Synthesis and Characterisation of Unitary, Binary and Ternary Photocatalysts Based on Polyaniline, Tin Oxide and Multiwalled Carbon Nanotube for the Photodegradation of the Toxic Dye RB5

Low, Wai Leon (2026) Synthesis and Characterisation of Unitary, Binary and Ternary Photocatalysts Based on Polyaniline, Tin Oxide and Multiwalled Carbon Nanotube for the Photodegradation of the Toxic Dye RB5. Doctoral thesis, Tunku Abdul Rahman University of Management and Technology.

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Abstract

The widespread use of azo dyes in the textile industry has raised environmental concerns due to their non-biodegradable and toxic nature. This thesis presents a comprehensive study on the synthesis and characterisation of unitary, binary and ternary photocatalysts based on polyaniline (PAni), tin oxide (SnO2), and multiwalled carbon nanotubes (MWCNTs) for the photodegradation of the toxic dye Reactive Black 5 (RB5). The research is structured into three phases: first, the fabrication of unitary photocatalyst (PAni); second, the synthesis of binary photocatalysts (PAni-SnO2 with varying SnO2 loadings and PAni-MWCNT); and third, the development of ternary photocatalysts (PAni-SnO2-MWCNT based on the best performed binary photocatalyst PAni-SnO2) with different MWCNT weight percentages, all via a template-free method. Characterisation techniques, including Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-Vis) spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), conductivity analysis and Brunauer-Emmett-Teller (BET) nitrogen physisorption analysis, were employed to validate chemical structure, oxidation states, morphological features, electrical conductivity, surface area and pore morphology. Electrical conductivity measurements revealed enhanced conductivity for the ternary photocatalyst (PAni-SnO2-MWCNT), with values ranging from 3.29 × 10-3 to 4.42 × 10-2 S cm-1, which is significantly higher than that of the binary photocatalysts (PAni-SnO2) (6.55 × 10-6 – 2.66 × 10-3 S cm-1). Meanwhile, the optical properties – specifically the band gap energy and electron-hole recombination rate – of both binary and ternary photocatalysts were studied using a diffuse reflectance ultraviolet-visible-near-infrared (DR UV-vis-NIR) spectrophotometer and a photoluminescence (PL) Spectrometer. The photocatalytic performance of the unitary, binary and ternary photocatalysts was evaluated based on the degradation efficiency of RB5 dye under xenon light irradiation. The binary photocatalyst PAni-SnO2 (10 %), denoted as PS10, achieved a maximum photodegradation efficiency of 72.94 %, attributed to its nanotubular morphology, optimal surface area (28.09 m2 g-1), high conductivity (2.66  10-3 S cm-1), low band gap (1.98 eV), and reduced electron-hole recombination (as evidenced by low PL intensity, 7.29  103 a.u.). In contrast, the ternary photocatalyst PAni-SnO2-MWCNT (20 %), denoted as PSM20, demonstrated a superior photodegradation efficiency of 94.12 %, attributed to the synergistic interaction between PAni, SnO2 and MWCNT, which results in improved charge separation (i.e. a low electron-hole recombination rate with a PL intensity 1.52  104 a.u.), enhanced visible light absorption, and increased dye adsorption capacity. Further validation work on the photocatalytic performance of PSM20 was also conducted. It was found that 15 mg of PSM20 demonstrated excellent photodegradation of 97.92 % under the following optimum photodegradation conditions: 40 min dark adsorption time, 90 min light reaction time, and 10 ppm RB5 solution at pH 6. Long-term stability studies showed that PSM20 remained photocatalytically active over a 6-month period, with the percentage photodegradation of RB5 varying between 92.36 % and 96.67 %. In terms of recyclability, PSM20 retained approximately 80 % of its initial photodegradation efficiency after three cycles. In summary, this work underscores the potential of PAni-based photocatalysts, particularly the ternary photocatalyst (PAni-SnO2-MWCNT) system, as effective photocatalysts with high potential for the remediation of dye-laden industrial wastewater.