ABSTRACT
Thermal insulation materials with good flame-retardant properties have attracted widespread attention because of their huge application potential. Traditional petrochemical-based polymer insulation materials are flammable and have problems with environmental pollution. The microtubule structure is a perfect microstructure with excellent thermal insulation performance. In addition, the microtubule structure also has low density and high elasticity. Therefore, the microtubule structure is an important reference microstructure for the development of efficient thermal insulation materials. In this paper, a cellulose/SiO2 composite microtube thermal insulation superfoam has been successfully prepared. Cellulose microtubules were successfully prepared from poplar sawdust by chemical methods. The SiO2 aerogel precursor solution can be quickly adsorbed by the delignified cellulose microtubes. The SiO2 aerogel shells are evenly distributed only on the inner and outer walls of the delignified cellulose microtubes. The cellulose/SiO2 microtube composite (CSMC) superfoam exhibits low density, good mechanical properties, and low thermal conductivity (as low as 0.042 ± 0.0018 W m-1 K-1). The CSMC superfoam exhibits excellent self-extinguishing and flame-retardant properties. After being burned by a butane flame, the superfoam still has certain mechanical properties. The thermal conductivity of the B-CSMC superfoam (the CSMC superfoam burned by a butane flame) is about 0.050 W m-1 K-1. The B-CSMC superfoam remained almost unchanged after being continuously ablated by a butane flame for 3600 seconds.
ABSTRACT
High-performance thermal insulation materials with broad application prospects have attracted great attention. The introduction of new microstructures into thermal protection materials can significantly improve the thermal insulation performance. The tubular microstructure has obvious advantages such as thermal insulation, lightweight, mechanical, and other properties. Therefore, the microtubular structure has become an important reference microstructure for the development of high-performance thermal insulation materials. In this paper, the carbon/ZrO2 aerogel composite microtube superfoams with excellent thermal protection properties were prepared by a vacuum filtration and high-temperature carbonization method. The ZrO2 aerogel precursor solution can be quickly and uniformly adsorbed on the inner and outer walls of cellulose microtubules. These adsorbed ZrO2 aerogel precursor solution films can be converted into ZrO2 alcohol gel shells under the acceleration and promotion effect of citric acid at 65 °C. The micromorphology of the ZrO2 aerogel shell on the inner and outer walls of the composite microtubes can be efficiently controlled by the concentration of the ZrO2 aerogel precursor solution and the carbonization temperature. The carbon/ZrO2 aerogel composite microtube superfoam exhibits a lower thermal conductivity, lower density, good mechanical properties, and high ablation resistance. The thermal conductivity of the carbon/ZrO2 aerogel composite microtube superfoam is as low as 0.040 ± 0.001 W m-1 K-1. The residual rate of the carbon/ZrO2 aerogel composite microtube superfoam is still as high as 84.33% after butane flame ablation for up to 3600 seconds.
ABSTRACT
The detection of foodborne pathogens is crucial for food hygiene regulation and disease diagnosis. Colorimetry has become one of the main analytical methods in studying foodborne pathogens due to its advantages of visualization, low cost, simple operation, and no complex instrument. However, the low sensitivity limits its applications in early identification and on-site detection for trace analytes. In order to overcome such a limitation, herein we propose a joint strategy featuring dual signal amplification based on the hybridization chain reaction (HCR) and DNA-enhanced peroxidase-like activity of gold nanoparticles (AuNPs) for the sensitive visual detection of Escherichia coli. Target bacteria bound specifically to the aptamer domain in the capture hairpin probe, exposing the trigger domain for HCR and forming the extended double-stranded DNA (dsDNA) structures. The peroxidase-like catalytic capacity of AuNPs can be enhanced significantly by dsDNAs with the sticky ends of dsDNAs being adsorbed on AuNPs and the rigidity of dsDNAs causing the spatial regulation of AuNP concentration. The intensity of the enhancement was linearly related to the number of target bacteria. With the above strategy, the detection limit of our colorimetric method for Escherichia coli was down to 28 CFU mL-1 within a short analytical time (50 min). This study provides a new perspective for the sensitive and visual detection of early bacterial contamination in foods.
