Techniques for scaling-up the direct-current (dc) triboelectricity generation in MoS 2 multilayer-based Schottky nanocontacts are vital for exploiting the nanoscale phenomenon for real-world applications of energy harvesting and sensing. Here, we show that scaling-up the dc output can be realized by using various MoS 2 multilayer-based heterojunctions including metal/semiconductor (MS), metal/insulator (tens of nanometers)/semiconductor (MIS), and semiconductor/insulator (a few nanometers)/semiconductor (SIS) moving structures. It is shown that the tribo-excited energetic charge carriers can overcome the interfacial potential barrier by different mechanisms, such as thermionic emission, defect conduction, and quantum tunneling in the case of MS, MIS, and SIS moving structures. By tailoring the interface structure, it is possible to trigger electrical conduction resulting in optimized power output. We also show that the band bending in the surfacecharged region of MoS 2 determines the direction of the dc power output. Our experimental results show that engineering the interface structure opens up new avenues for developing next-generation semiconductor-based mechanical energy conversion with high performance.

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A carbon quantum dot-based chitosan hydrogel was prepared in this work as a fluorescence sensor for the selective sensing of Hg 2+ ions. Among the eight tested metal ions, the prepared hydrogel exhibited remarkable sensing selectivity and sensitivity toward Hg 2+ . The results demonstrated that a prominent fluorescence quenching at 450 nm was observed in the presence of Hg 2+ with a linear response range of 0–100.0 nM and an estimated limit of detection of 9.07 nM. The as-prepared hydrogel demonstrates pH-dependent fluorescence intensity and sensitivity. The highest fluorescence intensity and sensitivity were obtained under pH 5.0. The excellent sensing selectivity could be attributed to a strong interaction between the hydrogel film and Hg 2+ ions to form complexes, which provokes an effective electron transfer for fluorescence quenching. Results from density functional theory (DFT) calculation confirm that the interaction energies (ΔIE) of the hydrogel with three toxic metal ions (Hg 2+ , Cd 2+ , and Pb 2+ ) are in the following order: Hg 2+ > Cd 2+ > Pb 2+ .