Abstract
Gold nanoparticles (AuNPs) were synthesized under ambient conditions from chloroauric acid in aqueous solution at pH 4. Tannin-rich extract from Xylocarpus granatum bark was used as both reducing and capping agent, rapidly converting Au (I) salt to AuNPs. Transmission electron microscopy showed the as-prepared AuNPs to be predominantly spherical, with an average diameter of 17 nm. The AuNPs were tested for catalytic reduction of Congo red (CR), a carcinogenic azo dye, in aqueous sodium borohydride solution. Cotton samples were coated with the AuNPs, taking on a reddish-purple color. The samples showed significantly reduced tearing strength after coating, though tensile strength was unaffected. UV-visible spectroscopy was used to determine the dye concentration in the water. CR degradation was observed only when AuNPs were present, and the efficiency of degradation was strongly linked to the AuNP loading. The AuNP-coated fabrics left only a 4.7% CR concentration in the solution after 24 h and therefore promise as a heterogeneous catalyst for degradation of CR in aqueous solution.
Highlights
Nanostructured materials are known to be promising candidates for conversion or removal of toxic pollutants
Ey are increasingly used as sensory probes as well as in drug delivery, catalysis, and electronic devices [3,4,5,6]. e color of spherical AuNPs depends on their dimensions and may be brown, orange, red, or purple [7]
Successful tannin-assisted synthesis of AuNPs at pH 4 was confirmed as the solution rapidly changed color from yellow to reddish-purple
Summary
Nanostructured materials are known to be promising candidates for conversion or removal of toxic pollutants. Gold nanoparticles (AuNPs) offer a large surface-to-volume ratio, low toxicity, good biocompatibility, and unique optoelectronic properties [2]. AuNPs have been used for the catalytic reduction of organic compounds including 4-nitrophenol [8], nitrobenzene, and Congo red [9]. E large surface area of nanocatalysts makes them suitable as an electron transfer mediator, promoting electron transfer from the borohydride ions (electron donor) to dye molecules (electron acceptor). If the correct metal nanoparticles are used, the reduction process becomes kinetically feasible. A range of nanocatalysts have been employed in CR reduction, and rapid catalytic degradation of the dye has been demonstrated. To avoid overlapping between the surface plasmon resonance band of the nanoparticle and the absorption band of the dye, very small amounts of metal
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