Energy-efficient process for water desalination and organic dye separation is urgently needed to meet the dramatically increasing demand for fresh water globally. Nb2CTx MXene, as one type of 2D transition metal carbides (TMDCs) family, has attracted tremendous research interest in the fields of separation technology over the past decade. However, it has been challenging to fabricate surface-modified Nb2CTx MXene nanosheet films with superior performance for desalination and separation applications. Herein, we report a novel, facile and scalable sodium alginate (SA)-assisted surface termination method to fabricate SA-modified Nb2CTx MXene (NbSA) nanosheets. It is found that films of the NbSA nanosheets demonstrate overall better performance than bare Nb2CTx MXene nanosheet film. The NbSA film with a thickness of 5 mm shows >95% rejection towards various cations under forward osmosis process. The film also shows a fast water flux of 2200 +/- 100 L m(-2) h(-1) bar(-1) (LMHB) with almost 100% rejection rate towards multiple dyes under vacuum-driven filtration mode. Moreover, the NbSA film has exhibited selective separation performance on Li+/Mg2+ mixture solution under forward osmosis process. This work reports a novel NbSA film with excellent performances for desalination and separation, with useful implications for developing 2D material films in separation processes and environmental engineering. (C) 2020 Elsevier Inc. All rights reserved.