Topochemical polymerization of hydrogen-bonded organic framework for supporting ultrafine palladium nanoparticles

Topochemical polymerization of molecular crystals into porous materials is of significance due to their promising applications in the field of adsorption and catalysis,yet rarely reported due to the synthesis difficulty.Herein,a hydrogen-bonded organic framework(HOF-45)has been fabricated by the crystallization of a cage-like building block containing three alkynyl groups.It exhibits almost mesoporous structure demonstrated by single crystal X-ray diffraction study.Light-driven topochemical polymerization of HOF-45 with ethanedithiol covalently links alkynyl groups in HOF-45,generating a hydrogen-bond and covalentbond cross-linked material(HOF-45C).In contrast to HOF-45,cross-linked HOF-45C retains the crystalline nature and displays improved solution resistence according to the powder X-ray diffraction data.In particular,HOF-45C is able to support the growth of ultrafine palladium nanoparticles with the average size of ca.1.9 nm for rapidly promoting the degradation of nitrophenol,methyl orange,and congo red with the help of NaBH_(4)as well as Suzuki-Miyaura coupling reaction.This work inputs a new idea on the HOFs application in preparing covalent-linked porous organic materials.

Silicon-based nanosheets synthesized by a topochemical reaction for use as anodes for lithium ion batteries

Silicon is the most promising anode material for the next generation high- performance lithium ion batteries. However, its commercial application is hindered by its poor performance due to the huge volume change during cycling. Although two-dimensional silicon-based materials show significantly improved performance, flexible synthesis of such materials is still a challenge. In this work, silicon-based nanosheets with a multilayer structure are synthesized for the first time by a topochemical reaction. The morphology and oxidation state of these nanosheets can be controlled by appropriate choice of reaction media and oxidants. Benefiting from the hierarchical structure and ultrathin size, when the silicon-based nanosheets are employed as anodes they exhibit a charge （delithiation） capacity of 800 mAh/g after 50 cycles with a maximum coulombic efficiency of 99.4% and good rate performance （647 mAh/g at 1 A/g）. This work demonstrates a novel method for preparing nanosheets not only for lithium ion batteries but also having various potential applications in other fields, such as catalysts, electronics and photonics.

Block copolymer assisted topochemical polymerization:A facile and efficient route to robust polymeric nanoporous membranes decorated with versatile amino acids

Based on block copolymer assisted topochemical polymerization,a new strategy for facilely producing robust nanoporous membranes with controlled incorporation of functional groups onto nanopores is developed.As exemplified by preparing nanoporous polypyrrole decorated with amino acids,this strategy exhibits a high degree of freedom for tailoring the surface functionality in the created pores.

Synthesis of NiFe2O4 Nanowires with NiO Nanosheet as Precursor via a Topochemical Solid State Method

Large scale NiFe2O4 nanowires were synthesized with NiO nanosheets as precursor by means of the topochemical solid state method. The morphologies and magnetic properties of NiFe2O4 annealed at different temperatures were studied. An appropriate annealing temperature was requested to transfer NiO nanosheets and Feions into NiFe2O4 nanowires. In the beginning stage of synthesizing process, the shape ofNiO nanosheets remained unchanged at low temperatures. And then, NiO nanosheets split into nanowires from 400 ℃ to 600 ℃. At last they transformed into nanoparticles from 700 ℃ to 1000 ℃. Thus, the optimized annealing temperature was selected as 600 ℃ because the NiFe2O4 obtained at 600 ℃（N600） exhibited a maximum aspect ratio of 50 with a diameter of 20 nm and a length of 1 μm. Furthermore, N600 also displayed the largest magnetization value of 26.86 A·m^2/kg and the lowest coercivity（Hc） of 8914 A/m.

Topochemical polymerization of diphenyldiacetylene-based materials and the relevant application in photocatalysis

The diphenyldiacetylene （DPDA） and the corresponding polymers has become one of hot research topics in the field of functional materials, due to its highly π-conjugated system and outstanding electrochemical properties. Compared with routine polydiacetylenes, polydiphenyldiacetylene （PDPDA） has wider π-extension within the whole polymer structure and a larger internlolecular stacking tendency. Since the preorganization of monomers is essential for the topochemical polymerization, we here introduce several self-assembled methods and external-templated methods for the proper alignment of DPDA. From the perspective of morphology, the monomer structures and external templates are two of the important factors towards polymerization. Based on its structure, PDPDA can become a promising intelligent material for various optoelectical applications, and specifically we summarize the application of PDPDA as an effective phtocatalyst in organic pollutants degradation

Morphology-controlled synthesis of SrTiO_3 micro-scale particles

A novel and simple strategy of morphology-controlled Sr Ti O3（ST） micro-scale particle synthesis by the flux method is reported. Systematic experiments are designed to realize the tunable morphologies of the particles when the flux salt,sintering process, and the precursors are changed. The ST plates can be synthesized by plate-like Bi4Ti3O12（BIT） precursors in Na Cl flux. However, the as-synthesized Bi4Ti3O12 grains transform into reticular particles and finally into rods at higher temperature in Na Cl and KCl compounds. Besides, cubic ST particles are also prepared using different precursors as a comparative experiment. This study provides a strategy for further investigations in designing the morphology-controlled particles and efficient anisotropic materials of perovskite structure such as ferroelectric and photocatalyst.

Defect-manipulated magnetoresistance and above-room-temperature ferromagnetism in two-dimensional BaNi_(2)V_(2)O_(8)

The intricate correlation between multiple degrees of freedom and physical properties is a fascinating area in solid state chemistry and condensed matter physics.Here,we report a quantum-magnetic system BaNi_(2)V_(2)O_(8)(BNVO),in which the spin correlation was modulated by unusual oxidation state,leading to different magnetic behavior.The BNVO was modified with topochemical reduction(TR)to yield TR-BNVO with partially reduced valance state of Ni^(+)in the two-dimensional NiO_(6)-honeycomb lattice.Accordingly,the antiferromagnetic order is suppressed by the introduction of locally interposed Ni^(+)and oxygen vacancies,resulting in a ferromagnetic ground state with the transition temperature up to 710 K.A positive magnetoresistance(7.5%)was observed in the TR-BNVO at 40 K under 7 T.These findings show that topological reduction is a powerful approach to engineer low-dimensional materials and accelerate the discovery of new quantum magnetism.

Ultrathin nanosheets of Mn3O4： A new two-dimensional ferromagnetic material with strong magnetocrystalline anisotropy

Two-dimensional （2D） materials with robust ferromagnetism have played a key role in realizing next- generation spin-electronic devices, but many challenges remain, especially the lack of intrinsic ferro- magnetic behavior in almost all 2D materials. Here, we highlight ultrathin Mn3O4 nanosheets as a new 2D ferromagnetic material with strong magnetocrystalline anisotropy. Magnetic measurements along the in-plane and out-of-plane directions confirm that the out-of-plane direction is the easy axis. The 2D-confined environment and Rashba-type spin-orbit coupling are thought to be responsible for the magnetocrystaUine anisotropy. The robust ferromagnetism in 2D MnaO4 nanosheets with magne- tocrystalline anisotropy not only paves a new way for realizing the intrinsic ferromagnetic behavior in 2D materials but also provides a novel candidate for building next-generation spin-electronic devices.

Enhancing sodium-ion storage performance of MoO/N-doped carbon through interfacial Mo–N–C bond

Na-ion batteries(SIBs)have attracted considerable attention as promising alternatives to commercial Li-ion batteries(LIBs)due to comparable redox potential,and natural abundance of Na.However,it remains challenging to explore suitable anodes for SIBs.Herein,a MoO2/N-doped carbon(MoO2/N-C)composite composed of MoO2 nanocrystals embedded within carbon matrix with a Mo–N–C chemical bond is prepared by a simple yet effective carbonization-induced topochemical transformation route.Na-ion half-cells using MoO2/N-C exhibit excellent cycling stability over 5000 cycles at 5 A g^-1 and superior rate capability.Physicochemical characterizations and first-principles density functional theory(DFT)simulations reveal that the formation of chemical bond at the interface between MoO2 and N-doped carbon plays an important role in the excellent charge storage properties of MoO2/N-C.More importantly,the interfacial coupling can efficiently promote interface charge transfer.Benefiting from this,Na-ion capacitors(SICs)constructed with the MoO2/N-C anode and activated carbon cathode can deliver an impressive energy density of 15 W h kg^-1 at a power density of 1760 W kg^-1,together with a capacitance retention of 92.4%over 1000 cycles at 10 A g^-1.The proposed strategy in this paper based on interfacial chemical bond may hold promises for the design of high-performance electrodes for energy storage devices.

Incubation of PbSe Thin Films in a Tin(Ⅱ) Salt Aqueous Solution:Modification and Ion-Exchange Reactions

Topochemical ion-exchange reactions between solid micro- and nanostructured metal chalcogenides and aqueous salt solutions are generally used for formation of composite structures based on initial metal chalcogenides and products of their ion-exchange transformation. However, ion exchange has promises as a route to obtaining both composites and solid solutions based on the initial and the end chalcogenide phases. With the help of the ion-exchange technique, single-phase films of Phi xSnxSe substitutional solid solutions with a tin content up to -2 at.%, which are promising for mid- and long-wavelength infrared radiation （IR） optoelectronics, have been obtained at the interface between PbSe poly- crystalline thin films and SnCl2 aqueous solutions containing sodium citrate. It has been shown that the pH value and temperature of the reaction system play an important role in the ion-exchange process. Incubation of lead selenide （PbSe） films in a tin（II） salt aqueous solution also leads to their modification with oxygen-containing tin compounds to a depth of-3 nm. Differences in the film structure, such as changes in the coherent scattering region sizes and orientation of crystallites along the [220] direction, which arise during the contact with citrate-containing SnCl2 solutions, have also been revealed. For the first time, an idea of the existence of a relatively wide reaction zone of an intragranular topochemical ion-exchange reaction in an aqueous solution, within which substitutional solid solutions can form in micro- and nanostructured systems, has been set forth.