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

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.

Automated summary

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.