2.4.1. Adsorption Kinetics Experiment

For the method, 30 mg of SF@Cu-NFs was first dispersed into 300 mL 300 mg L−<sup>1</sup> Pb(II) solution under continuous stirring. The suspension was sealed and oscillated at room temperature to ensure equilibration. Then 3 mL of the suspension sample was taken from the system for filtration at a regular interval time. The residual Pb(II) concentration in the solution was also detected by AAS measurement like for thermodynamic adsorption. The amount of Pb(II) adsorbed on SF@Cu-NFs ( *Q*t) was calculated by subtracting the concentration of free Pb(II) at the time of t from the initial Pb(II) concentration as

$$Q\_{\rm l} = \frac{(C\_0 - C\_{\rm l}) \times V}{M} \tag{1}$$

where *C*0 and *C*t (mg <sup>L</sup>−1) were the initial and *t* time Pb(II) concentrations in liquid-phase, *V* (L) was the taken volume of dye solution, and *M* (g) was the mass of the SF@Cu-NFs adsorbent used. The data obtained were used to draw the kinetic adsorption curves for pseudo-first-order, pseudo-second-order, and intraparticle di ffusion analysis.

### 2.4.2. Adsorption Isotherm Experiment and Adsorption Thermodynamics

The thermodynamic adsorption experiment of SF@Cu-NFs was carried out by a typical batch method. First, 7 pieces of 1 mg washed and dried SF@Cu-NFs were added into 7 pieces of 10.0 mL di fferent concentration Pb(II) solutions (5, 20, 50, 80, 100, 400, 500 mg <sup>L</sup>−1) placed in the tube at 298 K, respectively. Then the suspensions were sealed and were vibrated for 2 h at room temperature to ensure the complete adsorption. After filtrating the mixture for solid–liquid separation, the residual

Pb(II) concentration in the solution was detected by AAS measurement. The amount of Pb(II) adsorbed on SF@Cu-NFs (*Q*e) was calculated by subtracting the concentration of Pb(II) from the initial concentration as

$$Q\_{\mathbf{e}} = \frac{(C\_0 - C\_{\mathbf{e}}) \times V}{M} \tag{2}$$

where *C*0 and *C*e (mg <sup>L</sup>−1) were the initial and equilibrium Pb(II) concentrations in liquid-phase, *V* (L) was the volume of Pb(II) solution, and *M* (g) was the mass of the SF@Cu-NFs adsorbent used. The data obtained were used to draw the adsorption isotherms for Langmuir, Freundlich, and Temkin analysis.

In order to obtain the experimental parameters of adsorption thermodynamics on the Pb(II) adsorption by SF@Cu-NFs, the adsorption capacity at three different temperatures of 298 K, 308 K, and 328 K were investigated with the initial Pb(II) concentration of 100 and 500 mg <sup>L</sup>−1, respectively.
