双功能离子液体催化剂实现废弃聚苯乙烯向苯甲酸的高效光氧化升级回收

doi:10.1016/S1872-2067(26)64984-4

摘要/Abstract

摘要：

塑料污染已成为全球性的环境挑战, 其中聚苯乙烯(PS)作为一种被广泛应用的通用塑料, 由于其具有化学惰性的碳-碳骨架和稳定的苯环结构, 废弃后极难自然降解. 目前全球PS的回收率不足1%, 造成了严重的白色污染和产生微塑料的潜在环境风险. 传统的化学回收方法(如热裂解)通常需要高温高压, 能耗高且产物分布复杂、选择性低; 而生物降解速率缓慢, 难以满足处理需求. 近年来, 光催化氧化技术因其温和的反应条件备受关注, 但如何实现聚合物长链的快速断裂与中间体的高选择性氧化仍是主要瓶颈. 因此, 开发一种在温和条件下能高效、高选择性地将废弃PS转化为高附加值化学品(如苯甲酸)的催化体系, 对于缓解环境压力和推动碳资源的循环利用具有重要意义.
针对上述挑战, 本文设计并合成了一种双功能离子液体催化剂, 由4-苯磺酸吡啶鎓三氟甲磺酸盐([BSPy][OTf])与三氟甲磺酸铁热混合构建, 红外光谱、拉曼光谱及X射线光电子能谱证实, 三价铁离子(Fe³⁺)与三氟甲磺酸根阴离子之间存在直接的配位作用, 构建了布朗斯特酸位点与路易斯酸位点在微观上紧密邻近的协同催化环境. 结果表明, 在室温(25 °C)、常压氧气和405 nm LED蓝光照射的温和条件下, 该催化剂在乙腈/二氯甲烷溶剂中反应24 h, 可将聚苯乙烯高效转化为苯甲酸, 产率可达76.43%, 显著优于单一组分三氟甲磺酸铁或[BSPy][OTf])及其物理混合物(产率仅为50.71%), 强有力地证实了结构集成带来的协同效应. 机理研究显示, 该反应遵循“单电子转移断链-单线态氧氧化”的双路径协同机制: (1)快速断链阶段: 凝胶渗透色谱显示, 反应初期(前4 h)PS分子量急剧下降, 离子液体中的Fe³⁺通过单电子转移机制诱导聚合物主链C-C键和C-H键断裂, 生成低分子量的含氧中间体; (2)选择性氧化阶段: 布朗斯特酸性离子液体组分通过质子化辅助的光敏化过程, 高效产生单线态氧, 这些中间体通过单线态氧(¹O₂)进一步转化为苯甲酸. 该反应路径也得到动力学同位素效应实验与密度泛函理论计算结果的支持. 紫外-可见光谱和电子顺磁共振光谱分析进一步证实了催化剂促进¹O₂生成的能力. 该方法同样适用于消费后聚苯乙烯废塑料, 所得苯甲酸产率在56.01%‒74.57%. 催化剂通过简单的液液萃取即可回收, 循环使用5次后活性未见明显衰减, 具有良好的回收性和工业应用潜力.
综上, 本文提出了一种基于机理导向的双功能离子液体催化策略, 成功实现了在室温光照下将废弃聚苯乙烯转化为高价值有机化学品. 该工作阐明了金属中心引发的断链与离子液体光敏化氧化之间的时空协同机制, 为废塑料的化学循环利用提供了一条低能耗、高原子经济性的新途径, 有助于推动塑料循环碳经济的发展.

关键词: 聚苯乙烯升级回收, 酸性离子液体催化剂, 光氧化降解, 单线态氧, 单电子转移, 消费后塑料废物

Abstract:

Polystyrene, a widely used yet chemically inert plastic, poses major recycling challenges due to its low degradability and global recovery rate below 1%, calling for innovative upcycling strategies under mild conditions. Herein, we report a dual-functional ionic liquid catalyst, [BSPy][OTf]-Fe(OTf)₃, that enables room-temperature photooxidative upcycling of PS into benzoic acid with a yield of 76.43% in 24 h under an oxygen atmosphere. This catalytic performance is substantially higher than that of control systems using individual components or their physical mixture, indicating a strong synergistic effect. Mechanistic investigations revealed that Fe³⁺ in the ionic liquid initiates chain scission via a single-electron transfer process, generating oxidized intermediates. These intermediates are subsequently converted to benzoic acid through singlet oxygen, as supported by kinetic isotope effect studies and density functional theory calculations. The generation of singlet oxygen is facilitated by the ionic liquid catalyst, as confirmed by ultraviolet-visible and electron paramagnetic resonance spectroscopy. The approach is applicable to post-consumer Polystyrene products, with benzoic acid yields ranging from 56.01% to 74.57%. This study establishes a mechanistically guided strategy for low-energy, selective upcycling of PS, offering a viable alternative to conventional high-temperature or harsh-oxidant approaches.

Key words: Polystyrene upcycling, Acidic ionic liquid catalyst, Photooxidative degradation, Singlet oxygen, Single-electron transfer, Post-consumer plastic waste

王浩伊, 张延凯, 司春英, 齐运彪, 张全兴, 江伟. 双功能离子液体催化剂实现废弃聚苯乙烯向苯甲酸的高效光氧化升级回收[J]. 催化学报, 2026, 83: 231-243.

Haoyi Wang, Yankai Zhang, Chunying Si, Yunbiao Qi, Quanxing Zhang, Wei Jiang. Dual-functional ionic liquid catalysts for efficient photooxidative upcycling of polystyrene to benzoic acid[J]. Chinese Journal of Catalysis, 2026, 83: 231-243.

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链接本文: https://www.cjcatal.com/CN/10.1016/S1872-2067(26)64984-4

https://www.cjcatal.com/CN/Y2026/V83/I4/231

图/表 11

Scheme 1. (a) Previously reported pathways for PS photooxidation. (b) Photooxidation of alkyl aromatics mediated by BAILs. (c) This work: dual-pathway PS photooxidation enabled by ionic liquid catalyst.

Table 1 Reaction conditions optimization for PS photooxidation with Br?nsted acidic ILs a.

Entry	Catalyst ^b (mol%)	Solvent (3 mL)	T (h)	M_w ^c (g/mol)	PDI ^c	Yield ^d (mol%)
1	[BSPy][OTf] (100)	MeCN/CH₂Cl₂(1:2)	24	—^e	—	25.38
2	[BSPy][HSO₄^‒] (100)	MeCN/CH₂Cl₂(1:2)	24	21193	5.76	—
3	[BSPy][OTf] (100)	MeCN	24	260912	5.03	—
4	[BSPy][OTf] (100)	CH₂Cl₂	24	204066	6.32	—
5	[BSPy][OTf] (20)	MeCN/CH₂Cl₂(1:2)	24	—	—	9.21
6	[BSPy][OTf] (50)	MeCN/CH₂Cl₂(1:2)	24	—	—	17.28
7	[BSPy][OTf] (200)	MeCN/CH₂Cl₂(1:2)	24	—	—	28.46
8	[BSPy][OTf] (100)	MeCN/CH₂Cl₂(1:2)	48	—	—	48.35

Fig. 1. (a) Visual comparison of samples with varying Fe3+ loadings and chemical structure. (b) FT-IR spectra of [BSPy][OTf] with different Fe3+ loadings. Spectroscopic comparison of “pure IL” and “Fe-IL”: Raman spectra (c) and XPS survey (d) and high-resolution Fe 2p (e), C 1s (f), O 1s (g), and S 2p (h) spectra.

Fig. 2. (a) Benzoic acid yield with a Fe3+ loading range at 100 mol% [BSPy][OTf] loading. (b) Benzoic acid yield with a [BSPy][OTf] loading range at 2 mol% Fe3+ loading. (c) Catalytic performance comparison between structured catalyst and physical mixture. (d) 3D response surface of benzoic acid yield versus [BSPy][OTf] and Fe(OTf)3. (e) Comparison of PS photooxidation catalytic performance over [BSPy][OTf]-Fe(OTf)3 and catalysts from other literature. The data points, labeled Ref. 1-9 within the plot, are categorized as follows: Transition metal catalysis (blue diamonds), corresponding to: Ref. 1 (FeBr3) [30]; Ref. 2 (FeCl2) [31]; Ref. 3 (FeCl3) [32]. Selective acid catalysis (yellow circles), corresponding to: Ref. 4 (HOTf) [50]; Ref. 5 (PPOP-1) [51]. HAT catalysts (gray triangles), corresponding to: Ref. 6 (NBS) [28]; Ref. 7 (Fluorenone) [29]; Ref. 8 (anthraquinone) [55]; Ref. 9 (Ph-Acr-Ph) [56].

Fig. 3. (a) Molecular weight (Mw)-time and yield-time curves under optimized reaction conditions. (b) GPC characterization of PS photooxidative degradation. (c) Mw evolution of PS over time under different catalysts. (d) Color changes during degradation. (e) Water contact angle measurements. (f) FT-IR characterization of PS photooxidative degradation.

Fig. 4. Investigation of reaction mechanism. (a) Quenching experiment. (b) UV-vis absorption spectrum. (c) EPR spectra under in-situ irradiation at 405 nm with TEMP and DMPO spin traps, respectively. A nitroxyl radical (TEMPO, from 1O2) [g = 2.0056, aiso(14N) = 1.50 mT], an oxygen-centered DMPO adduct (DMPO-?O2-) [g = 2.0057, aiso (14N) = 1.31 mT, aiso (β-1H) = 0.81 mT], an oxygen-centered DMPO adduct (DMPO-?OH) [g = 2.0058, aiso (14N) = 1.55 mT, aiso (β-1H) = 1.55 mT], and a carbon-centered DMPO adduct (DMPO-?R) [g = 2.0055, aiso (14N) = 1.60 mT, aiso (β-1H) = 2.19 mT]. (d) 1H NMR spectra of PS before and after deuteration; (e) Schematic illustration of 1O2 generation. (f) Mass spectra of benzoic acid products from PS and d-PS photodegradation. (g) Schematic comparison of KIE effects in Fe3+ induced SET and 1O2 oxidation pathways.

Table 2 Summary of deuteration rates in PS and d-PS determined by 1H NMR.

Peak No.	Chemical shift (δ, ppm)	Assigned proton position	Abbreviation	PS integration	d-PS integration	Deuteration rate
	~3.8	internal standard trimethoxybenzene	IS (6H)	1	1	—
1	6.3-6.6	aromatic proton (para)	Ar-H(1)	1.76	0.2	88.63%
2	6.6-7.3	aromatic protons (meta/ortho)	Ar-H(2)	1.19	0.7	41.17%
3	1.85-2.05	α-hydrogen	α-H	0.93	0.21	77.42%
4	1.35-1.85	β-hydrogen	β-H	1.57	0.62	60.50%

Table 3 Kinetic isotope effect in PS/d-PS degradation.

Entry	Substrate	Product	m/z (‒)	Intensity	Yield (%)	KIE_int^a
1	PS	M1	121.0329	10166	76.4	—
2	D-PS	M2	124.0049	3633	23	10.3
		M3	123.9056
		M4	125.0042

Fig. 5. (a) Gibbs free energy profile and optimized structures for the oxidation of a polystyrene intermediate by 1O2. Energies are given in kcal/mol relative to intermediate 1. Structures were optimized at B3LYP/6-31G(d), energies refined at cc-pVTZ level. (b) Mechanistic pathway for dual functional ionic liquid catalyst enabling cooperative activation through SET and singlet oxygen oxidation in polystyrene upcycling.

Table 4 Photooxidation capacity of post-consumer PS plastic waste by the IL catalyst.

Entry	Name	Molecular weight ^b	Conv.^c(%)	Yield ^d(%)
1	EPS foam waste	M_w = 244439 M_n = 96707	100	66.57
2	Polystyrene culture dish waste from lab	M_w = 241155 M_n = 70543	100	69.54
3	Polystyrene cup waste	M_w = 233715 M_n = 68616	100	74.57
4	Polystyrene food container waste	M_w = 278450 M_n = 95631	100	63.74
5	Polystyrene ruler	M_w = 245133 M_n = 69682	100	63.28
6	Polystyrene mousse cup waste	M_w = 232466 M_n = 79055	100	64.45
7	Polystyrene cup lid waste (white)	M_w = 174668 M_n = 80913	100	60.12
8	Polystyrene cup lid waste (black）	M_w = 174490 M_n = 76745	100	56.01
9	Styrene-butadiene-styrene	M_w = 140579 M_n = 57674 styrene 30 wt.%	100	60.17

Fig. 6. (a) Process for separating and purifying IL catalyst and photooxidation products. (b) FT-IR spectrum of IL catalyst before and after reaction. (c) Reusability of IL catalyst in PS photooxidation. *Cycle 5 was performed after replenishing the catalyst to its initial amount. (d) 1H NMR (DMSO-d6) of recrystallized benzoic acid.

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