Effect of mixing ratios of SiO2 nanoparticles synthesized from metakaolin on the physicochemical properties of ZnO/SiO2 nanocomposites

Abstract

Nanomaterials have distinguished themselves as an outstanding class of materials due to their unique physical and chemical characteristics compared to bulk materials. The physicochemical properties of nanomaterials can be improved by forming nanocomposites and manipulating different nanoparticles by varying their mixing ratios. In this study, ZnO and SiO2 nanoparticles and ZnO/SiO2 nanocomposites were produced using a sol–gel method based on the variation of mixing ratios (1:1, 1:2 and 2:1). The monometallic oxide nanoparticles (ZnO, SiO2) and the corresponding nanocomposites (ZnO/SiO2) were characterized using HRSEM, EDX, XRD, FTIR, BET and XPS. Regardless of the mixing ratio of ZnO and SiO2 nanoparticles used, the HRSEM pictures demonstrated a morphological change from the irregular and spherical forms produced for SiO2 and ZnO nanoparticles to rod-like shapes for the ZnO/SiO2 nanocomposite. The quartz phase of SiO2 nanoparticles, with a crystallite size of 43.67 nm, and the hexagonal wurtzite phase of ZnO nanoparticles, with a crystallite size of 31.52 nm, were both synthesized, as revealed by the XRD results. As opposed to this, the XRD patterns of the ZnO/SiO2 nanocomposites synthesized with 1:1, 1:2 and 2:1 mixing ratios showed a mixture of α-quartz (SiO2) and hexagonal wurtzite (ZnO) with crystallite sizes of 21.24, 29.56 and 15.36 nm, respectively. The EDS results confirmed the existence of Zn and O for ZnO; Si and O for SiO2 nanoparticles and Zn, Si and O in the prepared ZnO/SiO2 nanocomposite, irrespective of the mixing ratios. The XPS results showed the existence of Zn in the +1 oxidation state in ZnO/SiO2 compared to single ZnO with the Zn2+ valence. The BET surface area indicates that the ZnO/SiO2 nanocomposites had a higher surface area (1:1 (39.042 m2 /g), 1:2 (55.602 m2 /g) and 2:1 (82.243 m2 /g)), irrespective of the mixing ratios, compared to the surface area for the ZnO (8.620 m2 /g) and SiO2(0.386 m2 /g) nanoparticles. The mixing ratio of the ZnO and SiO2 nanoparticles influenced the crystallite sizes, surface elements oxidation states and morphology of the ZnO/SiO2 nanocomposite formed and the optima mixing ratio for the formation of ZnO/SiO2 nanocomposite was found to be 2:1 of ZnO:SiO2 nanoparticles.