Photothermal-Mediated Catalytic Reduction of 4-Nitrophenol Using Poly(N-isopropylacrylamide-acrylamide) and Hollow Gold Nanoparticles

Hollow gold nanoparticles (HAuNPs) have received significant attention for photothermal applications owing to their strong absorbance in the near-field region, resulting in high photothermal conversion efficiency. Localized surface plasmon resonance (LSPR)-mediated heating, which is a non-radiative property of AuNPs, has been shown to enhance photothermal-mediated catalytic reactions. In addition, the modification of the structure and interparticle distance of plasmonic NPs induce the surface plasmon resonance-coupling effect. In this study, we prepared the core-satellite structure used in the photothermal-mediated catalytic reduction of 4-nitrophenol with poly(N-isopropylacrylamide-acrylamide) [p(NIPAM-AA)] and HAuNPs. The amount of satellite HAuNPs (80 ppm) on 10 μL of 0.18 M p(NIPAM-AA) core varied from 6 to 12 mL. As-made p(NIPAM-AA)@HAuNP-8 sample reached a photothermal conversion efficiency of 56.9% and showed a high photothermal-mediated catalytic reduction rate. The reaction rate was enhanced from 0.162 to 0.354 min–1 by near-infrared irradiation, resulting in the effective photothermal effect of satellite HAuNPs and the enhanced LSPR-coupling between neighboring HAuNPs through the shrinkage of the p(NIPAM-AA) core. The results showed that the localized heating of p(NIPAM-AA)@HAuNP-8s effectively enhances the catalytic activity through the photothermal effect without the need to heat the entire solution with additional heating.