Faliang Li

A Family of High‐Efficiency Hydrogen‐Generation Catalysts Based on Ammonium Species

Development of highly active, low cost, ecologically friendly, and durable homogenous catalysts for hydrogen generation from hydrolysis of borohydride is one of the most desirable pathways for future hydrogen utilization. The unexpected catalytic activities of inorganic ammonium species and the corresponding mechanisms underpinning them are studied. The catalytic activities of the ammonium species are higher than or comparable to those of mostly investigated noble-metal/transition-metal catalysts (such as Pd, Pt, Ni, and Co) but are considerably cheaper, more environmentally friendly, and more readily available. Quantum chemical calculations indicate that the unique ammonium-induced reaction pathway involved with a barrierless elementary reaction at the reaction entrance and the formation of the highly active intermediate BH3 are responsible for the unexpected catalytic activities and the significantly accelerated hydrogen generation.

Theoretical study of complexation of resveratrol with cyclodextrins and cucurbiturils: structure and antioxidative activity

Resveratrol is an outstanding natural antioxidant which is often found in a wide variety of plant species; its antioxidative activity has been recently reported as being influenced by complexation with macromolecules such as cyclodextrins (CDs). In this work, the complexation of resveratrol with CDs and cucurbiturils (CBs) has been studied by density functional theory calculations, the equilibrium geometries and the electronic structures of the complexes are investigated at the B3LYP/6-311G(d, p) level of theory, the antioxidative capabilities of the inclusion complexes have been elucidated based on H-atom transfer (HAT), sequential proton loss electron transfer (SPLET) and single electron transfer (SET) antioxidative mechanisms. The influence of inclusion complexation on the structure and antioxidative activity of resveratrol has been investigated. Our results show that resveratrol exhibits a non-planar geometry when it is included in CDs and CBs. Complexation of resveratrol with these two macromolecules results in negligible change in frontier orbital distribution, but distinct change in orbital energies. Different inclusion complexes and inclusion modes show different influences on 4′-OH bond dissociation enthalpy (4′-OH BDE), proton affinity (PA) and the electron transfer enthalpy (ETE) of the 4′-phenolate anion, and the ionization potential (IP) of resveratrol. Compared to cyclodextrins, cucurbiturils exhibit better performance in improving the antioxidative capacity of resveratrol.

Catalytic Effects of Cr on Nitridation of Silicon and Formation of One-dimensional Silicon Nitride Nanostructure

The catalytic effects of chromium (Cr) on the direct nitridation of silicon (Si) and morphology of nitridation product were investigated. Cr dramatically improved the conversation of Si to silicon nitride (Si3N4). The complete conversion was achieved at 1350 °C upon addition of 1.25 wt% Cr. This temperature was much lower than that required in the case without using a catalyst. Meanwhile, Cr played an important role in the in-situ growth of one-dimensional (1-D) α-Si3N4 nanostructures. α-Si3N4 nanowires and nanobelts became the primary product phases when 5 wt% Cr was used as the catalyst. The growth processes of the 1-D α-Si3N4 nanostructures were governed by the vapor-solid mechanism. First-principle calculations suggest that electrons can be transferred from Cr atoms to N atoms, facilitating the Si nitridation.

Carbon Nanotube Reinforced Ceramic Composites: A Review

Carbon nanotubes (CNTs) have been extensively studied over the last two decades because of their excellent properties. In particular, they have been considered as promising reinforcements for development of novel ceramic composites (CCs). In this paper, current researches on CNT-reinforced CCs are briefly highlighted and reviewed. CNT-reinforced CCs possess remarkable electrical and thermal properties as well as superior mechanical properties compared to conventional CCs without using CNTs.

Preparation of Hierarchically Porous Graphitic Carbon Spheres and Their Applications in Supercapacitors and Dye Adsorption

Hierarchical micro-/mesoporous graphitic carbon spheres (HGCS) with a uniform diameter of ~0.35 μm were synthesized by Fe-catalyzed graphitization of amorphous carbon spheres resultant from hydrothermal carbonization. The HGCS resultant from 3 h at 900 °C with 1.0 wt % Fe catalyst had a high graphitization degree and surface area as high as 564 m2/g. They also exhibited high specific capacitance of 140 F/g at 0.2 A/g and good electrochemical stability with 94% capacitance retention after consecutive 2500 cycles. The graphitization degree of the HGCS contributed to 60% of their specific capacitance, and their specific capacitance per unit surface area was as high as 0.2 F/m2, which was much higher than in the most cases of porous amorphous carbon materials reported before. In addition, the HGCS showed a high adsorption capacity of 182.8 mg/g for methylene blue (MB), which was 12 times as high as that in the case of carbon spheres before graphitization.

Preparation of ZrB2-SiC Powders via Carbothermal Reduction of Zircon and Prediction of Product Composition by Back-Propagation Artificial Neural Network

Phase pure ZrB2-SiC composite powders were prepared after 1 450 °C/3 h via carbothermal reduction route, by using ZrSiO4, B2O3 and carbon as the raw materials. The influences of firing temperature as well as the type and amount of additive on the phase composition of final products were detailedly investigated. The results indicated that the onset formation temperature of ZrB2-SiC was reduced to 1 400 °C by the present conditions, and oxide additive (including CoSO4·7H2O, Y2O3 and TiO2) was effective in enhancing the decomposition of raw ZrSiO4, therefore accelerating the synthesis of ZrB2-SiC. Moreover, microstructural observation showed that the as-prepared ZrB2 and SiC respectively had well-defined hexagonal columnar and fibrous morphology. Furthermore, the methodology of back-propagation artificial neural networks (BP-ANNs) was adopted to establish a model for predicting the reaction extent (e g, the content of ZrB2-SiC in final product) in terms of various processing conditions. The results predicted by the as-established BP-ANNs model matched well with that of testing experiment (with a mean square error in 10-3 degree), verifying good effectiveness of the proposed strategy.

Research Progress in Preparation of Porous Ceramics

Porous ceramics have been extensively studied during the last two decades because of their potential application in the fields of thermal insulators, gas filters, catalytic supports, separation membranes, kiln furniture, and biomedical substitutes for bone and teeth. The properties of porous ceramics are highly dependent on their method of preparation. This mini-review summarizes recent developments in innovative fabrication of porous ceramics such as three-dimensional printing, molten salt synthesis, and the sacrificial template and replica methods. Finally, we conclude with our personal perspectives and recommendations for future research in porous ceramics.

Large-Scale Preparation of Carbon Nanotubes via Catalytic Pyrolysis of Phenolic Resin at Low Temperature

Carbon nanotubes (CNTs) were prepared through catalytic pyrolysis of phenol resin at 600°C under Ar atmosphere using ferric nitrate as the catalyst precursor. The structure and morphology of pyrolyzed resin were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the optimum growth temperature of the CNTs is 600°C, and other heating temperatures lower or higher than 600°C are not suitable for large-scale preparation of CNTs. Moreover, the ferric nitrate experienced the following phase transformation: Fe3O4 at 400°C, catalytically active Fe at 600°C and catalytically inactive (Fe, C) carbide at 800 and 1000°C. Based on the SEM and TEM results, a four-step mode of Vapour-solid-solid (VSS) and tip growth mechanism was revealed for the formation of CNTs from catalytic pyrolysis of phenol resin.

Fabrication of Porous Ceramics by Direct Foaming

Porous ceramics have been extensively studied during the last two decades because of their application potentials in various fields including thermal insulators, radome materials, gas or molten metal filters, catalytic supports and biomedical substitutes for bone. This paper gives a brief review on the recent developments of preparation of porous ceramics by direct foaming method, it shows that the direct foaming method is a more effective way for preparation of high performance porous ceramics with high porosity, high mechanical strength and an even pore size distribution compared with conventional methods.