In this study, three typical D–π–A type heteroaromatic organic dyes containing carbazole (CBZ), phenothiazine (PTZ), and phenoxazine (POZ) moiety as electron donor cores and linked to g-C 3 N 4 with amide covalent bonds were synthesized. Thereafter, we studied the long-term photochemical stability and degradation mechanism of the associated dye-sensitised g-C 3 N 4 with covalent linkage or weak interaction. The results revealed that most of the dyes degraded and became unstable after absorption on g-C 3 N 4 under light irradiation. Interestingly, after the target dyes were linked to g-C 3 N 4 with amide covalent bonds, the photostability could be effectively promoted and improved to high levels of stability. For POZ-S dye covalent bond-linked sample g-C 3 N 4 /POZ-S, ∼90.5% percent of the dyes were reserved, whereas only ∼25.3% remained for the physically absorbed dye sample g-C 3 N 4 +POZ-S after 30 min of irradiation aging test. Moreover, the obtained g-C 3 N 4 /POZ-S sample exhibited enhanced H 2 evolution activity with photocatalytic H 2 production rates that were approximately 96- fold of that of pure g-C 3 N 4 . Then, we applied various instrumental analysis and DFT calculation to clarify the mechanism involved with dye photostability and degradation pathway. The typical decarboxylation process was confirmed, and such an unfavourable reaction process could be effectively inhibited if the target dye is linked to g-C 3 N 4 with amide covalent bond instead of the weak interaction. Overall, the existed covalent bond is the key factor for enhancing both the photochemical stability and photocatalytic activity of organic dye-sensitised g-C 3 N 4 for hydrogen evolution .
Mengna Qin,Guibao Wu,Kai Zheng,Xiaofei Yu,Juan Xu,Jianyu Cao
The pH-neutral aqueous redox flow battery (ARFB) is one of the most attractive flow batteries due to its non-corrosiveness, low-cost, and wider electrochemical stability window compared to those with acidic or alkaline electrolytes. However, there are few families of organic redox-active molecules available as catholyte materials for pH-neutral ARFBs. Herein, through incorporation of quaternary ammonium moiety into the redox-active phenoxazine nucleus, an organic catholyte material, N , N , N -trimethyl-2-(10H-phenoxazin-10-yl) ethan-1-aminium chloride (NEt-POZ) is achieved for pH-neutral ARFBs. The NEt-POZ has a high redox potential of 0.79 V versus SHE and rapid redox kinetics (0.23 cm s −1 ) as well as high water-solubility (∼2.6 M in H 2 O). Paired with a methyl viologen (MV) anolyte in the pH-neutral aqueous electrolyte, a viologen-phenoxazine ARFB full cell is assembled, which shows an open circuit voltage of ∼1.23 V. However, the results of long-term cycling experiments indicate low Coulomb efficiency and rapid declining capacity of the NEt-POZ catholyte. The mechanism analysis unveils that the unstable doubly oxidized tri-cations (NEt-POZ 3+ ) formed via the disproportionation of radical di-cations (NEt-POZ 2+ ) in solution readily react with chloride anions to form poly-chlorinated derivatives, which precipitate from the catholyte due to their poor water solubility, leading to a rapid decrease in capacity. When there is no chloride present in the electrolyte solution, highly reactive NEt-POZ 3+ cations can interact with other counter-anions (such as sulfate and carbonate ions) and even water to form complex adducts.
Yixuan Xu,Changchang Teng,Yating Wang,Dejia Chen,Dalong Yin,Lifeng Yan
Stable organic radicals have emerged as a promising option to enhance fluorescence quantum yield (QY), gaining traction in medical treatment due to their unique electronic transitions from the ground state (D 0 ) to the doublet excited state (D 1 ). We synthesized a stable dicyanomethyl radical with a NIR-II fluorescence QY of 0.86 %, surpassing many NIR-II organic dyes. Subsequently, amphiphilic polymer-encapsulated nanoparticles (NPs) containing the radical were created, achieving a NIR-II fluorescence QY of 0.32 %, facilitating high-contrast bio-imaging. These CNPPs exhibit self-enhanced photothermal properties, elevating photothermal conversion efficiency (PCE) from 43.5 % to 57.5 % under 915 nm laser irradiation. This advancement enables more efficient photothermal therapy (PTT) with lower dye concentrations and reduced laser power, enhancing both feasibility and safety. Through regular fractionated mild photothermal therapy, we observed the release of damage-associated molecular patterns (DAMPs) and an increase in cytokine expression, culminating in combined mild phototherapy (m-PTT)-mediated immunogenic cell death (ICD). Consequently, we developed an immunostimulatory tumor vaccine, showcasing a novel approach for refining photothermal agents (PTA) and optimizing the PTT process.
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