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. 2021 May 25;6(22):14493-14503.
doi: 10.1021/acsomega.1c01458. eCollection 2021 Jun 8.

Titanium Dioxide/Polyvinyl Alcohol/Cork Nanocomposite: A Floating Photocatalyst for the Degradation of Methylene Blue under Irradiation of a Visible Light Source

Nurul Hidayah Mohamad Idris  1 , Jayalakshmi Rajakumar  1 , Kuan Yew Cheong  2 , Brendan J Kennedy  3 , Teruhisa Ohno  4 , Akira Yamakata  5 , Hooi Ling Lee  1   3
Affiliations

Titanium Dioxide/Polyvinyl Alcohol/Cork Nanocomposite: A Floating Photocatalyst for the Degradation of Methylene Blue under Irradiation of a Visible Light Source

Nurul Hidayah Mohamad Idris et al. ACS Omega. .

Abstract

Photocatalytic degradation by the titanium dioxide (TiO2) photocatalyst attracts tremendous interest due to its promising strategy to eliminate pollutants from wastewater. The floating photocatalysts are explored as potential candidates for practical wastewater treatment applications that could overcome the drawbacks posed by the suspended TiO2 photocatalysis system. The problem occurs when the powdered TiO2 applied directly into the treated solution will form a slurry, making its reuse become a difficult step after treatment. In this study, the immobilization of titanium dioxide nanoparticles (TiO2 NPs) on the floating substrate (cork) employing polyvinyl alcohol (PVA) as a binder to anchor TiO2 NPs on the surface of the cork was carried out. Characterizations such as Fourier transformer infrared, X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-vis), zeta potential, photoluminescence spectroscopy, femtosecond to millisecond time-resolved visible to mid-IR absorption spectroscopy, ion chromatography, and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) analyses were employed. XRD analysis revealed the formation of anatase-phase TiO2 NPs. The results demonstrated that the crystallite size was 9.36 nm. The band gap energy of TiO2 NPs was determined as 3.0 eV. PL analysis verified that TiO2 NPs possessed a slower recombination rate of electron-hole pairs as compared to anatase TiO2. The result was attributed by the behavior of photogenerated charge carriers on TiO2 NPs, which existed as shallowly trapped electrons that could survive longer than a few milliseconds in this study. Furthermore, SEM-EDX analysis indicated that TiO2 NPs were well distributed on the surface of the cork. At the optimal mole ratio of TiO2/PVA (1:8), the TiO2/PVA/cork floating photocatalyst degraded at 98.43% of methylene blue (MB) under a visible light source which performed better than under sunlight irradiation (77.09% of MB removal) for 120 min. Besides, the mineralization result has measured the presence of sulfate anions after photocatalytic activities, which achieved 86.13% (under a visible light source) and 65.34% (under sunlight). The superior photodegradation performance for MB was mainly controlled by the reactive oxygen species of the superoxide radical (•O2 -). The degradation kinetics of MB followed the first-order kinetics. Meanwhile, the Langmuir isotherm model was fitted for the adsorption isotherm. The floating photocatalyst presented good reusability, resulting in 78.13% of MB removal efficiency even after five cycles. Our TiO2/PVA/cork floating photocatalyst fabrication and high photocatalytic performance are potentially used in wastewater treatment, especially under visible light irradiation.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
XRD spectrum of the as-synthesized TiO2 NPs. The Miller indices of the reflections are indicated.
Figure 2
Figure 2
FTIR spectrum of the as-synthesized TiO2 NPs.
Figure 3
Figure 3
SEM images of the (a) plain cork (250×), (b) plain cork (1000×), (c) TiO2/PVA/cork floating photocatalyst (250×), and (d) TiO2/PVA/cork floating photocatalyst (1000×).
Figure 4
Figure 4
Absorption of the as-synthesized TiO2 NPs, and the inset shows the band gap.
Figure 5
Figure 5
PL spectra of the as-synthesized TiO2 NPs and anatase TiO2 with an excitation wavelength of 300 nm.
Figure 6
Figure 6
Plot of zeta potential vs pH for the as-synthesized TiO2 NPs.
Figure 7
Figure 7
Degradation efficiency of MB under the irradiation of the light source with TiO2/PVA mole ratios of 1:6, 1:8, and 1:10 (n = 3).
Figure 8
Figure 8
First-order linear transforms ln(C0/Ct) of MB degradation plots against time for mole ratios (TiO2/PVA) of 1:6, 1:8, and 1:10.
Figure 9
Figure 9
Degradation efficiency of MB under the irradiation of sunlight and visible light source with a TiO2/PVA ratio of 1:8 (n = 3).
Figure 10
Figure 10
First-order linear transform ln(C0/Ct) of MB degradation plots against time for the irradiation of the visible light source and sunlight with a mole ratio of 1:8.
Figure 11
Figure 11
Langmuir isotherm showing the variation of adsorption (Ce/qm) against the equilibrium concentration (Ce) for adsorption of the TiO2/PVA/cork floating photocatalyst.
Figure 12
Figure 12
Freundlich isotherm showing the variation of adsorption (ln qe) against the equilibrium concentration (ln Ce) for adsorption of the TiO2/PVA/cork floating photocatalyst.
Figure 13
Figure 13
Radical scavenging test of the TiO2/PVA/cork floating photocatalyst using methanol, acetonitrile, silver nitrate, sodium pyruvate, and ascorbic acid (n = 3).
Figure 14
Figure 14
Transient absorption spectrum of the as-synthesized TiO2 NPs measured in 20 Torr N2 after 450 nm laser pulse (5 mL/pulse at 5 Hz) irradiation. The negative signal at 3500–2800 cm–1 is due to the desorption of water.
Scheme 1
Scheme 1. Schematic of the Band Gap Structure of TiO2 NPs and the Proposed Degradation Mechanism of Methylene Blue under Visible Light Irradiation
Figure 15
Figure 15
Reusability test of the TiO2/PVA/cork floating photocatalyst (n = 3).
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