**4. Conclusions**

Modification of nanoporous carbon was conducted using mild oxidation of hydrogen peroxide. The results showed that the oxidation process alters the porosity of nanoporous carbon and amount of oxygen functional group. After oxidation, a higher amount of oxygen functional groups of porous carbon is seen and only a little decrease in the specific surface area, but more porosity is exhibited. In the application, oxidized carbon showed remarkably higher metronidazole uptake capacity. The increase in the adsorption capacity seems to be more related to the change in pore textural property rather than amount of oxygen functional group.

**Author Contributions:** Conceptualization, T.A. and I.P.; methodology, T.A. and I.P.; formal analysis, R.A.G.S. and Y.M.N.A.; investigation, R.A.G.S. and Y.M.N.A.; resources, T.A. and I.P.; writing—original draft preparation, T.A.; writing—review and editing, T.A. and I.P.; visualization, W.T.L.; supervision, T.A. and I.P; funding acquisition, T.A.

**Funding:** This research and APC were funded by program of Rekognisi Tugas Akhir (RTA), Universitas Gadjah Mada, grant number 2129/UN1/DITLIT/DIT-LIT/LT/2019.

**Acknowledgments:** The authors thank the PT Home System Indonesia for providing the porous carbon synthesized from coconut shell as a gift.

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