Lei Lecheng

Degradation kinetics and mechanisms of phenol in photo-Fenton process.

Phenol degradation in photochemically enhanced Fenton process was investigated in this work. UV-VIS spectra of phenol degradation showed the difference between photo-Fenton process and UV/H2O2, which is a typical hydroxyl radical process. A possible pathway diagram for phenol degradation in photo-Fenton process was proposed, and a mathematical model for chemical oxygen demand (COD) removal was developed. Operating parameters such as dosage of H2O2 and ferrous ions, pH, suitable carrier gas were found to impact the removal of COD significantly. The results and analysis of kinetic parameters calculated from the kinetic model showed that complex degradation of phenol was the main pathway for removal of COD; while hydroxyl radicals acted weakly in the photo-Fenton degradation of phenol.

Heterogeneous UV/Fenton catalytic degradation of wastewater containing phenol with Fe-Cu-Mn-Y catalyst

The heterogeneous UV/Fenton process with the appropriate amount of Fe-Mn-Cu-Y as catalyst was developed and various operation conditions for the degradation of phenol were evaluated. The results indicated that by using the heterogeneous UV/Fenton process, the CODcr removal rate reached almost 100% for wastewater containing phenol. Compared with the homogeneous process, the developed catalyst could be used at wider pH range in the UV/Fenton process. Comparison of various heterogeneous process showed that heterogeneous UV/Fenton process was best. The heterogeneous UV/Fenton process with Fe-Mn-Cu-Y catalyst is highly efficient in degrading various organic pollutants.

Preparation of TiO 2 /ITO film electrode by AP-MOCVD for photoelectrocatalytic application

Titanium dioxide (TiO2) thin films were grown onto Indium tin oxide (ITO) glass under atmospheric pressure by chemical vapor deposition (AP-MOCVD) using titanium tetraisopropoxide astitanium precursor. The as-prepared TiO2/ITO films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and photoelectrochemical measurements. Their photocatalytic (PC) and photoelectrocatalytic (PEC) activities were evaluated based on the results of methyl orange dye (MO) degradation experiments in aqueous solution. The difference between the front side (EE, electrolyte/electrode interface) and the back side (SE, substrate/electrode interface) illumination was evaluated in both photocurrent and MO degradation experiments. The effect of the film thickness on degradation rate by PEC under the two illumination directions was also studied. Stability of TiO2/ITO film electrode was investigated in repetitive degradation experiments. Overall, the TiO2/ITO film with thickness ranging from 321 to1440 nm deposited by MOCVD method is an effective photoelectrode for MO degradation under SE illumination in PEC reaction system.

The Catalytic Effect of Metal Ions on the Degradation of 4-Chlorophenol Induced by an Aqueous Pulsed Discharge Plasma

The influence of metal ions, such as Fe2+, Fe3+, Cu2+ and Mn2+, on 4-CP degradation was investigated in an aqueous pulsed discharge plasma system with or without the addition of a TiO2 photo-catalyst. From an analysis of the pseudo first-order rate constant (kCP) and energy efficiency (G50%) for 4-CP degradation, the experimental results show that the degradation of 4-CP is much enhanced in the presence of ferrous ions at the optimal concentration of 0.2~0.8 mmol/L or 0.2 mmol/L in an aqueous pulsed discharge plasma without or with the TiO2 system, respectively, and the enhancement is ascribed to plasma induced Fenton and photo-Fenton reactions. Meanwhile, the rank of such metal ions for catalytic effect on 4-CP degradation was Fe2+> Fe3+ > Cu2+ > Mn2+ and Fe2+ > Fe3+ > Mn2+ > Cu2+ for the former and the latter systems, respectively, and the reasons behind this were discussed through the analysis of active species, especially hydrogen peroxide.

Visible-Light-Driven Catalytic Properties and First-Principles Study of Fluorine-Doped TiO(2) Nanotubes

Improving the photocatalytic activity and the utilization of visible light of TiO2 is the most important research topics in the photocatalytic field. To improve the photocatalytic activity of TiO2, we used chemical vapor deposition (CVD) to dope TiO2 nanotubes with fluorine. Scanning electron microscopy (SEM) images showed that the annealing temperature significantly affected the morphological integrity of TiO2 nanotubes. Upon annealing at 550 and 700 °C, the structure of F-doped TiO2 nanotubes suffered from an observable disintegration of morphological integrity. X-ray diffraction (XRD) results indicated that the F impurity retarded the anatase-rutile phase transition. Fluorine was successfully doped into TiO2 by CVD, as indicated by the X-ray photoelectron spectroscopy (XPS) results. F-doped TiO2 nanotubes showed higher photocatalytic activity. First-principles calculations suggested that the F 2p states were located in the lower-energy range of valence band (VB) and less mixed with O 2p states. It thus contributed little to the reduction of the optical band gap. This is consistent with the finding that the band gap of F-doped TiO2 is very close to that of undoped TiO2. Therefore, the higher catalytic activity of F-doped TiO2 should be attributed to the creation of surface oxygen vacancies upon F-doping, which enhances surface acidity and increases the amount of Ti3+ ions.

High Conductivity Water Treatment Using Water Surface Discharge with Nonmetallic Electrodes

Although electrohydraulic discharge is effective for wastewater treatment, its application is restricted by water conductivity and limited to the treatment of low conductivity water. For high conductivity water treatment, water-surface discharge is the preferred choice. However, the metallic electrodes are easily corroded because of the high temperature and strong oxidative environment caused by gas phase discharge and the electrochemical reaction in water. As a result, the efficiency of the water treatment might be affected and the service life of the reactor might be shortened. In order to avoid the corrosion problem, nonmetallic electrode water-surface discharge is introduced into high conductivity water treatment in the present study. Carbon-felt and water were used as the high voltage electrode and ground electrode, respectively. A comparison of the electrical and chemical characteristics showed that nonmetallic electrode discharge maintained the discharge characteristics and enhanced the energy efficiency, and furthermore, the corrosion of metal electrodes was avoided.

Characteristics of Electrode-Water-Electrode Discharge and its Application to Water Treatment

Atmospheric air discharge above the surface of water is an effective method for water treatment. The leakage current and Joule heating of water are reduced by the air gap, which raises the energy efficiency of the water treatment. However, the application of this kind of discharge is limited by a pair of conflicting factors: the chemical efficiency grows as the discharge gap distance decreases, while the spark breakdown voltage decreases as the gap distance decreases. To raise the spark breakdown voltage and the chemical efficiency of atmospheric pressure water surface discharge, both the high-voltage electrode and the ground electrode are suspended above the water surface to form an electrode-water-electrode discharge system. For this system, there are two potential discharge directions: from one electrode to another directly, and from the electrodes to the water surface. The first step in utilizing the electrode-water-electrode discharge is to find out the discharge direction transition criterion. In this paper, the discharge direction transition criterions of spark discharge and streamer discharge are presented. By comparing the discharge characteristics and the chemical efficiencies, the discharge propagating from the electrodes to the water surface is proved to be more suitable for water treatment than that propagating directly between the electrodes.

Oxidation of S(IV) in Seawater by Pulsed High Voltage Discharge Plasma with TiO2/Ti Electrode as Catalyst

Oxidation of S(IV) to S(VI) in the effluent of a flue gas desulfurization(FGD) system is very critical for industrial applications of seawater FGD. This paper reports a pulsed corona discharge oxidation process combined with a TiO2 photocatalyst to convert S(IV) to S(VI) in artificial seawater. Experimental results show that the oxidation of S(IV) in artificial seawater is enhanced in the pulsed discharge plasma process through the application of TiO2 coating electrodes. The oxidation rate of S(IV) using Ti metal as a ground electrode is about 2.0×10−4 mol L−1 min−1, the oxidation rate using TiO2/Ti electrode prepared by annealing at 500°C in air is 4.5×10−4 mol L−1 min−1, an increase with a factor 2.25. The annealing temperature for preparing TiO2/Ti electrode has a strong effect on the oxidation of S(IV) in artificial seawater. The results of in-situ emission spectroscopic analysis show that chemically active species (i.e. hydroxyl radicals and oxygen radicals) are produced in the pulsed discharge plasma process. Compared with the traditional air oxidation process and the sole plasma-induced oxidation process, the combined application of TiO2 photocatalysts and a pulsed high-voltage electrical discharge process is useful in enhancing the energy and conversion efficiency of S(IV) for the seawater FGD system.

Inactivation of Bacteria in Oil Field Injected Water by a Pulsed Plasma Discharge Process

Pulsed plasma discharge was employed to inactivate bacteria in the injection water for an oil field. The effects of water conductivity and initial concentration of bacteria on elimination efficiency were investigated in the batch and continuous flow modes. It was demonstrated that Fe2+ contained in injection water could enhance the elimination efficiency greatly. The addition of reducing agent glutathione (GSH) indicated that active radicals generated by pulsed plasma discharges played an important role in the inactivation of bacteria. Moreover, it was found that the microbial inactivation process for both batch and continuous flow mode well fitted the model based on the Weibulls survival function.

Catalysis-assisted Decomposition of Aqueous 2, 4, 6-Trinitrotoluene by Pulsed High Voltage Discharge Process

TNT removal by the combination of high voltage pulsed discharge plasma and different catalysts with various concentration was investigated. In the case of 9.8 kV peak pulsed voltage and 120Hz pulsed frequency, the degradation rate of 30 mg/L TNT solution with pH value of 6.8 reached 66.1% after 60 min treatment. It was showed that Fe2+ had a remarkable catalytic effect on degradation of TNT. When the concentration of Fe2+ was 0.15 mmol/L, it promoted the TNT degradation, and 84.0% removal was obtained. However, addition of H2O2 into TNT solution inhibited the TNT removal, especially at the initial reaction. After 120min treatment, the degradation efficiency of 100mg/L TNT was 87%, and COD reduced 80%. The results indicated that TNT could be efficiently removed by high voltage pulsed discharge plasma.