Photoelectrocatalytic Technology Research Articles

Novel ZnFe2O4/TiO2/flake graphite composite as particle electrodes for efficient photoelectrocatalytic degradation of rhodamine B in water.

A novel ZnFe2O4/TiO2/flake graphite composite material was synthesized and used as particle electrodes in a photoelectrocatalytic (PEC) system to investigate the degradation of rhodamine B as a model dye pollutant in water. Results showed that a PEC process with the new composite evidently led to enhanced degradation of rhodamine B due to a synergistic effect of photocatalysis and electrocatalysis. Operating variables including electrolyte concentration, applied cell voltage, air flow, composite dosage, solution pH, and dye concentration were also found to play important roles in rhodamine B removal. A 99.0% removal efficiency was observed within 30 min of treatment under optimum conditions of 0.01 mol/L Na2SO4, applied cell voltage of 15 V, air flow of 20 mL/min, composite dosage of 10 g/L, solution pH of 2, and rhodamine B concentration of 20 mg/L, with a pseudo-first-order rate constant of 0.278 min-1. These findings could provide new insights into the development of efficient PEC technologies on degradation of residual dyes in water.

Soft-sensing modeling of chemical oxygen demand in photo-electro-catalytic oxidation treatment of papermaking wastewater

Photo-electro-catalytic (PEC) oxidation has been widely recognized as an effective technology for advanced treatment of papermaking wastewater. To optimize the oxidation process, it is important of monitor continuously the chemical oxygen demand (COD) of inflow and outflow wastewater. However, online COD sensors are expensive difficult to maintain, and therefore COD is usually analyzed off-line in laboratories in most cases. The objective of this study is to develop an inexpensive method for on-line COD measurement. The oxidation-reduction potential (ORP), pH, and dissolved oxygen (DO) of wastewater were selected as the key parameters, which consists of four different types of artificial neural network (ANNs) methods:multi-layer perceptron neural network (MLP), back propagation neural network (BPNN), radial basis neural network (RBNN) and generalized regression neural network (GRNN). These parameters were applied in the development of COD soft-sensing models. Six batches of papermaking wastewater with different pollution loads were treated with PEC technology over a period of 90 minutes, and a total of 546 data points was collected, including the on-line measurements of ORP, pH and DO, as well as off-line COD data. The 546 data points were divided into training set (410 data, 75% of total) and validation set (136 data, 25% of total). Four statistical criteria, namely, root mean square error (RMSE), mean absolute error (MAE), mean absolute relative error (MARE), and determination coefficient (R²) were used to assess the performance of the models developed with the training set of data. The comparison of results for the four ANN models for COD soft-sensing indicated that the RBNN model behaved most favorably, which possessed precise and predictable results with R²=0.913 for the validation set. Lastly, the proposed RBNN model was applied to a new batch of PEC oxidation of papermaking wastewater, and the results indicated that the model could be applied successfully for COD soft-sensing for the wastewater.

Removal of COD and colour in real pharmaceutical wastewater by photoelectrocatalytic oxidation method

In this study, TiO2/Ni photo-anode and multi-walled carbon nano-tubes (MWCNTs) air cathode were prepared by the dip-coating method, and the photoelectrocatalytic degradation of real pharmaceutical wastewater was investigated in the self-made reactor. The combination of the TiO2/Ni electrode and MWCNTs air cathode was adopted to treat the pharmaceutical wastewater by the process of photoelectrocatalysis. Various operational parameters to achieve optimum efficiency of this photoelectrocatalytic degradation system are presented, such as applied bias voltage, NaCl concentration, pH and different degradation methods. Under the optimal conditions, the removal of chemical oxygen demand (COD) and colour are 93.5% and 78.5% respectively. The possible roles of the anode–cathode on the reactions and the probable mechanisms of effect were also discussed. The photoelectrocatalytic technology can be used for the long-term treatment of real pharmaceutical wastewater.

Photoelectrocatalytic technologies for environmental applications

This paper summarizes recent research works dealing with the development of photoelectrocatalytic oxidation technologies combining both electrolytic and photocatalytic processes. Photoelectrocatalytic technologies have received particular attention due to their potential and effectiveness in the photodegradation of refractory organic and microbial pollutants present in water and wastewater. Here, titanium dioxide (TiO2) plays the most important role compared to other semiconductor photocatalysts (CdS, ZnO, SnO2, etc.) due to its excellent chemical and physical properties. The recombination of the photogenerated electrons and holes is the main factor that generally limits the application of photocatalytic processes (PCPs) in the environmental field. Considerable efforts have been made to increase the photocatalytic efficiency and decrease the charge recombination by means of photoelectrocatalytic processes (PECPs), also referred to as electrochemically assisted photocatalytic processes, which consists of applying an external potential on photocatalysts. This paper deals with the mechanism of photoelectrocatalytic processes, the characteristics and methods for preparing a TiO2 electrode, the irradiation sources, and the types of reactors used. Moreover, the key factors affecting the photoelectrocatalytic oxidation efficiency are discussed, including the applied electrical potential, light intensity, pH, dissolved oxygen concentration, electrolyte concentration, and temperature. Finally, the paper emphasizes the recent applications of photoelectrocatalytic processes and suggests new research directions for the development of this promising technology.

Approach to a pulse photoelectrocatalytic process for the degradation of organic pollutants

AbstractAg–TiO2 composite film was supported on indium–tin oxide glass (ITO) by a dip‐coating and subsequent photodeposition procedure. The composite film was employed as the photoanode for photoelectrocatalytic (PEC) degradation of Acid Orange II. The degradation efficiency for the PEC process on the Ag–TiO2/ITO electrode with a 0.8 V anodic bias is significantly higher than that for a photocatalytic process on Ag–TiO2/ITO film or for a PEC process on a neat TiO2/ITO photoanode. A new PEC technology with a pulse anodic bias was also proposed in order to solve the problem of the loss of deposited Ag from the Ag–TiO2/ITO. It was found that the PEC process with a 4.2 V pulse anodic bias could much more efficiently degrade Acid Orange II than that with a constant anodic bias of 0.8 V or 4.2 V. Moreover, when the duration of the open and close circuit time was identical, the treatment efficiency was observed to be optimal. Copyright © 2003 Society of Chemical Industry

Photoelectrochemical performance of Ag–TiO 2/ITO film and photoelectrocatalytic activity towards the oxidation of organic pollutants

Ag–TiO 2 composite film was supported on indium–tin oxide glass (ITO) by a dip-coating and subsequent photodeposition procedure. The composite film was characterised by UV-Vis diffuse reflectance spectra, X-ray reflection diffraction (XRD) spectra, scanning electron microscope (SEM) and photoelectrochemical measurement. It was used as a photoanode in a two-compartment photoelectrochemical cell to investigate the feasibility of a hybrid technology of Ag deposition combined with the application of an external electric field. The experimental results show that the combination has an apparent additive effect with respect to suppressing the recombination between the photogenerated charge carriers and enhancing the photoelectrocatalytic (PEC) oxidation of formic acid. A primary approach to a pulse PEC technology presents the possibility that the Ag–TiO 2/ITO film electrode is performed at an anodic bias over the oxidation potential of the deposited Ag.