The adsorption kinetics of TCP to GO and G are displayed in Figure 2. For GO and G, the adsorption equilibrium can be reached in less than 6 h. G has a higher adsorption rate than GO, which may be attributed to the higher specific surface areas of G (Table S1, available online). In order to illustrate the adsorption kinetics process, the pseudo-first-order, pseudo-second-order and intraparticle diffusion models were employed to fit experimental data. Results are shown in Figure 2 and Figure S2 (available online), and fitting parameters are listed in Table 1. For GO and G, the correlation coefficients (R^{2}) for the pseudo-second-order were relatively higher than those of the pseudo-first-order model, indicating that the pseudo-second-order kinetic model was suitably fitted with the kinetic data. As shown in Figure S2(c), the regressions of *q*_{t} versus *t*^{1/2} were linear, but it did not pass through the origin, suggesting that the adsorption involves intraparticle diffusion but it is not the only rate-controlling step (Zhang *et al.* 2012; Wang *et al.* 2016).

Table 1

Adsorbent . | Pseudo-first-order model . | Pseudo-second-order model . | Particle diffusion model . | |||
---|---|---|---|---|---|---|

k_{1} (min^{−1})
. | R^{2}
. | k_{2} (g·mg^{−1}·min^{−1})
. | R^{2}
. | k_{i} (g·mg^{−1}·min^{−1/2})
. | R^{2}
. | |

GO | 0.0097 | 0.8872 | 0.0064 | 0.9947 | 0.3590 | 0.8456 |

G | 0.0286 | 0.9188 | 0.0021 | 0.9982 | 1.2872 | 0.8076 |

Adsorbent . | Pseudo-first-order model . | Pseudo-second-order model . | Particle diffusion model . | |||
---|---|---|---|---|---|---|

k_{1} (min^{−1})
. | R^{2}
. | k_{2} (g·mg^{−1}·min^{−1})
. | R^{2}
. | k_{i} (g·mg^{−1}·min^{−1/2})
. | R^{2}
. | |

GO | 0.0097 | 0.8872 | 0.0064 | 0.9947 | 0.3590 | 0.8456 |

G | 0.0286 | 0.9188 | 0.0021 | 0.9982 | 1.2872 | 0.8076 |

Figure 2

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