A non-MPD-type reverse osmosis membrane with enhanced permselectivity for brackish water desalination

Easily Accessible and Solution-Stable Ni(0) Precatalysts for High-Throughput Experimentation

We report the synthesis, characterization, and catalytic applications of N,N'-diaryl diazabutadiene (DAB) Ni(0) complexes stabilized by alkene ligands. These complexes are soluble and stable in several organic solvents, making them ideal candidates for in situ catalyst formation during high-throughput experimentation (HTE). We used HTE to evaluate these Ni(0) precatalysts in a variety of Suzuki and C-N coupling reactions, and they were found to have equal or better performance than the still-standard Ni(0) source, Ni(COD)2.

Thin film nanocomposite hollow fiber membranes comprising Na+-functionalized carbon quantum dots for brackish water desalination

We have incorporated Na⁺-functionalized carbon quantum dots (Na-CQDs) into the polyamide layer via interfacial polymerization reaction and developed novel thin film nanocomposite (TFN) hollow fiber membranes for brackish water desalination. Comparing with the conventional thin film composite (TFC) membranes, the TFN membranes comprising Na-CQDs have a larger effective surface area, thinner polyamide layer and more hydrophilic oxygen-containing groups in the polyamide layer. Besides, the interstitial space among the polyamide chains becomes larger due to the presence of Na-CQDs. As a result, the incorporation of 1 wt% Na-CQDs into the polyamide layer could improve the pure water permeability (PWP) of the membranes from 1.74 LMH/bar to 2.56 LMH/bar by 47.1% without compromising their NaCl rejection of 97.7%. Interestingly, stabilization of the TFN hollow fiber membranes containing 1 wt% Na-CQDs at 23 bar could further promote the PWP to 4.27 LMH/bar and the salt rejection to 98.6% under the same testing conditions due to the deformation of the membranes under a high hydraulic pressure. When using a 2000 ppm NaCl aqueous solution as the feed, the optimal water flux and rejection of the newly developed TFN membranes at 15 bar are 57.65 ± 3.26 LMH and 98.6% ± 0.35% respectively. The Na-CQDs incorporated TFN hollow fiber membranes show promising applications in the field of brackish water desalination.

Toward Enhancing the Chlorine Resistance of Reverse Osmosis Membranes: An Effective Strategy via an End-capping Technology

Polyamide reverse osmosis (RO) membranes suffer performance decay when exposed to free chlorine because of their unique chemical structure. The decay limits their lifespan and increases operating cost. Herein, the secondary interfacial polymerization method was performed, for the first time, using isophthaloyl chloride (IPC) as the chain-terminating reagent, to eliminate the negative effect when the unreacted amino groups interact with chlorine. The surface zeta potential of the as-prepared membrane remained almost constant over a wide pH range, which greatly demonstrated the high conversion ratio of the end-capping procedure. However, neither the surface morphology nor the separation properties were conspicuously influenced. Because of the absence of the terminated amino groups in the polyamide layer, the IPC-modified membrane exhibited significantly improved chlorine resistance, particularly at high pH. Its desalination performance remained unchanged as the total chlorine exposure approached 10 000 ppm·h, whereas only 80.3% of the NaCl was rejected by the unmodified membrane under the same conditions. Such SIP technology can be applied directly to the commercial SW30 seawater desalination membrane, making it more tolerant to free chlorine. Overall, our results strongly proved the IPC-assisted end-capping process as a promising, practicable, and scalable technology for enhancing the chlorine resistance of an RO membrane.