Xingzhong Guo

Sol–gel synthesis of nanocrystal-constructed hierarchically porous TiO2 based composites for lithium ion batteries

Hierarchically porous TiO2 based composites (pure TiO2 and TiO2/carbon (TiO2/C) composite) were synthesized by a facile sol–gel process followed by post-calcination. Poly(vinylpyrrolidone) (PVP) acts as a phase separation inducer as well as a carbon source. The as-prepared TiO2 based composites possess an interesting hierarchically porous structure constructed of cocontinuous macropores and mesoporous skeletons consisting of interconnected nanocrystals and in situ distributed carbon. The hierarchically porous TiO2/C composite shows excellent electrochemical performance with fast lithium ion diffusion and electronic transport, resulting from the hierarchically porous structure and conductive carbon material. The TiO2/C composite calcined at 500 °C exhibits the highest BET surface area of 170 m2 g−1, superior cycling stability (delivers a remarkable discharge capacity of 132 mA h g−1 at 1 C after 100 cycles) and excellent rate capability (over 96 mA h g−1 at 30 C rate). The results indicate that these hierarchically porous TiO2 based composites could be promising anode materials for high performance lithium ion batteries.

Preparation of monolithic titania aerogels with high surface area by a sol–gel process combined surface modification

Monolithic titania (TiO2) aerogels with high surface area were successfully synthesized by the sol–gel process combined surface modification, followed by ambient pressure drying to remove the solvents from the gels. The effects of surface modification used polyethylene glycol (PEG) 2000 as surfactant on the gelation and microstructure of the aerogel were studied in detail. The resultant aerogel with the PEG 2000:TBOT (molar ratio) of 0.005 exhibits specific surface area as high as 495 m2 g−1, apparent density of 0.716 g cm−3 and porosity of 81.6%. The crystallization of aerogels after heat-treatment does not spoil the monolithic shape and morphology of the aerogel basically, and the specific surface area still keeps a relatively high value of 209 m2 g−1. The facile route provides a low-cost strategy for the preparation of metal oxide aerogels with high surface area.

Synthesis and electrochemical performance of Li4Ti5O12/TiO2/C nanocrystallines for high-rate lithium ion batteries

A Li4Ti5O12/TiO2/carbon (Li4Ti5O12/TiO2/C) nanocrystalline composite has been successfully synthesized by a facile sol–gel method and subsequent calcination treatment. Moreover, pure Li4Ti5O12, Li4Ti5O12/C and Li4Ti5O12/TiO2 composites have also been synthesized for comparison. All the samples present a nanocrystalline structure with a uniform size distribution, and abundant phase interfaces can be detected for the Li4Ti5O12/TiO2 and Li4Ti5O12/TiO2/C composites. Electrochemical measurements demonstrate that the resultant Li4Ti5O12/TiO2/C composite exhibits a superior rate capability and cycle stability in comparison with pure Li4Ti5O12, Li4Ti5O12/C and Li4Ti5O12/TiO2 composites, which can be attributed to a high grain boundary density, abundant phase interfaces and in situ formed carbon, for storing extra lithium ions, enhancing rapid lithium insertion/extraction kinetics and improving the electron transport rate.

Facile synthesis of monolithic mayenite with well-defined macropores via an epoxide-mediated sol–gel process accompanied by phase separation

Monolithic mayenite with well-defined macropores has been successfully synthesized from ionic precursors via a sol–gel process accompanied by phase separation. The addition of propylene oxide (PO) to the starting solution leads to homogenous gelation and modifies the gel skeleton, whereas the addition of poly(ethylene oxide) (PEO) induces phase separation. Glycol acts as a chelating agent to suppress the precipitation of Ca2+ ions, and formamide works as a drying control chemical additive to enhance the drying behavior. Appropriate amounts of solvents, PEO, and PO allow the formation of calcium aluminate gels with co-continuous macroporous structure. The reaction mechanism of the sol–gel process of the Ca–Al–O system is also investigated by TG-DSC, FT-IR and NMR. The dried gels are amorphous and the crystalline phase Ca12Al14O32Cl2 forms after heat-treatment at 1000 °C in air, while the macroporous structure is preserved. The resultant monoliths before and after heat-treatment possess both high porosity and smooth and dense skeletons.

Preparation of a hierarchically porous AlPO4 monolith via an epoxide-mediated sol–gel process accompanied by phase separation

Abstract Monolithic aluminum phosphate (AlPO4) with a macro–mesoporous structure has been successfully prepared via the sol–gel process accompanied by phase separation in the presence of poly(ethylene oxide) (PEO). Gelation of the system has been mediated by propylene oxide (PO), while PEO induces a phase separation. The dried gel is amorphous, whereas the crystalline tridymite phase precipitates upon heating above 1000 °C. Heat treatment does not spoil the macroporous morphology of the AlPO4 monoliths. Nitrogen adsorption–desorption measurements revealed that the skeletons of the dried gels possess a mesostructure with a median pore size of about 30 nm and a surface area as high as 120 m2 g−1. Hydrothermal treatment before heat treatment can increase the surface area to 282 m2 g−1.

Synthesis and application of several sol–gel-derived materials via sol–gel process combining with other technologies: a review

AbstractSol–gel process is a very unique wet chemical method for producing advanced materials in various areas of research. An increasingly evolution trend of this process is to combine with other technologies, such as surface modification, hybridization, templating induction, self-assembly, and phase separation, for preparing new materials possessing controllable shape, unique microstructure, superior properties, and special application. The review aims to present the synthesis of several typical sol–gel-derived materials (monodisperse nanoparticles, hybrid coatings, hollow microspheres, aerogels, and porous monoliths) via sol–gel process combining with other technologies . Some examples of application of the sol–gel-derived materials are also included.

Preparation of macroporous zirconia monoliths from ionic precursors via an epoxide-mediated sol-gel process accompanied by phase separation

Abstract Monolithic macroporous zirconia (ZrO2) derived from ionic precursors has been successfully fabricated via the epoxide-mediated sol-gel route accompanied by phase separation in the presence of propylene oxide (PO) and poly(ethylene oxide) (PEO). The addition of PO used as an acid scavenger mediates the gelation, whereas PEO enhances the polymerization-induced phase separation. The appropriate choice of the starting compositions allows the production of a macroporous zirconia monolith with a porosity of 52.9% and a Brunauer–Emmett–Teller (BET) surface area of 171.9 m2 · g−1. The resultant dried gel is amorphous, whereas tetragonal ZrO2 and monoclinic ZrO2 are precipitated at 400 and 600 °C, respectively, without spoiling the macroporous morphology. After solvothermal treatment with an ethanol solution of ammonia, tetragonal ZrO2 monoliths with smooth skeletons and well-defined mesopores can be obtained, and the BET surface area is enhanced to 583.8 m2 · g−1.

The novel and facile preparation of multilayer MoS2 crystals by a chelation-assisted sol–gel method and their electrochemical performance

Multilayer molybdenum disulfide (MoS2) was facilely prepared by a chelation-assisted sol–gel method with ammonium molybdate tetrahydrate ((NH4)6Mo7O24·4H2O) as the molybdenum source, thioacetamide (CH3CSNH2) as the sulfur source and diethylenetriamine pentaacetic acid (Dtpa) as the chelating agent, subsequently followed by high-temperature calcination. The chelating agent Dtpa ingeniously mediated the chelation reaction of the system and promoted the formation of a monolithic gel. The hexagonal MoS2 crystal (2H-MoS2) with good crystallinity precipitated after calcination at 1000 °C with the Mo and S mass ratio of 1 : 3. The adjustable MoS2 layers stacked together to form MoS2 flakes, and these flakes aggregated to construct crystalline MoS2 particles. The electrochemical tests showed the possibility of as-prepared MoS2 crystals applied as a negative electrode for lithium ion batteries.

Ellipsoid-like Li4Ti5O12–TiO2 composites constructed by nanocrystals for lithium ion batteries

Porous ellipsoid-like Li4Ti5O12–TiO2 composites with a unique micro/nano structure have been successfully fabricated via a facile sol–gel route followed by calcination. The porous ellipsoid-like particles with micro/nano structures are formed through phase-separation induced by poly(ethylene oxide) (PEO), which are constructed using numerous nanocrystals with sizes of about 50–100 nm consisting of lithium titanate, anatase and rutile. The resultant Li4Ti5O12–TiO2 composite shows a superior rate capability and cycling stability in comparison with pure Li4Ti5O12, which delivers a reversible capacity over 92 mA h g−1 at 10C after 100 cycles as well as an acceptable rate capacity of 89 mA h g−1 at a high rate of 30C. The excellent electrochemical performance of the Li4Ti5O12–TiO2 composite is attributed to the unique micro/nano and multiphase structures. The micro/nano structure enhances the structure stability and shortens the diffusion distance for both electron and lithium ions. Moreover, the abundant phase interfaces and grain boundaries store extra lithium ions and guarantee rapid lithium insertion/extraction kinetics.

Pore structure control of macroporous methylsilsesquioxane monoliths prepared by in situ two-step processing

Macroporous methylsilsesquioxane (MSQ) monoliths have been prepared by in situ two-step processing using an initial acid catalysis step accompanied by an epoxide-mediated condensation step in the presence of ammonium chloride (NH4Cl). We investigate the effects of duration time of acidic step, heat-treatment and hydrothermal treatment on the macroporous morphology and pore structures of MSQ monoliths. The duration time of acidic step gives an important effect on the macroporous morphology and pore structures of MSQ monoliths, resulting from the polymerization of MSQ. Heat-treatment and hydrothermal treatment basically do not spoil the macroporous morphology of MSQ monoliths, while obviously varies the mesopore/micropore structures including pore size, pore volume, and pore size distribution. The macroporous MSQ materials with thick skeleton and intrinsic hydrophobicity are promising for wide applications such as ultra performance liquid chromatography (UPLC), superhydrophobic materials and so on.