Mechanistic insights into CTAB assisted TiO2 crystal growth with largely exposed high energy crystal facets

Abstract

Pristine anatase titanium dioxide (TiO2) photocatalysts were prepared by a modified hydrothermal method using cetyltrimethylammonium bromide (CTAB) as the capping agent. The so-formed TiO2 crystals showed superhydrophilic behavior in a short irradiation time span, without adopting any modifications to TiO2 like doping or hybridizing with organic monolayers. At an optimum pH of 3, the CTAB molecules were effectively adhered to the high energy facets of TiO2 favoring a crystal growth elongation in [001] direction leading to the exposure of high energy {101}/{100} and {001} facets. Variations in crystal morphology, size and exposing facets are investigated in detail using XRD, Raman and TEM, whereas the optical properties are studied using UV–vis diffuse reflectance spectroscopy, PL and TSCPC techniques. Acetic acid acting as a bridging ligand attaching the Ti centres in a twisted conformation effectively led to the anatase phase of TiO2. The shape and size of the CTAB micelles were greatly dependent on the pH of the reaction system, which in turn decided the exposure percentage of different facets. Anatase TiO2 prepared at optimum pH 3 were ellipsoidal and showed 83% photocatalytic degradation (k = 9.23 × 10−3 min-1) of Methylene Blue as the model dye, and the water contact angle of 17° under UV irradiation. When synthesis is repeated with double the quantity of water, TiO2 shared ellipsoidal and cuboidal morphologies and were superhydrophilic showing contact angle of 9° within 5 min UV irradiation, along with a superior photodegradation of 93% (k = 12.9 × 10−3 min-1).