Pengtao Sheng

A novel method for the preparation of a photocorrosion stable core/shell CdTe/CdS quantum dot TiO2 nanotube array photoelectrode demonstrating an AM 1.5G photoconversion efficiency of 6.12%

Type-II core/shell CdTe/CdS quantum dots (QDs) are assembled onto TiO2 nanotube array (NTA) films using a bi-functional linker molecule with the help of a hydrothermal method coupled with successive ionic layer adsorption and reaction process. Spatial separation of the electron and hole wave functions within the core/shell heterostructured nanocrystals appears to result in an extended charge separation state, resulting in a significant increase in photocurrent and excellent device stability. When only CdS or CdTe QDs are used as the sensitizer, the largest photocurrent densities are 1.31 mA cm−2 and 1.23 mA cm−2, respectively. For the core/shell CdTe/CdS QDs sensitized TiO2 NTA photoelectrodes the photocurrent density increases to ≈9.17 mA cm−2, dramatically larger than the values obtained with only one sensitizer. The core/shell CdTe/CdS QDs sensitized TiO2 NTA photoelectrodes provide a remarkable photoelectrochemical cell efficiency of 6.12%. To the best of our knowledge this photoconversion efficiency is the highest in the field of QD-sensitized photoelectrodes. A corresponding hydrogen evolution rate as high as 1560 μmol h−1 W−1 was achieved.

Label-free photoelectrochemical immunosensor based on CdTe/CdS co-sensitized TiO2 nanotube array structure for octachlorostyrene detection

An octachlorostyrene (OCS) photoelectrochemical (PEC) immunosensor was developed by cross-linking anti-OCS antibody onto a CdTe/CdS-sensitized TiO2 nanotube arrays (NTAs). The anti-OCS polyclonal antibody was developed in rabbit as a result of immunization with BSA-OCS hapten conjugate. TiO2 NTAs were immobilized firstly with hydrothermally synthesized CdTe quantum dots (QDs), and then CdS which filled the spaces within the CdTe-TiO2 composite and encapsulated the CdTe QDs, forming an ideal stepwise bandedge structure, which benefited the light harvesting. The PEC immunosensor therefore shows high specificity and high sensitivity with a limit of detection of 2.58 pM, and a linear range from 5 pM to 50 nM. The testing time is 4 min. The analysis of river water reveals that the proposed sensor can be applied in the analysis of OCS in real water samples without complicated pre-treatments.

Fluorescence immunoassay of octachlorostyrene based on Fo¨rster resonance energy transfer between CdTe quantum dots and rhodamine B

Octachlorostyrene (OCS), a persistent and bioaccumulative toxicant (PBT), was assayed by fluorescence immunoassay based on the Förster resonance energy transfer (FRET) between CdTe quantum dots (QDs) and rhodamine B-labeled OCS (RB-OCS). Anti-OCS antibody produced in this lab is adsorbed on a microtiter plate. The RB-OCS competes with OCS for the highly specific immunoreaction with the anti-OCS antibodies adsorbed on the microtiter plate. The solution is then isolated and mixed with CdTe QDs as fluorescent donor which excite the emission of RB-OCS through FRET. As a result, the emission of CdTe QDs at 530 nm decreases, whereas the emission of RB-OCS at 580 nm increases. The ratio of fluorescence intensity at 580 nm to that at 530 nm is proportional to the RB-OCS concentration at a fixed CdTe QDs concentration, and consequently proportional to the OCS concentration. Selective and sensitive responses to OCS are achieved with a linear range of 8-80 nM and a LOD of 3.8 nM. Because OCS is quantified based on the fluorescence ratio, the sensor-to-sensor difference is greatly eliminated, making the proposed method a useful approach for in site scanning of OCS.

Surface enhanced Raman scattering detecting polycyclic aromatic hydrocarbons with gold nanoparticle-modified TiO2 nanotube arrays

A metal-semiconductor heterojunction material was fabricated by photocatalytically depositing Au nanoparticles (NPs) inside titania nanotubes, and have been applied, for the first time, to the surface enhanced Raman (SER) scattering detection of polycyclic aromatic hydrocarbons (PAHs). Due to the nanotubular structure of the Au-NPs/TiO2 nanotubes (NTs), a localized surface plasmon resonance is generated within the Au-NPs/TiO2 NTs, which results in an enhanced three-dimensional electromagnetic field. Raman enhancement occurs when the PAH molecules are spatially confined within the zone of the Au-NPs/TiO2 NTs. The achieved detection limit of 12.6 nM, by utilizing a low-cost small Raman spectrometer, is comparable to the published values obtained with surface enhanced Raman scattering. The recovery rates measured with different water samples range from 89.97% to 116.2%.

Stable core/shell CdTe/Mn-CdS quantum dots sensitized three-dimensional, macroporous ZnO nanosheet photoelectrode and their photoelectrochemical properties.

A novel photoelectrode based on ZnS/CdTe/Mn-CdS/ZnS-sensitized three-dimensional macroporous ZnO nanosheet (NS) has been prepared by electrodeposition and successive ion layer adsorption and reaction (SILAR) method. The photoelectrode performances were significantly improved through the coupling of the core/shell CdTe/Mn-CdS quantum dots (QDs) with ZnO NS, and the introduction of the ZnS layer as a potential barrier. The photocurrent density systematically increases from ZnO NS (0.45 mA/cm(2)), CdTe/Mn-CdS/ZnO NS (4.98 mA/cm(2)), to ZnS/CdTe/Mn-CdS/ZnS/ZnO (6.23 mA/cm(2)) under the irradiation of AM 1.5G simulated sunlight. More important, the ZnS/CdTe/Mn-CdS/ZnS-sensitized ZnO NS photoelectrode provides a remarkable photoelectrochemical cell efficiency of 4.20% at -0.39 V vs Ag/AgCl.

A CdS/ZnSe/TiO2 nanotube array and its visible light photocatalytic activities.

A novel CdS/ZnSe/TiO2 nanotube array (NTA) photoelectrode was prepared by deposition of ZnSe nanoparticles (NPs) using pulse electrodeposition technique onto a TiO2 NTA. By successive ion layer adsorption and reaction (SILAR), CdS quantum dots (QDs) deposit onto a ZnSe/TiO2 NTA photoelectrode. The as-prepared CdS/ZnSe/TiO2 NTA photoelectrode performance is significantly improved, which not only greatly extends spatial separation of charges, but also enhance the utilization efficiency of visible-light. This system exhibits excellent charges transport property. The maximum photocurrent density of an 8.25mAcm(-2) was observed in the CdS/ZnSe/TiO2 NTA photoelectrode, which is 37.5, 15.86 and 1.56 times higher than bare TiO2 NTA, ZnSe/TiO2 NTA, and CdS/TiO2NTA photoelectrodes, respectively. The photocatalytic activity of CdS/ZnSe/TiO2 NTA is tested by the degradation of methyl orange (MO) in distilled water under solar light irradiation of 100mW/cm(2). Within about 120min of irradiation, 90.05% MO are removed.

Development of a high performance hollow CuInSe2 nanospheres-based photoelectrochemical cell for hydrogen evolution

Hollow chalcopyrite CuInSe2 nanospheres are prepared by colloidal synthesis, for the first time, and assembled inside TiO2 nanotube arrays (NTAs) as a high performance photocatalyst for hydrogen evolution. In order to improve the charge separation, we engineer the CuInSe2-based photoelectrode with a novel strategy: thin layer ZnS (pre-treatment), hollow CuInSe2 nanocrystals, Mn-doped CdS, and thin layer ZnS (post-treatment) are assembled onto TiO2 NTAs in sequence. The Mn–CdS shell, closely packed around the earlier-modified CuInSe2 nanocrystals, provides high surface coverage to passivate surface states and enhance light absorption intensity. Double ZnS layers as a quasi-quantum well yield much longer electron diffusion length favoring a high photoresponse. Cyclic voltammetry (CV) is used to confirm the stepwise conduction band edge and electrochemically active surface areas. A type II-like core/shell heterojunction model is proposed to elucidate the charge transfer mechanism. Electrochemical impedance spectroscopy (EIS) and open-circuit dark–light–dark photovoltage response support a two-channel charge transport mechanism in this type of photoelectrode. Photoluminescence (PL) spectroscopy indicates a dramatically reduced electron transfer from TiO2 NTAs to the sensitizer. The saturated short circle photocurrent achieved by the quantum well structure photoelectrode under illumination of AM 1.5 (100 mW cm−2) is 22.4 mA cm−2. The corresponding measured hydrogen evolution rate is 7.93 ml cm−2 h−1.

Multi-functional CuO nanowire/TiO2 nanotube arrays photoelectrode synthesis, characterization, photocatalysis and SERS applications.

Vertically aligned single crystalline CuO nanowire arrays (NWs) grown directly on TiO2 nanotube arrays (NTAs) supporting by Ti foil have been successfully fabricated using facile thermal oxidation of Cu nanocrystals in static air. CuO NWs growth behavior dependent on parent Cu nanocrystals sizes has been well investigated. Mass transport channel of Cu ions in horizontal and vertical for supporting CuO NWs diameter and length changes has been confirmed through a novel step-by-step surface diffusion process. CuO NWs, nano-mushrooms and nanosheets can be easily obtained by varying growth conditions. After photocatalytic synthesis of snow-like Ag nanocrystals upon CuO NWs/TiO2 NTAs, the hybrid photoelectrode exhibits superior catalytic property and detection sensitivity, which can clean themselves by photocatalytic degradation of RhB molecules adsorbed to the substrate under irradiation using surface enhanced Raman scattering (SERS) detection, a recycling can been achieved.

CdS/ZnIn2S4/TiO2 3D-heterostructures and their photoelectrochemical properties

We describe the synthesis and application of a three-dimensional (3D) CdS quantum dot/ZnIn2S4 nanosheet/TiO2 nanotube array (CdS/ZnIn2S4/TiO2) heterostructured material architecture. TiO2 nanotube arrays (TiO2 NTAs) are used as the synthetic template, subsequently sensitized using hydrothermal and successive ion layer adsorption and reaction (SILAR) techniques. The described synthesis approach offers a powerful technique in the design of 3D heterostructure systems. Under AM1.5G illumination, the 3D CdS/ZnIn2S4/TiO2 samples generate a photocurrent of approximately 4.3 mA cm−2, with a photoconversion efficiency of 2%. Samples are tested for their ability to photocatalytically degrade target agents; it is noteworthy that after 90 min illumination 100% of 2,4-dichlorophenoxyacetic acid (2,4-D) is removed.

Advance in the detection techniques of persistent organic pollutants

Persistent organic pollutants can be transported long distances through various environmental media (atmosphere, water, organisms, etc.) with bio-accumulating, toxic, mutagenic, and carcinogenic, and highly toxicserious harm to human health and the environment. Determination of these chemicals in the natural environment is of great interest, and various detection techniques have been proposed, including combining techniques of instrumental analysis and fast analysis methods. These methods can be divided into, chromatography-mass analysis, spectroscopic analysis, bioanalysis, photo/electric analysis, biosensor analysis. These methods have their own advantages and disadvantages and can complement each other. Here, we review progress about the above analytical metheds in POPs analysis.