Hydrothermal Synthesis of K2Ti6O13 Nanotubes/Nanoparticles: A Photodegradation Study on Methylene Blue and Rhodamine B Dyes

Abstract

The degradation of methylene blue and rhodamine B dyes using potassium hexatitanate nanoparticles (KTNPs) and potassium hexatitanate nanotubes (KTNTs) synthesized via a hydrothermal method as efficient photocatalysts under UV light irradiation was investigated. The kinetics of degradation was determined for the two different catalysts--KTNPs and KTNTs--by monitoring the optical absorption of the dyes. The as-synthesized KTNPs were found to be spherical in shape with an average particle size of ∼36 ± 1.7 nm, whereas the KTNTs evidenced a tubular hollow structure with ∼7 nm internal diameter and ∼12 nm external diameter, as perused by structural and morphological studies. The larger surface area of KTNTs showed a greater impact on the photodegradation of dyes manifesting their high potential as compared to KTNPs under UV irradiation, and the reusability studies showed more than 90% (KTNTs) and 80% (KTNPs) degradation of the dyes even after the fourth cycle elucidating their stability.

Figure 1

Crystal structure of potassium titanate (K₂Ti₆O₁₃) nanotubes.

Figure 2

Schematic representation of the synthesis process flow of potassium titanate nanotubes.

Figure 3

Intensity vs 2θ profile obtained for KTNTs/KTNPs revealing the monoclinic phase structure of K₂Ti₆O₁₃ with the c2/m space group.

Figure 4

EDAX profile: (a,d) as-synthesized KTNPs and KTNTs with elemental analysis (inset), respectively. SEM images: (b,c) as-synthesized KTNPs and KTNTs, respectively. TEM images: (e) d-spacing of the (200) crystallographic planes of the monoclinic structure of KTNTs and (f) as-synthesized KTNTs with magnifications of 2 and 10 nm, respectively.

Figure 5

(a) FTIR transmittance spectra and (b) band gap determination from the UV–vis absorption spectra (inset) of the as-synthesized KTNPs and KTNTs.

Figure 6

Schematic representation of the photocatalytic activity of KTNTs/KTNPs.

Figure 7

(a,d) Percentage degradation vs time (min); (b,c,e,f) absorbance vs wavelength (nm); (g,h) photocatalytic activity plot of C/C₀ vs irradiation time (min); and (i,j) rate constant of the photocatalytic activity.

Figure 8

Trapping experiment plot (a). Concentration C/C₀ vs time (min) (b). Percentage degradation of dye vs scavengers.

Figure 9

BET surface area plots: relative pressure P/P₀ vs P/V_a(P₀ – P) of (a) KTNPs and (b) KTNTs.

Figure 10

Plot of percentage degradation vs number of reusability runs of (a) KTNPs and (b) KTNTs.