The Influence of Ag[sup.+]/Ti[sup.4+] Ratio on Structural, Optical and Photocatalytic Properties of MWCNT–TiO[sub.2]–Ag Nanocomposites

In this paper, we propose a simple procedure to obtain multi-walled carbon nanotubes (MWCNTs) decorated with TiO[sub.2] –Ag nanoparticles (MWCNT–TiO[sub.2] –Ag). The MWCNTs were decorated with TiO[sub.2] –Ag via combined functionalization with –OH and –COOH groups and a polymer-wrapping technique using poly(allylamine)hydrochloride (PAH). TiO[sub.2] -modified Ag nanoparticles were synthesized via the Pechini method using a mixture of acetylacetonate-modified titanium (IV) isopropoxide with silver nitrate (with Ag[sup.+] /Ti[sup.4+] atomic ratios of 0.5%, 1.0%, 1.5%, 2.0%, and 2.5%) and L(+)-ascorbic acid as reducing agents. XRD analysis revealed the formation of nanocomposites containing CNT, anatase TiO[sub.2] , and Ag. The presence of nanoparticles on the MWCNT surfaces was determined using TEM. The morphology of the TiO[sub.2] –Ag nanoparticles on the MWCNT surfaces was also determined using TEM. UV–Vis investigations revealed that an increase in the ratio between Ag[sup.+] and Ti[sup.4+] decreased the band gap energy of the samples. The characteristic vibrations of the TiO[sub.2] , Ag, and C atoms of the graphite were identified using Raman spectroscopy. The photocatalytic activity of the MWCNT–TiO[sub.2] –Ag nanocomposite was assessed by examining the degradation of Allura Red (E129) aqueous solution under UV irradiation. The dye photodegradation process followed a pseudo-first-order kinetic with respect to the Langmuir–Hinshelwood reaction mechanism. The spin-trapping technique evidenced that •O[sup.2−] was the main species generated responsible for the Allura Red degradation.