Mengmeng Xu

Bio: Mengmeng Xu is an academic researcher from Northwestern Polytechnical University. The author has contributed to research in topics: Charge carrier & Indium tin oxide. The author has an hindex of 8, co-authored 9 publications receiving 304 citations.

Ni-doped ZnO nanorods gas sensor: Enhanced gas-sensing properties, AC and DC electrical behaviors

Abstract: Ni-doped zinc oxide (ZnO) nanorods had been successfully fabricated via a fast microwave-assisted hydrothermal synthesis at 150 °C. The morphology and composition were carefully characterized by X-ray diffraction, field emission scanning electronic microscopy, and transmission electron microscopy. Gas-sensing testing results demonstrated that Ni-doped ZnO nanorods had enhanced gas-sensing performance. Furthermore, AC impedance spectroscopy and DC current–voltage curves were observed to investigate the gas-sensing mechanism. Current–voltage curves are approximately close to a linear function, indicating the potential barriers formed at the electron-depleted surface layer occupy a dominant when carriers transport in the gas sensor, and AC impedance spectra indicates the potential barriers height of the electron-depleted surface layer.

Phase transformation (cubic to rhombohedral): the effect on the NO2 sensing performance of Zn-doped flower-like In2O3 structures

Abstract: Cubic In2O3 (bcc-In2O3) was transformed into a mixture of bcc-In2O3 and rhombohedral In2O3 (rh-In2O3) by Zn doping The Zn-doped flower-like In2O3 structures consisted of many thin sheets with a length of 04–1 μm, and cubes with a length of 200 nm, while the size of the microflowers was 1–35 μm The Zn doping concentration significantly affected the phase transformation and the overall morphology of In2O3 Furthermore, the analysis of N2 adsorption–desorption measurements showed that the Zn-doped flower-like In2O3 structures (sample S5) adsorbed the largest amount of N2 and had the biggest surface area (4641 m2 g−1), which contributed to an improvement in gas sensing performance Finally, sensors based on the mixture of bcc- and rh-In2O3 structures exhibited a much higher response to NO2 than the pure bcc-In2O3 (sample S1), and the Zn-doped flower-like In2O3 structures (sample S5) exhibited the highest response of 274 ± 25 for 5 ppm NO2 Thus, the gas sensing performance of In2O3 was enhanced significantly by the phase transformation

Fast economical synthesis of Fe-doped ZnO hierarchical nanostructures and their high gas-sensing performance

Abstract: The Fe-doped ZnO with excellent porous features was successfully fabricated via a fast economical solution combustion synthesis. The morphology and the porous nature were characterized by SEM, TEM and BET – N2 adsorption–desorption analysis. The results of XRD Rietveld refinements and Raman spectra demonstrate that the dopant was successfully incorporated into the nanostructure ZnO lattice. The gas-sensing tests show that the sensors based on Zn0.97Fe0.03O have high sensitivity, quick response, excellent selectivity and long-time stability for detecting ethanol vapor. AC impedance spectroscopy and DC electrical conductivity measurements were used to investigate the gas-sensing mechanism, and the results demonstrate that the O− (300–400 °C) on the surface is the most reactive species with ethanol gas.

Solution Combustion Synthesis of Nanoscale Materials

Abstract: Solution combustion is an exciting phenomenon, which involves propagation of self-sustained exothermic reactions along an aqueous or sol–gel media. This process allows for the synthesis of a variety of nanoscale materials, including oxides, metals, alloys, and sulfides. This Review focuses on the analysis of new approaches and results in the field of solution combustion synthesis (SCS) obtained during recent years. Thermodynamics and kinetics of reactive solutions used in different chemical routes are considered, and the role of process parameters is discussed, emphasizing the chemical mechanisms that are responsible for rapid self-sustained combustion reactions. The basic principles for controlling the composition, structure, and nanostructure of SCS products, and routes to regulate the size and morphology of the nanoscale materials are also reviewed. Recently developed systems that lead to the formation of novel materials and unique structures (e.g., thin films and two-dimensional crystals) with unusual...

Magnetically separable nanocomposites based on ZnO and their applications in photocatalytic processes: A review

Abstract: Among the most challenging problems that human beings appear to face are depleting energy sources and increasing environmental pollutions. Heterogeneous photocatalytic processes are the most reward...

Solution combustion synthesis of metal oxide nanomaterials for energy storage and conversion

Abstract: The design and synthesis of metal oxide nanomaterials is one of the key steps for achieving highly efficient energy conversion and storage on an industrial scale. Solution combustion synthesis (SCS) is a time- and energy-saving method as compared with other routes, especially for the preparation of complex oxides which can be easily adapted for scale-up applications. This review summarizes the synthesis of various metal oxide nanomaterials and their applications for energy conversion and storage, including lithium-ion batteries, supercapacitors, hydrogen and methane production, fuel cells and solar cells. In particular, some novel concepts such as reverse support combustion, self-combustion of ionic liquids, and creation of oxygen vacancies are presented. SCS has some unique advantages such as its capability for in situ doping of oxides and construction of heterojunctions. The well-developed porosity and large specific surface area caused by gas evolution during the combustion process endow the resulting materials with exceptional properties. The relationship between the structural properties of the metal oxides studied and their performance is discussed. Finally, the conclusions and perspectives are briefly presented.

High-performance gas sensor based on ZnO nanowires functionalized by Au nanoparticles

Abstract: One-dimensional (1D) semiconductor nanostructure has been widely used for gas sensor devices. In this work, a high performance gas sensor based on Au-functionalized ZnO nanorods was fabricated. Au nanoparticles were successfully immobilized onto the surface of ZnO nanorods to serve as a sensitizer by a facile solution reduction process. The hybrid Au/ZnO nanorods have been systematically characterized by XRD, SEM, EDS, TEM and optical absorption spectrum. Gas sensing tests reveal that the Au/ZnO sensor has remarkably enhanced performance compared to pure ZnO. It could detect ethanol gas in a wide concentration range with very high response, fast response–recovery time, good selectivity and stable repeatability. The possible sensing mechanism is discussed. The superior sensing features indicate the present Au/ZnO nanorods are promising for gas sensors.

Design, synthesis and applications of core–shell, hollow core, and nanorattle multifunctional nanostructures

Abstract: With the evolution of nanoscience and nanotechnology, studies have been focused on manipulating nanoparticle properties through the control of their size, composition, and morphology. As nanomaterial research has progressed, the foremost focus has gradually shifted from synthesis, morphology control, and characterization of properties to the investigation of function and the utility of integrating these materials and chemical sciences with the physical, biological, and medical fields, which therefore necessitates the development of novel materials that are capable of performing multiple tasks and functions. The construction of multifunctional nanomaterials that integrate two or more functions into a single geometry has been achieved through the surface-coating technique, which created a new class of substances designated as core–shell nanoparticles. Core–shell materials have growing and expanding applications due to the multifunctionality that is achieved through the formation of multiple shells as well as the manipulation of core/shell materials. Moreover, core removal from core–shell-based structures offers excellent opportunities to construct multifunctional hollow core architectures that possess huge storage capacities, low densities, and tunable optical properties. Furthermore, the fabrication of nanomaterials that have the combined properties of a core–shell structure with that of a hollow one has resulted in the creation of a new and important class of substances, known as the rattle core–shell nanoparticles, or nanorattles. The design strategies of these new multifunctional nanostructures (core–shell, hollow core, and nanorattle) are discussed in the first part of this review. In the second part, different synthesis and fabrication approaches for multifunctional core–shell, hollow core–shell and rattle core–shell architectures are highlighted. Finally, in the last part of the article, the versatile and diverse applications of these nanoarchitectures in catalysis, energy storage, sensing, and biomedicine are presented.