3.2. Biocompatibility of composite materials and FACHB-314
We studied the effects of nanoparticles of rGO-TiO2 on the biomass and nitrate consumption of FACHB-314 and its cell structure or subcellular structure to determine the biocompatibility of the material with FACHB-314 . rGO-TiO2 composite nanoparticles were added to the FACHB-314 culture medium to determine the change in dry cell weight and the residual nitrate content in the culture medium. FACHB-314 cultured without nanoparticles was used as a control group. It can be observed from Figure 5 that the dry cell weight of FACHB-314 added with composite photocatalytic nanomaterials changes relative to the blank group and the remaining nitrate content in the culture medium. Among them, Figure 5(a) shows the growth trend of the two groups of FACHB-314 and gradually increases. On day 9, the weight of FACHB-314 stem cells cultured on the composite photocatalytic nanomaterials reached 1.24g/L, and the blank group reached 1.36g/L. Compared with the blank group, the experimental group only changed by 8.8%. Then, the residual nitrate content in the two sets of culture media was determined. The result is shown in Figure 5(b). The residual nitrate content also tends to be consistent. Based on this, we concluded that, compared with the blank group, nanoparticle rGO-TiO2 will not adversely affect the two indicators of FACHB-314 biomass and remaining nitrate content.
Figure 6 shows a photomicrograph of the effect of rGO-TiO2 and TiO2 nanoparticles on the morphology of FACHB-314 cells. Figure 6(a), (c), (e) shows the morphology of the three types of microalgae on the first day, (a) is a control group of FACHB-314 under an optical microscope, (c) isFACHB-314 with TiO2 nanoparticles added under an optical microscope, and (e) is a control group of FACHB-314 under an optical microscope. FACHB-314 and rGO-TiO2nanoparticles. The morphology of these three kinds of FACHB-314is normal, showing unidirectional growth and left-handed spiral arrangement. Unlike the control group, the FACHB-314 filaments of the two experimental groups are all attached with nanoparticles, but they have no effect on the morphology and structure of FACHB-314 . On the sixth day, the subcellular structures of the three microalgae are as follows: Figure 6 (b) is the control group FACHB-314 under the transmission electron microscope (d) is the FACHB-314 doped with nanoparticle TiO2 under the transmission electron microscope, and (f) is the transmission electron microscope.FACHB-314 doped with nanoparticles of rGO-TiO2under the electron microscope. By observing the microstructure of the three groups of FACHB-314 , it is found that the vegetative cells undergo two divisions during unidirectional growth, and there are obvious transfers on the transverse wall. The trichomes are wrapped in a thin sheath, and there are obvious structures at the crossing walls (Li et al., 2017; Lupatini et al., 2017). In the trichomes of the experimental group, especially under the treatment of titanium dioxide nanoparticles, the transverse wall structure of the trichomes became difficult to distinguish, the morphological abnormalities ofFACHB-314 were clearly visible, and the cell membrane and transverse wall were twisted. The horizontal wall structure in the middle disappeared. The cell shape of the control group showed a flat surface, and the cell membrane was not damaged. The mixing ofFACHB-314 and composite photocatalytic nanoparticles rGO-TiO2 has a certain effect on the cell morphology ofFACHB-314 . For example, the horizontal wall is opaque, the cell wall is wrinkled, etc., but it still maintains the basic morphological characteristics and will not cause obvious damage to the sexual structure. The above results indicate that rGO-TiO2nanoparticles have good biocompatibility for the growth ofFACHB-314 .