Inspired by the enhanced gas-sensing performance by the one-dimensional hierarchical structure, one-dimensional hierarchical polyaniline/multi-walled carbon nanotubes (PANI/CNT) fibers were prepared. Interestingly, the simple heating changed the sensing characteristics of PANI from p-type to n-type and n-type PANI and p-type CNTs form p–n hetero junctions at the core–shell interface of hierarchical PANI/CNT composites. The p-type PANI/CNT (p-PANI/CNT) and n-type PANI/CNT (n-PANI/CNT) performed the higher sensitivity to NO₂ and NH₃, respectively. The response times of p-PANI/CNT and n-PANI/CNT to 50 ppm of NO₂ and NH₃ are only 5.2 and 1.8 s, respectively, showing the real-time response. The estimated limit of detection for NO₂ and NH₃ is as low as to 16.7 and 6.4 ppb, respectively. After three months, the responses of p-PANI/CNT and n-PANI/CNT decreased by 19.1% and 11.3%, respectively. It was found that one-dimensional hierarchical structures and the deeper charge depletion layer enhanced by structural changes of PANI contributed to the sensitive and fast responses to NH₃ and NO₂. The formation process of the hierarchical PANI/CNT fibers, p–n transition, and the enhanced gas-sensing performance were systematically analyzed. This work also predicts the development prospects of cost-effective, high-performance PANI/CNT-based sensors.

Inspired by the similarity between the pleated structure of rose petals and the pleated structure of a dog's maxillary turbinate, porous biomass carbon materials with a pleated structure have been successfully prepared from rose petals by direct carbonization. Detailed SEM and TEM characterization showed that the carbonized rose tea (CRT) at 600 °C exhibited a mimetic structure very similar to the dog's maxillary turbinate. The trace K element was detected in the prepared CRT materials, which effectively improved the adsorption capacity of the CRT materials for NH₃ as revealed by density functional theory based on first-principles calculations. As a result, the CRT sensor showed an ultra-high response (60.16k%) to 500 ppm NH₃ with a theoretical detection limit of only 4.82 ppb, in addition to showing a fast recovery (2.0 s), excellent repeatability and long-term stability. Moreover, the formation of nanopores in the pleated structure of the CRT and the sensing mechanism of NH₃ were analyzed. Through a simple, inexpensive and efficient method, this study provides a new strategy for the preparation of a high-performance gas sensor with a bionic structure by directly using the similarity between the biomass structure and dog nose structure.

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.

The lowest-energy geometrical and electronic structures of Cu₃₈ cluster are investigated by density-functional calculations combined with a genetic algorithm based on a many body semi-empirical interatomic potential, the traditional FCC-truncated Octahedron (OH) and an incomplete-Mackay icosahedron (IMI) are recognized as the two lowest energy structures (energetically degenerate isomers) but with different electronic structures: a semiconductor-type with the energy-gap of 0.356 eV for the IMI and a metallic-type with negligible gap for the OH, which is in good agreement with the experimental results. The electron affinity and ionization potential of Cu₃₈ are also discussed and compared with the observations of the ultraviolet photoelectron spectroscopy experiments. The dynamical isomerization of the OH-like and IMI-like structures of Cu₃₈ is revealed to dominate the pre-melting stage through the investigation by the molecular dynamics annealing simulations.