Adsorptive Removal of Cd,Cu, Ni and Mn from Environmental Samples Using Fe3O4-Zro2@APS Nanocomposite: Kinetic and Equilibrium Isotherm Studies

In this study, Fe₃O₄-ZrO₂ functionalized with 3-aminopropyltriethoxysilane (Fe₃O₄-ZrO₂@APS) nanocomposite was investigated as a nanoadsorbent for the removal of Cd(II), Cu(II), Mn (II) and Ni(II) ions from aqueous solution and real samples in batch mode systems. The prepared magnetic nanomaterials were characterized using X-ray powder diffraction (XRD), scanning electron microscopy/energy dispersion x-ray (SEM/EDX) Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Factors (such as adsorbent dose and sample pH) affecting the adsorption behavior of the removal process were studied using the response surface methodology. Under optimized condition, equilibrium data obtained were fitted into the Langmuir and Freundlich isotherms and the data fitted well with Langmuir isotherms. Langmuir adsorption capacities (mg/g) were found to be 113, 111, 128, and 123 mg/g for Cd, Cu, Ni and Mn, respectively. In addition, the adsorption kinetics was analyzed using five kinetic models, pseudo-first order, pseudo-second order, intraparticle diffusion and Boyd models. The adsorbent was successfully applied for removal of Cd(II), Cu(II), Mn (II) and Ni(II) ions in wastewater samples.     

过渡态理论在化学体系中的2个应用实例*

在大学本科一二年级的物理化学教学中,化学动力学章节的学习涉及到对不同时间尺度的认识。本文利用过渡态理论得到的速率常数表达公式,以乙烷分子碳/碳单键旋转和水分子氢键交换的动力学过程为例,对这2个应用实例的动力学过程所发生的时间尺度做出估算。这些时间尺度的估算对于学生理解不同动力学过程的物理图像至关重要,同时也有助于加强学生对重要公式的理解并能够将这些公式在化学体系中灵活运用。     

Expanding the Ligand Classes Used for Mn(II) Complexation: Oxa-aza Macrocycles Make the Difference

We report two macrocyclic ligands based on a 1,7-diaza-12-crown-4 platform functionalized with acetate (tO2DO2A²⁻) or piperidineacetamide (tO2DO2AM^Pip) pendant arms and a detailed characterization of the corresponding Mn(II) complexes. The X−ray structure of [Mn(tO2DO2A)(H₂O)]·2H₂O shows that the metal ion is coordinated by six donor atoms of the macrocyclic ligand and one water molecule, to result in seven-coordination. The Cu(II) analogue presents a distorted octahedral coordination environment. The protonation constants of the ligands and the stability constants of the complexes formed with Mn(II) and other biologically relevant metal ions (Mg(II), Ca(II), Cu(II) and Zn(II)) were determined using potentiometric titrations (I = 0.15 M NaCl, T = 25 °C). The conditional stabilities of Mn(II) complexes at pH 7.4 are comparable to those reported for the cyclen-based tDO2A²⁻ ligand. The dissociation of the Mn(II) chelates were investigated by evaluating the rate constants of metal exchange reactions with Cu(II) under acidic conditions (I = 0.15 M NaCl, T = 25 °C). Dissociation of the [Mn(tO2DO2A)(H₂O)] complex occurs through both proton− and metal−assisted pathways, while the [Mn(tO2DO2AM^Pip)(H₂O)] analogue dissociates through spontaneous and proton-assisted mechanisms. The Mn(II) complex of tO2DO2A²⁻ is remarkably inert with respect to its dissociation, while the amide analogue is significantly more labile. The presence of a water molecule coordinated to Mn(II) imparts relatively high relaxivities to the complexes. The parameters determining this key property were investigated using ¹⁷O NMR (Nuclear Magnetic Resonance) transverse relaxation rates and ¹H nuclear magnetic relaxation dispersion (NMRD) profiles.     

Facial Synthesis of Adsorbent from Hemicelluloses for Cr(VI) Adsorption

It is challenging work to develop a low-cost, efficient, and environmentally friendly Cr(VI) adsorbent for waste water treatment. In this paper, we used hemicelluloses from chemical fiber factory waste as the raw material, and prepared two kinds of carbon materials by the green hydrothermal method as adsorbent for Cr(VI). The results showed that hemicelluloses hydrothermally treated with citric acid (HTC) presented spherical shapes, and hemicelluloses hydrothermally treated with ammonia solution (HTC-NH₂) provided spongy structures. The adsorption capacity of the samples can be obtained by the Langmuir model, and the adsorption kinetics could be described by the pseudo-second-order model at pH 1.0. The maximum adsorption capacity of HTC-NH₂ in the Langmuir model is 74.60 mg/g, much higher than that of HTC (61.25 mg/g). The green hydrothermal treatment of biomass with ammonia solution will provide a simple and feasible way to prepare adsorbent for Cr(VI) in waste water treatment.     

Reactivities of mixed organozinc and mixed organocopper reagents. Part 13 Kinetic study for phosphine‐catalyzed acylation of alkylarylzincs and effect of residual group on the transfer rate of alkyl group

Kinetics of reactions of di‐n‐butylzinc, n‐Bu₂Zn, and mixed n‐butyl(substituted phenyl)zinc reagents and n‐Bu(functional group (FG)?C₆H₄)Zn with benzoyl chloride in the presence of tri‐n‐butylphosphine have been investigated. Reaction rates of transferable n‐butyl group have been determined in tetrahydrofuran at 0 °C to compare the transfer rate of n‐butyl group in homo and mixed diorganozincs. Rate law is consistent with a third‐order reaction, which is first order in diorganozinc, benzoyl chloride, and n‐Bu₃P, and a mechanism was proposed. The lower reaction rate of n‐BuPhZn than that of n‐Bu₂Zn and negative reaction constant in Hammett plot are in accordance with the carbanionic charge of transferable n‐butyl group in the acylation reaction. These findings support the hypothesis that the reaction rate of transferable group, R_T, changes depending upon the residual group, R_R, in R_RR_TZn reagents. Copyright © 2016 John Wiley & Sons, Ltd.     

Kinetics and mechanism of uncatalysed and ruthenium(III) catalysed oxidation of allyl alcohol by diperiodatoargentate(III) in aqueous alkaline medium

The oxidation of allyl alcohol by diperiodatoargentate(III) (DPA) is carried out both in the absence and presence of ruthenium(III) catalyst in alkaline medium at 298 K and a constant ionic strength of 1.1 mol dm^?3 was studied spectrophotometrically. The oxidation products in both the cases were acrolein and Ag(I), identified by spectral studies. The stoichiometry is same in both the cases, that is, [AA]/[DPA] = 1:1. The reaction shows first order in [DPA] and has less than unit order dependence each in both [AA] and [Alkali] and retarding effect of [IO] in both the catalysed and uncatalysed cases. The order in [Ru(III)] is unity. The active species of DPA is understood to be as monoperiodatoargentate(III) (MPA) in both the cases. The uncatalysed reaction in alkaline medium has been shown to proceed via a MPA–allyl alcohol complex, which decomposes in a rate determining step to give the products. In catalysed reaction, it has been shown to proceed via a Ru(III)‐allyl alcohol complex, which further reacts with one molecule of MPA in a rate determining step to give the products. The reaction constants involved in the different steps of the mechanisms were calculated for both reactions. The catalytic constant (K_c) was also calculated for catalysed reaction at different temperatures. The activation parameters with respect to slow step of the mechanisms were computed and discussed for both the cases. The thermodynamic quantities were also determined for both reactions. Copyright © 2007 John Wiley & Sons, Ltd.     

Non-linear scission/recombination kinetics of living polymerization

Living polymers are formed by reversible association of primary units (unimers). Generally the chain statistical weight involves a factor σ < 1 suppressing short chains in comparison with free unimers. Living polymerization is a sharp thermodynamic transition for σ ≪ 1 which is typically the case. We show that this sharpness has an important effect on the kinetics of living polymerization (one-dimensional association). The kinetic model involves i) the unimer activation step (a transition to an assembly-competent state); ii) the scission/recombination processes providing growth of polymer chains and relaxation of their length distribution. Analyzing the polymerization with no chains but unimers at t = 0 , with initial concentration of unimers M ≳ M ^* (M^* is the critical polymerization concentration), we determine the time evolution of the chain length distribution and find that: 1) for M ^* ≪ M ≪ M ^*/σ the kinetics is characterized by 5 distinct time stages demarcated by 4 characteristic times t₁, t₂, t₃ and t^*; 2) there are transient regimes (t ₁ ≲ t ≲ t ₃) when the molecular-weight distribution is strongly non-exponential; 3) the chain scissions are negligible at times shorter than t₂. The chain growth is auto-accelerated for t ₁ ≲ t ≲ t ₂ : the cut-off chain length (= polymerization degree 〈n〉_w N ₁ ∝ t ² in this regime. 4) For t ₂ < t < t ₃ the length distribution is characterized by essentially 2 non-linear modes; the shorter cut-off length N₁ is decreasing with time in this regime, while the length scale N₂ of the second mode is increasing. (5) The terminal relaxation time of the polymer length distribution, t^*, shows a sharp maximum in the vicinity of M^*; the effective exponent is as high as ∼ σ^-1/3 just above M^*.     

High-temperature measurements of the rates of the reactions CH2O + Ar → Products and CH2O + O2 → Products

The two-channel thermal decomposition of formaldehyde [CH₂O], (1a) CH₂O + Ar → HCO + H + Ar, and (1b) CH₂O + Ar → H₂ + CO + Ar, was studied in shock tube experiments in the 2258-2687 K temperature range, at an average total pressure of 1.6 atm. OH radicals, generated on shock heating trioxane-O₂-Ar mixtures, were monitored behind the reflected shock front using narrow-linewidth laser absorption. 1,3,5 trioxane [C₃H₆O₃] was used as the CH₂O precursor in the current experiments. H-atoms formed upon CH₂O and HCO decomposition rapidly react with O₂ to produce OH via H + O₂ → O + OH. The recorded OH time-histories show dominant sensitivity to the formaldehyde decomposition pathways. The second-order reaction rate coefficients were inferred by matching measured and modeled OH profiles behind the reflected shock. Two-parameter fits for k_1a and k_1b, applicable in this temperature range, are:

     

纳米氧化锌的过饱和控制生长与大小分布控制.

"在非水介质中合成了纳米氧化锌,测定了纳米氧化锌的紫外吸收光谱,并用有效质量模型计算了粒子大小,开发并命名了一种称之为纳米粒子过饱和控制生长的技术,该技术涉及将小的纳米粒子悬浊液加入到大的粒子悬浊液中,结果因为不同大小粒子间的溶解度差异小的粒子将全部溶解,大的粒子将整体长大,大粒子悬浊液的粒子数将保持不变,大粒子的生长速度显著比Ostwald老化的高．该技术最显著的特征是只要最初两悬浊液粒子大小的差异足够大,分布不是太宽,则粒子大小的分布将会因为粒子如此长大而变窄．"     

Factors affecting the morphology of benzoyl peroxide microsponges

Benzoyl peroxide (BPO) is primarily used in the treatment of mild to moderate acne. However, its application is associated with skin irritation. It has been shown that encapsulation and controlled release of BPO could reduce the side effect while also reducing percutaneous absorption when administered to the skin. The aim of the present investigation was to design and formulate an appropriate encapsulated form of BPO, using microsponge technology, and explore the parameters affecting the morphology and other characteristics of the resultant products employing scanning electron microscopy (SEM). Benzoyl peroxide particles were prepared using an emulsion solvent diffusion method by adding an organic internal phase containing benzoyl peroxide, ethyl cellulose and dichloromethane into a stirred aqueous phase containing polyvinyl alcohol (PVA). Different concentrations of BPO microsponges were incorporated in lotion formulations and the drug release from these formulations were studied. The SEM micrographs of the BPO microsponges enabled measurement of their size and showed that they were spherical and porous. Results showed that the morphology and particle size of microsponges were affected by drug:polymer ratio, stirring rate and the amount of emulsifier used. The results obtained also showed that an increase in the ratio of drug:polymer resulted in a reduction in the release rate of BPO from the microsponges. The release data showed that the highest and the lowest release rates were obtained from lotions containing plain BPO particles and BPO microsponges with the drug:polymer ratio of 13:1, respectively. The kinetics of release study showed that the release data followed Peppas model and the main mechanism of drug release from BPO microsponges was diffusion.