Highly flexible carbon nitride-polyethylene glycol-cellulose acetate film with photocatalytic antibacterial activity for fruit preservation

Cellulose acetate film, as a biodegradable and biomass-derived material, has great potential applications in food packaging. However, the poor mechanical and antibacterial properties limit its applications. Herein, a highly flexible carbon nitride-polyethylene glycol-cellulose acetate (CN-PEG-CA) film was successfully prepared by combining graphitic carbon nitride (g-C3N4) photocatalyst with cellulose acetate (CA). The g-C3N4 enables the film with antibacterial activity, as a green photocatalyst. PEG softens the rigid polymer CA and crosslinks CA, PEG, and g-C3N4 together by hydrogen bonding, as a flexible crosslinker. X-ray diffractometer (XRD), scanning electron microscope (SEM), and Fourier transform infrared spectrum (FT-IR) characterizations confirmed the successful preparation of the CN-PEG-CA film. The mechanical property tests demonstrated that adding PEG increased the elongation at break of the film by about 4 times. The composite film had high antibacterial activity, and the bactericidal rates on Escherichia coli and Staphylococcus aureus were 99.98 % and 99.89 %, respectively. It effectively extended the shelf life of strawberries to 96 h and effectively maintained the quality of strawberries during storage. After 96 h, the weight loss rate of strawberries packaged with 15 % CN-PEG-CA film was 21.83 %, vitamin C content was 45.47 %, titratable acidity content was 0.89 %, and color, hardness and total soluble solids were well maintained. And biocompatibility test results showed that the film was safe and nontoxic. From the ecological and economic point of view, the highly flexible and biodegradable films with efficient photocatalytic antibacterial activity synthesized in this paper have great potential in the field of food packaging.

Mechanism analysis of surface structure-regulated Cu2O in photocatalytic antibacterial process

The effects of exposing crystal planes and vacancy defect engineering can induce unique surface atom arrangements that strongly influence the physicochemical properties of semiconductor materials. This paper used Cu2O with different surface structures as a research model. A liquid-phase method was chosen for surface structure regulation to prepare Cu2O semiconductors (Vo-(111)Cu2O, Vo-(100)Cu2O, Vo-(110)Cu2O) with different exposed crystalline surfaces analyze the antibacterial mechanisms of other faceted models in the photodynamic antibacterial process. The bactericidal effect of Vo-(111)Cu2O (40 μg/mL, 100%) was better than that of Vo-(100)Cu2O and Vo-(110)Cu2O. DFT simulations show that the photocatalytic antimicrobial performance of Vo-(111)Cu2O is improved due to surface defect structures caused by unsaturated coordination bonds and suspension bonds on its exposed crystalline surfaces. The suspension bonds act as active centres for trapping electrons, leading to a lower carrier complexation rate on the material surface. The antibacterial mechanism of Vo-(111)Cu2O showed that oxidative sterilization by reactive oxygen species (ROS) was the dominant factor (61.98%) in the antibacterial process. The most potent depolarizing effect on E. coli, the highest copper ion solubilization, and the highest ROS yield. Therefore, ROS oxidative sterilization, copper ion leaching sterilization, and contact damage synergistically affect E. coli from the inside out.

New pectin-induced green fabrication of Ag@AgCl/ZnO nanocomposites for visible-light triggered antibacterial activity

The pectin (CEP) was used as matrix material to prepare Ag@AgCl/ZnO nanocomposites with a green method for photocatalytic antibacterial activity in visible-light. Briefly, Ag@AgCl plasmonic hybrids were prepared in the CEP macromolecule matrix with size control, which was attributed to the stability of carboxyl and hydroxyl groups on the CEP. Subsequently, an effective and green two-steps approach was explored for the fabrication of CEP-Ag@AgCl/ZnO nanocomposites with resource saving and environment friendly. Interestingly, more Ag⁺ was converted into metallic Ag in the CEP-Ag@AgCl/ZnO than that in the CEP-Ag@AgCl. This phenomenon was attributed that the reducibility of free hemiacetal hydroxyl groups on CEP was realized with the help of NaOH in the preparation of CEP-ZnO. In addition, the CEP chains were not obviously destroyed except for the change in the crystallinity after the preparation of the CEP-Ag@AgCl/ZnO nanocomposites, indicating that the method was non-destructive. Moreover, the pH triggered release of Zn²⁺ and low release of Ag⁺ in CEP-Ag@AgCl/ZnO nanocomposites with excellent photocatalytic antibacterial activity were confirmed in this work. The proposed green process provides a new idea for the large-scale production of antibacterial pectin-based nanocomposites in industry with a low-cost.

Photocatalytic antibacterial agent incorporated double-network hydrogel for wound healing

A novel antibacterial hydrogel was prepared through the addition of IT to a chitin (CT) and polyvinyl alcohol (PVA) hydrogel, creating a promising material for wound dressings. The addition of nano particles IT endowed the anti-bacterial activity of hydrogel as well as had a positive impact on the mechanical properties of the hydrogels. The structure of the prepared hydrogel dressing was characterized by FTIR, XPS, XRD, SEM and TEM. The composite hydrogel exhibited excellent anti-bacterial activity under the visible light. Cytotoxicity tests (L929 fibroblast cells) showed all samples achieving up to 80% cell viability. Furthermore, compared with conventional dressings, wound healing test revealed that CT/PVA/IT hydrogel could accelerated wound healing in vivo, wound closure rates reached 95.5% after 10 days. This study suggests that the novel hydrogel has considerable potential for applications in wound dressings.