecular sieve with titanium: impregnation, grafting and modification with colloidal titania. The resulting materials were characterized various spectroscopic techniques. All modified materials have showed a significant activity towards the degradation of 4-chlorophenol.
Finally, we have explored the strategies of shifting the activity of catalysts into visible region. The advantage of visible light active as compared to UV light active materials is much more efficient energy utilization, as the solar spectrum contains only a small UV component. We have developed various photocatalytic materials, more active than the conventional materials under both UV and visible light. Based on theoretical calculations and model system studies we have addressed the issues of reproducibility and activity of N-doped, B-doped and B,N-codoped catalysts.
Patrick SM Dunlop, Nanotechnology and Integrated Bioengineering Centre (NIBEC), University of Ulster, Northern Ireland
The use of titanium dioxide photocatalysis for environmental remediation of air and water is well documented and explored. Photocatalysis research at the University of Ulster has been ongoing for several years with particular emphasis on water treatment applications utilising immobilised nanoparticle films. Significant research has been carried out with regards the degradation of organic pollutants in water using a range of titanium dioxide powder films, including the research standard Degussa P25. Recent attention has been focused on the development of novel photocatalytic nanoparticles which offer beneficial properties based upon the increased surface area available redox chemistry.
This presentation will focus on the photocatalytic research undertaken at the University of Ulster to remove persistent organic pollutants (POP’s) and microorganisms from drinking water sources. POP’s present a significant threat to human health and the environment due to their tendency to bio-accumulate in the tissues of living organisms and progress through the food chain. Many of these pollutants have also been reported to have endocrine disrupting capabilities. Photocatalysis using immobilised titania nanoparticles has been shown to be effective for the degradation of pesticides and endocrine disrupting chemicals. Chlorine resistant organisms also represent a significant problem to the drinking water industry. Photocatalysis has again shown promise towards disinfection of microorganisms including Clostridium spores and Cryptosporidium oocysts. Photocatalytic disinfection using solar radiation shows particular promise in relation to water purification in developing regions. Materials research into the production, characterisation and application of novel photocatalytic nanorods and nanotubes will also be discussed.
Marc A. Anderson, Environmental Chemistry and Technology Program, University of Wisconsin – Madison, USA
Capacitive Deionization (CD) or sometimes referred to as electro-sorption is a low pressure process of deionization that can directly compete with membrane or distillation as a means to deliver waters free of ions at reduced cost and operating expense. This process operates by sequestering ions near charged surfaces in the electrical double layer. A schematic pictorial of how this process works is shown in Figure 1. A solution of ions flows through a highly porous conducting pair of electrodes and the anions or other negatively charged species are removed at anode while the cations or positively charged species are removed at the anode.
This process is more efficient and uses less energy than either Reverse Osmosis (RO) or Multi Stage Flash Distillation (MFD), the two most used methods of desalination in the world today. Furthermore, because ions are stored at the interface of a charged surface this device is actually capable of storing its own energy. It thus is energy efficient. This process is 10 years old and in its early stages of adoption. Using new nanoporous materials that are 30-60% more efficient, and a novel method of regeneration, we have shown we can greatly improve this capacitive deionization making it even more competitive with RO and CFD.
In comparison to present desalination techniques these systems use low voltage and low pressure. In addition, they are not subject to as much fouling as RO is, thereby reducing the cost of cleaning. In summary, capital and operating cost are expected to be significantly lower than RO and MFD technologies.
We hope that in the not too distant future our novel method of capacitive deionization using nanoporous oxide materials will become cost competitive with conventional desalination systems and present some interesting alternatives for water treatment.
Nanofiltration and Adsorption for Water Treatment – The Need of Nanotechnologies
Jean-Yves BOTTERO* ; Jérôme ROSE* ; Mélanie AUFFAN& ; Matthew HOTZE* ; Armand MASION* ; Jérôme LABILLE* ; Mark-Robert WIESNER&
* CEREGE UMR 6635 CNRS-Aix-Marseille Université. Europole de l’Arbois BP 80 13545 Aix-en-Provence France. International Consortium for Implications of Nanotechnology (CNRS-CEA) & Center for the Environmental Implications of NanoTechnology (CEINT). Pratt School of Engineering. Nicholas School of the Environment. Duke University. Box 90287. 120 Hudson Hall . Durham, NC 27708-0287. International Consortium for Implications of Nanotechnology (CNRS-CEA)
In the environmental technology industry alone, nanomatériaux will enable new means of reducing the production of industrial wastes, using resources more sparingly, remediating industrial contamination, providing potable water, and improving the efficiency of energy production. Three new kinds of nanotechnology materials that should be developped in the future : Membranes, Oxidants, Adsorbents . Nanoscale control of membrane architecture may yield membranes of greater selectivity and lower cost in water treatment. Fullerene-basded oxidant nanomatériaux such as C60 have a high electron affinity and reactivity, and are capable of producing reactive oxygen species such as single oxygen and superoxides. Fullerene might be used in engineered systems to photocatalytically oxidize organic contaminant, or inhibit or inactivate microbes or viruses. In the same way the use of nano zero valence iron (ZVI) to treat in-situ polluted ground water is based on the oxidation of ZVI and réduction of organic pollutants. The high capacity of nanomaghemite or nanomagnetite to (ad)(ab)sorb metals as As, Co….is due to the existence of new adsorbing sites when size is lower than ~20 nm could open a new route for developping new adsorbents.