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.     

Characterization and investigation on the difference of hydrothermal stability for ordered mesoporous aluminosilicate sieves

Ordered hexagonal mesoporous aluminosilicates molecular sieves, designated as MSAMS-2A, MSAMS-2G and MSAMS-2, have been synthesized via re-crystallization of mesoporous SBA-15 within the diluted solution of aluminosilicate sol–gel, glycerol, and both of them, respectively. The three materials have been characterized by XRD, N₂ adsorption–desorption, FT-IR, FE-SEM, ²⁷Al MAS NMR and ²⁹Si MAS NMR, and the corresponding hydrothermal stability of these three sieves is in the order of MSAMS-2 > MSAMS-2G ? MSAMS-2A. The hydrothermal stability difference between MSAMS-2 and MSAMS-2G might be attributed to the synergistic effect of the higher condensation of silanol groups and insertion of all non-framework Al atoms into the framework of MSAMS-2. The hydrothermal stability of MSAMS-2G is higher than that of MSAMS-2A, which is likely because the high viscosity of glycerol will be in favor of the silanol groups interacting with zeolite-like subunits and moreover glycerol can act as a stabilizing guest molecule.     

CdS nanoparticles incorporated onion-like mesoporous silica films: Ageing-induced large stokes shifted intense PL emission

CdS nanoparticles (NPs) were generated in onion-like ordered mesoporous SiO₂ films through a modified sol–gel process using P123 as a structure directing agent. Initially Cd²⁺ doped (12 equivalent mol% with respect to the SiO₂) mesoporous SiO₂ films were prepared on glass substrate. These films after heat-treatment at 350 °C in air yielded transparent mesoporous SiO₂ films having hexagonally ordered onion-like pore channels embedded with uniformly dispersed CdO NPs. The generated CdO NPs were transformed into CdS NPs after exposing the films in H₂S gas at 200 °C for 2 h. The as-prepared CdS NPs incorporated mesoporous SiO₂ films (transparent and bright yellow in color) showed a band-edge emission at 485 nm and a weak surface defect related emission at 530 nm. During ageing of the films in ambient condition the band-edge emission gradually weakened with time and almost disappeared after about 15 days with concomitant increase of defect related strong surface state emission band near 615 nm. This transformation was related to the decay of initially formed well crystalline CdS to relatively smaller and weakly crystalline CdS NPs with surface defects due to gradual oxidation of surface sulfide. At this condition the embedded CdS NPs show large Stokes shifted (∼180 nm) intense broad emission which could be useful for luminescent solar concentrators. The detailed process was monitored by UV–Visible, FTIR and Raman spectroscopy, XPS, XRD and TEM studies. The evolution of photoluminescence (PL) and life times of CdS/SiO₂ films were monitored with respect to the ageing time.     

Fabrication and characterization of a zirconia/multi-walled carbon nanotube mesoporous composite

A zirconia/multi-walled carbon nanotube (ZrO₂/MWCNT) mesoporous composite was fabricated via a simple method using a hydrothermal process with the aid of the cationic surfactant cetyltrimethylammonium bromide (CTAB). Transmission electron microscopy (TEM), N₂ adsorption–desorption, Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) techniques were used to characterize the as-made samples. The cubic ZrO₂ nanocrystallites were observed to overlay the surface of MWCNTs, which resulted in the formation of a novel mesoporous–nanotube composite. On the basis of a TEM analysis of the products from controlled experiment, the role of the acid-treated MWCNTs and CTAB was proposed to explain the formation of the mesoporous–nanotube structure. The as-made composite possessed novel properties, such as a high surface area (312 m² · g^? 1) and a bimodal mesoporous structure (3.18 nm and 12.4 nm). It was concluded that this composite has important application value due to its one-dimensional hollow structure, excellent electric conductivity and large surface area.     

Hydrothermal synthesis and magnetic properties of α-MnO2 nanowires

In the present study, one-dimensional (1D) α-MnO₂ nanowires with width of 50–60 nm, length about several micrometers have been successfully prepared under hydrothermal conditions in the presence of sodium carboxymethyl cellulose. The samples were characterized by X-ray diffraction, scanning electron microscope, superconducting quantum interference device and N₂ adsorption–desorption experiment. The magnetic measurement reveals that the α-MnO₂ nanowires exhibit a ferromagnetic behavior at 5 K and a paramagnetic behavior at 300 K. The N₂ adsorption–desorption experiment shows that surface area is 160.4 m² g^?1, which is even larger than those of mesoporous nanostructures. At the same time, the possible formation mechanism for the formation of α-MnO₂ nanowires has been proposed according to the experimental results.     

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.     

Tannin-immobilized mesoporous silica bead (BT–SiO2) as an effective adsorbent of Cr(III) in aqueous solutions

This study describes a new approach for the preparation of tannin-immobilized adsorbent by using mesoporous silica bead as the supporting matrix. Bayberry tannin-immobilized mesoporous silica bead (BT–SiO₂) was characterized by powder X-ray diffraction to verify the crystallinity, field-emission scanning electron microscopy to observe the surface morphology, and surface area and porosity analyzer to measure the mesoporous porous structure. Subsequently, the adsorption experiments to Cr(III) were applied to evaluate the adsorption performances of BT–SiO₂. It was found that the adsorption of Cr(III) onto BT–SiO₂ was pH-dependent, and the maximum adsorption capacity was obtained in the pH range of 5.0–5.5. The adsorption capacity was 1.30 mmol g^?1 at 303 K and pH 5.5 when the initial concentration of Cr(III) was 2.0 mmol L^?1. Based on proton nuclear magnetic resonance (HNMR) analyses, the adsorption mechanism of Cr(III) on BT–SiO₂ was proved to be a chelating interaction. The adsorption kinetic data can be well described using pseudo-first-order model and the equilibrium data can be well fitted by the Langmuir isothermal model. Importantly, no bayberry tannin was leached out during the adsorption process and BT–SiO₂ can simultaneously remove coexisting metal ions from aqueous solutions. In conclusion, this study provides a new strategy for the preparation of tannin-immobilized adsorbents that are highly effective in removal of heavy metals from aqueous solutions.     

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.     

Nanocrystalline ruthenium oxide of fine mesoporosity prepared by templating for electrochemical capacitor applications

Hydrous ruthenium-oxide (RuO_xH_y) particles composed of nanocrystallites of ～5 nm in size were prepared, using hexagonal self-ordered mesoporous SiO₂ (SBA-15) as a template and RuCl₃ as the ruthenium precursor. The material has a highly mesoporous structure with a sharp distribution of fine pores of size around 3–4 nm. A high specific capacitance of 954 F g^?1 for the RuO_xH_y in 1 M H₂SO₄(aq) and a high energy density of 118.9 J g^?1 (or 32.7 W h kg^?1) were obtained from an electrochemical capacitor made with the material. Rectangular shape of the cyclic voltammetry was observed even increasing the scan rate to about 100 mV s^?1.     

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.     

Adsorption and dissociation of N2O molecule on Fe(1 1 1) surface: A DFT study

We have used spin-polarized density functional theory to investigate the adsorption and dissociation of N₂O molecule on Fe(1 1 1) surface. Several adsorption geometries and sites were examined in detail. In our computational results, the Fe–N₂O–η²-[N_t(1,2), O_t(1)] exhibited the greatest adsorption energy, 1.16 eV, on Fe(1 1 1) surface, whereas the other binding modes still have effective adsorption and dissociation behaviors. For the N₂O dissociation mechanisms, our calculated results indicate that the most favorable pathway is the production of N₂ + O fragments on the Fe(1 1 1) surface. Formation of NO + N is also possible, although this pathway involves a higher energy barrier.     

Mesoporous structure and evolution mechanism of hydroxycarbonate apatite microspheres

Monodisperse mesoporous hydroxycarbonate apatite microspheres (MHAMs) were fabricated by soaking calcium carbonate microspheres (CCMs) in a cetyltrimethylammonium bromide (CTAB)/Na₂HPO₄/cyclohexane/n-butanol emulsion system. After soaking CCMs in the emulsion system at 20 °C, hydroxycarbonate apatite nanocrystals nucleate heterogeneously on the surfaces of CCMs via a dissolution–precipitation reaction. The as-formed nanocrystals aggregate to form mesopores with the pore size of ～ 3.9 nm and ～ 9.0 nm. The smaller mesopores are derived from the direct aggregation of the nanocrystals, which do not change obviously with the reaction time. In contrast, the larger mesopores are formed by using CTAB micelles as templates, and their pore size decreases from ～ 9.0 nm to ～ 7.4 nm with increasing the reaction time from 6 h to 1 day. After reaction for 3 or 5 days, the larger mesopores disappear because of unstability of the CTAB micelles. If reaction temperature is kept at 50 °C, the conversion rate of CCMs to MHAMs is greater than that at 20 °C, and the corresponding mesoporous structure is unimodal with the pore size of ～ 3.9 nm. Simulated body fluid immersion tests reveal that MHAMs have a great in vitro bioactivity, which is attributed to the mesoporous structure and B-type CO₃^2? substitution of MHAMs.     

Thermodynamic and kinetic studies for the adsorption of Hg(II) by nano-TiO2 from aqueous solution

Titanium dioxide nanocrystals were employed, for the first time, for the sorption of Hg(II) ions from aqueous solutions. The effects of varying parameters such as pH, temperature, initial metal concentration, and contact time on the adsorption process were examined. Adsorption equilibrium was established in 420 min and the maximum adsorption of Hg(II) on the TiO₂ was observed to occur at pH 8.0. The adsorption data correlated with Freundlich, Langmuir, Dubinin–Radushkevich (D–R), and Temkin isotherms. The Freundlich isotherm showed the best fit to the equilibrium data. The Pseudo-first order and pseudo-second-order kinetic models were studied to analyze the kinetic data. A second-order kinetic model fit the data with the (k₂ = 2.8126 × 10^?3 g mg^?1min^?1, 303 K). The intraparticle diffusion models were applied to ascertain the rate-controlling step. The thermodynamic parameters (ΔG°, ΔH°, and ΔS°) were calculated which showed an endothermic adsorption process. The equilibrium parameter (R_L) indicated that TiO₂ nanocrystals are useful for Hg(II) removal from aqueous solutions.     

A facile method for production of high-purity silica xerogels from bagasse ash

In this paper, we systematically report the synthesis of mesoporous silica xerogels in high purity from bagasse ash. The bagasse ash was chosen as the raw material due to its availability and low-price, and environmental considerations also were important. Silica was extracted as sodium silicate from bagasse ash using NaOH solution. The sodium silicate was then reacted with HCl to produce silica gel. To produce high-purity silica xerogels, three different purification methods were investigated, i.e., acid treatment, ion exchange treatment, and washing with de-mineralized water. We were able to produce high-purity silica (>99 wt.%) by washing the produced gels with either de-mineralized water or with ion exchange resin. The specific surface area of the prepared silica xerogels ranged from 69 to 152 m² g^?1 and the pore volume ranged from 0.059 to 0.137 cm³ g^?1. The pore radii were 3.2–3.4 nm, which indicated that the silica xerogels was mesoporous. From the adsorption characterization, it was obvious that adsorptive capacity was better for high-purity silica xerogels compared with low-purity. The maximum adsorption capacity by high-purity silica xerogel was 0.18 g-H₂O/g-SiO₂. Finally, we demonstrate the potential of bagasse ash for mesoporous silica production with its excellent adsorptive capacity that makes it beneficial as an environmental solution.     

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.     

Lithium selective adsorption on 1-D MnO2 nanostructure ion-sieve

β-MnO₂, spinel-type Li₄Mn₅O₁₂ and pure cubic phase MnO₂ nanorod, with the size about 20–140 nm in diameter and 0.8–4 μm in length, were synthesized via a combination of hydrothermal synthesis and low temperature solid-phase reaction, more favorable to control the nanocrystalline structure with well-defined pore size distribution and high surface area than the traditional high temperature calcination process. Further, the MnO₂ ion-sieves with lithium selective adsorption property were prepared by the acid treatment process to completely extract lithium from the spinel Li₄Mn₅O₁₂ precursor with little change to the Mn–O lattice structure and the 1-D nanorod morphology. The effects of hydrothermal and solid-phase reaction process on the nanostructure, chemical stability and ion-exchange property of the ion-sieve material were examined with powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), N₂ adsorption–desorption at 77 K, and Li⁺ selective adsorption measurements. The lithium selective adsorption capacity was improved remarkably to 6.62 mmol g^?1 at equilibrium and about 5 mmol g^?1 at the initial lithium concentration of only 5.0 mmol l^?1, which is significant for lithium extraction from aqueous solutions with very low lithium content.     

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.     

Study of physical properties of cobalt oxide (Co3O4) nanocrystals

Cobalt oxide nanocrystals of size 10–15 nm have been prepared by a simple co-precipitation method. The structural investigations have been performed with X-ray diffraction and Transmission Electron Microscopy. Specific surface area of the nanocrystals is 77.5 × 10⁴ cm²/g which have been calculated by X-ray diffraction data. Optical properties are discussed with UV/visible spectroscopy which shows the multiple band gap energies 2.28 eV (O^? II → Co^II) and 1.57 eV (O^? II → Co^III) which suggest the possibility of degeneracy of the valence band. The magnetic behavior is investigated using Vibrating Sample Magnetometer. The Co₃O₄ nanocrystals possess paramagnetic character at room temperature.     

Novel rosette-shaped CdS microparticle with high surface area fabricated by lyotropic liquid crystal templating

Semiconductor CdS microparticle covered with wrinkle-like nanotexture was prepared under ambient condition by using the lyotropic liquid crystal mesophase as a structural template. The prepared CdS microparticle resembles a rosette shape with a diameter of 0.5–1.5 μm and the wrinkle-like nanotexture on its surface. This rosette-shaped CdS consists of small nanocrystals with a diameter of ∼4 nm, and the nanocrystal building block has the zinc-blende crystal structure. The characteristic band-to-band absorption and near band-edge emission are observed in this unique semiconductor particle. Nitrogen gas physisorption measurement reveals that the material has the high BET surface area of 38 m² g⁻¹ and nanoporous nature.     

Synthesis of SnO2 nanoparticles inside mesoporous carbon via a sonochemical method for highly reversible lithium batteries

A sonochemical method was introduced to synthesize SnO₂ nanoparticles in the pores of mesoporous carbon without any other agents. The nitrogen adsorption measurement and transmission electron microscopy results revealed that the SnO₂ nanoparticles with the average particle size of around 10 nm were homogeneous distribution in the matrix. The aggregation of SnO₂ was hindered by the three-dimensioned porous frameworks, resulting in a relatively large surface area of 362 m² g^? 1, which is beneficial for lithium-ion storage in batteries. The resultant composites with 43% SnO₂ exhibited a high reversible capacity of 200 mAh g^? 1 even after 300 cycles, which is 186% higher than that of the initial mesoporous carbon matrix. This strategy is expected to incorporate other functional nanoparticles inside mesoporous carbon for many applications.