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. 2023 May 6;26(6):106833.
doi: 10.1016/j.isci.2023.106833. eCollection 2023 Jun 16.

Efficient photodegradation of polystyrene microplastics integrated with hydrogen evolution: Uncovering degradation pathways

Jiehong He  1   2 , Lanfang Han  1   2 , Weiwei Ma  1 , Liying Chen  1 , Chuanxin Ma  1   2 , Chao Xu  3 , Zhifeng Yang  1   2
Affiliations

Efficient photodegradation of polystyrene microplastics integrated with hydrogen evolution: Uncovering degradation pathways

Jiehong He et al. iScience. .

Abstract

Photocatalytic microplastics (MPs) conversion into valuable products is a promising approach to alleviate MPs pollution in aquatic environments. Herein, we developed an amorphous alloy/photocatalyst composite (FeB/TiO2) that can successfully convert polystyrene (PS) MPs to clean H2 fuel and valuable organic compounds (92.3% particle size reduction of PS-MPs and 103.5 μmol H2 production in 12 h). FeB effectively enhanced the light-absorption and carrier separation of TiO2, thereby promoting more reactive oxygen species generation (especially ‧OH) and combination of photoelectrons with protons. The main products (e.g., benzaldehyde, benzoic acid, etc.) were identified. Additionally, the dominant PS-MPs photoconversion pathway was elucidated based on density functional theory calculations, by which the significant role of ‧OH was demonstrated in combination with radical quenching data. This study provides a prospective approach to mitigate MPs pollution in aquatic environments and reveals the synergistic mechanism governing the photocatalytic conversion of MPs and generation of H2 fuel.

Keywords: Applied chemistry; Interface science; Physical inorganic chemistry.

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Conflict of interest statement

The authors declare no competing interests.

Figures

None
Graphical abstract
Figure 1
Figure 1
Structural characterization of samples (A) X-ray diffraction (XRD) patterns of CST, FeB, and xFBT. (B–E) Scanning electron microscope (SEM) images of CST (B and C) and 7FBT (D and E). (F–I) Transmission electron microscopy (TEM) images of 7FBT with different scales. (J) Elemental mapping images of 7FBT. Note that CST, FeB, 7FBT were short for core-shell structured TiO2, iron boron amorphous alloy, FeB/TiO2 composites with 7 % theoretical mass ratio of Fe, respectively.
Figure 2
Figure 2
X-ray photoelectron spectroscopy (XPS) spectra of samples (A–D) XPS spectra for the (A) Ti 2p, (B) O 1s, (C) Fe 2p, and (D) B 1s levels of CST, FeB, and 7FBT. Note that CST, FeB, 7FBT were short for core-shell structured TiO2, iron boron amorphous alloy, FeB/TiO2 composites with 7 % theoretical mass ratio of Fe, respectively.
Figure 3
Figure 3
Photoelectrochemical characterization of samples (A and B) UV-vis diffuse reflection spectra (UV-vis DRS) (A) and the corresponding plots of (αhν)1/2 as a function of hν (B). (C) Steady-state fluorescence spectra at an excitation wavelength of 350 nm. (D) Photocurrent response spectra under irradiation by a 300 W Xe lamp. (E) Electrochemical impedance analysis with the equivalent circuit diagram in the inset. CPE: constant phase element; Rs: diffusion electric resistance; Rct: charge transfer resistance. (F) Luminescence decay curves with the enlarged patterns in the inset (excitation wavelength = 350 nm). τ: the average lifetime.
Figure 4
Figure 4
The performance of photocatalytic polystyrene microplastics (PS-MPs) degradation synergetic H2 production (A and B) Average particle size reduction (A) and corresponding In(D0/Dt)-time plot (B) on FeB, CST, and xFBT. (C and D) Carbonyl index (C) and H2 production (D) on FeB, CST, and xFBT. Note that “D0” and “Dt” presented the average diameter of the original and degraded MPs particles during the photocatalytic reaction. CST, FeB, xFBT were short for core-shell structured TiO2, iron boron amorphous alloy, FeB/TiO2 composites with x % theoretical mass ratio of Fe, respectively. Data are represented as mean ± SEM.
Figure 5
Figure 5
Reactive oxygen species identification and mechanism investigation (A and B) Average particle size reduction (A) and H2 production (B) on 7FBT under different conditions. (C) Electron paramagnetic resonance (EPR) spectrum of ⋅OH. (D) Plausible mechanism for the photocatalytic polystyrene microplastics (PS-MPs) degradation synergetic H2 evolution. Note that CST, FeB, 7FBT were short for core-shell structured TiO2, iron boron amorphous alloy, FeB/TiO2 composites with 7 % theoretical mass ratio of Fe, respectively. Data are represented as mean ± SEM.
Figure 6
Figure 6
Reaction pathways and related theoretical calculations (A–C) The pathway of photocatalytic polystyrene microplastics (PS-MPs) degradation including chain initiation (A), propagation (B), and termination (C). (D) Potential energy diagram from density functional theory (DFT) calculations of PS-MPs degradation. Note that TS is short for transition state.
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