Lu Jun-Yi, Chen Hsi-An, Yang Chia-Min, Chu Li-Kang
Department of Chemistry, National Tsing Hua University, 101, Sec. 2, Kuang-Fu Road, Hsinchu 300044, Taiwan.
Frontier Research Center on Fundamental and Applied Sciences of Matters, National Tsing Hua University, 101, Sec. 2, Kuang-Fu Road, Hsinchu 300044, Taiwan.
ACS Appl Mater Interfaces. 2021 Dec 22;13(50):60018-60026. doi: 10.1021/acsami.1c19613. Epub 2021 Dec 13.
Gold nanorods (AuNRs) have been widely used in photothermal conversion, and a coating of silica (SiO) provides higher thermal stability, better biocompatibility, and versatile chemical functionalization. In this work, two gold nanorods coated with surfactant-templated mesoporous silica layers of the same thickness but different porosities, and thus different specific surface areas, were prepared. Upon irradiation with 1064 nm nanosecond pulsed laser, the transient infrared emissions of AuNR@SiO enveloped the stretching mode of the Si-O-Si bridge (1000-1250 cm), the bending mode of adsorbed HO (1600-1650 cm) within the mesoporous silica layer, and blackbody radiation, in terms of an underlying broad band (1000-2000 cm) probed with a step-scan Fourier transform spectrometer. The mesoporous silica shell and the adsorbed HO gained populations of their vibrationally excited states, and the whole AuNR@SiO was heated up via the photothermal energy of the core AuNRs. An average temperature after 5-10 μs within 80% of the emission intensity was ca. 200 °C. The decay of the emission at 1000-1250 and 1500-1750 cm was both accelerated, and the blackbody radiation components were negatively correlated with the porosity of the mesoporous silica layer. Higher porosity of the mesoporous silica layer was associated with more effective depopulation of the vibrationally excited states of the silica layers on the AuNRs via the nonradiative thermal conduction of the adsorbed HO, since HO has a larger thermal conduction coefficient than that of silica, in concomitance with the accelerated emission kinetics. This work unveils the roles of the porosity, capping materials, and entrapping molecules of a core-shell nanostructure during the thermalization after photoexcitation.
金纳米棒（AuNRs）已被广泛应用于光热转换，而二氧化硅（SiO₂）涂层具有更高的热稳定性、更好的生物相容性以及多样的化学功能化特性。在本研究中，制备了两根涂覆有相同厚度但孔隙率不同（因而比表面积也不同）的表面活性剂模板介孔二氧化硅层的金纳米棒。在用1064 nm纳秒脉冲激光照射时，AuNR@SiO₂的瞬态红外发射包含了介孔二氧化硅层内Si - O - Si桥的伸缩模式（1000 - 1250 cm⁻¹）、吸附的H₂O的弯曲模式（1600 - 1650 cm⁻¹）以及黑体辐射，这是通过步进扫描傅里叶变换光谱仪探测到的一个潜在宽带（1000 - 2000 cm⁻¹）。介孔二氧化硅壳层和吸附的H₂O获得了它们振动激发态的粒子数，并且整个AuNR@SiO₂通过核心AuNRs的光热能被加热。在发射强度的80%范围内，5 - 10 μs后的平均温度约为200℃。在1000 - 1250 cm⁻¹和1500 - 1750 cm⁻¹处发射的衰减都加快了，并且黑体辐射成分与介孔二氧化硅层的孔隙率呈负相关。介孔二氧化硅层较高的孔隙率与通过吸附的H₂O的非辐射热传导使AuNRs上二氧化硅层振动激发态更有效地去粒子化有关，因为H₂O的热传导系数比二氧化硅大，同时发射动力学也加快了。这项工作揭示了核壳纳米结构的孔隙率、封端材料和捕获分子在光激发后的热化过程中的作用。
