Ligia Sierra

New perspectives for coal ash utilization: synthesis of zeolitic materials☆

Abstract An alternative use for coal ash was investigated, based on the metakaolin-type material present in the ash. In this study, fly ash from Amaga coal (Colombia) was used. The ash was treated with sodium hydroxide at different concentrations and various times and temperatures of crystallization. The zeolite produced contained 50–75% of a faujasite type material, and had an adsorption capacity ≈70–80% of that of the commercial zeolite 13X.

Preparation of mesoporous silica particles with controlled morphology from sodium silicate solutions and a non-ionic surfactant at pH values between 2 and 6

Abstract Isometric particles of mesoporous silica could be synthesized between 25°C and 45°C from reaction mixtures containing silicic acids, sodium chloride and a non-ionic surfactant (Triton X100). The size decreases from some tens of micrometers to less than 1 μm when the pH increases from 1.85 to 6. At pH lower than 3.5, glassy material forms a cement between the particles. The particle size distribution narrows at higher pH and at long reaction times (several days). A spheroidal shape is favored by low pH and high temperature, and a more polyhedral shape appears at high pH whatever the temperature. This behavior could be related to the polycondensation rate of the silicic acids, to the lifetime and disorder of the micelles and to the micelles–silicic acid interactions.

Interplay between structure and dynamics in chitosan films investigated with solid-state NMR, dynamic mechanical analysis, and X-ray diffraction.

Modern solid-state NMR techniques, combined with X-ray diffraction, revealed the molecular origin of the difference in mechanical properties of self-associated chitosan films. Films cast from acidic aqueous solutions were compared before and after neutralization, and the role of the counterion (acetate vs Cl−) was investigated. There is a competition between local structure and long-range order. Hydrogen bonding gives good mechanical strength to neutralized films, which lack long-range organization. The long-range structure is better defined in films cast from acidic solutions in which strong electrostatic interactions cause rotational distortion around the chitosan chains. Plasticization by acetate counterions enhances long-range molecular organization and film flexibility. In contrast, Cl− counterions act as a defect and impair the long-range organization by immobilizing hydration water. Molecular motion and proton exchange are restricted, resulting in brittle films despite the high moisture content.

Application of Hierarchical Porous Silica with a Stable Large Porosity for β‐Galactosidase Immobilization

Hierarchical porous silica, particles or monoliths, were synthesized by polycondensation of sodium silicate in the presence of cetyltrimethylammonium bromide and ethyl acetate at different concentrations under hydrothermal conditions. They were used as the support for the immobilization of β‐galactosidase from Kluyveromyces lactis by adsorption. The enzyme loading capacity (higher than 50 mg g−1 support) and the retention ability (lixiviation less than 20 % after 72 h of catalysis) of these supports were explained as a function of the hierarchical porosity, mesopore sizes of 10–40 nm, and macropore sizes of 0.07–20 μm and the presence of ionized silanol groups on the surface. The optimum pH value and temperature for the maximum activity of the obtained hybrid biocatalyst were evaluated, indicating that the three‐dimensional structure of the lactase was not significantly affected during the immobilization process. The stability under extreme conditions was improved in comparison with soluble lactase. The porous supports exhibited morphological and porous stability under the immobilization and catalytic processes. These results show that the obtained materials are good candidates for the immobilization of large enzymes, such as β‐galactosidase.

Design of β-galactosidase/silica biocatalysts: Impact of the enzyme properties and immobilization pathways on their catalytic performance

The use of heterogeneous biocatalysis in industrial applications is advantageous and the enzyme stability improvement is a continuous challenge. Therefore, we designed β‐galactosidase heterogeneous biocatalysts by immobilization, involving the support synthesis and enzyme selection (from Bacillus circulans, Kluyveromyces lactis, and Aspergillus oryzae). The underivatized, tailored, macro‐mesoporous silica exhibited high surface area, offered high enzyme immobilization yields and activity. Its chemical activation with glyoxyl groups bound the enzyme covalently, which suppressed lixiviation and conferred higher pH and thermal stability (120‐fold than for the soluble enzyme), without observable reduction of activity/stability due to the presence of silica. The best balance between the immobilization yield (68%), activity (48%), and stability was achieved for Bacillus circulans β‐galactosidase immobilized on glyoxyl‐activated silica, without using stabilizing agents or modifying the enzyme. The enzyme stabilization after immobilization in glyoxyl‐activated silica was similar to that observed in macroporous agarose‐glyoxyl support, with the reported microbiological and mechanical advantages of inorganic supports. The whey lactolysis at pH 6.0 and 25°C by using this catalyst (1 mg ml−1, 290 UI g−1) was still 90%, even after 10 cycles of 10 min, in batch process but it could be also implemented on continuous processes at industrial level with similar results.

PEG-g-chitosan nanoparticles functionalized with the monoclonal antibody OX26 for brain drug targeting

AIM Drug targeting to the CNS is challenging due to the presence of blood-brain barrier. We investigated chitosan (Cs) nanoparticles (NPs) as drug transporter system across the blood-brain barrier, based on mAb OX26 modified Cs. MATERIALS & METHODS Cs NPs functionalized with PEG, modified and unmodified with OX26 (Cs-PEG-OX26) were prepared and chemico-physically characterized. These NPs were administered (intraperitoneal) in mice to define their ability to reach the brain. RESULTS Brain uptake of OX26-conjugated NPs is much higher than of unmodified NPs, because: long-circulating abilities (conferred by PEG), interaction between cationic Cs and brain endothelium negative charges and OX26 TfR receptor affinity. CONCLUSION Cs-PEG-OX26 NPs are promising drug delivery system to the CNS.

Synthesis of new silicas with high stable and large mesopores and macropores for biocatalysis applications

Monomodal or bimodal porous silicas with large mesopores, constituted by particles or having a monolithic (block type) morphology, respectively, are synthesized using sodium silicate as siliceous species source, cetyltrimethylammonium bromide (CTAB) as pore template and ethyl acetate (EtAc) as pH modifier. The monomodal porosity is represented by 20-30 nm pores and the bimodal one by these pores and also macropores. These characteristics are modulated in function of the CTAB and EtAc concentrations as well as the pH and hydrothermal treatment. The role of these reagents upon the porosity is rationalized. The presence of high CTAB concentration and a rather low pH decreasing rate (function of EtAc concentration and hydrothermal treatment) are essential for having the already known bimodal mesoporous silicas (BMS). On the contrary a rather high pH decreasing rate promotes the formation of the new bimodal mesoporous-macroporous silicas (BMMS) synthesized in this work, where the EtAc also plays the role of emulsion forming agent. The hydrolytic stability of the synthesized silica under aqueous conditions, at different pH values, makes these silicas good candidates for application in different areas of catalysis, especially in the enzymatic one.

Characterization of a heteropolyacid supported on mesoporous silica and its application in the aromatization of α-pinene

H3PW12O40.xH2O was loaded (33 wt%) by impregnation into a calcined mesoporous silica. The Keggin structure was characterized by XRD, TGA, N2 adsorption and 31P MAS NMR. The bi-functionality (acid/redox) of this catalyst was then studied using the transformation of α-pinene between 40 and 160 °C in a batch reactor. The substrate is transformed into camphene and terpinene by isomerization on the acid sites. The latter is transformed in a second step at higher temperature into p-cymene by a dehydrogenation on the acid and redox sites. 3-p-menthene and carvomenthene are produced, in low yield, together with p-cymene, by a disproportionation reaction of the terpinenes.

Biodegradation of poly(vinylalcohol-co-ethylene) with the fungus phanerochaete chrysosporium

Abstract  Under appropriate conditions for lignine peroxidase production in a culture medium that contains spores of Phanerochaete Chrysosporium fungus, the biodegradation of ethylene vinyl alcohol (EVOH) pellets with 27% mole of ethylene content was observed after 30 days. The oxidative degradation was detected by Fourier Transform Infrared Spectroscopy (FTIR) through the formation of hydroperoxides containing chains which were broken with degradation time. Differential Scanning Calorimetry (DSC) initially showed only one melting peak and after 30 days two peaks appeared on the thermogram, one due to the remaining copolymer that did not change with degradation time and the other due to the polymer degradation sequence.When EVOH film with a similar amount of ethylene was used, the initial melting temperature (Tm) decreased during degradation and a second crystalline sequence with a lower Tm was produced, indicating that both copolymer sequences were degraded. Observed differences in the biodegradative behavior between EVOH pellets and EVOH film were mainly due to the changes in crystallinity of the copolymer induced by film processing. The initial EVOH film showed a lower crystallinity and the presence of double bonds, which favors the degradative process.

Contribution to the study of the formation mechanism of ordered porous carbons from a soft-template method using the copolymer triblock (PEO140PPO39PEO140) and a phenolic resin

Different porous carbons were synthesized using direct self-assembly of a nonionic surfactant (PEO140PPO39PEO140, PEO poly(ethylene oxide) and PPO poly(propylene oxide)) and a phenolic resin. According to dynamic light scattering (DLS) experiments realized before the flocculation, the formation of covered hybrid micelles (precursors of ordered mesoporous materials) competes with the formation of resol particles depending on the surfactant concentration. High synthesis temperature increases the formation of mesoporosity. When monomers (instead of oligomers) are used as resin precursors, the mesoporosity is also enhanced. However in this case, the formation of resol particles is also favored. The obtained materials are mainly microporous, indicating that the formed polymer/surfactant hybrid micelles are not stable enough to template the formation of highly mesoporous carbons. Appropriate interaction between the surfactant micelles and resin precursor species, as well as the polymerization degree of the resin, is crucial for obtaining polymer/surfactant hybrid micelles that conduce to mesoporous carbons.