L-lysine mediated facile synthesis of SnO₂-biochar nanocomposite and its excellent photocatalytic activity for the reduction of Cr(VI) and degradation of acid yellow 23 dye

SnO₂- biochar (AC) nanocomposite was fabricated employing microwave method by using L-lysine (as a capping agent and complexing agent) and biochar obtained from dried leaves of Canavalia gladiate. The fabricated SnO₂-AC nanocomposite was employed as a photocatalyst to reduce noxious heavy metal Cr(VI) and degrade acid yellow 23 dye from the aqueous phase under direct sunlight. The various techniques, namely TEM, HRTEM, SAED, EDX, UV–vis, and FTIR analysis, were used to characterize SnO₂-AC nanocomposites and SnO₂ nanoparticles. In addition to this, the surface area and pore size of the fabricated SnO₂-AC nanocomposite and SnO₂ NPs were also analyzed by nitrogen adsorption–desorption measurements using Quanta Chrome Nova 1000 gas adsorption analyzer. Further, the fabricated SnO₂-AC nanocomposite was utilized as a catalyst in the photoreduction of Cr(VI), where it showed excellent photocatalytic activity under direct sunlight by reducing 94% of Cr(VI) from aqueous solution with a catalytic concentration of 35 mg/L in 60 min. In contrast, pure SnO₂ NPs showed no response for Cr(VI) photoreduction. Besides, the fabricated SnO₂-AC nanocomposite also showed brilliant performance in the degradation of 99% of acid yellow 23 dye (AY23) in 60 min, whereas pure SnO₂ NPs showed removal of 71%. The kinetic study of photoreduction and photodegradation experiments showed a high rate constant of 4.8 × 10^–2 min⁻¹ and 8.3 × 10^–2 min⁻¹, respectively. Whereas in the case of pure SnO₂ NPs, the rate constant for photoreduction was almost negligible, and for photodegradation, it was only 2.07 × 10^–2 min⁻¹. The high rate constant in the case of SnO₂-AC nanocomposite is due to the synergic effect of SnO₂ and AC, which makes it an excellent photocatalyst.