Hierarchically Ordered Nanoporous Carbon with Exclusively Surface-Anchored Cobalt as Efficient Electrocatalyst

A hierarchically ordered porous carbon electrocatalyst with exclusively surface-anchored cobalt species, dubbed Co@HOPC, is synthesized from polyaniline and cobalt-functionalized silica microparticles templates, and its high electrocatalytic activity for the oxygen evolution reaction (OER) is demonstrated. The material requires a small potential (320 mV) to drive the reaction with a current density of 10 mA cm^-2 and a small Tafel slope of 31.2 mV dec^-1 . Moreover, Co@HOPC shows better catalytic activity for OER than in situ cobalt-doped and surface cobalt-loaded hierarchically ordered porous carbon materials synthesized by traditional methods. This is due to the abundant surface cobalt species present in Co@HOPC and the material's good electrical conductivity. This work provides a new strategy to utilize functionalized silica microparticles as templates to synthesize hierarchically ordered porous carbon materials with metal-rich surfaces and efficient electrocatalytic activities.

Fluorescent SiO2@Tb3+(PET-TEG)3Phen Hybrids as Nucleating Additive for Enhancement of Crystallinity of PET

A hybrid polymer of SiO₂@Tb³⁺(poly(ethylene terephthalate)-tetraglycol)₃ phenanthroline (SiO₂@Tb³⁺(PET-TEG)₃Phen) was synthesized by mixing of inorganic SiO₂ nanoparticles with polymeric segments of PET-TEG, whereas PET-TEG was achieved through multi-step functionalization strategy. Tb³⁺ ions and β-diketonate ligand Phen were added in resulting material. The experimental results demonstrated that it was well blended with PET as a robust additive, and not only promoted the crystallinity, but also possessed excellent luminescence properties. An investigation of the mechanism revealed that the SiO₂ nanoparticles functioned as a crystallization promotor; the Tb³⁺ acted as the fluorescent centre; and the PET-TEG segments played the role of linker and buffer, providing better compatibility of PET matrix with the inorganic component. This work demonstrated that hybrid polymers are appealing as multifunctional additives in the polymer processing and polymer luminescence field.

Recent Advances in the Nanocatalysts-assisted NaBH4 Reduction of Nitroaromatics in water

In view of the increasing applications of nanocatalysis in chemical transformations, this article illustrates recent advances on the use of nanocatalysts for an important reduction reaction, the hydrogenation of nitroaromatics to significant aminoaromatics with aqueous NaBH₄ solution; the utility of mono- and multi-metal nanocatalysts with special emphasis on heterogeneous nanocatalysts are included. A progressive trend on the applicability of nanocatalysts is also incorporated with large scale application and their sustainable recyclization and reuse utilizing supported and magnetic nanocatalysts; representative methods for the synthesis of such reusable nanocatalysts are featured.

Bringing attention to metal (un)availability in encapsulated catalysts

The encapsulation method significantly affects the shell porosity, the availability of active sites and the catalytic behavior of Pd@SiO₂ materials in methane combustion.

Oxygen deficient Pr6O11 nanorod supported palladium nanoparticles: highly active nanocatalysts for styrene and 4-nitrophenol hydrogenation reactions

The design and development of highly efficient and long lifetime Pd-based catalysts for hydrogenation reactions have attracted significant research interest over the past few decades. Rational selection of supports for Pd loadings with strong metal-support interaction (SMSI) is beneficial for boosting catalytic activity and stability. In this context, we have developed a facile approach for uniformly immobilizing ultra-small Pd nanoparticles (NPs) with a clean surface on a Pr₆O₁₁ support by a hydrogen thermal reduction method. The hydrogenations of p-nitrophenol and styrene are used as model reactions to evaluate the catalytic efficiency. The results show highly efficient styrene hydrogenation performance under 1 atm H₂ at room temperature with a TOF value as high as 8957.7 h⁻¹, and the rate constant value of p-nitrophenol reduction is 0.0191 s⁻¹. Strong metal-support interaction and good dispersion of Pd nanoparticles, as demonstrated by XPS and HRTEM results, contribute to the excellent hydrogenation performance. Electron paramagnetic resonance (EPR) results suggest the presence of oxygen vacancies in the support, which serve as electron donors and enhance the adsorption and activation of reactants and subsequent conversion into products. Moreover, the catalyst can be recovered and reused up to 10 consecutive cycles without marked loss of activity. Overall, our results indicate that oxygen-deficient Pr₆O₁₁ nanorods (NRs) not only play a role as support but also work as the promoter to substantially boost the catalytic activities for organic transformations, therefore, providing a novel strategy to develop other high-performance nanostructured catalysts for environmental sustainability.

Oxygen-deficient Pd/Pr₆O₁₁ nanocatalysts with strong metal-support interaction exhibit highly efficient styrene and 4-NP hydrogenation reactions performance.

Nano-K2CO3: preparation, characterization and evaluation of reactive activities

Nano-K₂CO₃ shows higher basicity and can replace sodium (potassium) alkoxide to carry out monoalkylation and oximation of active methylene compounds.

Pd(0) encapsulated nanocatalysts as superior catalytic systems for Pd-catalyzed organic transformations

In the last decade, Pd(0) nanoparticles have attracted increasing attention due to their outstanding utility as nanocatalysts in a wide variety of key chemical reactions.

Towards rational design of core–shell catalytic nanoreactor with high performance catalytic hydrogenation of levulinic acid

Core–shell catalytic nanoreactor was designed, exhibiting high catalytic activity for levulinic acid hydrogenation.

Continuous-flow hydrogenation of olefins and nitrobenzenes catalyzed by platinum nanoparticles dispersed in an amphiphilic polymer

Continuous-flow hydrogenation of olefins and nitrobenzenes with ARP-Pt.

A comparative study of two different approaches for the incorporation of silver nanoparticles into layer-by-layer films

In this work, a comparative study about the incorporation of silver nanoparticles (AgNPs) into thin films is presented using two alternative methods, the in situ synthesis process and the layer-by-layer embedding deposition technique. The influence of several parameters such as color of the films, thickness evolution, thermal post-treatment, or distribution of the AgNPs along the coatings has been studied. Thermal post-treatment was used to induce the formation of hydrogel-like AgNPs-loaded thin films. Cross-sectional transmission electron microscopy micrographs, atomic force microscopy images, and UV-vis spectra reveal significant differences in the size and distribution of the AgNPs into the films as well as the maximal absorbance and wavelength position of the localized surface plasmon resonance absorption bands before and after thermal post-treatment. This work contributes for a better understanding of these two approaches for the incorporation of AgNPs into thin films using wet chemistry.

A Pd/CNT-SiC monolith as a robust catalyst for Suzuki coupling reactions

A Pd/CNT-SiC monolith prepared by a simple two-step method exhibits robust catalytic activity and recycling ability in Suzuki coupling reactions.

Strawberry-like SiO2@Pd and Pt nanomaterials

Pd and Pt nanoparticles (NPs) supported on silica particles were prepared via a straightforward protocol in non-alcoholic medium. The metallic NPs are remarkably dense, homogeneous and well-dispersed at the silica surface.

Ordered mesoporous materials based on interfacial assembly and engineering

Ordered mesoporous materials have inspired prominent research interest due to their unique properties and functionalities and potential applications in adsorption, separation, catalysis, sensors, drug delivery, energy conversion and storage, and so on. Thanks to continuous efforts over the past two decades, great achievements have been made in the synthesis and structural characterization of mesoporous materials. In this review, we summarize recent progresses in preparing ordered mesoporous materials from the viewpoint of interfacial assembly and engineering. Five interfacial assembly and synthesis are comprehensively highlighted, including liquid-solid interfacial assembly, gas-liquid interfacial assembly, liquid-liquid interfacial assembly, gas-solid interfacial synthesis, and solid-solid interfacial synthesis, basics about their synthesis pathways, princples and interface engineering strategies.

Porosity control of Pd@SiO2 yolk-shell nanocatalysts by the formation of nickel phyllosilicate and its influence on Suzuki coupling reactions

The surface of Pd@SiO(2) core-shell nanoparticles (1) was simply modified by the formation of nickel phyllosilicate. The addition of nickel salts formed branched nickel phyllosilicates and generated pores in the silica shells, yielding Pd@SiO(2)-Niphy nanoparticles (Niphy = nickel phyllosilicate; 2, 3). By removal of the silica residue, Pd@Niphy yolk-shell nanoparticles (4) was uniformly obtained. The four distinct nanostructures (1-4) were employed as catalysts for Suzuki coupling reactions with aryl bromide and phenylboronic acid, and the conversion yields were in the order of 1 < 2 < 3 < 4 as the pore volume and surface area of the catalysts increased. The reaction rates were strongly correlated with shell porosity and surface exposure of the metal cores. The chemical inertness of nickel phyllosilicate under the basic conditions rendered the catalysts reusable for more than five times without loss of activity.

Synthesis of a multinanoparticle-embedded core/mesoporous silica shell structure as a durable heterogeneous catalyst

A multi-nanoparticle-embedded amorphous aluminum/magnesium oxides (AAMO) core/mesoporous silica (mSiO(2)) shell structure has been successfully synthesized by calcining the presynthesized catalyst precursor-containing layered double hydroxide (LDH) core/mesoporous silica shell composite. The well-dispersed catalytic nanoparticles were fixed at the interface between AAMO core and mesoporous SiO(2) shell, i.e., at the inner pore mouths of the mesoporous SiO(2) shell, which could effectively prevent nanoparticles from growth and/or aggregation with each other and in the meantime allow efficient access of reactants to the catalytic NPs. The final core/shell composite was found to be an efficient and highly recyclable heterogeneous catalyst.

Assembling nanostructures for effective catalysis: supported palladium nanoparticle multicores coated by a hollow and nanoporous zirconia shell

We report the synthesis and catalytic activities of highly stable, hollow nanoreactors, called SiO(2)/Pd/h-ZrO(2), which consist of silica microsphere (SiO(2))-supported Pd nanoparticle multicores (Pd) that are encapsulated with a hollow and nanoporous ZrO(2) shell (h-ZrO(2)). The SiO(2)/Pd/h-ZrO(2) nanoreactors are fabricated by first synthesizing SiO(2)/Pd/SiO(2)/ZrO(2) microspheres, and then etching the inner SiO(2) shell with dilute NaOH solution. The hollow and nanoporous ZrO(2) shell of the nanoreactors serves two important functions: 1) it provides reactants direct access to the Pd nanoparticle multicores inside the SiO(2)/Pd/h-ZrO(2) nanoreactors during catalysis, and 2) it stabilizes the Pd nanoparticles or protects them from aggregation/sintering. The fabrication of such structures capable of protecting the Pd nanoparticles from aggregation/sintering is of particular interest considering the fact that Pd nanoparticles generally have a high tendency to aggregate because of their high surface energies. Furthermore, the structures are interesting because the Pd nanoparticles are designed and synthesized here to have 'naked' surfaces or no organic surface-passivating ligands-that are often necessary to stabilize metallic nanoparticles-in order to increase their catalytic efficiency. The resulting SiO(2)/Pd/h-ZrO(2) nanoreactors show excellent catalytic activity, as shown in the hydrogenation of olefins and nitro groups, even at room temperature under moderate hydrogen pressure. This stems from the SiO(2)/Pd/h-ZrO(2) microspheres' high surface area and their small, stable, and bare Pd nanoparticles. Furthermore, the SiO(2)/Pd/h-ZrO(2) nanoreactor catalysts remain fairly stable after reaction and can be recycled multiple times without losing their high catalytic activities.

Silica-dendrimer core-shell microspheres with encapsulated ultrasmall palladium nanoparticles: efficient and easily recyclable heterogeneous nanocatalysts

We report the synthesis, characterization, and catalytic properties of novel monodisperse SiO(2)@Pd-PAMAM core-shell microspheres containing SiO(2) microsphere cores and PAMAM dendrimer-encapsulated Pd nanoparticle (Pd-PAMAM) shells. First, SiO(2) microspheres, which were prepared by the Stöber method, were functionalized with vinyl groups by grafting their surfaces with vinyltriethoxysilane (VTS). The vinyl groups were then converted into epoxides by using m-chloroperoxybenzoic acid. Upon treatment with amine-terminated G4 poly(amidoamine) (PAMAM) dendrimers, the SiO(2)-supported epoxides underwent ring-opening and gave SiO(2)@PAMAM core-shell microspheres. Pd nanoparticles within the cores of the SiO(2)-supported PAMAM dendrimers were synthesized by letting Pd(II) ions complex with the amine groups in the cores of the dendrimers and then reducing them into Pd(0) with NaBH(4). This produced the SiO(2)@Pd-PAMAM core-shell microspheres. The presence of the different functional groups on the materials was monitored by following the changes in FTIR spectra, elemental analyses, and weight losses on thermogravimetric traces. Transmission electron microscopy (TEM) images showed the presence of Pd nanoparticles with average size of 1.56 ± 0.67 nm on the surface of the monodisperse SiO(2)@Pd-PAMAM core-shell microspheres. The SiO(2)@Pd-PAMAM core-shell microspheres were successfully used as an easily recyclable catalyst for hydrogenation of various olefins, alkynes, keto, and nitro groups, giving ~100% conversion and high turnover numbers (TONs) under 10 bar H(2) pressure, at room temperature and in times ranging from 10 min to 3 h. In addition, the SiO(2)@Pd-PAMAM core-shell microspheres were proven to be recyclable catalysts up to five times with barely any leaching of palladium into the reaction mixture.