Zheng-Ming Wang

Graphene Oxide−Periodic Mesoporous Silica Sandwich Nanocomposites with Vertically Oriented Channels

This paper describes the synthesis and characterization of single-layer graphene oxide-periodic mesoporous silica sandwich nanocomposites. Through a comprehensive exploration of the synthesis conditions, it has proven possible to create the first example of a graphene oxide-periodic mesoporous silica nanocomposite in which hexagonal symmetry PMS film grows on both sides of the graphene oxide sheets with the mesoporous channels vertically aligned with respect to the graphene oxide surface. The formation of this novel architecture is found to be very sensitive to pH, the ratio of surfactant template to graphene oxide, the amount of silica precursor, and the temperature of the synthesis. On the basis of the collected data of a multi-technique analysis, it is proposed that the mode of formation of the nanocomposite involves the co-assembly of silicate-surfactant admicelles on opposite sides of graphene oxide platelets acting thereby as a template for growth of vertical mesopores off the platelet surface. These composites showed semiconductive behavior with electrical conductivity sensitively responding to analyte vapor exposure. The discovery of graphene oxide-periodic mesoporous silica sandwich nanocomposites will provide new opportunities for research that exploits the synergism of the graphene oxide and periodic mesoporous silica parts.

Synthesis and Characteristics of Graphene Oxide-Derived Carbon Nanosheet−Pd Nanosized Particle Composites

Carbon nanosheet (CNS)-Pd nanosized particle (NP) composites were synthesized by using graphite oxide (GO) and bis(ethylenediamine)palladium(II) (Pd(en)(2)(2+)) as the precursors, and their structure and adsorption properties were examined. It was found that the Pd(en)(2)(2+) complex ions can be intercalated into GO layers highly efficiently to form a layered structure containing a large amount of Pd (approximately 12 wt %). By the subsequent chemical reduction, Pd NPs (2-6 nm in size) are well dispersed between CNS to form a CNS-Pd NP composite and serve as spacers to increase the porosity of the composite. Hydrogen adsorption results demonstrate that both Pd NPs and CNS play important roles in hydrogen adsorption, particularly at a lower temperature and for CNS with deficient sites, which bring about a H(2) adsorption greater than those on other Pd-loaded nanocarbon materials reported so far. The unique composite nanostructure having large contents of Pd NPs (20-25 wt %) stabilized by CNSs is hopeful to be applied to the fields of H(2)-related catalysis, sensing, and so forth.

Structural and surface property changes of macadamia nut-shell char upon activation and high temperature treatment

Structural and surface property changes of macadamia nut-shell (MNS) char upon activation and high temperature treatment (HTT) were studied by high-resolution nitrogen adsorption, diffuse reflectance infra-red Fourier transform spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed desorption. It is found that activation of MNS char can be divided into the low extent activation which may involve the reactions of internal oxygen-containing groups and leads to the formation of comparatively uniform micropores, and the high extent activation which induces reactions between carbon and activating gas and produces a large amount of micropores. The surface functional groups (SFGs) basically increase with the increase of activation extent, but high extent activation preferentially increases the amount of -C-O and -C=O. HTT in air for a short tithe at a high temperature (1173 K) greatly increases the micropore volume and the amounts of SFGs. By appropriately choosing the activation and HTT conditions, it is possible to control both the textural structure and the type and amounts of SFG

Comparative examination of titania nanocrystals synthesized by peroxo titanic acid approach from different precursors

Titanium dioxide nanocrystalline particles were synthesized by peroxo titanium acid (PTA) approach from titanium alkoxide and inorganic salt precursors, and their structural and surface properties, porosities, and photocatalytic activities were comparatively examined by XRD, TG/DTA, DRIFT, UV-vis, low temperature N(2) adsorption, and methyl orange (MO) degradation. It was found that nanoparticles with single anatase phase can be obtained from alkoxide precursor even near room temperature if synthesis conditions are appropriately controlled. PTA-derived anatase nanoparticles from titanium alkoxide precursor have smaller crystalline sizes and better porosities, and contain less amount of peroxo group and no organic impurities as compared to those from TiCl(4) precursor. The advantages in structural property, porosity, and surface properties (few deficiencies) lead to a much better photocatalytic activity for TiO(2) nanoparticles from titanium alkoxide precursor in comparison with those from TiCl(4) precursor.

Fabrication and characterization of mesoporous carbon nanosheets-1D TiO2 nanostructures

Carbon nanosheet (CNS)–titanate nanotube (TNT) composites were prepared by hydrothermal treatment of Ti species-intercalated graphite oxide, and their bulk and surface structures, formation mechanism and porosities were investigated by XRD, DRIFT, TG-DTA, FE-SEM and N2 adsorption. It was found that CNS functions as a template for two-dimensional deposition of the TNTs, forming a TNT-loaded CNS composing structure with tubular axes parallel to the sheet surface, which then gathers together to form secondary mesoporous aggregates. The titanate nanotubes in the composites were gradually transformed into single-crystal anatase nanorods by further calcination under inert atmosphere with the composing structure unchanged. Behaviors in adsorption and photocatalytic activity toward methyl orange indicated the establishment of adsorption-concentration-promoted photocatalysis in these composites with unique structures due to the synergy effect of carbon nanosheets and rod-like TiO2 nanoparticles, achieving up to 6 times higher photoactivity in comparison with a commercial high-activity photocatalyst.

Selective D2 adsorption enhanced by the quantum sieving effect on entangled single-wall carbon nanotubes

The quantum sieving effect of D(2) over H(2) is examined at 40 and 77 K by means of experiments and GCMC simulations, for two types of single-wall carbon nanotubes that are distinguishable by their unique entangled structures; (1) a well-bundled SWCNT and (2) loosely-assembled SWCNT produced by the super growth method (SG-SWCNT). Oxidized SWCNT samples of which the so-called internal sites are accessible for H(2) and D(2), are also studied. Experimental H(2) and D(2) adsorption properties on the well-bundled SWCNTs are compared with the simulated ones, revealing that pore-blocking and restricted diffusion of the molecules suppress the high selectivity of D(2) over H(2). The non-oxidized SG-SWCNT assembly shows the highest selectivity among the SWCNT samples, both at 40 and 77 K. The high selectivity of the SG-SWCNT assembly, which is pronounced even at 77 K, is ascribed to their unique assembly structure.

NH3 desorption and decomposition behavior on microporous hollandite-type hydrous manganese oxide

Abstract In order to figure out the catalytic property of hollandite-type hydrous manganese oxide (H-Hol) to remove NH3, the desorption and decomposition properties of NH3 from NH3-chemically adsorbed H-Hol were examined and these properties and NH3 adsorptivity were compared with those of other manganese oxides and a de-NOx catalyst. It was found that the presence of NO accelerates the oxidation of NH3 to form N2 at a lower temperature. Comparison of NH3 pulse reaction in a flow containing NO on H-Hol with those on a high surface area-manganese oxide and a commercial de-NOx catalyst shows that H-Hol has the greatest N2 production, but less selectivity to form N2. H-Hol has a comparable amount of the strong H+ sites with the high surface area manganese oxide, which have relationship with NH3 decomposition.

Quiescent hydrothermal synthesis of reduced graphene oxide–periodic mesoporous silica sandwich nanocomposites with perpendicular mesochannel alignments

Abstract Quiescent hydrothermal conditions were applied to synthesis of the sandwich nanocomposites of reduced graphite oxide (rGO) and periodic mesoporous silica (PMS) with vertically aligned mesochannels. It was found that the formation of the PMS–rGO–PMS sandwich structure is very sensitive to the surface and synthesis conditions. Although a higher temperature hydrothermal condition promotes reduction of GO and formation of bulky mesoporous nanoparticles, quiescent hydrothermal condition can serve as an alternative approach to obtain the unusual nanocomposites and slightly promote the structural stability of PMS on the surface of rGO.

Synergetic photocatalysts derived from porous organo Ti–O clusters pillared graphene oxide frameworks (GOFs)

Unique nanocomposites comprising thin TiO2 nanoplates and lamellar carbon sheets were derived from organo Ti–O clusters pillared graphene oxide (GO), a porous layered framework synthesized by intercalating GO layers with organo-Ti reagents via a simultaneous intercalation and hydrolysis process. The nanocomposites display both high adsorption capacity and enhanced photocatalytic activity towards methyl orange (MO), promising as synergetic photocatalysts for the removal of organic contaminates in a water environment.

Gaseous adsorption properties of a silica-pillared layered manganese oxide.

Adsorptions of N(2), H(2)O, and organic vapors including CH(2)Cl(2), CCl(4), c-C(6)H(12), C(6)H(6), n-C(6)H(14), and n-C(9)H(20) on a silica-pillared layered manganese oxide (SiHMnO) and nonane-preadsorbed SiHMnO were examined. It is found that SiHMnO has a microporosity with a wide pore width distribution showing different pore wall affinities. Micropores with smaller width preferentially accommodate the nonane preadsorbate while the surface hydrophilicity of pore wall leads to an easier detachment of the adsorbed nonane molecules. H(2)O adsorption influences both the porosity and the surface properties by accelerating a sufficient hydrolysis of the remained TEOS molecules in SiHMnO. Examinations using Dubinin-Radeshkevich (DR) equation and isosteric heat of adsorption of organic molecules provide evidences that the wall surface of micropores with smaller and larger width have less affinity toward nonpolar and polar organic vapors, respectively.