Zhengping Hao

Mesoporous Co3O4 and Au/Co3O4 Catalysts for Low-Temperature Oxidation of Trace Ethylene

Low-temperature catalysts of mesoporous Co(3)O(4) and Au/Co(3)O(4) with high catalytic activities for the trace ethylene oxidation at 0 degrees C are reported in this paper. The catalysts were prepared by using the nanocasting method, and the mesostructure was replicated from three-dimensional (3D) cubic KIT-6 silicas. High resolution transmission electron microscopy (HRTEM) studies revealed that {110} facets were the exposed active surfaces in the mesoporous Co(3)O(4), whereas the Co(3)O(4) nanosheets prepared by the precipitation method exhibited the most exposed {112} facets. We found that the mesoporous Co(3)O(4) was significantly more active for ethylene oxidation than the Co(3)O(4) nanosheets. The results indicated that the crystal facet {110} of Co(3)O(4) played an essential role in determining its catalytic oxidation performance. The synthesized Au/Co(3)O(4) materials, in which the gold nanoparticles were assembled into the pore walls of the Co(3)O(4) mesoporous support, exhibited stable, highly dispersed, and exposed gold sites. Gold nanoparticles present on Co(3)O(4) readily produced surface-active oxygen species and promoted ethylene oxidation to achieve a 76% conversion at 0 degrees C, which is the highest conversion reported yet.

Photocatalytic degradation of triazine-containing azo dyes in aqueous TiO2 suspensions

The photocatalytic degradation of triazine-containing azo dyes, Procion Red MX-5B and Reactive Brilliant Red K-2G, in aqueous TiO2 dispersions was investigated. Total organic carbon (TOC), ion chromatography (IC), HPLC, UV-Vis, FTIR and GC-MS analyses were employed to obtain the details of the photodegradation of the selected dyes. The results verified that decolorization and desulfuration occurred at almost the same rate in the first step of photo-oxidation. The substituents attached to the naphthalene group of a dye molecule were hydroxylated more easily than those linked to the triazine group. Intermediates include mainly organic aromatic and aliphatic carboxylic acids, which were further oxidized slowly to CO2. TiO2/UV-based photocatalysis was able to oxidize the dyes with partial mineralization of carbon, nitrogen and sulfur heteroatoms into CO2, NH4+, NO3− and SO42−, respectively. Cyanuric acid (OOOT) was one of the final products for both azo dyes, showing no sign of decomposition by heterogeneous photocatalysis. The residual nitrogen-containing organics after prolonged-photocatalytic oxidation (PCO) appeared to be the PCO-resistant OOOT. There was a similar degradation pathway for photodegradation of the two dyes. The selected dyes were completely detoxified as indicated by the results of Microtox® tests.

Effects of acidity and inorganic ions on the photocatalytic degradation of different azo dyes

Effects of acidity and inorganic ions that are common in industrial effluent on the photocatalytic degradation of azo dyes, Procion Red MX-5B (MX-5B) and Cationic Blue X-GRL (CBX), have been investigated in UV illuminated TiO2 dispersions. There are significant differences between adsorption and photodegradation of MX-5B and those of CBX to the change of solution pH. The results indicated that CBX photodegradation was favored at the surface of TiO2, while that of MX-5B occurred in the aqueous phase. At pH 2.4, SO42-, H2PO4-, ClO4- and F- in general increased the decolorization rates of MX-5B and CBX by enhancing the adsorption of the selected dyes on the surface of TiO2. At pH 10.8, most of the selected anions inhibited the photocatalytic oxidation (PCO) to decolorize and degrade CBX and MX-5B. These results demonstrated that inorganic anions affect the photodegradation of dyes by their adsorption onto the surface of TiO2 and trapping positive hole (h(+)) and (OH)-O-.. Inorganic cationic ions, such as Cu2+ and Ni2+ had strong inhibition on the PCO decolorization of MX-5B at pH 10.8. On the contrary, no significant effect was observed at the same concentration of metal cations at pH 2.4

Improving Adsorbent Properties of Cage-like Ordered Amine Functionalized Mesoporous Silica with Very Large Pores for Bioadsorption

In this paper, we report the successful synthesis of amine-functionalized FDU-12-type mesoporous silica with a very large pore (30.2 nm) and a highly ordered mesostructure by using 3-aminopropyltriethoxysilane (APTES) as an organosilane source. Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) measurements confirmed that the materials possessed a face-centered cubic (space group Fm3m) mesostructure. Different techniques were used to obtain a significant pore and entrance size enlargement: low synthesis temperature and high hydrothermal treatment temperature. The amount of amine organosilane influenced the mesostructure of the mesoporous silica. It was found that the addition of inorganic salt (KCl) could help to maintain an ordered structure of the large pore mesoporous material. X-ray photoelectron spectroscopy (XPS), solid-state magic-angle spinning (MAS) 13C nuclear magnetic resonance (NMR) and thermogravimetric analysis (TGA) verified the incorporation of amine functional groups on the surface of the materials. The addition of amine organosilane extended the synthesis temperature domain of ordered FDU-12 materials. The amine functional group significantly enhanced the adsorption capacity of the mesoporous materials, e.g., the amine functionalized mesoporous silica had 8-fold higher bovine serum albumin (BSA) adsorption capacity than that of the unfunctionalized one. It also had 2 times higher adsorption capacity for large cellulase enzymes. The amine functional group introduced positively charged groups on the surface of the mesoporous silica, which created strong electrostatic interactions between the protein and the silica.

Synthesis of graphene–NiFe2O4 nanocomposites and their electrochemical capacitive behavior

Reduced graphite oxide-NiFe2O4 (RGO-NiFe2O4) composites were synthesized by adding different amounts of NH3 center dot H2O into a mixed aqueous solution of graphite oxide, Ni(NO3)(2) and Fe(NO3)(3) at room temperature. NH3 center dot H2O was used to adjust the synthesis systems pH value. The morphology and the microstructure of the as-prepared composites were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and transmission electron microscope (TEM) techniques. The structure characterizations indicate that NiFe2O4 successfully deposited on the surface of the RGO and the morphologies of RGO-NiFe2O4 show a transparent structure with NiFe2O4 homogeneously distributed on the RGO surfaces. Capacitive properties of the synthesized electrodes were studied using cyclic voltammetry and electrochemical impedance spectroscopy in a three-electrode experimental setup using 1 M Na2SO4 aqueous solution as electrolyte. It is found that the pH value plays an important role in controlling the electrochemical properties of these electrodes. Among the synthesized electrodes, RGO-NiFe10 (pH = 10) shows the best capacitive properties because of its suitable particle size and good dispersion property. It could be anticipated that the synthesized electrodes will gain promising applications as novel electrode materials in supercapacitors and other devices by virtue of their outstanding characteristics of controllable capacitance and facile synthesis.

Surface charging of layered double hydroxides during dynamic interactions of anions at the interfaces

In this research, we investigated the effect of dynamic anion adsorption/exchange on the surface charging property of Mg(2)AlClLDH and Mg(2)AlCO(3)LDH particles that show the average zeta potential of 41 and 34 mV in the as-prepared suspension, respectively. The addition of NaCl up to 3x10(-3) M in the suspension does not obviously affect the zeta potential of both LDHs, which can be attributed to the less affinity of Cl(-) to LDH. The introduction of Na(2)CO(3) severely reduces the zeta potential at the CO(3)(2-) concentration higher than 1x10(-4) M, and to the negative value in both LDH systems at ca. 2x10(-3) M, which is presumably resulted from the exchange and the re-orientation of CO(3)(2-) in a tilt/vertical style on the surface. All four organic anions (dodecyl sulfate, folate, citrate and polyacrylate) also significantly affect the zeta potential of the LDH particles. At the lower concentrations of organic anionic groups (<1x10(-4) M), the zeta potential was slightly affected, i.e. limited exchange/adsorption. However, the concentration increasing to some point suddenly decreases and reverses the zeta potential of the LDH particles, which is presumably caused by the hydrophobic interactions that bind the hydrophobic hydrocarbon chains (especially in dodecyl sulfate) into the micelle-like bilayer bunches on the LDH surface. In addition, the effect of pH in 5.5-11.0 on the LDH particle surface charging is mainly reflected through the conversion of CO(3)(2-) to HCO(3)(-)/H(2)CO(3) when pH decreases from ca. 11 to 6, with limited contribution from protonation/deprotonation and exchange/adsorption.

Adsorption performance of VOCs in ordered mesoporous silicas with different pore structures and surface chemistry.

Ordered mesoporous silicas with different pore structures, including SBA-15, MCM-41, MCM-48 and KIT-6, were functionalized with phenyltriethoxysilane by a post-synthesis grafting approach. It was found that phenyl groups were covalently anchored onto the surface of mesoporous silicas, and the long-range ordering of the mesoporous channels was well retained after the surface functionalization. The static adsorption of benzene and the dynamic adsorption of single component (benzene) and bicomponent (benzene and cyclohexane) on the original and functionalized materials were investigated. As indicated by the adsorption study, the functionalized silicas exhibit improvement in the surface hydrophobicity and affinity for aromatic compounds as compared with the original silicas. Furthermore, the pore structure and the surface chemistry of materials can significantly influence adsorption performance. A larger pore diameter and cubic pore structure are favorable to surface functionalization and adsorption performance. In particular, the best adsorption performance observed with phenyl-grafted KIT-6 is probably related to the highest degree of surface functionalization, arising from the relatively large mesopores and bi-continuous cubic pore structure which allow great accessibility for the functional groups. In contrast, functionalized MCM-41 exhibits the lowest adsorption efficiency, probably owing to the small size of mesopores and 1D mesoporous channels.

Supported gold catalysts used for ozone decomposition and simultaneous elimination of ozone and carbon monoxide at ambient temperature

Investigations of catalytic ozone decomposition and CO oxidation show that Au/Fe2O3 catalyst was a good catalytic material for ozone decomposition and simultaneous elimination of ozone and carbon monoxide at ambient temperature, and also suitable for use in relatively severe conditions, without the stoichiometric limitations. The structure of Au/Fe2O3 catalyst was studied by BET, XRD, XPS, XAFS and O-2-TPD characterization techniques. This new type of Au catalytic material shows great potential as an environmental catalyst, particularly for indoor environmental pollution control, (C) 2001 Elsevier Science B.V. All rights reserved.

Characterization and photocatalytic activity of noble-metal-supported surface TiO2/SiO2

M-TiO2/SiO2 photocatalysts were prepared by the photodeposition method using noble-metal salts (M: Pt4+, Pd2+, and Ag+) as precursors and the surface bond-conjugated TiO2/SiO2 as supporter in N2 atmosphere. The photocatalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflection spectra (DRS), photoluminescence (PL) spectra, and zeta-potential. Their photocatalytic activities were evaluated using reactive Brilliant Red K-2G (K-2G) and Cationic Blue X-GRL (CBX) that showed different types of adsorption behavior on the oxides. XPS analysis verified that the introduction of noble metal led to the changes of the electronic environmental of Ti cations and the zeta-potential of oxides. As a result, K-2G has higher adsorption on Pt-TiO2/SiO2 than on TiO2/SiO2, while the adsorption of CBX has little change on the modified TiO2/SiO2 catalysts. At the same time, Pt-modified catalyst shows 2.8 times higher photoactivity than TiO2/SiO2 for the photodegradation of K-2G, but has a decrease in activity for CBX degradation. These noble-metal-supported TiO2/SiO2 can efficiently extend the light absorption to the visible region. The PL results demonstrated that the noble metal dopant acted as electron acceptor to hinder the recombination of the photoinduced electron–hole pairs.

Influence of pretreatment conditions on low-temperature CO oxidation over Au/MOx/Al2O3 catalysts

Composite oxide MOx/Al2O3 supported gold catalysts for low-temperature CO oxidation were prepared and investigated. The presence of transition metal oxide was proved to be beneficial to the improvement of catalytic performance of Au/Al2O3 catalysts for low-temperature CO oxidation. Furthermore, the influence of various pretreatment conditions on Au/MOx/Al2O3 catalysts was studied carefully. The image of TEM showed that gold catalyst with small gold particles only in the form of a fine dispersion exhibited highly catalytic activity. The XPS, Fourier transform infrared (FTIR) spectroscopy characterization results of Au/FeOx/Al2O3 catalyst showed that gold catalysts having partially oxidized gold species have the best catalytic performance. One possible pathway for CO oxidation on Au/FeOx/Al2O3 catalyst is that the CO adsorbed on gold particles reacts with adsorbed oxygen, which is possible to occur on oxygen vacancies on the support or at the metal–support interface.