多孔TiO_2/SiO_2复合薄膜的制备及其超亲水性机理

采用溶胶-凝胶法,以钛酸四丁酯和正硅酸乙酯为前驱体,利用乙酰丙酮和二乙醇胺为络合剂,制备多孔TiO2/SiO2复合薄膜。通过扫描电子显微镜(SEM)、原子力显微镜(AFM)、傅里叶变换红外光谱(FTIR)、X射线衍射分析(XRD)、接触角测试仪(WCA)等对薄膜的结构和性能进行了表征。结果表明,TiO2/SiO2复合薄膜表面相对孤立或连通的孔结构是由缩聚反应诱导的相分离以及溶胶-凝胶转化过程同步作用产生的。多孔复合薄膜具有优异的超亲水性能,自然条件下与水接触角仅为2.5°,而普通致密TiO2薄膜在相同条件下接触角为19.3°。复合薄膜的超亲水性是由多孔结构和SiO2复合的共同作用产生,受到表面微观形貌和表面化学组成(羟基含量)的共同影响。     

Fabrication of SiO2-ZrO2 composite fiber mats via electrospinning

(1 ? x)SiO₂-(x)ZrO₂ (x = 0.1, 0.2) composite fiber mats were prepared by electrospinning their sol-gel precursors of zirconium acetate and tetraethyl orthosilicate (TEOS) without using a polymer binder. The electrospun composite fibers were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR) and mercury porosimetry. The composite fibers having a tetragonal crystalline ZrO₂ were obtained by calcining the electrospun composite fibers at high temperatures. The results show that the structure and crystallization of ZrO₂ in the composite fibers can be controlled by sintering temperature, while the porosity and morphology of the fiber mats did not depend on the sintering temperature.     

以稻壳-TiO_2为原料化学活化制备TiO_2/SiO_2/AC光催化剂

以钛酸四丁酯[Ti(OBu)4]为钛源,采用溶胶-凝胶法将TiO2前驱体负载于稻壳表面,进一步以该复合物为原料,经炭化和KOH化学活化制得具有可见光激发活性的活性炭负载TiO2/SiO2光催化剂。以对亚甲基蓝的脱色率为依据探讨了钛酸四丁酯的用量及煅烧温度对催化剂光催化性能的影响。利用傅立叶变换红外光谱、扫描电镜及X射线衍射等测试手段对光催化剂的结构、表面形态及晶相结构进行了表征。结果表明,TiO2晶型为锐钛矿相结构,并且与SiO2作用形成了Ti—O—Si键。     

Low-temperature fabrication of porous ZrC/C composite material from molten salts

In this work, biological ceramic-wood porous ZrC/C materials were prepared in a KCl-KF molten salt reaction medium, using Zr as a metal source and a C template as C source. The effects of reaction temperature and salts/Zr mole ratio on the formation of porous biomorphic ZrC/C ceramics were investigated. The phase compositions and morphological structures of the C templates and porous ZrC/C ceramics were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and pore size analysis. The results showed that the ZrC grains were equiaxed and enhanced the oxidation resistance of the material. Furthermore, a possible reaction mechanism for the formation of porous biomorphic ZrC/C ceramics in molten salt is proposed.     

从稻壳中获得二氧化硅气凝胶的研究

研究了稻壳在盐酸中浸泡、煮沸、回流、干燥后,置于600℃燃烧,并保温2 h,制得了一系列二氧化硅气凝胶样品。重量法分析表明这些二氧化硅气凝胶中二氧化硅质量分数为99%以上,并采用了激光粒度仪、比表面测定仪（BET方法）、X射线衍射仪（XRD）、红外光谱仪（FT-IR）和扫描电镜（SEM）等研究了二氧化硅气凝胶样品,同时对使用稻壳能够成功制备二氧化硅气凝胶方法进行了探讨。     

高分散SiO2/石油沥青基多孔碳用于锂离子电池负极

二氧化硅(SiO₂)作为锂离子电池负极材料具有理论容量高、放电电位低、成本较低等特点,但存在导电性差、充放电过程体积膨胀严重以及容量衰减过快等问题。以石油沥青为碳源,利用硅烷偶联剂KH-540对纳米α-Fe₂O₃模板剂进行表面化学包覆,然后将硅源修饰模板剂与碳源混合,经碳化、酸洗等步骤得到高分散SiO₂/石油沥青基多孔碳(SiO₂/PC)。所得SiO₂/PC作为锂离子电池负极材料,在1 A·g^-1电流密度下,循环900圈后仍具有640 mA·h·g^-1的高可逆比容量。研究结果表明,高度纳米化的SiO₂在高温碳化过程原位生成,紧密牢固地负载于多孔碳表面,提高了其导电性,同时能够有效缓解SiO₂在充放电过程中的体积膨胀,抑制SiO₂的团聚或粉化,从而表现出优异的电化学性能。     

SiO2 migration mechanism at the joints of SiO2f/SiO2 composite brazed by bismuth glass

Joining is an indispensable process for expanding the application of ceramics and composites. Recently, glasses have been extensively explored for ceramic/composite joining owing to their unique functional needs. However, the difficulty in detecting amorphous materials and lack of enthalpy data make the interfacial reaction mechanism challenging to investigate. In this study, the interfacial reaction mechanism of joints of SiO_2f/SiO₂ composite-brazed bismuth glass was thoroughly explored. SiO₂ was dissolved from the matrix and used throughout the brazing process. In the initial stage, silica reacts with the brazing glass to form Bi₄(SiO₄)₃. Then, owing to the decomposition of Bi₄(SiO₄)₃, the silicate glass replaced the bismuth glass. Finally, some precipitation of SiO₂ occurred at the brazing seam owing to an entropy–enthalpy dominating mode. This study may instigate the design of brazing glasses for joining SiO_2f/SiO₂ composites.     

C2 oxygenate synthesis from CO hydrogenation on AgRh/SiO2

The effect of silver on carbon monoxide hydrogenation over Rh/SiO₂ has been studied. Silver is found to decrease the rates of formation for methane and C₂₊ hydrocarbons more than those for C₂ oxygenates resulting in a marked increase in C₂ oxygenate selectivity. Infrared spectroscopic studies reveal that Ag blocks the bridge-CO sites. Ethylene addition studies show that Ag promotes carbon monoxide insertion and suppresses hydrogenation. The results suggest that the number of Rh atoms required for carbon monoxide insertion may be less than that for hydrogenation and methanation.     

Fabrication of porous SiC nanostructured coatings on C/C composite by laser chemical vapor deposition for improving the thermal shock resistance

Recently, fabricating one-dimensional (1D) nanomaterials on C/C composite has been recognized effective to improve the thermal shock resistance of the coated composites. However, the remaining metal catalyst in CVD process and the week bond of 1D nanomaterials with substrate limit the strengthening effect. Herein, laser chemical vapor deposition (LCVD) was proposed for fabricating porous SiC nanostructured coating on C/C composite without metal catalyst. The laser heating resulted in a temperature gradient between the top and bottom of the coating, providing an external driving force for the vertical growth of whiskers with side-branches, forming a porous network nanostructure. The porous nanostructure was beneficial to reduce CTE and effectively relieve thermal stress. After 10 times of thermal shock test from RT to 1723 K, the porous SiC nanostructured coating remained intact. This work provides a novel methodology to produce functional coating on C/C composite with outstanding thermal shock resistance.     

Fabrication of Carbon Nanotube/SiO2 and Carbon Nanotube/SiO2/Ag Nanoparticles Hybrids by Using Plasma Treatment

Based on plasma-treated single wall carbon nanotubes (SWCNTs), SWCNT/SiO₂ and thiol groups-functionalized SWCNT/SiO₂ hybrids have been fabricated through a sol–gel process. By means of thiol groups, Ag nanoparticles have been in situ synthesized and bonded onto the SiO₂ shell of SWCNT/SiO₂ in the absence of external reducing agent, resulting in the stable carbon nanotube/SiO₂/Ag nanoparticles hybrids. This strategy provides a facile, low–cost, and green methodology for the creation of carbon nanotube/inorganic oxides-metal nanoparticles hybrids.     

Kinetic studies on production of silicon carbide from rice husks

Abstract

A kinetic study on a non-conventional route for the production of silicon carbide was carried out on a laboratory scale. Silicon carbide was produced by vacuum pyrolysis of rice husks in the temperature range 1200–1600°C. The resulting products were characterised by XRD and chemical analysis. Attempts were made to develop the parametric relationships correlating the yield of silicon carbide to the process variables and starting material characteristics. Empirical relationships defining the rate of silicon carbide formation as a function of temperature, compaction pressure, CO gas diffusion, and compact porosity are proposed.     

废纸纤维素/SiO2复合气凝胶的性能

对废纸纤维素进行处理，以甲基三甲氧基硅烷（MTMS）作为硅源，制备纤维素/SiO₂复合水凝胶，经过冷冻干燥得到性能良好的纤维素/SiO₂复合气凝胶。利用扫描电镜（SEM）、接触角测量仪及热重分析（TGA）等对制得的气凝胶进行了表征测试。结果显示材料由大孔、介孔、微孔组成，最低密度为0.107 g/cm³，具有较好的疏水性能，静态疏水接触角可达148.5°，力学性能良好，可实现50%范围内压缩后100%恢复，材料具备良好的吸附性能，吸附油污可达到本身质量的12.7倍，热稳定性提高。在处理有机废水，尤其是水体油污方面有着广阔的应用前景。     

纳米SiO2/PS复合材料的制备及性能

以无水乙醇为溶剂,使用偶联剂γ-(甲基丙烯酰氧)丙基三甲氧基硅烷(KH-570)对纳米SiO2表面进行了化学改性,采用溶液聚合法在改性后的纳米粒子表面接枝苯乙烯,然后通过熔融共混法制备了纳米SiO2/PS复合材料。利用红外光谱考察了改性前后纳米SiO2与硅烷偶联剂、苯乙烯的相互作用;利用扫描电镜观察了复合材料的断面形貌结构,研究了纳米SiO2含量对复合材料力学性能的影响。结果表明:与纯聚苯乙烯相比,纳米SiO2质量分数为4%时,复合材料的缺口冲击强度提高了7.6%、拉伸强度提高了0.98%,显示出纳米SiO2对聚苯乙烯具有同时增强增韧的效果。     

Simultaneous SO2 and NO removal using sorbents derived from rice husks: An optimisation study

In this study, rice husk-derived ash (RHA) was hydrated with CaO and then impregnated with copper to synthesize a sorbent that was subsequently tested for its capacity in simultaneous removal of SO₂ and NO from a simulated flue gas. The effect of various sorbent preparation parameters, including copper loading, RHA/CaO ratio, hydration period and NaOH concentration, on the desulphurisation/denitrification capacity of the sorbents was studied using Design-Expert Version 6.0.6 software. Specifically, central composite design (CCD) coupled with response surface method (RSM) was used. The individual parameters that were found to significantly affect the sorbent capacity were RHA/CaO ratio and NaOH concentration. In addition, the interactive effect between RHA/CaO ratio, hydration period and NaOH concentration was also found to have a significant effect on the sorbent activity. The preparation condition for optimal sorbent activity was found to be CuO loading of 3.0%, RHA/CaO ratio of 1.4, hydration period of 20.0 h and NaOH concentration of 0.2 M. Characterisation of the sorbent was performed using scanning electron microscopy (SEM), X-ray diffraction (XRD) and nitrogen adsorption-desorption method to describe the effect of the sorbent preparation parameters on its desulphurisation/denitrification activity.     

二氧化硅/二氧化锆核壳复合材料的制备及性能

合成了一种新型的二氧化硅/二氧化锆(SiO2/ZrO2)核壳型复合材料。利用异丙醇锆的水解缩合在SiO2微球表面沉积ZrO2层,得到二氧化锆包覆的SiO2/ZrO2核壳型复合氧化物。采用SEM、EDX、XRD等对复合材料的形貌及性质进行表征。利用IR-1红外发射率测量仪测定复合粒子在8～14μm波段的红外发射率。结果显示:该复合物具有明显的核壳结构。随着沉积次数的增加,ZrO2在SiO2表面的含量增加。ZrO2层经高温热处理可分别形成四方和单斜两种晶型。ZrO2层沉积在SiO2表面后,得到的SiO2/ZrO2核壳复合粒子的红外发射率较基底SiO2的有所降低。ZrO2的晶型也影响着复合材料的红外发射性能。ZrO2层为单斜晶的SiO2/ZrO2核壳复合物在8～14μm波段的红外发射率值比ZrO2层为四方晶时的更小。ZrO2层和SiO2球之间的界面作用解释了该复合材料红外发射率降低的原因。     

Fabrication of porous Cu supported Ni-P/CeO2 composite coatings for enhanced hydrogen evolution reaction in alkaline solution

Cost-effective electrodes with high activity for hydrogen evolution reaction (HER) and durability are required to develop clean and renewable hydrogen energy. In this work, a porous Cu supported Ni-P/CeO₂ composite coating was fabricated by a facile electrodeposition technique. Owing to the contribution from the 3D porous Cu support and the incorporating agglomeration-free and uniformly distributed CeO₂ particles into the Ni-P matrix, the optimal composite coating (porous Cu supported Ni-P/CeO₂ (20 g L^-1)) exhibits outstanding electrocatalytic performance with small overpotentials (η) of 118 and 320 mV at a cathodic current density of 10 and 100 mA cm². Moreover, the composite electrode also presents excellent electrochemical stability in the alkaline solution. This work provides a feasible option to fabricate composite electrodes that may have desirable electrochemical properties for HER.     

SiC whisker reinforced multi-carbides composites prepared from B4C and pyrolyzed rice husks via reactive infiltration

SiC whisker reinfored carbide-based composites were fabricated by a reactive infiltration method by using Si as the infiltrate. Rice husks (RHs) were pyrolyzed to SiC whiskers, particles and amorphous carbon, and were then mixed with different contents of B₄C as well as Mo powders. The mixtures were molded to porous preforms for the infiltration. The SiC whiskers and particles in the preform remained in the composite. Molten Si reacted with the amorphous carbon, B₄C as well as Mo in the preform during the infiltration, forming newly SiC, B₁₂(C,Si,B)₃ as well as MoSi₂. The upper values of elastic modulus, hardness and fracture toughness of the composites are 297.8 GPa, 16.8 ± 0.8 GPa, and 3.8 ± 0.2 MPa m^1/2, respectively. The influence of the phase composition of the composites on the mechanical properties and the fracture mechanism are discussed.