Chengjun Dong

Combustion synthesis of porous Pt-functionalized SnO2 sheets for isopropanol gas detection with a significant enhancement in response

Pt-functionalized SnO2 sheets with Pt contents of 0, 0.5, 1, and 2 wt% were synthesized by a facile solution combustion synthesis, and their crystal structure, morphology, and chemistry have been thoroughly characterized. In the combustion process, the urea (CO(NH2)2) has been employed as a fuel. The obtained products appear as porous sheets formed by the interconnected and loosely packed SnO2 nanoparticles. Pt nanoparticles are assembled together with SnO2 nanoparticles in several up to tens of nanometer clusters. The as-synthesized products were used as sensing materials in the sensors to detect the isopropanol (IPA) gas. Gas sensing tests exhibited that the Pt-functionalized SnO2 are highly promising for gas sensor applications, as the operating temperature was lower than current IPA sensors and the response to IPA was significantly enhanced. The 2 wt% Pt–SnO2 sheet based gas sensor displayed a response value of 190.50 for 100 ppm IPA at an optimized operating temperature of 220 °C, whereas the pristine SnO2 based gas sensor only showed a response of 21.53 under the same conditions. The roles of Pt nanoparticles on electronic sensitization of SnO2, catalytic oxidation (spillover effect), and the increased quantities of oxygen species on the surface of SnO2 are plausible reasons to explain the significant enhancement in response to a Pt-functionalized SnO2 sheet based gas sensor.

Ag–ZnO heterostructure nanoparticles with plasmon-enhanced catalytic degradation for Congo red under visible light

Ag–ZnO heterostructure nanoparticles were synthesized by a one-step solvothermal route from zinc acetate dihydrate (Zn(CH3COO)2·2H2O), silver nitrate (AgNO3), potassium hydroxide (KOH) and methanol (CH3OH). The structure, morphology, component and optical properties were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV-vis spectroscopy and photoluminescence spectroscopy, respectively. The results show that highly crystalline wurtzite-type ZnO nanoparticles matrices with an average grain size of 7.4 nm are obtained. Highly crystalline metallic Ag nanoparticles are observed on the ZnO matrix with a good combination. The absorption spectra of the Ag–ZnO heterostructure nanoparticles show the existence of a special two-absorption-region (strong UV-light and weak visible-light at 421 nm). The intensities of photoluminescence in the visible light region have a regular decrease with the increase in the load amount of Ag. The photoactivity of the as-synthesized samples was tested by measuring the degradation of azo dye Congo red (CR) under visible light irradiation. And it is found that both ZnO nanoparticles and Ag–ZnO heterostructured nanoparticles have better photocatalytic efficiency than commercial TiO2 (P-25), and an appropriate loading amount of Ag nanoparticles can significantly enhance the photocatalytic efficiency. The photodegradation mechanism as well as enhancement of the photoactivity in the presence of silver nanoparticles is further investigated. The experimental results indicate the potential of using Ag–ZnO heterostructured nanoparticles for degradation of Congo red dye.

Porous NiO nanosheets self-grown on alumina tube using a novel flash synthesis and their gas sensing properties

Porous NiO nanosheets were self-grown on an alumina tube with a pair of Au electrodes connected by platinum wires via a simple solution combustion synthesis. A cubic NiO phase was obtained by a mixed solution of an oxidizer of nickel nitrate and a fuel of ethylene glycol (EG) at 400 °C. The phases and the morphologies of the materials self-grown on an alumina tube were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results showed that the alumina tube was entirely covered by NiO nanosheets with several micrometers in thickness. The NiO nanosheets on the surface of the tube were assembled by a large number of nanoparticles of irregular shapes and pores with different sizes. The electronic and gas-sensing characteristics of the self-grown porous NiO nanosheets for volatile organic compound (VOC) vapours (ethanol, acetone, methanol, and formaldehyde) were investigated. The resistance of the sensor directly based on the self-grown NiO dramatically drops from 100–240 °C, and then slightly decreases with further increasing temperature to about 28 kΩ at 400 °C. The sensor based on the self-grown NiO exhibits low detection limit, fast response and recovery and wide dynamic range detection to VOC vapours, especially ethanol, at the respectively optimal operating temperatures.

Hydrothermal growth of ZnO nanorods on Zn substrates and their application in degradation of azo dyes under ambient conditions

A new type of catalytic material, large-scale ZnO nanorod arrays grown on self-source substrate, was directly synthesized by a facile hydrothermal approach. The catalytic activity of the ZnO nanocrystals with different exposed surfaces, including ZnO hexagonal nanorods with exposed reactive {0001} facets, hexagonal ZnO nanopyramids with nonpolar {010} planes, and pencil-like morphology with exposed {101} polar planes, was tested towards the degradation of the azo dyes (Congo red (CR) and methyl orange (MO)). The aqueous azo dyes can be degraded efficiently under ambient conditions, requiring neither light illumination nor additional energy (agitation, ultrasonic, etc.). Systematic experiments suggested that the dye degradation proceeds through electron transfers from the anionic dye molecules to the catalyst and then to electron acceptors such as dissolved oxygen. It strongly depends on the exposed polar surfaces of the ZnO nanocrystals, giving rise to the relatively higher catalytic activity and stability of the ZnO hexagonal nanopencils. The present ZnO nanorod arrays grown on the Zn substrate require no additional reagents or external energy input, which thus provides a potentially low-cost alternative for the remediation of azo-dye effluents.

Butane detection: W-doped TiO2 nanoparticles for a butane gas sensor with high sensitivity and fast response/recovery

This article describes a new option for butane detection: W-doped TiO2 nanoparticles with high sensitivity and fast response/recovery toward butane, which were obtained from a simple, non-aqueous sol–gel route. The structure, morphology, surface chemical state and specific surface area were analyzed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectrum (XPS) and N2-sorption isotherm, respectively. The obtained products are anatase-type TiO2 with a small grain size (7.5 ± 1.4 nm) and a high specific surface area (181.15 m2 g−1). Tungsten element presents in the +6 oxidation state. The resistance–temperature measurements indicate that tungsten dopant leads to the decrease in resistance. The as-prepared pure and W-doped TiO2 nanoparticles were used to fabricate gas sensor devices. Gas response toward 3000 ppm butane is increased from 6 to 17.8 through the doping of 5% tungsten. Meanwhile, the response and recovery time toward 3000 ppm butane are as fast as 2 and 12 s, respectively. Moreover, the sensor also possesses low detection limit, good linear dependence, good repeatability and long-term stability, indicating the potential of using W-doped TiO2 nanoparticles for butane gas detection. In addition, a possible mechanism for the enhanced sensitivity of W-doped TiO2 nanoparticles toward butane is also offered.

Facile synthesis of CuO micro-sheets over Cu foil in oxalic acid solution and their sensing properties towards n-butanol

Here, CuO micro-sheets were successfully synthesized from Cu foil using the annealing procedure. Cupric oxalate (CuC2O4·xH2O) micro-sheets were firstly peeled off by immersing Cu foil in oxalic acid solution at room temperature, and then they were converted into CuO with preserved configuration after thermal treatment at 350 °C. Various techniques were employed for the characterization of the structure and morphology of as-prepared products. Results revealed that the samples were composed of a large amount of porous CuO micro-sheets, which were constructed by plenty of nano-sized primary particles. A gas sensor was fabricated using as-prepared CuO micro-sheets and was systematically investigated for its ability to detect n-butanol. Due to the porous structure of CuO micro-sheets, the sensor based on CuO micro-sheets manifests a remarkably improved sensing performance, including high response, good selectivity, excellent reproducibility and stability, and limit of detection as low as 10 ppm at 160 °C, suggesting its greatly promising applications in gas sensing.

Facile synthesis of core–shell carbon nanotubes@MnOOH nanocomposites with remarkable dielectric loss and electromagnetic shielding properties

Carbon nanotubes (CNTs)@MnOOH core–shell nanocomposites, in which the CNTs core is uniformly coated with a shell of MnOOH nanoflakes, were successfully synthesized using a facile hydrothermal method. The appearance of sodium dodecyl benzene sulfonate (SDBS) plays a key role in forming the unique CNTs@MnOOH core–shell. A high dielectric loss tangent value was observed for the samples with/without SDBS. Significantly, the CNTs@MnOOH core–shell nanocomposites exhibit an electromagnetic shielding effectiveness of 13–15 dB in the frequency range of 8–18 GHz, which can be attributed to the improved absorption loss, resulting from the increased electrical conductivity, and the improved impedance matching of the core–shell structure. Moreover, the increasing interfaces between the MnOOH and CNTs favor the electromagnetic attenuation performance. Our findings strongly confirm that the CNTs@MnOOH core–shell nanocomposites can be considered as a potential candidate for electromagnetic applications.

Carbon spheres@MnO 2 core-shell nanocomposites with enhanced dielectric properties for electromagnetic shielding

Carbon spheres (CS)@MnO2 core-shell nanocomposites, with MnO2 nanoflakes uniformly coating at the surface of CS cores, were successfully synthesized by a facile water-bathing method. MnO2 amounts is estimated to be 24.7 wt% in CS@MnO2 nanocomposites. A high dielectric loss value and an electromagnetic shielding effectiveness of 16‒23 dB were observed for the CS@MnO2 in the frequency range of 8‒18 GHz, which is mainly attributed to the enhanced absorption loss. The incorporation of the CS with MnO2 improves the electrical conductivity. Meanwhile, the electromagnetic impendence matching has been significantly ameliorated. Moreover, the increasing interfaces between the CS and MnO2 facilitate the microwave attenuation as well. Thus, the electromagnetic shielding performances were greatly enhanced. Our findings provide an effective methodology for the synthesis of the CS@MnO2 core-shell nanocomposite for potential electromagnetic applications.

Cu2O templating strategy for the synthesis of octahedral Cu2O@Mn(OH)2 core–shell hierarchical structures with a superior performance supercapacitor

We demonstrate the design and fabrication of novel Cu2O@Mn(OH)2 core–shell hierarchical structures using octahedral Cu2O as a template. The Cu2O backbone supports the growth of an ultrathin Mn(OH)2 nanoflake shell, leading to a relatively large surface area (65.8 m2 g−1) for sufficient utilization of active materials. Cyclic voltammetry (CV) and galvanostatic charge–discharge measurements (GCD), as well as cycling stability and electrochemical impedance spectroscopy (EIS) were performed to examine the electrochemical performances of the Cu2O@Mn(OH)2 core–shell structure. Applied as a supercapacitor electrode, the Cu2O@Mn(OH)2 composite delivers a high specific capacitance of 540.9 F g−1 at 1 A g−1 and an energy density of 6.4–18.2 Wh kg−1. After conducting 3000 cycles at 5.0 A g−1, the capacitance retention of 71.5% was achieved. The unique core–shell structure of the Cu2O@Mn(OH)2 composite favours the effective transport of electrolytes and shortens the ion diffusion path. In addition, the synergetic effects from both Cu2O and Mn(OH)2 significantly enhance the electrochemical performances. Our findings suggest that this Cu2O@Mn(OH)2 core–shell is very promising for next generation high-performance supercapacitors.