Handi Yin,Zhiguo Hao,Jihua Zhao,Peizhu Zheng,Weiguo Shen
The kinetics of the Diels–Alder (D–A) reactions of N-ethylmaleimide with 2,3-dimethyl-1,3-butadiene and of 9,10-dimethyl-anthracene with diethyl maleate in two critical binary solutions n -tetradecane + dimethyl carbonate and n -nonane + diethyl maleate have been studied by the three-wavelength UV-spectrophotometry. It was found that neither speeding up nor slowing down effect for the first reaction was observed, which obeyed the Griffiths–Wheeler rule; while a very weak slowing down effect was detected for the second reaction, but significantly weaker as compared with the prediction by the Griffiths–Wheeler rule. It was attributed to that only less than 0.002% of diethyl maleate changed to the products during the reaction, hence the concentration of diethyl maleate may be considered as a fixed thermodynamic density in the critical reaction system, resulting in no thermodynamic slowing down being detected.
Rates of SN1 hydrolysis reactions for 2-chloro-2-methylbutane in the critical solution of isobutyric acid + water and for 2-bromo-2-methylpropane in the critical solution of triethylamine + water in the one-phase region and at various temperatures have been determined respectively by conductance measurements. It was found that the reaction rates at different temperatures for those two SN1 reactions were well described by the Arrhenius equation in the noncritical region, whereas near the critical points the critical slowing down was clearly detected. These results are inconsistent with a previous report in the literature ( J. Phys. Chem. A 2003, 107, 8435−8443). Reanalyzing the literature data, we found that if an Arrhenius equation appropriate to either the one-phase region or the two-phase region being examined was used as the background, a critical slowing down rather than a speeding up was detected for the reaction in both the one-phase region and the two-phase region. The experimental data from different sources were fitted with a simplified crossover formalism characterizing the critical effect on the reactions to determine the critical slowing down exponents, which were found to be about 0.04, showing that only a dynamic critical slowing down could be detected for these reaction systems. This phenomenon was attributed to the fact that the SN1 hydrolysis reaction is neither a first-order nor a pseudo-first-order reaction in the reverse direction and the kinetic measurements were carried out in a region quite far from the equilibrium of the reactions.
Lang Liu,Ying Jing,Tielin Du,Xinzheng Li,Jiasheng Song
In this study, zeolite beta nanoparticles were incorporated into an interfacial polymerization procedure for the fabrication of thin film nanocomposites (TFNs). The successful introduction of zeolite beta into the polyamide (PA) selective layer was confirmed by surface attenuated total reflection infrared spectroscopy (ATR-FTIR), and x-ray photoelectron spectroscopy (XPS). The introduction of porous structured zeolite beta improved the water flux and rejection rate of the TFN membrane compared to the PA thin film composite (TFC) membrane. A quantitative performance coefficient is further proposed in this work, comprehensively considering the flux and rejection rate to evaluate the performance of TFNs. For five salt solutions, we found that the TFN0.3 membrane with 0.3 wt% of zeolite particles had a high coefficient of performance. With the help of zeolite particles, the TFN0.3 membrane achieved a high flux of 92.53 L/(m 2 ·h) under an operating pressure of 5 bar. For ion separation from binary solutions, the TFN0.2 membrane with 0.2 wt% zeolite content was a better choice for a wide range of binary mixtures, which is because the addition of zeolite beta resulted in smaller pore sizes, the strongest zeta potential, and the thickest thickness (scanning electron microscope, SEM determined) of the TFN0.2 membrane. All these factors contribute to the selectivity of the TFN0.2 membrane. Our study provides an efficient and cost-effective method to simultaneously improve the permeability and rejection of nanofiltration membranes, facilitating the development of nanofiltration for water recovery.
This study investigated the adsorption characteristics of Cr(VI) and methyl orange (MO) onto polyethyleneimine (PEI) cryogels. The morphology and physicochemical properties of this prepared adsorbent were characterized with various techniques. Its adsorption behaviors towards MO and Cr(VI) were systematically investigated. In single-component systems, PEI cryogels exhibited significant adsorption capacities for Cr(VI) (875 mg/g) and MO (1777 mg/g), respectively. In binary systems, the cryogels demonstrated a stronger affinity for Cr(VI) than for MO. Column adsorption studies in single-component systems explored the effects of bed height, flow rate, and inlet concentration using breakthrough curves, with the modified dose–response model proving effective in describing these curves. Moreover, repeated dynamic adsorption experiments highlighted that the cryogels exhibited exceptional reusability. Results from column adsorption in binary systems indicated that the presence of MO did not significantly affect the adsorption of Cr(VI), while the presence of Cr(VI) enhanced the affinity of the cryogels for MO adsorption. The adsorption mechanism of PEI cryogels towards Cr(VI) primarily involved electrostatic attraction and reduction, whereas for MO, it predominantly entailed electrostatic attraction and hydrogen bonding. These findings collectively emphasize the significant potential of PEI cryogels for treating dyeing wastewater.
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