Carbon-based composite materials for water treatment

Water scarcity and pollution are now urgent problems around the world. Thus efficient water treatment is an important research topic. Forward osmosis (FO) and solar evaporation are two most important desalination technologies that could overcome water scarcity problem since seawater is abundant. FO is an emerging desalination technology taking advantage of natural osmosis-driven movement of water, while solar evaporation pond is widely used to produce fresh water and sea salts at the same time by harnessing solar energy. And a wide range of sorbent materials have been developed for spilled oil cleanup to prevent seawater pollution. Although present materials for water treatment have been widely applied in industry, novel materials are stilled required to achieve better performance with lower energy consumption and less environmental pollution. Carbon-based composites have a bright application prospect due to the broad available precursors, relatively low cost and excellent properties of carbon materials. This thesis studies novel environmentally friendly carbon-based composite materials in the field of water treatment including FO, solar evaporation and oil sorption with high performance and relatively low cost by recycle or using free solar energy. Draw agent is a major issue required to be addressed to promote commercial implementation of FO. Incorporation of reduced graphene oxide (rGO) in polymer hydrogels greatly increased the softness of composite hydrogels and improved inter-particle and particle-membrane contact, leading to over double water fluxes of pure hydrogels. Furthermore, the light-absorbing property of rGO accelerated dewatering process, in which pure water from the hydrogels was harvested using heat induced from absorbed solar energy at twice the rate of the pure hydrogels. In another desalination process, solar evaporation, water evaporation enhancement by floating photothermal material which aims to increase water surface temperature was carried out. Fe3O4/C magnetic particles were synthesized by carbonization of poly(furfuryl alcohol) (PFA) incorporated with Fe3O4 nanoparticles. The results indicated that these floating Fe3O4/C particles led to an increase as high as 230% in water evaporation rate. In addition, Fe3O4/C particles were easily recycled using a magnet, and stable after recycled three times. To make particles more easily collected and handled, another millimetre-sized hollow carbon beads were also prepared for solar evaporation. These hydrophobic hollow carbon beads were obtained after carbonization of polymer/silica beads synthesized by phase inversion method. Monodispersed hollow carbon beads with 1.5 mm in diameter achieved a maximum evaporation rate of 1.28 L m-2 h-1, which is around 234 % of the rate attained without carbon beads, and also higher than that of Fe3O4/C particles, indicating the particle size had an impact on evaporation rate. Moreover, the good recyclability was also demonstrated. Due to the hydrophobic nature and porous structure, hollow carbon beads were also applied as sorbents in oil cleanup process. Especially, the toluene sorption capacity was as high as 5.25 times of carbon beads in volume. The effects of silica content in beads and oil molecule size on oil sorption capacity were investigated. Heat treatment was revealed to be a good recycle method to collect carbon beads and oils simultaneously