High-strength, antifogging and antibacterial ZnO/carboxymethyl starch/chitosan film with unique "Steel Wire Mesh" structure for strawberry preservation.

In this work, a multifunctional preservative film of ZnO/carboxymethyl starch/chitosan (ZnO/CMS/CS) with the unique "Steel Wire Mesh" structure is fabricated by the chemical crosslinked of ZnO NPs, CMS and CS. Unlike traditional nano-filled polymer film, the formation of the "Steel Wire Mesh" structure of ZnO/CMS/CS film is based on the synergistic effect of ZnO NPs filled CMS/CS and the coordination crosslinked between CMS/CS and Zn2+ derived from ZnO NPs. Thanks to the "Steel Wire Mesh" structure, the tensile strength and water vapor barrier of 2.5ZnO/10CMS/CS film are 2.47 and 1.73 times than that of CS film, respectively. Furthermore, the transmittance of 2.5ZnO/10CMS/CS film during antifogging test is close to 89 %, confirming its excellent antifogging effects. And the 2.5ZnO/10CMS/CS film also exhibits excellent long-acting antibacterial activity (up to 202 h), so it can maintain the freshness and appearance of strawberries at least 5 days. More importantly, the 2.5ZnO/10CMS/CS film is sensitive to humidity changes, which achieves real-time humidity monitoring of the fruit storage environment. Note that the preparation method of the film is safe, simple and environmentally friendly, and its excellent degradation performance will not bring any problems of food safety and environmental pollution.

High strength, controlled release of curcumin-loaded ZIF-8/chitosan/zein film with excellence gas barrier and antibacterial activity for litchi preservation.

Polysaccharide films containing protein additives have good application prospects in agriculture and food field. However, interfacial incompatibility between hydrophobic proteins and hydrophilic polymers remains a major technical challenge. In this work, the interfacial compatibility between hydrophobic zein and hydrophilic chitosan (CS) is improved by the chemical crosslinking between zinc ions of curcumin-loaded zeolitic imidazolate framework-8 (Cur-ZIF-8) with CS and zein. With the improvement of interface compatibility, the results show that the elongation at break and O2 barrier property of synthesized Cur-ZIF-8/CS/Zein are 9.2 and 1.5 times higher than CS/Zein, respectively. And the Cur-ZIF-8/CS/Zein exhibits superior antibacterial and antioxidant properties as well. Importantly, Cur-ZIF-8/CS/Zein can also be used as an intelligent-responsive release platform for curcumin. As a result, Cur-ZIF-8/CS/Zein can keep the freshness and appearance of litchi at least 8 days longer than that of CS/Zein. Therefore, this study provides a novel method to improve the interfacial compatibility between hydrophobic proteins and hydrophilic polymers, and is expected to expand the application of protein/polymer composites in agriculture and food field.

Green and multifunctional chitosan-based conformal coating as a controlled release platform for fruit preservation.

Food waste caused by the decay of perishable foods is a serious global issue. However, traditional preservative materials don't perform well in preventing food decay. Here, a green and multifunctional conformal coating is prepared by the hydrogen-bonding interactions among chitosan, nano-humic acid and curcumin, which is different from traditional preservative films obtained by solution blending. Thanks to the formation of hydrogen-bonding network, the surface roughness of the coating increased from 9.43 nm to 33.3 nm, which makes it more matches with the micro/nano structure of the fruit surface and obtains a good coating effect for various fruits. Furthermore, this coating shows distinctive mechanical properties (the tensile strength of 31.4 MPa), antioxidant and antibacterial activities (the inhibition zone ≥5 mm), and can be used to control the long-term release (up to 38 days) of natural preservative onto fruit surfaces. Through the demonstration of four perishable fruits, the coating can keep freshness and appearance at least 9 days longer than the uncoated samples, confirming the universal effectiveness of the coating in preventing fruit decay. This coating is easy to produce and use, washable, degradable, and makes from cheap or waste renewable biomaterials, which does not cause additional health and environmental concerns.

A self-matching, ultra-fast film forming and washable removal bio-crosslinked hydrogel films for perishable fruits.

Spoilage of food has aggravated the issue of food shortage worldwide. Here, we report a strategy for ultrafast hydrogel film forming within 10 s on fruit surfaces with good self-matching, washable removal and preservative property. This carboxymethyl chitosan (CMCS)/tannic acid (TA) hydrogel film (CTHF) is fabricated by bio-material of CMCS and TA via in-situ rapidly crosslinking with high-density hydrogen bonds. Simply blending TA and CMCS solution at room temperature can form CTHF with different roughness (Ra: ranges from 123 to 1.55 nm) on different fruit surfaces, so as to perfectly match the hydrogel protective layer of pericarp. The CTHF slows down fruit decay by its outstanding antioxidant and antibacterial activity. It is soluble and easily removed (within 3-5 min) by washing without environmental pollution and food safety issues. As natural polymer, CTHF shows high promise as sustainable substitutes for conventional plastics packing because of its non-toxic, edible, biodegradable, and environmentally friendly.

Curcumin-loaded nanoMOFs@CMFP: A biological preserving paste with antibacterial properties and long-acting, controllable release.

Food spoilage is one of the biggest concerns for food safety worldwide. Here, we describe the construction of a carrier for biological agents by chemical combination of porous nanoMOFs and carboxymethylated filter paper (CMFP). When curcumin was encapsulated in nanoMOFs@CMFP, they showed the ability to act as super-long-acting food preserving agents with controllable release of curcumin. Although only 22.3% of curcumin was released into water in 600 h, 65.8% was released into PBS in the same time, and the release into PBS could be tuned by adding citric acid at the time of greatest requirement. Furthermore, the chemical stability of curcumin in nanoMOFs@CMFP was >4.9 times greater than for free curcumin. The outstanding antioxidant and antimicrobial activity of curcumin-loaded nanoMOFs@CMFP paste was demonstrated by prolonging the shelf life of pitayas, which illustrates its potential for development as long-acting and stable preserving paste for use in food preservation.

Hybridization of carboxymethyl chitosan with MOFs to construct recyclable, long-acting and intelligent antibacterial agent carrier.

This study posed a novel strategy of interweaving carboxymethyl chitosan (CMCS) and HKUST-1 to build eco-friendly, recyclable, long-acting and intelligent antibacterial agent carrier of HKUST-1@CMCS. Combined characterizations revealed that the structure of HKUST-1@CMCS was destroyed step by step through different intensity of the stimulation of phosphate, thereby realizing intelligent release of antibacterial agent. The results showed that dimethyl fumarate-loaded HKUST-1@CMCS was much intelligent and long-acting (384 h, 0.04 M PBS) release performance than pure dimethyl fumarate, thus its inhibition zone diameters with and without stimulation of phosphate on S. aureus were 17.4 ±â€¯0.1, 10.2 ±â€¯0.7 mm at 7 d, respectively, while that of pure dimethyl fumarate had lost antibacterial activity at 2 d. With superior and long-acting antimicrobial activity, dimethyl fumarate-loaded HKUST-1@CMCS could effectively prolong the shelf life of strawberries as food packaging. Furthermore, HKUST-1@CMCS could easily regenerate, and regenerated HKSUT-1@CMCS still maintained intelligent response property at one cycle.

High-efficiency removal of dyes from wastewater by fully recycling litchi peel biochar.

Litchi peel biochar was prepared by hydrothermal carbonization and subsequent activation process, and its adsorption on congo red and malachite green were investigated. The structural characteristics and adsorption properties of litchi peel biochar were studied by Scanning electron microscopy, X-ray diffractometer, Brunauer-Emmett-Teller, and dye adsorption experiments, and the adsorption mechanism between litchi peel biochar and dye molecules was analyzed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The results showed that the litchi peel biochar had a high specific surface area and pore volume of 1006 m2 g-1 and 0.588 cm3 g-1, respectively, and its adsorption capacity for congo red and malachite green was 404.4 and 2468 mg g-1, respectively. The excellent adsorption properties were due to hydrogen bonding, π-π interaction, pore filling and electrostatic interactions. In addition, the reactivated litchi peel biochar also showed good adsorption performance, and all the adsorbed dyes were completely removed by reactivation, which realized complete recycling of the litchi peel biochar without causing secondary environmental pollution. Therefore, litchi peel biochar was expected to be an effective and recyclable adsorbent for removing congo red and malachite green from aqueous solutions.

Facile Method To Prepare a Novel Biological HKUST-1@CMCS with Macroscopic Shape Control for the Long-Acting and Sustained Release.

We have developed a green and versatile method to prepare hierarchically porous Cu3(BTC)2@carboxymethyl chitosan (HKUST-1@CMCS) with a macroscopic shape control and designable performance via the cross-linking of Cu(II) ions with CMCS. Furthermore, atomic force microscopy, scanning electron microscopy, powder X-ray diffraction, Brunauer-Emmett-Teller, and X-ray photoelectron spectroscopy analyses showed that the morphology of HKUST-1 could be controlled and changed by tailoring the surface roughness ( Rq) of polymer matrix. For the ball-like, fiberlike, and membrane-like composites, the matrix Rq values were 887, 88.4, and 18.2 nm and the average sizes of HKUST-1 crystals were about 10.2, 5.9, and 1.7 µm, respectively. It was found that the larger the Rq of the polymer matrix, the higher the drug payload. The results of drug release showed that the release percentage of dimethyl fumarate from HKUST-1@CMCS was 66% in 326 h, whereas that of Cu@CMCS was only 12 h. Obviously, the HKUST-1@CMCS had a long-acting and sustained release property compared to that of Cu@CMCS due to its complementary advantages of metal-organic frameworks (MOFs) and polymers. Therefore, this study not only provided an interesting way to make up for the shortcomings of MOFs and natural polymer but also developed a long-acting delivery system for a huge potential application prospect.

Adsorption of Cu(ii), Zn(ii), and Pb(ii) from aqueous single and binary metal solutions by regenerated cellulose and sodium alginate chemically modified with polyethyleneimine.

In this paper, crosslinked cellulose/sodium alginate (SA) was modified with polyethyleneimine (PEI) as an adsorbent (PEI-RCSA) for comparative and competitive adsorption of Cu(ii), Zn(ii), and Pb(ii) in single and binary aqueous solutions. FTIR, SEM, TGA and specific surface area analysis were used to characterize the structural characteristics of PEI-RCSA. The effects of initial pH of solutions, contact time and initial concentration of heavy metal ions on the adsorption capacity of PEI-RCSA were investigated. The experimental results revealed that the removal of metal ions on the PEI-RCSA was a pH-dependent process with the maximum adsorption capacity at the initial solution pH of 5-6. The adsorption kinetics were followed by a pseudo-second-order kinetics model, and the diffusion properties played a significant role in the control of the adsorption kinetics. Meanwhile, adsorption isotherms were successfully described by the Langmuir model in a single aqueous solution system. The maximum adsorption capacities of PEI-RCSA for Cu(ii), Zn(ii), and Pb(ii) in a single system were 177.1, 110.2 and 234.2 mg g-1, respectively. The binary-component system was better described with the Langmuir competitive isotherm model. The removal efficiencies didn't change significantly when three adsorption-desorption experimental cycles were conducted. All the above results indicated that PEI-RCSA has promising applications in the treatment of toxic metal pollution.