Thermal stability of high surface area silicon carbide materials

The synthesis of mesoporous silicon carbide by chemical vapor infiltration of dimethyl dichlorosilane into mesoporous silica SBA-15 and subsequent dissolution of the silica matrix with HF was investigated. The influence of the synthesis parameters of the composite material (SiC/SBA-15) on the final product (mesoporous SiC) was determined. Depending on the preparation conditions, materials with specific surface areas from 410 to 830 m² g⁻¹ and pore sizes between 2 and 10 nm with high mesopore volume (0.31-0.96 cm³ g⁻¹) were prepared. Additionally, the thermal stability of mesoporous silicon carbide at 1573 K in an inert atmosphere (argon) was investigated, and compared to that of SBA-15 and ordered mesoporous carbon (CMK-1). Mesoporous SiC has a much higher thermal textural stability as compared to SBA-15, but a lower stability than ordered mesoporous carbon CMK-1.     

Synthesis of activated carbon foams with high specific surface area using polyurethane elastomer templates for effective removal of methylene blue

Carbon foams have gained significant attention due to their tuneable properties that enable a wide range of applications including catalysis, energy storage and wastewater treatment. Novel synthesis pathways enable novel applications via yielding complex, hierarchical material structure. In this work, activated carbon foams (ACFs) were produced from waste polyurethane elastomer templates using different synthesis pathways, including a novel one-step method. Uniquely, the produced foams exhibited complex structure and contained carbon microspheres. The ACFs were synthesized by impregnating the elastomers in an acidified sucrose solution followed by direct activation using CO₂ at 1000 ℃. Different pyrolysis and activation conditions were investigated. The ACFs were characterized by a high specific surface area (S_BET) of 2172 m²/g and an enhanced pore volume of 1.08 cm³/g. Computer tomography and morphological studies revealed an inhomogeneous porous structure and the presence of numerous carbon spheres of varying sizes embedded in the porous network of the three-dimensional carbon foam. X-ray diffraction (XRD) and Raman spectroscopy indicated that the obtained carbon foam was amorphous and of turbostratic structure. Moreover, the activation process enhanced the surface of the carbon foam, making it more hydrophilic via altering pore size distribution and introducing oxygen functional groups. In equilibrium, the adsorption of methylene blue on ACF followed the Langmuir isotherm model with a maximum adsorption capacity of 592 mg/g. Based on these results, the produced ACFs have potential applications as adsorbents, catalyst support and electrode material in energy storage systems.     

The study of the conversion of intercalated compounds synthesized from a sol-gel procedure

Intercalated materials containing iron and carbonate species were synthesized in this work to study their hydrolysis and condensation from sol to gel transition. The former material was designated as PV (perovskite) and the latter HT (hydrotalcite). Another sample containing neither of the indicated ions was designated as AlMg(OH)₅ (aluminum magnesium hydroxide). The conversion energy of these materials for the hydrolysis and condensation reaction during the transition was estimated to be ≈14 cal/mol, much lower than the hydration energy of 10–14 kcal/mol computed using molecular dynamic simulation from the previous work. The energy consumed was interpreted as equivalent to the drop of temperature due to the endothermic reaction. PV material exhibited the highest swelling ratio, amounting to 76% from its dried weight, demonstrating its ability to intercalate water readily. HT sample, on the other hand, was completely saturated and did not dilate.     

高比表面SiC的合成及其在CO氧化反应中的应用

采用蔗糖为碳源, 正硅酸乙酯(TEOS)为硅源, 分别以草酸、硝酸铁、硝酸镍为催化剂, 用溶胶-凝胶法制备碳化硅前驱体, 考察了制备过程中催化剂的种类以及反应温度和时间对凝胶形成的影响. 发现以硝酸铁为催化剂最有利于凝胶的形成, 碳/硅物质的量比为4的前驱体在氩气气氛1350 ℃下加热10 h, 碳热还原反应趋于完成. 以该条件下合成的多孔碳化硅(比表面积133 m2·g-1)作为催化剂载体, 通过等量浸渍法获得Pt/SiC催化剂, 将其应用于一氧化碳氧化的模型反应中. 研究结果表明该催化剂有较好的催化活性和稳定性. 引入镍助剂的PtNi/SiC催化剂能进一步提高一氧化碳催化氧化反应的活性.     

高比表面碳化硅制备及其作为催化剂载体的应用

介绍了模板法、溶胶-凝胶法以及聚碳硅烷裂解法制备高比表面积碳化硅的主要过程和结果, 并介绍了碳化硅作为催化剂载体在多相催化中应用的研究进展. 对碳化硅在多相催化中的应用前景进行了展望.     

肼溶胶-凝胶法制备高比表面积纳米氮化钛粉体的研究

以无水肼作氮源, 采用肼溶胶-凝胶技术(HSG)成功地制备了TiN粉体, 研究了不同钛源、处理气氛及焙烧温度对TiN粉体晶化过程的影响, 并对其形成机理进行了讨论. 与氨气氮化法相比, 该方法所需温度低、TiN的粒径小、比表面积大, 并且分散均匀.     

Recent advances in high surface area electrodes for bioelectrochemical applications

The search for high surface area electrodes for bioelectrochemical applications is becoming more intense. In the last few years, new strategies have emerged to develop three-dimensional electrode materials with very well controlled architecture providing at the same time high specific surface, bendability and flexibility. This review will highlight some of the recent work published in the last 2 years and will discuss the issue of mathematical modeling of porous electrodes and what could be the future of high surface area electrodes materials.     

Occlusion of transition metal ions by new adsorbents synthesized from plant polyphenols and animal fibrous proteins

Removing and collecting heavy and rare metal ions from industrial effluents and waste aqueous solutions are improtant problems. Our previous studies showed that animal fibrous proteins (AFPs) such as hen eggshell membrane, chicken feather (CF), wool, and silk were stable and insoluble proteins and had an excellent ability to bind not only hard (Mn²⁺ and Fe³⁺) but alsosoft (Ag⁺, Au⁺, Pd²⁺, Pt²⁺, and Hg²⁺) acids from aqueous solutions. In this study, we syntheszed some adsorbents for transition (Cr⁶⁺, Mn²⁺, Co²⁺, Ni²⁺, and Cu²⁺) and heavy (Cd²⁺) metalions from AFPs (gelatin, CF, and wool) and plant polyphenols (lignin and tannin) by heating a mixture of AFPs and plant polyphenols under acidic conditions. In batch experiments, pH profile, time dependency, and isotherm analysis were performed to determine binding properties of adsorbents for transition and heavy metal ions. Columnexperiments were also performed to removecopper ion from aqueous solution. The results showed that the new adsorbents were effective for collecting and removing transition and heavy metal ions from aqueous solutions.     

Joint neighbors approximation of macromolecular solvent accessible surface area

A new method for approximate analytical calculations of solvent accessible surface area (SASA) for arbitrary molecules and their gradients with respect to their atomic coordinates was developed. This method is based on the recursive procedure of pairwise joining of neighboring atoms. Unlike other available methods of approximate SASA calculations, the method has no empirical parameters, and therefore can be used with comparable accuracy in calculations of SASA in folded and unfolded conformations of macromolecules of any chemical nature. As shown by tests with globular proteins in folded conformations, average errors in absolute atomic surface area is around 1 A2, while for unfolded protein conformations it varies from 1.65 to 1.87 A2. Computational times of the method are comparable with those by GETAREA, one of the fastest exact analytical methods available today.     

A fast pairwise evaluation of molecular surface area

A fast and general analytical approach was developed for the calculation of the approximate van der Waals and solvent-accessible surface areas. The method is based on three basic ideas: the use of the Lorentz transformation formula, a rigid-geometry approximation, and a single fitting parameter that can be refitted on the fly during a simulation. The Lorentz transformation equation is used for the summation of the areas of an atom buried by its neighboring contacting atoms, and implies that a sum of the buried pairwise areas cannot be larger than the surface area of the isolated spherical atom itself. In a rigid-geometry approximation we numerically calculate and keep constant the surface of each atom buried by the atoms involved in 1-2 and 1-3 interactions. Only the contributions from the nonbonded atoms (1-4 and higher interactions) are considered in terms of the pairwise approximation. The accuracy and speed of the method is competitive with other pairwise algorithms. A major strength of the method is the ease of parametrization.     

Porous silicon oxycarbide glasses from organically modified silica gels of high surface area

High surface area alkyl-substituted silica aerogels and xerogels were successfully prepared by sol-gel processing and supercritical drying. The gels were further heat treated in inert atmosphere to temperatures as high as 1000°C. Surface areas and pore structure of the gels and gels pyrolyzed at high temperatures were determined by multipoint BET surface area measurement. The aerogels and xerogels exhibited surface areas of about 1100 m²/g. No significant effect of pH was found on the surface areas of gels in the two step sol-gel process, but gels of low pH showed smaller pore diameter and higher density. Xerogels showed smaller surface area, pore size, and pore volume compared to aerogels. Upon pyrolyzing in inert atmosphere, the surface areas of all the gels decreased with temperature as a result of collapse of micropores and shrinkage of mesopores. Unlike pure silica gel, which loses almost all surface area and densifies at 1000°C, the advantage of the alkyl-substituted gels is that they maintained a high surface area of 400 m²/g at 1000°C.Also with the Department of Agronomy.     

Mixed metal fluorides as doped Lewis acidic catalyst systems: a comparative study involving novel high surface area metal fluorides

MF₃-doped/MgF₂ systems with enhanced Lewis acidity are reported, which are obtained either by the conventional aqueous route of co-precipitation or, by a novel non-aqueous soft chemistry route. The latter gives outstanding high surface areas and exhibits potent Lewis acid catalyst behaviour. The doped solid metal fluorides with dopant metals such as Ga, In, Fe, V are discussed in terms of the modified Tanabe model, which is adopted for metal fluoride systems. The two doped but differently prepared systems are analysed according to their surface characteristics by BET surface area, pore-size distribution and XPS/XAES as well as for the solid state structure by scanning electron microscopy (SEM), XRD and -MAS-NMR. The surface properties were evaluated by photoacoustic IR-spectroscopy of pyridine adsorbates and selected catalytic reactions.The exemplarily investigated GaF₃-doped/MgF₂ system reveals modified intrinsic properties of the solid mixture culminating in very high surface areas of a structurally distorted mesoporous solid and electrostatic charge rearrangements causing increased Lewis acid sites.     

A generalized expression for the ratio of the critical temperature to the critical pressure with the van der Waals surface area

Using an extensive database of experimental critical properties for heavy compounds, which have been compiled mostly from recent literature sources, it is shown that the ratio T_c: P_c (critical temperature over critical pressure) can be expressed in terms of the van der Waals surface area (Q_w), which is readily available for any compound from the group contributions of Bondi (given also in UNIFAC tables). The proposed correlation is based on the hole theory of Kurata and Isida for n-paraffin liquids, which is mathematically equivalent to Flory's theory of polymer solutions. The method is suitable for medium to high molecular weight compounds with unknown critical constants. For example, if only one of the two critical constants is available, then the proposed generalized equation offers a useful rapid procedure for the estimation of the other critical property for use in corresponding states, and other relevant applications where knowledge of the critical properties is required. Furthermore, the T_c: P_c method can be used in many cases for identifying the most suitable among the existing group contribution methods for estimating the critical properties of heavy and complex compounds for which experimental values are, very often, not available.     

Sol-gel-fluorination synthesis of amorphous magnesium fluoride

The sol-gel fluorination process is discussed for the reaction of magnesium alkoxides with HF in non-aqueous solvents to give X-ray amorphous nano-sized magnesium fluoride with high surface areas in the range of 150-350 m²/g (HS-MgF₂). The H2 type hysteresis of nitrogen adsorption-desorption BET-isotherms is indicative for mesoporous solids. A highly distorted structure causes quite high Lewis acidity, shown by NH₃ temperature-programmed desorption (NH₃-TPD) and catalytic test reactions. XPS data of amorphous and conventionally crystalline MgF₂ are compared, both show octahedral coordination at the metal site. Thermal analysis, F-MAS NMR- and IR-spectroscopy give information on composition and structure of the precursor intermediate as well as of the final metal fluoride. The preparation of complex fluorides, M⁺MgF₃⁻, by the sol-gel route is reported. From the magnesium fluoride gel of the above process thin films for optical application are obtained by, e.g., spin coating.     

Extended structural materials constructed from sulfate-centered Preyssler-type polyoxometalate with excellent electrocatalytic property

The sulfate-centered Preyssler-type polyoxometalate was firstly used to construct inorganic-organic hybrid materials, which exhibits excellent electrocatalytic activity toward reduction of H₂O₂ and NO₂^-.     

Recent developments in the preparation of high surface area metal fluorides

An overview of the main procedures for the preparation of fluorides with very high surface areas is given. Three processes are outlined: (i) plasma fluorination, (ii) sol–gel route and (iii) oxidative decomposition of inorganic precursors. From all three processes nanostructured metal fluorides with 100–400 m² g⁻¹ can be obtained. Prevention of the local overheating during fluorination seems to be the key factor to obtain the high surface area fluorides. TEM investigations of AlF₃ and CrF₃ obtained by oxidative decomposition revealed considerable differences in their morphologies and crystallinity. CrF₃ is completely amorphous and unstable under beam. AlF₃ contains an amorphous phase and nanocrystalline phases of α-AlF₃ and β-AlF₃. Nanocrystals are uniformly distributed within the amorphous phase. Also present are the rod-like nanostructures that consist of β-AlF₃ and are 5–10 nm wide.     

The specific surface area of methane hydrate formed in different conditions and manners

The specific surface area of methane hydrates, formed both in the presence and absence of sodium dodecyl sulfate (SDS) and processed in different manners (stirring, compacting, holding the hydrates at the formation conditions for different periods of time, cooling the hydrates for different periods of time before depressurizing them), was measured under atmospheric pressure and temperatures below ice point. It was found that the specific surface area of hydrate increased with the decreasing temperature. The methane hydrate in the presence of SDS was shown to be of bigger specific surface areas than pure methane hydrates. The experimental results further demonstrated that the manners of forming and processing hydrates affected the specific surface area of hydrate samples. Stirring or compacting made the hydrate become finer and led to a bigger specific surface area. Supported by the National natural Science Foundation of China (Grant Nos.20490207, 2076145, uo633003), Program for New Century Excellent Talents in University and National The National High Technology Research and Development Program of China Project.     

Preparation of high surface area ZrO2 and ZrO2-Y2O3 from the alkoxide

In order to obtain a catalyst support with a high surface area, ZrO₂ and ZrO₂-Y₂O₃ were prepared by the hydrolytic decomposition of the corresponding isopropoxide dissolved in benzene. The hydrolysis was carried out at 80°C using an excess amount of distilled water in flowing dry nitrogen. The precipitates thus obtained were dried at 100°C followed by calcination at 500°C in air or nitrogen for 1 h. The specific surface areas for both of the ZrO₂ and ZrO₂-Y₂O₃ increased with increasing amount of water added for hydrolysis, and the surface areas for ZrO₂-Y₂O₃ increased with increasing yttrium content. A ZrO₂ having a surface area of 130 m²/g was produced, and a stabilized tetragonal ZrO₂ with 15 mol% Y³⁺ having a surface area of 200 m²/g was produced. Furthermore, despite the difference in the ZrO₂ and ZrO₂-Y₂O₃ crystal structures, the lattice-strain of ZrO₂ has been unequivocally related to the surface area.     

耐高温高比表面氧化铬/氧化锆体系的制备和表征

采用浸渍法和共沉淀法制备了CrOx/ZrO2样品.制备过程中所得沉淀都经100 ℃碱液回流老化24 h.通过X射线衍射、X射线光电子能谱、氮吸附、差热-热重分析等手段对样品进行了表征.结果证实,碱液回流过程中会有SiO2从所用的玻璃器皿进入样品， SiO2的表面修饰作用提高了载体的热稳定性.氧化铬的引入进一步提高了所得样品的比表面和热稳定性.与浸渍法相比，共沉淀法制备的样品具有更好的性能.其中铬锆摩尔比为0.15时，用NaOH作沉淀剂， pH值为13的条件下制备的样品在1000 ℃焙烧后比表面仍达到121 m2•g－1.     

Maintaining solvent accessible surface area under rotamer substitution for protein design

Although quantities derived from solvent accessible surface areas (SASA) are useful in many applications in protein design and structural biology, the computational cost of accurate SASA calculation makes SASA-based scores difficult to integrate into commonly used protein design methodologies. We demonstrate a method for maintaining accurate SASA during a Monte Carlo search of sequence and rotamer space for a fixed protein backbone. We extend the fast Le Grand and Merz algorithm (Le Grand and Merz, J Comput Chem, 14, 349), which discretizes the solvent accessible surface for each atom by placing dots on a sphere and combines Boolean masks to determine which dots are exposed. By replacing semigroup operations with group operations (from Boolean logic to counting dot coverage) we support SASA updates. Our algorithm takes time proportional to the number of atoms affected by rotamer substitution, rather than the number of atoms in the protein. For design simulations with a one hundred residue protein our approach is approximately 145 times faster than performing a Le Grand and Merz SASA calculation from scratch following each rotamer substitution. To demonstrate practical effectiveness, we optimize a SASA-based measure of protein packing in the complete redesign of a large set of proteins and protein-protein interfaces.