Hongchong Chen

Efficient electricity production and simultaneously wastewater treatment via a high-performance photocatalytic fuel cell

A great quantity of wastewater were discharged into water body, causing serious environmental pollution. Meanwhile, the organic compounds in wastewater are important sources of energy. In this work, a high-performance short TiO(2) nanotube array (STNA) electrode was applied as photoanode material in a novel photocatalytic fuel cell (PFC) system for electricity production and simultaneously wastewater treatment. The results of current work demonstrate that various model compounds as well as real wastewater samples can be used as substrates for the PFC system. As a representative of model compounds, the acetic acid solution produces the highest cell performance with short-circuit current density 1.42 mA cm(-2), open-circuit voltage 1.48 V and maximum power density output 0.67 mW cm(-2). The STNA photoanode reveals obviously enhanced cell performance compared with TiO(2) nanoparticulate film electrode or other long nanotubes electrode. Moreover, the photoanode material, electrolyte concentration, pH of the initial solution, and cathode material were found to be important factors influencing the system performance of PFC. Therefore, the proposed fuel cell system provides a novel way of energy conversion and effective disposal mode of organics and serves well as a promising technology for wastewater treatment.

Enhanced Photoelectrochemical Properties of Cu2O-loaded Short TiO2 Nanotube Array Electrode Prepared by Sonoelectrochemical Deposition

Copper and titanium remain relatively plentiful in earth crust. Therefore, using them in solar energy conversion technologies are of significant interest. In this work, cuprous oxide (Cu2O-modified short TiO2 nanotube array electrode was prepared based on the following two design ideas: first, the short titania nanotubes obtained from sonoelectrochemical anodization possess excellent charge separation and transportation properties as well as desirable mechanical stability; second, the sonoelectrochemical deposition technique favours the improvement in the combination between Cu2O and TiO2 nanotubes, and favours the dispersion of Cu2O particles. UV-Vis absorption and photo- electronchemical measurements proved that the Cu2O coating extended the visible spectrum absorption and the solar spectrum-induced photocurrent response. Under AM1.5 irradiation, the photocurrent density of the composite electrode (i.e. sonoelectrochemical deposition for 5 min) was more than 4.75 times as high as the pure nanotube electrode. Comparing the photoactivity of the Cu2O/TiO2 electrode obtained using sonoelectrochemical deposition with others that synthesized using plain electrochemical deposition, the photocurrent density of the former electrode was ∼2.2 times higher than that of the latter when biased at 1.0 V (vs. Ag/AgCl). The reproducible photocurrent response under intermittent illumination demonstrated the excellent stability of the composite electrode. Such kind of composite electrode material will have many potential applications in solar cell and other fields.

Assessment of a COD analytical method based on the photoelectrocatalysis of a TiO2 nanotube array sensor

This work mainly describes assessment of a photoelectrocatalytic method to determine chemical oxygen demand (COD) in refractory and low-concentration organics using a highly effective TiO2 nanotube array sensor in a thin-cell reactor. Twenty organic compounds, including recalcitrant organics from six categories, were used as model compounds to evaluate the accuracy of the method. The correlation between theoretical oxygen demand (ThCOD) and response COD was studied. The linear regression equation COD = α × ThCOD was obtained, where α is the slope of the regression equation representing the conformity between the actual COD value and the theoretical value. Results of the photoelectrochemical method used in the present paper show excellent conformity between ThOD and response COD for all model compounds, with α and correlation coefficient r values of 0.9903 and 0.9901, respectively. However, results using the standard dichromate method show poor conformity, with α and r values of only 0.8359 and 0.8213, respectively. Hence, we conclude that this photoelectrocatalytic method is superior to the dichromate method for determination of COD in refractory and low-concentration organics. The photoelectrocatalytic method possesses a detection limit of 0.5 mg L−1, while dichromate COD values lower than 20 mg L−1 could not accurately be detected, with the exception of sugars.

Characterization and Mechanism of the Photoelectrocatalytic Oxidation of Organic Pollutants in a Thin-Layer Reactor

Abstract The characterization and mechanism of the photoelectrocatalytic oxidation of a typical endocrine disrupting chemical, bisphenol-A (BPA), on TiO2 nanotube arrays (TNAs) were investigated using a thin-layer reactor where BPA was rapidly and exhaustively oxidized. Physical parameters such as the photocurrent, the initial peak photocurrent, the exhaustive charge quantity, and the blank photocurrent were found to be related to the degradation rate and the reaction mechanism. The Langmuir equation was used to fit the relationship between the initial peak photocurrent response and the BPA concentration indicating the proportionality between the photocurrent responses and the adsorbed organic concentration. A first-order exponential decay fitting of transient photocurrent profiles indicated the validity of first-order organic degradation kinetics for the photoelectrocatalysis. These relationships were found to be valid for many other organics including urea, glycol, glumatic acid, tartaric acid, methanol, and diethanolamine. The quantitative relationship found in this study provides a theoretical foundation for the real-time determination of the degradability of toxic organics by photoelectrocatalytic sensors.

Adsorption and photoelectrocatalytic characteristics of organics on TiO2 nanotube arrays

The adsorption and photoelectrocatalytic characteristics of four different kinds of organic compounds (d-fructose, glutamic acid, fumaric acid, and nicotinic acid) on TiO2 nanotube arrays (TNAs) were investigated using a thin-layer cell, wherein the compounds were rapidly and exhaustively oxidized. The photogenerated current–time (Iph–t) profiles were found to be related to the adsorption, the degradation rate, and the reaction mechanism. The relationship between the initial organic compounds concentrations and photocurrent peaks (I0ph) fit the Langmuir type adsorption model well, thereby confirming that the adsorption of organic compounds on TNAs was via monolayer adsorption. The adsorption equilibrium constant was obtained from the Langmuir equation. The results indicate that the adsorption performance of the organic compounds on TNAs were in the following order: nicotinic acid < d-fructose < glutamic acid < fumaric acid. The degradation of organic compounds on TNAs was classified as either easy or difficult based on the time of complete mineralization (tend) of the organic samples under an equal holes consumption; the degree of degradation were as follows: fumaric acid < d-fructose < glutamic acid < nicotinic acid. The photoelectrocatalytic characteristics of the organic compounds on TNAs were also discussed by analyzing the changes in the Iph–t profiles.

Photoelectrocatalytic Performance of Benzoic Acid on Nanotube Array Electrodes

The photoelectrocatalytic performance of benzoic acid on TiO2 nanotube array electrodes was investigated. A thin-cell was used to discuss the effect of the bias voltage, illumination intensity, and electrolyte concentration on the photoelectrocatalytic degradation efficiency of benzoic acid. The photogenerated current-time (I-t) profiles were found to be related to the adsorption and the degradation process. The relationship between the initial concentration and the photocurrent peaks () fits the Langmuir-type adsorption model, thus confirming that the adsorption of benzoic acid on TiO2 nanotube arrays (TNAs) was single monolayer adsorption. At low concentrations, the I-t profiles simply decay after the initial transient peak due to the sufficient holes on the TNAs which would oxidize the benzoic acid quickly. However, the I-t profiles varied with increasing benzoic acid concentrations because the rate of diffusion in the bulk solution and the degradation of the intermediate products affect the photoelectrocatalysis on the electrode surface.