Microwave-assisted ionic liquid preparation and characterization of cellulose/calcium silicate nanocomposites in ethylene glycol

Preparation of cellulose-based nanocomposites by microwave-assisted ionic liquid method allows the high value-added applications of cellulose by combining three major green chemistry principles: using environmentally preferable solvents, environmentally friendly method and renewable biomaterials. In this paper, we report the microwave-assisted ionic liquid method for the fast controlled synthesis of the cellulose/calcium silicate nanocomposites by using the microcrystalline cellulose, Ca(NO₃)₂·4H₂O and Na₂SiO₃·9H₂O in ethylene glycol. The calcium silicate nanoparticles were homogeneously dispersed in the cellulose matrix. The experimental results showed that the additive of ionic liquid favored the composite of cellulose and calcium silicate. The weight loss of nanocomposites was decreased with the increasing ionic liquid concentrations. The influences of heating times, heating temperatures, and ionic liquid concentrations on the products were investigated. This method is fast, environmentally friendly and suitable for the large-scale production of cellulose-based nanocomposites.     

Synthesis of sodium iron silicate(NaFe(III)[SiO3]2) nanorods and electrochemical characterization

Sodium iron silicate (NaFe(III)[SiO₃]₂) nanorods have been synthesized using iron nitrate (Fe(NO₃)₃) and sodium silicate (Na₂SiO₃) solutions by means of hydrothermal method. The mixture solution is processed in hydrothermal autoclave first at 180-200 °C for two days and then dried at 70 °C to obtain nanotructured NaFe(III)[SiO₃]₂. It was revealed that NaFe(III)[SiO₃]₂ nanorod with the average diameter of ~ 15 nm and length of several hundreds nm was confirmed by X-ray power diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Cyclic voltammeter (CV) and electrochemical impedance spectra (EIS) investigations show that this kind of NaFe(III)[SiO₃]₂ nanostructures have evident and stable electrochemical redox behavior between potential range of − 0.1-0.55 V in alkaline solution.     

Structure and micro-nanomechanical characterization of synthetic calcium–silicate–hydrate with Poly(Vinyl Alcohol)

The principal phase of hardened Portland cement pastes is calcium silicate hydrate (C–S–H), which influences the physical and mechanical properties of construction materials. In this work calcium silicate hydrate (C–S–H) was synthesized, with the addition of Poly(Vinyl Alcohol) (PVA), for the development of C–S–H/polymer nanocomposites. Among the polymers available, PVA is indicated by the literature as one of the most viable for producing C–S–H/polymer complexes. However, no consensus exists regarding the kind of interaction. The resulting compounds were characterized by XRD, FT-IR, TGA, carbon content (CHN), TEM, SEM and elastic modulus and hardness were measured by instrumented indentation. The set of results presented do not confirm the intercalation of PVA in the interlayer space of C–S–H, but presented evidence of the potential for intercalation, since changes in the structure clearly occurred. A significant change in the micro-nanomechanical properties of C–S–H occurred in the presence of PVA.     

Microwave-assisted preparation of calcium sulfate nanowires

We have successfully developed a new synthetic route for the rapid preparation of calcium sulfate nanowires by thermal transformation of calcium dodecyl sulfate (CDS) in organic solvents of ethylene glycol (EG) and N,N-dimethylformamide (DMF). The products are characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM), and determined to be single-phase CaSO₄·0.5H₂O consisting of single-crystalline nanowires with aspect ratio up to about 62. In this method, the different types of organic solvents used have no obvious influences on the morphology, phase, and formation time of the product. The microwave heating can remarkably shorten the reaction time compared with conventional heating methods.     

Synthesis and characterization of calcium hydroxide nanoparticles by hydrogen plasma-metal reaction method

Ca(OH)₂ nanoparticles have been synthesized with high purity and yield using the hydrogen plasma-metal reaction method. They are spherical in shape with a mean particle size of approximately 100 nm. The morphology of nanoparticles is spongy with mesopores, mostly less than 10 nm. The pore volume and surface area of Ca(OH)₂ nanoparticles are 0.084 cm³/g and 28.7 m²/g, respectively. Both transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis demonstrated that these nanoparticles possess poly-nanocrystalline structure with an average grain size of about 10 nm. The formation mechanism of Ca(OH)₂ nanoparticles was discussed in terms of chemical reactions and coalescence during the processing.     

Synthesis and characterization of novel ferromagnetic PPy-based nanocomposite

Polypyrrole(PPy)/Zn_0.5Cu_0.5Fe₂O₄ nanocomposite was prepared by a simple, general and inexpensive in situ polymerization of pyrrole in the presence of Zn_0.5Cu_0.5Fe₂O₄ nanoparticles in w/o microemulsion. The effects of PPy coating on the magnetic properties of Zn_0.5Cu_0.5Fe₂O₄ were investigated. By means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectra, scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM) technique, the microstructure and magnetic property of samples were characterized. The SEM analysis indicated that PPy was deposited on the porous surface of Zn_0.5Cu_0.5Fe₂O₄. The results were shown that the magnetic parameters such as saturation magnetization and coercivity of Zn_0.5Cu_0.5Fe₂O₄ decreased upon PPy coating.     

Synthesis and characterization of novel nanocomposite membrane of sodium titanate/Nafion

Novel nanocomposite membrane of sodium titanate/Nafion based on sodium titanate nanotubes with Nafion^® were prepared by solvent casting techniques. Nanotubes of sodium titanate were synthesized by hydrothermal method. TEM, XRD, and FTIR were employed to characterize the crystal phase, microstructure, and other physicochemical properties of the membrane and the nanotube samples. FTIR results showed us that the nanotube material of Na₂Ti₃O₇ has existed in the nanocomposite membrane of Na₂Ti₃O₇/Nafion. The existence of sodium titanate nanotubes in Nafion^® improves the methanol crossover and makes promising practical value of blocking methanol in direct methanol fuel cells.     

Preparation and characterization of multifunctional magnetic mesoporous calcium silicate materials

Abstract

We have prepared multifunctional magnetic mesoporous Fe–CaSiO₃ materials using triblock copolymer (P123) as a structure-directing agent. The effects of Fe substitution on the mesoporous structure, in vitro bioactivity, magnetic heating ability and drug delivery property of mesoporous CaSiO₃ materials were investigated. Mesoporous Fe–CaSiO₃ materials had similar mesoporous channels (5–6 nm) with different Fe substitution. When 5 and 10% Fe were substituted for Ca in mesoporous CaSiO₃ materials, mesoporous Fe–CaSiO₃ materials still showed good apatite-formation ability and had no cytotoxic effect on osteoblast-like MC3T3-E1 cells evaluated by the elution cell culture assay. On the other hand, mesoporous Fe–CaSiO₃ materials could generate heat to raise the temperature of the surrounding environment in an alternating magnetic field due to their superparamagnetic property. When we use gentamicin (GS) as a model drug, mesoporous Fe–CaSiO₃ materials release GS in a sustained manner. Therefore, magnetic mesoporous Fe–CaSiO₃ materials would be a promising multifunctional platform with bone regeneration, local drug delivery and magnetic hyperthermia.     

Synthesis and characterization of NiAl2O4 nanoparticles obtained through gelatin

Nanoparticles of NiAl₂O₄ were synthesized by heating (500-1000 °C) the dried resin resultant of a mixture in aqueous solution of gelatin, NiCl₂·6H₂O and AlCl₃·6H₂O. The particle size and microstrain were calculated from the line broadening of X-ray powder diffraction peaks through the Rietveld method refinement: these are 3.9-16 nm and − 0.743-0.139%, respectively. The NiAl₂O₄ nanoparticles were characterized by X-ray powder diffraction (XRPD), thermo gravimetric analysis (TG), BET and TEM techniques.     

High temperature ablation of kaolinite layered silicate/phenolic resin/asbestos cloth nanocomposite

The successful return of re-entry space vehicle, which is subjected to severe aerodynamic heating, is largely accompanied by some provisions to reduce the heat transfer to the structure. Heat shield is the best protection means which undergoes physical, chemical, and mostly endothermal transformations. The objective of this work is to investigate the ablating, charring, and thermal degradation behaviour of heat shield resol-type phenolic resin/kaolinite/asbestos cloth nanocomposite by oxyacetylene flame test with an external heat flux of 8 x 10(9)W/m(2) and 3000 K hot gas temperature and thermal analyzer techniques. Kinetic parameters of thermal degradation and temperature distribution at the back surface of the nanocomposite heat shield were determined and compared with that of composite counterpart.     

Single-step synthesis of MWCNT/ZnO nanocomposite using co-chemical vapor deposition method

Single-step synthesis of MWCNT and ZnO nanocomposite was conducted by co-chemical vapor deposition method. Electron microscopic analysis revealed that the fabricated nanostructures consisted of MWCNTs with a diameter of 60-70 nm which were coated with ZnO nanoparticles with an average size of 20-30 nm. The growth of ZnO nanoparticles took place after the formation of MWCNTs. EDS and XRD analyses could confirm the high crystallinity of ZnO deposited on the MWCNT surface. In comparison with pristine MWCNTs and ZnO nanoparticles, the UV absorption of MWCNT/ZnO nanocomposite was changed through modification with ZnO nanoparticles.     

A new model for the formation of calcium silicate hydrate (C-S-H)

2 S) and tricalcium silicate (C₃S) pastes are generally based on the notion that the dimeric calcium silicate hydrate (C-S-H) that begins to form at the end of the induction period is not a stable phase. It is implied that its formation simply marks the beginning of a rather lengthy equilibration process. This statement is based on the fact that the arrangement of Ca²⁺, OH^– and (Si₂O₇)^6– ions in the C-S-H at this time has no long range order (C-S-H is X-ray amorphous) and the fact that the dimers present in the C-S-H will seemingly polymerize and form dreierketten of the 3n-1 type with time. It has been suggested that the localized layers of C-S-H that contain these dreierketten are structurally related to tobermorite that has been modified in various ways, including omission of bridging tetrahedra and partial replacement of silicate ions by OH^– groups. As an alternative, it is suggested that the dimeric C-S-H that forms soon after setting and hardening may actually be a metastable phase in its own right, a rigid gel precursor phase whose stability is related to its calcium content. Should calcium concentrations fall below the level needed to stabilize the phase (a phenomenon that can be initiated by rising temperatures and/or portlandite precipitation), the dimeric C-S-H will undergo a phase change forming nano-sized fragments of tobermorite/jennite-like C-S-H. The proposed model differs from current models in that it proposes a relatively rapid equilibration followed by a much slower diffusion-controlled phase change process. Although both models predict the same outcome, i.e. a mature paste sample will normally contain a mixture of dimer and dreierketten, the new model gives a raison d’être for the presence of consistently large amounts of dimer throughout the entire hydration process. Received: 17 June, 1999 / Reviewed and accepted: 13 July, 1999     

Synthesis,characterization and modelling of zinc and silicate co-substituted hydroxyapatite

Experimental chemistry and atomic modelling studies were performed here to investigate a novel ionic co-substitution in hydroxyapatite (HA). Zinc, silicate co-substituted HA (ZnSiHA) remained phase pure after heating to 1100°C with Zn and Si amounts of 0.6 wt% and 1.2 wt%, respectively. Unique lattice expansions in ZnSiHA, silicate Fourier transform infrared peaks and changes to the hydroxyl IR stretching region suggested Zn and silicate co-substitution in ZnSiHA. Zn and silicate insertion into HA was modelled using density functional theory (DFT). Different scenarios were considered where Zn substituted for different calcium sites or at a 2b site along the c-axis, which was suspected in singly substituted ZnHA. The most energetically favourable site in ZnSiHA was Zn positioned at a previously unreported interstitial site just off the c-axis near a silicate tetrahedron sitting on a phosphate site. A combination of experimental chemistry and DFT modelling provided insight into these complex co-substituted calcium phosphates that could find biomedical application as a synthetic bone mineral substitute.     

Synthesis and characterization of porous κ-carrageenan/calcium phosphate nanocomposite scaffolds

The polysaccharide κ-carrageenan was used in the production of macroporous composites containing nanosized hydroxyapatite, with potential application in bone tissue engineering. Biodegradable composite scaffolds were prepared combining in situ co-precipitation of calcium phosphates with a freeze-drying technique. The effect of the Ca/P molar ratio and total ceramic content on the chemical composition, microstructure and mechanical performance of the scaffolds were investigated by thermal analysis, X-ray diffraction, FTIR, transmission electron microscopy, scanning electron microscopy, He porosimetry and compressive tests. A mixture of amorphous calcium phosphates and/or nanosized calcium-deficient hydroxyapatite was obtained in most of the composites. The formation of hydroxyapatite was induced by higher Ca/P ratios, probably due to competing reticulation of the biopolymer with calcium cations. The composite scaffolds presented interconnected pores (50–400 μm) and porosity around 97% and calcium phosphates were uniformly dispersed in the κ-carrageenan matrix. Both microstructure and compressive mechanical properties of the scaffolds were affected by the ceramic content and, for a Ca/P molar ratio of 1.67, maximum compressive strength was achieved for a ceramic content of ca. 25 wt%. Above this value the structural integrity of the composite was damaged and a dramatic decrease in mechanical strength was verified. Compressive mechanical properties of the composites were improved by increasing Ca/P atom ratio.     

Influence of curing temperatures on the hydration of calcium aluminate cement/Portland cement/calcium sulfate blends

In this paper, the effects of curing temperature on the hydration of calcium aluminate cement (CAC) dominated ternary binders (studied CAC: Portland cement: calcium sulfate mass ratio were 22.5: 51.7: 25.8) were estimated at 0, 10, 20 and 40 °C, respectively. Both α-hemihydrate and natural anhydrite were employed as the main source of sulfate. The impacts of temperature on the phase assemblages, morphology and pore structure of pastes hydrated up to 3 days were determined by using X-ray diffraction (XRD), backscattered electron imaging (BEI) and mercury intrusion porosimetry (MIP). Results reveal that the main hydration products are firmly related to calcium sulphoaluminate based phases. Increasing temperature would result in a faster conversion from ettringite to plate-like monosulfate for both calcium sulfate doped systems. When the temperature increases to 40 °C, an extraordinary formation of strätlingite (C₂ASH₈) and aluminium hydroxide is observed in anhydrite doped pastes. Additionally, increased temperature exerts different effects on the pore structure, i.e. the critical pore diameter shifts to finer one for pastes prepared with α-hemihydrate, but changes to coarser one for those made with anhydrite. From the mechanical point of view, increased temperature accelerates the 1-day strength development prominently, while exerts marginal influence on the development of 3-day strength.     

Synthesis and magnetic studies of nano-crystalline GdFeO3

Nano-crystalline GdFeO₃ was synthesized by three different soft-chemical routes viz. hydrothermal, co-precipitation and combustion. The hydrothermal and co-precipitation methods resulted in amorphous powder which on further heating resulted in GdFeO₃. The combustion method produced phase pure GdFeO₃ in a single step. The particle size was in the range of 50-70 nm as calculated by Scherrer's formula. The transmission electron micrographs (TEM) showed the presence of fairly regular particles. Magnetic studies revealed a paramagnetic behavior. The magnetic susceptibility (in emu/g-Oe) of GdFeO₃ samples as synthesized by hydrothermal, co-precipitation and combustion routes was found to be 9.6 × 10^− 5, 6.7 × 10^− 5 and 4.4 × 10^− 5 respectively.     

Processing of bovine hydroxyapatite (HA) powders and synthesis of calcium phosphate silicate glass ceramics using DC thermal plasma torch

In the present work, hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) was prepared from bovine bones with calcination method (up to 850 °C).The calcinated hydroxyapatite was powdered (30-40 μm) using a mechanical grinder; the particles were highly irregular in shape with sharp edges, angular, rounded, circular, dentric, porous and fragmented morphologies. The irregular shaped calcinated hydroxyapatite was plasma processed to produce spherical powders for thermal spray coating applications. More over; calcium phosphate silicate glass ceramics was produced by plasma melting of ball milled hydroxyapatite-borosilicate glass (50 wt.%) mixture. The samples were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometer (XRD) and energy dispersive X-ray analysis (EDX). The morphology was determined using scanning electron (SEM) and optical microscopy (OM). The microhardness, density and porosity measurements for the synthesized samples were made.     

Synthesis and characterization of Zn/Al2O3 nanocomposite by mechanical alloying

In this study, fabrication and characterization of zinc-based metal matrix nanocomposite reinforced by Al₂O₃ particles was investigated. Aluminum and zinc oxide powder mixture was milled in a planetary ball mill in order to produce Zn/Al₂O₃ nanocomposite. The structural evaluation milled and annealed powders studied by X-ray diffraction, SEM observation and hardness measurement. The zinc crystallite size estimated with broadening of XRD peaks by Williamson-Hall formula. The zinc oxide was found to react with Al through a rapid self-sustaining combustion reaction process. As a result a zinc matrix composite reinforced by Al₂O₃ particulate was formed. The microhardness value of produced nanocomposite powder was about 350 HV which was 10–15 times higher than the microhardness of pure zinc (20–30 HV).     

Synthesis and characterization of novel Ag-polypyrrole@poly(styrene-co-methacrylic acid) nanocomposite particles

Novel raspberry-like Ag-polypyrrole/poly(styrene-co-methacrylic acid) (Ag-PPy/P(St-co-MAA)) colloidal nanocomposite particles were prepared by aqueous oxidative polymerization of pyrrole using AgNO₃ as the oxidant. The polymerization was carried out in the pre-synthesized polymer-emulsion of P(St-co-MAA) with emulsifier-free P(St-co-MAA) latex particles serving as both the templates and the stabilizers. Without any extra surfactants or polymer stabilizers, the polymerization proceeded steadily with the in-situ produced Ag-PPy nanocomposites depositing on the surface of the template particles. The obtained product is typical of raspberry-like morphology, whose nanostructures and compositions were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), powder X-ray diffraction (XRD) and electron dispersive X-ray spectrometer (EDS), respectively. The results confirmed that the surface of the P(St-co-MAA) latex was coated by Ag-PPy nanocomposite particles with a size range from 2 nm to 50 nm. Most of Ag nanoparticles are encapsulated by the PPy sheath or dispersed in the PPy layer.     

Synthesis and humidity control performances of natural opoka based porous calcium silicate hydrate

In this work, a porous calcium silicate hydrate (CSH) humidity control material was prepared by hydrothermal synthesis with opoka (ROP) and slaked lime. The microstructures and humidity control properties of the prepared sample were characterized and analyzed in detail. Results show that CSH possesses plenty of mesoporous structures with the pore size range of 3–20 nm, which are superior to ROP. The maximum moisture adsorption capacity of CSH is about 2–3 times of ROP. The superior humidity control performance of CSH can be attributed to the increase of specific surface area and pore volume and the more reasonable and uniform pore size distribution. Moreover, CSH also exhibits good reusability within three cycles of adsorption/desorption. Furthermore, the synthesized CSH was added to an interior wall coating to test its humidity control performance in practical building materials. The result indicated that the moisture adsorption capacity of the coating with CSH in 24 h at high humidity can reach 110 g/m², and the moisture desorption capacity can also reach 70 g/m². The as received CSH shows excellent humidity control performance and can be used as a smart indoor humidity control material for various construction applications.