Red light photocatalysis of conjugated microporous polymers based on fused thiophenes for selective oxidation of amines

Photocatalytic oxidation of glycerol with red light employing quinacridone sensitized TiO2 nanoparticles

Photocatalytic nanomaterials combining organic dyes and inorganic semiconductor nanoparticles (NPs) are extensively investigated for light-driven production of solar fuels and for conversion of organic feedstocks. However, their applications for the valorization of abundant raw materials by exploiting low-energy visible light remain limited. In this study, we report a facile preparation of TiO2 nanoparticles sensitized with a quinacridone (QA) industrial pigment for the aqueous oxidation of glycerol to glyceraldehyde with red light (λ = 620 nm), reaching 47.5 ± 5.0 μmol gNP -1 h-1 of productivity and 80% selectivity in the presence of TEMPO co-catalyst. The hybrid material outperforms the single components and shows recyclability up to at least 5 additional times under red light while maintaining intact productivity; furthermore, it demonstrates versatility by operating also under green, yellow or white light irradiation. We believe that this work will provide a new avenue for using industrial pigment-sensitized materials in photocatalysis exploiting low energy light, providing novel strategies for the future development of this field.

Enhancing Spin-Orbit coupling in covalent organic polymers to facilitate intersystem crossing for uranium (VI) photoreduction

Photocatalytic removal and recovery of uranium from wastewater by heightening reactive oxygen species, especially superoxide radical (O2•-), is of great significance for radioactive contamination remediation. However, limited by the sluggish intersystem crossing (ISC) rates, the generation of triplet excited states is inefficient in polymeric semiconductors, thereby lower the level of O2•-. Herein, we first furnish a heteroatomic nitrogen-embedded strategy to enhance spin-orbit coupling (SOC) capacity of covalent organic polymers (COPs) by decorating benzo[c][1,2,5]thiadiazole-based COPs with the benzene, triazine, and tris([1,2,4]triazolo)[4,3-a:4',3'-c:4'',3''-e][1,3,5]triazine (TTT) cores, resulting in SOC value of 0.03, 0.10 and 0.41 cm-1, respectively. Thus, the TTT-functionalized COPs exhibited the highest ISC rates and the longest triplet excited state with a lifetime of 30.5 μs, dramatically facilitating the photoreduction of U(VI) (95.0 %, 1.5 h). This work validates that enhancing SOC ability is an effective strategy to improve ISC rate, which contributed to the rational design of polymeric semiconductors with intersystem crossing behaviors.

Donor-acceptor conjugated porous polymers from truxene and triazine: Effect of connecting units on photocatalytic activity for selective oxidation of amines and sulfides

Donor-acceptor (D-A) conjugated polymers have been widely reported as promising photocatalysts for organic conversion. However, achieving excellent photocatalytic performance still relies on the rational design of molecular structures and the careful selection of appropriate building blocks. In this study, we designed two D-A type conjugated porous polymers (CPPs) using 2,7,12-tribromo-5,5,10,10,15,15-hexamethyl-10,15-dihydro-5H-diindeno[1,2-a:1',2'-c]fluorene (Tx) as the donor unit and two 1,3,5-triazine-based derivatives, namely 2,4,6-tri(thiophen-2-yl)-1,3,5-triazine (TTT) and 2,4,6-triphenyl-1,3,5-triazine (TPT), as the acceptor units. The resulting CPPs are named ThTx-CPP and PhTx-CPP, respectively. The research findings emphasize the profound impact of minute structural changes in the triazine peripheral groups on the photocatalytic activity of the polymers. Compared to PhTx-CPP, ThTx-CPP exhibits superior light-harvesting capabilities, narrower bandgaps, and improved efficiency in charge separation. Specifically, ThTx-CPP demonstrates outstanding activity and selectivity in both amine coupling and sulfide oxidation reactions, surpassing PhTx-CPP by a significant margin. Furthermore, the catalyst retains its consistent activity even after five cycles of reuse, showcasing its high stability and excellent reusability.

Study on photocatalytic degradation and antibacterial properties of conjugated microporous polymers/TiO2 composite membranes

Conjugated microporous polymers (CMPs) are widely used in the field of photocatalysis due to their unique conjugated structures and various synthesis methods. Herein, we report the design and synthesis of conjugated microporous polymers hollow spheres (CMPs-HS) superhydrophilic modified by acetylcysteine (CMPs-HS-S) and compounded with the inorganic semiconductor material titanium dioxide (CMPs-HS-S/TiO2) for efficient photocatalytic degradation. To facilitate recycling, the composite membrane material was prepared by combining the materials mentioned above with PVDF membrane. The composite membrane materials had good hydrophilic and photocatalytic properties. Under visible light, the degradation rate of tetracycline (TC) (10 mg/L 180 min) reached 90 %, and the bactericidal rates for Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were 89 % and 99.99 %, respectively. The efficient photocatalytic performance of the composite membranes could be attributed to the hollow sphere structure of CMPs and the role of TiO2 as a photogenic electron transfer platform. Additionally, the hydrophilicity of the membrane also helped to accelerate the occurrence of photocatalytic reactions. After electron paramagnetic resonance (EPR) detection, h+, 1O2 and O2- were proved to be important reactive substances, which played a major role in degradation. These studies reflect the versatility of CMPs-based photocatalysts and provide a new idea for the future development of CMPs-based photocatalysts.

Low-temperature synthesis of porous organic polymers with donor-acceptor structure and β-ketoenamine for photocatalytic oxidative coupling of amines

In light of the widespread use of fossil fuels and the resulting environmental pollution, it is crucial to develop efficient photocatalysts for renewable energy applications that utilize visible light. Organic photocatalysts based on β-ketoenamine offer several advantages, including facile preparation, high stability, structural controllability, and excellent photovoltaic properties. However, in previous studies, the synthesis of porous organic polymers (POPs) often involved long, high-temperature processes. In this study, POPs with donor (D)-acceptor (A) structure were constructed by utilizing various branched bridging groups and 2,4,6-triformylphloroglucinol, across multiple temperature gradients. Through adjustments in hydrothermal temperature, we successfully synthesized a series of POPs with varying enol-keto structure ratios. Among these POPs, the dimethoxybenzidine-POPs (DMDPOPs) with methoxy electron-rich branched chains exhibited superior photovoltaic performance, electron transfer rate, and photocatalytic activity compared to the dihydroxybenzidine-POPs (DHDPOPs) with electron-deficient hydroxyl branched chains. Notably, DMDPOP-30 demonstrated outstanding performance, achieving a conversion rate of 98% within 3 h. Additionally, other POPs exhibited favorable conversions (90%), further confirming the feasibility of this synthetic approach. Moreover, the synthesis of DMDPOP-30 was achieved under mild conditions at room temperature, highlighting its significant potential for practical applications.