A Universal Formation Mechanism of Hollow Multi-Shelled Structures Dominated by Concentration Waves.

Hollow multi-shelled structures (HoMS), a new family of hierarchical nano/micro-structured materials, have evoked intensive studies to discover their unique temporal-spatial ordering features. The theoretical understanding of the general synthetic methods of HoMS, i.e. the sequential templating approach (STA), makes it possible to understand, predict, and control the shell formation process. Herein, a mathematical model is established based on the experiment results, which reveal the appearance of concentration waves in the STA. The numerical simulation results not only correspond well to the experimental observations but also explain the regulation methods. Whereby, the underlying physical essence of STA is elucidated, suggesting that HoMS is the concrete representation of the concentration waves. Thereafter the formation of HoMS is not limited to the solid-gas reactions through high-temperature calcination, but could be extended to solution systems under low-temperature conditions.

Hollow Multishell-Structured TiO2/MAPbI3 Composite Improves Charge Utilization for Visible-Light Photocatalytic Hydrogen Evolution.

Interfacial photogenerated charge separation and transport have demonstrated great influence on photocatalytic performance. Herein, the composite photocatalysts of methylammonium lead iodide perovskite (MAPbI3) in TiO2 with a hollow multishell structure (HoMS) are designed and synthesized. The results indicate that the heterogeneous interface within the MAPbI3/Pt/TiO2-HoMS can help enhance the separation of photogenerated charges. HoMSs assembled with multiple shells can not only support large surfaces available for building a heterogeneous interface and photocatalytic reactions but also improve the light absorption capability of photocatalysts. Besides, the thin shell structure can also reduce the transmission distance of carriers so as to hinder charge recombination and improve charge utilization. As a result, samples of MAPbI3/Pt/triple-shelled TiO2 hollow structure displayed a H2 yield of 6856.2 µmol h-1 g-1 under visible light, which is greatly better than that of bare MAPbI3 (268.6 µmol h-1 g-1).

PEG-Functionalized Hollow Multishelled Structures with On-Off Switch and Rate-Regulation for Controllable Antimicrobial Release.

The construction of responsive antimicrobial carriers with multifunctional and controllable release is an attractive but challenging proposition. Recently developed hollow multishelled structures (HoMSs) offers structural advantages, such as easily modifiable surfaces and mutually influenced shells. Herein, we report a novel pH-responsive antimicrobial carrier having hierarchical shells as multilevel responsive bodies using polyethylene glycol (PEG) as a gated regulator. The interaction between PEG-functionalized shells endows them with a pH-responsive switch and rate-regulator capability. These features are present in the form of rapid release of molecules wrapped in the outer shell, and controlled diffusion of antimicrobials stored in the inner shell by electrostatic interaction, resulting in a long-lasting mildew resistance for up to 71 days. The versatility of the hierarchical interactions of HoMSs will inspire the design of promising smart drug carriers.

Heterogeneous Hollow Multi-Shelled Structures with Amorphous-Crystalline Outer-Shells for Sequential Photoreduction of CO2.

Constructing delicate nano-/microreactors with tandem active sites in hierarchical architectures is a promising strategy for designing photocatalysts to realize the challenging but attractive CO2 reduction. Herein, hollow multi-shelled structure (HoMS) based microreactors with spatial ordered hetero-shells are fabricated, which achieve two-step CO2 -to-CH4 photoreduction. The multiple inner CeO2 shells increase the number of active catalytic sites to ensure efficient first-step reaction for generating CO, along with enriching the local CO concentration. The second-step CO-to-CH4 reaction is consequently induced by amorphous TiO2 (A-TiO2 ) composites on the adjacent outer-most shell, thus realizing the CO2 -to-CH4 conversion capability using one CeO2 @CeO2 /A-TiO2 HoMS. In-depth explorations in the microreactors provide compositional, structural, and interfacial guidance for engineering HoMS-based microreactors with temporally-spatially ordered shells toward efficient tandem catalysis.

Self-Assembled Open Porous Nanoparticle Superstructures.

Imparting porosity to inorganic nanoparticle assemblies to build up self-assembled open porous nanoparticle superstructures represents one of the most challenging issues and will reshape the property and application scope of traditional inorganic nanoparticle solids. Herein, we discovered how to engineer open pores into diverse ordered nanoparticle superstructures via their inclusion-induced assembly within 1D nanotubes, akin to the molecular host-guest complexation. The open porous structure of self-assembled composites is generated from nonclose-packing of nanoparticles in 1D confined space. Tuning the size ratios of the tube-to-nanoparticle enables the structural modulation of these porous nanoparticle superstructures, with symmetries such as C1, zigzag, C2, C4, and C5. Moreover, when the internal surface of the nanotubes is blocked by molecular additives, the nanoparticles would switch their assembly pathway and self-assemble on the external surface of the nanotubes without the formation of porous nanoparticle assemblies. We also show that the open porous nanoparticle superstructures can be ideal candidate for catalysis with accelerated reaction rates.

CdSe 1D/2D Mixed-Dimensional Heterostructures: Curvature-Complementary Self-Assembly for Enhanced Visible-Light Photocatalysis.

Mixed-dimensional heterostructures (MDHs), which combine nanomaterials of different dimensionalities deliver on the promise to bypass intrinsic limitations of a given low-dimensional material. Here, a strategy to engineer MDHs between two low-dimensional materials by curvature-complementary self-assembly is described. CdSe nanotubes rolled from 2D nanosheets and 1D CdSe nanorods, with negative and positive curvatures, respectively, are selected to illustrate complementary curvature self-assembly. The assembly process, optical, and photoelectrical properties of the CdSe MDHs are thoroughly investigated. Several remarkable features of CdSe MDHs, including increased light absorption, efficient charge separation, and appropriate bandgap structure are confirmed. The MDHs significantly alleviate the sluggish kinetics of electron transfer in the quantum sized CdSe subunits (onset potential of 0.21 V vs RHE for MDHs; 0.4 V lower than their low-dimensional building blocks), while the spatial nano-confinement effect in the CdSe MDHs also assists the interfacial reaction kinetics to render them ideal photocatalysts for benzylamine oxidation (conversion > 99% in 4 h with a two times higher rate than simple mixtures). The results highlight opportunities for building MDHs from low-dimensional building blocks with curvature-complementary features and expand the application spectrum of low dimensional materials in artificial photosynthesis.

Hollow Multishelled Structured SrTiO3 with La/Rh Co-Doping for Enhanced Photocatalytic Water Splitting under Visible Light.

La- and Rh-co-doped SrTiO3 (STO:La/Rh) hollow multishelled structures (HoMSs) are fabricated by adding La3+ and Rh3+ ions during the hydrothermal process of converting TiO2 HoMSs to STO HoMSs. STO:La/Rh HoMSs have successfully expanded the light absorption edge to 520 nm. Accompanied with the benefits of the unique hierarchical structure and relatively thin shells, STO:La/Rh HoMSs exhibit elevated light-harvesting capacity and charge separation efficiency. Compared with STO:La/Rh nanoparticles (NPs), STO:La/Rh HoMSs demonstrate enhanced photocurrent response, photocatalytic hydrogen evolution activity, and the quantum efficiency. Moreover, overall water splitting is realized by a Z-scheme system combining STO:La/Rh HoMSs with BiVO4 (BVO) nanosheets with 1 wt% Pt as the co-catalyst. Steady evolution of hydrogen and oxygen is performed under both visible light and simulated sunlight irradiation. The solar-to-hydrogen efficiency of double-shelled STO:La/Rh HoMS-BVO photocatalysts reaches 0.08%, which is twofold higher than STO:La/Rh NP-BVO photocatalysts.

Anisotropic Assembly of Nanocrystal/Molecular Hierarchical Superlattices Decoding from Tris-Amide Triarylamines Supramolecular Networks.

Directed assembly of nanocrystals from conventional templates suffers from poor control over the periodicity of the nanocrystal assembly, which is largely due to the fact that the template exists prior to the assembly and is not generally adaptive. Herein, small organic molecules (tris-amide triarylamines, TATA) are demonstrated as conceptual templates from self-assembly through noncovalent interactions. The as-formed supramolecular structures with terminated alkyl chains, resembling the structure of as-synthesized nanocrystals capped with alkyl chains, are able to interact with nanocrystals through van der Waals attractive forces, thereby enabling directed assembly of nanocrystals into ordered superlattices. Specifically, it is found that, as determined by the substituted alkyl chains of TATA, either H or J-aggregates of TATA can be achieved, which eventually produce several distinct supramolecular structures, from rods to spindles, to rings, and to spheres, serving as on-pathway intermediate that directs the assembly of nanocrystals into diverse nanocrystal superlattices. The approach described can be applicable to produce ordered nanocrystal assemblies of a wide range of nanocrystals, independent of size and shape and without ligand exchange process. Strikingly, a helical TATA stacking can direct assembly of binary nanocrystal mixtures into NaZn13 binary superhelix.

Constructing SrTiO3 -TiO2 Heterogeneous Hollow Multi-shelled Structures for Enhanced Solar Water Splitting.

Constructing hollow multi-shelled structures (HoMSs) has a significant effect on promoting light absorption property of catalysts and enhancing their performance in solar energy conversion applications. A facile hydrothermal method is used to design the SrTiO3 -TiO2 heterogeneous HoMSs by hydrothermal crystallization of SrTiO3 on the surface of the TiO2 HoMSs, which will realize a full coverage of SrTiO3 on the TiO2 surface and construct the SrTiO3 /TiO2 junctions. The broccoli-like SrTiO3 -TiO2 heterogeneous HoMSs exhibited a fourfold higher overall water splitting performance of 10.6 µmol h-1 for H2 production and 5.1 µmol h-1 for O2 evolution than that of SrTiO3 nanoparticles and the apparent quantum efficiency (AQE) of 8.6 % at 365 nm, which can be mainly attributed to 1) HoMS increased the light absorption ability of the constructed photocatalysts and 2) the SrTiO3 -TiO2 junctions boosted the separation efficiency of the photogenerated charge carriers.

High Phase-Purity 1T-MoS2 Ultrathin Nanosheets by a Spatially Confined Template.

The crystal phase plays an important role in controlling the properties of a nanomaterial; however, it is a great challenge to obtain a nanomaterial with high purity of the metastable phase. For instance, the large-scale synthesis of the metallic phase MoS2 (1T-MoS2 ) is important for enhancing electrocatalytic reaction, but it can only be obtained under harsh conditions. Herein, a spatially confined template method is proposed to synthesize high phase-purity MoS2 with a 1T content of 83 %. Moreover, both the confined space and the structure of template will affect the purity of 1T-MoS2 ; in this case, this approach was extended to other similar spatially confined templates to obtain the high-purity material. The obtained ultrathin nanosheets exhibit good electrocatalytic activity and excellent stability in the hydrogen evolution reaction.

Mesoscience in Hollow Multi-Shelled Structures.

The prevalence of mesoscale complexity in materials science underscores the significance of the compromise in competition principle, which gives rise to the emergence of mesoscience. This principle offers valuable insights into understanding the formation process, characteristics, and performance of complex material systems, ultimately guiding the future design of such intricate materials. Hollow multi-shelled structures (HoMS) represent a groundbreaking multifunctional structural system that encompasses several spatial regimes. A plethora of mesoscale cases within HoMS present remarkable opportunities for exploring, understanding, and utilizing mesoscience, varying from the formation process of HoMS, to the mesoscale structural parameters, and finally the distinctive mass/energy transfer behaviors exhibited by HoMS. The compromise in competition between the diffusion and reaction contributes to the successful formation of multi-shells of HoMS, allowing for precise regulation of the structural parameters by dynamically varying the interplay between two dominances. Moreover, the distinct roles played by the shells and cavities within HoMS significantly influence the energy/mass transfer processes with the unique temporal-spatial resolution, providing guidance for customizing the application performance. Hopefully, the empirical and theoretical anatomy of HoMS following mesoscience would fuel new discoveries within this promising and complex multifunctional material system.

Interfaces Engineering of Ultrafine Ni@Ni2P/C Core-Shell Heterostructure for High Yield Hydrogen Peroxide Electrosynthesis.

Developing cost-effective and sustainable catalysts with exceptional activity and selectivity is essential for the practical implementation of on-site H2O2 electrosynthesis, yet it remains a formidable challenge. Metal phosphide core-shell heterostructures anchored in carbon nanosheets (denoted as Ni@Ni2P/C NSs) are designed and synthesized via carbonization and phosphidation of the 2D Ni-BDC precursor. This core-shell nanostructure provides more accessible active sites and enhanced durability, while the 2D carbon nanosheet substrate prevents heterostructure aggregation and facilitates mass transfer. Theoretical calculations further reveal that the Ni/Ni2P heterostructure-induced optimization of geometric and electronic structures enables the favored adsorption of OOH* intermediate. All these features endow the Ni@Ni2P/C NSs with remarkable performance in 2e ORR for H2O2 synthesis, achieving a top yield rate of 95.6 mg L-1 h-1 with both selectivity and Faradaic efficiency exceeding 90% under a wide range of applied potentials. Furthermore, when utilized as the anode of an assembled gas diffusion electrode (GDE) device, the Ni@Ni2P/C NSs achieve in situ H2O2 production with excellent long-term durability (>32 h). Evidently, this work provides a unique insight into the origin of 2e ORR and proposes optimization of H2O2 production through nano-interface manipulation.

Rational Design of Coordination Polymers Composited Hollow Multishelled Structures for Drug Delivery.

Multifunctional drug delivery systems (DDS) are in high demand for effectively targeting specific cells, necessitating excellent biocompatibility, precise release mechanisms, and sustained release capabilities. The hollow multishelled structure (HoMS) presents a promising solution, integrating structural and compositional design for efficient DDS development amidst complex cellular environments. Herein, starting from a Fe-based metal-organic framework (MOF), amorphous coordination polymers (CP) composited HoMS with controlled shell numbers are fabricated by balancing the rate of MOF decomposition and shell formation. Fe-CP HoMS loaded with DOX is utilized for synergistic chemotherapy and chemodynamic therapy, offering excellent responsive drug release capability (excellent pH-triggered drug release 82% within 72 h at pH 5.0 solution with doxorubicin (DOX) loading capacity of 284 mg g-1). In addition to its potent chemotherapy attributes, Fe-CP-HoMS possesses chemodynamic therapy potential by continuously catalyzing H2O2 to generate ·OH species within cancer cells, thus effectively inhibiting cancer cell proliferation. DOX@3S-Fe-CP-HoMS, at a concentration of 12.5 µg mL-1, demonstrates significant inhibitory effects on cancer cells while maintaining minimal cytotoxicity toward normal cells. It is envisioned that CP-HoMS could serve as an effective and biocompatible platform for the advancement of intelligent drug delivery systems in the realm of cancer therapy.

Chiral superstructures of inorganic nanorods by macroscopic mechanical grinding.

The development of mechanochemistry substantially expands the traditional synthetic realm at the molecular level. Here, we extend the concept of mechanochemistry from atomic/molecular solids to the nanoparticle solids, and show how the macroscopic grinding is being capable of generating chirality in self-assembled nanorod (NR) assemblies. Specifically, the weak van der Waals interaction is dominated in self-assembled NR assemblies when their surface is coated with aliphatic chains, which can be overwhelmed by a press-and-rotate mechanic force macroscopically. The chiral sign of the NR assemblies can be well-controlled by the rotating directions, where the clockwise and counter-clockwise rotation leads to the positive and negative Cotton effect in circular dichroism and circularly polarized luminescence spectra, respectively. Importantly, we show that the present approach can be applied to NRs of diverse inorganic materials, including CdSe, CdSe/CdS, and TiO2. Equally important, the as-prepared chiral NR assemblies could be served as porous yet robust chiral substrates, which enable to host other molecular materials and induce the chirality transfer from substrate to the molecular system.

Semicrystalline SrTiO3 -Decorated Anatase TiO2 Nanopie as Heterostructure for Efficient Photocatalytic Hydrogen Evolution.

The coupling of TiO2 and SrTiO3 through elaborate bandgap engineering can provide synergies for highly efficient photocatalysts. To further improve the separation between photogenerated electrons and holes, a nano-heterostructured combination of semicrystalline SrTiO3 (S-SrTiO3 ) and anatase TiO2 nanoparticles is designed, and an optimized interface is achieved between uniformly grown S-SrTiO3 and metal organic framework (MOF)-derived anatase TiO2 through a controlled hydrothermal process. Besides tuning of the bandgap and broadening of the absorption spectral range, S-SrTiO3 particles alleviate charge carrier recombination benefiting from the coupling of the semicrystalline SrTiO3 around the interface. Additionally, highly dispersed S-SrTiO3 on TiO2 provides a good spatial distribution of active sites and the abundant carbon remained from MOF may reduce charge transport resistance. Moreover, the rapid transfer within the nano-heterostructure promotes the separation of the photogenerated charge carriers. With the above predominant architecture, when used as a photocatalyst, the as-synthesized S-SrTiO3 /TiO2 heterostructure exhibits exceptionally high photocatalytic performance of 13 005 µmol h-1 g-1 for H2 production, exceeding most oxide-based photocatalysts reported. This study might provide mechanistic insights into a new perspective for the design and preparation of photocatalysts with novel structure and enhanced catalysis activity.

Steering Hollow Multishelled Structures in Photocatalysis: Optimizing Surface and Mass Transport.

Hollow multishelled structures (HoMSs) provide a promising platform for fabricating photocatalysts, because the unique structure optimizes the effective surface and mass transport, showing enhanced light absorption, optimized mass transport and highly effective active sites exposed. Subsequently, the rational design on HoMS photocatalytsts is elaborated to boost the photocatalytic activity with efforts in all dimensions, from nanoscale to microscale. Breakthroughs in synthetic methodology of HoMSs have greatly evoked the prosperous photocatalytic researches for HoMSs since the developing of sequential templating approach in 2009. The dawn of HoMS photocatalyst is coming after revealing the temporal-spatial ordering property, which is also discussed in this paper with pioneer works demonstrating the greatly enhanced energy/mass transfer processes. Some insights into the key challenges and perspectives of HoMSs photocatalysts are also discussed. With the reviewed fate and future of HoMSs photocatalysts, hopefully new concepts and innovative works can be inspired to flourish this sun-rise field.

In-situ exfoliation of graphitic carbon nitride with metal-organic framework via a sonication-assisted approach for dispersive solid-phase extraction of perfluorinated compounds in drinking water samples.

Monitoring the levels of perfluorinated compounds (PFCs) in the environment is of vital importance, owing to their sustained environmental presence, extensive distribution, and associated health risks. The development of cost-effective and efficient sorbents for the establishment of sensitive analytical methods is critical for achieving trace-level detection. In this study, a graphitic carbon nitride (g-C3N4)-based sorbent is synthesized by a facile sonication-assisted method exfoliated by zeolitic imidazolate framework-67 (ZIF-67) in situ. The novel ZIF-67/g-C3N4 composites were systematically characterized by transmission electron microscopy, scanning electron microscopy, atomic force microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, and N2 adsorption-desorption analysis, exhibiting good dispersity and a large surface area. Moreover, molecular dynamics simulations indicated that g-C3N4 structures can be effectively exfoliated by the introduced ZIF-67 molecules. The hybrid material was successfully utilized as a dispersive solid-phase extraction sorbent, and the extraction factors were systematically optimized by response surface methodology. Under optimal conditions, the synthesized sorbent exhibited desirable linear correlations (R2 > 0.99), a low detection limit (0.3-2 ng L-1), and good repeatability (relative standard deviation <15%, n = 6). The developed method was applied for the analysis of natural and spiked water samples. The study demonstrated that the ZIF-67/g-C3N4 composites are promising materials for pollutant adsorption from drinking water samples.

Efficient sequential harvesting of solar light by heterogeneous hollow shells with hierarchical pores.

In nature, sequential harvesting of light widely exists in the old life entity, i.e. cyanobacteria, to maximize the light absorption and enhance the photosynthesis efficiency. Inspired by nature, we propose a brand new concept of temporally-spatially sequential harvesting of light in one single particle, which has purpose-designed heterogeneous hollow multi-shelled structures (HoMSs) with porous shells composed of nanoparticle subunits. Structurally, HoMSs consist of different band-gap materials outside-in, thus realizing the efficient harvesting of light with different wavelengths. Moreover, introducing oxygen vacancies into each nanoparticle subunit can also enhance the light absorption. With the benefit of sequential harvesting of light in HoMSs, the quantum efficiency at wavelength of 400 nm is enhanced by six times compared with the corresponding nanoparticles. Impressively, using these aforementioned materials as photocatalysts, highly efficient photocatalytic water splitting is realized, which cannot be achieved by using the nanoparticle counterparts. This new concept of temporally-spatially sequential harvesting of solar light paves the way for solving the ever-growing energy demand.

Few-Layer Graphdiyne Nanosheets Applied for Multiplexed Real-Time DNA Detection.

Despite recent progress in 2D nanomaterials-based biosensing, it remains challenging to achieve sensitive and high selective detection. This study develops few-layer graphdiyne (GD) nanosheets (NSs) that are used as novel sensing platforms for a variety of fluorophores real-time detection of DNA with low background and high signal-to-noise ratio, which show a distinguished fluorescence quenching ability and different affinities toward single-stranded DNA and double-stranded DNA. Importantly, for the first time, a few-layer GD NSs-based multiplexed DNA sensor is developed.

Dually Ordered Porous TiO2 -rGO Composites with Controllable Light Absorption Properties for Efficient Solar Energy Conversion.

Quadruple-layered TiO2 films with controllable macropore size are prepared via a confinement self-assembly method. The inverse opal structure with ordered mesoporous (IOM) presents unique light reflection and scattering ability with different wavelengths. Cyan light (400-600 nm) is reflected and scattered by IOM-195, which is in accord with N719 absorption spectra. By manipulating the macropore size, different light responses are obtained.