A Facile Green Tea Assisted Synthesis of Palladium Nanoparticles Using Recovered Palladium from Spent Palladium Impregnated Carbon

Abstract

Palladium impregnated activated carbon (Pd/C) filters play a major role in air quality management by the removal of toxic carbon monoxide from confined environments. However, Pd is an expensive metal and therefore, recovery and reuse of Pd from spent filter cartridges is highly desirable. The objective of the present study was to biosynthesise Pd nanoparticles (NPs) using green tea as a reducing agent. The source of Pd for the NP synthesis was spent Pd/C. Three different acid based Pd extraction protocols constituting of hydrochloric acid-hydrogen peroxide (HCl-H2O2), 2 M HCl and aqua regia were systematically explored. The Pd impregnated carbon was characterised using scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), ultraviolet-visible (UV-vis) spectroscopy, X-ray powder diffraction (XRD) and atomic absorption spectrometry (AAS) before and after Pd extraction. It was found that the aqua regia based extraction protocol was the most efficient among the three chosen acid or acid mixtures with an average absolute yield of 96%. Finally, an attempt was made towards one pot biosynthesis of Pd NPs from the recovered extract by using green tea as a reducing agent. The synthesised NPs were characterised using UV-vis spectroscopy, SEM and XRD.

Simple, green approach for the synthesis of solid support‐embedded PdNPs for ligand exchange

“…The size and crystalline structure of the formed PdNPs were next determined by X-ray diffraction (XRD). [18]. Unknown sharp reflections at 28˚ possibly can be rendered to some protected molecules of the plant; this confirmed the average size of PdNPs as calculated by the Scherrer equation [32]: 21.86 nm for PdNPs, less than the value calculated by TEM and [4,32].…”

“…Generally, and according to electrochemical studies, GT polyphenols are characterised by two types of hydroxyl groups. Hydroxyl groups donate electrons to Pd(II) ions more easily than others during reduction according to biomolecule conformation [18]. Generally, the formed NPs were partially or completely suspended and not completely deposited in the investigated extract.…”

“…3 shows XRD patterns of PdNPs and reveals the presence of three distinctive sharp peaks corresponding to (111), (200), and (220) planes Bragg reflection sat 2 θ = 40°, 46.88°, and 68.2°, which are the characteristic peaks of face‐centred cubic (FCC) crystalline Pd (Ref. JCPDS file: 46‐1043) [18]. Unknown sharp reflections at 28˚ possibly can be rendered to some protected molecules of the plant; this confirmed the average size of PdNPs as calculated by the Scherrer equation [32]: 21.86 nm for PdNPs, less than the value calculated by TEM and [4, 32].…”

“…The simplicity of green NP biosynthesis, which can take as little as minutes [11] and result in specific NP morphology based on plant type, has a further fuelled interest [12]. NPs are important products with a wide variety of applications including in nanoscale sensors [13], catalysts [14], medical diagnostics [15], and other applications [16], and indeed green tea (GT) extracts rich in polyphenols have successfully been used to synthesise Pd and AgNPs [17,18].…”

An Experimental and Theoretical Investigation on the Oxidation of CO over Pd/C Derived from the Spent Pd Catalyst

“…To prepare the Pd/C catalyst, Pd recovered from the spent Pd/C was impregnated onto 10 g of GAC‐Acid. A detailed methodology for Pd recovery is given in our previous work [8b] . The recovery was done by using aqua regia as extraction media.…”