# Enhanced Performance of nZVI/MXene@CNTs for Rapid As(III) Removal from Aqueous Solutions
## 3 Results and Discussion  
### Synthesis and Characterization of nZVI/MXene@CNTs  
The three-dimensional mesh interlayered nZVI/MXene@CNTs nanomaterials were self-assembled in the given aqueous solution. As shown in Figure 1, the synthesis schematic design of nZVI/MXene@CNTs was depicted. Briefly, the functionalized CNTs and Ti\({}_{3}\)C\({}_{2}\)T\({}_{x}\)-Mxene nanosheet dispersions were obtained by acid drenching the CNTs and etching the graphite phase MAX (Ti\({}_{3}\)AlC\({}_{2}\)), respectively. Then, the functionalized CNTs and MXene nanosheet mixture were distributed in the prepared ferrous-sulfate solution, while stirring constantly under N\({}_{2}\) protection. Due to the high surface energy and numerous hydrophilic groups, Fe(II) could be evenly disseminated on the surface of the CNTs and MXene. It would be generated by the sequential assembly of MXene and CNTs and the ordered placement of Fe(II) on their surfaces by water shear and zeta potential difference, producing a three-dimensional interconnected interlayer structure of Fe(II)/MXene@CNTs. Fe(II) was reduced to nZVI and deposited in the layer gaps and interstitial spaces of MXene and MXene@CNTs by the addition of a dilute reducing agent (NaBH\({}_{4}\)). In this way, a nanomaterial (nZVI/MXene@CNTs), with three-dimensional interlayer structure and excellent adsorption and catalytic properties, was prepared. Additionally, this approach allowed for the simultaneous self-assembly of three-dimensional interlayer nanostructures with a variety of functional groups cross-linked for catalytic or interfacial activities, exhibiting the characteristics of simplicity, efficacy and environmental friendliness. The microscopic morphology and elemental composition of the CNTs, functionalized CNTs, MXene and nZVI/MXene@CNTs were observed by SEM and EDS-mapping (Figure 2). As shown in Figure 2a, there were numerous impurities, such as amorphous carbon and agglomerates, on the original CNTs surface. However, following acidification, the surface of the CNTs became rough, showing a considerable reduction in length, diameter and impurity (Figure 2b). The prepared MXene showed a two-dimensional stack of lamellae (Figure 2c). With the addition of the nZVI and functionalized CNTs, a cross-linked and interlaced three-dimensional intercalation structure was produced, and many nZVI catalytic units were evenly coated on the surface or embedded within (Figure 2d). A considerable number of C, O, Ti and Fe elements were visible in the EDS-mapping energy spectrum (Figure 2e-h), and each element was evenly distributed on the material surface. The original morphology of nZVI/MXene@CNTs was retained after repeated ultrasonic treatment, demonstrating good stability. The functional groups of the MXene, functionalized CNTs and nZVI/MXene@CNTs nanohybrid were identified via Fourier-Transform infrared spectroscopy (FTIR) (Figure 3a). It was obvious that the number of groups on the surface of MXene was limited. In addition, the peaks at 3429 and 1325 cm\({}^{-1}\) should be attributed to C-OH stretching, whereas at 2920 and 1625 cm\({}^{-1}\) the peaks should be assigned to -CH\({}_{3}\) symmetric bending and C=O stretching of the carboxyl group, respectively [48]. Significantly, the new peak at 556 cm\({}^{-1}\) corresponded to the Fe-O stretching vibration, indicating that the element of Fe was effectively deposited onto the surface [49]. The surface of the successfully synthesized nZVI/MXene@CNTs contained a specific quantity of iron and abundant oxygen-containing groups, indicating that nZVI and the functionalized CNTs were successfully grafted onto the MXene nanosheets. It would also be inferred that nZVI and functionalized CNTs  
Figure 1: Schematic illustration of the self-assembly synthesis of nZVI/MXene@CNTs. improved the active sites and some functional groups on MXene, hence improving its performance.