Crystal Phase and Morphology-Controlled Synthesis of Tungsten Oxide Nanostructures for Remarkably Ultrafast Adsorption and Separation of Organic Dyes.

Simple inorganic routes for the synthesis of WO3 nanostructures with variable crystal phases, WO3·(H2O)0.5 and (NH4)0.33WO3, and their self-assembled structures as nanoplates and nanospheres, respectively, were reported. The morphologies and formation of nanoplates and nanospheres were controlled by changing the solvent amount (H2O/n-propanol) in the solvothermal reactions without any stabilizing agent or surfactant. The adsorption properties of the WO3 nanostructures were studied, and it was found that nanospheres show remarkably higher and ultrafast adsorption of methylene blue (MB) in comparison to nanoplates and commercial WO3. The adsorption isotherms, kinetics, mechanism, and reusability of (NH4)0.33WO3 nanospheres were systematically studied. The nanospheres exhibited an exceptionally high adsorption rate K2 of 17.24 g·mg-1·min-1 and the maximum adsorption capacity of 116 mg·g-1 for MB. The adsorption cycle of nanospheres was examined, and the removal efficiency of MB remained at ∼98-99% even after three regeneration cycles. In addition, (NH4)0.33WO3 nanospheres exhibited excellent selective adsorption performance toward several cationic dyes, including MB, malachite green (MG), safranin O (SO), crystal violet (CV), and separate MO, a negatively charged dye, with a separation efficiency of 99.93 and 77.31% from binary and pentanary dye mixture solutions, respectively, at neutral pH.

An Organic-Inorganic Perovskitoid with Zwitterion Cysteamine Linker and its Crystal-Crystal Transformation to Ruddlesden-Popper Phase.

We demonstrate synthesis of a new low-D hybrid perovskitoid (a perovskite-like hybrid halide structure, yellow crystals, P21/n space group) using zwitterion cysteamine (2-aminoethanethiol) linker, and its remarkable molecular diffusion-controlled crystal-to-crystal transformation to Ruddlesden-Popper phase (Red crystals, Pnma space group). Our stable intermediate perovskitoid distinctly differs from all previous reports by way of a unique staggered arrangement of holes in the puckered 2D configuration with a face-sharing connection between the corrugated-1D double chains. The PL intensity for the yellow phase is 5 orders higher as compared to the red phase and the corresponding average lifetime is also fairly long (143 ns). First principles DFT calculations conform very well with the experimental band gap data. We demonstrate applicability of the new perovskitoid yellow phase as an excellent active layer in a self-powered photodetector and for selective detection of Ni2+ via On-Off-On photoluminescence (PL) based on its composite with few-layer black phosphorous.

Scalable Mechanochemical Synthesis of ß-Ketoenamine-linked Covalent Organic Frameworks for Methane Storage.

In the current scenario of increased pollution and releasing toxic gases by burning petroleum products, switching to natural gas is more promising for reducing CO2 emissions and air pollutants. Hence, research on Liquefied Natural Gas and Compressed Natural Gas is gaining more value. However, natural gas primarily consists of CH4 , which has less energy density than conventional fuels. Interestingly, since the C-H ratio of CH4 gas is 1 : 4, it is easily combustible, gives less carbon footprint, and reduces unburnt hydrocarbon pollution. Hence, research on storing and transporting CH4 has utmost importance, and porous materials are one of the suitable candidates for storing CH4 . Herein we report the scalable synthesis of highly porous and crystalline covalent organic frameworks for storing CH4 at room temperature and pressure. Two COFs, namely, Tp-Azo and Tp-Azo-BD(Me)2 , synthesized in 1 kg at ∼45 g batch scale using a Planetary mixer, displayed a maximum BET surface area of around 3345 m2 /g, and 2342 m2 /g and CH4 storage of 174.10 cc/cc and 151 cc/cc, respectively. A comparison of the CH4 sorption of Tp-Azo and Tp-Azo-BD(Me)2 COFs synthesized in different batches has a variation of only ±5 cc/cc and shows the consistency in bulk scale synthesis of COFs. The cyclic equilibrium CH4 adsorption studies showed the COFs are stable with consistent CH4 adsorption and desorption cycles. The present study is a step towards the scalable mechanochemical synthesis of COFs for gas storage applications.