Preparation And Performance Of High Flux Polyamide Thin Film Composite Membrane

Polyamide thin film composite（PA-TFC）membranes are widely used due to excellent selective separation performance,low energy consumption,and environmental friendliness.However,PA-TFC membranes have shortcomings such as low permeation flux and poor selective separation performance in practical applications.In this study,zero-dimensional carbon nanomaterials and new amine monomers were used to control the structure and morphology of polyamide active layers.Graphene oxide quantum dots（GOQDs）and 3,5-diamino-1,2,4-triazole（GAZ）were introduced into aqueous solution to optimize the separation performance of PA-TFC membrane,and the specific work is as follows:The effect of graphene oxide quantum dots（GOQDs）on the properties and separation performance of GOQDs/PA-TFC membrane was studied.Zero-dimensional carbon nanomaterials—GOQDs with a large number of oxygen-containing groups on the surface improve the hydrophilicity of PA-TFC membranes,and the pure water flux of the membrane was 1.5-folds of the pristine PA-TFC membrane（5.4 L/（m²·h·bar）to 8.2L/（m²·h·bar））.Compared with pristine PA-TFC membrane,the rejection rates of GOQDs/PA-TFC membrane to Na₂SO₄,sulfamethoxazole and carbamazepine were almost unchanged.GOQDs/PA-TFC membrane not only had good separation performance for micro-pollutants and inorganic salts in water,but also improved the chlorine resistance of the composite membrane and overcomes the trade-off effects.The effect of GAZ on the structure morphology and separation performance of the GAZ/PA-TFC membrane was systematically studied.Firstly,the optimized conditions for the preparation of PA-TFC membranes were obtained and are displayed as follows:0.5 wt.%of PIP concentration,0.1 wt.%of TMC concentration,and 30 s of reaction time.Under this condition,the pure water flux of the PA-TFC membrane was 14.9 L/（m²·h·bar）with a 97.9%rejection rate of Na₂SO₄.FTIR and XPS analysis proved the successful incorporation of GAZ in the polyamide layer and the reduction of crosslinking degree.SEM and AFM analysis showed that with increasing GAZ,the thickness of the active layer of the membrane gradually decreased from 148.5 nm to 40.0 nm,and the membrane had a smoother and looser surface.The average pore size gradually increased with the increase of GAZ content.Zeta potential and contact angle analysis showed that the negative charge was increased and the hydrophilicity of the membrane surface was decreased.The thinner loose active layer increased the flux of the GAZ/PA-TFC membrane to 57.7 L/（m²·h·bar）,which was 4.3 times that of the unmodified membrane.Futhermore,the rejection rates of the GAZ/PA-TFC membrane for methyl orange,methylene blue,and crystal violet decreased with the increase of GAZ content.Water flux of the two anionic dyes Congo red（CR）and rose bengal（RB）increased from 9.5 and 10.6 L/（m²·h·bar）to 23.5 and 23.0L/（m²·h·bar）,respectively.In addition,the synergistic effect of size sieving and electrostatic repulsion maintained the rejection rate of CR and RB of GAZ/PA-TFC membrane above 97.0%and 99.5%,respectively.It can be concluded that GAZ overcomes the trade-off effects of PA-TFC membrane in the separation process of anionic dyes.Therefore,the incorporation of zero-dimensional carbon nanomaterials（GOQDs）and novel amine monomers（GAZ）could regulate the structural morphology of PA-TFC membranes and optimize the water separation performance of the membranes for desalination and dye recycling.