*4.4. Characterizations of Fe–Zr@PDA@CMCS and Fe–Zr@PDA*

To observe the microscopic morphology and elemental distribution of the CMCS and Fe–Zr@PDA@CMCS hydrogel, firstly, the conductive glue was carefully pasted on the test sample table, and the freeze-dried CMCS and Fe–Zr@PDA@CMCS hydrogel were cut into thin pieces and placed on the conductive glue. Then, an infrared baking lamp was used to dry the surface of the hydrogel. After that, its morphology was examined using a scanning electron microscope (SEM, Zeiss Sigma 300). Similarly, the morphology and particle size of Fe–Zr@PDA were observed using SEM, and the elemental composition of Fe–Zr@PDA nanoparticles was further analyzed using an X-ray energy spectrometer.

### *4.5. Characteristics of Photothermal Conversion*

To explore the influence of different power densities on the temperature change, Fe–Zr@PDA@CMCS hydrogel was irradiated with the near-infrared laser electricity with strength densities of 0.5 W/cm<sup>2</sup> , 0.8 W/cm<sup>2</sup> , or 1 W/cm<sup>2</sup> . Then, we recorded the temperature change using an FLIRE60 camera. Finally, the photothermal stability of the hydrogel was explored. Specifically, the near-infrared laser with a power density of 0.8 W/cm<sup>2</sup> was used to irradiate the hydrogel for 6 cycles, and the cycle was set at 20 min each time. During the experiment, the thermal images and temperature changes of the experimental each cycle were recorded using a near-infrared thermal imager. The photothermal conversion efficiency (η) of Fe–Zr@PDA@CMCS was calculated by the modified Korgel formula (1):

$$\mathfrak{n}(\%) = \frac{h\mathcal{S}(T\_{\max} - T\_{\text{surr}}) - Q\_{\text{in.surr}}}{I\left(1 - 10^{(-A(\_{\lambda}))}\right)} \tag{1}$$

In the above formula, η is the photothermal conversion efficiency, *h* is the warmness switch coefficient, *I* replace the power of the laser, *Tmax* is the highest temperature of Fe–Zr@PDA@CMCS solution under the laser irradiation for 6 min, *Tsurr* represents the ambient temperature throughout the test period, *hS* is the heat transfer coefficient, *A*(*λ*) is the absorbance of Fe–Zr@PDA@CMCS at wavelength 808 nm, *S* is the effective area of laser radiation, and *Qin.surr* is the heat loss of Fe–Zr@PDA@CMCS in the heating process.
