In-line measurement of absorbed solar irradiance using nanofluids

In this paper a novel technique for the in-line evaluation of the absorption rate of solar radiation by nanofluids in a volumetric solar receiver is presented. This method allows to experimentally investigate the optical behaviour of a nanofluid when circulating in a volumetric solar receiver under non-concentrated solar irradiance and it is based on the combined use of pyranometers. This technique is used in the present work to study the absorption capability of a Single-Wall-Carbon-NanoHorns (SWCNHs) based nanofluid. From the experiments, it can be seen that after some hours of circulation, the absorption rate of the nanofluid decreases, due to a loss of nanoparticles in the suspension.

Efficient Optical Limiting in Carbon-Nanohorn Suspensions

Nonlinear optical properties of aqueous dispersions of single-wall carbon nanohorns (SWCNH) are investigated by a simple and original technique, relating nonlinear transmittance measurements with semi-empirical model fitting and allowing to identify the dominant nonlinear mechanism. The nanofluids shown a particularly strong optical limiting under irradiation by nanosecond laser pulses at 355, 532 and 1064 nm, much stronger than that previously reported in SWCNHs with smaller aggregate size. The effect is more relevant at 355 nm, where a nearly ideal optical limiting behavior with output energy practically independent on the input one is obtained, and it is attributed to the massive production of bubbles under the effect of light irradiation. This result opens interesting perspectives for the use of SWNCH-based suspensions for smart materials applications and green energy.

Investigation of nanofluids circulating in a volumetric solar receiver

Single-Wall-Carbon-Nanohorns (SWCNHs) based nanofluids have been proven to be promising media for the direct absorption of solar radiation due to their favourable optical properties and potential low cost. Still, their stability in real working conditions is an open issue because they have been studied mainly under stagnant conditions while limited information is available on the performance of these nanofluids during circulation in real systems. In the present work, the optical behaviour of SWCNHs based nanofluids has been investigated with the aim of detecting possible effects of circulation and exposure to radiation, avoiding other effects such as thermal instability. An ad-hoc experimental apparatus has been realized to check the stability of the circulating fluids in-situ using a novel approach based on the use of pyranometers. Three suspensions are tested, two are surfactant-stabilized and one is based on pre-oxidised and functionalised SWCNHs. Efficiency values higher than 90 % were measured for more than 65 hours of circulation. The effects of fluid circulation and exposure to solar radiation have been addressed, finding that the absorption efficiency decreases during tests due to the degradation of the optical properties and the nanofluid circulation is the main responsible for such degradation.

Optical Limiting of Carbon Nanohorn-Based Aqueous Nanofluids: A Systematic Study

Nowadays, the use of lasers has become commonplace in everyday life, and laser protection has become an important field of scientific investigation, as well as a security issue. In this context, optical limiters are receiving increasing attention. This work focuses on the identification of the significant parameters affecting optical limiting properties of aqueous suspensions of pristine single-wall carbon nanohorns. The study is carried out on the spectral range, spanning from ultraviolet to near-infrared (355, 532 and 1064 nm). Optical nonlinear properties are systematically investigated as a function of nanohorn morphology, concentration, dimensions of aggregates, sample preparation procedure, nanostructure oxidation and the presence and concentration of surfactants to identify the role of each parameter in the nonlinear optical behavior of colloids. The size and morphology of individual nanoparticles were identified to primarily determine optical limiting. A cluster size effect was also demonstrated, showing more effective optical limiting in larger aggregates. Most importantly, we describe an original approach to identify the dominant nonlinear mechanism. This method requires simple transmittance measurements and a fitting procedure. In our suspensions, nonlinearity was identified to be of electronic origin at a 532 nm wavelength, while at 355 nm, it was found in the generation of bubbles.

Properties and biological potential of single wall carbon nanohorns (SWCNH)

Nanohorns (or nanocons) are formed when pentagons are accumulated at the top of the formed nanocarbon structure. hey are a cone formed by one layer of graphene with a diameter of 24 nm and a length of 4050 nm. The review considers the structure of these structures and their properties. The possibilities of using these structures in biology are described in detail.