Efficient removal of non-biodegradable and hazardous dyes from wastewater remains a hot research topic.Herein,a rationally designed a Cu(Ⅱ)-based metal-organic gel(Cu-MOG)with a nanoporous 3D network structure prepared via a simple one-step mixing method was successfully employed for the removal of cationic dyes.The Cu-MOG exhibited high efficiency,with an adsorption capacity of up to 650.32 mg/g,and rapid adsorption efficiency,with the ability to adsorb 80％of Neutral Red within 1 min.The high adsorption efficiency was attributed to its large specific surface area,which enabled it to massively bind cationic dyes through electrostatic interaction,and a nanoporous structure that promoted intra-pore diffusion.Remarkably,the Cu-MOG displayed size-selective adsorp-tion,based on adsorption studies concing dyes of different sizes as calculated by density functional theory.Additionally,the adsorption performance of the Cu-MOG still maintained removal efficiency of 100％after three regeneration cycles.These results suggested that the Cu-MOG could be expected to be a promising and competitive candidate to conveniently process wastewater.