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The adsorption isotherms of TCP on GO and G at 303, 323, and 343 K are shown in Figure 3. The Langmuir and Freundlich models were used to fit the isotherms. Results are shown in Figure 3 and Figure S3 (available online), and the regression parameters are listed in Table 2. Compared with the Freundlich model, the Langmuir model is much better able to describe the adsorption isotherms with relatively higher R2 (Table 2), suggesting that the adsorption of TCP on GO and G is monolayer coverage (Liu et al. 2015b). The Langmuir maximum adsorption capacity for TCP on G (qm = 87.7 mg·g−1) at 303 K was found to be higher than that of GO (qm = 30.7 mg·g−1). Furthermore, an increase in the adsorption capacity is observed with an increase in temperature, which can be attributed to the increase in chemical interactions caused by an increased mobility of TCP towards the active sorption sites of GO and G at higher temperatures (Setshedi et al. 2015).
Table 2

Parameters for Langmuir and Freundlich isotherm model

AdsorbentTLangmuir
Freundlich
KL (L·mg−1)qm (mg·g−1)R2KF (L1/n·g−1· mg1-1/n)R2
GO 303 K 0.1155 30.7 0.9790 6.0818 0.9784 
323 K 0.1029 32.3 0.9598 7.0604 0.9421 
343 K 0.1065 35.2 0.9456 8.2813 0.9211 
303 K 0.1010 87.7 0.9886 10.9507 0.9153 
323 K 0.1297 90.1 0.9896 14.5691 0.8949 
343 K 0.1695 96.2 0.9884 19.6603 0.9145 
AdsorbentTLangmuir
Freundlich
KL (L·mg−1)qm (mg·g−1)R2KF (L1/n·g−1· mg1-1/n)R2
GO 303 K 0.1155 30.7 0.9790 6.0818 0.9784 
323 K 0.1029 32.3 0.9598 7.0604 0.9421 
343 K 0.1065 35.2 0.9456 8.2813 0.9211 
303 K 0.1010 87.7 0.9886 10.9507 0.9153 
323 K 0.1297 90.1 0.9896 14.5691 0.8949 
343 K 0.1695 96.2 0.9884 19.6603 0.9145 
Figure 3

Adsorption isotherms of TCP on GO (a) and (b) and G (c) and (d) at 303 K (), 323 K (), and 343 K (). Langmuir (a) and (c) and Freundlich (b) and (d) fitting for GO and G, respectively. Conditions: C0: 5–50 mg L−1 of TCP solution; mass of adsorbent: 10 mg; time: 0–360 min at pH 5.

Figure 3

Adsorption isotherms of TCP on GO (a) and (b) and G (c) and (d) at 303 K (), 323 K (), and 343 K (). Langmuir (a) and (c) and Freundlich (b) and (d) fitting for GO and G, respectively. Conditions: C0: 5–50 mg L−1 of TCP solution; mass of adsorbent: 10 mg; time: 0–360 min at pH 5.

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