Yunfa Chen

Hollow and Cage-Bell Structured Nanomaterials of Noble Metals

Mastery of the structure of nanomaterials enables control of their properties to enhance their performance for a given application. Herein we demonstrate the synthesis of metal nanomaterials with hollow interiors or cage-bell structures based on the inside-out diffusion of Ag in core-shell structured nanoparticles. It begins with the synthesis of core-shell Ag-M or core-shell-shell M(A)-Ag-M(B) nanoparticles in an organic solvent. Ag is then extracted from the core or the inner shell by bis(p-sulfonatophenyl)phenylphosphane, which binds strongly with Ag(I)/Ag(0) to allow the complete removal of Ag in 24-48 h, leaving behind an organosol of hollow or cage-bell structured metal nanomaterials. Because of their relatively lower densities, which usually translate to a higher surface area than their solid counterparts, the hollow and cage-bell structured metal nanomaterials are especially relevant to catalysis. For example, cage-bell structured Pt-Ru nanoparticles were found to display outstanding methanol tolerance for the cathode reaction of direct methanol fuel cells (DMFCs) as a result of the differential diffusion of methanol and oxygen in the cage-bell structure.

Synthesis of network reduced graphene oxide in polystyrene matrix by a two-step reduction method for superior conductivity of the composite

Polymer/graphene composites have attracted much attention due to their unique organic–inorganic hybrid structure and exceptional properties. In this paper, we report the synthesis of polystyrene/reduced graphene oxide (PS/r-GO) composites by a two-step in situ reduction technique, which consists of a hydrazine hydrate reduction and a subsequent thermal reduction at 200 °C for 12 h. The structure and micromorphology of PS/r-GO composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis. The results show that the GO can be efficiently reduced by the two-step in situ reduction method, and the r-GO sheets are well dispersed and ultimately form a continuous network structure in the polymer matrix. PS/r-GO composite films (5 wt% GO) are prepared by the hot press molding method, possessing a conductivity as high as 22.68 S m−1. The superior conductivity arises from the high reduction degree of GO and its high dispersion and the formation of a network structure in the polymer matrix. These polymer/r-GO composites are expected to be applied in multiple electric devices. The techniques for preparing polymer/r-GO composite films could be further extended to other similar systems.

Oxalate route for promoting activity of manganese oxide catalysts in total VOCs’ oxidation: effect of calcination temperature and preparation method

A novel template-free oxalate route was applied to synthesize mesoporous manganese oxides with high surface area (355 m2 g−1) and well-defined mesopores which can be obtained in large quantities. The physicochemical properties of the materials were characterized by means of TG, XRD, SEM, TEM, H2-TPR and XPS techniques. All catalysts were tested on catalytic deep oxidation of benzene, and the effects of calcination temperature on the features of catalyst structure and catalytic activity were investigated. Manganese oxides prepared by oxalate route exhibited better catalytic activities for complete oxidation of benzene, toluene and o-xylene as compared with related manganese oxides prepared by other different methods (NaOH route, NH4HCO3 route and nanocasting strategy), and especially the temperature for benzene conversion of 90% on the oxalate-derived manganese oxide catalysts was 209 °C, which is 132 °C lower than required for the catalyst prepared by NaOH route. The catalytic performance of manganese oxide is correlated with surface area, pore size, low-temperature reducibility and distribution of surface species. The mole ratio of Mn4+/Mn2+ on the samples which performed with better catalytic activity was close to 1.0. This is good for the redox process of Mn4+ ↔ Mn3+ ↔ Mn2+ which is the key factor in determining the activity on MnOx, further indicating that the oxalate route is good for keeping the distribution of manganese oxidation states at an appropriate degree. A possible process of VOCs’ complete oxidation on manganese oxide catalysts is discussed. In addition, the best catalyst was highly stable with prolonged time on stream and was resistant to water vapor.

Scalable Synthesis of Interconnected Porous Silicon/Carbon Composites by the Rochow Reaction as High‐Performance Anodes of Lithium Ion Batteries

Despite the promising application of porous Si-based anodes in future Li ion batteries, the large-scale synthesis of these materials is still a great challenge. A scalable synthesis of porous Si materials is presented by the Rochow reaction, which is commonly used to produce organosilane monomers for synthesizing organosilane products in chemical industry. Commercial Si microparticles reacted with gas CH3 Cl over various Cu-based catalyst particles to substantially create macropores within the unreacted Si accompanying with carbon deposition to generate porous Si/C composites. Taking advantage of the interconnected porous structure and conductive carbon-coated layer after simple post treatment, these composites as anodes exhibit high reversible capacity and long cycle life. It is expected that by integrating the organosilane synthesis process and controlling reaction conditions, the manufacture of porous Si-based anodes on an industrial scale is highly possible.

Preparation of a new sorbent with hydrated lime and blast furnace slag for phosphorus removal from aqueous solution

The removal of dissolvable inorganic phosphate (H(2)PO(4)(-)) by sorbents prepared from hydrated lime (HL) and blast furnace slag (BFS) was fundamentally studied by an orthogonal experiment design. Based on statistic analysis, it is revealed that the weight ratio of BFS/HL is the most significant variable, and an optimized preparation condition is figured out. With the increase of HL content, the adsorption capacity increases, suggesting that the HL plays the important role in the removal process in the gross. However, in the lower HL content, it is interesting that the adsorption capacity of as-prepared sorbents exceed the sum of the capacities of the same ratio of BFS and HL. The further analysis indicate the excess capacities linearly depend on the specific surface area of sorbents, suggesting that the removal of H(2)PO(4)(-) is closely related with the microstructure of sorbents in the lower HL content, according to the characterization with SEM, XRD and pore analysis. Additionally, an adsorption model and kinetic are discussed in this paper.

Efficient photocatalytic reduction of aqueous Cr(VI) over flower-like SnIn4S8 microspheres under visible light illumination.

Photocatalytic reduction of aqueous Cr(VI) was successfully achieved on nanostructured SnIn(4)S(8). The SnIn(4)S(8) particles with flower-like nanostructure were synthesized via a facile solvothermal method. UV-vis diffuse reflectance spectra (DRS) indicated that the SnIn(4)S(8) particles had strong absorption in visible region and the band gap was estimated to be from 2.27 to 2.35 eV. The photocatalytic reduction of aqueous Cr(VI) by flower-like SnIn(4)S(8) was evaluated under visible light (λ>400 nm) irradiation. The polyvinyl pyrrolidone (PVP) assisted SnIn(4)S(8) sample exhibits excellent removal efficiency of Cr(VI) (~97%) and good photocatalytic stability. The predominant photocatalytic activity is due to its large surface area, strong absorption in visible-light region and excellent charge separation characteristics.

Comparative Study of CeO2 and Doped CeO2 with Tailored Oxygen Vacancies for CO Oxidation

We report on the preparation and characterization of CeO(2) nanofibers (CeO(2)-NFs) and nanocubes (CeO(2)-NCs), as well as Sm- and Gd-doped CeO(2) nanocubes (Sm-CeO(2)-NCs and Gd-CeO(2)-NCs), synthesized by a simple hydrothermal process for CO catalytic oxidation. The samples were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Raman spectroscopy, and photoluminescence spectroscopy. Their oxygen-storing capacity (OSC) was examined by means of hydrogen temperature-programmed reduction (H(2)-TPR) and oxygen pulse techniques. Their catalytic properties for CO catalytic oxidation were comparatively investigated. The results showed that the CeO(2)-NFs possessed a higher catalytic activity compared to the CeO(2)-NCs because of their smaller size and the greater number of oxygen vacancies. The activity of the Sm-CeO(2)-NCs was higher than that of the CeO(2)-NCs due to an increase in the number of oxygen vacancies, which results from the substitution of Ce(4+) species with Sm(3+) ions. In contrast, Gd doping had a negative effect on the CO catalytic oxidation due to the special electron configuration of Gd(3+) (4f(7)). Our work demonstrates that the oxygen vacancies in pure CeO(2) and the electron configuration of the dopants in doped CeO(2) play an important role in CO oxidation.

Graphene oxide as an effective interfacial layer for enhanced graphene/silicon solar cell performance

We show that interface tailoring is an effective approach towards high performance G/Si Schottky-barrier solar cells. Inserting a thin graphene oxide (GO) interfacial layer can improve the efficiency of graphene/silicon solar cells by >100%. The role of the GO interfacial layer is systematically investigated by varying the annealing temperature and thickness of the GO film. It is found that GO cannot be treated as the common thought, i.e., an insulator. In other words, the G/GO/Si solar cell is not suitable to be treated as a “MIS” cell. In contrast, it should be regarded as a p-doped thin layer. The effects of GO film thickness on device response are also studied and there exists an optimal thickness for device performance. A record 12.3% (device size: 3 × 3 mm2) power conversion efficiency is achieved by further performance optimization (chemical doping graphene and antireflection coating).

Photo-crosslinking polymerization to prepare polyanhydride/needle-like hydroxyapatite biodegradable nanocomposite for orthopedic application

The biodegradable nanocomposite of poly(methacrylated pyromellitylimidoalanine) (PM(PMA-ala)) and hydroxyapatite (HAp) was prepared by dispersing nanosized needle-like HAp particles prepared by homogeneous precipitation under hydrothermal condition into the crosslinked PM(PMA-ala) network via in-situ photo-polymerization. The conversion of carbon carbon double bonds of multifunctional anhydride monomers after the heat treatment can be over 90%, and the HAp needles are distributed homogeneously in the PM(PMA-ala) crosslinking network. By increasing the content of HAp, the mechanical properties of HAp/PM(PMA-ala) nanocomposite is improved two to three times those of PM(PMA-ala) itself. Furthermore, in contrast with PM(PMA-ala), the nanocomposite HAp/PM(PMA-ala) has higher modulus retention and lower mass loss at the same degradation time, and this tendency will be enhanced as the increase of the content of HAp

Regulation of pore size distribution in coal-based activated carbon

An approach to regulating the pore size distribution of coal-based activated carbon was proposed and studied by potassium-catalyzed steam activation. Activated carbons were prepared from coal in the presence of different amounts of KOH in the raw materials, and in the process of which, delicate acid washing was performed to change the amount Of K-containing compounds left in chars after carbonization and before steam activation. Then, the activated carbons were characterized by nitrogen adsorption, scanning electron microscopy, and X-Ray energy spectrometry, and their adsorption capacity was determined. Results show that the content of K-containing compounds left in the char can be controlled jointly by changing the amount of KOH added to the precursor and subsequent washing with 5% mass fraction acid after carbonization. With increasing amount of KOH, the adsorption capacity of the resulting activated carbon becomes greater. The average pore size of the activated carbons gradually increases from 2.379 to 2.636 nm, and the mesoporosity increases front 30.9 to 46.1%. The principles for the regulation of pore size distribution in activated carbon were discussed.