Fabrication of three-dimensional (3D) raspberry-like copper chromite spinel catalyst in a facile hydrothermal route and its activity in selective hydroxylation of benzene to phenol

Fractal-like gold nanonetworks formed by templated electrodeposition through 3D-mesoporous silica films

Fractal-like networks of gold nanoparticles created by templated electrodeposition are described. Templated electrodeposition is a powerful and efficient technique for the bottom-up fabrication of nanostructures which can effectively control the size and shape of the electrodeposits. In this work, mesoporous silica films with highly ordered mesopores and three-dimensional mesostructure are synthesised and are used as templates for the electrodeposition of gold nanoparticles. The mesoporous silica films have small mesopores (∼8 nm) and complex mesopore channels (Fmmm structure with the [0 1 0] axis perpendicular to the substrate). A variety of nucleation conditions were applied to investigate their effect on the nanoparticles' arrangement and growth in templated electrodeposition. The electrodeposited gold particles are characterised by electron microscopy and grazing incidence small-angle X-ray scattering (GISAXS). GISAXS shows changes in the lattice parameters of the mesostructure after gold electrodeposition that relate to dimensional changes in directions linked to the shortest distances between the main spherical pores. Top-view SEM shows large areas of gold nanoparticles were deposited into the film and they were growing towards the surface. After removing the silica film templates, the gold nanoparticles display interesting fractal morphologies: the linked gold nanonetworks form a branched structure. The lengths of branches vary from the applied nucleation deposition conditions. Generally, with increasing nucleation time, fractal gold nanoparticles with longer branches are more likely to be obtained.

What is the role of PEO chains in the assembly of core-corona supraparticles in aqueous dispersions?

Hypothesis The assembly of core-corona supraparticles in aqueous dispersions has been regularly assisted by auxiliary monomers/oligomers which modify the individual particles with, e.g., surface grafting of polyethylene oxide (PEO) chains or other hydrophilic monomers. However, this modification complicates the preparation and purification procedures and increases potential upscaling efforts. Hybrid polymer-silica core-corona supracolloids could be more simply assembled if the PEO chains from surfactants, typically used by default as polymer stabilizers, concomitantly act as assembly promotors. The supracolloids assembly could therefore be more easily achieved without requiring particles functionalization or post-purification steps. Methods The self-assembly of supracolloidal particles prepared with PEO-surfactant stabilized (Triton X-405) and/or PEO-grafted polymer particles is compared to differentiate the roles of the PEO chains in the assembly of core-corona supraparticles. Using time-resolved dynamic light scattering (DLS) and cryogenic transmission electron microscopy(cryo-TEM), the effect of concentration of PEO chains (from surfactant) on the kinetics and dynamics of supracolloids assembly is investigated. Self-consistent field (SCF) lattice theory was used to numerically study the distribution of PEO chains at the interfaces present in the supracolloidal dispersions. Findings The PEO based surfactant can be used as assembly promoter of core-corona hybrid supracolloids due to its amphiphilic nature and via establishing hydrophobic interactions. The concentration of the PEO surfactant, and especially the PEO chains distribution over the different interfaces, crucially affect the supracolloids assembly. A simplified pathway for preparing hybrid supracolloidal particles with a well-controlled corona coverage over polymer cores is presented.

Template and interfacial reaction engaged synthesis of CeMnO x hollow nanospheres and their performance for toluene oxidation

A series of well-dispersed CeMnO x hollow nanospheres with uniform diameter and thickness were synthesized by a novel approach combining the template method and interfacial reaction. A SiO2 template was used as a hard template for preparation of SiO2@CeO2 nanospheres by solvothermal reaction. SiO2@CeMnO x could be formed after KMnO4 was reacted with SiO2@CeO2 by interfacial reaction between MnO4 - and Ce3+. Among all the prepared catalysts, CeMnO x -3 with a moderate content of Mn (15 wt%) exhibited the lowest temperature for complete combustion of toluene (280 °C). Moreover, it showed high stability for 36 h with toluene conversion above 97.7% and good water tolerance with 5 vol% H2O. With characterization, we found that the reaction between Ce and Mn in the Ce-Mn binary oxides gave rise to increased Ce3+ and oxygen vacancies, which led to the formation of enhanced reducibility and more surface-absorbed oxygens (O2 2-, O2- and O-), and improved the catalytic performance further.

Assembly of partially covered strawberry supracolloids in dilute and concentrate aqueous dispersions

HYPOTHESIS

Core-corona supracolloids can be assembled in aqueous dispersions by controlling the physical interactions between the corona and core colloidal particles. A raspberry corona configuration with full surface coverage of the core can be reached by inducing strong attractive interactions between the individual particles. A controlled partial surface coverage of the core, i.e. strawberry configuration, is however, more difficult to achieve. Supracolloids with different surface coverage ratio exhibit unique and multifunctional surface properties.

EXPERIMENTS

By counterbalancing the multiple physical interactions playing a role during the assembly, the configuration and stability of the assemblies could be fine-tuned over a wide range of concentrations. Supracolloids consisting of polyethylene glycol (PEO)-grafted polymer particles covered by silica nanoparticles were assembled with different configurations, by adjusting the pH and ionic strength of the dispersion, the PEO grafting density and the particles concentration. The self-assembly process and resulting configurations were monitored via cryogenic transmission electron microscopy (Cryo-TEM) and light scattering.

FINDINGS

The suitable conditions to assemble supracolloids with partial corona coverage have been established. Stable strawberry supracolloids could be prepared, both for diluted (1 wt%) and concentrated (12 wt%) dispersions. These hybrid supracolloids with well-defined configuration are highly relevant to developing advanced water-borne paints and inks, food dispersions, cosmetic and healthcare products.

A green approach for the preparation of a surfactant embedded sulfonated carbon catalyst towards glycerol acetalization reactions

A surfactant embedded carbon-based acid catalyst was prepared via simple physical mixing and thermal treatment to establish the relationship between hydrophobicity and acidic site density for efficient glycerol acetalization reaction.

Single Atomic Cu-N2 Catalytic Sites for Highly Active and Selective Hydroxylation of Benzene to Phenol

Searching for an efficient single-atom catalyst for benzene hydroxylation to phenol is of critical importance, but it still remains a challenge. Herein, a single-atom catalyst with unique Cu-N₂ moieties (Cu₁-N₂/HCNS) was prepared and confirmed by HAADF-STEM and EXAFS. Turnover number (TON) over Cu₁-N₂/HCNS (6,935) is 3.4 times of Cu₁-N₃/HCNS (2,034) under the same reaction conditions, and both exhibit much higher phenol selectivity (close to 99%) and stability compared with Cu nanoparticles and nanoclusters. Experiments and DFT calculations reveal that atomically dispersed Cu species are active sites for benzene hydroxylation to phenol, and the Cu-N₂ is more active than Cu-N₃ owing to its much lower energy barrier concerning the activation of H₂O₂ led by its unique coordination state of local atomic structure. We envision that this work opens a new window for modulating coordination environments of single metallic atoms in catalysis design.

Morphology-Tailored Gold Nanoraspberries Based on Seed-Mediated Space-Confined Self-Assembly

Raspberry-like structure, providing a high degree of symmetry and strong interparticle coupling, has received extensive attention from the community of functional material synthesis. Such structure constructed in the nanoscale using gold nanoparticles has broad applicability due to its tunable collective plasmon resonances, while the synthetic process with precise control of the morphology is critical in realizing its target functions. Here, we demonstrate a synthetic strategy of seed-mediated space-confined self-assembly using the virus-like silica (V-SiO₂) nanoparticles as the templates, which can yield gold nanoraspberries (AuNRbs) with uniform size and controllable morphology. The spikes on V-SiO₂ templates serve dual functions of providing more growth sites for gold nanoseeds and activating the space-confined effect for gold nanoparticles. AuNRbs with wide-range tunability of plasmon resonances from the visible to near infrared (NIR) region have been successfully synthesized, and how their geometric configurations affect their optical properties is thoroughly discussed. The close-packed AuNRbs have also demonstrated huge potential in Raman sensing due to their abundant “built-in” hotspots. This strategy offers a new route towards synthesizing high-quality AuNRbs with the capability of engineering the morphology to achieve target functions, which is highly desirable for a large number of applications.

Raspberry-Like Polysilsesquioxane Particles with Hollow-Spheres-on-Sphere Structure: Rational Design, Controllable Synthesis, and Catalytic Application

Raspberry-like hollow-spheres-on-sphere (HSOS) particles with reactive surfaces, uniform sizes and monodisperse properties were rational designed and fabricated to immobilize gold nanoparticles for the catalytic reduction of 4-nitrophenol. HSOS polysilsesquioxane (PSQ) particles were constructed by an organic alkali catalyzed sol-gel process from trialkoxysilane precursors with stabilized polystyrene (PS) nanoparticles as both a sacrifice template and a Pickering emulsifier. The PSQ particles were fabricated in an ice bath with methyltrimethoxysilane and mercaptopropyltrimethoxysiane as a co-precursor, tetramethylammonium hydroxide (TMAH) as a catalyst, polyvinylpyrrolidone (PVP) and sodium lignosulfonat as co-stabilizers and PS latex as a hard template. The formation mechanism of the hierarchical particles was investigated in detail by the time study through imaging the particles at regular time intervals during the reaction process. Various effect factors on the morphology were studied systematically which showed that the precursor composition, the content of PS, TMAH and PVP are the most important factors. The hierarchical structure combined with the mercaptopropyl groups on both the surface and the skeleton to make it possible to adsorb guest molecules. Au nanoparticles were immobilized on the particles for the catalytic reduction of 4-nitrophenol to 4-aminophenol. The unique PSQ colloids with hollow-spheres-on-sphere extended the family of the hierarchical structures and has shown the potential applications in separations, drug delivery and heterogeneous catalysts.

NH3 -Driven Benzene C-H Activation with O2 that Opens a New Way for Selective Phenol Synthesis

Catalytic benzene C-H activation toward selective phenol synthesis with O₂ remains a stimulating challenge to be tackled. Phenol is currently produced industrially by the three-steps cumene process in liquid phase, which is energy-intensive and not environmentally friendly. Hence, there is a strong demand for an alternative gas-phase single-path reaction process. This account documents the pivotal confined single metal ion site platform with a sufficiently large coordination sphere in β zeolite pores, which promotes the unprecedented catalysis for the selective benzene hydroxylation with O₂ under coexisting NH₃ by the new inter-ligand concerted mechanism. Among alkali and alkaline-earth metal ions and transition and precious metal ions, single Cs⁺ and Rb⁺ sites with ion diameters >0.300 nm in the β pores exhibited good performances for the direct phenol synthesis in a gas-phase single-path reaction process. The single Cs⁺ and Rb⁺ sites that possess neither significant Lewis acidic-basic property nor redox property, cannot activate benzene, O₂ , and NH₃ , respectively, whereas when they coadsorbed together, the reaction of the inter-coadsorbates on the single alkali-metal ion site proceeds concertedly (the inter-ligand concerted mechanism), bringing about the benzene C-H activation toward phenol synthesis. The NH₃ -driven benzene C-H activation with O₂ was compared to the switchover of the reaction pathways from the deep oxidation to selective oxidation of benzene by coexisting NH₃ on Pt₆ metallic cluster/β and Ni₄ O₄ oxide cluster/β. The NH₃ -driven selective oxidation mechanism observed with the Cs⁺ /β and Rb⁺ /β differs from the traditional redox catalysis (Mars-van Krevelen) mechanism, simple Langmuir-Hinshelwood mechanism, and acid-base catalysis mechanism involving clearly defined interaction modes. The present catalysis concept opens a new way for catalytic selective oxidation processes involving direct phenol synthesis.

A new iron-based metal-organic framework with enhancing catalysis activity for benzene hydroxylation

A new Fe-based metal-organic framework (MOF), termed Fe-TBAPy Fe2(OH)2(TBAPy)·4.4H2O, was solvothermally synthesized. Structural analysis revealed that Fe-TBAPy is built from [Fe(OH)(CO2)2]∞ rod-shaped SBUs (SBUs = secondary building units) and 1,3,6,8-tetrakis(p-benzoate)pyrene (TBAPy4-) linker to form the frz topological structure highlighted by 7 Å channels and 3.4 Å narrow pores sandwiching between the pyrene cores of TBAPy4-. Consequently, Fe-TBAPy was used as a recyclable heterogeneous catalyst for benzene hydroxylation. Remarkably, the catalysis reaction resulted in high phenol yield and selectivity of 64.5% and 92.9%, respectively, which are higher than that of the other Fe-based MOFs and comparable with those of the best-performing heterogeneous catalysts for benzene hydroxylation. This finding demonstrated the potential for the design of MOFs with enhancing catalysis activity for benzene hydroxylation.

Heterogeneity of polyoxometalates by confining within ordered mesopores: toward efficient oxidation of benzene to phenol

Polyoxometalates@ordered mesoporous polymers have been prepared by a mechanochemical coordination assembly with tannin as the renewable precursor.

A cocoon silk chemistry strategy to ultrathin N-doped carbon nanosheet with metal single-site catalysts

Development of single-site catalysts supported by ultrathin two-dimensional (2D) porous matrix with ultrahigh surface area is highly desired but also challenging. Here we report a cocoon silk chemistry strategy to synthesize isolated metal single-site catalysts embedded in ultrathin 2D porous N-doped carbon nanosheets (M-ISA/CNS, M = Fe, Co, Ni). X-ray absorption fine structure analysis and spherical aberration correction electron microscopy demonstrate an atomic dispersion of metal atoms on N-doped carbon matrix. In particular, the Co-ISA/CNS exhibit ultrahigh specific surface area (2105 m² g⁻¹) and high activity for C–H bond activation in the direct catalytic oxidation of benzene to phenol with hydrogen peroxide at room temperature, while the Co species in the form of phthalocyanine and metal nanoparticle show a negligible activity. Density functional theory calculations discover that the generated O = Co = O center intermediates on the single Co sites are responsible for the high activity of benzene oxidation to phenol.

Single-site catalysts supported by ultrathin two-dimensional (2D) porous matrix are desirable for catalytic reactions, yet their synthesis remains a great challenge. Herein the authors report a cocoon silk chemistry strategy to synthesize isolated metal single-site catalysts embedded in ultrathin 2D porous N-doped carbon nanosheets.

CuCr2O4@rGO Nanocomposites as High-Performance Cathode Catalyst for Rechargeable Lithium-Oxygen Batteries

Rechargeable lithium-oxygen batteries have been considered as a promising energy storage technology because of their ultra-high theoretical energy densities which are comparable to gasoline. In order to improve the electrochemical properties of lithium-oxygen batteries (LOBs), especially the cycling performance, a high-efficiency cathode catalyst is the most important component. Hence, we aim to demonstrate that CuCr₂O₄@rGO (CCO@rGO) nanocomposites, which are synthesized using a facile hydrothermal method and followed by a series of calcination processes, are an effective cathode catalyst. The obtained CCO@rGO nanocomposites which served as the cathode catalyst of the LOBs exhibited an outstanding cycling performance for over 100 cycles with a fixed capacity of 1000 mAh g^-1 at a current density of 200 mA g^-1. The enhanced properties were attributed to the synergistic effect between the high catalytic efficiency of the spinel-structured CCO nanoparticles, the high specific surface area, and high conductivity of the rGO.

Ruthenium Nanoparticles Decorated Tungsten Oxide as a Bifunctional Catalyst for Electrocatalytic and Catalytic Applications

The syntheses of highly stable ruthenium nanoparticles supported on tungsten oxides (Ru-WO₃) bifunctional nanocomposites by means of a facial microwave-assisted route are reported. The physicochemical properties of these Ru-WO₃ catalysts with varied Ru contents were characterized by a variety of analytical and spectroscopic methods such as XRD, SEM/TEM, EDX, XPS, N₂ physisorption, TGA, UV-vis, and FT-IR. The Ru-WO₃ nanocomposite catalysts so prepared were utilized for electrocatalytic of hydrazine (N₂H₄) and catalytic oxidation of diphenyl sulfide (DPS). The Ru-WO₃-modified electrodes were found to show extraordinary electrochemical performances for sensitive and selective detection of N₂H₄ with a desirable wide linear range of 0.7-709.2 μM and a detection limit and sensitivity of 0.3625 μM and 4.357 μA μM^-1 cm^-2, respectively, surpassing other modified electrodes. The modified GCEs were also found to have desirable selectivity, stability, and reproducibility as N₂H₄ sensors, even for analyses of real samples. This is ascribed to the well-dispersed metallic Ru NPs on the WO₃ support, as revealed by UV-vis and photoluminescence studies. Moreover, these Ru-WO₃ bifunctional catalysts were also found to exhibit excellent catalytic activities for oxidation of DPS in the presence of H₂O₂ oxidant with desirable sulfoxide yields.

Fabrication of Ag nanoparticles supported on one-dimensional (1D) Mn3O4 spinel nanorods for selective oxidation of cyclohexane at room temperature

Silver nanoparticles supported on spinel Mn₃O₄ nanorods efficiently catalyze cyclohexane to cyclohexanone with high yield at room-temperature.

Ni-based chromite spinel for high-performance supercapacitors

NiCr₂O₄ has been prepared through the easy precipitation reaction of Ni²⁺ and Cr³⁺ (1 : 2 mol ratio) in aqueous NH₃ followed by annealing at a high temperature.

Catalytic oxidation of aromatic amines to azoxy compounds over a Cu–CeO2 catalyst using H2O2 as an oxidant

Highly dispersed Cu-nanoparticles supported on nanocrystalline CeO₂ were prepared which showed good catalytic activity toward selective oxidation of aromatic amines.

A facile strategy to fabricate covalently linked raspberry-like nanocomposites with pH and thermo tunable structures

A simple and controllable route to prepare covalently bonded raspberry-like composite particles with pH and thermal dual-responsiveness.

Fabrication of Ag/Mn3O4 nano-architectures for the one-step selective oxidation of 3-picoline to niacin: a key to vitamin B3 production

Silver nanoparticles supported on spinel Mn₃O₄ nanorods efficiently transformed 3-methylpyridine to niacin using hydrogen peroxide as an oxidant.

Chloride promoted room temperature preparation of silver nanoparticles on two dimensional tungsten oxide nanoarchitectures for the catalytic oxidation of tertiary N-compounds to N-oxides

A halide ion promoted two dimensional silver tungsten-based nanomaterial was synthesized by a facile one-pot synthesis protocol at room temperature. The 2D morphology features high activity and selectivity for the oxidation of a wide range of tertiary N-compounds to their corresponding N-oxides. The morphology of Ag/WO3 materials can be varied by changing the synthesis parameters. The unique 2D plate like morphology of tungsten oxide increases adsorption sites of the support, leading to less sintering and higher dispersion of silver nanoparticles, resulting in significantly enhanced activity for the reaction. The influence of reaction parameters such as temperature, substrate to oxidant molar ratio, reaction time, etc. was investigated in detail. The catalyst was characterized by XRD, XPS, ICP-AES, TGA, FT-IR, UV-vis, Raman, SEM, TEM and STEM. Raman studies further provide mechanistic insight which proves that the formation of peroxo tungsten species is responsible for the N-oxidation reaction. High stability and recyclability of the 2D Ag/WO3 nanoplates are also observed under the investigated conditions.

Cetyl alcohol mediated fabrication of forest of Ag/Mn3O4 nanowhiskers catalyst for the selective oxidation of styrene with molecular oxygen

Cetyl alcohol-mediated water-based preparation of nanocrystalline Ag/Mn₃O₄ catalyst has been reported in a one-pot preparation method.

One-pot preparation of nanocrystalline Ag–WO3 catalyst for the selective oxidation of styrene

Cationic surfactant cetyltrimethylammonium bromide-mediated water-based preparation of nanocrystalline Ag–WO₃ catalyst has been reported in a one-pot preparation method.

Fabrication of three dimensional (3D) hierarchical Ag/WO3 flower-like catalyst materials for the selective oxidation of m-xylene to isophthalic acid

A three dimensional (3D) hierarchical silver supported tungsten oxide flower-like microsphere catalyst has been fabricated using a cationic surfactant CTAB.