Mingce Long

Synthesis of Visible-Light Responsive Graphene Oxide/TiO2 Composites with p/n Heterojunction

Graphene oxide/TiO(2) composites were prepared by using TiCl(3) and graphene oxide as reactants. The concentration of graphene oxide in starting solution played an important role in photoelectronic and photocatalytic performance of graphene oxide/TiO(2) composites. Either a p-type or n-type semiconductor was formed by graphene oxide in graphene oxide/TiO(2) composites. These semiconductors could be excited by visible light with wavelengths longer than 510 nm and acted as sensitizer in graphene oxide/TiO(2) composites. Visible-light driven photocatalytic performance of graphene oxide/TiO(2) composites in degradation of methyl orange was also studied. Crystalline quality and chemical states of carbon elements from graphene oxide in graphene oxide/TiO(2) composites depended on the concentration of graphene oxide in the starting solution. This study shows a possible way to fabricate graphene oxide/semiconductor composites with different properties by using a tunable semiconductor conductivity type of graphene oxide.

Preparation of photocatalytic anatase nanowire films by in situ oxidation of titanium plate

Photocatalytic anatase TiO2 nanowire thin films have been prepared by in situ oxidation of Ti plate in a mixture solution of concentrated H(2)O(2) and NaOH, followed by proton exchange and calcination. The morphologies and properties of the titanate and titania films have been investigated by means of field emission scanning electron microscopy, energy-dispersive x-ray spectrometry, high resolution transmission electron microscopy, x-ray diffraction and Raman spectrometry. The mechanism of formation of the porous microstructure has been discussed; it is the result of the balance between dissolution and precipitation. And sodium ions in the solution are needed to combine with titanate species for the nanowire formation. The anatase TiO2 nanowire thin films exhibited enhanced photocatalytic activity and stability in phenol degradation. The combination effects of the porous morphology and nanowire characteristics are favorable for improved photocatalytic performance. This novel nanowire film is promising for practical aqueous purification.

Magnetically separable core-shell structural γ-Fe2O3@Cu/Al-MCM-41 nanocomposite and its performance in heterogeneous Fenton catalysis.

To target the low catalytic activity and the inconvenient separation of copper loading nanocatalysts in heterogeneous Fenton-like reaction, a core-shell structural magnetically separable catalyst, with γ-Fe2O3 nanoparticles as the core layer and the copper and aluminum containing MCM-41 as the shell layer, has been fabricated. The role of aluminum has been discussed by comparing the copper containing mesoporous silica with various Cu contents. Their physiochemical properties have been characterized by XRD, UV-vis, FT-IR, TEM, nitrogen physisorption and magnetite susceptibility measurements. Double content Cu incorporation results in an improved catalytic activity for phenol degradation at the given condition (40°C, initial pH=4), but leads to a declined BET surface area and less ordered mesophase structure. Aluminum incorporation helps to retain the high BET surface area (785.2m(2)/g) and the regular hexagonal mesoporous structure of MCM-41, which make the catalyst possess a lower copper content and even a higher catalytic activity than that with the double copper content in the absence of aluminum. The catalysts can be facilely separated by an external magnetic field for recycle usage.

RhB Adsorption Performance of Magnetic Adsorbent Fe3O4/RGO Composite and Its Regeneration through A Fenton-like Reaction

Adsorption is one of the most effective technologies in the treatment of colored matter containing wastewater. Graphene related composites display potential to be an effective adsorbent. However, the adsorption mechanism and their regeneration approach are still demanding more efforts. An effective magnetically separable absorbent, Fe3O4 and reduced graphene oxide (RGO) composite has been prepared by an in situ coprecipitation and reduction method. According to the characterizations of TEM, XRD, XPS, Raman spectra and BET analyses, Fe3O4 nanoparticles in sizes of 10–20 nm are well dispersed over the RGO nanosheets, resulting in a highest specific area of 296.2 m2/g. The rhodamine B adsorption mechanism on the composites was investigated by the adsorption kinetics and isotherms. The isotherms are fitting better by Langmuir model, and the adsorption kinetic rates depend much on the chemical components of RGO. Compared to active carbon, the composite shows 3.7 times higher adsorption capacity and thirty times faster adsorption rates. Furthermore, with Fe3O4 nanoparticles as the in situ catalysts, the adsorption performance of composites can be restored by carrying out a Fenton-like reaction, which could be a promising regeneration way for the adsorbents in the organic pollutant removal of wastewater.

Effect of Gold Nanoparticles on the Photocatalytic and Photoelectrochemical Performance of Au Modified BiVO 4

An efficient visible light driven photocatalyst, gold nanoparticles (NPs) modified BiVO4 (Au/BiVO4), has been synthesized by deposition-precipitation with urea method. Au/BiVO4 exhibits enhanced photocatalytic activity for phenol degradation under λ>400 nm irradiation but negligible activity under λ>535 nm, indicating that the surface plasmon resonance (SPR) effect is too weak for organic photodegradation. According to the photoelectrochemical results of the porous powder electrodes of BiVO4 and Au/BiVO4, the SPR effect of Au NPs has been assessed. The role of Au NPs as electron sinks or sources, which is controllable by incident photon energy and applied potentials, has been discussed.

Trading oxidation power for efficiency: Differential inhibition of photo-generated hydroxyl radicals versus singlet oxygen

The ability of reactive oxygen species (ROS) to interact with target pollutants is crucial for efficient water treatment using advanced oxidation processes (AOPs), and inhibition by natural organic matter (NOM) can significantly reduce degradation efficiency. We compare OH-based degradation (H2O2-UV) to (1)O2-based degradation (Rose Bengal) of several probe compounds (furfuryl alcohol, ranitidine, cimetidine) interacting in water containing background constituents likely to be found in treatment water such as natural organic matter (NOM) and phosphate, as well as in effluent from a waste-water treatment plant (WWTP). Hydroxyl radicals were much more susceptible to hindrance by all three background matrices (NOM, phosphate and WWTP effluent) tested, while (1)O2 was only slightly inhibited by NOM and not by phosphate or WWTP effluent. A mechanistic model accounting for this inhibition in terms of radical scavenging and inner filter effects was developed, and accurately simulated the results of the NOM interactions. These results underscore the importance of considering the effect of background constituents in the selection of photocatalysts and in the design of AOPs for emerging applications in tertiary treatment of wastewater effluent and disinfection of natural waters.

Reduction of graphene oxide by an in-situ photoelectrochemical method in a dye-sensitized solar cell assembly

Reduction of graphene oxide [GO] has been achieved by an in-situ photoelectrochemical method in a dye-sensitized solar cell [DSSC] assembly, in which the semiconductor behavior of the reduced graphene oxide [RGO] is controllable. GO and RGO were characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, high-resolution transmission electron microscope, and Fourier-transform infrared spectroscopy. It was found that the GO film, which assembled in the DSSC assembly as the counter electrode, was partly reduced. An optimized photoelectrochemical assembly is promising for modulating the reduction degree of RGO and controlling the band structure of the resulting RGO. Moreover, this method appeared to be a green progress for the production of RGO electrodes.

Inhibitory effect of natural organic matter or other background constituents on photocatalytic advanced oxidation processes: Mechanistic model development and validation.

The ability of reactive oxygen species (ROS) to interact with priority pollutants is crucial for efficient water treatment by photocatalytic advanced oxidation processes (AOPs). However, background compounds in water such as natural organic matter (NOM) can significantly hinder targeted reactions and removal efficiency. This inhibition can be complex, interfering with degradation in solution and at the photocatalyst surface as well as hindering illumination efficiency and ROS production. We developed an analytical model to account for various inhibition mechanisms in catalytic AOPs, including competitive adsorption of inhibitors, scavenging of produced ROS at the surface and in solution, and the inner filtering of the excitation illumination, which combine to decrease ROS-mediated degradation. This model was validated with batch experiments using a variety of ROS producing systems (OH-generating TiO2 photocatalyst and H2O2-UV; (1)O2-generating photosensitive functionalized fullerenes and rose bengal) and inhibitory compounds (NOM, tert-butyl alcohol). Competitive adsorption by NOM and ROS scavenging were the most influential inhibitory mechanisms. Overall, this model enables accurate simulation of photocatalytic AOP performance when one or more inhibitory mechanisms are at work in a wide variety of application scenarios, and underscores the need to consider the effects of background constituents on degradation efficiency.

Understanding the composition and electronic structure dependent photocatalytic performance of bismuth oxyiodides

A series of bismuth oxyiodides were obtained by calcining the precursor compound (Bi7O9I3). Their compositions and electronic structures were analyzed by various physicochemical characterizations, slurry method measurements and theoretical calculations. Iodine vacancies appearing at elevated temperatures before the phase transition contribute to the increased photocatalytic activity, which can be attributed to the increase of band gaps, downward shifts of band potentials and the change of semiconductor behavior from p type to n type. The catalyst obtained at 400 °C displayed an excellent photocatalytic performance for phenol degradation, and it was characterized as a composite of two components with well-matched band potentials and good contact interfaces. Photogenerated holes were revealed as the main active species in the phenol degradation. This study could bring insights into the fabrication of novel highly efficient bismuth oxyiodide composites by simultaneously controlling the extent of phase transition and the amount of iodine vacancies.

Template-free sol–gel preparation and characterization of free-standing visible light responsive C,N-modified porous monolithic TiO2

Visible light responsive C,N-modified porous monolithic titania (MT(f)) has been successfully synthesized. The template-free sol-gel synthesis method accompanied by phase separation and in situ C,N-modification has been used. The molar ratio of water to tetrabutyl titanate (f) in starting solution plays an important role in the porous structure and photoactivity of MT(f). Scanning electron microscopy (SEM) analysis and N(2) adsorption-desorption analysis show that MT(f) possess mesoporous structure as well as macroporous structure. MT(22) has been further characterized by using X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflectance spectra (DRS). The results show that both nitrogen and carbon elements exist in MT(22) and result in the visible light photocatalytic activity of MT(22). The observed reaction rate of decolorization of methyl orange is 0.0026 min(-1).