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nanoscale iron particles were essentially suspended in solution. Therefore slow transport or diffusion of chlorinated methanes to the settled Aldrich iron surfaces may have caused the slow reaction for the commercial grade iron particles. A major advantage of the nanoscale particles for treatment of CT is the low yield of DCM. Yield of DCM was merely 55% with the nanoscale Fe, compared to 70% with the Aldrich iron. Reductions of CT by the nanoscale iron particles also tend to be more complete with higher yields of methane. For example, yield of methane was 41% for CT reaction with nanoscale iron particles, compared to only 23% with the Aldrich iron. This study demonstrated the potential of the nanoscale metal particles for transformation of CT. Combining the effects of larger surface area (~39 times) and higher surface reactivity (~5.3 times), performance of the nanoscale system versus conventional zero-valent iron barrier is expected to be appreciably (-206 times) higher. However, our knowledge on the underlying reaction mechanisms at the metal-solution interface is still primitive at the best. Important questions need to be investigated include: (1) the exact role of palladium for the dechlorination, (2) optimal amount of surface palladium coverage, (3) effects of naturally occurring oxidants (e.g., oxygen) and reductant (e.g., sulfide) on the long term performance of nanoscale iron particles, (4) cause for the slow DCM dechlorination. Clearly, for this technology to be fully optimized for environmental applications, a better understanding of the fundamental chemical mechanism is essential. REFERENCES 1. Wang, C. B. and Zhang, W. 1997. “Nanoscale Metal Particles for Dechlorination of PCE and PCBs,” Environ. Sci. Technol., 31(7):2154-2156. 2. Wang, C. B. and Zhang, W. 1997. “Catalytic Reduction of Chlorinated hydrocarbons by Pd/Fe, Pt/Fe, and Pd/Zn Bimetals,” 15th Meeting of the North American Catalysis Society, May 18-23, 1997, Chicago. 3. Lien, H and Zhang, W. 1998. “Transformation of Chlorinated Ethylenes in Aqueous Solution Using Nanoscale Bimetallic Particles,” submitted to Journal of Environmental Engineering. 4. Johson, T.L., M.M. Scherer, and P.G. Tratnyek. 1996. “Kinetics of halogenated organic compound degradation by iron metal,” Environ. Sci. Technol., 30(8):2634-2640.
DOI link for nanoscale iron particles were essentially suspended in solution. Therefore slow transport or diffusion of chlorinated methanes to the settled Aldrich iron surfaces may have caused the slow reaction for the commercial grade iron particles. A major advantage of the nanoscale particles for treatment of CT is the low yield of DCM. Yield of DCM was merely 55% with the nanoscale Fe, compared to 70% with the Aldrich iron. Reductions of CT by the nanoscale iron particles also tend to be more complete with higher yields of methane. For example, yield of methane was 41% for CT reaction with nanoscale iron particles, compared to only 23% with the Aldrich iron. This study demonstrated the potential of the nanoscale metal particles for transformation of CT. Combining the effects of larger surface area (~39 times) and higher surface reactivity (~5.3 times), performance of the nanoscale system versus conventional zero-valent iron barrier is expected to be appreciably (-206 times) higher. However, our knowledge on the underlying reaction mechanisms at the metal-solution interface is still primitive at the best. Important questions need to be investigated include: (1) the exact role of palladium for the dechlorination, (2) optimal amount of surface palladium coverage, (3) effects of naturally occurring oxidants (e.g., oxygen) and reductant (e.g., sulfide) on the long term performance of nanoscale iron particles, (4) cause for the slow DCM dechlorination. Clearly, for this technology to be fully optimized for environmental applications, a better understanding of the fundamental chemical mechanism is essential. REFERENCES 1. Wang, C. B. and Zhang, W. 1997. “Nanoscale Metal Particles for Dechlorination of PCE and PCBs,” Environ. Sci. Technol., 31(7):2154-2156. 2. Wang, C. B. and Zhang, W. 1997. “Catalytic Reduction of Chlorinated hydrocarbons by Pd/Fe, Pt/Fe, and Pd/Zn Bimetals,” 15th Meeting of the North American Catalysis Society, May 18-23, 1997, Chicago. 3. Lien, H and Zhang, W. 1998. “Transformation of Chlorinated Ethylenes in Aqueous Solution Using Nanoscale Bimetallic Particles,” submitted to Journal of Environmental Engineering. 4. Johson, T.L., M.M. Scherer, and P.G. Tratnyek. 1996. “Kinetics of halogenated organic compound degradation by iron metal,” Environ. Sci. Technol., 30(8):2634-2640.
nanoscale iron particles were essentially suspended in solution. Therefore slow transport or diffusion of chlorinated methanes to the settled Aldrich iron surfaces may have caused the slow reaction for the commercial grade iron particles. A major advantage of the nanoscale particles for treatment of CT is the low yield of DCM. Yield of DCM was merely 55% with the nanoscale Fe, compared to 70% with the Aldrich iron. Reductions of CT by the nanoscale iron particles also tend to be more complete with higher yields of methane. For example, yield of methane was 41% for CT reaction with nanoscale iron particles, compared to only 23% with the Aldrich iron. This study demonstrated the potential of the nanoscale metal particles for transformation of CT. Combining the effects of larger surface area (~39 times) and higher surface reactivity (~5.3 times), performance of the nanoscale system versus conventional zero-valent iron barrier is expected to be appreciably (-206 times) higher. However, our knowledge on the underlying reaction mechanisms at the metal-solution interface is still primitive at the best. Important questions need to be investigated include: (1) the exact role of palladium for the dechlorination, (2) optimal amount of surface palladium coverage, (3) effects of naturally occurring oxidants (e.g., oxygen) and reductant (e.g., sulfide) on the long term performance of nanoscale iron particles, (4) cause for the slow DCM dechlorination. Clearly, for this technology to be fully optimized for environmental applications, a better understanding of the fundamental chemical mechanism is essential. REFERENCES 1. Wang, C. B. and Zhang, W. 1997. “Nanoscale Metal Particles for Dechlorination of PCE and PCBs,” Environ. Sci. Technol., 31(7):2154-2156. 2. Wang, C. B. and Zhang, W. 1997. “Catalytic Reduction of Chlorinated hydrocarbons by Pd/Fe, Pt/Fe, and Pd/Zn Bimetals,” 15th Meeting of the North American Catalysis Society, May 18-23, 1997, Chicago. 3. Lien, H and Zhang, W. 1998. “Transformation of Chlorinated Ethylenes in Aqueous Solution Using Nanoscale Bimetallic Particles,” submitted to Journal of Environmental Engineering. 4. Johson, T.L., M.M. Scherer, and P.G. Tratnyek. 1996. “Kinetics of halogenated organic compound degradation by iron metal,” Environ. Sci. Technol., 30(8):2634-2640.
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ABSTRACT
Io n iz in g rad ia tio n is a n o rm al p a r t o f e v e ry o n e ’s day. E x p o su re to b ac k g ro u n d rad ia tio n o cc u rs th ro u g h several paths. E x p o su re to sun ligh t, and n a tu ra lly o c c u rrin g ra d io a c tiv e m a te ria ls in ro c k and soil, m ed ica l tre a tm e n ts fo r ca n ce r and th y ro id co n d itio n s , and d en ta l x - ra y s1. F o o d and w a te r w e in g est a lso co n ta in s sm all am o u n ts o f n a tu ra l rad io a c tiv e m a te r ia ls1. B a c k g ro u n d rad ia tio n fo rm N o rm a lly O cc u rr in g R a d io a c tiv e M a te r ia ls (N O R M ) fo r an av e rag e p e rso n is e s tim a ted to b e 30 0 m illia re m s p e r y ea r2.
