Pan Wang

Enhanced HCHO gas sensing properties by Ag-loaded sunflower-like In2O3 hierarchical nanostructures

Nanoscale Ag-loaded sunflower-like In2O3 hierarchical nanostructures are developed for HCHO detection. Such unique architectures are synthesized by an ambient temperature and pressure hydrolysis reaction combined with a subsequent chemical reduction process. Morphology characterizations confirm that homodisperse nanochains assembled by nanoparticles along the same direction are radially linked to a center to construct sunflower-like hierarchical nanostructures. Novel highly porous and branched structure of the 3D hierarchical architectures and the chemical and electronic sensitization effect of Ag nanoparticles endow Ag-loaded In2O3 nanostructures-based sensors with enhanced gas sensing performances in terms of fast response time (0.9 s), recovery time (14 s), high sensitivity and good sensing selectivity for 20 ppm HCHO. A multistage reaction formation mechanism of the sunflower-like hierarchical nanostructures, and a morphology-dependent sensing mechanism are proposed.

Low-temperature solvothermal synthesis of hierarchical flower-like WO3 nanostructures and their sensing properties for H2S

In this work, hierarchical flower-like tungsten trioxide (WO3) nanostructures assembled by needle-like single-crystalline nanosheets were fabricated. These were synthesized via a facile and simple solvothermal method at a rather low temperature (100 °C) without any surfactants or templates. Time-dependent experiments were carried out to understand the formation process, which undergoes four stages: polymerizing, nucleating, assembling and growing from WO42− to the flower-like WO3. The as-prepared WO3 microflowers exhibit a good reversibility, fast response time (0.9 s) and recovery time (19 s) and good sensing selectivity at a relatively low working temperature (160 °C) after exposing to hydrogen sulfide (H2S). Such excellent performance can be attributed to the highly exposed surface area and the assembling of single-crystalline nanosheets. The sensing process is tentatively explained in terms of the adsorption-desorption mechanism and chemical kinetics theories are discussed in detail.

Facile fabrication and enhanced gas sensing properties of In2O3 nanoparticles

Nanoscale single crystalline In2O3 nanoparticles with sizes of 10–40 nm are prepared by annealing gas-liquid phase chemical deposition-synthesized In2S3 nanoparticles and are developed for the detection of acetone gas. The In2O3 nanoparticles are characterized by TEM, HRTEM, SAED, EDX and XRD. Moreover, the products are further studied by room temperature UV-absorption and photoluminescence (PL) spectroscopy. To demonstrate the usage of such nanoparticles, gas sensors based on the as-synthesized In2O3 nanoparticles are fabricated and exhibit good selectivity, high sensitivity, rapid response, a low concentration detection limit and better repeatability towards acetone gas at a relatively low operating temperature. Such excellent gas sensing performances are attributed to small crystal sizes and the existence of abundant oxygen vacancies. As demonstrated, the single crystalline In2O3 nanoparticles are highly promising for real-time monitoring gas sensor applications.

Enhanced acetone gas sensing properties by aurelia-like SnO2 micro-nanostructures

In this research, well defined, three-dimensional, aurelia-like tin dioxide (SnO2) micro-nanostructures have been successfully obtained using a simple and easy one-step, low temperature, hydrothermal strategy in the presence of cetyltrimethylammonium bromide and poly(vinylpyrrolidone). The use of these SnO2 nanostructures was further developed for use in acetone gas detection. The unique structure and morphology of the SnO2 nanostructures were comprehensively characterized using techniques such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM) and high-resolution TEM. The results revealed that the aurelia-like SnO2 micro-nanostructures were composed of two parts: the crown and tentacles. The crown and tentacles were assembled from a chassis of mass stunted, disorderly, cumulate nanosheets and a large number of curvy, uneven nanobelts, respectively. The special aurelia-like structure of the SnO2 micro-nanostructures endows the nanostructure-based sensors with enhanced acetone gas sensing performance such as a fast response time (2 s)/recovery time (23 s), high sensitivity, good repeatability and good sensing selectivity at lower working temperatures. The possible formation growth mechanism of the aurelia-like micro-nanostructures and a morphology dependent sensing mechanism are proposed.

Facile synthesis and enhanced gas sensing properties of In2O3 nanoparticle-decorated ZnO hierarchical architectures

In2O3 nanoparticle-decorated flowerlike ZnO hierarchical architectures are fabricated by a simple and facile two-step approach, including the room temperature synthesis of flowerlike ZnO and the subsequent decoration with In2O3 nanoparticles, and developed for HCHO gas detection. The SEM, TEM and HRTEM images indicate that the In2O3 nanoparticles have successfully grown and are closely attached to the surface of the ZnO. The special 3D hierarchical architectures, the appropriate decoration amount of In2O3 nanoparticles and the incorporation of interfaces between ZnO nanosheets and the In2O3 nanoparticles endow In2O3-decorated ZnO nanostructured sensors with enhanced HCHO gas sensing performances. A multistage reaction formation mechanism of flowerlike hierarchical nanostructures and a morphology-dependent sensing mechanism are proposed.

Ce doping influence on the magnetic phase transition in In2S3:Ce nanoparticles

The classical thermally driven transition from supermagnetic to blocked supermagnetic and quantum phase transition from magnetic long-range order to quantum superparamagnetic state have been observed in ultrasmall In2S3:Ce diluted magnetic semiconductors (DMSs). The In2S3:Ce nanoparticles (5–6 nm) were synthesized by a facile gas–liquid phase chemical deposition process using Ce(COOCH3)3, In(COOCH3)3 and H2S as source materials. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM) were used to characterize the structure, components, morphology and size. Photoluminescence emission spectroscopy (PL) demonstrates that the luminescence quantum efficiency increases with Ce addition and indicates the existence of Ce atoms in the structure. The magnetic properties reflect a strong f–f exchange interaction between the Ce ions. The Ce doped In2S3 nanoparticles are shown to exhibit a higher blocking temperature from superparamagnetic to magnetic long-range order state, and even show room-temperature ferromagnetism. The larger ionic radius of Ce results in a larger influence on carrier concentration, affecting the blocking temperature of the magnetic phase transition.

Highly enhanced methanol gas sensing properties by Pd0.5Pd3O4 nanoparticle loaded ZnO hierarchical structures

Pd0.5Pd3O4 nanoparticle loaded ZnO hierarchical architectures have been successfully synthesized via a facile solution route at room temperature followed by a subsequent thermal treatment. Morphology and component characterizations reveal that Pd0.5Pd3O4 nanoparticles are uniformly deposited on the surface of the ZnO hierarchical architecture. A gas sensor based on the as-prepared Pd0.5Pd3O4 loaded ZnO hierarchical architecture shows excellent gas sensing performances in terms of fast response time (1 s), recovery time (5 s) and a high sensitivity for 50 ppm methanol at a relatively low temperature, which are evidently modified by the appropriate decoration of Pd0.5Pd3O4 nanoparticles in comparison with pure ZnO. The enhanced gas sensing performances are attributed to the appropriate sensitization effect of Pd0.5Pd3O4 nanoparticles. A multistage reaction formation mechanism of such flowerlike hierarchical architecture, and the morphology-dependent gas sensing mechanism are proposed.

Co effect on zinc blende–rocksalt phase transition in CdS nanocrystals

The influence of Co doping on zinc blende-to-rocksalt (ZB–RS) phase transformation in CdS nanocrystals (NCs) has been investigated. Analysis is performed using in situ high pressure X-ray powder diffraction with synchrotron radiation. Pure cadmium sulphide (CdS) and cobalt-doped cadmium sulphide (CdS:Co) are prepared by gas–liquid phase chemical deposition. The experimental data indicates that doping with Co ions reduces the phase transition pressure (PT) (CdS = 4.89 GPa and CdS:Co = 4.06 GPa) and increases the bulk modulus (B0) of the initial and high-pressure phases. The phase transitions of all samples are reversible. Density functional theory calculations are also performed to study the phase transition. The enthalpy variation is in accord with the experimental data.

Synthesis of ZnO nanosheets decorated with Au nanoparticles and its application in recyclable 3D surface-enhanced Raman scattering substrates

Au decorated ZnO (Au/ZnO) nanosheets were prepared by ultra-thin liquid layer electrodeposition and galvanic reduction route. Polycrystalline Zn backbones with dense single-crystalline ZnO nanosheets covering the surface were electrodeposited on SiO2 by controlling the ion concentration and deposition potential. The Zn/ZnO micro/nanostructure was used as a template and reducing reagent for preparing Au/ZnO composite nanosheets via a low-cost and convenient galvanic reduction method. The coverage and size of Au nanoparticles (NPs) on ZnO nanosheets surface can be changed by tuning the concentration of Au precursor. The Au protrusions and gaps between them contribute to 3D SERS “hot spots” which can be modulated by simply controlling the HAuCl4 concentration. The substrates can be easily self-cleaned and reactivated by UV irradiation to eliminate the single-use problem of traditional SERS substrates. This study suggested that the Au decorated ZnO nanosheets would be promising as high SERS-active substrates with UV-cleanable and regenerated property.

Magnetic phase transition of Ag2S:Eu diluted magnetic semiconductor nanoparticles

In this study, we synthesize europium doped Ag2S diluted magnetic semiconductor (DMS) nanoparticles using a gas–liquid phase chemical deposition process. It has been found that the Ag2S:Eu nanoparticles have room-temperature ferromagnetism (RTF) and display two remarkable magnetic phase transitions with decreasing temperature, i.e., the classic thermally driven transition from superparamagnetism to blocked superparamagnetism and the quantum phase transition from magnetic long-range order to quantum superparamagnetism state. When the blocking temperature (TB, 300 K) is reached, the first magnetic phase transition from superparamagnetism to blocked superparamagnetism is observed; after further temperature decrease to the critical phase transition temperature (TC, 11 K) the second magnetic phase transition which is from magnetic long-range order to quantum superparamagnetism is observed because of the quantum tunnelling effect. The spin-resolved density of states is calculated by the software VASP (Vienna Ab-initio Simulation Package) to investigate the origin of magnetism of the Ag2S:Eu nanoparticles. It is found that the magnetism originates from the doped Eu atoms and is caused by an f–f exchange interaction of Eu ions.