The effect of ionic Co presence on the structural, optical and photocatalytic properties of modified cobalt–titanate nanotubes

Abstract

With the aim of producing materials with enhanced optical and photocatalytic properties, titanate nanotubes (TNTs) modified by cobalt doping (Co-TNT) and by Na(+)→ Co ion-exchange (TNT/Co) were successfully prepared by a hydrothermal method. The influence of the doping level and of the cobalt position in the TNT crystalline structure was studied. Although no perceptible influence of the cobalt ion position on the morphology of the prepared titanate nanotubes was observed, the optical behaviour of the cobalt modified samples is clearly dependent on the cobalt ions either substituting the Ti(4+) ions in the TiO6 octahedra building blocks of the TNT structure (doped samples) or replacing the Na(+) ions between the TiO6 interlayers (ion-exchange samples). The catalytic ability of these materials on pollutant photodegradation was investigated. First, the evaluation of hydroxyl radical formation using the terephthalic acid as a probe was performed. Afterwards, phenol, naphthol yellow S and brilliant green were used as model pollutants. Anticipating real world situations, photocatalytic experiments were performed using solutions combining these pollutants. The results show that the Co modified TNT materials (Co-TNT and TNT/Co) are good catalysts, the photocatalytic performance being dependent on the Co/Ti ratio and on the structural metal location. The Co(1%)-TNT doped sample was the best photocatalyst for all the degradation processes studied.

Tuning the band gap of M-doped titanate nanotubes (M = Fe, Co, Ni, and Cu): an experimental and theoretical study

“…The observed absorption redshi is attributed to the insertion of the metal 3d orbitals within the forbidden band and the subsequent charge-transfer transition between the d-electrons of the dopant and the conduction band of the Ti-NT. 34,48 In fact, it seems that there is a relationship between d-electrons of the transition metal and the light absorption properties of the materials; a lower number of delectrons corresponds to a higher absorption redshi. Besides, other absorption edges are observed in all the M-doped Ti-NT.…”

“…S1 †); by ion-exchange, the protonated titanates can be easily modied into M x H 2Àx Ti 3 O 7 , a transition-metal-doped protonated titanate. 47,48 Therefore, the substitution of hydrogen atoms for metal cations only should cause a change in the "a" lattice parameter and not in the other two parameters because the layers of (Ti 3 O 7 ) 2À remain untouched. It is worth to notice that no relationship between the "a" lattice parameter and the ionic radii of the metal was found.…”

Influence of Re and Ru doping on the structural, optical and photocatalytic properties of nanocrystalline TiO2

“…Among them, semiconductor heterogeneous photocatalysis has enormous potential to treat organic contaminants, having gained growing acceptance as an effective wastewater treatment method to degrade a broad variety of harmful compounds. Although a wide variety of semiconductors have been reported to be effective photocatalysts [4][5][6][7][8][9][10][11][12][13], TiO 2 is still the most widely used semiconductor in photocatalysis because it is a cost effective non-toxic compound, chemically and biologically inert, thermally stable, superhydrophilic, and capable of promoting the oxidation of numerous organic compounds [14][15][16][17][18][19][20].…”

Ruthenium-Modified Titanate Nanowires for the Photocatalytic Oxidative Removal of Organic Pollutants from Water

“…The prepared powders were analyzed by XRD using a Philips Analytical X-ray diffractometer and the experimental protocol described in ref . For crystallite size calculations, the acquisitions were done in the 5–15° 2θ range, using an acquisition time of 600 s/step.…”

“…For instance, to produce upgraded photocatalysts, by incorporating foreign active species, such as metallic or other cationic entities. , Depending on the synthesis methodology, these foreign metallic ions can replace Na + , and/or can substitute some Ti 4+ in lattice positions, or can be localized in interstitial sites. In this context, improvements on photocatalytic performance were recently obtained, using Co-modified titanate nanoparticles, with the dopant localized in two distinct positions: partial substitution of Ti 4+ and replacement of Na + in the interlayers …”