Facile and efficient synthesis of carboxylic terminated Ti3C2Tx nanosheets using citric acid

•High-quality carboxylic terminated Ti3C2Tx nanosheets were successfully synthesized by incorporating non-hazardous citric acid with NH4HF2 through an efficient and one-pot protocol.•The nanosheeets showed superior exfoliation, better morphology, few-layered thickness, enhanced specific surface area, better thermal stability, and numerous active sites in terms of terminal functional groups.•The MXenes nanosheets displayed an extraordinary adsorption capacity for toxic Cr(VI) and Pb(II) in water.•The nanosheets were regenerated and reused over six cycles of adsorption–desorption effectively.