ZnO nanoparticles dispersed in nitrogen-enriched carbon matrix for the efficient adsorption and photocatalytic degradation of aqueous methylene blue molecules

Abstract

In the present study, ZnO nanoparticles dispersed in graphitic carbon nitride (g-C3N4) composite is synthesized via hydrothermal route at 150 °C. The synthesized material (ZnO/g-C3N4) is further heat-treated at an optimized temperature of 500 °C in an air-rich environment and the heat-treated material is denoted as the ZnO/g-C3N4-HT. Physicochemical properties of the as-synthesized material are evaluated by various analytical and spectroscopic techniques. The obtained results confirm good dispersion of the ZnO nanoparticles on the surface of the g-C3N4. The ZnO/g-C3N4-HT is further tested for its adsorption ability and photocatalytic activity towards aqueous methylene blue (abbreviated as MB). The data show that the ZnO/g-C3N4-HT possesses remarkably high MB adsorption capacity of 251.70 mg/g at the pH value of 7. The MB adsorption capacity obtained in the present study is superior to most of the carbon-based adsorbents. The kinetic curve is found to be in good agreement with pseudo-second-order kinetic model. The remarkably high MB adsorption capacity is ascribed to the combined effects of surface area, wettability characteristic, and the negative surface charge of the material. The photocatalytic MB-degradation study over the ZnO/g-C3N4-HT yields a maximum degradation efficiency of 90% with pseudo-first-order rate constant value of 0.0113 min−1. The high MB-degradation efficiency of the material is attributed to the modified band gap and morphological properties of the material. With adequate optimization, the ZnO/g-C3N4-HT may be useful in the removal of several other recalcitrant organic pollutants from water.