Temperature-Responsive Smart Nanoreactors: Poly(N‑isopropylacrylamide)-Coated Au@Mesoporous-SiO2 Hollow Nanospheres

• Published in: Langmuir Vol. 28; no. 37; pp. 13452 - 13458
• Main Authors: Chen, Zhe, Cui, Zhi-Min, Cao, Chang-Yan, He, Wei-Dong, Jiang, Lei, Song, Wei-Guo
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 18.09.2012
• Subjects: Acrylamides - chemistry; Acrylic Resins; Catalysis; Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Gold - chemistry; Metal Nanoparticles - chemistry; Models, Molecular; Nanospheres - chemistry; Particle Size; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Polymers - chemistry; Porosity; Porous materials; Silicon Dioxide - chemistry; Surface Properties; Temperature; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Critical property; Binary compound; Catalytic reaction; Separation; Nanoparticle; Thermogravimetry; Temperature effect; Porous material; Transmittance; Grafting; Silica; Mesoporosity; Chemical reduction; Infrared spectrometry; Transmission electron microscopy; Pore; Silicon oxides; Nanosphere; Kinetics; Critical temperature; Diffusion; Catalyst
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la3022535

A nanoreactor with temperature-responsive poly(N-isopopylacrylamide) (PNIPAM) coated on the external pore mouth of mesoporous silica hollow spheres and Au nanoparticles at the internal pore mouth were fabricated. Such spatial separation allows both Au nanoparticles and PNIPAM to function without interfering with each other. Transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectra, and temperature-dependent optical transmittance curves demonstrate successful grafting of PNIPAM. This nanoreactor shows repeated on/off catalytic activity switched by temperature control. It shows excellent catalytic activity toward 4-nitrophenol (4-NP) reduction at 30 °C [below lower critical solution temperature (LCST) of PNIPAM] with a turnover frequency (TOF) of 14.8 h–1. However, when the temperature was 50 °C (above LCST), the TOF dropped to 2.4 h–1. Kinetic studies indicated that diffusion into the mesopores of the catalyst was the key factor, and the temperature-responsive behavior of PNIPAM was able to control this diffusion.