Carbon deposition behavior on biochar during chemical vapor deposition process

In addressing contemporary plastic pollution, catalytic - chemical vapor deposition (CVD) emerges as an effective method for converting plastic to carbon nanomaterials. Biochar, widely employed in plastic pyrolysis–CVD processes as a catalyst, is often modified with metals or other chemicals in existing studies. To enhance the understanding of biochar's role in this process, it is crucial to investigate carbon nanomaterials growth mechanisms on pure biochar. This comprehensive study employs two representative plastic pyrolysis vapors in the CVD process for treating woody-chips derived biochar: ring-rich vapor from polystyrene (PS) and chain-rich vapor from polyethylene (PE). When ring-rich vapor was employed as the carbon precursor, three types of carbon nanomaterials were observed on the spent biochar: bulk amorphous carbon (BAC), monolayer amorphous carbon (MAC) and carbon nanofibers (CNFs). Conversely, only BAC and CNFs are found in spent biochar treated with chain-rich vapor, suggesting divergent behaviors. The substantial carbon deposition on biochar surfaces (164 mg/gPS and 21 mg/gPE at 900 °C), compared to inert catalyst supports, results from the stable carbon–carbon bond formed between plastic and biochar. MAC growth is attributed to the presence of aromatic rings in ring-rich vapor, while CNF growth is linked to sp2 carbon on biochar. These findings lay a strong theoretical foundation for the further development of biochar catalysts in the CVD process for the production of carbon nanomaterials.