Herein, we report the novel nanostructural interfaces of self-assembled hierarchical ZnO nanotubes/graphene (ZNT/G) with three different growing times of ZNTs on graphene substrates (namely, SH, SH, and SH). Each sample was fabricated with interdigitated electrodes to form hydrogen sensors, and their hydrogen sensing properties were comprehensively studied. The systematic investigation revealed that SH sensor exhibits an ultrahigh sensor response even at a low detection level of 10 ppm (14.3%) to 100 ppm (28.1%) compared to those of the SH and SH sensors. The SH sensor was also found to be well-retained with repeatability, reliability, and long-term stability of 90 days under hydrogenation/dehydrogenation processes. This outstanding enhancement in sensing properties of SH is attributed to the formation of a strong metalized region in the ZNT/G interface due to the inner/outer surfaces of ZNTs, establishing a multiple depletion layer. Furthermore, the respective band models of each nanostructure were also purposed to describe their heterostructure, which illustrates the hydrogen sensing properties. Moreover, the long-term stability can be ascribed by the heterostructured combination of ZNTs and graphene via a spillover effect. The salient features of this self-assembled nanostructure are its reliability, simple synthesis method, and long-term stability, which makes it a promising candidate for new generation hydrogen sensors and hydrogen storage materials.
Granular activated carbon (GAC) materials were prepared via simple gas activation of silkworm cocoons and were coated on ZnO nanorods (ZNRs) by the facile hydrothermal method. The present combination of GAC and ZNRs shows a core-shell structure (where the GAC is coated on the surface of ZNRs) and is exposed by systematic material analysis. The as-prepared samples were then fabricated as dual-functional sensors and, most fascinatingly, the as-fabricated core-shell structure exhibits better UV and H sensing properties than those of as-fabricated ZNRs and GAC. Thus, the present core-shell structure-based H sensor exhibits fast responses of 11% (10 ppm) and 23.2% (200 ppm) with ultrafast response and recovery. However, the UV sensor offers an ultrahigh photoresponsivity of 57.9 A W, which is superior to that of as-grown ZNRs (0.6 A W). Besides this, switching photoresponse of GAC/ZNR core-shell structures exhibits a higher switching ratio (between dark and photocurrent) of 1585, with ultrafast response and recovery, than that of as-grown ZNRs (40). Because of the fast adsorption ability of GAC, it was observed that the finest distribution of GAC on ZNRs results in rapid electron transportation between the conduction bands of GAC and ZNRs while sensing H and UV. Furthermore, the present core-shell structure-based UV and H sensors also well-retained excellent sensitivity, repeatability, and long-term stability. Thus, the salient feature of this combination is that it provides a dual-functional sensor with biowaste cocoon and ZnO, which is ecological and inexpensive.
Due to environmental problems such as global warming and ozone depletion, it is essential to detect harmful UV rays from sunlight and to commercialize a clean energy source (H2), and both issues require a reliable sensor.
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