ZnO nanoparticles synthesized by co-precipitation method: characterization and application in dye photodegradation and petroleum wastewater remediation via hydrocarbon degradation and heavy metal adsorption

Petroleum wastewater, contaminated with organic dyes, hydrocarbons, and heavy metals (e.g., As, Cd, Pb, Zn), poses significant ecological and health risks, demanding effective remediation. This study details the synthesis of ZnO nanoparticles (NPs) via co-precipitation, optimized with calcination at 500 °C for 3 h to boost crystallinity. Characterization via UV-Vis spectrophotometry revealed a strong absorption peak at 310 nm and a 3.08 eV bandgap, ideal for photocatalysis. X-ray diffraction (XRD) confirmed a hexagonal wurtzite structure with a 23 ± 4 nm crystallite size, while FTIR identified Zn-O modes at 418 cm⁻¹ and 833 cm⁻¹. SEM displayed asymmetric particles (peaking at 60–70 nm), and a -27.6 mV zeta potential indicated excellent colloidal stability. Thermogravimetric analysis (TGA-DSC) showed a 14.3% mass loss up to 1000 °C, with an endothermic peak at 685 °C, reflecting thermal stability. Photocatalytically, ZnO NPs degraded 97.5% of methylene blue in 60 min (kapp = 0.06637 min⁻¹) and removed 93.3% oil-in-water, 91.4% chemical oxygen demand, and 97.7% total suspended solids from petroleum wastewater in 30 min. They also achieved >99.9% heavy metal adsorption, with 100% removal for Be, Cr, Mo, Sb, and Se. These results establish ZnO NPs as a potent, sustainable solution for wastewater treatment, tackling diverse pollutants. Graphical Abstract