Preparation and Characterization of Porous Titania by Modified Sol-Gel Method

Mesoporous titania, especially anatase, is attractive due to its potential applications. A novel method to control pore structure of titania, surfactant- or polymer modification, is proposed. The wet gels and gel films, prepared from Ti(O-nC₄H₉)₄ were dried at 90°C and annealed at 500°C after immersion in surfactant or polymer solutions, and mesoporous anatase was obtained. The pore size, pore volume and specific surface area of the surfactant-modified bulk gels, estimated from N₂ absorption-desorption curves, are more than twice larger than those of the gels without modification. The pore size of the surfactant-modified gel films, observed by SEM, are similar to that of the bulk gels. The pore size obviously depended on the size of micelles. The pore size of the gels modified with hydrophilic polymers hardly increased, but the pore volume and the specific surface area increased.     

Physicochemical features of the formation of siliceous porous mesophases. 4. Effect of duration and temperature of the hydrothermal treatment on the structural and textural properties

The results of investigation of mesoporous mesophase materials C12--SiO₂--MMM and C16--SiO₂--MMM prepared at the optimized composition of the reaction mixture and different durations of hydrothermal treatment (HTT) at 120 °C and 140 °C are presented. Hydrothermal treatment at 120 °C influences slightly the specific surface area and the volume of the mesopores but gives a more ordered structure. Prolonged HTT at 140 °C results in irreversible structure degradation. The samples obtained with the optimal HTT duration are characterized by the minimum width of X-ray reflections, the maximum surface and volume of mesopores, and the minimum external surface.     

Zr 改性MnOx/MWCNTs催化剂的结构特征与低温SCR活性

以ZrO（NO₃）₂·2H₂O为前驱体对多壁碳纳米管（MWCNTs）进行了改性并负载MnO_x制备了MnO_x/ZrO₂/MWCNTs 催化剂. 考察了Zr 对催化剂低温选择性催化还原（SCR）反应活性的影响,并通过多种分析手段对催化剂的结构进行了表征. 结果表明Zr 的添加对催化剂的低温SCR活性具有显著的促进作用,当Zr 负载量为30%时,催化剂活性最佳. X射线衍射（XRD）、拉曼（Raman）光谱、透射电镜（TEM）、N₂吸附-脱附的表征结果分析表明,适量的Zr 改性促进了MnO_x在载体表面的分散,增强金属氧化物与MWCNTs 之间的作用,也能增加催化剂的比表面积、孔容和孔径. X 射线光电子能谱（XPS）、H₂程序升温还原（H₂-TPR）和NH₃程序升温脱附（NH₃-TPD）的分析结果则显示,Zr 能提高催化剂表面化学吸附氧浓度,促进Mn³⁺转化为Mn⁴⁺,从而使催化剂表面的活性位点增多,氧化还原能力增强,同时还提高了催化剂表面酸性位点的数量和强度,促进了NH₃的吸附,是MnO_x/ZrO₂/MWCNTs 催化剂低温SCR活性提高的主要原因.     

Characterization of Hydrophobic SiO2 Powders Prepared by Surface Modification on Wet Gel

Hydrophobic porous silica has been prepared by surface modification of TEOS (tetraethylorthosilicate) wet gel with 6 and 12 vol.% of TMCS (trimethylchlorosilane). We characterized the products by using FT-IR, TGA, DTA, N₂ adsorption/desorption, contact angle and SEM. Surface silanol groups of the gel were widely replaced by–Si(CH₃)₃ to result in a hydrophobic SiO₂ powder as confirmed by contact angle measurements with H₂O, 1-butanol and ethanol. The modified dried gels had a surface area of 950–1000 m²/g (average pore size 120 Å), compared to the non-modified surface which had a surface area of 690 m²/g (average pore size 36 Å). The adsorption/desorption isotherm curves indicated they had similar pore characteristics as aerogels prepared by the supercritical drying process.     

Porosity control in nanoporous carbide-derived carbon by oxidation in air and carbon dioxide

Carbide-derived carbons (CDC) allow a precise control over the pore size through the selection of the carbide precursor and varying of the synthesis conditions. However, their pore volume is limited by the carbide stoichiometry. While activation of carbons derived from various organic precursors has been widely studied, this process may similarly be able to increase the pore volume and specific surface area of CDC. Oxidation of carbide-derived carbon in air and CO₂ at different temperatures and times allows for significant increase in pore volume and specific surface area as well as control over average pore size with subnanometer accuracy. The effect of activation and associated changes in the pore volume and surface area on the hydrogen uptake are also discussed.     

Template-free sol–gel synthesis of microporous NiO–SiO2 composite with high surface area and narrow pore size distribution

Microporous NiO–SiO₂ composites were synthesized by a new sol–gel chemistry strategy using propylene oxide as gelation agent. Simple procedure, using of cheap precursor and high quality of the synthesized target materials were recognized as the advantages of the process. The obtained maximum pore surface area of the composites is about 718 m² g^?1 with narrow pore size distribution around 9 Å and micropore volume of 0.31 cm³ g^?1. It was found that the surface area of the samples decreases with the increase of Ni/Si molar ratio. However, the micropore size distributions of the samples were not altered with the increase of Ni/Si molar ratio. The unique chemistry of this sol–gel route assures the effectivity, simplicity and low cost of the whole process, showing the characteristics for the potential large scale preparation of microporous mixed oxide composites with very high pore area and very narrow pore size distribution.     

KIT-1介孔分子筛的化学修饰及吸附性能

介孔分子筛MCM-41具有较大、可调的孔径和较高的比表面积，其骨架组成具有较强的可调变性．为该材料的应用提供了很大的空间。但全硅MCM-41分子筛在潮湿空气中，即使在室温条件下也会发生水解反应，使其介孔结构遭到破坏。前人已针对MCM-41分子筛稳定性不足的问题相继合成了稳定性较高的介孔分子筛KIT-1,     

HY Zeolite Modified by Liquid Silane Deposition and Its Catalytic Activity in Selective tert-Butylation of Naphthalene

HY zeolites were modified by chemical liquid deposition with i-C₄H₉Si(OC₂H₅)₃, followed by hydrothermal treatment. The samples were characterized by X-ray diffraction, N₂ adsorption and pulse mass analysis to investigate the influence on framework structure, specific surface area, pore diameter and adsorption behaviors. The catalytic performances of HY zeolite and the modified samples in the alkylation of naphthalene with tert-butyl alcohol were also evaluated. The results showed the modification of HY zeolite did not change framework structure but increased specific surface area, decreased average pore diameter, and reduced the size of pore opening. Catalytic activity of the modified HY zeolite catalyst for tert-butylation of naphthalene was decreased compared with that of HY zeolite catalyst while shape-selectivity of 2,6-di-tert-butylnaphthalene (2,6-DTBN) was increased obviously, the highest 2,6-DTBN/2,7-DTBN ratio of 6.62 obtained.     

The impact of microwave energy on the results of silica gel hydrothermal modification

Two series of the hydrothermally treated (HTT) silica gel samples using the microwave reactor or the classical autoclave have been prepared. The HTT modification processes have been performed under the liquid water layer or in the water vapour. The initial and HTT silica samples were examined by means of adsorption (N₂), thermogravimetric (TG) and infra red (FTIR-ATR) methods. On the basis of the obtained results it was stated that even a short time of HTT modification using microwaves is enough to make distinct changes in the porous structure of silica. The time and pressure are the most influential parameters during HTT using microwaves. However, in the case of the samples modified in the classical autoclave the most important factors are temperature and time. The hydrothermally modified silica samples possess different concentration of intraglobular water dependently on applied treatment conditions and water state.     

Effect of pore structure on surface characteristics of zirconium phosphate-modified silica

Three samples of silica of different pore structure-predominantly microporous, S1; mesoporous, S2; and nonporous, S3-were modified with zirconium phosphate and examined. Pore structure analysis showed that modification had taken place in wider pores of S1 leaving a totally microporous sample, and in large pores of S2 giving a mesoporous sample of narrower pore size distribution. The modification of the nonporous sample decreased the surface area and pore volume to a lower extent than in the other two samples, but resulted in a surface of lower energy toward N2. The different distribution of surface silanol groups on the surfaces of different porosity may result in variable pictures on the modified surfaces as reflected in the differences observed in Br?nsted acidity of modified surfaces. The use of these modified silica samples for amino acid adsorption (L-glutamic acid and L-alanine) indicated that both the isoelectric point of the amino acid and the distribution of surface groups on modified solids are controlling the adsorption process.     

Preparation of SnO2 Monolithic Gel by Sol-Gel Method

The effects of aging of a wet gel at room temperature and a use of a drying control chemical additive (DCCA) were investigated on the prevention of cracking of the gel during drying. N,N-Dimethylformamide (DMF) having low surface tension was used as a DCCA in this study. Before drying, the aged wet gel was immersed in DMF for several days to replace the pore liquid in the wet gel with DMF.The longer the aging and DMF immersing times became, a fewer cracks generated during drying. Especially, the immersion in DMF for over 8 days made it possible to obtain the SnO₂ gel monolith without cracking from the wet gel aged for short time (1 day). However, the wet gel aged for long time without immersing in DMF could not be dried without cracking. Therefore, the replacement of the pore liquid in the wet gel with DMF having low surface tension is thought to be more effective on avoiding a crack generation than aging. From a pore size distribution measurement by N₂ gas adsorption, it was found that the pore size and the breadth of the pore size distribution of the dried gel became larger and narrower respectively with increasing DMF immersing time. DMF is thought to be capable of forming strong hydrogen bonding to hydroxyl groups remaining on the surface of the wet gel and providing a shielding cage around the reactants (Sn–OH), thus further condensation reaction is probably suppressed. Consequently, a large pore distribution is developed in the gel, which reduces the magnitude of capillary stress induced during drying.     

Preparation of Mesoporous Titania by Templating with Polymer and Surfactant and its Characterization

Mesoporous titania was obtained by gelation from Ti-alkoxide in alcoholic solutions with addition of polymer and/or surfactant. The structure and surface morphology of the gels were characterized by N₂-adsorption measurements, scanning electron microscopy and X-ray diffraction. The specific surface area and pore volume of the gels can be increased with addition of hydrophilic polymer such as polyethyleneglycol. Surfactants like cetyltrimetylammoniumchloride are effective to control the pore size and to increase the pore volume and surface area. The surface morphology of the gels can be modified by the mixing method with polymer and/or surfactant. The effects of the templating on pore size distribution, pore shape, surface area and crystallization behaviors have been discussed.     

Influence of the pore structure parameters of mesoporous anatase microspheres on their performance in lithium-ion batteries

Monodisperse mesoporous anatase microspheres were prepared by a combination of sol–gel and liquid–crystal template methods. With the change in annealing temperature, the pore structure parameters of samples were regulated. The influence of pore structure parameters on lithium-ion battery performance was systematically investigated. Results of electrochemical test and analysis demonstrated that the pore structure parameters significantly influenced the specific capacity, charging and discharging curves, rate capability, and cycle performance of the batteries. The first irreversible capacity increased with increased specific surface area. Materials with larger specific surface area showed better rate capability. When the average pore size was too small, the transport of Li⁺ in the electrolyte was impeded, which affected the rate capability of the materials. Based on the charging and discharging curves, the capacity of the plateau section corresponding to lithium insertion/extraction ions in the interstitial octahedral sites of anatase became smaller with increased specific surface area. By contrast, the capacity of the oblique line section corresponding to the Li⁺ insertion/extraction into/from the surface layer of anatase became larger. The pore volume influenced the cycling stability.     

Dynamics and isotherms of water vapor sorption on mesoporous silica gels modified by different salts

The mesoporous silica gels impregnated with different metal salts were prepared and studied. The pore structure and specific surface area of adsorbents were evaluated using nitrogen adsorption. Then, the sorption isotherms and dynamics of water vapor were carried out at 303 K and different relative humidity (RH). The temperature programmed desorption experiments were conducted to estimate the activation energy (E _d) of water desorption on the silica gels. The results showed that the sorption capacity for water decreased with the increase of the ionic radius (except the calcium ion) and that CaCl₂ and LiCl were particularly suitable for use in modification of the mesoporous silica gel to improve their sorption rates and capacities for water vapor at the lower and medium RH (RH < 80%). The larger the average pore diameter and pore volume of the initial silica gels, higher the accrual rates of the water vapor sorption rate and capacity were after modification with hygroscopic salts. The activation energy of the water desorption on the mesoporous silica gel modified by CaCl₂ were much higher than that on the silica gel modified by LiCl, because the polarizability of the Ca²⁺ was higher than that of Li⁺.     

Effect of sulfate synthesis conditions on characteristics of samples with the nanosized η-TiO2 modification

The nanosized titania modification ??-TiO₂ has been obtained from titanyl sulfate with different starting precursor concentration, under different hydrolysis and coagulation conditions. Characteristics of samples (nanoparticle and crystallite size, specific surface, pore volume) have been determined by scanning electron microscopy, small-angle and wide-angle X-ray diffraction, and nitrogen physical adsorption at ?196°C, and their correlation with the synthesis conditions has been established. Optimal technological regimes ensuring fabrication of samples with a high yield of ??-TiO₂ modification and specified functional characteristics have been found.     

Influence of cross profile of PE fibers on thermal properties of materials

Molecular sieves MCM-41 were synthesized from rice husk ash (RHA) as alternative sources of silica, called RHA MCM-41. The material was synthesized by a hydrothermal method from a gel with the molar composition 1.00 CTMABr:4.00 SiO₂:1.00 Na₂O:200.00 H₂O at 100 °C for 120 h with pH correction. The cetyltrimethylammonium bromide (CTMABr) was used as a structure template. The material was characterized by X-ray powder diffraction, FTIR, TG/DTG, and surface area determination by the BET method. The kinetics models proposed by Ozawa, Flynn–Wall, and Vyazovkin were used to determine the apparent activation energy for CTMA⁺ species decomposition from the pores of MCM-41 material. The results were compared with those obtained from the MCM-41 synthesized with silica gel. The synthesized material had specific surface area, size, and pore volume as specified by mesoporous materials developed from conventional sources of silica.     

Sorption equilibria of CO2 on silica-gels in the presence of water

The sorption equilibria of carbon dioxide on three types of silica gel (SG) with different pore size distributions in the presence of water were studied experimentally using a volumetric method at 275?K with pressures from 0 to 3.7?MPa. Both the pore size distribution of the silica gel and the quantity of pre-sorbed water impact the formation of the CO₂ hydrates. For wet silicon gel A(SG-A) with water loading ratio of 0.75, the highest CO₂ sorption was about 2.5?mmol of CO₂ per gram of dry sorbent at 275?K. Similarly, the highest sorption was about 2.7?mmol for wet SG-B with R _w =0.81. However, CO₂ hydrate did not form on the wet surface of SG-C due to its large pore sizes.     

Effective synthesis of nanoscale anatase TiO2 single crystals using activated carbon template to enhance the photodegradation of crystal violet

Nanoscale anatase TiO₂ single crystals were successfully synthesized using three kinds of activated carbon (AC) templates through a simple sol–gel method. The optimal photocatalyst (T‐WOAC) was obtained using wood‐based AC template. X‐ray diffraction, transmission electron microscopy and Brunauer–Emmett–Teller analyses revealed that T‐WOAC possessed a small crystallite size of 8.7 nm and a clear mesoporous structure. The photocatalytic properties of samples were then evaluated through photodegradation of crystal violet (CV). Results implied that the photocatalysts prepared using the AC templates exhibited superior photocatalytic activity to that of the original TiO₂. This enhancement may be due to the small crystallite size, large specific surface area and pore volume of the catalysts prepared with ACs. T‐WOAC showed high photocatalytic activity, CV degradation of 99.01% after 120 min of irradiation and k = 0.03914 min^?1, which is 3.9 times higher than that of the original TiO₂ (k = 0.00994 min^?1). This result can be mainly attributed to the application of WOAC with moderate specific surface area and pore volume to produce T‐WOAC. Alkaline conditions benefitted the photodegradation of CV over photocatalysts. This work proposes a possible degradation mechanism of CV and indicates that the fabricated photocatalysts can be used to effectively remove CV from aqueous solutions.     

Structure and electrorheological properties of nanoporous BaTiO<Subscript>3</Subscript> crystalline powders prepared by sol–gel method

In this paper, a novel nanoporous barium titanate (BaTiO₃) crystalline powder was synthesized by using triblock poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) based systems (P-123) as the soft template via a sol–gel method and their structure-dependent electro rheological property was studied. The pore diameter and specific surface area of BaTiO₃ were precisely controlled by varing the calcined temperature. The chemical composition, structure and surface morphology of BaTiO₃ were characterized by X-ray diffraction (XRD), thermo gravimetric analysis (TGA), and nitrogen adsorption–desorption method, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The result revealed that the pore volume and specific surface area of BaTiO₃ decreased with the increment of calcined temperature. The electro rheological fluids (ERFs) were obtained by dispersing BaTiO₃ crystallites in silicon oil and three kinds ERFs were fabricated by using three kinds of BaTiO₃ which were prepared under different calcined temperature (550, 600 and 900 °C) as the precursors. The behaviors of the ERFs were evaluated via a rotational rheometer fixed with electric field generator. The results showed that electro rheological effect was related to the pore volume and specific surface area of BaTiO₃. Due to the distinct advantage of sol–gel method for preparing nanoporous BaTiO₃ without contamination of the materials, the markedly low current destiny of the ERFs was obtained. The yield stress of ERFs with large specific surface area of BaTiO₃ reached the maximum of 3 kPa, which is higher than that of ERFs using traditional pure BaTiO₃ crystallites (lower than 1 kPa).     

Synthesis of micro/mesoporous silica using poly(ethylene glycol) as a template

Analysis of isotherms of low-temperature nitrogen adsorption-desorption has revealed the formation of a micro/mesoporous structure in silica resulting from the sol-gel transition of SiO₂ in the presence of poly(ethylene glycol)s with different molecular masses used as templates. The specific surface area of pores has been determined by the BET and Langmuir methods; the volume and surface area of micropores have been estimated by the t-plot method; and the surface area and volume of pores, mesopore size distribution, and average pore diameter have been assessed using the Barrett-Joyner-Halenda method.