Desenvolvimento de uma membrana composta de grafeno sobre substrato polimérico poroso de PMMA para dessalinização e purificação de água

Abstract

In the current global scenario, the development of a process of desalination and purification of marine waters by membranes is a strategic factor to guarantee drinking water resources worldwide. In this context, the search for new materials has been one of the main focuses of the study of the membrane separation process. Among the recent advances in the development of new membrane systems for water desalination, one of the most promising technologies is the use of graphene-based membranes. Even with great interest and due to the recent nature, there are still few published experimental studies on the subject. There are also no studies in the literature using polymethylmethacrylate (PMMA) as porous support for graphene, and likewise, there are also few reports of the use of PMMA exclusively as a basis for the production of a porous membrane even without the use of nanoparticles. This dissertation aims to produce and characterize a membrane composed of graphene in a porous PMMA substrate. The experimental strategy consisted of the growth by chemical vapor deposition (CVD) of graphene monolayers, the formation of the PMMA porous membrane, by different systems, and subsequent wet transfer of graphene to the surface of the PMMA porous substrate. Characterization of the resulting membranes was carried out through contact angle, rheology of the matrix solution, scanning electron microscopy, atomic force microscopy, spectroscopy/Raman map, permeation measurement in liquid and gas phase, in addition to salt retention test. The synthesized CVD graphene showed a predominance of monolayers and low defect density, indicating good quality, being the same application in the production process of the composite membrane. Membranes produced with PMMA solution with different solvents, dimethylformamide, acetone, and chlorobenzene, are possible to be formed through phase inversion. Membranes originated from the PMMA/Acetone solution showed dense morphology, gas selectivity (αN2/CO2 of 5.6), but fragile structure. Membranes originated from the PMMA/Chlorobenzene solution showed asymmetric structure and sponge-like morphology, preservation of the structural characteristic in a long time, gas selectivity (αN2/CO2 of 1.5) and characteristics suitable for application of the graphene layer. The transfer of graphene film to PMMA membranes proved to be feasible, thus producing membranes composed of graphene on the PMMA substrate. The membrane composed of graphene on PMMA formed from acetone solution showed an improvement in gas selectivity of ~10% compared to the pure membrane. The pure PMMA membrane showed complete saline retention in a 24-hour direct osmosis test, indicating the possibility of applying for the desalination process. The measurements with the composite membrane showed a gaseous permeability for CO2 in GPU of 6.08x10-2, representing a decrease of approximately 81.9% when compared to the pure membrane. Concerning N2, the permeability was 0.9x10-2, representing a decrease of 83.7%.