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1.
Nanoscale Horiz ; 5(3): 541-552, 2020 Mar 02.
Artigo em Inglês | MEDLINE | ID: mdl-32118233

RESUMO

Flexible tactile sensors that imitate the skin tactile system have attracted extensive research interest due to their potential applications in medical diagnosis, intelligent robots and so on. However, it is still a great challenge to date to fabricate tactile sensors with both high sensitivity and wide detection range due to the difficulties in modulating the resistance variation in the sensing materials in a wide pressure range. Here, a tactile sensor with a novel design based on the hierarchical pressure-peak effect (HPPE) consisting of PVP nanowires and electroless deposition (ELD) silver PDMS micro-pyramids is reported. The HPPE can effectively modulate the resistance change rate by adjusting the change of contact area during compression deformation, and the HPPE tactile sensor was demonstrated to have both ultrahigh sensitivity (11.60-1108.75 kPa-1) and ultrawide pressure range (0.04-600 kPa). The designed HPPE tactile sensor is successfully utilized in detecting multi-level pressures including respiration, finger heart rate, pulse and foot pressures. Moreover, it is used to sense a subtle clamping force in the Leonardo Da Vinci surgical robot demonstrating the potential of the sensor in surgical robot applications. In all these cases, the sensor exhibits enough capability to respond quickly to ultrawide-range pressures with high accuracy and stability.

2.
Macromol Rapid Commun ; 41(6): e1900573, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-32022971

RESUMO

Nanocomposite hydrogels (NCs) with mechanical properties suitable for a diverse range of applications can be made by combining polymer hydrogel networks with various inorganic nanoparticles. However, the mechanical properties and functions of conventional NCs are seriously limited by the poor structural or functional tunability of common nanofillers and by the low amounts of such fillers that can be added. Here, the fabrication of novel elastically stretchable and compressible nanocomposite hydrogels (MIL-101-MAAm/PAAm) with a distinctive pearl-net microstructure and a metal-organic framework (MOF) content in the range of 20-60 wt% through post-synthetic polymerization (PSP) is reported. The MOFs, which are compatible with polymers and have a high degree of modifiability in structure and functions, are used as nanofillers. Such MOF-laden hydrogels can withstand 500% tensile strain or 90% compressive strain without fracture and recover quickly upon unloading. They are also resistant to freezing at -25 °C. In addition, the problems associated with poor flexibility and processability of MOFs are overcome by the hybridization of hydrogel polymer matrices with MOFs. The results of this work not only provide a new perspective on preparing NCs but also indicate a promising path for applying MOFs in flexible devices.

3.
Nanomaterials (Basel) ; 9(11)2019 Nov 16.
Artigo em Inglês | MEDLINE | ID: mdl-31744070

RESUMO

In this work, TiO2 QDs-modified NiO nanosheets were employed to improve the room temperature NO2 sensing properties of NiO. The gas sensing studies showed that the response of nanocomposites with the optimal ratio to 60 ppm NO2 was nearly 10 times larger than that of bare NiO, exhibiting a potential application in gas sensing. Considering the commonly reported immature mechanism that the effective charge transfer between two phases contributes to an enhanced sensitivity, the QDs sensitization mechanism was further detailed by designing a series of contrast experiments. First, the important role of the QDs size effect was revealed by comparing the little enhanced sensitivity of TiO2 particle-modified NiO with the largely enhanced sensitivity of TiO2 QDs-NiO. Second, and more importantly, direct evidence of the heterointerface charge transfer efficiency was detailed by the extracted interface bond (Ti-O-Ni) using XPS peak fitting. This work can thus provide guidelines to design more QDs-modified nanocomposites with higher sensitivity for practical applications.

4.
Chem Commun (Camb) ; 55(89): 13386-13389, 2019 Nov 18.
Artigo em Inglês | MEDLINE | ID: mdl-31633713

RESUMO

The formation path of hollow complex nanocages prepared via Na2WO4·2H2O etching, using Prussian blue as a template, is tracked, which confirms the existence of a central cross structure inside the etching products. A mechanism based on etching along edges is described. The gas sensor designed with an Fe-W hollow complex exhibits excellent performance toward CH3S3CH3.

5.
ACS Nano ; 13(9): 10768-10775, 2019 Sep 24.
Artigo em Inglês | MEDLINE | ID: mdl-31491079

RESUMO

Controlled substitutional doping of two-dimensional transition-metal dichalcogenides (TMDs) is of fundamental importance for their applications in electronics and optoelectronics. However, achieving p-type conductivity in MoS2 and WS2 is challenging because of their natural tendency to form n-type vacancy defects. Here, we report versatile growth of p-type monolayer WS2 by liquid-phase mixing of a host tungsten source and niobium dopant. We show that crystallites of WS2 with different concentrations of substitutionally doped Nb up to 1014 cm-2 can be grown by reacting solution-deposited precursor film with sulfur vapor at 850 °C, reflecting the good miscibility of the precursors in the liquid phase. Atomic-resolution characterization with aberration-corrected scanning transmission electron microscopy reveals that the Nb concentration along the outer edge region of the flakes increases consistently with the molar concentration of Nb in the precursor solution. We further demonstrate that ambipolar field-effect transistors can be fabricated based on Nb-doped monolayer WS2.

6.
Chem Commun (Camb) ; 55(74): 11045-11048, 2019 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-31453574

RESUMO

Ag NPs are encapsulated into ZIF-71 via a deposition-reduction method. The resulting products are tested as adjustable molecular sieves for hydrogen and acetone. The gas sensing performances show that the response to acetone is reduced and that to hydrogen increased, demonstrating an engineered selectivity. A novel design of molecular sieving MOF materials for gas separation in gas-sensing selectivity is thus provided.

7.
ACS Appl Mater Interfaces ; 11(22): 20535-20544, 2019 Jun 05.
Artigo em Inglês | MEDLINE | ID: mdl-31081609

RESUMO

For the stretchable electrode, strong interface adhesion is the primary guarantee for long service life, and the maximization of the tensile limit with remarkable electrical stability can expand the scope of its use. Here, a cost-effective strategy is proposed to fabricate a high-adhesion stretchable electrode. By modifying dopamine and functionalized silane on a polydimethylsiloxane (PDMS) substrate in sequence before the electroless deposition process, super-high adhesion up to 3.1 MPa is achieved between the PDMS substrate and silver layer, and the electrode exhibits extraordinary conductivity of 4.0 × 107 S/m. This process is also suitable for other common flexible substrates and metals. Moreover, inspired by the micro-/nanostructure on the surface of lotus leaf, a biomimetic elastomeric micropore film with a uniformly distributed micropore is fabricated by the one-step soft lithography replication process. The electrode exhibits a large tensile limit exceeding 70% uniaxial tensile and superior electrical stability from 6.3 to 11.5 Ω under 20% uniaxial tensile for more than 10 000 cycles. This study seeks a promising method to manufacture stretchable electrodes with high adhesion, large tensile limit, and excellent electrical stability, showing great potential to detect various biological signals including joint movement, surface electromyography, and so forth.

8.
Small ; 15(10): e1804559, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30714294

RESUMO

Flexible pressure sensors as electronic skins have attracted wide attention to their potential applications for healthcare and intelligent robotics. However, the tradeoff between their sensitivity and pressure range restricts their practical applications in various healthcare fields. Herein, a cost-effective flexible pressure sensor with an ultrahigh sensitivity over an ultrawide pressure-range is developed by combining a sandpaper-molded multilevel microstructured polydimethylsiloxane and a reduced oxide graphene film. The unique multilevel microstructure via a two-step sandpaper-molding method leads to an ultrahigh sensitivity (2.5-1051 kPa-1 ) and can detect subtle and large pressure over an ultrawide range (0.01-400 kPa), which covers the overall pressure regime in daily life. Sharp increases in the contact area and additional contact sites caused by the multilevel microstructures jointly contribute to such unprecedented performance, which is confirmed by in situ observation of the gap variations and the contact states of the sensor under different pressures. Examples of the flexible pressure sensors are shown in potential applications involving the detection of various human physiological signals, such as breathing rate, vocal-cord vibration, heart rate, wrist pulse, and foot plantar pressure. Another object manipulation application is also demonstrated, where the material shows its great potential as electronic skin intelligent robotics and prosthetic limbs.

9.
Langmuir ; 35(9): 3248-3255, 2019 Mar 05.
Artigo em Inglês | MEDLINE | ID: mdl-30759983

RESUMO

The detection of trace amount of volatile organic compounds (VOCs) has been covered by tons of researches, which are dedicated to improve the detection limit and insensitivity to humidity. In this work, we have synthesized ZnO@ZIF-71 nanorod arrays (NRAs) equipped with the adsorption effect at metal site that promoted the detection limit of ethanol and acetone, to which also have great selectivity. The gas sensor not only exhibits shorter response/recovery time (53/55% for ethanol, 48/31% for acetone), but also excellent insensitivity to humidity and improved detection limit (10× improved at 21 ppb for ethanol, 4× at 3 ppb for acetone) at low working temperature (150 °C). By the analysis of in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and calculation of density functional theory (DFT), the mechanism of enhanced gas sensing performance from ZnO@ZIF-71 NRAs is proved. It shows ethanol and acetone gas molecules can be adsorbed at the metal sites of ZIF-71. This work provides a new idea to improve the detection limit and humidity-insensitivity of gas sensor toward specific gas molecules.

10.
ACS Sens ; 3(12): 2629-2636, 2018 12 28.
Artigo em Inglês | MEDLINE | ID: mdl-30456951

RESUMO

Black and blue phosphorus (both allotropes of elementary phosphorus) have recently been widely explored as an active material for electronic devices, and their potential in gas sensing applications has been demonstrated. On the other hand, amorphous red phosphorus (a-RP), a much cheaper and readily available phosphorus allotrope, has seldom been investigated as an electronic material, and its gas sensing properties have never been studied. In this work we have investigated these properties of a-RP by combining experimental characterizations with theoretical calculations. We found that a-RP exhibited an amphoteric character for detecting both commonly regarded reducing and oxidizing gas molecules, featuring a negative correlation between the electrical resistance of a-RP and the gas concentration. Interestingly, the a-RP based sensors appear to be particularly suitable for room-temperature NO2 detection, exhibiting excellent sensitivity and selectivity, as well as fast temporal response and recovery. A unique sensing feature of a-RP toward NO2 was identified, which is associated with the expansion of P-P bonds upon NO2 chemisorption. Based on density functional theory calculations we proposed a physiochemical model to elaborate the synergistic effects of the P-P bond expansion and Langmuir isotherm adsorption on the electronic properties and gas sensing processes of a-RP.


Assuntos
Dióxido de Nitrogênio/análise , Fósforo/química , Semicondutores , Adsorção , Teoria da Densidade Funcional , Técnicas Eletroquímicas/métodos , Gases/análise , Gases/química , Modelos Químicos , Dióxido de Nitrogênio/química , Oxirredução , Temperatura Ambiente
11.
Langmuir ; 34(48): 14577-14585, 2018 12 04.
Artigo em Inglês | MEDLINE | ID: mdl-30423250

RESUMO

In this work, we report a metal-organic framework (MOF)-assisted strategy to synthesize necklace-like TiO2/Co3O4 nanofibers with highly ordered heterostructures via a facile approach including electrospinning and subsequent calcination. Polycrystalline TiO2 nanofibers and Co3O4 nanocages are consummately interconnected to form a highly ordered heterogeneous nanostructure, which can be of benefit for precisely accommodating the interface resistance of the p-n heterojunctions and the future realization of improved material performance. The ethanol-gas-sensing investigation showed that TiO2/Co3O4 nanofiber sensors exhibited a strong ethanol response ( Rair/ Rgas -1 = 16.7 @ 150 ppm) and a low operating temperature of 150 °C. The sensing enhancement mechanism of the TiO2/Co3O4 nanofibers is related to the formation of heterojunctions at interfaces and the high catalytic activity of MOF-derived Co3O4. Furthermore, this versatile method is a promising approach to constructing ordered heterostructures and extending the MOF-based heterogeneous materials toward wide applications.

12.
ACS Appl Mater Interfaces ; 9(32): 27102-27110, 2017 Aug 16.
Artigo em Inglês | MEDLINE | ID: mdl-28745045

RESUMO

Two-dimensional (2D) ultrathin metal chalcogenides represent a class of promising materials for various applications thanks to attractive physicochemical properties. However, a reliable pathway for fabricating ultrathin metal chalcogenides nanosheets, regardless of the bulk crystals of their 3D counterparts, still remains a challenge. Herein, we present a versatile solution-processed template synthesis strategy, in which a single molecular-level precursor anneals to ultrathin single-crystal nanosheets with the aid of lattice-matching templates, following the Frank-van der Merwe growth mode and featuring high quality, low cost, scalability, and processability. Following this strategy, Sb2S3, MoS2, and ZnS nanosheets are successfully prepared as representatives for materials whose bulk counterparts possess 1D, 2D, and 3D crystal structures, respectively, and the growth mechanism is confirmed by crystal mode analysis. As a proof-of-concept application, MoS2 and Sb2S3 nanosheets are used for gas sensor and flexible photodetector applications, respectively, which exhibit excellent performance. The method can also be easily extended to other ultrathin nanosheets like single metals, metal oxide, metal nitride, and heterostructures.

13.
Phys Chem Chem Phys ; 19(9): 6313-6329, 2017 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-28198897

RESUMO

Metal-oxide-semiconductor (MOS) based gas sensors have been considered a promising candidate for gas detection over the past few years. However, the sensing properties of MOS-based gas sensors also need to be further enhanced to satisfy the higher requirements for specific applications, such as medical diagnosis based on human breath, gas detection in harsh environments, etc. In these fields, excellent selectivity, low power consumption, a fast response/recovery rate, low humidity dependence and a low limit of detection concentration should be fulfilled simultaneously, which pose great challenges to the MOS-based gas sensors. Recently, in order to improve the sensing performances of MOS-based gas sensors, more and more researchers have carried out extensive research from theory to practice. For a similar purpose, on the basis of the whole fabrication process of gas sensors, this review gives a presentation of the important role of screening and the recent developments in high throughput screening. Subsequently, together with the sensing mechanism, the factors influencing the sensing properties of MOSs involved in material preparation processes were also discussed in detail. It was concluded that the sensing properties of MOSs not only depend on the morphological structure (particle size, morphology, pore size, etc.), but also rely on the defect structure and heterointerface structure (grain boundaries, heterointerfaces, defect concentrations, etc.). Therefore, the material-sensor integration was also introduced to maintain the structural stability in the sensor fabrication process, ensuring the sensing stability of MOS-based gas sensors. Finally, the perspectives of the MOS-based gas sensors in the aspects of fundamental research and the improvements in the sensing properties are pointed out.

14.
Phys Chem Chem Phys ; 19(16): 10695-10697, 2017 04 19.
Artigo em Inglês | MEDLINE | ID: mdl-27352959

RESUMO

Correction for 'Enhanced room temperature NO2 response of NiO-SnO2 nanocomposites induced by interface bonds at the p-n heterojunction' by Jian Zhang et al., Phys. Chem. Chem. Phys., 2016, 18, 5386-5396.

15.
Sci Rep ; 6: 32310, 2016 08 26.
Artigo em Inglês | MEDLINE | ID: mdl-27561350

RESUMO

Recently, graphene nanomesh (GNM) has attracted great attentions due to its unique porous structure, abundant active sites, finite band gap and possesses potential applications in the fields of electronics, gas sensor/storage, catalysis, etc. Therefore, diverse GNMs with different physical and chemical properties are required urgently to meet different applications. Herein we demonstrate a facile synthetic method based on the famous Fenton reaction to prepare GNM, by using economically fabricated graphene oxide (GO) as a starting material. By precisely controlling the reaction time, simultaneous regulation of pore size from 2.9 to 11.1 nm and surface structure can be realized. Ultimately, diverse GNMs with tunable band gap and work function can be obtained. Specially, the band gap decreases from 4.5-2.3 eV for GO, which is an insulator, to 3.9-1.24 eV for GNM-5 h, which approaches to a semiconductor. The dual nature of electrophilic addition and oxidizability of HO(•) is responsible for this controllable synthesis. This efficient, low-cost, inherently scalable synthetic method is suitable for provide diverse and optional GNMs, and may be generalized to a universal technique.

16.
Phys Chem Chem Phys ; 18(7): 5386-96, 2016 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-26818788

RESUMO

Recently, heterostructured nanomaterials have attracted great attention in gas sensing applications. However, the sensing mechanism of the enhanced sensitivity of heterostructured nanomaterials remains unclear, which is not conducive to further improvements in their sensing performances. In order to detail the fundamental studies on the gas sensing mechanism of heterostructured nanomaterials and improve the room temperature NO2 sensing properties of NiO-based nanomaterials, NiO-SnO2 heterojunction nanocomposites were fabricated. It was found that the sensitivity of the nanocomposites was largely enhanced compared to the bare NiO. On the basis of the intrinsic characteristics of the p-n heterojunction and the band structure of the NiO-SnO2 heterojunction, the largely enhanced room temperature NO2 response of the nanocomposites could be attributed to two factors. One was the significantly decreased initial conductance, and the increase in the equivalent hole concentration of the nanocomposites after exposure to NO2, associated with the effective electron transfer via the interface bonds at the heterojunction. Another was that the variation of contact potential in the nanocomposites, before and after exposure to NO2, exerted a drastic effect on the transducer function for gas sensing. According to the differentiation in the sensitivity of the nanocomposites with different molar ratios, the important role of interface bonds in gas sensing properties was further illustrated by the dependency of the sensitivity on the interface bond number and the interface resistance. Here, we hope that this work could give us a better understanding of the gas sensing mechanism of the p-n heterojunction, and provide a proper approach for heterojunction materials to further improve their sensing performances.

17.
Phys Chem Chem Phys ; 17(41): 27437-45, 2015 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-26421631

RESUMO

Lowering the working temperature without sacrificing other good gas-sensing properties is of particular interest to gas sensors for an excellent performance. In this work, La surface doped ZnO nanocrystals were successfully prepared by a facile thermal treatment with lanthanum nitrate (La(NO3)3) solution injected into ZnO thick films, which exhibited a remarkable decrease in the optimal working temperature for formaldehyde (HCHO) sensing properties. This was probably attributed to the formation of surface LaZn defects in the ZnO nanocrystals which was evidenced by XRD, XPS results and DFT calculations. The surface LaZn defects can introduce a shallower donor level than oxygen vacancies, and probably facilitate the charge transfer from oxygen species to ZnO for producing chemisorbed oxygen species more easily. This was in good agreement with the DFT results that the absorption energy of oxygen molecules on the surface of La doped ZnO was only -10.61 eV, much lower than that of pure ZnO. Moreover, the optimal working temperature of the La doped ZnO based sensor was significantly decreased from 350 to 250 °C without sacrificing the high and quick response to HCHO gas as the content of surface LaZn defects was increased gradually. Therefore, the behavior of the surface LaZn defects in the optimal working temperature revealed a HCHO response mechanism in ZnO, which can provide new insights into the enhanced HCHO sensing performance of gas sensors.

18.
ACS Appl Mater Interfaces ; 7(21): 11359-68, 2015 Jun 03.
Artigo em Inglês | MEDLINE | ID: mdl-25955292

RESUMO

Unique gas-sensing properties of semiconducting hybrids that are mainly related to the heterogeneous interfaces have been considerably reported. However, the effect of heterogeneous interfaces on the gas-sensing properties is still unclear, which hinders the development of semiconducting hybrids in gas-sensing applications. In this work, SnO2-SnS2 hybrids were synthesized by the oxidation of SnS2 at 300 °C with different times and exhibited high response to NH3 at room temperature. With the increasing oxidation time, the relative concentration of interfacial Sn bonds, O-Sn-S, among the total Sn species of the SnO2-SnS2 hybrids increased first and then decreased. Interestingly, it can be found that the response of SnO2-SnS2 hybrids to NH3 at room temperature exhibited a strong dependence on the interfacial bonds. With more chemical bonds at the interface, the lower interface state density and the higher charge density of SnO2 led to more chemisorbed oxygen, resulting in a high response to NH3. Our results revealed the real roles of the heterogeneous interface in gas-sensing properties of hybrids and the importance of the interfacial bonds, which offers guidance for the material design to develop hybrid-based sensors.

19.
Phys Chem Chem Phys ; 17(22): 14903-11, 2015 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-25982556

RESUMO

In recent years, there has been increasing interest in synthesis of reduced graphene oxide (rGO)-metal oxide semiconductor (MOS) nanocomposites for room temperature gas sensing applications. Generally, the sensitivity of a MOS can be obviously enhanced by the incorporation of rGO. However, a lack of knowledge regarding how rGO can enhance gas-sensing performances of MOSs impedes its sensing applications. Herein, in order to get an insight into the sensing mechanism of rGO-MOS nanocomposites and further improve the sensing performances of NiO-based sensors at room temperature, an rGO-NiO nanocomposite was synthesized. Through a comparison study on room temperature NO2 sensing of rGO-NiO and pristine NiO, an inverse gas-sensing behavior in different NO2 concentration ranges was observed and the sensitivity of rGO-NiO was enhanced obviously in the high concentration range (7-60 ppm). Significantly, the stimulating effect of rGO on the recovery rate was confirmed by the sensing characteristics of rGO-NiO that was advantageous for the development of NO2 sensors at room temperature. By comprehending the electronic interactions between the rGO-MOS nanocomposite and the target gas, this work may open up new possibilities for further improvement of graphene-based hybrid materials with even higher sensing performances.

20.
Phys Chem Chem Phys ; 16(39): 21349-55, 2014 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-25179434

RESUMO

First-principle calculations have been carried out to investigate structural stabilities, electronic structures and optical properties of tungsten doped bismuth oxychloride (BiOCl). The structures of substitutional and interstitial tungsten, and in the form of WO6-ligand-doped BiOCl are examined. The substitutional and interstitial tungsten doping leads to discrete midgap states within the forbidden band gap, which has an adverse effect on the photocatalytic properties. On the other hand, the WO6-ligand-doped BiOCl structure induces a continuum of hybridized states in the forbidden gap, which favors transport of electrons and holes and could result in enhancement of visible light activity. In addition, the band gap of WO6-BiOCl decreases by 0.25 eV with valence band maximum (VBM) shifting upwards compared to that of pure BiOCl. By calculating optical absorption spectra of pure BiOCl and WO6-ligand-doped BiOCl structure, it is found that the absorption peak of the WO6-ligand-doped BiOCl structure has a red shift towards visible light compared with that of pure BiOCl, which agrees well with experimental observations. These results reveal the tungsten doped BiOCl system as a promising material in photocatalytic decomposition of organics and water splitting under sunlight irradiation.

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