Reusability in visible light of titanate nanotubes for the removal of organic pollutants: role of calcination temperature

ABSTRACT

Titanate nanotubes (NTs) were synthesised by the hydrothermal method and later calcined at temperatures between 100–500°C. The calcined NTs were characterised and evaluated in the physicochemical adsorption of the safranin dye and photocatalytic degradation of caffeine. The materials calcined at low temperatures displayed a tubular structure and the H₂Ti₃O₇ crystalline phase, which was transformed into anatase nanoparticles at 400°C. The NTs treated at 100°C showed the highest adsorption capacity (94%). Safranin was adsorbed through an ion-exchange mechanism, following the Langmuir isotherm and a pseudo-second-order kinetic model. While NTs calcined at lower temperatures were better for adsorption, the photocatalytic degradation of caffeine increased in samples calcined at higher temperatures with a maximum removal of 72%. The photocatalytic behaviour of the NT samples confirmed that the crystalline anatase structure in conjunction with structural OH groups enhanced the photocatalytic activity. The addition of isopropanol as a scavenger confirmed the important role played by the •OH radicals in the photocatalytic process. NTs calcined at 300°C were efficient for both adsorption and photocatalytic processes. Due to its efficiency, this sample was reused after dye adsorption for the photocatalytic degradation of caffeine under visible light due to its enhanced absorbance in the visible region. This research work shows the potential of NTs for wastewater purification.

GRAPHICAL ABSTRACT

KEYWORDS:

• Titanate nanotubes
• calcination temperature
• adsorption
• photocatalysis
• visible light

Acknowledgements

This work was supported by the SEP CONACYT-2014 S-2780 and CB-2010-01-153675 projects. M. Hinojosa-Reyes thanks the postdoctoral scholarship funding by Consejo Nacional de Ciencia y Tecnología (CONACYT). A.L. Ruiz-Castillo would like to acknowledge CONACYT for the doctoral scholarship. The authors thank Vicente Rodríguez González for the provided support and infrastructure at Instituto Potosino de Investigación Científica y Tecnológica (IPICYT).

Disclosure statement

The authors declare that there is not conflict of interest. There are neither competing financial interests nor personal relationships that could have appeared to influence the work reported in this paper.

Additional information

Funding

This work was supported by Consejo Nacional de Ciencia y Tecnología [grant number 289571].