More multipurpose and convenient demand driven by Radio Frequency Identification (RFID) and intelligent packaging require flexible power sources. A VO₂(B)/graphene (VO₂(B)/GN) core-shell composite was successfully synthesized by the hydrothermal treatment with V₂O₅ and graphite. The as-obtained sample was characterized by XRD, FT-IR, SEM, TEM, and XPS measurements. In addition, the electrochemical properties of VO₂(B)/GN were tested. Due to its great electrochemical performance and mechanical properties, graphene could increase the electrochemical performance and strengthen the structural stability of the material at the same time. With increasing loading amount of GN, the specific capacitance of VO₂(B)/GN increased correspondingly. With 20% GN loading, the initial discharge specific capacity could reach 197 F g⁻¹ at 0.5 A g⁻¹, and 160 F g⁻¹ at 1 A g⁻¹ in 0.5 M Na₂SO₄ electrolyte, which is better than that of pure rod-like VO₂(B). The capacitance of the VO₂(B)/GN (20%) composite electrode retains 95.49% after 1000 cycles, which is higher than that of a pure VO₂(B) electrode (85.43%), indicating that the VO₂(B)/GN composite possesses better cycling stability. Moreover, a symmetrical solid-state supercapacitor (SCs) using VO₂(B)/GN(20%) as the anode was assembled. Four printed SCs were connected in series to light up a 1.5 V red LED. This demonstrates its potential application in intelligent packaging to trace food safety.

In this work, 1,3,6,8-pyrenesulfonic acid sodium salt (PTSA) was successfully synthesized via a one-step sulfonating reaction. This method is more convenient, effective and eco-friendly than the traditional one. The as-prepared PTSA exhibits pure blue fluorescence under UV light. Due to its excellent fluorescent properties and water solubility, PTSA was used to prepare water-soluble invisible inks based on hydroxyethyl cellulose (HEC) aqueous solution. Notably, the resulting inks possessed acceptable stability after being stored for 30 days. Besides, the red/green/blue fluorescent inks were obtained by adding extra pigments, all of which exhibited excellent rheology and thixotropy properties. Subsequently, various patterns, including a QR code, the logo of Wuhan University, Chinese characters and so on, were printed on non-background paper through ink-jet and screen printing, and the as-prepared materials exhibited good water solubility and outstanding fluorescence performances, indicating that the fluorescent PTSA material is a promising candidate for anti-counterfeiting applications.