Comparative Removal of Hexavalent Chromium from Aqueous Solution Using Plant-Derived and Industrial Zirconia Nanoparticles

This study presents a plant-fabricated nanoparticle system of zirconia (ZrO2) using Sonchus asper plant extract, compared with conventionally synthesized ZrO2, for their efficacy in Cr(VI) removal from aqueous solutions. The nanoparticles were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) for elemental composition, Fourier-transform infrared spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET) analysis. The plant-fabricated ZrO2 exhibited mesoporosity and enhanced surface functionality, attributed to bioactive compounds from Sonchus asper, which improved adsorption performance via increased surface area and residual organic functional groups. Batch adsorption experiments showed that Cr(VI) removal was optimized at 100 mg/L Cr(VI), 300 mg/L adsorbent dosage, pH 5, and 30 min reaction time at 25 °C. Adsorption followed the Langmuir isotherm and pseudo-second-order kinetics models. According to Langmuir model fitting, the maximum adsorption capacity (qmax) reached 142.24 mg/g for PF-ZrO2 NPs and 133.11 mg/g for conventional ZrO2 NPs, indicating the superior adsorption performance of the green-synthesized material. This work highlights the sustainable potential of plant-fabricated ZrO2 nanoparticles as cost-effective and environmentally friendly nano-adsorbents for heavy metal remediation, contributing to the achievement of UN SDG No. 6 by providing clean water solutions.