Xidong Wang

Density-controlled hydrothermal growth of well-aligned ZnO nanorod arrays

Density-controlled ZnO nanorod arrays (ZNAs) were prepared on pre-treatment substrates by a hydrothermal approach under different conditions. The effect of substrate pre-treatment conditions on controlling the density of ZNAs was systematically studied by scanning electron microscopy and x-ray diffraction. It is demonstrated that the substrate pre-treatment conditions such as the concentration of the ZnO colloid, spin coating times, and substrate annealing treatment have their respective influence on controlling the density of the ZNAs. The introduction of a ZnO nanoparticle layer on the substrate not only helps to control the nanorod density but also has a strong impact on the orientation of the nanorod arrays. Although controlling the spin coating process has a similar mechanism to controlling the concentration of colloid, it offers a convenient method to prepare a series of ZNAs with variable density. An annealing treatment of the substrate can influence the microstructure of the ZnO seed layer and then influence the density of the ZNAs.

Electrodeposition of Hierarchical ZnO Nanorod-Nanosheet Structures and Their Applications in Dye-Sensitized Solar Cells

We present a two-step electrochemical deposition process to synthesize hierarchical zinc oxide (ZnO) nanorod-nanosheet structures on indium tin oxide (ITO) substrate, which involves electrodeposition of ZnO nanosheet arrays on the conductive glass substrate, followed by electrochemical growth of secondary ZnO nanorods on the backbone of the primary ZnO nanosheets. The formation mechanism of the hierarchical nanostructure is discussed. It is demonstrated that annealing treatment of the primary nanosheets synthesized by the first-step deposition process plays a key role in synthesizing the hierarchical nanostructure. Photovoltaic properties of dye-sensitized solar cells (DSSCs) based on hierarchical ZnO nanostructures are investigated. The hierarchical ZnO nanorod-nanosheet DSSC exhibits improved device performance compared to the DSSC constructed using photoelectrode of bare ZnO nanosheet arrays. The improvement can be attributed to the enhanced dye loading, which is caused by the enlargement of internal surface area within the nanostructure photoelectrode. Furthermore, we perform a parametric study to determine the optimum geometric dimensions of the hierarchical ZnO nanorod-nanosheet photoelectrode through adjusting the preparation conditions of the first- and second-step deposition process. By utilizing a hierarchical nanostructure photoelectrode with film thickness of about 7 μm, the DSSC with an open-circuit voltage of 0.74 V and an overall power conversion efficiency of 3.12% is successfully obtained.

Hydrothermal preparation and photoelectrochemical performance of size-controlled SnO2 nanorod arrays

Single crystalline SnO2 nanorod arrays with controlled size and high orientation consistency have been fabricated on a substrate in large scale by using a hydrothermal approach, and used as the photoanode in a Gratzel-type solar cell.

Tailoring CoO–ZnO nanorod and nanotube arrays for Li-ion battery anode materials

Hydrothermal treatment of cobalt nitrate in the presence of ZnO nanorod templates results in the generation of free-standing CoO–ZnO composite arrays on a copper substrate. The result shows that tuning the molar concentration of cobalt nitrate can controllably prepare CoO–ZnO nanotube and ZnCo2O4 hierarchical nanorod structures. The electrochemical properties of the resultant nanorod and nanotube arrays are investigated. Due to the short insertion and extraction length for lithium ions, the free space between the adjacent tubes or rods, and the high contact area, the as-prepared one-dimensional CoO–ZnO composites exhibit excellent cycling performance and high capacities as anode materials for Li-ion batteries.

Promoting effect of Nd on the reduction of NO with NH3 over CeO2 supported by activated semi-coke: an in situ DRIFTS study

Cerium oxides and neodymium-cerium composite oxides were loaded onto activated semi-coke (ASC) by a hydrothermal method for the selective catalytic reduction (SCR) of NO with NH3. The catalytic activity of CeO2/ASC was greatly enhanced by the addition of Nd. The mechanistic cause of the promoting effect of Nd was systematically investigated using various characterization techniques, including XRD, SEM, TEM and in situ DRIFTS. The results revealed that the reaction route for NH3-SCR followed both the E–R and L–H mechanisms over CeO2/ASC and CeO2-Nd/ASC catalysts. Nevertheless, the Nd doping process was beneficial for the formation of Ce3+ and gave rise to the transformation of Lewis acid sites into Bronsted acid sites, which influenced the mechanism of SCR reaction. The generation of oxygen vacancies was in favor of the oxidation of NO to NO2 and thus facilitated the proceeding of the following reduction reactions. Thus, the presence of the Ce3+ state and oxygen vacancies played a primary role in the improvement of the low-temperature SCR performance of the CeO2-Nd/ASC catalyst.

Integrated carbon dioxide/sludge gasification using waste heat from hot slags: syngas production and sulfur dioxide fixation.

The integrated CO2/sludge gasification using the waste heat in hot slags, was explored with the aim of syngas production, waste heat recovery and sewage sludge disposal. The results demonstrated that hot slags presented multiple roles on sludge gasification, i.e., not only a good heat carrier (500-950 °C) but also an effective desulfurizer (800-900 °C). The total gas yields increased from 0.022 kg/kgsludge at 500 °C to 0.422 kg/kgsludge at 900 °C; meanwhile, the SO2 concentration at 900 °C remarkably reduced from 164 ppm to 114 ppm by blast furnace slags (BFS) and 93 ppm by steel slags (SS), respectively. A three-stage reaction was clarified including volatile release, char transformation and fixed carbon using Gaussian fittings and the kinetic model was analyzed. Accordingly, a decline process using the integrated method was designed and the optimum slag/sludge ratio was deduced. These deciphered results appealed potential ways of reasonable disposal of sewage sludge and efficient recovery of waste heat from hot slags.

Viscosities Behavior of CaO-SiO2-MgO-Al2O3 Slag With Low Mass Ratio of CaO to SiO2 and Wide Range of Al2O3 Content

The present paper is aimed at recycling of coal ash and blast furnace slag to produce mineral wool. Considering the mineralogical constitutions of coal ash and blast furnace slag, the primary quaternary slag compositions of CaO-SiO2-MgO-Al2O3 with basicity (mass ratio of CaO to SiO2) ranging from 0. 5 to 0. 9 and alumina ranging from 5% to 20% were investigated through a rotating cylinder method. The experimental results indicated that the viscosities decreased with increasing basicity above the liquidus temperature, and increased with increasing alumina content, and the maximum values were reached and as the alumina content was 20%, followed by the decrease with further increasing alumina content due to its amphoteric behavior. The amphoteric behavior of Al2O3 also performed in the relationship between viscosity and non-bridging oxygen per tetrahedrally-coordinated atom (NBO/T), and the viscosities decreased with increasing the NBO/T except the slag with a basicity 0. 5 and Al2O3 20% which have a low NBO/T value and a low viscosity than others.

Two-stage high temperature sludge gasification using the waste heat from hot blast furnace slags

Nowadays, disposal of sewage sludge from wastewater treatment plants and recovery of waste heat from steel industry, become two important environmental issues and to integrate these two problems, a two-stage high temperature sludge gasification approach was investigated using the waste heat in hot slags herein. The whole process was divided into two stages, i.e., the low temperature sludge pyrolysis at ⩽ 900°C in argon agent and the high temperature char gasification at ⩾ 900°C in CO2 agent, during which the heat required was supplied by hot slags in different temperature ranges. Both the thermodynamic and kinetic mechanisms were identified and it was indicated that an Avrami-Erofeev model could best interpret the stage of char gasification. Furthermore, a schematic concept of this strategy was portrayed, based on which the potential CO yield and CO2 emission reduction achieved in China could be ∼1.92∗10(9)m(3) and 1.93∗10(6)t, respectively.

Environmental investigation on co-combustion of sewage sludge and coal gangue: SO2, NOx and trace elements emissions

To promote the utilization of waste material as alternative fuel, the mono- and co-combustion characteristics of sewage sludge (SS) and coal gangue (CG) were systematically investigated, with emphasis on environmental influences. The emission of SO2, NOx as well as the trace elements during combustion of SS and CG were studied with regard to the effects of their chemistries, structures and interactions. Results showed that co-combustion can be beneficial for ignition performance. A synergic effect on both desulfurization and denitrification can be expected at ca. 800°C. Further, an enhanced retention of trace elements during co-combustion was also observed, especially for Pb and Zn. On the basis of the results, it can be expected that, with proper operation, co-combustion of SS and CG can be a promising method for the disposal of these two wastes.

Hydrothermal synthesis and automotive exhaust catalytic performance of CeO2 nanotube arrays

Ceria (CeO2) nanotube arrays with precisely defined size and density were directly synthesized on glass and cordierite substrates using a ZnO nanorods-assisted hydrothermal method. Eliminating the procedures of template removal and film coating, the one-step synthesis approach could greatly broaden the applications for materials with tubular structures. The proper concentration of cerium nitrate precursor solution acts a vital role to adjust the instantaneous precipitation of CeO2 and dissolution of ZnO templates. The as-prepared CeO2 tube arrays were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) techniques, which reveal a regular tubular structure with the average diameter of 500 nm and length of 3 μm. The automotive exhaust catalytic performance of CeO2 tube arrays prepared on the cordierite was evaluated. Compared with the ceria nanoparticles film, the target CeO2 tubes exhibit improved catalytic activities at a low start-up temperature for oxycarbide and hydrocarbon. Furthermore, the palladium-decorated CeO2 tubes exhibit a higher catalytic activity for the degradation of oxynitride than that of palladium/ceria particles/cordierite.