A novel green synthesis approach for improved photocatalytic activity and antibacterial properties of zinc sulfide nanoparticles using plant extract of Acalypha indica and Tridax procumbens

In this present work, improved photocatalytic activity and antibacterial properties of zinc sulfide (ZnS) nanoparticles using plant extract of Acalypha indica (A:ZnS) and Tridax procumbens (T:ZnS) via novel green synthesis route had been reported. X-ray diffraction (XRD), transmission electron microscopy (TEM), and Energy dispersive X-ray spectroscopy (EDX) were used to investigate the crystal structure, surface morphology, and elemental composition analysis, respectively. The optical properties and functional group analysis of the samples were done using UV-visible, photoluminescence, and Fourier transform infrared spectroscopy (FTIR). The influence of Acalypha indica (A:ZnS) and Tridax procumbens (T:ZnS) plant extract concentration on the structural, surface morphology, optical, antibacterial, and photocatalytic activity has been systematically investigated. XRD results are suggested that ZnS hexagonal wurtzite crystal structure formed during biosynthesis process. TEM and SAED images show the hexagonal- and spherical-shaped structure in morphology with average diameter around 5-20 nm which is good agreement with the grain size calculated from XRD. Optical properties were found to have considerable red shift in the absorption edge and decreasing band gap was observed for A:ZnS/T:ZnS (2.96 eV) when compared to pure ZnS (3.36 eV). The antibacterial properties of ZnS/A:ZnS/T:ZnS nanoparticles were investigated using in vitro disk diffusion method against human pathogenic microorganisms. The inhibition zone of biosynthesized ZnS nanoparticles increased by increasing plant extracts concentration. This result conformed that A:ZnS/T:ZnS nanoparticles have more potential as antibiotic when compared with pure ZnS. Besides, Biosynthesized T:ZnS (40 ml) nanoparticles showed high surface area (131.84 m(2)/g) and larger pore size (12.15 nm) than pure ZnS sample; this high surface area may offer more active sites to enhance photocatalytic ability. The dye degradation properties of methylene blue dye (MBD) were investigated using the ZnS/A:ZnS/T:ZnS nanoparticles under visible light irradiation. The results show that T:ZnS (40 ml) has excellent photocatalytic performance towards MBD such as high degradation efficiency (98%) and more cyclic stability than other ZnS samples. The role of plant extract on dye degradation properties was discussed based on the possible inhibition of photogenerated electron-hole pair recombination during dye degradation under visible light irradiation.