Facile diazonium modification of pomegranate peel biochar: A stupendous derived relationship between thermal and Raman analyses

There is an ever growing interest worldwide in the development of biochar from a large variety of agrowastes. This work contributes to the domain by tackling an agrowaste represented in pomegranate peels powder. The latter was activated by acid treatment and then pyrolyzed to generate low cost biochar. To enrich the surface of the resulting biochar, it was arylated with various in-situ generated diazonium salts of 4-aminobenzoic acid (H2N-C6H4-COOH), sulfanilic acid (H2N-C6H4-SO3H) and Azure A dye. At a certain point, it was important to monitor the effect of diazonium nature and concentration on the arylation process. Surface modification of biochar was characterized with TGA and Raman analyses which showed gradual changes in the arylation of biochar at low concentrations of 10-5, 10-4 and 10-3 M of 4-aminobenzoic acid. Interestingly, Azure A diazonium salt induces lower extent of surface modification, likely due to steric hindrance. One key feature of this work is the correlation between D/G Raman peak intensity ratios and the mass loading of the aryl groups. To the very best of our knowledge this is the first report ever on diazonium modification of biochar and opens new avenues for this carbon allotrope, its surface arylation and applications.