Preparation and photocatalytic activity of highly ordered mesoporous TiO2–SBA-15

TiO₂–SBA-15 complex materials with highly ordered mesostructures have been prepared by a one-step hydrothermal synthesis method of titanium tetraisopropoxide (TTIP) and tetraethoxysilane (TEOS) in an acidic solution using surfactant P123 (EO₂₀PO₇₀EO₂₀) as structure-directing reagent. The prepared materials were characterized by transmission electron microscopy (TEM), small-angle X-ray diffraction patterns (SAXRD), Fourier transformed infrared spectroscopy (FT-IR) and N₂ adsorption–desorption experiments. The resulting TiO₂–SBA-15 complex materials showed highly ordered mesoporous structure with uniform pore sizes of 5.95 and 8.24 nm, high specific surface areas S_BET of 689 m² g^? 1 and 347 m² g^? 1 at different hydrothermal temperatures (100 °C and 130 °C). The photocatalytic activity of these TiO₂–SBA-15 mesoporous materials has been studied by 4-chlorophenol decomposition under UV light irradiation. The TiO₂–SBA-15 mesoporous materials prepared at the TiO₂:SiO₂ mass ratios of 25:75, 40:60 and 50:50 showed higher photocatalytic activity than that prepared at the TiO₂:SiO₂ mass ratio of 75:25.     

Controlled synthesis of semiconductor PbWO4 nanocrystals inside silica SBA-15 materials

A new flexible approach is developed to synthesize PbWO₄ nanoparticles inside the channels of mesoporous silica SBA-15. Mesoporous SBA-15 silica with 7 nm pores was produced by a hydrothermal process and used as a hard template. PbWO₄ nanoparticles were synthesized and incorporated into the mesoporous silicate support in a low-power ultrasonication condition. The as-synthesized samples were characterized by Raman spectroscopy, diffuse reflectance UV–vis spectroscopy (UV–vis), powder X-ray diffraction (XRD), small-angle X-ray diffraction (SAXRD), nitrogen adsorption and transmission electron microscopy (TEM). It was found that PbWO₄ nanoparticles appeared among the channels of SBA-15. Blue shift was observed in UV–vis absorption spectra due to the quantum size effect of PbWO₄ nanoparticles. This preparation method is also capable of synthesis of various semiconductor nanoparticles with controlled size and morphology inside the channels of mesoporous materials.     

Inclusion of cefalexin in SBA-15 mesoporus material and release property

SBA-15 (Santa Barbara Amorphous-15) is a high ordered mesoporous material. It has the advantages of a non-toxic property, good hydrothermal stability and thermal stability, etc. Inside inner surface a lot of silanols exist. Pore diameter size is uniform and pore size distribution is narrow. This structural feature makes SBA-15 have a higher loading drug amount and be able to effectively extend the drug release cycle. In this paper, polyethylene glycol-block-polypropylene glycol-block-polyethylene glycol was used as template and tetraethyl orthosilicate was used as silica source to prepare SBA-15 by hydrothermal synthesis method. Cefalexin was included in SBA-15 and the included cefalexin drug content was 158.72 mg/g. The composite materials were characterized by using chemical analysis, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), infrared (IR) spectroscopy, and low temperature nitrogen adsorption–desorption. The results showed that cefalexin had been successfully included in host SBA-15 pore channels. Rational analyses of the release processes of cefalexin drug from the pores of SBA-15 to the simulated body fluid, simulated gastric juice and simulated intestinal fluid were made and sustained-release effects of the drug in complex system were studied. The results showed that in simulated body fluid within 1–5 h cefalexin was fast released and the cumulative release reached 50.00% at 5 h. In 15–20 h, the sustained release speed of cefalexin drug in the composite material decreased and the sustained-release cumulative amount reached 99.87% at 20 h. The release of cefalexin was basically complete. In simulated gastric fluid, composite material sustained-release ended at 4 h, the cumulative sustained release ratio reaching 26.10%. In simulated gastric fluid, the sustained-release was complete at 7 h, the cumulative sustained release ratio reaching 32.46%. The composite material of SBA-15 and cefalexin could improve efficiency of the sustained-release of drug and has a very great potential applicable value.     

The morphology and size of nanostructured Au in Au/SBA-15 affected by preparation conditions

Template-free mesoporous silica SBA-15 was reacted with TPTAC to generate positively charged functional groups PTA⁺ on the pore surface. Through ion exchange, a uniform distribution of anionic metal complexes on the intrachannel surface of host silica was achieved. In this study, ethanol and water were used as solvent for HAuCl₄ precursor solutions impregnated on SBA-15 mesoporous silica. The solvent used can affect the size and location of the resulting nanoparticles. Large Au nanoparticles (15–43 nm) were found on the as-prepared Au/SBA-15 as observed by PXRD, XAS, UV–vis and TEM. This may have originated through Si–OH reduction of chloroaurate complexes generated in the aqueous solution of HAuCl₄, and such particles were not present when ethanolic solution was used. After NaBH₄ and H₂ reduction, the average size of Au nanoparticles, which was incorporated into the channels of SBA-15, was found to be limited to ≤  7 nm.     

Magnetic separation and adsorptive performance for methylene blue of mesoporous NiFe2O4/SBA-15 nanocomposites

Magnetic NiFe₂O₄/SBA-15 nanocomposites were synthesized by a facile impregnation method, and NiFe₂O₄ nanoparticles presented spinel phase structure and existed in the mesopores of SBA-15. Partial mesopores were blocked by NiFe₂O₄ nanoparticles and micropores formed, which the capillarity of micropores played a decisive role for methylene blue (MB) adsorption. The saturation magnetization increased from 2.34 emu g^?1 to 10.03 emu g^?1 with the NiFe₂O₄ content, while the specific surface area decreased from 552.18 m² g^?1 to 260.40 m² g^?1 and pore volume decreased from 1.13 cm³ g^?1 to 0.49 cm³ g^?1. MB adsorption could be improved by optimizing the NiFe₂O₄ content of the nanocomposites. MB could be adsorbed completely in 60 min with the optimum nanocomposites and could be separated easily from water by magnetic separation technique.     

Photocatalytic properties of the SBA-15 mesoporous silica molecular sieve modified with titanium

We describe three methods of post-synthesis modification of the SBA-15 mesoporous molecular sieve with titanium: impregnation with Ti(OEt)₄ in an ethanolic solution, grafting with titanocene dichloride, and modification with colloidal titania. The products were characterized using X-ray diffraction (XRD) and N₂ adsorption as well as Fourier-transform infrared and ²⁹Si NMR spectroscopies. All three methods yield materials containing 1.4--4.7 wt.% titanium and with high surface areas. The absorbance at 960 cm⁻¹ in SBA-15 modified with colloidal titania and SBA-15 grafted with titanocene indicates the formation of Ti–O bonds. All products showed significant activity towards the degradation of p-chlorophenol. UV-vis absorption spectra of SBA-15 samples modified with titanium indicate that the variation in the photocatalytic activity is governed by isolated titanium sites.     

Synthesis of nano titania particles embedded in mesoporous SBA-15: characterization and photocatalytic activity

Supported nanocrystalline titanium dioxide (TiO2) has been prepared by a post-synthesis step via Ti-alkoxide hydrolysis through the use of mesoporous SBA-15 silica. TiO2/SBA-15 composites with various TiO2 loading have been prepared and characterized by X-ray diffraction, nitrogen adsorption, Fourier transform infrared spectroscopy and diffusive reflective UV-vis spectroscopy. The addition of mesoporous SBA-15 prevents the anatase to rutile phase transformation and the growth of crystal grain. TiO2 did not block the SBA-15 pores, and their surface was fully accessible for nitrogen adsorption. Calcination in air of the composites up to 800 degrees C did not change the nanocrystal phase and slightly increased the domain size from 5.0 to 7.5 nm, indicating that the anatase TiO2 grains in the mesostructures have a relatively high thermal stability and proper pore diameter allows controlling the size of obtained titania particles. The TiO2/SBA-15 composites prepared by this study showed much higher photodegradation ability for methylene blue (MB) than commercial pure TiO2 nanoparticles P-25. Experimental results indicate that the photocatalytic activity of titania/silica mixed materials depends on the adsorption ability of composite and the photocatalytic activity of the titania, and there is an optimal ratio of Ti:Si, too high or low Ti:Si ratio will lower the photodegradation ability of the composites.     

Enhanced stability of catalase covalently immobilized on functionalized titania submicrospheres

In this study, a novel approach combing the chelation and covalent binding was explored for facile and efficient enzyme immobilization. The unique capability of titania to chelate with catecholic derivatives at ambient conditions was utilized for titania surface functionalization. The functionalized titania was then used for enzyme immobilization. Titania submicrospheres (500–600 nm) were synthesized by a modified sol–gel method and functionalized with carboxylic acid groups through a facile chelation method by using 3-(3,4-dihydroxyphenyl) propionic acid as the chelating agent. Then, catalase (CAT) was covalently immobilized on these functionalized titania submicrospheres through 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride/N-hydroxysuccinimide (EDC/NHS) coupling reaction. The immobilized CAT retained 65% of its free form activity with a loading capacity of 100–150 mg/g titania. The pH stability, thermostability, recycling stability and storage stability of the immobilized CAT were evaluated. A remarkable enhancement in enzyme stability was achieved. The immobilized CAT retained 90% and 76% of its initial activity after 10 and 16 successive cycles of decomposition of hydrogen peroxide, respectively. Both the K_m and the V_max values of the immobilized CAT (27.4 mM, 13.36 mM/min) were close to those of the free CAT (25.7 mM, 13.46 mM/min).     

Enhanced photoactivity and anatase thermal stability of silica–alumina mixed oxide additives on sol–gel nanocrystalline titania

Nanocrystalline titania with silica and silica–alumina mixed oxide as additives has been prepared through a sequential approach sol–gel method starting from titanyl sulphate in aqueous medium. The mixed oxide added titania shows increased anatase phase stability and high surface area. The complete transformation of anatase to rutile in the mixed oxide added titania occurs only above 1100 °C. The silica and silica–alumina added titania precursor even after calcination at 800 °C show specific surface area of 53 m² g^− 1 and 63 m² g^− 1 respectively. Further, the mixed oxide added titania sample shows excellent photoactivity compared to the commercially available Hombikat UV 100 titania, with respect to degradation of methylene blue. The addition of mixed oxide has resulted in better properties with respect to specific surface area, increased anatase to rutile phase transformation and photocatalytic activity of titania.     

Development of amperometric laccase biosensor through immobilizing enzyme in copper-containing ordered mesoporous carbon (Cu-OMC)/chitosan matrix

A functionalized copper-containing ordered mesoporous carbon (Cu-OMC) which shows good electrical properties was synthesized by carbonization of sucrose in the presence of cupric acetate inside SBA-15 mesoporous silica template. Based on this, a facilely fabricated amperometric biosensor by entrapping laccase into the Cu-OMC/chitosan (CS) film was developed. Laccase from Trametes versicolor was assembled on a composite film of Cu-OMC/chitosan (CS) modified Au electrode and the electrode was characterized. The optimum experimental conditions of biosensor for the detection of catechol were studied in details. Under the optimal conditions, the detection limit was 0.67 μM and the linear detection range was from 0.67 μM to 15.75 μM for catechol. The apparent Michaelis–Menten (K_M^app) was estimated using the Lineweaver–Burk equation and the K_M^app value was 40.2 μM. This work demonstrated that the Cu-OMC/CS composite provides a suitable support for laccase immobilization and construction of biosensor.     

Thermal stability of silica-coated magnetite nanoparticles prepared by an electrochemical method

Magnetite nanoparticles have been prepared by electrooxidation of iron in water. Surface modifications have been conducted by coating the nanoparticles with silica by a one-step synthesis in dilute sodium silicate solution. The mean size of particles was approximately 10–30 nm for the uncoated particles and 9–12 nm for the coated particles. The results obtained from thermal gravimetric/differential thermal analysis (TG/DTA) revealed that the silica layer formed by the electrochemical method was stable and could serve as a protective layer. Annealing the nanoparticles at 550 °C for 30 min converts magnetite into maghemite for the silica-coated particles, and it further converts the uncoated particles into hematite. The conversions cause the saturation magnetization to decrease for all samples.     

Influence of Nd dopant amount on microstructure and photoluminescence of TiO2:Nd thin films

TiO₂ and TiO₂:Nd thin films were deposited using reactive magnetron sputtering process from mosaic Ti–Nd targets with various Nd concentration. The thin films were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and spectroscopic techniques. Photoluminescence (PL) in the near infrared obtained upon 514.5 nm excitation was also examined. The relationship between the Nd concentration, structural, optical and photoluminescence properties of prepared thin films was investigated and discussed. XRD and TEM measurements showed that an increase in the Nd concentration in the thin films hinders the crystal growth in the deposited coatings. Depending on the Nd amount in the thin films, TiO₂ with the rutile, mixed rutile–amorphous or amorphous phase was obtained. Transmittance measurements revealed that addition of Nd dopant to titania matrix did not deteriorate optical transparency of the coatings, however it influenced on the position of the fundamental absorption edge and therefore on the width of optical band gap energy. All TiO₂:Nd thin films exhibited PL emission that occurred at ca. 0.91, 1.09 and 1.38 μm. Finally, results obtained for deposited coatings showed that titania with the rutile structure and 1.0 at.% of Nd was the most efficient in VIS to NIR photon conversion.     

Blending effect of sucrose and surfactant templating agents on silica mesostructure

We report the blending effect of surfactant and sucrose as a nonsurfactant templating agent on the silica mesostructure. The CTAB/sucrose-templated mesoporous silica (SCS) was compared with CTAB-templated MCM-41. The MCM-41 showed spherical morphology with a particle diameter of 1.1–1.5 μm, and gave a bimodal size distribution, centered at 2.1 nm and 8.9 nm, which is assigned to hexagonally-arrayed cylindrical pores and interparticle-pores between small MCM-41 clusters, respectively. SCS gave unique and extraordinary morphology in which two different mesostructures have grown with both of them facing each other. The ordered MCM-41 pore structure clung to silica nanosphere-framed wormlike mesostructure, resulting in a bimodal pore size distribution centered at 2.1 nm and 7.0 nm. It was revealed that both of CTAB and sucrose act independently as a surfactant and a nonsurfactant template.     

Comparative study on the structural and catalytic properties of mesoporous hexagonal silica anchored with H3PW12O40: Green synthesis of benzoic acid from benzaldehyde

Mesoporous silica anchored with 25 wt.% 12-tungstophosphoric acid (H₃PW₁₂O₄₀, HPW) were comparatively characterized on their structures and catalytic activities for benzaldehyde oxidation with H₂O₂. The results revealed that the mesoporous materials retained the typical hexagonal mesopores for the supports of HPW. It was found that HPW exhibited higher dispersion within MCM-41 than those within SBA-15 and other mesoporous molecular sieves. Moreover, the as-prepared materials were found to be the efficient catalysts for the green synthesis of benzoic acid. In particular, HPW/MCM-41 exhibited the best catalytic properties due to its suitable textural and structural characteristics.     

Recovery of high surface area mesoporous silica from waste hexafluorosilicic acid (H2SiF6) of fertilizer industry

In this article we report recovery of mesoporous silica from the waste material (hexafluorosilicic acid) of phosphate fertilizer industry. The process involves the reaction of hexafluorosilicic acid (50 ml, 24 wt% H₂SiF₆) and 100 ml, 0.297 M Na₂CO₃ to generate the alkaline aqueous slurry. Silica was separated from the slurry by filtration and the sodium fluoride was extracted from the aqueous solution by evaporation method. The obtained mesoporous silica was characterized by N₂ absorption/desorption (BET), thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscope (SEM), and EDS. The results confirm that the separation of silica and NaF was successful and the final products have high purity. The silica product was found to have an average pore diameter of 4.14 nm and a high surface area (up to 800 m²/g). The process reported in this study may significantly reduce the release of hazardous materials into the environment and it might confer economic benefits to the responsible industries.     

Preparation and characterization of V/TiO2 nanocatalyst with magnetic nucleus of iron

A magnetic composite containing V/TiO₂ was prepared by combination of sol–gel and wetness impregnation methods. The effects of synthesis temperature, different weight percents of Fe supported on TiO₂, vanadium loading and the heating rate of calcination on the structure and morphology of nanocatalyst were investigated. The optimum conditions for synthesized catalyst were 40 wt.% of Fe, 15 wt.% of V and synthesis temperature equal to 30 °C. Characterization of catalyst is carried out using XRD, TGA, DSC, SEM, FTIR and N₂ physisorption measurements. The magnetic character of nanocatalyst was measured using VSM, which showed the typical paramagnetic behavior of sample at room temperature with a saturation magnetization value equal to 8.283 emu/g. The nanocatalyst has a particle size about 56 nm and can easily be separated from medium by a magnet.     

Multistep loading of titania nanoparticles in the mesopores of SBA-15 for enhanced photocatalytic activity

A multistep deposition of anatase nanoparticles was employed to incorporate high amounts of titania into the mesopores of SBA-15. Anatase nanoparticles were synthesized and deposited following the Acid Catalyzed Sol Gel method. With this method, the size of the anatase nanoparticles can be controlled and therefore, the titania loading into the mesopores of SBA-15 can be controlled. Through multistep deposition of anatase nanoparticles, a further increase of titania loading into the mesoporous channels can be obtained. For the degradation of Rhodamine-6G, the samples synthesized by multistep deposition showed an enhanced photocatalytic activity.     

Synthesis and characterization of Co/SiO2 as catalyst catalyze hydrogen generation

Novel composites of porous SiO₂-LP and SiO₂-HP supports are synthesized by the silica–polyethylene glycol monooleyl ether surfactant self-assembly method to obtain a large surface area. Cobalt is immobilized in the supports by incipient wetness impregnation. A stable and active Co/SiO₂ catalyst is examined using FE-SEM, BET and XRD. Further, the catalyst is tested for catalytic hydrolysis of alkaline sodium borohydride (NaBH₄) solution: the rate of hydrogen generation is found to increase with increasing cobalt loading of the Co/SiO₂ catalyst. The hydrogen generation rates increase dramatically when the temperature is increased from 17 to 40 °C. The highest hydrogen generation rates of Co/SiO₂ catalyst are obtained at 2513 mL min^? 1 g^? 1 in 20 mL of 5 wt.% NaBH₄ solution containing 5 wt.% NaOH at 40 °C.     

Selective adsorption and release of cationic organic dye molecules on mesoporous borosilicates

Mesoporous materials can play a pivotal role as a host material for delivery application to a specific part of a system. In this work we explore the selective adsorption and release of cationic organic dye molecules such as safranine T (ST) and malachite green (MG) on mesoporous borosilicate materials. The mesoporous silica SBA-15 and borosilicate materials (MBS) were prepared using non-ionic surfactant Pluronic P123 as template via evaporation induced self-assembly (EISA) method. After template removal the materials show high surface areas and in some cases ordered mesopores of dimensions ca. 6–7 nm. High surface area, mesoporosity and the presence of heteroatom (boron) help this mesoporous borosilicate material to adsorb high amount of cationic dye molecules at its surface from the respective aqueous solutions. Furthermore, the mesoporous borosilicate samples containing higher percentage adsorbed dyes show excellent release of ST or MG dye in simulated body fluid (SBF) solution at physiological pH = 7.4 and temperature 310 K. The adsorption and release efficiency of mesoporous borosilicate samples are compared with reference boron-free mesoporous pure silica material to understand the nature of adsorbate–adsorbent interaction at the surfaces.     

Properties of highly oriented K(Sr,Ba)2Nb5O15 thin films derived from a metal-alkoxide precursor solution

Highly oriented tungsten–bronze K(Sr,Ba)₂Nb₅O₁₅ (KSBN) thin films have been fabricated by a chemical solution deposition method. Alkoxy-derived K(Sr_0.5Ba_0.5)₂Nb₅O₁₅ (KSBN50) thin films directly crystallized into a tetragonal tungsten–bronze phase on fused silica, MgO(1 0 0), and Pt(1 0 0)/MgO(1 0 0) substrates with c-axis preferred orientation at 700 °C by optimizing the processing conditions. Ferroelectric KSBN50 thin films on Pt(1 0 0)/MgO(1 0 0) exhibited the diffuse-phase transition and typical relaxor-type dielectric behavior, which are characteristic properties along the c-axis of the tungsten–bronze (Sr,Ba)Nb₂O₆ crystal. The KSBN thin films synthesized on fused silica and MgO(1 0 0) showed high transparency over a wide wavelength range. The propagation modes of the synthesized KSBN thin films were characterized by the prism coupling method. The values of their refractive indices in TE and TM modes were 2.27 and 2.25, respectively.