Efficient defect-controlled photocatalytic hydrogen generation based on near-infrared Cu-In-Zn-S quantum dots

The development of photocatalysts that can effectively harvest visible light is essential for advances in high-efficiency solar-driven hydrogen generation. Herein, we synthesized water soluble CuInS₂ (CIS) and Cu-In-Zn-S (CIZS) quantum dots (QDs) by using one-pot aqueous method. The CIZS QDs are well passivated by glutathione ligands and are highly stable in aqueous conditions. We subsequently applied these QDs as a light harvesting material for photocatalytic hydrogen generation. Unlike most small band gap materials that show extremely low efficiency, these new QDs display remarkable energy conversion efficiency in the visible and near-infrared regions. The external quantum efficiency at 650 nm is ～1.5%, which, to the best of our knowledge, is the highest value achieved until now in the near-infrared region.

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In situ RHEED control of self-organized Ge quantum dots

In situ registration of high-energy electron diffraction patterns was used for constructing the diagram of structural and morphological states of the Ge film on the Si(100) surface. The following regions identified in the diagram: two-dimensional (2D)-growth, ‘hut’- and ‘dome’-clusters, ‘dome’-clusters with misfit dislocations at the interface. Variations in the lattice constants of the Ge film during the MBE growth on the Si(100) surface were determined. An increase in the lattice constant at the (100) surface was attributed to the elastic deformation at the stage of 2D growth and formation of ‘hut’-clusters and to the plastic relaxation for the ‘dome’-clusters. As a result, epitaxial silicon structures with germanium quantum dots of 15 nm base size at the density of 3×10¹¹ cm⁻² were synthesized. The total electron structure of the hole spectrum of Ge quantum dots in Si was established.     

Gate-defined quantum dots on carbon nanotubes

We report the realization of nanotube-based multiple quantum dots that are fully defined and controlled with electrostatic gates. Metallic top-gates are used to produce localized depletion regions in the underlying tubes; a pair of such depletion regions in a nanotube with ohmic contact electrodes defines the quantum dot. Top-gate voltages tune the transparencies of tunnel barriers as well as the electrostatic energies within single and multiple dots. This approach allows precise control over multiple devices on a single tube, and serves as a design paradigm for nanotube-based electronics and quantum systems.     

MWCNTs上原位生长CdSe量子点及与牛血清蛋白的偶联

以巯基乙酸为稳定剂在水溶液中实现了CdSe量子点(QDs)在MWCNTs(多壁碳纳米管)上的原位生长,并与生物分子牛血清蛋白(BSA)偶联,通过电镜、荧光、紫外、X射线衍射等技术对CdSe量子点-MWCNTs异质结(CdSe-MWCNTs)及异质结-牛血清蛋白偶联体(CdSe-MWCNTs-BSA)进行了表征。结果表明,CdSe量子点可在碳纳米管活化部位发生原位组装得到CdSe-MWCNTs异质结,该异质结可与牛血清蛋白偶联,CdSe-MWCNTs异质结及偶联后的复合物(CdSe-MWCNTs-BSA)均具有荧光性质。     

Solution processed high performance perovskite quantum dots/ZnO phototransistors

Phototransistors that can detect visible light have been fabricated using solution processed zinc oxide channel/zirconium oxide gate insulator thin film transis...     

Preparation of well-dispersed Mg-doped LaCoO3 nanocrystals with controllable particle size and high visible-light photocatalytic activity

Mg-doped LaCoO3 nanocrystals are prepared by a modified sol-gel method. Excess MgO is used to inhibit the crystal growth and agglomeration during the calcination process. A series of Mg-doped LaCoO3 nanocrystals with average crystallite size varying from 13.4 to 31.6 nm can be obtained by changing the molar ratio of Mg:La from 4:1 to 1:10 in the reaction mixture. The largest BET surface area observed is 64.5 m2/g if the molar ratio of Mg:La is 4:1. The product can be well dispersed in water and a very stable colloid formed without any stabilizer. The photocatalytic performance of Mg-doped LaCoO3 nanocrystals is evaluated by the degradation of Reactive Brilliant Red X-3B solution. The well-dispersed Mg-doped LaCoO3 nanocrystals exhibit high visible-light photocatalytic activity.     

Sensitization of ZnO nanorods with CdSe quantum dots

We have optimized the low-temperature growth of aligned arrays of zinc oxide nanorods of controlled length and diameter on conductive substrates. Varying the solution concentration and growth time, we were able to tune the nanorod diameter and length in the ranges 40–600 nm and 0.5–15 μm, respectively. The grown zinc oxide nanorods were photosensitized with CdSe quantum dots (QDs) in an oleic shell, which was replaced by pyridine. We studied the optical and transport properties of the ZnO nanorod arrays, with and without CdSe QDs on their surface. The current-voltage characteristics of the ZnO nanorod arrays with CdSe QDs are significantly influenced by illumination with light at a wavelength under the absorption band of the QDs, which points to effective interaction between the QDs and ZnO matrix.     

CdS量子点沉积的钛基纳米管的制备及其光催化性能研究

采用水热法制备了钛基纳米管,利用双官能团物质2-巯基丙酸为连接剂,将CdS量子点沉积在纳米管表面,研究了2-巯基丙酸浓度对样品的物相、微观结构和光催化活性的影响。利用X射线衍射仪、透射电子显微镜、紫外可见分光度计和光催化反应仪对样品进行了表征。结果表明,CdS量子点成功沉积在纳米管表面,改变2-巯基丙酸浓度可以调节CdS量子点的沉积数量,随着CdS量子点在纳米管表面的沉积,样品不仅在紫外光区有吸收,在可见光区也出现吸收,其吸收边在540nm左右。CdS量子点的沉积提高了样品在可见光下的光催化活性,2-巯基丙酸浓度为0.7mol/L时制备的样品对甲基橙降解的光催化活性最好。     

MOF-derived ZnO and ZnO@C composites with high photocatalytic activity and adsorption capacity

Nanostructured ZnO materials have unique and highly attractive properties and have inspired interest in their research and development. This paper presents a facile method for the preparation of novel ZnO-based nanostructured architectures using a metal organic framework (MOF) as a precursor. In this approach, ZnO nanoparticles and ZnO@C hybrid composites were produced under several heating and atmospheric (air or nitrogen) conditions. The resultant ZnO nanoparticles formed hierarchical aggregates with a three-dimensional cubic morphology, whereas ZnO@C hybrid composites consisted of faceted ZnO crystals embedded within a highly porous carbonaceous species, as determined by several characterization methods. The newly synthesized nanomaterials showed relatively high photocatalytic decomposition activity and significantly enhanced adsorption capacities for organic pollutants.     

Growth of ZnO quantum dots on Si nano ripples

Substrates with nano-scale ripples are excellent templates for the deposition of semiconductor nanostructures. We have prepared quasi periodical nano-scale ripples on Si (100) substrates with spatial wavelength λ from ~ 70 to ~ 150 nm by ion beam sputtering. ZnO QDs with diameters from 17 to ~ 30 nm and heights from 2 to ~ 4 nm have been successfully deposited by reactive ion beam sputter deposition. The QD size and distribution were found to be dependent both on growth conditions and spatial wavelength of the nano-scale ripple. On substrates with λ ~ 150 nm, ZnO QDs were distributed evenly across the wafer, while on substrates with λ ~ 70 nm, ZnO QDs were preferentially located along the crest of the nano-scale ripples. As the QD height decreases from ~ 4 to 2 nm, room temperature photoluminescence UV emission energy blue shifts by 80 meV. Possible sources of the blue shift are presented.     

In situ encapsulation of horseradish peroxidase in electrospun porous silica fibers for potential biosensor applications

Nanoporous silica nanofibers have been employed as a matrix to encapsulate horseradish peroxide enzymes via a simple electrospinning method. A viscous solution of prehydrolyzed tetramethyl orthosilicate, beta-d-glucose, poly(vinyl alcohol), and enzymes were employed as spinning solution to generate porous fibers in the form of nonwoven mats. The silica fiber mats thus produced have a high surface area because of the small diameter (100 to 200 nm) of the fibers as well as the extreme porosity (2 to 4 nm) of individual fibers caused by the glucose template present in them. The high surface area, mechanical flexibility, thermal stability, reusability, and freedom of encapsulating various enzymes make porous silica nanofibers excellent biosensors.     

Electronic transport properties of coupled quantum dots on carbon nanotubes

We investigate the electronic transport properties of coupled quantum dots, controlled by local gates on carbon nanotubes. The inter-dot coupling can be tuned from weak to strong by changing gate voltages, and oscillates in short and long period with the distance between two gates. We introduce a one-dimensional scattering model to describe the mechanism of the electron transport through the carbon nanotube quantum dots. We show that pi and PI* channels contribute differently to the inter-dot coupling and the transport phase plays a key role in the oscillations of the coupling.     

量子点/TiO2复合光催化材料的研究进展

近年,光催化技术已被广泛应用于污水处理、CO₂还原、制氢等多个领域。在光催化材料中,TiO₂由于具有化学稳定性高、来源广泛、价格低廉等优点,应用最广泛。但较宽的带隙及较高的电子及空穴复合效率使TiO₂的光催化性能受到极大限制。量子点(QDs)作为一种受量子约束效应影响的纳米尺度粒子,具有载流子易调控和表面位点丰富等优势。因此,研究人员采用不同方法将TiO₂与QDs复合,以增强TiO₂的光催化性能,获得了系列具有优异光催化性能的QDs/TiO₂复合光催化材料。本文主要综述了QDs/TiO₂复合光催化材料的研究进展。首先,阐述了QDs/TiO₂复合光催化材料的制备方法,并就QDs对TiO₂光催化性能的增强机制进行了剖析;然后,总结了QDs/TiO₂复合光催化材料在有机污染物降解、制氢及CO₂还原方面的应用研究进展;最后,围绕QDs/TiO₂复合光催化材料现阶段研究中的关键问题及未来的研究前景进行了展望。      

Photosensitization of ZnO nanowires with CdSe quantum dots for photovoltaic devices

We combine CdSe semiconductor nanocrystals (or quantum dots) and single-crystal ZnO nanowires to demonstrate a new type of quantum-dot-sensitized solar cell. An array of ZnO nanowires was grown vertically from a fluorine-doped tin oxide conducting substrate. CdSe quantum dots, capped with mercaptopropionic acid, were attached to the surface of the nanowires. When illuminated with visible light, the excited CdSe quantum dots injected electrons across the quantum dot-nanowire interface. The morphology of the nanowires then provided the photoinjected electrons with a direct electrical pathway to the photoanode. With a liquid electrolyte as the hole transport medium, quantum-dot-sensitized nanowire solar cells exhibited short-circuit currents ranging from 1 to 2 mA/cm2 and open-circuit voltages of 0.5-0.6 V when illuminated with 100 mW/cm2 simulated AM1.5 spectrum. Internal quantum efficiencies as high as 50-60% were also obtained.     

Microwave-assisted silica coating and photocatalytic activities of ZnO nanoparticles

A new and rapid method for silica coating of ZnO nanoparticles by the simple microwave irradiation technique is reported. Silica-coated ZnO nanoparticles were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), high-resolution transmission electron microscopy (HR-TEM), CHN elemental analysis and zeta potential measurements. The FT-IR spectra and XPS clearly confirmed the silica coating on ZnO nanoparticles. The results of XPS analysis showed that the elements in the coating at the surface of the ZnO nanoparticles were Zn, O and Si. HR-TEM micrographs revealed a continuous and uniform dense silica coating layer of about 3 nm in thickness on the surface of ZnO nanoparticles. In addition, the silica coating on the ZnO nanoparticles was confirmed by the agreement in the zeta potential of the silica-coated ZnO nanoparticles with that of SiO₂. The results of the photocatalytic degradation of methylene blue (MB) in aqueous solution showed that silica coating effectively reduced the photocatalytic activity of ZnO nanoparticles. Silica-coated ZnO nanoparticles showed excellent UV shielding ability and visible light transparency.     

Graphene oxide modified ZnO nanorods hybrid with high reusable photocatalytic activity under UV-LED irradiation

In this work, graphene oxide/zinc oxide (GO/ZnO) hybrid was prepared through a facile hydrothermal process. Transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectra and N₂ adsorption and desorption isotherms were used to investigate the morphology, crystal structure, optical properties and specific surface area of GO/ZnO hybrid. It was shown that the well-dispersed ZnO nanorods were deposited on GO homogeneously. Photocatalytic properties of GO/ZnO nanorods hybrid were evaluated under 375 nm light-emitting diode light irradiation for photodegradation of methylene blue (MB). The synergic effect between GO and ZnO was found to lead to an improved photo-generated carrier separation. An optimal GO content has been determined to be 3 wt%, and corresponding the apparent pseudo-first-order rate constant kapp$k_{\text{app}}$ is 0.0248 min⁻¹, 4.3 times and 2.5 times more than that of pure ZnO nanorods and commercial P25 photocatalyst, respectively. Moreover, the cyclic photocatalytic test indicated that GO/ZnO hybrid can be reused for degradation of MB, suggesting the possible application of GO/ZnO hybrid as excellent candidate for water treatment.     

Nanostructured porous ZnO film with enhanced photocatalytic activity

Well-defined ZnO nanostructured films have been fabricated directly on Zn foil via hydrothermal synthesis. During the fabrication of the ZnO nanostructured films, the Zn foil serves as the Zn source and also the substrate. Porous nanosheet-based, nanotube-based and nanoflower-based ZnO films can all be easily prepared by adjusting the alkali type, reaction time and reaction temperature. The composition, morphology and structure of ZnO films are characterized by X-ray diffraction, scanning electron microscope and high-resolution transmission electron microscope. The porous ZnO nanosheet-based film exhibits enhanced photocatalytic activity in the degradation of Rhodamine B under UV light irradiation. This can be attributed to the high surface area of the ZnO nanosheet and the large percentage of the exposed [001] facet. Moreover, the self-supporting, recyclable and stable ZnO photocatalytic film can be readily recovered and potentially applied for pollution disposal.     

Carbon quantum dots/attapulgite nanocomposites with enhanced photocatalytic performance for desulfurization

Carbon quantum dots (CQDs)/attapulgite (ATP) nanocomposite was prepared by a simple impregnation method. The ATP was initially modified with hydrochloric acid solution, which favored for the combination of CQDs due to the generation of hydroxyl group on the surface. XRD shows the decrease of interplanar spacing of ATP (1 1 0) plane, suggesting that the CQDs are immobilized on the surface of ATP. UV–Vis shows that the absorption peak of modified ATP is apparently red-shifted and the absorbance intensity of CQDs/ATP is higher than others. FT-IR and XPS show that the CQDs are immobilized on the surface of ATP through hydroxylation reaction. TEM shows that the average diameter of CQDs nanoparticles is about 5 nm and they are coated on the surface of ATP uniformly. The CQDs/ATP nanocomposite was employed as catalyst for photocatalytic degradation of dibenzothiophene (DBT) in model gasoline under visible light irradiation. The influence of the mass ratio of CQDs to ATP on desulfurization performance was investigated. The desulfurization rate of DBT could reach 93% when the mass ratio of CQDs/ATP is 3:10. The enhanced photocatalytic oxidative desulfurization was attributed to the sensitizing effect and up-conversion property of CQDs.     

Observation of quantum confinement effect on ZnO embedded mesoporous silica

Nonionic surfactant as liquid organic template and tetraethoxysilane as silica precursor were used for the synthesis of mesoporous silica with ordered arrangement of nanopores (diameters are about 1-6 nm). The synthesized mesoporous silica was used as the template for the synthesis of ZnO nanoparticles using zinc acetylacetonate as ZnO precursor. The as synthesized ZnO incorporated in the mesoporous silica nanocomposite were analyzed using X-ray diffraction, TEM and Photoluminescent spectrum. ZnO introduction has no extensive influence on the mesoporous structure of silica. Quantum confinement effects are observed in the case of ZnO nanoparticles embedded in mesoporous silica. The particle size of ZnO is about 3.2 nm. The band gap is broadening to 3.47 eV.