Abstract
This study presents a simple and green approach for the synthesis of Siraitia grosvenorii fruit extract capped gold nanoparticles (SG-AuNPs). The SG-AuNPs samples prepared under the optimized conditions were characterized by various techniques (UV-Vis, XRD, FTIR, HR-TEM, EDX, DLS). The biosynthesized nanoparticles were then studied for the reduction of 2-nitrophenol (2-NP) and 3-nitrophenols (3-NP) and for colorimetric detection of Pb2+ ions. The characterization results revealed that the crystals of SG-AuNPs were spherical with an average size of 7.5 nm. The FTIR and DLS analyses proved the presence of the biomolecule layer around AuNPs, which played an important role in stabilizing the nanoparticles. The SG-AuNPs showed excellent catalytic activity in the reduction of 3-NP and 2-NP, achieving complete conversion within 14 min. The catalytic process was endothermic and followed pseudo-first-order kinetics. The activation energy was determined to be 10.64 and 26.53 kJ mol−1 for 2-NP and 3-NP, respectively. SG-AuNPs maintained high catalytic performance after five recycles. The fabricated material was also found to be highly sensitive and selective to Pb2+ ions with the detection limit of 0.018 μM in a linear range of 0–1000 μM. The practicality of the material was validated through the analyses of Pb2+ in mimic pond water samples. The developed nanoparticles could find tremendous applications in environmental monitoring.
Highlights
Heavy metals and organic substances are considered as the major pollutants in wastewater, and have caused many serious problems for the environment and human health.[1,2,3] Heavy metals like Pb2+, Cd2+, Hg2+, Ni2+, and Cr6+, even at trace level concentrations, in water bodies have been reported to be potential environmental pollutants.[4]
It can be seen that the intensity of the surface plasmon resonance (SPR) peak for AuNPs at 540 nm increased as the concentration of gold ions increased from 0.25 to 0.75 mM; and decreased signi cantly with further rising the amount of gold ions rate up to 1.25 mM
The high concentration of gold ions used (>0.75 mM) led to the shi ing of the SPR peak from 540 nm to 560 nm, re ecting that varying the concentration of Au3+ solution affected the shape and size of the synthesized AuNPs.[24]
Summary
Heavy metals and organic substances are considered as the major pollutants in wastewater, and have caused many serious problems for the environment and human health.[1,2,3] Heavy metals like Pb2+, Cd2+, Hg2+, Ni2+, and Cr6+, even at trace level concentrations, in water bodies have been reported to be potential environmental pollutants.[4]. Those methods provide excellent sensitivity, high accuracy, and multi-element analysis, they have shortcomings associated with the complicated sample preparation, complex and costly instrumentation, and time-consuming procedures.[5] In recent years, nanomaterial-based colorimetric sensors have been extensively studied for the detection of heavy metal ions in environmental and biological samples owing to their simple operations, cost-effective, highly sensitive and selective detection, and rapid analysis.[6] This method can allow the direct tracking of target heavy metal ions by the naked eyes through color changes without expensive instruments compared with other methods. The development of various colorimetric sensors for detecting metal contaminants is of great interest
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