Yuchen Li

The development of phosphorescent materials with time-dependent phosphorescence colors (TDPCs) is of considerable interest for application in advanced dynamic information encryption. In this study, TDPC is realized in carbon dots (CDs) synthesized by the one-pot hydrothermal treatment of levofloxacin. CD ink printed on paper (CD@paper) exhibits a change in phosphorescence color from orange to green, 1 s after irradiation with 395 nm light. However, when irradiated with wavelengths shorter or longer than 395 nm, the CD@paper exhibits only green or red phosphorescence, respectively. The red and green phosphorescence originates from the low-energy surface oxide triplet state and high-energy N-related triplet state, respectively. When irradiated with a suitable light energy (around 395 nm wavelength), the two phosphorescent centers can be simultaneously activated, emitting red and green phosphorescence with different decay rates. The red and green phosphorescence merge into an orange phosphorescence initially, exhibiting the TDPC phenomenon. Based on the unusual phosphorescent properties of the CDs, a kind of multilevel, dynamic phosphorescence colored 3D code is designed for advanced dynamic information encryption.

Graphene is the strongest and stiffest material, leading to the development of promising applications in many fields. However, the assembly of graphene nanosheets into macrosized nanocomposites for practical applications remains a challenge. Nacre in its natural form sets the “gold standard” for toughness and strength, which serves as a guide to the assembly of graphene nanosheets into high-performance nanocomposites. Here we show the strong, tough, conductive artificial nacre based on graphene oxide through synergistic interactions of hydrogen and covalent bonding. Tensile strength and toughness was 4 and 10 times higher, respectively, than that of natural nacre. The exceptional integrated strong and tough artificial nacre has promising applications in aerospace, artificial muscle, and tissue engineering, especially for flexible supercapacitor electrodes due to its high electrical conductivity. The use of synergistic interactions is a strategy for the development of high-performance nanocomposites.

We here show that infiltrated bridging agents can convert inexpensively fabricated graphene platelet sheets into high-performance materials, thereby avoiding the need for a polymer matrix. Two types of bridging agents were investigated for interconnecting graphene sheets, which attach to sheets by either π-π bonding or covalent bonding. When applied alone, the π-π bonding agent is most effective. However, successive application of the optimized ratio of π-π bonding and covalent bonding agents provides graphene sheets with the highest strength, toughness, fatigue resistance, electrical conductivity, electromagnetic interference shielding efficiency, and resistance to ultrasonic dissolution. Raman spectroscopy measurements of stress transfer to graphene platelets allow us to decipher the mechanisms of property improvement. In addition, the degree of orientation of graphene platelets increases with increasing effectiveness of the bonding agents, and the interlayer spacing increases. Compared with other materials that are strong in all directions within a sheet, the realized tensile strength (945 MPa) of the resin-free graphene platelet sheets was higher than for carbon nanotube or graphene platelet composites, and comparable to that of commercially available carbon fiber composites. The toughness of these composites, containing the combination of π-π bonding and covalent bonding, was much higher than for these other materials having high strengths for all in-plane directions, thereby opening the path to materials design of layered nanocomposites using multiple types of quantitatively engineered chemical bonds between nanoscale building blocks.

Abstract Most of the ancient buildings are made of inflammable wooden structures, which have serious potential safety hazards. Applying fire‐retardant coating is one of the simplest and most effective means of fire prevention in ancient wooden buildings. In this work, we have demonstrated that the Ti 3 C 2 T x transition metal carbide/carbonitride (MXene) was applied as the synergetic agent, waterborne epoxy resin as the film‐forming agent, ammonium polyphosphate, dipentaerythritol, and melamine (P‐C‐N system) as the intumescent fire‐retardant system to prepare Ti 3 C 2 T x /epoxy intumescent fire‐retardant coating (TEIFC). The results showed that MXene has significantly improved the fire‐retardant performance of the coating. By incorporating 3 wt% Ti 3 C 2 T x (TEIFC‐3, with 62 wt% P‐C‐N system), the coating displayed UL‐94 V‐0 rating with the limiting oxygen index value of 38%. In addition, the combination of Ti 3 C 2 T x and P‐C‐N system enhanced the Shore hardness of the coating to 95 SHD (TEIFC‐3). Furthermore, TEIFC‐3 presented high thermal stability with the T HRI of 177.0°C and T dmax of 380.5°C. This work provides a novel strategy for the design and preparation of intumescent fire‐retardant coating, which will greatly broaden the industrial applications of MXene‐based polymer composites in the field of fire prevention of ancient buildings.

Enantioselective analysis of biological thiols, including cysteine (Cys) and glutathione (GSH), is extremely important because of their unique role in bioentities. Here we demonstrated that the end-to-end assemblies of plasmonic gold nanorods with chiral Cys or GSH can be used as a distinctive chiroptical sensor for reliable determination of the absolute configuration of Cys and GSH at the visible light region. The end-to-end assemblies of Au nanorods induced by Cys or GSH exhibit strong circular dichroism (CD) signals in the region of 500-850 nm, which is attributed to chiral current inside Au nanorods induced by the mixed biothiols. The CD intensity of the assemblies shows good linearity with the amount of Cys and GSH. The limit of detection for Cys and GSH using end-to-end assemblies is at micromolar concentrations. In addition, the sensing system exhibits good selectively toward Cys and GSH in the presence of other amino acids.