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The electrocatalytic N2 reduction reaction (NRR) is a very attractive yet challenging route for sustainable NH3 synthesis under ambient conditions, for which efficient catalysts are required due to the highly strong NN bond. In this work, B decorated C9N4 monolayer (B-C9N4) for NRR is studied by using first-principles calculations. It is found that the inert N2 can be sufficiently activated through the electron “acceptance-donation” pattern between N2 and the B dopant. The subsequent N2 reduction prefers the alternating mechanism, and the reduction of *N2 to *N2H is the potential-limiting step with an overpotential of 0.56 V. Furthermore, B-C9N4 exhibits a metallic nature, which can promote charge transfer during the reduction process. The stability of B-C9N4 can be confirmed by the calculated B adsorption energies and the ab initio molecular dynamic simulation. Consequently, owing to its high activity, good electrical conductivity, and excellent stability, B-C9N4 is a promising metal-free N2 reduction catalyst. Our work not only provides an efficient electrocatalyst for NH3 production, but also opens up a promising avenue to develop highly active and robust metal-free catalysts for other applications.

Metal oxide gas sensors with porous structures are widely used in numerous applications ranging from health monitoring and medical detection to safety; in this study, we report a highly sensitive SnO2 gas sensor with a multi-level tube/pore structure prepared via biomimetic technology using flax waste as a bio-template and a simple wet chemical process combined with subsequent annealing. Indeed, MLTPS not only maintained and improved the excellence of porous structure gas sensing materials with abundant active sites and large surface-to-volume ratios, but also overcame the deficiency of the lack of gas diffusion channels in porous gas sensing materials. Thus, this novel multi-level tube/pore SnO2 gas sensor exhibited significantly enhanced sensing performance, e.g. an ultra-low response concentration (250 ppb), a high response (87.9), a fast response (9.2 s), a low operating temperature (130 °C) and good stability, for formaldehyde. On the basis of these results, via the reuse of agricultural waste, this study provides a new concept for the low-cost synthesis of environmentally friendly and effective multi-level tube/pore gas sensor materials.

In this study, the carbon-matrix Ag wing with a hierarchical sub-micron antireflection quasi-photonic crystal structure (HSAS) was fabricated by a simple and promising method. This method combines chemosynthesis with biomimetic techniques, without the requirement of expensive equipment and energy intensive processes. Here, the Troides helena (Linnaeus) (T. helena) forewing (T_FW) was chosen as the biomimetic template. The carbon-matrix Ag butterfly wing (Ag@C_T_FW) achieves a drastically enhanced infrared absorption over a broad spectral range, especially, over the near infrared region. Here, we report methods to enhance and modify the plasmonic resonances in such structures by strongly coupling plasmonic resonances to HSAS. Using the finite difference time domain (FDTD) method, the absorption spectra and the distribution of the energy density near the Ag NPs surface were simulated. Based on the experiment and simulation results, these findings demonstrate that the enhanced infrared absorption over a broad spectral range is due to the mechanism that the plasmon and the coherent coupling between adjacent resonance systems integrate with the HSAS.

Templated from the bristles on Papilio maacki wings, single porous SnO2 microtubes (SPSMs) have been synthesized by soaking and sintering. The delicate microstructure and morphology of SPSMs were characterized by SEM and TEM. Silver electrodes were precisely contacted on the two ends of an SPSM for gas-sensing measurement in reducing gases. The SPSMs were highly sensitive to trace ammonia, formaldehyde, and ethanol at room temperature. They also exhibited low working temperature and short response/recovery times. The average response and recovery times were only about 3 s and 30 s. Compared with the non-porous structure and the filled structure, the SPSMs showed higher sensitivity. The fascinating biomorphic structure of the SPSMs will open a new way for the design and application of sensor devices for the detection of harmful and toxic gases.