氢氧直接合成过氧化氢用PdO/γ-Al2O3催化剂过渡金属改性研究

采用等体积浸渍法制得过渡金属改性的系列催化剂MOx-PdO/γ-Al2O3 (M=La、Mn、Ni、Ce).在10℃、常压下考察了过渡金属种类及氧化镧负载量对催化剂MOx-PdO/γ-Al2O3催化氢氧直接合成过氧化氢性能的影响.采用能谱(EDS)、X射线衍射(XRD)、程序升温还原(H2-TPR)等手段对催化剂进行表征分析.结果表明,经过渡金属改性后的MOx-PdO/γ-Al2O3催化剂活性高于未改性的催化剂PdO/γ-Al2O3;以镧为助剂制得的La2O3-PdO/γ-Al2O3(氧化镧质量分数为1％、氧化钯质量分数为2.5％)催化剂性能优于其他过渡金属改性的催化剂,与PdO/γ-AhO3相比,所得过氧化氢的浓度、收率、选择性分别提高了76.54％、76.61％、44.21％.     

Experimental improvement of preparation of acrylic acid‐modified middle deacetylated chitosan and its application in absorbing paraquat

Chitosan with 45% deacetylation (CS45) grafted poly (acrylic acid) (CS45‐g‐PAA) was synthesized and characterized as an adsorbent of paraquat. CS45‐g‐PAA copolymers were prepared using H₂O_2(aq) as an initiator and NH₄OH_(aq) as a promoter. The highest grafting percentage of 44.2% was obtained using the traditional kinetic method. However, a maximum grafting percentage of 52.6% was calculated for the central composite design (CCD). Experimental results based on the reaction conditions that were predicted from the CCD are consistent with theoretical calculations. The grafted copolymer was characterized by FTIR, BET, and SEM. A representative CS45‐g‐PAA copolymer was hydrolyzed to a salt type (CS45‐g‐PANa) and used in the adsorption of paraquat. The adsorption equilibrium data correlate more closely with the Langmuir isotherm than with the Freundlich equation. The maximum adsorption capacity of CS45‐g‐PANa is 396.7 mg/g‐adsorbent. This value clearly exceeds that of Fuller's earth and the activated carbon which is the most commonly used binding agent for paraquat. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Structure and Reactivity of Spruce Mechanical Pulp Lignins Part I. Bleaching and Photoyellowing of in situ Lignins

This paper reports the structural investigation of a series of in situ spruce lignins in wood, thermomechanical pulp (TMP) and the corresponding bleached (BTMP) and photoyellowed (YBTMP) samples. This was achieved by using an original two-step degradative technique, thioacidolysis followed by Raney nickel desulfuration. The determination of thioacidolysis monomeric and dimeric products allowed an estimate of various lignin building units and interunit bonds, respectively. It was observed that the thermomechanical and bleaching treatments did not affect spruce lignin structure to an appreciable extent. On the contrary, the photoyellowing treatment caused marked structural changes in lignin, particularly when run in severe conditions. These changes were essentially a decrease in the amount of β-O-4 and β-1 interunit bonds and a relative increase in catechol units and in vanillin end-groups.     

EVAPORATION FROM SINGLE DROPLETS IMPINGING ON HEATED SURFACES

Thermal behaviour of liquid droplets on a heated solid surface was studied experimentally using metallic/nonmetallic solids of different characteristics and variety of liquids, from distilled water through pure organic solvents and binary mixtures to solutions, suspensions and emulsions. Nearly spherical particles were obtained from solutions and suspensions. Kraft black liquor was used as a model complex suspension with organic and inorganic components. Evaporation rates were measured for single droplets.     

EFFECT OF VIBRATION ON THE DRYING RATE DURING THE FALLING RATE PERIOD

The results of an experimental study on the drying characteristics in vibrated fluidized beds of corn plumule, silica gel and citric acid are presented. Application of vibration was found to enhance the drying rate during the falling rate period. In the optimum range of vibration parameters, the critical moisture content decreased significantly as compared with that in conventional fluidized beds of the same material.     

Effects of saliva contamination on bonding performance of self-etching adhesives

Purpose: This study investigated the effects of saliva contamination on bonding performance of two self-etching adhesives. Materials and Methods: Forty caries-free extracted human third molars’ cusps were cut off to expose mid-coronal dentin surfaces. Two one-step self-etching adhesives and the respective resin composite from the same manufacturer (Adper Easy One?+?Filtek Z350 (3?M ESPE); Clearfil S3 Bond?+?Clearfil Majesty (Kuraray Co.)) were applied onto the dentin surfaces for micro-tensile bond strength (MTBS) test. The dentin surfaces were not contaminated (A), were contaminated with saliva before/after priming (B/C), or they were water-sprayed after saliva contamination occurred before/after priming (D/E). The resin–dentin interfaces were analyzed by scanning electron microscopy. After the two adhesives were polymerized on saliva-contaminated or uncontaminated conditions, they were determined by Fourier transform infrared spectroscopy for degree of conversion (DC), and analyzed by AFM spectroscopy for spatial homogeneity of the adhesives. The data were analyzed using factorial design ANOVA and one-way ANOVA. Results: Compared with control group (A), the saliva contamination after priming significantly reduced both dentin MTBS (p?<?0.05). Thorough water-spraying could significantly improve the MTBS of the saliva-contaminated dentin (p?<?0.05) or completely restore it. Saliva contamination deteriorated the resin–dentin adaptation, DC, and spatial homogeneity of adhesives. Conclusions: Saliva contamination had a negative effect on bonding performance of self-etching adhesives regarding their dentin MTBS, resin–dentin adaptation, DC, and spatial homogeneity. However, the effect of saliva contamination on the dentin MTBS was related to the individual adhesive used and the time point of contamination.     

Selective Deflection and Localization of Flowing Aerosols onto a Substrate

Pulsed airflow cued by the fluorescence spectrum of a particular aerosol can be used to distinguish and deflect particles of biological origin out of an aerosol stream, permitting concentration of these particles for subsequent analysis (Pan et al. 2004 Pan, Y. L., Boutou, V., Bottiger, J. R., Zhang, S. S., Wolf, J. P. and Chang, R. K. 2004. A Puff of Air Sorts Bioaerosols for Pathogen Identification. Aerosol Sci. Technol., 38: 598–602. [CROSSREF][CSA][Taylor & Francis Online], [Web of Science ®] , [Google Scholar]). However, these high velocity pulses of air have an inherent tendency to scatter particles, confounding efforts to concentrate these deflected particles for analysis. The ability to concentrate large numbers of biological particles into a small area on a collection substrate is particularly important for more species-specific techniques such as Raman and FTIR (Fourier Transform Infra-Red) spectroscopy, which require long integration times due to their weak signal strength. In the present work, a simple method is developed for deflecting and localizing particles after classification by a pulsed airflow. The concept is both modeled and experimentally tested. A specially designed funnel is used to localize the scattered particles onto an area of substrate as small as 1 mm in diameter. Computational fluid dynamics simulations were performed to investigate the interaction of the pulsed airflow with the deflected particles and the localizing funnel, in order to gain insight into design parameters and operating conditions that affect the efficiency of this technique. The results show that the combination of pulsed airflow with a localizing funnel effectively deflects and localizes the concentrated bioaerosol onto a small area of substrate or an opening of a microfluidic cell.     

Layer‐by‐layer self‐assembled multilayer films of single‐walled carbon nanotubes and tin disulfide nanoparticles with chitosan for the fabrication of biosensors

In this study, multilayer films containing chitosan, tin disulfide (SnS₂) nanoparticles, and single‐walled carbon nanotubes were prepared on glassy carbon electrodes with the use of a layer‐by‐layer assembly technique. The resulting films were characterized with cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy, and ultraviolet–visible absorption spectroscopy. The results of CV and EIS indicates that the peak currents and charge‐transfer resistance all had linear responses to the number of assembled layers. The multilayer‐film‐modified electrode showed excellent electrocatalytic properties for some species, such as dopamine hydrochloride (DA), ascorbic acid (AA), and uric acid (UA). The well‐separated voltammetric signals of DA, UA, and AA could be obtained on the assembled multilayer‐film‐modified electrode, and the peak‐to‐peak potential separations were 171, 136, and 307 mV for DA–UA, DA–AA, and UA–AA on CV, respectively. These facts showed that the multilayer‐film‐modified electrode could be used as a new sensor for the simultaneous detection of DA and UA in the presence of AA in a real sample. In addition, the multilayer films were stable, selective, and reproducible. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and properties of 4, 4′‐diphenylmethane diisocyanate blocking modified poly(propylene carbonate)

Poly(propylene carbonate) (PPC) is inferior in thermal stability and liable to incur thermal degradation, especially in the existence of residual bimetal catalyst. In this article, PPC containing residual catalyst was end‐capped with 4, 4′‐diphenylmethane diisocyanate (MDI) through melt compounding. The blends were characterized by infrared spectra, melt flow index (MFI), gel permeation chromatography (GPC), gel content measurement, thermogravimetric analysis, scanning electron microscopy, and tensile test. The effect of MDI on thermal stability, molecular weight, and tensile properties of PPC was studied. Thermal degradation kinetics of neat PPC and PPC+MDI blending samples was discussed with Friedman method. MFI, GPC, and gel content measurements showed that mainly end‐capping reaction was carried out on PPC chains when 0.1% of MDI was added. However, as the amount of MDI exceeded to 0.3%, end‐capping, chain‐extension, and crosslinking reactions were synchronously carried out on PPC. Results showed that the end‐capping, chain‐extension, and crosslinking reaction occurring between PPC and MDI could effectively inhibit the unzipping degradation even when the residual catalyst was not removed thoroughly. When the content of MDI reached 1.0%, the initial degradation temperatures (T_‐5%) increased from 176.26°C for neat PPC to 259.56°C. As a result, the processing temperature range and processing time were largely extended, and the heat resistance of PPC was improved remarkably. Meanwhile, the tensile property of the modified PPC was enhanced obviously. It may be due to the fact that the molecular weight and gel content of PPC were increased with the increasing amount of MDI. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013