De-Suo Yang

As a typical cation-exchangeable layered compound, layered titanate has a unique open layered structure. Its excellent physical and chemical properties allow its wide use in the energy, environmental protection, electronics, biology, and other fields. This paper reviews the recent progress in the research on the structure, synthesis, properties, and application of layered titanates. Various reactivities, as well as the advantages and disadvantages, of different synthetic methods are discussed. The reaction mechanism and influencing factors of the ion exchange reaction, intercalation reaction, and exfoliation reaction are analyzed. The latest research progress on layered titanates and their modified products in the fields of photocatalysis, adsorption, electrochemistry, and other applications is summarized. Finally, the future development of layered titanate and its exfoliated product two-dimensional nanosheets is proposed.

An iodine-mediated oxidative [4+1] cyclization of enamines with TMSN₃ for the synthesis of 2,5-disubstituted imidazole-4-carboxylic derivatives has been developed. The mechanistic studies revealed that the reaction proceeds through a sequential removal of two nitrogen atoms from TMSN₃. The synthetic utility was further demonstrated with a gram-scale reaction and various derivatization transformations of the products.

A novel and efficient iron-catalyzed cycloaddition reaction using readily available 2,3-diaryl-2H-azirines and primary amides is reported. A wide range of trisubstituted oxazoles could be achieved in good yields with good functional group compatibility. In this transformation, two C–N bonds were cleaed and new C–N and C–O bonds were formed.

Additive manufacturing technology has attracted unprecedented attention in industry because it provides infinite possibilities for rapid prototyping and enormous potential and opportunities for the production of electronic devices of various complex shapes. This paper focuses on the progress of additive manufacturing of piezoelectric materials in recent years, summarizing the advantages of additive manufacturing technology and its technical impact on the production of piezoelectric materials. It identifies the likely future research development direction of additive manufacturing technology, as well as the limitations of the current additive manufacturing technology in the context of piezoelectric materials. First, the various processes involved in additive manufacturing of piezoelectric devices and the impact of various processes on device performance are systematically summarized. Then, the development of additive manufacturing technology and slurry preparation of piezoelectric ceramic materials, piezoelectric polymer materials, and piezoelectric composites are introduced. Finally, the technical difficulties and potential research directions associated with additive manufacturing of piezoelectric materials are discussed. With the continuous development of additive manufacturing technology and piezoelectric materials, additive manufacturing of piezoelectric devices with excellent performance, high energy storage density, and high electromechanical conversion efficiency will be applied in a wider range of fields in the future.

An IBX-mediated selected oxidative cyclization of N-hydroxyalkyl enamines was developed. Through this strategy, a variety of 2,3-disubstituted pyrroles and pyridines were produced in good selectivity involving oxidation of alcohol, followed by condensation of aldehyde and α-C of enamines. Furthermore, this metal-free method has several advantages, including the use of environment-friendly reagents, broad substrate scope, mild reaction conditions and high efficiency.

A new energetic coordination polymer (ECP) composite, namely GO–Cu(II)–AmTZ, has been synthesized by 3-amino-1,2,4-triazole (AmTZ) and multifunctional graphene oxide (GO) coordination with Cu(II) successively. The ECP composite was further characterized through SEM, EDS and XPS analysis as well as FTIR and Raman spectroscopy. It shows high thermostability, high decomposition heat release and insensitivity to mechanical stimuli. What's more, thermal analysis data for ammonium perchlorate (AP) have been obtained by mechanically mixing GO–Cu(II)–AmTZ and AP. The low-temperature decomposition (LTD, 335.3 °C) and high-temperature decomposition (HTD, 441.3 °C) peaks of AP were reduced to an exothermic peak at 298.4 °C at a heating rate of 10 °C min⁻¹. GO–Cu(II)–AmTZ exhibits outstanding catalytic performance by decreasing the activation energy from 168.7 kJ mol⁻¹ to 122.4 kJ mol⁻¹, indicating its promising application as a combustion catalyst for improving the thermal-catalytic decomposition performance of energetic materials largely. In addition, thermal analysis techniques including thermogravimetry coupled with mass spectrometry (TG/MS) and thermogravimetry coupled with infrared spectrometry (TG/IR) were employed to determine the decomposition mechanisms.

Hybrid halide perovskites are emerging semiconducting materials with a diverse set of remarkable optoelectronic properties. Besides the widely studied lead halide perovskites, Pb-free metal halides such as Bi- and Sb-containing hybrid organic–inorganic materials have shown potential as semiconductors and have been deemed candidates for optoelectronic devices. Here, we report a series of 1D Sb/Bi-based organic–inorganic hybrid alloys: [4ApyH]Sb_xBi_1–xI_yBr_4–y, where 4ApyH stands for the 4-aminopyridine cations. These compounds are assembled by edge-sharing octahedral [MX₆] units stabilizing 1D chains with organic cations filled in between. The crystallographic data of eight selected complexes show that [4ApyH]Sb_xBi_1–xI_yBr_4–y has at least five phases (space group) with the difference metal and halogen content: Pbca ([4ApyH]BiI₄), Pca2₁ ([4ApyH]Sb_0.5Bi_0.5I₄), P2₁/c ([4ApyH]SbI₄ (100 K), [4ApyH]BiI₂Br₂, [4ApyH]BiBr₄, and [4ApyH]SbBr₄ (100 K)), I2/a ([4ApyH]Sb_0.5Bi_0.5I₂Br₂and [4ApyH]SbI₂Br₂), and C2/c ([4ApyH]SbI₄ (298 K) and [4ApyH]SbBr₄ (298 K)). Powder X-ray diffraction shows that the phase of the sample changes with a change of the metal and halogen ratios, and the change law accords with Vegard’s law. The optical band gaps are heavily affected by the metal and halide contents, ranging from 1.94 eV for [4ApyH]BiI₄ to 2.73 eV for [4ApyH]SbBr₄. When Sb substitutes for Bi to form an alloy, the band gap increases from 1.94 for [4ApyH]BiI₄ to 1.67 eV for [4ApyH]SbI₄, from 2.13 eV for [4ApyH]BiI₂Br₂ to 2.41 eV for [4ApyH]SbI₂Br₂, and from 2.55 eV for [4ApyH]BiBr₄ to 2.73 eV for [4ApyH]SbBr₄. The conductivity of [4ApyH]Sb_xBi_1–xI₄ increased from ∼1.00 × 10^–15 to 2.14 × 10^–8 S cm^–1 with an increase of the Sb content. Solution-deposited thin films of the nine complexes show the same (110) orientation, displaying a parallel growth orientation with respect to the substrate. The devices of [4ApyH]Sb_0.8Bi_0.2I₄ and [4ApyH]SbI₄ demonstrated stable open-circuit photovoltages of 0.55 and 0.44 V, steady-state short-circuit photocurrent densities of 1.52 and 1.81 mA cm^–2, and light-to-electrical energy conversion efficiencies of 0.29% and 0.30%, respectively.

Metal halide perovskites have fascinating electronic properties and have already been implemented in various devices. Although the behavior of the properties of lead halide perovskite nanocrystals has been studied, the properties of lead-free perovskite nanocrystals are less well-understood because synthesizing them is still very challenging. Here, a simple and popularizable method has been demonstrated to grow monodisperse bismuth-halide double perovskite nanocrystals, Cs₂AgBiBr₆ (1), inside three kinds of mesoporous silica templates. The size and morphology of nanocrystals depend on the structure and pore size of the template. Structural analysis shows that the nanocrystals of various sizes and morphologies retain the crystal structure of bimetallic perovskite. 1 exhibits different morphologies in the silicon channels of three templates: square nanoparticles in KIT-6, spherical and rodlike particles in SBA-15, and nanowires in MCM-41. UV–vis–NIR and photoluminescence measurements show us the variation of band gap and carrier recombination time due to quantum confinement of nanocrystals in mesoporous silicon materials. The band gaps of nanocrystals in the template exhibit an obvious blue shift compared with that of the bulk sample, and the carrier recombination time is significantly shortened. We show that mesoporous silicon templates can be used to prepare lead-free perovskite nanocrystals, and the controllable preparation of nanocrystals can be achieved by the template’s own characteristics. This provides a new idea for us to find new functional materials of lead-free metal halide solid-state light-emitting diodes.

Brønsted acid-catalyzed allylic substitution reactions of the in-situ generated 3-hydroxy indanones with alcohols and sulfamides were investigated, which provided a facile route for the synthesis of a large variety of 3-alkoxy and 3-sulfamido indanones. The key intermediates, 3-hydroxy indanones, were obtained through intramolecular Meyer-Schuster rearrangement of o-propargyl alcohol benzaldehydes. The resulting 3-benzyloxy indanone could be selectively modified by allylic sulfonamidation and reduction reactions.