Synthesis and characterization of porphyrin nanotubes/rods for solar radiation harvesting and solar cells

Energy transfer and electron transfer events as they occur between well arranged light harvesting antenna molecules, the reaction center and other factors determine the function of natural photosynthesis. The overall small reorganization energy and the well-balanced electronic coupling between each component bear key characters for the unique efficiency of natural photosynthesis. Such aspects permit the design and assembly of artificial systems that efficiently process solar energy, replicating the natural processes. The rich and extensive transitions seen in porphyrin-based materials hold great expectation as light harvesting building blocks in the construction of molecular architectures, allowing an efficient use of the solar spectrum. Hence in this study porphyrin nanorods are synthesized and characterized for future application in the construction of the artificial light harvesting system. Understanding the sizes and growth mechanism of porphyrins nanorods by self-assembly and molecular recognition is essential for their successful implementation in nanodevices. Spectroscopic and microscopic studies were carried out to investigate the effect that time, concentration and solvents have on the fabrication of porphyrin nanorods by ionic self-assembly of two oppositely charged porphyrins. We investigate in details the heteroaggregate behavior formation of [H₄TPPS₄]²⁻ and [SnTPyP]²⁺ mixture by means of the UV–vis spectroscopy and aggregates structure and morphology by transmission electron microscopy (TEM). This study demonstrates the potential for using different concentrations and solvents to influence the physical and optical properties of porphyrin based nanorods.     

Silver nanostructures embedding in polymethyl methacrylate patterns fabricated using proton beam writing

Proton beam writing (PBW) on polymethyl methacrylate (PMMA) followed by embedding of biosynthesized silver nanoparticles (AgNPs) was investigated. This is the first demonstration of the use of 3 MV Tandetron accelerator at iThemba LABS for fabricating patterns using PBW technique. The irradiation of PMMA was carried out using 3.0-MeV proton beam focused down to micrometer spot size. The fluence of protons was counted as electrical charge per unit monitored by exposure time, beam current, and irradiated area. As expected, the PMMA behaved as a positive resist because of chain scissioning induced from the interaction with proton beam. Morphological characterization using scanning electron microscope (SEM) revealed fabrication of square-like patterns, and atomic force microscopy (AFM) provided the possibility of observing the presence of AgNPs that stood out of the PMMA matrix.     

Black Cr/α-Cr2O3 nanoparticles based solar absorbers

Monodisperse spherical core–shell particles of Cr/α-Cr₂O₃ with high adhesion were successfully coated on rough copper substrates by a simple self-assembly-like method for the use in solar thermal absorbers. The structure and morphology of the core-shell particles of Cr/α-Cr₂O₃ were effectively controlled by deposition temperature and the pH of the initial precursor solution. Their characterizations were carried out with X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry and attenuated total reflection, as well as UV–vis diffuse reflectance spectroscopy. The samples aged for more than 40 h at 75 °C exhibit the targeted high absorbing optical characteristic “Black chrome” while those aged for ≤40 h show a significant high UV–vis diffuse reflectance “green color”.