Abstract
Hexavalent chromium is extremely toxic and increasingly prevalent owing to industrialisation, thereby posing serious human health and environmental risks. Therefore, new approaches for detoxifying high concentrations of Cr (VI) using an ultralow amount of catalyst with high recyclability are increasingly being considered. The catalytic conversion of Cr (VI) into Cr (III) was previously reported; however, it required a large amount of catalyst to reduce a low concentration of Cr (VI); further, pH adjustment and catalyst separation had to be performed, causing issues with large-scale remediation. In this study, an unprecedented eco-friendly and cost-effective method was developed for the synthesis of Pd nanoparticles (PdNPs) with a significantly narrow size distribution of 3–25 nm. PdNPs demonstrated the presence of elemental Pd with the zero oxidation state when analysed by energy-dispersive X-ray analysis and X-ray photoelectron spectroscopy. The PdNPs could detoxify a high concentration of Cr (VI), without the need to adjust the pH or purify the nanoparticles for reusability. The reusability of the PdNPs for the catalytic conversion of Cr (VI) into Cr (III) was >90% for subsequent cycles without the further addition of formic acid. Thus, the study provides new insights into the catalytic reclamation of Cr (VI) for industrial wastewater treatment.
Highlights
Heavy-metal pollution is a serious hazard and a global issue due to the increase in industrial and agricultural activities
It can be applied to industrial wastewater treatment because once the biogenic Pd nanoparticles (PdNPs) are added to the wastewater, additional PdNPs need not be added for several consecutive cycles, and no further addition of formic acid is required
This shows that the biosynthesis time was 30 min, whereas in a previous study involving the biosynthesis of PdNPs, the peak corresponding to Pd2+ ions only vanished after 3 h45
Summary
Heavy-metal pollution is a serious hazard and a global issue due to the increase in industrial and agricultural activities. The effectiveness of PdNPs in the reduction of Cr (VI) (in the presence of formic acid) is owing to their distinguished features of high selectivity and activity in catalytic hydrogenation reactions[9,10,11]. The objectives of this study were to develop a simple, cost-effective, and eco-friendly method for the biosynthesis of PdNPs using a leaf extract of Erigeron canadensis L (E. canadensis) and to investigate their effectiveness and reusability for the reduction of Cr (VI) without the separation of PdNPs. The novelty of the present work is indicated by Table 1. Erigeron species is a source of γ-pyranone derivatives, flavonoids, and phenolic acids[25], and is important for the synthesis of nanoparticles[26,27,28] This plant has medicinal value in the treatment of indigestion, hematuria, enteritis, and epidemic hepatitis[29]. It can be applied to industrial wastewater treatment because once the biogenic PdNPs are added to the wastewater, additional PdNPs need not be added for several consecutive cycles, and no further addition of formic acid is required
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