Promise Otuokere Master’s Thesis Defense, Tuesday, December 2, 2025 @ 11:00 am Central Time

COMMITTEE CHAIR: Dr. Yunxiang Gao

TITLE: DYE ADSORPTION ON CURVED CARBON LATTICES FOR SUSTAINABLE ENVIRONMENTAL AND ENERGY APPLICATIONS

ABSTRACT: Dye contamination in industrial wastewater remains a major environmental challenge, requiring selective and reusable treatment materials. This study comprehensively evaluates the adsorption performance and surface interactions of pristine and acid-modified single-walled carbon nanotubes (SWCNTs) for removing cationic dyes. Using UV-Vis, FT-IR, and Raman spectroscopy, the effects of HF and HCl treatments on dye adsorption and electronic structure were analyzed. Pristine SWCNTs demonstrated strong adsorption, following the selectivity order: methylene green > crystal violet > malachite green > methylene blue. Adsorption involved conjugated electron p-p stacking and electrostatic forces. A complementary investigation utilizing Surface-Enhanced Raman Scattering (SERS) provided molecular mechanistic insight into Crystal Violet (CV) adsorption. SERS revealed a strong chemical enhancement mechanism governed by an interfacial charge transfer (ICT) resonance at 1.96 eV (633 nm Raman laser excitation). This excitation triggered a massive, selective enhancement of non-totally symmetric torsional modes, such as the 205 cm?¹ propeller torsion vibration. This phenomenon confirms the Herzberg-Teller vibronic coupling principle, where skeletal torsion breaks molecular symmetry to enable the electron transition between the metallic nanotube and the dye LUMO. The SERS response was concentration-dependent, exhibiting a “geometric switch”: the signal vanished at low coverage (0.1 ppm) due to the possible flat-on-substrate geometric locking and ultrafast energy transfer, but was enabled at high coverage (50 ppm) by crowding-induced torsional freedom. Collectively, the results define design rules that processing history, morphology, and electronic structure to both adsorption and chemical SERS enhancement. By toggling excitation energy (electronic resonance) and surface state (protonation/defects vs densification), SWCNT platforms can be engineered for selective dye capture, rapid regeneration, and symmetry-forbidden mode readout—advancing recyclable nanocarbon adsorbents for wastewater treatment and mechanism-aware molecular sensing.

Keywords: Carbon nanotubes, dye adsorption, Raman spectroscopy (SERS), Hofmeister Effect, Wastewater remediation

Room Location: E.E. O’Banion Science Building, Room 203