Organosulfonic acid-functionalized mesoporous composites based on natural rubber and hexagonal mesoporous silica

This study is the first report on synthesis, characterization and catalytic application of propylsulfonic acid-functionalized mesoporous composites based on natural rubber (NR) and hexagonal mesoporous silica (HMS). In comparison with propylsulfonic acid-functionalized HMS (HMS-SO₃H), a series of NR/HMS-SO₃H composites were prepared via an in situ sol–gel process using tetrahydrofuran as the synthesis media. Tetraethylorthosilicate as the silica source, was simultaneously condensed with 3-mercaptopropyltrimethoxysilane in a solution of NR followed by oxidation with hydrogen peroxide to achieve the mesoporous composites containing propylsulfonic acid groups. Fourier-transform infrared spectroscopy and ²⁹Si MAS nuclear magnetic resonance spectroscopy results verified that the silica surfaces of the NR/HMS-SO₃H composites were functionalized with propylsulfonic acid groups and covered with NR molecules. After the incorporation of NR and organo-functional group into HMS, the hexagonal mesostructure remained intact concomitantly with an increased framework wall thickness and unit cell size, as evidenced by the X-ray powder diffraction analysis. Scanning electron microscopy analysis indicated a high interparticle porosity of NR/HMS-SO₃H composites. The textural properties of NR/HMS-SO₃H were affected by the amount of MPTMS loading to a smaller extent than that of HMS-SO₃H. NR/HMS-SO₃H exhibited higher hydrophobicity than HMS-SO₃H, as revealed by H₂O adsorption–desorption measurements. Moreover, the NR/HMS-SO₃H catalysts possessed a superior specific activity to HMS-SO₃H in the esterification of lauric acid with ethanol, resulting in a higher conversion level.     

Superhydrophobic sodium silicate based silica aerogel prepared by ambient pressure drying

The superhydrophobic silica aerogel was prepared by using less expensive sodium silicate as a main silica source through a cost-effective and simple route via ambient pressure drying. The sodium impurity was first eliminated by mixing sodium silicate with a co-precursor methyltriethoxysilane (MTES) followed by ion exchange process. The hydrogel was formed by gelation and the alcogel was further obtained by alcoholization of the hydrogel. The surface of alcogel was modified by reacting with trimethylchlorosilane (TMCS) diluted in n-hexane. It was suggested that MTES accelerated water expelling from the hydrogel, while TMCS modified the surface of silica network by replacing Si–OH with Si–C. As a result, the obtained silica aerogel exhibited excellent physical properties with less than 10% volume shrinkage. The density, surface area and cumulative pore volume were 0.12 g cm⁻³, 684.44 m² g⁻¹, and 3.55 cm³ g⁻¹, respectively. The optical transmission reached 82.8% with the water contact angle of 146°.     

Weak acid–base interaction induced assembly for the formation of berry-like polystyrene/SiO2 composite particles

To investigate the formation mechanism of berry-like polystyrene/silica (PS/SiO₂) with carboxyl-functional templates through in-situ sol–gel process, different alkalis were adopted to catalyze the hydrolysis reaction of tetraethoxysilane (TEOS) and the morphology of composite particles was observed by TEM. The results showed that the weak acid–base interaction (–COO⁻/–N⁺/–SiO⁻) drove the silica particle nucleated and growth on the surface of PS spheres and berry-like structure can be easily adjusted by alkalis and volume ratio of ethanol/water. The present work implied that the weak acid–base interaction can be used to control the nano/micro or hierarchically structures. In addition, the particulate films were constructed by assembling these berry-like particles on the glass substrates. After surface modification with dodecyltrichlorosilane, hydrophobic surface can be obtained and the contact angle of water on the dual-sized structured surface can be adjusted.     

Gold nanoparticles into Ti1−xZnxO2 films: Synthesis,structure and application

The gold particles of certain size were incorporated into Ti_1−xZn_xO₂ films by sol–gel method. The synthesis conditions predetermine the size and shape of gold nanoparticles, which were monitored by the absorption spectra and SEM images. The results of Raman spectra measurements indicate that Au nanoparticles inhibit the grain growth of anatase within the film. The photocatalytic activity of Au/Ti_1−xZn_xO₂ films in the degradation of tetracycline hydrochloride depends on the sizes of Au particles.     

Structural and electrochemical properties of multifunctional silica/lignin materials

Synthesis and characterisation of silica/lignin materials is described. Silica was synthesised by the modified Stöber method and its surface was functionalised with aminosilane. The organic matrix was the activated Kraft lignin (KL). The materials obtained were subjected to thorough characterisation (physicochemical, dispersive, morphological and electrochemical) by the NIBS, SEM, FT–IR, and XPS methods. Results of the characterisation permitted evaluation of the application possibilities of the products and the choice of the best ones for specific applications. Because of high negative ionic charge the material particles could be effectively deposited on positively polarised glassy carbon electrode by electrophoretic deposition. The silica/lignin modified electrode showed enhanced charge transfer resistance for anionic redox probe (ferrocyanide/ferricyanide couple) and an enhanced capability to the adsorption of silver cations. The latter property could be exploited in anodic striping voltammetry of silver.     

Hard-templating synthesis of mesoporous carbon spheres with controlled particle size and mesoporous structure for enzyme immobilization

Mesoporous carbon spheres (MCSs) with controlled particle size and pore structure were synthesized via a combined hard templating and sol–gel processing within water-in-oil emulsions, using resorcinol–formaldehyde polymer as carbon precursor and colloidal silica nanoparticles as hard templates. The addition of silica nanoparticles in polymer sol not only served as the pore structure reagents but also shortened the gelation time, making it easy to control the emulsion process. The sphere size of MCSs can be controlled in the range from 10 to 500 μm by changing the emulsification conditions. The pore structure of MCSs can be tuned by adjusting the mass ratio of resorcinol–formaldehyde polymer to silica nanoparticles and the diameter of silica nanoparticles. The as-prepared MCSs possessed large surface area (>600 m² g⁻¹), large pore volume (>1 cm³ g⁻¹) and a narrow pore size distribution replicated from the silica nanoparticles used. These MCSs exhibited extraordinary high adsorption capacities (ca. 1100 mg g⁻¹) for α-Chymotrypsin (Chy) in solution. Due to their well-developed pore structure and the controllable pore size, as well as the unique shape and good affinity to biomolecules, the as-prepared MCSs should have a good potential in enzyme immobilization.     

Polyacrolein/mesoporous silica nanocomposite: Synthesis,thermal stability and covalent lipase immobilization

In this work, new polyacrolein/MCM-41 nanocomposites with good phase mixing behavior were prepared through an emulsion polymerization technique. Mesoporous silica was synthesized by in situ assembly of tetraethyl orthosilicate (TEOS) and cetyl trimethyl ammonium bromide (CTAB). The structure and properties of polyacrolein containing nanosized MCM-41 particle (5 and 10 wt%), were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, Dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption techniques, and thermogravimetric (TGA) analyses. The SEM images from the final powder have revealed good dispersion of the MCM-41 nanoparticles throughout polymeric matrix with no distinct voids between two phases. The results indicated that the thermal properties of the nanocomposite were enhanced by addition of MCM-41. Thermomyces lanuginosa lipase (TLL) was used as a model biocatalyst and successfully immobilized with polyacrolein and the nanocomposite via covalent bonds with the aldehyde groups. The activity between free enzyme, polyacrolein, and MCM-41 nanocomposite (10 wt%)-immobilized TLL was compared. The immobilized lipase with the nanocomposite shows better operational stability such as pH tolerance, thermal and storage stability. In addition, the immobilized lipase with the nanocomposite can be easily recovered and retained at 74% of its initial activity after 15 time reuses.     

Synthesis and characterization of KNd2Ti3O9.5 nanocrystal and its catalytic effect on decomposition of ammonium perchlorate

A novel kind of perovskite type oxide KNd₂Ti₃O_9.5 nanocrystals with an average size of 12 nm were successfully fabricated by a stearic acid sol–gel method (SAM) using Ti(OBu)₄, KOH, Nd₂O₃ and stearic acid as the raw materials. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the products. The catalytic effect of the KNd₂Ti₃O_9.5 nanoparticles on thermal decomposition of ammonium perchlorate (AP) was investigated by differential thermal analysis (DTA) and thermal gravimetry (TG) experiments. Results indicated that the obtained KNd₂Ti₃O_9.5 nanocrystals took on cubic structure and presented both good dispersibility and uniform crystallite size. Also, they have an intense catalytic effect on the thermal decomposition of AP. Adding 2% of KNd₂Ti₃O_9.5 nanoparticles to AP can obviously decrease the thermal decomposition temperature of AP by 50 °C, increase the heat of decomposition from 590 J g⁻¹ to 1659 J g⁻¹ and obviously quicken the decomposition reaction rate.     

Organic/inorganic flame retardants containing phosphorus,nitrogen and silicon: Preparation and their performance on the flame retardancy of epoxy resins as a novel intumescent flame retardant system

This paper presents the preparation of novel organic/inorganic flame retardants containing phosphorus, nitrogen and silicon (organic/inorganic FRs). The organic/inorganic FRs were highly water resistant, as suggested by the water contact angle and water solubility tests. The organic/inorganic FRs were then incorporated into epoxy resins (EP) at different phosphorus/nitrogen ratios and the flame retardancy of EP/FRs composites was characterized. The results showed that synergistic effects on the flame retardancy of EP composites existed between the DOPO-VTS and TGIC-KH. The char residues for EP/FRs composites were increased, and the highest char residues were obtained in air atmosphere (3.8 wt.%) when the DOPO-VTS/TGIC-KH is 4/1. The MCC results also showed that the THR of epoxy resins were also decreased when the DOPO-VTS/TGIC-KH is 4/1, which was in accordance with the highest LOI and UL-94 results. The SEM, FTIR, XPS and TG-FTIR results of pyrolysis products in both condensed and gases phases indicated that the strategy of organic/inorganic FRs combined condensed phase and gases phase flame retardant strategies such as the phosphorus–nitrogen synergism systems, the silicon reinforced effects in the condensed phase and DOPO flame retardant systems in the gases phase, resulting in significant improvements in the flame retardancy of epoxy resins.     

The study of photoluminescence properties of Rhodamine B encapsulated in mesoporous silica

Rhodamine B (Rh B), a kind of fluorescent dye, was encapsulated into the pores of various mesoporous silica materials through postgrafting method. Small angle X-ray diffraction (XRD), nitrogen adsorption–desorption and Fourier transform infrared (FTIR) spectrometry were used to characterize those composites. After encapsulation, the composites showed significant blue-shift in photoluminescence (PL) spectra. The extent of shift changed upon varying mesoporous silica host. This phenomenon is related to the topological structure of mesopores. For the first time, it was observed that not only the size, but also the structure and the curvature of the mesopores have a great influence on PL properties of the composites, and a possible mechanism was also provided.     

Preparation and characterization of aminosilane-modified silicate supported with silver for antibacterial behavior

The objective of the study was to develop and evaluate aminosilanes-modified silicate impregnated with silver (Ag) nanoparticles, in which Ag dispersion is stabilized, to create a composite that protects against biological warfare agents. A composite based on Ag and organically modified silicate (Ormosil) was prepared by an in situ reduction method, in which silver nitrate, tetraethoxysilane (TEOS) and 3-(2-aminoethylaminopropyl)trimethoxysilane (AES) acted as precursor, linker and colloidal suspension stabilizer, respectively. The physical properties of the Ormosil hybrid and Ormosil/Ag composite were examined using NMR, ESR, SEM, TEM, and TGA spectroscopy, the results of which indicated that Ag was incorporated in the Ormosil matrix after impregnation. Morphological analysis by TEM showed the resulting Ag nanoparticles to be spherical and of a mean size of less than 50 nm. The antibacterial effects of the Ormosil hybrid and the Ormosil/Ag composite were assessed by the zone of inhibition and plate-counting methods, and an excellent antibacterial performance was discovered.     

Synergistic effect of composite template and La-doping on microdynamic behavior of photogenerated carriers in mesoporous nano-TiO2

The traditional view that the role of the composite template that is adopted in the preparation of nano-TiO₂ is only for forming a pore structure and increasing the material's specific surface area is challenged by this study. The complex impact of the composite template and La-doping on the microdynamic behavior of photo-generation free charge carriers (FCCs) in the mesoporous nano-TiO₂ is investigated using the transient photovoltaic (TPV) technique, supplemented by electric field-induced surface photovoltaic spectroscopy and a computer simulation method. The experimental results reveal that utilizing an appropriate composite template, such as polyethylene glycol and octadecylamine with a molar ratio of 1:1, may result in the rapid separation and prolonged diffusion distance of electron–hole pairs that were excited by a 355 nm and 50 μJ laser pulse. These may be responsible for the stronger and broader TPV response in the microsecond and millisecond regions of the La-doped nano-TiO₂ in TPV spectroscopy, as compared with that for materials that used other composite templates. This response is closely related to the reduced content of the surface state located at 367 nm. A suitable level of La-doping, however, was only responsible for the stronger and broader TPV response in the microsecond region of the spectrum of the nano-TiO₂. The computer simulation results confirm that the photo-generation FCCs microdynamic characteristics in the microsecond region may partially originate from the state density distribution of both the d-electron in the antibonding orbital and the p-electron in the bonding orbital moving up to higher levels, and from a broader band-gap after La-doping in the anatase lattice cell.     

Synthesis of porous micro-sized titania cages and their photocatalytic property

Micro-sized TiO₂ cage consisted of anatase nanoparticles on the edges of each cube, was synthesized using TTIP as the reagent and NaF submicrometer sized cubes as the template. When a salt of cube was adopted as the template, the reactants prefer to grow on the active sites, edges and corners of the cube, after removing the NaF template, the skeleton of the cube remain as the cage-shaped materials. The hierarchical structures with nano-sized anatase particles and micro scaled cage architecture markedly enlarge the surface area and enhance the light harvesting by light scattering of TiO₂ frame, resulting in great photo-catalytic performance, which leads to the photo-degradation of methylene blue by 40% higher than that was achieved by crushed nanoparticles.     

Rapid erasing of wettability patterns based on TiO2-PDMS composite films

TiO₂-polydimethylsiloxane (TiO₂-PDMS) composite films are prepared using the sol–gel method from a Ti(OBu)₄–benzoylacetone solution containing PDMS. The prepared films are cured by irradiation with ultraviolet (UV) light. Structural changes in the films after UV irradiation are confirmed by UV–vis absorption experiments, which show that an absorption band characteristic of the benzoylacetonate chelate rings disappears. This finding is ascribed to structural changes associated with the dissociation of the chelate rings. The IR spectra of the thin films exhibit a broad absorption band after UV irradiation, indicating that a Ti–O–Ti network forms in the thin film. Contact angles are measured for the TiO₂-PDMS thin films, showing wettability conversion from hydrophobic to superhydrophilic states by irradiation with oxygen plasma for 1 s. This phenomenon is explained by XPS experiments which reveal that the number of carbon atoms decreases, whereas the number of oxygen atoms increases on the surface of the TiO₂-PDMS composite films. Finally, hydrophobic–superhydrophilic patterns are fabricated based on a patterned TiO₂-PDMS composite film. The film displays a rapid change to superhydrophilicity over the whole film surface upon plasma irradiation for 1 s, which means that the wettability patterns are rapidly erasable.     

Synthesis of Zr-MCM-41 by the assistance of sodium chloride in the self-generated acid conditions

Zr-MCM-41 materials were synthesized by the hydrothermal method in the presence of ZrOCl₂ and NaCl. The characterization results showed that Zr was highly dispersed in the tetrahedral environment of silica framework. In the synthesis process, the self-generated acidity by the hydrolysis of ZrOCl₂ acted as the catalyst for TEOS hydrolysis. In order to form the ordered structure of Zr-MCM-41, the addition of NaCl in the synthesis gel was essential and the optimum NaCl/Si molar ratio was 1.0. The ordering of Zr-MCM-41 was also influenced by the content of Zr, which decreased gradually with the increase of Zr content.     

In vitro study of nano-sized zinc doped bioactive glass

Surface reactivity in physiological fluid has been linked to bioactivity of a material. Past research has shown that bioactive glass containing zinc has the potential in bone regeneration field due to its enhanced bioactivity. However, results from literature are always contradictory. Therefore, in this study, surface reactivity of bioactive glass containing zinc was evaluated through the study of morphology and composition of apatite layer formed after immersion in simulated body fluid (SBF). Nano-sized bioactive glass with 5 and 10 mol% zinc were synthesized through quick alkali sol–gel method. The synthesized Zn–bioglass was characterized using field emission scanning electron microscope (FESEM), energy dispersive X-ray spectrometer (EDX), X-ray diffractometer (XRD) and Fourier transform infrared spectrometer (FTIR). Samples after SBF immersion were characterized using scanning electron microscope (SEM) and EDX. Morphological study through SEM showed the formation of spherical apatite particles with Ca/P ratio closer to 1.67 on the surface of 5 mol% Zn–bioglass. Whereas, the 10 mol% Zn–bioglass samples induced the formation of flake-like structure of calcite in addition to the spherical apatite particles with much higher Ca/P ratio. Our results suggest that the higher Zn content increases the bioactivity through the formation of bone-bonding calcite as well as the spherical apatite particles.     

Studies in structural characterization of silica–heteropolyacids composites prepared by sol–gel method

Heteropolyacids (HPAs) which are included in mesoporous silica, H₃PMo₁₂O₄₀/SiO₂ and H₄PMo₁₁VO₄₀/SiO₂ have been synthesized by a sol–gel technique that involves hydrolysis of ethyl orthosilicate. The effect of incorporation of heteropolyacids species on silica matrix was studied by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Raman spectroscopy, thermo gravimetric analysis (TGA) and differential thermal analysis (DTA), N₂ adsorption–desorption, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).     

Room temperature ferromagnetism in Zn0.99La0.01O and pure ZnO nanoparticles

Room temperature ferromagnetism (RTFM) was observed in both La-doped and pure ZnO nanoparticles synthesized by the sol–gel method. RTFM is intrinsic according to the results of X-ray diffraction and X-ray photoelectron spectroscopy. The saturation magnetization (M_S), the remnant magnetization at zero field and coercive field are 5 × 10⁻³, 7 × 10⁻⁴ emu g⁻¹, 100 Oe for Zn_0.99La_0.01O nanoparticles and 1.5 × 10⁻⁴, 1 × 10⁻⁵ emu g⁻¹, 50 Oe for pure ZnO nanoparticles, respectively. The magnetization is enhanced greatly by doping of La. Furthermore, the M_S of Zn_0.99La_0.01O nanoparticles decreases from 0.005 to 0.001 emu g⁻¹ as the annealing temperature increases from 500 to 700 °C. The doping of La introduces more oxygen vacancies into ZnO. The decrease of annealing temperature also produces more oxygen vacancies in La-doped ZnO. These results indicate that the origin of the RTFM is related to oxygen vacancies.     

Synthesis of ferrofluid based nanoarchitectured polypyrrole composites and its application for electromagnetic shielding

The monodispersion of magnetic nanoparticles in conducting polymer is the prerequisite to make a high quality composite for tunable electromagnetic interference (EMI) shielding. To meet this challenge, we have designed and synthesized ferrofluid based nanoarchitectured polypyrrole composites containing Fe₃O₄ (8–12 nm) via in situ oxidative polymerization. To tune the microwave signals, polypyrrole composites (PFF) with different monomer/ferrofluid weight ratios have been prepared and characterized in microwave frequency domain. A maximum shielding effectiveness value of SE_A(max) = 20.4 dB (∼99% attenuation) due to the absorption of microwave has been observed in the frequency range of 12.4–18 GHz and attenuation level varied with ferrofluid loading. The electrical conductivity of PFF composite is of the order of 10⁻² S cm⁻¹ order and having superparamagnetic nature with saturation magnetization (M_s) of 5.5 emu g⁻¹. The lightweight PFF composites with high attenuations can provide full control over the atomic structure and are favorable for the practical EMI shielding application for commercial electronic appliances.     

Synthesis and characterization of conductive copper-based metal-organic framework/graphene-like composites

Metal-organic framework (MOF) incorporating conductive graphene-like layers were synthesized and characterized. The selected MOF, HKUST-1, combines high surface area, water stability, simple preparation and low costs. Graphene-like layers incorporated into the MOF structure were obtained by a two-step oxidation/reduction wet treatment of a high surface carbon black. MOF composites were produced at different carbonaceous layers content. It was shown, through a wide characterization of the samples, that the composites preserve the main features of the parent MOF, additional exhibiting a tunable electrical conductivity.