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[Display omitted] • The membranes were fabricated by filtering g-C 3 N 4 nanosheets and CTS onto HPAN. • The membranes demonstrated selective separation of monovalent and divalent ions. • The membranes exhibited high water permeability at low pressure. • The diffusion behaviors of water and ions through g-C 3 N 4 membranes was studied by MD simulations. The complex transport mechanism of water and ions in the membrane hinders the design of free standing membranes. The mechanism of the mass transport characteristics of traditional nanofiltration membranes is no longer applicable to free standing membranes due to the change of the driving force in the membrane. In this study, the vacuum filtration of the g-C 3 N 4 suspension was simulated to form a free standing membrane model for the first time by using the molecular dynamics (MD) simulations. In the nanochannels formed by the g-C 3 N 4 nanosheets, the water molecules rapidly penetrated across the free standing membrane due to ultra-low friction. On the other hand, the hydrated Na+ and Mg2+ ions needed energy to partially dehydrate and penetrate across the free standing membrane. Moreover, the MD simulations indicated that the speed of Mg2+ ions penetrating across the g-C 3 N 4 nanochannels was lower than that of Na+ ions. Combined with the computational works, salt retention experiments were conducted to demonstrate the correctness of the proposed model. Further, the developed membranes exhibited excellent non-swelling stability and antibacterial activity in aqueous solutions. The g-C 3 N 4 free standing membranes prepared in this study can effectively realize the separation of monovalent and divalent ions, accompanied with high permeability. [ABSTRACT FROM AUTHOR]

[Display omitted] • pH-response attapulgite (p-ATP) nanofibers were prepared by surface grafting. • The compatibility between PVDF and t-ATP resulted in excellent tensile strength. • Anti-fouling performance of membrane increased due to the hydrophilic p-ATP. • Adsorption and desorption of H 2 O from p-ATP occurred with the change in pH. • The membrane is easy-cleaning due to the pH-response property of p-ATP. Membrane separation is an efficient strategy to disrupt the spread of pathogens in an aqueous solution and produce clean water, but its performance is seriously affected by fouling caused by bioadhesive. In this study, novel pH-response attapulgite (p-ATP) nanofibers were prepared and applied in the modification of poly(vinylidene fluoride) (PVDF) ultrafiltration membrane for bovine serum albumin (BSA) solution purification. Poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) was grafted onto the surface of attapulgite (ATP) to offer pH-response property and to improve compatibility with PVDF. p-ATP is a hydrophilic material, which can increase the anti-biofouling performance of PVDF, and its one-dimensional structure is beneficial for enhancing the inter-entanglement with organic chains in the membrane matrix. The resultant composite membrane loaded with 7% p-ATP presented 77.2% and 108.1% increase in stationary permeance and mechanical strength, respectively, than that of the pristine PVDF membrane. Furthermore, the PDMAEMA chains in p-ATP will be shrunken or swollen with the change of pH value, resulting in adsorbing or releasing water molecules. This process is effective to mitigate the adhesion between biofoulants and membrane and can break the already formed biofouling layer. So, the composite membranes are easily to be cleaned via a simple pH-change cleaning process. The molecular dynamic simulation was also conducted to analyze the high performance of the PVDF/p-ATP membrane to provide theoretical support. [ABSTRACT FROM AUTHOR]