Nanoscale zinc oxide (ZnO NPs)–alginate–PEG–activated carbon nanocomposite for efficient Cr(VI) removal from electroplating wastewater: adsorption isotherms and eco-toxicity evaluation

BACKGROUND: Wastewater treatment utilizing nanotechnology principles has gained more attention recently due to the high removal efficacy of toxic pollutants with high biocompatibility and eco-friendliness. This research utilizes an in situ green synthesis method to synthesize a nanoscale zinc oxide–sodium alginate–poly(ethylene glycol)–activated carbon nanocomposite coated with Clitoria ternatea extract (CLT-PEG-AC-ZnO) for the effective remediation of hexavalent chromium (Cr(VI)) from electroplating industry effluent. RESULTS: Structural characterization via UV–visible spectroscopy and X-ray diffraction (XRD) validated the synthesis of ZnO nanoparticles at 340 nm, while scanning electron microscopy and energy-dispersive X-ray analyses verified a heterogeneous, porous morphology with particle dimensions ranging from 10 to 100 nm. Fourier transform infrared analysis revealed functional groups that indicate good molecular interactions in the nanocomposite. The XRD patterns of the CLT-PEG-AC-ZnO nanocomposite exhibited distinct peaks at 2θ values of 31°, 34°, and 36°, aligning with ZnO (JCPDS card no. 36-1451), hence confirming its primarily amorphous structure. Optimal conditions for Cr(VI) removal were pH = 7, temperature of 40 °C, a 90 min contact time, and 0.5 g adsorbent dosage. Under these conditions, the equilibrium data adhered to the Langmuir isotherm model (R² = 0.8765), indicating a monolayer adsorption mechanism on particular localized sites with a maximum adsorption capacity of 6.5091 mg g⁻¹. Zebrafish embryos exposed to in vivo biocompatibility profiling showed no negative effects on morphological development, heart rate, or survival. Vigna radiata seedlings exhibited minimal toxicity, identifying this composite as a nontoxic alternative to traditional chemical treatments. CONCLUSION: The results indicate the significant potential of the CLT-PEG-AC-ZnO nanocomposite as a scalable, biocompatible, and environmentally safe material for the sustained removal of potentially toxic heavy metals from intricate environmental matrices.