Water Treatment Technology with Nanocarbon

Abstract

Nano-carbon materials such as carbon nanotube and graphene have been studied over the last 2 decades with great attention for their feasibility in future applications due to their exceptional properties like high current carrying capacity, ballistic charge transport, high thermal conductivity, chemical inertness, and high mechanical strength and so on. The materials has received considerable attention in the fields of water treatment because of fast mass transport resulted from surface hydrophobicity, large surface area and anti-microbial activity. In the thesis, the structures consisting only of nano-carbon materials are synthesized and then characterisitics undiscoverable in the existing water treatment matrials and possibility of the structures as materials for water treatment is reported. 1) A Carbon Nanotube Wall Membrane for Water Treatment: Various forms of carbon nanotubes have been utilized in water treatment applications. The unique characteristics of carbon nanotubes, however, have not been fully exploited for such applications. Herein, a millimeter-thick ultrafiltration carbon nanotubes membrane that can provide a water permeability that approaches 30,000 L m-2 h-1 bar-1, compared to the best water permeability of 2,400 L m-2 h-1 bar-1 reported for carbon nanotube membranes, is developed. The developed membrane consists only of vertically aligned carbon nanotube walls that provide 6 nm wide inner pores and 7 nm wide outer pores that form between the walls of the carbon nanotubes when the carbon nanotube forest is densified. The experimental results reveal that the permeance increases as the pore size decreases. The carbon nanotube walls of the membrane were observed to impede bacterial adhesion and resist biofilm formation. 2) Graphene membranes for nanofiltration: Graphene membranes for water treatment that are functionalized with chelates is presented. With the present of charged molecules on graphene, vastly improved ion rejection result. Although graphene membranes reported so far showed much higher permeability than commercial nanofiltration membrane (NF), Rejection of monovalent and divalent salts is similar to that of commercial NF. Herein, to fabricate the graphene membrane with high rejection to salts, graphene oxide is functionalized with N-(trimethoxysilylpropyl) ethylenediamine triacetic acid (EDTA-silane) positively charged at one side and then reduced it. The graphene membrane shows more than 80 % rejection rate for NaCl2. A significant increase in rejection rate is comparable with performance of commercial NF. The excellent performance of the graphene membrane is resulted in charge effect and size exclusion based on positively charged chelate molecules and small interlayer spacing in wetted. 3) Carbon Nanotube-Bonded Graphene Hybrid Aerogel Sorbents: Carbon nanotube (CNT)-bonded graphene hybrid aerogels are prepared by growing CNTs on graphene aerogel surface with nickel catalyst. With the presence of bonded CNTs in graphene aerogel, vastly improved mechanical and electrical properties result. A significant increase in specific surface area is also realized. The presence of CNTs transforms the hybrid aerogels into a mesoporous material. Viscoelasticity of the hybrid aerogels are found to be invariant with respect to temperature over a range between -150 ℃ and 450 ℃. These characteristics along with improved properties would make the hybrid aerogels an entirely different class of material for applications in the fields of biotechnology and electrochemistry. Mesoporous nature of the material along with a high specific surface area also makes the hybrid aerogel attractive as a water treatment substance. Both anionic and cationic dyes can be removed effectively from water with the hybrid aerogel. A number of organics and oils can selectively be separated from water by the hybrid aerogel. The hybrid aerogel is easy to handle and separate due to its magnetic nature, and can readily be recycled and reused.