Banana Peel-Supported Sulfonic Acid Catalysts

Four batches of banana peel-supported sulfonic acid (BP-SO₃H) catalysts were prepared by varying the banana peel-to-sulfuric acid ratio, reaction time, and temperature. Catalysts prepared in the initial batch include dried banana peel powder (1 g) mixed thoroughly with conc. H₂SO_4. Banana peel powder: H₂SO₄ ratios (g L⁻¹) of 1:5, 1:10, 1:15, and 1:20 were used, whereas the reaction temperature varied between 80 and 120 °C while reaction time was monitored for 16, 18, 20, 22, and 24 h. In order to remove residual sulfate ions in the filtrate, 50–60 mL of deionized water was added to the mixture. It was washed several times with hot deionized water until no residual sulfate ions could be detected (a 6 mol L⁻¹ solution of BaCl₂ was used for testing). The resultant sulfonic acid functionalized banana peel (BP-SO₃H) was dried in an oven overnight. All the synthesized BP-SO₃H catalysts were assigned a code based on their synthesis procedure; BP-SO₃H-X-Y-Z, where X is the wt/volume ratio of banana peel/H₂SO₄, Y is the 'in 'situ' hydrothermal-sulfonation time, and Z stands for reaction temperature. Accordingly, the catalyst prepared using a 1:10 (wt/volume) banana peel/sulfuric acid ratio, hydrothermal sulfonation time of 16 h, and reaction temperature of 80 °C were designated as BP-SO₃H-10-16-80.