Luminescent Thin Films Enabled by CsPbX3 (X=Cl,Br, I) Precursor Solution

Inorganic cesium lead halide perovskite nanocrystals are candidates for lighting and display materials due to their outstanding optoelectronic properties. However, the dissolution issue of perovskite nanocrystals in polar solvents remains a challenge for practical applications. Herein, we present a newly designed one-step spin-coating strategy to prepare a novel multicolor-tunable CsPbX₃ (X=Cl, Br, I) nanocrystal film, where the CsPbX₃ precursor solution was formed by dissolving PbO, Cs₂CO₃, and CH₃NH₃X into the ionic liquid n-butylammonium butyrate. The as-designed CsPbX₃ nanocrystal films show high color purity with a narrow emission width. Also, the blue CsPb(Cl/Br)₃ film demonstrates an absolute photoluminescence quantum yields (PLQY) of 15.6 %, which is higher than 11.7 % of green CsPbBr₃ and 8.3 % of red CsPb(Br/I)₃ film. This study develops an effective approach to preparing CsPbX₃ nanocrystal thin films, opening a new avenue to design perovskite nanocrystals-based devices for lighting and display applications.     

A Series of MAX Phases with MA‐Triangular‐Prism Bilayers and Elastic Properties

We report a new type of MAX phase (M=transition metals, A=main group elements, and X=C/N), Nb₃As₂C, designated as 321 phase. It differs from all the previous M_n+1AX_n phases in that it consists of an alternate stacking of one MX layer and two MA layers in its unit cell, while only one MA layer is allowed in usual MAX phases. The new 321 phase exhibits a bulk modulus of Nb₃As₂C up to 225(3) GPa as determined by high‐pressure synchrotron X‐ray diffraction, one of the highest values among MAX phases. Isostructural 321 phases V₃As₂C, Nb₃P₂C, and Ta₃P₂C are also found to exist. First‐principles calculations reveal the outstanding elastic stiffness in 321 phases. Among all 321 phases, Nb₃P₂C is predicted to have the highest elastic properties. These 321 phases, represented by a chemical formula M_n+1A_nX, were added as new members to the MAX family and their other properties deserve future investigations.     

聚甲基丙烯酸甲酯包覆(CH3NH3)PbBr3纳米晶静电纺丝膜的制备及对氨气的荧光传感

采用原位合成法制备了聚甲基丙烯酸甲酯包覆MAPbBr₃纳米晶(MAPbBr₃@PMMA,MA=甲铵离子)静电纺丝膜。当氨气(NH₃)通入MAPbBr₃@PMMA纤维膜时与MAPbBr₃中的MA发生取代,能显著降低MAPbBr₃@PMMA纤维的荧光强度,以此构建了基于MAPbBr₃@PMMA纤维荧光猝灭的NH₃传感器。通过扫描电镜、透射电镜、粉末X射线衍射和红外对静电纺丝膜的形貌和结构进行表征,通过紫外可见光谱、荧光光谱对其光学特性进行表征。结果表明,传感器的荧光强度与NH₃浓度在8~90 mg·L^-1之间呈现出良好的线性关系(r=0.995 9),NH₃的检出限低(3 mg·L^-1),且具有良好的重现性和选择性。在实际样品气体的测定中,加标回收率为92.2%~102.1%,相对标准偏差(RSD)为1.8%~3.2%。     

聚甲基丙烯酸甲酯包覆(CH3NH3) PbBr3纳米晶静电纺丝膜的制备及对氨气的荧光传感

采用原位合成法制备了聚甲基丙烯酸甲酯包覆MAPbBr₃纳米晶（MAPbBr₃@PMMA,MA=甲铵离子）静电纺丝膜。当氨气（NH₃）通入MAPbBr₃@PMMA纤维膜时与MAPbBr₃中的MA发生取代,能显著降低MAPbBr₃@PMMA纤维的荧光强度,以此构建了基于MAPbBr₃@PMMA纤维荧光猝灭的NH₃传感器。通过扫描电镜、透射电镜、粉末X射线衍射和红外对静电纺丝膜的形貌和结构进行表征,通过紫外可见光谱、荧光光谱对其光学特性进行表征。结果表明,传感器的荧光强度与NH₃浓度在8~90 mg·L^-1之间呈现出良好的线性关系（r=0.995 9）,NH₃的检出限低（3 mg·L^-1）,且具有良好的重现性和选择性。在实际样品气体的测定中,加标回收率为92.2%~102.1%,相对标准偏差（RSD）为1.8%~3.2%。     

Hydrochromic CsPbBr3 Nanocrystals for Anti‐Counterfeiting

Hydrochromic materials that can reversibly change color upon water treatment have attracted much attention owing to their potential applications in diverse fields. Herein, for the first time, we report that space‐confined CsPbBr₃ nanocrystals (NCs) are hydrochromic. When CsPbBr₃ NCs are loaded into a porous matrix, reversible transition between luminescent CsPbBr₃ and non‐luminescent CsPb₂Br₅ can be achieved upon the exposure/removal of water. The potential applications of hydrochromic CsPbBr₃ NCs in anti‐counterfeiting are demonstrated by using CsPbBr₃ NCs@mesoporous silica nanospheres (around 100 nm) as the starting material. Owing to the small particle size and negatively charged surface, the as‐prepared particles can be laser‐jet printed with high precision and high speed. We demonstrate the excellent stability over repeated transformation cycles without color fade. This new discovery may not only deepen the understanding of CsPbX₃, but also open a new way to design CsPbX₃ materials for new applications.     

Hydrochromic CsPbBr3 Nanocrystals for Anti-Counterfeiting

Hydrochromic materials that can reversibly change color upon water treatment have attracted much attention owing to their potential applications in diverse fields. Herein, for the first time, we report that space-confined CsPbBr₃ nanocrystals (NCs) are hydrochromic. When CsPbBr₃ NCs are loaded into a porous matrix, reversible transition between luminescent CsPbBr₃ and non-luminescent CsPb₂Br₅ can be achieved upon the exposure/removal of water. The potential applications of hydrochromic CsPbBr₃ NCs in anti-counterfeiting are demonstrated by using CsPbBr₃ NCs@mesoporous silica nanospheres (around 100 nm) as the starting material. Owing to the small particle size and negatively charged surface, the as-prepared particles can be laser-jet printed with high precision and high speed. We demonstrate the excellent stability over repeated transformation cycles without color fade. This new discovery may not only deepen the understanding of CsPbX₃, but also open a new way to design CsPbX₃ materials for new applications.     

A strategy for constructing sensitive and renewable molecularly imprinted electrochemical sensors for melamine detection

A novel strategy for preparing highly sensitive and easily renewable molecularly imprinted polymer (MIP) sensors was proposed. Using melamine (MA) as the template molecule, MIP particles were synthesized and embedded in a solid paraffin carbon paste to prepare the MIP sensor. MA was indirectly determined from the competition between the reactions of MA and horseradish peroxidase-labeled MA (MA-HRP) with the vacant cavities. The detection signals were amplified because of enzymatic reaction to the H₂O₂ catalytic oxidation. Sensitivity was markedly improved. Sensor renewal was achieved by a simple mechanical polishing of the sensitive film. The linear range for MA detection was 0.005–1 μmol L⁻¹ and the detection limit was 0.7 nmol L⁻¹. The molecularly imprinted solid paraffin carbon paste sensor was used for MA detection in milk samples.     

All‐Inorganic CsPbX3 Perovskite Solar Cells: Progress and Prospects

Recently, lead halide‐based perovskites have become one of the hottest topics in photovoltaic research because of their excellent optoelectronic properties. Among them, organic‐inorganic hybrid perovskite solar cells (PSCs) have made very rapid progress with their power conversion efficiency (PCE) now at 23.7 %. However, the intrinsically unstable nature of these materials, particularly to moisture and heat, may be a problem for their long‐term stability. Replacing the fragile organic group with more robust inorganic Cs⁺ cations forms the cesium lead halide system (CsPbX₃, X is halide) as all‐inorganic perovskites which are much more thermally stable and often more stable to other factors. From the first report in 2015 to now, the PCE of CsPbX₃‐based PSCs has abruptly increased from 2.9 % to 17.1 % with much enhanced stability. In this Review, we summarize the field up to now, propose solutions in terms of development bottlenecks, and attempt to boost further research in CsPbX₃ PSCs.     

基于硫堇掺杂的聚乙烯醇薄膜的光波导传感器检测硫化氢气体

采用旋转甩涂法将硫堇掺杂的聚乙烯醇薄膜固定在K⁺交换玻璃光波导表面,研制出一种高灵敏硫化氢气体传感器。 传感膜与硫化氢(H₂S)气体作用时,薄膜颜色从紫色变为无色,从而降低薄膜对倏逝波的吸收,使传感器的输出光强度（信号）增强。 采用流动注射法对H₂S气体进行检测。 实验结果表明,H₂S传感器对浓度在0.14~56 mg/m3范围的H₂S气体具有良好的线性响应（r=0.99667）,检出限为0.11 mg/m³(S/N=3),相对标准偏差为4.0%,响应时间（t90）＜2 s。 该传感器具有灵敏度高、响应快、可逆性和重复性好等特点。     

Synthesis,crystal structure,absorption properties,photoelectric behavior of organic–inorganic hybrid (CH3NH3)2CoCl4

Lead‐free and organic–inorganic hybrid (CH₃NH₃)₂CoCl₄ [(MA)₂CoCl₄] single crystal and thin film are prepared. The single crystal diffraction data of (MA)₂CoCl₄ are assigned to monoclinic, P2(1)/C space group (7.6590 × 12.6908 × 10.89350 Å, 90.0 × 96.5320 × 90.000). The absorption edge of (MA)₂CoCl₄ reaches 730 nm. The band gap for (MA)₂CoCl₄ is determined to be approximately 1.63 eV. To the best of our knowledge, this is the first study on (MA)₂CoCl₄ for optoelectronic applications. A low‐cost photodetector based on (MA)₂CoCl₄ thin film is efficient under different monochromatic light from 330 nm to 400 nm with different chopping frequencies (1.33–60 Hz). The strongest photoresponse (I_on ? I_off) is under 330 nm monochromatic light with 1.33 Hz according to our optimal condition. The calculational results by density functional theory show that the narrow valence bands and conduction bands are derived from the 3p orbitals of Cl and 3d orbitals of Co.     

Cesium Lead Halide Perovskite Nanostructures: Tunable Morphology and Halide Composition

Inorganic halide perovskite (CsPbX₃) nanostructures have gained considerable interest in recent years owing to their enhanced stability and optoelectronic applications. Recent developments in the synthesis of nanostructures are reviewed. The impact of the precursor and ligand nature, temperature and growth time on the morphology and shape tuning of CsPbX₃ nanostructures is described in relation to their optical properties. The presynthetic and postsynthetic anion exchange strategies to retain pre‐existing crystal phase and shape are discussed in this minireview.     

Correlation amongst gas barrier behaviour,temperature and thickness in BOPP films for food packaging usage: A lab-scale testing experience

Permeability of gases in polymers depends strongly upon the polymer structure, the gas type, as well as the conditions of temperature and film thickness. The in-use temperature and thickness of the polymer membrane can play the most important role on preservation and prolongation of food shelf-life. In this work the gas transmission parameters of six Bi-axially Oriented Polypropylene (BOPP) films were investigated as a function of temperature, gas type and thickness. O₂, CO₂, N₂, N₂O, C₂H₄, Air (79%N₂/21%O₂) and Modified Atmosphere (MA) of 79%N₂O/21%O₂ were used as test gas. In order to understand the kinetic of the process, by the activation energy determination, samples were tested at a different temperature, from 10 °C to 40 °C. Gas Transmission Rate (GTR), solubility (S) and diffusion (D) relationship was investigated. The gas/thickness/temperature correlation was reflected in the obtained perm-selectivity ratios and a good linear correlation was found only at 23 °C. Deviations recorded were attributed to temperature fluctuations. Gas transmission process follows the Arrhenius model while the solubility/diffusion process shows consistent deviation, correlated to the temperature and the thickness of the film. By Differential Scanning Calorimetry (DSC) a different crystallinity percentage was recorded, whose influence was evidenced only in the sorption/diffusion processes. The melting temperature remained unchanged. FT-IR Spectroscopy was also carried out to confirm the morphology.     

Unveiling the Photo- and Thermal-Stability of Cesium Lead Halide Perovskite Nanocrystals

Lead halide perovskites possess unique characteristics that are well-suited for optoelectronic and energy capture devices, however, concerns about their long-term stability remain. Limited stability is often linked to the methylammonium cation, and all-inorganic CsPbX₃ (X=Cl, Br, I) perovskite nanocrystals have been reported with improved stability. In this work, the photostability and thermal stability properties of CsPbX₃ (X=Cl, Br, I) nanocrystals were investigated by means of electron microscopy, X-ray diffraction, thermogravimetric analysis coupled with FTIR (TGA-FTIR), ensemble and single particle spectral characterization. CsPbBr₃ was found to be stable under 1-sun illumination for 16 h in ambient conditions, although single crystal luminescence analysis after illumination using a solar simulator indicates that the luminescence states are changing over time. CsPbBr₃ was also stable to heating to 250 °C. Large CsPbI₃ crystals (34±5 nm) were shown to be the least stable composition under the same conditions as both XRD reflections and Raman bands diminish under irradiation; and with heating the γ (black) phase reverts to the non-luminescent δ phase. Smaller CsPbI₃ nanocrystals (14±2 nm) purified by a different washing strategy exhibited improved photostability with no evidence of crystal growth but were still thermally unstable. Both CsPbCl₃ and CsPbBr₃ show crystal growth under irradiation or heat, likely with a preferential orientation based on XRD patterns. TGA-FTIR revealed nanocrystal mass loss was only from liberation and subsequent degradation of surface ligands. Encapsulation or other protective strategies should be employed for long-term stability of these materials under conditions of high irradiance or temperature.     

The Ti3AlC2 MAX Phase as an Efficient Catalyst for Oxidative Dehydrogenation of n‐Butane

Dehydrogenation or oxidative dehydrogenation (ODH) of alkanes to produce alkenes directly from natural gas/shale gas is gaining in importance. Ti₃AlC₂, a MAX phase, which hitherto had not been used in catalysis, efficiently catalyzes the ODH of n‐butane to butenes and butadiene, which are important intermediates for the synthesis of polymers and other compounds. The catalyst, which combines both metallic and ceramic properties, is stable for at least 30 h on stream, even at low O₂:butane ratios, without suffering from coking. This material has neither lattice oxygens nor noble metals, yet a unique combination of numerous defects and a thin surface Ti_1?yAl_yO_2?y/2 layer that is rich in oxygen vacancies makes it an active catalyst. Given the large number of compositions available, MAX phases may find applications in several heterogeneously catalyzed reactions.     

A thioacetamide additive-based hybrid (MA0.5FA0.5)PbI3 perovskite solar cells crossing 21 % efficiency with excellent long term stability

An additive in hybrid perovskite is playing a vital role in the increment of power conversion efficiency (PCE), stability, and reproducibility of perovskite solar cells (PVSCs). Although, single-phase α-FAPbI₃ perovskite has an ideal band gap but is continuously transforming to δ–FAPbI₃, which is non-photoactive. Here, we controlled the methylammonium (MA) and formamidinium (FA) ratio in the (MA_xFA_1-x)PbI₃ perovskite composition and tuned its morphology with the help of the thioacetamide (TAA) Lewis base additive. The optimum MA:FA ratio and fine-tuning of TAA additive result in a highly crystalline, large grain size and smooth surface of the (MA_0.5FA_0.5)PbI₃ perovskite film. These highly uniform thin films with 850 nm grain size offered a superior interaction between the perovskite material and the electron transport layer (ETL) and a longer lifetime yielding a high PCE. The (MA_0.5FA_0.5)PbI₃+1% TAA-based champion device exhibited the highest PCE of 21.29% for a small area (0.09 cm²) and 18.32% PCE for a large area (1 cm²). The TAA-assisted devices exhibited high stability with >85% retention over 500 h. These results suggest that the (MA_0.5FA_0.5)PbI₃ along with the 1% TAA additive is a promising absorber layer that can produce >21% PCE.     

Nanothin Polyaniline Film for Highly Sensitive Chemiresistive Gas Sensing

This study developed a facile technique for site‐specific synthesis of nanometer‐thick polyaniline (PANI) film for fabrication of field‐effect transistor/chemiresistor sensors. The nanothin film had a thickness of 9–20 nm and was of carpet‐like morphology offering a highly accessible surface geometry that enhanced gas adsorption and promoted surface reaction/interaction. When applied for sensing of ammonia (NH₃) and nitrogen dioxide (NO₂), the performance of the nanothin film device was comparable to that of a 1‐dimensional (1‐D) nanostructure, with a great advantage in ease of processing. Sensing mechanism study indicated electrostatic gating as the dominating mode of sensing.     

Self-assembly of TiO2/polypyrrole nanocomposite ultrathin films and application for an NH3 gas sensor

TiO₂/polypyrrole (PPy) nanocomposite ultrathin films for NH₃ gas detection were fabricated by the in situ self-assembly technique. The films were characterized by UV–Vis absorption, FT–IR spectroscopy, and atomic force microscopy (AFM). The electrical properties of TiO₂/PPy ultrathin film NH₃ gas sensors, such as sensitivity, selectivity, reproducibility, and stability were investigated at room temperature in air as well as in N₂. The results showed that the optimum gas-sensing characteristics of TiO₂/PPy ultrathin film were obtained in the presence of 0.1?wt% colloidal TiO₂ for 20-min deposition. Compared with pure PPy thin-film sensors, the TiO₂/PPy film gas sensor has a shorter response/recovery time. It was also found that both humidity and temperature had an effect on the operation of the TiO₂/PPy film gas sensor at low NH₃ concentrations.     

Selective Etching of Silicon from Ti3SiC2 (MAX) To Obtain 2D Titanium Carbide (MXene)

Until now, MXenes could only be produced from MAX phases containing aluminum, such as Ti₃AlC₂. Here, we report on the synthesis of Ti₃C₂ (MXene) through selective etching of silicon from titanium silicon carbide—the most common MAX phase. Liters of colloidal solutions of delaminated Ti₃SiC₂‐derived MXene (0.5–1.3 mg mL^?1) were produced and processed into flexible and electrically conductive films, which show higher oxidation resistance than MXene synthesized from Ti₃AlC₂. This new synthesis method greatly widens the range of precursors for MXene synthesis.     

Completely Amine-Free Open-Atmospheric Synthesis of High-Quality Cesium Lead Bromide (CsPbBr3) Perovskite Nanocrystals

Cesium lead halide perovskite nanocrystals (NCs) CsPbX₃ (X=Cl, Br, and I) have been prominent materials in the last few years due to their high photoluminescence quantum yield (PLQY) for light-emitting diodes and other significant applications in photovoltaics and optoelectronics. In colloidal CsPbX₃ synthesis, the most commonly used ligands are oleic acid and oleylamine. The latter plays an important role in surface passivation but may also be responsible for poor colloidal stability as a result of facile proton exchange leading to the formation of labile oleylammonium halide, which pulls halide ions out of the NC surface. Herein, a facile, efficient, completely amine-free synthesis of cesium lead bromide perovskite nanocrystals using hydrobromic acid as halide source and tri-n-octylphosphane as ligand under open-atmospheric conditions is demonstrated. Hydrobromic acid serves as labile source of bromide ion, and thus this three-precursor approach (separate precursors for Cs, Pb, Br) gives more control than a conventional single-source precursor for Pb and Br (PbBr₂). The use of HBr paved the way to eliminate oleylamine, and thus the formation of labile oleylammonium halide can be completely excluded. Various Cs:Pb:Br molar ratios were studied and optimum conditions for making very stable CsPbBr₃ NCs with high PLQY were found. These completely amine-free CsPbBr₃ perovskite NCs synthesized under bromine-rich conditions exhibit good stability and durability for more than three months in the form of colloidal solutions and films, respectively. Furthermore, stable tunable emission across a wide spectral range through anion exchange was demonstrated. More importantly, this work reports open-atmosphere-stable CsPbBr₃ NCs films exhibiting strong PL, which can be further used for optoelectronic device applications.     

Direct Conversion of Syngas into Methyl Acetate,Ethanol, and Ethylene by Relay Catalysis via the Intermediate Dimethyl Ether

Selective conversion of syngas (CO/H₂) into C₂₊ oxygenates is a highly attractive but challenging target. Herein, we report the direct conversion of syngas into methyl acetate (MA) by relay catalysis. MA can be formed at a lower temperature (ca. 473 K) using Cu‐Zn‐Al oxide/H‐ZSM‐5 and zeolite mordenite (H‐MOR) catalysts separated by quartz wool (denoted as Cu‐Zn‐Al/H‐ZSM‐5|H‐MOR) and also at higher temperatures (603–643 K) without significant deactivation using spinel‐structured ZnAl₂O₄|H‐MOR. The selectivity of MA and acetic acid (AA) reaches 87 % at a CO conversion of 11 % at 643 K. Dimethyl ether (DME) is the key intermediate and the carbonylation of DME results in MA with high selectivity. We found that the relay catalysis using ZnAl₂O₄|H‐MOR|ZnAl₂O₄ gives ethanol as the major product, while ethylene is formed with a layer‐by‐layer ZnAl₂O₄|H‐MOR|ZnAl₂O₄|H‐MOR combination. Close proximity between ZnAl₂O₄ and H‐MOR increases ethylene selectivity to 65 %.