Fe-species-loaded mesoporous MnO2 superstructural requirements for enhanced catalysis.

In this work, a novel catalyst, Fe-species-loaded mesoporous manganese dioxide (Fe/M-MnO2) urchinlike superstructures, has been fabricated successfully in a two-step technique. First, mesoporous manganese dioxide (M-MnO2) urchinlike superstructures have been synthesized by a facile method on a soft interface between CH2Cl2 and H2O without templates. Then the M-MnO2-immobilized iron oxide catalyst was obtained through wetness impregnation and calcination. Microstructural analysis indicated that the M-MnO2 was composed of urchinlike hollow submicrospheres assembled by nanorod building blocks with rich mesoporosity. The Fe/M-MnO2 retained the hollow submicrospheres, which were covered by hybridized composites with broken and shortened MnO2 nanorods. Energy-dispersive X-ray microanalysis was used to determine the availability of Fe loading processes and the homogeneity of Fe in Fe/M-MnO2. Catalytic performances of the M-MnO2 and Fe/M-MnO2 were evaluated in catalytic wet hydrogen peroxide oxidation of methylene blue (MB), a typical organic pollutant in dyeing wastewater. The catalytic degradation displayed highly efficient discoloration of MB when using the Fe/M-MnO2 catalyst, e.g., ca. 94.8% of MB was decomposed when the reaction was conducted for 120 min. The remarkable stability of this Fe/M-MnO2 catalyst in the reaction medium was confirmed by an iron leaching test and reuse experiments. Mechanism analysis revealed that the hydroxyl free radical was responsible for the removal of MB and catalyzed by M-MnO2 and Fe/M-MnO2. MB was transformed into small organic compounds and then further degraded into CO2 and H2O. The new insights obtained in this study will be beneficial for the practical applications of heterogeneous catalysts in wastewater treatments.

Multifunctional tin dioxide materials: advances in preparation strategies, microstructure, and performance.

Tin oxide materials are a class of unique semiconductor materials with widespread technological applications because of their valuable semiconducting, gas sensing, electrical and optical properties in the fields of macro/mesoscopic materials and micro/nanodevices. In this review, we describe the efforts toward understanding the synthetic strategies and formation mechanisms of the micro/nanostructures of various tin dioxide thin films prepared by pulsed laser ablation, highlighting contributions from our laboratory. First, we present the preparation and formation processes of tetragonal-phase tin dioxide thin films with interesting fractal clusters. In addition, the quantum-dot formation and dynamic scaling behavior in tetragonal-phase tin dioxide thin films induced by pulsed delivery will be discussed experimentally and theoretically. Finally, we emphasize the fabrication, properties and formation mechanism of orthorhombic-phase tin dioxide thin films by using pulsed laser deposition. This research may provide a novel approach to modulate their competent performance and promote rational design of micro/nanodevices. Once mastered, tin dioxide thin films with a variety of fascinating micro/nanostructures will offer vast and unforeseen opportunities in the semiconductor industry as well as in other fields of science and technology.

Hierarchical mesoporous MnO2 superstructures synthesized by soft-interface method and their catalytic performances.

To obtain a highly efficient and stable heterogeneous catalyst in catalytic wet hydrogen peroxide oxidation, we have successfully synthesized hierarchical mesoporous manganese dioxide (MnO2) superstructures by a facile and environmental friendly method on a soft-interface between CH2Cl2 and H2O without templates. The main crystal phase of as-prepared MnO2 was proved to be ε-MnO2 by X-ray diffraction techniques. The structure characterizations indicated that the hierarchical MnO2 superstructures were composed of urchin-like MnO2 hollow submicrospheres assembled by one-dimension nanorods building blocks with rich mesoporosity. The nitrogen sorption analysis confirmed that the as-synthesized MnO2 has an average pore diameter of 5.87 nm, mesoporous volume of 0.451 cm(3) g(-1), and specific surface area of 219.3 m(2) g(-1). Further investigations revealed that a possible formation mechanism of this unique hierarchical superstructure depended upon the synthesis conditions. The catalytic performances of the hierarchical mesoporous MnO2 superstructures were evaluated in catalytic degradation of methylene blue in the presence of H2O2 at neutral pH, which demonstrated highly efficient catalytic degradation of the organic pollutant methylene blue using hierarchical mesoporous MnO2 superstructures as catalyst at room temperature.

Advances in fractal germanium micro/nanoclusters induced by gold: microstructures and properties.

Germanium materials are a class of unique semiconductor materials with widespread technological applications because of their valuable semiconducting, electrical, optical, and thermoelectric power properties in the fields of macro/mesoscopic materials and micro/nanodevices. In this review, we describe the efforts toward understanding the microstructures and various properties of the fractal germanium micro/nanoclusters induced by gold prepared by high vacuum thermal evaporation techniques, highlighting contributions from our laboratory. First, we present the integer and non-integer dimensional germanium micro/nanoclusters such as nanoparticles, nanorings, and nanofractals induced by gold and annealing. In particular, the nonlinear electrical behavior of a gold/germanium bilayer film with the interesting nanofractal is discussed in detail. In addition, the third-order optical nonlinearities of the fractal germanium nanocrystals embedded in gold matrix will be summarized by using the sensitive and reliable Z-scan techniques aimed to determine the nonlinear absorption coefficient and nonlinear refractive index. Finally, we emphasize the thermoelectric power properties of the gold/germanium bilayer films. The thermoelectric power measurement is considered to be a more effective method than the conductivity for investigating superlocalization in a percolating system. This research may provide a novel insight to modulate their competent performance and promote rational design of micro/nanodevices. Once mastered, germanium thin films with a variety of fascinating micro/nanoclusters will offer vast and unforeseen opportunities in the semiconductor industry as well as in other fields of science and technology.

Characterization strategies for Mn2O3 nanomaterials.

Transition metal oxides belong to a class of versatile materials that are vitally important for developing new materials with functionality and smartness. Research on manganese oxides has been a key topic among studies on transition metal oxides. This is due to their potential applications in diverse areas, including rechargeable lithium ion batteries, catalysis, molecular adsorption, gas sensors, energy storage, and magnetics. In this review, we will elucidate in detail various characterization strategies, including temperature-dependent growth, micro/nanostructures, Raman, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and electron spin resonance, for Mn2O3 nanocrystals, highlighting contributions from our laboratory. This review article mainly focuses on the wide-ranging research effort on the development of preparation methodologies and the assessment of various characterization strategies in Mn2O3 nanomaterials. The main purpose is to provide the readers a comprehensive understanding of the research progress of manganese oxides. This is an interdisciplinary work that integrates the areas of physics, chemistry, materials science, and nanotechnology.

Assembling tin dioxide quantum dots to graphene nanosheets by a facile ultrasonic route.

Nanocomposites have significant potential in the development of advanced materials for numerous applications. Tin dioxide (SnO2) is a functional material with wide-ranging prospects because of its high electronic mobility and wide band gap. Graphene as the basic plane of graphite is a single atomic layer two-dimensional sp(2) hybridized carbon material. Both have excellent physical and chemical properties. Here, SnO2 quantum dots/graphene composites have been successfully fabricated by a facile ultrasonic method. The experimental investigations indicated that the graphene was exfoliated and decorated with SnO2 quantum dots, which was dispersed uniformly on both sides of the graphene. The size distribution of SnO2 quantum dots was estimated to be ranging from 4 to 6 nm and their average size was calculated to be about 4.8 ± 0.2 nm. This facile ultrasonic route demonstrated that the loading of SnO2 quantum dots was an effective way to prevent graphene nanosheets from being restacked during the reduction. During the calcination process, the graphene nanosheets distributed between SnO2 nanoparticles have also prevented the agglomeration of SnO2 nanoparticles, which were beneficial to the formation of SnO2 quantum dots.

Al-induced crystallization of amorphous Ge and formation of fractal Ge micro-/nanoclusters.

Results on Al-induced crystallization of amorphous Ge (a-Ge) deposited by vacuum thermal evaporation techniques under thermal annealing in N(2) atmosphere are presented in detail. The a-Ge crystallization and fractal Ge pattern formation on the free surface of annealed Al/Ge bilayer films deposited on single-crystal Si (100) substrates were investigated by using scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive X-ray spectrometry (EDS), and Raman spectra. It is found that the temperature field effects play an extremely crucial role in a-Ge crystallization and fractal Ge formation process. The open branched structure of fractal Ge clusters in Al/Ge bilayer films was effectively prepared by Al-induced crystallization when they were annealed at 400 °C for 60 min. These films with fractal Ge clusters exhibit charming noninteger dimensional nanostructures, which differ from those of conventional integer dimensional materials such as one-dimensional nanowires/nanorods, nanotubes, nanobelts/nanoribbons, two-dimensional heterojunctions, thin films, and zero-dimensional nanoparticles. The SEM image shows that a big Al grain was found located near the center of a fractal Ge cluster after the films were annealed at 400 and 500 °C for 60 min. This suggests that the grain boundaries of polycrystalline Al films are the initial nucleation sites of a-Ge. It also validates the preferred nucleation theory of a-Ge at triple-point grain boundaries of polycrystalline Al at the interface. This discovery may be explained by the metal-induced nucleation (MIN) mechanism.

Preparation methodologies and nano/microstructural evaluation of metal/semiconductor thin films.

Metal/semiconductor thin films are a class of unique materials that are widespread technological applications, particularly in the field of microelectronic devices. Assessment strategies of fractal and tures are of fundamental importance in the development of nano/microdevices. This review presents the preparation methodologies and nano/microstructural evaluation of metal/semiconductor thin films including Au/Ge bilayer films and Pd-Ge alloy thin films, which show in the form of fractals and nanocrystals. Firstly, the extended version of Au/Ge thin films for the fractal crystallization of amorphous Ge and the formation of nanocrystals developed with improved micro- and nanostructured features are described in Section 2. Secondly, the nano/microstructural characteristics of Pd/Ge alloy thin films during annealing have been investigated in detail and described in Section 3. Finally, we will draw the conclusions from the present work as shown in Section 4. It is expected that the preparation methodologies developed and the knowledge of nano/microstructural evolution gained in metal/semiconductor thin films, including Au/Ge bilayer films and Pd-Ge alloy thin films, will provide an important fundamental basis underpinning further interdisciplinary research in these fields such as physics, chemistry, materials science, and nanoscience and nanotechnology, leading to promising exciting opportunities for future technological applications involving these thin films.

Microstructure evolution and advanced performance of Mn3O4 nanomorphologies.

Mn(3)O(4) morphologies with tetragonal single-crystal nanostructures including nanoparticles, nanorods and nanofractals were successfully prepared by a widely applicable chemical reaction route. The morphologies were synthesized using the reactants MnCl(2)·4H(2)O, H(2)O(2), and NaOH in a suitable surfactant and alkaline solution. The dripping speed of the NaOH solution plays an important role in the microstructure evolution of Mn(3)O(4) morphologies. The difference in the dripping speed of NaOH solutions leads to different Mn(3)O(4) nanomorphologies, which are called nanoparticles, nanorods and nanofractals. The average grain size of the Mn(3)O(4) nanoparticles ranged from a few to several tens of nanometers. The Mn(3)O(4) nanorods were smooth, straight, and the geometrical shape was structurally perfect. Their lengths ranged from several hundred nanometers to a few micrometers, and their diameters ranged from 10 nm to 30 nm. The fractal branches of the Mn(3)O(4) nanofractals were a few micrometers in length and several hundred nanometers in width. The catalytic properties of these Mn(3)O(4) nanomorphologies for the degradation of phenol were evaluated in detail. The results indicated that the Mn(3)O(4) nanofractals possess remarkable catalytic activity for the degradation of phenol in water treatment.

Probing into interesting effects of fractal Ge nanoclusters induced by Pd nanoparticles.

Metal/semiconductor thin films are a class of unique materials that have widespread technological applications, particularly in the field of microelectronic devices. New strategies of fractal assessment for Pd/Ge bilayer films formed at various annealing temperatures are of fundamental importance in the development of micro/nanodevices. Herein, Pd/Ge bilayer films with interesting fractal nanoclusters were successfully prepared by evaporation techniques. Temperature-dependent properties of resistance and fractal dimensions in Pd/Ge bilayer films with self-similar Ge fractal nanoclusters were investigated in detail. Experimental results indicated that the fractal crystallization behavior and film resistance in Pd/Ge bilayer films are influenced significantly by annealing temperatures and fractal dimensions. The measurements of film resistance confirmed that there is an evident relationship between the film resistance and the fractal dimension. These phenomena were reasonably explained by the random tunneling junction network mechanism.

Dependence of electrical properties on thermal temperature in nanocrystalline SnO2 thin films.

Nanocrystalline SnO2 thin films were prepared by pulsed laser deposition techniques on clean glass substrates, and the films were then annealed for 30 min from 50 to 550 degrees C with a step of 50 degrees C, respectively. The investigation of X-ray diffraction confirmed that the various SnO2 thin films were consisted of nanoparticles with average grain size in the range of 23.7-28.9 nm. Root-mean-square surface roughness of the as-prepared SnO2 thin film was measured to be 25.6 nm which decreases to 16.2 nm with thermal annealing. Electrical resistivity and refractive index were measured as a function of annealing temperature, and found to lie between 1.24 to 1.45 momega-cm, and 1.502 to 1.349, respectively. The results indicate that nearly opposite actions to root-mean-square surface roughness and electrical resistivity make a unique performance with thermal annealing temperature. The post annealing shows greater tendency to affect the structural and electrical properties of SnO2 thin films which composed of nanoparticles.

Insight on fractal assessment strategies for tin dioxide thin films.

Tin oxide is a unique material of widespread technological applications, particularly in the field of environmental functional materials. New strategies of fractal assessment for tin dioxide thin films formed at different substrate temperatures are of fundamental importance in the development of microdevices, such as gas sensors for the detection of environmental pollutants. Here, tin dioxide thin films with interesting fractal features were successfully prepared by pulsed laser deposition techniques under different substrate temperatures. Fractal method has been first applied to the evaluation of this material. The measurements of carbon monoxide gas sensitivity confirmed that the gas sensing behavior is sensitively dependent on fractal dimensions, fractal densities, and average sizes of the fractal clusters. The random tunneling junction network mechanism was proposed to provide a rational explanation for this gas sensing behavior. The formation process of tin dioxide nanocrystals and fractal clusters could be reasonably described by a novel model.

Evolution of electronic structure and spectral evaluation in single-crystal Mn3O4 nanorods.

Single-crystal Mn3O4 nanorods with tetragonal structure have been successfully prepared by a chemical reaction route. Transmission electron microscopy (TEM) and high-resolution TEM studies prove that the single-crystal Mn3O4 nanorod is smooth and straight, and that the geometrical shape is structurally perfect. We investigated the electronic characteristics of Mn3O4 nanorods by various spectral evaluations. The present study confirms that the hybridization between oxygen 2p and manganese 3d orbits plays an important role when considering electronic structures of Mn3O4 nanorods.