Isotherm, kinetics, thermodynamics, recyclability and mechanism of ultrasonic assisted adsorption of methylene blue and lead (II) ions using green synthesized nickel oxide nanoparticles

One of the urgent global problems demanding effective mitigation strategies is the pollution caused by organic dyes and metal ions like methylene blue and lead (II) ions. In recent times, the increasing applications of nickel oxide nanoparticles in biomedicine, catalysis, sensors in optoelectronic materials, and the prevention of environmental pollution have attracted researchers' interest across the globe. Herein, Psidium guajava leaves extract was utilized to synthesize green nickel oxide nanoparticles (PG-NiONPs). Surface and analytical techniques were employed to characterize PG-NiONPs and were thereafter applied to remove methylene blue and lead (II) ions from wastewater. The results revealed the quantified presence of phytochemicals such as alkaloids, phenols, tannins, flavonoids and saponins in the Psidium guajava leaves extract. The prepared PG-NiONPs revealed a crystalline phase, functional groups, mesoporous and microstructural arrangements typical of nickel oxide nanoparticles. The surface area of PG-NiONPs was obtained as 85.40 m2/g. The best ultrasonic-assisted adsorption of MB and Pb(II) ions was achieved at pH values of 6 and 5 for MB and Pb(II), a contact time of 60 min, an adsorbent mass of 40 mg/L, and a temperature of 50 °C, respectively. The maximum MB and Pb(II) adsorption capacities of 495.58 and 508.56 mg/g were evaluated. The experimental data corroborated with the pseudo-second-order and Toth isotherm models. The adsorption of MB and Pb(II) over green PG-NiONPs was a thermodynamically spontaneous process. The PG-NiONPs indicated good recyclability with high stability even after 8 adsorption cycles. Overall, the PG-NiONPs is a potential adsorbent for improved toxic dyes, metal ions and other scavengers removal from wastewater.