Competitive adsorption and desorption of a bi-solute mixture: effect of activated carbon type

This study aims to clarify the effects of carbon activation type and physical form on the extent of adsorption capacity and desorption capacity of a bi-solute mixture of phenol and 2-chlorophenol (2-CP). For this purpose, two different PACs; thermally activated Norit SA4 and chemically activated Norit CA1, and their granular countertypes with similar physical characteristics, thermally activated Norit PKDA and chemically activated Norit CAgran, were used. The thermally activated carbons were better adsorbers for phenol and 2-CP compared with chemically activated carbons, but adsorption was more reversible in the latter case. 2-CP was adsorbed preferentially by each type of activated carbon, but adsorption of phenol was strongly suppressed in the presence of 2-CP. The simplified ideal adsorbed solution (SIAS) model underestimated the 2-CP loadings and overestimated the phenol loadings. However, the improved and modified forms of the SIAS model could better predict the competitive adsorption. The type of carbon activation was decisive in the application of these models. For each activated carbon type, phenol was desorbed more readily in the bi-solute case, but desorption of 2-CP was less compared with single-solute. This was attributed to higher energies of 2-CP adsorption.     

Synthesis and polymerization of racemic and optically active β-substituted β-propiolactones. II: β-monosubstituted and β-disubstituted monomers and polymers with different optical purities

β-(trichloromethyl)-β-propiolactone (CCl₃-PL), β-(trifluoromethyl,methyl)-β-propiolactone (CF₃, Me-PL) and β-(trifluoromethyl,ethyl)-β-propiolactone (CF₃,Et-PL) have been obtained by the reaction of ketene with chloral, 1,1,1-trifluoroacetone and 1,1,1-trifluorobutanone, respectively. Chiral catalysis lead to optically active monomers. The enantiomeric excess of the lactones has been measured by ¹H-NMR spectroscopy, in the presence of 2,2,2-trifluoro-1-(9-anthryl)ethanol or an europium chiral shift reagent. Polymerizations have been carried out in bulk or in toluene, at 60°C or 80°C, using mainly organometallic initiators. The Polymers become insoluble and crystalline at enantiomeric excesses over 80% for CCl₃-PL and 70% for CF₃,Me-PL. Melting temperatures were recorded from 238 to 268°C for poly(CCl₃-PL) and from 78 to 100°C for poly(CF₃,Me-PL), depending upon the molecular weight and the enantiomeric excess. The ¹³C-NMR specroscopy of poly(CCL₃-PL) indicates that the polymerization of the corresponding lactone leads to polymers of increasing degrees of isotacticity with the enantiomeric excess of the monomer.     

Interactions in water-alcohol mixtures studied by NMR and infrared spectroscopy

By using low temperatures and largely deuterated solvents, the rate of OH proton exchange for aqueous solutions of alcohols is reduced sufficiently to give separate NMR signals from water and alcohol OH protons. The limiting shifts for dilute alcohols in water are down-field of both the water resonance and those of the pure alcohols. This contrasts with the limiting shift for water in the alcohols, which is to high field of the bulk water resonance. The resonance shifts initially to low fields as [ROH] increases, the rate of shift being greatest for t-butyl alcohol. For dilute aqueous solutions, all the alcohols reduce the total concentration of free OH groups, as judged by the overtone infrared spectra. Some of these results are interpreted in terms of a scavenging of free OH groups by the excess lone-pairs of the alcohol molecules. An extra, temperature dependent, down-field shift in the water proton resonance induced by t-butyl alcohol is assigned to a clathrate cage effect.     

Synthesis of 9-methyl-1H-[1,4]thiazino[3,2-g]quinoline-2,5,10(3H)-trione, the B,C,D ring core of the shermilamine alkaloids

Synthesis of 9-methyl-1H-[1,4]thiazino[3,2-g]quinoline-2,5,10(3H)-trione (4), from N-(4-bromo-2,5-dimethoxyphenyl)acetamide (23) is described. Oxidative cyclisation of 2,2'-disulfanediylbis[N-(2,5-dimethoxyphenyl)acetamide] (19) to 5,8-dimethoxy-2H-1,4-benzothiazin-3(4H)-one (7b) is also reported.     

Elastic properties of crosslinked poly(vinyl alcohol) gels: Network topology

Current network theory exhibits inconsistencies which show up particularly clearly in deformation of networks prepared by crosslinking a polymer in solution. A check of theory can be obtained if one knows precisely the number of crosslinks in the network and if a range of deformations is applied to the network. In an effort to explore this problem we have examined the relation of shear modulus to crosslink density, primary molecular weight, and polymer concentration for a series of poly(vinyl alcohol) gels at low to intermediate concentrations. Aqueous poly(vinyl alcohol) solutions were crosslinked to form infinite networks using terephthalaldehyde. We find a large discrepancy with these poly(vinyl alcohol) gels between measured shear modulus and that calculated from classical elasticity theory assuming quantitative reaction of crosslinking. The ratio of measured to calculated modulus is independent of crosslink density for a given primary molecular weight and concentration. It shows linear dependence on polymer concentration prior to crosslinking and extrapolates to a critical concentration which is consistent with the effective sizes of the polymer molecules.     

Laser studies of vibrational energy transfer and relaxation of CO trapped in solid neon and argon

The infrared emission of CO trapped in solid Ne and Ar is observed at low temperature. The first vibrational level of ¹²C¹⁶O is excited by a Q-switched frequency doubled CO₂ laser. The emission spectrum consists of several lines arising from upper vibrational levels of ¹²C¹⁶O and also of ¹³C¹⁶O and ¹²C¹⁸O which are present in natural abundance. An interpretation is proposed which is based on the assumption that long range dipole—dipole interaction is the main physical process involved in these experiments. Resonance energy transfer produces an energy migration among ¹²C¹⁶O molecules without any change in vibrational populations. Phonon assisted energy transfer takes place between vibrational levels of the various isotopic species present in the solution. In order to satisfy the resonance condition a phonon is emitted or absorbed whose energy compensates for the energy mismatch between the transitions in each interacting molecule due to isotopic effect and or vibrational anharmonicity. The range of this process is greatly extended by energy migration. At the low phonon bath temperature phonon emission is much more probable than phonon absorption. So a strong excitation of upper vibrational levels with in some cases population inversions is observed.Molecular impurities act as efficient quenching centers even at very low concentration. When highly purified samples are used, the fluorescence decay time is found to be 20.6 ms in Ne and 14.5 ms in Ar and does not significantly depend upon concentration and temperature. It is concluded that radiationless relaxation is unimportant.     

Photocatalytic TiO2 Coatings: Effect of Substrate and Template

Transparent TiO₂ films with a high photodegradation activity towards an azo dye in aqueous solution were prepared by sol–gel processing. Films on soda–lime glass supports protected with a thin silica barrier layer exhibited better crystallization and monodisperse nanoparticles, higher absorption of light below 370 nm, and higher photocatalytic activity than those films deposited on bare glass supports proving the detrimental effect of interdiffused sodium ions on the development of the anatase nanostructure. The effect of substrate was more pronounced in thinner films (300 nm) than in thicker ones (1200 nm), which were achieved by adding a template (i.e. Pluronic F127) to the sol.     

Reinvestigation of CS2 dissociation at 193 nm by means of product state-selective vacuum ultraviolet laser ionization and velocity imaging

A branching ratio of 1.6 +/- 0.3 for S(3P)/S(1D) is obtained for the dissociation of CS2 with very low fluence 193 nm laser (less than 2 mJ/cm2), in which the S(3P) and S(1D) have been state-selectively ionized using VUV lasers at different wavelengths. The anisotropy parameters betamax(3P) = 0.8 and betamax(1D) = 1.9 indicate that these channels are preferentially populated at different geometries and the lifetime is very short.     

Thermal behavior of glutamic acid and its sodium,lithium and ammonium salts

Glutamic acid (H2_glu) and its lithium, sodium and ammonium monosalts were submitted to thermal analysis using thermogravimetry (TG) and differential thermal analysis (DTA). The main goal of these studies was to compare the relative thermal stability and to evaluate the effect of the counter ion in the thermal decomposition pathways. Salts were obtained by direct neutralization of the purified acid with LiOH, NaOH or NH₄OH and were characterized by elemental analysis (C, H and N) and IR spectroscopy. Decomposition occurred after conversion to the pyroglutamic acid or the respective pyroglutamates and ammonium salt loosing NH₃ being converted to H₂glu before decomposition.     

Biotreatment of tannin-rich beer-factory wastewater with white-rot basidiomycete Coriolopsis gallica monitored by pyrolysis/gas chromatography/mass spectrometry

Some fractions of beer-factory wastewaters represent an important environmental concern owing to their high content of polyphenols and dark-brown color. The capacity of Coriolopsis gallica to preferentially degrade lignin has been successfully applied in our laboratory to the biotreatment and decolorization of paper-industry effluents. In this work, the ability of this white-rot fungus to degrade high-tannin-containing wastewaters is evaluated. Under all the conditions studied, effluent decolorization and chemical oxygen demand reduction achieved by C. gallica at day 12 of incubation were close to 50 and 65%, respectively. No adhesion of dark color to the fungal mycelium was observed suggesting that decolorization could be ascribed to C. gallica degradation systems. Mycelium dry-weight values showed that C. gallica is tolerant to relatively high tannin content present in the effluent samples. In the sample containing the highest effluent concentration (60% v/v), dry-weight values suggested an inhibition of fungal growth at day 6 of incubation and a further adaptation of the fungus to the stressing tannin effect at day 12 of fungal treatment. Pyrolysis/gas chromatography/mass spectrometry results showed a decrease of polyphenols pyrolysis products, mainly phenol and guaiacol, with the incubation time. All these results indicate the potential use of C. gallica in bioremediation of tannin-containing industrial wastewaters and in other applications where a reduction in polyphenols content is required.