2.2 Photothermal Performance of the PTEH-Interlocking
For the photothermal performance assessment, the surface temperature of PA-PEI-Fe photothermal film constructed with different concentrations of polyphenolic PA (0-0.2 mol L−1) were measured under simulated sunlight with an intensity of 100 mW cm−2 for 1 h. The surface temperature rises to 63.4 ± 1.87oC as the proportion of PA increases to 0.1 mol L−1, then that temperature remained steady (Figure 3a ). As can be seen from the digital photos, that film gradually darkens as the PA content increases (Figure S5 ). The PA-PEI-Fe photothermal film prepared via the oxidation of PA (0.1 mol L−1) and PEI (0.2 g L−1) by [Fe(CN)6]3− is thus used as the prototype in all experiments. In the UV diffuse reflection spectra (Figure 3b ), the PA-PEI-Fe photothermal film shows an enhanced absorbance coefficient compared with the pure PA-PEI film ranging from the UV to NIR region. We compared the photothermal conversion effect of the PA-PEI and PA-PEI-Fe film in this work and the classic commercially available photothermal materials of carbon nanotubes (CNT). CNT and pure PA film have a similar increase in temperature (rising to ~57oC), whereas that temperature of the PA-PEI-Fe photothermal film rise to a higher temperature of ~66oC (Figure 3c and d ). The corresponding photothermal conversion efficiency of the PA-PEI-Fe photothermal film is 43.83% higher than those of pure PA-PEI film and CNT film (Figure 3e ). After 10 UV light “on-off” cycles (UV light intensity of 70 mW cm−1 for 1 h), the temperature of the PA-PEI-Fe and PA-PEI film remained stable (Figure 3f ), and after UV photobleaching for 13 h (70 mW cm−1), the PA-PEI-Fe and PA-PEI film still keep at a higher temperature of ~59oC and 50oC (Figure 3f ). which indicating the satisfactory UV tolerance. These results demonstrate that the as-prepared PA-PEI-Fe photothermal film have good and stable photothermal performance. As a result, temperature differences (ΔT) between the upper and lower surface of the PTEH-Interlocking is high as 1.9K, while that ΔT of the TEH and TEH-CNT is only 0.1K and 1K, respectively (Figure 3g ).