Synthesis and Characterization of ZnO-Nanostructured Particles Produced by Solar Ablation

Nowadays, nanotechnology offers opportunities to create new features and functions of emerging materials. Correlation studies of nanostructured materials' development processes with morphology, structure, and properties represent one of the most important topics today due to potential applications in all fields: chemistry, mechanics, electronics, optics, medicine, food, or defense. Our research was motivated by the fact that in the nanometric domain, the crystalline structure and morphology are determined by the elaboration mechanism. The objective of this paper is to provide an introduction to the fundamentals of nanotechnology and nanopowder production using the sun's energy. Solar energy, as part of renewable energy sources, is one of the sources that remain to be exploited in the future. The basic principle involved in the production of nanopowders consists of the use of a solar energy reactor concentrated on sintered targets made of commercial micropowders. As part of our study, for the first time, we report the solar ablation synthesis and characterization of Ni-doped ZnO performed in the CNRS-PROMES laboratory, UPR 8521, a member of the CNRS (French National Centre for Scientific Research). Also, we study the effect of the elaboration method on structural and morphological characteristics of pure and doped ZnO nanoparticles determined by XRD, SEM, and UV-Vis.

The modification effect of Fe2O3 nanoparticles on ZnO nanorods improves the adsorption and detection capabilities of TEA

The depletion layer and more active sites are the key factors for improving the gas sensitivity of an Fe2O3/ZnO sensor.

Gas Sensor Detecting 3-Hydroxy-2-butanone Biomarkers: Boosted Response via Decorating Pd Nanoparticles onto the {010} Facets of BiVO4 Decahedrons

The newly emerged gas sensing detection of 3-hydroxy-2-butanone (3H-2B) biomarker is deemed as an effective avenue to indirectly monitor Listeria monocytogenes (LM). However, 3H-2B sensing materials requiring critically high sensitivity and selectivity, and ppb-level detection limit, remain challenging. Here, we report the advanced gas sensors built with bismuth vanadate microdecahedron (BiVO₄ MDCD) {010} facets selectively decorated with Pd nanoparticles (Pd NPs, Pd-{010}BiVO₄ MDCDs) for boosted detection of the 3H-2B biomarker. Meanwhile, BiVO₄ MDCDs with overall facets are randomly deposited with Pd NPs (Pd-BiVO₄ MDCDs). Comparatively, Pd-{010}BiVO₄ MDCD sensors show 1 order of magnitude higher response toward the 3H-2B biomarker at 200 °C. Further, Pd-{010}BiVO₄ MDCD sensors enable to detect as low as 0.2 ppm 3H-2B and show best selectivity and stability, and fastest response and recovery. Density functional theory calculations reveal a lower adsorption energy of 3H-2B onto Pd-{010}BiVO₄ MDCDs than those of pristine and Pd-BiVO₄ MDCDs. The extraordinary Pd-{010}BiVO₄ sensing performance is ascribed to the Pd NP-assisted synergetic effect of the preferential adsorption of 3H-2B target molecules, accumulated sensing agent of ionic oxygen species, and concentrated catalysts on the {010} facets. This strategy offers rapid and noninvasive detection of LMs and is thus of great potential in the upcoming Internet of Things.

Nanoparticles: synthesis and applications

This chapter focuses on the synthesis, functionalization, and applications of metallic, semiconductor, magnetic, and multifunctional nanoparticles. Synthesis methods such as chemical reduction, coprecipitation, seeding, microemulsion, hydrothermal synthesis, and sonoelectrodeposition are outlined. Functionalized nanoparticles are suitable for numerous applications. Several applications of nanoparticles in life sciences and the enviromment are discussed. Finally, some future trends are pointed out.

Highly selective and sensitive methanol gas sensor based on molecular imprinted silver-doped LaFeO3 core-shell and cage structures

Silver-doped LaFeO₃ molecularly imprinted polymers (SLMIPs) were synthesized by a sol-gel method combined with molecularly imprinted technology as precursors. The precursors were then used to prepare SLMIPs cage (SLM-cage) and SLMIPs core-shell (SLM-core-shell) structures by using a carbon sphere as the template and hydrothermal synthesis, respectively. The structures, morphologies, and surface areas of these materials were determined, as well as their gas-sensing properties and related mechanisms. The SLM-cage and SLM-core-shell samples exhibited good responses to methanol gas, with excellent selectivity. The response and optimum working temperature were 16.98 °C and 215 °C, 33.7 °C and 195 °C, respectively, with corresponding response and recovery times of 45 and 50 s (SLM-cage) and 42 and 57 s (SLM-core-shell) for 5 ppm methanol gas. Notably, the SLM-cage and SLM-core-shell samples exhibited lower responses (≤5 and ≤7, respectively) to other gases, including ethanol, ammonia, benzene, acetone, and toluene. Thus, these materials show potential as practical methanol detectors.

A 3D Chemically Modified Graphene Hydrogel for Fast, Highly Sensitive, and Selective Gas Sensor

Reduced graphene oxide (RGO) has proved to be a promising candidate in high-performance gas sensing in ambient conditions. However, trace detection of different kinds of gases with simultaneously high sensitivity and selectivity is challenging. Here, a chemiresistor-type sensor based on 3D sulfonated RGO hydrogel (S-RGOH) is reported, which can detect a variety of important gases with high sensitivity, boosted selectivity, fast response, and good reversibility. The NaHSO3 functionalized RGOH displays remarkable 118.6 and 58.9 times higher responses to NO2 and NH3, respectively, compared with its unmodified RGOH counterpart. In addition, the S-RGOH sensor is highly responsive to volatile organic compounds. More importantly, the characteristic patterns on the linearly fitted response-temperature curves are employed to distinguish various gases for the first time. The temperature of the sensor is elevated rapidly by an imbedded microheater with little power consumption. The 3D S-RGOH is characterized and the sensing mechanisms are proposed. This work gains new insights into boosting the sensitivity of detecting various gases by combining chemical modification and 3D structural engineering of RGO, and improving the selectivity of gas sensing by employing temperature dependent response characteristics of RGO for different gases.

One-step hydrothermal preparation of Ce-doped MoO3 nanobelts with enhanced gas sensing properties

Rare earth ions are considered as the ideal dopants to modify the crystal structure, electronics structure, and gas sensing performance of metal oxides semiconductors.

Template-free synthesis of hierarchical ZnFe2O4 yolk-shell microspheres for high-sensitivity acetone sensors

Metal oxides with hierarchical microstructures have attracted tremendous attention with respect to their enhanced gas sensing properties. Herein, we reported the facile synthesis of hierarchical ZnFe2O4 yolk-shell microspheres via a template-free solvothermal strategy and the subsequent annealing and chemical etching process. Electron microscopy images undoubtedly demonstrated that the novel ZnFe2O4 architecture was constructed of a large number of nanosheet subunits with a thickness around 20 nm. As a proof-of-concept demonstration of the function, when evaluated as gas sensing materials, the as-prepared ZnFe2O4 yolk-shell microspheres manifested an extremely high response and a low detection limit to acetone at the operating temperature of 200 °C. Significantly, the response to 20 ppm acetone was retained well even after 200 cycles and continuous measurement for 30 days, indicating superior cyclability and long-term stability.

Temperature-Dependent Abnormal and Tunable p-n Response of Tungsten Oxide--Tin Oxide Based Gas Sensors

We observed the sensing response of temperature-dependent abnormal p-n transitions in WO3-SnO2 hybrid hollow sphere based gas sensors for the first time. The sensors presented a normal n-type response to ethanol at elevated temperatures but abnormal p-type responses in a wide range of operation temperatures (room temperature to about 95 °C). By measuring various reducing gases and applying complex impedance plotting techniques, we demonstrated the abnormal p-type sensing behavior to be a pseudo-response resulting from the reaction between target gas and adsorbed water on the material surface. The temperature-controlled n-p switch is ascribed to the competition of intrinsic and extrinsic sensing behaviors, which resulted from the reaction of target gas with adsorbed oxygen ions and protons from adsorbed water, respectively. The former can modulate the intrinsic conductivity of the sensor by changing the electron concentration of the sensing materials, while the latter can regulate the conduction of the water layer, which contributes to the total conductivity as an external part. The hollow and hybrid nanostructures facilitated the observation of extrinsic sensing behaviors due to its large-area active sites and abundant oxygen vacancies, which could enhance the adsorption of water. This work might give new insight into gas sensing mechanisms and opens up a promising way to develop practical temperature and humidity controllable gas sensors with little power consumption based on the extrinsic properties.

Nanosheet-assembled ZnFe2O4 hollow microspheres for high-sensitive acetone sensor

Semiconductor oxides with hierarchically hollow architecture can provide significant advantages as sensing materials for gas sensors by facilitating the diffusion of target gases. Herein, we develop a facile template-free solvothermal strategy combined with the subsequent thermal treatment process toward the successful synthesis of novel ZnFe2O4 hollow flower-like microspheres. The images of electron microscopy unambiguously indicated that the ZnFe2O4 nanosheets with thickness of around 20 nm assembled hierarchically to form the unique flower-like architecture. As a proof-of-concept demonstration of the function, the as-prepared product was utilized as sensing material for gas sensor. Significantly, in virtue of the porous shell structure, hollow interior, and large surface area, ZnFe2O4 hierarchical microspheres exhibited high response, excellent cyclability, and long-term stability to acetone at the operating temperature of 215 °C.

TiO2 Fibers Supported β-FeOOH Nanostructures as Efficient Visible Light Photocatalyst and Room Temperature Sensor

Hierarchical heterostructures of beta-iron oxyhydroxide (β-FeOOH) nanostructures on electrospun TiO₂ nanofibers were synthesized by a facile hydrothermal method. This synthesis method proves to be versatile to tailoring of β-FeOOH structural design that cuts across zero-dimensional particles (TF-P), one-dimensional needles (TF-N) to two-dimensional flakes (TF-F). In addition, synthesizing such oxyhyroxide nanostructures presents the advantage of exhibiting similar functional performances to its oxides counterpart however, without the need to undergo any annealing step which leads to undesirable structural collapse or sintering. The as-prepared hierarchical heterostructures possess high surface area for dye adsorptivity, efficient charge separation and visible photocatalytic activity. Also, for the first time, hydrogen gas sensing has been demonstrated on β-FeOOH nanostructures at room temperature. The reported hierarchical heterostructures of β-FeOOH on TiO₂ nanofibers afford multiple functions of photocatalysis and sensing which are highly promising for environment monitoring and clean up applications.

Highly Enhanced Sensing Properties for ZnO Nanoparticle-Decorated Round-Edged α-Fe₂O₃ Hexahedrons

ZnO/α-Fe2O3 composites built from plenty of ZnO nanoparticles decorated on the surfaces of uniform round-edged α-Fe2O3 hexahedrons were successfully prepared via a facile solvothermal method. Various techniques were employed to obtain the crystalline and morphological characterization of the as-prepared samples. In addition, a comparative sensing performance investigation between the two kinds of sensing materials clearly demonstrated that the sensing properties of ZnO/α-Fe2O3 composites were substantially enhanced compared with those of the single α-Fe2O3 component, which manifest the superiority of the ZnO decoration as we expected. For instance, the response of ZnO/α-Fe2O3 composites to 100 ppm acetone is ∼30, which is ∼3.15-fold higher than that of primary α-Fe2O3 hexahedrons. The synergetic effect is believed to be the source of the improvement of gas-sensing properties.

Facile synthesis of anisotropic single crystalline α-Fe2O3 nanoplates and their facet-dependent catalytic performance

Facet-dependent photocatalytic degradation of methylene blue was carried out using hexagonal and cylindrical hematite nanoplates.

Fabrication of porous g-C3N4/Ag/Fe2O3 composites with enhanced visible light photocatalysis performance

Porous graphitic carbon nitride (pg-C₃N₄) synthetized by pyrolysis of urea was hybridized with Ag-doped Fe₂O₃ to form a visible-light-driven photocatalyst pg-C₃N₄/Ag/Fe₂O₃via a simple chemical adsorption method.

Facile fabrication and enhanced gas sensing properties of hierarchical MoO3 nanostructures

Hierarchical MoO₃ nanostructures, synthesized through oxidization conversion of hydrothermally synthesized MoS₂ precursors, show superior gas sensing performance toward ethanol.

Dispersed SnO2 nanoparticles on MoS2 nanosheets for superior gas-sensing performances to ethanol

Novel composites with superior gas-sensing performance were successfully obtained by dispersing SnO₂ nanoparticles on the surfaces of MoS₂ nanosheets.

Vertically ordered hematite nanotube array as an ultrasensitive and rapid response acetone sensor

Vertically ordered nanotube array is a desirable configuration to improve gas sensing properties of the hematite which is the most abundant and cheapest metal oxide semiconductor on earth but has low and sluggish chemiresistive responses. We have synthesized a vertically aligned, highly ordered hematite nanotube array directly on a patterned SiO2/Si substrate and then it used as a gas sensor without additional processing. The nanotube array sensor shows unprecedentedly ultrahigh and selective responses to acetone with detection limits down to a few parts per billion and response time shorter than 3 s.

Nanocasting synthesis of In2O3 with appropriate mesostructured ordering and enhanced gas-sensing property

Ordered mesoporous In2O3 gas-sensing materials with controlled mesostructured morphology and high thermal stability have been successfully synthesized via a nanocasting method in conjunction with the container effect. The mesostructured ordering, as well as the particle size, crystallinity and pore size distribution have been proved to vary in a large range by using the XRD, SAXRD, SEM, TEM, and nitrogen physisorption techniques. The control of the mesostructured morphology was carried out by tuning the transportation rate of indium precursor in template channel resulting from the different escape rate of the decomposed byproducts via the varied container opening and shapes. The particular relation between the mesostructured ordering and gas sensing property of mesoporous In2O3 was examined in detail. It was found that the ordered mesoporous In2O3 with appropriate mesostructured morphology exhibited significantly improved ethanol sensitivity, response and selectivity performances in comparison with the other ordered mesoporous In2O3, which benefits from the large surface area with enough sensing active sites, proper pore distribution for sufficient gas diffusion, and appropriate particle size for effective electron depletion. The resulting sensing behaviors lead to a better understanding of designing and using such mesoporous metal oxides for a number of gas-sensing applications.

Flower-like In2O3 hierarchical nanostructures: synthesis, characterization, and gas sensing properties

Flower-like In₂O₃ nanostructures with superior ethanol sensing performance were synthesized by annealing In(OH)₃ precursor prepared via a one-step hydrothermal method.

C-isolated Ag-C-Co sandwich sphere-nanostructures and their high activity catalysis induced by surface plasmon resonance

Magnetic C-isolated Ag-C-Co sandwich sphere nanostructures have been fabricated through a synchronous growth and assembly process, in which the outer Co sphere-shells assemble around the surface of synchronously grown Ag-C sphere-cores. Raman and UV-vis absorption spectroscopy studies show that the covering of Co shell on Ag-C sphere cores weakens the surface-enhanced Raman scattering (SERS) and surface plasmon resonance (SPR) of Ag-C sphere cores. Owing to its ferromagnetic behaviour, the as-prepared C-isolated Ag-C-Co sandwich nanospheres can be easily separated and recycled by an external magnet field for application. Compared with Ag-Co, C-Co, and Co nanospheres of the same size, the resultant magnetic Ag-C-Co sandwich nanospheres exhibit markedly high catalytic activity toward ammonia borane hydrolytic dehydrogenation at atmospheric pressure and room temperature, which is induced by SPR from C-isolated sandwich structural and electronic synergistic effects.