Monodisperse hollow spheres with sandwich heterostructured shells as high-performance catalysts via an extended SiO2 template method

Molecular Exchange of Dynamic Imine Bond for the Etching of Polymer Particles

The underlying trend of colloidal synthesis has focused on extending the structure and composition complexity of colloidal particles. Hollow and yolk-shell particles are successful examples that have potential applications in frontier fields. In this paper, we develop a facile and controllable etching method based on the molecular exchange of the dynamic imine bond to generate cavities in polymer particles. Starting from boronate ester polymer particles and inorganic@boronate core-shell particles with the imine bonds incorporated in the polymer networks, our etching method easily affords hollow and yolk-shell particles with tunable shell thicknesses. The molecular exchange dynamics analysis indicates that guest amine molecules cause the reconstruction of imine bonds and the leakage of molecular and oligomer fragments, resulting in the formation of the hollow structure. This molecular exchange-based etching method may be of interest in the construction of polymer architectures with increased composition and structure complexities. This article is protected by copyright. All rights reserved.

Hierarchical Multicavity Nitrogen-Doped Carbon Nanospheres as Efficient Polyselenide Reservoir for Fast and Long-Life Sodium-Selenium Batteries

Sodium-selenium (Na-Se) battery has been emerging as one of the most prospective energy storage systems owing to their high volumetric energy density and cost effectiveness. Nevertheless, the shuttle effect of sodium polyselenide (NaPSe) and sluggish electrochemical reaction kinetics present the main bottlenecks for its practical implementation. Herein, a new Se host of 3D nitrogen-doped hierarchical multicavity carbon nanospheres (3D NHMCs) is designed and synthesized via a facile self-sacrifice templating strategy. The 3D NHMCs are verified to hold a favorable structure of a hollow macropore core and numerous micro/mesopores hollow shell for hosting Se, which can not only maximize Se utilization and alleviate the volumetric expansion but also promote the electrical/ionic conductivity and electrolyte infiltration. Moreover, the abundant self-functionalized surfaces as an efficient NaPSe scavenger via robust physical-chemical dual blocking effects demonstrate high-efficiency in situ anchoring-diffusion-conversion of NaPSe, rendering rapid reaction kinetics and remarkable suppressive shuttle effect, as evidenced by systematic experimental analysis and density functional theory calculations. As a result, the high-Se-loading 3D NHMCs/Se cathode exhibits an ultrahigh volumetric capacity (863 mAh cm^-3 ) and rate capability (377 mAh g^-1 at 20 C) and unexceptionable stability over 2000 cycles at 2 C.

Zirconia Hybrid Nanoshells for Nutrient and Toxin Detection

Monitoring milk quality is of fundamental importance in food industry, because of the nutritional value and resulting position of milk in daily diet. The detection of small nutrients and toxins in milk is challenging, considering high sample complexity and low analyte abundance. In addition, the slow analysis and tedious sample preparation hinder the large-scale application of conventional detection techniques. Herein, zirconia hybrid nanoshells are constructed to enhance the performance of laser desorption/ionization mass spectrometry (LDI MS). Zirconia nanoshells with the optimized structures and compositions are used as matrices in LDI MS and achieve direct analysis of small molecules from 5 nL of native milk in ≈1 min, without any purification or separation. Accurate quantitation of small nutrient is achieved by introducing isotope into the zirconia nanoshell-assisted LDI MS as the internal standard, offering good consistency to biochemical analysis (BCA) with R²  = 0.94. Further, trace toxin is enriched and identified with limit-of-detection (LOD) down to 4 pm, outperforming the current analytical methods. This work sheds light on the personalized design of material-based tool for real-case bioanalysis and opens up new opportunities for the simple, fast, and cost-effective detection of various small molecules in a broad field.

Hollow Nano-Mesosilica Spheres Containing Rhodium Nanoparticles Supported on Nitrogen-Doped Carbon: An Efficient Catalyst for the Reduction of Nitroarenes under Mild Conditions

Atom efficiency, low temperature, low pressure, and a nontoxic hydrogen source as a reducing agent are ideal reaction conditions for the reduction of nitroarenes. In this work, an efficient catalyst comprising hollow nano-mesosilica spheres loaded with Rh nanoparticles supported on nitrogen-doped carbon was developed. Rh nanoparticles were stabilized and uniformly dispersed by nitrogen atoms, and the inner N-doped carbon shell was used to adsorb reaction substrates and improve catalytic activity. The catalyst showed remarkable activity (maximum yield at 1.5 h) and selectivity (100 %) for the reduction of nitrobenzene at lower temperature (80 °C), atmospheric pressure (1 atm), and without base under aqueous conditions. Moreover, the hydrothermal stability of this nanocatalyst was better than other catalysts in boiling water at 100 °C for 48 h and effectively prevented the aggregation and leaching of Rh NPs during the reaction.

Hollow Metal-Organic-Framework Micro/Nanostructures and their Derivatives: Emerging Multifunctional Materials

Hollow metal-organic framework (MOF) micro/nanostructures and their derivatives are attracting a great amount of research interest in recent years because their hierarchical porous structures not only provide abundant, easily accessed metal sites but also endow 3D channels for rapid mass transport. As a result, they demonstrate significant advantages in many applications including catalysis, gas sensors, batteries, supercapacitors, and so on. Nevertheless, studies on hollow MOFs and their derivatives are still at the beginning of this field, and the relationship between their structures and application performances is not yet reviewed comprehensively. Herein, the synthetic strategies and practical applications of hollow micro/nanostructured MOFs and their derivatives are summarized, and their corresponding prospects are also discussed.

In situ construction of hollow carbon spheres with N, Co, and Fe co-doping as electrochemical sensors for simultaneous determination of dihydroxybenzene isomers

Control of the active sites/centers plays an important role in the design of novel electrode materials with unusual properties and achievement of sensors with high performance. In this study, three-dimensional (3D) freestanding multi-doped hollow carbon spheres (N-Co-Fe-HCS) with a layer thickness of 30 nm, which contained multiple active sites of the heteroatom N and transition metals (Co and Fe), were synthesized via a simple template method (with SiO2 as the template) and cost-efficient in situ self-polymerization, self-adsorption/reduction and carbonization strategies. Moreover, a series of hollow carbon sphere composites of the same family (N-HCS, N-Co-HCS and N-Fe-HCS) were prepared by this sensible process using the same method and precursors but different doping elements. These differences lead to different active sites/centers from hollow carbon spheres and improved electrocatalytic activities for dihydroxybenzene isomers. Furthermore, N-Co-Fe-HCS as an electrochemical sensor exhibited excellent simultaneous qualitative and quantitative determination performance for catechol (CC) and hydroquinone (HQ). The detection limit and the linear range were 75 nmol L-1 and 0.5-500 μmol L-1 for CC and 80 nmol L-1 and 0.5-1500 μmol L-1 for HQ, respectively. The interference from the components coexisting in river water on the detection of CC and HQ was not observed. These results indicate that high-performance electrochemical sensors can be constructed by in situ multi-element doping into electrode materials to achieve multi-active sites.

The rational design of sandwich-like MnO2-Pd-CeO2 hollow spheres with enhanced activity and stability for CO oxidation

The development of strategies for the facile fabrication of noble metal/metal oxide nanomaterials with high catalytic activity and thermal stability is very challenging in the field of catalysis and for other relevant applications. Herein, we report a delicate multi-assembly method to prepare sandwich-like MnO2-Pd-CeO2 hollow spheres wherein carbon spheres were employed as sacrificial templates. Typically, tiny Pd nanoparticles were deposited on the outer surface of the MnO2 shell, and the CeO2 overcoating served as a nanotrap to anchor the Pd particles on the MnO2 supports. The unique sandwich-like structure effectively prevents the Pd nanoparticles from aggregation during high-temperature calcination and catalyzation. The as-prepared MnO2-Pd-CeO2 hollow spheres exhibited enhanced stability and activity for CO oxidation. The excellent stability and activity exhibited by the as-synthesized MnO2-Pd-CeO2 hollow spheres can be ascribed to the sandwich-like structure and the strong synergistic effects between Pd and the hierarchical porous MnO2-CeO2 shell. We believe that this optimal structure design demonstrates a new approach for the synthesis of noble-metal-based catalysts with superior activity and stability.

A facile synthetic strategy for the creation of hollow noble metal/transition metal oxide nanocomposites

We have reported an efficient synthetic protocol to build different hollow hybrid nanocomposites with tunable compositions, such as Au/TiO2, Pt/ZrO2, and Au/CexTi1-xO2. The noble metal nanoparticles were well encapsulated in a wall composed of the designated transition metal oxides, showing promising potential as stable catalysts as demonstrated by Pt/ZrO2 for methane combustion.

A green and general strategy for the synthesis of hollow Ag/CdS nanocomposites for superior SERS performance

In this study, we developed a convenient, environmentally friendly approach for the fabrication of hollow Ag/CdS composites, which presented superior SERS performance.

Novel formation of Bi@BiFe-glycolate hollow spheres and their conversion into Bi2O3/BiFeO3 composite hollow spheres with enhanced activity and durability in visible photocatalysis

Novel passion fruit-like Bi@BiFe-glycolate hollow spheres are synthesized and explained by an interesting mechanism of “spit and swallow” process.

Component-Customizable Porous Rare-Earth-Based Colloidal Spheres towards Highly Effective Catalysts and Bioimaging Applications

Multicomponent porous colloidal spheres are of interest because they not only show a combination of the properties associated with all different components, but also usually present synergy effects. However, a combination of different components in a single porous sphere is still greatly challenged due to the different precipitation behaviors of each component. In this work, we have developed a general synthetic route to prepare several categories of porous monodisperse rare-earth (RE)-based colloidal spheres with customizable elemental compositions and a uniform element distribution. The two-step synthetic strategy is based on the integration of coordination chemistry precipitation of RE ions and a subsequent ion-exchange process, which steers clear of obstacles, such as differences in solubility product constant, that are to be found in traditional co-precipitation methods. Our approach provides a new mixing mechanism to realize homogeneous distribution of each element within the porous spheres. An array of binary, ternary, and even senary RE colloidal porous spheres with diameters of 500 nm to 700 nm has been successfully synthesized. Taking advantage of their good dispersibility, porosity, and customizable components, these porous RE oxide spheres show excellent catalytic activity for the reduction of 4-nitrophenol, and promising application in single-phase multifunctional bioprobes.

Preparation of Hollow Biopolymer Nanospheres Employing Starch Nanoparticle Templates for Enhancement of Phenolic Acid Antioxidant Activities

Phenolic acids have been extensively studied because of their bioactive properties and disease prevention and control capacities. However, undesired odors and taste, low aqueous solubility, and thermal and ultraviolet (UV) light instability severely restrict their application. The aim of this work was to evaluate the enhancement in antioxidative activities of phenolic acids in hollow nanospheres and their stability in terms of their antioxidative activities under harsh conditions. For the first time, we have successfully fabricated hollow short linear glucan (SLG)@gum arabic (GA) nanospheres and hollow in situ SLG/GA hybrid nanospheres by removing the sacrificial starch nanoparticle templates through α-amylase treatment and Ostwald ripening. These two hollow nanospheres had a huge cavity area for the encapsulation of phenolic acids, and their loading capacities were >20%. Furthermore, they can be used as nanoreactors to immobilize phenolic acids, enhance their antioxidative activities, and improve their stability when exposed to high salt concentrations, UV light, or heat treatments.

Template-free synthesis of inorganic hollow spheres at water/"water-brother" interfaces as Fenton-like reagents for water treatment

This paper reports a template-free method to synthesize a series of inorganic hollow spheres (IHSs) including Cu-1, Cu-2, Ni-1, Ni-2 based on mineralization reactions at water/"water-brother" interfaces. "Water-brother" was defined as a solvent which is miscible with water, such as ethanol and acetone. The water/"water-brother" interfaces are very different from water/oil interfaces. The "water-brother" solvent will usually form a homogenous phase with water. Interestingly, in our method, these interfaces can be formed, observed and utilized to synthesize hollow spheres. Utilizing the unique porous properties of the spheres, their potential application in water treatment was demonstrated by using Cu-1 IHSs as Fenton-like reagents for adsorption and decomposition of Congo Red from aqueous solution. The final adsorption equilibrium was achieved after 30min with the maximum adsorption capacity of 86.1mg/g, and 97.3% removal of the dye in 80min after adsorption equilibrium. The IHSs can be reused as least 5 times after treatment by NaOH. This method is facile and suitable for large-scale production, and shows great potential for watertreatment.

Functionalized Metal-Organic Framework as a Biomimetic Heterogeneous Catalyst for Transfer Hydrogenation of Imines

Mimicking a biocatalytic system has been one of the prevalent strategies for the design of novel and efficient chemical transformations. Among the enzyme-catalyzed reactions, the cooperative interplay of Lewis- and Brønsted-acidic functionalities at active sites represents a common feature in activating reactants. Employing MIL-101(Cr) as a biomimetic platform, we customize a sulfonic group (SO₃H) into its hierarchical pores to generate a heterogeneous catalyst for transfer hydrogenation of imines by using Hantzsch ester as the reductant. Both aldimines and ketimines were efficiently converted to their hydrogenated counterparts in a manner similar to metal enzymes. The Cr³⁺ node and sulfonic acid functionality encapsulated in MOF cages worked cooperatively in promoting this transformation, resulting in an enhanced reactivity as compared to its homogeneous analogue. Furthermore, MIL-101(Cr)-SO₃H could be recycled for many times without considerable loss in reactivity.

Polystyrene-based Hollow Microsphere Synthesized by γ-ray Irradiation-assisted Polymerization and Self-Assembly and Its Application in Detection of Ionizing Radiation

To simply and multitudinously synthesize hollow microspheres in a pure system is important for relevant research and application. Here, a simple and novel one-pot synthetic strategy to prepare polystyrene (PS) hollow microspheres via irradiation-assisted free-radical polymerizing and self-assembly (IFPS) approach under γ-ray irradiation with no additives introduced into the system is presented. And PS/2,5-Diphenyloxazole (PPO) fluorescent microspheres have been prepared successfully by IFPS reaction, which can be used as scintillators for the detection of ionizing radiation. A linear relationship between emitted luminescence and dose-activity in water is obtained, which suggests that composite microspheres could be used as liquid scintillation in specific environment.

Carbon-embedded Ni nanocatalysts derived from MOFs by a sacrificial template method for efficient hydrogenation of furfural to tetrahydrofurfuryl alcohol

A Ni/C catalyst prepared by the pyrolysis of Ni-MOFs, synthesized by a facile oil-bath method, showed high activity of hydrogenation of FAL.

Preparation of TiO2–ZrO2/Au/CeO2 hollow sandwich-like nanostructures for excellent catalytic activity and thermal stability

This work reports a novel type of sandwich-like hollow Au-based nanocatalyst, including a TiO₂–ZrO₂ shell, a hollow CeO₂ core and Au nanoparticles of 2–5 nm.

Highly efficient large-scale preparation and electromagnetic property control of silica–NiFeP double shell composite hollow particles

Micron-sized double shell composite hollow particles with excellent electromagnetic behavior are prepared using a highly efficient and large scale method.

Radiolytic syntheses of hollow UO2 nanospheres in Triton X-100-based lyotropic liquid crystals

Hollow nanospheres (ϕ: 60–80 nm, wall thickness: 10–20 nm), consisted of UO2 nanoparticles (ϕ: 3–5 nm), were successfully prepared in a Triton X-100-water (50:50, w/w) hexagonal lyotropic liquid crystal (LLC) by γ-irradiation, where water soluble ammonium uranyl tricarbonate was added as precursor. The product was stable at least up to 300°C. Furthermore, whether the nanospheres were hollow or not, and the wall thickness of the hollow nanospheres could be easily controlled via adjusting dose rate. While in the Triton X-100 based micellar systems, only solid nanospheres were obtained. At last, a possible combination mechanism containing adsorption, aggregation and fracturing processes was proposed.

Cu2O-directed in situ growth of Au nanoparticles inside HKUST-1 nanocages

Controllable integration of metal nanoparticles (MNPs) and metal-organic frameworks (MOFs) is attracting considerable attention as the obtained composite materials always show synergistic effects in applications of catalysis, delivery, as well as sensing. Herein, a Cu₂O-directed in situ growth strategy was developed to integrate Au nanoparticles and HKUST-1. In this strategy, Cu₂O@HKUST-1 core-shell heterostructures, HKUST-1 nanocages, Cu₂O@Au@HKUST-1 sandwich core-shell heterostructures and Au@HKUST-1 balls-in-cage heterostructures were successfully synthesized. Cu₂O@HKUST-1 core-shell heterostructures were synthesized by soaking Cu₂O nanocrystals in benzene-1,3,5-tricarboxylic acid solution. The well-defined Cu₂O@HKUST-1 core-shell heterostructures were demonstrated to be dominated by the ratio of Cu²⁺ cations to btc^3- ligands in solution during the period of HKUST-1 formation. Cu₂O@Au@HKUST-1 sandwich core-shell or Au@HKUST-1 balls-in-cage heterostructures were obtained by impregnating HAuCl₄ into Cu₂O@HKUST-1 core-shell heterostructures. Due to the porosity of HKUST-1 and reducibility of Cu₂O, HAuCl₄ could pass through the HKUST-1 shell and be reduced by the Cu₂O core in situ forming Au nanoparticles. Finally, CO oxidation reaction at high temperatures was carried out to assess the catalytic functionality of the obtained composite heterostructures. This strategy can circumvent some drawbacks of the existing approaches for integrating MNPs and MOFs, such as nonselective deposition of MNPs at the outer surface of the MOF matrices, extreme treatment conditions and additional surface modifications.

A covalent organic framework-based route to the in situ encapsulation of metal nanoparticles in N-rich hollow carbon spheres

Metal nanoparticles (NPs) encapsulated in hollow nanostructures hold great promise for a variety of applications. Herein, we demonstrate a new concept where covalent organic frameworks (COFs) doped with metal cations can be readily used as novel precursors for the in situ encapsulation of metal NPs into N doped hollow carbon spheres (NHCS) through a controlled carbonization process. The obtained Pd@NHCS composites show a significantly enhanced catalytic activity and selectivity in the hydrogenation of nitrobenzene in ethanol and oxidation of cinnamyl alcohol compared with that of the conventional Pd/N-C and commercial Pd/C catalysts. The excellent catalytic performance should be related to the synergism of the porous hollow spheric structure, highly dispersed Pd NPs, and uniform distribution of N dopants on the materials. We believe that this newly developed methodology could be extended to the synthesis of other metal NPs@NHCS composites for a variety of advanced applications.

Yolk-Shell Nanocomposites of a Gold Nanocore Encapsulated in an Electroactive Polyaniline Shell for Catalytic Aerobic Oxidation

Noble metal nanoparticles (NPs) have been widely applied in nanocatalysis owing to the benefits associated with their miniature size. However, improving their stability and reusability during catalytic applications still remains a great challenge. To this end, monodispersed gold@void@polyaniline yolk-shell nanocomposites (Au@void@PANI YSNs) were synthesized using bottom-up template-assisted methods. Au@SiO2 NPs, prepared from a modified sol-gel process, were used as templates for the thiol-ene click reaction with 4-vinylaniline (VAn) to immobilize the aniline moieties, which later performed as the initiation sites for the oxidative copolymerization of aniline from the outer surface of the Au@SiO2-VAn NPs with an electroactive PANI shell (Au@SiO2@PANI NPs). The silica layer sandwiched between the Au core and PANI shell was selectively removed by aqueous hydrofluoric acid to produce Au@void@PANI YSNs with a movable Au core. The electroactive PANI shell not only serves as a physical barrier that prevents the self-association of Au cores and provides a vacant cavity where chemical transformations take place on the Au cores in a controlled manner but also improves the activity and stability of Au cores due to the electrons delocalization and transfer from the Au d orbitals of the nanocores to the π-conjugated ligands of the PANI shell, as proved by the X-ray photoelectron spectroscopy results. The as-synthesized YSNs were found to perform as flexible and reusable heterogeneous catalysts with high catalytic efficiency for the aerobic oxidation of alcohol in aqueous solution. One may find the present study to be a general and effective way to fabricate monodispersed hollow nanomaterials in a controlled and green manner.

Design, synthesis and applications of core-shell, hollow core, and nanorattle multifunctional nanostructures

With the evolution of nanoscience and nanotechnology, studies have been focused on manipulating nanoparticle properties through the control of their size, composition, and morphology. As nanomaterial research has progressed, the foremost focus has gradually shifted from synthesis, morphology control, and characterization of properties to the investigation of function and the utility of integrating these materials and chemical sciences with the physical, biological, and medical fields, which therefore necessitates the development of novel materials that are capable of performing multiple tasks and functions. The construction of multifunctional nanomaterials that integrate two or more functions into a single geometry has been achieved through the surface-coating technique, which created a new class of substances designated as core-shell nanoparticles. Core-shell materials have growing and expanding applications due to the multifunctionality that is achieved through the formation of multiple shells as well as the manipulation of core/shell materials. Moreover, core removal from core-shell-based structures offers excellent opportunities to construct multifunctional hollow core architectures that possess huge storage capacities, low densities, and tunable optical properties. Furthermore, the fabrication of nanomaterials that have the combined properties of a core-shell structure with that of a hollow one has resulted in the creation of a new and important class of substances, known as the rattle core-shell nanoparticles, or nanorattles. The design strategies of these new multifunctional nanostructures (core-shell, hollow core, and nanorattle) are discussed in the first part of this review. In the second part, different synthesis and fabrication approaches for multifunctional core-shell, hollow core-shell and rattle core-shell architectures are highlighted. Finally, in the last part of the article, the versatile and diverse applications of these nanoarchitectures in catalysis, energy storage, sensing, and biomedicine are presented.

Understanding the carbon-monoxide oxidation mechanism on ultrathin palladium nanowires: a density functional theory study

The CO oxidation mechanism catalyzed by ultrathin helical palladium nanowires (PdNW) was investigated by density functional theory (DFT) calculation. The helical PdNW structure was constructed on the basis of the simulated annealing basin-hopping (SABH) method with the tight-binding potential and the penalty method in our previous studies (J. Mater. Chem., 2012, 22, 20319). The low-lying adsorption configurations as well as the adsorption energies for O2 and CO molecules on different PdNW adsorption sites were obtained by DFT calculation. The most stable adsorption configurations for the Langmuir-Hinshelwood (LH) mechanism processes were considered for investigating the CO oxidation mechanism. The nudged elastic band (NEB) method was adopted to obtain the transition state configuration and the minimum energy pathways (MEPs).

A 3D Co–CN framework as a high performance electrocatalyst for the hydrogen evolution reaction

A 3D Co–CN framework was synthesized with the Co–CN electrode showing exceptionally high catalytic activity and good durability. Only requiring overpotentials of 181 mV and 266 mV to afford current densities of 10 mA cm⁻² in acid and alkaline electrolytes, respectively.

Anti-bacterial PES-cellulose composite spheres: dual character toward extraction and catalytic reduction of nitrophenol

Polyethersulfone (PES) based hybrid adsorbents were used for the removal of different phenols from aqueous solutions, which are categorized as major aquatic organic pollutants.

Synthesis and applications of porous non-silica metal oxide submicrospheres

A variety of metal oxide particles of spherical morphology from nano to micrometer size have been reviewed with a special emphasis on the appraisal of synthetic strategies and applications in biomedical, environmental and energy-related areas.

Enhanced photocatalytic activity of a hollow TiO2–Au–TiO2 sandwich structured nanocomposite

The hollow mesoporous TiO₂–Au–TiO₂ nanospheres with stability, large specific surface area can enhance visible-light-induced photocatalytic activity.

A metal-assisted templating route (S0M+I−) for fabricating thin-layer CoO covered on the channel of nanospherical-HMS with improved catalytic properties

Nanospherical hexagonal mesoporous silica (HMS) with a functional mesochannel covered with thin-layer-dispersed cobalt oxide species was directly fabricatedviaa novel metal-assisted templating method (S⁰M⁺I⁻).

Formation of Uniform Fe3 O4 Hollow Spheres Organized by Ultrathin Nanosheets and Their Excellent Lithium Storage Properties

Hierarchical Fe3 O4 hollow spheres constructed by nanosheets are obtained from solvothermally synthesized Fe-glycerate hollow spheres. With the unique structural features, these hierarchical Fe3 O4 hollow spheres exhibit excellent electrochemical lithium-storage performance.

Photomechanically Controlled Encapsulation and Release from pH-Responsive and Photoresponsive Microcapsules

Poly(acrylic acid)/azobenzene microcapsules were obtained through distillation precipitation polymerization and the selective removal of silica templates by hydrofluoric acid etching. The uniform, robust, and monodisperse microcapsules, confirmed by transmission electron microscopy and scanning electron microscopy, had reversible photoisomerization under ultraviolet (UV) and visible light. Under UV irradiation, azobenzene cross-linking sites in the main chain transformed from the trans to cis isomer, which induced the shrinkage of microcapsules. These photomechanical effects of azobenzene moieties were applied to the encapsulation and release of model molecules. After loading with rhodamine B (RhB), the release behaviors were completely distinct. Under steady UV irradiation, the shrinkage adjusted the permeability of the capsule, providing a novel way to encapsulate RhB molecules. Under alternate UV/visible light irradiation, a maximal release amount was reached due to the continual movement of shell networks by cyclic trans-cis photoisomerization. Also, microcapsules had absolute pH responsiveness. The diffusion rate and the final release percentage of RhB both increased with pH. The release behaviors under different irradiation modes and pH values were in excellent agreement with the Baker-Lonsdale model, indicating a diffusion-controlled release behavior. Important applications are expected in the development of photocontrolled encapsulation and release systems as well as in pH-sensitive materials and membranes.

γ-Al2O3 supported Pd@CeO2 core@shell nanospheres: salting-out assisted growth and self-assembly, and their catalytic performance in CO oxidation

In this paper, we have successfully demonstrated the clean synthesis of high-quality Pd@CeO2 core@shell nanospheres with tunable Pd core sizes in water, and furthermore loaded the as-obtained Pd@CeO2 products on commercial γ-Al2O3via electrostatic interaction. KBr here plays two key roles in inducing the growth and self-assembly of Pd@CeO2 core@shell nanospheres. First, Br- ions can retard the reduction of Pd2+ ions via the formation of the more stable complex of [PdBr4]2- so as to tune the size of Pd cores. Second, it greatly decreases the colloidal stability, and hence the surface polarity-weakened Pd and CeO2 NPs have to spontaneously self-assemble into more stable and ordered structures. Among different-sized Pd samples, the as-obtained 8 nm-Pd@CeO2/Al2O3 one exhibits the best performance in catalytic CO oxidation, which can catalyze 100% CO conversion into CO2 at 95 °C, which is much lower than the previously reported CeO2-encapsulated Pd samples.

Copper doped ceria porous nanostructures towards a highly efficient bifunctional catalyst for carbon monoxide and nitric oxide elimination

Cu²⁺ doped CeO₂ porous nanomaterials were synthesized by calcining CeCu–MOF nanocrystals. They exhibited a superior bifunctional catalytic performance for CO oxidation and selective catalytic reduction of NO.

Copper doped ceria porous nanostructures with a tunable BET surface area were prepared using an efficient and general metal–organic-framework-driven, self-template route. The XRD, SEM and TEM results indicate that Cu²⁺ was successfully substituted into the CeO₂ lattice and well dispersed in the CeO₂:Cu²⁺ nanocrystals. The CeO₂:Cu²⁺ nanocrystals exhibit a superior bifunctional catalytic performance for CO oxidation and selective catalytic reduction of NO. Interestingly, CO oxidation reactivity over the CeO₂:Cu²⁺ nanocrystals was found to be dependent on the Cu²⁺ dopants and BET surface area. By tuning the content of Cu²⁺ and BET surface area through choosing different organic ligands, the 100% conversion temperature of CO over CeO₂:Cu²⁺ nanocrystals obtained from thermolysis of CeCu–BPDC nanocrystals can be decreased to 110 °C. The porous nanomaterials show a high CO conversion rate without any loss in activity even after five cycles. Furthermore, the activity of the catalysts for NO reduction increased with the increase of BET surface, which is in accordance with the results of CO oxidation.

A novel structural Fenton-like nanocatalyst with highly improved catalytic performance for generalized preparation of iron oxide@organic dye polymer core–shell nanospheres

Fe_xO_y@Fe_xO_y/C nanoparticles as excellent catalysts and precursors could catalyze organic dye molecules to form iron oxide@organic dye polymer core–shell nanospheres.