Synthetic Roadmap to a Large Library of Colloidal High-Entropy Rare Earth Oxyhalide Nanoparticles Containing up to Thirteen Metals

Nanoparticles of high-entropy materials that incorporate five or more elements randomized on a crystalline lattice often exhibit synergistic properties that can be influenced by both the identity and number of elements combined. These considerations are especially important for structurally and compositionally complex materials such as multimetal multianion compounds, where cation and anion mixing can influence properties in competitive and contradictory ways. Here, we demonstrate the synthesis of a large library of colloidal high-entropy rare earth oxyhalide (REOX) nanoparticles. We begin with the synthesis of (LaCePrNdSmEuGdDyHoErYbScY)OCl, which homogeneously incorporates 13 distinct rare earth elements. Through time point studies, we find that (LaNdSmGdDy)OCl, a 5-metal analogue, forms through in situ generation of compositionally segregated core@shell@shell intermediates that convert to homogeneously mixed products through apparent core-shell interdiffusion. Assuming that all possible combinations of 5 through 13 rare earth metals are synthetically accessible, we propose the existence of a 7099-member REOCl nanoparticle library, of which we synthesize and characterize 40 distinct members. We experimentally validate the incorporation of a large number of rare earth elements using energy dispersive X-ray spectra, despite closely spaced and overlapping X-ray energy lines, using several fingerprint matching strategies to uniquely correlate experimental and simulated spectra. We confirm homogeneous mixing by analyzing elemental distributions in high-entropy nanoparticles versus physical mixtures of their constituent compounds. Finally, we characterize the band gaps of the 5- and 13-metal REOCl nanoparticles and find a significantly narrowed band gap, relative to the constituent REOCl phases, in (LaCePrNdSmEuGdDyHoErYbScY)OCl but not in (LaNdSmGdDy)OCl.

Regioselective epitaxial growth of metallic heterostructures

Constructing regioselective architectures in heterostructures is important for many applications; however, the targeted design of regioselective architectures is challenging due to the sophisticated processes, impurity pollution and an unclear growth mechanism. Here we successfully realized a one-pot kinetically controlled synthetic framework for constructing regioselective architectures in metallic heterostructures. The key objective was to simultaneously consider the reduction rates of metal precursors and the lattice matching relationship at heterogeneous interfaces. More importantly, this synthetic method also provided phase- and morphology-independent behaviours as foundations for choosing substrate materials, including phase regulation from Pd20Sb7 hexagonal nanoplates (HPs) to Pd8Sb3 HPs, and morphology regulation from Pd20Sb7 HPs to Pd20Sb7 rhombohedra and Pd20Sb7 nanoparticles. Consequently, the activity of regioselective epitaxially grown Pt on Pd20Sb7 HPs was greatly enhanced towards the ethanol oxidation reaction; its activity was 57 times greater than that of commercial Pt/C, and the catalyst showed increased stability (decreasing by 16.3% after 2,000 cycles) and selectivity (72.4%) compared with those of commercial Pt/C (56.0%, 18.2%). This work paves the way for the design of unconventional well-defined heterostructures for use in various applications.

Remnant Copper Cation-Assisted Atom Mixing in Multicomponent Nanoparticles

Nanostructured high-/medium-entropy compounds have emerged as important catalytic materials for energy conversion technologies, but complex thermodynamic relationships involved with the element mixing enthalpy have been a considerable roadblock to the formation of stable single-phase structures. Cation exchange reactions (CERs), in particular with copper sulfide templates, have been extensively investigated for the synthesis of multicomponent heteronanoparticles with unconventional structural features. Because copper cations within the host copper sulfide templates are stoichiometrically released with incoming foreign cations in CERs to maintain the overall charge balance, the complete absence of Cu cations in the nanocrystals after initial CERs would mean that further compositional variation would not be possible by subsequent CERs. Herin, we successfully retained a portion of Cu cations within the silver sulfide (Ag2S) and gold sulfide (Au2S) phases of Janus Cu2-xS-M2S (M = Ag, Au) nanocrystals after the CERs, by partially suppressing the transformation of the anion sublattice that inevitably occurs during the introduction of external cations. Interestingly, the subsequent CERs on Janus Cu1.81S-M2S (M = Ag, Au), by utilizing the remnant Cu cations, allowed the construction of Janus Cu1.81S-AgxAuyS, which preserved the initial heterointerface. The synthetic strategy described in this work to suppress the complete removal of the Cu cation from the template could fabricate the CER-driven heterostructures with greatly diversified compositions, which exhibit unusual optical and catalytic properties.

Inhomogeneous Au2S for Photoacoustic Imaging and Photodynamic Tumor Therapy Based on Different Forms of Energy Dissipation

Nanomaterials with unique structures and components play a crucial role in nanomedicine. In this study, we discovered that the inhomogeneous Au2S constructed by cation exchange and acid etching could dissipate energy in different forms after absorbing multichromatic light, which could be used to achieve the integrated diagnosis and treatment of tumors, respectively. Folic acid modified Au2S ringed nanoparticles (FA-Au2S RNs) with an assembly-like structure were demonstrated to result in better PA imaging performance and generate more reactive oxygen species (O2·-, ·OH, and 1O2) than folic acid modified Au2S triangular nanoparticles (FA-Au2S TNs). Finite element analyses determined the reason for the high absorbance properties and synergistic enhancement of plasma resonance in the assembly-like structure of Au2S RNs. Both FA-Au2S nanostructures were modified with folic acid and injected into 4T1 tumor-bearing mice via the tail vein. The best PA imaging contrast was obtained under 700 nm laser illumination, and the most effective PDT antitumor activity was achieved under 1064 nm laser illumination. The PA average of the tumor in the FA-Au2S RN group was approximately 2 times higher than that of the FA-Au2S TN group at 24 h of injection. The PA imaging results of intratumorally injected FA-Au2S RNs proved that they were still able to show better PA signal enhancement at 24 h postinjection. Our study demonstrates that FA-Au2S nanomaterials with unique structures and special properties can be reliably produced using strictly controlled chemical synthesis. It further provides a strategy for the construction of highly sensitive PA imaging platforms and efficient PDT antitumor agents that exploit wavelength-dependent energy dissipation mechanisms.

Waning-and-waxing shape changes in ionic nanoplates upon cation exchange

Flexible control of the composition and morphology of nanocrystals (NCs) over a wide range is an essential technology for the creation of functional nanomaterials. Cation exchange (CE) is a facile method by which to finely tune the compositions of ionic NCs, providing an opportunity to obtain complex nanostructures that are difficult to form using conventional chemical synthesis procedures. However, due to their robust anion frameworks, CE cannot typically be used to modify the original morphology of the host NCs. In this study, we report an anisotropic morphological transformation of Cu1.8S NCs during CE. Upon partial CE of Cu1.8S nanoplates (NPLs) with Mn2+, the hexagonal NPLs are transformed into crescent-shaped Cu1.8S-MnS NPLs. Upon further CE, these crescent-shaped NPLs evolve back into completely hexagonal MnS NPLs. Comprehensive characterization of the intermediates reveals that this waxing-and-waning shape-evolution process is due to dissolution, redeposition, and intraparticle migration of Cu+ and S2-. Furthermore, in addition to Mn2+, this CE-induced transformation process occurs with Zn2+, Cd2+ and Fe3+. This finding presents a strategy by which to create heterostructured NCs with various morphologies and compositions under mild conditions.

Complete miscibility of immiscible elements at the nanometre scale

Understanding the mixing behaviour of elements in a multielement material is important to control its structure and property. When the size of a multielement material is decreased to the nanoscale, the miscibility of elements in the nanomaterial often changes from its bulk counterpart. However, there is a lack of comprehensive and quantitative experimental insight into this process. Here we explored how the miscibility of Au and Rh evolves in nanoparticles of sizes varying from 4 to 1 nm and composition changing from 15% Au to 85% Au. We found that the two immiscible elements exhibit a phase-separation-to-alloy transition in nanoparticles with decreased size and become completely miscible in sub-2 nm particles across the entire compositional range. Quantitative electron microscopy analysis and theoretical calculations were used to show that the observed immiscibility-to-miscibility transition is dictated by particle size, composition and possible surface adsorbates present under the synthesis conditions.

Using Surface Composition and Energy to Control the Formation of Either Tetrahexahedral or Hexoctahedral High-Index Facet Nanostructures

High-index facet nanoparticles with structurally complex shapes, such as tetrahexahedron (THH) and hexoctahedron (HOH), represent a class of materials that are important for catalysis, and the study of them provides a fundamental understanding of the relationship between surface structures and catalytic properties. However, the high surface energies render them thermodynamically unfavorable compared to low-index facets, thereby making their syntheses challenging. Herein, we report a method to control the shape of high-index facet Cu nanoparticles (either THH with {210} facets or HOH with {421} facets) by tuning the facet surface energy with trace amounts of Te atoms. Density functional theory (DFT) calculations reveal that the density of Te atoms on Cu nanoparticles can change the relative stability of the high-index facets associated with either the THH or HOH structures. By controlling the annealing conditions and the rate of Te dealloying from CuTe nanoparticles, the surface density of Te atoms can be deliberately adjusted, which can be used to force the formation of either THH (higher surface Te density) or HOH (lower surface Te density) nanoparticles.

Cation Exchange in Colloidal Transition Metal Nitride Nanocrystals

Transition metal nitride (TMN)-based nanostructures have emerged as promising materials for diverse applications in electronics, photonics, energy storage, and catalysis due to their highly desirable physicochemical properties. However, synthesizing TMN-based nanostructures with designed compositions and morphologies poses challenges, especially in the solution phase. The cation exchange reaction (CER) stands out as a versatile postsynthetic strategy for preparing nanostructures that are otherwise inaccessible through direct synthesis. Nevertheless, exploration of the CER in TMNs lags behind that in metal chalcogenides and metal phosphides. Here, we demonstrate cation exchange in colloidal metal nitride nanocrystals, employing Cu3N nanocrystals as starting materials to synthesize Ni4N and CoN nanocrystals. By controlling the reaction conditions, Cu3N@Ni4N and Cu3N@CoN core@shell heterostructures with tunable compositions can also be obtained. The Ni4N and CoN nanocrystals are evaluated as catalysts for the electrochemical oxygen evolution reaction (OER). Remarkably, CoN nanocrystals demonstrate superior OER performance with a low overpotential of 286 mV at 10 mA·cm-2, a small Tafel slope of 89 mV·dec-1, and long-term stability. Our CER approach in colloidal TMNs offers a new strategy for preparing other metal nitride nanocrystals and their heterostructures, paving the way for prospective applications.

Stress-induced ordering evolution of 1D segmented heteronanostructures and their chemical post-transformations

Investigations of one-dimensional segmented heteronanostructures (1D-SHs) have recently attracted much attention due to their potentials for applications resulting from their structure and synergistic effects between compositions and interfaces. Unfortunately, developing a simple, versatile and controlled synthetic method to fabricate 1D-SHs is still a challenge. Here we demonstrate a stress-induced axial ordering mechanism to describe the synthesis of 1D-SHs by a general under-stoichiometric reaction strategy. Using the continuum phase-field simulations, we elaborate a three-stage evolution process of the regular segment alternations. This strategy, accompanied by easy chemical post-transformations, enables to synthesize 25 1D-SHs, including 17 nanowire-nanowire and 8 nanowire-nanotube nanostructures with 13 elements (Ag, Te, Cu, Pt, Pb, Cd, Sb, Se, Bi, Rh, Ir, Ru, Zn) involved. This ordering evolution-driven synthesis will help to investigate the ordering reconstruction and potential applications of 1D-SHs.

Pre-phase transition of a Cu2-xS template enables polymorph selective synthesis of MS (M = Zn, Cd, Mn) nanocrystals via cation exchange reactions

Utilization of copper-deficient Cu2-xS nanocrystals (NCs) with diverse crystal phases and stoichiometries as cation exchange (CE) templates is a potential route to overcome the current limitations in the polymorph selective synthesis of desired nanomaterials. Among the Cu2-xS NCs, covellite CuS is emerging as an attractive CE template to produce complicated and metastable metal sulfide NCs. The presence of a reducing agent is essential to induce a phase transition of CuS into other Cu2-xS phases prior to the CE reactions. Nevertheless, the effect of the reducing agent on the phase transition of CuS, especially into the hexagonal close packing (hcp) phase and the cubic close packing (ccp) phase, has been scarcely exploited, but it is highly important for the polymorphic production of metal sulfides with the wurtzite phase and zinc blende phase. Herein, we report a reducing agent dependent pre-phase transition of CuS nanodisks (NDs) into hcp and ccp Cu2-xS NCs. 1-Dodecanethiol molecules and oleylamine molecules selectively reduced CuS NDs into hcp djurleite Cu1.94S NDs and ccp digenite Cu1.8S NCs. Afterward, the hcp Cu1.94S NDs and ccp Cu1.8S NCs were exchanged by Zn2+/Cd2+/Mn2+, and the wurtzite phase and the zinc blende phase of ZnS, CdS, and MnS NCs were produced. Without the pre-phase transition, direct CE reactions of CuS NDs are incapable of synthesizing the above wurtzite and zinc blende metal sulfide NCs. Therefore, our findings suggest the importance of the pre-phase transition of the CE template in polymorphic syntheses, holding great promise in the fabrication of other polymorphic nanomaterials with novel physical and chemical properties.

Synergy of copper vacancies and amorphous regions in copper sulfides enables superior capacity for Hg0 adsorption

Adsorption is a high-efficiency and low-cost approach to control elemental mercury emission from industrial flue gas. However, the adsorption capacity is unsatisfactory due to its surface-only adsorption. In this work, a facile method was used for preparing the crystalline-amorphous co-existed copper sulfides (CA-CuS) with an abundance of copper vacancies and amorphous regions through temperature-controlled ultrasonic cavitation. The CA-CuS was used in the flue gas wet scrubbing and displayed outstanding Hg0 capture performance, achieving a removal efficiency of 99.8% and an adsorption capacity up to 573.8 mg·g-1 with a sulfur atomic utilization ratio of 27.5%. Experimental results and density functional theory (DFT) calculation verified that the copper vacancies at di-coordinated sites led to the formation of robust mercury binding sites (i.e., S2-(CN=3)) and unsaturated coordinated oxidizing sites (i.e., S22-). Meanwhile, the amorphous regions facilitated the internal migration of adsorbed mercury on the surface and promote the exchange with Cu2+ in the interior of adsorbents. The synergistic effect of copper vacancies and amorphous regions enables superior mercury adsorption capability and high atomic utilization.

Solution-Processed 1D Wurtzite ZnS Nanostructures with Controlled Crystallographic Orientation and Tunable Band-Edge Emission

1D compound semiconductor nanomaterials possess unique physicochemical properties that strongly depend on their size, composition, and structures. ZnS has been widely investigated as one of the most important semiconductors, and the control of crystallographic orientation of 1D ZnS nanostructures is still challenging and crucial to exploring their anisotropic properties. Herein, a solution-processed strategy is developed to synthesize 1D wurtzite (w-)ZnS nanostructures with the specific <002> and <210> orientations by co-decomposing the copper dibutyldithiocarbamate {[(C4 H9 )2 NCS2 ]2 Cu, i.e., R2 Cu} and zinc dibutyldithiocarbamate (R2 Zn) precursors in the mixed solvents of oleylamine and 1-dodecanethoil. A solution-solid-solid (SSS)-Oriented growth mechanism is proposed, which includes oriented nucleation dominated and SSS growth dominated stages. The crystallographic orientation mainly depends on the interfacial energy and ligand effect. The 1D w-ZnS nanostructures with controlled crystallographic orientation display unique morphologies, i.e., <002>-oriented w-ZnS nanorod enclosed with {110} facets while <210>-oriented w-ZnS nanobelt enclosed with wide (002) and narrow (110) facets. The bandgap of 1D w-ZnS nanostructures can be tuned from 3.94 to 3.82 eV with the crystallographic growth direction varied from <002> to <210>, thus leading to the tunable band-edge emission from ≈338 to ≈345 nm.

Hierarchical Flower-like Sulfides with Increased Entropy for Electromagnetic Wave Absorption

The concept of high entropy is considered promising to enhance electromagnetic wave absorption properties. However, preparing high-entropy sulfides with unique structures for high-performance electromagnetic absorption remains a challenge. In this study, hierarchical porous flower-like dual-phase sulfides were designed with increased entropy and fabricated using a versatile approach. The porous flower configuration enhanced the scattering of electromagnetic waves and the impedance-matching characteristics. Additionally, the effect of high entropy induced diverse defects that were favorable for electromagnetic wave dissipation in dual-phase sulfides. The design of the dual-phase structure generated strong interface polarization, and the composition and content of the phases exhibited clear changes with the increase in the number of metal elements. Interestingly, apparent lattice distortions, defects, and shear strains were directly observed near the dual-phase interface of millerite (102) and pyrite (220) planes, facilitating the occurrence of dipole polarization. Consequently, the developed dual-phase high-entropy sulfide exhibited outstanding microwave absorption properties. The minimum reflection loss value of (FeCoNiCuZn)S was -45.8 dB at a thickness of 1.5 mm, and the optimal effective absorption bandwidth was 3.8 GHz at a thickness of 1.4 mm thickness. Thus, the design of high-entropy sulfides brings meaningful guidance for tuning the wave absorption properties in sulfides.

Amorphization-Induced Cation Exchange in Indium Oxide Nanosheets for CO2-to-Ethanol Conversion

Cation exchange (CE) in metal oxides under mild conditions remains an imperative yet challenging goal to tailor their composition and enable practical applications. Herein, we first develop an amorphization-induced strategy to achieve room-temperature CE for universally synthesizing single-atom doped In2O3 nanosheets (NSs). Density functional theory (DFT) calculations elucidate that the abundant coordination-unsaturated sites present in a-In2O3 NSs are instrumental in surmounting the energy barriers of CE reactions. Empirically, a-In2O3 NSs as the host materials successfully undergo exchange with unary cations (Cu2+, Co2+, Mn2+, Ni2+), binary cations (Co2+Mn2+, Co2+Ni2+, Mn2+Ni2+), and ternary cations (Co2+Mn2+Ni2+). Impressively, high-loading single-atom doped (over 10 atom %) In2O3 NSs were obtained. Additionally, Cu/a-In2O3 NSs exhibit an excellent ethanol yield (798.7 μmol g-1 h-1) with a high selectivity of 99.5% for the CO2 photoreduction. This work offers a new approach to induce CE reactions in metal oxides under mild conditions and constructs scalable single-atom doped catalysts for critical applications.

Facile aqueous synthesis and comparative evaluation of TiO2-semiconductor and TiO2-metal nanohybrid photocatalysts in antibiotics degradation under visible light

Advanced oxidation processes using TiO2-based nanomaterials are sustainable technologies that hold great promise for the degradation of many types of pollutants including pharmaceutical residues. A wide variety of heterostructures coupling TiO2 with visible-light active nanomaterials have been explored to shift its photocatalytic properties to harness sun irradiation but a systematic comparison between them is lacking in the current literature. Furthermore, the high number of proposed nanostructures with different size, morphology, and surface area, and the often complex synthesis processes hamper the transition of these materials into commercial and effective solutions for environmental remediation. Herein, we have designed a facile and cost-effective method to synthesize two heterostructured photocatalysts representative of two main families of novel structures proposed, hybrids of TiO2 with metal (Au) and semiconductor (CeO2) nanomaterials. The photocatalysts have been extensively characterized to ensure a good comparability in terms of co-catalyst doping characteristics, morphology and surface area. The photocatalytic degradation of ciprofloxacin and sulfamethoxazole as target pollutants, two antibiotics of high concern polluting water sources, has been evaluated and CeO2/TiO2 exhibited the highest activity, achieving complete antibiotic degradation at very low photocatalyst concentrations. Our study provides new insights into the development of inexpensive heterostructured photocatalysts and suggests that the non-stoichiometry and characteristic d and f electronic orbital configuration of CeO2 have a significantly improved role in the enhancement of the photocatalytic reaction.

Recent Advances of Seed-Mediated Growth of Metal Nanoparticles: from Growth to Applications

Unprecedented advances in metal nanoparticle synthesis have paved the way for broad applications in sensing, imaging, catalysis, diagnosis, and therapy by tuning the optical properties, enhancing catalytic performance, and improving chemical and biological properties of metal nanoparticles. The central guiding concept for regulating the size and morphology of metal nanoparticles is identified as the precise manipulation of nucleation and subsequent growth, often known as seed-mediated growth methods. However, since the growth process is sensitive not only to the metal seeds but also to capping agents, metal precursors, growth solution, growth/incubation time, reductants, and other influencing factors, the precise control of metal nanoparticle morphology is multifactorial. Further, multiple reaction parameters are entangled with each other, so it is necessary to clarify the mechanism by which each factor precisely regulates the morphology of metal nanoparticles. In this review, to exploit the generality and extendibility of metal nanoparticle synthesis, the mechanisms of growth influencing factors in seed-mediated growth methods are systematically summarized. Second, a variety of critical properties and applications enabled by grown metal nanoparticles are focused upon. Finally, the current progress and offer insights on the challenges, opportunities, and future directions for the growth and applications of grown metal nanoparticles are reviewed.

Thermally Induced Domain Migration and Interfacial Restructuring in Cation Exchanged ZnS-Cu1.8S Heterostructured Nanorods

Partial cation exchange reactions can be used to rationally design and synthesize heterostructured nanoparticles that are useful targets for applications in photocatalysis, nanophotonics, thermoelectrics, and medicine. Such reactions introduce intraparticle frameworks that define the spatial arrangements of different materials within a heterostructured nanoparticle, as well as the orientations and locations of their interfaces. Here, we show that upon heating to temperatures relevant to their synthesis and applications, the ZnS regions and Cu1.8S/ZnS interfaces of heterostructured ZnS-Cu1.8S nanorods migrate and restructure. We first use partial cation exchange reactions to synthesize a library of seven distinct samples containing various patches, bands, and tips of ZnS embedded within Cu1.8S nanorods. Upon annealing in solution or in air, ex situ TEM analysis shows evidence that the ZnS domains migrate in different ways, depending upon their sizes and locations. Using differential scanning calorimetry, we correlate the threshold temperature for ZnS migration to the superionic transition temperature of Cu1.8S, which facilitates rapid diffusion throughout the nanorods. We then use in situ thermal TEM to study the evolution of individual ZnS-Cu1.8S nanorods upon heating. We find that ZnS domain migration occurs through a ripening process that minimizes small patches with higher-energy interfaces in favor of larger bands and tips having lower-energy interfaces, as well as through restructuring of higher-energy Cu1.8S/ZnS interfaces. Notably, Cu1.8S nanorods containing multiple patches of ZnS thermally transform into ZnS-Cu1.8S heterostructured nanorods having ZnS tips and/or central bands, which provides mechanistic insights into how these commonly observed products form during synthesis.

Functional Zonation Strategy of Heterodimer Nanozyme for Multiple Chemiluminescence Imaging Immunoassay

Although nanozymes with intrinsic enzyme-like characteristics have aroused great interest in the biosensing field, the challenge is to keep high enzyme-like activity of the nanozyme after the modification of biomolecules onto nanozymes. Herein, a functional zonation strategy of a heterodimer nanozyme was proposed to tackle the challenge and further construct a multiple chemiluminescence (CL) imaging immunoassay. Here Fe3O4-Au as a heterodimer nanozyme model was divided into two zones, in which Fe3O4 nanoparticles (NPs) were regarded as a nanozyme zone and AuNPs were defined as an antibody immobilization zone. A signal amplification probe (Fe3O4-Au-Ab2) was prepared by modifying the secondary antibody (Ab2) on AuNPs of the Fe3O4-Au heterodimer owing to the Au-S bond. The exposed Fe3O4 of the Fe3O4-Au-Ab2 probe shows very high peroxidase-like activity and can efficiently catalyze H2O2-luminol to produce strong CL imaging signals for multiple antigens detection. Using chicken interleukin-4 (ChIL-4) and chicken gamma interferon (ChIFN-γ) as models, the proposed CL imaging immunoassay shows wide linear ranges (0.005-0.10 ng/mL for both ChIL-4 and ChIFN-γ) and low detection limits (0.58 pg/mL for ChIL-4, 0.47 pg/mL for ChIFN-γ) with the characteristics of high sensitivity, high specificity, and good stability. This work provides a promising functional zonation concept for nanozymes to construct new types of nanozyme probes for immunoassay of multiple biomolecules.

Versatile synthesis of nano-icosapods via cation exchange for effective photocatalytic conversion of biomass-relevant alcohols

Branched metal chalcogenide nanostructures with well-defined composition and configuration are appealing photocatalysts for solar-driven organic transformations. However, precise design and controlled synthesis of such nanostructures still remain a great challenge. Herein, we report the construction of a variety of highly symmetrical metal sulfides and heterostructured icosapods based on them, in which twenty branches were radially grown in spatially ordered arrangement, with a high degree of structure homogeneity. Impressively, the as-obtained CdS-PdxS icosapods manifest a significantly improved photocatalytic activity for the selective oxidation of biomass-relevant alcohols into corresponding aldehydes coupled with H2 evolution under visible-light irradiation (>420 nm), and the apparent quantum yield of the benzyl alcohol reforming can be achieved as high as 31.4% at 420 nm. The photoreforming process over the CdS-PdxS icosapods is found to be directly triggered by the photogenerated electrons and holes without participation of radicals. The enhanced photocatalytic performance is attributed to the fast charge separation and abundant active sites originating from the well-defined configuration and spatial organization of the components in the branched heterostructures.

Three-dimensional reconstruction of Y-IrNi rhombic dodecahedron nanoframe by STEM/EDS tomography

The structural analysis of nanocrystals via transmission electron microscopy (TEM) is a valuable technique for the material science field. Recently, two-dimensional images by scanning TEM (STEM) and energy-dispersive X-ray spectroscopy (EDS) have successfully extended to three-dimensional (3D) imaging by tomography. However, despite improving TEM instruments and measurement techniques, detector shadowing, the missing-wedge problem, X-ray absorption effects, etc., significant challenges still remain; therefore, the various required corrections should be considered and applied when performing quantitative tomography. Nonetheless, this 3D reconstruction technique can facilitate active site analysis and the development of nanocatalyst systems, such as water electrolysis and fuel cell. Herein, we present a 3D reconstruction technique to obtain tomograms of IrNi rhombic dodecahedral nanoframes (IrNi-RFs) from STEM and EDS images by applying simultaneous iterative reconstruction technique and total variation minimization algorithms. From characterizing the morphology and spatial chemical composition of the Ir and Ni atoms in the nanoframes, we were able to infer the origin of the physical and catalytic durability of IrNi-RFs. Also, by calculating the surface area and volume of the 3D reconstructed model, we were able to quantify the Ir-to-Ni composition ratio and compare it to the EDS measurement result.

Colloidal semiconductor nanocrystals: from bottom-up nanoarchitectonics to energy harvesting applications

Colloidal semiconductor nanocrystals (NCs) have been extensively investigated owing to their unique properties induced by the quantum confinement effect. The advent of colloidal synthesis routes led to the design of stable colloidal NCs with uniform size, shape, and composition. Metal oxides, phosphides, and chalcogenides (ZnE, CdE, PbE, where E = S, Se, or Te) are few of the most important monocomponent semiconductor NCs, which show excellent optoelectronic properties. The ability to build quantum confined heterostructures comprising two or more semiconductor NCs offer greater customization and tunability of properties compared to their monocomponent counterparts. More recently, the halide perovskite NCs showed exceptional optoelectronic properties for energy generation and harvesting applications. Numerous applications including photovoltaic, photodetectors, light emitting devices, catalysis, photochemical devices, and solar driven fuel cells have demonstrated using these NCs in the recent past. Overall, semiconductor NCs prepared via the colloidal synthesis route offer immense potential to become an alternative to the presently available device applications. This feature article will explore the progress of NCs syntheses with outstanding potential to control the shape and spatial dimensionality required for photovoltaic, light emitting diode, and photocatalytic applications. We also attempt to address the challenges associated with achieving high efficiency devices with the NCs and possible solutions including interface engineering, packing control, encapsulation chemistry, and device architecture engineering.

Heterogeneity in Cation Exchange Ag+ Doping of CdSe Nanocrystals

Cation exchange is becoming extensively used for nanocrystal (NC) doping in order to produce NCs with unique optical and electronic properties. However, despite its ever-increasing use, the relationships between the cation exchange process, its doped NC products, and the resulting NC photophysics are not well characterized. For example, similar doping procedures on NCs with the same chemical compositions have resulted in quite different photophysics. Through a detailed single molecule investigation of a postsynthesis Ag+ doping of CdSe NCs, a number of species were identified within a single doped NC sample, suggesting the differences in the optical properties of the various synthesis methods are due to the varied contributions of each species. Electrostatic force microscopy (EFM), electron energy loss spectroscopy (EELS) mapping, and single molecule photoluminescence (PL) studies were used to identify four possible species resulting from the Ag+-CdSe cation exchange doping process. The heterogeneity of these samples shows the difficulty in controlling a postsynthesis cation exchange method to produce homogeneous samples needed for use in any potential application. Additionally, the heterogeneity in the doped samples demonstrates that significant care must be taken in describing the ensemble or average characteristics of the sample.

Unexpected Multi-Step Transformation of AgCuS to AgAuS During Nanoparticle Cation Exchange

Cation exchange reactions can modify the compositions of colloidal nanoparticles, providing easy access to compounds or nanoparticles that may not be accessible directly. The most common nanoparticle cation exchange reactions replace monovalent cations with divalent cations or vice versa, but some monovalent-to-monovalent exchanges have been reported. Here, we dissect the reaction of as-synthesized AgCuS nanocrystals with Au+ to form AgAuS, initially hypothesizing that Au+ could be selective for Cu+ (rather than for Ag+) based on a known Au+-for-Cu+ exchange and the stability of the targeted AgAuS product. Unexpectedly, we found this system and the putative cation exchange reaction to be much more complex than anticipated. First, the starting AgCuS nanoparticles, which match literature reports, are more accurately described as a hybrid of Ag and a variant of AgCuS that is structurally related to mckinstryite Ag5Cu3S4. Second, the initial reaction of Ag-AgCuS with Au+ results in a galvanic replacement to transform the Ag component to a AuyAg1-y alloy. Third, continued reaction with Au+ initiates cation exchange with Cu+ in AuyAg1-y-AgCuS to form AuyAg1-y-Ag3CuxAu1-xS2 and then AuyAg1-y-AgAuS, which is the final product. Crystal structure relationships among mckinstryite-type AgCuS, Ag3CuxAu1-xS2, and AgAuS help to rationalize the transformation pathway. These insights into the reaction of AgCuS with Au+ reveal the potential complexity of seemingly simple nanoparticle reactions and highlight the importance of thorough compositional, structural, and morphological characterization before, during, and after such reactions.

Ligand-Controlled Electroreduction of CO2 to Formate over Facet-Defined Bimetallic Sulfide Nanoplates

CO₂ reduction (CO₂R) catalyzed by an efficient, stable, and earth-abundant electrocatalyst offers an attractive means to store energy derived from renewable sources. Here, we describe the synthesis of facet-defined Cu₂SnS₃ nanoplates and the ligand-controlled CO₂R property. We show that thiocyanate-capped Cu₂SnS₃ nanoplates possess excellent selectivity toward formate over a wide range of potentials and current densities, attaining a maximum formate Faradaic efficiency of 92% and partial current densities as high as 181 mA cm^-2 when tested using a flow cell with gas-diffusion electrode. In situ spectroscopic measurements and theoretical calculations reveal that the high formate selectivity originates from favorable adsorption of HCOO* intermediates on cationic Sn sites that are electronically modulated by thiocyanates bound to adjacent Cu sites. Our work illustrates that well-defined multimetallic sulfide nanocrystals with tailored surface chemistries could provide a new avenue for future CO₂R electrocatalyst design.

Quantifiable Regulation of Chemical Kinetics Barriers for Creation of Single-Atom Metal Sites on Photocatalytic Atomic Layers

Cation exchange (CE) under mild conditions promises a facile strategy to anchor single metal sites on colloidal chalcogenides toward catalytic applications, which however has seldom been demonstrated. The dilemma behind this is the rapid kinetics and high efficiency of the reaction disfavoring atomic dispersion of the metal species. Here we report that a fine-tuning of the affinity between the incoming metal cations and the deliberately introduced ligands can be exploited to manipulate the kinetics of the CE reaction, in a quantitative and systematic manner defined by the Tolman electronic parameter of the ligands used. Moreover, the steric effect of metal-ligand complexes offers thermodynamic preference for spatial isolation of the metal atoms. These thereby allow the rational construction of single atom catalysts (SACs) via simple one-step CE reactions, as exemplified by the CE-derived incorporation of single metal atoms (M = Cu, Ag, Au, Pd) on SnS₂ two-unit-cell layers through M-S coordination.

Region-Controlled Framework Interface Mediated Anion Exchange Chemical Transformation to Designed Metal Phosphosulfide Heteronanostructures

Postsynthetic chemical transformation provides a powerful platform for creating heteronanostructures (HNs) with well-defined materials and interfaces that generate synergy or enhancement. However, it remains a synthetic bottleneck for the precise construction of HNs with increased degrees of complexity and more elaborate functions in a predictable manner. Herein, we define a general transformative protocol for metal phosphosulfide HNs based on tunable hexagonal Cu_1.81S frameworks with corner-, edge- and face-controlled growth of Co₂P domains. The region-controlled Cu_1.81S-Co₂P framework interfaces can serve as "kinetic barriers" in mediating the direction and rate between P and S anion exchange reactions, thus leading to a family of morphology and phase designed Cu₃P_1-xS_x-Co₂P HNs with hollow (branched, dotted and crown), porous and core-shell architectures. This study reveals the internal transformation mechanism between metal sulfide and phosphide nanocrystals, and opens up a new way for the rational synthesis of metastable HNs that are otherwise inaccessible.

Engineering the Au-Cu2 O Crystalline Interfaces for Structural and Catalytic Integration

Precise structural control has attracted tremendous interest in pursuit of the tailoring of physical properties. Here, this work shows that through strong ligand-mediated interfacial energy control, Au-Cu₂ O dumbbell structures where both the Au nanorod (AuNR) and the partially encapsulating Cu₂ O domains are highly crystalline. The synthetic advance allows physical separation of the Au and Cu₂ O domains, in addition to the use of long nanorods with tunable absorption wavelength, and the crystalline Cu₂ O domain with well-defined facets. The interplay of plasmon and Schottky effects boosts the photocatalytic performance in the model photodegradation of methyl orange, showing superior catalytic efficiency than the AuNR@Cu₂ O core-shell structures. In addition, compared to the typical core-shell structures, the AuNR-Cu₂ O dumbbells can effectively electrochemically catalyze the CO₂ to C₂₊ products (ethanol and ethylene) via a cascade reaction pathway. The excellent dual function of both photo- and electrocatalysis can be attributed to the fine physical separation of the crystalline Au and Cu₂ O domains.

Multimetallic post-synthetic modifications of copper selenide nanoparticles

In this report, we investigate the addition of two metal cations, simultaneously and sequentially to Cu_2-xSe nanoparticles. The metal combinations (Ag-Au, Ag-Pt, Hg-Au and Hg-Pt) are chosen such that one metal adds to the structure via cation exchange and the other adds to the structure via metal deposition when added individually to Cu_2-xSe nanoparticles. Surprisingly, we find that for each metal combination, across all three synthesis routes, cation exchange and metal deposition products are obtained without deviation from the outcomes seen in the binary metal systems. However, within those outcomes the data show several types of heterogeneities in the morphologies formed including extent and composition of cation exchange products as well as the extent and composition of the metal deposited products. Taken together, these results suggest a hierarchical control for nanoheterostructure morphologies where the pathways of cation exchange or metal deposition in post-synthetic modification of Cu_2-xSe exhibit relatively general outcomes as a function of metal, regardless of synthetic approach or metal combination. However, the detailed composition and interface populations of the resulting materials are more sensitive to both metal identities and synthetic procedure (e.g. order of reagent addition), suggesting that certain principles of metal chalcogenide post-synthetic modification are excitingly robust, while also revealing new avenues for both mechanistic discovery and structural control.

Plate-Like Colloidal Metal Nanoparticles

The pseudo-two-dimensional (2D) morphology of plate-like metal nanoparticles makes them one of the most anisotropic, mechanistically understood, and tunable structures available. Although well-known for their superior plasmonic properties, recent progress in the 2D growth of various other materials has led to an increasingly diverse family of plate-like metal nanoparticles, giving rise to numerous appealing properties and applications. In this review, we summarize recent progress on the solution-phase growth of colloidal plate-like metal nanoparticles, including plasmonic and other metals, with an emphasis on mechanistic insights for different synthetic strategies, the crystallographic habits of different metals, and the use of nanoplates as scaffolds for the synthesis of other derivative structures. We additionally highlight representative self-assembly techniques and provide a brief overview on the attractive properties and unique versatility benefiting from the 2D morphology. Finally, we share our opinions on the existing challenges and future perspectives for plate-like metal nanomaterials.

Formation and Transformation of Cu2-xSe1-yTey Nanoparticles Synthesized by Tellurium Anion Exchange of Copper Selenide

Ion exchange reactions of colloidal nanoparticles post-synthetically modify the composition while maintaining the morphology and crystal structure and therefore are important for tuning properties and producing otherwise inaccessible and/or metastable materials. Reactions involving anion exchange of metal chalcogenides are particularly interesting, as they involve the replacement of the sublattice that defines the structure while also requiring high temperatures that can be disruptive. Here, we show that the tellurium anion exchange of weissite Cu_2-xSe nanoparticles using a trioctylphosphine-tellurium complex (TOP═Te) yields weissite Cu_2-xSe_1-yTe_y solid solutions, rather than complete exchange to weissite Cu_2-xTe, with compositions that are tunable based on the amount of TOP═Te used. Upon storage at room temperature in either solvent or air, tellurium-rich Cu_2-xSe_1-yTe_y solid solution nanoparticles transform, over the span of several days, to a selenium-rich Cu_2-xSe_1-yTe_y composition. The tellurium that is expelled from the solid solution during this process migrates to the surface and forms a tellurium oxide shell, which correlates with the onset of particle agglomeration due to the change in surface chemistry. Collectively, this study demonstrates tunable composition during tellurium anion exchange of copper selenide nanoparticles along with unusual post-exchange reactivity that transforms the composition, surface chemistry, and colloidal dispersibility due to the apparent metastable nature of the solid solution product.

Morphology Engineering in Multicomponent Hollow Metal Chalcogenide Nanoparticles

Hollow metal chalcogenide nanoparticles are widely applicable in environmental and energy-related processes. Herein, we synthesized such particles with large compositional and morphological diversity by combining scanning probe block copolymer lithography with a Kirkendall effect-based sulfidation process. We explored the influence of temperature-dependent diffusion kinetics, elemental composition and miscibility, and phase boundaries on the resulting particle morphologies. Specifically, CoNi alloys form single-shell sulfides for the synthetic conditions explored because Co and Ni exhibit similar diffusion rates, while CuNi alloys form sulfides with various types of morphologies (yolk-shell, double-shell, and single-shell) because Cu and Ni have different diffusion rates. In contrast, Co-Cu heterodimers form hollow heterostructured sulfides with varying void numbers and locations depending on synthesis temperature and phase boundary. At higher temperatures, the increased miscibility of CoS₂ and CuS makes it energetically favorable for the heterostructure to adopt a single alloy shell morphology, which is rationalized using density functional theory-based calculations.

Electronic Structure and Excited State Dynamics of Cadmium Chalcogenide Nanorods

The cylindrical quasi-one-dimensional shape of colloidal semiconductor nanorods (NRs) gives them unique electronic structure and optical properties. In addition to the band gap tunability common to nanocrystals, NRs have polarized light absorption and emission and high molar absorptivities. NR-shaped heterostructures feature control of electron and hole locations as well as light emission energy and efficiency. We comprehensively review the electronic structure and optical properties of Cd-chalcogenide NRs and NR heterostructures (e.g., CdSe/CdS dot-in-rods, CdSe/ZnS rod-in-rods), which have been widely investigated over the last two decades due in part to promising optoelectronic applications. We start by describing methods for synthesizing these colloidal NRs. We then detail the electronic structure of single-component and heterostructure NRs and follow with a discussion of light absorption and emission in these materials. Next, we describe the excited state dynamics of these NRs, including carrier cooling, carrier and exciton migration, radiative and nonradiative recombination, multiexciton generation and dynamics, and processes that involve trapped carriers. Finally, we describe charge transfer from photoexcited NRs and connect the dynamics of these processes with light-driven chemistry. We end with an outlook that highlights some of the outstanding questions about the excited state properties of Cd-chalcogenide NRs.

Kinetic Analysis of the Cation Exchange in Nanorods from Cu2-xS to CuInS2: Influence of Djurleite's Phase Transition Temperature on the Mechanism

In the syntheses of ternary I-III-VI₂ compounds, such as CuInS₂, it is often difficult to balance three precursor reactivities to achieve the desired size, shape, and atomic composition of nanocrystals. Cation exchange reactions offer an attractive two-step alternative, by producing a binary compound with the desired morphology and incorporating another atomic species postsynthetically. However, the kinetics of such cation exchange reactions, especially for anisotropic nanocrystals, are still not fully understood. Here, we present the cation exchange reaction from Cu-deficient djurleite Cu_2-xS nanorods to wurtzite CuInS₂, with size and shape retention. With reaction parameters in a broad temperature range between 40 °C and 160 °C, we were able to obtain various intermediates. Djurleite has a bulk phase transition temperature at 93 °C, which influences the cation exchange considerably. Below the phase transition temperature, indium is only incorporated into the surface of the nanorods, while, at temperatures above the phase transition temperature, we observe a Janus-type exchange mechanism and the formation of CuInS₂ bands in the djurleite nanorods. The findings suggest that the diffusion above the phase transition temperature is strongly favored along the copper planes of the copper sulfide nanorods over the diffusion through the sulfur planes. This results in a difference of 37 kJ mol^-1 in the activation energy of the cation exchange below and above the phase transition temperature.

Multipod Bi(Cu2-xS)n Nanocrystals formed by Dynamic Cation-Ligand Complexation and Their Use as Anodes for Potassium-Ion Batteries

We report the formation of an intermediate lamellar Cu-thiolate complex, and tuning its relative stability using alkylphosphonic acids are crucial to enabling controlled heteronucleation to form Bi(Cu_2-xS)_n heterostructures with a tunable number of Cu_2-xS stems on a Bi core. The denticity of the phosphonic acid group, concentration, and chain length of alkylphosphonic acids are critical factors determining the stability of the Cu-thiolate complex. Increasing the stability of the Cu-thiolate results in single Cu_2-xS stem formation, and decreased stability of the Cu-thiolate complex increases the degree of heteronucleation to form multiple Cu_2-xS stems on the Bi core. Spatially separated multiple Cu_2-xS stems transform into a support network to hold a fragmented Bi core when used as an anode in a K-ion battery, leading to a more stable cycling performance showing a specific capacity of ∼170 mAh·g^-1 after 200 cycles compared to ∼111 mAh·g^-1 for Bi-Cu_2-xS single-stem heterostructures.

A one-dimensional conductive metal-organic framework with extended π-d conjugated nanoribbon layers

Conductive metal-organic frameworks (MOFs) have performed well in the fields of energy and catalysis, among which two-dimensional (2D) and three-dimensional (3D) MOFs are well-known. Here, we have synthesized a one-dimensional (1D) conductive metal-organic framework (MOF) in which hexacoordinated 1,5-Diamino-4,8-dihydroxy-9,10-anthraceneedione (DDA) ligands are connected by double Cu ions, resulting in nanoribbon layers with 1D π-d conjugated nanoribbon plane and out-of-plane π-π stacking, which facilitates charge transport along two dimensions. The DDA-Cu as a highly conductive n-type MOF has high crystalline quality with a conductivity of ~ 9.4 S·m^-1, which is at least two orders of magnitude higher than that of conventional 1D MOFs. Its electrical band gap (E_g) and exciton binding energy (E_b) are approximately 0.49 eV and 0.3 eV, respectively. When utilized as electrode material in a supercapacitor, the DDA-Cu exhibits good charge storage capacity and cycle stability. Meanwhile, as thse active semiconductor layer, it successfully simulates the artificial visual perception system with excellent bending resistance and air stability as a MOF-based flexible optoelectronic synaptic case. The controllable preparation of high-quality 1D DDA-Cu MOF may enable new architectural designs and various applications in the future.

Exceptional Anisotropic Noncovalent Interactions in Ultrathin Nanorods: The Terminal σ-Hole

Nanomaterial is the Holy Grail of material science, which has been widely applied in the fields of energy, environment, chemistry, and biomedicine. Its catalytic merits were usually ascribed to the advantages of size effect, strain effect, and covalent effect. Noncovalent interactions are critical in the catalysis processes but often overlooked. Herein, different from the traditional understandings, we discover for the first time and give systematic insights into a unique noncovalent terminal σ-hole phenomenon in the 3d-metal-based nanorods, which should be one of the key origins of nanomaterial activity. As a proof-of-concept, pure metal and alloyed core-shell nanoclusters/nanorods composed of the two most important 3d metals (Co and Ni) growing from 0.5 to 2.5 nm are investigated. Unlike nanoclusters, the σ-hole only appears at the terminal sites of nanorods and the magnitude of the terminal σ-hole generally enhances with the growing processes. Further investigations show that this terminal σ-hole is closely related to the important physicochemical properties of nanorods. For example, the work function along the axis of the terminal σ-hole is smaller than other directions, contributing to the facile electronic transport along the axis of the terminal σ-hole. Most importantly, we find that the d-orbital center of the atoms around the terminal σ-hole shifts closer to the Fermi level as compared with other atoms, which can endow the terminal sites in nanorods with the higher chemical adsorption capability. We believe that this work will provide critical guidance for the rational design of nanomaterials in many potential applications.

Low-Dimensional Organic Crystals: From Precise Synthesis to Advanced Applications

Low-dimensional organic crystals (LOCs) have attracted increasing attention recently for their potential applications in miniaturized optoelectronics and integrated photonics. Such applications are possible owing to their tunable physicochemical properties and excellent charge/photon transport features. As a result, the precise synthesis of LOCs has been examined in terms of morphology modulation, large-area pattern arrays, and complex architectures, and this has led to a series of appealing structure-dependent properties for future optoelectronic applications. This review summarizes the recent advances in the precise synthesis of LOCs in addition to discussing their structure-property relationships in the context of optoelectronic applications. It also presents the current challenges related to organic crystals with specific structures and desired performances, and the outlook regarding their use in next-generation integrated optoelectronic applications.

Design Principles of Colloidal Nanorod Heterostructures

Anisotropic heterostructures of colloidal nanocrystals embed size-, shape-, and composition-dependent electronic structure within variable three-dimensional morphology, enabling intricate design of solution-processable materials with high performance and programmable functionality. The key to designing and synthesizing such complex materials lies in understanding the fundamental thermodynamic and kinetic factors that govern nanocrystal growth. In this review, nanorod heterostructures, the simplest of anisotropic nanocrystal heterostructures, are discussed with respect to their growth mechanisms. The effects of crystal structure, surface faceting/energies, lattice strain, ligand sterics, precursor reactivity, and reaction temperature on the growth of nanorod heterostructures through heteroepitaxy and cation exchange reactions are explored with currently known examples. Understanding the role of various thermodynamic and kinetic parameters enables the controlled synthesis of complex nanorod heterostructures that can exhibit unique tailored properties. Selected application prospects arising from such capabilities are then discussed.

Solution-Processed Inorganic Thermoelectric Materials: Opportunities and Challenges

Thermoelectric technology requires synthesizing complex materials where not only the crystal structure but also other structural features such as defects, grain size and orientation, and interfaces must be controlled. To date, conventional solid-state techniques are unable to provide this level of control. Herein, we present a synthetic approach in which dense inorganic thermoelectric materials are produced by the consolidation of well-defined nanoparticle powders. The idea is that controlling the characteristics of the powder allows the chemical transformations that take place during consolidation to be guided, ultimately yielding inorganic solids with targeted features. Different from conventional methods, syntheses in solution can produce particles with unprecedented control over their size, shape, crystal structure, composition, and surface chemistry. However, to date, most works have focused only on the low-cost benefits of this strategy. In this perspective, we first cover the opportunities that solution processing of the powder offers, emphasizing the potential structural features that can be controlled by precisely engineering the inorganic core of the particle, the surface, and the organization of the particles before consolidation. We then discuss the challenges of this synthetic approach and more practical matters related to solution processing. Finally, we suggest some good practices for adequate knowledge transfer and improving reproducibility among different laboratories.

Atomically Precise Enantiopure Bimetallic Janus Clusters

Asymmetric bimetallic Janus nanocrystals with a side-by-side interface have unique properties and important applications. However, understanding their fundamental issues, including their formation mechanism, interfacial linkage, and related properties, remains challenging, as does the preparation of enantiopure samples. Atomically precise Janus bimetal nanoclusters would unequivocally resolve these issues, yet they have not been realized. Here, based on Au and transition metals (Cu/Cd), and employing an S/P biligand strategy, we prepare and structurally resolve four Janus nanoclusters, including racemate 6e Au ₈ /Cu ₄ , 6e R -/ S-Au ₈ /Cu ₄ enantiomers, and 2e racemate Au ₃ /Cd. Their interfacial linkage is unambiguously resolved at the atomic level, superatomic orbital splitting emerges, and unique molecule-like electronic transitions and chiroptical properties are present; more importantly, the dipolar distribution of bicomponents leads to a maximum dipole moment of up to 45 D, which drives the formation of 1D nanowires through self-assembly. This work provides a fundamental knowledge of intermetallic nanomaterials and an avenue for the synthesis of Janus nanoclusters.

Selective-Epitaxial Hybrid of Tripartite Semiconducting Sulfides for Enhanced Solar-to-Hydrogen Conversion

The design and synthesis of advanced semiconductors is crucial for the full utilization of solar energy. Herein, colloidal selective-epitaxial hybrid of tripartite semiconducting sulfides CuInS₂ Cd(In)SMoS₂ heteronanostructures (HNs) via lateral- and vertical-epitaxial growths, followed by cation exchange reactions, are reported. The lateral-epitaxial CuInS₂ and Cd(In)S enable effective visible to near-infrared (NIR) solar spectrum absorption, and the vertical-epitaxial ultrathin MoS₂ offer sufficient edge sulfur sites for the hydrogen evolution reaction (HER). Furthermore, the integrated structures exhibit unique epitaxial-staggered type II band alignments for continuous charge separation. They achieve the H₂ evolution rate up to 8 mmol h^-1 g^-1 , which is ≈35 times higher than bare CdS and show no deactivation after long-term cycling, representing one of the most efficient and robust noble-metal-free photocatalysts. This design principle and transformation protocol open a new way for creating all-in-one multifunctional catalysts in a predictable manner.

Site-selective modification of metallic nanoparticles

Surface patterning of inorganic nanoparticles through site-selective functionalization with mixed-ligand shells or additional inorganic material is an intriguing approach to developing tailored nanomaterials with potentially novel and/or multifunctional properties. The unique physicochemical properties of such nanoparticles are likely to impact their behavior and functionality in biological environments, catalytic systems, and electronics applications, making it vital to understand how we can achieve and characterize such regioselective surface functionalization. This Feature Article will review methods by which chemists have selectively modified the surface of colloidal nanoparticles to obtain both two-sided Janus particles and nanoparticles with patchy or stripey mixed-ligand shells, as well as to achieve directed growth of mesoporous oxide materials and metals onto existing nanoparticle templates in a spatially and compositionally controlled manner. The advantages and drawbacks of various techniques used to characterize the regiospecificity of anisotropic surface coatings are discussed, as well as areas for improvement, and future directions for this field.

Solution-Mediated Inversion of SnSe to Sb2Se3 Thin-Films

New facile and controllable approaches to fabricating metal chalcogenide thin films with adjustable properties can significantly expand the scope of these materials in numerous optoelectronic and photovoltaic devices. Most traditional and especially wet-chemical synthetic pathways suffer from a sluggish ability to regulate the composition and have difficulty achieving the high-quality structural properties of the sought-after metal chalcogenides, especially at large 2D length scales. In this effort, and for the first time, we illustrated the fast and complete inversion of continuous SnSe thin-films to Sb₂Se₃ using a scalable top-down ion-exchange approach. Processing in dense solution systems yielded the formation of Sb₂Se₃ films with favorable structural characteristics, while oxide phases, which are typically present in most Sb₂Se₃ films regardless of the synthetic protocols used, were eliminated. Density functional theory (DFT) calculations performed on intermediate phases show strong relaxations of the atomic lattice due to the presence of substitutional and vacancy defects, which likely enhances the mobility of cationic species during cation exchange. Our concept can be applied to customize the properties of other metal chalcogenides or manufacture layered structures.

Tailoring CsPbBr3 Growth via Non-Polar Solvent Choice and Heating Methods

This study describes an investigation of the role of non-polar solvents on the growth of cesium lead halide (CsPbX₃ X = Br and I) nanoplatelets. We employed two solvents, benzyl ether (BE) and 1-octadecene (ODE), as well as two nucleation and growth mechanisms, one-pot, facilitated by microwave irradiation (MWI)-based heating, and hot-injection, using convection. Using BE and MWI, large mesoscale CsPbBr₃ nanoplatelets were produced, whereas use of ODE produced small crystallites. Differences between the products were observed by optical spectroscopies, which showed first band edge absorptions consistent with thicknesses of ∼9 nm [∼15 monolayer (ML)] for the BE-CsPbBr₃ and ∼5 nm (∼9 ML) for ODE-CsPbBr₃. Both products had orthorhombic crystal structures, with the BE-CsPbBr₃ revealing significant preferred orientation diffraction signals consistent with the asymmetric and two-dimensional platelet morphology. The differences in the final morphology were also observed for products formed via hot injection, with BE-CsPbBr₃ showing thinner square platelets with thicknesses of ∼2 ML and ODE-CsPbBr₃ showing similar morphologies and small crystallite sizes. To understand the role solvent plays in crystal growth, we studied lead plumbate precursor (PbBr_n^2-n) formation in both solvents, as well as solvent plus ligand solutions. The findings suggest that BE dissolves PbBr₂ salts to a higher degree than ODE, and that this BE to precursor affinity persists during growth.

Hollow nanoparticles synthesized via Ostwald ripening and their upconversion luminescence-mediated Boltzmann thermometry over a wide temperature range

Upconversion nanoparticles (UCNPs) with hollow structures exhibit many fascinating optical properties due to their special morphology. However, there are few reports on the exploration of hollow UCNPs and their optical applications, mainly because of the difficulty in constructing hollow structures by conventional methods. Here, we report a one-step template-free method to synthesize NaBiF₄:Yb,Er (NBFYE) hollow UCNPs via Ostwald ripening under solvothermal conditions. Moreover, we also elucidate the possible formation mechanism of hollow nanoparticles (HNPs) by studying the growth process of nanoparticles in detail. By changing the contents of polyacrylic acid and H₂O in the reaction system, the central cavity size of NBFYE nanoparticles can be adjusted. Benefiting from the structural characteristics of large internal surface area and high surface permeability, NBFYE HNPs exhibit excellent luminescence properties under 980 nm near-infrared irradiation. Importantly, NBFYE hollow UCNPs can act as self-referenced ratiometric luminescent thermometers under 980 nm laser irradiation, which are effective over a wide temperature range from 223 K to 548 K and have a maximum sensitivity value of 0.0065 K^-1 at 514 K. Our work clearly demonstrates a novel method for synthesizing HNPs and develops their applications, which provides a new idea for constructing hollow structure UCNPs and will also encourage researchers to further explore the optical applications of hollow UCNPs.

Expanded Tunability of Intraparticle Frameworks in Spherical Heterostructured Nanoparticles through Substoichiometric Partial Cation Exchange

Partial cation exchange reactions provide a synthetic pathway for rationally constructing heterostructured nanoparticles that incorporate different materials at precise locations. Multiple sequential partial cation exchange reactions can produce libraries of exceptionally complex heterostructured nanoparticles, but the first partial exchange reaction is responsible for defining the intraparticle frameworks that persist throughout and help to direct subsequent exchanges. Here, we studied the partial cation exchange behavior of spherical nanoparticles of roxbyite copper sulfide, Cu_1.8S, with substoichiometric amounts of Zn²⁺. We observed the formation of ZnS–Cu_1.8S–ZnS sandwich spheres, which are already well known in this system, as well as ZnS–Cu_1.8S Janus spheres and Cu_1.8S–ZnS–Cu_1.8S central band spheres, which have not been observed previously as significant subpopulations of samples. Aliquots taken during the formation of the heterostructured nanoparticles suggest that substoichiometric amounts of Zn²⁺ limit the number of sites per particle where exchange initiates and/or propagates, thereby helping to define intraparticle frameworks that are different from those observed using excess amounts of exchanging cations. We applied these insights from mixed-population samples to the higher-yield synthesis of ZnS–Cu_1.8S Janus spheres, as well as the higher-order derivatives ZnS–(CdS–Cu_1.8S), ZnS–(CdS–ZnS), and ZnS–(CdS–CoS), which have unique features relative to previously reported analogues. These results demonstrate how the diversity of intraparticle frameworks in spherical nanoparticles can be expanded to produce a broader range of downstream heterostructured products.

Solid-State Reaction Synthesis of Nanoscale Materials: Strategies and Applications

Nanomaterials (NMs) with unique structures and compositions can give rise to exotic physicochemical properties and applications. Despite the advancement in solution-based methods, scalable access to a wide range of crystal phases and intricate compositions is still challenging. Solid-state reaction (SSR) syntheses have high potential owing to their flexibility toward multielemental phases under feasibly high temperatures and solvent-free conditions as well as their scalability and simplicity. Controlling the nanoscale features through SSRs demands a strategic nanospace-confinement approach due to the risk of heat-induced reshaping and sintering. Here, we describe advanced SSR strategies for NM synthesis, focusing on mechanistic insights, novel nanoscale phenomena, and underlying principles using a series of examples under different categories. After introducing the history of classical SSRs, key theories, and definitions central to the topic, we categorize various modern SSR strategies based on the surrounding solid-state media used for nanostructure growth, conversion, and migration under nanospace or dimensional confinement. This comprehensive review will advance the quest for new materials design, synthesis, and applications.