Carbon-sulfur surface compounds (CχS), in which sulfur is chemically bound, have been prepared with a sulfur content greater than 30 wt.%. X-Ray diffractometry and electron microscopy show that the structure of the material is similar to that of disordered carbons. CχS compounds are chemically stable in base and after an initial loss of several per cent of sulfur, they are stable in strong acids such as HCl and HNO3. In inert atmosphere, no measurable loss of sulfur was detected after being heated to 700°C. The XPS spectra (C1s,: 284.3 eV; S2p3/2: 163.7 eV) and the Fourier transform IR absorption spectra (1180,1550 cm?1) of CχS materials indicate no significant charge separation in carbon-sulfur bonds. Furthermore, these results suggest that, on CχS, carbon-sulfur surface groups exist in the form of thiocarbonyls, C and thiolactones, C, analogous to carbonyls and lactones existing on activated carbons. 相似文献
The catalytic conversion of 2-propanol on carbon based acid catalysts obtained by chemical activation of lignocellulosic waste with H3PO4 was investigated. The carbon acid catalysts were prepared in a single step, without the need for incorporating acid surface groups in a complementary step by chemical oxidation of the carbon surface. The porous structure was characterized by N2 and CO2 adsorption, showing a strong dependence on the impregnation ratio. The surface chemistry was studied by XPS and TPD. A significant amount of phosphorus remains on the catalysts surface, as phosphate and/or polyphosphate esters, stable at relatively high temperature (<700 °C), despite the washing process carried out during the preparation of the catalysts. The total acidity and acid strength distribution were determined by NH3-TPD. The conversion of 2-propanol yielded only dehydration products, mainly propylene with very low amounts of di-isopropyl ether, confirming the acidic nature of the catalyst sites. The amount and strength of acid sites affected the catalytic activity but did not change significantly the apparent activation energy of the dehydration reaction. The catalysts were stable at the operation conditions. The presence of water vapor did not affect significantly the conversion and the product distribution. 相似文献
A new polymeric system containing hydrolysable ester bond linked to salicylic acid to be used for controlled drug release
was synthesized. Poly(2-hydroxyethyl methacrylate) (PHEMA) functionalized with chloroacetate groups was obtained by the reaction
between PHEMA and chloroacetyl chloride using the N,N-dimethylacetamide/5% lithium chloride system as a solvent and pyridine as a catalyst. The degree of substitution was calculated
from the chlorine content and ranged from 32.2 to 98.1 mol.% depending on the ratio of chloroacetyl chloride to PHEMA. The
coupling of salicylic acid to PHEMA functionalized with chloroacetate groups was carried out by the reaction between PHEMA
and the sodium salt of salicylic acid. The structures of chloroacetylated PHEMA and PHEMA–salicylic acid conjugates were determined
by means of FTIR, 1H-NMR and 13C-NMR spectra. The hydrolysis in the heterogeneous system of PHEMA–salicylic acid conjugates were performed in buffer solutions
(pH 7.6 and 8.5) at 37 °C and showed that the release of the drug (sodium salicylate) from tablets was dependent on the hydrophilic
character of conjugate as well as on the pH value of the medium. 相似文献
Clay modification was carried out by treatment of fatty nitrogen compounds (FNCs); fatty hydrazide (FH), hydroxy methyl fattyamide
(HMFA), and difatty acyl thiourea (DFAT) were synthesized from vegetable oils with a sodium montmorillonite (MMT) as natural
clay. This process was accomplished by stirring the clay particles in an aqueous solution of FH, HMFA, and DFAT, by which
the clay layer thickness increased from 1.23 to 2.69, 2.89 and 3.21 nm, respectively. The modified clay was then used in the
preparation of the polylactic acid/epoxidized palm oil (PLA/ EPO) blend nanocomposites. The interaction of the modifier in
the clay layer was characterized by X-ray diffraction (XRD) and Fourier transform infrared (FTIR). Elemental analysis was
used to estimate the presence of FNCs in the clay. The nanocomposites were synthesized by solution casting of the modified
clay and a PLA/EPO blend at the weight ratio of 80/20, which has the highest elongation at break. The nanocomposites were
then characterized using XRD, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and tensile properties
measurements. Improvement in mechanical properties of the FH-MMT, HMFA-MMT, and DFAT-MMT nanocomposites was obtained when
2% of the DFAT-MMT and 3% of both FH-MMT and HMFA-MMT loadings were used. PLA/EPO modified clay nanocomposites show higher
thermal stability in comparison with those of the PLA/EPO blend. The XRD and TEM results confirmed the production of nanocomposites. 相似文献
Two new uranyl-organic coordination compounds, UO2(NDC)[(CH3)2SO)]2 (1) and [UO2(NDC)(CH2OH)2] (2) (H2NDC = 1,4-naphthalene dicarboxylate), have been synthesized from the solutions of dimethyl sulfoxide (DMSO) and ethylene glycol (EG), respectively, through a volatilization method. Single-crystal X-ray diffraction analyses show that compound 1 consists of novel straight chains modified by pairs of DMSO molecules, whereas compound 2 features one-dimensional zigzag chains which are cross-linked by non-coordinating solvent molecules through hydrogen bonding interactions, forming a two-dimensional network. Both 1 and 2 decompose rhodamine B (RhB) molecules efficiently under the irradiation of UV and visible light. 相似文献
Nonionic, cationic and anionic surfactants, derivatives ofcis-13-docosenoic acid (erucic acid), have been prepared and characterized, and their performance has been evaluated and compared
with the corresponding derivatives of fatty acids with shorter alkyl chain length.
Nonionic erucic acid ethoxylates give a solution behavior anticipated from the hydrophilic-lipophilic balance of the molecule;
however, the increased molecular size as compared to ordinary surfactants results, e.g., in higher temperature stability of
the surfactant aggregates. Anomalous solution behavior was found and investigated for anionic surfactants, triethanolammonium
salts of erucic acid, and some shorter homologues. The effects are discussed in terms of the acid-base equilibria of the alkanolammonium
counterion and the acid, together with effects due to the molecular size of the counterion. 相似文献