Abstract
M.Tech.
Studies on the removal of nickel and platinum are increasing due to the toxicities
of these metals. Several methods are currently used to extract these metals
however they present limitations. There is hence a need to develop an efficient
method for the removal of nickel and platinum from aqueous solution. A study on
the use of purified multiwalled carbon nanotubes (purified MWCNTs) and a
phosphine derivatized multiwalled carbon nanotubes for the extraction of these
metal ions from solution was therefore undertaken. Multiwalled carbon nanotubes
(MWCNTs) were produced by nebulised spray pyrolysis, purified by a multi-step
technique and functionalized. Phosphine moieties were attached to the bromoarylated-
MWCNTs by metallated phosphide route leading to triphenylphoshine
linked MWCNTs (Tpp-MWCNTs). As produced, purified and triphenylphosphine
linked multiwalled carbon nanotubes were characterized by various techniques,
including microscopic and spectroscopic techniques, thermal, elemental and
surface analysis. Transmission and scanning electron microscopy used revealed
purified MWCNTs had insignificant impurities. X-ray photoelectron spectroscopy
(XPS) results showed that triphenylphosphine linked multiwalled carbon
nanotubes had 2.6% phosphorus. Zeta potential results demonstrated that purified
MWCNTs had positive surface charges at acidic pH. Triphenylphosphine linked
multiwalled carbon nanotubes were negatively charged on the surface in acidic
media. Batch adsorption experiments were carried out to investigate the removal
of nickel and platinum from aqueous solutions. Several parameters which
influence the adsorption process were studied, including the effect of pH, the
contact time and the effect of initial concentration on adsorption. The adsorption
models for the Freundlich and Langmuir isotherms were employed to fit the
experimental data. Triphenylphosphine linked MWCNTs removed more nickel
(84.68 mg/g) than purified MWCNTs (77.39 mg/g). In contrast, purified MWCNTs
removed more platinum (10.5 mg/g) than triphenylphosphine linked MWCNTs
(6.01 mg/g). Experimental data for nickel fitted both Freundlich and Langmuir
models well whereas only Langmuir model fitted well for platinum. The adsorption
of nickel and platinum was indeed found to be pH, time and initial concentration
dependent. Metal species (nickel and platinum) in solution had also influenced the
uptake of these metals using purified-and Tpp-MWCNTs.