PREPARATION AND CHARACTERISATION OF PALLADIUM/SILVER/CARBON NANOTUBES COMPOSITES FOR THE TREATMENT OF INDUSTRIAL ANIMAL FEEDS PROCESSING WASTEWATER

Abstract

This study focused on the development of Pd-Ag-CNTs nanocomposites for the removal of selected heavy metals and other water quality indicators in industrial animal feed processing wastewater. Silver and palladium nanoparticles were produced using green synthesis method. While Carbon nanotubes (CNTs) were produced via catalytic chemical vapour deposition (CCVD) method and then purified by acid treatment by mixture of H2SO4 and HNO3. The solution of 2-mercaptpoethylamine in N, N’-dicyclohexylcarbondiimide (DCC) was used as a coupling and dehydrating agent for the formation of amide group on the purified CNTs. Pd-CNTs and Ag-CNTs were produced along with Pd-Ag-CNTs through a combination of ultrasonic-assisted wet impregnation method. Different analytical tools such as HRSEM, HRTEM, EDS, SAED, XRD and BET were used to characterise the prepared nanostructured materials. The HRSEM results revealed that PdNPs and AgNPs were well dispersed on the CNTs matrix. The EDS confirmed that Pd and Ag were successfully deposited on CNTs. XRD pattern confirmed a graphitic, face-centred cubic structure upon modifications with Ag and Pd nanoparticles with an average crystallite sizes of 26.10 nm (Pd-Ag-CNTs) > 18.74 nm (Pd-CNTs) > 13.6 nm (Ag-CNTs) > 13.00 nm (P-CNTs). The BET results showed increased in surface area of Pd-Ag-CNTs compared to CNTs and the order ofthe increment were: 392.5 m2/g (Pd-Ag-CNTs) >356.3 m2/g (Pd-CNTs) > 352.5 m2/g (Ag-CNTs) >227.63 m2/g (P-CNTs). Pd-Ag-CNTs nanocomposites were used as an adsorbent for the treatment of industrial animal feed processing wastewater. The effect of the nano-adsorbent removal on wastewater indicator parameters and selected heavy metals such as copper (Cu), iron (Fe), manganese (Mn) and nickel (Ni) were investigated. Effect of contact time, adsorbent dosage and temperature on the adsorption potentials of Pd/Ag/CNTs were assessed via a batch mode process. Linear and nonlinear regression methods were used for determination of the optimum adsorption isotherms and kinetics using the experimental adsorption equilibrium data. The coefficient of determination (R2), the sum of the squares errors (SSE) and Chi-square (χ2) were used in the nonlinear regression. The optimum condition based on each parameters was 90 min of contact time, 60 mg of adsorbent dosage and 80 ℃ of temperature, where the adsorption of Ni ions (99.84 %) was higher in removal efficiency than other analyzed metal ions: Fe (88.36 %), Cu (77.86 %) and Mn (77.64 %). The isotherm data best fitted Florry-Huggins isotherm model based on the χ2, SSE and regression co-efficient values of 0.9947 (Cu), 0.9787 (Fe), 0.9924 (Mn) and 0.7098 (Ni), while the kinetic data suited pseudo-second order and thus predicted best the experimental data.The thermodynamic study was found to be non-spontaneous and endothermic in nature due to positive values of standard Gibb’s free energy and enthalpy change respectively. This study demonstrated that Pd/Ag/CNTs exhibits exceptional adsorptive properties for the removal of selected metal ions from industrial animal feed processing wastewater.