Characterization of carbon-based materials obtained from sunflower waste with boric acid additive

In this study, the yields and properties of biochar, bio-oil and biogas products were investigated through pyrolysis of sunflower meal biomass sourced from the Thrace region, with varying additions of boric acid (BA). The feedstock mixtures were prepared with four different BA concentrations (5.3%, 6.0%, 7.8% and 8.4%) and subjected to pyrolysis at 400, 450, 500 and 550°C. The mass yields, elemental compositions, and structural characteristics of the resulting products were comprehensively analyzed. In BA-free samples (Pure A), the highest yield of liquid products was observed, while increasing BA content led to a reduction in liquid yield and an increase in solid product yield with rising temperature and BA concentration. Elemental analysis showed an increase in carbon content from 64.8% to 78.6% with higher pyrolysis temperature while hydrogen and nitrogen contents decreased. The C/H, C/N and H/C ratios were evaluated to assess aromaticity and inertness; samples A550 and 0.8BA550 exhibited high aromatic characteristics. SEM images revealed significant increases in porosity with BA addition and temperature, particularly in the 1.3BA550 sample which demonstrated a honeycomb-like interconnected microporous structure. BET analysis showed that the 1.2BA400 sample achieved the highest surface area measuring 7.4 m²/g. FT-IR and TGA-DTA analyses confirmed chemical bond transformations and supported thermal stability. Overall, the addition of boric acid and the increase in pyrolysis temperature enhanced the structural properties of biochar derived from sunflower meal, significantly improving its water retention capacity and demonstrating high potential for applications in agricultural irrigation, drought management, and as an adsorbent or catalyst support.