Synergistic Surface Modification for High-Efficiency Perovskite Nanocrystal Light-Emitting Diodes: Divalent Metal Ion Doping and Halide-Based Ligand Passivation.

Surface defects of metal halide perovskite nanocrystals (PNCs) substantially compromise the optoelectronic performances of the materials and devices via undesired charge recombination. However, those defects, mainly the vacancies, are structurally entangled with each other in the PNC lattice, necessitating a delicately designed strategy for effective passivation. Here, a synergistic metal ion doping and surface ligand exchange strategy is proposed to passivate the surface defects of CsPbBr3 PNCs with various divalent metal (e.g., Cd2+ , Zn2+, and Hg2+ ) acetate salts and didodecyldimethylammonium (DDA+ ) via one-step post-treatment. The addition of metal acetate salts to PNCs is demonstrated to suppress the defect formation energy effectively via the ab initio calculations. The developed PNCs not only have near-unity photoluminescence quantum yield and excellent stability but also show luminance of 1175 cd m-2 , current efficiency of 65.48 cd A-1 , external quantum efficiency of 20.79%, wavelength of 514 nm in optimized PNC light-emitting diodes with Cd2+ passivator and DDA ligand. The "organic-inorganic" hybrid engineering approach is completely general and can be straightforwardly applied to any combination of quaternary ammonium ligands and source of metal, which will be useful in PNC-based optoelectronic devices such as solar cells, photodetectors, and transistors.

In-Bi Electrocatalyst for the Reduction of CO2 to Formate in a Wide Potential Window.

The CO2 atmospheric concentration level hit the record at more than 400 ppm and is predicted to keep increasing as the dependence on fossil fuels is inevitable. The CO2 electrocatalytic conversion becomes an alternative due to its environmental and energy-friendly properties and benign operation condition. Lately, bimetallic materials have drawn significant interest as electrocatalysts due to their distinct properties, which the parents' metal cannot mimic. Herein, the indium-bismuth nanosphere (In16Bi84 NS) was fabricated via the facile liquid-polyol technique. The In16Bi84 NS exhibits exceptional performance for CO2 reduction to formate, with the faradaic efficiency (FE) approaching ∼100% and a corresponding partial current density of 14.1 mA cm-2 at -0.94 V [vs the reversible hydrogen electrode (RHE)]. Furthermore, the FE could be maintained above 90% in a wide potential window (-0.84 to -1.54 V vs the RHE). This superior performance is attributed to the tuned electronic properties induced by the synergistic interaction between In and Bi, enabling the intermediates to be stably adsorbed on the catalyst surface to generate more formate ions.

Highly sensitive and selective visual detection of Cr(VI) ions based on etching of silver-coated gold nanorods.

We report a visual detection of Cr(VI) ions using silver-coated gold nanorods (AuNR@Ag) as sensing probes. Au NRs were prepared by a seed-mediated growth process and AuNR@Ag nanostructures were synthesized by growing Ag nanoshells on Au NRs. Successful coating of Ag nanoshells on the surface of Au NRs was demonstrated with TEM, EDS, and UV-vis spectrometer. By increasing the overall amount of the deposited Ag on Au NRs, the localized surface plasmon resonance (LSPR) band was significantly blue-shifted, which allowed tuning across the visible spectrum. The sensing mechanism relies on the redox reaction between Cr(VI) ions and Ag nanoshells on Au NRs. As the concentration of Cr(VI) ions increased, more significant red-shift of the longitudinal peak and intensity decrease of the transverse peak could be observed using UV-vis spectrometer. Several parameters such as concentration of CTAB, thickness of the Ag nanoshells and pH of the sample were carefully optimized to determine Cr(VI) ions. Under optimized condition, this method showed a low detection limit of 0.4 µM and high selectivity towards Cr(VI) over other metal ions, and the detection range of Cr(VI) was tuned by controlling thickness of the Ag nanoshells. From multiple evaluations in real sample, it is clear that this method is a promising Cr(VI) ion colorimetric sensor with rapid, sensitive, and selective sensing ability.

A silver/graphene oxide nanocomposite film as a flexible SERS substrate for reliable quantitative analysis using high-speed spiral scanning spectrometry.

Excellent uniformity (∼1.5% RSD) in SERS signals was obtained from an Ag/GO decorated adhesive tape on a simple in-house cylindrical scanning system. The calibration curve for the quantitative analysis of CV shows reliable linearity ranging from 75 nM to 50 µM. This novel method is promising to be an adept tool for universal quantitative analysis and be used complementarily with the conventional Raman mapping method for a more time efficient and reliable analysis.