## 2 Materials and Methods
### Characterization  
The samples were studied using a set of complementary methods: thermogravimetric analysis (TGA), derivative thermogravimetric analysis (DTGA) and differential scanning calorimetry (DSC), Raman spectroscopy, scanning electron microscopy (SEM), near-edge X-ray absorption fine structure (NEXAFS), and photoelectron (XPS) spectroscopy.  
Thermal analysis is the primary method for determining the thermal properties of chemicals. The TGA-DTGA-DSC measurements provide information on the thermal stability of a substance and its modification during thermal exposure to increasing temperature. Simultaneous differential thermal TGA-DTGA-DSC analyses were performed on SDTQ600 simultaneous differential technics (\"TA Instruments\", USA). The marine sponge samples with approximately m \(\approx\) 2.5-3 mg were heated at a heating rate of \(\beta\) = 5 \({}^{\circ}\)C min\({}^{-1}\) in an Ar atmosphere (argon flow \(\varphi\) = 100 mL\(\cdot\)min\({}^{-1}\)) in the temperature range of \(\Delta\)T = 20-1200 \({}^{\circ}\)C. Raman spectroscopy research was conducted at room temperature in the 80-3500 cm\({}^{-1}\) interval using a Horiba-Yvon Jobin LabRam HR800 spectrometer equipped with a 600 g/mm grating and an Ar laser with a 1 mW and 488 nm wavelength. Lenses of \(\times\)50 and \(\times\)100 were used for analysis. The spectrometer was fitted with neutral filters to limit the laser radiation power. The spectral and spatial resolution was about 1 cm\({}^{-1}\) and 1 \(\upmu\)m, respectively.  
The surface morphology of the sponge samples was analyzed using a couple of scanning electron microscopes (XL 30 ESEM, Philips; ULTRA55, Carl Zeiss, Jena, Germany). The elements were analyzed using energy-dispersive X-ray spectroscopy in an EDX analysis system from EDX (Mahwah, NJ, USA).  
The NEXAFS spectroscopy studies were carried out using the synchrotron radiation of the Russian-German dipole beamline at the BESSY II (Berlin, Germany). All NEXAFS spectra were measured in total electron yield (TEY) mode. The energy calibrations of the C 1s NEXAFS spectra were performed using the well-resolved \(\pi^{*}\)-resonance at 285.38 eV in the C 1s spectrum of HOPG [34]. The photon flux spectral dependence was monitored using the TEY signal from a clean Au photocathode. The photon energy resolution was below 0.05 eV. The samples for absorption measurements were prepared ex situ in air via pressing sample powders into the clean surface of a copper or indium plate.  
XPS studies were carried out at the resource center \"Physical methods of surface investigation\" of the Saint Petersburg University Research Park (St. Petersburg, Russia). XPS analysis was performed on a Thermo Fisher Scientific ESCALAB 250 Xi X-ray photoelectron spectrometer. The X-ray tube with Al K\({}_{\alpha}\) radiation (1486.6 eV) was used as a source of ionizing radiation. The survey spectra and high-resolution core-level spectra were measured with pass energies of 100 eV and 50 eV, respectively. To neutralize the sample charging during the experiments, an electron-ion charge compensation system was used. The experimental data were processed using the ESCALAB 250 Xi spectrometer software.