Qing Kang

MoS2/Graphene Cocatalyst for Efficient Photocatalytic H2 Evolution under Visible Light Irradiation

Exploiting noble-metal-free cocatalysts is of huge interest for photocatalytic water splitting using solar energy. Here we report a composite material consisting of CdS nanocrystals grown on the suface of a nanosized MoS2/graphene hybrid as a high-performance noble-metal-free photocatalyst for H2 evolution under visible light irradiation. Through the optimizing of each component proportion, the MoS2/G-CdS composite showed the highest photocatalytic H2 production activity when the content of the MoS2/graphene cocatalyst is 2.0 wt % and the molar ratio of MoS2 to graphene is 1:2. The photocatalytic H2 evolution activity of the proposed MoS2/G-CdS composite was tested and compared in Na2S-Na2SO3 solution and lactic acid solution. A 1.8 mmol/h H2 evolution rate in lactic acid solution corresponding to an AQE of 28.1% at 420 nm is not only higher than the case in Na2S-Na2SO3 solution of 1.2 mmol/h but also much higher than that of Pt/CdS in lactic acid solution. The relative mechanism has been investigated. It is believed that this kind of MoS2/G-CdS composite would have great potential as a promising photocatalyst with high efficiency and low cost for photocatalytic H2 evolution reaction.

High Efficient Photocatalytic Degradation of p-Nitrophenol on a Unique Cu2O/TiO2 p-n Heterojunction Network Catalyst

p-Nitrophenol (PNP) is a difficultly decomposed organic pollutant under solar light in the absence of strong oxidants. This study shows that under artificial solar light PNP can be effectively degraded by a Cu(2)O/TiO(2) p-n junction network which is fabricated by anodizing Cu(0) particles-loaded TiO(2) nanotubes (NTs). The network is composed of p-type Cu(2)O nanowires on the top surface and Cu(2)O nanoparticles on the inner walls of the n-type TiO(2) NT arrays. The Cu(2)O/TiO(2) network shows much higher degradation rate (1.97 μg/min cm(2)) than the unmodified TiO(2) NTs (0.85 μg/min cm(2)). The enhanced photocatalytic acitivity can be attributed to the extended absorption in the visible resulting from the Cu(2)O nanowire networks and the effective separation of photogenerated carriers driven by the photoinduced potential difference generated at the Cu(2)O/TiO(2) p-n junction interface.

Reduced TiO2 nanotube arrays for photoelectrochemical water splitting

We report a facile one-step chemical method to synthesize partially reduced TiO2 nanotube arrays (NTAs). The NaBH4 treatment introduces oxygen vacancies on the surface and interior of TiO2. Oxygen vacancy extends the photocatalytic activity of TiO2 NTAs from the UV to visible light region, and enhances the electrical conductivity as well as charge transportation. Surface oxygen vacancies serve as charge carrier traps as well as adsorption sites where the charge transfer to adsorbed species inhibits the surface charge recombination, whereas bulk oxygen vacancies tend to act as charge carrier traps where e–h recombination occurs. The optimally reduced TiO2 NTAs yield a photocurrent density of 0.73 mA cm−2 at 1.23 VRHE and a highest photoconversion efficiency of 1.31% at a rather low bias of 0.40 VRHE under a standard AM 1.5G solar illumination. Not only does the incident photon to current conversion efficiency (IPCE) spectrum increase in the UV region, but photoactivity in visible light also emerged. Surface oxygen vacancies, serving as electron donors, cause a noticeable negative flatband shift and increase the donor density of TiO2 NTAs 2-fold. Electron paramagnetic resonance (EPR) spectra confirm the presence of oxygen vacancies on the surface and interior of TiO2. Benefitting from the oxygen vacancy, a narrowed band gap of 2.46 eV and suitable localized states for hydrogen production are observed.

Photoelectrochemical detection of pentachlorophenol with a Multiple Hybrid CdSexTe1−x/TiO2 Nanotube Structure-Based Label-Free Immunosensor

Driven by the urgent demand of detecting trace amounts of pentachlorophenol (PCP) in contaminative water, a label-free immunosensor with ultra sensitivity and high selectivity was constructed based on a hybrid CdSe(x)Te(1-x) (0 ≤ x ≤ 1) nanocrystal (NCs)-modified TiO(2) nanotube (NT) arrays for the first time. The CdSe(x)Te(1-x) NCs were photoelectrodeposited on inner and outer space of the TiO(2) NTs, leading to high photoelectrical conversion efficiency in the visible region. PCP antibodies are covalently conjugated on the TiO(2) NTs due to the large surface area and good biocompatibility. Since the photocurrent is highly dependent on the TiO(2) surface properties, the specific interaction between PCP and the antibodies results in a sensitive change in the photocurrent, with a limit of detection (LOD) of 1 pM. High sensor-to-sensor reproducibility is achieved. The sensor was applied for the direct analysis of river water samples.

Fabrication of PbS nanoparticle-sensitized TiO₂ nanotube arrays and their photoelectrochemical properties.

TiO(2) nanotube arrays (NTAs) are modified with PbS nanoparticles by successive ionic layer adsorption and reaction (SILAR) or electrodeposition, with an aim towards tuning the photoelectrochemical cell to the visible region. The PbS modification of the TiO(2) NTAs results in an increase in the visible light adsorption, however the increase in photocurrent is dependent on the modification method. PbS/TiO(2) NTAs prepared by SILAR and electrodeposition show, respectively, photocurrents of 11.02 and 5.72 mA/cm(2). The increase in photocurrent is attributed to enhanced charge separation efficiency and improved electron transport.

Photocatalytic Reduction of Carbon Dioxide by Hydrous Hydrazine over Au–Cu Alloy Nanoparticles Supported on SrTiO3/TiO2 Coaxial Nanotube Arrays

Efficient photocatalytic conversion of CO2 into CO and hydrocarbons by hydrous hydrazine (N2H4⋅H2O) is achieved on SrTiO3/TiO2 coaxial nanotube arrays loaded with Au-Cu bimetallic alloy nanoparticles. The synergetic catalytic effect by the Au-Cu alloy nanoparticles and the fast electron-transfer in SrTiO3/TiO2 coaxial nanoarchitecture are the main reasons for the efficiency, while N2H4⋅H2O as the H source and electron donor provides a reducing atmosphere to protect the surface Cu atoms from oxidation, therefore maintaining the alloying effect which is the basis for the high photocatalytic activity and stability. This approach opens a feasible route to enhance the photocatalytic efficiency, which also benefits the development of photocatalysts and co-catalysts.

A ternary hybrid CdS/Pt–TiO2 nanotube structure for photoelectrocatalytic bactericidal effects on Escherichia Coli

A ternary hybrid CdS/Pt-TiO(2) nanotube (NT) photoelectrode was developed by dipping and deposition technique as well as successive ionic layer adsorption and reaction (SILAR). Small Pt nanoparticles (NPs) and CdS NPs were effectively deposited on both the inside and outside of the TiO(2) NTs. The as-prepared hybrid shows enhanced photon absorption and photocurrent generation efficiency. Higher bactericidal effect to Escherichia coli was observed on the ternary hybrid CdS/Pt-TiO(2) NTs as compared with Pt-TiO(2) NTs or pure TiO(2) NTs.

An electro-catalytic biosensor fabricated with Pt–Au nanoparticle-decorated titania nanotube array

A Gold-Platinum nanoparticle-decorated titania nanotubular electrode is fabricated by electrochemically depositing Au and Pt nanoparticles onto a highly-oriented titania nanotube array. The prepared electrode, characterized by SEM and EDX, shows remarkably improved catalytic activities in the oxidation of hydrogen peroxide. By modifying the electrode with glucose oxidase (GOx) the resultant glucose biosensor exhibits a high sensitivity to glucose in the range of 0 to 1.8 mM with a response time of 3 s and detection limit of 0.1 mM.

In situ synthesis of ordered mesoporous Co-doped TiO2 and its enhanced photocatalytic activity and selectivity for the reduction of CO2

Ordered mesoporous cobalt-doped titanium dioxide was successfully synthesized by a multicomponent self-assembly process. The doped Co species change the construction of the conduction band and valence band of TiO2, leading to visible-light absorption for TiO2. The designed cobalt-doped titanium dioxide exhibits a higher visible light activity for the reduction of CO2 among the commonly reported photocatalysts. In addition, the selectivity of the reduction products is improved by optimizing the energy-band configurations of cobalt-doped titanium dioxide through varying the molar ratio of Co/Ti. When the doping content of cobalt species increases to some extent, Co3O4/Co-doped TiO2 nanocomposites with oxygen vacancies were obtained, which markedly improve the generation rate of CH4.

Nickel Confined in the Interlayer Region of Birnessite: an Active Electrocatalyst for Water Oxidation

We report a synthetic method to enhance the electrocatalytic activity of birnessite for the oxygen evolution reaction (OER) by intercalating Ni(2+) ions into the interlayer region. Electrocatalytic studies showed that nickel (7.7 atomic %)-intercalated birnessite exhibits an overpotential (η) of 400 mV for OER at an anodic current of 10 mA cm(-2) . This η is significantly lower than the η values for birnessite (η≈700 mV) and the active OER catalyst β-Ni(OH)2 (η≈550 mV). Molecular dynamics simulations suggest that a competition among the interactions between the nickel cation, water, and birnessite promote redox chemistry in the spatially confined interlayer region.