Facile Preparative Access to Bioactive Silicon Oxycarbides with Tunable Porosity

In the present work, Ca-containing silicon oxycarbides (SiCaOC) with varying Ca content have been synthesized via sol-gel processing and thermal treatment in inert gas atmosphere (pyrolysis). It has been shown that the as-prepared SiCaOC materials with low Ca loadings (Ca/Si molar ratios = 0.05 or 0.12) were X-ray amorphous; their glassy network contains Q3 sites, indicating the presence of Ca2+ at non-bridging-oxygen sites. SiCaOC with high Ca content (i.e., Ca/Si molar ratio = 0.50) exhibits the presence of crystalline calcium silicate (mainly pseudowollastonite). Furthermore, it has been shown that the incorporation of Ca into the SiOC glassy network has a significant effect on its porosity and specific surface area. Thus, the as-prepared Ca-free SiOC material is shown to be non-porous and having a specific surface area (SSA) of 22.5 m2/g; whereas SiCaOC with Ca/Si molar ratio of 0.05 exhibits mesoporosity and a SSA value of 123.4 m2/g. The further increase of Ca content leads to a decrease of the SSA and the generation of macroporosity in SiCaOC; thus, SiCaOC with Ca/Si molar ratio of 0.12 is macroporous and exhibits a SSA value of 39.5 m2/g. Bioactivity assessment in simulated body fluid (SBF) confirms the hydroxyapatite formation on all SiCaOC samples after seven days soaking, unlike the relatively inert ternary silicon oxycarbide reference. In particular, SiCaOC with a Ca/Si molar ratio of 0.05 shows an increased apatite forming ability compared to that of SiCaOC with Ca/Si molar ratio of 0.12; this difference is considered to be a direct consequence of the significantly higher SSA of the sample with the Ca/Si ratio of 0.05. The present work indicates two effects of Ca incorporation into the silicon oxycarbide glassy network on its bioactivity: Firstly, Ca2+ is shown to contribute to the slight depolymerization of the network, which clearly triggers the hydroxyapatite formation (compare the bioactive behavior of SiOC to that of SiCaOC with Ca/Si molar ratio 0.12 upon SBF exposure); secondly, the Ca2+ incorporation seems to strongly affect the porosity and SSA in the prepared SiCaOC materials. There is an optimum of Ca loading into the silicon oxycarbide glassy network (at a Ca/Si molar ration of 0.05), which provides mesoporosity and reaches maximum SSA, both highly beneficial for the bioactive behavior of the materials. An increase of the Ca loading leads, in addition to the crystallization of calcium silicates, to a coarsening of the pores (i.e., macroporosity) and a significant decrease of the SSA, both negatively affecting the bioactivity.

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Effect of pH, Molar Ratio of Fuel to Nitrates and Calcination Temperature on the Glycine-Nitrate Synthesis of Nano CoAl2O4

Advances in Science and Technology ◽

10.4028/www.scientific.net/ast.68.176 ◽

2010 ◽

Vol 68 ◽

pp. 176-181 ◽

Cited By ~ 2

Author(s):

Seyyed Hamid Jazayeri ◽

Federica Bondioli ◽

Shiva Salem ◽

Ali Allahverdi ◽

Mansoor Shirvani ◽

...

Keyword(s):

Specific Surface ◽

Surface Area ◽

Calcination Temperature ◽

Specific Surface Area ◽

Precursor Solution ◽

Molar Ratio ◽

Effect Of Ph ◽

Molar Ratios ◽

Metal Nitrates ◽

Powder Characteristics

In this research, solution-based combustion synthesis is applied to prepare the spinel CoAl2O4 pigment from precursor solution of Al(NO3)3 .9H2O, Co(NO3)2 .6H2O and glycine. Effect of pH values (2.5, 7, 10.5), molar ratio of fuel to metal nitrates in the precursor solutions (1.5, 2) and subsequent calcination temperature (800, 1000, 1200 °C) on the powder characteristics are described. Gel formation, morphologies, specific surface area and colour of the powder are characterized using DTA/TG, XRD, TEM, BET and UV-Vis. The results indicate that the crystalline spinel CoAl2O4 is formed at all different Gl/(metal nitrates) molar ratios, pH and temperatures and higher temperature promote the increase of the crystallite size. According to TEM figures most of the particles calcined at 800 and 1000 °C has sizes less than 50 and 100 nm, respectively. Corresponding to results of BET experiment, specific surface area has its maximum values at pH 7 and decreases with increasing of temperature. Finally, colorability test indicates the complete stability of the synthesized powder in the glass matrix.

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Preparation and Characterization of Ultralow Density Silica Aerogels by Acetonitrile Supercritical Drying

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.519.83 ◽

2012 ◽

Vol 519 ◽

pp. 83-86 ◽

Cited By ~ 6

Author(s):

Guang Wu Liu ◽

Xing Yuan Ni ◽

Bin Zhou ◽

Qiu Jie Yu

Keyword(s):

Specific Surface ◽

Surface Area ◽

Specific Surface Area ◽

Silica Aerogel ◽

Sol Gel ◽

Supercritical Drying ◽

Silica Aerogels ◽

High Specific Surface Area ◽

Molar Ratio ◽

Sol Gel Process

This paper deals with the synthesis of ultralow density silica aerogels using tetramethyl orthosilicate (TMOS) as the precursor via sol-gel process followed by supercritical drying using acetonitrile solvent extraction. Ultralow density silica aerogels with 6 mg/cc of density was made for the molar ratio by this method. The microstructure and morphology of the ultralow density silica aerogels was characterized by the specific surface area, SBET, SEM, and the pore size distribution techniques. The results show that the ultralow density silica aerogel has the high specific surface area of 812m2/g. Thermal conductivities at desired temperatures were analyzed by the transient plane heat source method. Thermal conductivity coefficients of silica aerogel monoliths changed from 0.024 to 0.043W/ (m K) as temperature increased to 400°C, revealed an excellent heat insulation effect during thermal process.

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Novel Al2O3–SiO2composite aerogels with high specific surface area at elevated temperatures with different alumina/silica molar ratios prepared by a non-alkoxide sol–gel method

RSC Advances ◽

10.1039/c5ra19764c ◽

2016 ◽

Vol 6 (7) ◽

pp. 5611-5620 ◽

Cited By ~ 40

Author(s):

Xiaodong Wu ◽

Gaofeng Shao ◽

Xiaodong Shen ◽

Sheng Cui ◽

Ling Wang

Keyword(s):

Specific Surface ◽

Surface Area ◽

Specific Surface Area ◽

Elevated Temperatures ◽

Inorganic Salt ◽

Sol Gel ◽

High Specific Surface Area ◽

Gel Method ◽

Molar Ratios ◽

Composite Aerogels

We have developed a new sol–gel route to synthesise Al2O3–SiO2composite aerogels with different alumina/silica (Al/Si) molar ratios using an inexpensive inorganic salt.

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Synthesis and Structural Characterization of SiO2-Al2O3 Xerogels

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.336-338.2286 ◽

2007 ◽

Vol 336-338 ◽

pp. 2286-2289

Author(s):

Fei He ◽

Xiao Dong He ◽

Yao Li

Keyword(s):

Structural Change ◽

Specific Surface ◽

Surface Area ◽

Specific Surface Area ◽

Sol Gel ◽

Nitrogen Adsorption ◽

Mesoporous Structure ◽

Supercritical Drying ◽

High Specific Surface Area ◽

Molar Ratio

Low-density xSiO2-(1-x)Al2O3 xerogels with x=0.9, 0.8, 0.7, 0.6 (mole fractions) were prepared by sol-gel and non-supercritical drying. Silica alkogels, which were the framework of binary composite materials, formed from tetraethyl orthosilicate (TEOS) by hydrolytic condensation with a molar ratio of TEOS: H2O: alcohol: hydrochloric acid: ammonia =1: 4: 10: 7.5×10-4: 0.0375. Aluminum hydroxide derived from Al(NO3)3·9H2O and NH4OH acting in the alcohol solution under the condition of catalyst. After filtrating and washing, the precipitation was mixed into silica sols to form SiO2-Al2O3 mixed oxide gels with different silicon and aluminum molar ratio. The structural change and crystallization of the binary xerogels were investigated after heat treatment at 600 for 2 h by the means of X-ray diffraction. Nitrogen adsorption experiment was performed to estimate specific surface area, porous volume and pore size distribution. The structural change of xerogels was observed by FT-IR spectroscopy. The resulting mixed xerogels possess of mesoporous structure which is characteristic of cylindrical pores, high specific surface area of 596-863 m2/g and a relatively narrow pore distribution of 2.8-30 nm. Al2O3 is introduced into the SiO2 phase and some of Al-O-Si bonds form.

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Chemical Structure and Microstructure Characterization of Ladder-Like Silsesquioxanes Derived Porous Silicon Oxycarbide Materials

Materials ◽

10.3390/ma14061340 ◽

2021 ◽

Vol 14 (6) ◽

pp. 1340

Author(s):

Jakub Marchewka ◽

Piotr Jeleń ◽

Izabela Rutkowska ◽

Patryk Bezkosty ◽

Maciej Sitarz

Keyword(s):

Specific Surface ◽

Surface Area ◽

Specific Surface Area ◽

Porous Ceramic ◽

Sol Gel ◽

Ceramic Materials ◽

Porous Ceramics ◽

Silicon Oxycarbide ◽

Bet Analysis ◽

Structure And Microstructure

The aim of this work was to synthesize porous ceramic materials from the SiOC system by the sol-gel method and the subsequent pyrolysis. The usage of two types of precursors (siloxanes) was determined by Si/C ratio in starting materials. It allows us to control the size of the pores and specific surface area, which are crucial for the potential applications of the final product after thermal processing. Methyltrimethoxysilane and dimethyldiethoxysilane were mixed in three different molar ratios: 4:1, 2:1, and 1:1 to emphasize Si/C ratio impact on silicon oxycarbide glasses properties. Structure and microstructure were examined both for xerogels and obtained silicon oxycarbide materials. Brunauer-Emmett-Teller (BET) analysis was performed to confirm that obtained materials are porous and Si/C ratio in siloxanes precursors affects porosity and specific surface area. This kind of porous ceramics could be potentially applied as gas sensors in high temperatures, catalyst supports, filters, adsorbents, or advanced drug delivery systems.

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Sol-gel preparation and properties of amorphous iron-containing aluminosilicate

Butlerov Communications ◽

10.37952/roi-jbc-01/20-64-11-102 ◽

2020 ◽

Vol 64 (11) ◽

pp. 102-107

Author(s):

Lyubov V. Furda ◽

◽

Evgeniya A. Tarasenko ◽

Sofya N. Dudina ◽

Olga E. Lebedeva ◽

...

Keyword(s):

Specific Surface ◽

Surface Area ◽

Specific Surface Area ◽

Active Sites ◽

Sol Gel ◽

Reference Sample ◽

Acid Sites ◽

Molar Ratio ◽

Indicator Method ◽

Gel Preparation

The objective of the present study includes a modification of synthetic aluminosilicate with iron cations and an estimation of the modificator influence at structure and properties of the aluminosilicate. The iron-containing aluminosilicate (Si/Al = 4.72) with an Al/Fe molar ratio of 5:1 was prepared by the sol-gel method at pH = 1-2. Amorphous aluminosilicate (Si/Al = 4.72), which was synthesized by analogous procedure, was applied as a reference sample. By scanning electron microscopy, it was found that the powders had particles of 1-20 micrometers in size. The results of low-temperature adsorption-thermal desorption of nitrogen showed that the modification with Fe3+ ions affected the specific surface area and porosity of the material under study. The iron-containing sample has a higher specific surface area and pore volume comparing to the initial aluminosilicate. The Hammett indicator method was used to evaluate the surface centers of the samples. It was found that the materials under study were characterized by the presence of active sites with pKax values in the range from - 4.4 to 12.8 with a pronounced maximum at pKax = 1.02. For an iron-containing sample, the concentration of acid sites significantly decreases at pKax = 1.02, while at pKax 0.80, 1.03, 2.10, 2.50, 4.10, 5.00, 8.00, and 12.80, an increase in the number of acid sites is observed. The values of the Hammett function are practically the same for the studied samples and characterizes them as materials of medium acidity. For iron-containing aluminosilicate, the larger number of active sites was noted, it amounted to 313.5 mmol/g.

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Functional Silica Aerogels with High Specific Surface Area: Influence of Preparation Conditions on Structure Properties

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.79-82.2039 ◽

2009 ◽

Vol 79-82 ◽

pp. 2039-2042

Author(s):

Li Ye ◽

Wei Jian Han ◽

Zhi Hong Ji ◽

Ji Dong Hu ◽

Tong Zhao

Keyword(s):

Specific Surface ◽

Bulk Density ◽

Surface Area ◽

Specific Surface Area ◽

Sol Gel ◽

Silica Aerogels ◽

Pore Distribution ◽

Nano Particles ◽

Molar Ratio ◽

Electron Microscopic

A series monolithic silica aerogels modified by amino-substituted organic groups were synthesized by sol-gel processing of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) mixtures, followed by drying of the wet gels with supercritical carbon dioxide (SCCO2). The molar ratios of EtOH/TEOS and DMF/ (TEOS+APTES) were fixed at 5 and 0.4, respectively, and APTES/TEOS ratio was varied between 1:9 and 3:7. HCl was added to obtain a narrow pore distribution, and the ratio of HCl/ (TEOS+APTES) was varied between 0 and 0.004. When APTES/TEOS ratio was kept at constant, gelling of the precursor mixtures was accelerated with an increasing ratio of HCl/ (TEOS+APTES). The physical properties of the aerogels have been investigated in detail by the bulk density, porosity, nitrogen sorption measurements and scanning electron microscopic (SEM). The results showed that adding HCl did increase the specific surface areas of the aerogels and make the aerogels have narrow pore distributions, but also resulted in some increase in bulk densities and decrease in porosities. The bulk density of the aerogels was 0.13-0.32 g/cm3, the corresponding porosity between 80% and 92%. Microscopically, the framework of the functional aerogels consists of spherical secondary nano-particles, which stack into grape-like aggregate and interconnect in different directions into a network. The specific surface area of the aerogels were in the range of 362-1044 m2/g, and uniform pore distribution aerogels were obtained when the molar ratio of APTES/ (TEOS+APTES)/HCl at 1/10/0.002 and 1/10/0.004.

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Effect of Different Reaction Solvents on the Hydrophobic and Structural Properties of Silica Cryogels

Materials Science Forum ◽

10.4028/www.scientific.net/msf.663-665.1238 ◽

2010 ◽

Vol 663-665 ◽

pp. 1238-1241

Author(s):

Li Fen Su ◽

Lei Miao ◽

Sakae Tanemura ◽

Gang Xu

Keyword(s):

Specific Surface ◽

Surface Area ◽

Specific Surface Area ◽

Freeze Drying ◽

Sol Gel ◽

Base Catalysis ◽

Molar Ratio ◽

Nitrogen Absorption ◽

Acid Base ◽

Sol Gel Process

The experimental results on the microstructural and physical properties of the TEOS-based silica cryogels have been reported. The cryogels were produced by two-step sol-gel process followed by vacuum freeze drying. The wet gels were synthesized via acid-base catalysis using tetraethoxysilane (TEOS) as a silica precursor, the different solvents containing ethanol (EtOH), methanol (MeOH) and tert-butanol (TBA), the molar ratio of TEOS / solvent were varied from 1:6 to 1:13. Further, the microstructure and specific surface area of the cryogels were analysed by Scanning Electron Microscopy (SEM) and nitrogen absorption/desorption isotherms. The hydrophobicity of the cryogels was studied by contact angle. It was found that the highest specific surface area (1040.17 m2 / g) was obtained with the solvent of MeOH. The lowest density (0.074 g/cm3) was acquired with the solvent of EtOH.

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The Influence of Fe/Al Molar Ratio on Microreactor-Based Catalyst Preparation and Carbon Nanotube Preparation

Materials Science Forum ◽

10.4028/www.scientific.net/msf.1036.130 ◽

2021 ◽

Vol 1036 ◽

pp. 130-136

Author(s):

Ting Qun Tan ◽

Lei Geng ◽

Yan Lin ◽

Yan He

Keyword(s):

Carbon Nanotubes ◽

Catalytic Activity ◽

Specific Surface ◽

Surface Area ◽

Specific Surface Area ◽

Small Diameter ◽

High Specific Surface Area ◽

Detection Methods ◽

Molar Ratio ◽

High Catalytic Activity

In order to prepare carbon nanotubes with high specific surface area, small diameter, low resistivity, high purity and high catalytic activity, the Fe-Mo/Al2O3 catalyst was prepared based on the microreactor. The influence of different Fe/Al molar ratios on the catalyst and the carbon nanotubes prepared was studied through BET, SEM, TEM and other detection methods. Studies have shown that the pore structure of the catalyst is dominated by slit pores at a lower Fe/Al molar ratio. The catalytic activity is the highest when the Fe/Al molar ratio is 1:1, reaching 74.1%. When the Fe/Al molar ratio is 1:2, the catalyst has a higher specific surface area, the maximum pore size is 8.63 nm, and the four-probe resistivity and ash content of the corresponding carbon nanotubes are the lowest. The higher the proportion of aluminum, the higher the specific surface area of the catalyst and the carbon nanotubes, and the finer the diameter of the carbon nanotubes, which gradually tends to relax. The results show that when the Fe/Al molar ratio is 1:2, although the catalytic activity of the catalyst is not the highest, the carbon nanotubes prepared have the best performance.

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Tuning the Morphological Properties of Cellulose Aerogels: An Investigation of Salt-Mediated Preparation

10.21203/rs.3.rs-333138/v1 ◽

2021 ◽

Author(s):

Prakash Parajuli ◽

Sanjit Acharya ◽

Julia Shamshina ◽

Noureddine Abidi

Keyword(s):

Specific Surface ◽

Surface Area ◽

Specific Surface Area ◽

Sol Gel ◽

Earth Metal ◽

Morphological Properties ◽

Cellulose Solution ◽

Bet Analysis ◽

Sol Gel Transition ◽

Gel Transition

Abstract In this study, alkali and alkaline earth metal chlorides with different cationic radii (LiCl, NaCl, and KCl, MgCl2, and CaCl2) were used to gain insight into the behavior of cellulose solutions in the presence of salts. The specific focus of the study was evaluation of the effect of salts’ addition on the sol-gel transition of the cellulose solutions and on their ability to form monoliths, as well as evaluation of the morphology (e.g., specific surface area, pore characteristics, and microstructure) of aerocelluloses prepared from these solutions. The effect of the salt addition on the sol-gel transition of cellulose solutions was studied using rheology, and morphology of resultant aerogels was evaluated by Scanning Electron Microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis, while the salt influence on the aerocelluloses’ crystalline structure and thermal stability was evaluated using powder X-Ray Diffraction (pXRD) and Thermogravimetric Analysis (TGA), respectively. The study revealed that the effect of salts’ addition was dependent on the component ions and their concentration. The addition of salts in the amount below certain concentration limit significantly improved the ability of the cellulose solutions to form monoliths and reduced the sol-gel transition time. Salts of lower cationic radii had a greater effect on gelation. However, excessive amount of salts resulted in the formation of fragile monoliths or no formation of gels at all. Analysis of surface morphology demonstrated that the addition of salts resulted in a significant increase in porosity and specific surface area, with salts of lower cationic radii leading to aerogels with much larger (~1.5 and 1.6-fold for LiCl and MgCl2, respectively) specific surface area compared to aerocelluloses prepared with no added salt. Thus, by adding the appropriate salt into the cellulose solution prior to gelation, the properties of aerocelluloses that control material’s performance (specific surface area, density, and porosity) could be tailored for a specific application.

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