The role of cationic surfactant in the photocatalytic properties of sodium and hydrogen titanates heterojunctions

In this work, we have investigated the photoluminescent and photocatalysis properties of sodium and hydrogen titanate heterojunctions obtained in the hydrothermal microwave assisted method. The influence of a cationic surfactants cetyltrimethyl ammonium bromide (CTAB) and hexamethylene tetramine (HMTA) was investigated compared to the pure titanate. Structural analysis revealed the formation of two crystalline phases, hydrogen titanate and sodium titanate, and that the insertion of the CTAB surfactant influences the direction of the crystalline plane (201) of the sodium titanate phase. Electronic results showed that surfactants influence the band gap energy and photoluminescent emission depending on the crystalline structure and crystallite size of the material. The samples synthesized in the presence of cationic surfactants (CTAB and HMTA) show greater contribution of emission peaks in the blue region, which may be associated with cluster distortions, originating shallow-level defects within the crystalline lattice, while for pure titanate a strong green emission suggests deep-level originate from oxygen vacancies. The photocatalytic activity of the samples modified with CTAB and HMTA showed similar efficiencies (∼85 % discoloration in 15 min of activity). The article demonstrates the mechanism of action of surfactants on the titanate structure and their influence on photonic and photocatalytic properties.