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Owing to their excellent photoluminescence (PL) properties, good biocompatibility, and low toxicity, graphene quantum dots (GQDs) are widely applied in bioimaging, biosensing, and so forth. However, further development of GQDs is limited by their synthetic methodology and unclear PL mechanism. Therefore, it is urgent to find efficient and universal methods for the synthesis of GQDs with high stability, controllable surface properties, and tunable PL emission wavelength. By coating with polyethyleneimine (PEI) of different molecular weights, blue-, yellow-, and red-emitting GQDs were successfully prepared. By transmission electron microscopy, atomic force microscopy, and dynamic light scattering, the characterization of size and morphology revealed that blue-emitting PEI GQDs were monocoated, like jelly beans, and red-emitting PEI GQDs were multicoated, like capsules. The amidation reaction between carboxyl and amide functional groups played an important role in the coating process, as evidenced by IR spectroscopy and theoretical calculation with density functional theory B3LYP/6-31G*. The PL-tunable GQDs exhibited an excellent chemical stability and extremely low cytotoxicity, and they had been shown to be feasible for bioimaging, making these GQDs highly attractive for a wide variety of applications, including multicolor imaging and bioanalysis.

Photoelectrochemical (PEC) cells based on silicon nanowire arrays (SiNWs) have, to date, exhibited modest power conversion efficiency (PCE) and suffered serious degradation, though they exhibit advantageous properties of charge-transfer/transport properties at the radial-junction and strong light-trap capabilities. The main challenge for this low-cost PEC cell is the surface photooxidation and photocorrosion of the silicon surface when contacting with the electrolyte. In this report, SiNWs derivatized with covalently attached methyl groups, prepared via a two-step chlorination/methylation procedure, demonstrate excellent stability even in the presence of water. Furthermore, SiNWs PEC cells utilizing a room temperature ion liquid (IL) acting as an electrolyte solvent display neglectable surface oxidation. A PEC cell based on a platinum (Pt) nanodots decorated and methylated (-CH(3)) SiNWs electrode in combination with an IL electrolyte yields a PCE of 6.0% and shows excellent stability under simulated air mass (AM) 1.5 solar spectrum irradiation, while the PCE of a PEC cell based on planar silicon only exhibits 0.003%. The inherent performance of these structures indicates that a -CH(3) (Pt) SiNWs electrode in combination with an IL is a new approach to develop a high-performance and low-cost solar cell.

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