Zinc-Reduced CQDs with Highly Improved Stability, Enhanced Fluorescence, and Refined Solid-State Applications

Carbon quantum dots (CQDs) have attracted considerable interest because of their advantages of low cost, nontoxicity, easy preparation, and diverse optical properties. Photophysical properties and stability are two key issues that affect the further use of CQDs, especially for solid-state applications. Here, we report a facile and effective method to enhance the fluorescence and moisture-resistance of CQDs. CQDs were synthesized by the thermolysis of citric acid on a multigram scale and were readily used to react with zinc powder in an aqueous solution to produce zinc-reduced CQDs (Zn-CQDs). The process was operated under mild conditions and completed in 10 min. The fluorescence intensity of the CQDs increased more than three times after reacting with zinc. In contrast to the pristine CQD solids, which easily absorbed moisture and turned into viscous liquids, the as-prepared Zn-CQD blocks possessed an ordered porous structure and were immune to moisture in the air. They remained stable under ambient conditions for months. Comprehensive studies were carried out to explore the reaction mechanism and material properties. It was revealed that zinc likely served as a reductant in the process. On the basis of the satisfactory properties of the Zn-CQD blocks, their solid-state applications were studied. A Zn-CQD-based fluorescent film for temperature monitoring was fabricated with favorable linear response and reversibility. Moreover, the as-obtained Zn-CQD blocks showed remarkable adsorption of particulate matter (PM). Therefore, it is expected that they may find practical use in the purification of PM-polluted air

Experimental Studies on A New Fluorescent Ensemble of Calix[4]pyrrole and Its Sensing Performance in the Film State

The supramolecular approach plays a pivotal role in the construction of smart and functional materials due to the reversible nature of noncovalent interactions. In the present work, two compounds, cholesterol-functionalized calix[4]­pyrrole (CCP) and perylene bisimide diacid (PDA), were synthesized. Little fluorescence is observed in the ethanol solution of the mixture of CCP and PDA, while the solution turns fluorescent upon introduction of ammonia, which is attributed to the formation of a supramolecular ensemble, PDA/(CCP)₂/NH₃. The fluorescence emission of the as-formed ensemble is sensitive to the presence of phenol, an electron-rich analyte. Interestingly, the sensing can also be observed in the film state, and the relevant detection limit (DL) is lower than 1 ppb. Moreover, the sensing could also be performed in a visualized manner. Upon the basis of the findings, a sensor device with instant response and good reversibility was developed. Further studies revealed that the as-developed fluorescent ensemble is also sensitive to the presence of TNT, an electron-poor compound. The DL for this sensing is ∼80 nM. To our knowledge, this is the first report that a fluorescent sensor could be used for phenol sensing in the vapor state, and for sensing of both electron-rich and electron-poor analytes in solution state. It is believed that the present study presents a distinctive example that demonstrates how smart sensing is realized via combination of the host–guest chemistry of calix[4]­pyrrole and the aggregation and disaggregation property of PBI derivatives

Facile Method for Modification of the Silicon Nanowires and Its Application in Fabrication of pH-Sensitive Chips

A novel, facile, and effective method for modification of SiNWs or SiNW arrays has been developed. In this method, reaction between reductive Si–H bonds on the surface of SiNWs and the aldehyde group containing in organic molecules has been used for immobilization of organic molecules onto the surface of SiNW arrays. The method is time saving and can be operated at room temperature without any other complex reaction requirement. Fluorescence images, XPS, fluorescence spectra, and IR spectra were used for characterization of the modification. Through this method, a SiNW array-based pH sensitive chip was realized by covalently immobilizing 5-aminofluorescein molecules onto the surface of SiNW arrays with glutaraldehyde as linker molecules. Fluorescence intensity of the chip increased with increasing of pH value and a linear relationship between fluorescence intensity and pH values was acquired. In addition, the chip has been successfully used for real-time and in situ monitoring of extracellular pH changes for live HeLa cells and the result exhibited fine resolution of time and space