Abstract
Abstract The forward osmosis (FO) membrane exhibits great performance degradation when contacting with chlorine solutions. The damage of chlorine to membrane material will seriously reduce the lifetime of the membrane and increase the cost of membrane treatment technology. Here, we prepared chlorine-stable membranes by a covalent modification method with cyclohexylamine. The cyclohexylamine observably changed the surface morphology, the roughness (arithmetic average) of the membrane decreased from 22 to 17.2 nm. The addition of cyclohexylamine produced a denser sacrificial layer of short chain polyamide, which made modified membranes possess significantly better chlorine resistance with slightly declined water flux. The water flux of the optimal modified membrane was 10.78 Lm−2 h−1, only 13% less than that of the pristine membrane. Importantly, after 20,000 ppm·h chlorine exposure, the membrane with 1.5 wt% cyclohexylamine had a salt rejection of 77.2% and showed 26.0% lower water flux than pristine TFC (thin film composite) membrane in FO mode. Notably, the grafting membranes could maintain a high performance under acidic chlorination conditions. The membrane with best performance had a salt rejection of 81.6%, exhibiting 24.4% higher salt rejection than pristine membrane with 20,000 ppm·h chlorine exposure at a pH of 4. The cyclohexylamine endowed the FO membrane with better chlorine resistance, making it attractive for the development of chlorine-resistant membrane for environmental and desalination processes.
Highlights
At present, the world’s available fresh water resources are still in short supply and water quality problems are still severe
With the cyclohexylamine concentration increased to 1.0 wt% and 1.5 wt%, the Ra decreased to 18.7 nm and 17.2 nm, respectively
The composite structures composed of the long-chain PA were formed by TMC and MPD and the short-chain PA were formed by cyclohexylamine and TMC
Summary
The world’s available fresh water resources are still in short supply and water quality problems are still severe. The FO technology uses only the osmotic pressure of the solution on both sides of the membrane to provide power without applying external pressure to achieve the separation of pollutants and water. It has the advantages of low energy consumption, strong retention capacity, strong resistance to membrane fouling, and low membrane fouling. At present, it is mainly used for seawater desalination, sewage treatment and water purification. As the most common and effective disinfectant in the water treatment process, chlorine can make the membrane sharply lose its salt rejection function
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