Magnetic Iron Oxide Nanoparticles: Synthesis and Surface Functionalization Strategies

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

Biotechnological Perspective of Reactive Oxygen Species (ROS)-Mediated Stress Tolerance in Plants

All environmental cues lead to develop secondary stress conditions like osmotic and oxidative stress conditions that reduces average crop yields by more than 50% every year. The univalent reduction of molecular oxygen (O2) in metabolic reactions consequently produces superoxide anions (O2•−) and other reactive oxygen species (ROS) ubiquitously in all compartments of the cell that disturbs redox potential and causes threat to cellular organelles. The production of ROS further increases under stress conditions and especially in combination with high light intensity. Plants have evolved different strategies to minimize the accumulation of excess ROS like avoidance mechanisms such as physiological adaptation, efficient photosystems such as C4 or CAM metabolism and scavenging mechanisms through production of antioxidants and antioxidative enzymes. Ascorbate-glutathione pathway plays an important role in detoxifying excess ROS in plant cells, which includes superoxide dismutase (SOD) and ascorbate peroxidase (APX) in detoxifying O2•−radical and hydrogen peroxide (H2O2) respectively, monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) involved in recycling of reduced substrates such as ascorbate and glutathione. Efficient ROS management is one of the strategies used by tolerant plants to survive and perform cellular activities under stress conditions. The present chapter describes different sites of ROS generation and and their consequences under abiotic stress conditions and also described the approaches to overcome oxidative stress through genomics and genetic engineering

Spectroscopic ellipsometry study of barrier width effect in self-organized InGaAs/GaAs QDs laser diodes

725-731Molecular beam epitaxy (MBE) is used to grow InGaAs/GaAs quantum dots (QDs) laser diodes (LDs) with different barrier widths (5, 10 and 15 nm) at 580 ºC on GaAs substrates. Optical properties of the InGaAs/GaAs QDs LDs have been investigated by using the spectroscopic ellipsometry (SE) technique. A general oscillator optical model has been utilized to fit the experimental data in order to obtain the LD layer thicknesses, refractive index and absorption coefficient. The dielectric function, the energy band gap and the surface and volume energy loss functions are computed in the energy range 1-6 eV. The optical properties of the deposited InGaAs/GaAs QDs LDs are found to be affected by the barrier width, which give more insight into carriers dynamics and optical parameters in these devices. The refractive indices, the extinction coefficients and the dielectric constants of the LDs with barrier widths 15 and 10 nm are relatively larger than those of the LD with barrier width 5 nm. These indicate that optical properties of LDs with larger barrier widths (15 and 10 nm) will be improved. The interband transition energies in the three devices have calculated and identified. Two energy gaps at 1.04 and ~1.37 eV are obtained for all the heterostructures which indicates that fabricated LDs may be operating for a wavelength of 1.23 m at room temperature

Effect of Mn loading onto MnFeO nanocomposites for the CO2 hydrogenation reaction

This work describes the preparation of mesoporous xMnFe oxide (x = 0, 0.05, 0.1, 0.2, 0.3 and 0.5 molar ratios) nanocomposites through a one-step sol–gel process in the presence of a triblock copolymer as a structure-directing agent. The prepared oxides were used as catalysts in the CO2 hydrogenation via Fischer–Tropsch reactions for the production of valuable hydrocarbons. Among the catalysts, the 0.05MnFe catalyst performed best under the selected reaction conditions: a reaction temperature of 340 °C, overall pressure of 20 bar, reactant mixture of 23% CO2/69% H2/8% N2 and flow rate of 20 mL min−1. This catalyst provided a much higher conversion of CO2 to hydrocarbons (63.2% C2–C5, 3.9% to C6+ and 3.6% to oxygenates) and the lowest levels of CO and methane formation among the xMnFe series. Moreover, 0.05MnFe was the only catalyst with a mesoporous structure, and it had a substantially lower reduction temperature than did the other members of the series. The enhanced catalytic activity of the 0.05MnFe catalyst, which contains only a small amount of Mn, appears to result primarily from its high specific area and relatively easy reduction.This research was supported by Najran University, Najran, the Kingdom of Saudi Arabia.Peer Reviewe

Influence of Ni evironment on the reactivity of Ni-Mg-Al catalyst for the acetone steam reforming reaction

Steam reforming of acetone, as representative molecule of bio-oil, was investigated over different Ni-Mg-Al oxides with different Ni-environments which were obtained by the preparation of different Ni-Mg-Al materials: Ni-supported, Ni-mixed oxides and Ni like-spinel structures. Physico-chemical characterization of samples showed different Ni-support interactions depending on the nature of the support and the method of preparation. Ni-incorporation into the Mg-Al structure increases its stability. Reforming activity results showed that the Ni-environment interaction plays an essential role on the catalytic behaviour of Ni-Mg-Al catalysts. The sequence of gasification capacity over Ni-Mg-Al samples points out that acidity of supports participates in the acetone reforming mechanism over these catalystsThis research was supported by the Autonomous Government of Madrid (Spain) under project S2013/MAE-2882. Partial support to this work came from Najran University, The Kingdom of Saudi Arabia.Peer reviewe

Ni- and PtNi-catalysts supported on Al2O3 for acetone steam reforming: Effect of the modification of support with Ce, la and Mg

Hydrogen production from acetone steam reforming was studied using bimetallic PtNi catalysts supported on modified alumina. La-, Ce- and Mg-oxides were used as support modifiers in order to neutralize acidity and/or to improve water adsorption and OH− surface mobility of Al2O3 support. Characterization of the sample showed that metal-support interactions and the size of metallic Ni at surface differ depending on the oxide added to the alumina support. Reforming activity on Ni and Pt–Ni supported on X-modified-Al2O3 catalysts (X = La, Ce, or Mg) showed that both metal and support, play an essential role in the catalytic behavior on the steam reforming of acetone. The sequence of gasification capacity over monometallic samples (Ni/LaAl > Ni/MgAl > Ni/CeAl) points out that acidity of supports participates in the acetone reforming mechanism over these catalysts. Addition of Pt to monometallic Ni catalysts only has a beneficial effect on the reforming capacity of the Ni/LaAl sample. Improvement in the reforming capacity of the PtNi/LaAl catalyst is believed to be a consequence of the promoting effect of Pt that leads to an increase in the stability of metallic Ni particles on catalyst surface together with the ability of Pt to enhance the mobility of the H-atoms formed in the reaction could help the gasification of carbon precursors formed during the reforming of acetone.This research was supported by the Ministry of Science and Innovation (Spain) and the Autonomous Government of Madrid, Madrid (Spain) under grants ENE2010-21198-C04-01 and S2009ENE-1743, respectively. Partial support to this work came from Najran University, The Kingdom of Saudi Arabia.Peer Reviewe

Role of Pt in the Activity and Stability of PtNi/CeO2¿Al2O3 Catalysts in Ethanol Steam Reforming for H2 Production

Hydrogen production from ethanol reforming was investigated on bimetallic PtNi catalysts supported on CeO2/Al2O3. Pt content was varied from 0.5 to 2.5 %. Physico-chemical characterization of the as-prepared and H2-reduced catalysts by TPR, XRD and XPS showed that Pt phase interacted with the Ni and Ce species present at the surface of the catalysts. This interaction leads to an enhancement of the reducibility of both Ni and Ce species. Loadings of Pt higher than 1.0 wt% improved the activity and stability of the Ni/CeO2–Al2O3 catalyst in ethanol steam reforming, in terms of lower formation of coke, C2 secondary products and a constant production of CO2 and H2. The amount and type of carbon deposited on the catalyst was analyzed by TG–TPO while the changes in crystalline phases after reaction were studied by XRD. It was found that for Pt contents higher than 1 wt% in the catalysts, a better contact between Pt and Ce species is achieved. This Pt–Ce interaction facilitates the dispersion of small particles of Pt and thereby improves the reducibility of both Ce and Ni components at low temperatures. In this type of catalysts, the cooperative effect between Pt0, Ni0 and reduced Ce phases leads to an improvement in the stability of the catalysts: Ni provides activity in C–C bond breakage, Pt particles enhance the hydrogenation of coke precursors (CxHy) formed in the reaction, and Ce increases the availability of oxygen at the surface and thereby further enhances the gasification of carbon precursors.This research was supported by the Ministry of Science and Innovation (Spain) and the Autonomous Government of Madrid, Madrid (Spain) under grants ENE2010-21198-C04-01 and S2009ENE-1743, respectively.Peer Reviewe

Structure and Reactivity of sol–gel V/SiO2 Catalysts for the Direct Conversion of Methane to Formaldehyde

[EN] Vanadium oxide-silica catalysts prepared by the sol–gel method were characterized by different techniques (nitrogen adsorption–desorption isotherms, scanning electron microscopy, X-ray diffraction, temperature-programmed reduction, Raman spectroscopy and X-ray photoelectron spectroscopy) and applied in the direct conversion of methane to C1 oxygenates. The addition of a small amount of nitric oxide to the reaction mixture reduced the energy barrier for H-abstraction, increasing the methane conversion and formaldehyde yield. Correlations between the characterization and activity results indicate that the reaction occurs on tetrahedrally coordinated vanadium sites, as the maximum formaldehyde yield was found for the catalyst with a vanadium content of 1.5 wt%, which has a high surface density of well-dispersed tetrahedrally coordinated monomeric or slightly oligomerized VO species. On the other hand, a high space velocity and CH:O ratio decrease the subsequent oxidation to carbon oxides, increasing oxygenate formation.This work was supported by Najran University, Najran, The Kingdom of Saudi Arabia. This is a post-peer-review, pre-copyedit version of an article published in Topics in Catalysis. The final authenticated version is available online at: http://dx.doi.org/10.1007/s11244-017-0809-