Viorica Parvulescu

Modified SBA-15 mesoporous silica for heavy metal ions remediation

N-Propylsalicylaldimino-functionalized SBA-15 mesoporous silica was prepared, characterized and used as an adsorbent for heavy metal ions. The organic-inorganic hybrid material was obtained using successive grafting procedures of SBA-15 silica with 3-aminopropyl-triethoxysilane and salicylaldehyde, respectively. For comparison an amorphous silica gel was functionalized using the same procedure. The structure and physicochemical properties of the materials were characterized by means of elemental analysis, X-ray diffraction (XRD), nitrogen adsorption-desorption, thermogravimetric analysis and FTIR spectroscopy. The organic functional groups were successfully grafted on the SBA-15 surfaces and the ordering of the support was not affected by the chemical modification. The behavior of the grafted solids for the adsorption of heavy metals ions from aqueous solutions was investigated. The hybrid materials showed high adsorption capacity and high selectivity for copper ions. Other ions, such as nickel, zinc, and cobalt were adsorbed by the modified SBA-15 material. The adsorbent can be regenerated by acid treatment without altering its properties.

Acidic and textural properties of H-ZSM-5 impregnated with gallium, indium or thallium

Abstract ZSM-5 samples with a silicon-to-aluminium atomic ratio of 25 were impregnated with gallium, indium or thallium salts. The acidic and textural properties of the samples were determined either before or after reduction. The acidity was investigated by infrared spectroscopy using pyridine (Py) as test molecule, titration with KOH or Py as well as ammonia adsorption. Differences were revealed concerning the dispersion of impregnated species and the distribution of the acidic sites. The sites containing ionic thallium were spectroscopically identified; the other sites were indirectly evidenced. Under our impregnation conditions, gallium species seem to enter inside the zeolite to a higher extent than was reported for similar samples. The contribution of indium to the sample acidity was reduced because it is deposited as a distinct phase onto the external surface. An adsorption mechanism operating during impregnation was proposed on the basis of electrochemical measurements; it was used to account for the acidity data. The textural properties were interpreted in terms of the deposition of the impregnation species near the pore mouth, hindering the entrance of the test molecules.

Structure and surface chemistry in crystalline mesoporous (CeO2−δ)–YSZ

Mesoporous metal oxides (CeO(2-δ))-YSZ have been synthesized by a versatile direct synthesis method using ionic cetyltrimethylammonium bromide (CTAB) and different nonionic (block copolymers) as surfactants and urea as hydrolyzing agent. The synthesis was realized at pH=9 using tetraethylammonium hydroxide (TEAOH) as pH mediator. Calcination at 550 °C led to the formation of crystalline metal oxides with uniform mesoporosity. The obtained materials have been characterized by thermogravimetric analysis (TG-DTG), wide and small-angle X-ray diffraction (XRD), Raman spectroscopy, Brunauer, Emmett and Teller (BET) surface area analysis, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). All the obtained materials exhibits mesoporous structure, crystalline structure indexed in a cubic symmetry, showing a high surface area, a uniform and narrow pore size distribution, spherical morphology typical for the mesoporous materials. The crystalline and mesoporous structures, surface chemistry and stoichiometry for the samples synthesized using ionic and nonionic surfactants have been discussed.

Styrene-co-divinylbenzene/silica hybrid supports for immobilization transitional metals and their application in catalysis

The functionalization of S–1% DVB copolymer was carried out with aminophosphonate groups, and then the samples were covered with silica to obtain hybrid materials. The obtained hybrid materials were used as supports for impregnation of transition metal ions [Cu(II) and Mn(II)], and they were subsequently used as catalysts in oxidation reactions. The supports and catalysts were characterized by FTIR and UV–Vis spectroscopy, thermal analysis, SEM, and TEM electron microscopy. The results of FTIR spectroscopy indicated the formation of a hybrid of silica and an aminophosphonate polymer by the sol–gel route. The UV–Vis spectra showed a strong interaction of Cu(II) and a weak interaction of Mn(II) with aminophosphonate groups of the supports. The catalytic tests confirm different interactions between the metal cations and obtained supports. The formation of the immobilized Cu(II) complexes shows the possibility of using these materials selectively in oxidation of various organic compounds (anisole, cyclohexene, toluene, styrene, phenol). The purpose of this article is to develop some new poly(aminophosphonates)/silica hybrid materials immobilized with transition metal such as Cu(II) and Mn(II) ions for future use in the oxidation process.

Platinum Mesoporous Silica Catalysts for Liquid Media Oxidation

ABSTRACT Mono- and bimetallic heterogeneous catalysts with mesoporous structure were prepared in two steps. In the first step, SBA-15 and amino-SBA-15 supports were prepared, and in the second, these materials were impregnated with Pt and Co precursors. High-surface-area supports like SBA-15 afford highly dispersed metal oxide species which are the key parameter in the rather difficult oxidation of alkenes with hydrogen peroxide. The obtained mesoporous catalysts with 0.1% Pt and 1% Co were characterized by nitrogen adsorption, ultraviolet–visible, Fourier-transform infrared, and X-ray absorption spectroscopies. X-ray absorption spectroscopy demonstrated the presence of Pt–oxygen for both Pt–SBA-15 and Pt–amino-SBA-15 samples, suggesting a higher number of oxidized platinum species in the second material. The adopted procedure was simple, green, and efficient for 3-butene-1-ol, cis-2-butene-1, 4-diol, and cyclohexene oxidation. The use of H2O2, a clean oxidant, is an important feature of a green chemical reaction since it produces only water as the by-product. The mesoporous structure of the silica-supported catalysts enables better accessibility of active sites to bulky substrate molecules, reflected in the high conversions and enhanced selectivity.

Effect of polymer support functionalization on enzyme immobilization and catalytic activity

Abstract Two enzymes, laccase and peroxidase, were immobilized on chloromethylated styrene-divinylbenzene copolymers supports functionalized with phosphonates ((RO)2PO) or mixed ammonium and phosphonium groups (N+R3Cl–, P+Ph3Cl–). Phosphonates groups and quaternary ammonium salts were grafted on the “gel-type” copolymer by Michaelis–Becker polymer analogue reaction. Mixed polymer-supported ammonium and phosphonium salts were obtained by transquaternization of the ammonium groups to phosphonium group. The degrees of functionalization for obtained polymers were relatively high ensuring a sufficient concentration of active centers per unit mass of the copolymer. The obtained materials were characterized by thermal analysis, FTIR spectroscopy and SEM microscopy. The effects of OR1 and R2 radicals from phosphonate and respectively ammonium groups, as well as those of glutaraldehyde utilization on the immobilization yield and the catalytic properties of the supported enzymes were indicated. The activity of enzymes increased after immobilization and high immobilization yield was obtained for all the samples. The higher interaction of enzymes with support was indicated for mixed ammonium and phosphonium functions. A higher catalytic activity was obtained for peroxidase in oxidation of phenol and laccase in oxidation of anisole. The low effect of glutaraldehyde on enzyme activity reveals the strong interaction of enzyme with the polymer support, respectively with the functional groups.