Improving structural and functional properties of starch-catechin-based green nanofiber mats for active food packaging by electrospinning and crosslinking techniques.

The hydrophilic and low mechanical properties limited the application of starch-based films. In this work, a hydrophobic starch-based nanofiber mat was first successfully prepared from aqueous solution at room temperature by using electrospinning and glutaraldehyde (GTA) vapor phase crosslinking techniques for active packaging applications. Catechin (CAT) was immobilized in the nanofibers by electrospinning, resulting in higher thermal stability (Tdmax = 315.23 °C), antioxidant (DPPH scavenging activity = 94.31 ± 2.70 %) and antimicrobial (inhibition zone diameter = 15.6 ± 0.3 mm) of the fibers, which further demonstrated hydrogen bonding and electrostatic interaction between CAT and fibers. Nanofibers after GTA vapor phase crosslinking exhibited enhanced hydrophobicity (water contact angle: 15.6 ± 1.5° â†’ 93.5 ± 2.3°) and mechanical properties (tensile strength: 1.82 ± 0.06 MPa â†’ 7.64 ± 0.24 MPa, elastic modulus: 19.35 ± 0.63 MPa â†’ 45.34 ± 0.51 MPa). The results demonstrated that preparation of starch-based electrospun nanofiber mats in aqueous system at room temperature overcame the challenges of organic solvent pollution and thermosensitive material encapsulation, while GTA vapor phase crosslinking technique improved the hydrophobicity and mechanical properties of nanofiber mats, which facilitated the application of starch-based materials in the field of packaging.

Photoelectron Migration Boosted by Hollow Double-Shell Dyads Based on Covalent Organic Frameworks for Highly Efficient Photocatalytic Hydrogen Generation.

Photocatalytic hydrogen production based on noble metal-free systems is a promising technology for the conversion of solar energy into green hydrogen, it is pivotal and challenging to tailor-make photocatalysts for achieving high photocatalytic efficiency. Herein, we reported a hollow double-shell dyad through uniformly coating covalent organic frameworks (COFs) on the surface of hollow Co9S8. The double shell architecture enhances the scattering and refraction efficiency of incident light, shortens the transmission distance of the photogenerated charge carriers, and exposes more active sites for photocatalytic conversion. The hydrogen evolution rate is as high as 23.15 mmol g-1 h-1, which is significantly enhanced when compared with that of their physical mixture (0.30 mmol g-1 h-1) and Pt-based counterpart (11.84 mmol g-1 h-1). This work provides a rational approach to the construction of noble-metal-free photocatalytic systems based on COFs to enhance hydrogen evolution performance.

Intelligent food tag: A starch-anthocyanin-based pH-sensitive electrospun nanofiber mat for real-time food freshness monitoring.

A starch-based nanofiber mat was prepared for real-time monitoring of food freshness for the first time. UV-vis results showed that roselle anthocyanins (RS) conferred a wide pH sensing range on the nanofiber mat. The prepared nanofiber mats demonstrated good color visibility (total color difference value (ΔE) increased to 56.4 ± 0.7) and a reversible response (within 120 s). Scanning electron microscopy and Fourier transform infrared spectroscopy results suggested that the nanofibers had smooth surfaces without beaded fibers and that RS was well embedded into the nanofibers. The introduction of RS improved the thermal stability of the nanofibers. Color stability tests revealed that the nanofibers exhibited excellent color stability (maximum change ΔE = 1.57 ± 0.03) after 14 days of storage. Pork and shrimp freshness tests verified that the nanofibers could effectively reflect the dynamic freshness of pork and shrimp. Nontoxic, degradable and responsive characteristics make the pH-sensitive nanofiber mat a smart food label with great application potential.

Comparison of volatile and nonvolatile metabolites in green tea under hot-air drying and four heat-conduction drying patterns using widely targeted metabolomics.

Hot-air and heat-conduction drying are the most common drying patterns in green tea production. However, the differences between them in terms of the resulting green tea chemical compounds have not been illustrated systematically. In this study, 515 volatile and 204 nonvolatile metabolites were selected to compare the differences between hot-air drying green tea (HAGT) and four heat-conduction drying green teas (HCDGTs) using widely targeted metabolomics. The results showed notable changes in volatile compounds; for example, two kinds of HCDGTs preferred to form chestnut-like and caramel-like key odorants. In addition, 14 flavonol glycosides, 10 catechins, 9 phenolic acids, 8 amino acids, 7 flavonols, and 3 sugars were significantly changed between HAGT and HCDGTs (p < 0.05), presenting a tremendous discrepancy in the transformation of nonvolatile compounds. Our results provide clear guidance for the precise manufacturing of green tea by four common heat-drying patterns and hot air-drying patterns.

Organic solvent-free starch-based green electrospun nanofiber mats for curcumin encapsulation and delivery.

Developing green and efficient methods for the delivery of active food substances is a sustained demand for food scientists and industries. In this work, for the first time, we prepared a curcumin (CUR)-loaded starch-based fast-dissolving nanofiber by electrospinning technology. This green nanofiber was obtained by incorporating CUR with octenyl succinic anhydride starch (OSA) and pullulan (PUL) matrix using pure water as the solvent. To overcome the poor water-solubility and bioavailability of CUR, hydroxypropyl-beta-cyclodextrin (HPßCD) was used to form inclusion complexes. Phase solubility test results showed that by introducing HPßCD, the water-solubility of CUR was obviously improved. The prepared electrospun nanofibers were systematically characterized through scanning electron microscopy (SEM), X-ray diffraction (XRD), proton nuclear magnetic resonance spectroscopy (1H NMR), Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), encapsulation efficiency testing, solubility testing and antioxidant activity testing. The results demonstrated that CUR was well encapsulated into HPßCD and OSA/PUL/CUR-HPßCD electrospun nanofibers with fine morphology and fast-dissolving character were successfully prepared. It is worth noting that the whole process and raw materials were green, suggesting that the prepared fast-dissolving nanofiber has great application potential in the food and pharmaceutical fields.

Effect of red light on the composition of metabolites in tea leaves during the withering process using untargeted metabolomics.

BACKGROUND: Red light withering significantly improves the sensory flavor qualities of tea, although changes in metabolites during this process have not been systematically studied until now. The present study comprehensively analyzes metabolites in withered tea leaves at 2-h intervals up to 12 h under red light (630 nm) and dark conditions using ultra performance liquid chromatography-high resolution mass spectrometry (untargeted metabolomics). RESULTS: Ninety-four non-volatile compounds are identified and relatively quantified, including amino acids, catechins, dimeric catechins, flavonol glycosides, glycosidically-bound volatiles, phenolic acids and nucleosides. The results show that amino acids, catechins and dimeric catechins are most affected by red light treatment. Ten free amino acids, theaflavins and theasinensin A increase after red light irradiation, whereas epigallocatechin gallate and catechin fall. CONCLUSION: The present study provides a comprehensive and systematic profile of the dynamic effects of red light on withering tea and a rationale for its use in tea processing quality control. © 2021 Society of Chemical Industry.

Transformation of Covalent Organic Frameworks from N-Acylhydrazone to Oxadiazole Linkages for Smooth Electron Transfer in Photocatalysis.

Covalent organic frameworks (COFs) are regarded as new platforms for solar-to-chemical energy conversion due to their tailor-made functions and pre-designable structures. Their intrinsic reversibility and the high polarization of organic linkages inevitably result in poor chemical stability and weak optoelectronic properties. Herein, one N-acylhydrazone-linked COF (H-COF) was converted into a stable and π-conjugated oxadiazole-linked COF via post-oxidative cyclization. Both chemical stability and π-electron delocalization throughout the reticular framework are significantly improved, leading to a high hydrogen evolution rate of 2615 µmol g-1 h-1 upon visible light irradiation, which is over four times higher than that of H-COF. This work provides a facile protocol for the fabrication of π-conjugated COFs and the modulation of photophysical properties for photocatalytic application.

Regulating Utilization Efficiency of the Photogenerated Charge Carriers by Constructing Donor-π-Acceptor Polymers for Upgrading Photocatalytic CO2 Reduction.

Photocatalytic CO2 reduction offers a promising approach for managing global carbon balance. The smooth delivery of the photoexcited electrons to the active sites without the extra photosensitizers is still challenging. Herein, a series of donor-π-acceptor conjugated organic polymers (COPs) were produced using anthracene, cobalt-coordinated bipyridyl, and benzene as donor, acceptor, and π linker units, respectively. The introduction of phenyl linker significantly improved the activities of photocatalytic CO2 reduction upon visible light illumination. Structure-performance relationship examinations uncovered that donor-π-acceptor structure promotes mobility of charge carriers and utilization efficiency on the catalytically active sites, resulting in high photocatalytic activity and durability for CO2 photoreduction. The in-depth insights into the electron transport processes open new perspectives for further optimization and rational design of photoactive polymers with high efficiency for solar-energy conversion.

The Electrostatic Attraction and Catalytic Effect Enabled by Ionic-Covalent Organic Nanosheets on MXene for Separator Modification of Lithium-Sulfur Batteries.

It is of great significance to mediate the redox kinetics and shuttle effect of polysulfides in pursuit of high-energy-density and long-life lithium-sulfur (Li-S) batteries. Herein, a new strategy is proposed based on the electrostatic attraction and catalytic effect of polysulfides for the modification of the polypropylene (PP) separator. Guanidinium-based ionic-covalent organic nanosheets (iCON) on the surface of Ti3 C2 is presented as a coating layer for the PP separator. The synergetic effects of Ti3 C2 and iCON provide new platforms to suppress the shuttle effect of polysulfides, expedite the redox kinetics of sulfur species, and promote efficient conversion of the intercepted polysulfides. The functional separator endows carbon nanotube/sulfur cathodes with excellent electrochemical performance. The average capacity decay per cycle within 2000 cycles at 2 C is as low as 0.006%. The separator is even effective in the case of sulfur content of 90 wt% and sulfur loading of 7.6 mg cm-2 ; the reversible capacity, areal capacity, and volumetric capacity at 0.1 C are as high as 1186 mA h g-1 , 9.01 mA h cm-2 , and 1201 mA h cm-3 , respectively. This work provides a promising approach toward separator modification for the development of high-performance Li-S batteries.

Recent Advances on Metalloporphyrin-Based Materials for Visible-Light-Driven CO2 Reduction.

Photocatalytic CO2 reduction is a promising technology to mitigate environmental issue and the energy crisis. The four nitrogen atoms in the porphyrin ring can incorporate transition metals to form stable active sites for CO2 activation and photoreduction. Nevertheless, the photocatalytic efficiency of metalloporphyrins is still low due to the insufficient photoelectron injection to drive CO2 photoreduction upon visible light irradiation. To address this issue, considerable efforts have been made to introduce photosensitizers for constructing homogeneous or heterogeneous metalloporphyrin-based photocatalytic systems. In this Review, recent advances of metalloporphyrin-based materials for visible-light-driven CO2 reduction were summarized. The methods for the modulation of photosensitizing process at molecular level were presented for the promotion of photocatalytic performance. The mechanism of CO2 activation and photocatalytic conversion was illustrated. Better insight into the structure-activity relationship provides guidance to the design of metalloporphyrin-related photocatalytic systems.

Flexible Porous Organic Polymer Membranes for Protonic Field-Effect Transistors.

Artificial transistors represent an ideal means for meeting the requirements in interfacing with biological systems. It is pivotal to develop new proton-conductive materials for the transduction between biochemical events and electronic signals. Herein, the first demonstration of a porous organic polymer membrane (POPM) as a proton-conductive material for protonic field-effect transistors is presented. The POPM is readily prepared through a thiourea-formation condensation reaction. Under hydrated conditions and at room temperature, the POPM delivers a proton mobility of 5.7 × 10-3 cm2 V-1 s-1 ; the charge carrier densities are successfully modulated from 4.3 × 1017 to 14.1 × 1017 cm-3 by the gate voltage. This study provides a type of promising modular proton-conductive materials for bioelectronics application.