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Integrating multiple switching behaviors in a single material is conducive to the development of smart devices, but still faces challenges, especially in finding new types of multiresponsive materials. Hybrid metal halides have been becoming promising candidates with the potential to exhibit changes in various physical and chemical properties upon structural phase transitions. Herein, a pair of enantiomers (R/S‐3‐OHPD)PbI3 (1R/1S; 3‐HOPD = 3‐hydroxypiperidine cation) is reported to show multichannel switching behaviors around room temperature triggered by a combined order‐disorder and displacive type phase transition that arouses a large lattice reorganization and shape change of the crystals. Owing to the inherent chiral, noncentrosymmetric, and semiconducting characteristics of the compounds, five other switching behaviors are realized besides the macroscopic deformation, that is, enthalpy, dielectric permittivity, photoluminescence, circularly polarized light excited photoluminescence, and photoelectric response. This study provides an exciting example of phase transition crystals for the development of integrated multifunctional materials. [ABSTRACT FROM AUTHOR]

Multiferroics refer to materials with two or more ferroic orders in one phase within a specific temperature range, including ferroelectricity, ferroelasticity, and ferromagnetism which have been widely used in sensors, actuators, and memory devices. Among them, hybrid perovskites exhibiting multiferroicity are generally limited to low dimensions (0D–2D). Designing 3D lead‐free perovskite multiferroics remains a challenge due to Goldschmidt's tolerance factor limitation. Here, a multiferroic perovskite (R‐3AP)RbBr3 (1; 3AP = 3‐ammoniopyrrolidinium) is successfully synthesized by introducing homochirality to the 3D ferroelectric (Rac‐3AP)RbBr3, achieving both ferroelasticity and ferroelectricity. Compound 1 undergoes a structure phase transition at 401 K belonging to Aizu notation 432F2(s), which has 12 ferroelectric equivalent polarization directions and 6 polar axes. Furthermore, 1 exhibits reversible second harmonic generation switching effects. Moreover, while the temperature varies, the reversible and rapid changes of ferroelastic domains in 1 are observed using a polarizing microscope, indicating that it is a ferroelastic material. This work provides a practical method for designing and synthesizing molecule‐based multiferroics. [ABSTRACT FROM AUTHOR]

Hybrid metal halides (HMHs) based phase transition materials have received widespread attention due to their excellent performance and potential applications in energy harvesting, optoelectronics, ferroics, and actuators. Nevertheless, effectively regulating the properties of phase transitions is still a thorny problem. In this work, two chiral lead‐free HMHs (R‐3FP)2SbCl5 (1; 3FP=3‐fluoropyrrolidinium) and (R‐3FP)2SbBr5 (2) were synthesized. By replacing the halide ions in the inorganic skeleton, the phase transition temperature of 2 changes with an increase of about 20 K, compared with 1. Meanwhile, both compounds display reversible dielectric switching properties. Through crystal structure analysis and Hirshfeld surface analysis, their phase transitions are ascribed to the disorder of the cations and deformation of the inorganic chains. [ABSTRACT FROM AUTHOR]

The thickness dependence of cadmium telluride/cadmium selenide (CdTe/CdSe) heterojunctions is studied in order to maximize the performance of solar cells. The best overall performance of 3.02% efficiency at air mass 1.5 was achieved from a device with 300 nanometers (nm) of sintered CdTe and 100 nm CdSe, using indium tin oxide and evaporated aluminum as the electrodes. In contrast to thin film CdTe solar cells, the power efficiency was strongly dependent on the thickness of the nanoparticle layer, indicating that the device efficiency is limited by charge transport. [ABSTRACT FROM AUTHOR]

A variety of N-substituted 3-aminocyclohex-2-enones were converted into the corresponding N-arylated α-iodo enaminones in high yields via concurrent α-iodination and N-arylation mediated by ArI(OAc)2. A mechanism is postulated to account for the reaction differences between the cyclic and the acyclic β-enamin�ones, which undergo predominant α-acetoxylation under the same reaction conditions. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs), with their regularly organized structures and solvent resistance, offer distinct advantages for constructing liquid-phase separation membranes. In nearly a decade of development, research has mainly focused on two-dimensional (2D) COFs, which yet give insufficient molecular selectivity due to inherent large pores. Here, we present a mixed-dimensional strategy of growing three-dimensional (3D) COFs on 2D COFs to build bilayered membranes for efficient organic solvent nanofiltration (OSN). The pores of 3D COFs interlace with those of 2D counterparts, resulting in a subnanoporous composite. We develop this 3D-/2D-COFs composite as robust membranes with a nanoscale thickness. The optimal bilayered membrane yields ethanol permeance of 12.2 L m−2 h−1 bar−1 with a molecular weight cutoff as low as ∼400 g mol−1, surpassing conventional COF-based OSN membranes. Importantly, the designed 3D-/2D-COFs membrane exhibits stable separation performance and excellent sieving ability to discriminate molecular mixtures. This exceptional molecular selectivity ultimately allows the separation of bioactive pharmaceuticals from impurities through our membrane. Overall, this work provides a design strategy for producing mixed-dimensional COF membranes to advance molecular separation in liquids. [Display omitted] • Mixed-dimensional covalent organic framework composites show reduced pore sizes. • Robust membranes of mixed-dimensional covalent organic frameworks are developed. • The optimal membrane exhibits high molecular selectivity with substantial permeances. • Our membrane performs high-selectivity purification of pharmaceuticals from impurities. [ABSTRACT FROM AUTHOR]

Covalent organic polymers (COPs) with abundant micropores are deemed as promising materials for building molecular separation membranes. In spite of this potential, fabricating COP separation membranes through an efficient and scalable method remains a significant challenge. Herein, we report a simple and efficient strategy for the synthesis of COP membranes with three-dimensionally interconnected micropores. Utilizing transition-metal nitrates as a catalyst, we achieve fast polymerization of amorphous COPs with relatively uniform micropores (0.7 nm in diameter). The rational design of organic-aqueous interface allows for the direct fabrication of robust COP membranes with an ultrathin thickness of ∼20 nm on porous polyacrylonitrile substrates. The resulting hydrophobic but pore-uniform frameworks in these membranes permit fast permeation of organic liquids with a notable molecular weight cutoff of 388 g mol−1 in ethanol. To demonstrate scalability, we show that our strategy can produce large-size COP membranes with a prominent area of 200 cm2, which exhibit performances similar to that of small membrane coupons. The present study offers a potentially scalable method for producing highly microporous COP membranes toward efficient molecular separation in organic liquids. [Display omitted] • A three-dimensional COP with uniform and subnanometer pores is synthesized. • Ultrathin COP membranes are rapidly prepared at ambient conditions. • The optimal COP membrane shows high selectivities with decent solvent permeances. • We produce large-size COP membranes without losing their separation performance. [ABSTRACT FROM AUTHOR]

Permanently microporous materials have evolved as focal point of research for tackling issues in separation science and membrane technology. Covalent organic frameworks (COFs) stand out for their distinctive synergy of crystalline nature, uniform channels, and structural diversities. Three-dimensional (3D) COFs, distinguished by angstrom-sized and interconnected channels, hold special promise for separating small targets; however, this potential remains underexplored. Here, we report feasible growth of cationic 3D COF membranes on a flexible polymer substrate for versatile nanofiltration toward both molecules and ions. Through comprehensive performance evaluations, we reveal that the resultant membrane exhibits durable and prominent molecular selectivity to separate fine species with molecular weights above 300 g mol−1 at fast methanol permeation. Lanthanide ions of industrial value also can be harvested by the membrane with rejection rates of up to 91.4%. Together with its nonselectivity to competing ions, our membrane implements efficient extraction of rare earth elements from ion mixtures. These findings illuminate the potential of 3D COFs for liquid separation and offer a solution to building versatile membranes. [Display omitted] • A cationic three-dimensional covalent organic framework membrane is prepared. • The membrane shows exceptional molecular selectivity with high methanol permeance. • Efficient sieving of small molecules is achieved by the membrane. • Our membrane performs selective separation of rare earth elements. [ABSTRACT FROM AUTHOR]

Microporous polyamide membranes that allow lithium ions to pass through easily but exclude magnesium ions hold vast potential in the lithium extraction from brine lakes. The efficacy, nevertheless, has long been limited by a trade-off that the magnesium/lithium selectivity is received at the expense of the permeability, arising from the highly cross-linked polyamide. This work describes that rationally lowering the internal density of polyamides by embedding functionalized covalent organic framework (COF) nanosheets can boost the selectivity and permeability simultaneously. A cationic COF, TpTG Cl , is used to build transport highways in membranes, which shows the double role that not only lowers the polyamide density in a controllable way, but also strengthens the positive charge property. The resulting membrane exhibits a large water permeance of 19.6 L m−2 h−1 bar−1, along with an excellent separation factor of up to 21.3 under a high magnesium/lithium ratio of 30. This engineering strategy offers a means by which charged and nanoporous two-dimensional frameworks can be leveraged as a booster for microporous membranes enabling fast and precise ion transports. [Display omitted] • COF nanosheets are embedded in polyamides to build transport highways. • Polyamide density is lowered and positive charge property is strengthened. • Membranes show large permeance and high Mg2+/Li+ separation factor. • Membranes have the ability to process highly concentrated Mg2+/Li+ brines. [ABSTRACT FROM AUTHOR]

Tight ultrafiltration (TUF) membranes featuring specific pore sizes are increasingly developed to bridge the gap between nanofiltration and ultrafiltration. So far, a wealth of efforts has been devoted to tackle the limitation found in TUF, but there still lacks a facile accessibility to upgrade TUF membranes with simultaneously improved permeance and selectivity. Herein, we report a large-pore covalent organic framework (LP-COF) as the building material to prepare ultra-permeable TUF membranes for fast separations. The LP-COF layers with an exceptionally large aperture size of up to ~3.6 nm are synthesized on macroporous substrates through a unidirectional diffusion method. The resultant LP-COF layers show a moderate crystallinity and low thickness down to ~60 nm, and allow ultrafast water permeation. Surprisingly, the optimal LP-COF membrane exhibits an unprecedented water permeance of ~3147 L m−2 h−1 MPa−1 with a high Congo red rejection (~92.6%), which is basically unchanged after several cycles of filtration. Moreover, the large-pore channels enable an unimpeded pass of ions, thus affording the membrane an excellent dye/salt separation competence, and largely exceeding state-of-the-art membranes. Therefore, this work opens up a new opportunity in producing high-performance TUF membranes by large-pore COFs for rapid and precise separations. [Display omitted] • A large-pore covalent organic framework (LP-COF) is designed to prepare TUF membranes. • Local nucleation and interfacial polymerization collectively promote the growth of ultrathin LP-COF layers. • Ordered channels of LP-COF membranes promise fast separations with high selectivities. • The optimized LP-COF membrane shows a preeminent dye/salt separation performance. • The extraction of nanoparticles from aggressive solvents is realized by the LP-COF membrane. [ABSTRACT FROM AUTHOR]