Photostability of J -aggregates adsorbed on TiO 2 nanoparticles and AFM imaging of J -aggregates on a glass surface

Abstract. Spectral properties and photostability of the 5,5'-6,6'-tetrachloro-1,1'-dioctyl-3,3'-bis-(3-carboxypropyl)-benzimidacarbocyanine (Dye 1) J-aggregate was investigated in solution and upon adsorption on TiO 2 nano-particles. Dye 1 was found to photodegrade on the surface of TiO 2 . Additionally, the self-assembly of Dye 1 was studied on a glass surface by non-contact atomic force microscopy (NCAFM). The dye molecules form a well-defined fiber like structure that extends for tens of micrometers. The internal structure of the fibers was clearly resolved and showed a number of small tubes wrapped around each other to form a helical structure

Flexible Bench-Scale Recirculating Flow CPC Photoreactor for Solar Photocatalytic Degradation of Methylene Blue Using Removable TiO 2

TiO2 immobilized on polyethylene (PET) nonwoven sheet was used in the solar photocatalytic degradation of methylene blue (MB). TiO2 Evonik Aeroxide P25 was used in this study. The amount of loaded TiO2 on PET was approximately 24%. Immobilization of TiO2 on PET was conducted by dip coating process followed by exposing to mild heat and pressure. TiO2/PET sheets were wrapped on removable Teflon rods inside home-made bench-scale recirculating flow Compound Parabolic Concentrator (CPC) photoreactor prototype (platform 0.7 × 0.2 × 0.4 m3). CPC photoreactor is made up of seven low iron borosilicate glass tubes connected in series. CPC reflectors are made of stainless steel 304. The prototype was mounted on a platform tilted at 30°N local latitude in Cairo. A centrifugal pump was used to circulate water containing methylene blue (MB) dye inside the glass tubes. Efficient photocatalytic degradation of MB using TiO2/PET was achieved upon the exposure to direct sunlight. Chemical oxygen demand (COD) analyses reveal the complete mineralization of MB. Durability of TiO2/PET composite was also tested under sunlight irradiation. Results indicate only 6% reduction in the amount of TiO2 after seven cycles. No significant change was observed for the physicochemical characteristics of TiO2/PET after the successive irradiation processes

J-Aggregates of Amphiphilic Cyanine Dyes for Dye-Sensitized Solar Cells: A Combination between Computational Chemistry and Experimental Device Physics

We report on the design and structure principles of 5,5′-6,6′-tetrachloro-1,1′-dioctyl-3,3′-bis-(3-carboxypropyl)-benzimidacarbocyanine (Dye 1). Such metal-free amphiphilic cyanine dyes have many applications in dye-sensitized solar cells. AFM surface topographic investigation of amphiphilic molecules of Dye 1 adsorbed on TiO2 anode reveals the ability of spontaneous self-organization into highly ordered aggregates of fiber-like structure. These aggregates are known to exhibit outstanding optical properties of J-aggregates, namely, efficient exciton coupling and fast exciton energy migration, which are essential for building up artificial light harvesting to the photovoltaic device. A light-to-electricity conversion efficiency of DSSC based on the metal free amphiphilic Dye 1 is η=3.75, which is about 50% of that based on metal-based N719 Ru-dye (Di-tetrabutylammoniumcis-bis(isothiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)ruthenium(II)). DFT and TD-DFT studies show that large intramolecular charge transfer takes place from the HOMO to LUMO. HOMO is localized on a part of the molecule with almost no contribution from the carboxylic moiety. This clearly indicates that the anchoring carboxylic group plays a minor role

Catalytic Decomposition of Natural Gas to CO/CO2-Free Hydrogen Production and Carbon Nanomaterials Using MgO-Supported Monometallic Iron Family Catalysts

Monometallic Fe, Co, and Ni/MgO catalysts with 50 wt.% metal loadings were prepared and examined for natural gas decomposition to nanocarbonaceous materials, particularly multiwalled carbon nanotubes (MWCNTs) and co-valuable hydrogen. The catalytic testing was carried out in a fixed-bed horizontal reactor at 700°C under atmospheric pressure. The fresh and/or used catalysts were characterized using XRD, TPR, HRTEM, SEM, TG/DTA, Raman spectroscopy, and BET surface measurements. The resulting data showed that the 50%Co/MgO catalyst displayed higher catalytic decomposition activity of natural gas to CO x -free hydrogen production (∼88%), higher yield of MWCNTs, and excellent stability up to 10 h time-on-stream. On the other hand, the Ni-containing catalyst showed lower catalytic activity toward hydrogen and CNTs production, principally due to the formation of rock-salt Mg x Ni (1-x) O solid solution as observed from XRD and TPR data. Accordingly, the concentration of Ni particles required for natural gas feed was extremely low. The d orbital of Ni was presumed to be occupied during the formation of the solid solution, which inhibits the solublization or adsorption of hydrocarbons on Ni particles. The MWCNTs obtained over Ni-based catalyst had narrow and homogeneous diameters (∼11-13 nm). However, the Fe/MgO catalyst exhibited intermediate activity between those of Ni and Co˭MgO catalysts toward hydrogen production (∼44%). This catalyst produced mixtures of carbon nanofibers and nanotubes

Photophysics of molecular rotors of functionalized surface-active styrylcyanine dyes

This paper describes the essential photophysical properties of a newly synthesized 1-cetyl-4-( p - NN -dimethylamino styryl)-pyridinium bromide and its parent short-chain styrylcyanine dye. These dyes exhibit similar fluorescence behaviour and are characterized by extensive non-radiative processes. The observed main differences are related to the long-chain hydrocarbon group and are found to be an enhanced sensitivity of the organized surfactant molecules to solvent interactions. The influence of various macro-and micro-scopic solvent properties on the photophysical properties of the dyes is investigated, with particular focus on the interplay of dye structure and specific solvent-solute interactions that govern the competition between radiative and non-radiative decay. It is found that specific interactions by hydrogen-bonding solvents are the key controlling factors in the relaxation processes. The results are expressed in terms of linear and multilinear relationships. Correlating the experimental results with theory (CNDO and PPP-SCF-CI calculations) provides a better insight into the excited-state properties of these dyes