The biosorbent (Lagenaria, LG) was ground, washed, dried (40-50 oC) and ground (<150 µm) (LG in natura (LG-in)). Part of LG-in was chemically modified by basic hydrolysis using 0.1 mol L-1 NaOH solution for 24 h, to delignify the biomass1 and increasing the pH (LG-b). The LG-b was again washed with distilled water, dried (40-50 oC) and ground (<150 µm). The pH was determined using 0.1500 g±0.0003 g of LG in 20 mL of distilled water for 30 min (LG-in pH=8.4; LG-b pH=11.4). Kinetic tests were carried out until equilibrium (t=30 min; T=25 oC; tartrazina cationic azo dye (CAD) concentration 7.5 x 10-5 mol L-1) using 0.1500 g of each biomass in 20 mL of aqueous CAD solution. Data did not fit for the pseudo-first-order model (physical adsorption). The kinetic parameters (Tab.1) demonstrate that the amount of CAD adsorbed calculated at equilibrium obtained from the pseudo-second-order kinetics (chemical adsorption) is equivalent to the maximum amount of CAD adsorbed in equilibrium at 25 oC (Tab.1). The highest correlation coefficient (R2,Tab.1) was obtained for the pseudo-second kinetics indicating that the sorption is determined by the rate of adsorption reactions, occurring at the solid/liquid interface.2 It is observed that the basic hydrolysis reduces the amount of CAD adsorbed in equilibrium (Tab.1). In intraparticle diffusion, the adsorbate molecules infiltrate the interior of the adsorbent particles.3 The data indicate that other interaction mechanisms may be acting simultaneously. There are two linearities (Tab.1): First (R2 dif,1) represents the instantaneous adsorption or on the external surface; Second (R2 dif,2), represents the stage of gradual adsorption by diffusion intraparticle.4 There is no kinetic adjustment to LG-b biomass using Elovich model (chemical adsorption).5
Table 1. Coefficients of Pseudo-second-order, Elovich and Intraparticle diffusion kinetic constants

Pseudo-second-order:6 qe (mg g-1): amount adsorbed in equilibrium; k2 (g mg-1 min-1): second-order adsorption constant. Intraparticle diffusion:4 C (mg g-1): constant related to diffusion resistance; Kp (dif,2) (mg g-1 min-1/2): intraparticle diffusion coefficient. Elovich:6 α (mg g-1 min-1): initial adsorption rate; β (g mg-1): desorption constant.
LACOPPI, IFPR, PIBIC/CNPQ, CNPq
1. Santos, R.d.; Mello Júnior, J.A.d.; Caraschi, J.C.; Ventorim, G.; Pereira, F.A.; Cie. Florestal 2016, 26, 1281.
2. Bojić, D.V.; Ranđelović, M.S.; Zarubica, A.R.; Mitrović, J.Z.; Radović, M.D.; Purenović, M.M.; Bojić, A.L.; Desalin. Water Treat. 2013, 51, 6871.
3. Dada, A.O.; Adekola, F.A.; Odebunmi, E.O.; Ogunlaja, A.S.; Bello, O.S.; Sci. Rep. 2021, 11, 16454.
4. Carvalho, T.E.M.d.; Fungaro, D.A.; Izidoro, J.d.C.; Quim. Nova 2010, 33, 358.
5. Treto-Suárez, M.A.; Prieto-García, J.O.; Mollineda-Trujillo, Á.; Lamazares, E.; Hidalgo-Rosa, Y.; Mena-Ulecia, K.; Sci. Rep. 2020, 10, 1.
6. Debrassi, A.; Largura, M.C.T.; Rodrigues, C.A.; Quim. Nova 2011, 34, 764.