One of the most intriguing protein materials found in nature is bone, a material composed of assemblies of tropocollagen molecules and tiny hydroxyapatite mineral crystals that form an extremely tough, yet lightweight, adaptive and multifunctional material. Bone has evolved to provide structural support to organisms, and therefore its mechanical properties are of great physiological relevance. In this article, we review the structure and properties of bone, focusing on mechanical deformation and fracture behavior from the perspective of the multidimensional hierarchical nature of its structure. In fact, bone derives its resistance to fracture with a multitude of deformation and toughening mechanisms at many size scales ranging from the nanoscale structure of its protein molecules to the macroscopic physiological scale.

On the Mechanistic Origins of Toughness in Bone

In this study, a straightforward coassembly strategy is demonstrated to synthesize Pt sensitized mesoporous WO3 with crystalline framework through the simultaneous coassembly of amphiphilic poly(ethylene oxide)-b-polystyrene, hydrophobic platinum precursors, and hydrophilic tungsten precursors. The obtained WO3/Pt nanocomposites possess large pore size (≈13 nm), high surface area (128 m2 g−1), large pore volume (0.32 cm3 g−1), and Pt nanoparticles (≈4 nm) in situ homogeneously distributed in mesopores, and they exhibit excellent catalytic sensing response to CO of low concentration at low working temperature with good sensitivity, ultrashort response-recovery time (16 s/1 s), and high selectivity. In-depth study reveals that besides the contribution from the fast diffusion of gaseous molecules and rich interfaces in mesoporous WO3/Pt nanocomposites, the partially oxidized Pt nanoparticles that chemically and electronically sensitize the crystalline WO3 matrix, dramatically enhance the sensitivity and selectivity.

Pt Nanoparticles Sensitized Ordered Mesoporous WO 3 Semiconductor: Gas Sensing Performance and Mechanism Study

In this study, SnO2 nanosheets (NSs) was firstly prepared by the hydro-solvothermal treatment, and then decorated with Pd, Au and PdAu bimetallic nanoparticles (NPs) by an in situ reduction with ascorbic acid (AA). Their morphology, chemistry, and crystal structure were characterized at the nanoscale. It was found that SnO2 NSs were flower-like with thickness of 7–12 nm, and PdAu NPs with the size of 3–10 nm were dispersed uniformly on the surface of SnO2 NSs. Their gas sensing properties were carefully studied. The results demonstrated that the PdAu/SnO2 sensor can not only effectively detect acetone at 250 °C with response of 6.6 to 2 ppm acetone, but also detect formaldehyde at 110 °C with response of 4.1–2 ppm formaldehyde, and the corresponding detection limit is as low as 45 ppb and 30 ppb, respectively. Moreover, the PdAu/SnO2 sensor exhibited excellent reusability, and reliability to the low concentration of acetone and good anti-interference to humidity and other biomarkers in human breath. Compared with that decorated with their parent metal (Pd or Au), the enhanced response of SnO2 NSs decorated with PdAu bimetallic NPs may be ascribed to the chemical sensitization of Au, the electronic sensitization of Pd and the synergistic effect of PdAu bimetallic NPs. The PdAu/SnO2 sensor has a great potential application in detecting formaldehyde and diabetes diagnosis.

Bimetal PdAu decorated SnO2 nanosheets based gas sensor with temperature-dependent dual selectivity for detecting formaldehyde and acetone

The alarming rise of indoor pollution and the need to combat the associated negative effects have promoted increasing attention in modernizing the chemical sensing technologies by newly designed materials with rich and tunable functionalities at atomic or molecular levels. With the appealing physical, chemical, optical, and electronic properties for various potential applications, the state-of-art gas-sensing nanomaterials and their future perspectives are well-documented and summarized in this paper. Specifically, the key performance attributes are addressed in detail such as the sensitivity, selectivity, reversibility, operating temperature, response time, and detection limit. As such, this review provides both critical insights in exploring and understanding various gas sensing nanomaterials and points out limitations and opportunities for further developments, such as morphology control, doping and surface alteration, atomic-scale characterization, and applications in different fields. Finally, the challenges and outlooks are discussed on the basis of the current developments.

Functional gas sensing nanomaterials: A panoramic view

Benzene, toluene, and xylene gases, which are known collectively as BTX gases, are volatile organic compounds (VOCs) that are used extensively in many industrial products. Nevertheless, BTX gases are quite toxic and need to be detected by sensitive sensors as fast as possible. Among the various gas sensors available, resistive-based gas sensors are among the most promising candidates for the detection of these gases. On the other hand, it is difficult to realize resistive-based gas sensors with high sensitivity to BTX gases owing to their relatively low chemical reactivity. In addition, the selective detection of a single gas among the BTX gases is challenging because of their similar nature and structure. This review discusses the different strategies employed in resistive-based gas sensors for the realization of high performance BTX gas sensors.

Resistive-based gas sensors for detection of benzene, toluene and xylene (BTX) gases: a review

In this work, Au was employed as an ideal dopant to obtain enhanced sensing performance of xylene gas sensor. Firstly, the as-perpared Au-doped WO 3 ·H 2 O powder was synthesized by a facile and efficient hydrothermal method. Then various techniques including X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectrometer (EDX) were employed to investigate the morphology, microstructure, crystalline nature and chemical compositions of the as-prepared Au-doped WO 3 ·H 2 O nanomaterials. The morphologies of the nanomaterials could be easily controlled by changing the atomic percentage (at%) of Au (0.15 at%, 0.30 at%, 0.45 at%) in the precursor solutions. And it have been attested that the 0.30 at% Au-doped WO 3 ·H 2 O-based sensor realized higher gas response of 26.4–5 ppm xylene at 255 °C, faster response/recovery speed and stronger selectivity to target gas compared with the unloaded one. Furthermore, the detection limit could be as low as 200 ppb level. Hence, Au-loaded WO 3 ·H 2 O nanomaterial could be a promising material applied in xylene gas sensor. Also, the mechanism involved in the improving xylene sensing properties of Au/WO 3 ·H 2 O was discussed.

Xylene gas sensor based on Au-loaded WO3·H2O nanocubes with enhanced sensing performance

Preparation of Pd nanoparticle-decorated hollow SnO2 nanofibers and their enhanced formaldehyde sensing properties

Metal sulfide Zn1–xCdxS nanowires (NWs) covering the entire compositional range prepared by one step solvothermal method were used to fabricate gas sensors. This is the first time for ternary metal sulfide nanostructures to be used in the field of gas sensing. Surprisingly, the sensors based on Zn1–xCdxS nanowires were found to exhibit enhanced response to ethanol compared to those of binary CdS and ZnS NWs. Especially for the sensor based on the Zn1–xCdxS (x = 0.4) NWs, a large sensor response (s = 12.8) and a quick rise time (2 s) and recovery time (1 s) were observed at 206 °C toward 20 ppm ethanol, showing preferred selectivity. A dynamic equilibrium mechanism of oxygen molecules absorption process and carrier intensity change in the NWs was used to explain the higher response of Zn1–xCdxS. The reason for the much quicker response and recovery speed of the Zn1–xCdxS NWs than those of the binary ZnS NWs was also discussed. These results demonstrated that the growth of metal sulfide Zn1–xCdxS nanostruct...

Gas Sensors Based on Metal Sulfide Zn1–xCdxS Nanowires with Excellent Performance

α-MoO3/α-Fe2O3 nanostructure composites were fabricated via a facile and low-cost hydrothermal strategy. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) were used to characterize the samples. The results revealed that the α-Fe2O3 nanorods grew on the surface of α-MoO3 nanobelts. The result shows the length and the width of α-MoO3 nanobelts to be about 6 μm and 200 nm. The average length of an α-Fe2O3 nanorod was 10 nm. The sensing properties towards various kinds of gases were tested and the heater-type gas sensors based on α-MoO3 nanobelts and α-MoO3/α-Fe2O3 nanostructure composites showed excellent performance towards xylene. It was found that such heterostructure composites exhibited enhanced xylene sensing properties compared with α-MoO3 nanobelts. For example, at a xylene concentration of 5 ppm, the response of the α-MoO3/α-Fe2O3 composites was 4.79, which was about 3 times higher than that of α-MoO3 nanostructures at 206 °C.

Dongming Sun

Papers

Xylene gas sensor based on Au-loaded WO3·H2O nanocubes with enhanced sensing performance

Preparation of Pd nanoparticle-decorated hollow SnO2 nanofibers and their enhanced formaldehyde sensing properties

Gas Sensors Based on Metal Sulfide Zn1–xCdxS Nanowires with Excellent Performance

Xylene gas sensor based on α-MoO3/α-Fe2O3 heterostructure with high response and low operating temperature

Highly stabilized and rapid sensing acetone sensor based on Au nanoparticle-decorated flower-like ZnO microstructures