9.8.3 Short description
Nanosized metal oxide halogen adducts have been reported in the literature for high surface reactivity due to their unique surface morphology. These can be used against vegetative cells and viruses. These adducts in three nanosized metal oxides of aluminium, titanium and cerium have been mentioned for applications in decontamination and disinfection. A comparative analysis of the three oxides produced varying degree of results. The macrocrystalline counterparts of the same oxides did not produce a result .
Nanocrystals of magnesium oxide have been reported in the literature to absorb organophosphorus compounds. The chemisorption has been demonstrated at room temperature. The high surface area and high surface reactivity make this material suitable for decontamination of chemical warfare agents. The advantage offered by nanocrystalline magnesium oxide over activated charcoal is that it is much faster, and organophosphorus compounds are destructively absorbed while in activated carbon they are only phsisorbed . It has also been reported in the literature that nanoscale powders of magnesium and calcium oxides possess antimicrobial properties. These nanocrystalline forms carry active halogens. Vegetative cells of Escherichia coli, Bacillus cereus, or Bacillus globigii were reported to be decontaminated within a few minutes and spores of spores of Bacillus within several hours. These formulations also decontaminated water carrying Escherichia coli, Bacillus cereus, or Bacillus globigii within minutes . Nanoscale Corporation has been reported to be commercialising a chemical hazard system that combines magnesium oxide and photocatalytic titanium dioxide nanoparticles. The system has been demonstrated to neutralise 99.9% of nerve gas VX within 10 minutes .
Bacillus anthracis attacks and Escherichia coli contamination of produce has made it necessary for the development of a decontamination method that does not rely on time consuming cell culture development. Magnetic glyconanparticles have been considered advantageous due to the pace, high acquisition of pathogens due high surface to volume ratio and due to its non-destructive nature. The functionalization of silica coated nanoparticles, was done with triazole linker in the experimental investigation. High capture and removal efficiency for bacteria were demonstrated with the carbohydrate coated magnetic glyconanoparticles .
Nanocrystalline zeolite surfaces have been researched for the absorption, desorption and thermal oxidation of mustard gas stimulant, 2-chloro-ethyl ethyl sulphide. The research compares the nanocrystalline zeolites, ZSM-5 (Si/Al~20) and silicalite -1 (purely siliceous form) for decontamination of chemical warfare agents. It was experimentally demonstrated that the ZSM-5 form was more reactive than the silicalite form due to a higher surface area. The absorption was suggested to take place both on the external surface and on the internal. It was shown that chemical agent was stored in a stable state in the zeolite until destruction .
Experimental research has been conducted to analyse the reaction of nanocrystalline NaY with dimethyl methylphosphonate (DMMP), a nerve gas stimulant. Nanocrystalline NaY with a crystal size of approximately 30nm were used investigate the adsorption and thermal reaction. The reaction and products were studied with FTIR and solid state NMR spectroscopy. Successful decomposition of the stimulant was demonstrated, and the reactivity per gram of the zeolite was reported to be similar to other studies conducted on metal oxides such as magnesium, aluminium and titanium .
The benefits of using titanium dioxide as a photo catalyst and for decontamination of environment pollutant are that TiO2 is inexpensive, non-toxic and biocompatible [185, 186]. The processing of nano-sized titanium dioxide was reported in the literature to have been produced by sol-gel processing at temperatures of less than 100 degree centigrade. The thin titanium dioxide film constituted by a of particle size in the range of 3 -5 nm adhere strongly to the substrate and are photoactive. The research reported high photo catalytic efficiency in decomposing the stimulant methylene blue and heptane extracted bitumen fraction. The titanium dioxide while decomposing environmental pollutant did not promote the degradation of fibres . Nano titanium dioxide particles loaded on to activated carbon fibres have been studied in the literature for air purification. The experimental study examined the photo degradation efficiency of formaldehyde gas. The research showed excellent decontamination effect, by the photo catalytic action of titanium dioxide and absorption of activated carbon fibers. The research also investigated parameter such as concentration of nano-titanium dioxide, ratio of nano-titanium dioxide to activated carbon fibre, drying temperature and time . Materials coated with doped photo catalysts have been reported to degrade solute toxic substances such as chlorophenol and azo dyes. They can also degrade harmful gases such as acetaldehyde, benzene, and carbon monoxide in diffuse daylight within closed spaces .
Research and development in photocatalytic nanowires has been reported in the literature. Free standing membranes produced from titanium dioxide nanowire have been grown through a hydrothermal heating process. These membranes give a paper like appearance and are highly chemically inert, robust and can be heated to high temperatures. These can be potentially also used as a filtration membrane in gas masks allowing oxygen but blocking toxic gases. The technology is waiting to be commercialised by the University of Arkansas researchers .
CoOx-doped silica xerogels with high surface area have been reported in the literature for decontamination of acetaldehyde gas. The xerogel with maximum pore size of 3 nm show high catalytic activity. Carbon dioxide and traces of methane are produced as a result of air oxidation of acetaldehyde .
Nanoporous keratin fibers have been reported in the literature for removing heavy metal from solution. Keratin fibres are considered suitable due to their stability over a wide range of pH, toughness of the structure and high surface area. A multi-fold increase in metal uptake by the nano-porous keratin fibres was reported on alkaline ultrasonic treatment. The resulted indicated high uptake and reusability of keratin as a biosorbent .
The development of a fibrous membrane has been mentioned in the literature for removing particulates from liquid. Polyvinylidene fluoride nanofibers were electrospun into membranes for this application. The structural properties were related to membrane separation properties and its performance. The membranes were reported to be successful in separating 90% of the polystyrene particles from the solution. This application has potential applications in pre-treatment to minimise fouling and contamination .
Permeable reactive barriers have been mentioned in the literature for the remediation of ground water. Permeable reactive barriers development investigation presents methods that rely on injection and deposition of nano sized iron sulphide particles. The chemical conditions necessary for optimum performance were reported to be moderately alkaline to establish optimal coverage of iron sulphide in sand .
Nanoporous membranes have been developed using stable nickel based super alloys by researchers in Germany. The nanoporous mechanical membranes offer high structural integrity, porosity of between 30-70%, thermal and electrical conductivity and weldability. Such membranes are suitable for applications filtering bacterial spores and dust from respiratory air and gas separation. These are advantageous as they can be thermally sterilized. Design and development challenges need to be overcome for such membranes can be cost effectively used with reproducible quality .
Nanoceramic membranes with a mesoporous sponge structure have been developed through self assembly of monolayers. The nanosponge is produced from mesoporous silicon dioxide ceramics. The average pore size of these ceramics is 6nm and is known to remove toxins from water more effectively than activated carbon fibers. The pores are filled with the self assembly layer. Mercury is decontaminated using mercapton molecules while chelating ligands have been reported to remove chromates. The investigation conducted by Pacific National Laboratory reported to have achieved 99.9% decontamination within 5 minutes. Potential application for the technology has also been mentioned for radio nucleotides and for non-fluid medium .
Water borne pathogens are an important cause of infections . The most commonly known pathogens are Legionella pneumophila, Pseudomonas aeruginosa and moulds  Point of use filters have been mentioned in the literature as a means of providing pathogen free water [195,196]. This is expected to reduce infections in transmission of pathogens through water used in washing hands and rinsing wounds in emergency wards . Filters with inner coatings of nanocrystalline silver have been reported in the literature for decontamination of water. The research on the functionality lifetime retention of the filtering efficiency of pathogens recommended that filters should be changed every 4 weeks in high risk areas and every 8 weeks in moderate risk areas .
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Tags: nano metal oxides, nanocrystals, magnesium oxide, magnetic glyconanoparticles, nanocrystalline zeolites, photocatalytic titanium dioxide, silica xerogel, nanoporus keratin fibre, nanofibres, iron sulphide