An invasive plant Ageratum houstonianum L. as an adsorbent for the removal of triphenylmethane dye (malachite green): isotherm, kinetics, and thermodynamic studies

The present study has focused on the biosorption of a triphenylmethane dye malachite green (MG) onto the leaf biomass of an undesired weed plant Ageratum houstonianum (AHLB). The effects of different contact time, temperature, biomass dose, and initial dye concentration are investigated on the biosorption of the test dye by the given adsorbent. Adsorption isotherm and kinetics of MG removal using AHLB followed the Freundlich’s isotherm model and pseudo-first-order model of kinetics, indicating that the process of chemisorption occurred. The MG adsorption data fitted best to the Langmuir’s model having the highest correlation coefficient value R 2 = 0.998. The magnitude of adsorption capacity of Langmuir’s isotherm model ( q max = 161.29 mg/g) was found to be comparable with experimental to the value obtained experimentally ( q e = 103.22 mg/g). This maximum adsorption capacity has occurred with 20 mg/100 ml biomass dose, in 20-min contact time, at 45 °C temperature, from 500 ppm initial dye concentration. Thermodynamic parameters were calculated in order to identify the adsorption process. It revealed that, because of the positive values of ∆H ‡ (+ 1.75 KJmol −1 ) and negative values ∆G ‡ (–5.16 KJmol −1 to –5.51 KJmol −1 ) as well as positive value of ∆S ‡ (+ 17.34 JK −1 mol −1 ), the adsorption processes have endothermic, chemical and spontaneous nature. The experimental data found to be in good agreement with pseudo-first-order kinetic model ( R 2 = 0.971). The identification of active sites on AHLB surface was done via FT-IR spectroscopy. Thus, C = S, C = O, C≡C, –NO 2 , –N = N–, –NCS, C≡N, and N≡N stretches contained in the AHLB were the causable elements for effective adsorption of MG from the aqueous medium. The results revealed that MG can be removed from aqueous solutions using this weed adsorbent growing in abundance on earth. The use of such biosorbents could also be helpful in maintaining the undesired plants and their sequel problems through their exploitation as biosorbent.