Xiaofeng Chang

Photodegradation of Rhodamine B over unexcited semiconductor compounds of BiOCl and BiOBr

This study reported, for the first time systematically, photodegradation of Rhodamine B (RhB) in aqueous solution over BiOCl and BiOBr semiconductors. Under visible light irradiation (λ>400 nm, λ>420 nm and λ=550±15 nm), RhB adsorbed on the surface of BiOCl and BiOBr was photosensitized and decomposed effectively over unexcited BiOCl and BiOBr. The degradation of Methyl Orange (MO) and Methylene Blue (MB) over BiOCl and BiOBr was investigated as well, and the results were compared with RhB photodegradation. It was found that MB molecules having the lowest LUMO could not be degraded by this process. Utilizing the quantum chemical calculation (Gaussian 03 program), the relationship between frontier orbital energy of selected dye molecules and photodegradation rate was established for the first time in this study.

Rapid removal of bisphenol A on highly ordered mesoporous carbon

Bisphenol A (BPA) is of global concern due to its disruption of endocrine systems and ubiquity in the aquatic environment. It is important, therefore, that efforts are made to remove it from the aqueous phase. A novel adsorbent, mesoporous carbon CMK-3, prepared from hexagonal SBA-15 mesoporous silica was studied for BPA removal from aqueous phase, and compared with conventional powdered activated carbon (PAC). Characterization of CMK-3 by transmission electron microscopy (TEM), X-ray diffraction, and nitrogen adsorption indicated that prepared CMK-3 had an ordered mesoporous structure with a high specific surface area of 920 m2/g and a pore-size of about 4.9 nm. The adsorption of BPA on CMK-3 followed a pseudo second-order kinetic model. The kinetic constant was 0.00049 g/(mg x min), much higher than the adsorption of BPA on PAC. The adsorption isotherm fitted slightly better with the Freundlich model than the Langmuir model, and adsorption capacity decreased as temperature increased from 10 to 40 degrees C. No significant influence of pH on adsorption was observed at pH 3 to 9; however, adsorption capacity decreased dramatically from pH 9 to 13.

Photocatalytic decomposition of 4-t-octylphenol over NaBiO3 driven by visible light: Catalytic kinetics and corrosion products characterization

The photocatalytic decomposition of 4-t-octylphenol (4-t-OP) by NaBiO(3) photocatalyst and the catalyst stability in aqueous solution were investigated systematically for the first time. The results showed that some parameters such as catalyst dosage, initial 4-t-OP concentration and pH value of the solution had great effects on the photocatalytic activity. The NaBiO(3) photocatalyst maintained considerable catalytic performance under visible light (lambda>400 nm) irradiation and exhibited a higher photocatalytic activity compared to the commercialized photocatalyst P25. In addition, the corrosion products of NaBiO(3) catalyst under acid condition (HCl aqueous solution contained) were characterized by X-ray diffraction (XRD), transmittance electronic microscopy (TEM), selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS) and UV-vis transmittance spectrum analysis. The results showed that NaBiO(3) was unstable under the acidic condition and the catalyst could convert into Bi(3+)-containing compounds such as Bi(2)O(3), etc. The experiment demonstrates that NaBiO(3) can be corroded to nano-sized BiOCl crystal in the presence of hydrogen chloride, the band gap of which was estimated to be 3.28 eV by Taucs approach.

Synthesis and magnetic properties of crystalline mesoporous CoFe2O4 with large specific surface area

Based on the nanocasting strategy, highly crystalline mesoporous CoFe2O4 were synthesized for the first time through the pyrolysis of hybrid metal nitrates within the pores of two kinds of mesoporous silica, SBA-15 and KIT-6, respectively. The Brunauer–Emmet–Teller (BET) surface areas of the samples could be as high as 155.7 m2 g−1 (templated by SBA-15) and 129.4 m2 g−1 (templated by KIT-6). Characterization results revealed that the mesoporous structures of the templates can be negatively replicated by the crystals of CoFe2O4, and the probable phase formation mechanism was also proposed initially. Magnetic test showed that both samples had rather low coercivity (106.5 and 212.1 Oe, respectively) due to the presence of a prominent proportion of superparamagnetic particles. It has also been found that the impregnation steps had a great influence on the stucture and properties of the products.

Rapid photocatalytic degradation of PCP―Na over NaBiO3 driven by visible light irradiation

The photocatalytic performance of sodium pentachlorophenate (PCP-Na) over NaBiO(3) under visible light irradiation was first investigated systematically. After 1h of photocatalytic reaction, the degradation rate of PCP-Na could reach to 90.5% in appropriate conditions. OH is the dominant photooxidant rather than O(2)(-) based on the experiment results and density of states (DOS) analysis. The PCP-Na solution became basic (pH value increased to approximately 9) with the progress of photocatalytic reaction which may be attributed to the PCP(-) oxidized to the pentachlorophenoxy radical by an attack on PCP(-) by OH. The photocatalytic reaction over NaBiO(3) follows the rule of first-order reaction according to the Langmuir-Hinshelwood model. The initial concentration of the PCP-Na, the initial pH value of PCP-Na aqueous solution and the amount of NaBiO(3) used have great influences on the photocatalytic performance. Three kinds of photocatalytic systems (P25, Bi(2)O(3) and P25-Bi(2)O(3) heterojunction) exhibited relative lower photocatalytic activity compared to NaBiO(3) powder.

Highly-active direct Z-scheme Si/TiO2 photocatalyst for boosted CO2 reduction into value-added methanol

In the present study, direct Z-scheme Si/TiO2 photocatalyst was synthesized via a facile hydrothermal reaction using tetrabutyl titanate and Si powder prepared from magnesiothermic reduction of SiO2 nanospheres. The Si/TiO2 nanospheres were composed of porous Si nanospheres with a diameter of ∼300 nm and TiO2 nanosheets with a diameter of 50 nm and thickness of 10 nm, and demonstrated superior visible light harvesting ability to either Si nanospheres or TiO2 nanosheets. CO2 photocatalytic reduction proved that Si/TiO2 nanocomposites exhibit high activity in conversion of CO2 to methanol with the maximum photonic efficiency of 18.1%, while pure Si and TiO2 catalyst are almost inactive, which can be ascribed to the integrated suitable band composition in the Si/TiO2 Z-scheme system for CO2 reduction. The enhanced photocatalytic property of Z-scheme Si/TiO2 nanospheres was ascribed to the formation of Si/TiO2 Z-scheme system, which improved the separation efficiency of the photogenerated carriers, prolonged their longevity, and therefore boosted their photocatalytic activity.

Structural Characterization of Mesoporous Silica Nanofibers Synthesized Within Porous Alumina Membranes

Mesoporous silica nanofibers were synthesized within the pores of the anodic aluminum oxide template using a simple sol–gel method. Transmission electron microscopy investigation indicated that the concentration of the structure-directing agent (EO20PO70EO20) had a significant impact on the mesostructure of mesoporous silica nanofibers. Samples with alignment of nanochannels along the axis of mesoporous silica nanofibers could be formed under the P123 concentration of 0.15 mg/mL. When the P123 concentration increased to 0.3 mg/mL, samples with a circular lamellar mesostructure could be obtained. The mechanism for the effect of the P123 concentration on the mesostructure of mesoporous silica nanofibres was proposed and discussed.

Enhanced photoactivity on Ag/Ag3PO4 composites by plasmonic effect

The work presented here deals with the photoreduction in metallic silver nanoparticles onto the surface of Ag(3)PO(4) and resulting photocatalytic activity enhancement toward degradation of dye molecules, namely Rhodamine B (Rh. B) as a model compound, from aqueous solution under UV or visible light irradiation. Our results clearly indicated that the photoactivity of Ag(3)PO(4) was significantly enhanced by depositing an optimum amount of silver nanoparticles, even though the adsorption kinetics rate and capacity decreased after the silver nanoparticles agglomerate extensively. The surface plasmon resonance (SPR) excited between the silver nanoparticles and Rh. B interface is a physical origin and responsible for the boosted photoactivity, which strongly depends on the specific wavelength of the incident light. This work provides and suggests a novel scheme for Ag/Ag(3)PO(4) composites having plasmonic effect on the interface with detailed experimental and theoretical study.

Microwave-assisted synthesis of Sb2Se3 submicron tetragonal tubular and spherical crystals

Sb(2)Se(3) submicron tetragonal tubes have been prepared by a microwave-assisted polyol method using antimony trichloride and sodium selenite as the Sb and Se precursors. Scanning electron microscopy (SEM) results showed a novel transformation of Sb(2)Se(3) microstructures from submicron tubes to submicron spheres during the microwave heating process. The potential growth mechanism has been investigated by analyzing the samples at different growth stages. Transmission electron microscopy (TEM) analyses confirmed that samples prepared under 10 min microwave heating possessed tetragonal tubular structure with lengths in the range of 10-30 microm, thicknesses in the range of 0.5-1 microm and wall thicknesses in the range of 100-200 nm. High-resolution TEM (HRTEM) and selected area electron diffraction (SAED) results revealed that Sb(2)Se(3) submicron tubes were single-crystalline along the [001] direction. The optical properties of Sb(2)Se(3) submicron tubes and submicron spheres were characterized by UV-vis diffuse reflectance spectroscopy, and the band gap (E(g)) derived to be 1.161 and 1.173 eV, respectively.

Synthesis of silver nanoparticles within ordered CMK-3 mesoporous carbon

Silver nanoparticles have been prepared using ordered mesoporous carbon CMK-3 as host by a simple chemical method, which involves AgNO 3 precursor impregnation, followed by thermal decomposition. Advantage of template method is that it provides good control over size and shape of the nanomaterials. Silver nanoparticles formation inside the channels of CMK-3 is confirmed by transmission electron microscopy (TEM), which shows silver nanoparticles with diameter of ca. 3 nm coincident with channel diameter of CMK-3. The powder X-ray diffraction (XRD) pattern also shows presence of silver. N 2 sorption measurements confirm that Ag nanoparticles are indeed located within CMK-3. The new Ag/CMK-3 nanomaterial is of much importance and would provide wider applications in catalysis and optical property.