Abstract
This study compares a green reducing agent (ascorbic acid, AA) with chemical reducing
agents (borohydride, BH, and hydrazine hydrate, HH) for the immobilization of Pd0 nanoparticles
(NPs) onto activated carbon to evaluate their antibacterial properties. The activated carbon prepared
from black cumin seeds was used as a substrate on which Pd nanoparticles (Pd NPs) were deposited
in situ using the three reducing agents. The reducing agents were used over a concentration range
of 2-10 mM at 20ºC. The Pd(0) loading was 45.4±0.5 (mg/g), 45.2±0.4 (mg/g), and 39.9±1.9 (mg/g)
for BH, AA, and HH, respectively, when different amounts of reducing agents were used. X-ray powder
diffraction (XRPD), scanning electron microscopy (SEM), and transmission electron microscopy
(TEM) showed the presence of Pd NPs in different crystallite sizes, particle sizes, and morphologies.
Pd particles produced by BH reduction were larger than those reduced by HH or AA. Crystallite size
decreases as the concentration of the reducing agent increases for BH and AA, while with the increase
in HH concentration, a slight increase in the average crystallite size was observed. The antibacterial
efficacy against S. aureus, B. cereus, and E. coli was qualitatively assessed by inhibition zone size
and quantitatively by turbidity. Growth inhibition zones for reduced Pd nanoparticles follow the order:
AA>HH>BH. For the quantitative turbidity method, growth inhibition showed efficient antibacterial
results for Pd NPs reduced by AA and HH more than those reduced by BH. This can be attributed to
their smaller particle size compared with those reduced by BH.