Facile synthesis of catalase@ZIF-8 composite by biomimetic mineralization for efficient biocatalysis.

Enzymes immobilized in metal-organic frameworks (MOFs) have attracted great attention as a promising hybrid material. In the study, a novel biomimetic mineralization encapsulation process for a highly stable and easily reusable catalase (CAT)@ZIF-8 composite has been designed. This immobilization process provides a high enzyme loading of 70 wt %. The CAT@ZIF-8 composites exhibited a much lower Km value and better enzyme activity than those of free CAT, exhibiting good stability against enzymatic hydrolysis and protein denaturation under harsh conditions. The inhibitory effects of pesticides such as pH, temperature, solvent (i.e., methanol, dimethyl sulfoxide and tetrahydrofuran) and storage at room temperature (6 months) on the activity of free and immobilized catalase enzyme were investigated. The CAT@MOF composites also exhibited excellent reusability, an obvious advantage for treating a wastewater from food processing. The CAT@MOF developed is promising for the efficient removal of H2O2 under harsh conditions.

Photocatalytic degradation of an organophosphorus pesticide using a ZnO/rGO composite.

A zinc oxide (ZnO)/reduced graphene oxide (rGO) nanocomposite was synthesized via a hydrothermal synthesis method and used for the photocatalytic degradation of dimethoate. In the synthesis process of the ZnO/rGO nanocomposite, hexamethylenetetramine (HMT) was used as both a mineralizer and reducing agent. When the ZnO nanoparticles formed on the surfaces of graphene oxide sheets, the sheets were simultaneously reduced by HMT to form rGO. The photodegradation rate and photodegradation efficiency of dimethoate by the ZnO/rGO nanocomposite were 4 and 1.5 times, respectively, higher than those of bare ZnO. The ZnO/rGO nanocomposite possessed a high surface area of 41.0 m2 g-1 and pore volume of 4.72 × 10-3 cm3 g-1, which were conducive to the adsorption and mass transfer of pesticides and oxygen. The enhanced photocatalytic performance of the ZnO/rGO nanocomposite was attributed to the decrease in electron-hole recombination rate and effective carrier transport caused by the presence of rGO. Photoelectrochemical measurements confirmed that the nanocomposite exhibited a high charge transfer rate at the ZnO/rGO interface. These results indicate that ZnO/rGO nanocomposites have great application potential in pollutant degradation.

Facile synthesis of highly efficient fluorescent carbon dots for tetracycline detection.

Rampant use of tetracycline in animal feed is a threat to food security, the environment, and human health because of the risk of drug residues. Therefore, it is necessary to establish a sensitive, efficient, and reliable method for qualitative and quantitative detection of tetracycline. In this paper, we synthesized fluorescent carbon dots (FCDs) by thermal cracking of crab shell waste, and obtained a fluorescence quantum yield of 30%. Characterization of the FCDs by transmission electron microscopy, Fourier-transform infrared spectroscopy, ultraviolet visible absorption spectroscopy, and photoluminescence spectroscopy showed that they were fluorescent and evenly distributed with an average size of approximately 10 nm. We designed a sensitive probe for detecting tetracycline using the fluorescence intensity change of the FCDs. This method is sensitive, inexpensive, and environmentally friendly. The concentration of tetracycline was examined by comparing the fluorescence intensities of the FCDs before and after tetracycline addition. The limit of detection for tetracycline was 0.005 mg/L (signal-to-noise ratio = 3), which is promising for method development.

In situ synthesis of ZnO-GO/CGH composites for visible light photocatalytic degradation of methylene blue.

A novel ZnO-GO/CGH composite was prepared using an in situ synthesis process for photodegradation of methylene blue under visible light illumination. The chitin-graphene composite hydrogel (CGH) was used to provide uniform binding of the nano ZnO-GO composite to the hydrogel surface and prevent their agglomeration. GO provides multi-dimensional protons and electron transport channels for ZnO with a flower-like structure, which possessed improved photo-catalytic activity. SEM analysis indicates that the hydrogel has good adsorption properties with rougher surfaces and porous microstructure, which enables it to adsorb the dyes effectively. Under synergetic enhancement of adsorption and photo-catalysis, catalytic activity and nano ZnO-GO/CGH recycling improved greatly. Synthesized nano ZnO-GO/CGH showed high dye removal efficiency of 99%, about 2.2 times that of the pure chitin gel under the same condition. This suggests the potential application of the new photocatalytic composites to remove organic dyes from wastewater.

Use of long-term stable CsPbBr3 perovskite quantum dots in phospho-silicate glass for highly efficient white LEDs.

We report the synthesis of CsPbBr3 QDs with great stability and high quantum yield in phospho-silicate glass, which was fabricated by using a heat-treatment approach, for white light emitting devices. QD glasses exhibited excellent photo- and thermal stability, and significantly prolonged the lifetime of light emitters under ambient air conditions.