Adsorptive Stripping Voltammetric Determination of 2,4-Dichlorophenol by Laponite Modified Carbon Paste Electrode

A laponite modified carbon paste electrode was prepared, characterized and applied for the 2,4-dichlorophenol (2,4-DCP) voltammetric determination. It takes advantage of the ability of laponite to adsorb phenols, as well as of its availability and very low cost. Kinetic and equilibrium data for 2,4-DCP adsorption by laponite in aqueous dispersions demonstrated that the adsorption process obeyed a pseudo first order kinetic model and was consistent with the formation of adsorbed multilayers on a surface with heterogeneous pore distribution. The composite paste electrode exhibited a heterogeneous surface with 65 % increased surface area and 27 % enhanced catalytic activity compared to the unmodified one. The adsorptive stripping voltammetric determination of 2,4-DCP at an electrode with an optimized graphite:laponite ratio of 55 : 15 w% using a 3 min accumulation time at pH 5.5 was found to be suitable for its quantification in the linear concentration range extended up to 50 μmol L⁻¹ with a sensitivity of 0.56 μA L μmol⁻¹ and a LOD of 0.2 μmol L⁻¹ (S/N=3).The 2,4-DCP electrochemical response was not affected by the presence of some structurally similar phenols, like catechol and p-nitrophenol, while resorcinol, 2-chlorophenol, and 4-chlorophenol presented interferences. The results were validated by 2,4-DCP determination in spiked tap water.     

Manipulating electronic and magnetic properties of black phosphorene with 4d series transition metal adsorption

We carry out first-principles calculations within density-functional theory to investigate the structural, electronic and magnetic properties of 4d transition metal (TM) decorated monolayer black phosphorene (BP). The results indicate that the TM adsorption on BP can have dilute magnetic semiconductor (DMS) properties. The spin polarized semiconducting state is realized in BP by adsorption of Y, Nb and Ru, while a half-metal state is obtained by Tc adsorption. In the case of two same types of TMs adsorption on BP, only [email protected] shows DMS state. In particular, two different types of TMs decorated BP can induce magnetic moments, localized mainly on the 4d TMs and the neighboring P atoms. Furthermore, the 4d TMs may enrich the electronic properties of BP, such as half-metallic, metallic and semiconducting features. These findings suggest that the 4d TM adsorbed BP can be used as a potential next-generation spintronics and magnetic storage material.     

Adsorption properties of the double-imprinted electrospun crosslinked chitosan nanofibers

Pb(II)-Cd(II) double-imprinted electrospun crosslinked chitosan nanofibers (Pd/Cd-DIECCNs) were prepared by combining electrospinning and ion-imprinting methods, which showed excellent adsorption capacity for both Pb(II) and Cd(II).     

Adsorption performance and stability of the modified straws and their extracts of cellulose,lignin, and hemicellulose for Pb2+: pH effect

Adsorption performance and stability of the carboxyl groups modified straws and their extracts of cellulose, lignin, and hemicellulose for Pb²⁺ were investigated, and the optimum pH range for Pb²⁺ adsorption was determined by considering both the stability and capacity of the modified biosorbents for the first time. Results showed that adsorption capacity and stability of the straws and extracts were both improved significantly after modification. Adsorption capacities of the modified straws and extracts followed the order: modified hemicellulose > modified lignin, modified straw > modified cellulose, while stability of them followed the reverse order. In the optimum pH range from 4.0 to 5.0, modified rape and cotton straw showed better stability than the modified maize straw, and total organic carbon (TOC) values determined from the two modified straws and extracts were lower than 5.0 mg L⁻¹ even after adsorption for 30 days, which reached the drinking water standard in China.     

碳纤维汞膜微电极1.5次微分伏安法测定胆固醇的研究

将胆固醇吸附在碳纤维汞膜微电极表面，阳极溶出时，可产生一个灵敏的１．５次微分溶出峰，其峰电位为－０．０６Ｖ（ｖｓ，ＳＣＥ，下同），峰电流和样品浓度在１．０×１０－５～１．０×１０－７ｍｏｌ／Ｌ范围内有良好的线性关系。检出限可达１．０×１０－８ｍｏｌ／Ｌ。本文讨论了测定条件，建立了测定胆固醇的新方法，并对实际样品进行了分析。     

CMC-Na/TETA-B62型蛇笼树脂对Ag+、Cr3+和Hg2+的吸附性能

研究了自合成的蛇笼型螯合树脂三乙烯四胺交联甘油环氧树脂／羧甲基纤维素体系对Ag^ 、Cr^3 、Hg^2＋的吸附量，吸附动力学，等温吸附过程等静态吸附性能，同时研究了PH值等因素对吸附性能的影响。实验结果表明，该树脂对Ag^ 、Cr^3 具有较强的吸附选择性，在Ag^ 、Cr^3 、Hg^2＋3种离子共存时能选择吸附Ag^ ，其选择性系数分别为KAg/Hg^2 ＝10．31、KAg^ /Cr^3 =1.77,KCr^3 /Hg^2 =5.83。该树脂对上述3种离子的吸附量分别达2.99mmol/g、1．69mmol/g、0．29mmol/g，该类树树可用于含重金属离子污水的处理和金属离子的分离等方面。     

The influence of a small amount of active sites on the adsorption kinetics of nitrogen on ruthenium

Recently, Dahl et al. [S. Dahl, A. Logadottir, R.C. Egeberg, J.H. Larsen, I. Chorkendorff, E. Törnqvist, J.K. Nørskov, Phys. Rev. Lett. 83 (1999) 1814; S. Dahl, E. Törnqvist, I. Chorkendorff, J. Catal. 192 (2000) 381] have proposed very interesting hypothesis that the rate of dissociation and adsorption of nitrogen on Ru(0 0 0 1) facet is totally dominated by the presence of a small amount of step sites on Ru(0 0 0 1) terraces. Following this idea, a kinetic model, based on applying the Statistical Rate Theory approach, was developed in order to explain if such mechanism is able to explain the observed features of the system N₂/Ru(0 0 0 1). As a result, it was stated that the activation barrier for adsorption on the active (step) sites is equal to 36 kJ/mol; in turn, the adsorption energy of nitrogen atoms on the active sites is 43 kJ/mol. It implies that the rate of adsorption via the active sites is much faster than direct adsorption on the three-fold hollow sites; moreover, the occupation of the active sites is always close to zero at the investigated temperatures, so they are not blocked and may act as an indirect channel for adsorption. Thus, the rate of nitrogen adsorption on Ru(0 0 0 1) surface is governed by the rate of diffusion of nitrogen atoms from the active sites into the three-fold hollow sites. The analysis of thermodesorption spectra revealed an important role of repulsive interactions between the N atoms adsorbed on the hollow sites, the associated interaction parameter between nearest neighbors was estimated to be 5 kJ/mol. The presence of small amount of gold on Ru(0 0 0 1), apart of blocking the active sites, seems to remove the repulsion between nitrogen atoms.     

Surface resistance measurements at the metal/electrolyte interface of Ag(100) and Ag(111) thin film electrodes

The conductivity of thin film metal electrodes with a thickness of the order of the mean free path of the conduction electrons (50 nm at 300 K) is sensitive to several processes on the metal surface (e.g. adsorption and desorption of ions). We developed epitaxially grown Ag(100)/MgO(100) and Ag(111)/TiO₂(110) electrodes of 20 nm thickness. The change in the surface resistance of Ag(100) thin film electrodes during adsorption of the halide ions Cl⁻, Br⁻ and I⁻ shows the different strengths of specific adsorption. We investigated the phase transition of thiocyanate (SCN⁻) on Ag(100) electrodes by combining the surface resistance method with voltammetric, capacitance and ex-situ XPS measurements. The influence of adsorbed uracil on the resistance of Ag(100) films was demonstrated. The surface resistance is very sensitive to small concentrations of metal cations (e.g. Tl⁺). The surface resistance of Ag(100) and Ag(111) thin film electrodes shows the typical difference in the stripping potential of Tl⁺ of about 100 mV.     

Bond polarization and image-potential screening in adsorbed C6F6 on Cu(1 1 1)

The orientation of hexafluorobenzene (C₆F₆) on the Cu(1 1 1) surface has been determined for different coverages with the help of near edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS). The adsorption geometry and the bonding mode of C₆F₆ differ significantly in comparison to its hydrocarbon analog C₆H₆. C₆F₆ is found to adsorb on Cu(1 1 1) with the ring plane parallel to the surface for coverages below 10 ML. Next to the distinct multilayer, bilayer and monolayer phases we also present evidence of sub-monolayer (i.e., 1/2 ML) coverage with different electronic structure. These findings are explained in a phenomenological model based on fluorine’s property as a σ-acceptor and a π-donor and the resulting bond polarization within the molecule, which is stabilized by image-potential screening within the substrate.