One-step preparation of Cr2O3-based inks with long-term dispersion stability for inkjet applications

A light scattering camouflage membrane with similar solar spectrum reflectance to leaves based on a chlorophyll and titanium dioxide composite

To counter the hyperspectral detection under the background of vegetation, a light scattering camouflage polyvinyl alcohol membrane containing lithium chloride, chlorophyll (Chl) and titanium dioxide (TD) particles was developed according to the bionic principle. Based on the reflectance and transmittance of the membrane, the optical constants of all components of the membrane were inverted via the ray tracing model and four flux Kubelka-Munk model. Using the determined optical constants, the reflectances of the membranes with different component contents were predicted through the model, and the effects of TD, Chl and water contents on the reflectance of the membrane were elucidated, respectively. Besides, a military specification of the USA in the region of 760 to 1200 nm and an Osmanthus fragrans leaf were used as a spectrum requirement and a simulation object of the camouflage membrane, respectively, to determine the appropriate contents of TD, Chl and water. It is found that when the volume fractions of TD, Chl and water are 0.7%, 5% and 50%, respectively, the 0.3 mm thick membrane can not only meet the military specification but also exhibit a reflection spectrum similar to that of the leaf with a similarity of 0.976.

Fabrication and Characterization of Dielectric ZnCr2O4 Nanopowders and Thin Films for Parallel-Plate Capacitor Applications

We report here the successful shape-controlled synthesis of dielectric spinel-type ZnCr2O4 nanoparticles by using a simple sol-gel auto-combustion method followed by successive heat treatment steps of the resulting powders at temperatures from 500 to 900 °C and from 5 to 11 h, in air. A systematic study of the dependence of the morphology of the nanoparticles on the annealing time and temperature was performed by using field effect scanning electron microscopy (FE-SEM), powder X-ray diffraction (PXRD) and structure refinement by the Rietveld method, dynamic lattice analysis and broadband dielectric spectrometry, respectively. It was observed for the first time that when the aerobic post-synthesis heat treatment temperature increases progressively from 500 to 900 °C, the ZnCr2O4 nanoparticles: (i) increase in size from 10 to 350 nm and (ii) develop well-defined facets, changing their shape from shapeless to truncated octahedrons and eventually pseudo-octahedra. The samples were found to exhibit high dielectric constant values and low dielectric losses with the best dielectric performance characteristics displayed by the 350 nm pseudo-octahedral nanoparticles whose permittivity reaches a value of ε = 1500 and a dielectric loss tan δ = 5 × 10-4 at a frequency of 1 Hz. Nanoparticulate ZnCr2O4-based thin films with a thickness varying from 0.5 to 2 μm were fabricated by the drop-casting method and subsequently incorporated into planar capacitors whose dielectric performance was characterized. This study undoubtedly shows that the dielectric properties of nanostructured zinc chromite powders can be engineered by the rational control of their morphology upon the variation of the post-synthesis heat treatment process.

Disposable solar microcell array-based addressable photoelectrochemical sensor for high-throughput and multiplexed analysis of salivary metabolites

The high-throughput detection of multiple metabolites in saliva by electrochemical sensors is usually a challenge, which however is essential to the comprehensive evaluation of health status or screening of diseases. Here, a light-addressable and paper-based hydrogen peroxide (H₂O₂) photoelectrochemical (PEC) sensor for the high-throughput detection of multiple salivary metabolites is reported. This sensor has a unique solar microcell array structure with a silver nanowires/fullerene-Congo red (AgNWs/C₆₀-CR) disc working electrode (WE) and a single-walled carbon nanotubes/platinum nanowires (SWCNTs/PtNWs) ring reference/counter electrode (RE/CE) in each microcell. Enzymes of different metabolites are immobilized on different separated microcells of a cover slide over the sensor, from which enzymatically produced H₂O₂ can react with p-hydroxyphenyl boric acid (4-HPBA) on the WE of the sensor to generate hydroquinone (HQ) for photocurrent responses. Based on this strategy, a disposable PEC sensor of saliva was developed, which allows the multiplexed detection of uric acid (UA), glucose (GLU) and lactate (LA) in diluted human saliva with high sensitivity and selectivity. Moreover, the detection throughput and application field of the sensor can be easily extended by connecting a series of sensors in parallel or varying the enzymes. The present work thus establishes a cost-effective approach to the scalable construction of versatile biosensing platforms with tunable throughput and varied analytes.

Porous Cr2O3 Architecture Assembled by Nano-Sized Cylinders/Ellipsoids for Enhanced Sensing to Trace H2S Gas

How to achieve high sensing of Cr₂O₃-based sensors for harmful inorganic gases is still a challenge. To this end, Cr₂O₃ nanomaterials assembled from different building blocks were simply prepared by chromium salt immersion and air calcination with waste scallion roots as the biomass template. The hierarchical architecture calcined at 600 °C is constructed from nanocylinders and nanoellipsoids (named as Cr₂O₃-600), and also possesses multistage pore distribution for target gas accessibility. Interestingly, the synergism of two shapes of nanocrystals enables the Cr₂O₃-based sensor to realize highly sensitive detection of trace H₂S gas. At 170 °C, Cr₂O₃-600 exhibits a high response of 42.8 to 100 ppm H₂S gas, which is 3.45 times larger than that of Cr₂O₃-500 assembled from nanocylinders. Meanwhile, this sensor has a low detection limit of 1.0 ppb (S = 1.4), good selectivity, stability, and moisture resistance. These results show that the combination of nanosized cylinders/ellipsoids together with exposed (104) facet can effectively improve the sensing performance of the p-type Cr₂O₃ material. In addition, the Cr₂O₃-600 sensor shows satisfactory results for actual monitoring of the corruption process of fresh chicken.