Acylisoxazolone-impregnated Si-MCM-41 mesoporous materials as promising liquid-solid extractants of metals

The solid-liquid extraction of Cu(II) from 0.33 M (Na⁺, H⁺)SO₄²⁻ sulphate medium at 25 °C by calcined mesoporous materials type Si-MCM-41, impregnated by the acidic extractant 3-phenyl-4-benzoyl-isoxazol-5-one (HPBI), has been tested. The Si-MCM-41 material was impregnated by HPBI using the dry impregnation method. It was characterized by physico-chemical methods: N₂-sorption, XRD, SEM and determination of the amount of HPBI in the solid. The extraction rate was determined as a function of pH and extractant concentration in the material. The extraction of Cu(II) into impregnated mesoporous material can reach 99%.     

Hydrothermal synthesis, characterization, photocatalytic activity and dye-sensitized solar cell performance of mesoporous anatase TiO2 nanopowders

Mesoporous anatase TiO₂ nanopowder was synthesized by hydrothermal method at 130 °C for 12 h. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), HRTEM, and Brunauer-Emmett-Teller (BET) surface area. The as-synthesized sample with narrow pore size distribution had average pore diameter about 3-4 nm. The specific BET surface area of the as-synthesized sample was about 193 m²/g. Mesoporous anatase TiO₂ nanopowders (prepared by this study) showed higher photocatalytic activity than the nanorods TiO₂, nanofibers TiO₂ mesoporous TiO₂, and commercial TiO₂ nanoparticles (P-25, JRC-01, and JRC-03). The solar energy conversion efficiency (η) of the cell using the mesoporous anatase TiO₂ was about 6.30% with the short-circuit current density (Jsc) of 13.28 mA/cm², the open-circuit voltage (Voc) of 0.702 V and the fill factor (ff) of 0.676; while η of the cell using P-25 reached 5.82% with Jsc of 12.74 mA/cm², Voc of 0.704 V and ff of 0.649.     

Photoinduced charge property of nanosized perovskite-type LaFeO3 and its relationships with photocatalytic activity under visible irradiation

In this paper, ABO₃-type perovskite LaFeO₃ nanosized photocatalysts were synthesized by a sol-gel method, using citric acid (HOOCCH₂C(OH)(COOH)CH₂COOH) as complexing reagent and La(NO₃)₃·6H₂O and Fe (NO₃)₃·9H₂O as raw materials. The as-prepared samples also were characterized by several testing techniques, such as thermogravimetry-differential thermal analysis (TG-DTA), X-ray powder diffraction (XRD), Brunauer-Emmett-Teller (BET), infrared spectrum (IR), ultraviolet-visible diffuse reflection spectrum (UV-vis DRS), photoluminescence spectrum (PL), surface photovoltage spectroscopy (SPS) and electrical field induced surface photovoltage spectroscopy (EFISPS). The sample activity of different LaFeO₃ nanoparticles for degrading Rhodamine B solution under visible irradiation (λ > 400 nm) was evaluated. The effects of thermal treatment temperature on photoinduced charge property and photocatalytic activity were mainly investigated, together with their relationships. The results show that the LaFeO₃ sample calcined at 500 °C exhibits higher activity, and the activity decreases with increasing calcination temperature, which is in good agreement with the characterization results. The weaker is the PL and SPS signal, the higher is the photocatalytic activity. Moreover, the activity of all as-prepared LaFeO₃ samples is higher than that of international P-25 TiO₂ under visible irradiation.     

M2Y8(SiO4)6O2: Tb (M = Ca, Sr) phosphors: Sol-gel synthesis from N-2-aminoethylic-3-aminopropyldiethoxysilane and different photoluminescence behavior

M₂Y₈(SiO₄)₆O₂: Tb³⁺ (M = Ca, Sr) phosphors have been synthesized with a new silicon source silane crosslinking reagent (N-2-aminoethylic-3-aminopropyldiethoxysilane [NH₂(CH₂)₂NH(CH₂)₃SiCH₃(OCH₃)₂], abbreviated as AEAPMMS) through the sol-gel process, both of which present the characteristic emission ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) of Tb³⁺ ions. It is interesting to be found that the high energy level blue emission (⁵D₃ → ⁷F_J (J = 6, 5, 4, 3) transition) still can be found in the emission spectrum of Ca₂Y₈(SiO₄)₆O₂: Tb³⁺ while it disappears in the emission spectrum of Sr₂Y₈(SiO₄)₆O₂: Tb³⁺ for the cross-relaxation-induced quenching.     

pH-Controlled drug release from mesoporous silica tablets coated with hydroxypropyl methylcellulose phthalate

A simple pH-controlled drug release system was successfully prepared by coating pH-sensitive polymer hydroxypropyl methylcellulose phthalate (HPMCP) on drug-loaded mesoporous SBA-15 tablet. Using famotidine (Famo) as a model drug, the effects of coating times and drying temperature on drug release were studied in detail to optimize the drug release system. In simulated gastric fluid (SGF, pH 1.2), it took only 2 h for Famo to be completely released from mesoporous silica tablet without HPMCP coating. Also in SGF, with the increase of coating times and drying temperature, the release of Famo was greatly delayed by HPMCP coating. For the tablet with twice coating of HPMCP and dried at 80 °C, only 4.0 wt.% of Famo could be released within 4 h. However, in simulated intestinal fluid (SIF, pH 7.4), HPMCP coating did not show obvious effect on the release of Famo.     

An aqueous sol-gel synthesis of chromium(III) doped mesoporous titanium dioxide for visible light photocatalysis

Nanoparticles of titanium dioxide doped with Cr³⁺ ions have been prepared through an aqueous sol-gel method. The mesoporous nature of both pure and Cr³⁺ doped TiO₂ powders, with specific surface area of 7.4 and 6.6 m² g⁻¹, respectively, is maintained even at calcination temperature of 800 °C. The transformation of TiO₂ from the anatase to rutile phase is suppressed up to 800 °C by Cr³⁺ ion doping. Even though surface area values are decreased, the doped materials show improved photocatalytic activity, which may be due to increased crystallinity of the anatase phase without the formation of rutile. Doped materials have a red-shift in the band gap energy and hence, photoactivity under visible light. The rate of photodegradation of methylene blue dye for both pure and doped TiO₂ under visible light has been monitored in this study. The 0.25 mol% Cr(III) doped photocatalyst, calcined at 800 °C, shows the highest photocatalytic activity under visible light with a rate constant of ∼15.8 × 10⁻³ min⁻¹, which is nearly three times higher than that of commercially available Degussa P25 titania (5.8 × 10⁻³ min⁻¹).     

One-step synthesis of hydrophobic mesoporous silica ellipsoidal particles with a bimodal mesopore system

Highly CH₃-functionalized mesoporous silica ellipsoidal particles with bimodal mesopore structure were prepared via a one-step route using polymethylhydrosiloxane (PMHS) and tetraethoxysilane (TEOS) with triblock copolymer P123 as template under acidic conditions. N₂ adsorption–desorption, XRD, HRTEM, SEM and ²⁹Si MAS NMR were used to characterize the obtained material. The introduction of PMHS into the synthetic system led to the formation of a bimodal mesopore system consisting of framework mesopores of ∼7.2 nm and textural mesopores of ∼29.4 nm. The two scale pores were directly observed in HRTEM images and indirectly proved by the two-step increase in N₂ adsorption–desorption isotherm. Also, PMHS played an important role in morphology controlling and organic functionalization, ensuring monodisperse ellipsoidal particle morphology and high CH₃ functionalization degree of the mesoporous silica product. Subjected to removing highly diluted nonylphenol from aqueous solution, the hydrophobic bimodal mesoporous silica ellipsoidal particles showed high adsorption performance.     

Aluminum doped zirconia nanopowders: Wet-chemical synthesis and structural analysis by Rietveld refinement

Alumina/zirconia nanopowders, with up to 20 mol% Al₂O₃, were prepared by wet-chemical synthesis technique, using controlled hydrolysis of alkoxides. The as-synthesized powders are amorphous, have very high specific surface area and the corresponding particle size smaller than 4 nm. Amorphous powders with 0, 10 and 20 mol% Al₂O₃ crystallize at 460, 692 and 749 °C, respectively, as a single-phase tetragonal zirconia, without any traces of alumina phases. Rietvled refinement of X-ray diffraction data, used for the detailed structural analysis of annealed nanopowders, showed that the high-temperature zirconia phase is stabilized due to the formation of ZrO₂/Al₂O₃ solid solutions. High solubility of alumina in the tetragonal zirconia (up to 28.6 at% Al³⁺) and stabilization of tetragonal zirconia solid solution up to high temperature (as high as 1150 °C) were also confirmed.     

Preparation and characterization of morph-genetic aluminum nitride/carbon composites from filter paper

Morph-genetic aluminum nitride/carbon composites with cablelike structure were prepared from filter paper template through the surface sol-gel process and carbothermal nitridation reaction. The resulting materials have a hierarchical structure originating from the morphology of cellulose paper. The aluminum nitride/carbon composites have the core-shell microstructure, the core is graphitic carbon, and the shell is aluminum nitride nanocoating formed by carbothermal nitridation reduction of alumina with the interfacial carbon in nitrogen atmosphere. Scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and transmission electron microscope were employed to characterize the structural morphology and phase compositions of the final products.     

Nonaqueous sol-gel synthesis and growth mechanism of single crystalline TiO2 nanorods with high photocatalytic activity

In this paper, we report on a nonaqueous synthesis of single crystalline anatase TiO₂ nanorods by reaction between TiCl₄ and benzyl alcohol at a low temperature of 80 °C. The resulting samples were characterized with X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, nitrogen adsorption, X-ray photoelectron spectrometry and UV-vis diffuse reflectance spectroscopy. We proposed that the TiO₂ nanorods were formed through an oriented attachment mechanism. More importantly, these single crystalline anatase TiO₂ nanorods exhibited significantly higher photocatalytic activities than commercial photocatalyst P25. This study provides an environmentally friendly and economic approach to produce highly active TiO₂ photocatalyst.     

Chainlike assembly of magnetite coated with SiO2 nanostructures induced by an applied magnetic field

The assembly of silica coated magnetite nanoparticles into chainlike nanostructures is reported in the presence of applied magnetic field. The coating of SiO₂ onto the surface of magnetite nanoparticles was successfully conducted with the hydrolysis and condensation of tetraethyl orthosilicate. X-ray diffraction and transmission electron microscopy were used to characterize the microstructure and morphology. Vibrating sample magnetometry reveals that the coercivity is dependent on the coating thickness and can be controlled to a certain extent.     

Hydrothermal synthesis of hierarchical titanium silicalite-1 using single template

Hierarchical nano-crystalline TS-1 can be directly synthesized using tetrapropylammonium hydroxide (TPAOH) as single template in the presence of a ‘seed’ gel. The hierarchical nano-crystalline TS-1 was characterized by scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, UV-Vis diffuse reflectance spectroscopy and nitrogen adsorption-desoprtion. Compared with the conventional TS-1, the hierarchical nano-crystalline TS-1 contained an additional porosity including supermicro/mesopores, which attributed to the interstitial voids existing between the nanocrystals. The secondary porosity in the TS-1 material provided an enhanced external surface area and high mesopore volume in favor of fast diffusion of both reactants and products, which resulted in an enhanced activity in the epoxidation of bulky molecules cyclohexene using aqueous H₂O₂ solution as oxidant.     

Bio-inspired titanium dioxide film with extremely stable super-amphilicity

TiO₂ nanofibers with diameters of 200-550 nm were obtained by high temperature calcinations of the as-electrospun tetrabutyl titanate (Ti(OC₄H₉)₄)/polystyrene (PS) composite fibers prepared by sol-gel processing and electrospinning technique. The fiber films exhibit extremely stable super-amphilicity and self-cleaning properties. The wetting of both watery and oily liquid was observed even after the storage for 240 days in darkness or the contamination of organic compound. And the microstructure of the TiO₂ fibers could be well controlled by different fabrication condition. In addition, the approach shown in this report solved the problem of the stability of the super-amphilicity of titanium dioxide, which very important for the real application.     

Studies on synthesis of alumina nanopowder from synthetic Bayer liquor

Procedure for synthesis of alumina nanopowder from Bayer liquor (synthetic sodium aluminate solution) is investigated. Cooling, ageing and then addition of 3 ml/l Tiron (1,2-dihydroxy-3,5-benzene disulfonic acid disodium salt) to the supersaturated liquor affect purity and fineness of the nanopowder product. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray (EDAX) analyses indicate that purity of the alumina nanopowder increases with the aging time. Experimental observations show that highly pure alumina nanopowders could be produced by direct calcination of cold gelatinous sodium aluminate solution followed by careful washing at a Tiron concentration of 3 ml/l NaOH.     

Chemical synthesis of environment-friendly nanosized yellow titanate pigments

As yellow pigments, nanosized rutile structured Ni_0.1W_0.1Ti_0.8O₂ and priderite structured BaNiTi₇O₁₆ have been prepared through pyrolysis of precursor solution containing nickel nitrate, dimethyl tungstate, titanium oxalate, triethanolamine (TEA) for the former composition and barium nitrate, nickel nitrate, titanium oxalate, TEA for the later composition, respectively. In the reaction, TEA acts to minimize the agglomeration in the products through formation of a highly branched polymeric framework, which anchors the metal ions for producing nanocrystalline powders. The rutile and priderite structured titanates obtained on heat-treatment of the precursor powders at 800 °C and 850 °C, respectively, have been characterized by XRD, TGA-DTA, BET surface area measurement, UV-vis spectroscopy, CIE L^*a^*b^* colour parameter measurements, TEM and HRTEM. XRD reveals the purity of the resulting rutile and priderite phases. Their crystallite sizes, average particle sizes and specific surface areas determined from XRD, TEM, and BET surface area measurement are found to be in the range between 25 nm and 30 nm, 25-45 nm and 100-120 m²/g, respectively, for both compositions.     

Structural and chemical characterization of BaTiO3 nanorods

An electron-microscopy investigation was performed on BaTiO₃ nanorods that were processed by sol-gel electrophoretic deposition (EPD) into anodic aluminium oxide (AAO) membranes. The BaTiO₃ nanorods grown within the template membranes had diameters ranging from 150 to 200 nm, with an average length of 10-50 μm. By using various electron-microscopy techniques we showed that the processed BaTiO₃ nanorods were homogeneous in their chemical composition. The BaTiO₃ nanorods were always polycrystalline and were composed of well-crystallized, defect-free, pseudo-cubic BaTiO₃ grains, ranging from 10 to 30 nm. No intergranular phases were observed between the BaTiO₃ grains. A low-temperature hexagonal polymorph that is coherently intergrown with the BaTiO₃ perovskite matrix was also observed as a minor phase. When annealing the AAO templates containing the BaTiO₃ sol in an oxygen atmosphere the presence of the hexagonal polymorph was diminished.     

A modified method for barium titanate nanoparticles synthesis

In this research, a modified, cost effective sol-gel procedure applied to synthesize BaTiO₃ nanoparticles. XRD and electron microscopy (SEM and TEM) applied for microstructural characterization of powders. The obtained results showed that the type of precursors, their ratio and the hydrolysis conditions had a great effect on time, temperature and therefore the costs of the synthesis process. By selection, utilization of optimized precursor's type, hydrolysis conditions, fine cubic BaTiO₃ nanoparticles were synthesized at low temperature and in short time span (1 h calcination at 800 °C). The proposed procedure seems to be more preferable for mass production.The result indicated that the polymorphic transformation to tetragonal (ferroelectric characteristic) occurred at 900 °C, which might be an indication of being nanosized.     

Synthesis of zeolite NaY in anionic, cationic and nonionic emulsions

Zeolite NaY has been first synthesized respectively in the anionic, cationic and nonionic emulsions. The emulsion systems can accelerate zeolite NaY crystallization and in some cases retard the growth of impurity. Compared to the conventional zeolite NaY synthesized in the absence of emulsion, the emulsion-mediated NaY samples show different morphologies, larger surface areas and higher pore volumes depending on the charge nature of the surfactants involved. In particular, the NaY sample synthesized in the nonionic emulsion system presents a hierarchical pore structure with the highest BET surface area of 646.85 m² g⁻¹. The increase of surface areas for the NaY products made in emulsion media is due to the removal of emulsion components occluded in the pore structures through calcination. These features of the NaY zeolites synthesized in emulsion media, such as various product morphologies and high surface areas, may bestow the materials unique catalytic properties in their potential applications.     

Mass-synthesized anatase titania nanocrystals with tunable size and shape via sol-gel in organic solvents with adsorbing ligands

High-quality anatase titania (TiO₂) nanoparticles, nanowires, and nanorods have been mass-synthesized by the modified sol-gel method in the saturated fatty alcohol, acid, and amine systems with adsorbing ligands, respectively. These obtained quasi-spherical TiO₂ nanoparticles showed the mean size of 16.5 nm with a narrow size-distribution. These resulting TiO₂ nanowires had the uniform diameter of 3.8 nm with the length range of 80-180 nm, and TiO₂ nanorods had the uniform diameter of 7.5 nm with the length range of 40-70 nm, respectively. We demonstrated that the shapes, sizes and morphology of these anatase TiO₂ nanocrystals could be controlled systematically by adjusting certain reaction parameters, such as the kind of organic solvents, the alkyl length of organic solvents, and the reaction time. It has been found that the shape of the products was primarily determined by the kind of organic solvents. However, their sizes, size-distributions, and morphology could be controlled by adjusting the alkyl length of organic solvents and the reaction time. Based on the analysis of all experiment results, we have investigated the growth mechanism of these TiO₂ nanocrystals with the different shape. Meanwhile, this synthetic method can be extended further for the preparation of other oxides nanocrystals.     

Synthesis and photocatalytic activity of titania microspheres with hierarchical structures

A combined sol-gel and solvothermal process was introduced to fabricate the titania microspheres with hierarchical structures by using lauryl alcohol as the structure-directing agent. Scanning electron microscope, high-resolution transmission electron microscope, Fourier transform infrared spectrograph and powder X-ray powder diffraction indicated that the molar ratio of lauryl alcohol, water and tetra-n-butyl titanate was the key factor for the formation of the mono-dispersed titania with anatase phase and the optimal ratio was 1.2:4:1. The diameter of the end-product was 523 ± 74 nm and it was composed of smaller nanoparticles with about 6.8 nm size in diameter. Photocatalytic activity of the end-product was investigated by employing Rhodamine B and Methylene blue as the model compounds. The target microspheres exhibited the higher photocatalytic efficiency compared with commercial Degussa P25 titania and this result might be due to the hierarchical structures of microspheres according to the analysis of Brunauer-Emmett-Teller specific surface areas.