Search

Infections caused by multidrug-resistant (MDR) bacteria pose an impending threat to humanity, as the evolution of MDR bacteria outpaces the development of effective antibiotics. In this work, we use indium phosphide (InP) quantum dots (QDs) to treat infections caused by MDR bacteria via photodynamic therapy (PDT), which shows superior bactericidal efficiency over common antibiotics. PDT in the presence of InP QDs results in high-efficiency bactericidal activity towards various bacterial species, including Staphylococcus aureus, Bacillus cereus, Escherichia coli and Pseudomonas aeruginosa. Upon light absorption, InP QDs generate superoxide (O-2(-)), which leads to efficient and selective killing of MDR bacteria while mammalian cells remain intact. The cytotoxicity evaluation reveals that InP QDs are bio- and blood-compatible in a wide therapeutic window. For the in vivo study, we drop a solution of InP QDs at a concentration within the therapeutic window onto MDR S. aureus-infected skin wounds of mice and perform PDT for 15 min. InP QDs show excellent therapeutic and prophylactic efficacy in treating MDR bacterial infection. These findings show that InP QDs have great potential to serve as antibacterial agents for MDR bacterial infection treatment, as an effective and complementary alternative to conventional antibiotics.

In photocatalysis, photons are absorbed by semiconductor materials and photogenerated electrons and holes migrate to the catalytic surface for desired reactions. Photocatalytic reduction and oxidation of organic molecules pose significant challenges and opportunities, with the surging demand for energy-efficient and carbon-neutral organic synthesis. In this review, we highlight the recent progress in the expanding area of radical-driven photocatalytic transformation of organic molecules. Our focus expands from heterogeneous catalysts to quantum dots, summarizing the reaction mechanism and photocatalytic activity, in reference to conventional molecular catalysts.

Advances in nanotechnology have enabled precise design of catalytic sites for CO

There is an evergrowing demand for environment-friendly processes to synthesize ammonia (NH

Semiconductor nanocrystals with an anisotropic morphology exhibit unique properties, most notably their linear polarization. The colloidal growth of semiconductor nanorods with core dots inside, also referred to as dot-in-rod (DIR) structure, has enabled the synthesis of anisotropic nanocrystals with better stability and controllable fluorescence polarization. In this study, we synthesize CdSe/CdS DIR nanocrystals, in which the position of the CdSe core particle can be controlled by using different ligand compositions during the CdS growth. Varying the core position within the DIR structure, e.g., from the center to the end of the DIR particles, results in a change in the degree of linear polarization. When the core is positioned at the center of the nanorod, the linear polarization turns out to be higher compared with tip-core DIRs. Time-resolved photoluminescence analysis reveals that the center-core DIRs have higher electron–hole interaction than tip-core DIRs because of weak uniaxial strain in center-core DIR that arises from lattice dislocations at the interface to relieve accumulated strain.

The correlation between polymer architecture and molecular-level forces has long been a challenging research subject. Herein, spiropyran, a mechanophore that exhibits fluorescence change under force, was incorporated as a cross-linker between PMMA backbone segments. Using an in situ opto-mechanical setup to probe the molecular-level forces, the mechano-response of SP-linked PMMA as a function of the cross-link density was monitored during deformation. The dependence of the molecular-level force on cross-link density was quantitatively examined and revealed. First, a higher cross-link density shifted the fluorescence onset, that is, the onset of the spiropyran-to-merocyanine transition, to lower strains, eventually shifting the onset long before yield, without requiring sufficient chain mobility, owing to the higher efficiency of the force transfer. Under the same energy, the increase in cross-link density allowed for faster force transfer, but only to a certain level. Finally, the overall amount of spiropyran-to-merocyanine conversion linearly decreased with increasing cross-link density.

Colloidal quantum dots (QDs) stand at the forefront of a variety of photonic applications given their narrow spectral bandwidth and near-unity luminescence efficiency. Integrating desired forms of QD films into photonic systems without compromising their optical or transport characteristics is the key to bridging the gap between expectations and outcomes. Here, we devise a dual-ligand passivation system comprising photocrosslinkable ligands and dispersing ligands to enable QDs to be universally compatible with solution-based patterning techniques. The successful control on the structure of both ligands allows multiscale, direct patterning of the dual-ligand QDs on various substrates via commercialized photolithography (i-line) or inkjet printing systems without compromising the optical properties of QDs or the optoelectronic performances of the devices implementing them. Our approach offers a versatile way of creating various structures of luminescent QDs in a cost-effective and non-destructive manner, and thus enables the implementation of QDs in a range of photonic applications.

Due to the strong confinement of carriers, electronic interactions play a major role on the performance of colloidal nanocrystals (NCs) as material for optical gain. Therefore, understanding how to...

Because of the large surface-to-volume ratio of colloidal nanocrystals (NCs), surfactant molecules grafted at the NC surface play an important role in NC growth, interparticle interaction, processing, and application. For this reason, much progress has been made in understanding the surface chemistry of NCs along with the organic ligand shell, particularly in terms of grafted polar groups. However, most explanations of aliphatic counterparts are based on spherical NCs that usually have a dilute ligand layer. In anisotropic NCs such as nanorods and nanoplatelets, the linearly extended dimension results in a high-density aliphatic layer on the NC surface. Unlike spherical NCs, the compact organic shell could serve as a permeation membrane, effectively impeding a penetration of foreign molecules toward the NC surface. In this Perspective, we highlight the effects of ligand configuration on the properties of anisotropic NCs by exploring morphologies, assembled superstructures, and surface reaction of anisotropic NCs.

Carbon-based electrocatalysts for oxygen reduction reaction (ORR), especially in anion exchange membrane fuel cells (AEMFCs), have received a lot of attention because they exhibit excellent stability and are comparable to commercial Pt/C catalysts. Currently, to maximize the catalytic activity of carbon-based electrocatalysts, there are two major strategies: heteroatom doping or exposing active edge sites. However, the approach of increasing heteroatomic dopants of active edge sites has been rarely addressed. In this study, we present a simple strategy to prepare edge-enriched graphene catalysts with an increased ratio of heteroatomic dopants suitable for ORR of AEMFCs. The catalysts were prepared under harsh oxidation conditions, followed by a simple co-doping process with boron and nitrogen. The ORR activity of the catalysts was observed to be related to an increase of edge sites with heteroatomic dopants. We believe that the edge-enriched structure leads to accelerated electron transfer with enhanced oxygen adsorption.

The multiple ligands with different functionalities enable atomic-precision control of NCs morphology and subtle inter-NC interactions, which paves the way for novel optoelectronic applications., Successful exploitation of semiconductor nanocrystals (NCs) in commercial products is due to the remarkable progress in the wet-chemical synthesis and controlled assembly of NCs. Central to the cadence of this progress is the ability to understand how NC growth and assembly can be controlled kinetically and thermodynamically. The arrested precipitation strategy offers a wide opportunity for materials selection, size uniformity, and morphology control. In this colloidal approach, capping ligands play an instrumental role in determining growth parameters and inter-NC interactions. The impetus for exquisite control over the size and shape of NCs and orientation of NCs in an ensemble has called for the use of two or more types of ligands in the system. In multiple ligand approaches, ligands with different functionalities confer extended tunability, hinting at the possibility of atomic-precision growth and long-range ordering of desired superlattices. Here, we highlight the progress in understanding the roles of ligands in size and shape control and assembly of NCs. We discuss the implication of the advances in the context of optoelectronic applications.

The state-of-the-art quantum dot (QD) based light-emitting diodes (QD-LEDs) reach near-unity internal quantum efficiency thanks to organic materials used for efficient hole transportation within the devices. However, toward high-current-density LEDs, such as augmented reality, virtual reality, and head-up display, thermal vulnerability of organic components often results in device instability or breakdown. The adoption of a thermally robust inorganic hole transport layer (HTL), such as NiO, becomes a promising alternative, but the large energy offset between the NiO HTL and the QD emissive layer impedes the efficient operation of QD-LEDs. Here, we demonstrate bright and stable all-inorganic QD-LEDs by steering the orientation of molecular dipoles at the surfaces of both the NiO HTL and QDs. We show that the molecular dipoles not only induce the vacuum level shift that helps alleviate the energy offset between the NiO HTL and QDs but also passivate the surface trap states of the NiO HTL that act as nonradiative recombination centers. With the facilitated hole injection into QDs and suppressed electron leakage toward trap sites in the NiO HTL, we achieve all-inorganic QD-LEDs with high external quantum efficiency (6.5% at peak) and brightness (peak luminance exceeding 77 000 cd/m

The past decade has witnessed remarkable progress in the device efficiency of quantum dot light-emitting diodes based on the framework of organic-inorganic hybrid device structure. The striking improvement notwithstanding, the following conundrum remains underexplored: state-of-the-art devices with seemingly unfavorable energy landscape exhibit barrierless hole injection initiated even at sub-band gap voltages. Here, we unravel that the cause of barrierless hole injection stems from the Fermi level alignment derived by the surface states. The reorganized energy landscape provides macroscopic electrostatic potential gain to promote hole injection to quantum dots. The energy level alignment surpasses the Coulombic attraction induced by a charge employed in quantum dots which adjust the local carrier injection barrier of opposite charges by a relatively small margin. Our finding elucidates how quantum dots accommodate barrierless carrier injection and paves the way to a generalized design principle for efficient electroluminescent devices employing nanocrystal emitters., Hybrid quantum dot light-emitting diodes exhibit barrier-less carrier injection despite a seemingly unfavourable energy landscape. Here, Lee et al. unravel the origin of this barrier-less carrier injection, showing the critical role of surface states of quantum dots.

We report gas-phase photocatalytic CO2 reduction with Cu2O/TiO2 photocatalysts of varying surface passivation. With taurine adsorbed on the photocatalyst surface, the CH4 production rate increases ...

Commercially viable synthesis of InP nanocrystals (NCs) involves highly pyrophoric phosphorus (P) precursor, tris(trimethylsilyl) phosphine (TMS3P). Finding a cheap and safe alternative would be the holy grail. We report the synthesis of InP NCs using triphenyl phosphite, an inexpensive and relatively safe phosphorous source. By reacting indium chloride and triphenyl phosphite, we obtained large-sized and black-colored InP NCs, yet without any distinct feature that shows quantum confinement effect. Addition of ZnCl2 resulted in InP NCs with controlled size, which was manifested in the shift of 1S peak in absorption spectra. By coating ZnS shell on InP NCs, we achieved photoluminescence with some extent of trap emission, showing maximum total quantum yield (QY) of 23% (8% of band-edge emission QY). We used 31P nuclear magnetic resonance (NMR), diffusion-ordered spectroscopy (DOSY), and mass spectrometry (MS) to assign intermediates and following mechanisms of the InP synthesis using triphenyl phosphite. The development of this safe and cost-effective P precursor opens broader opportunity space for large-scale production of InP NC.

Graphene quantum dots (GQDs) are promising materials for optoelectronic devices because their band-gap, derived from quantum confinement and edge effects, can be easily tuned via their size or surface/edge states. In this paper, a novel approach to synthesize nitrogen- and oxygen-doped GQDs (NO-GQDs) is presented. Nitrogen and oxygen are mainly bound at the GQD edges, resulting in high crystallinity and good electrical properties. A simple solvothermal reaction using N-methyl-2-pyrrolidone (NMP), whose surface energy is similar to that of graphite as a raw material, can simultaneously exfoliate, cut, and finally transform the graphite into the GQDs with heteroatoms derived from the decomposed NMP solution. The synthesized NO-GQDs have a less defective and more selectively edge-functionalized structure compared to other reported GQDs. The electrical properties of NO-GQDs are investigated using them as the additive of hole-transporting materials (HTMs) in an optoelectronic device such as perovskite solar cells (PeSCs). Compared with PEDOT:PSS, a mixture of NO-GQDs and PEDOT:PSS shows a 36.2% increase in the power conversion efficiency (PCE) (maximum PCE: 11.47%) and good device stability. Therefore, it is believed that the improvement of photovoltaics is solely attributed from NO-GQDs which act as a positive role of faster hole transfer. We could confirm that the NO-GQDs facilitate hole-extraction from a photoactive layer and guarantee the more stable operation of PeSCs.

We examined the packing structure of polystyrene-coated gold nanoparticles (Au@PS) as a function of grafting density. A series of Au@PS nanoparticles with grafting densities in the range of 0.51–1.94 chains nm–2 were prepared by a ligand exchange process using thiol-terminated PS and then self-assembled at a liquid–air interface. We observed a transition from disordered to body-centered cubic (bcc) to face-centered cubic (fcc) arrangements with increasing grafting density, even though the ligand length-to-core radius ratio (λ) was as high as 3.0, a condition that typically favors nonclose-packed bcc symmetry in the self-assembly of hard nanoparticles. To explain this phenomenon, we define λeff to include the concentrated polymer brush regime as part of the “hard core”, which predicts that the softness of Au@PS nanoparticles is reduced from 1.53 to 0.14 in a theta solvent as the grafting density increases from 0.51 to 1.94 chains nm–2. This new definition of λ can also predict the effective radii of nanopa...

Colloidal semiconductor nanocrystals hold great promise in display technologies, as the tunable energy levels and narrow emission bandwidth allow for wide gamut in color space. Impetus for energy-e...

Advance in wet chemistry enables the sophisticated design of nanocrystal quantum dots (QDs) and allows unprecedented color purity and brightness, promising their useful applications in a variety of...

Relatively large faces of colloidal CdSe nanoplatelets (NPLs) drive the anisotropic nanomaterials into one-dimensional superstructures through stacking of NPLs when solvent evaporates. We observe that the assembly could result in the formation of twisted ribbon superstructures with varying pitch length depending on lateral dimensions of CdSe NPLs. Transmission electron microscopy images and simulated projection reveal that stacked NPLs are distorted. The estimation of the contact area between distorted NPLs suggests that this distortion leads to lower energy of overall nanoribbon superstructures. The average pitch length of superstructures on the lateral dimension of NPLs depends on the dimension of NPLs as it alters the distortion angle of NPLs and thus the rotation angle between NPLs. We investigate the energy transfer between NPLs in the context of the lateral dimension of NPLs and the geometric structure of their superstructures via transient photoluminescence decay measurements. Our analysis on the e...

Synthesis of colloidal nanocrystals (NCs), which are not readily available via the wet-chemical approach based on arrested precipitation, has often relied on templated growth. Cation exchange, in which guest cations in bulk solution replace host cations in template NCs, has evolved as one of the most powerful examples. Despite its versatility and facileness, there are caveats because most of the cation-exchange processes presuppose the formation of crystalline defects, which are more or less uncontrolled in terms of population and locations. The defect formation is a consequence of the imbalance between extraction and incorporation of host and guest cations. Here, we demonstrate the controlling of ion-exchange balance in the Cu+-to-In3+ cation-exchange reaction of Cu3–xP nanoplatelets (NPLs), which triggers the nanoscale Kirkendall effect, a representative phenomenon of crystal defect generation, clearly shown by morphology change of NPLs. Cation-exchanged NPLs exhibit various morphologies depending on th...

Stable electrode materials with guaranteed long-term cyclability are indispensable for advanced lithium-ion batteries. Recently, delafossite CuFeO2 has received considerable attention, due to its relative structural integrity and cycling stability. Nevertheless, the low conductivity of delafossite and its relatively low theoretical capacity prevent its use as feasible electrodes for next-generation batteries that require higher reversible capacities. In this work, we suggest a simple and straightforward approach to prepare CuFeO2–NiFe2O4 by introducing Ni precursor into Cu and Fe precursor to form NiFe2O4, which exhibits higher capacity but suffers from capacity fading, through sol–gel process and subsequent heat treatments. The presence of both NiFe2O4 and CuFeO2 is apparent, and the heterostructure arising from the formation of NiFe2O4 within CuFeO2 renders some synergistic effects between the two active materials. As a result, the CuFeO2–NiFe2O4 hybrid sample exhibits excellent cycling stability and improved rate capability, and can deliver stable electrochemical performance for 800 cycles at a current density of 5.0 A g−1. This work is an early report on introducing a foreign element into the sol–gel process to fabricate heterostructures as electrodes for batteries, which open up various research opportunities in the near future.

Due to their anisotropic structure, quantum rods (QRs) feature unique properties that differ from quantum dots, such as suppression of non-radiative Auger recombination and linearly polarized light emission. Despite many potential advantages, the progress of QR-based light-emitting diodes (QR-LEDs) is left behind due to the difficulty in aligning QRs. In this study, polarized electroluminescence emission is reported in high-performance QR-LEDs by employing the Langmuir-Blodgett (LB) technique. The adoption of the LB technique successfully produces a highly dense and smooth QR film with a high degree of alignment. As a result, the aligned QR films exhibit polarized photoluminescence emission with a degree of linear polarization of 2.1. Advantageous features of the LB technique, such as nondestructiveness, precise thickness control, and the nonnecessity of an additional matrix material, allow to fabricate QR-LEDs with the same procedure as the standard spin coating-based scheme. The device is fabricated via the LB technique, which shows excellent device performance, such as the low turn-on voltage of 1.8 V, peak luminance of 56 287 cd m-2 , and peak external quantum efficiency (EQE) of 10.33%. Furthermore, these devices clearly exhibit an indication of polarized electroluminescence emission, which opens new opportunities for QRs in display technologies.

The potential profile and the energy level offset of core/shell heterostructured nanocrystals (h-NCs) determine the photophysical properties and the charge transport characteristics of h-NC solids. However, limited material choices for heavy metal-free III-V/II-VI h-NCs pose challenges in comprehensive control of the potential profile. Herein, we present an unprecedented approach to such control by steering dipole moments at the interface of III-V/II-VI h-NCs. The controllable heterovalency at the interface is responsible for interfacial dipole moments that result in the vacuum-level shift, providing an additional knob for the control of optical and electrical characteristics of h-NCs. We capitalize on the atomic precision with which to synthesize h-NCs by correlating interfacial dipole moments to photochemical stability and optoelectronic performance of resulting h-NCs.

The potential profile and the energy level offset of core–shell heterostructured nanocrystals (h-NCs) determine the photophysical properties and the charge transport characteristics of h-NC solids. However, limited material choices for heavy metal-free III-V–II-VI h-NCs pose challenges in comprehensive control of the potential profile. Herein, we present an approach to such a control by steering dipole densities at the interface of III-V–II-VI h-NCs. The controllable heterovalency at the interface is responsible for interfacial dipole densities that result in the vacuum-level shift, providing an additional knob for the control of optical and electrical characteristics of h-NCs. The synthesis of h-NCs with atomic precision allows us to correlate interfacial dipole moments with the NCs’ photochemical stability and optoelectronic performance. Controlled synthesis of heterostructured III-V–II-VI nanocrystals shows that dipole moments formed at the core–shell interface can tune the optoelectronic properties of these nanomaterials and their performance in light-emitting devices.

Achieving ordered arrays of nanoparticles (NPs) with controlled packing symmetry and interparticle spacing is of great importance to design complex metamaterials. Herein, we report softness- and size-dependent self-assembly behavior of polystyrene-grafted Au NPs (Au@PS NPs). We varied the core size of Au NPs from 1.9 to 9.6 nm and the number-average molecular weight (Mn) of thiol-terminated polystyrene from 1.8 to 7.9 kg mol-1. The optimal packing model based on an "effective softness" parameter λeff that accounts for close-packed and semidilute brush regimes could predict the effective radius of Au@PS NPs (within ±9%) for a wide range of PS Mn, grafting density, and Au core size. With increasing λeff, the self-assembled Au@PS NP superlattices undergo a symmetry transition from hexagonal close packed (hcp) to body-centered tetragonal (bct) to body-centered cubic (bcc). This work demonstrates the effective softness model as a simple but robust tool for the design of NP superlattices with precisely controlled interparticle distance and packing symmetry, both of which are critical for the development of sophisticated materials through control of nanoscale structure.

Endowing quantum dots (QDs) with robustness and durability have been one of the most important issues in this field, since the major limitations of QDs in practical applications are their thermal and oxidative instabilities. In this work, we propose a facile and effective passivation method to enhance the photochemical stability of QDs using polymeric double shell structures from thiol-terminated poly(methyl methacrylate-b-glycidyl methacrylate) (P(MMA-b-GMA)-SH) block copolymer ligands. To generate a densely cross-linked network, the cross-linking reaction of GMA epoxides in the PGMA block was conducted using a Lewis acid catalyst under an ambient environment to avoid affecting the photophysical properties of the pristine QDs. This provides QDs encapsulated with robust double layers consisting of highly transparent PMMA outer-shell and oxidation-protective cross-linked inner shell. Consequently, the resulting QDs exhibited exceptional tolerance to heat and oxidants when dispersed in organic solvents or QD-nanocomposite films, as demonstrated under various harsh conditions with respect to temperature and oxidant species. The present approach not only provides simple yet effective chemical means to enhance the thermochemical stability of QDs, but also offers a promising platform for the hybridization of QDs with polymeric materials for developing robust light-emitting or light-harvesting devices. A treatment that makes nanoparticles robust and thus more useful for optoelectronics has been developed by researchers in South Korea. Quantum dots are semiconductor particles just a few tens of nanometers in diameter. These tiny dimensions restrict the motion of electrons, which gives the dots properties similar to those of an atom. Specifically, they efficiently absorb and emit spectrally pure light, making them useful for displays, photodetectors and solar cells. However, quantum dots are sensitive to heat, moisture and oxidization. Joona Bang, Korea University, Seoul, and colleagues improved the thermochemical stability of quantum dots by surrounding them with a physical barrier to suppress the creation of surface defects. This protective shell was made using a cross-linkable polymer ligand and was shown to reduce the deleterious effects of exposure to high temperatures and an oxidizing agent. Quantum Dot: Shell cross-linking endows stability: Simple and facile cross-linking chemistry was employed to form the robust network shell on the quantum dot (QD) surface without altering the photoluminescence property of pristine QDs. The resulting shell cross-linked QDs exhibited exceptional tolerance against heat or chemical oxidations. And the exterior brush in QDs can be readily tunable and provide the miscibility with host polymer matrix, resulting in well-defined QD-nanocomposite films. This encapsulation strategy can be generally applicable to many other nanoparticles that are vulnerable to various external stimuli.