Accepted Manuscript Molecular mechanism of anionic dyes adsorption on cationized

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17 
Fig. 6. Reusability of CRHC. 
3.5 Adsorption kinetics 
The non-linearized kinetics of the adsorption was studied by analyzing the 
adsorption capacity of Diamine Green B (DG-B), Acid Black 24 (AB-24) and Congo 
Red (CR) at different time intervals. The adsorption kinetics of Pseudo-first-order, 
Pseudo-two-order and Elovich models are given in Table 2[36]. All the data used for 
the above analysis are the mean values from three replicate tests.
Table 2 Lists of adsorption kinetics models 
Models 
Nonlinear form 
Plot 
Pseudo-first-order 
q
t 
= q
e
 (1−e
− k1t
) 
t vs q
t
Pseudo-second-order 
q
t 
= k
2
q
e
2
t/(1 + k
2
q
e
t) 
t vs q
t
Elovich 
q
t 
= ln(1 + αβt)/β 
t vs q
t
Pseudo-first-order kinetics mainly reveals the physical adsorption behavior that 
plays a dominant role in the adsorption process. Pseudo-second-order kinetics is 
generally more suitable for describing adsorption processes where chemisorption 
plays a dominant role. The Elovich kinetic model is commonly used to describe the 
adsorption behavior of contaminants on uneven solid adsorbents. The non-linear 
fitting results of the purification of Diamine Green B (DG-B), Acid Black 24 (AB-24) 
and Congo red (CR) by CRHC at different temperatures are shown in Table 3.
The correlation R
2
values are typically used to evaluate the correlation 
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18 
coefficients, so as to determine the adsorption kinetics during the adsorption process. 
In this experiment, at the different temperatures (303.15 K, 308.15 K, 313.15 K), the 
R
2
value of the pseudo-second-order kinetics is higher than that of pseudo-first-order 
kinetics models from nonlinear fitting results. The higher correlation R
2
value reveals 
that it would be more appropriate to use pseudo-second-order kinetics to analyze the 
purification behavior of Diamine Green B (DG-B), Acid Black 24 (AB-24) and 
Congo red (CR) onto CRHC. In addition, the more closely of adsorption capacity 
(q
e
(cal)) obtained by the pseudo-secondary kinetics and the experimentally measured 
adsorption capacity (q
e
(exp)) support the above conclusion from another aspect. 
Therefore, the pseudo-second-order kinetics was applied in this experiment to 
evaluate and analyze the purification of Diamine Green B (DG-B), Acid Black 24 
(AB-24) and Congo red (CR) by CRHC. The purification of the three dyes by CRHC 
may be a chemical process. However, the activation energies of Diamine Green B 
(DG-B), Acid Black 24 (AB-24) and Congo red (CR) are 13.16 kJ mol
-1
, 4.29 kJ mol
-1
and 1.93 kJ mol
-1
, which are all lower than 40 kJ mol
-1
, so the purification process 
belongs to physical adsorption [37]. Moreover, the non-linear fitting of Elovich model 
has a high correlation R
2
value indicating that the surface of solid adsorbent may have 
non-uniformities existed. Furthermore, as can been seen from Table 2, the adsorption 
capacities of Diamine Green B (DG-B), Acid Black 24 (AB-24) and Congo red (CR) 
dye onto CRHC were increased with the increasing of temperature. Raising the 
temperature favors the adsorption process. 

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