Surface　modification　with　advanced　nanomaterials　(i.e.,　2D　nanosheets)　can　be　used　to　strategically　tailor　membrane　properties,　providing　improved　solute　permselectivity　to　targeted　molecules.　In　particular,　2D　graphite-like　carbon　nitride　(g-C3N4)　nanosheets　are　a　promising　alternative　for　membrane　modification,　due　to　their　exceptional　physicochemical　properties　and　facile　synthesis.　Herein,　high-flux　nanofiltration　(NF)　membranes　were　designed　using　bio-inspired　co-deposition　of　hydrophilic　g-C3N4　nanosheets　with　a　polydopamine　(PDA)/polyethylenimine　(PEI)　layer　onto　porous　ultrafiltration　(UF)　substrates.　The　g-C3N4　nanosheets　created　additional　nanochannels　in　the　PDA/PEI　layer　to　facilitate　water　molecule　transport,　resulting　in　high　permeability　(28.4　±　1.2　L　m-2　h-1　bar-1).　Particularly,　the　bio-inspired　layer　structure　was　tailored　from　the　UF　to　the　NF　(592　Da)　scale　by　incorporating　g-C3N4　nanosheets,　thereby　breaking　through　the　permeability-selectivity　trade-off　effect.　The　tailored　NF　membrane　enabled　ultrahigh　retention　of　three　reactive　dyes　(610-630　Da,　>99.3%)　and　low　salt　rejection　(2.9%　for　NaCl;　7.6%　for　Na2SO4),　significantly　promoting　the　fractionation　of　dyes　and　salts　for　dye　desalination.　Additionally,　the　hydrophilic　g-C3N4　nanosheets　with　oxygen　plasma　treatment　further　enhanced　the　wettability　of　the　membrane　surfaces,　resulting　in　a　superior　antifouling　performance.　This　study　indicates　the　promise　of　g-C3N4　nanosheets　to　engineer　high-flux　NF　membranes　with　desirable　fractionation　performance　for　sustainable　treatment　of　highly　saline　wastewater.　This　journal　is　©　The　Royal　Society　of　Chemistry.