Hongyun Xuan

A Smart Colorful Supercapacitor with One Dimensional Photonic Crystals

To meet the pressing demands for portable and flexible equipment in contemporary society, developing flexible, lightweight, and sustainable supercapacitor systems with large power densities, long cycle life, and ease of strongly required. However, estimating the state-of-charge of existing supercapacitors is difficult, and thus their service life is limited. In this study, we fabricate a flexible color indicative supercapacitor device with mesoporous polyaniline (mPANI)/Poly(N-Isopropyl acrylamide-Graphene Oxide-Acrylic Acid) (P(NiPPAm-GO-AA)) one dimensional photonic crystals (1DPCs) as the electrode material through a low-cost, eco-friendly, and scalable fabrication process. We found that the state-of-charge could be monitored by the structural color oscillation due to the change in the photonic band gap position of the 1DPCs. The flexible 1DPCs supercapacitor is thin at 3 mm and exhibits good specific capacitance of 22.6 F g−1 with retention of 91.1% after 3,000 cycles. This study shows the application of the 1DPCs supercapacitor as a visual ultrathin power source. The technology may find many applications in future wearable electronics.

Highly transparent and self-healing films based on the dynamic Schiff base linkage

Self-healing optically transparent coatings have attracted significant attention due to their high transparency and ability to heal damages at the same time. In this study, we report an optically transparent and self-healing film via a layer by layer assembly. This film is based on chitosan (CS) and poly(ethylene glycol) functionalized by dialdehyde groups (DF-PEG). The dynamic equilibrium of Schiff base linkage between the aldehyde groups on DF-PEG and amino groups on CS resulted in the self-healing property of the film. The CS/DF-PEG film can heal damages several times at the same location. Moreover, the Schiff base-bonded CS/DF-PEG films are highly transparent with a transmittance of up to 99.47%, and the transmittance of the film can remain at 99% after ten damage/healing processes. The combination of self-healing property and high transparency provides a new method for fabricating the optically transparent devices.

Aptamer-functionalized P(NIPAM-AA) hydrogel fabricated one-dimensional photonic crystals (1DPCs) for colorimetric sensing

As heavy metals cannot be biodegraded and are easily accumulated in food chain organisms and so enter the human body, a simple detection method becomes particularly important for human health. A robust means for the visual detection of highly toxic mercury ion (Hg2+) is developed with aptamer-functionalized one-dimensional photonic crystals (1DPCs). 1DPCs consisting of TiO2 and poly(N-isopropylacrylamide-acrylic acid), P(NIPAM-AA), were successfully fabricated by a spin-coating technique, whose stopbands span the total visible range. When the 1DPCs were exposed to mercury ion solution, the specific binding of cross-linked single-stranded aptamers and heavy metal ions in the hydrogel network caused the hydrogel to shrink. At the same time, there was a homologous blue shift in the Bragg diffraction peak position of the TiO2/P(NIPAM-AA) 1DPCs. The shift value could be used to estimate the number of target ions quantitatively. It was found that the 1DPCs apta-sensor could screen a wide concentration range of heavy metal ions with selectivity and sensitivity. It is expected that the technology may also be widely used in screening a wide range of metal ions in drugs, food, and the environment.

Humidity responsive self-healing based on intermolecular hydrogen bonding and metal–ligand coordination

Here, we report the fabrication of a self-healing, colorful polyelectrolyte multilayer (PEM) composite film with humidity responsive properties, based on intermolecular hydrogen bonding and metal–ligand coordination. The synthetic strategy involves the fabrication of multilayer chitosan (CS)/polyacrylic acid (PAA) film with a layer-by-layer (LbL) self-assembly technique, followed by immersing the resulting CS/PAA PEM film in a cobalt chloride solution. According to the theory calculation and experimental results, cobalt chloride annealing treatment plays a critical role in rebuilding the reversible interactions that facilitate the PEM film to heal the mechanical damages and endow the PEM film with the property of reversibly changing its color in different conditions of humidity. Such a metal induced, humidity responsive, self-healing PEM film may broaden the application of the self-healing materials.

Graphene oxide hydrogel improved sensitivity in one-dimensional photonic crystals for detection of beta-glucan

Hydrogels are environment sensitive and they were introduced to 1DPhCs to improve the sensitivity in our previous research. In this paper, a new method was developed for quantitative determination of beta-glucan in oats by introducing graphene oxide (GO) hydrogels in one-dimensional photonic crystals (1DPhCs) with a polyaniline (PANI) defect layer. GO hydrogels were synthesized via a one-step hydrothermal method, characterized with scanning electronic microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR), and then they were employed as a component to fabricate 1DPhCs using a spin-coating method. Synthesized 1DPhCs combined with Congo red dye were in use for the quantification of beta-glucan. Reflection spectra demonstrated that a linear relationship existed between the photonic band gap and the beta-glucan concentration within 1–10 mg mL−1. The detection limit for beta-glucan is 0.18 mg mL−1 with a sensitivity of 7.53 nm mL mg−1.

Anti-Oxidative and Antibacterial Self-Healing Edible Polyelectrolyte Multilayer Film in Fresh-Cut Fruits.

The consumption of fresh-cut fruits is limited because of the oxidation browning and pathogenic bacterias growth on the fruit surface. Besides, crack of the fresh-keeping film may shorten the preservation time of fruit. In this work, polyelectrolyte multilayer (PEM) film was fabricated by layer-by-layer (LBL) electrostatic deposition method. The film was made by carboxy methylcellulose sodium (CMC) and chitosan (CS). The as-prepared PEM film had good anti-oxidative and antibacterial capability. It inhibited the growth of Gram-negative bacteria and the antibacterial rate was more than 95%. The stratified structure and linear increase of the absorbance in the film verified a linear increase of film thickness. The slight scratched film could self-heal rapidly after the stimulation of water whatever the layer number was. Moreover, the film could heal cracks whose width was far bigger than the thickness. The application of PEM film on fresh-cut apples showed that PEM film had good browning, weight loss and metabolic activity inhibition ability. These results showed that the PEM film is a good candidate as edible film in fresh-cut fruits applications.

Beta-glucan quantification by fluorescence analysis using photonic crystals

One-dimensional photonic crystal (1DPhC) was fabricated using a spin-coating method to be utilized as a Bragg reflection mirror. Gold was deposited on 1DPhC films by thermal evaporation under a vacuum. The beta-glucan–fluorochrome complex, whose emission wavelength was largely consistent with the photonic stopband of the 1DPhC, spin coated on the surface of 1DPhC with Au. The fluorescence of beta-glucan–fluorochrome complex deposited on 1DPhCs with Au was obviously enhanced in comparison with that on glass. There was 10-fold fluorescence enhancement. In this study, 1DPhCs with Au were used for the quantitative determination of beta-glucan. Fluorescence spectra demonstrated that a linear relationship existed between the fluorescence intensity and the beta-glucan concentration within 1–6 μg mL−1. The detection limit for beta-glucan is 0.083 μg mL−1 with a sensitivity of 19.53 mL μg−1.