Browsing by Author "Wang, Po-Yen"
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Item Determination of perchlorate in soil and air samples during fireworks displays in Taiwan and USA(University of Delaware, 2015) Wang, Po-YenPerchlorate is considered an emerging persistent inorganic environmental contaminant. Perchlorate has been suspected of disrupting the thyroid uptake of iodide and subsequently causing the malfunction of metabolic processes. Firework displays are commonly referred to as a source of perchlorate in the environment. There are two types of fireworks displays: Near-ground fireworks or firecrackers and sky fireworks. During the explosion process, fireworks generate large amounts of smoke that is dispersed into the atmosphere, and the residuals of firecrackers or fireworks would further deposit on the ground or in the water. In this study, sample analysis from the near-ground fireworks and firecracker events demonstrate that during the high time of the fireworks event, the concentration of perchlorate increased dramatically in the air. The outdoor air quality was more deteriorate than the indoor air quality during the fireworks events. However, when the events ended after 12 hours, both the anions and cations concentration in the air recovered to the original level. Unlike air samples, the cations and anions concentrations in the soil increased after the fireworks events. Sample analysis from the sky fireworks display also showed the concentration of perchlorate in the air and soil. However, the concentration of perchlorate during the sky fireworks was smaller than during the near-ground fireworks. In addition, the concentration of cations, such as Ba(II), K(I), Na(I), Mg(II) and Sr(II) in the air and soil samples all increased as the concentration of perchlorate increased. The risk of exposure to perchlorate during the near-ground fireworks/firecrackers events is higher than that during the sky fireworks event. It is found that all the age groups, adults, child age of 6-12 and child age of 2-6 were shown to have high hazard index when exposed to perchlorate during the near-ground fireworks events.Item Removal of pechlorate from dilute aqueous solutions: synthesis, characterization and testing of perchlorate selective and permselective membranes and bimetallic catalysts(University of Delaware, 2015) Wang, Po-YenPerchlorate is an emerging inorganic contaminant in the United States. The Environmental Protection Agency (EPA) expects to issue a national primary drinking water regulation (NPDWR) for perchlorate in March 2017. Therefore, methods that are effective in eliminating perchlorate from water are needed. The objective of this study is to synthesize a perchlorate selective and permselective membrane for detection and separation of perchlorate and to integrate electrodialysis and catalytic electrochemical techniques for the simultaneous separation and reduction of perchlorate. First, a highly sensitive polymeric membrane electrode was synthesized for the detection of perchlorate in water. The membrane electrode exhibited favorable selectivity toward perchlorate over interfering anions such as chloride, nitrate, sulfate, and bicarbonate in water and had a response time of ca. 5 s over the perchlorate concentration (activity) range of 10-6 to 10-1 M and a Nernstian slope of 58.5 ± 0.4 mV at room temperature. The potentiometric response of the electrode was pH independent in the range of 3.0 to 11.0 and had a perchlorate detection limit of 7.0 ×10-7 M (or 70 ppb). The polymeric membrane electrode was able to detect perchlorate ion at the sub-micro-molar level under conditions mimicking those of natural water systems. Next, perchlorate permselective membranes were synthesized and characterized in this study. A membrane with a thickness of ~300?m was prepared with polyvinyl chloride (PVC) and quaternary ammonium salts in solvent under room temperature. Among 12 different quaternary ammonium salts, methyltributylammonium chloride (MTBA) showed superior perchlorate permselectivity due to in part to the favorable steric effect of the alkyl chain length. In addition, results from contact angle measurements indicated that modification with quaternary ammonium salts rendered the membranes hydrophobic. Results from Fourier transform infrared (FTIR) spectrum analysis showed that the functional groups responsible for ion exchange were incorporated in the membrane matrix successfully. The surface roughness, averaged pore radius, and ion exchange capacity of the MTBA membrane were 3.23±2.58 (nm), 83.6 (Å), and 0.12 (meq/g), respectively. In the presence of an electric field, about 60% of perchlorate ions were separated from the solution while only less than 9% of other anions, specifically, nitrate, sulfate and bicarbonate passed through the membrane under otherwise identical operation conditions simultaneously. After the membranes were prepared for the separation of perchlorate, catalysts for the reduction of perchlorate were also examined. Monometallic and bimetallic catalysts were prepared for perchlorate reduction in the study. The electrodes were characterized for surface structure and chemical composition using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that with applying the same current and pH in the system, perchlorate reduction efficiency of monometallic-doped electrodes were in the order of Rh>Cu>Ru>Mo>Pd. For bimetallic-doped electrodes, Rh-Cu (75% reduction) was found to be more effective than Rh-Ru (60% reduction). The mass balance of chlorine species (chloride and perchlorate) in the system can be up to 95%. The imbalance part of chlorine species mass would be due to the adsorption of perchlorate by the electrode. The testing results of the catalytic electrochemical technique showed its suitability for reduction of perchlorate. X-ray photoelectron spectroscopy (XPS) analysis of the bimetallic catalyst indicated the presence of metal oxide and elemental metals. X-ray diffraction (XRD) spectra showed the presence of both crystalline and amorphous metallic catalysts. Finally, an integrated process for the separation and reduction of perchlorate from water was constructed. With the perchlorate permselevtive membrane, perchlorate can be exclusively separated and concentrated from water in presence of other anions. Followed by using perchlorate reduction electrodes, perchlorate can be reduced to chloride. A proposed model for perchlorate reduction was developed and successfully used to calculate the rate constants of anions passing through the membranes. Thus, it has been shown that 80% of perchlorate could be separated by MTBA membrane in electrodialysis process and up to 95% of separated perchlorate can be readily reduced to chloride within 6 hours. No other oxyanions of chlorine, such as ClO3-, ClO2- or ClO- was detected as the intermediates during the reduction process. This integrated ED-CECR process can be applied for the removal of low concentrations of perchlorate from drinking water sources.Item The Role of Biochar in Regulating the Carbon, Phosphorus, and Nitrogen Cycles Exemplified by Soil Systems(Sustainability, 2021-05-18) Pan, Shu-Yuan; Dong, Cheng-Di; Su, Jenn-Fang; Wang, Po-Yen; Chen, Chiu-Wen; Chang, Jo-Shu; Kim, Hyunook; Huang, Chin-Pao; Hung, Chang-MaoBiochar is a carbon-rich material prepared from the pyrolysis of biomass under various conditions. Recently, biochar drew great attention due to its promising potential in climate change mitigation, soil amendment, and environmental control. Obviously, biochar can be a beneficial soil amendment in several ways including preventing nutrients loss due to leaching, increasing N and P mineralization, and enabling the microbial mediation of N2O and CO2 emissions. However, there are also conflicting reports on biochar effects, such as water logging and weathering induced change of surface properties that ultimately affects microbial growth and soil fertility. Despite the voluminous reports on soil and biochar properties, few studies have systematically addressed the effects of biochar on the sequestration of carbon, nitrogen, and phosphorus in soils. Information on microbially-mediated transformation of carbon (C), nitrogen (N), and phosphorus (P) species in the soil environment remains relatively uncertain. A systematic documentation of how biochar influences the fate and transport of carbon, phosphorus, and nitrogen in soil is crucial to promoting biochar applications toward environmental sustainability. This report first provides an overview on the adsorption of carbon, phosphorus, and nitrogen species on biochar, particularly in soil systems. Then, the biochar-mediated transformation of organic species, and the transport of carbon, nitrogen, and phosphorus in soil systems are discussed. This review also reports on the weathering process of biochar and implications in the soil environment. Lastly, the current knowledge gaps and priority research directions for the biochar-amended systems in the future are assessed. This review focuses on literatures published in the past decade (2009–2021) on the adsorption, degradation, transport, weathering, and transformation of C, N, and P species in soil systems with respect to biochar applications.