Hierarchical morphology-dependent gas-sensing performances have been demonstrated for three-dimensional SnO nanostructures. First, hierarchical SnO nanostructures assembled with ultrathin shuttle-shaped nanosheets have been synthesized via a facile and one-step hydrothermal approach. Due to thermal instability of hierarchical nanosheets, they are gradually shrunk into cone-shaped nanostructures and finally deduced into rod-shaped ones under a thermal treatment. Given the intrinsic advantages of three-dimensional hierarchical nanostructures, their gas-sensing properties have been further explored. The results indicate that their sensing behaviors are greatly related with their hierarchical morphologies. Among the achieved hierarchical morphologies, three-dimensional cone-shaped hierarchical SnO nanostructures display the highest relative response up to about 175 toward 100 ppm of acetone as an example. Furthermore, they also exhibit good sensing responses toward other typical volatile organic compounds (VOCs). Microstructured analyses suggest that these results are mainly ascribed to the formation of more active surface defects and mismatches for the cone-shaped hierarchical nanostructures during the process of thermal recrystallization. Promisingly, this surface-engineering strategy can be extended to prepare other three-dimensional metal oxide hierarchical nanostructures with good gas-sensing performances.

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Porous and single-crystalline ZnO nanobelts have been prepared through annealing precursors of ZnSe · 0.5N2H4 well-defined and smooth nanobelts, which have been synthesized via a simple hydrothermal method. The composition and morphology evolutions with the calcination temperatures have been investigated in detail for as-prepared precursor nanobelts, suggesting that they can be easily transformed into ZnO nanobelts by preserving their initial morphology via calcination in air. In contrast, the obtained ZnO nanobelts are densely porous, owing to the thermal decomposition and oxidization of the precursor nanobelts. More importantly, the achieved porous ZnO nanobelts are single-crystalline, different from previously reported ones. Motivated by the intrinsic properties of the porous structure and good electronic transporting ability of single crystals, their gas-sensing performance has been further explored. It is demonstrated that porous ZnO single-crystalline nanobelts exhibit high response and repeatability toward volatile organic compounds, such as ethanol and acetone, with a short response/recovery time. Furthermore, their optoelectronic behaviors indicate that they can be promisingly employed to fabricate photoelectrochemical sensors.

Achieving highly sensitive and selective detection of trace-level As­(III) and clarifying the underlying mechanism is still a intractable problem. The electroanalysis of As­(III) relies on the electrocatalytic ability of the sensing interface. Herein, we first adopt single-atom catalysts as the electrocatalyst in As­(III) detection. Cobalt single-atoms anchored on nitrogen-doped carbon material (Co SAC) were found to have an extraordinary sensitivity of 11.44 μA ppb–1 with excellent stability and repeatability, which so far is the highest among non-noble metal nanomaterials. Co SAC also exhibited a superior selectivity toward As­(III) compared with some bivalent heavy metal ions (HMIs). Combining X-ray absorption spectroscopy (XAFS), density functional theory (DFT) calculation, and reaction kinetics simulation, we demonstrated that Co single atoms stabilized in N2C2 support serve as active sites to catalyze H3AsO3 reduction via the formation of Co–O hybridization bond, leading to a lower energy barrier, promoting the breakage of As–O bonds. Importantly, the first electron transfer is the rate-limiting step of arsenic reduction and is found to be more favorable on Co-SAC both thermodynamically and kinetically. This work not only expands the potential applicaiton of single-atom catalysts in the detection and treatment of As­(III), but also provides atomic-level catalytic insights into HMIs sensing interfaces.

Nanocrystals generally suffer from agglomeration because of the spontaneous reduction of the system surface energy, resulting in blocking the active sites from reacting with target ions, and then severely reducing the electrochemical sensitivity. In this article, a highly ordered self-assembled monolayer array is successfully constructed using ∼14 nm CoFeO nanocubes uniformly and controllably distributed on the surface of a working electrode (glass carbon plate). The large area and high exposure of the surface defects on CoFeO nanocubes are clearly characterized by high-resolution transmission electron microscopy (HRTEM) and atomic-resolution high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Expectedly, a considerable sensitivity of 2.12 μA ppb and a low limit of detection of 0.093 ppb are achieved for As(III) detection on this highly homogeneous sensing interface; this excellent electroanalysis performance is even better than that of noble metals electrodes. Most importantly, this approach of uniformly distributing the small-sized defective nanoparticles on the electrode surface provides a new opportunity for modifying the electrodes, as well as the realization of their applications in the field of environmental electroanalysis for heavy metal ions.

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Cu 2 Se nanobelts have been developed via a facile cation-exchange approach at room temperature, employing ZnSe•0.5N 2 H 4 hybrid nanobelts as the templated precursors. Detailed characterizations demonstrate that the morphologies of the templated precursors are well-preserved in the cation-exchange reaction, because of the spatial confinement effect from the coated layer of poly-(vinylpyrrolidone) (PVP) surfactant. Simultaneously, Cu 2+ cations diffusing through the coated layer of PVP are in situ reduced to be Cu + cations by the ligands of N 2 H 4 , thereby forming Cu 2 Se nanobelts with the complete replacement of Zn 2+ cations in the templated precursors. After thermal oxidation in air, the obtained Cu 2 Se nanobelts are further converted into porous CuO nanobelts. Considering that this special morphology processes a large active surface area and is favorable for gas diffusion, gas-sensing properties of porous CuO nanobelts have been explored. The results indicate that porous CuO nanobelts exhibit highly selective sensing toward H 2 S with a low detection limit less than 10 ppb. Moreover, they also present a good sensing reproducibility. Finally, their sensing mechanism toward H 2 S has been discussed.

A direct Z-scheme ZnS/Co9S8 heterojunction-based photoelectrochemical sensor for analyzing organophosphorus chlorpyrifos.