**4. Conclusions**

In this study, the mp-CA/GO with controlled pore structure was used as an efficient solid adsorbent to remove heavy metal ion in wastewater. The fabrication of a controlled porous structure has two advantages. First, the porous structure increases the surface area of the material itself, thereby enabling the adsorbent material to provide additional binding sites for heavy metal ions. The removal rates for Pb2+, Cu2+, and Cd2+ were 95.4%, 81.2%, and 73.2%, respectively. Second, existing porous structure significantly accelerates the diffusion rate of ions in the adsorption process, thus enabling the adsorption process to complete within 40 min. Furthermore, the mp-CA/GO could be regenerated through a simple acid washing process and used repeatedly with little loss in performance. Additionally, the wide pH application range and the weak sensitivity to temperature also allowed the mp-CA/GO to be potentially applied to actual heavy metal sewage treatment.

**Author Contributions:** Z.W. and L.P. conceived and designed the experiments; L.P. performed the experiments; L.P. and Q.Y. analyzed the data; Z.W. and L.P. wrote the paper; R.H. made revisions of the manuscript.

**Acknowledgments:** We gratefully acknowledge the national natural science foundation of China (21407004), Anhui province office of education (KJ2017A345) and Program for Innovative Research Team in Anqing Normal University for financial support.

**Conflicts of Interest:** The authors declare no conflict of interest.
