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.

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.

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.

Protein folding is a complex multidimensional process that is difficult to illustrate by the traditional analyses based on one- or two-dimensional profiles. Analyses based on transition networks have become an alternative approach that has the potential to reveal detailed features of protein folding dynamics. However, due to the lack of successful reversible folding of proteins from conventional molecular-dynamics simulations, this approach has rarely been utilized. Here, we analyzed the folding network from several 10 μs conventional molecular-dynamics reversible folding trajectories of villin headpiece subdomain (HP35). The folding network revealed more complexity than the traditional two-dimensional map and demonstrated a variety of conformations in the unfolded state, intermediate states, and the native state. Of note, deep enthalpic traps at the unfolded state were observed on the folding landscape. Furthermore, in contrast to the clear separation of the native state and the primary intermediate state shown on the two-dimensional map, the two states were mingled on the folding network, and prevalent interstate transitions were observed between these two states. A more complete picture of the folding mechanism of HP35 emerged when the traditional and network analyses were considered together.

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Porous single-crystalline nanostructures are of tremendous interest for their application in the catalytic, electronic and sensing fields due to their large active surfaces, favorable diffusion, and good electronic transport. Despite the recent advances of various other components, photoelectric chalcogenides remain almost undeveloped. The present study contributes a facile strategy to prepare porous single-crystalline CdSe nanobelts through a cation-exchange reaction, in which ZnSe⋅0.5 N H hybrid nanobelts are employed as precursors. The detailed characterizations indicate the preservation of the belt-like morphology of the precursors due to the spatial confinement effect, which arises from the coated surfactant layer during the cation-exchange process. Simultaneously, CdSe nanobelts with porous and single-crystalline structures are formed following a complete exchange between Zn and Cd , the release of N H , and the atomic arrangement. The native photoelectric properties of the as-prepared porous single-crystalline CdSe nanobelts are systematically addressed based on the nanodevices fabricated with a single nanobelt and assembled nanobelt array. The results indicate that they present a rapid, stable, and repeatable photoelectric response. Moreover, as-prepared nanobelts exhibit highly selective photoelectric sensing toward Cu with a low detection limit down to 0.1 ppm. To illuminate this phenomenon, a possible sensing mechanism is also discussed.

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Although the post-doping approach as a typical and effective method has been widely employed to improve the gas sensing performance of nanostructured metal oxides, it easily breaks their porous nanostructures. Herein a facile partial cation-exchange strategy combined with thermal oxidation has been developed to prepare porous CuO-doped ZnO nanobelts. Using ZnSe$0.5N 2 H 4 nanobelts as the precursor template, Cu 2 Se-doped precursor nanobelts were obtained with Zn 2+ cations partially exchanged by Cu 2+ cations. After annealing in air, they are further oxidized into well-defined porous CuO-doped ZnO nanobelts. Through manipulating the amount of exchanged Cu 2+ cations, the CuOdoping concentration can be precisely tuned. Based on the assembly approach and in situ thermal oxidation, a uniform and stable sensing film consisting of porous CuO-doped nanobelts was fabricated.Compared with pristine porous ZnO nanobelts, the as-prepared porous CuO-doped nanobelts with ptype CuO|n-type ZnO heterojunctions exhibited better sensing performance toward volatile organic compounds (VOCs). Especially for 3 at% CuO-doped porous ZnO nanobelts, the relative responses toward 100 ppm of ethanol, acetone and formaldehyde were greatly enhanced more than two, four and ten times, respectively. Due to the porous structure, they also displayed a fast response/recovery time.Finally, this enhanced sensing mechanism was discussed for porous CuO-doped ZnO nanobelts.Scheme 1 The process of preparation of porous CuO-doped ZnO nanobelts: (1) Zn 2+ cations of ZnSe$0.5N 2 H 4 nanobelts as a precursor template partially exchanged by Cu 2+ , (2) the transformation from Cu 2 Se doped precursor nanobelts to porous CuO-doped ZnO nanobelts via thermal oxidation.This journal is