Photocatalytic Decomposition of an Alkylammonium Cation in a Langmuir−Blodgett Film of a Titania Nanosheet

Abstract

The formation of inorganic-organic hybrid films of a titania nanosheet and an amphiphilic alkylammonium cation has been investigated, and the photocatalytic decomposition of the alkylammonium cation in the film has been pursued. When a solution of the amphiphilic alkylammonium salt (octadecylammonium chloride: ODAH+ Cl-) was spread on an interface between the air and a titania nanosheet suspension, the negatively charged nanosheets were adsorbed onto the floating monolayer of ODAH+ to form a hybrid monolayer. The hybridization was confirmed by pi-A isotherm measurements, atomic force microscopy, and X-ray photoelectron spectroscopy. Multilayered films were fabricated in a layer-by-layer way by transferring the hybrid monolayers onto glass plates. Areas per ODAH+ cation in the films were estimated from the infrared (IR) spectra of the films, but these areas were smaller than those estimated from the pi-A isotherm curves. The orientation of the alkyl chain of ODAH+ in the hybrid film was determined by means of polarized IR spectroscopy. The alkyl chains were tilted 41 +/- 1 degrees and 47 +/- 1 degrees from the surface normal for the films prepared from the 8 and 20 ppm (ppm = mg dm(-3)) suspensions, respectively. Together with X-ray diffraction data of the films, the structure of the hybrid film was discussed. When the films were illuminated with a UV light, the absorption intensities due to the alkyl chain of ODAH+ decreased exponentially, indicating the photocatalytic decomposition of ODAH+ by the titania nanosheets in the films. Deviation from the exponential trend in the decomposition rate was observed in the initial period for the hybrid films prepared from the suspensions at low concentrations. Interestingly, the layered structure of the hybrid film was disturbed significantly after the ODAH+ cations were decomposed.

Recent development in 2D materials beyond graphene

“…In the typical LB deposition process, a monolayer of nanosheets is formed on the liquid surface by the careful maneuver of LB trough arms. Uniform dispersion of nanosheets in water usually achieved using surfactants [517,[557][558][559][560]. Movement of LB trough arms create sufficient/optimum compression to make dense monolayer.…”

Photoinduced electron accumulation in colloidally dispersed wide band-gap semiconductor nanosheets

“…No spectral alteration is observed before and after the irradiation, indicating that the niobate(e -) species does not form in the absence of propylammonium ions. A previous study has also reported oxidative photocatalytic decomposition of alkylammonium ions over niobate nanosheets [15].…”

“…Since the exfoliated nanosheets easily reform layered solids with appropriate techniques such as layer-by-layer assembling, various photoactive nanomaterials have been constructed by restacking the exfoliated niobate and titanate nanosheets [9,12]. Photofunctions observed for these nanoassemblies are photocatalysis [13][14][15], photoinduced electron and energy transfer [16], photoinduced hydrophilic conversion [17], and photocurrent generation [18]. On the other hand, the exfoliated nanosheets of the layered niobates and titanates can exhibit characteristic photochemical behavior in the colloidal system that is the ''as-prepared state" of the nanosheets.…”

Soft Langmuir–Blodgett Technique for Hard Nanomaterials

“…Umemura and coworkers demonstrated the formation of inorganic-organic hybrid films of a titania nanosheet and an amphiphilic alkylammonium cation and the photocatalytic decomposition of the alkylammonium cation in the film. [112] It was revealed that the titania nanosheet in the hybrid film decomposed octadecylammonium chloride by UV-light illumination, indicating photocatalytic activity of titania nanosheet even when contained in the hybrid film. The decomposition proceeded exponentially.…”