Yanqiu Jiang

Simulation-guided synthesis of graphitic carbon nitride beads with 3D interconnected and continuous meso/macropore channels for enhanced light absorption and photocatalytic performance

An optical simulation is adopted to examine the effects of the pore channels with different sizes and architectures on the ability of light absorption in photocatalysts. The simulation results are utilized to guide the synthesis of a novel porous graphitic carbon nitride (g-C3N4) material in bead form, using millimeter-scale porous SiO2 beads as a template. The obtained g-C3N4 beads possess a unique porous architecture with 3D interconnected and continuous meso/macropore channels at 30–90 nm in size, which is identical to the simulation result. Compared with pristine g-C3N4, the prepared material exhibits significantly enhanced visible light-induced catalytic performances for H2 evolution (8 times), photoreduction of nitrobenzene (3 times) and degradations of rhodamine B (4 times), methyl orange (2 times) and phenol (3 times). The unique pores and skeleton structures not only promote light penetration inside the material and light absorption at the edge of pore channels, but also improve mass transfer and inhibit the recombination of photogenerated electrons and holes. Moreover, this optical simulation approach could be adopted to guide the synthesis of other porous photocatalysts, and to verify their light absorption and infiltration properties in photocatalysis.

Mesoporous TiO2/Carbon Beads: One-Pot Preparation and Their Application in Visible-Light-Induced Photodegradation

Mesoporous TiO2/Carbon beads have been prepared via a facile impregnation-carbonization approach, in which a porous anion-exchange resin and K2TiO(C2O4)2 were used as hard carbon and titanium source, respectively. Characterization results reveal that the self-assembled composites have disordered mesostructure, uniform mesopores, large pore volumes, and high surface areas. The mesopore walls are composed of amorphous carbon, well-dispersed and confined anatase or rutile nanoparticles. Some anatase phase of TiO2 was transformed to rutile phase via an increase of carbonization temperature or repeated impregnation of the resin with TiO(C2O4)22− species. X-ray photoelectron spectroscopy, carbon, hydrogen, and nitrogen element analysis, and thermal gravity analysis results indicate the doping of carbon into the TiO2 lattice and strong interaction between carbon and TiO2 nanoparticles. A synergy effect by carbon and TiO2 in the composites has been discussed herein on the degradation of methyl orange under visible light. The dye removal process involves adsorption of the dye from water by the mesopores in the composites, followed by photodegradation on the separated dye-loaded catalysts. Mesopores allow full access of the dye molecules to the surface of TiO2 nanoparticles. Importantly, the bead format of such composite enables their straightforward separation from the reaction mixture in their application as a liquid-phase heterogeneous photodegradation catalyst.

Nitrogen Doped Macroporous Carbon as Electrode Materials for High Capacity of Supercapacitor

Nitrogen doped carbon materials as electrodes of supercapacitors have attracted abundant attention. Herein, we demonstrated a method to synthesize N-doped macroporous carbon materials (NMC) with continuous channels and large size pores carbonized from polyaniline using multiporous silica beads as sacrificial templates to act as electrode materials in supercapacitors. By the nice carbonized process, i.e., pre-carbonization at 400 °C and then pyrolysis at 700/800/900/1000 °C, NMC replicas with high BET specific surface areas exhibit excellent stability and recyclability as well as superb capacitance behavior (~413 F⋅g−1) in alkaline electrolyte. This research may provide a method to synthesize macroporous materials with continuous channels and hierarchical pores to enhance the infiltration and mass transfer not only used as electrode, but also as catalyst somewhere micro- or mesopores do not work well.

Mesoporous titanosilicate nanoparticles: facile preparation and application in heterogeneous epoxidation of cyclohexene

Mesoporous titanosilicate nanoparticles with a size of 40 to 75 nm (Nano-Ti-MCM-41) were hydrothermally synthesized from a titanosilicate (TiSil) solution with cetyltrimethylammonium bromide (CTAB) as the template and with a cationic polymer as the size-controlling agent. The particle size is proposed to be controlled by adjusting the size of TiSil-CTA+ micelles influenced by the charge interaction between negatively charged titanosilicate and polymer cationic ions during the formation of TiSil-CTA+ micelles. The presence of n-hexane and hydrogen peroxide in the preparation process proved to favor a well-ordered mesostructure in these nanoparticles: the mesostructure became disordered without using hexane and hydrogen peroxide although the size of mesoporous titanosilicate particles remained in the nanometer scale. The characterization results showed that Nano-Ti-MCM-41 possesses hierarchical porosity (bimodal mesopores) and an ordered mesoporous structure and that the titanium species are predominately located in tetrahedral framework positions. Nano-Ti-MCM-41 is a highly active catalyst for the epoxidation of cyclohexene with hydrogen peroxide, and displayed higher turnover numbers (TONs) based on the cyclohexene conversions and higher selectivity ratio between cyclohexene epoxide and 1,2-cyclohexanediol compared with traditional Ti-MCM-41 prepared without the cationic polymer. The improved catalytic performances are mainly ascribed to the decrease in the particle size of Ti-MCM-41, resulting in the enhanced accessibility of the reactants to the catalytic Ti species via the shorter channels of Nano-Ti-MCM-41 and in the shorter residence time of cyclohexene epoxide in the mesopores of the nanoparticles. Importantly, the mesoporous titanosilicate nanoparticles are stable catalysts immune to titanium leaching, suggesting their good recyclability potential in the epoxidation with aqueous H2O2.

Synthesis of submicrometer-sized Sn-MCM-41 particles and their catalytic performance in Baeyer-Villiger oxidation

Submicrometer-sized tin-containing MCM-41 particles with a size of several hundred nanometers(Sn-MCM-41/SMPs) were rapidly prepared with tin chloride as tin source and tetraethyl orthosilicate as silicon source via a dilute solution route in sodium hydroxide medium at room temperature. The characterization results show the highly ordered hexagonal mesopores and tetrahedral Sn species in Sn-MCM-41/SMPs. The material proved to be active and selective for Baeyer-Villiger oxidation of adamantanone with aqueous H2O2. Notably, Sn-MCM-41/SMPs displayed a higher initial reaction rate and turnover number(TON) than common micrometer-sized Sn-MCM-41 large particles(Sn-MCM-41/LPs), mainly attributed to the accelerated diffusion of the reactants and enhanced accessibility to the catalytic Sn species via shorter mesopore channels in Sn-MCM-41/SMPs. Furthermore, Sn-MCM-41/SMPs could be reused without the loss of activity after five runs, indicating that Sn active sites in the submicrometer-sized particles are remarkably stable. The study shows that decreasing particle size of Sn-MCM-41 in submicrometer scale is an effective way to achieve catalysts for Baeyer-Villiger oxidations with improved catalytic performance.

The influence of dwell time on reliability of SMT solder joints under thermal cycling

Abstract The influence of dwell time on mechanical behaviour and fatigue life of SMT solder joints under thermal cycling has been investigated. The dwell time has two effects on the mechanical behaviour of SMT solder joints under thermal cycling: first, in the dwell time of high-temperature part, the stress in SMT solder joints will notably relax, and secondly, as the dwell time increase, the stress in solder joints in the low-temperature part of thermal cycling increases. With the increase of dwell time, the life of SMT solder joints under thermal cycling exponentially decreases.

A dislocation model of shear fatigue damage and life prediction of SMT solder joints under thermal cycles

Abstract In this paper, a damage model of low-cycle shear fatigue has been developed in the dislocation theory. On the basis of this model, a formula including the factors of thermal cycle temperature, dwell time and atmospheric oxidation has been established to predict the life of SMT solder joints under thermal cycles, and this has been verified by experiments on the specimens of true SMT assemblies. The results show that the life formula established in this paper coincides with the experimental results.

A study of the rheological behaviour of SnPb solders under varying temperature

Abstract An integral constitutive equation for one-dimensional shearing deformation of a soldered joint under varying temperature has been established based on viscoelasticity theory, and this has been verified by experiments on a sample subjected to simulated loading by thermal expansion. The theoretical results coincide well with the experimental ones. An important application of this integral constitutive equation is in the analyzing of the mechanical behaviour of the soldered joints in surface mount technology (SMT) under thermal cycling. An example of analyzing the relationship between stress and temperature in a SMT soldered joint under thermal cycling is also given.

Double-shelled hollow mesoporous silica nanospheres as an acid–base bifunctional catalyst for cascade reactions

Double-shelled hollow mesoporous silica nanospheres (HMS-Al@MS-NH2) have been successfully obtained using the shell-by-shell strategy, by which the isolated acidic (–Al) and basic (–NH2) sites were spatially incorporated in different shells. The characterization results indicate that HMS-Al@MS-NH2 possesses a hollow void and mesopores in both shells, and this favors the mass transfer of the reactants and products. As a spatially isolated acid–base bifunctional catalyst, HMS-Al@MS-NH2 proved to exhibit high catalytic performances in the one-pot deacetalization-Knoevenagel cascade reaction. Under the optimized conditions, the conversion of benzaldehyde dimethyl acetal approached ca. 100% for 2 h at 110 °C, mainly attributed to the isolated acidic and basic sites and to the hollow architecture and mesopores in the shells. Notably, the catalyst could be reused up to 4 times without obvious loss of activity and selectivity, indicating the high stability of the active acidic and basic sites in the framework. Moreover, the double-shelled hollow mesoporous silica spheres are also active and selective for the other cascade sequence of the deacetalization-Henry reaction.

Easily separated and recyclable amino-functionalized porous SiO2 beads with 3D continuous meso/macropore channels

Amino-functionalized porous SiO2 beads with a diameter of 200—800 μm(PSB-NH2) have been success-fully synthesized by grafting 3-aminopropyl-triethoxysilane onto meso/macroporous silica beads(PSB), in which the PSB was prepared by hydrothermal synthetic method with a porous hard template anion-exchange resin. The as-prepared materials were characterized by means of nitrogen sorption and transmission electron micrographs(TEM), showing the presence of 3D interconnected and continuous large mesopores and macropores inside. The beads were used to catalyze Knoevenagel condensation and proved to be highly active and selective due to the high accessibility of the reactants to the amino groups via the continuous 3D meso/macopores. Notably, such material in bead format facilitates the extremely straightforward separation from reaction solution without any centrifugation or filtration. Moreover, PSB-NH2 proved to be a stable catalyst via leaching experiment test, and can be easily recovered and reused without significant loss of activity in successive catalytic cycles.