## 4 Combined Applications of NCs and BCs for Elimination of Hydrocarbon Pollutants
These results open up new prospects for the joint use of photochemistry and biocatalytic technologies to solve urgent problems of environmental biotechnology, particularly for the removal of hydrocarbon pollutants. For hybrid systems involving the combined use of chemical and biological catalysis, it is important to not only ensure the biocompatibility of components but also protect the activity of BCs. A hybrid photo-controlled reversible photocatalytic ICPB system has been developed with a mechanism of protecting microorganisms from the attack of reactive oxidative species formed during photocatalysis [109]. The surface of the CdS-photocatalyst was coated with SiO\({}_{2}\), and then a thermosensitive polymer (TRP) was applied to cover the surface of CDs@SiO\({}_{2}\). This polymer was composed of \(N\)-isopropyl acrylamide, acrylamide, and the cross-linker (\(N\),\(N^{\prime}\)-methylenebisacrylamide). The resulting CdS@SiO\({}_{2}\)@TRP was attached to the surface of graphene (photothermal converter) to form a photo-controlled reversible photocatalytic system. Without light irradiation, soluble pollutants were biofegraded or absorbed by the CdS@SiO\({}_{2}\)@TRP. Under light irradiation, reactive oxidative species, photogenerated due to the activation of the protective polymer cover, were formed inside CDs@SiO\({}_{2}\)@TRP and photocatalytically decomposed the pollutants without contact between reactive oxidative species and microorganisms. It should be noted that in hybrid systems, in addition to chemical and biocatalytic components, there is most often an important component such as a carrier, whose role is not limited to protecting BCs from the influence of negative environmental factors, particularly free radicals [111]. Among carriers, priority is given to biocompatible materials (cellulose, ceramics and loofah) [98,112]. Microcapsules based on Ca-alginate gel and carboxymethyl cellulose successfully protected BCs from direct contact with the photocatalyst and free radicals, increasing the life of BCs during the photocatalytic decomposition of PAHs [103]. Cellulose used as a carrier provided conditions for the growth of cells of the genus _Ruminic-clostridium_ used as BCs and played an additional role of co-substrate [108]. In this case, the cellulose carrier was not only biocompatible but also biodegradable. The presence of a co-substrate or its formation in the workflow can contribute to improving the efficiency of the implementation of hybrid processes. Not only the carrier but also low-molecular-weight substances (acetic or propionic acids formed in the bioreactor or introduced from outside) can also act as co-substrates and electron donors and contribute to the course of photocatalytic reactions [108]. Today, the development of hybrid processes depends on the development of three-dimensional carriers characterized as affordable, high strength, biocompatible, porous and reproducible in characteristics. It should be noted that the effective use of hybrid processes is influenced by temperature and pH. Currently, a significant part of chemical reactions occurring in the presence of NCs do not require the use of extreme temperatures (Table 1), and this allows them to be considered in combination with BCs (Tables 2 and 3). The use of sewage with natural microbial consortia, possessing activity at pH 5.5-7.4 (Table 2), can be considered optimal for simultaneous physical-chemical treatment and biodegradation, which generally corresponds to most modern approaches to the degradation of hydrocarbon pollutants using NCs (Table 1). If necessary, the range of operating pH values can be expanded when using microscopic fungi as BCs [110] and synthetic or adaptedconsortia [46]. Thus, the use of _Aspergillus niger_ cells in combination with NPs of ZS provides 100% destruction of 100 mg/L verenzene, 100 mg/L toluene and 100 mg/L xylene w for 1 h at pH 4 [110]. BCs themselves play an important role in achieving the effective destruction of toxicants in the organization and implementation of hybrid processes [113].