Amit Adhikary
Missouri University of Science and Technology, USA
Title: Unusual atmospheric water capture and reversible structural transformation OF NaGaS2
Biography
Biography: Amit Adhikary
Abstract
A newly synthesized ternary sulfide composition, NaGaS2 (1) has remarkable ability to capture atmospheric water molecules. The absorption of water was verified by PXRD, TG analysis, FT-IR and XPS studies. The process of water absorption leads to stable distinct material NaGaS2• ~H2O (2), the structure of which is different from original crystal structure of anhydrous phase. Interestingly the transformed structure 2 can go back to original structure 1 by simple heating under inert atmosphere, unveiling reversibility of structural transformation. Single crystal XRD study shows adamantane like Ga4S10 super tetrahedral units form the fundamental building unit of the structure and further corner sharing between these units forms the [GaS2]–∞ layers. The charge-balancing Na ions are present in between the layers. Moreover, structural transformation also effects the physical properties as initial compound 1 possesses Na+ ion conductivity of 1.49 x 10-7 S cm-1 at 22°C with Ea of 0.14 eV whereas 2 displays ion conductivity of 1.85 x 10-8 S cm-1 at 23°C with Ea of 0.19 eV. Experimental DRS study shows an optical band gap of 2.40 eV which closely corroborates with the theoretical band gap of 2.35 eV obtained by DFT-based band structure calculation. Vapor sorption studies indicate exclusively adsorption of water over MeOH, EtOH and CH3CN, revealing ‘Single Molecule Trap’1 behavior with maximum water uptake of 372 cm3 g-1 at P/P0 = 0.9.2 DFT calculations3 reveal that exergonic hydration reaction takes place outlined as NaGaS2 + H2O → NaGaS2•H2O with the energy release ΔE of -73.9 kJ.mol-1.