Carboxylic Anchoring Dye p-Ethyl Red Does Not Adsorb Directly onto TiO₂ Particles in Protic Solvents

Abstract

Adsorption of the carboxylic anchoring dye, p-ethyl red (p-ER), onto TiO2 nanoparticles in protic vs aprotic solvents was studied in situ using the surface-specific technique, second harmonic light scattering (SHS). Two different adsorption schemes were proposed to account for p-ER interactions with TiO2 under different solvent environments. In aprotic solvents, p-ER adsorbs directly onto TiO2. Conversely, in protic solvents, in which solvent molecules bind stronger than p-ER with TiO2, the dye molecules adsorb onto the solvent shell around the particle but not directly to the TiO2 surface. In addition, a portion of the p-ER molecules form hydrogen bonds with the protic solvent molecules. The two different adsorption models reproduce the measured adsorption isotherms detected by SHS. Specifically, the p-ER molecules adsorb with a smaller free energy change and a larger density in protic solvents than in aprotic solvents. Our results indicate that protic solvents are undesirable for administering adsorption of carboxylic dyes in dye-sensitized solar cell applications as the dye molecules do not directly adsorb onto the TiO2 particle.

Photovoltaic properties of the flavonoid‐based photosensitizers: Molecular‐scale perspective on the natural dye solar cells

“…The naringenin‐based dye (set a ), and isorhamnetin‐ and quercetin‐based dyes (set b ) represent a more favorable kinetic behavior of the exciton formation and dissociation. Water molecules decrease the electronic charge transfer of the dyes and shorten the path of the electron transfer toward TiO 2 , through the hydrogen bond formation with the functional groups of the flavonoids …”

Influence of Solvent on Dye‐Sensitized Solar Cell Efficiency: What is so Special About Acetonitrile?

“…Reproduced with permission. [ 84 ] Copyright 2019, American Chemical Society.…”

“…The remainder of the review will focus on specific examples taken from our own works investigating the influence of various solvents on critical DSSC characteristics. Specifically, we show how the type of solvent (i.e., protic or aprotic) and solvent polarity affect dye adsorption free energy and density, [83,84] as well as the injection rate of electrons from excited dye molecules to TiO 2 particles. [85] By combing these prior observations, we present a holistic and comprehensive understanding on how the solvent used may affect the efficacy of DSSC.…”

“…b)The normalized SHS intensity of p-ER onto TiO 2 in the three solvents. Reproduced with permission [84]. Copyright 2019, American Chemical Society.…”

“…The normalized SHS signal from a sample containing 10 × 10 −6 m p-ER in the TiO 2 in ACN colloid as a function of EtOH concentration added. The decrease of the SHS signal indicates that EtOH can displace adsorbed p-ER molecules from the TiO 2 surface in ACN.Reproduced with permission [84]. Copyright 2019 American Chemical Society.…”