Juncheng Hu

Sunflower and rapeseed oil transesterification to biodiesel over different nanocrystalline MgO catalysts

The catalytic activity for the production of biodiesel with three morphologically different nanocrystalline MgO materials prepared using simple, green and reproducible methods was investigated. The nanocrystalline samples studied were MgO(111) nanosheets (MgO (I)), conventionally prepared MgO (MgO (II)) and aerogel prepared MgO (MgO (III)). The methods to produce the catalysts included: (a) 4-methoxy-benzyl alcohol templated sol-gel process followed by supercritical drying and calcination in air at 773 K (MgO (I)), (b) from a commercial MgO that was boiled in water, followed by drying at 393 K, and dehydration under vacuum at 773 K (MgO (II)), and (c) viahydrolysis of Mg(OCH3)2 in a methanol–toluene mixture, followed by supercritical solvent removal with the formation of a Mg(OH)2 aerogel that was dehydrated under vacuum at 773 K (MgO (III)). These catalysts were characterized by TEM, DRIFT, and DR-UV-Vis and tested in the transesterification of sunflower and rapeseed vegetable oils at low temperatures, under different experimental conditions: autoclave, microwave and ultrasound. Working with these materials under microwave conditions provided higher conversions and selectivities to methylesters compared to autoclave or ultrasound conditions. Under ultrasound, a leaching of the magnesium has been evidenced as a direct consequence of a saponification reaction. These systems also allow working with much lower ratios of methanol to vegetable oil than reported in the literature for other heterogeneous systems. The activation temperature providing the most active catalysts was found to vary depending on the exposed facet: for MgO(111) structures (i.e.MgO (I)) this was 773 K, while for MgO (110) and (100) (i.e.MgO (II) and MgO (III)) this was 583 K.

One-pot synthesis of CdS and Ni-doped CdS hollow spheres with enhanced photocatalytic activity and durability.

CdS and Ni-doped CdS hollow spheres were synthesized via a simple template-free one-pot method. The products were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, energy-dispersive spectroscopy analysis, X-ray photoelectron spectroscopy, and UV-vis absorption spectroscopy. The formation mechanism for the Ni-doped CdS hollow spheres was discussed. The prepared CdS and Ni-doped CdS hollow spheres showed the superior photocatalytic activity for the degradation of RhB under visible light (λ > 420 nm) irradiation, and 1.2 mol % Ni-doped CdS hollow spheres were found to be highly efficient for organic pollutants RhB and phenol removal. Moreover, this catalyst showed improved stability, and the activity did not decrease significantly after four recycles. The unique hollow spheres structure may favor the harvesting of exciting light due to multiple scattering within the interior space, and the doping of Ni(2+) may facilitate the generation of electrons and holes pairs and inhibit their recombination rate by act as a temporary trapping sites of photoinduced electrons.

NiO(111) nanosheets as efficient and recyclable adsorbents for dye pollutant removal from wastewater

Semiconductor single-crystalline polar NiO(111) nanosheets with well-defined hexagonal holes have been investigated for application in dye adsorption and combustion processes. With regard to adsorption technologies, high surface area metal oxides have an advantage over activated carbon in that the adsorbed species can be combusted and the adsorbent reused in the case of metal oxides while regeneration of activated carbon remains challenging and thus the adsorbent/adsorbate system must be disposed of. Here, three typical textile dyes, reactive brilliant red X-3B, congo red and fuchsin red, were studied for removal from wastewater with two NiO systems and activated carbon. These studies revealed that the NiO(111) nanosheets exhibited much more favorable adsorptive properties than conventionally prepared nickel oxide powder (CP-NiO) obtained from thermal decomposition of nickel nitrate. The maximum adsorption capabilities of the three dyes on NiO(111) nanosheets reached 30.4 mg g(-1), 35.15 mg g(-1) and 22 mg g(-1) for reactive brilliant red X-3B, congo red and fuchsin acid, respectively, while the maximum adsorption capabilities of the three dyes on CP-NiO were only 8.4, 13.2 and 12 mg g(-1) for reactive brilliant red X-3B, congo red and fuchsin acid. To simulate the adsorption isotherm, two commonly employed models, the Langmuir and the Freundlich isotherms, were selected to explicate the interaction of the dye and NiO(111). The isotherm evaluations revealed that the Langmuir model demonstrated better fit to experimental equilibrium data than the Freundlich model. The maximum predicted adsorption capacity was 36.1 mg g(-1). In addition, adsorption kinetic data of NiO(111) followed a pseudo-second-order rate for congo red. These studies infer that NiO(111) nanosheets possess desirable properties for application in adsorption and combustion applications.

Size-tunable fabrication of multifunctional Bi2O3 porous nanospheres for photocatalysis, bacteria inactivation and template-synthesis

Multifunctional Bi2O3 porous nanospheres (PNs) with tunable size have been successfully synthesized via a facile solvothermal method. The obtained Bi2O3 porous nanospheres demonstrate outstanding performance in visible-light-driven photocatalysis for Cr(VI) and organic dye removal, inactivation of Gram-negative and Gram-positive bacteria, as well as template-synthesis for fabrication of bismuth-related hollow nanostructures.

Controlled strategy to synthesize SnO2 decorated SnS2 nanosheets with enhanced visible light photocatalytic activity

Novel SnO2 nanoparticle-decorated SnS2 nanosheets were synthesized via a one-pot solvothermal process using SnCl4·5H2O and CH4N2S as precursors. SnS2@SnO2 nanosheets were characterized by XRD, TEM, FESEM, XPS and UV-vis diffuse reflectance spectra (DRS). The band-gap of SnO2@SnS2 can be easily tuned by the controlled experimental strategy. Anisole and ethanol with different volume ratios were used as binary solvent to tune the composition of SnS2@SnO2 nanocomposites (NCs) continuously and the composites gradually change from hexagonal SnS2 into tetragonal SnO2. All of the SnS2@SnO2 nanosheets exhibited enhanced visible light photocatalytic activity, which was remarkably superior to SnS2, SnO2 and Degussa P-25. The obtained SnS2@SnO2 NCs with Vethanol/Vanisole = 1 : 2 showed the best photocatalytic capability. Furthermore, the formation mechanism of SnS2@SnO2 nanosheets has also been discussed.

Mass production and photocatalytic activity of highly crystalline metastable single-phase Bi20TiO32 nanosheets.

Highly crystalline metastable bismuth titanate (Bi₂₀TiO₃₂) nanosheets are prepared via a simple green wet chemical route for the first time. The Bi₂₀TiO₃₂)photocatalysts were characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive spectrum analysis (EDS), X-ray diffraction (XRD), N₂ adsorption-desorption (BET), and UV-vis diffuse reflectance spectroscopy (DRS). Inspiringly, Bi₂₀TiO₃₂ nanosheets showed high photocatalytic activity for the degradation of nonbiodegradable azo dye under simulated sunlight and visible-light irradiation. The experimental results showed that the photocatalytic activity of the Bi₂₀TiO₃₂ nanosheets was superior to the commercial Degussa P25 TiO₂, and demonstrated that the morphology and crystal structure have a distinct effect on the photocatalytic activity. The reasons for the high photocatalytic activity and the formation mechanism of Bi₂₀TiO₃₂ nanosheets are also discussed.

Mesoporous bimetallic PdCl2-CuCl2 catalysts for dimethyl carbonate synthesis by vapor phase oxidative carbonylation of methanol

Dimethyl carbonate (DMC) synthesis reaction by oxidative carbonylation of methanol has been studied in a flow reaction system at atmospheric pressure in the presence of quaternary ammonium salt (QAS)-promoted bimetallic PdCl2-CuCl2 catalyst system supported on mesoporous HMS silica. The effects of the various QAS promoters, the promoter doping level and the Cu/Pd mole ratio were investigated, as well as the reaction conditions on the catalytic reactivates. The results showed that the tetrabutylammonium bromide (TBAB) promoted PdCl2-CuCl2/HMS catalyst system has the best catalytic performance. The characterization of PdCl2-CuCl2-TBAB/HMS catalysts was performed by means of BET, X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The essential role of TBAB promoter is to facilitate the Pd(0)/Pd(II) and Cu(II)/Cu(I) redox processes. The formation of substantial amounts of surface stabilized cuprous species on the bimetallic HMS catalysts may account for the significant enhancement of the catalytic performance in DMC synthesis.

Synthesis and surface activity of single-crystalline Co3O4 (111) holey nanosheets

Single crystalline, thermally stable, Co(3)O(4) (111) holey nano-sheets were prepared by an efficient, template-free, wet chemical synthetic approach. The high energy (111) surfaces formed can be used as highly active heterogeneous catalysts for methanol decomposition.

Nitrogen-doped graphene/CdS hollow spheres nanocomposite with enhanced photocatalytic performance

A novel N-doped graphene/CdS hollow sphere nanocomposite photocatalyst was synthesized by a simple, template-free one-pot method. The samples were characterized by X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, N2 adsorption-desorption, photoluminescence spectroscopy, and X-ray photoelectron spectroscopy. Photocatalytic degradations of methylene blue and salicylic acid were carried out to evaluate the photocatalytic activity of the nanocomposites under visible light irradiation. The N-graphene/CdS nanocomposites exhibited excellent stability and high photocatalytic activity, exceeding those of graphene oxide/CdS hollow sphere nanocomposites and pure CdS hollow spheres. This excellent photocatalytic activity of the nanocomposite was due to N-graphene acting as an excellent electron acceptor and transporter, thus reducing charge carrier recombination. It was also found that •OH acted as the main reactive species in the degradation of methylene blue under visible-light irradiation.

Characterization of high-surface-area zirconia aerogel synthesized from combined alcohothermal and supercritical fluid drying techniques

Thermally stable tetragonal zirconia aerogel with a high surface area can be obtained by a novel alcohothermal route, followed by the supercritical fluid drying technique. In addition, a cheaper inorganic salt was used as raw material instead of the expensive and harmful zirconium alkoxides. The zirconia aerogel samples were characterized using X-ray diffraction, thermal analysis, N2 adsorption measurements, diffuse reflectance infrared Fourier transform spectroscopy, and transmission electron microscopies. The results show that the resulting zirconia aerogel was composed primarily of narrowly distributed nanoparticles with loose aggregation. It is shown that the thermally stable zirconia aerogel has a high specific surface area and a well-developed textural mesoporosity with narrow pore size distribution, which is highly attractive for potential applications in heterogeneous catalysis.