Jun Hee Lee

Chromium removal from aqueous solution by a PEI-silica nanocomposite

It is essential and important to determine the adsorption mechanism as well as removal efficiency when using an adsorption technique to remove toxic heavy metals from wastewater. In this research, the removal efficiency and mechanism of chromium removal by a silica-based nanoparticle were investigated. A PEI-silica nanoparticle was synthesized by a one-pot technique and exhibited uniformly well-dispersed PEI polymers in silica particles. The adsorption capacity of chromium ions was determined by a batch adsorption test, with the PEI-silica nanoparticle having a value of 183.7u2009mg/g and monolayer sorption. Adsorption of chromium ions was affected by the solution pH and altered the nanoparticle surface chemically. First principles calculations of the adsorption energies for the relevant adsorption configurations and XPS peaks of Cr and N showed that Cr(VI), [HCrO4]− is reduced to two species, Cr(III), CrOH2+ and Cr3+, by an amine group and that Cr(III) and Cr(VI) ions are adsorbed on different functional groups, oxidized N and NH3+.

Investigation of the mechanism of chromium removal in (3-aminopropyl)trimethoxysilane functionalized mesoporous silica

We are proposed that a possible mechanism for Cr(VI) removal by functionalized mesoporous silica. Mesoporous silica was functionalized with (3-aminopropyl)trimethoxysilane (APTMS) using the post-synthesis grafting method. The synthesized materials were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), N2 adsorption-desorption analysis, Fourier-transform infrared (FT-IR), thermogravimetric analyses (TGA), and X-ray photoelectron spectroscopy (XPS) to confirm the pore structure and functionalization of amine groups, and were subsequently used as adsorbents for the removal of Cr(VI) from aqueous solution. As the concentration of APTMS increases from 0.01u2009M to 0.25u2009M, the surface area of mesoporous silica decreases from 857.9u2009m2/g to 402.6u2009m2/g. In contrast, Cr(VI) uptake increases from 36.95u2009mg/g to 83.50u2009mg/g. This indicates that the enhanced Cr(VI) removal was primarily due to the activity of functional groups. It is thought that the optimum concentration of APTMS for functionalization is approximately 0.05u2009M. According to XPS data, NH3+ and protonated NH2 from APTMS adsorbed anionic Cr(VI) by electrostatic interaction and changed the solution pH. Equilibrium data are well fitted by Temkin and Sips isotherms. This research shows promising results for the application of amino functionalized mesoporous silica as an adsorbent to removal Cr(VI) from aqueous solution.

Enhanced efficiency in lead-free bismuth iodide with post treatment based on a hole-conductor-free perovskite solar cell

Despite the excellent merits of lead perovskite solar cells, their instability and toxicity still present a bottleneck for practical applications. Bismuth perovskite has emerged as a candidate for photovoltaic (PV) applications, because it not only has a low toxicity but is also stable in air. However, the power conversion efficiency (PCE) remains an unsolved problem. We performed band gap tuning experiments to improve the efficiency. The absorption of ABi3I10 structure films was extended within the visible region, and the optical band gap was decreased considerably compared to that for Cs3Bi2I9. Furthermore, we explained the correlation between the structure and the optical properties via a first-principles study. A device employing CsBi3I10 as a photoactive layer exhibits a PCE of 1.51% and an excellent ambient stability over 30 days.

Solution-derived glass-ceramic NaI·Na3SbS4 superionic conductors for all-solid-state Na-ion batteries

Bulk-type all-solid-state Na-ion batteries (ASNBs) employing inorganic Na-ion conductors and operating at room temperature are considered as promising candidates for large-scale energy storage systems. However, their realization has been impeded by low ionic conductivity, instability in air of the solid electrolytes, and poor ionic contacts among the constituents of the electrodes. Here, we report novel glass-ceramic xNaI·(1 − x)Na3SbS4 superionic conductors (maximum Na+ conductivity of 0.74 mS cm−1 at 30 °C, for x = 0.10) obtained from scalable methanol solutions. Comprehensive spectroscopic evidence, density functional theory calculations, and electrochemical analysis suggest the decisive role of I− incorporated in the disordered domains at the nanoscale in the overall Na+ transport. Furthermore, the solution-derived NaI·Na3SbS4 forms uniform coating layers on the surface of the active material FeS2, providing unobstructed ionic transport pathways in the electrodes. The good electrochemical performance of FeS2/Na–Sn ASNBs at 30 °C is demonstrated.