Hollow Nanocages Research Articles

Prussian blue analogues-derived nitrogen-doped carbon-coated FeO/CoO hollow nanocages as a high-performance anode material for Li storage

Prussian blue analogues-derived nitrogen-doped carbon-coated FeO/CoO hollow nanocages as a high-performance anode material for Li storage

A controllable design of ZIF-67 based magnetic carbon nanotubes as efficient oxidase mimetics for sensitive detection of alkaline phosphatase in serum

The activity of alkaline phosphatase (ALP) is related to various pathological processes. Therefore, developing an ALP activity detection technology with high sensitivity and accuracy is of great significance for clinical diagnosis and cancer screening. To solve uncontrollable carbon nanotubes (CNTs) structure and lack of solubility, FeCo hollow nanocages (HNCs)@CNTs catalysts were prepared by facile pyrolysis of ZIF-67 precursor mixed with Fe-Co catalyst, displaying an oxidase-like activity. From the characterization, formation of CNTs was observed on the surface of FeCo HNCs@CNTs with the mole ratio of Fe3+ to Co2+ of 3:1. Density functional theory calculations demonstrated that the performed catalytic activity of FeCo HNCs@CNTs derived from active orbital of Co-3d band, which enabled the activation and decomposition of O2 with a feasible thermodynamic process. ·O2− and 1O2 were the main reactive oxygen species as electron acceptors. ALP catalyzed the hydrolysis of ascorbic acid 2-phosphate (AAP) to convert it into ascorbic acid (AA), which could effectively reduce the FeCo HNCs@CNTs-mediated chromogenic reaction of TMB oxidation. The performance of the FeCo HNCs@CNTs-linked biosensing assay showed a broad detection range from 0.1 U/L to 150 U/L and a relatively low limit of detection of 0.083 U/L. The ALP activity of the mouse serum sample obtained by the proposed biosensing assay was highly consistent with that via the clinical method, indicating a promising technology in biomolecule detection.

Ultra-thin WS2 decorated Co-based Metal‒organic framework derived materials for synergistic electrocatalysis towards pH-Universal hydrogen evolution reaction

Rational designing of a WS2-based hybrid material is extremely important to resolve low-edge sites and poor conductivity of bare WS2, but it is still challenging to construct applicable structures. In this study, an electrocatalyst with ultra-thin WS2 nanosheets homogeneously decorated on Co–N-co-doped carbon hollow nanocages (WS2-3/Co–N–CN-750) is developed, which has favorable hydrogen evolution reaction (HER) activity and stability. The performance of WS2-3/Co–N–CN-750 is significantly improved due to the collective synergy of the specific micro-morphology, interfacial structure, and electronic property. The hybridization of WS2 and Co9S8 can optimize the electronic structure, reduce hydrogen adsorption energy, slash the decomposition barrier of H2O, and accelerate the electron transfer to WS2. Furthermore, the marginal sites of WS2 are significantly increased by optimizing the aggregation growth of WS2. Besides, the precipitation of appropriate Co particles and the Co-based metal-organic framework (Co-MOF) lay a solid foundation for the favorable conductivity of the hybrid material. However, samples after stability tests reveal that cobalt sulfide is corroded and transformed in a locally strong alkali condition. This study highlights the synergies of multicomponent hybridization and provides insights into the stability of congeneric materials.

Synthesis of unique three-dimensional CoMn2O4@Ni(OH)2 nanocages via Kirkendall effect for non-enzymatic glucose sensing

Transition metal oxides / hydroxides, which have the advantages of wide distribution, low price, low toxicity, and stable chemical properties, have attracted much attention from researchers. Therefore, this work reports the construction of the unique CoMn2O4 nanocages assisted by the Kirkendall effect, and worm-like Ni(OH)2 nanoparticles were grown on the surface via hydrothermal method, the final product CoMn2O4@Ni(OH)2 nanocages were applied to construct efficient and sensitive non-enzymatic glucose electrochemical sensing. The stable three-dimensional hollow CoMn2O4 nanocages structure, not only can provide a wider specific surface area and more abundant active sites, its porous structure also can effectively inhibit the aggregation of nanoparticles, increase the ion diffusion path, shorten the electron transport distance, and improve the electrical conductivity. Loading Ni(OH)2 nanoparticles on the CoMn2O4 nanocages can increase catalytic sites, and further strengthen the electrocatalytic performance. Due to the good synergistic effect between CoMn2O4 and Ni(OH)2, CoMn2O4@Ni(OH)2 nanocages electrochemical sensor can achieve sensitive and rapid detection of trace glucose, with excellent linear range (8.5–1830.5 μM), low limit of detection (0.264 μM), high sensitivity of 0.00646 μA mM−1 cm−2, and outstanding repeatability. More importantly, the sensor has been successfully applied to the determination of blood glucose in human serum with good recoveries (95.64–104.3 %). This work provides a novel scheme for blood glucose detection and expands the application of transition metal oxides / hydroxides in the field of electrochemical sensing.

Sugar gourd-like NiCo layered double hydroxide @ NiMoO4 hierarchical core-shell material for high-performance asymmetric supercapacitors

As one of the strategies for preparing electrode materials with excellent electrochemical properties, reasonable structural design has been widely used to improve the performance of electrode materials. In this work, a core-shell structure with a unique sugar gourd-like appearance is designed, in which NiMoO4 (NMO) nanorods string together multiple NiCo-LDH (NCL) hollow nanocages to form NCL@NMO/NF composite electrode. The unique structure and the synergistic effect between the two substances give it high cycle stability and excellent capacity. DFT calculations show that the electronic structure at the NCL@NMO heterogeneous interface changes after compounding, so that electrons are transferred from the NCL to the NMO surface, and the difference in the work function promotes the transfer of electrons and accelerates the reaction rate. When used as the positive electrode of asymmetric supercapacitor (ASC), the material exhibits a specific capacity of 1186 C g−1 at a current density of 1 A g−1, and a capacity retention rate of 85.5 % after 5000 cycles at 5 A g−1. In addition, the assembled NCL@NMO/NF//AC ASC exhibits a high energy density of 80.38 Wh kg−1 at a power density of 800 W kg−1, and has high cycle stability (89.2 % after 5000 cycles).

FeCo alloy modified and carbon nanotube linked hollow carbon nanocages as efficient sulfur hosts for Li-S batteries

Although lithium-sulfur batteries have a high theoretical energy density, the lithium polysulfide (Li2Sn, n = 4 ∼ 8) shuttle effect and slow electrochemical reaction kinetics always arouse the poor rate performance, fast capacity decay and low Coulombic efficiency. Therefore, efficiently adsorption and timely catalytic conversion of Li2Sn by sulfur host is critical to overcome the above challenges of lithium sulfur batteries. In this work, an FeCo alloy modified and carbon nanotube linked hollow carbon nanocages host (CoFe-CHC-X) is constructed by in situ transformation of Fe and Co elements doped Zn-based metal-organic frameworks and melamine. Moreover, the catalytic properties of the CoFe-CHC-X with different Fe and Co ratios are investigated. The results reveal that both small and excessive amounts of Co metal nanoparticles in CoFe-CHC-1 and CoFe-CHC-2 composites are not conducive to the adsorption and conversion of Li2Sn. In contrast, the separated and uniformly dispersed FeCo alloy nanoparticles in CoFe-CHC-3 composite not only can effectively adsorb Li2Sn, but also reduce it conversion reaction energy barriers, accelerate conversion kinetics and inhibit shuttle effects. Meanwhile, the hollow carbon nanocages linked by carbon nanotube can facilitate the transport of electrons on the cathode and physical adsorption Li2Sn. Benefiting from these synergistic modulations, the Li-S batteries assembled by S@FeCo-CHC-3 cathode can stably cycle for 700 cycles at 1.0 C. During cycle, the Coulombic efficiency is maintained at about 98%, and the capacity decay is as low as 0.052% per cycle.

Co/CoS2 Heterojunction Embedded in N, S-Doped Hollow Nanocage for Enhanced Polysulfides Conversion in High-Performance Lithium-Sulfur Batteries.

Modulating the electronic configuration of the substrate to achieve the optimal chemisorption toward polysulfides (LiPSs) for boosting polysulfide conversion is a promising way to the efficient Li-S batteries but filled with challenges. Herein, a Co/CoS2 heterostructure is elaborately built to tuning d-orbital electronic structure of CoS2 for a high-performance electrocatalyst. Theoretical simulations first evidence that Co metal as the electron donator can form a built-in electric field with CoS2 and downshift the d-band center, leading to the well-optimized adsorption strength for lithium polysulfides on CoS2 , thus contributing a favorable way for expediting the redox reaction kinetics of LiPSs. As verification of prediction, a Co/CoS2 heterostructure implanted in porous hollow N, S co-doped carbon nanocage (Co/CoS2 @NSC) is designed to realize the electronic configuration regulation and promote the electrochemical performance. Consequently, the batteries assembled with Co/CoS2 @NSC cathode display an outstanding specific capacity and an admirable cycling property as well as a salient property of 8.25mAhcm-2 under 8.18mgcm-2 . The DFT calculation also reveals the synergistic effect of N, S co-doping for enhancing polysulfide adsorption as well as the detriment of excessive sulfur doping.

An Overview of Heavy Chain Ferritin in Cancer.

As a spherical protein that acts as a repository for intracellular iron, Ferritin is the most important iron storage form and is known to influence tumor immunity. Unbound ferritin is composed of 24 subunits, made up of ferritin light chain (FTL) and ferritin heavy chain (FTH). Ferritin can be automatically put together to form hollow nanocages that measure 12 nm around the outside and 8 nm around the inside. Cancer causes the second-most deaths worldwide, effective elimination of tumor cells while protecting normal cells is the foundation of modern tumor therapy. To this end, the innate tumor-targeting activity of human FTH1, first identified ten years ago, is highly appealing. Unmodified human FTH1 binds to its receptor, transferrin receptor 1 (TfR1), which is frequently overexpressed in cancer cells. FTH1-TfR1 binding permits improved drug efficacy by promoting ferritin-mediated targeted delivery. In addition, FTH is also associated with the prognosis of multiple typies of cancer. The level of FTH1 is significantly and positively correlated with the infiltration of tumor-associated macrophages. FTH1 also plays an important role in regulating the tumor immunity of solid cancer. As such, FTH1 has been extensively applied in the targeted delivery of anticancer drugs, diagnostic molecules (e.g., radioisotopes and fluorophones), and inorganic nanoparticles (NPs) to tumors.This article reviews the role of FTH in cancer and its potential as a therapeutic target.

Deciphering the Space Charge Effect of the CoNiLDH/FeOOH n-n Heterojunction for Efficient Electrocatalytic Oxygen Evolution.

Space charge transfer is an effective strategy to regulate the electron density of narrow bandgap semiconductors for enhancing electrocatalytic activity. Herein, the CoNiLDH/FeOOH n-n heterojunction hollow nanocages structure is constructed. The hollow structure provides abundant catalytic active sites and enhances mass transfer. The space charge region in the n-n heterojunction significantly promotes the adsorption of OH- and electron transfer; and the built-in electric field accelerates the electron transport, optimizes the electronic structure during the catalytic reaction process, and ensures the stability of surface charged active center sites in the heterojunction. Thus, CoNiLDH/FeOOH delivers an excellent oxygen evolution reaction (OER) overpotential of 250mV to achieve a current density of 10mA cm-2 with a small Tafel slope of 60mV dec-1 , and superior electrocatalytic durability for 210h at a high current density. Density functional theory calculations further verify that the space charge effect and built-in electric field in the n-n heterojunction of CoNiLDH/FeOOH can improve the electron transfer and lower the adsorption energy of OH- and the reaction energy barrier of the rate-determining step. This work provides a new fundamental understanding of the space charge effect of semiconductor heterojunction during the electrocatalytic process for developing more efficient OER electrocatalysts.

Chemically Etched Prussian Blue Analog-WS2 Composite as a Precatalyst for Enhanced Electrocatalytic Water Oxidation in Alkaline Media.

The electrochemical water-splitting reaction is a promising source of ecofriendly hydrogen fuel. However, the oxygen evolution reaction (OER) at the anode impedes the overall process due to its four-electron oxidation steps. To address this issue, we developed a highly efficient and cost-effective electrocatalyst by transforming Co-Fe Prussian blue analog nanocubes into hollow nanocages using dimethylformamide as a mild etchant and then anchoring tungsten disulfide (WS2) nanoflowers onto the cages to boost OER efficiency. The resulting hybrid catalyst-derived oxide demonstrated a low overpotential of 290 mV at a current density of 10 mA cm-2 with a Tafel slope of 75 mV dec-1 in 1.0 M KOH and a high faradaic efficiency of 89.4%. These results were achieved through the abundant electrocatalytically active sites, enhanced surface permeability, and high electronic conductivity provided by WS2 nanoflowers and the porous three-dimensional (3D) architecture of the nanocages. Our research work uniquely combines surface etching of Co-Fe PBA with WS2 growth to create a promising OER electrocatalyst. This study provides a potential solution to the challenge of the OER in electrochemical water-splitting, contributing to UN SDG 7: Affordable and clean energy.

A bi-functional catalyst strategy to selectively regulate sulfur redox kinetics in lithium–sulfur batteries

Designing electrochemical catalysts has become a research hotspot due to their accelerating the polysulfide conversion of the sulfur cathode to inhibit the “shuttle effect” in lithium–sulfur batteries. However, it is still a great challenge to design the heterogeneous selective electrochemical catalyst for inhibiting the “shuttle effect”. Herein, nickel cobalt phosphide and cobalt phosphide as the heterogeneous catalyst active sites embedded in the nitrogen-doped hollow carbon nanocages (NiCoP@CoP/NC) are reported, used for multi-step and multi-phase sulfur electrode reaction, and it is found that metal-sulfur d-p hybridization can effectively indicate the intrinsic catalytic activity of metal site. Division of labor and cooperation of the bi-active NiCoP@CoP as heterogeneous catalysts propel the stepwise polysulfide conversion. NiCoP and CoP sites preferentially accelerate the long-chain polysulfide conversion reaction (S8⇌LiPSs) and the short-chain polysulfide conversion reactions (LiPSs⇌Li2S), respectively. Moreover, the hollow and porous N-doped carbon structure can successfully suppress the volume effect and improve the conductivity of the sulfur cathode. The unique design can obtain an effective inhibition of the shuttle effect and rapid electrode reaction. As a result, LiS batteries demonstrate a high initial capacity of 1063 mAh g−1 and a low-capacity decay of 0.04% per cycle within 1000 cycles. Our work provides a feasible idea for the design of host materials in Li–S batteries.

Terephthalic Acid Intercalated CoNi-LDH Materials for Improved Li-O2 Battery.

CoNi-LDH (layered CoNi double hydroxides) hollow nanocages with specific morphology are obtained by Ni ion etching of ZIF-67 (Zeolitic imidazolate framework-67). The structure of the layered materials is further modified by molecular intercalation. The original interlayer anions are replaced by the ion exchange effect of terephthalic acid, which helps to increase the interlayer distance of the material. The intercalated cage-like structures not only benefit for the storage of oxygen, and the discharge product reaction, but also have more support between the material layers. The experimental results show that the excessive use of intercalation agent will affect structural stability of the intercalated CoNi-LDH. By adjusting the amount of terephthalic acid, the intercalated CoNi-LDH-2 (with 0.02mmol terephthalic acid intercalated) is not easy to collapse after 209 cycles and shows the best electrochemical performance in Li-O2 battery.

N, S co-doped hollow carbon nanocages confined Fe, Co bimetallic sites for bifunctional oxygen electrocatalysis

Regulating pore architecture and electronic structure is of significance for improving oxygen electrocatalytic activity of M−N−C catalysts. Herein, N, S co-doped hollow carbon nanocages confined Fe, Co bimetallic sites (FeCo-NS-HNCs) are constructed through an efficient surface bridging strategy. The surface modifier of trithiocyanuric acid trisodium salt bridges Co doped ZIF-8 surface with Fe ions to promote the formation of Fe/Co-Nx sites. The synergistic coupling of metal sites and N, S co-doping manipulates the adsorption/desorption characteristics of M−Nx sites to optimize intrinsic activity. The Kirkendall effect constructs the hollow carbon nanocages, improving the accessibility of M−Nx sites. Benefiting from the ameliorated electronic structure and hollow porous architecture, FeCo-NS-HNCs displays excellent bifunctional oxygen electrocatalytic activity (ΔE = 0.655 V). The liquid and flexible Zn-air batteries of FeCo-NS-HNCs offer prominent power density and cycling stability. This work provides estimable insights into the structure design and activity regulation of M−N−C catalysts for Zn-air battery.

Design of ZnSe-CoSe heterostructure decorated in hollow N-doped carbon nanocage with generous adsorption and catalysis sites for the reversibly fast kinetics of polysulfide conversion

Although lithium-sulfur batteries (LiSBs) are regarded as one of the most promising candidates for the next-generation energy storage system, the actual industrial application is hindered by the sluggish solid–liquid phase conversion kinetics, severe shuttle effect, and low sulfur loadings. Herein, a zeolitic imidazolate framework (ZIF) derived heterogeneous ZnSe-CoSe nanoparticles encapsulated in hollow N-doped carbon nanocage (ZnSe-CoSe-HNC) was designed by etching with tannic acid as a multifunctional electrocatalyst to boost the polysulfide conversion kinetics in LiSBs. The hollow structure in ZIF ensures large inner voids for sulfur and buffering volume expansions. Abundant exposed ZnSe-CoSe heterogeneous interfaces serve as bifunctional adsorption-catalytic centers to accelerate the conversion kinetics and alleviate the shuttle effect. Together with the highly conductive framework, the ZnSe-CoSe-HNC/S cathode exhibits a high initial reversible capacity of 1305.3 mA h g−1 at 0.2 C, high-rate capability, and reliable cycling stability under high sulfur loading and lean electrolyte (maintaining at 745 mA h g−1 after 200 cycles with a high sulfur loading of 6.4 mg cm−2 and a low electrolyte/sulfur ratio of 6 μL mg−1). Theoretical calculations have demonstrated the heterostructures of ZnSe-CoSe offer higher binding energy to lithium polysulfides than that of ZnSe or CoSe, facilitating the electron transfer to lithium polysulfides. This work provides a novel heterostructure with superior catalytic ability and hollow conductive architecture, paving the way for the practical application of functional sulfur electrodes.

Under-Coordinated CoFe Layered Double Hydroxide Nanocages Derived from Nanoconfined Hydrolysis of Bimetal Organic Compounds for Efficient Electrocatalytic Water Oxidation.

Hierarchically structured bimetal hydroxides are promising for electrocatalytic oxygen evolution reaction (OER), yet synthetically challenging. Here, the nanoconfined hydrolysis of a hitherto unknown CoFe-bimetal-organic compound (b-MOC) is reported for the controllable synthesis of highly OER active nanostructures of CoFe layered double hydroxide (LDH). The nanoporous structures trigger the nanoconfined hydrolysis in the sacrificial b-MOC template, producing CoFe LDH core-shell octahedrons, nanoporous octahedrons, and hollow nanocages with abundant under-coordinated metal sites. The hollow nanocages of CoFe LDH demonstrate a remarkable turnover frequency (TOF) of 0.0505s-1 for OER catalysis at an overpotential of 300mV. It is durable in up to 50h of electrolysis at step current densities of 10-100mAcm-2 . Ex situ and in situ X-ray absorption spectroscopic analysis combined with theoretical calculations suggests that under-coordinated Co cations can bind with deprotonated Fe-OH motifs to form OER active Fe-O-Co dimmers in the electrochemical oxidation process, thereby contributing to the good catalytic activity. This work presents an efficient strategy for the synthesis of highly under-coordinated bimetal hydroxide nanostructures. The mechanistic understanding underscores the power of maximizing the amount of bimetal-dimer sites for efficient OER catalysis.

Optimization of sodium storage performance by structure engineering in nickel-cobalt-sulfide.

The development of high-performance electrode materials is crucial for the advancement of sodium ion batteries (SIBs), and NiCo2S4 has been identified as a promising anode material due to its high theoretical capacity and abundant redox centers. However, its practical application in SIBs is hampered by issues such as severe volume variations and poor cycle stability. Herein, the Mn-doped NiCo2S4@GNs composite electrodes with hollow nanocages were designed using a structure engineering method to relieve the volume expansion and improve the transport kinetics and conductivity of the NiCo2S4 electrode during cycling. Physical characterization and electrochemical tests, combined with Density functional theory (DFT) calculations indicate that the resulting 3% Mn-NCS@GNs electrode demonstrates excellent electrochemical performance (352.9 mA h g-1 (200 mA g-1) after 200 cycles, and 315.3 mA h g-1 (5000 mA g-1)). This work provides a promising strategy for enhancing the sodium storage performance of metal sulfide electrodes.

Self-powered photoelectrochemical immunosensor with triple enhanced photoelectric response for sensitive detection of cTnI

A self-powered photoelectrochemical (PEC) immunosensor triple enhanced photoelectric response was proposed for the sensitive cardiac troponin (cTnI) detection. The self-powered PEC platform was constructed by sulfur indium copper hollow nanocage as a photocathode and hollow nanometer sphere heterojunction (In2S3 @CdIn2S4) as a photoanode, where the coulomb force of distinct photoelectrodes as the driving force effectively improves the photoelectric response without redox-mediator or external potential. In addition, the reverse transfer of photo-generated charge carriers increases the photoelectric response capacity due to the internal electric field effect in type II heterojunction. What is more exciting is that carefully designed hollow materials playing energy conversion function possess compelling properties. Given the advantages of multiple reflection effects in the cavity, thin-shell configuration and large surface, the designed hollow materials possessed a higher photon capture rate, a shorter-range transfer for photon-generated charges, and more active site points for the associated redox reactions, which facilitated the entire photoelectric response process. Based on the above strategies, the proposed PEC immunosensor achieved triple enhanced photoelectric response to present high sensitivity for detecting cTnI. The present study has gone some way to design nanomaterials with superior photoelectric activity, which paves a way for detecting other disease markers in high sensitivity.

Nitrogen and atomic Fe co-doped hollow carbon nanocages supporting RuPd nanoclusters as extraordinary high-performance nanoreactor-like cathode for lithium–oxygen batteries

Lithium−oxygen batteries (LOBs) have attracted considerable worldwide attention due to their exceptionally high theoretical energy density. Finding outstanding catalysts whereby Li2O2 can be directly and efficiently formed/decomposed is essential for achieving highly efficient LOBs. Herein, we report the design and preparation of an atomic Fe-dispersed hollow carbon nanocage supporting Ru-Pd binary nanoclusters. This catalyst exhibits extraordinarily high, top-ranking cathode performance towards the LOB. For our optimal sample, Ru0.8Pd0.2/Fe-CNCs, the specific capacity reaches 31,211 mAh g−1 with a very low charge overpotential of 0.64 V, and ultra-long cycle life of 300 cycles is realized. Systematic experimental and calculation results reveal the crucial role of the RuPd alloy nanoclusters in greatly improving OER activity and preventing the occurrence of side reactions. Meanwhile, the hollow nanocages, which have ultrathin mesoporous walls, act as “nanoreactors”. The encouraging performance of our rationally designed cathode may provide a new pathway to develop advanced catalysts for LOBs.

Regulating Electrochemical Kinetics of CoP by Incorporating Oxygen on Surface for High-Performance Li-S Batteries.

Lithium-sulfur (Li-S) batteries are widely studied because of their high theoretical specific capacity and environmental friendliness. However, the further development of Li-S batteries is hindered by the shuttle effect of lithium polysulfides (LiPSs) and the sluggish redox kinetics. Since the adsorption and catalytic conversion of LiPSs mainly occur on the surface of the electrocatalyst, regulating the surface structure of electrocatalysts is an advisable strategy to solve the obstacles in Li-S batteries. Herein, CoP nanoparticles with high oxygen content on surface embedded in hollow carbon nanocages (C/O-CoP) is employed to functionalize the separators and the effect of the surface oxygen content of CoP on the electrochemical performance is systematically explored. Increasing the oxygen content on CoP surface can enhance the chemical adsorption to lithium polysulfides and accelerate the redox conversions kinetics of polysulfides. The cell with C/O-CoP modified separator can achieve the capacity of 1033 mAh g-1 and maintain 749mAh g-1 after 200 cycles at 2C. Moreover, DFT calculations are used to reveal the enhancement mechanism of oxygen content on surface of CoP in Li-S chemistry. This work offers a new insight into developing high-performance Li-S batteries from the perspective of surface engineering.

Rapid, one-pot, non-toxic and scalable synthesis of boron nitride nano-onions via lamp ablation

We report the generation of boron nitride nano-onions (BNNOs) from pure hexagonal-BN crystallite powder in vacuum, via a one-pot, non-toxic, catalyst-free, rapid and potentially scalable high-temperature lamp ablation procedure. An array of characterization procedures revealed nanoparticle (a) shapes and sizes, morphing from polyhedral for diameters of order 101 nm to quasi-spherical at diameters of order 102 nm, and (b) composition, with a 1:1 B:N ratio while also confirming the absence of contaminants. A formation mechanism is proposed whereby BNNOs evolve from the initial thermal exfoliation of the bulk precursor powder into nano-platelets. They fold and close into hollow nano-cages that are more stable thermodynamically. Reactor temperatures were measured to be ∼ 1500–1600 K for experiments yielding the largest amounts of BNNOs. A relatively narrow range of ∼ 1300–1800 K can be established for viable BNNO generation. Structural modeling sheds light on the relative stability of the nanostructures as a function of shape, size and number of layers.