Guixiang Quan

Adsorption, immobilization, and activity of β-glucosidase on different soil colloids

For a better understanding of enzyme stabilization and the subsequent catalytic process in a soil environment, the adsorption, immobilization, and activity of beta-glucosidase on various soil colloids from a paddy soil were studied. The calculated parameters maximum adsorption capacity (q(0)) for fine soil colloids ranged from 169.6 to 203.7 microg mg(-1), which was higher than coarse soil colloids in the range of 81.0-94.6 microg mg(-1), but the lower adsorption affinity (K(L)) was found on fine soil colloids. The percentages of beta-glucosidase desorbed from external surfaces of the coarse soil colloids (27.6-28.5%) were higher than those from the fine soil colloids (17.5-20.2%). Beta-glucosidase immobilized on the coarse inorganic and organic soil colloids retained 72.4% and 69.8% of activity, respectively, which indicated the facilitated effect of soil organic matter in the inhibition of enzyme activity. The residual activity for the fine soil clay is 79-81%. After 30 days of storage at 40 degrees C the free beta-glucosidase retained 66.2% of its initial activity, whereas the soil colloidal particle-immobilized enzyme retained 77.1-82.4% of its activity. The half-lives of free beta-glucosidase appeared to be 95.9 and 50.4 days at 25 and 40 degrees C. Immobilization of beta-glucosidase on various soil colloids enhanced the thermal stability at all temperatures, and the thermal stability was greatly affected by the affinity between the beta-glucosidase molecules and the surface of soil colloidal particles. Due to the protective effect of supports, soil colloidal particle-immobilized enzymes were less sensitive to pH and temperature changes than free enzymes. Data obtained in this study are helpful for further research on the enzymatic mechanisms in carbon cycling and soil carbon storage.

Kinetic and thermodynamic parameters of β-glucosidase immobilized on various colloidal particles from a paddy soil

To better understanding of enzyme stabilization and the subsequent catalytic process in soil environment, the kinetic and thermodynamic parameters of beta-glucosidase immobilized on different-sized colloidal particles from a paddy soil were studied. Higher adsorption and lower desorption of beta-glucosidase were found on fine soil colloids, which were attributed to their higher surface area and the large content of iron oxides. Immobilization of beta-glucosidase decreased the V(max) values and increased the K(m) values, which indicated that the immobilized enzyme has an apparently lower affinity for its substrate due to structural changes of beta-glucosidase or less accessibility of substrate to the active site of immobilized enzymes. The values of activation energy (E(a)), activation enthalpy (DeltaH(a)) and temperature coefficient (Q(10)) for the immobilized enzymes were smaller than those with free enzyme, implying that the immobilized enzymes are less temperature sensitive. Furthermore, mean values of Q(10) were ranged from 1.32 to 1.50. These results indicated the higher stability of beta-glucosidase after immobilization on various soil colloidal particles.

Degradation of Herbicide Mesotrione in Three Soils with Differing Physicochemical Properties from China.

The movement and fate of herbicides in soils under various environmental factors are important in evaluating their mobility and ecological impact. The effects of sterilization, solarization, and soil physicochemical properties on the degradation of herbicide mesotrione in three soils from China were evaluated using laboratory incubation method, and the degradation kinetics were also simulated using pseudo first-order reaction model. The calculated half-lives () of mesotrione were found to be 3.78- to 5.24-fold increased in sterilized soils than nonsterilized soils, which indicated that the degradation of mesotrione was strongly affected by soil microbial activity. A certain role of promoting degradation effect of natural light was found, and the values appeared to be only 7.90, 15.89, and 25.29 d in the surface of paddy soil, sandy loess, and silt clay loam, respectively. Correlation analysis between the observed first-order reaction rate constant () values and the selected soil properties revealed that the degradation of mesotrione was highly dependent on soil pH value ( > 0.992) and organic matter content ( > 0.932), but less related with clay content (<0.02 mm) with < 0.761 and nonrelated with cation exchange capacity (CEC) ( < 0.164). Data obtained in this study are helpful for further research on the prediction of the movement and fate of mesotrione in soils in limiting its environmental impact.

Effects of chemical oxidation on surface oxygen-containing functional groups and adsorption behavior of biochar

Biochar is a beneficial soil amendment but the changes in its surface properties during the aging process, especially the oxygen-containing functional groups and the associated adsorption behaviors, are not well documented. In this paper, the aged wheat straw biochar was simulated by chemical oxidation with HNO3-H2SO4 and NaOH-H2O2 systems. Characterization results showed that carbon loss and oxygen incorporation ran throughout the aging process. Surface oxygen-containing functional groups were found to be increased in all treated biochars, especially for carboxyl. Much more developed mesopores were observed in aging biochar, specific surface area was increased by 126% for biochar treated with NaOH-H2O2, and 226% for biochar treated with 40% of HNO3-H2SO4. Thermogravimetric analysis showed that the increasing oxygen-containing functional groups led to 14% and 30% mass loss by treating biochar with alkali and acid, respectively. The improved biochar surface through the increase of oxygen-containing functional groups enhanced the cadmium sorption capacity, and the sorption capacity increased by 21.2% in maximum. Roughed surface from oxidation was another reason for increasing cadmium adsorption. Results indicated that the adsorption performance of biochar on pollutant would be changed during aging process along with the changing surface properties.

Adsorption Behaviour of Pymetrozine by Four Kinds of Biochar from Aqueous Solution

A laboratory experiment was performed to investigate the potential of biochar (BC) as an adsorbent for removing pymetrozine from aqueous solution. The adsorption data were well described by Langmuir isotherm, with maximum pymetrozine adsorption capacities of 13.8, 20.6, 11.0 and 18.8 mg g−1 for bush-, wheat straw-, peanut- and corn-derived BC in a single solution at 25 °C, respectively. The functional groups of BCs were –NH (1628.25 cm−1), –OH (3443.78 cm−1), –PO4 (1089.2 cm−1) and –C–Cl (769.23 cm−1), which were responsible for binding pymetrozine. The adsorption capacity of BC was increased by 7.2–106.4% at different solution pH (1, 3, 5 and 7). The removal efficiency increased with the addition of BCs and over 70% pymetrozine removal was observed upon addition of up to 8 g l−1. The rate of pymetrozine adsorption was fast, with 50–80% of the adsorption occurring in the first 120 minutes, followed by a much slower approach to equilibrium. The ΔG° values decreased (increasingly negative) from −165.3% to 235.9% at 298 K compared with 318 K for the adsorption of pymetrozine onto different BCs in a single solution. The study results indicate that plant residue- or agricultural waste-derived BC can act as an effective surface sorbent, but their ability to treat mixed waste streams needs to be carefully evaluated on an individual basis.

Colorimetric Determination of Hypochlorite Based on the Oxidative Leaching of Gold Nanorods

Hypochlorite plays a critical role in killing microorganisms in the water. However, it can also cause cardiovascular diseases, neuron degeneration, and cancer to humans. Although traditional methods feature excellent sensitivity and reliability in detecting hypochlorite, the expensive instruments and strict determination conditions have limited their application in environmental analysis to some extent. Thus, it is necessary and urgent to propose a cheap, facile, and quick analytical assay for hypochlorite. This paper proposes a colorimetric assay for hypochlorite utilizing gold nanorods (AuNRs) as the nanoreactor and color reader. The AuNRs were acquired via a reported seed-mediated method. NaClO with strong oxidation property can cause the etching of gold from the longitudinal tips of AuNRs, which could shorten the aspect ratio of AuNRs, decrease the absorption in the UV–Vis spectrum and also induce the solution color changing from red to pale yellow. Thus, according to the solution color change and the absorbance of longitudinal surface plasmon resonance of AuNRs, we established the calibration curve of NaClO within 0.08 μM to 125 μM (∆Abs = 0.0547 + 0.004 CNaClO, R2 = 0.9631). Compared to traditional method, we obtained the conversion formula between the concentration of residual-chlorine in tap water and the concentration of hypochlorite detected by the proposed colorimetric assay, which is Cresidual-chlorine = 0.24 CNaClO. Finally, the real application of the colorimetric assay in tap water was successfully performed, and the accuracy of the colorimetric method can reach from −6.78% to +8.53%.

Cellulase Activity in Physically Isolated Fractions of a Paddy Soil

Speci¿c location of extracellular enzymes within the soil matrix was related to soil organic matter (SOM) quality and carbon turnover. A physical fractionation procedure was used to investigate whether soil carbon was spatially isolated from degradative enzymes in a paddy soil. In POM fractions of this study, high C concentrations are found because they are derived from inputs of recent plant materials with high C-to-N ratios and low mineral content. Total nitrogen was highest in the clay-sized fraction and lowest in the silt-sized fraction. The C-to-N ratios were decreased with decreasing particle size, lowest in the clay-sized fraction, greatest in the POM fractions, and inter-mediate in the bulk soil and silt-sized fractions. Different distribution trend in physically isolated fractions indicated that there was fundamental difference in the factors determining their location. The absolute activity of carboxymethyl cellulase activity was greatest in coarse POM fractions and generally decreased from the coarse POM fractions to the silt-size fraction, following a decrease of Corg as well as an increase in biostability of the organic material, as indicated by a decrease in the C-to-N ratio.