Ultra small cobalt nanoparticles supported on MCM41: One-pot synthesis and catalytic hydrogen production from alkaline borohydride

Insights into the hydrogen generation and catalytic mechanism on Co-based nanocomposites derived from pyrolysis of organic metal precursor

Hydrogen generation from boron hydride is important for the development of hydrogen economy. Cobalt (Co) element has been widely used in the hydrolysis of boron hydride. Pyrolysis is a common method for materials synthesis in catalytic fields. Herein, Co-based nanocomposites derived from the pyrolysis of organic metal precursors and used for hydrolysis of boron hydride are summarized and discussed. The different precursors consisting of MOF, supported, metal, and metal phosphide precursors are summarized. The catalytic mechanism consisting of dissociation mechanism based on oxidative addition-reduction elimination, pre-activation mechanism, SN2 mechanism, four-membered ring mechanism, and acid-base mechanism is intensively discussed. Finally, conclusions and outlooks are conveyed from the design of high-efficiency catalysts, the characterization of catalyst structure, the enhancement of catalytic activities, the investigation of the catalytic mechanism, and the catalytic stability of active structure. This review can provide guidance for designing high-efficiency catalysts and boosting development of hydrogen economy.

Current Methods for Synthesis and Potential Applications of Cobalt Nanoparticles: A Review

Cobalt nanoparticles (CoNPs) are promising nanomaterials with exceptional catalytic magnetic, electronic, and chemical properties. The nano size and developed surface open a wide range of applications of cobalt nanoparticles in biomedicine along with those properties. The present review assessed the current environmentally friendly synthesis methods used to synthesize CoNPs with various properties, such as size, zeta potential, surface area, and magnetic properties. We systematized several methods and provided some examples to illustrate the synthetic process of CoNPs, along with the properties, the chemical formula of obtained CoNPs, and their method of analysis. In addition, we also looked at the potential application of CoNPs from water purification cytostatic agents against cancer to theranostic and diagnostic agents. Moreover, CoNPs also can be used as contrast agents in magnetic resonance imaging and photoacoustic methods. This review features a comprehensive understanding of the synthesis methods and applications of CoNPs, which will help guide future studies on CoNPs.

Cobalt nanoparticle supported on layered double hydroxide: Effect of nanoparticle size on catalytic hydrogen production by NaBH4 hydrolysis

Catalytic hydrolysis of sodium borohydride (NaBH₄) is a promising method to provide clean hydrogen (H₂) energy for portable devices. Therefore, designing a non-noble metal catalyst that performs well in this hydrolysis is essential. Cobalt-nanoparticles (Co-NPs) supported on magnesium-aluminium layered double hydroxide (LDH) with various mean diameter were synthesized by changing concentration of cobalt-citrate anion (Co-citrate) precursor used for ion exchange with the LDH host. Then the Co-citrate intercalated LDHs were reduced with NaBH₄ to form Co-NPs. Evidence of successful intercalation was shown by X-ray diffraction (XRD) and Fourier-Transform Infrared spectroscopy (FT-IR). Transmission Electron Microscope (TEM) and Scanning TEM (STEM) observations revealed that Co-NPs were in metallic state and their mean diameter increased with the concentration of Co-citrate solution. Nitrogen physisorption isotherms showed that the surface structure of LDHs transformed from non-porous to mesoporous after chemical reduction, which indicated that the Co-NPs were formed in the interlayer of LDHs. Catalytic hydrolysis of NaBH₄ at 25 °C clarified that the catalyst synthesized from 6 mM Co-citrate solution showed the highest H₂ generation rate of 4520 ± 251 mL min^-1·g_Co^-1, indicating the catalyst had the optimum size of Co-NP. This activity could be considered relatively higher compared to unsupported cobalt and many other supported cobalt-base catalysts previously reported. It was also clearly shown that size of Co-NPs supported on LDH could be a significant parameter as it allowed better accessibility of reactants to the active catalyst surface to obtain maximum activity. For this optimum catalyst, the activation energy was evaluated to be 56.9 kJ mol^-1. Although the catalyst was able to achieve almost the same conversion when the catalyst was repeatedly tested five times under the same condition, the catalytic activity decreased gradually. Overall, it could be revealed that Co-NPs supported on LDHs have a huge potential to be used for H₂ energy production.

Rehydrogenation of Sodium Borates to Close the NaBH4-H2 Cycle: A Review

In 2007, the US Department of Energy recommended a no-go on NaBH4 hydrolysis for onboard applications; however, the concept of a NaBH4-H2-PEMFC system has the potential to become a primary source for on-demand power supply. Despite the many efforts to study this technology, most of the published papers focus on catalytic performance. Nevertheless, the development of a practical reaction system to close the NaBH4-H2 cycle remains a critical issue. Therefore, this work provides an overview of the research progress on the solutions for the by-product rehydrogenation leading to the regeneration of NaBH4 with economic potential. It is the first to compare and analyze the main types of processes to regenerate NaBH4: thermo-, mechano-, and electrochemical. Moreover, it considers the report by Demirci et al. on the main by-product of sodium borohydride hydrolysis. The published literature already reported efficient NaBH4 regeneration; however, the processes still need more improvements. Moreover, it is noteworthy that a transition to clean methods, through the years, was observed.

High Energy Ball Milling and Liquid Crystal Template Method: A Successful Combination for the Preparation of Magnetic Nano-Platforms

In this study, we present the preparation of superparamagnetic ordered mesoporous silica (SOMS) for biomedical applications by the combination of high energy ball milling (HEBM) and the liquid crystal template method (LCT) to produce a material comprised of room temperature superparamagnetic Fe₃O₄ nanoparticles in a MCM-41 like mesostructured silica. In a typical synthesis, a mixture of Fe₂O₃ and silica was sealed in a stainless-steel vial with steel balls. Ball milling experiments were performed in a vibratory mill apparatus. The milling process produced nanocomposites with an average size ranging from ∼100-200 nm, where the Fe₃O₄ nanoparticles (4.8 nm size) are homogeneously dispersed into the amorphous SiO₂ matrix. The obtained nanocomposite has been used for the preparation of the SOMS through the LCT method. Structural, morphological and textural characterization were performed using X-ray powder diffraction, transmission electron microscopy and nitrogen sorption analysis. Field dependence of magnetization was investigated and showed superparamagnetic behaviour at 300 K with a value of saturation magnetization (M_s) that is of interest for biomedical applications.

Preparation and characterization of self-electrical stimuli conductive gellan based nano scaffold for nerve regeneration containing chopped short spun nanofibers of PVDF/MCM41 and polyaniline/graphene nanoparticles: Physical, mechanical and morphological studies

Conductive self -electrical stimuli bioactive scaffolds could be used the potential for peripheral nerve regeneration with the maximum efficiency. To produce such conductive self-electrical stimuli bioactive scaffolds, chopped spun piezoelectric nanofibers of polyvinylidene fluoride/mesoporous silica nanoparticle (PVDF/MCM41) are prepared and incorporated in gellan/polyaniline/graphene (gellan/PAG) nanocomposites which have been previously prepared by incorporation of polyaniline/graphene (PAG) nanoparticles in gellan gel at 80 °C. Highly conductive binary doped polyaniline/graphene nanoparticles are prepared by chemical oxidative polymerization of aniline monomer using in-suite precipitation polymerization method in presence of graphene nanoparticles and sodium dodecyl sulfate. All intermediate and final products including spun PVDF/MCM41 nanofibers, PAG nanoparticles, and gellan-gelatin gel scaffolds containing PVDF/MCM41 nano spun fibers and PAG nanoparticles are characterized using different analysis methods. Chemical and structural analyses of PAG nanoparticles and PVDF/MCM41 nanofibers have been done using FTIR and XRD methods. The morphological structure of different samples is investigated using SEM. Morphological investigation and DLS results confirm fabrication of MCM41 nanoparticle with a completely spherical shape and the average size of 50 nm of which have been dispersed in electrospun PVDF nanofibers very well. Also, the preparation of PAG nanoparticle with high conductivity is verified with morphological and conductivity tests. MTT easy and biocompatibility test results indicate potential applicability of the prepared conductive self -stimuli nano-scaffold for nerve regeneration applications.

Recent Advances in Noble Metal Catalysts for Hydrogen Production from Ammonia Borane

Interest in chemical hydrogen storage has increased, because the supply of fossil fuels are limited and the harmful effects of burning fossil fuels on the environment have become a focus of public concern. Hydrogen, as one of the energy carriers, is useful for the sustainable development. However, it is widely known that controlled storage and release of hydrogen are the biggest barriers in large-scale application of hydrogen energy. Ammonia borane (NH3BH3, AB) is deemed as one of the most promising hydrogen storage candidates on account of its high hydrogen to mass ratio and environmental benignity. Development of efficient catalysts to further improve the properties of chemical kinetics in the dehydrogenation of AB under appropriate conditions is of importance for the practical application of this system. In previous studies, a variety of noble metal catalysts and their supported metal catalysts (Pt, Pd, Au, Rh, etc.) have presented great properties in decomposing the chemical hydride to generate hydrogen, thus, promoting their application in dehydrogenation of AB is urgent. We analyzed the hydrolysis of AB from the mechanism of hydrogen release reaction to understand more deeply. Based on these characteristics, we aimed to summarize recent advances in the development of noble metal catalysts, which had excellent activity and stability for AB dehydrogenation, with prospect towards realization of efficient noble metal catalysts.

A modified 'skeleton/skin' strategy for designing CoNiP nanosheets arrayed on graphene foam for on/off switching of NaBH4 hydrolysis

CoNiP nanosheet array catalysts were successfully prepared on three-dimensional (3D) graphene foam using hydrothermal synthesis. These catalysts were prepared using 3D Ni-graphene foam (Ni/GF), comprising nickel foam as the 'skeleton' and reduced graphene oxide as the 'skin'. This unique continuous modified 'skeleton/skin' structure ensure that the catalysts had a large surface area, excellent conductivity, and sufficient surface functional groups, which promoted in situ CoNiP growth, while also optimizing the hydrolysis of sodium borohydride. The nanosheet arrays were fully characterized and showed excellent catalytic performance, as supported by density functional theory calculations. The hydrogen generation rate and activation energy are 6681.34 mL min-1 g-1 and 31.2 kJ mol-1, respectively, outperforming most reported cobalt-based catalysts and other precious metal catalysts. Furthermore, the stability of mockstrawberry-like CoNiP catalyst was investigated, with 74.9% of the initial hydrogen generation rate remaining after 15 cycles. The catalytic properties, durability, and stability of the catalyst were better than those of other catalysts reported previously.