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Plotting Qt vs. t1/2 give straight line did not pass through the origin with Ki (constant of intraparticle diffusion) =0.74, 0.85 and 0.57 mg/g min0.5, (R2 = 0.53, 0.59, 0.73) as shown in fig.1b. The C values (film thickness) were 1.01, 0.71 and 1.03 for the sorption of Br.G, To.B and Tr.B. the boundary layer effect is higher for Tr.B as a great value of C. two stages are the formation of linear deviation (Moawed et el., 2014), the first stage, the diffusion rate is high then, decreased with the time change forward in the second stage. The values of ki (1), ki (2) of these stages are (2.74, 0.089 mg g-1 min1/2) for Br.G, (2.65, 0.032 mg/g min1/2) for To.B and (1.35, 0.2 mg/g min1/2) for Tr.B. ki (2) always lower as active centers were blocked by adsorbed dye molecules. The first stage is a transport step for the adsorbed solution into adsorbent, it is too fast step. The second stage is diffusion of adsorbate molecules from the external of the adsorbent into the pores of adsorbent molecules at equilibrum (Tran et el., 2017), proving adsorption process controlled by double steps. Rate of diffusion of To.B > Br.G >Tr.B which mean ki dependent on the molecular weight of dyes. The lighter molecule’s weight as To.B will diffuse faster in contract Tr.B which has heavier molecule’s weight. Larger ki, better adsorption mechanism which related to improved bonding between adsorbate molecules with adsorbent particles.

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