Mingfang Li

Electrosorption-promoted Photodegradation of Opaque Wastewater on A Novel TiO2/Carbon Aerogel Electrode

A novel electrosorption-photocatalysis synergistic electrode of TiO(2)/carbon aerogel (TiO(2)/CA) is prepared. The thermal stability and dispersion of the anatase TiO(2) particles are well facilitated by the porous and discontinuous microstructure of CA. The degradation experiments show that the TiO(2)/CA material is not only a good photocatalyst but also an excellent electrosorptive electrode. The TiO(2)/CA is easily molded to an agglomerate electrode. The opaque wastewater with dyestuff is degraded effectively by the electrosorption-promoted photocatalytic process on this electrode. For the simulated methylene blue (MB) wastewater (150 mg L(-1)), the rate constant of MB degradation in the electro-assisted photocatalytic process with the conventional ITO-supported TiO(2) (TiO(2)/ITO) is 0.55 x 10(-3) min(-1) and that the electrosorption-promoted photocatalysis with TiO(2)/CA is 10.27 x 10(-3) min(-1), which is 18 times the former. In the electrosorption-promoted photocatalytic process with TiO(2)/CA, the energy consumption removing per unit TOC is only 15% of that in the electro-assisted photocatalysis with TiO(2)/ITO, because the electrosorption is a nonfaradic process irrelative to any electron transfer and requires very low consumption. This study provides a new method for exploring highly efficient electrosorption-promoted photocatalytics technology in the treatment of opaque wastewater.

Applicability of boron-doped diamond electrode to the degradation of chloride-mediated and chloride-free wastewaters

The electrochemical degradation of chloride-mediated and chloride-free dye wastewaters was investigated on a boron-doped diamond (BDD) electrode in comparison with that on a dimensionally stable anode (DSA), and the applicability of BDD electrode to the degradation of these two kinds of wastewaters was explored. In chloride-free wastewater, the electrochemical degradation efficiency of dye on BDD electrode was much higher than that on DSA, with a chemical oxygen demand (COD) removal of 100% and 26% for BDD and DSA, respectively. In chloride-mediated dye wastewater, COD removal was faster than that in chloride-free wastewater on both BDD and DSA electrodes with COD removal efficiencies higher than 95%, whereas the rate of COD removal on DSA was faster than that on BDD electrode. The investigation indicates that DSA is more suitable than BDD electrode in degradation of originally chloride contained dye wastewaters for the sake of energy and time saving. However, for chloride-free dye wastewaters, with the aim of environmental protection, BDD electrode is more appropriate to realize complete mineralization. At the same time, the secondary pollution can be avoided.

Selective photoelectrocatalytic degradation of recalcitrant contaminant driven by an n-P heterojunction nanoelectrode with molecular recognition ability.

With in situ molecular imprinting technique, a novel nanoelectrode (MI, n-P)-TiO(2) with n-P heterojunction and molecular recognition ability was fabricated by liquid phase deposition at low temperature. Using bisphenol A (BPA) as template, the spindle-like TiO(2) particles 40-80 nm in size compactly grew on the boron-doped diamond (BDD) substrate. Several spectroscopy measurements demonstrate that the BPA molecules were successfully imprinted on the TiO(2) matrix and numerous specific recognition sites to template were formed after calcination. The transient photocurrent response experiments have confirmed that the (MI, n-P)-TiO(2) nanoelectrode displays outstanding photoelectrocatalytic (PEC) activity and selectivity. The (MI, n-P)-TiO(2) is further employed in degrading the mixture containing BPA and interference 2-naphthol (2-NP). After 2 h, BPA removal reaches 97%, and corresponding kinetic constant is 1.76 h(-1), which is 4.6 times that of 2-NP removal even if 2-NP is much more concentrated. On the electrode without molecular imprint, the removal rate constants of BPA and 2-NP approximately equal, only about 0.5 h(-1). The results indicate that selective PEC oxidation can be realized readily on the (MI, n-P)-TiO(2) nanoelectrode due to the synergetic effects including strong recognition adsorption, formation of n-P heteojunction, and external electrostatic field. The effect of formation of n-P heterojunction on the enhanced PEC performances is also discussed.

The mechanism and kinetics of ultrasound-enhanced electrochemical oxidation of phenol on boron-doped diamond and Pt electrodes.

The research on ultrasound (US) enhanced electrochemical oxidation of Phenol (Ph) on boron-doped diamond (BDD) and Pt electrodes is studied. The enhancement by US on BDD is much greater than for Pt. With the assistance of US, the degradation rate and current efficiency on BDD are increased by 301% and 100%, respectively, while those on Pt are 51% and 49%. The difference of the enhancement on these two electrodes is caused by the fact that mass transport, adsorption amount and electrode reaction affected by US on BDD are different from those of Pt. The kinetics investigation on intermediates formed during electrochemical degradation show that the variety of intermediates produced on BDD is less than for Pt. In the presence of US, on both electrodes, no change occurred to the amounts of the intermediate species. However, time for intermediates to reach the highest concentration is cut down. This effect for degradation of Ph on BDD is more obvious than for Pt. The present research indicates that BDD is suitable for degradation of Ph by US assisted electrochemical oxidation.

A simple, stable and picomole level lead sensor fabricated on DNA-based carbon hybridized TiO2 nanotube arrays.

An electrochemical lead sensor is developed on DNA-based vertically aligned conductive carbon hybridized TiO(2) nanotube arrays (DNA/C-TiO(2) NTs). The designed DNA/C-TiO(2) NTs sensor is superior in determination of lead with high sensitivity, selectivity and repeatability, as well as wide pH adaptability, fast electro-accumulation capacity for lead and easy regeneration. Such remarkable characteristics for lead sensing are attributed to the immobilization of abundant target biomolecules, DNA, and the enhanced bioelectrochemical activity. The controllable carbon hybridization of the TiO(2) NTs increases the conductivity of the electrode, while retaining the tubular structure, biocompatibility, and hydrophilicity. The results show that the lead sensor possesses a wide linear calibration ranging from 0.01 to 160 nM with the detection limitation at a picomole level (3.3 pM). The application of the present sensor is realized for determination of Pb(2+) in real water samples.

Facile electrocatalytic redox of hemoglobin by flower-like gold nanoparticles on boron-doped diamond surface.

The flower-like gold nanoparticles together with spherical and convex polyhedron gold nanoparticles were fabricated on boron-doped diamond (BDD) surface by one-step and simple electrochemical method through easily controlling the applied potential and the concentration of HAuCl(4). The recorded X-ray diffraction (XRD) patterns confirmed that these three shapes of gold nanoparticles were dominated by different crystal facets. The cyclic voltammetric results indicated that the morphology of gold nanoparticles plays big role in their electrochemical behaviors. The direct electrochemistry of hemoglobin (Hb) was realized on all the three different shapes of nanogold-attached BDD surface without the aid of any electron mediator. In pH 4.5 acetate buffer solutions (ABS), Hb showed a pair of well defined and quasi-reversible redox peaks. However, the results obtained demonstrated that the redox peak potential, the average surface concentration of electroactive heme, and the electron transfer rates of Hb are greatly dependent upon the surface morphology of gold nanoparticles. The electron transfer rate constant of hemoglobin over flower-like nanogold/BDD electrode was more than two times higher than that over spherical and convex polyhedron nanogold. The observed differences may be ascribed to the difference in gold particle characteristics including surface roughness, exposed surface area, and crystal structure.

Hydrothermally enhanced electrochemical oxidation of high concentration refractory perfluorooctanoic acid.

A green hydrothermally enhanced electrochemical oxidation (HTEO) technique is developed to treat the high concentration refractory perfluorooctanoic acid (PFOA) wastewater on boron-doped diamond (BDD) film electrode. Results show that HTEO can demonstrate higher degradation efficiency for PFOA than the normal electrochemical oxidation (EO) process, with the removal of PFOA, total organic carbon (TOC), and organic fluorine in the HTEO process increasing by 1.1, 1.8, and 2.1 times, respectively. The kinetics study indicates that the degradation of PFOA follows a first-order reaction in the HTEO process with the apparent reaction rate constant 3.1 times higher than that in the EO process. The higher degradation efficiency of PFOA is due to the hydrothermal enhancement in electrochemical properties of the electrode and solution. Compared with EO, during the HTEO process, the conductivity and ionic migration rate of the solution is improved by 540% and 60%, respectively. In addition, the Tafel slope is increased to 343 from 279 mV dec(-1), indicating an inhibition effect of oxygen evolution reaction and a more effective oxidation of PFOA. In particular, the hydrothermal condition promotes a high formation rate of hydroxyl radical with the concentration almost 2 times of that in EO, which is considered the inner factor leading to the higher degradation efficiency. The density functional theory simulations demonstrate that the nonterminal C-C bonds in the main carbon chain can be easily destructed in the hydrothermal condition, as confirmed by the experimental detection of intermediates of C(5)F(11)COOH, C(4)F(9)COOH, C(3)F(7)COOH, C(2)F(5)COOH, CF(3)COOH, and some dicarboxylic acids. As a result, a reaction pathway is tentatively proposed.

Fabrication of a novel atrazine biosensor and its subpart-per-trillion levels sensitive performance.

The present study describes an atrazine biosensor with the detection limit of 0.1 part-per-trillion (ppt). The atrazine biosensor is fabricated on tyrosinase-immobilized vertical growth TiO(2) nanotubes (Tyr/TiO(2)-NTs), based on the inhibition of tyrosinase by atrazine. The designed Tyr/TiO(2)-NTs present excellent applicability in atrazine determination, with high sensitivity and stability, and rapid response. The outstanding sensing characteristics for atrazine is attributed to the appropriate bioelectrochemical interface of Tyr/TiO(2)-NTs, resulting from the preponderant tubular structure, excellent biocompatibility, and hydrophilicity of TiO(2)-NTs. The atrazine biosensor possesses a wide detection range from 0.2 ppt to 2 part-per-billion (ppb). The practical application of the biosensor is realized for the determination of atrazine and the analysis of its transport in soil samples. A new method for determination of atrazine in soil samples is thus established, which greatly simplifies the preparation procedure of sample and is helpful to evaluate the pollution risk of atrazine to soil, groundwater, and surface water.

Photoelectrocatalytic properties of a vertically aligned Ti-W alloy oxide nanotubes array and its applications in dye wastewater degradation

A highly ordered and vertically oriented array of nanotubes (NTs) of mixed oxide was prepared in situ by Ti-W alloy anodization. Compared with the traditional TiO2 NTs, the photoelectrocatalytic activity of the resulting Ti-W-O NTs was greatly enhanced. Results indicated a narrowing of the band gap from 3.2 eV for pristine TiO2 to 2.7 eV for Ti-W-O NTs. Under irradiation with 254 and 365 nm UV lights, Ti-W-O NTs showed much higher photoelectroconversion efficiency (η) than TiO2 NTs and TiO2-WO3 coating. The η254 and η365 on Ti-W-O NTs reached as high as 51.8% and 57.0% respectively, four to five times those on TiO2 NTs and TiO2-WO3 coating. As a result of its narrow band gap energy and fast electron–hole separation, Ti-W-O NTs presented outstanding photoelectrocatalytic features. The electrochemically assisted photocatalytic degradation of highly concentrated Rhodamine 6G wastewaters was studied. The results showed that the rates of colour and TOC removal were much higher on Ti-W-O NTs than on TiO2 NTs and TiO2-WO3 coating. The photocatalytic material obtained by alloy anodization is of significance in the advanced oxidation of environmental pollutants.

Enhanced electron transfer by bovine serum albumin covalently attached to glassy carbon electrode and its application to determination of hydroquinone

Bovine serum albumin (BSA) was covalently attached to glassy carbon electrode (GCE) surface by the electrochemical method. An enhancement for the redox of hydroquinone (HQ) on BSA/GCE was confirmed by cyclic voltammetry and electrochemical impedance spectroscopy measurement. The electron transfer rate constant (k s) on the BSA/GCE electrode is almost three orders of magnitude higher than that on bare GCE. The enhancing effect can be attributed to the electrostatic force between the positively charged HQ and negatively charged BSA. It is found that the enhanced redox process of HQ can be used to determine HQ sensitively. The oxidation current can reach 95% of its steady-state value within 30 s. The linear range for HQ determination is from 2.5 × 10−8 M to 1.325 × 10−6 M with a detection limit of 8.6 × 10−9 M at a signal-to-noise ratio of 3. The study may provide a simple, rapid and sensitive method for determination of HQ which is present in the natural environment and in chemical industry effluent.