Uniform Nanocrystals Research Articles

A Library of Nanocrystal‐Inserted Ordered Mesoporous Frameworks with Ultrahigh Density and Spatial Dispersity

AbstractIt is a great challenge to integrate incompatible subunits into ordered macroscopic materials with tailored functionalities. Herein, a facile modular assembly strategy is demonstrated to link incompatible colloidal nanocrystals and polymer micelles by using the phenolic resol as the “molecule glue” for the synthesis of nanocrystal‐inserted mesoporous frameworks with diverse functionalities. It is found that the uniform nanocrystals can be inserted into the mesoporous frameworks with outstanding spatial dispersity, even in the case of high incorporation density. This modular assembly route is versatile, a library of nanocrystals with diverse diameters, shapes, and compositions can be integrated into various kinds of mesoporous frameworks (carbon, carbon‐SiO2, and carbon‐TiO2 composites). Unprecedently, this strategy also allows the controllable assembly of two, even three types of nanocrystals within the mesoporous frameworks to achieve multiple functionalities. The as‐prepared nanocomposites can simultaneously exhibit catalytic, magnetic, and adsorption properties independently, and show synergistic effects for tandem catalytic applications.

CdTe nanocrystals doped with Sm3+: blueshift and enhanced emission

This work used an aqueous-phase method to prepare Sm-doped CdTe nanocrystals (NCs). The successful doping of Sm into the CdTe lattice was confirmed by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), as well as UV–Visible (UV–Vis) absorption and emission spectroscopies. The CdTe and CdTe:Sm NCs are monodispersed as uniform spherical nanocrystals with cubic structures. The particle diameters are ∼4.2, ∼3.3, and ∼2.6 nm for CdTe, CdTe:Sm(5%) and CdTe:Sm(10%) NCs, respectively. Compared with pure CdTe, the CdTe:Sm(5%) NCs exhibit a blueshift of 9–23 nm in their absorption bands and a blueshift of 8–17 nm in their emission bands. With increasing concentration of Sm3+, the quantum yield (QY) of the CdTe:Sm NCs increases initially and then decreases. The CdTe:Sm NCs have longer fluorescence lifetimes than CdTe, probably due to the introduction of trap states. Due to charge compensation, the CdTe:Sm NCs have much stronger emission peaks.

Shape-controlled synthesis and self-assembly of highly uniform upconverting calcium fluoride nanocrystals

A novel synthetic method to tailor the shapes of highly uniform upconverting CaF2 NCs is demonstrated. We investigate the shape-dependent self-assemblies, and size, shape, and dopant composition-dependent upconversion luminescence of CaF2 NCs.

One-pot synthesis of an ultrafine Cu2O nanocrystal/porous polymer heterostructure for photocatalytic hydrogen production

This work provides a facile method for inorganic/organic heterostructures synthesis in a one-pot “click” reaction, in which ultrafine and uniform Cu2O nanocrystals were in situ deposited on triazole polymer nanosheets for the first time.

Observation of Sub-10 nm Transition Metal Dichalcogenide Nanocrystals in Rapidly Heated van der Waals Heterostructures.

Two-dimensional materials, such as transition metal dichalcogenides (TMDCs), have the potential to revolutionize the field of electronics and photonics due to their unique physical and structural properties. This research presents a novel method for synthesizing crystalline TMDCs crystals with <10 nm size using ultrafast migration of vacancies at elevated temperatures. Through in situ and ex situ processing and using atomic-level characterization techniques, we analyzed the shape, size, crystallinity, composition, and strain distribution of these nanocrystals. These nanocrystals exhibit electronic structure signatures that differ from the 2D bulk: i.e., uniform mono- and multilayers. Further, our in situ, vacuum-based synthesis technique allows observation and comparison of defect and phase evolution in these crystals formed under van der Waals heterostructure confinement versus unconfined conditions. Overall, this research demonstrates a solid-state route to synthesizing uniform nanocrystals of TMDCs and lays the foundation for materials science in confined 2D spaces under extreme conditions.

Highly stable lead-free perovskite Cs2AgBiBr6/UiO-66 Z-scheme heterostructures with enhanced photocatalytic activity for CO2 photoreduction and organic dyes degradation

Excessive combustion of traditional fossil fuels causes seriously global warming (Carbon dioxide, CO2) and energy crisis. Photocatalytic CO2 conversion to fuels has emerged as one of the most effective strategies. Herein, an environmentally friendly nanocomposite based on lead-free Cs2AgBiBr6 (CABB) perovskite nanocrystals and the UiO-66 metal–organic framework was fabricated by a facile ultrasonic process for efficient CO2 photoreduction. The obtained CABB/UiO-66 consisted of uniform CABB nanocrystals (10–12 nm) attached to the UiO-66 surface and exhibited a high surface area (1031 m2/g). The composite displayed enhanced light-harvesting capacity than the individual components and provided sufficient active sites for promoting photocatalytic activity. A typical Z-scheme heterostructure between the CABB and UiO-66 was realized by forming an inner electric field, leading to the occurrence of efficient excited state charge transfer. The efficient charge transfer of CABB/UiO-66 inspired its use as an active photocatalyst for the reduction of CO2 with significantly improved photocatalytic activity against its individual components. Specifically, CABB/UiO-66 exhibited 38 and 40-fold improvement in catalytic activity compared to respective CABB and UiO-66 in terms of the total yield of CO, CH4, and C2H6. Moreover, the nanocomposite displayed excellent activity towards the oxidative photocatalytic degradation of aqueous environmental contaminant rhodamine B. We believe that this work provides a guide for designing lead-free perovskite-based renewable catalysts and offers new opportunities for the photocatalytic conversion of CO2 photoreduction.

Stable Perovskite Quantum Dots Light-Emitting Diodes with Efficiency Exceeding 24.

Perovskite nanocrystals for light-emitting diodes are often synthesized by uncontrollable metathesis reactions, suffering from low product yield, nonuniform growth, and poor stability. Herein, by controlling the nucleation kinetics with high dissociation constant (Ka or Kb) acids or bases, homogenous one-route nucleation of perovskite nanocrystals is achieved as the cluster intermediates are eliminated. The stable, shape uniform, and narrow size distribution green nanocrystals are synthesized. The perovskite nanocrystal film exhibites excellent stability in 80% humidity air with only a 10% photoluminescence intensity drop after 16h. Efficient and stable electroluminescence is demonstrated with an FWHM of 16nm at 517nm. The green devices shows a peak EQE of 24.13% with a lifetime T50 of 54min at 10 000cdm-2 .

Enabling cobblestone-like zinc deposition via uniform ZnSnO3 perovskite nanocrystal nucleus towards dendrites-free and high-rate zinc batteries

Although the plating/stripping mechanism of zinc metal anode brings high energy density for rechargeable aqueous zinc metal batteries (AZMBs), zinc tends to plating/stripping along dendrite planes and induces severe parasitic reactions, which reduces its coulombic efficiency and shortens its cycling life. Here, uniform perovskite nanocrystals nucleus with rich-exposed ZnSnO3(111) as zinc deposition sites was prepared to achieve cobblestone-like zinc deposition. Due to the high lattice match rate (93.7%) of ZnSnO3(111) with Zn(002) and the moderating effect of ZnSnO3 nanocrystals on zinc deposition/dissolution, the zinc anode allows for 3D deposition/dissolution with a highly exposed Zn(002) facet (referred to as 3D-Zn), resulting in accelerated reaction kinetics. In symmetrical battery, the 3D-Zn exhibits an ultra-low polarization voltage of 15 mV at 1 mA cm−2 and a high exchange current density of 13.53 mA cm−2for Zn0↔Zn2+, indicating the 3D stripping/plating delivers fast kinetics process. A full cell with 3D-Zn anode and NaV3O8·H2O (NVO) cathode shows a stable CE (average value ~ 99.3%) at 0.5 A g−1. Moreover, the full cell with 3D-Zn anode still works up to 600 cycles at 3A g−1. This work provides new insights into the design of dendrite-free metal anodes with fast kinetics for high-rate and stable AZMBs.

Significantly improved thermoelectric performance of Ag-doped Bi0.5Sb1.5Te3 films deriving from high-efficient carrier filtering effect

Selective carrier energy filtering effect is an important strategy to promote the power factor of a thermoelectrical materials, which requires an appropriate potential barrier and coherent interfaces between the secondary phase and the host matrix. Although the energy filtering effect has been realized in various bulk systems, its efficiency in promoting their thermoelectric performance is limited. Herein, simultaneously increased electrical conductivity and Seebeck coefficient are investigated in Ag-doped Bi0.5Sb1.5Te3 films, leading to an increasement of the power factor up to 700%. Microstructure analysis reveals that the thin films prepared from magnetron sputtering consist of highly uniform nanocrystal domains, which construct coherent interfaces somewhere. Moreover, the local Ag doping might depress the Fermi level, providing the possibility to form a suitable potential barrier between the adjacent nanograins. This study suggests a facile method to significantly enhance the thermoelectric performance via energy filtering effect in high quality thin films.

Fabrication and Characterization of Antimony doped Iron oxide Nanoparticles

Antimony oxide (Sb2O3) and Antimony-doped iron oxide (Sb-Fe2O3) nanomaterials of different (2 &amp;3 %) concentrations were fabricated by wet synthesis technique and characterized by FTIR, XRD and XRF techniques, respectively. X-RD results showed uniform Iron oxide nanocrystals of almost 15 nm, whereas FTIR and XRF were employed to detect elemental composition of Antimony in doped (Sb-Fe2O3) samples.

Highly Active Nanocrystalline ZnO and Its Photo-Oxidative Properties towards Acetone Vapor.

Zinc oxide is one of the well-known photocatalysts, the potential applications of which are of great importance in photoactivated gas sensing, water and air purification, photocatalytic synthesis, among others. However, the photocatalytic performance of ZnO strongly depends on its morphology, composition of impurities, defect structure, and other parameters. In this paper, we present a route for the synthesis of highly active nanocrystalline ZnO using commercial ZnO micropowder and ammonium bicarbonate as starting precursors in aqueous solutions under mild conditions. As an intermediate product, hydrozincite is formed with a unique morphology of nanoplates with a thickness of about 14-15 nm, the thermal decomposition of which leads to the formation of uniform ZnO nanocrystals with an average size of 10-16 nm. The synthesized highly active ZnO powder has a mesoporous structure with a BET surface area of 79.5 ± 4.0 m2/g, an average pore size of 20 ± 2 nm, and a cumulative pore volume of 0.507 ± 0.051 cm3/g. The defect-related PL of the synthesized ZnO is represented by a broad band with a maximum at 575 nm. The crystal structure, Raman spectra, morphology, atomic charge state, and optical and photoluminescence properties of the synthesized compounds are also discussed. The photo-oxidation of acetone vapor over ZnO is studied by in situ mass spectrometry at room temperature and UV irradiation (λmax = 365 nm). The main products of the acetone photo-oxidation reaction, water and carbon dioxide, are detected by mass spectrometry, and the kinetics of their release under irradiation are studied. The effect of morphology and microstructure on the photo-oxidative activity of ZnO samples is demonstrated.

Bis(stearoyl) Sulfide: A Stable, Odor‐Free Sulfur Precursor for High‐Efficiency Metal Sulfide Quantum Dot Photovoltaics

AbstractThe synthesis of metal sulfide nanocrystals is a crucial step in the fabrication of quantum dot (QD) photovoltaics. Control over the QD size during synthesis allows for precise tuning of their optical and electronic properties, making them an appealing choice for electronic applications. This flexibility has led to the implementation of QDs in both highly‐efficient single junction solar cells and other optoelectronic devices including photodetectors and transistors. Most commonly, metal sulfide QDs are synthesized using the hot‐injection method utilizing a toxic, and air‐ and moisture‐sensitive sulfur source: bis(trimethylsilyl) sulfide ((TMS)2S). Here, bis(stearoyl) sulfide (St2S) is presented as a new type of air‐stable sulfur precursor for the synthesis of sulfide‐based QDs, which yields uniform, pure, and stable nanocrystals. Photovoltaic devices based on these QDs are equally efficient as those fabricated by (TMS)2S but exhibit enhanced operational stability. These results highlight that St2S can be widely adopted for the synthesis of metal sulfide QDs for a range of optoelectronic applications.

Uniform Catalytic Nanocrystals: From Model Catalysts to Efficient Catalysts

ConspectusSolid catalysts play a key role in the chemical industry, energy, and the environment. Fundamental understanding of heterogeneous catalysis exerted by solid surfaces is useful for structural designs of efficient catalysts but is challenging due to the complexity. Emerging uniform catalytic nanocrystals (NCs) with controlled and well-defined surface structures have brought new opportunities for fundamental understanding and directed explorations of efficient catalysts. In a previous Account ( Acc. Chem. Res. 2016, 49, 520−527), I postulated and exemplified a concept of oxide nanocrystal model catalysts for the fundamental investigations of oxide catalysis without the “materials gap” and “pressure gap” which are often encountered using the traditional single crystal model catalysts. In this Account, I summarize our effort in fabricating efficient uniform nanocrystal catalysts based on the fundamental understanding of structure–activity relations and reaction mechanisms acquired by oxide nanocrystal model catalyst studies. Directed by the fundamental understanding that the Cu2O{110} facet is active in catalyzing propylene epoxidation with O2 and the fine Cu2O nanocube exposes high densities of Cu2O{110} edge sites, we successfully explore fine Cu2O nanocubes as a highly selective catalyst for propylene epoxidation with O2. Directed by the fundamental understanding that the Cu{100} facet is the active Cu facet in catalyzing the water–gas shift (WGS) reaction, we successfully fabricate a highly active ZnO/fine Cu nanocube WGS catalyst with enhanced ZnO-CuCu{100} active site density. Directed by the fundamental understanding of TiO2 facet effects on the surface band bending and adsorbate–surface interfacial energy level alignment, and consequent photocatalytic performance, we successfully fabricate highly active TiO2{001} NC-based photocatalysts for photocatalytic CH4 conversions. These results adequately exemplify the concept of fundamental understanding-directed explorations of efficient catalysts following a strategy of “identification of active site structure + maximization of active site density”, which, together with the advancement of controlled-synthesis methods, is expected to greatly accelerate the explorations of novel and efficient catalysts in future.

Synthesis of Thermally Stable and Highly Luminescent Cs5 Cu3 Cl6 I2 Nanocrystals with Nonlinear Optical Response.

Low-dimensional Cu(I)-based metal halide materials are gaining attention due to their low toxicity, high stability and unique luminescence mechanism, which is mediated by self-trapped excitons (STEs). Among them, Cs5 Cu3 Cl6 I2 , which emits blue light, is a promising candidate for applications as a next-generation blue-emitting material. In this article, an optimized colloidal process to synthesize uniform Cs5 Cu3 Cl6 I2 nanocrystals (NCs) with a superior quantum yield (QY) is proposed. In addition, precise control of the synthesis parameters, enabling anisotropic growth and emission wavelength shifting is demonstrated. The synthesized Cs5 Cu3 Cl6 I2 NCs have an excellent photoluminescence (PL) retention rate, even at high temperature, and exhibit high stability over multiple heating-cooling cycles under ambient conditions. Moreover, under 850-nm femtosecond laser irradiation, the NCs exhibit three-photon absorption (3PA)-induced PL, highlighting the possibility of utilizing their nonlinear optical properties. Such thermally stable and highly luminescent Cs5 Cu3 Cl6 I2 NCs with nonlinear optical properties overcome the limitations of conventional blue-emitting nanomaterials. These findings provide insights into the mechanism of the colloidal synthesis of Cs5 Cu3 Cl6 I2 NCs and a foundation for further research.

Achieving Ultralong-Cycle Zinc-Ion Battery via Synergistically Electronic and Structural Regulation of a MnO2 Nanocrystal-Carbon Hybrid Framework.

Aqueous rechargeable zinc-ion batteries (ZIBs) have attracted burgeoning interests owing to the prospect in large-scale and safe energy storage application. Although manganese oxides are one of the typical cathodes of ZIBs, their practical usage is still hindered by poor service life and rate performance. Here, a MnO2 -carbon hybrid framework is reported, which is obtained in a reaction between the dimethylimidazole ligand from a rational designed MOF array and potassium permanganate, achieving ultralong-cycle-life ZIBs. The unique structural feature of uniform MnO2 nanocrystals which are well-distributed in the carbon matrix leads to a 90.4% capacity retention after 50 000 cycles. In situ characterization and theoretical calculations verify the co-ions intercalation with boosted reaction kinetics. The hybridization between MnO2 and carbon endows the hybrid with enhanced electrons/ions transport kinetics and robust structural stability. This work provides a facile strategy to enhance the battery performance of manganese oxide-based ZIBs.

Eu3+-doped CdSe nanocrystals with blueshift emission and high quantum yield

In this work, we used an oil phase method to synthesize Eu3+-doped CdSe nanocrystals (NCs), which were characterized extensively with X-ray powder diffraction (XRD), transmission electron microscopy (TEM), UV–visible (UV–vis) absorption and emission. The CdSe:Eu NCs were monodispersed and uniform spherical nanocrystals with a cubic structure resembling CdSe NCs. The particle diameter depended on the content of the Eu3+ dopant and ranged from 5.57to 4.27 nm, respectively. The CdSe:Eu NCs containing 20 mol% Eu3+ (denoted as a-20) has a 31nm blueshift in absorption and a 25 nm blueshift in emission with comparison to the pure CdSe NCs. The efficiency of energy transfer from CdSe to Eu3+ can be calculated from the variation of fluorescence lifetime to be 22%. The quantum yield (QY) of the CdSe:Eu NCs is the highest when the concentration of the Eu3+ dopant is 20 mol%. High reaction temperature and charge compensation can effectively improve the QY of the CdSe:Eu NCs.

Directional growth of quasi-2D Cu2O monocrystals on rGO membranes in aqueous environments.

The preparation technology of unconventional low-dimensional Cu2O monocrystals, which exhibit specific crystal planes and present significantly unique interfacial and physicochemical properties, is attracting increasing attention and interest. Herein, by integrating a high-temperature oxidation process under vacuum and a pure-water incubation process under ambient conditions, we propose the self-assembled growth and synthesis of quasi-two-dimensional Cu2O monocrystals on reduced graphene oxide (rGO) membranes. The prepared Cu2O crystals have a single (110) crystal plane, regular rectangular morphology, and potentially well conductivity. Experimental and theoretical results suggest that this assembly is attributed to the pre-nucleation clusters aggregation and directional attachment of Cu and O on the rGO membranes in aqueous environment and cation-π interactions between the (110) crystal plane of Cu2O and rGO surface. Our findings offer a potential avenue for the discovery and design of advanced low-dimensional single-crystal materials with specific interfacial properties in a pure aqueous environment.

Synthesis of CsPbX3 lead halide perovskite nanocrystals in flower-like TiO2 matrices with enhanced stability

The instability of the cesium lead halide perovskite (CsPbX3, X = Cl, Br, I) upon exposure to humidity or heat strongly hinders their applications in optoelectronic devices. In this work, an in situ adsorption strategy is adopted to directly grow uniform CsPbX3 nanocrystals (NCs) on flower-like TiO2 microspheres to achieve a hybrid structure. Benefiting from the isolation effect of flower-like structure, the as-synthesized TiO2–CsPbBr3 composites exhibit excellent water stability when soaked in water for 35 days and retain 62.7% of the initial photoluminescence (PL) emission intensity. CsPbBr3 NCs also present enhanced thermal stability under the protection of TiO2 matrix. It is intriguing that the TiO2-CsPbX3 composites with blue, green and red emissions are fabricated successfully by this method with excellent moisture and thermal stability, which provides a feasible solution for the effective application of CsPbX3 NCs in light emitting diode (LED) devices.

(Digital Presentation) Controllable Preparation of Ultrasmall Pt-Based Intermetallic Nanocrystals Via Atomic Layer Deposition for Hydrogen Fuel Cell

The cost and endurance anxiety about proton exchange membrane fuel cells (PEMFCs) has prompted the rapid development of platinum-based (Pt-based) oxygen reduction electrocatalysts towards smaller particle sizes, higher durability and alloying. However, well-balanced these advanced trends by a simple approach is difficult in practice, because the existing solutions are problematic in removing the protective organic coating or oxide shell that preventing the high-temperature agglomeration of Pt-based nanocrystals, or broadening the size range of Pt-based nanocrystals which caused by the heterogeneous distribution of heteroatom anchor points on supports. With a self-developed strategy that based on the atomic layer deposition (ALD), we have addressed these problems in two aspects. One is directly loading size and distribution controllable Pt nanocrystals on diverse supports, and another is indirectly depositing easily removed ultra-thin metal oxide coating with dual functions on prefabricated ultrasmall Pt nanocrystals to restrain their sintering effect during high temperature ordering. By controlling the temperature and pulse time of ALD, we successfully synthesized ultrasmall (< 2 nm) Pt nanocrystals on surface inactive TiC nanoparticles and nanowires. These two new electrocatalysts exhibited comparable oxygen reduction activity and durability on par with commercial Pt/C with lower Pt loading. And using this strategy, about 1 nm ZnO coating on Pt nanocrystals was performed to construct uniform PtZn intermetallic nanocrystals with the ultrasmall size of 2.50 ± 0.65 nm and excellent stability for oxygen reduction reaction. The mass activity of PtZn intermetallic nanocrystals reaches to 0.60 A mgPt -1 at 0.9 V (6 times than commercial Pt/C) and only 13 mV decrease of half-wave potential after 30000 cycles of accelerated durability testing rivaling the most recently reported PtZn catalysts. Ultrasmall sizes and excellent features of our Pt and Pt-based intermetallic nanocrystals are all attributed to the accurate control of ALD and could be a promising method applying to other Pt-based intermetallic nanocrystals.

Proficient One-Step Heat-Up Synthesis of Manganese Sulfide Quantum Dots for Solar Cell Applications.

The necessity to develop renewable energy resources that are highly durable and flexible with superior energy density and capacitance ability has attracted considerable interest in the field of solar cell research. Semiconducting compound materials that are easily available, hazard-free and cost-effective are emerging as potential solutions to tackle this challenge. Herein, we present multiple molecular precursors used to grow manganese sulfide nanoparticles through a proficient one-step heat-up approach. For all of the tested samples, the X-ray diffraction peaks correspond to a γ-MnS hexagonal wurtzite structure. UV-Vis spectroscopy yielded absorption wavelengths of 359–420 nm and band-gap energies of 3.78–4.0 eV. Photoluminescence analysis shows characteristics of red and blue shift from 451–602 nm. High-resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED) reveal a narrow size distribution with nanosticks and large contact areas, which are critical for improved catalytic performance. The current study provides an improved pathway to a well-grown and uniform nanocrystal structure for applications in energy devices.