Room-Temperature Ionic-Liquid-Assisted Microwave Preparation of Tunable Photoluminescent Copper-Indium-Zinc-Sulfide Quantum Dots.

A facile approach towards photoluminescent (PL) Cu-In-Zn-S quantum dots (CIZS QDs) has been developed, comprising microwave treatment with the assist of room-temperature ionic liquid (RTIL). Because of its high polarizability, RTIL served as a microwave absorbent, which resulted in the increase of the instantaneous nucleation rate and the rapid synthesis of CIZS QDs at low temperature. Moreover, the surface decoration of QDs with RTIL can passivate the surface defects greatly. The PL intensity of the CIZS QDs depends on the anion species, alkyl chain length of the RTIL, and the metal element ratios of the QDs. On the basis of the variable PL peak position and extended luminescence lifetime of the CIZS QDs, the superior emission behavior of the QDs was confirmed by surface etching with fluoride produced by the hydrolysis of RTIL 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4 ). Moreover, the intermediate alkyl chain length of the RTIL can avoid aggregation, which results in the construction of CIZS QDs with homogenous size distribution. The shape-controlled CIZS QDs show a broadened tunable emission peak from 677 to 579 nm compared with that of QDs prepared by a conventional one-pot method by mixing the raw materials. CIZS QDs also exhibit a high quantum yield (QY) of 24.1 % after coating with a ZnS shell. This method is expected to be a useful technique for the rapid synthesis of multiple QDs with a wider range of emission wavelengths and higher QY for a variety of applications.

Luminescent properties of novel red-emitting M7 Sn(PO4 )6 :Eu3+ (M = Sr, Ba) for light-emitting diodes.

Novel red-emitting phosphors, Eu3+ -activated M7 Sn(PO4 )6 (M = Sr, Ba), were synthesized at 1200°C by conventional solid-state reaction method. The luminescent properties of M7 Sn(PO4 )6 :Eu3+ (M = Sr, Ba) phosphors were investigated, and the critical concentration of the activator (Eu3+ ) concentration were found to be 0.175 mol and 0.21 mol per formula unit for Sr7-x Sn(PO4 )6 :xEu3+ and Ba7-x Sn(PO4 )6 :xEu3+ , respectively. These phosphors presented red luminescence under the excitation of 395 or 465 nm, perfectly matching with the emissions wavelength of near-ultraviolet (UV) light-emitting diodes (LEDs) and InGaN blue LED.

Highly efficient silica coated perovskite nanocrystals with the assistance of ionic liquids for warm white LEDs.

Given the inherent characteristics of defect-tolerant, tunable emission performance, and high extinction coefficient, lead halide perovskite nanocrystals (NCs) have attracted widespread attention as a promising material in optoelectronic fields. However, their poor structural stability greatly impedes their practical applications. Herein, a novel strategy for synthesizing stable CsPbBr3@SiO2 NCs via the hydrolytic polycondensation of (3-aminopropyl)triethoxysilane (APTES) in the presence of ionic liquids (ILs) is deliberately designed. The problems of fluorescence quenching and undesirable agglomeration of NCs resulting from ligand loss and surface erosion existing in common encapsulation methods can be effectively resolved. The fast and controllable growth of the SiO2 shell around the CsPbBr3 NCs is realized owing to the high polarity and hygroscopicity of the IL. Moreover, the dual effects of the IL for passivating the surface defects and avoiding the structural degradation of NCs during the hydrolysis process of APTES are demonstrated. As a result, CsPbBr3@SiO2 NCs with a high photoluminescence quantum yield of 85.7% and excellent stability are realized. Furthermore, this method proves to be a versatile tool to obtain CsPbX3@SiO2 NCs with different halide compositions, realizing a broad tunable wavelength from 421.2 nm to 651.6 nm. A warm white LED with a high color rending index was assembled through packaging CsPbBr3@SiO2 NCs and Cu-In-Zn-S/ZnS/PVP composites on a commercial blue chip. These findings are expected to facilitate the development of perovskite NCs, which provides access to their optoelectronic applications.

Two-Dimensional V2O5 Inverse Opal: Fabrication and Electrochromic Application.

The open-layered structure of Vanadium pentoxide (V2O5) has triggered significant interest in exploring its energy-related application as lithium (Li) intercalation cathode material. Various methods are extensively studied to improve the Li diffusion using thin films or nanoarchitecture. In this work, high-quality two-dimensional (2D) inverse opal α-V2O5 films were synthesized via a modified 'dynamic hard template' infiltration strategy using sacrificial polystyrene spheres (PS, a diameter of 530 nm) photonic crystal as a template. The new material exhibited an excellent porous array with featured structural colors in a large area. The electrochromic behavior was explored by combining bandgap and electrochemical characterization. On the one hand, the intercalation/deintercalation of Li+ played an important role in the bandgap (Eg), and thereafter on the visible range transmittance through changing the film's stoichiometry and the valence of vanadium ions. On the other hand, the asymmetry of the lattice due to the disordered distribution of Li+ within the V2O5 interlayer and/or the formation of an irreversible phase explained the change in transmittance with voltage.

In situ passivation of Pb0 traps by fluoride acid-based ionic liquids enables enhanced emission and stability of CsPbBr3 nanocrystals for efficient white light-emitting diodes.

A great hurdle restricting the optoelectronic applications of cesium lead halide perovskite (CsPbX3) nanocrystals (NCs) is due to the uncoordinated lead atoms (Pb0) on the surface, where most attempts to address the challenges in the literature depend on complicated post-treatment processes. Here we report a simple in situ surface engineering strategy to obtain highly fluorescent and stable perovskite NCs, wherein the introduction of the multifunctional additive 1-butyl-3-methyl-imidazolium tetrafluoroborate ([Bmim]BF4) can significantly eliminate the Pb0 traps. The photoluminescence quantum yield (PLQY) of the as-synthesized NCs was improved from 63.82% to 94.63% due to the good passivation of the surface defects. We also confirm the universality of this in situ passivation pathway to remove Pb0 deep traps by using fluoride acid-based ionic liquids (ILs). Due to the high hydrophobicity of the cations of ILs, the as-prepared CsPbBr3 NCs exhibit robust water resistance stability, maintaining 67.5% of the initial photoluminescence (PL) intensity after immersion in water for 21 days. A white light emitting diode (LED), assembled by mixing the as-synthesized CsPbBr3 NCs and red K2SiF6:Mn4+ phosphors onto a blue chip, exhibits high luminous efficiency (100.07 lm W-1) and wide color gamut (140.64% of the National Television System Committee (NTSC) standard). This work provides a promising and facile technique to eliminate the Pb0 traps and improve the optical performance and stability of halide perovskite NCs, facilitating their applications in optoelectronic fields.

Lead-Free Halide Double Perovskite Nanocrystals for Light-Emitting Applications: Strategies for Boosting Efficiency and Stability.

Lead-free halide double perovskite (HDP) nanocrystals are considered as one of the most promising alternatives to the lead halide perovskite nanocrystals due to their unique characteristics of nontoxicity, robust intrinsic thermodynamic stability, rich and tunable optoelectronic properties. Although lead-free HDP variants with highly efficient emission are synthesized and characterized, the photoluminescent (PL) properties of colloidal HDP nanocrystals still have enormous challenges for application in light-emitting diode (LED) devices due to their intrinsic and surface defects, indirect band, and disallowable optical transitions. Herein, recent progress on the synthetic strategies, ligands passivation, and metal doping/alloying for boosting efficiency and stability of HDP nanocrystals is comprehensive summarized. It begins by introducing the crystalline structure, electronic structure, and PL mechanism of lead-free HDPs. Next, the limiting factors on PL properties and origins of instability are analyzed, followed by highlighting the effects of synthesis strategies, ligands passivation, and metal doping/alloying on the PL properties and stability of the HDPs. Then, their preliminary applications for LED devices are emphasized. Finally, the challenges and prospects concerning the development of highly efficient and stable HDP nanocrystals-based LED devices in the future are proposed.

Ionic liquid assisted preparation and modulation of the photoluminescence kinetics for highly efficient CsPbX3 nanocrystals with improved stability.

CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) are competitive fluorescent materials for lighting and displays owing to their excellent photophysical properties. However, the stability and optoelectronic performance of the perovskite NCs are severely limited by the highly dynamic binding feature of the present ligand strategy. Herein, a facile approach was employed to synthesize CsPbBr3 NCs with the assistance of the ionic liquid (IL) 1-butyl-3-methylimidazolium bromide ([Bmim]Br). By strictly controlling the addition dose of [Bmim]Br (nIL/nPb = 0.125) into the reaction precursor, it is possible to obtain the desired cube-shaped and monodisperse CsPbBr3 NCs with simultaneous enhancement of the storage and irradiation stability as well as photoluminescence quantum yields (PLQYs, ∼91%). Stability tests show that the emission intensity of the parent CsPbBr3 NCs drops to 50% of its initial emission intensity after storage under an open atmosphere for 91 days, while the sample prepared with the assistance of [Bmim]Br can maintain 82% of the PL intensity. Meanwhile, the modified CsPbBr3 NCs also present superior photo-stability, and still maintain 81% of the original PL intensity after continuous illumination under an ultraviolet lamp for 24 h, but the intensity of the parent CsPbBr3 NCs reduces to 35% of the original intensity. Through the morphology, composition, and luminescence kinetics evolution of CsPbBr3 NCs, these benefits were attributed to the modulation by [Bmim]Br, which could effectively provide Br ions for the formation and growth of NCs, resulting in the reduction of surface traps. Moreover, [Bmim]Br exhibited strong interactions with NCs, and the deprotonation of oleic acid (OA) was inhibited, resulting in the effective passivation of surface defects. Finally, CsPbX3 NCs with different compositions were obtained via a facile anion exchange reaction, leading to the tunable emission in the range of 462-665 nm and a wide colour gamut (129.65% NTSC standard). This work opens a new avenue for modulating the surface properties of CsPbX3 NCs, which will create opportunities for their application in the photoelectric field.

Cellulose Nanofibril/Carbon Nanomaterial Hybrid Aerogels for Adsorption Removal of Cationic and Anionic Organic Dyes.

Advances in nanoscale science and engineering are providing new opportunities to develop promising adsorbents for environmental remediation. Here, hybrid aerogels are assembled from cellulose nanofibrils (CNFs) and carbon nanomaterials to remove cationic dye methylene blue (MB) and anionic dye Congo red (CR) in single and binary systems. Two classes of carbon nanomaterials, carbon nanotubes (CNTs) and graphene nanoplates (GnPs), are incorporated into CNFs with various amounts, respectively. The adsorption, mechanics and structure properties of the hybrid aerogels are investigated and compared among different combinations. The results demonstrate CNF-GnP 3:1 hybrid exhibits the best performance among all composites. Regarding a single dye system, both dye adsorptions follow a pseudo-second-order adsorption kinetic and monolayer Langmuir adsorption isotherm. The maximal adsorption capacities of CNF-GnP aerogels for MB and CR are 1178.5 mg g-1 and 585.3 mg g-1, respectively. CNF-GnP hybrid show a superior binary dye adsorption capacity than pristine CNF or GnP. Furthermore, nearly 80% of MB or CR can be desorbed from CNF-GNP using ethanol as the desorption agent, indicating the reusability of this hybrid material. Hence, the CNF-GnP aerogels show great promise as adsorption materials for wastewater treatment.

A novel porous egg-white (EW)/titania composite photocatalytic material for efficient photodegradation applications.

A novel porous egg-white (EW)/titania composite material was prepared via a facile nonaqueous precipitation method with EW as the porous skeleton. In a typical process, tetrabutyl titanate, a titanium precursor, was dissolved in ethanol to undergo a non-hydrolytic reaction with the aid of anhydrous formic acid under ultrasonication and form a porous structure with EW. The composite material was characterized by BET, XRD, FTIR spectroscopy, TEM, FE-SEM and photocatalytic degradation test. The results show that formic acid changes the characteristic structure of tetrabutyl titanate, increases the polarity of its C-O and Ti-O bonds, and promotes the non-hydrolytic de-etherization poly-condensation reaction. After ultrasonic treatment, the reaction product was rearranged to form anatase titania on EW to form a porous structure. The porous composite material had a mean pore size of 15.8 nm, BET surface area of 325.5 m2 g-1 and exhibited an excellent photocatalytic activity. The degradation rate of methyl orange using the EW/titania composite material reached 99.9% in 50 minutes, exhibiting an attractive prospect in wastewater treatment.

Comparison of Fe2TiO5/C photocatalysts synthesized via a nonhydrolytic sol-gel method and solid-state reaction method.

Fe2TiO5/C photocatalysts were synthesized by a solid-state reaction method (Fe2TiO5/C(S)) and nonhydrolytic sol-gel (NHSG) method (Fe2TiO5/C(N)), where C was introduced by external carbon and in situ carbon sources, respectively. The Fe2TiO5/C(N) photocatalyst with in situ carbon has much better photocatalytic degradation efficiency than that of Fe2TiO5/C(S) synthesized by doping external carbon. The superiorities of in situ carbon were demonstrated by SEM, EDS, BET and photoelectrochemical analysis. Compared with Fe2TiO5/C(S) using external carbon as a carbon source, Fe2TiO5/C(N) with in situ carbon exhibits more uniform elemental distribution, much larger surface area, higher photocurrent density and lower resistivity of interfacial charge transfer. The results show that the introduction of in situ carbon via the NHSG method more easily promotes the separation of photogenerated electron-hole pairs, owing to the uniformity of the carbon element, thereby improving the photocatalytic activity of the photocatalyst.

Pressure Field Assisted Polycondensation Nonaqueous Precipitation Synthesis of Mullite Whiskers and Their Application as Epoxy Resin Reinforcement.

Mullite whiskers were novelty prepared via pressure field assisted polycondensation nonaqueous precipitation method. The precipitate phase transition in heating process, phase compositions and microstructure of samples calcined at different temperatures, effect of pressure field on precursors polycondensation and AlF3 amount on sample morphology, the structure and the growth mechanism of whiskers were investigated. The results indicate that pressure field caused by kettle treatment promotes the polycondensation reaction between AlF3 and tetraethyl orthosilicate (TEOS), the excess aluminum fluoride coordinates with the precipitate skeleton of the =Al-O-Si≡, which brings about the low mullitization temperature (900 °C). The sample prepared with the optimal amount of aluminum fluoride (1.3 of the theoretical amount) calcined at 1100 °C presents high yield and aspect ratio (>15, 100 nm in diameter) of mullite whiskers. Growth of whiskers prepared via pressure field assisted polycondensation nonaqueous precipitation method is attributed to a vapor-solid (VS) mechanism with the inducement of screw. These mullite whiskers with the structure of multi-needle whiskers connected in the same center can be distributed evenly in epoxy resin, which greatly improves the mechanical properties of epoxy resin.

The off-stoichiometry effect on the optical properties of water-soluble copper indium zinc sulfide quantum dots.

CuInZnS quantum dots (CIZS QDs) were prepared via reflux method in aqueous solution using CuCl2·2H2O, InCl3·4H2O, Zn(OAc)2·2H2O and Na2S·9H2O as raw materials, l-glutathione (GSH) and sodiumcitrate (SC) as stabilizing agents, respectively. The effects of off-stoichiometry (Cu/In and Zn/Cu ratios) on the crystal structure and morphology were systematically studied by means of X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM), and the relative optical properties were also investigated by absorption and fluorescence spectra. The as-prepared water-dispersible CIZS QDs were around 3-4nm and possessed the tetragonal chalcopyrite crystal structure. The photoluminescence (PL) intensity of QDs was significantly increased with decreasing the Cu/In ratio. Compared with the Cu/In ratio variation, changing Zn/Cu ratio was an effective strategy to realize a more uniform irradiation and a wide range of emission wavelength tunability.