Electrochemical Behaviors of Glucose Oxidase Based on Biocatalytic Deposition of Gold Nanoparticles

Coupling nanotechnology with biocatalysis, a highly sensitive glucose biosensor for the study of electrochemical behaviors of glucose oxidase (GOx) was proposed by using monkshoodvine root–bark like carbon (MLC) as the platform for the biocatalytic deposition of AuNPs. The biosensor showed a linear range from 0.25 to 130 μM with a detection limit of 0.1 μM (S/N = 3) towards glucose and sensitivity of 3010 μA/mM. K value was calculated to be 67.4 μM. Furthermore, the proposed AuNPs/GOx–MLC modified pyrolytic graphite electrode (AuNPs/GOx–MLC/PGE) achieved direct electron transfer of GOx. Γ* was calculated to be 2.79 × 10^?11 mol/cm² and k_s was 1.79 s^?1. It also showed a remarkable electrocatalysis towards glucose.     

原子吸收光谱法测定粉煤灰中氧化钾、氧化钠

采用火焰原子吸收光谱法测定粉煤灰中氧化钾、氧化钠含量。采用氢氟酸-高氯酸混合酸分解样品,以氯化锶消除其他元素的干扰。本方法操作简便、再现性好、灵敏度高,适用于粉煤灰中氧化钾、氧化钠含量的测定。     

分光光度法研究粉煤灰对亚甲基蓝的吸附及其机理研究

以龙岩雁石火电厂粉煤灰对亚甲基蓝进行吸附实验,探讨了改性粉煤灰、粉煤灰用量、吸附时间、温度对亚甲基蓝吸附的影响。当粉煤灰投加量为4g/L,亚甲基蓝浓度15mg/L,常温条件下,在60min左右,亚甲基蓝降解率达到了98%以上。结果表明,利用粉煤灰处理亚甲基蓝,具有处理效果好、简单,经济等特点。利用Freundlich等温式和Langmuir等温式对其吸附行为进行描述,表明粉煤灰易于吸附亚甲基蓝,吸附属于化学吸附;用颗粒内扩散方程和准二级吸附动力学方程对实验数据进行回归分析,更好地描述亚甲基蓝在粉煤灰上的吸附。准二级吸附动力学方程能够反映亚甲基蓝在粉煤灰上的吸附机理,准二级吸附速率常数k2=0.5758g/(mg.min)。本研究为粉煤灰处理印染废水提供了理论依据和实践依据。     

Effects of mechanical stresses around single tube on ash shedding in pulverized coal combustor

In this study, the effects of mechanical stresses on the shedding of ash deposits in a coal-fired boiler were evaluated. We have confirmed that the shedding occurred because of the fracture within the initial deposit layer, which was formed by powdered ash residues. Therefore, assuming that the mechanical stress acting on the initial layer influenced the shedding, the distribution of the tensile stress and shear stresses acting on the initial deposit was calculated on the basis of elastic mechanism. Because the ash deposits were brittle in nature, it was assumed that the initial deposit failed on the basis of the maximum principal stress theory (MPST). The stress values were calculated based on the data for deposit shapes, which were obtained through previous ash deposition experiments on two bituminous coals, one subbituminous coal, and two lignite coals. The fracture strength of the deposit increased with a decrease in the ash fusion temperature. This result indicated that the strength of the deposit increased because of ash coalescence. Moreover, as the MPST, the starting point of fracture was estimated from the position where the principal stress became the largest, and the stress value was used to presume whether the fracture depended on tensile stress or shear stress. The deposit with a narrow adherence region failed because of tensile stress, and the signature of peeling due to tensile stress was observed in the cross-sectional scanning electron microscopy (SEM) image of the deposit after ash shedding. In contrast, the deposit with a wide adherence region failed because of shear stress. Therefore, peeling was not observed in the cross-sectional SEM image of the deposit after ash shedding. The results obtained from the analysis on the basis of the MPST well with the actual behavior of ash shedding.     

Dynamic evolution of impaction and sticking behaviors of fly ash particle in pulverized coal combustion

This paper aims to reveal the mechanisms governing the impaction and sticking dynamics of fly ash particles in pulverized coal combustion. The modeling work is of relevance to experiments in a 25?kW self-sustained down-fired furnace, which provides a sequence of real deposit shapes as varied boundary conditions for CFD simulations. Although the formed ash deposit has a comparable length scale with the probe, it has little effect on the global impaction efficiency of newly-coming particles. However, as the deposit builds up, incident particles impact the deposit and probe at generally larger impact angles and smaller normal velocities despite the almost invariant global impaction efficiency. It results in an enhanced local sticking probability in the center region of the probe, but a decreased one in the lateral regions. The incident kinetic energy of newly sticking particles to the deposit exhibits a converse correlation with their impact angle. The relationship of the averaged local sticking probability as a function of the azimuthal angle of probe is illustrated. Finally, the effect of Reynolds number on global particle impaction efficiency is examined. A universal formula is proposed, which is of importance to bridge lab-scale experiments and practical applications.     

A chromatographic and chemometric study of the bark phenolic compounds of two poplar clones with different resistance toDiscosporium populeum

Summary Reversed-phase high performance liquid chromatography with diode array detection was used to analyze phenolic compounds contained in bark extracts of two different poplar clones known to have different resistance toDiscosporium populeum infection. Statistical treatments both monovariate and multivariate were applied to the results in order to identify regularities useful to discriminate the polar resistance and to check the importance of seasonal and cultivation site related factors. For the two clones examined phenolic compounds showed great discrimination ability not influenced by either sample collection period or cultivation site.     

Some natural aqueous extracts of plants as green inhibitor for carbon steel corrosion in 0.5 M sulfuric acid

The inhibiting impact of natural aqueous extracts of some plants such as curcumin, parsley and cassia bark extracts for the corrosion of carbon steel (C-steel) in 0.5 M H₂SO₄ solution was inspected utilizing some techniques such as galvanostatic and potentiodynamic anodic polarization and weight loss measurements. Outcomes indicated that the percentage inhibition efficiency increases with increasing the concentration of the extract due to its horizontal adsorption on the C-steel surface. The process of adsorption is followed by the Temkin isotherm. These natural extracts acted as pitting corrosion inhibitors by shifting the pitting potential to more noble values. The sequence of inhibition efficiency of the natural extracts decreases in the following order: cassia bark extract > parsley extract > curcumin extract. This arrangement is related to the molecular size of the major components of the three natural extracts used.     

Measurement uncertainty for total ash and acid-insoluble ash determination of Chinese materia medica

The total ash and acid-insoluble ash contents of Chinese materia medica (CMM) have been widely used as one of the indices to illustrate the quality as well as purity of herbal medicines. Such an approach has also been adopted by many official organizations in writing monographs for pharmacopoeia worldwide. In the present study, a full validation on the methodology was conducted with the inclusion of various commonly encountered matrices in herbs, namely, leaf, flower, fruit, stem and root. The practice ensures method suitability for a wider scope of matrix variation in CMM. Moreover, in order to comply with the technical requirement of International Organization of Standardization 17025 quality assurance system, the concept of measurement uncertainty has also been incorporated in the present study. Measurement uncertainties for total ash and acid-insoluble ash contents have been estimated.     

The Utilization of Douglas-Fir Bark for the Production of Oxalic Acid and High Density Carbon Pellets

The production of oxalic acid by the catalytic oxidation of Douglas-fir (Psedotsuga menfiesii (Mirb) Franco) bark and subsequent pyrolysis of the residue to produce high density carbon pellets is discussed. Kinetic rate data are presented for oxalic acid production from Douglasfir bark. A maximum yield of 38 wt% oxalic acid has been obtained in 8 h at 80°C with 62.5 vol% HNO₃ and 0.5 mg V₂O₅/g of bark. Additional oxalic acid can be produced by the conversion of pyrolytic oils and tars (obtained during carbonization of the residue) to increase the total yield to 45 wt%. An economic analysis based on the current cost of oxalic acid indicates the viability of the proposed process.     

Curing Kinetics Of Tannin-Phenol-Formal- dehyde Adhesives As Determined By DSC

Differential scanning calorimetry (DSC) was used to compare the thermal curing of two adhesives suitable for using in the manufacture of exterior-grade plywood boards: a commercial phenol-formaldehyde (PF) resin, and a tannin-phenol-formaldehyde (TPF) resin developed in our laboratory. The experimental curves were well simulated by means of the Model Free Kinetics isoconversional method incorporated in the Mettler-Toledo STAR^e software package. The corresponding kinetic calculations predict that the TPF resin cures faster than the PF resin. This finding implies the possibility that the TPF resin may allow the achievement of higher productivity by permitting the use of shorter press times than with conventional PF resins. This revised version was published online in July 2006 with corrections to the Cover Date.