Preparation of novel heterogeneous catalysts by adsorption of a cationic tetrapyrrole on to bentonite: equilibrium, kinetics, and thermodynamics

Abstract  

Adsorption of an octacationic tetrapyrrole, octakis(2-trimethylammoniumethylsulfanyl)porphyrazinatocobalt octaiodide (QCoPz), from aqueous solutions on to negatively charged bentonite was investigated. Effects of temperature, dye concentration, solid concentration, and contact time on adsorption were determined. Zeta potential and ion-release measurements were also used as supporting experiments. Experimental data were analyzed using four adsorption kinetic models; a pseudo second-order kinetic model resulted in better correlation with experimental results than the others. Experimental equilibrium data were analyzed by non-linear regression using five adsorption isotherm models with two, three, or four terms. Free energies, enthalpies, and entropies for the adsorption process were determined. The results indicated that adsorption of QCoPz on bentonite was exothermic and spontaneous in nature. FT-IR spectroscopy of the composite and its desorptive behavior were also investigated to identify the mechanism of adsorption. The novel QCoPz–bentonite composites obtained are likely to be used in “green chemistry” and in a wide range of optical and/or catalytic applications, especially those crucially important in the petroleum and pulp/paper industries for waste water cleaning (destruction of mercaptans, sulfides, phenol, and halogenated aromatics, etc.) and removal of bad odor.     

Selective Determination of Total Capsaicinoids in Plant Material Using Poly(Gallic Acid)‐modified Electrode

Novel voltammetric approach for the selective determination of total capsaicinoids has been developed using glassy carbon electrode modified with multi‐walled carbon nanotubes and poly(gallic acid) (PGA/MWNT/GCE). The modified electrode provides significant improvements in the capsaicinoids voltammetric characteristics in comparison to GCE and MWNT/GCE. The electrooxidation of capsaicinoids is irreversible adsorption‐controlled process with the anodic transfer coefficient of 0.49–0.53 and heterogeneous electron transfer rate constant of 1300–2400 s^?1. The analytical ranges of 0.010–1.0 and 1.0–50 μM for capsaicin, 0.025–0.75 and 0.75–75 μM for dihydrocapsaicin and 0.025–5.0 and 5.0–75 μM for nonivamide with the detection limits of 2.9, 5.9 and 6.1 nM, respectively, have been obtained using differential pulse voltammetry (DPV). The selectivity of the capsaicinoids quantification in the presence of ascorbic acid, α‐tocopherol and carotenoids is shown. The method has been tested on the samples of red hot pepper spices and Capsicum annuum L. tinctures. The results correspond to the chromatographic data.     

Complexes of podand-containing bis(dithiophosphonate) ligands with cobalt(II), nickel(II) and cadmium(II): recognition of CH<Subscript>2</Subscript>Cl<Subscript>2</Subscript>

Reaction of the potassium salts of podand-containing bis(dithiophosphonate)s [PhO(4-C₆H₄)P(S)(SH)OCH₂CH₂]₂O (H ₂ L) with Co(II), Ni(II) and Cd(II) in aqueous EtOH leads to complexes of formulae M₂(L-S,S′)₂. The structural formulae of the compounds were deduced by physico-chemical and spectroscopic methods. It was established that complex Ni ₂ L ₂ recognizes CH₂Cl₂.     

Dissociative Electron Attachment to Hexachlorobenzene

Gas phase molecules of hexachlorobenzene (C₆Cl₆) were investigated by means of dissociative electron attachment spectroscopy (DEAS). Three channels of molecular negative ions decay have been identified: abstraction of Cl⁻ and Cl₂⁻ as well as electron detachment (τ_a∼250 μs at 343 K). All three channels exhibit temperature dependence. The adiabatic electron affinity estimated using a simple but typically accurate Arrhenius model (EA_a=1.6–1.9 eV) turns out to be much higher than the quantum-chemical predictions (EA_a=0.9–1.0 eV). We discuss the possible reasons behind the observed discrepancy.     

Specific Features of the Structure of Chelate Complexes of <Emphasis Type="Italic">N</Emphasis>-Thiocarbamoylamidophosphates with Zn(II) and Cd(II) Cations

The reaction of potassium salts of N-thiocarbamoylamidophosphates RC(S)NHP(O)(OPr-i)₂X [X = PhNH, p-MeOPhNH, p-BrPhNH, i-PrNH, t-BuNH, Et₂N, C₅H10N, OC₄H₈N, C₆H₁₁NH] with Zn(II) cation gives complexes of the composition Zn(L-O,S)₂. The Cd(II) complexes could not be isolated under analogous conditions because of their hydrolytic lability. The reaction of thioureas (X = PhNH, p-MeOPhNH) with Cd(II) acetate in DMF provides stable solvato complexes of the composition Cd(DMF)₂L₂. The structure of the resulting compounds was studied by means of IR, ¹H, and ³¹P NMR spectroscopy and EI and ESI mass spectrometry.