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Capacitive deionization (CDI) technology, based on the electric field ion capture mechanism, holds significant application prospects for purifying copper ions (Cu2+) from industrial wastewater. The development of electrode materials is crucial for enhancing capacitive Cu2+ removal. Herein, the three-dimensional nanoporous carbon network is prepared from agricultural waste rice husk using basic zinc carbonate as the pyrolytic activator. It is found that the ZnO site-occupying effect, stemming from the pyrolysis activator, exerts a pronounced regulatory influence on the porous structure of carbon network. The carbon electrode exhibits a satisfactory specific capacitance of 256.2 F g−1 at 0.5 A g−1. More importantly, the assembled symmetrical CDI cell demonstrates an excellent electrochemical adsorption capacity of 60.5 mg g−1 for Cu2+. Such exceptional capacitive deionization performance can be attributed to the synergistic effect of the electrochemical double-layer and electrochemical reduction during the adsorption process of Cu2+. Thus, this research offers a promising strategy for efficient wastewater treatment. [Display omitted] • ZnO site-occupying effect on pore formation has been thoroughly investigated. • The CDI cell presents a superb Cu2+ adsorption capacity of 60.5 mg g−1. • The electrochemical synergistic effect enhances the ability to purify Cu2+. [ABSTRACT FROM AUTHOR]