Porphyrin-Nanocarbon Complexes to Control the Photodegradation of Rhodamine.

Porphyrin-nanocarbon systems were used to generate a photocatalyst for the control of rhodamine B and rhodamine 6G photodegradation. Carboxylic functionalized multi-walled carbon nanotubes (o-MWCNTs) were decorated by two different porphyrin moieties: 5-(4-aminophenyl)-10,15,20-(triphenyl)porphyrin (a-TPP) with an amine linker and 5-(4-carboxyphenyl)-10,15,20-(triphenyl)porphyrin (c-TPP) with a carboxyl linker to the o-MWCNT, respectively, with their photocatalyst performances investigated. The optical properties of the mixed nanocomposite materials were investigated to reveal the intrinsic energy levels and mechanisms of degradation. The charge-transfer states of the o-MWCNTs were directly correlated with the performance of the complexes as well as the affinity of the porphyrin moiety to the o-MWCNT anchor, thus extending our understanding of energy-transfer kinetics in porphyrin-CNT systems. Both a-TPP and c-TPP o-MWCNT complexes offered improved photocatalytic performance for both RhB and Rh6G compared to the reference o-MWCNTs and both porphyrins in isolated form. The photocatalytic performance improved with higher concentration of o-MWCNTs in the complexed sample, indicating the presence of greater numbers of -H/-OH groups necessary to more efficient photodegradation. The large presence of the -H/-OH group in the complexes was expected and was related to the functionalization of the o-MWCNTs needed for high porphyrin attachment. However, the photocatalytic efficiency was affected at higher o-MWCNT concentrations due to the decomposition of the porphyrins and changes to the size of the CNT agglomerates, thus reducing the surface area of the reactant. These findings demonstrate a system that displays solar-based degradation of rhodamine moieties that are on par, or an improvement to, state-of-the-art organic systems.

Ultra-broadband light trapping using nanotextured decoupled graphene multilayers.

The ability to engineer a thin two-dimensional surface for light trapping across an ultra-broad spectral range is central for an increasing number of applications including energy, optoelectronics, and spectroscopy. Although broadband light trapping has been obtained in tall structures of carbon nanotubes with millimeter-tall dimensions, obtaining such broadband light-trapping behavior from nanometer-scale absorbers remains elusive. We report a method for trapping the optical field coincident with few-layer decoupled graphene using field localization within a disordered distribution of subwavelength-sized nanotexturing metal particles. We show that the combination of the broadband light-coupling effect from the disordered nanotexture combined with the natural thinness and remarkably high and wavelength-independent absorption of graphene results in an ultrathin (15 nm thin) yet ultra-broadband blackbody absorber, featuring 99% absorption spanning from the mid-infrared to the ultraviolet. We demonstrate the utility of our approach to produce the blackbody absorber on delicate opto-microelectromechanical infrared emitters, using a low-temperature, noncontact fabrication method, which is also large-area compatible. This development may pave a way to new fabrication methodologies for optical devices requiring light management at the nanoscale.