Removal of Cd(II), Cu(II), and Pb(II) by adsorption onto natural clay: a kinetic and thermodynamic study

In this work, we study the elimination of three bivalent metal ions (Cd²⁺, Cu²⁺, and Pb²⁺) by adsorption onto natural illitic clay (AM) collected from Marrakech region in Morocco. The characterization of the adsorbent was carried out by X-ray fluorescence, Fourier transform infrared spectroscopy and X-ray diffraction. The influence of physicochemical parameters on the clay adsorption capacity for ions Cd²⁺, Cu²⁺, and Pb²⁺, namely the adsorbent dose, the contact time, the initial pH imposed on the aqueous solution, the initial concentration of the metal solution and the temperature, was studied. The adsorption process is evaluated by different kinetic models such as the pseudo-first-order, pseudo-second-order, and Elovich. The adsorption mechanism was determined by the use of adsorption isotherms such as Langmuir, Freundlich, and Temkin models. Experiments have shown that heavy metals adsorption kinetics onto clay follows the same order, the pseudo-second order. The isotherms of adsorption of metal cations by AM clay are satisfactorily described by the Langmuir model and the maximum adsorption capacities obtained from the natural clay, using the Langmuir isotherm model equation, are 5.25, 13.41, and 15.90 mg/g, respectively for Cd(II), Cu(II), and Pb(II) ions. Adsorption of heavy metals on clay is a spontaneous and endothermic process characterized by a disorder of the medium. The values of ΔH are greater than 40 kJ/mol, which means that the interactions between clay and heavy metals are chemical in nature.     

Synthesis and evaluation of some new hydrazones as corrosion inhibitors for mild steel in acidic media

Research on Chemical Intermediates - Mild steel corrosion in HCl solution is an example of corrosion in acidic mediums. The ongoing research efforts to develop novel environmentally friendly...     

Copper(I) Zeolites as Heterogeneous and Ligand‐Free Catalysts: [3+2] Cycloaddition of Azomethine Imines

Clicking in zeolites : Copper(I)‐exchanged zeolites proved to be practical and efficient catalysts for the cycloaddition of azomethine imines with alkynes, providing a convenient access to N,N‐bicyclic pyrazolidinone derivatives (see scheme). With high regioselectivity, 100 % atom economy, and convenient product isolation, this heterogeneously catalyzed version of the Dorn cycloaddition corresponds to click‐chemistry criteria.

     

Solvent-dependent behavior of arylvinylketones in HUSY-zeolite: a green alternative to liquid superacid medium

Depending on the reaction conditions, arylvinylketones can be directly and efficiently converted using zeolites to indanones by cyclization or to dihydrochalcones through regioselective aryl addition or chemoselective hydride transfer.     

Ac electrical parameters of Al-ZnPc-Al organic semiconducting films

The ac electrical parameters of thermally evaporated zinc phthalocyanine, ZnPc, semiconducting thin films was measured in the temperature range of 180–390 K and frequency between 0.1 and 20 kHz. Aluminum electrode contacts were utilized to sandwich the organic ZnPc semiconducting films. Capacitance and loss tangent decreased rapidly with frequency at high temperatures, but at lower temperatures a weak variation is observed. An equivalent circuit model assuming ohmic contacts could qualitatively and successfully explains capacitance and loss tangent behavior. The ac conductivity showed strong dependence on both temperature and frequency depending on the relevant temperature and frequency range under consideration. Ac conductivity σ (ω) is found to vary with ω, as ω ^s with the index s ≤ 1.35 suggesting a dominant hopping conduction process at low temperatures (< 250 K) and high frequency. The conductivity of some samples did not increase monotonically with temperature. This behavior was attributed to oxygen exhaustion of the sample as its temperature is increased. The ac conductivity behavior at low temperatures of ZnPc films could be described well by Elliott model assuming hopping of charge carriers between localized sites.     

Control of an axially moving viscoelastic Kirchhoff string

The control problem of axially moving strings occurs in a large class of mechanical systems. In addition to the longitudinal displacement, the strings are subject to undesirable transversal vibrations. In this work, in order to suppress these vibrations, we consider a control by a hydraulic touch-roll actuator at the right boundary. We prove uniform stability of the system using a viscoelastic material and an appropriate boundary control force applied to the touch rolls of the actuator. The features of the present work are: taking into account the mass flow entering in and out at the boundaries due to the axial movement of the string and overcoming the difficulty raised by the Kirchhoff coefficient which does not allow us to profit from the dissipativity of the system (as in the existing works so far). We shall make use of an inequality which is new in this theory.     

Chiral Separation of 4-Iminoflavan Derivatives on Several Polysaccharide-Based Chiral Stationary Phases by HPLC

The HPLC enantiomeric separation of seven 4-iminoflavans was successfully accomplished in the normal phase mode using six polysaccharide-based chiral stationary phases namely, Chiralcel^®OD-H, Chiralcel^®OD, Chiralcel^®OJ, Chiralpak^®AD, Chiralpak^®IA and Chiralpak^®IB under normal and polar organic phase modes. The resolution depended on nature and concentration of alcoholic modifier. The results demonstrate clearly that the chromatographic system based on the coated and immobilized type Chiralpak^®IB and Chiralcel^®OD-H CSPs provide a powerful analytical tool for enantiomeric separation of all the 4-iminoflavans used in this study.     

The Dω—classical orthogonal polynomials

This is an expository paper; it aims to give an essentially self-contained overview of discrete classical polynomials from their characterizations by Hahn’s property and a Rodrigues’ formula which allows us to construct it. The integral representations of corresponding forms are given.