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 °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 (red-TMB) that found the lowest limit of detection (LOD) of 2.25 µM.