Abdulmohsen Ali Alshehri

Direct fabrication of tri-metallic PtPdCu tripods with branched exteriors for the oxygen reduction reaction

Design of multi-metallic nanocrystals with branched structures is very important for catalytic applications. Herein, a one-step synthesis of unique tri-metallic PtPdCu tripods with branched exteriors (PtPdCu TPs) in an aqueous solution is presented. Benefiting from their spatially and locally separated branches and tri-metallic compositions, the PtPdCu TPs exhibit superior activity and durability for the oxygen reduction reaction. The newly designed PtPdCu TPs are quite different from previous tripods in their branched exteriors. The developed one-step method is very feasible for the preparation of Pt-based multi-metallic tripods with designed compositions and desired performances.

Effect of TiO2 morphology on the benzyl alcohol oxidation activity of Fe2O3–TiO2 nanomaterials

Three series of Fe loaded TiO2 anatase (1, 3, 5 and 7 mol% Fe) nanomaterials with different morphologies: nanoparticles (NP), nanotubes (NT) and nanofibers (NF) were synthesized and calcined at 400 °C. The physico-chemical properties of the catalysts were studied by using elemental analysis, XRD, UV-vis, N2-physisorption, SEM, TEM, XPS, pyridine adsorption using FTIR and H2-TPR techniques. It was observed that iron oxide was highly dispersed on the TiO2-NP support due to its strong interaction. The catalytic activity of the catalysts was tested in the oxidation of benzyl alcohol with hydrogen peroxide at mild reaction temperatures (70–100 °C) and atmospheric pressure. The highest activity was observed with 3 mol% Fe supported on TiO2-NP at 100 °C. It seems that TiO2-NP is unique in stabilizing small Fe2O3 nanoparticles. A greater number of surface hydroxyl groups in TiO2-NT and NF tend to increase the density of adsorption sites and/or the affinity of the surfaces with the Fe2O3 precursor. This appears to favor agglomeration, which results in a higher density of larger iron oxide particles. Fe-TiO2-NP catalysts display high activities due to a detrimental morphology effect, high surface area of the TiO2 support, dispersion of Fe2O3, more Lewis acid sites and easy reducibility of total catalysts. It was also observed that the Fe-TiO2 nanomaterials possessed two types of Fe3+ ions on the support surface; one dispersed in which Fe3+ ions interact with the TiO2 surface and another in which Fe2O3 crystals are located on the surface of the catalyst. The catalyst which possessed the former species exhibited the best performance in the oxidation of benzyl alcohol. Metal oxide leaching studies prove the true heterogeneous nature of the reaction. The catalysts are found to be reusable and resistant to rapid deactivation.

Gold nanoparticles supported on mesoporous iron oxide for enhanced CO oxidation reaction

Herein, we report the synthesis of gold (Au)-loaded mesoporous iron oxide (Fe2O3) as a catalyst for both CO and NH3 oxidation. The mesoporous Fe2O3 is firstly prepared using polymeric micelles made of an asymmetric triblock copolymer poly(styrene-b-acrylic acid-b-ethylene glycol) (PS-b-PAA-b-PEG). Owing to its unique porous structure and large surface area (87.0 m2 g-1), the as-prepared mesoporous Fe2O3 can be loaded with a considerably higher amount of Au nanoparticles (Au NPs) (7.9 wt%) compared to the commercial Fe2O3 powder (0.8 wt%). Following the Au loading, the mesoporous Fe2O3 structure is still well-retained and Au NPs with varying sizes of 3-10 nm are dispersed throughout the mesoporous support. When evaluated for CO oxidation, the Au-loaded mesoporous Fe2O3 catalyst shows up to 20% higher CO conversion efficiency compared to the commercial Au/Fe2O3 catalyst, especially at lower temperatures (25-150 °C), suggesting the promising potential of this catalyst for low-temperature CO oxidation. Furthermore, the Au-loaded mesoporous Fe2O3 catalyst also displays a higher catalytic activity for NH3 oxidation with a respectable conversion efficiency of 37.4% compared to the commercial Au/Fe2O3 catalyst (15.6%) at 200 °C. The significant enhancement in the catalytic performance of the Au-loaded mesoporous Fe2O3 catalyst for both CO and NH3 oxidation may be attributed to the improved dispersion of the Au NPs and enhanced diffusivity of the reactant molecules due to the presence of mesopores and a higher oxygen activation rate contributed by the increased number of active sites, respectively.

Few-layer graphitic shells networked by low temperature pyrolysis of zeolitic imidazolate frameworks

Few-layer graphitic shell networks show great promise in energy storage applications such as electrochemical accommodation of alkaline ions. However, the networking and graphitization processes remain a challenge because of the complicated procedures and high temperature used for fabrication. In this work, we report a simple synthetic method by employing low-temperature solid-state pyrolysis of ZIF-67 crystals to weave graphitic shells consisting of 3–10 layers into capsules. Owing to their unique structure, the few-layer graphitic shell networks show excellent electrochemical performance for fast sodium ion storage.

Biofabrication of Fe nanoparticles in aqueous extract of Hibiscus sabdariffa with enhanced photocatalytic activities

Hibiscus sabdariffa is a strongly basic dye with a large number of medicinal applications and is used for various diagnostic purposes. The biofabrication of Fe nanoparticles using Hibiscus sabdariffa (Roselle) flower extract is an eco-friendly and cost-effective protocol reported for the first time in the present investigation. The natural plant extract acts as a non-toxic, biodegradable and economical reducing agent in the biosynthesis of the Fe nanoparticles. Different well-known complementary characterization techniques such as UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X-ray diffraction (XRD), dynamic light scattering (DLS) and thermogravimetric analysis-differential scanning calorimetry (TGA-DSC) were used to investigate the morphological, structural and optical properties of the as-synthesised Fe nanoparticles. The resulting nanoparticles were then utilized as a photocatalyst for the degradation of the toxic organic dye Congo red (CR). UV-visible spectroscopy was used to determine the photocatalytic performance of the Fe nanoparticles under UV irradiation. The results of the photocatalytic degradation of Congo red in aqueous solution under UV light showed a higher photocatalytic activity. A reasonable mechanism was proposed for the enhanced photocatalytic activity of the Fe nanoparticles.

Facile synthesis of palladium-nanoparticle-embedded N-doped carbon fibers for electrochemical sensing

In recent years, there have been many studies on metal/carbon hybrid materials for electrochemical applications. However, reducing the metal content in catalysts is still a challenge. Here, a facile synthesis of palladium (Pd) nanoparticle-embedded N-doped carbon fibers (Pd/N-C) through electropolymerization and reduction methods is demonstrated. The as-prepared Pd/N-C contains only 1.5 wt % Pd. Under optimal conditions, bisphenol A is detected by using amperometry in two dynamic ranges from 0.1 to 10 μm and from 10 to 200 μm, and the obtained correlation coefficients are close to 0.9836 and 0.9987, respectively. The detection limit (DL) for bisphenol A is determined to be 29.44 (±0.77) nm.

Electrochemical Synthesis of Mesoporous Au–Cu Alloy Films with Vertically Oriented Mesochannels Using Block Copolymer Micelles

We synthesized Au-Cu bimetallic alloy films with a controlled mesoporous architecture through electrochemical deposition using an electrolyte solution containing spherical polymeric micelles. The composition of the alloy films can be easily controlled by tuning the ratio between the Au and Cu species present in the electrolyte solution. At low Cu content, cage-type mesopores are formed, reflecting the parent micellar template. Surprisingly, upon increasing the Cu content, the cage-type mesopores fuse to form vertically aligned one-dimensional mesochannels. The vertical alignment of these mesopores is favorable for enhanced mass and ion transfer within the channels due to low diffusion resistance. The atomic distribution of Au and Cu is uniform over the entire film and free of any phase segregation. The as-synthesized mesoporous Au-Cu films exhibit excellent performance as a nonenzymatic glucose sensor with high sensitivity and selectivity, and the current response is linear over a wide range of concentrations. This work identifies the properties responsible for the promising performance of such mesoporous alloy films for the clinical diagnosis of diabetes. This micelle-assisted electrodeposition approach has a high degree of flexibility and can be simply extended from monometallic compounds to a multimetallic system, enabling the fabrication of various mesoporous alloy films suitable for different applications.

Mesoporous Manganese Phosphonate Nanorods as a Prospective Anode for Lithium-Ion Batteries

Mesoporous materials can serve as well-performed electrode candidates for lithium-ion batteries (LIBs). Mesoporous manganese phosphonate (MnP) nanorods are composed of an interconnected network of pores that have high infiltration capacity for electrolyte and less tortuous transport pathways for lithium/electron charge carriers. The mesoporous architecture should also help alleviate stress from volume variation upon lithium intercalation/deintercalation cycles. We used MnP as an LIB anode and observed an initial reversible capacity of 420 mA h g-1 and a modest Coulombic efficiency of 68.7% at a relatively high current density of 144 mA g-1. The reversible capacity stabilizes at 253 mA h g-1 after 100 repetitive cycles, while most of the time, the Coulombic efficiency remains around 100%. The results show that, as a prospective LIB anode, the mesoporous MnP can achieve desirable capacity with decent durability and rate capability.

Low Temperature Oxidation of Carbon Monoxide over Mesoporous Au-Fe2O3 Catalysts

Low temperature active and stable mesoporous Au (0.1, 0.2, 0.5, and 1.0 wt.%) supported α-Fe2O3 catalysts were prepared via deposition-precipitation method. The H2-pretreated catalyst with 0.5 wt.% Au loading offered CO conversion of 100% at 323 K and showed continual activity for at least 120 h. X-ray diffraction and transmission electron microscopy analysis indicate that Au species were highly dispersed as nanoparticles (20–40 nm) on the surface of α-Fe2O3 support even after thermal treatment at 773 K. The N2-physisorption measurements show that the synthesized α-Fe2O3 support and Au-Fe2O3 nanocomposites possessed mesopores with high specific surface area of about 158 m2 g−1. X-ray photoelectron spectroscopy and H2-TPR results reveal that the Au species exist in metallic and partially oxidized state due to strong interaction with the support. Effective Au-Fe2O3 interaction resulted in a high activity for Au nanoparticles, locally generated by the thermal treatment at 773 K in air.

Effects of morphology of Mg powder precursor on phase formation and superconducting properties of Mg11B2 low activation superconductor

The effect of morphology with magnesium (Mg) powder on phase formation and critical current density (Jc,) of sintered Mg11B2 bulk was studied. As a precursor for the formation of Mg11B2, the morphology of spherical and plate-like of Mg powder were separately synthesized using atomization and chemical reduction methods. From differential thermal analyses of the sintering process, the solid–solid reaction of a Mg11B2 sample using spherical Mg powder was confirmed to be much weaker than the plate-like one, and the second exothermic peak place was shifted back and its intensity was increased due to a special microstructure of spherical Mg powder. XRD analysis of Mg11B2 samples showed that the volume fraction of Mg11B2 in the sintered sample with plate-like Mg was higher than that with the spherical one, and for all the samples MgB2 is the main phase. The Mg11B2 sample using spherical Mg powder had two different kinds of microstructures because of differences in their diffusivity and their contact interfaces. The Jc value of an Mg11B2 sample using spherical Mg powder enhanced the entire field; it was twice as high as that using plate-like Mg, and it was even better than all the Jc values reported in previous literature using the same kind of Mg powder as precursor.