Showing papers on "Mesoporous silicate published in 2018"

Comparison of different kinetic models for adsorption of acid blue 62 as an environmental pollutant from aqueous solution onto mesoporous Silicate SBA-15 modified by Tannic acid

Abstract: In this work, adsorption kinetics were investigated in order to remove the acid blue 62 off the aqueous solutions using mesoporous silicate SBA-15 loaded with tannic acid (tannin-SBA-15). Nitrogen adsorption and desorption test (BET), X-ray diffraction (XRD) and Fourier transform infra-red spectroscopy (FT-IR) analysis characterize synthesized composite. The impacts of some parameters such as PH, adsorbent dosage as well as contact time were studied and optimized at temperatures between 25 to 45 oC. The study also was conducted on intra-particle diffusion, pseudo first-order, pseudo second-order and Elovich kinetic models. In order to have the best correlation with the experimental data, the model of the second-order kinetics was discovered. The model of the intra-particle diffusion represents that both boundary layer and intra-particle diffusion processes control the mechanisms of adsorption of acid blue 62 onto tannin-SBA-15.

Substitutions of zinc in mesoporous silicate-based glasses and their physicochemical and biological properties

Abstract: Mesoporous bioactive silicate-based glasses in the system of (38-x)CaO–xZnO–58SiO2– 4P2O5 (mol.%), where x varies between 0 and 20, have been prepared by the sol–gel method. The influence of zinc addition on glass physicochemical properties, degradability and apatite- formation ability was comprehensively investigated. The nitrogen adsorption/desorption results confirmed the glasses mesoporous structure. The degradability of glass was studied in Tris–HCl, the addition of zinc would lead to a decrease. Furthermore, the glass apatite-formation ability was assessed by immersion of samples in simulated body fluid (SBF) solution for up to 7 days. The changes in glass surface morphology and composition were detected using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) and fourier transform infrared spectroscopy (FTIR). It was observed that the apatite precipitation rate slowed down with the increase of zinc, suggesting that the incorporation of zinc could be a promising route to regulate the dissolution and apatite formation of silicate-based glasses.

Synthesis of MCM-41 nanoparticles from stem of common reed ash silica and their application as substrate in electrooxidation of methanol

Abstract: In this work, stem of common reed ash (SCRA) is introduced as a new source of silica in the preparation of mesoporous materials. Mesoporous silicate MCM-41 nanoparticles were synthesized hydrothermally using sodium silicate prepared from SCRA as a silica source. The characterization of MCM-41was carried out by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), N $$_{2}$$ adsorption/desorption (BET) and transmission electron microscopy (TEM). SEM shows that MCM-41 nanoparticles are sphere-like with size in the range of 30–50 nm with some degree of agglomeration. TEM image of the synthesized sample shows the open framework structure of MCM-41. A type IV isotherm can be observed from adsorption/desorption curves, which is the characteristic of mesoporous materials. The prepared MCM-41 nanoparticles were used as substrate to facilitate the oxidation of methanol through the modification with an electroactive species. The modification was achieved by impregnation of MCM-41 pores with $$\hbox {Ni}^{2+}$$ ions (Ni-doped MCM-41). A modified carbon paste electrode (CPE) was prepared by mixing Ni-doped MCM-41 with carbon paste (NiMCM-41CPE). Cyclic voltammetry of NiMCM-41CPE shows an increment in current density of methanol oxidation in comparison with CPE in alkaline solution. Moreover, a decrease in the overpotential of methanol oxidation occurred on the surface of modified electrode. The effects of some parameters such as scan rate and methanol concentration are also investigated on the behaviour of NiMCM-41CPE. Also, the heterogeneous electron transfer rate for the catalytic reaction (k) of methanol is calculated.

Identification of the Basic Sites on Nitrogen-Substituted Microporous and Mesoporous Silicate Frameworks Using CO2 as a Probe Molecule.

Abstract: Carbon dioxide was shown to identify surface basic properties of nitrogen-substituted microporous and mesoporous silicas, in addition to conventional basic oxides, by a detailed study using isotherm and heat of adsorption measurements as well as by infrared spectroscopy. A hydrogen-bonded weak interaction was primarily observed between CO2 and silanol (Si-OH) and silamine (Si-NH-Si) groups. The heat of adsorption of CO2 demonstrated that the latter adspecies were formed preferentially over the former, although a much higher amount of linear CO2 adspecies were found on SBA-15 mesoporous silica because of the presence of a large quantity of silanol groups on its surface. Carbamate-type chemisorbed adspecies were not detected on silamino sites, whereas carbonate-type adspecies were formed on alkali ion-exchanged zeolites and also residual sodium ions on the surface of silicalite-1. CO2 was shown to be a successful probe molecule for identifying weakly interactive hydrogen-bonding sites, and it has potential as a surface probe for strongly interactive nucleophilic sites derived from alkaline ions or a methylated silamino group, Si-N(CH3)-Si.

Radiation response of cubic mesoporous silicate and borosilicate thin films

Abstract: The radiation response has been studied of cubic mesoporous silicate and borosilicate thin films having different boron contents prepared using the block copolymer template Brij 58 and the dip coating technique. The degree of pore ordering of the films was analysed using low-angle X-ray diffraction and film thickness measured by X-ray reflectivity. For films calcined at 350 °C, the incorporation of boron resulted in a reproducible oscillatory variation in the d-spacing and intensity of the primary reflection as a function of boron content. A clear peak was observed in the d-spacing at 5–10 mol% boron incorporation. For borosilicate films of a given composition an overall suppression of d-spacing was observed as a function of aging time relative to films that did not contain boron. This was ascribed to a slow condensation process. The films were irradiated in pile with neutrons and with iodine ions at energies of 180 keV and 70 MeV. Neutron irradiation of the silicate thin films for periods up to 30 days and aged for 400 days resulted in little reduction in either d-spacing or intensity of the primary low-angle X-ray reflection indicating that the films retained their mesopore ordering. In contrast borosilicate films for which the B (n, α) reaction was expected to result in enhanced displacement damage showed much larger variations in X-ray parameters. For these films short irradiation times resulted in a reduction of the d-spacing and intensity of the primary reflections considerably beyond that observed through aging. It is concluded that prolonged neutron irradiation and internal α irradiation have only a small, although measurable, impact on mesoporous borosilicate thin films increasing the degree of condensation and increasing unit cell contraction. When these borosilicate films were irradiated with iodine ions, more profound changes occurred. The pore ordering of the films was significantly degraded when low energy ions were used. In some cases the degree of damage was such that no low-angle reflection could be observed. This degradation of pore ordering was confirmed in scanning electron microscopy images of the irradiated films.

Controlled and localized delivery of c-myc AS-ODN to cells by 3-aminopropyl-trimethoxylsilane modified SBA-15 mesoporous silica

Abstract: SBA-15 mesoporous silicate was synthesized and functionalized with 3-aminopropyl organic groups through a post-synthesis method. The materials were characterized consecutively by powder X-ray diffraction (XRD), N2 adsorption/desorption analysis and solid-state magic-angle spinning 29Si nuclear magnetic resonance (MAS NMR). Human c-myc anti-sense oligodeoxyneucleotide (AS-ODN) was selected as a model molecule to be loaded onto the surface of bare and functionalized SBA-15 via different loading conditions. It has been found that the amount of AS-ODN incorporated into the porous matrix is strongly dependent on the surface properties, pH of the loading solvent and AS-ODN concentration. The release behaviour of AS-ODN from modified SBA-15 materials was also investigated and depended on conditions chosen. Cellular uptake of the eluted AS-ODN into Hela cells was observed by fluorescent microscopy. The materials showed excellent cytocompatibility. The AS-ODN keeps full transfection and expression activities indic...