*3.1. Characterization of the RCMs and RPMs*

SEM was used to study the surface morphology of RCMs and RPMs, and the results are represented in Figure 2. As can be seen in Figure 2a,b, the RPMs are found to be spherical or nearly spherical objects, and the surfaces of the microspheres had a porous, large surface area. These pores are formed as a result of the diffusion of methanol from the particle to the surface during the polymerization of the polymer. This interconnected porous network provides accessibility and active sites for dencichine adsorption, thus facilitating adsorption. In Figure 2b, it can be seen that the RCMs and the RPMs form a three-dimensional network structure, and the polymers are encased in the membranes. As can be seen from Figure 2c,d, the diameter of the composite membrane fiber prepared by electrostatic spinning is at the nanometer level, with a range of 322.9 ± 73.49 nm. The RCMs present random distributions and are very uniform with dense structure and interconnected large pores. Therefore, electrospinning can provide a rigid frame for the RPMs, which is conducive to the further recycling of the RPMs.

**Figure 2.** (**a**) SEM images of RPMs; (**b**,**c**) SEM images of RCMs; (**d**) Average particle size and particle size distribution images of RCMs.

The structure of the RCMs and RPMs was investigated by FT-IR spectroscopy, and the results are represented in Figure 3. In Figure 3a, the RPMs display a stretching vibration peak of -NH occurs at 3308 cm<sup>−</sup>1, a stretching vibration peak of -C=O occurs at 1653 cm−1, a -C=C stretching vibration absorption peak is observed at 1521 cm−<sup>1</sup> and a -COO- stretching vibration absorption peak is observed at 2359 cm<sup>−</sup>1, indicating the successful preparation of RPMs. In the RCM curve, the stretching vibration absorption peak of -C≡N is observed at 2243 cm<sup>−</sup>1, indicating the presence of PAN. Compared with RPMs, the presence of PAN leads to a blue shift in -C=O and a red shift in -C=C. In addition, the FT-IR spectra of the RCMs and RPMs samples are similar, indicating the successful preparation of RCMs.

N2 adsorption–desorption experiments were carried out to study the pore volumes [48], pore size distributions, average pore diameters and specific surface areas of the RPMs, and the results are shown in Figure 3b. The pore volume and surface area of the RPMs are 2.756 × <sup>10</sup>−<sup>3</sup> cm3/g and 6.1776 ± 0.1204 m2/g, respectively. The RPMs have a high specific surface area, which was favorable for the adsorption and extraction of analytes.

TGA curves were presented in Figure 3c, and they were used to describe the thermal stability of the RCMs and RPMs. The RPMs start to decompose at 360 ◦C, the temperature of the fastest decomposition rate occurs at 381 ◦C and the maximum decomposition temperature (Tmax) is 462 ◦C. The decomposition process is divided into two stages, including dehydration in the low temperature zone (100–360 ◦C) and decomposition in the high temperature zone (381–462 ◦C). The initial decomposition temperature for the RCMs is 297 ◦C, the temperature of the fastest decomposition rate occurred at 306 ◦C, and the Tmax is 333 ◦C. Decomposition occurs in two stages, including dehydration (100–297 ◦C) and decomposition (297–333 ◦C). The second stage of decomposition is due to the breakdown of the PAN in the RCMs. Compared with RCMs, the RPMs have different thermal degradation behavior. The RPMs lost more mass in the high-temperature region from 360 to 500 ◦C. The TGA results demonstrate that the RCMs and RPMs have excellent thermal stability.

The mechanical properties stability of the membrane long-term stability is one of the significant parameters. Figure 3e shows the stress–strain curves of the as-prepared membranes measured by a dynamic mechanical analyzer. In Figure 3e, it can be seen that the RCMs exhibited excellent mechanical stability with the tensile strength of 2.15 MPa, along with the elongation at the break of 215.1%. The stress–strain curve results demonstrate that the RCMs had excellent mechanical properties.

**Figure 3.** (**a**) FI-IR images of RCMs and RPMs; (**b**) N2 adsorption–desorption of RPMs; (**c**) TGA of RCMs and RPMs; (**d**) DTG of RCMs and RPMs (**e**) Stress−strain curves of RCMs.

#### *3.2. Optimization Preparation Conditions of the RCMs*

The results of the investigation into the preparation conditions of the RCMs are represented in Figure 4. As can be seen in Figure 4a, the adsorption amount of dencichine increases as the RPM concentration increases. When the RPM concentration exceeds 1 wt%, the adsorption amount decreases with the increase in the RPM concentration. The sediment volume is also increased, for a certain PAN concentration, when the polymer concentration

increases. Thus, the optimal concentration of the RPMs is 1.0 wt%. In Figure 4b, it can be seen that the adsorption amount of dencichine increases with the increase in the PAN concentration. When the concentration exceeds 10 wt%, the adsorption amount decreases with the increase in the PAN concentration. This may be because the spinning solution with low PAN content has low adhesion, poor spinning effect and poor adsorption amount of the dencichine. PAN content continues to increase, the spinning effect is excellent, and the preparation of the RCMs has also increased the adsorption amount. However, as the content of PAN continues to increase, the spinning solution surface tension increases, the droplet formation of jet flow in the electric field tension is difficult, even blocking the syringe needle which affects the spinning, and the preparation of the morphology of the RCMs will become worse, reducing the adsorption amount. In Figure 4c, it can be seen that the adsorption amount of dencichine increased as the voltage increased. When the concentration exceeds 20 KV, the adsorption amount decreases with the increased voltage. When the voltage concentration is increased, membranes thickness is also increased. With the further increase in the electric field, the drop gradually stays in the electric field for a shorter time and the radius of the RCM center circle decreases. This may be due to the RPMs being wrapped in membranes, thus reduce reducing the adsorption amount.

**Figure 4.** Optimization preparation conditions of the RCMs: (**a**) Polymer content; (**b**) PAN content; (**c**) Voltage adsorption amount.

## *3.3. Adsorption of Dencichine on Different Mass RCMs and RPMs*

The adsorption of dencichine (0.1 mg/mL) on different mass RCMs and RPMs is represented in Figure 5. As can be seen in Figure 5a, the adsorption amount of dencichine is increased by increasing the mass of the RPMs. When the mass exceeds 20 mg, the adsorption amount decreases with the increase in the RPM mass. In Figure 5b, it can be seen that the adsorption amount of dencichine increases with the increase in the RCM mass. When the mass exceeds 150 mg, the adsorption amount decreases with the increase in the RCM mass. Under the same concentration conditions, more adsorption sites are provided to dencichine at a small increase, which raises the effective contact area and the amount of dencichine adsorption. With the increase in mass, the RCMs and RPMs had inadequate adsorption of dencichine, and the adsorption amount decreased. In other words, the adsorption of the sorption system stays correlated with the availability of adsorption sites on the surface of the adsorbent and the concentration of the dencichine solution.

**Figure 5.** Adsorption of dencichine on different mass RCMs and RPMs; (**a**) RPM adsorption amount; (**b**) RCM adsorption amount.
