Adsorptive Removal of Methylene Blue Dye from Water Using Activated Carbon Made from Abutilon Indicum Fruit: Kinetics, Isotherms, Thermodynamics, and A Side-By-Side Check

Abstract

Methylene blue still colors textile wastewater and blocks light that water plants need. We turned dried fruit of Abutilon indicum, picked in Nalgonda District, Telangana, into activated carbon. Fruit powder was soaked in 50% phosphoric acid and heated at 500 °C under nitrogen. The yield was 42.5%. The carbon had a BET area of 625 m2/g, a mean pore width of 2.8 nm, and a point of zero charge of 6.8. Infrared bands at 3420 and 1620 cm−1 showed hydroxyl and carbonyl groups. Both bands grew weaker after the dye stuck. In shaken flasks, the best removal from a 100 mg/L dye solution was 98.7% (65.8 mg/g) at pH 8, 1.5 g/L carbon, 120 min, and 35 °C. When the starting dye level rose from 50 to 300 mg/L, uptake rose from 32.1 to 118.6 mg/g, but the share removed fell from 96.4% to 59.3%. Time data fitted the pseudo-second-order model (R2 = 0.997). The Redlich–Peterson isotherm fitted best (R2 = 0.999). The Langmuir fit gave a maximum capacity of 285.4 mg/g (R2 = 0.998). The free-energy change ran from −2.5 to −4.1 kJ/mol between 25 and 45 °C. Enthalpy was 12.5 kJ/mol and entropy was 45.2 J/mol·K. After five wash cycles with 0.1 M hydrochloric acid, removal was still 75.4%. The fruit carbon takes up methylene blue under mild conditions and can be used again. Column tests with real dyehouse water are still needed.