Cuijin Pei

Charge Separation between Polar {111} Surfaces of CoO Octahedrons and Their Enhanced Visible-Light Photocatalytic Activity

Crystal facet engineering of semiconductors has been proven to be an effective strategy to increase photocatalytic performances. However, the mechanism involved in the photocatalysis is not yet known. Herein, we report our success in that photocatalytic performances of the Cl(-) ion capped CoO octahedrons with exposed {111} facets were activated by a treatment using AgNO3 and NH3·H2O solutions. The clean CoO {111} facets were found to be highly reactivity faces. On the basis of the polar structure of the exposed {111} surfaces, a charge separation model between polar {111} surfaces is proposed. There is an internal electric field between polar {111} surfaces due to the spontaneous polarization. The internal electric field provides a driving force for charge separation. The reduction and oxidation reactions selectively take place on the positive and negative polar {111} surfaces. The charge separation model provides a clear insight into charge transfer in the semiconductor nanocrystals with high photocatalytic activities and offer guidance to design more effective photocatalysts, solar cells, photoelectrodes, and other photoelectronic devices.

Superior adsorption performance for triphenylmethane dyes on 3D architectures assembled by ZnO nanosheets as thin as ∼1.5 nm

The 3-dimensional hierarchical ZnO flower-like architectures have been synthesized in a Zn(Ac)2·2H2O-Na2SeO3-KBH4-pyridine solvothermal system at 100°C for 24h. The flower-like architecture is assembled from ZnO nanosheets with a thickness of ∼1.5nm, and the flower-like architecture specific surface area is 132m(2)/g. When the ZnO flower-like architecture is used as the adsorbent for acid fuschin (AF), malachite green (MG), basic fuchsin (BF), congo red (CR) and acid red (AR) in water, the adsorption capacities for AF, MG, BF, CR and AR are 7154.9, 2587.0, 1377.9, 85.0 and 38.0mg/g, respectively. Evidently, the as-obtained ZnO flower-like architectures show excellent adsorption performances for triphenylmethane dyes, and the adsorption capacity of 7154.9mg/g for AF is the highest of all adsorbents for dyes. The adsorption mechanism can be attributed to the electrostatic attraction and the formation of ion-association complex between triphenylmethane dyes and ZnO hierarchical flower-like architectures.

Enhancing the Sensing Properties of TiO2 Nanosheets with Exposed {001} Facets by a Hydrogenation and Sensing Mechanism

Hydrogenation is successfully employed to improve sensing performances of the gas sensors based on TiO2 nanosheets with exposed {001} facets for the first time. The hydrogenated TiO2 nanosheets show a significantly higher response toward ethanol, acetone, triethylamine, or formaldehyde than the samples without hydrogenation, and the response further increases with an increase of the hydrogenation temperature. The excellent sensing performances are ascribed to an increase of the density of unsaturated Ti5c atoms on the {001} surface resulting from the hydrogenation process. The unsaturated Ti5c atoms are considered to serve as sensing reaction active sites. They can generate noncontributing (free) electrons and adsorb oxygen molecules, and the detailed sensing mechanism is described at atomic and molecule level. The hydrogenated strategy may be employed to enhance the sensing performances of other metal oxide sensors and catalytic reaction activities of catalyst. The concept of the surface unsaturated metal atoms serving as sensing reaction active sites not only deepens the understanding of the sensing reaction and catalytic reaction mechanism but also provides new insights into the design of advanced gas sensing materials, catalysts, and photoelectronic devices.

Enhanced Gas Sensitivity and Sensing Mechanism of Network Structures Assembled from α-Fe2O3 Nanosheets with Exposed {104} Facets

Network structures assembled from α-Fe2O3 nanosheets with exposed {104} facets were successfully prepared by heating Fe(NO3)3 solution containing polyvinylpyrrolidone (PVP) in air. The α-Fe2O3 nanosheet-based network structures demonstrate significantly higher response to ethanol and triethylamine than α-Fe2O3 commercial powders. The excellent sensing performances can be ascribed to the exposed (104) facet terminated with Fe atoms. A concept of the unsaturated Fe atoms serving as the sensing reaction active sites is thus proposed, and the sensing reaction mechanism is described at the atomic and molecular level for the first time in detail. The concept of the surface metal atoms with dangling bonds serving as active sites can deepen understanding of the sensing and other catalytic reaction mechanisms and provides new insight into the design and fabrication of highly efficient sensing materials, catalysts, and photoelectronic devices.

Effect of Unsaturated Sn Atoms on Gas-Sensing Property in Hydrogenated SnO 2 Nanocrystals and Sensing Mechanism

Sensing reaction mechanism is crucial for enhancing the sensing performance of semiconductor-based sensing materials. Here we show a new strategy to enhancing sensing performance of SnO2 nanocrystals by increasing the density of unsaturated Sn atoms with dangling bonds at the SnO2 surface through hydrogenation. A concept of the surface unsaturated Sn atoms serving as active sites for the sensing reaction is proposed, and the sensing mechanism is described in detail at atomic and molecule level for the first time. Sensing properties of other metal oxide sensors and catalytic activity of other catalysts may be improved by using the hydrogenation strategy. The concept of the surface unsaturated metal atoms serving as active sites may be very useful for understanding the sensing and catalytic reaction mechanisms and designing advanced sensing sensors, catalysts and photoelectronic devices.

Flowerlike Cu2Te architectures constructed from ultrathin nanoflakes as superior dye adsorbents for wastewater treatment

Flowerlike architectures assembled from Cu2Te nanoflakes have been synthesized using a hydrothermal reaction of Te, Cu foils, and KBH4 with H2O in the presence of ethanol amine (EA) at 200 °C for 12 h. The Cu2Te flowerlike architectures with diameters of 4.0–6.0 μm are assembled from the nanoflakes with a thickness of 4.0–6.0 nm. When the as-synthesized Cu2Te flowerlike nanoarchitectures serve as adsorbents for acid fuschin (AF), malachite green (MG), methylene blue (MB) and rhodamine B (RhB) in water, the adsorption capacities are 3798.1, 1122.8, 77 and 14.4 mg g−1, respectively. This suggests that the Cu2Te flowerlike architectures are excellent adsorbents for AF and MG and are promising materials for the removal of AF and MG pollutants from wastewater. The excellent adsorption performance is attributed to the renewed assembly of the constituent ultrathin Cu2Te nanoflakes with thickness of 4.0–6.0 nm.

The photovoltaic effect in a [001] orientated ZnO thin film and its physical mechanism

We report a new type of photovoltaic effect. The photovoltaic device was constructed using a [001] orientated wurtzite ZnO thin film synthesized by heating Zn(NO3)2 solution. The open-circuit voltage (Voc) and short-circuit current (Isc) of the ZnO photovoltaic device are 0.16 mV and 0.25 μA, respectively, under 365 nm ultraviolet lamp (3 W) illumination. Current rectification across the top and bottom planes of the ZnO thin film was observed. The photovoltaic and rectifying properties of the ZnO thin film are related to the magnitude of the TC(002). An internal electric field is produced in the ZnO film by spontaneous polarization in the [001] direction. The presence of the internal electric field is the fundamental physical basis of the photovoltaic effect, and a new physical mechanism of photon-to-electron conversion is proposed. The electrostatic potential provides a driving force for flow of the photogenerated electrons and holes in the semiconductor and in an external load, and thus the photo-to-electron conversion is achieved. Our result suggests thin film texturing as a strategy to develop photovoltaic devices beyond p–n junction. In addition, the photo-to-electron conversion model provides new insights into the understanding of the photovoltaic effect in ferroelectric and pyroelectric materials as well as the design and fabrication of advanced solar cells and other electronic and optoelectronic devices.

Synthesis of ultralong NiSe nanobelts and their excellent adsorption properties towards malachite green in water

NiSe ultralong nanobelts were synthesized by a solvothermal reaction of Ni with Se and KBH4 in ethylenediamine and subsequent annealing in Ar. The aspect ratios of NiSe ultralong nanobelts can be tuned by altering the reaction time. The adsorption performance of NiSe nanostructures with different aspect ratios was investigated, and the as-obtained NiSe ultralong nanobelts exhibited excellent adsorption capability of malachite green in wastewater, which could be attributed to their unique honeycomb-like assembly and high surface area. The adsorption process agreed well with the pseudo-second-order kinetics and the Langmuir isotherm equation. Thermodynamic parameters indicated that the adsorbent processes were spontaneous. Electrostatic attraction between malachite green and NiSe ultralong nanobelts was considered as the adsorption mechanism. The NiSe ultralong nanobelts could be regarded as a promising adsorbent for the removal of MG in wastewaters.