Use of surfactant bilayer modified silica for evolution and application of size variable solid Ag nanoparticle catalyst

Zero valent arsenic nanoparticles (As(0)) in two different size ranges such as 55 & PLUSMN; 8 and 61 & PLUSMN; 9 nm were prepared by reducing As(III) using NaBH4, and designated as As1 and As2. Galvanic replacement reaction (GRR) of As(0) was employed for the synthesis of Ag nanoparticles (AgNPs) in two different size ranges. The as-prepared AgNPs i.e. AgNP1 and AgNP2 were then converted to heterogeneous catalyst by adsolubilizing them onto surfactant-modified silica (SMS) surface, and the immobilized AgNPs were designated as Ag1-SMS and Ag2-SMS, respectively. The AgNPs thus formed in both homogeneous and heterogeneous phases were utilized as catalyst for 4-nitrophenol (4-NP) reduction in borohydride medium. The homogeneous catalysts were found to be more efficient compared to the supported catalysts. As for example, the complete reduction of 4-NP using homoge-neous Ag(0) catalyst was achieved within 12 min with a first order rate constant of 0.1513 min(-1) using AgNP1 at a dose of 1.86 mg/L. On the other hand, when it was immobilized on SMS surface it showed a rate constant 0.0259 min(-1) at a dose of 9 mg/L. The size effect of the AgNPs was also realized in both homogeneous and heterogeneous catalytic reactions. At a constant catalyst dose (in terms of Ag), smaller sized particles showed higher reaction rate compared to the larger particles. The TON and TOF as calculated for all the catalysts showed that homogeneous AgNPs were more efficient (> 24 times) than the AgNPs when they are immobilized on SMS surface.

Automated summary

This study prepared zero valent arsenic nanoparticles in two different size ranges and used them to synthesize silver nanoparticles. The prepared nanoparticles were immobilized onto surfactant-modified silica and used as catalysts for the reduction of 4-nitrophenol. The homogeneous catalysts were found to be more efficient than the supported catalysts. In addition, smaller sized nanoparticles showed higher reaction rates in both homogeneous and heterogeneous catalytic reactions.