Yanjun Lin

Study on UV-shielding mechanism of layered double hydroxide materials

The development of UV-shielding materials has attracted considerable attention in the field of coatings and sunscreen. This paper reports the UV-shielding mechanism of layered double hydroxide (LDH) materials in terms of chemical composition, structure and morphology, by using (LDH/PAA)n films (n stands for bilayer number) through alternate LBL assembly of LDH nanoparticles and poly(acrylic acid) (PAA) on quartz substrates as a model system. A combination investigation based on experimental and theoretical study demonstrates that the maximum UV scattering can be achieved when λ/d ≈ 1.98; the introduction of Zn element is an effective way to tune the electron structure, band gap, transition mode and resulting UV-shielding property of LDH materials. A UV-shielding efficiency as high as 95% can be obtained by modulating the particle size, composition and thickness of the LDHs. Furthermore, the UV anti-aging capacity of LDH-modified bitumen was studied, which demonstrates a large improvement in UV-resistance performance of bitumen by the incorporation of LDH materials. Therefore, this work systematically discloses the relationship between UV-shielding property and chemical/structural parameters of LDH materials, which can be potentially used as anti-aging agents in various organic matrices and polymer areas.

Patterned fluorescence films with reversible thermal response based on the host–guest superarchitecture

This paper reports patterned films with thermal colorimetric and fluorescent response fabricated by a combined approach based on electrophoretic deposition (EPD)–photolithography. A composite film of diacetylene (DA)/layered double hydroxide (LDH) was prepared by the method of EPD, and the photolithography technique was subsequently employed to further obtain a polydiacetylene (PDA)/LDH patterned fluorescence film via UV-induced polymerization of DA in the two-dimensional (2D) gallery of LDH matrix. The PDA/LDH film shows a well c-orientation of LDH platelets (the ab plane of the LDH platelets parallel to the substrate) confirmed by XRD and SEM. Both the in situUV-vis absorption and fluorescence emission spectroscopy indicate that the composite film exhibits marked thermal colorimetric and fluorescent behavior in the temperature range 20–130 °C, which is reversible over a number of heating/cooling cycles. It should be noted that the pristine PDA shows no reversible thermal colorimetric and fluorescent performance at all. The transformation of an organic chromophore from irreversible to reversible thermal response material upon incorporation into a 2D layered matrix is the most distinct feature in this work. It was demonstrated that the thermally response behavior resulted from the strong hydrogen bond interaction between the PDA and LDH matrix, which was confirmed by in situ Raman and in situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy. Therefore, this work provides new opportunities for the fabrication of thermally responsive patterned films with high stability and reversibility, which can be used in intelligent response and display devices.

Bactericidal properties of ZnO–Al2O3 composites formed from layered double hydroxide precursors

ZnO–Al2O3 composites with different Zn/Al molar ratios (R) have been prepared using zinc–aluminium layered double hydroxides (LDHs) ZnRAl–CO3 as precursor. The samples were characterized by XRD, ICP, EDX, EPR and FT-IR. The results show that ZnO is highly dispersed in all of the ZnO–Al2O3 composites. Bactericidal experiments against Staphylococcus aureus ATCC 6538 and Bacillus subtilis var. niger ATCC 9372 were carried out by contacting the bacteria and spores with the ZnO–Al2O3 composites. The composites all showed high bactericidal activity against Staphylococcus aureus ATCC 6538, and the bactericidal efficiency against Bacillus subtilis var. niger ATCC 9372 increased with increasing content of ZnO. The mechanism of bactericidal activity of ZnO–Al2O3 has also been investigated. It is suggested that highly active O2− and •OH species generated on the surface of ZnO–Al2O3 particles react with the peptide linkages in the cell walls of bacteria or spores resulting in their destruction.