首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
《中国化学会会志》2017,64(8):978-985
Alumina/titania composite aerogels with different titania contents were synthesized by the sol–gel process and supercritical ethanol drying. The structures and morphologies of synthesized aerogels were analyzed by X‐ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetry, and N2 adsorption–desorption tests. Supercritical ethanol drying induced the crystallization of titania, which prompted the transformation of the structure from pseudoboehmite to γ‐Al2O3 . Reversely, alumina retarded the anatase‐to‐rutile transformation of titania. The content of titania significantly affected the structure and morphology of alumina/titania composite aerogels. A high content of titania (≥40%) resulted in the phase separation of titania particles, which grew to form the anatase phase octahedral particles with well‐developed facets. When the titania content was low, titania particles could be homogeneously dispersed in alumina particles to form spherical clusters with the poor crystallinity. Titania particles were in the anatase phase, and no rutile phase was formed until the temperature rose to 1000°C. In addition, titania addition resulted in a decrease in the specific surface area (SSA) of alumina aerogels because the SSA of titania was lower than that of alumina aerogels.  相似文献   

2.
Zeolite rho was prepared by hydrothermal synthesis using an 18-crown-6 ether (18C6) as a structure-directing agent, and the effects of the calcination temperature for removal of 18C6 on the physicochemical properties and CO2-adsorption properties were investigated. CO2 adsorption on zeolite rho calcined at 150 °C was lower than that on samples calcined at temperatures above 300 °C. For samples calcined above 300 °C, CO2 adsorption increased with increasing calcination temperature up to 400 °C. It is thought that the pore volume for adsorption of CO2 increased as a result of 18C6 removal, resulting in increasing CO2 adsorption. A decrease in CO2 adsorption for calcination from 400 °C to 500 °C was observed. The particle size of zeolite rho increased with increasing 18C6 molar ratio. Particle sizes of 1.0-2.1 μm and 1.4-2.6 μm were found by field-emission scanning electron microscopy and dynamic light-scattering, respectively. The particle size is controlled in these regions by adjusting the 18C6 molar ratio. XRD showed that zeolite rho samples with 18C6 molar ratios of 0.25-1.5 had high crystallinity. The adsorbed amount of CO2 is almost constant, at 3.4 mmol-CO2 g−1, regardless of the 18C6 molar ratio. However, CO2 selectivity, which is the CO2/N2 adsorption ratio, decreased. The amount of CO2 adsorbed on zeolite rho is lower than that on zeolite NaX, but higher than that on SAPO-34. The CO2/N2 adsorption ratio for zeolite rho was higher than those for SAPO-34 and zeolite NaX.  相似文献   

3.
NaY zeolite particles with a high surface area of 723 m2/g were synthesized by a hydrothermal method. Adsorption isotherms of pure gases CO2 and N2 on the synthesized NaY particles were measured at temperatures 303, 323, 348, 373, 398, 423, 448 and 473 K and pressures up to 100 kPa. It was found that the adsorption isotherm of CO2 on the synthesized zeolite is higher than that on other porous media reported in the literature. All measured adsorption isotherms of CO2 and N2 were fitted to adsorption models Sips, Toth, and UNILAN in the measured temperature/pressure range and Henry’s law adsorption equilibrium constants were obtained for all three adsorption models. The adsorption isotherms measured in this work suggest that the NaY zeolite may be capable of capturing CO2 from flue gas at high temperatures. In addition, isosteric heats of adsorption were calculated from these adsorption isotherms. It was found that temperature has little effect on N2 adsorption, while it presents marked decrease for CO2 with an increase of adsorbate loading, which suggests heterogeneous interactions between CO2 and the zeolite cavity.  相似文献   

4.
The Cu-doped SiO2 composite aerogels were successfully prepared by sol–gel process and subsequently supercritical drying with ethanol and CO2. The Cu-doped SiO2 composite aerogels had porous texture, low density (<100 mg cm?3) and high specific surface area (>800 m2 g?1), which were investigated by FESEM and nitrogen adsorption desorption porosimetry. The FTIR spectra of the aerogels showed that the ethanol-dried aerogels had been modified by ethyl while the corresponding CO2-dried aerogels had more Si–OH groups. The phase structure and thermal stability were investigated by XRD and TGA, respectively. Due to the reducibility of ethanol, the copper was crystalline in ethanol-dried sample. The Cu-doped SiO2 composite aerogels dried with supercritical ethanol had larger pore diameter and better thermal stability under 400 °C in comparison with CO2-dried composite aerogels. The structures and properties of Cu-doped SiO2 composite aerogels are obviously affected by supercritical drying conditions. The effect research could instruct the synthesis of different state of Cu in composite aerogels.  相似文献   

5.
Effective adsorption of CO2 at low partial pressures is required for many technical processes, such as gas purification or CO2 removal in closed loop environmental control systems. Since the concentration of CO2 in such applications is rather low, a high adsorption capacity is a required property for the adsorbent. Silica aerogels possessing an open pore structure, a high porosity and a high surface area, have a great potential for utilisation as CO2 adsorbents. Nonetheless in order to reach high adsorption capacities, silica aerogels should be functionalised, for instance by amino functionalisation. In this work, two different functionalisation methods were applied for the generation of amino functionalised aerogels: co-condensation during the sol-gel process and post-treatment of the gel. The co-condensation functionalisation allows the introduction of up to 1.44 wt.% nitrogen into the aerogel structure with minor reductions in surface area, leading however only to minor increases in the adsorption capacity at low partial pressures. The post functionalisation of the gel causes a greater loss in surface area, but the CO2 adsorption capacity increases, due to the introduction of higher amounts of amino groups into the aerogel structure (up to 5.2 wt.% nitrogen). Respectively, 0.523 mmol CO2/g aerogel could be adsorbed at 250 Pa. This value is comparable with the adsorption capacity at this pressure of a standard commercially available adsorbent, Zeolite 13X.  相似文献   

6.
Adsorption may be a potentially attractive alternative to capturing CO2 from stationary sources in the context of Carbon Capture and Sequestration (CCS) technologies. Activated carbon and zeolites are state-of-art adsorbents which may be used for CO2 adsorption, however physisorption alone tends to be insignificant at high temperatures. In the present work, commercial adsorbents have been impregnated with monoethanolamine (MEA) and triethanolamine (TEA) in order to investigate the effect of the modified surface chemistry on CO2 adsorption, especially above room temperature. Adsorption isotherms for CO2, N2 and CH4 were measured in a gravimetrically system in the pressure range of UHV to 10 bar, at 298 and 348 K for activated carbon and zeolite 13X supports. The adsorbed concentration of CO2 was significantly higher than those of CH4 and N2 for both adsorbents in the whole pressure range studied, zeolite 13X showing a remarkable affinity for CO2 at very low pressures. However, at 348 K, the adsorbed concentration of CO2 decreases significantly. The supports impregnated with concentrated amine solutions and dried in air suffered a detrimental effect on the textural properties, although CO2 uptake became much less susceptible to temperature increase. Impregnations carried out with dilute solution followed by drying in inert atmosphere yielded materials with very similar textural characteristics as compared to the parent support. CO2 isotherms in such materials showed a significant change with similar capacities at 348 K as compared to the original support at 298 K in the case of activated carbons. The impregnated zeolite showed a decrease in adsorbed phase concentration in low pressures for a given temperature, but the adsorbed amount also seemed to be less affected by temperature. These results are promising and indicate that CO2 adsorption may be enhanced despite high process temperatures (e.g. 348 K), if convenient impregnation and drying methods are applied.  相似文献   

7.
Adsorption isotherms of H2S, CO2, and CH4 on the Si-CHA zeolite were measured over pressure range of 0–190 kPa and temperatures of 298, 323, and 348 K. Acid gases adsorption isotherms on this type of zeolite are reported for the first time. The isotherms follow a typical Type-I shape according to the Brunauer classification. Both Langmuir and Toth isotherms describe well the adsorption isotherms of methane and acid gases over the experimental conditions tested. At room temperature and pressure of 100 kPa, the amount of CO2 adsorption for Si-CHA zeolite is 29 % greater than that reported elsewhere (van den Bergh et al. J Mem Sci 316:35–45 (2008); Surf Sci Catal 170:1021–1027 (2007)) for the pure silica DD3R zeolite while the amounts of CH4 adsorption are reasonably the same. Si-CHA zeolite showed high ideal selectivities for acid gases over methane at 100 kPa (6.15 for H2S and 4.06 for CO2 at 298 K). Furthermore, H2S adsorption mechanism was found to be physical, and hence, Si-CHA can be utilized in pressure swing adsorption processes. Due to higher amount of carbon dioxide adsorbed and lower heats of adsorption as well as three dimensional channels of Si-CHA pore structure, this zeolite can remove acid gases from methane in a kinetic based process such as zeolite membrane.  相似文献   

8.
以SiO2为成核中心,钛酸四丁酯为钛源,分别以多羟基化合物乙二醇、丙三醇、葡萄糖和聚乙烯醇为联接剂,采用水解沉淀法制备了碳掺杂和包覆的多孔SiO2/TiO2-xCx/C可见光响应型光催化剂。采用X-射线衍射(XRD)、透射电子显微镜(TEM)、X-射线光电子能谱(XPS)、傅里叶变换-红外光谱(FTIR)、比表面积(BET)和紫外-可见(UV-Vis)漫反射光谱对样品进行表征。对不同结构样品的形成机理进行了分析。以次甲基蓝(MB)溶液为模拟废水,对样品的吸附性能和可见光催化性能进行了评价。结果表明,多羟基化合物对材料的结构和性能有重要影响。碳的掺杂和包覆使材料的吸收光谱包含了整个可见光区,而多孔结构使材料的吸附性能得到提高。以聚乙烯醇为原料所得样品吸附性能最好,30 min内吸附率达到70%;而以丙三醇为原料所得样品具有最好的可见光催化性能,40 min内次甲基蓝的降解率达到95%。  相似文献   

9.
Photocatalytic conversion of CO2 is of great interest but it often suffers sluggish oxidation half reaction and undesired by-products. Here, we report for the first the simultaneous co-photocatalytic CO2 reduction and ethanol oxidation towards one identical value-added CH3CHO product on a rubidium and potassium co-modified carbon nitride (CN-KRb). The CN-KRb offers a record photocatalytic activity of 1212.3 μmol h−1g−1 with a high selectivity of 93.3 % for CH3CHO production, outperforming all the state-of-art CO2 photocatalysts. It is disclosed that the introduced Rb boosts the *OHCCHO fromation and facilitates the CH3CHO desorption, while K promotes ethanol adsorption and activation. Moreover, the H+ stemming from ethanol oxidation is confirmed to participate in the CO2 reduction process, endowing near ideal overall atomic economy. This work provides a new strategy for effective use of the photoexcited electron and hole for high selective and sustainable conversion of CO2 paired with oxidation reaction into identical product.  相似文献   

10.
Titania (TiO2) and titania–silica (TiSi) aerogels are suitable for photocatalytic oxidation of volatile organic compounds for pollution mitigation; however, methods for fabricating these aerogels can be complex. In this work we describe the use of a rapid supercritical extraction (RSCE) technique to prepare TiO2 and TiSi aerogels in as little as 8 h. The RSCE technique uses a metal mold and a four-step hydraulic hot press procedure to bring the solvents in the sol–gel pores to a supercritical state and control the supercritical fluid release process. Resulting TiO2 aerogels were powdery with BET surface areas of 130–180 m2/g, pore volumes ~0.5 cm3/g and skeletal densities of 3.6 g/mL. Monolithic TiSi aerogels were made using two different methods. An impregnation process, in which titania precursor was added to a silica sol–gel, took 4–8 days to complete with a 7-h RSCE and resulted in translucent aerogels with high surface area (560–650 m2/g) and pore volume (2.0–2.6 cm3/g), bulk densities ranging from 0.1 to 0.4 g/mL and skeletal densities of 2.3 g/mL. A co-precursor method for preparing TiSi aerogels took 8 h to complete. The precursor chemical mixture was poured directly into the mold and processed in a 7-h RSCE process. The resulting aerogels were opaque, with high surface areas (510–580 m2/g), low bulk density (0.03 g/mL), skeletal densities of 2 g/mL and pore volumes of 2.6–3.5 cm3/g. Preliminary solar simulator studies show that TiO2 and TiSi aerogels are capable of photocatalytic degradation of methylene blue in aqueous solution.  相似文献   

11.
Anatase nanocrystals of 5 to 10 nm in diameter were formed in the silica-titania films by treatment with hot water. The formation of nanocrystals with hot water treatment was a unique phenomenon to the silica-titania system and the addition of organic polymers such as PEG was indispensable for the high dispersion of anatase nanocrystals in the films. The hydrolysis of Si—O—Ti bonds with hot water was considered to play an important role for the formation of anatase nanocrystals. The resultant films were transparent even after the formation of anatase nanocrystals. Acetaldehyde was photocatalytically decomposed into CO2 on the films which were subjected to a hot water treatment. The amounts of generated CO2 were twice of that of introduced acetaldehyde, indicating that the total acetaldehyde was completely decomposed to CO2. Anatase nanocrystals-dispersed films can be formed on various kinds of substrates including those with poor heat resistance such as organic polymers and organisms by this process, so that the substrates coated with the films are expected to be widely used for photocatalytic applications.  相似文献   

12.
High crystallinity of TiO_2 was prepared by a modified alcohothermal method, in which titanium isopropoxide was used as the titania precursor, absolute ethanol as the reaction medium, and NH_4HCO_3 as the raw materials for release of water, ammonia and carbon dioxides via in-situ decomposition. The X-ray powder diffraction(XRD) and transmission electron microscope(TEM) measurements showed that water and ammonia from the in-situ decomposition of NH_4HCO_3 played an important role in conducting the size, shape, crystallinity and microstructure of TiO_2. The photoluminescence spectroscopy and photocurrent measurements indicated that enhanced crystallinity could hinder the recombination and promote the separation of electron-hole pairs in TiO_2, which contribute to the improvement of photocatalytic activity.Methyl orange photodegradation under UV light confirmed that high crystallinity of TiO_2 did present a high photocatalytic activity due to the effective separation of photoinduced charges.  相似文献   

13.
Nitrogen adsorption at 77 K has been applied to the study of the texture of alginate aerogel microspheres obtained by CO2 supercritical drying of alcogels. The limited volume shrinkage suggests that the aerogels preserve the texture of the hydrogels. Alginate aerogels presents a N2 adsorption at small pressure higher than reference non-porous silica, to be attributed to the polarity of the surface or to a small microporous volume. The aggregated nanobead strings of the guluronic-rich gels accounts for a significant mesoporosity. The N2 adsorption results correspond to electron microscopy observations for features smaller than 50 nm.  相似文献   

14.
The permeation of CO2 and CH4 and their binary mixtures through a DDR membrane has been investigated over a wide range of temperatures and pressures. The synthesized DDR membrane exhibits a high permeance and maintains a very high selectivity for CO2. At a total pressure of 101 kPa, the highest selectivity for CO2 in a 50∶50 feed mixture was found to be over 4000 at 225 K. This is ascribed to the higher adsorption affinity, as well as to the higher mobility for the smaller CO2 molecules in the zeolite, preventing the bypassing of the CH4 through the membrane. An engineering model, based on the generalized Maxwell-Stefan equations, has been used to interpret the transport phenomena in the membrane. The feasibility of DDR membranes as applied to CO2 removal from natural gas or biogas is anticipated.  相似文献   

15.
Nanocrystalline mesoporous TiO2 was synthesized by hydrothermal method using titanium butoxide as starting material. XRD, SEM, and TEM analyses revealed that the synthesized TiO2 had anatase structure with crystalline size of about 8 nm. Moreover, the synthesized titania possessed a narrow pore size distribution with average pore diameter and high specific surface area of 215 m2/g. The photocatalytic activity of synthesized TiO2 was evaluated with photocatalytic H2 production from water-splitting reaction. The photocatalytic activity of synthesized TiO2 treated with appropriate calcination temperature was considerably higher than that of commercial TiO2 (Ishihara ST-01). The utilization of mesoporous TiO2 photocatalyst with high crystallinity of anatase phase promoted great H2 production. Furthermore, the reaction temperature significantly influences the water-splitting reaction.  相似文献   

16.
Mesoporous nanocrystalline Cd-doped titania was firstly prepared at low temperature by a modified sol–gel method, using dodecylamine as a template. The template could be easily removed by refluxing samples in nitric acid ethanol solution. The Fourier transform infrared spectrometer (FT-IR), low-angle and wide-angle X-ray diffraction (XRD), N2 adsorption–desorption, transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), and UV–visible diffuse reflectance spectroscopy were used for the characterization of catalysts. The characteristic results clearly showed that Cd2+ ions were doped into the titania lattice, and the mesoporous architecture of Cd-doped TiO2 was composed of mixed-phase crystal textures of anatase and brookite. The samples displayed high visible-light photocatalytic activity for photodegradating 2,4-dichlorophenol (2,4-DCP) solution. The high activities of samples were attributed to the bicrystalline framework, large BET surface area, small crystallite size, and Cd-doping.  相似文献   

17.
A series of carbon aerogels were synthesized by polycondensation of resorcinol and formaldehyde using cetyltrimethyl ammonium bromide (CTAB) as a catalyst. The structure and properties of carbon aerogels were characterized by X‐ray diffraction (XRD), Raman, scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT‐IR), and N2 adsorption‐desorption technologies. Besides, the CO2 capture behavior of carbon aerogels was also investigated. It was found that the amount of CTAB affected the structure and morphology of carbon aerogels, thus influenced the CO2 adsorption behavior. The sample CA‐125 (the ratio of resorcinol and CTAB is 125) had the highest CO2 adsorption capacity (63.71 cm3 · g–1 at 1 bar and 24.14 cm3 · g–1 at 0.15 bar) at 25 °C. In addition, the higher CO2 adsorption capacity was ascribed to the higher surface area, pore volume and appropriate pore size, as well as the more defects over carbon aerogels.  相似文献   

18.
Nanophase silica-titania particles were prepared by two different synthetic routes, namely, sol–gel and hydrothermal processing. The crystallinity and crystallographic phases, particle size and surface area of the materials were controlled by varying the calcination temperature, and/or the ratio of Si to Ti. It was determined by XRD that the crystallite sizes of SiO2-TiO2 prepared by sol–gel and hydrothermal processing decreased from 11 to 6 nm and 12 to 9 nm, respectively, as the mole fraction of silica was increased from 0.1 to 0.4. It is proposed that the presence of the amorphous silica suppresses the growth of anatase TiO2 grains and their phase transformation to rutile. The photocatalytic decomposition rate of 1,4-dichlorobenzene (DCB) in aqueous solution with the sol–gel derived SiO2-TiO2 powder prepared at 750 °C was about 10 ± 5% higher than that observed with Degussa P25, whereas the SiO2-TiO2 samples prepared by hydrothermal processing at 250 °C showed a slightly lower decomposition rate than P25.  相似文献   

19.
We demonstrate practical aerosol-assisted approach to synthesize spherical mesoporous titania particles with high surface areas. Scanning electron microscopy observation of the spray-dried products clearly shows spherical morphology. To remove surfactants and enhance crystallinity, the spray-dried products are calcined under various temperatures. The crystalline structures inside the particles are carefully detected by wide-angle XRD measurements. With increase of the calcination temperatures, anatase crystal growth proceeds and transformation from anatase to rutile is occurred. The effect of various calcination temperatures on the mesostructures is also studied by using N2 adsorption desorption isotherms. The mesoporous titania particles calcined at 350, 400, and 500 °C exhibit type IV isotherms with a capillary condensation step and shows a hysteresis loop, which is a characteristic of mesoporous materials. The reduction in the surface areas and the pore volumes is confirmed by increasing the calcination temperatures, while the average pore diameters are increased gradually. This is attributed to the distortion of the mesostructures due to the grain growth of the anatase phase and the transformation to the rutile phase during the calcination process. As a preliminary experimental photocatalytic activity, oxidative decomposition of acetaldehyde under UV irradiation is examined. The mesoporous titania calcined at 400 °C shows the highest photocatalytic activity, due to both high surface area and well-developed anatase crystalline phase.  相似文献   

20.
In this paper we describe a methodology to form a data base that will allow us to investigate the correlation between the morphology of Ti?2 aerogels and their photocatalytic activity with respect to photodecomposition of a water soluble organic compound. We start with a qualitative theoretical argument in which we show that any functionality that involves optimization of different length scale should require some kind of ramified structure. For photocatalytic activity we need to optimize substrate and light absorptions with diffusion of products and reactants. We proceed to describe the techniques that we use to analyze and parametrize the morphology of the aerogels, using nitrogen adsorption and Small Angle Neutron Scattering. The photocatalytic activity is monitored through the photodecomposition of salicylic acid. We compare the adsorption and photodegradation of salicylic acid on the aerogels to many other forms of TiO2 and report that under our experimental conditions the photocatalytic activity of the aerogels is superior.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号