Surface Ligands Research Articles

Engineering Colloidal Metal‐Semiconductor Nanorods Hybrid Nanostructures for Photocatalysis†

Comprehensive SummaryEmerging engineering strategies of colloidal metal‐semiconductor nanorod hybrid nanostructures spanning from type, size, dimension, and location of both metal nanoparticles and semiconductors, co‐catalyst, band gap structure, surface ligand to hole scavenger are elaborated symmetrically to rationalize the design of this type of intriguing materials for efficient photocatalytic applications.

Improvement of the Stability and Optical Properties of CsPbBr3 QDs.

All-inorganic perovskite quantum dots (CsPbX3 QDs) (X = Cl, Br, I) have the advantages of adjustable emission position, narrow emission spectrum, high fluorescence quantum efficiency (PLQY), easy preparation, and elevated defect tolerance; therefore, they are widely used in optoelectronic devices, such as solar cells, light-emitting diodes, and lasers. However, their stability still constrains their development due to their intrinsic crystal structure, ionic exchange of surface ligands, and exceptional sensitivity to environmental factors, such as light, water, oxygen, and heat. Therefore, in this paper, we investigate the stability improvement of CsPbX3 QDs and apply fabricated high-efficiency, stable perovskite QDs to solar cells to improve the performance of the cells further. In this paper, we focus on CsPbBr3 QDs with intrinsic extreme stability and optimize CsPbBr3 QDs using strategies, such as Mn+ doping, ligand regulation, and polymer encapsulation, which can improve optical properties while ensuring their stability. The test results show that the above five methods can improve the strength and luminescence performance of QDs, with the best stability achieved when PMMA encapsulates QDs with a ratio of PMMA = 2:1 and PLQY increases from 60.2% to 90.1%.

Direct photocatalytic patterning of colloidal emissive nanomaterials.

We present a universal direct photocatalytic patterning method that can completely preserve the optical properties of perovskite nanocrystals (PeNCs) and other emissive nanomaterials. Solubility change of PeNCs is achieved mainly by a photoinduced thiol-ene click reaction between specially tailored surface ligands and a dual-role photocatalytic reagent, pentaerythritol tetrakis(3-mercaptopropionate) (PTMP), where the thiol-ene reaction is enabled at a low light intensity dose (~ 30 millijoules per square centimeter) by the strong photocatalytic activity of PeNCs. The photochemical reaction mechanism was investigated using various analyses at each patterning step. The PTMP also acts as a defect passivation agent for the PeNCs and even enhances their photoluminescence quantum yield (by ~5%) and photostability. Multicolor patterns of cesium lead halide (CsPbX3)PeNCs were fabricated with high resolution (<1 micrometer). Our method is widely applicable to other classes of nanomaterials including colloidal cadmium selenide-based and indium phosphide-based quantum dots and light-emitting polymers; this generality provides a nondestructive and simple way to pattern various functional materials and devices.

Effect of the Ag+ in Ag25@ZnO nanocatalysts for the 4-nitrophenol reduction reactions

As catalysts, metal nanoclusters (NCs) have become the focus of research due to their precise structure and excellent catalytic activity. In general, it can greatly improve the catalytic activity of NCs by thermal treatment. In this work, the ZnO supported 2,4-dimethylbenzenethiol-protected-[Ag25(C8H9S)18]- NCs (Ag25@ZnO) nanocatalysts were subjected to activation temperatures of 100 °C, 200 °C and 300 °C to remove the surface ligands of Ag25 NCs and regulate the surface composition of Ag25@ZnO nanocatalysts. The structure of Ag25@ZnO nanocatalysts were characterized by XRD, SEM, TEM, EDS and XPS. In particular, the XPS results obviously confirmed that the concentration of Ag+ on the catalyst surface was positively correlated with the activation temperature. Finally, the effect of the Ag + content on the catalytic activity of the Ag25@ZnO nanocatalysts was also explored. Because the content of Ag+ in Ag25@ZnO-300 nanocatalysts is the highest, the 4-nitrophenol reduction reaction showed the best catalytic performance.

Recent Advances in Direct Optical Patterning of Inorganic Materials and Devices

AbstractDirect patterning technology holds significant promise owing to its ability to streamline complex patterning processes, fostering affordable design and production of various devices. Direct optical lithographic techniques have recently been applied to diverse ranges of functional inorganic nanomaterials, providing a viable alternative to conventional photolithography. These techniques facilitate the fabrication of diverse thin‐film devices and enable 3D printability for inorganic microarchitectures. This review discusses the recent progress in the direct patterning of inorganic materials and associated device fabrication. The chemical design of inorganic building blocks is delved into, which entails the photochemistry of surface ligands or additives that respond to external stimuli and the different patterning methodologies predicated on these external stimuli. Moreover, device fabrication is introduced through direct patterning methods, highlighting examples from optoelectronic, electronic, and energy devices. Last, the prospects of this field are presented, focusing on materials and processes.

Multifunctional Short-Chain 2-Thiophenealkylammonium Bromide Ligand-Assisted Perovskite Quantum Dots for Efficient Light-Emitting Diodes.

Lead halide perovskite quantum dots (QDs) have attracted great interest for application in light-emitting diodes (LEDs) due to their high photoluminescence quantum yield (PLQY), solution processability, and high color purity, showing great potential for next-generation full-color display and lighting technologies. Conventional long-chain insulating oleic acid (OA)/oleamine (OAm) ligands exhibit dynamic binding to the surface of QDs, resulting in a plethora of extra surface defects and inferior optoelectronic properties. Herein, a sole multifunctional ligand with optimized carbon chain length, that is, 2-thiophenepropylamine bromide (ThPABr), was creatively designed and introduced into CsPbBr3 QDs, which not only replaces OAm and provides a bromine source but also coordinates with the uncoordinated surface Pb2+ of QDs through the thiophene, passivating surface defects and increasing the PLQY of the film to 83%. More importantly, the interaction between the electron donor-thiophene ring and QDs can enhance electron injection and improve carrier balance. The resulting green LED exhibited significant performance improvement, showing ultrahigh spectral stability under high operating voltage, achieving a maximum external quantum efficiency of 10.5%, and extending the operating lifetime to 5-fold that of the reference. Designing a single multifunctional ligand presents a promising and convenient strategy for selecting surface ligands that can enhance the performance of LEDs or other optoelectronic devices.

Stimuli-Responsive Surface Ligands for Direct Lithography of Functional Inorganic Nanomaterials.

ConspectusColloidal nanocrystals (NCs) have emerged as a diverse class of materials with tunable composition, size, shape, and surface chemistry. From their facile syntheses to unique optoelectronic properties, these solution-processed nanomaterials are a promising alternative to materials grown as bulk crystals or by vapor-phase methods. However, the integration of colloidal nanomaterials in real-world devices is held back by challenges in making patterned NC films with the resolution, throughput, and cost demanded by device components and applications. Therefore, suitable approaches to pattern NCs need to be established to aid the transition from individual proof-of-concept NC devices to integrated and multiplexed technological systems.In this Account, we discuss the development of stimuli-sensitive surface ligands that enable NCs to be patterned directly with good pattern fidelity while retaining desirable properties. We focus on rationally selected ligands that enable changes in the NC dispersibility by responding to light, electron beam, and/or heat. First, we summarize the fundamental forces between colloidal NCs and discuss the principles behind NC stabilization/destabilization. These principles are applied to understanding the mechanisms of the NC dispersibility change upon stimuli-induced ligand modifications. Six ligand-based patterning mechanisms are introduced: ligand cross-linking, ligand decomposition, ligand desorption, in situ ligand exchange, ion/ligand binding, and ligand-aided increase of ionic strength. We discuss examples of stimuli-sensitive ligands that fall under each mechanism, including their chemical transformations, and address how these ligands are used to pattern either sterically or electrostatically stabilized colloidal NCs. Following that, we explain the rationale behind the exploration of different types of stimuli, as well as the advantages and disadvantages of each stimulus.We then discuss relevant figures-of-merit that should be considered when choosing a particular ligand chemistry or stimulus for patterning NCs. These figures-of-merit pertain to either the pattern quality (e.g., resolution, edge and surface roughness, layer thickness), or to the NC material quality (e.g., photo/electro-luminescence, electrical conductivity, inorganic fraction). We outline the importance of these properties and provide insights on optimizing them. Both the pattern quality and NC quality impact the performance of patterned NC devices such as field-effect transistors, light-emitting diodes, color-conversion pixels, photodetectors, and diffractive optical elements. We also give examples of proof-of-concept patterned NC devices and evaluate their performance. Finally, we provide an outlook on further expanding the chemistry of stimuli-sensitive ligands, improving the NC pattern quality, progress toward 3D printing, and other potential research directions. Ultimately, we hope that the development of a patterning toolbox for NCs will expedite their implementation in a broad range of applications.

Light-driven Transformation of Carbon Monoxide into Hydrocarbons using CdS@ZnS : VFe Protein Biohybrids.

Enzymatic Fisher-Tropsch (FT) process catalyzed by vanadium (V)-nitrogenase can convert carbon monoxide (CO) to longer-chain hydrocarbons (>C2) under ambient conditions, although this process requires high-cost reducing agent(s) and/or the ATP-dependent reductase as electron and energy sources. Using visible light-activated CdS@ZnS (CZS) core-shell quantum dots (QDs) as alternative reducing equivalent for the catalytic component (VFe protein) of V-nitrogenase, we first report a CZS : VFe biohybrid system that enables effective photo-enzymatic C-C coupling reactions, hydrogenating CO into hydrocarbon fuels (up to C4) that can be hardly achieved with conventional inorganic photocatalysts. Surface ligand engineering optimizes molecular and opto-electronic coupling between QDs and the VFe protein, realizing high efficiency (internal quantum yield >56 %), ATP-independent, photon-to-fuel production, achieving an electron turnover number of >900, that is 72 % compared to the natural ATP-coupled transformation of CO into hydrocarbons by V-nitrogenase. The selectivity of products can be controlled by irradiation conditions, with higher photon flux favoring (longer-chain) hydrocarbon generation. The CZS : VFe biohybrids not only can find applications in industrial CO removal for high-value-added chemical production by using the cheap, renewable solar energy, but also will inspire related research interests in understanding the molecular and electronic processes in photo-biocatalytic systems.

Atomically precise gold nanoclusters for CO oxidation: balancing activity and stability by ligand shedding

Ligand-protected gold (Au) nanoclusters (NCs) are fascinating for catalytic applications due to their unique electronic structure and catalytic activity endowed by quantum size effects. The identification of the number of ligands in NCs not only determines the catalytic behavior of their active sites, but also directly affects their stability. Therefore, establishing a physical picture including the number of ligands on the surface of NCs, geometric structure, thermodynamic stability and catalytic activity is crucial for balancing stability and catalytic performance. Combined with density functional theory calculations, the catalytic behavior of phosphine ligand-protected Au NCs (including [Au9(PPh3)8]3+, [Au10(PPhCy2)6Cl3]+, [Au11(PPh3)8Cl2]+ and [Au13(PMe2Ph)10Cl2]3+) with ligand shedding processes were systematically investigated using gas-phase CO oxidation as a probe reaction. The results show that the geometric configurations of these Au NCs evolve towards a planar structure with the shedding of ligands. Their chemical activity shows a distinct linear relationship with their d orbital centers, which are governed by the electron coupling between the surface ligands and the Au core for each ligand of Au NCs. The geometrical structure–chemical activity relationship was uncovered for these ligand Au NCs. These results provide important knowledge for precisely regulating the activity and stability of ligand-protected metal NCs for energy conversion at the atomic level.

Controlled Self-Assembly of Gold Nanotetrahedra into Quasicrystals and Complex Periodic Supracrystals.

The self-assembly of shape-anisotropic nanocrystals into large-scale structures is a versatile and scalable approach to creating multifunctional materials. The tetrahedral geometry is ubiquitous in natural and manmade materials, yet regular tetrahedra present a formidable challenge in understanding their self-assembly behavior as they do not tile space. Here, we report diverse supracrystals from gold nanotetrahedra including the quasicrystal (QC) and the dimer packing predicted more than a decade ago and hitherto unknown phases. We solve the complex three-dimensional (3D) structure of the QC by a combination of electron microscopy, tomography, and synchrotron X-ray scattering. Nanotetrahedron vertex sharpness, surface ligands, and assembly conditions work in concert to regulate supracrystal structure. We also discover that the surface curvature of supracrystals can induce structural changes of the QC tiling and eventually, for small supracrystals with high curvature, stabilize a hexagonal approximant. Our findings bridge the gap between computational design and experimental realization of soft matter assemblies and demonstrate the importance of accurate control over nanocrystal attributes and the assembly conditions to realize increasingly complex nanopolyhedron supracrystals.

Theoretical and Experimental Advances in High-Pressure Behaviors of Nanoparticles.

Using compressive mechanical forces, such as pressure, to induce crystallographic phase transitions and mesostructural changes while modulating material properties in nanoparticles (NPs) is a unique way to discover new phase behaviors, create novel nanostructures, and study emerging properties that are difficult to achieve under conventional conditions. In recent decades, NPs of a plethora of chemical compositions, sizes, shapes, surface ligands, and self-assembled mesostructures have been studied under pressure by in-situ scattering and/or spectroscopy techniques. As a result, the fundamental knowledge of pressure-structure-property relationships has been significantly improved, leading to a better understanding of the design guidelines for nanomaterial synthesis. In the present review, we discuss experimental progress in NP high-pressure research conducted primarily over roughly the past four years on semiconductor NPs, metal and metal oxide NPs, and perovskite NPs. We focus on the pressure-induced behaviors of NPs at both the atomic- and mesoscales, inorganic NP property changes upon compression, and the structural and property transitions of perovskite NPs under pressure. We further discuss in depth progress on molecular modeling, including simulations of ligand behavior, phase-change chalcogenides, layered transition metal dichalcogenides, boron nitride, and inorganic and hybrid organic-inorganic perovskites NPs. These models now provide both mechanistic explanations of experimental observations and predictive guidelines for future experimental design. We conclude with a summary and our insights on future directions for exploration of nanomaterial phase transition, coupling, growth, and nanoelectronic and photonic properties.

Synthesis of Layered Lead-Free Perovskite Nanocrystals with Precise Size and Shape Control and Their Photocatalytic Activity.

Halide perovskites have attracted enormous attention due to their potential applications in optoelectronics and photocatalysis. However, concerns over their instability, toxicity, and unsatisfactory efficiency have necessitated the development of lead-free all-inorganic halide perovskites. A major challenge in designing efficient halide perovskites for practical applications is the lack of effective methods for producing nanocrystals with precise size and shape control. In this work, a layered perovskite, Cs4ZnSb2Cl12 (CZS), is found from calculations to exhibit size- and facet-dependent optoelectronic properties in the nanoscale, and thus, a colloidal method is used to synthesize the CZS nanoparticles with size-tunable morphologies: zero- (nanodots), one- (nanowires and nanorods), two- (nanoplates), and three-dimensional (nanopolyhedra). The growth kinetics of the CZS nanostructures, along with the effects of surface ligands, reaction temperature, and time were investigated. The optoelectronic properties of the nanocrystals varied with size due to quantum confinement effects and with shape due to anisotropy within the crystals and the exposure of specific facets. These properties could be modulated to enhance the visible-light photocatalytic performance for toluene oxidation. In particular, the 9.7 nm CZS nanoplates displayed a toluene to benzaldehyde conversion rate of 1893 μmol g-1 h-1 (95% selectivity), 500 times higher than the bulk synthesized CZS, and comparable with the reported photocatalysts. This study demonstrates the integration of theoretical calculations and synthesis, revealing an approach to the design and fabrication of novel, high-performance colloidal perovskite nanocrystals for optoelectronic and photocatalytic applications.

A Chemist's View on Electronic and Steric Effects of Surface Ligands on Plasmonic Metal Nanostructures.

ConspectusPlasmonic metal nanostructures have been extensively developed over the past few decades because of their ability to confine light within the surfaces and manipulate strong light-matter interactions. The light energy stored by plasmonic nanomaterials in the form of surface plasmons can be utilized to initiate chemical reactions, so-called plasmon-induced catalysis, which stresses the importance of understanding the surface chemistry of the plasmonic materials. Nevertheless, only physical interpretation of plasmonic behaviors has been a dominant theme, largely excluding chemical intuitions that facilitate understanding of plasmonic systems from molecular perspectives. To overcome and address the lack of this complementary understanding based on molecular viewpoints, in this Account we provide a new concept encompassing the well-developed physics of plasmonics and the corresponding surface chemistry while reviewing and discussing related references. Inspired by Roald Hoffmann's descriptions of solid-state surfaces based on the molecular orbital picture, we treat molecular interfaces of plasmonic metal nanostructures as a series of metal-ligand complexes. Accordingly, the effects of the surface ligands can be described by bisecting them into electronic and steric contributions to the systems. By exploration of the quality of orbital overlaps and the symmetry of the plasmonic systems, electronic effects of surface ligands on localized surface plasmon resonances (LSPRs), surface diffusion rates, and hot-carrier transfer mechanisms are investigated. Specifically, the propensity of ligands to donate electrons in a σ-bonding manner can change the LSPR by shifting the density of states near the Fermi level, whereas other types of ligands donating or accepting electrons in a π-bonding manner modulate surface diffusion rates by affecting the metal-metal bond strength. In addition, the formation of metal-ligand bonds facilitates direct hot-carrier transfer by forming a sort of molecular orbital between a plasmonic structure and ligands. Furthermore, effects of steric environments are discussed in terms of ligand-ligand and ligand-surface nonbonding interactions. The steric hindrance allows for controlling the accessibility of the surrounding chemical species toward the metal surface by modulating the packing density of ligands and generating repulsive interactions with the surface atoms. This unconventional approach of considering the plasmonic system as a delocalized molecular entity could establish a basis for integrating chemical intuition with physical phenomena. Our chemist's outlook on a molecular interface of the plasmonic surface can provide insights and avenues for the design and development of more exquisite plasmonic catalysts with regio- and enantioselectivities as well as advanced sensors with unprecedented chemical controllability and specificity.

Interfacial modification of GO-FePt hybrid film leads to giant ultrafast optical nonlinearity

Excellent optical nonlinearity is highly promising for the development of multifunctional ultrafast photonics techniques and integrated optoelectronic devices. However, existing numerous optical materials commonly suffer from several challenges, such as bad functional integration, slow response speed, and weak optical nonlinearity thus severely hindering their extensive applications. Here, we first engineer new scalable graphene oxide (GO)-FePt films by chemistry induced self-assembly and then demonstrate the enhanced ultrafast optical nonlinearity by resorting to their interfacial modifications. It is found that the FePt magnetic nanoparticles (NPs) are easily assembled on the surface of the GO by exchanging the surface ligands of the former with evaporated solvent, leading to good water solubility and super-paramagnetism. The femtosecond Z-scan test results show that both the nonlinear saturation absorption and optical Kerr refraction of the pure GO are subjected to reversion once the FePt NPs are introduced. More importantly, we can greatly enhance the ultrafast nonlinear optics response of as-prepared GO-FePt hybrid film by promoting the concentration of magnetic NPs. In addition, the associated optical nonlinearity can be further boosted with femtosecond vectorial beams excitation instead of the linearly polarized one. In principle, the enhanced optical nonlinearity may arise from direct metal-to-semiconductor interfacial charge transfer transition (DICTT) related to the difference in work function and Fermi level together with complicated interaction between the vectorial light fields and the hybrid films. The GO-based magnetic hybrid films with giant ultrafast optical nonlinearity have potential wide-ranging applications in integrated optoelectronics, ultrafast nanophotonics, opto-magnetic storage, and beyond.

Controllable Black-to-Yellow Phase Transition by Tuning the Lattice Symmetry in Perovskite Quantum Dots.

The black-to-yellow phase transition in perovskite quantum dots (QDs) is more complex than in bulk perovskites, regarding the role of surface energy. Here, with the assistance of in situ grazing-incidence wide-angle and small-angle X-ray scattering (GIWAXS/GISAXS), distinct phase behaviors of cesium lead iodide(CsPbI3 ) QDfilms under two different temperature profiles-instant heating-up (IHU) and slow heating-up (SHU) is investigated. The IHU process can cause the phase transition from black phase to yellow phase, while under the SHU process, the majority remains in black phase. Detailed studies and structural refinement analysis reveal that the phase transition is triggered by the removal of surface ligands, which switches the energy landscape. The lattice symmetry determines the transition rate and the coexistence black-to-yellow phase ratio. The SHU process allows longer relaxation time for a more ordered QD packing, which helps sustain the lattice symmetry and stabilizes the black phase. Therefore, one can use the lattice symmetry as a general index to monitor the CsPbI3 QD phase transition and finetune the coexistence black-to-yellow phase ratio for niche applications.

Photochemical Route for Synthesizing Atomically Precise Metal Nanoclusters from Disulfide.

Practical approaches to the synthesis of atomically precise metal nanoclusters are in high demand as they provide the structural basis for investigating nanomaterials' structure-property correlations with atomic precision. The Brust-Schiffrin method has been widely used, while the essential reductive ligands (e.g., thiols) limit the application of this method for synthesizing metal nanoclusters with specific frameworks and surface ligands. In this work, we developed a photochemical route for synthesizing atomically precise metal nanoclusters by applying disulfide, which is a widely available, stable, and environmentally friendly sulfur source. This method enables the construction of structurally diverse metal nanoclusters and especially features the synthesis of PhS-protected metal nanoclusters that were not easily achieved previously and the gram-scale synthesis. A reduction-oxidation cascade mechanism has been revealed for the photochemical route. This work is expected to open up new opportunities for metal nanocluster synthesis and will contribute to the practical applications of this kind of nanomaterial.

Bonding and Acidity of the Formal Hydride in the Prototypical Au9 (PPh3 )8 H2+ Nanocluster.

The role of hydrogen atoms as surface ligands on metal nanoclusters is of profound importance but remains difficult to directly study. While hydrogen atoms often appear to be incorporated formally as hydrides, evidence suggests that they donate electrons to the cluster's delocalized superatomic orbitals and may consequently behave as acidic protons that play key roles in synthetic or catalytic mechanisms. Here we directly test this assertion for the prototypical Au9 (PPh3 )8 H2+ nanocluster, formed by addition of a hydride to the well-characterized Au9 (PPh3 )8 3+ . Using gas-phase infrared spectroscopy, we were able to unambiguously isolate Au9 (PPh3 )8 H2+ and Au9 (PPh3 )8 D2+ , revealing an Au-H stretching mode at 1528 cm-1 that shifts to 1038 cm-1 upon deuteration. This shift is greater than the maximum expected for a typical harmonic potential, suggesting a potential governing cluster-H bonding that has some square-well character consistent with the hydrogen nucleus behaving as a metal atom in the cluster core. Complexing this cluster with very weak bases reveals a redshift of 37 cm-1 in the Au-H vibration, consistent with those typically seen for moderately acidic groups in gas phase molecules and providing an estimate of the acidity of Au9 (PPh3 )8 H2+ , at least with regard to its surface reactivity.

Bonding and Acidity of the Formal Hydride in the Prototypical Au9(PPh3)8H2+ Nanocluster

AbstractThe role of hydrogen atoms as surface ligands on metal nanoclusters is of profound importance but remains difficult to directly study. While hydrogen atoms often appear to be incorporated formally as hydrides, evidence suggests that they donate electrons to the cluster's delocalized superatomic orbitals and may consequently behave as acidic protons that play key roles in synthetic or catalytic mechanisms. Here we directly test this assertion for the prototypical Au9(PPh3)8H2+ nanocluster, formed by addition of a hydride to the well‐characterized Au9(PPh3)83+. Using gas‐phase infrared spectroscopy, we were able to unambiguously isolate Au9(PPh3)8H2+ and Au9(PPh3)8D2+, revealing an Au−H stretching mode at 1528 cm−1 that shifts to 1038 cm−1 upon deuteration. This shift is greater than the maximum expected for a typical harmonic potential, suggesting a potential governing cluster‐H bonding that has some square‐well character consistent with the hydrogen nucleus behaving as a metal atom in the cluster core. Complexing this cluster with very weak bases reveals a redshift of 37 cm−1 in the Au−H vibration, consistent with those typically seen for moderately acidic groups in gas phase molecules and providing an estimate of the acidity of Au9(PPh3)8H2+, at least with regard to its surface reactivity.

N-Heterocyclic Carbene Boranes: Dual Reagents for the Synthesis of Gold Nanoparticles.

N-heterocyclic carbenes (NHCs) have drawn considerable interest in the field of nano-materials chemistry as highly stabilizing ligands enabling formation of strong and covalent C-metal bonds. Applied to gold nanoparticles synthesis, the most common strategy consists in the reduction of a preformed NHC-Au(I) complex with a large excess of a reducing agent rendering the particle size difficult to control. In this paper, we report on the straightforward synthesis of NHC-coated gold nanoparticles (NHC-AuNPs) by reacting a commercially-available gold(I) precursor with an easy-to-synthesize NHC-BH3reagent. The latter acts as both the reducing agent and the source of surface ligands operating under mild conditions. Mechanistic studies including NMR spectroscopy and mass spectrometry demonstrate that the reduction of gold(I) generates NHC-BH2Cl as a byproduct. This strategy garners efficient control over the nucleation and growth of gold particles by varying the NHC-borane/gold(I) ratio, allowing unparalleled particle size variation in the range of 4.9 ± 0.9 nm to 10.0 ± 2.7 nm. Our strategy also allows the unprecedented precise and controlled seeded growth of gold nanoparticles. In addition, the as-prepared NHC-AuNPs exhibit narrow size distributions without engaging extensive purification or size selectivity techniques and are stable over months.

Elucidating the Role of Capping Agents in Facet-Dependent Adsorption Performance of Hematite Nanostructures.

Organic capping agents are a ubiquitous and crucial part of preparing reproducible and homogeneous batches of nanomaterials, particularly nanocrystals with well-defined facets. Despite studies reporting surface ligands (e.g., capping agents) having a non-negligible role in catalytic behavior, their impact is less understood in contaminant adsorption, an important consideration given their potential to obfuscate facet-dependent trends in performance. To ascribe observed behaviors to the facet or the ligand, this report evaluates the impact of poly(N-vinyl-2-pyrrolidone) (PVP), a commonly utilized capping agent, on the adsorption performance of nanohematite particles of varying prevailing facet in the removal of selenite (Se(IV)) as a model system. The PVP capping agent reduces the available surface area for contaminant binding, thus resulting in a reduction in overall Se(IV) adsorbed. However, accounting for the effects of surface area, {012}-faceted nanohematite demonstrates a significantly higher sorption capacity for Se(IV) compared with that of {001}-faceted nanohematite. Notably, chemical treatment is minimally effective in removing strongly bound PVP, indicating that complete removal of surface ligands remains challenging.