Background: In this work, a detector based on optical fiber covered with Multi-Wall Carbon
Nanotubes (MWCNTs) was used for sensing and removal of Alizarin from wastewaters. Alizarin
is a strong anionic red dye that is part of the anthraquinone dye group. As a rule, this dye is used in the
textile industry as a coloring agent. Experiments showed a good efficiency of wastewater treatment.
This development could resolve the problem of water contamination with Alizarin red dye.
Methods: We used a single-mode fiber SMF-28e with a core diameter of 8.2 μm and a cladding diameter
of 125 μm as a base for the tapered optical fiber detector. An MWCNTs array was synthesized on
the tapered optical fiber detector surface by spray pyrolysis Chemical Vapor Deposition (CVD) method
at 800oC for 20 min inside a tubular furnace, using ferrocene solution in toluene as a catalyst precursor.
The formed structure was applied for Alizarin detection in water.
Results: According to the patent studies, the nanotubes completely covered the optical fiber surface
and the array had a high density with minimal distance between nearby nanotubes. Carbon nanotubes
were oriented along the radius of the optical fiber. The average diameter of carbon nanotubes was 24
nm. The optical absorbance levels increased as the Alizarin concentration increased from 50 mg/L to
1000 mg/L. MWCNTs on the optical fiber tapered section adsorbed the dye molecules from aqueous
solution. Three intensive absorption bands with the wavelength of the 700, 714 and 730 nm appeared
and their intensity increased as the Alizarin concentration increased. The accumulated Alizarin can be
recovered by multiple immersing clean water. This property may make tapered optical fiber detector
reusable and increase the economic expediency of the sensor application.
Conclusion: The study showed higher Alizarin adsorption efficiency of the tapered optical fiber detector
compared with relative detectors. This structure can be reusable for dye detection. Removal efficiency
for Alizarin reached 98.6%, which makes the tapered optical fiber detector promising for
wastewater treatment and dye elimination.