Junjie Lin

The decoloration and mineralization of azo dye C.I. Acid Red 14 by sonochemical process: rate improvement via Fenton's reactions.

The degradation of azo dye C.I. Acid Red 14 (AR14) was investigated using cast iron in the absence and presence of low frequency ultrasound (59 kHz). The effects of pH, amount of cast iron ([Fe](0)) and initial concentration of AR14 ([dye](0)) on the degradation of AR14 by cast iron combined with low frequency ultrasound had been assessed. The degradation followed the first-order kinetics model. The first-order rate constant of AR14 degradation by cast iron was 7.50 x 10(-2) min(-1) while that by US-cast iron was 2.58 x 10(-1) min(-1). A 3.4-fold increase in the reaction rate was observed in the presence of ultrasound compared with that of absence of ultrasound. This kinetic effect is quantitatively accounted for a simple kinetic model based on the reaction of Fe(II) from cast iron in aqueous solution with sonochemically produced H(2)O(2) (Fentons reaction). This latter effect illustrates a simple way of achieving a substantial improvement in the efficiency of sonochemical degradation reactions. It was found that for azo dye AR14, the rate of color decay was the first order with respect to the visible absorption of the dye. The destruction of the naphthalene rings in azo dyes was slower than that of color. A significant mineralization of AR14 was observed.

Effect of zinc incorporation manner on a Cu–ZnO/Al2O3 glycerol hydrogenation catalyst

A systematic study was undertaken to investigate the effects of zinc incorporation manner on the textural properties, bulk and surface phase compositions, reduction behaviors, and surface acidity of a copper based glycerol hydrogenation catalyst. The catalyst samples were characterized by N2 physisorption, X-ray photoelectron spectroscopy (XPS), X-ray diffraction, transmission electron microscopy, air thermal gravimetric analysis (air-TGA), H2 thermal gravimetric analysis (H2-TGA), and NH3 temperature-programmed desorption. The glycerol hydrogenation performance of the catalysts was studied in a fixed-bed reactor. The characterization results indicated that the zinc promoter incorporated by using the co-precipitation method could improve the dispersion of copper oxide, and decrease the particle size of the copper oxide. The zinc incorporated with the impregnation method is enriched on the catalyst surface. The catalyst prepared by adding zinc using the co-precipitation method provides higher glycerol conversion and 1,2-propanediol selectivity, and lower selectivity to acetol.

Total nitrogen and pH-controlled chemical speciation, bioavailability and ecological risk from Cd, Cr, Cu, Pb and Zn in the water level-fluctuating zone sediments of the Three Gorges Reservoir

Abstract We investigated the distribution and chemical speciation of Cd, Cr, Cu, Pb and Zn in the water level-fluctuating (WLF) zone of the main stream (MS) and tributaries (ZX and MX) of the Three Gorges Reservoir. We evaluated the ecological risk and pollution level from heavy metals based on the Potential Ecological Risk Index (RI), Risk Assessment Code (RAC), and Ratio of Secondary Phase and Primary Phase (RSP). Our results indicated that the total and bio-available heavy metal contents were higher in the tributaries than in the MS. Moderate pollution from Cd and light pollution from Pb were observed both at the MS and ZX sites, whereas the MX site exhibited a pattern of heavy Cd pollution and light Cr and Pb pollution. In our study area, the results indicated that Cd exhibited a higher ecological risk than did the other heavy metals. Finally, the pH and nitrogen content of sediments may play a key role in controlling the amount of heavy metal bioavailability, further inducing a higher potential ecological risk.

Mobility and potential risk of sediment-associated heavy metal fractions under continuous drought-rewetting cycles

Ecological decline in the water level fluctuating (WLF) zone of the Three Gorges Reservoir (TGR) has been well established over the past decades. However, the effect of heavy metal fractions present in the sediment and their potential ecological risk under the anti-seasonal hydrological regime are still unclear. The Pengxi River is a tributary of the Yangtze River and it has a typical annual water level fluctuation ranging from 145 to 175m above sea level. The current study examined heavy metal fractions in sediments containing Cr, Cd, Cu, Pb and Mn collected along the WLF zone using the Tessier sequential extraction scheme. The total organic carbon (TC), total nitrogen (TN), carbon/nitrogen ratio (C/N), pH, particle size composition and content of nitrate (NO3--N), and ammonium (NH4+-N) differed dramatically among the sampled altitudes and depths and was significantly correlated with the flooding time of the WLF zone. At lower altitudes of the WLF zone, the amounts of the exchangeable (EXC), carbonate-bound (CA) and total heavy metal contents of the surface sediment were much higher compared to those of higher altitudes of the WLF zone. The risk assessment code (RAC) for Cd and Mn showed an opposite trend to that of Cr, Cu, and Pb and mainly depended on the organic matter-bound fraction (OM). The modified RAC (mRAC) indicated a very high potential adverse effect for the whole WLF zone, although the risk value was much lower at the lower altitudes and upper depths of the WLF zone. Our results showed that the positive response of the loosely bound fractions (LOS) of heavy metals to the drought-rewetting (DRW) process minimizes the risk of heavy metals in the WLF zone sediment.

Application of Combustion Module Coupled with Cavity Ring-Down Spectroscopy for Simultaneous Measurement of SOC and δ13C-SOC

Quantifying the decomposition of soil organic carbon (SOC) fractions under climate change is essential to predict carbon-climate feedbacks. The accuracy and utility of a combustion module coupled with cavity ring-down spectroscopy (CM-CRDS) system were assessed for simultaneously determining SOC and δ13C-SOC. Using a range of standard materials as well as soil samples, we compared the results of the CM-CRDS system with those from other systems for determining C content and δ13C value. The CM-CRDS system can determine a vast range of δ13C values from −7.639‰ to −34.318‰. The δ13C values measured at C content > 0.2 mg C, corresponding to 1000 ppmv of CO2, were relatively stable. However, below a content of 0.2 mg C, the δ13C values appeared unsteady and seemed to be affected by background signal. We found that, with the increase of C content, the recovery rates (RRs) for soil samples also increased. On the contrary, the RRs for inorganic materials were much lower than organic material and soil samples. Overall, the CM-CRDS system provides a valid alternative method to determine SOC and δ13C-SOC for a sample simultaneously.

Effect of coupling process of wetting-drying cycles and seasonal temperature increasing on sediment nitrogen minerization in the water level fluctuating zone

To reveal the effect of coupling process of wetting-drying and seasonal temperature on sediment nitrogen (N) minerization, surface sediment samples were collected from the water level fluctuating zone(WLFZ) of Pengxi River crossing two hydrological sections. The sediment samples were incubated under drying and submerging conditions at the controlled temperature. The result showed that NO3--N and sand% in the sediment of higher altitude of water level (170 m) were higher than those in low altitudes (150 and 160 m), whereas contents of TN, NH4+-N and clay% and silt% in low altitudes were much higher. Generally, Net N mineralization rate and cumulation were lower in higher altitude of water level during the drying period and submerging period. The ammonification rate decreased rapidly at the initial stage of incubation (0-7 d), and then had no obvious change, and no significant differences among altitudes was observed. The nitrification rate at low altitude decreased with incubation time, while it had only a little change at higher altitude; The nitrification contributed a higher fraction of net N mineralization than ammonification. Net N mineralization rate and its cumulation were significantly higher in the drying period than in the submerging period, while net N mineralization rate decreased with incubation time at all altitudes. Net N mineralization cumulation tended to rise first and then declined at all altitudes of the drying period, whereas it was continuously decreasing at the low water level altitude during the submerging period. Net N nitrogen mineralization rate of the drying period was positively correlate to both the sediment organic matter content and its C:N ratio, while it showed a negative correlation in the submerging period(P<0.001). Net N mineralization was sensitive to temperature increase (Q10>1) in the drying period, while it was insensitive during the submerging period of low altitude (Q10<1). Thus, the impact of temperature on Net N mineralization was relatively low in submerging period of winter and N was accumulated with low releasing rate. In contrast to winter, summer exhibited warmer and drying period, this two factors would lead to higher N mineralization rate and further induce the potential risk of eutrophication as N releasing into water body.

Effects of DOM on the Migration of Cr (VI) in Soils

Dissolved organic matter is an important and active component in both terrestrial and aquatic ecosystem. It has become a hotspot in environment science, with active functional groups such as carboxyl, hydroxyl, amino that can influence adsorption and migration of heavy metal contaminants in soil system. Through soil column leaching experiment the article demonstrates that Cr (VI) is dominated by physical adsorption in soils. By using DOM eluent and distilled water to leach at different temperatures in soil, this article shows that release ability of Cr increases with temperature rising, while its deposition capacity increases with temperature decreasing in Water Level Fluctuating Zone. Combined with Gibbs theory, Cr (VI) may take complexation reaction with DOM in soil medium. Thus, new substances appear under the proof of XRD graph.

Analysis of the spatial variation of Pb in the water-level-fluctuating zone of Xiao River based on GIS mapping techniques

The geostatistical method was used for predicting the distribution of the content of Pb and tracing the hotspots in water-level-fluctuating zone. The hotspots of Pb pollution which indicated higher risk than other areas were identified to be mainly distributed in the water-level-fluctuating zone of soils near populated areas along the Xiao River. The mean contents of Pb in soils are more than 2 times greater than the reference values. The anthropogenic factors were the main sources for Pb concentration in soils of the study area, which obviously affect the distribution of Pb.

GIS-based approach to study the spatial distribution of Cr in the water-level-fluctuating zone along the Xiao River

The geo-statistical method was used for predicting the distribution of the content of Chrome (Cr) and tracing the hotspots in water-level-fluctuating zone. The hotspots of Cr pollution which indicated higher risk than other areas were identified to be mainly distributed in the water-level-fluctuating zone of soils near populated areas along the Xiao River. The mean contents of Cr in soils are more than 2 times greater than the reference values. The anthropogenic factors are the main sources for Cr concentration in soils of the study area, which obviously affect the distribution of Cr.