Green synthesis, characterization of N-doped ZnO@zeolite nanocomposite for enhanced simultaneous adsorptive removal of environmental contaminants.

Abstract

In this study, nitrogen-doped zinc oxide (N-ZnO) nanoparticles supported on zeolite matrix (N-ZnO@Zeolite) nanocomposite were synthesized and its adsorption capability tested against dangerous environmental pollutants such as hexavalent chromium (Cr(VI)), Rhodamine B (RhB), and Congo Red (CR) under single as well as binary component batch adsorption systems. The SEM and XRD results of N-ZnO@Zeolite nanocomposite validated the spherical morphology and effective embedding of N-ZnO particles within the porous zeolite matrix with average crystallite sizes of 32 nm (N-ZnO) and 41 nm (N-ZnO@Zeolite). The EDX analysis confirms the elemental composition and validates nitrogen doping and preservation of the zeolite framework. BET measurements indicate a high rise in surface area for the nanocomposite (29.01 m²/g) than pure N-ZnO (21.26 m²/g), implying increased surface-active sites. The lower photoluminescence intensity in the nanocomposite implies repressed electron-hole recombination, which is beneficial for photocatalytic and adsorptive behavior. Adsorption studies confirm that N-ZnO@Zeolite nanocomposite had considerably greater adsorption capacities compared with N-ZnO for removal of all three contaminants, with the best removal occurring at certain pH conditions: pH 3 for Cr(VI), pH 8 for RhB, and pH 6 for CR. The isotherm study confirms the Langmuir model, with maximum adsorption capacity of 147.62, 139.46, and 210.93 mg/g for Cr(VI), RhB, and CR, respectively, by N-ZnO@Zeolite nanocomposite. The enhanced adsorption capacity is due to higher surface area, greater porosity, stabilization of surface charge, and the synergic effect of the interaction between the zeolite support and N-ZnO. The findings in this paper highlight the use of N-ZnO@Zeolite nanocomposite as a multifunctional efficient adsorbent that is particularly promising for removing multiple co-existent pollutants in complicated wastewater.