Synthesis of Cd doped ZnO/CNT nanocomposite by using microwave method: Photocatalytic behavior, adsorption and kinetic study

Abstract

The Cd-doped ZnO/CNT nanocomposites (Cd@ZnO/CNT-NCs) were synthesized by the microwave assisted hydrothermal method. The as-synthesized Cd@ZnO/CNT-NCs was characterized in detail in term of their structural, morphological, chemical and optical properties using XRD; SEM, FE-TEM, BET and UV–Vis methods. The band gap energy measurements confirmed that the addition of Cd ions causes a decrease in the band gap energy of the nanocomposites. The photocatalytic properties of the synthesized nanocomposites were investigated by the measurements of methyl orange (MO) degradation under UV irradiation.The equilibrium adsorption data of all three nanocomposites (i.e. ZnO/CNT, CZC-1, CZC-0.25) were analyzed by Langmuir and Freundlich isotherm models, respectively. The best fit to the data was obtained from the Langmuir model. The decrease in MO dye concentration was examined by UV–Visible spectroscopy at different time intervals under ultraviolet light irradiation, until the dye was completely degraded to colorless end product. Rapid MO dye decomposition was observed with a degradation rate of ∼93, 70 and 44% on the CZC-1, CZC-0.25 and ZnO/CNT within the initial 110 min, respectively. The fast degradation rate and high degradation efficiency of CZC-1 and CZC-0.25 is attributed to the porous nature, large specific surface area (162.5 and 136.1 m2 g−1), narrow pore size distribution (7.46 and 12.98 nm) evaluated from N2 adsorption-desorption isotherms analysis and excellent electron accepting features of the engineered porous Cd@ZnO/CNT-NCs. The kinetic results revealed that the degradation rate of MO on the CZC-1 (i.e. Cd0.5Zn0.5O/CNT) and CZC-0.25 (i.e. Cd0.25Zn0.75O/CNT) is approximately 2- and 4-folds larger than the CNT/ZnO that can be explained by the replacement of Cd ions in the ZnO structure. The degradation of the model dyes was observed to follow pseudo first order degradation kinetics. Keywords: Adsorption, CNTs, CNT/ZnO nanocomposites, CNT/ZnO:Cd, Isotherm, Kinetics, Microwave, Photocatalytic performance