Enhancement the photocatalytic degradation of methylene blue dye using fabricated CNTs/TiO2/AgNPs/Surfactant nanocomposites

Abstract

In this work, the cotton stalks waste, as a woody biomass widely produced in Egypt, was used as a carbonaceous precursor for synthesis of carbon nanotubes (CNTs) with bamboo-like structure via subsequent catalytic hydrothermal and carbonization routes. Nanocomposite of TiO2@CNTs was prepared by sol-gel of titanium isopropoxide in presence of CNTs as a support and followed by calcination at 500 °C for 180 min under flowing of N2 gas. In addition, TiO2@CNTs was wrapped by silver nanoparticles (AgNPs) individually and in presence of synthesized cationic surfactant (C10) to produce TiO2@CNTs/AgNPs and TiO2@CNTs/AgNPs/C10, respectively. The resulting nanocomposites and unadorned CNTs were characterized by transmission-electron microscope (TEM), field emission-scanningelectron microscopy (FE-SEM) combined with energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Raman spectroscopy, N2 gas adsorption-desorption at −196 °C and UV–Vis diffuse reflectance spectroscopy (UV–vis DRS). The obtained photocatalysts were used to remediate aqueous solutions of methylene blue (MB) dye under visible light irradiation. The results affirmed that the surfactant improved the dispersion and surface interaction of AgNPs over TiO2@CNTs which formed effective photocatalytic sites. The synthesized CNTs enhanced the surface and electronic properties of TiO2 while AgNPs significantly reduced the recombination of electron–hole pairs over TiO2@CNTs/AgNPs/C10. Accordingly, TiO2@CNTs/AgNPs/C10 exhibited the superior photocatalytic degradation of MB dye and high stability as a result of good dispersion of AgNPs by the surfactant, the lower band-gap energy (2.25 eV) and the larger surface area (146 m2/g) than that of TiO2@CNTs/AgNPs.