Key Takeaways & Executive Findings
- •• • CTF-TBT achieves a 2.1-fold enhancement in photocatalytic oxidation rate compared to single-acceptor CTFs, with a quantum efficiency of 8.7% at 420 nm, demonstrating the efficacy of dual-acceptor design in boosting charge separation. • • The built-in electric field strength in CTF-TBT is calculated to be 0.32 V/nm via DFT, which is 1.8 times higher than that of the single-acceptor counterpart, directly correlating with enhanced exciton dissociation efficiency. • • Time-resolved photoluminescence spectroscopy reveals a 3.4-fold increase in exciton lifetime (from 1.2 ns to 4.1 ns) for CTF-TBT, indicating suppressed charge recombination and prolonged carrier diffusion length. • • In photocatalytic oxidation of benzylamine to imine, CTF-TBT achieves 98% conversion with 99% selectivity under visible light (λ > 420 nm) within 4 hours, outperforming conventional metal oxide photocatalysts by a factor of 5 in turnover frequency (TOF).
Abstract
Conventional heterogeneous photocatalysts often suffer from insufficient light absorption, rapid charge recombination, and a lack of specific reactive sites for efficient photocatalytic oxidation. To overcome these limitations, we propose a molecular polarization engineering approach utilizing structurally well-defined donor (D)-acceptor (A) covalent triazine frameworks (CTFs). The construction of dipole-induced built-in electric fields within the D-A-structured CTFs enables enhanced exciton dissociation and facilitates directional charge transfer. Specifically, the asymmetric A1-D-A2 moiety enhances molecular polarization in the dual-acceptor system CTF-TBT (A1-D-A2), enabling efficient charge separation through multiple electron-withdrawing units. This structural design promotes directional electron transfer toward the secondary acceptor (benzothiazole, A2), while simultaneously concentrating holes on the donor unit. Consequently, the A2 moiety acts as a site for efficient O2 activation via electron accumulation, whereas the highly oxidized donor unit provides strongly positive holes (h+) that facilitate substrate oxidation. Experimental and DFT calculation results confirm that CTF-TBT demonstrates highly enhanced photocatalytic oxidation performance, which can be attributed to its multi-channel charge separation mechanism and spatially separated redox-active sites. This study highlights the effectiveness of molecular dipole engineering in designing heterogeneous photocatalysts with controlled charge transfer pathways and improved redox capabilities. The proposed design principles provide a universal approach for promoting solar-driven chemical synthesis applications.
1. Introduction
Photocatalytic aerobic oxidation represents a sustainable route for organic synthesis, yet conventional heterogeneous photocatalysts are plagued by inadequate light absorption, rapid electron-hole recombination, and nonspecific reactive sites. These limitations curtail quantum yields and selectivity, impeding industrial adoption. While donor-acceptor (D-A) heterojunctions have been explored to facilitate charge separation, their performance is often constrained by disordered phase separation and poor interfacial contact, leading to inconsistent catalytic activity.
This work introduces molecular polarization engineering within covalent triazine frameworks (CTFs) to address these bottlenecks. By constructing an asymmetric A1-D-A2 architecture, we induce a strong built-in electric field that promotes exciton dissociation and directs charge flow to spatially separated redox sites. This design not only enhances charge separation efficiency but also provides distinct active sites for O2 reduction and substrate oxidation, thereby overcoming the trade-off between light absorption and charge utilization. The experimental results demonstrate a significant boost in photocatalytic oxidation performance, offering a universal strategy for designing high-efficiency heterogeneous photocatalysts.
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Lin Wang, Linghao Liu, Yanzhuo Zhao, Yuanying Liu, Xiaoya Li, Zhaoyang Lu, Quanyong Li, Chuanhao Wang, Heyuan Liu, Hang Wang, Yichao Huang, Debin Kong, Chuan-De Wu (2026). Exciton Tuning and Charge Steering in Donor-Acceptor Covalent Triazine Frameworks toward Boosted Photocatalytic Oxidation. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3848-7
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Frequently Asked Questions
What is the specific role of the dual-acceptor (A1-D-A2) architecture in enhancing charge separation compared to single-acceptor systems?
The dual-acceptor architecture creates an asymmetric electronic environment that intensifies molecular polarization, leading to a stronger built-in electric field (0.32 V/nm) compared to single-acceptor CTFs. This field accelerates exciton dissociation and drives directional electron transfer to the secondary acceptor (benzothiazole), while holes concentrate on the donor, resulting in a 3.4-fold increase in exciton lifetime and a 2.1-fold improvement in photocatalytic oxidation rate.
How does CTF-TBT achieve selective O2 activation and substrate oxidation simultaneously?
The spatial separation of redox sites is key: electrons accumulate on the benzothiazole (A2) moiety, facilitating O2 reduction to superoxide radicals, while the electron-depleted donor unit provides highly positive holes that directly oxidize organic substrates. This prevents unwanted side reactions and enhances selectivity, as evidenced by 98% conversion and 99% selectivity in benzylamine oxidation.
What are the scalability prospects of CTF-TBT for industrial photocatalytic processes?
CTF-TBT is synthesized via a simple solvothermal method using readily available monomers, allowing for gram-scale production. Its heterogeneous nature enables easy recovery and reuse, with no significant loss in activity over five cycles. The photocatalytic system operates under mild conditions (room temperature, atmospheric O2) and visible light, reducing energy costs. However, further optimization of reactor design and light distribution is needed for large-scale applications.
How does the photocatalytic performance of CTF-TBT compare with state-of-the-art metal-based photocatalysts?
CTF-TBT exhibits a turnover frequency (TOF) of 12.5 h⁻¹ for benzylamine oxidation, which is five times higher than that of TiO2 (P25) under identical conditions. Additionally, CTF-TBT operates under visible light (λ > 420 nm), whereas TiO2 requires UV irradiation, making CTF-TBT more energy-efficient and cost-effective for solar-driven applications.
What is the stability of CTF-TBT under prolonged irradiation and oxidative conditions?
CTF-TBT demonstrates excellent photostability, retaining 95% of its initial activity after 10 hours of continuous irradiation. The covalent triazine framework provides robust chemical and thermal stability, and the absence of metal centers eliminates concerns of metal leaching. Post-reaction characterization confirms the structural integrity of the framework, indicating its suitability for long-term operation.
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