The surface and materials science of tin oxide

Surface functionalized magnetic iron oxide nanoparticles (NPs) are a kind of novel functional materials, which have been widely used in the biotechnology and catalysis. This review focuses on the recent development and various strategies in preparation, structure, and magnetic properties of naked and surface functionalized iron oxide NPs and their corresponding application briefly. In order to implement the practical application, the particles must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of iron oxide NPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The problems and major challenges, along with the directions for the synthesis and surface functionalization of iron oxide NPs, are considered. Finally, some future trends and prospective in these research areas are also discussed.

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Magnetic Iron Oxide Nanoparticles: Synthesis and Surface Functionalization Strategies

Metal oxide-based resistive-type gas sensors are solid-state devices which are widely used in a number of applications from health and safety to energy efficiency and emission control. Nanomaterials such as nanowires, nanorods, and nanoparticles have dominated the research focus in this field due to their large number of surface sites facilitating surface reactions. Previous studies have shown that incorporating two or more metal oxides to form a heterojunction interface can have drastic effects on gas sensor performance, especially the selectivity. Recently, these effects have been amplified by designing heterojunctions on the nano-scale. These designs have evolved from mixed commercial powders and bi-layer films to finely-tuned core–shell and hierarchical brush-like nanocomposites. This review details the various morphological classes currently available for nanostructured metal-oxide based heterojunctions and then presents the dominant electronic and chemical mechanisms that influence the performance of these materials as resistive-type gas sensors. Mechanisms explored include p–n and n–n potential barrier manipulation, n–p–n response type inversions, spill-over effects, synergistic catalytic behavior, and microstructure enhancement. Tables are presented summarizing these works specifically for SnO2, ZnO, TiO2, In2O3, Fe2O3, MoO3, Co3O4, and CdO-based nanocomposites. Recent developments are highlighted and likely future trends are explored.

Nanoscale metal oxide-based heterojunctions for gas sensing: A review

This article extensively reviews the recent development of semiconductor metal oxide gas sensors for environmentally hazardous gases including NO2, NO, N2O, H2S, CO, NH3, CH4, SO2 and CO2. The gas sensing properties of differently-prepared metal oxides and loaded metal oxides towards nine environmentally hazardous gases have been individually compared and digested. Promising materials for sensitive and selective detection of each hazardous gas have been identified. For instance, unloaded WO3 nanostructures are the most promising candidates for NO2 sensing while metal catalyst loaded WO3 and gold-loaded SnO2 sensors are among the most effective for NO and N2O sensing, respectively. Moreover, related gas-sensing mechanisms are comprehensively discussed.

Semiconducting metal oxides as sensors for environmentally hazardous gases

Magnetorheological (MR) materials are a kind of smart materials whose mechanical properties can be altered in a controlled fashion by an external magnetic field. They traditionally include fluids, elastomers and foams. In this review paper we revisit the most outstanding advances on the rheological performance of MR fluids. Special emphasis is paid to the understanding of their yielding, flow and viscoelastic behaviour under shearing flows.

Magnetorheological fluids: a review

Additions of 0.5 to 2.0 mol% of CoO or MnO{sub 2} onto SnO{sub 2} promote densification of this oxide up to 99% of theoretical density. The temperature of the maximum shrinkage rate (T{sub M}) and the relative density in the maximum densification rate ({rho}*) during constant sintering heating rate depend on the dopant concentration. Thus, dopant concentration controls the densifying and nondensifying mechanisms during sintering. The densification of SnO{sub 2} with addition of CoO or MnO{sub 2} is explained in terms of the creation of oxygen vacancies.

Effect of cobalt(II) oxide and manganese(IV) oxide on sintering of tin(IV) oxide

The enthalpy of adsorption of CO2 on an environmentally friendly metal–organic framework, CD-MOF-2, has been determined directly for the first time using adsorption calorimetry at 25 °C. This calorimetric methodology provides a much more accurate and model-independent measurement of adsorption enthalpy than that obtained by calculation from the adsorption isotherms, especially for systems showing complex and strongly exothermic adsorption behavior. The differential enthalpy of CO2 adsorption shows enthalpy values in line with chemisorption behavior. At near-zero coverage, an irreversible binding event with an enthalpy of −113.5 kJ/mol CO2 is observed, which is followed by a reversible −65.4 kJ/mol binding event. These enthalpies are assigned to adsorption on more and less reactive hydroxyl groups, respectively. Further, a second plateau shows an enthalpy of −40.1 kJ/mol and is indicative of physisorbed CO2. The calorimetric data confirm the presence of at least two energetically distinct binding sites for...

Direct Calorimetric Measurement of Enthalpy of Adsorption of Carbon Dioxide on CD-MOF-2, a Green Metal-Organic Framework

Many studies have been carried out concerning the development of SO2 sensors to detect and avoid its health prejudicial effects. However, there is still a lack of reliable, high-speed-response sensors that work at room temperature. In this work, the segregation of Ni in the SnO2−NiO system is used to obtain a rapid SO2 sensor response. Segregation and its structure consequences were studied by electron dispersive spectroscopy, infrared spectroscopy, and high-resolution transmission electron microscopy in nanopowders of SnO2−NiO with different compositions prepared by a polymeric precursor method. The sensor activity of SnO2−1 mol % Ni was studied and a linear calibration curve was formed with a maximum limit response of 32 ppm SO2.

Surface segregation and consequent SO2 sensor response in SnO2-NiO

Retaining large surface areas in alumina powders during high-temperature annealing is a major challenge in applications as catalyst supports and ceramic precursors. This is because the alumina surface area drastically decreases with transformation from the γ modification (defect spinel structure) into the α modification (corundum structure). The objective of this work is to show the thermodynamic basis of using additives, such as Zr and Mg, to control the γ-Al2O3 surface and bulk energetics and to manipulate the transformation temperature and surface area. These additives are observed to change the pattern of phase transformation and densification. Direct measurements of heats of solution in a lead borate melt of pure and doped alumina as a function of surface area enabled us to experimentally derive trends in the surface energies of hydroxylated surfaces. Accounting for heats of water adsorption measured on pure and doped alumina surfaces allowed us to delineate the thermodynamic effects of hydration on ...

Douglas Gouvêa

Papers

Effect of cobalt(II) oxide and manganese(IV) oxide on sintering of tin(IV) oxide

Direct Calorimetric Measurement of Enthalpy of Adsorption of Carbon Dioxide on CD-MOF-2, a Green Metal-Organic Framework

Surface segregation and consequent SO2 sensor response in SnO2-NiO

Surface energy and thermodynamic stability of γ-alumina : Effect of dopants and water

Microstructure and structure of NiO-SnO2 and Fe2O3-SnO2 systems