## 3 Results and Discussion  
The results of a preliminary study of the native sponge after the cleaning procedure are shown in Figure 1a-d, which contains its photo (a) and the scanning electron microscopy data. The microphotographs clearly demonstrated the characteristic multilevel 3D structure of the spongin matrix of individual fibers up to 100 \(\upmu\)m thick, consisting of nanoscale collagen filaments, which together formed a complex three-dimensional structure with high microporosity. To elucidate the elemental composition of the sample, EDX was used, which, in addition to the presence of carbon (-74%), nitrogen (-3%), and oxygen (-20%), also showed traces of calcium, magnesium, sodium, aluminum, sulfur, and silicon. Quantitative elemental analysis of the native sponge was also carried out using XPS. Figure 2a shows the survey XPS spectrum of the native sponge, which contained two intense C 1s and O 1s peaks, as well as a set of low-intensity N 1s, Na 1s, Si 2p, and Ca 2p peaks. Figure 1: Photos of the native (**a**) and carbonized (**e**) marine sponges, along with the SEM images of the native marine sponge before (**b–d**) and after carbonization (**f–h**). Figure 2: XPS spectra of pristine and carbonized sponge: survey (**a**), N 1s (**b**), C 1s (**c**), and O 1s (**d**) spectra. The XPS data agreed well with the EDX results on the elemental composition of the native sponge, which showed 76.8 at.% carbon, 1.9 at.% nitrogen, 16.0 at.% oxygen, 2.6 at.% silicon, 1.1 at.% sodium, and 1.6 at.% calcium. The observed discrepancy in the content and atomic composition was caused by the different sensitivities of the methods to the atoms of the elements, as well as by the distribution of nitrogen, carbon, and oxygen atoms in the volume and on the surface of the sponge structural elements. It should be noted that EDX gives information on the relative concentration of atoms at a depth of several tenths to several micrometers, and for the XPS this depth is 1-2 nm. Therefore, the agreement of data on carbon, oxygen, and nitrogen indicates an equal distribution in the volume and on the surface of the studied sample. It should be noted that the ratio of atomic concentrations of carbon, nitrogen, and oxygen atoms in the sponge agrees with the data of other authors [35]. Despite the fact that mankind has been actively using sponges for more than a thousand years, data on the chemical properties of spongin are incomplete. To date, there is no clear definition of the chemical composition of this unique biological material. The pathways of spongin biosynthesis in sponges, as well as the genomics, proteomics, and protein sequences of this biopolymer, are still unknown. However, earlier studies [8] showed that spongin is built from amino acids similar to collagen, which consists of a Gly-Xaa-Yaa triplet motif, where the Xaa or Yaa position is usually occupied by hydroxproline and the remaining position by any of the amino acids present [36]. Hydroxproline was found in large amounts in several sponges of _Dictyoceratida_ (_Demosopgiae_) [9]. According to [37], the spongin _H. communis_ marine sponges contain 19 different amino acids, with the highest concentration (percentage per 100 g of spongin) of glycine C\({}_{2}\)H\({}_{5}\)NO\({}_{2}\) (31.9%), followed by aspartic acid C\({}_{4}\)H\({}_{7}\)NO\({}_{4}\) (9.4%), hydroxproline C\({}_{5}\)H\({}_{9}\)NO\({}_{3}\) (8.7%), alanine C\({}_{3}\)H\({}_{7}\)NO\({}_{3}\) (8.4%), and glutamic acid C\({}_{5}\)H\({}_{9}\)NO\({}_{4}\) (7.9%). These amino acids are characterized by the presence of -COOH, -NH\({}_{2}\), and -OH functional groups, which are responsible for the effective interaction with other substances in the sponge. Taking into account the data on the relative composition of carbon, oxygen, and nitrogen atoms in the native sponge, one can make a preliminary conclusion about the content of spongin in it.