Abstract
The effect of polyvinyl alcohol (PVA) stabilizers and gold nanoparticles supported on active carbon (AuNPs/AC) was investigated in this article. Polymers with different molecular weights and hydrolysis degrees have been synthesized and used, like the stabilizing agent of Au nano-catalysts obtained by the sol-immobilization method. The reduction of 4-nitrophenol with NaBH4 has been used as a model reaction to investigate the catalytic activity of synthesized Au/AC catalysts. In addition, we report several characterization techniques such as ultraviolet-visible spectroscopy (UV-Vis), dynamic light scattering (DLS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) in order to correlate the properties of the polymer with the metal nanoparticle size and the catalytic activity. A volcano plot was observed linking the catalytic performance with hydrolysis degree and the maximum of the curve was identified at a value of 60%. The Au:PVA-60 weight ratio was changed in order to explain how the amount of the polymer can influence catalytic properties. The effect of nitroaromatic ring substituents on the catalytic mechanism was examined by the Hammett theory. Moreover, the reusability of the catalyst was investigated, with little to no decrease in activity observed over five catalytic cycles. Morphological and kinetic studies reported in this paper reveal the effect of the PVA polymeric stabilizer properties on the size and catalytic activity of supported gold nanoparticles.
Highlights
Metal nanoparticles of different sizes, shapes, and compositions are of high interest in fields such as catalysis, nanomedicine, and pollution remediation [1,2,3,4,5,6]
The properties resulting from the combination of dimensional and quantum effects allowed the use of gold nanoparticles (AuNPs) in catalysis, which is in contrast with bulk gold that has a long-standing reputation of being an inert metal
Polymeric stabilizers based on polyvinyl alcohol (PVA) of different molecular weights were synthesized via solution radical polymerization of vinyl acetate, using different solvents in order to control the molecular weights of the polymers
Summary
Metal nanoparticles of different sizes, shapes, and compositions are of high interest in fields such as catalysis, nanomedicine, and pollution remediation [1,2,3,4,5,6]. Several studies have evidenced the importance of polymeric stabilizers on the catalytic activity of metal-supported nanoparticles in terms of slowing down the electron transfer kinetics in the redox catalysis mechanism on the surface of NPs. Recent works have proposed a different interpretation of the role of polymeric ligands in nano-catalysis. Different studies have investigated the role of PVA as steric stabilizers for the synthesis of mono-metallic and bimetallic nanoparticles [41,42,43,44] It is widely used in nano-catalysts preparation methods, few studies have reported the use of customized synthetic polyvinyl alcohol instead of commercial PVA. The effect of PVA on the catalytic activity of AuNP was elucidated using a combination of characterization techniques to connect morphological features to the catalytic activity of these systems, in order to demonstrate the active role of PVA stabilizers in the catalytic mechanism
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