Fabrication of spherical biochar by a two-step thermal process from waste potato peel.

The aim of this study was to develop a new approach for the preparation of spherical biochar (SBC) by employing a two-step thermal technology to potato peel waste (PPW). Potato starch (PS), as a carbon-rich material with microscale spherical shape, was separated from PPW as a precursor to synthesizing SBC. The synthesis process comprised (1) pre-oxidization (preheating under air) of PS at 220 °C and (2) subsequent pyrolysis of the pretreated sample at 700 °C. Results showed that the produced SBC successfully retained the original PS morphology and that pre-oxidization was the key for its shape maintenance, as it reduced surface tension and enhanced structural stability. The SBC possessed excellent chemical inertness (high aromaticity) and uniform particle size (10-30 μm). Zero-cost waste material with a facile and easy-to-control process allows the method to be readily scalable for industrialization, while offering a new perspective on the full use of PPW.