Phyto-mediated synthesis of nickel oxide (NiO) nanoparticles using leaves’ extract of Syzygium cumini for antioxidant and dyes removal studies from wastewater

[Display omitted] •The NiO-NPs were synthesized by using Syzygium cumini extract, through a low-cost, easy and reproducible approach.•Phytochemicals present in the extract are performed as the reducing or stabilizing agent for NiO nanoparticles synthesis.•The % scavenging of DPPH radical was found as 74.83% at 1000 µg concentration of nanoparticles which was found as moderate as compared to BHT.•The synthesized NiO nanoparticles also showed excellent removal efficiency for methylene blue and Congo red dyes. The present study reports the nickel oxide nanoparticles (NiO NPs) synthesis by green route using Syzygium cumini leaf extract. Secondary metabolites in Syzygium cumini extract reduced nickel ions by decreasing, stabilizing, and capping them. The absorption peak of NPs in the UV–visible spectrum was 320 nm, indicating that they were successfully synthesized. Fourier transform infrared spectroscopic (FTIR) analysis identified several functional groups present in the extract which were accountable for reduction. Scanning electron microscope (SEM) images showed the formation of spherical shape NiO NPs. X-ray diffraction spectroscopy (XRD) showed that the crystallite size of NiO-NPs was 10.4 nm. EDX determined the composition of NPs that confirmed the presence of elemental nickel and oxygen. The reducing property of leaves’ extract was due to the presence of antioxidants which were confirmed by measuring antioxidant potential. Antioxidant performance of synthesized NiO-NPs was assessed by DPPH radical scavenging activity, phosphomolydenum complex formation method, and total phenolic contents estimation. The percent scavenging of DPPH radical was found to be 74.83% at a 1000 µg/ml concentration of NPs. Total antioxidant activity was 0.5369 and total phenolic content was 310.8 mg/g GAE in NiO-NPs (Gallic Acid Equivalent). The adsorption of methylene blue and Congo red dyes on NiO-NPs was investigated. Temperature, pH, dye concentration, contact time, and adsorbent dosage were all tuned to ensure that both colors were removed as completely as possible. For Congo red and methylene blue (MB) dyes, NiO-NPs demonstrated high removal efficiency (CR).