Layer‐by‐Layer Assemblies of Catechol‐Functionalized TiO₂ Nanoparticles and Porphyrins through Electrostatic Interactions

Abstract

In the current work, we present the successful functionalization and stabilization of P-25 TiO2 nanoparticles by means of N1,N7-bis(3-(4-tert-butyl-pyridium-methyl)phenyl)-4-(3-(3-(4-tert-butyl-pyridinium-methyl)phenylamino)-3-oxopropyl)-4-(3,4-dihydroxybenzamido)heptanediamide tribromide (1). The design of the latter is aimed at nanoparticle functionalization and stabilization with organic building blocks. On one hand, 1 features a catechol anchor to enable its covalent grafting onto the TiO2 surface, and on the other hand, positively charged pyridine groups at its periphery to prevent TiO2 agglomeration through electrostatic repulsion. The success of functionalization and stabilization was corroborated by thermogravimetric analysis, dynamic light-scattering, and zeta potential measurements. As a complement to this, the formation of layer-by-layer assemblies, which are governed by electrostatic interactions, by alternate deposition of functionalized TiO2 nanoparticles and two negatively charged porphyrin derivatives, that is, 5,10,15,20-(phenoxyacetic acid)-porphyrin (2) and 5,10,15,20-(4-(2-ethoxycarbonyl)-4-(2-phenoxyacetamido)heptanedioic acid)-porphyrin (3), is documented. To this end, the layer-by-layer deposition is monitored by UV/Vis spectroscopy, scanning electron microscopy, ellipsometry, and profilometry techniques. The resulting assemblies are utilized for the construction and testing of novel solar cells. From stable and repeatable photocurrents generated during several "on-off" cycles of illumination, we derive monochromatic incident photo-to-current conversion efficiencies of around 3 %.

Synergy of Catechol‐Functionalized Zinc Oxide Nanorods and Porphyrins in Layer‐by‐Layer Assemblies

“…Considering that P1 and P2 feature different steric demands, as well as 4 and 12 negative charges, respectively, they are ideal building blocks for LbL assemblies. Both porphyrins show characteristic absorptions in the UV/Vis region, which allow the precise monitoring of successive layer formation by means of absorption spectroscopy …”

“…Herein, positively charged poly(diallyldimethylammonium) (PDDA) and negatively charged poly(sodium 4‐styrenesulfonate) (PSS) were utilized for the polyelectrolyte coating. Specifically, aqueous solutions of 0.5 % PDDA at pH 3 and 0.5 % PSS at pH 4 were prepared …”

“…The [ P2 ‐ Z1 ] 9 photoelectrodes feature efficiencies one order of magnitude higher than those of [ Z1 ‐ P2 ] 9 photoelectrodes: 1.5×10 −2 versus 4.3×10 −3 %. Relative to photoelectrodes based on catechol‐functionalized TiO 2 NPs ( T ) and P1 / P2 , significantly better results were realized in terms of performance and efficiency: 1×10 −3 % for [ T ‐ P1 ] and 2.5×10 −4 % for [ T ‐ P2 ] . In short, up to 15 times higher efficiencies were achieved by using [ P2 ‐ Z1 ].…”

“…Combining all of these concepts, we recently reported the successful formation of LbL assemblies by using catechol‐functionalized, cationic P‐25 TiO 2 NPs and anionic porphyrins . In the resulting multilayer assemblies, stable and repeatable photocurrent generations yielded monochromatic incident photo‐to‐current conversion efficiencies of around 3 %.…”

Synergistic Effect of Polyoxometalates and rGO for Enhancing the Photocurrents of TiO2-based Composite Film

“…18 TiO 2 nanoparticles are positively charged in dilute HNO 3 aqueous solution, subsequently the self-assembly with the negatively charged POMs will spontaneously occur via Coulombic force. 19 The basic LbL assembly process is schemed in Figure 1a, in which PEI and PSS are used as the bottom layer to facilitate the following anchoring of inorganic species.…”