Biomedical subjects

Da-hui Wang

Publications and source records attributed to Da-hui Wang.

10 recordsLinked to original sources

PubMed2006

Hg(0) absorption in potassium persulfate solution.

The aqueous phase oxidation of gaseous elemental mercury (Hg(0)) by potassium persulfate (KPS) catalyzed by Ag(+) was investigated using a glass bubble column reactor. Concentration of gaseous mercury and potassium persulfate were measured by cold vapor atom absorption (CVAA) and ion chromatograph (IC), respectively. The effects of pH value, concentration of potassium persulfate and silver nitrate (SN), temperature, Hg(0) concentration in the reactor inlet and tertiary butanol (TBA), free radical scavenger, on the removal efficiency of Hg(0) were studied. The results showed that the removal efficiency of Hg(0) increased with increasing concentration of potassium persulfate and silver nitrate, while temperature and TBA were negatively effective. Furthermore, the removal efficiency of Hg(0) was much better in neutral solution than in both acidic and alkaline solution. But the influence of pH was almost eliminated by adding AgNO(3). High Hg(0) concentration has positive effect. The possible reaction mechanism of gaseous mercury was also discussed.

Journal Article↗

PubMed2006

Characterization of on-road CO, HC and NO emissions for petrol vehicle fleet in China city.

Vehicle emissions are a major source of air pollution in urban areas. The impact on urban air quality could be reduced if the trends of vehicle emissions are well understood. In the present study, the real-world emissions of vehicles were measured using a remote sensing system at five sites in Hangzhou, China from February 2004 to August 2005. More than 48000 valid gasoline powered vehicle emissions of carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxide (NO) were measured. The results show that petrol vehicle fleet in Hangzhou has considerably high CO emissions, with the average emission concentration of 2.71%+/-0.02%, while HC and NO emissions are relatively lower, with the average emission concentration of (153.72+/-1.16)x10(-6) and (233.53+/-1.80)x10(-6), respectively. Quintile analysis of both average emission concentration and total amount emissions by model year suggests that in-use emission differences between well maintained and badly maintained vehicles are larger than the age-dependent deterioration of emissions. In addition, relatively new high polluting vehicles are the greatest contributors to fleet emissions with, for example, 46.55% of carbon monoxide fleet emissions being produced by the top quintile high emitting vehicles from model years 2000-2004. Therefore, fleet emissions could be significantly reduced if new highly polluting vehicles were subject to effective emissions testing followed by appropriate remedial action.

Automobiles↗

PubMed2006

Enhanced degradation of carbon tetrachloride by surfactant-modified zero-valent iron.

Sorption of carbon tetrachloride (CT) by zero-valent iron (ZVI) is the rate-limiting step in the degradation of CT, so the sorption capacity of ZVI is of great importance. This experiment was aimed at enhancing the sorption of CT by ZVI and the degradation rate of CT by modification of surfactants. This study showed that ZVI modified by cationic surfactants has favorable synergistic effect on the degradation of CT. The CT degradation rate of ZVI modified by cetyl pyridinium bromide (CPB) was higher than that of the unmodified ZVI by 130%, and the CT degradation rate of ZVI modified by cetyl trimethyl ammonium bromide (CTAB) was higher than that of the unmodified ZVI by 81%. This study also showed that the best degradation effect is obtained at the near critical micelle concentrations (CMC) and that high loaded cationic surfactant does not have good synergistic effect on the degradation due to its hydrophilicity and the block in surface reduction sites. Furthermore degradation of CT by ZVI modified by nonionic surfactant has not positive effect on the degradation as the ionic surfactant and the ZVI modified by anionic surfactant has hardly any obvious effects on the degradation.

Carbon Tetrachloride↗

PubMed2005

Study on US/O3 mechanism in p-chlorophenol decomposition.

Study on the effects of sonolysis, ozonolysis and US/O3 system on the decomposition of p-chlorophenol in aqueous solutions indicated that in the cases of US/O3 system, individual ozonolysis and sonolysis, the decomposition rate of p-chlorophenol reached 78.78%, 56.20%, 2.79% after a 16-min reaction while its CODcr (chemical oxygen demand) removal rate was 97.02%, 62.17%, 3.67% after a 120-min reaction. The decomposition reaction of p-chlorophenol follows pseudo-first-order kinetics. The enhancement factors of p-chlorophenol and its COD(cr) under US/O3 system reached 63% and 237% respectively. The main intermediates during the decomposition include catechol, hydroquinone, p-benzoquinone, phenol, fumaric acid, maleic acid, oxalic acid and formic acid. The decomposition mechanism of p-chlorophenol was also discussed.

Chlorophenols↗

PubMed2005

Enhanced catalytic degradation process of o-nitrochlorobenzene by palladium-catalyzed fe0 particles.

Over Pd/Fe bimetallic catalyst, o-nitrochlorobenzene (o-NCB), at a concentration of 20 mg/L in aqueous solutions, is rapidly converted to o-chloroaniline (o-CAN) first, and then quickly dechlorinated to aniline(AN) and Cl-, without other intermediate reaction products. The aminated and dechlorinated reactions are believed to take place on the surface site of the Pd/Fe. The o-NCB removal efficiency and the next dechlorination rate increase with an increase of bulk loading of palladium and catalysts addition due to the increase of both the surface loading of palladium and the total surface area. These results indicate that reduction, amination and dechlorination of o-NCB by palladium-catalyzed Fe0 particles, can be designed for remediation of contaminated groundwater.

Catalysis↗

PubMed2005

Mechanistic study of ozonation of p-nitrophenol in aqueous solution.

Ozonlysis in the treatment of p-nitrophenol solution was studied in this paper. The results indicated that the decomposition of p-nitrophenol was accelerated as the gas flow rate or pH value increased. When gaseous ozone concentration was 20.11 mg/L and pH was 3, after 24 min reaction, the removal rate of p-nitrophenol reached 73.04%, 86.11%, 91.71% and 95% at the gas flow rate of 32, 40, 48 and 56 ml/min respectively. And when pH was 3, 4, 5, 6, the decomposition rate was 66.38%, 82.09%, 90.46%, 97.50% after a 20 min reaction respectively. It was mainly O3 molecule that took part in the decomposition when pH was 3. The main intermediates during the decomposition include catechol, o-benzoquinone, hydroquinone, p-benzoquinone, phenol, fumaric acid, maleic acid, oxalic acid and formic acid. The decomposition mechanism of p-nitrophenol was also discussed.

Chromatography, High Pressure Liquid↗

PubMed2004

Modeling of mass transfer characteristics of bubble column reactor with surfactant present.

Danckwert's method was used to determine the specific interfacial area, a, and the individual mass transfer coefficient, k(L), during absorption of CO(2) in a bubble column with an anionic surfactant in the carbonate-bicarbonate buffer solution and NaAsO(2) as catalyst, the presence of which decreases the specific interfacial area and the individual mass transfer coefficient. The specific interfacial area and the individual mass transfer coefficient increase with increasing superficial gas velocity. The specific interfacial area decreases whereas the individual mass transfer coefficient increases with increasing temperature. The results of experiments were used to determine the dependence of a, k(L), and k(L)a on the surface tension, the temperature of the absorption phase, and the superficial velocity of the gas. The calculated results from the correlation were found to be within 10% deviation from the actual experimental results.

Journal Article↗

PubMed2004

Catalytic dechlorination of o-chlorophenol by nanoscale Pd/Fe.

Transformation of chlorophenols by nanoscale bimetallic particles represents one of the latest innovative technologies for environmental remediation. Nanoscale Pd/Fe bimetallic particles were synthesized in the laboratory for treatment of o-chlorophenol. Most of the nanoscale particles are in the size range of 20-100 nm. BET specific surface area of the nanoscale Pd/Fe particles is 12.4 m2/g. In comparison, a commercially available Fe powder( < 100 mesh) has a specific surface area of just 0.49 m2/g. Batch experiments demonstrated that the nanoscale Pd/Fe bimetallic particles can effectively dechlorinate o-chlorophenol. Dechlorination efficiency is affected by the mass fraction of Pd in the bimetal, nanoscale Pd/Fe mass concentration and mixing intensity.

Catalysis↗

PubMed2004

[Dechlorination of p-dichlorobenzene by metallic catalytic reduction technology].

Pd/Fe bimetallic catalysts were synthesized by chemical deposition and used to dechlorination treatment of p-DCB. Batch experiments demonstrated that the Pd/Fe bimetallic particles can effectively dechlorinate p-DCB. Dechlorination efficiency accounted for more than 90% at Pd weight ratio (Pd to Fe) 0.02% and metal to solution ratio about 4g/74mL in 90min. Dechlorination ratios were affected by reaction temperature, initial pH, Pd ratio and the addition of Pd/Fe. Chlorobenzene represented stable partially dechlorinated intermediates in the generation of benzene.

Catalysis↗

PubMed2003

2-Chlorophenol oxidation kinetic by photo-assisted Fenton process.

Experimental data are presented to test and validate a kinetic model for the oxidation of 2-chlorophenol wastewater by photo-assisted Fenton process. The data showed that this process had produced good effects under acidic conductions. Up to 90% 2-chlorophenol was removed after 90-minute reaction time with H2O2 of 25% COD(Cr, in), while in UV/H2O2 system only 16.8% 2-chlorophenol was removed after one hour treatment. The optimal pH in this reaction occurred between pH 3.0 and pH 4.0. The reaction kinetics for photo-assisted Fenton process experimented in this research was investigated. Kinetic models were proposed for the treatment of 2-chlorophenol wastewater. The reaction was found to follow the 2nd order. The equations of reaction kinetics are as follows: -d[RH]/dt = K(RH) [RH] [H2O2]0 exp(-K(H2O2) t); -d[COD(Cr)]/dt = K(COD(Cr)) [COD(Cr)] [H2O2]0 exp(-K' t). The prediction of the models was found to be in a good agreement with experimental results, thus confirming the proposed reaction mechanism.

Chlorophenols↗