*2.4. Batch Adsorption*

A series of adsorption experiments were conducted in the polyethylene vials at 30 ◦C under 150 rpm rotary shaking. 15 mg adsorbent was accurately weighed and added into the 50 mL Cr(VI) containing solution. The blank assay was carried out under the same condition without any adsorbent simultaneously. The adsorbents were filtrated from the solution by filter paper (pore size ~0.45 μm) after completion of adsorption. The analysis method of Cr(VI) concentration (and other pollutants) was given in Supplementary Section S1.3. Considering the chemical state of Cr, the concentration of Cr(III) can be calculated as Cr(III) = Crtotal − Cr(VI). To survey the effect of pH on adsorption capacity, the initial pH of solution was adjusted from 0~6 by 2 M HCl or 2 M NaOH. The adsorption isotherm experiment was implemented at pH 2 for 6 h with the initial Cr(VI) concentration varied from 100~500 mg L<sup>−</sup>1. For kinetics experiment, Cr(VI) solution with concentration of 400 mg L−<sup>1</sup> was experienced 1~240 min adsorption at pH 2. The concentration of Cu(II), Re(VII), Conga red, and Orange G solution varied from 50~500 mg L−<sup>1</sup> for 6 h adsorption to achieve their adsorption isotherm. The Cu(II), Re(VII) and Orange G was adjusted to pH 2 while the Conga red was adjusted to pH 5.5. The adsorption capacity for batch adsorption experiment was calculated as follows:

$$q\_t = \frac{\mathbf{C}\_0 - \mathbf{C}\_t}{\mathbf{m}} V \tag{2}$$

$$q\_{\varepsilon} = \frac{\mathbf{C}\_0 - \mathbf{C}\_{\varepsilon}}{\mathbf{m}} V \tag{3}$$

where *qt* is the adsorption capacity at time t (mg g<sup>−</sup>1), *C0* is the initial Cr(VI) concentration in solution (mg L<sup>−</sup>1), *Ct* is the Cr(VI) concentration in solution at time t (mg L<sup>−</sup>1), *qe* is the equilibrium adsorption capacity (mg g<sup>−</sup>1), *Ce* is the equilibrium concentration (mg L<sup>−</sup>1), m is the weight of adsorbent (g), and *V* is the volume of solution (L).

## *2.5. Dynamic Adsorption*

For the dynamic adsorption, 0.3 g adsorbent was compressed and squeezed in a glass column with length of 500 mm and ID of 8 mm. 25 mL Cr(VI) solution with concentration of 5~100 mg L−<sup>1</sup> was adjusted to pH 2 and fed into the top of column using the peristaltic pump with controlling the flow velocity from 28.42~85.26 μL min−<sup>1</sup> at ambient temperature. The concentration of Cr(VI) (and other pollutant) in effluent was measured by the same method as batch adsorption experiment. For other pollutant, the influent concentration of Cu(II), Re(VII), Conga red and Orange G were 50, 20, 20, and 50 mg L<sup>−</sup>1, respectively. The Cu(II), Re(VII), and Orange G was adjusted to pH 2 while the Conga red was adjusted to pH 5.5. The removal rate was calculated as follows:

$$R\% = \frac{C\_0 - C\_a}{C\_0} \times 100\% \tag{4}$$

where *R%* is the removal rate of effluent, *C0* is the influent concentration of pollutant (mg L<sup>−</sup>1), *Ca* is the concentration of pollutant in effluent (mg L<sup>−</sup>1).
