First-principles calculations are used to systematically investigate the geometric and electronic structures of both pure TM(n) (n=2-4) and Ag-modulated AgTM(n-1) (n=2-4; 3d-transition metal (TM): from Sc to Cu; 4d-TM: from Y to Ag elements) clusters. Some new ground state structures are found for the pure TM(n) clusters, such as a low symmetry configuration for Cr(3), which is found to be about 0.20 eV more stable than the previously reported C(2v) symmetry. In the most cases, Ag-doping can significantly elongate the bond lengths of the clusters and induce geometric distortions of the small clusters from the high dimensional to the low dimensional configurations. Importantly, introduction of Ag significantly changes the electronic structures of the small clusters and modulates the density of states in the proximity of the Fermi levels, which also varies with the size and the type of the cluster. The results contribute to future design of effective bimetallic alloy Ag/TM catalysts.

Sycamore villus fibers were used to prepare hollow and porous carbon microtubes (CMTs) and the ZnO/CMT composite with heterojunctions by simple carbonization for the first time. Because the hollow and porous structure provided more channels to facilitate the adsorption and desorption of gas molecules, both CMTs and ZnO/CMT exhibited higher sensitivity and quicker response (<16 s) to and recovery (<2 s) from multiple target analytes. Furthermore, ZnO nanoparticles were uniformly dispersed on the CMTs by zinc acetate-assisted carbonization, which avoided the agglomeration of ZnO and formed a large number of heterojunctions, greatly improving the sensitivity of ZnO/CMT. In comparison to the pure CMTs and ZnO, the response of ZnO/CMT to the four target gases increased by 1.4∼4.3 and 9.9∼18.1 times, respectively. Their limit of detection for NH 3 was calculated as 62.5 and 8.8 ppb, respectively. After 30 days, the responses of CMTs and ZnO/CMTs to 500 ppm NH 3 decreased by 9.4 and 6.5%, respectively. This indicated that CMTs and ZnO/CMT had high sensitivity and good long-term stability. This study provides a feasible way for the gas-sensing application of biomass carbon materials with heterojunction structures.

Triacetone triperoxide (TATP) is a self-made explosive synthesized from the commonly used chemical acetone (C3H6O) and hydrogen peroxide (H2O2). As C3H6O and H2O2 are the precursors of TATP, their detection is very important due to the high risk of the presence of TATP. In order to detect the precursors of TATP effectively, hierarchical molybdenum disulfide/reduced graphene oxide (MoS2/RGO) composites were synthesized by a hydrothermal method, using two-dimensional reduced graphene oxide (RGO) as template. The effects of the ratio of RGO to raw materials for the synthesis of MoS2 on the morphology, structure, and gas sensing properties of the MoS2/RGO composites were studied. It was found that after optimization, the response to 50 ppm of H2O2 vapor was increased from 29.0% to 373.1%, achieving an increase of about 12 times. Meanwhile, all three sensors based on MoS2/RGO composites exhibited excellent anti-interference performance to ozone with strong oxidation. Furthermore, three sensors based on MoS2/RGO composites were fabricated into a simple sensor array, realizing discriminative detection of three target analytes in 14.5 s at room temperature. This work shows that the synergistic effect between two-dimensional RGO and MoS2 provides new possibilities for the development of high performance sensors.

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