Carbothermic reduction using carbon as a sacrificial agent has been widely used in extractive metallurgy to convert extracted ores into pure metals. Here, we demonstrated that the carbothermic reduction could be an effective means to transform biowastes (e.g., the fallen leaves dumped each autumn in South Korea) into useful porous carbon with wide applicability. Amid speculation that metal oxide, not carbon, could also be functioned as a sacrificial agent, we coated ZnO on the fallen leaves using atomic layer deposition (ALD) and performed pyrolysis. We found that the pyrolysis of the ZnO-coated fallen leaves leads to carbonization as well as solid-state etching, thereby producing highly porous carbon. The carbothermically synthesized carbon exhibited a significantly increased volume fraction of the micropore (over 60%). Besides, the porous carbon showed far better electrochemical performance (-3 times increase in energy density) as well as higher dye removal efficiency than that synthesized by the simple pyrolysis. We expect that our approach could be employed as one of the effective upcycling methods for waste management. (c) 2021 Elsevier Ltd. All rights reserved.