4.7 Article

Kinetic analysis of nitrophenol reduction and colourimetric detection of hydrogen peroxide based on gold nanoparticles catalyst biosynthesised from Cynomorium songaricum

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ELSEVIER SCI LTD
DOI: 10.1016/j.jece.2021.106590

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Nitrophenol reduction; Kinetic; Colourimetric detection; Catalysis; Hydrogen peroxide; Gold nanoparticles

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In this study, gold nanoparticles (AuNPs) synthesized using an aqueous extract of Cynomorium songaricum (CS) were used as catalysts for the reduction of nitrophenols at various reaction temperatures. The biosynthesized CS-AuNPs showed good stability and low activation energy, and were capable of detecting hydrogen peroxide with a low detection limit of 2.25 µM. It was found that the reduction of nitrophenols followed a Langmuir-Hinshelwood mechanism with a half-order kinetic model, with activation energies as low as 4.88 kJ mol(-1) and 8.66 kJ mol(-1) for different nitrophenols.
The pseudo-first-order reaction kinetics of metallic nanocatalyst for the model reaction of nitrophenols/NaBH4 were early reported on low reaction temperatures. Here, we investigated reduction of nitrophenols in a wide range of reaction temperature with gold nanoparticles (AuNPs) catalyst that was fabricated via a low-cost and effective method using aqueous extract of Cynomorium songaricum (CS). The biosynthesised CS-AuNPs were well characterised by the analytic techniques such as X-ray diffraction (XRD), transmission electron microscope (TEM), scanning transmission electron microscopy (STEM). The TEM images showed multiple shapes and size in a range of 3-30 nm with an average size of 16 nm. The colloidal solutions were stored at the room temperature for 30 days with a stability of 63%. The kinetic study of the NiPs reduction showed that the reaction occurred via Langmuir-Hinshelwood mechanism with a half-order kinetic model for all tested reaction temperatures (30-70 degrees C). The thermodynamic parameters including activation energy, enthalpy, entropy and Gibbs free energy were calculated. The activation energies in the reduction of 2-nitrophenol and 3-nitrophenol were found to be as low as 4.88 kJ mol(-1) and 8.66 kJ mol(-1), respectively. Moreover, CS-AuNPs were used as a nanozyme for the detection of hydrogen peroxide (H2O2) via peroxidase-like reaction with 3,3',5,5'-tetramethylbenzidine (redTMB) that found the lowest limit of detection (LOD) of 2.25 mu M.

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