Preparation of engineered carbon nanotube materials and its application in water treatment for removal of hydrophobic natural organic matter (NOM)

Abstract

Organic matters in drinking water are composed of soluble and particulate fractions. Soluble organic matters generally originated from allochthonous, autochthonous, and synthetic organic. Silica sand filters, which are utilized in water treatment, have a low potential of removing the soluble organic matters. Traditional carbon-based media such as activated carbon and anthracite are among the choices for the removal of soluble organic. Carbon nanotubes (CNTs) have a higher potential in removing synthetic and natural organic materials than the other traditional carbon based media. Utilization of CNTs at the slurry state requires the removal of the nanotubes themselves at the end of the process which leads to yet another problem to take care of. The present study, therefore, aims at solving this problem. In so doing, oxidized CNTs (140°C, 5 h, Nitric acid) were bound to the surface of silica sand through 3-(triethoxysilyl)propylamine to act as a bonding agent. Humic acid was used as the index of natural organic matters. The removal potential of humic acid with the new adsorbent (CNTsand) was studied under various operational conditions (contact time, temperature, and initial concentration). According to the obtained data, CNTsand has a good potential in the removal of humic acid (qmax = 81.96 mg/g CNT). Additionally, the kinetic, isotherm, and thermodynamic of adsorption were investigated, for which the data followed the pseudo-second-order kinetic model and Langmuir isotherm. Evaluation of enthalpy change (ΔH = 11.02 kJ/mol) and free energy change (ΔG = –7.32 to –9.20 kJ/mol) indicated that the reaction is spontaneous, endothermic, and thermodynamically favorable. Regeneration study showed that the desorption step of humic acid was faster than its adsorption step. It was observed that after five cycles, the adsorption capacity amounted to roughly 50% of the initial adsorption capacity. The above data depict that the new engineered material is a good reusable adsorbent in water treatment.