Yolk-shell Nanoreactors Research Articles

MOF-derived Fe3O4@SiO2/Al2O3 yolk-shell nanoreactor for efficient furfural acetalization

Yolk-shell nanoreactors feature numbers of advantages in promoting catalytic performance. This work demonstrates the fabrication of yolk-shell Fe3O4@SiO2/Al2O3-T (T = 500–900 °C) from metal-organic framework. Characterizations indicate the Fe3O4 yolk and SiO2/Al2O3 shell of the obtained nanoreactors. Fe3O4@SiO2/Al2O3–800 showed excellent performance in furfural acetalization to 2-(dimethoxymethyl)furan, achieving a 97% yield at 60 °C, atmospheric pressure within 5 h. Control experiments reveal the high reactivity of Fe3O4 yolks for furfural acetalization, and acidic Al species are favorable for reactivity promotion. Besides, porous SiO2/Al2O3 shells facilitate mass transfer and increase the accessibility of active sites, also contribute to the high performance and stability.

Tumour‐microenvironment‐responsive Na2S2O8 nanocrystals encapsulated in hollow organosilica–metal–phenolic networks for cycling persistent tumour‐dynamic therapy

AbstractTraditional tumour‐dynamic therapy still inevitably faces the critical challenge of limited reactive oxygen species (ROS)‐generating efficiency due to tumour hypoxia, extreme pH condition for Fenton reaction, and unsustainable mono‐catalytic reaction. To fight against these issues, we skilfully develop a tumour‐microenvironment‐driven yolk‐shell nanoreactor to realize the high‐efficiency persistent dynamic therapy via cascade‐responsive dual cycling amplification of •SO4−/•OH radicals. The nanoreactor with an ultrahigh payload of free radical initiator is designed by encapsulating the Na2S2O8 nanocrystals into hollow tetra‐sulphide‐introduced mesoporous silica (HTSMS) and afterward enclosed by epigallocatechin gallate (EG)‐Fe(II) cross‐linking. Within the tumour microenvironment, the intracellular glutathione (GSH) can trigger the tetra‐sulphide cleavage of nanoreactors to explosively release Na+/S2O82−/Fe2+ and EG. Then a sequence of cascade reactions will be activated to efficiently generate •SO4− (Fe2+‐catalyzed S2O82− oxidation), proton (•SO4−‐catalyzed H2O decomposition), and •OH (proton‐intensified Fenton oxidation). Synchronously, the oxidation‐generated Fe3+ will be in turn recovered into Fe2+ by excessive EG to circularly amplify •SO4−/•OH radicals. The nanoreactors can also disrupt the intracellular osmolarity homeostasis by Na+ overload and weaken the ROS‐scavenging systems by GSH exhaustion to further amplify oxidative stress. Our yolk–shell nanoreactors can efficiently eradicate tumours via multiple oxidative stress amplification, which will provide a perspective to explore dynamic therapy.

Tailor-made yolk-shell nanocomposites of star-shape Au and porous organic polymer for nitrogen electroreduction to ammonia

Electrocatalytic nitrogen (N2) reduction reaction (NRR) is an energy-saving approach to synthesize ammonia (NH3), which significantly depends on the development of high-efficiency electrocatalysts. Inspired by the catalytic microenvironment of enzymes, a series of yolk-shell nanostructures of monodispersed Au nanostars within porous organic polymers (POPs) have been successfully prepared via a self-sacrificing template strategy. The obtained yolk-shell nanocomposites have highly active Au nanostar cores and permeable POP shells for ambient electrocatalytic NRR to NH3. The hydrophobic properties of yolk-shell nanoreactors can be tailored accurately by engineering the POP shells at an atomic level, which greatly improves the N2 fixation performance by inhibiting the hydrogen evolution reaction, resulting in the unprecedented NH3 yield rate (∼109.1 μg h−1 mgcat.−1) and Faradaic efficiency (∼68.3 %). This work pioneers an effective strategy to construct tailor-made electrocatalysts for the N2-to-NH3 fixation.

Efficient removal of organic pollution via photocatalytic degradation over a TiO2@HKUST-1 yolk-shell nanoreactor

Currently, the design and development of yolk-shell nanoreactors for photocatalytic organic pollution removal have received increasing attention because of their unique architecture. In this work, we developed a novel TiO2@HKUST-1 yolk-shell nanoreactor for the removal of tetracycline (TC) and rhodamine B (RhB) under visible light radiation with clearly increased photocatalytic activity and stability. The degradation efficiency of RhB and TC over the TiO2@HKUST-1 composite was significantly higher than that of pure TiO2 and HKUST-1. Within 60 min, the RhB and TC elimination rates reached 95.2% and 92.40%, respectively when exposed to visible light radiation. After the fifth cycle, the photocatalytic TC degradation efficiency by TiO2@HKUST-1 remained at 89.02%. In TiO2@HKUST-1, a yolk-shell nanoreactor structure with intimate interfacial contact significantly increased the carrier density, specified surface area, and separation effect of photogenerated electron-hole pairs, all of which were highly helpful for enhancing the photocatalytic performance. Additionally, by using electron spin resonance (ESR) spin-trap technology, density function theory (DFT) calculations, positive species trapping studies, and other methods, a potential photocatalytic degradation mechanism was proposed. It was discovered that h+ and •OH were the main active species. In view of its excellent gas properties, TiO2@HKUST-1 was used as an adsorbent for Rh B solution. The effect of mixing time and different initial mass concentration on the adsorption effect was investigated, and the adsorption isotherm and kinetic equation were fitted to the experimental results. This work's successful augmentation can effectively remove organic contaminants and has a wide range of potential environmental applications.

An ideal confined catalytic model via MOFs derived yolk-shell nanoreactors: The formation mechanism and catalytic performance for single-core and multi-core

Yolk-shell nanoreactors with diversified structure has received enormous attention in field of catalytic degradation due to the confined catalytic mechanism. Here, the single-core and multi-core yolk-shell nanoreactors are easily prepared by thermolysis of ZIF-67@SiO2 precursor, where the controllable single-core and multi-core structures are adjusted by variable pyrolysis process. In order to confirm the effect of structure on catalytic mechanism and performance, tetracycline hydrochloride (TTCH), a common antibiotic, was selected as the model pollutant for degradation. Under the optimal conditions, the reaction rate of single-core yolk-shell nanoreactors (SCYSN) reached 0.067 min−1, and the degradation efficiency of TTCH reached 85.05% within 25 min. However multi-core yolk-shell nanoreactors (MCYSN) reached 0.079 min−1, and the degradation efficiency of TTCH reached 93.7% at the same time. The radical mechanism was confirmed by quenching experiments and electron paramagnetic resonance. Degradation pathway was inferred by three-dimensional fluorescence spectrum and liquid chromatography-mass spectrograph. Biotoxicity tests was conducted on the degradation products by culturing Staphylococcus aureus. This work demonstrates an ideal confined catalytic model for yolk-shell nanoreactors in field of environmental remediation.

Metal Sulfides Yolk–Shell Nanoreactors with Dual Component for Enhanced Acidic Electrochemical Hydrogen Production

The activity of electrocatalysts can be optimized via constructing heterostructures, while it remains a challenge for the universal synthesis of heterocatalysts with covalent interface. Herein, a universal bifunctional‐S strategy for the preparation of covalently connected metal sulfides yolk–shell nanoreactors with dual components toward enhanced electrochemical hydrogen production in acid, is reported. Specifically, the yolk–shell MoS2‐(CTAB)2Sz host with abundant covalent S22− is first developed by a micelle‐confined microemulsion technology. The preencapsulated S22− in the precursor is utilized to in situ react with the additional M ions (M = Fe, Co, Ni, Cu, Zn, Mn, Cd, Sn), thus creating the covalent microenvironment at the heterointerface, which demonstrates a universal strategy to prepare dual‐component metal sulfides nanoreactors (MoS2/MxSy–BS). The resultant MoS2/CdS–BS nanoreactor exhibits excellent hydrogen evolution activity (27 mV at 10 mA cm−2) among the MoS2‐based heterocatalysts reported in the literature, while representing an improvement of four times than that of as‐prepared traditional MoS2/CdS heterocatalyst. Operando X‐ray diffractometer patterns are performed to study durability. The enhanced mechanism related to the transformation of catalytic center and the establishment of “electronic bridge” at the interface of MoS2/CdS–BS are revealed by theoretical calculations. This study inspires to develop covalently connected electrocatalysts via nanoreactors’ engineering.

Acidic Electrocatalytic CO2 Reduction Using Space-Confined Nanoreactors.

Electrochemical CO2 reduction reaction (CO2RR) is an attractive strategy for sustainable production of chemicals and has mainly been implemented in alkaline or neutral electrolytes. However, part of input CO2 is consumed by the formation of carbonate under these conditions. Herein, a space-confined strategy is proposed for CO2RR in acidic media, and Ni nanoparticles are encapsulated inside N-doped carbon nanocages as yolk-shell nanoreactors. By confining CO2RR in the cavities of nanoreactors, a Faradaic efficiency (FE) of 93.2% for CO is achieved at pH 7.2 and 84.3% FE for CO at pH 2.5. The inhibited proton diffusion within the Nernst layer of a nanoreactor is responsible for suppression of competing hydrogen evolution in acid. Moreover, CO2RR in an acidic flow electrolysis system offers enhanced current density and sustainable operation, in comparison with the conventional neutral pH system. This work shows that steering of mass transport via a unique structure is a viable avenue toward selective CO2 conversion, and it provides a further understanding of the structure-performance relationship of electrocatalysts.

Hierarchical multi-active component yolk-shell nanoreactors as highly active peroxymonosulfate activator for ciprofloxacin degradation

The reasonable design of the structure and composition of catalysts was essential to improve the catalytic performance of advanced oxidation processes (AOPs). Herein, we reported a simple strategy to synthesize hierarchical Co3O4-C@CoSiOx yolk-shell nanoreactors with multiple active components by using metal–organic frameworks (MOFs). The novel nanoreactors are further used to activate peroxymonosulfate (PMS) for ciprofloxacin (CIP) degradation. The effects of reaction parameters (pH value, co-existing ions, reaction temperature, etc.) on CIP degradation were systematically investigated. Especially, ∼98.2% of CIP was degraded within 17 min under the optimal conditions, together with the low cobalt leaching and excellent reusability. The appreciable catalytic performance improvement might be due to the synergistic effect of the structure and component design: (1) the hierarchical yolk-shell structure endowed the catalyst with high surface area (∼232.47 m2/g) and fully exposed active sites; (2) abundant highly active ≡Co-OH+ were formed on the surface of CoSiOx; (3) the presence of oxygen vacancies and nitrogen-doped carbon promoted the decomposition of PMS through a non-radical process. The results revealed both the radical (SO4∙-, ∙OH and O2∙-) and non-radical (1O2 and direct charge transfer) should be responsible for the CIP degradation. Moreover, the possible degradation pathways of CIP were proposed through the identification of intermediates using LC-MS/MS techniques and density functional theory (DFT) calculation. Our work highlights that multi-component catalysts derived from MOFs with novel structure have broad application prospects in AOPs.

A confinement approach to fabricate hybrid PBAs-derived FeCo@NC yolk-shell nanoreactors for bisphenol A degradation

In this study, a FeCo alloy@N-doped carbon yolk-shell nanoreactors (ANCYNs) was synthesized through the confinement pyrolysis of the polydopamine (PDA)-coated Fe/Co Prussian blue analogs (PBAs). The PDA-derived carbon shell formed preferentially via pyrolysis is of relevance to (i) protecting the framework structure from collapsing, (ii) increasing the specific surface areas and pore volumes, (iii) facilitating the adsorption of pollutants, and (iv) solving the metal leaching problem. The resulting ANCYNs exhibits good peroxomonosulfate (PMS) activation to degrade bisphenol A (BPA) (removing 98% of BPA in 5 mins), which is significantly better in catalytic performance and stability than those of the single-metal@NC or Nano-alloy catalysts. First-principles calculations indicate that the charge density redistribution becomes much more pronounced when adsorbed on nitrogen-doped graphene with the compressive strain, which leads to a higher density of active sites exposed. The radicals and non-radical processes were confirmed to be simultaneously responsible for BPA degradation.

The fabrication of hollow ZrO2 nanoreactors encapsulating Au-Fe2O3 dumbbell nanoparticles for CO oxidation.

Nanosized Au catalysts suffer from serious sintering problems during synthesis or catalytic reactions at high temperatures. In this work, we integrate dumbbell-shaped Au-Fe3O4 heterostructures into hollow ZrO2 nanocages to make Au-Fe2O3@ZrO2 yolk-shell nanoreactors with high activity as well as ultra-high sintering resistance for high-temperature CO oxidation. The synthesis starts with the fabrication of a (Au-Fe3O4)@SiO2@ZrO2 core-shell nanostructure with a Au-Fe3O4 dumbbell nanoparticle (DB) core and SiO2/ZrO2 double shells, followed by calcination and the selective removal of the inner SiO2 shell with alkaline solution to obtain Au-Fe2O3@ZrO2 nanoreactors. The retained ZrO2 hollow (outer) shells protect the Au NPs from aggregation at temperatures up to 900 °C and show excellent long-term stability. Compared to Au@ZrO2 yolk-shell nanoreactors, Au-Fe2O3@ZrO2 shows improved activity in CO oxidation due to the active Au-Fe2O3 interface. This strategy can be extended to other yolk-shell nanoreactors with various nanocomposites and for different catalytic reactions.

0D-1D hybrid nanoarchitectonics: tailored design of FeCo@N-C yolk-shell nanoreactors with dual sites for excellent Fenton-like catalysis.

Heterogeneous Fenton-like processes are very promising methods of treating organic pollutants through the generation of reactive oxygen containing radicals. Herein, we report novel 0D–1D hybrid nanoarchitectonics (necklace-like structures) consisting of FeCo@N–C yolk–shell nanoreactors as advanced catalysts for Fenton-like reactions. Each FeCo@N–C unit possesses a yolk–shell structure like a nanoreactor, which can accelerate the diffusion of reactive oxygen species and guard the active sites of FeCo. Furthermore, all the nanoreactors are threaded along carbon fibers, providing a highway for electron transport. FeCo@N–C nano-necklaces thereby exhibit excellent performance for pollutant removal via activation of peroxymonosulfate, achieving 100% bisphenol A (k = 0.8308 min−1) degradation in 10 min with good cycling stability. The experiments and density-functional theory calculations reveal that FeCo dual sites are beneficial for activation of O–O, which is crucial for enhancing Fenton-like processes.

Sequential Ultrafiltration-Catalysis Membrane for Excellent Removal of Multiple Pollutants in Water.

Clean water production calls for highly efficient and less energy-intensive technologies. Herein, a novel concept of a sequential ultrafiltration-catalysis membrane is developed by loading Co3O4/C@SiO2 yolk-shell nanoreactors into the fingerlike channels of a polymeric ultrafiltration membrane. Such a sequenced structure design successfully integrates selective separation with peroxymonosulfate-based catalysis to prepare a functionalized molecular sieve membrane, which exhibits excellent decontamination performance toward multipollutants by filtering the water matrices containing humic acid (HA) and bisphenol A (BPA). In this study, 100% rejection of HA and 95% catalytic degradation of BPA were achieved under a low pressure of 0.14 MPa and an ultrahigh flux of 229 L m-2 h-1, corresponding to a retention time of 3.1 s. Notably, the removal performance of multiple pollutants essentially depends on the ordered arrangement of ultrafiltration and catalysis. Moreover, the flow-through process demonstrated significant enhancement of BPA degradation kinetics, which is 21.9 times higher than that of a conventional batch reactor. This study provides a novel strategy for excellent removal of multiple pollutants in water.

Mesoporous Silica Encapsulated Metal-Organic Frameworks for Heterogeneous Catalysis

Encapsulation of metal-organic frameworks (MOFs) with a shell of mesoporous silica can boost overall performance of MOFs, offering versatility for synthetic architecture of integrated nanocatalysts with reactor-like features. Recently, Yu et al. report a green approach to make yolk-shell nanoreactors.

A Green Selective Water-Etching Approach to MOF@Mesoporous SiO2 Yolk-Shell Nanoreactors with Enhanced Catalytic Stabilities

<h2>Summary</h2> Despite their open and uniformly distributed active sites, the relatively low stability of coordination bonds in metal-organic frameworks (MOFs) limits their applications in catalytic reactions, especially under harsh environments. Here, we report a design of MOF@mesoporous SiO₂ yolk-shell nanoreactors via a mesoporous silica coating followed by selective water-etching strategy. Different from conventional alkali- or acid-etching methods, water etching of MOF surface presents a green and cost-effective way to form yolk-shell structures. The yolk-shell nanoreactors exhibit higher catalytic stability than bare MOF crystals in CO₂ cycloaddition with product yield remaining unchanged upon three cycles, owing to their permeable mesoporous SiO₂ shells, exposed active sites on MOF surfaces, and protective shells. The design concept and synthetic strategy via selective water etching may be used to construct other highly stable MOF-based nanocatalysts, broadening their applications in diverse catalytic reactions.

Efficient Removal of Organic Pollutants by Metal-organic Framework Derived Co/C Yolk-Shell Nanoreactors: Size-Exclusion and Confinement Effect.

Selective removal of organic pollutants from surface water with high efficiency is crucial in water purification. Here, yolk-shell Co/C nanoreactors (YSCCNs) are facilely synthesized via pyrolysis of controllably etched ZIF-67 by tannic acid, and their degradation performance on multiple pollutants is demonstrated. To present the structure-performance relationship between the designed nanocatalyst and the selective removal of organic pollutants, bisphenol A (BPA) was selected as the targeted pollutant with coexistence of humus acid (HA). For comparison, solid and hollow ZIF-67 derived Co/C nanoparticles denoted as SCCNs and HCCNs, were also tested. The results show that YSCCNs exhibit enhanced BPA degradation rate of 0.32 min-1, which is 23.1% and 45.4% higher than that of HCCNs and SCCNs in HA (10 ppm) system. The essential improvement can be ascribed to the synergetic effects from shell layer (size-exclusion) and core/shell (confinement effect). The degradation mechanism and pathway are further confirmed by radical quenching experiments and liquid chromatography-mass spectrograph (LC-MS), respectively. In addition, some influential factors, including reaction temperature, pH value, and peroxymonosulfate (PMS) dosage are investigated in detail. This work provides a possible way to selectively remove target contaminant from multiple pollutants in complex water system.

MOF-derived CoN/N-C@SiO2 yolk-shell nanoreactor with dual active sites for highly efficient catalytic advanced oxidation processes

Optimizing the structure and composition of the yolk-shell nanoreactors are one of the effective approaches to enhance their performance in heterogeneous catalysis, yet challenging. Here, we report a facile route to synthesize a highly efficient and recyclable yolk-shell CoN/N-C@SiO2 nanoreactor with dual active sites by the direct nitridation of MOF@SiO2 precursor. The CoN yolks (∼50–70 nm) as active sites were encapsulated by the hydrophilic SiO2 shells (∼30 nm), and some small dots (∼5–10 nm) was sandwiched between void spaces. In-situ formation of N-doped carbon layer not only served as active sites but also improved electron transfer. The yolk-shell nanoreactors were applied for catalytic tetracycline (TC) degradation by activation of peroxymonosulfate (PMS), and in the optimal case, it degraded >∼95% TC within 30 min in a wide pH value range of 2.02–9.94. The quenching experiments and EPR measurements further revealed that synergistic effect of the radicals and nonradical in PMS activation, O2−, OH, SO4− and 1O2 were involved in TC degradation. The improved catalytic performances could be ascribed to the following two aspects: (1) the hydrophilic SiO2 shell and the microenvironment formed by the yolk-shell structure not only enhance catalytic stability but also provide driving force to improve reaction rate (structural modulation); (2) CoN core and N doped carbon layer as dual active sites can achieve the synergistic effect of radicals and non-radicals in PMS activation (composition modulation). Moreover, possible degradation pathways of TC were proposed through the identification of intermediates using LC–MS/MS techniques. This research highlights the critical role of structure and component optimization in construction of advanced oxidation process systems and provides the possibility of utilizing MOF derivatives in the field of electrocatalysis, lithium battery and supercapacitor etc.

Well-Defined Metal Nanoparticles@Covalent Organic Framework Yolk-Shell Nanocages by ZIF-8 Template as Catalytic Nanoreactors.

Yolk-shell nanoreactors have received considerable interest for use in catalysis. However, the controlled synthesis of continuous crystalline shells without imperfections or cracks remains challenging. Here, a strategy for the synthesis of yolk-shell metal nanoparticles@covalent organic framework (MNPs@COF) nanoreactors by using MNPs@ZIF-8 core-shell nanostructures as a self-template is designed and developed. The COF shell is formed through an amorphous-to-crystalline transformation process of a polyimine shell in a mildly acidic solution, while the ZIF-8 is etched in situ, generating a void space between the MNPs core and the COF shell. With the protection of the COF shell, multiple ligand-free MNPs are confined inside of the hollow nanocages. Importantly, the synthetic strategy can be generalized to engineer the functions and properties of the designed yolk-shell nanocages by varying the structure of the COF shell and/or the composition of the core MNPs. Representative Pd@H-TpPa yolk-shell nanocages with active Pd NP cores and permeable TpPa shells exhibit high catalytic activity and stability in the reduction of 4-nitrophenol by NaBH4 at room temperature.

Fabrication of Smart Hybrid Nanoreactors from Platinum Nanodendrites Encapsulating in Hyperbranched Polyglycerol Hollow Shells

Hybrid nanorattles by spatial inclusion catalytic nanocores into hollow shells as nanoreactors have stimulated tremendous interests in advanced technologies for the sustainable production and conversion of energy. However, the nanoshells fabricated by inorganic compositions usually lack of desirable elasticity, permeability, and responsiveness to meet the requirement of increasingly complex and sophisticated catalytic systems. In this study, we describe a new strategy to construct a smart hybrid nanoreactor with an ultrathin and flexible polymer shell based on in situ thiol–ene photopolymerization. The morphological transitions in the hyperbranched poly(glycerol-co-N,N-diallyl glycidyl amine) (HPGD) shells of the Pt@hHPGD nanorattles result in the precise tuning of efficient mass transfer to encapsulated Pt nanocores in response to external stimuli. The fabricated Pt@hHPGD yolk–shell nanoreactors exhibited highly enhanced activity, longevity, and recyclability in catalyzing the hydrogenation of p-nitrophe...

Nanoreactor of MOF-Derived Yolk–Shell Co@C–N: Precisely Controllable Structure and Enhanced Catalytic Activity

Hollow yolk–shell nanoreactors are of great interest in heterogeneous catalysis owing to their improved mass transfer ability and stability. Here, we report a facile and straight route to synthesize a highly efficient and recyclable yolk–shell Co@C–N nanoreactor with controllable properties by the direct thermolysis of a hollow Zn/Co-ZIF precursor. Based on systematical optimization of the pyrolysis temperature and the shell-thickness of Zn/Co-ZIFs, we could completely anchor and stabilize uniform Co nanoparticles (NPs) in the hollow yolk, accommodated by the Co-ZIF derived N-doped carbon nanosheets. This nanosheet-assembled yolk was further confined by a permeable and robust N-doped carbon (C–N) shell to protect the Co NPs against leaching and also enabled the reaction to take place in the hollow void. Consequently, the optimal yolk–shell Co@C–N nanoreactor showed a significantly enhanced catalytic activity for the aqueous oxidation of alcohols, yielding >99% conversion under atmospheric air and base-fre...

Synthesis of NiO-TiO2 hybrids/mSiO2 yolk-shell architectures embedded with ultrasmall gold nanoparticles for enhanced reactivity

Novel NiO-TiO2 hybrids/mSiO2 yolk-shell architectures loaded with ultrasmall Au nanoparticles (STNVS-Au) were developed via the rational synthetic strategy. The hierarchical yolk-shell nanostructures (STNVS) with high surface areas were constructed by a facile “bottom-up” assembly process using SiO2 materials and polymer resins as cores/shells and sacrificial templates, accompanied by a simple hydrothermal incorporation of NiO into uniform amorphous TiO2 layers that were converted to NiO-anatase TiO2 p-n heterojunction hybrids. Then, numerous sub–3nm Au nanoparticles were post encapsulated within STNVS nanostructures through the low-temperature hydrogen reduction based on the unique deposition-precipitation method with Au(en)2Cl3 compounds as gold precursors. The NiO-TiO2 hybrids alloying with Au nanoparticles were effectively protected and entrapped within STNVS architectures, and interacted with outer mSiO2-Au shells, which comprised the powerful STNVS-Au yolk-shell nanoreactors and produced stronger configural synergies in enhancing the heterogeneous catalysis. Into catalyzing the reduction of 4-nitrophenol to 4-aminophenol, the STNVS-Au was shown with outstanding activity and reusability, and its pristine morphology was well retained during the recycling process.