Three-Dimensional Perovskite Phase Transition Materials with Switchable Second Harmonic Generation Properties Introduced by Homochiral (1S,4S)-2,5-Diazabicyclo[2.2.1]-heptane.

Switchable second harmonic generation (SHG) materials have potential applications in information storage, signal processing, and so on because they can switch between SHG-on and SHG-off states. In this work, we designed and synthesized three organic-inorganic hybrid Rb halide three-dimensional (3D) perovskite materials [1S,4S 2,5-2.2.1-H2dabch]RbX3·0.5H2O (X = Cl, 1; Br, 2; I, 3) based on the chiral 1S,4S-2,5-diazabicyclo[2.2.1]heptane (1S,4S-2,5-2.2.1-dabch). The selection of homochiral organic cations ensures that the compounds 1∼3 crystallize in the noncentrosymmetric and chiral space group P212121, which further leads to reversible SHG responses of the three compounds. Through differential scanning calorimetry (DSC) and dielectric measurements, it revealed that the phase transition point of the compounds 1∼3 increased with RbCl, RbBr, and RbI. This is because the hydrogen interaction H···X between the inorganic framework [RbX3]n and the organic cation [1S,4S-2,5-2.2.1-H2dabch]2+ is increased with the order of I > Br > Cl. This study can provide an effective molecular design strategy for the exploration and construction of temperature-tunable SHG switching materials.

Precise design and preparation of two 3D organic-inorganic perovskite ferroelectrics (1,5-diazabicyclo[3.2.2]nonane)RbX3 (X = Br, I).

Compared with the spherical molecule 1,4-diazoniabicyclo[2.2.2]-octane (2.2.2-dabco), 1,5-diazabicyclo[3.2.2]nonane (3.2.2-dabcn) bears a lower symmetry and larger size. As expected, reactions of 3.2.2-dabcn with rubidium halides gave two 3D molecular ferroelectrics [3.2.2-H2dabcn]RbX3 (X = Br for 1; X = I for 2) with Tc at 342 K (1) and 293 K (2).

The Role of Fluorine-Substituted Positions on the Phase Transition in Organic-Inorganic Hybrid Perovskite Compounds.

Although research on organic-inorganic hybrid perovskites (OIHPs) has grown exponentially in the past two decades, the high phase transition temperature of OIHP materials is still one of the insurmountable difficulties. Herein, a series of A2BX4 type OIHP materials [(2,n-DFBA)2PbCl4] (n = 3, for 1; n = 4, for 2; n = 5, for 3; n = 6, for 4) have been prepared by reactions of double-substituted difluorobenzylamine (difluorobenzylamine = DFBA) with lead chloride in concentrated HCl aqueous solution. It was found the OIHP compounds 1-3 proceed a switchable phase transition with phase transition temperatures (Tc) at 449 K (1), 462 K (2) and 500 K (3), higher than that of the parent compound [(BA)2PbCl4] (BA = benzylammonium) at 438 K, but compound 4 exhibits no phase transition. A crystal structure analysis elucidated that the organic template ligands DFBA lead in the inorganic part in compounds 1-3 to a two-dimensional (2D) perovskite structure, while that in compound 4 leads to a one-dimensional (1D) chain structure. The different double-substituted positions of fluorine atoms on benzylamine have important influences on the phase transition in compounds 1-4.

Flue gas desulfurization (FGD) steel slag ameliorates salinity, sodicity, and adverse physical properties of saline-sodic soil of middle Yellow River, China.

Saline-sodic soil is considered the most important low-yield soil in arid and semi-arid regions. Flue gas desulfurization (FGD) steel slag is a kind of by-product from wet FGD process, in which steel slag powder replaces lime as sorbent of SO2 emitted from coal-fired power plants. It could potentially be used to ameliorate saline-sodic soil. In this study, a large-scale field experiment of applying FGD steel slag as a new amendment of saline-sodic soils was conducted in the middle Yellow River, Inner Mongolia, China. The FGD steel slag was applied at a rate of 180 t/ha in 2015, 2016, and 2018, respectively. After FGD steel slag application for 1, 3, and 4 years, the soil samples were collected. The saline-sodic field without FGD steel slag amendment was used as the control treatment (CK). Compared with control, the application of FGD steel slag significantly (p < 0.05) decreased soil pH, electric conductivity (EC), salt content, sodium adsorption ratio (SAR), and exchangeable sodium percentage (ESP) of surface soil in saline-sodic soil. However, FGD steel slag increased the EC and salt content at the lower depth of soil profile because of the salt accumulation leached from surface soil. The FGD steel slag significantly increased the concentration of Ca2+ and reduced the concentrations of Na+, Cl-, CO32-, and HCO3- ions. FGD steel slag was beneficial for improving adverse physical properties of saline-sodic soil. The application of FGD steel slag significantly reduced the plastic index, tensile strength, and the formation of cracking in saline-sodic soil. The FGD steel slag reduced surface area density of crack (Dc) and average crack width (AW) by 49.1% and 58.7%, compared with the control. The reduction of soil cracking was contributed to the release of Ca2+ from FGD steel slag to exchange the Na+ on the soil cation exchange sites, which decrease the clay dispersion in soil. The findings of this study confirmed that FGD steel slag could effectively and rapidly remediate saline-sodic soils through decreasing soil sodicity and improving poor physical properties.