Adsorption Studies Of Acetaldehyde On TiO2 Nanosurface

Department of Chemistry, University of Delhi, Delhi 110007, India

Adv. Mater. Lett., 2013, 4 (10), pp 769-778

DOI: 10.5185/amlett.2013.2424

Publication Date (Web): Oct 13, 2013

Copyright © IAAM-VBRI Press

E-mail: rkakkar@chemistry.du.ac.in

Abstract

The present work deals with the adsorption of acetaldehyde, one of the most harmful volatile organic compounds (VOCs), on the TiO₂ anatase nanosurface. The research was undertaken due to environmental concerns, as the TiO₂ nanosurface serves as an excellent catalyst for the adsorption and decomposition of VOCs. The chemistry of aldehydes on metal oxides is complex and elaborate, as it can result in a variety of reactions, such as selective oxidation, alcohols disproportionation, etherification and reductive coupling to higher olefins. The structural properties of the various nanosurfaces were first examined and finally adsorption studies were made on the (TiO₂)17 cluster, as it shows least reconstruction and offers all kinds of coordination sites for the study. It is found that a myriad of different adsorption products are formed on the TiO₂ nanosurface, depending upon the coordination site. The low coordination (3c) sites are highly reactive and form stronger bonds with the acetaldehyde molecule, whereas adsorption at the four coordination site leads to the reconstruction of the nanosurface. Acetaldehyde chemisorbs onto the surface producing zwitterionic four-membered rings, in which the carbonyl C=O bond is considerably weakened, or it adsorbs on the TiO₂ surface in a H-bridge bonded form. The most feasible mode of adsorption on the TiO₂ nanosurface is found to be methyl hydrogen migration resulting in the formation of [CH2-C(H)O] species, which may further undergo transformation by β-aldolization to yield crotonaldehyde and butane. Other products investigated in this work include oxidation to acetate and reduction to ethoxy species. The results obtained in this work can be of significant help in deciding the fate of reaction of acetaldehyde on the TiO₂ nanosurface, and using it for decomposition of acetaldehyde to benign products.

Keywords

TiO₂ anatase nanosurface, adsorption on nanocrystals, acetaldehyde, density functional theory.