SYNTHESIS OF SILVER DOPED MULTI-WALLED CARBON NANOTUBES FOR THE TREATMENT OF FISHPOND WASTEWATER.

Abstract

Agglomeration of the carbonaceous material during and after the synthesis carbon nanotubes affects and limits its efficiency hence there is need to modify the surface of raw CNTs and enhance its adsorption capacity and dispersion rate. This study is aimed at the development of silver Nanoparticles doped on multi- walled carbon nanotube for the treatment of fish pond wastewater. This study investigated the treatment of fishpond wastewater using nanocomposites via batch adsorption by purified carbon nanotube and silver doped carbon nanotubes (CNTs) as nano-adsorbents. Synthesis of silver nanoparticles (AgNPs) was done using Carica papaya leaf extract. The synthesized AgNPs was confirmed by UV spectra, Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD) and Highresolution transmission electron microscopy (HRTEM). The peaks in XRD pattern are associated with that of face centered cubic (FCC) form of metallic silver. The results of HRTEM confirmed that the size of AgNPs are between 11-30 nm. Fe–Ni/kaolin catalyst was used for the production of carbon nanotubes (CNTs) by catalytic chemical vapour deposition method followed by acid purification treatment and doping with silver nanoparticles to give purified carbon nanotubes (P-CNTs) and silver doped carbon nanotubes (Ag-CNTs) respectively. The as-synthesized CNTs, P-CNTs and Ag-CNTs were characterized by HRTEM, High-resolution scanning electron microscopy (HRSEM), FTIR and Brunauer Emmett Teller (BET). The adsorption behavior of P-CNTs and Ag-CNTs to remove specifically Fe, Mn and Zn from fishpond wastewater were examined by the batch adsorption process as a function of different contact time, adsorbent dosage and temperature. The HRSEM/HRTEM/BET analysis confirmed that both nano adsorbents were tube-like in nature, highly porous and crystalline, with Ag-CNTs possessing high surface area (1068 m2/g) than P-CNTs (268.40 m2/g). The order of maximum Mn, Zn and Fe removal by the nano-adsorbents at equilibrium time of 100 min are as follows: Ag-CNTs (91.92%, 88.53% and 89.23%)>P-CNTs (91.85%, 81.60% and 52.14%). Equilibrium sorption data were better described by Freundlich isotherm than Langmuir isotherm. The adsorption kinetics for Mn, Zn and Fe removal from fishpond wastewater fitted well to the pseudo-second-order model. Thermodynamics analysis of the adsorption process revealed negative values of enthalpy (ΔH°) for Mn, Fe and Zn respectively on Ag-CNTs which indicates that the adsorption is exothermic in nature and for P-CNTs negative values of ΔH° for Mn and Fe except Zn has positive ΔH° and endothermic in nature. The Gibbs free energy (ΔG°) was negative which showed the feasibility and spontaneity of adsorption process, except Zn adsorbed by P-CNTs which possesses positive ΔG°. The change entropy (ΔS°) was positive which signifies a better adsorption of the heavy metals and increase randomness except for Zn adsorbed by PCNTs with negative ΔS° which signifies decrease in randomness of the process. In this study the adsorption isotherm and kinetic model was best fitted to Freundlich isotherm and pseudosecond-order model, which shows that it is a multilayer phenomenon. The adsorption process was spontaneous, random and exothermic in nature.