Engineering of Ag-nanoparticle-encapsulated intermediate layer by tannic acid-inspired chemistry towards thin film nanocomposite membranes of superior antibiofouling property

Biofouling severely limits the application of reverse osmosis (RO) for water treatment. In this work, a green surface in-situ reduction method based on the tannic acid-inspired chemistry was used to introduce silver nanoparticles (AgNPs) into the intermediate layer of a thin film nanocomposite (TFN) membrane, as effectively improved the anti-biofouling performance of the membrane without sacrificing its desalination performance. SEM, EDX, AFM, XPS, DSA, ATR-FTIR and zeta potential were used to characterize the membranes. The plate counting method and confocal laser scanning microscopy (CLSM) were used to evaluate the anti-biofouling performance. And the long-term Ag+ release rate was measured using ICP-MS. Compared with unmodified thin film composite (TFC) membranes, the permeation flux of TFN membrane is improved while retaining the salt rejection. By optimizing the soaking time of FeCl3 and AgNO3 on the PSF membrane surface during the preparation of the intermediate layer and the M-phenylenediamine (MPD) and trimesoyl chloride (TMC) concentration for the interfacial polymerization. A water flux of 34.5 ± 1.2 L/m2 h and a salt retention of 98.0 ± 0.3% were achieved under the operating pressure of 1.55 MPa and 25 °C, for a 2000 ppm NaCl solution. The killing rates of the membrane to E. coli and S. aureus are almost 100% for a 24 h and 48 h contacting time. The number of bacteria attached to the membrane surface is far less than that of the unmodified membrane. More importantly, the Ag+ release rate was stable and controllable, allowing for long-term antibacterial properties.