Structural insights into nano-porous zinc oxide carbon composites for sustainable hexavalent chromium removal

A novel method for synthesising nano-porous zinc oxide-carbon composites was developed using zinc nitrate, glycine and carbon nanofibres in a controlled setting. Despite the challenges posed by the exothermic solution combustion method, the approach effectively produced porous composites that maintained structural carbon, as verified by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Heat treatment between 350 and 650 °C resulted in the formation of hexagonal wurtzite zinc oxide, with crystal sizes shrinking from 15 nm to 11 nm as the temperature rose. Changes in morphology were noted, and energy dispersive spectroscopy (EDS) analysis confirmed the presence of zinc, oxygen, and carbon. The composites showed impressive efficiency in removing hexavalent chromium from water solutions, achieving a 91.27% removal rate under optimal conditions (200 ppm concentration, pH 7, 0.5 g adsorbent and 30 min of contact). The adsorption parameters were optimised using response surface methodology, with the findings indicating that chemisorption was the primary removal mechanism. This innovative synthesis method underscores the potential of solution combustion-synthesised composites for effective environmental remediation applications.