Partial nitrogen doping was performed during the catalytic chemical vapor deposition (CCVD) synthesis of multi-walled carbon nanotubes. A special reactor was created to facilitate the execution of syntheses with different reaction conditions. The synthesized samples were analyzed by transmission electron microscopy (TEM) in order to provide information about the tubular and nontubular morphology of particles and their deformation gained after the reaction conditions were changed. The incorporation of nitrogen into the carbon structure was studied by X-ray photoelectron spectroscopy (XPS), whereas X-ray diffraction (XRD) and Raman spectroscopy evaluations showed the degree of graphitization. The samples then were carboxyl functionalized in varied concentrations of nitric acid solutions and photosynthetic reaction center protein (RC-26) purified from purple bacteria was linked to the carboxyl groups in order to make the degree of functionalization visible. The protein-linked samples were characterized by atomic force microscopy (AFM). Our experiments indicated that the syntheses carried out in the new reactor were successful and resulted in carbon nanotubes partially doped with nitrogen. TEM studies revealed that the expected deformations are localized only in a defined segment of carbon nanotubes therefore nitrogen doping is most possibly presented there. The nitrogen content in the samples represented in atomic ratios was between 0.9% and 2.9%. The deformations facilitate the functionalization at that certain area, thus the location of carboxyl groups can be determined.

The reaction center protein is the unit in the photosynthetic organisms in which the primary events of the photoelectric energy conversion take place during photosynthesis. When the photochemistry following the excitation of the reaction center by light is oversaturated there is a large probability to form reactive oxygen species (ROS, e.g., singlet oxygen ( 1 O 2 )). Because the ROS components decrease the overall yield of the photochemical energy conversion there is a considerable effort in many laboratories to find conditions to reduce these harmful compounds. The aim of our work is to create a system by using carbon nanotubes (CNTs) and RCs for efficient lightenergy conversion. The role of the 1 O 2 that destroys the RC structure is discussed. 1,3-Diphenylisobenzofuran was used to detect the concentration of the 1 O 2 . Although, 1 O 2 can be sensitized by CNTs in certain conditions, in our experiments the main sources of the 1 O 2 are the RCs. The concentration of the 1 O 2 in the equilibrium is determined by the forward sensitization and the backward deactivation processes of the components and functions of the CNT/RC composite.

Carbon-based nanomaterials of different dimensions (1–3D, tubes, bundles, films, papers and sponges, graphene sheets) have been created and their characteristic properties have been discussed intensively in the literature. Due to their unique advantageous, tunable properties these materials became promising candidates in new generations of applications in many research laboratories and, recently, in industries as well. Protein-based bio-nanocomposites are referred to as materials of the future, which may serve as conceptual revolution in the development of integrated optical devices, e.g. optical switches, microimaging systems, sensors, telecommunication technologies or energy harvesting and biosensor applications. In our experiments, we designed various carbon-based nanomaterials either doped or not doped with nitrogen or sulfur during catalytic chemical vapor deposition synthesis. Radio- and isotope analytical studies have shown that the used starting materials, precursors and carriers have a strong influence on the geometry and physico-/chemical characteristics of the carbon nanotubes produced. After determining the 14C isotope constitution 53 m/m% balance was found in the reaction center protein/carbon nanotubes complex in a sensitive way that was prepared in our laboratory. The result is essential in determining the yield of conversion of light energy to chemical potential in this bio-hybrid system.

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