Tailoring Band Gap and Light Absorption in M-TiNT (M= Cu2+, Ni2+, Co2+ and Fe3+) for Water Remediation

Abstract The need for effective wastewater treatment is critical, particularly in light of increasing environmental concerns and the prevalence of persistent organic pollutants. Among the various strategies developed to address this challenge, photocatalysis has emerged as a promising approach due to its potential for sustainable and efficient pollutant degradation. In this context, developing novel photocatalytic materials remains a research priority. In the present study, we explore the simultaneous incorporation of transition metal cations (Cu²⁺, Ni²⁺, Co²⁺, and Fe³⁺) into the crystalline structure of titanate nanotubes (H₂Ti₃O₇, TiNT) via a simple ion-exchange method. This modification also facilitates the formation of an n–p heterostructure between TiNT and the respective metal oxides (CuO, NiO, CoO, and Fe₂O₃). Notably, the incorporation of metal cations results in a significant reduction of the band gap from 3.3 eV to 1.5 eV. At the same time, the formation of n–p heterojunctions contribute to the appearance of a new absorption feature. Together, these modifications effectively extend the light absorption capability of the material into the visible region. The photocatalytic activity of the resulting M-TiNT semiconductors was evaluated for the degradation of ibuprofen and indigo carmine, under UV and visible light irradiation. The observed enhancement in photocatalytic efficiency is directly correlated with improved light absorption and increased charge carrier density, contributing to the generation of reactive redox species. These findings offer valuable insights into the design of nanostructured semiconductors for environmental remediation and highlight the potential of metal-doped TiNTs as efficient and versatile photocatalysts.