Charge transfer tuning in TiO₂hybrid nanostructures with acceptor–acceptor systems

Abstract

An interesting interplay between two different modifiers and the surface of titanium dioxide leads to a significant change in photoelectrochemical properties of the designed hybrid materials. The semiconductor is photosensitized by one of the counterparts and exhibits the photoelectrochemical photocurrent switching effect thanks to interactions with graphene oxide -the second modifier mediates charge transfer processes in the system, allowing us to design the materials response at the molecular level. Based on the selection of molecular counterpart we may affect the behaviour of hybrids upon light irradiation in a different manner, which may be useful for the applications in photovoltaics, optoelectronics and photocatalysis. Here we focus particularly on the nanocomposites made of titanium dioxide with graphene oxide combined with either 2,3,5,6-tetrachlorobenzoquinone or 2,3-dichloro-5,6-dihydroxybenzoquinone -for these two materials we observed a major change in the charge transfer processes occurring in the system.

Light intensity-induced photocurrent switching effect

“…We have already mentioned that the most pronounced changes may be noticed in the oxygen-rich electrolytes-particularly, the strong amplification of cathodic photocurrents occurs when CA is present in the system and this effect is additionally enhanced upon the addition of COH. This observation is in agreement with previous investigations of TiO 2 , CdS and PbMoO 4 modified with CA or various anthraquinone dyes 12,13,30,31 . In these systems, depending on the applied potential, oxidation of water or reduction of dissolved oxygen can occur, which leads to the potential/wavelength photocurrent switching.…”

“…7c, d). It is generally consistent with a strongly acceptor character of CA and the mechanism behind the photocurrent switching may be of a similar nature as discussed in our previous works 12,13 . Additional, clear evidence for this new, strong interaction between ZnO surface and modifiers may be found in FTIR spectra-significant shifts and/or partial quenching of absorption bands originating from hydroxyl and carbonyl groups of CA may be noticed ( Supplementary Fig.…”

“…7b, d and f) -which are literally constructed from snapshots of the samples response in a state of the thermodynamic equilibrium-that upon modification with CA and CA-COH system the efficiency of the cathodic photocurrent generation process rises at the negative electrode potentials. It has been previously reported 13 that the presence of quinone derivatives may facilitate electron transfer to oxygen species in electrolyte, thus the photocurrent map profile from Supplementary Fig. 7d is easily explainable.…”

“…[9][10][11] , but may be also induced by an appropriately designed surface modification with organic compounds (e.g. anthraquinone derivatives) 12 and/or carbon nanostructures 13 .…”

Electrodeposition of Composite Ni-TiO2 Coatings from Aqueous Acetate Baths

“…In addition, hydrogen combustionresults in water formation, making it the most environmentally friendly available energy carrier. The location of nickel on the DH Me-H À log(i 0 ) dependence as well as the properties of specially photosensitized and modified TiO 2 , [3,4] and its resistance to photo corrosion, semiconducting properties as well as its efficiency of UV-Vis absorption allow for the assumption that a combination of these materials may allow for the synthesis of composites of the required properties suitable for photocatalytic water splitting. Common routes concerning the design of materials for hydrogen generation by water splitting are focused on platinum group metal (PGM) alloys, [5][6][7][8] or the synthesis of new PGM-free alloys, [9,10] semiconductors, [11,12] or metal-semiconductor composite materials.…”