Cyperus scariosus extract based greenly synthesized gold nanoparticles as colorimetric nanoprobe for Ni²⁺ detection and as antibacterial and photocatalytic agent

Nanoparticles (NPs) having diameter in the range of 1-100 nm has been extensively studied for their broad range applications in the field of catalysis, sensing, energy storage and biology. The NPs can be synthesized utilizing multiple approaches, such as sol-gel method, hydrothermal, chemical reduction and green synthesis etc. However, green synthesis utilizing the plant extract as reducing and capping agent has grabbed the special attention due to its eco-friendly, non-hazardous and cost-effective nature. Herein, green synthesis of gold nanoparticles (AuNPs) is being reported utilizing aqueous extract of Cyperus scariosus roots (CSRE) under sunlight irradiation. CSRE@AuNPs have been successfully characterized by UV-Visible and FTIR spectroscopy, Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), zeta potential (ZP), dynamic light scattering (DLS) and powder diffraction analysis (PXRD). Average size of the CSRE@AuNPs has been found similar to 50 nm. Due to appropriate band gap of CSRE@AuNPs in the range of visible light, these NPs have evaluated for the photocatalytic potential to degrade hazardous organic dye i.e., methylene blue (MB). The NPs were proved to be efficient catalyst by 80% degradation of MB dye in just 90 min exposure to sunlight. These NPs have also been screened for the selective sensing of heavy metal ions in spiked water. CSRE@AuNPs had shown selective colorimetric response for the detection of Ni2+ with limit of detection (LOD) of 118.5 nM and a linear range of 0-300 mu M at optimized temperature of 40 degrees C at wide range of pH (3-9). The zeta potential and hydrodynamic size measurements were carried out to study the effect of Ni2+ on nanoparticle aggregation. A decrease in value of zeta potential from -34.4 to -0.116 mV (ignore the sign) and increase in value of DLS size from 53.2 to 7553 nm of the AuNPs was observed with an increase in concentration of Ni2+ ions from 0 to 300 mu M. Furthermore, over 93% recovery and a relative standard deviation (RSD) of roughly 4% proved the effectiveness of this colorimetric nano-probe for Ni2+ detection in untreated natural water samples, such as river and tap water.