answer:Fig. 1a illustrates the process of creating ZnS/Ti3C2Tx MXene composites. To begin, Ti3AlC2 MAX was etched using LiF and HCl to produce ultrathin Ti3C2Tx MXene, as observed in the TEM image shown in Fig. 1b. The AFM image in Fig. 1c and 1d revealed that the average thickness of Ti3C2Tx MXene was approximately 3.5-4.5 nm, equivalent to three layers according to Bragg's Law. Subsequently, a hydrothermal method was employed to grow ZnS nanoparticles on the Ti3C2Tx MXene, resulting in the formation of ZnS/Ti3C2Tx MXene composites. TEM analysis was used to examine the morphology of the composites, revealing the presence of nanosheets and nanoparticles. HRTEM images of the composites displayed lattice spacings of two widths, as shown in Fig. 1f. One lattice stripe spacing of 0.22 nm corresponded to the (105) crystallographic plane of Ti3C2Tx MXene, while the other lattice stripe spacing of 0.31 nm corresponded to the (111) crystallographic plane of the cubic phase of ZnS. Fig. 1g presents the XRD pattern of Ti3AlC2, Ti3C2Tx MXene, and ZnS/Ti3C2Tx MXene composites, along with the standard card of Ti3AlC2 and ZnS. When compared to the pattern of Ti3AlC2 MAX, the strong peak at 38.6° in the Ti3C2Tx MXene pattern was conspicuously absent, indicating the removal of interlayer Al during the etching process. Additionally, the diffraction peak of the (002) plane shifted to a lower angle, suggesting an expansion of the layer spacing after etching. In the case of the ZnS/Ti3C2Tx MXene composites, the diffraction peaks of Ti3C2Tx MXene were retained, while new (111), (220), and (311) diffraction peaks associated with the cubic-phase structure of ZnS emerged (JCPDS card No. 05-0566). The (002) peak of the composites shifted to a lower angle compared to Ti3C2Tx MXene, indicating the widening of the layer spacing due to the in-situ growth of ZnS. Furthermore, no extraneous diffraction peaks were observed from the composites.

answer:The composition analysis of both MXene and ZnS/Ti3C2Tx MXene composites was carried out using energy dispersive spectrometry (EDS) and X-ray photoelectron spectroscopy (XPS), as shown in Fig. S1 and Fig. 2a. The results clearly indicate the presence of Zn, S, Ti, C, O, and F elements. Zn and S elements originated from ZnS, while Ti, C, O, and F elements came from MXene in ZnS/Ti3C2Tx MXene composites. The high-resolution XPS spectra of Ti 2p in Fig. 2b provide detailed information regarding the Ti-containing groups. The peaks at 455.1 and 461.2 eV correspond to Ti-C, while 456.5 and 462.3 eV correspond to Ti-O. The peaks at 459.2 eV and 464.5 eV are assigned to C-Ti-Fx. In ZnS/Ti3C2Tx MXene composites, these peaks closely resemble the ones observed in Ti3C2Tx MXene. The Raman spectra in Fig. S2 exhibit characteristic peaks at 203 cm-1, and the Raman hump around 392 cm-1 and 584 cm-1 indicate the in-plane and out-of-plane vibrational modes of Ti3C2Tx MXene with surface groups (-OH, -O, and -F) present in both Ti3C2Tx MXene and ZnS/Ti3C2Tx composites. Notably, the Raman intensity around 615 cm-1 (associated with -OH on the MXene surface) is reduced in ZnS/Ti3C2Tx MXene compared to the other peaks. This reduction could be attributed to the compositing of MXene with ZnS through -OH dehydrogenation. The O 1s region of Ti3C2Tx MXene, depicted in Fig. 2c, shows three peaks indicating the presence of Ti-O, Ti-OH, and adsorbed H2O. In contrast to Ti3C2Tx MXene, an additional peak at 530.8 eV is observed in the high-resolution XPS spectra of O 1s for ZnS/Ti3C2Tx MXene composites. This new peak is assigned to the Ti-O-Zn bond, suggesting the formation of a chemical bond at the interface between ZnS and Ti3C2Tx MXene. These findings support the conclusion that the binding of ZnS with Ti3C2Tx MXene was achieved through -OH dehydrogenation, confirming the formation of a Ti-O-Zn bond. Based on these comprehensive results, it can be concluded that the preparation of ZnS/Ti3C2Tx MXene composites was successful.

answer:In order to investigate the charge transfer interaction between ZnS and Ti3C2Tx MXene in the composites, the high-resolution XPS spectra of Zn 2p were examined for both ZnS and ZnS/Ti3C2Tx MXene, as shown in Fig. 2d. In the spectra, two peaks of 2p1/2 and 2p3/2 are observed. However, in ZnS/Ti3C2Tx MXene composites, the position of both the Zn 2p1/2 and Zn 2p3/2 peaks is lower in binding energy compared to ZnS alone. Additionally, the high-resolution XPS spectra of Ti 2p for the composites indicate that the peaks shift towards higher binding energy compared to Ti3C2Tx MXene (Fig. 2b). This trend suggests the occurrence of electron transfer from Ti3C2Tx MXene to ZnS, resulting in electron-rich properties for Zn 2p in the composites. Consequently, the degree of the barycenter shift on negative charges is enhanced, leading to increased polarizability of ZnS. This ultimately significantly improves the MRRS (magneto-rotation resonance signal) properties of ZnS/Ti3C2Tx MXene composites.

answer:The presence of Ti3C2Tx MXene in ZnS/Ti3C2Tx MXene composites enhances the magneto-rotation resonance signal (MRRS) effect, as evidenced by the strengthened Raman peaks at 350 cm-1, 699 cm-1, and 1047 cm-1. These peaks correspond to the first-order longitudinal optical (1 LO), second-order LO (2 LO), and third-order LO (3 LO) phonon modes of ZnS, as shown in Fig. 3a. As the concentration of Ti3C2Tx MXene increases, the intensity of MRRS in the composites also increases (Fig. 3b). The Raman peaks at 203 cm-1 and 521 cm-1 in Fig. 3a and Fig. 3b are attributed to Ti3C2Tx MXene and the Si substrate. To evaluate the enhancement effect of MXene on MRRS, the enhancement factor (EF) was calculated to be 1.5×107. The detailed calculation procedure can be found in the supporting information. The enhancement effect of Ti3C2Tx MXene on MRRS is further confirmed by calculating the strength of electron-phonon coupling, characterized by the Huang-Rhys parameter (S). The parameter S is calculated according to Equation (1), where n is the order of the LO phonon and I is the corresponding Raman integrated intensity. Based on the Raman spectra in Fig. 3a, the S1 value of ZnS was determined to be 0.95, while the S1 value of ZnS/Ti3C2Tx MXene composites was found to be 1.15. The increased S1 value indicates that the inclusion of MXene enhances the electron-phonon coupling in ZnS. The strength of electron-phonon coupling is positively correlated with the distance between electrons and holes. An increase in this separation suggests higher polarizability, resulting in an improvement in MRRS. It is worth noting that this is the first instance of using MXene to enhance MRRS in semiconductor materials.