Yi Shang,Zhihai Cao,Hangnan Chen,Yangyi Sun,Jia Yao,Lin Yang,Dongming Qi,Ulrich Ziener
In our previous paper, we reported the synthesis of easily recyclable and highly active rice roll-like (RR-like) Au/SiO 2 nanocatalysts (NCs) in inverse miniemulsions [Colloids Surf. A 517, 2017, 52–62]. In the present contribution, the influences of three key synthesis parameters, including the 3-aminopropyltriethoxysilane (APTES) content, reaction temperature, and urea amount, on the particle properties of the Au/SiO 2 NCs were systematically investigated. The role of these synthesis parameters in the formation of SiO 2 nanosupports and Au nanoparticles (NPs) was discovered. The RR-like SiO 2 nanosupports could only be formed in the systems within the range of 20–80 mol% of APTES content, at reaction temperatures above 60 °C, and with more than 0.72 mg of urea. The AuCl 4 − ions could be immobilized onto the aminopropyl-functionalized SiO 2 nanosupports through a coordination interaction. The immobilized ions were reduced by the aminopropyl groups at elevated temperatures. The APTES content and reaction temperature play an important role in controlling the particle size and its distribution of Au NPs. The catalytic activity of Au/SiO 2 NCs depends significantly on the APTES content. The RR-like Au/SiO 2 NCs with smaller immobilized Au NPs and higher specific surface area display higher catalytic activity towards hydrogenation of p -nitrophenol.
Rice roll-like (RR-like) Au/SiO 2 nanocatalysts (NCs) were synthesized through simultaneous sol–gel process of tetramethoxysilane and 3-aminopropyltriethoxysilane (APTES) and in situ reduction of gold salt in inverse miniemulsions. APTES played an important role in formation of RR-like SiO 2 nano-supports, reduction of gold salts to narrowly size-distributed sub–10 nm Au nanoparticles (NPs), and improved attachment of Au NPs to the SiO 2 nano-supports. The prepared RR-like Au/SiO 2 NCs displayed a pH-dependent, reversible colloidal stability in water, which facilitated to recycle them through tuning the pH value of the dispersion. Most importantly, the catalytic activity of the RR-like Au/SiO 2 NCs towards reduction of p -nitrophenol was about 7–9 times higher than that of the raspberry-like Au/SiO 2 NCs reported in our previous paper (Colloids Surf. A, 489, 2016, 223–233). The formation mechanism of the RR-like Au/SiO 2 NCs was also discussed.
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