Singlet Oxygen Generation Research Articles

Novel Halogenated Curcumin-Mediated Photodynamic Inactivation for the Preservation of Small Yellow Croaker (Larimichthys polyactis).

A novel class of halogenated curcumin, X-Cur (X = F, Cl, or Br), was synthesized, and its photosensitivity was evaluated. The results showed that Br-Cur with the highest singlet oxygen (1O2) generation capacity exhibited a better photodynamic inactivation (PDI) effect on the small yellow croaker (Larimichthys polyactis) than curcumin. This was attributed to the heavy atom effect of Br, which resulted in Br-Cur having the smallest singlet-triplet energy difference ΔEst(S1-T3) (0.140 eV) and the largest spin-orbit coupling value (0.642262 cm-1). When L. polyactis was treated with 0.025 wt % Br-Cur and exposed to blue LED irradiation (450 nm, 20 mW/cm2) for 20 min, the increase in the total volatile basic nitrogen content (28.23 ± 2.38 mg/100 g on day 6), pH, and total viable count (6.13 ± 0.06 log CFU/g on day 6) could be effectively controlled. Accordingly, Br-Cur is a promising photosensitizer for PDI preservation.

Synthesis and photophysical properties of symmetrical tetraaryltetranaphtho[2,3]porphyrin derivatives

The discovery of new photosensitizers with strong absorption near-infrared region, obvious fluorescence emission, and high reactive oxygen generation ability has attracted great attention as optical agents in life science and material industry. Herein a series of meso-tetraaryltetranaphtho[2,3]porphyrins (Ar 4TNPs) with different substitutions were designed and synthesized. They had strong absorptions at ∼730 nm and fluorescence emission at ∼760 nm after excitation with ∼503 nm light. All compounds possessed excellent reactive oxygen species (ROS) generation ability. The singlet oxygen generation rate of compound 10m (meso-5,10,15,20-tetra[2-(2-hydroxyethoxy)ethylbenzoate]tetrana-phthoporphyrin) is 0.1898 s−1 with a Φ△ value of 0.73, which is significantly higher than that of verteporfin. Therefore, Ar4TNPs have great potential as an effective optical material, bio-tracker, and photodynamic drug candidate.

Synthesis and evaluation of new tetrapyrrole derivatives with photodynamic anti-tumor effects

As a promising anti-tumor method, photodynamic therapy (PDT) has garnered increased interest over the past decades. Since the efficacy of PDT relies on the properties of photosensitizers, tremendous efforts have been exerted in the quest for novel photoactive agents with long wavelength absorbance and high phototoxicity. In this investigation, a series of five tetrapyrrole derivatives were newly synthesized and evaluated. They all manifested sharp UV–vis absorption peak at ∼680 nm, high molar extinction coefficient (>74200 L mol−1 cm−1), impressive reactive oxygen species generation abilities and obvious photo-damage on cancer in vitro and in vivo. Among them, I4 displayed the most excellent singlet oxygen generation slope (K = 0.0531 s−1, ΦΔ = 0.87), the strongest anti-proliferation effects towards human esophageal cancer cell line Eca-109 in vitro, and more remarkable tumor inhibition rates (90.2 %) than m-THPC in vivo. Subcellular localization experiments demonstrated that I4 could distribute in mitochondria, endoplasmic reticulum and lysosomes. Hence, compound I4 could be viewed as a potential photosensitizer drug for further studies in PDT.

Continuous peroxymonosufate activation for antibiotics degradation via fluorine-free-Ti3C2Tx-CoFe2O4 hydrogel beads: Performance, mechanism and application

This study explored the efficient, stable, and continuous treatment of antibiotic-containing wastewater through rapid electron transfer between layered fluorine-free Ti3C2Tx and CoFe2O4 nanomicrospheres. These materials were synthesized into hydrogel beads crosslinked with sodium alginate, resulting high reactivity and stability. Ff-Ti3C2Tx-CoFe2O4 catalyst facilitated peroxymonosufate (PMS) activation through rapid electron transfer and the formation of Ff-Ti3C2Tx-CoFe2O4-PMS* species, as confirmed by experiments and DFT calculations. The cleavage of the S-O bond on Ff-Ti3C2Tx-CoFe2O4 catalyst identified as the primary mechanism for the generation of singlet oxygen (1O2). In a continuous flow system, the degradation efficiency of antibiotics, such as sulfamethoxazole (SMX), remained above 96.9 % with ultra-low metal leaching (<1.3 μg·L−1, 72 h). This research provides significant insights into the practical application of PMS activation for antibiotic degradation, offering a sustainable solution for wastewater treatment.

A Photoinduced Annulation Strategy Towards a Novel Polycyclic Heteroaromatic Chromophore: Scope, Mechanism, Properties and Applications.

This article reports a detailed mechanistic and kinetic study of an unusual photoreaction leading to the (diazonia)tetrabenzonaphthacene skeleton. The photo‐triggered double intramolecular nucleophilic aromatic substitution (SNAr∗) has been investigated by varying the leaving groups. Photoreaction quantum yields have been determined and mechanistic insights have been supported by theoretical calculations using DFT and TD‐DFT methods. Additionally, we show that this light‐triggered formed diazonia constitutes a potent photosentitizer with a singlet oxygen generation quantum yield of 55 %, both in organic solvents and in water, which is an extremely relevant value in view of PDT applications or use as an oxidation photocatalyst in aqueous media. Once again, the experimental observations were supported by TD‐DFT calculations showing a large density of triplet states below the S1 excited state along with large spin‐orbit couplings. The reaction is not restricted to solutions but can also occur in solid PDMS matrices thus allowing for photochemical encoding of information that will progressively vanish upon prolonged UV‐exposure.

Antibacterial Photodynamic Therapy of the Metallosurfactant-Fluorescein Conjugate under Visible Light Illumination.

Antibacterial photodynamic therapy (APDT) has received increased attention as a treatment for multidrug-resistant bacterial infections caused by antibiotic abuse. However, photosensitizers used in APDT have disadvantages such as water insolubility, self-aggregation, and photobleaching. To address these limitations, metal complexes have been explored. However, the use of such complexes tends to confine their antibacterial effectiveness specific bacterial strains. In this study, we report iron (Fe)- and copper (Cu)-based metallosurfactants as unique moieties for antibacterial photodynamic therapy (PDT) under the illumination of visible light. Briefly, our formulated Fe and Cu metallosurfactants, when combined with a fluorescein photosensitizer, exhibit nearly 100% antibacterial efficacy. This high efficiency is primarily attributed to the enhanced generation of singlet oxygen using FL in the presence of metallosurfactants when targeting bacteria such as Escherichia coli and Staphylococcus aureus under laser light. In vitro experiments further confirmed the superior antimicrobial activity of these metallosurfactants against a diverse range of microbial cultures, encompassing Gram-negative and Gram-positive bacteria as well as fungi. This performance outpaces conventional surfactants like cetyltrimethylammonium chloride and cetylpyridinium chloride. The compelling results from MTT assays and flow cytometry endorsed the substantial enhancement in antimicrobial properties achieved through Fe and Cu doping, all without the need for additional secondary agents. Notably, this synergistic antibacterial approach using metallosurfactants in PDT holds significant promise for the elimination of various bacteria in vivo, with the added advantage of mitigating the emergence of multidrug resistance.

Differentiated management of ROS level in tumor and kidney to alleviate Cis-platinum induced acute kidney injury with improved efficacy

Cisplatin (DDP) is a prevalent chemotherapeutic agent used in tumor therapy, yet DDP-induced acute kidney injury (AKI) severely limits its clinical application. Antioxidants as reactive oxygen species (ROS) scavengers can circumvent this adverse effect while leading to the decrease of efficacy to tumor. Herein, we report ultrasmall ruthenium nanoparticles (URNPs) as switchable ROS scavengers/generators to alleviate DDP-induced AKI and improve its therapeutic efficacy. In the physiological environment of the kidney, URNPs mimic multi-enzyme activities, such as superoxide dismutase and catalase, effectively protecting the renal cell and tissue by down-regulating the increased ROS level caused by DDP and alleviating AKI. Specifically, URNPs are oxidized by high levels of H2O2 in the tumor microenvironment (TME), resulting in the generation of oxygen vacancies and Ru3+/Ru4+ ions. This unique structure transformation endows URNPs to generate singlet oxygen (1O2) under laser irradiation and hydroxyl radicals (∙OH) through a Fenton-like reaction in tumor cell and tissue. The simultaneous generation of multifarious ROS effectively improves the efficacy of DDP in vitro and in vivo. This TME-responsive ROS scavenger/generator acts as an adjuvant therapeutic agent to minimize side effects and improve the efficacy of chemotherapy drugs, providing a new avenue to chemotherapy and facilitating clinical tumor therapy.Graphical

Structure-Activity Relationship of Benzophenazine Derivatives for Homogeneous and Heterogenized Photooxygenation Catalysis.

Singlet oxygen is a powerful oxidant used in various applications, such as organic synthesis, medicine, and environmental remediation. Organic and inorganic photosensitizers are commonly used to generate this reactive species through energy transfer with the triplet ground state of oxygen. We describe here a series of novel benzophenazine derivatives as a promising class of photosensitizers for singlet oxygen photosensitization. In this study, we investigated the structure-activity relationship of these benzophenazine derivatives. Akin to a molecular compass, the southern fragment was first functionalized with either aromatic tertiary amines, alkyl tertiary amines, aromatic sulfur groups, alkyl sulfur groups, or cyclic ethers. Enhanced photophysical properties (in terms of triplet excited-state lifetime, absorption wavelength, triplet state energy, and O2 quenching capabilities) were obtained with cyclic ether and sulfur groups. Conversely, the presence of an amine moiety was detrimental to the photocatalysts. The western and northern fragments were also investigated and slightly undesirable to negligible changes in photophysical properties were observed. The most promising candidate was then immobilized on silica nanoparticles and its photoactivity was evaluated in the citronellol photooxidation reaction. A high NMR yield of 97 % in desired product was obtained, with only a slight decrease over several recycling runs (85 % in the fourth run). These results provide insights into the design of efficient photosensitizers for singlet oxygen generation and the development of heterogeneous systems.

The controllable of BODIPY dimers without installing blocking groups as both fluorescence and singlet oxygen generators

AbstractWe compared a range of BODIPY dimer derivatives without installing blocking groups by optimizing geometry structures and analyzing energies, frontier molecular orbitals, Chole&amp;Cele map, electron density difference, spin‐orbit coupling (SOC) matrix and decay rate constants from excited states. The dihedral angles of the β‐β‐linked BODIPY dimer and the α‐α‐linked BODIPY dimer tend to flatten in the T1 state, which is detrimental to the occurrence of the intersystem crossing (ISC). Conversely, the dihedral angle of the meso‐β‐linked BODIPY dimer, the meso‐meso‐linked BODIPY dimer and α‐γ‐linked BODIPY dimer is within the range of 125°–143° in the T1 state, facilitating ISC and the generation of singlet oxygen. Notably, the transition from S1 to S0 involving lowest unoccupied molecular orbital to highest occupied molecular orbital with long‐wavelength emission and moderate oscillator strength underpins the remarkable long emission peaks observed experimentally for α‐γ‐linked BODIPY dimer. Moreover, the apparent SOC matrix enhances the ISC process, resulting in a respectable efficiency in generating singlet oxygen for this dimer. In meso‐β‐linked BODIPY, meso‐meso‐linked BODIPY, and α‐γ‐linked BODIPY, the S1→T1 process is characterized by a significant charge transfer, specifically transitioning from the 1CT state to the 3LE state, indicative of a spin‐orbit charge transfer ISC (SOCT‐ISC) mechanism. The ability to regulate the photosensitivity of BODIPY dimers by adjusting the dihedral angle between the two units in the T1 state unveils new avenues for designing high‐performance photosensitizers for both therapeutic and imaging applications.

Membrane Disruption-Enhanced Photodynamic Therapy against Gram-Negative Bacteria by a Peptide-Photosensitizer Conjugate.

Photodynamic therapy (PDT) emerges as a promising strategy for combating bacteria with minimal drug resistance. However, a significant hurdle lies in the ineffectiveness of most photosensitizers against Gram-negative bacteria, primarily attributable to their characteristic impermeable outer membrane (OM) barrier. To tackle this obstacle, we herein report an amphipathic peptide-photosensitizer conjugate (PPC) with intrinsic outer membrane disruption capability to enhance PDT efficiency against Gram-negative bacteria. PPC is constructed by conjugating a hydrophilic ultrashort cationic peptide to a hydrophobic photosensitizer. PPC could efficiently bind to the OM of Gram-negative bacteria through electrostatic adsorption, and subsequently disrupt the structural integrity of the OM. Mechanistic investigations revealed that PPC triggers membrane disruption by binding to both lipopolysaccharide (LPS) and phospholipid leaflet in the OM, enabling effective penetration of PPC into the Gram-negative bacteria interior. Upon light irradiation, PPC inside bacteria generates singlet oxygen not only to effectively decrease the survival of Gram-negative bacteria P. aeruginosa and E. coli to nearly zero in vitro, but also successfully cure the full-thickness skin infection and bacterial keratitis (BK) induced by P. aeruginosa in animal models. Thus, this study provides a broad-spectrum antibacterial phototherapeutic design strategy by the synergistic action of membrane disruption and PDT to combat Gram-negative bacteria.

A Biocompatible Hydrogen-Bonded Organic Framework (HOF) as Sonosensitizer and Artificial Enzyme for In-Depth Treatment of Alzheimer's Disease.

Current phototherapeutic approaches for Alzheimer's disease (AD) exhibit restricted clinical outcomes due to the limited physical penetration and comprised brain microenvironment of noninvasive nanomedicine. Herein, a hydrogen-bonded organic framework (HOF) based sonosensitizer is designed and synthesized. Mn-TCPP, a planar molecule where Mn2+ ion is chelated in the core with a large p-conjugated system and 4 carboxylate acid groups, has been successfully used as building blocks to construct an ultrasound-sensitive HOF (USI-MHOF), which can go deep in the brain of AD animal models. The both in vitro and in vivo studies indicate that USI-MHOF can generate singlet oxygen (1O2) and oxidize β-amyloid (Aβ) to inhibit aggregation, consequently attenuating Aβ neurotoxicity. More intriguingly, USI-MHOF exhibits catalase (CAT)- and superoxide dismutase (SOD)-like activities, mitigating neuron oxidative stress and reprograming the brain microenvironment. For better crossing the blood-brain barrier (BBB), the peptide KLVFFAED (KD8) has been covalently grafted to USI-MHOF for improving BBB permeability and Aβ selectivity. Further, in vivo experiments demonstrate a significant reduction of the craniocerebral Aβ plaques and improvement of the cognition deficits in triple-transgenic AD (3×Tg-AD) mice models following deep-penetration ultrasound treatment. The work provides the first example of an ultrasound-responsive biocompatible HOF as non-invasive nanomedicine for in-depth treatment of AD.

NIR afterglow nanosystem for photodynamic therapy.

Within the milieu of immune dysfunction, reactive oxygen species (ROS) play a pivotal role in inducing immunogenic cell death (ICD), countering the dysregulated tumor microenvironment. However, the administration of ROS at indiscriminate dosages may provoke deleterious immune responses. Therefore, precise regulation of ROS production is crucial to achieve efficacious therapeutic outcomes. We engineered an innovative afterglow nanosystem which is capable of real-time monitoring of ROS levels. Our findings reveal that Ru/CYQ@CPPO exhibits a markedly enhanced and prolonged afterglow luminescence, coupled with superior singlet oxygen (O2) generation, compared to the commercially available indocyanine green (ICG). In vitro studies demonstrated that Ru/CYQ@CPPO exhibits remarkable efficacy in photodynamic therapy (PDT) under irradiation at a wavelength of 450 nm. Furthermore, a significant correlation (R 2 = 0.987) was observed between the intensity of afterglow luminescence and the rate of cancer cell inhibition.

Enhancing Emerging Pollutant Removal in Industrial Wastewater: Validation of a Photocatalysis Technology in Agri-Food Industry Effluents

Emerging pollutants in wastewater pose significant risks to human health and wildlife, particularly due to their persistence in treated effluents from WWTPs. Very recent research has focused on developing new techniques based on advanced oxidation processes using inorganic and organic photocatalysts for treating polluted effluents under visible light. This study investigates a pesticide-removal system utilizing heterogeneous photoactive polymeric materials P2, P3, and P4. These materials, engineered as hydrophilic polymeric microparticles and functionalized with Rose Bengal, have demonstrated efficient singlet oxygen generation and first-order kinetics in the degradation of AHMPD, a pyrimidine fungicide. Given that most studies in the literature have concentrated on urban WWTPs, with less emphasis on industrial wastewater treatment, this research focused on real water samples from the effluent of an industrial WWTP in the agri-food sector, which processes large volumes of citrus and where high concentrations of AHMPD and other pesticides were detected at certain times of the year. The degradation potential of photoactive materials P3 and P4 was evaluated, achieving removal rates of AHMPD up to 85% under conditions of pH = 11 with 48 h of exposure to visible light.

Rational Design and Evaluation of Photoactive Molecularly Imprinted Nanoparticles for Tetracycline Degradation Under Visible Light.

This work presents the use of photoactive molecularly imprinted nanoparticles (MINs) to promote antibiotic degradation under visible light irradiation. Prototype MINs for the model antibiotic tetracycline (TC) were developed using molecular dynamics simulations to predict the TC-binding capacity of seven pre-polymerization mixtures. The studied formulations contained varying proportions of functional monomers with diverse physicochemical profiles, namely N-isopropylacrylamide (NIPAM), N-tert-butylacrylamide (TBAM), acrylic acid (AA), and (N-(3-aminopropyl)methacrylamide hydrochloride) (APMA) and a constant ratio of the cross-linker N,N'-methylene-bis-acrylamide (BIS). Two monomer formulations showed markedly higher TC-binding capacities based on template-monomer interaction energies. These mixtures were used to synthesize photoactive MINs by high-dilution radical polymerization, followed by the EDC/NHS conjugation with the organic photosensitizer toluidine blue. MINs showed higher TC-binding capacities than non-imprinted nanoparticles (nINs) of identical composition. MINs and nINs exhibited photodynamic activity under visible light irradiation, as confirmed by singlet oxygen generation experiments. TC degradation was evaluated in 50 μmol L-1 solutions placed in microplate wells containing immobilized nanoparticles and irradiated with white LED light (150 W m-2) for 1 h at room temperature. Degradation followed pseudo-zero-order kinetics with accelerated profiles in MIN-containing wells. Our findings suggest a key role of molecularly imprinted cavities in bringing TC closer to the photosensitizing moieties, minimizing the loss of oxidative potential due to reactive oxygen species diffusion. This degradation strategy can potentially extend to any organic pollutants for which MINs can be synthesized and opens valuable opportunities for exploring novel applications for molecularly imprinted materials.

Functionalization of fibrous substrates with mesoporous silica nanoparticles as a strategy to obtain photodynamic antibacterial textiles

The insertion of various nanomaterials and technologies in the search for antimicrobial textiles has grown in recent years, especially after the SARS-CoV-2 pandemic. Despite the efficiency, the design of a safe, scalable, low-cost, and robust antimicrobial textiles that cover all the spectra of microorganisms continues to be challenging. This gap can be filled using antimicrobial Photodynamic Therapy, a new promising approach that inactivates microorganisms in a very efficient way. In this contribution, we develop antibacterial textiles using photodynamic inactivation. To achieve that, we firstly synthesized amino functionalized mesoporous silica nanoparticles that were loaded with either Azure A or Rose Bengal. First the nanoparticles were characterized by X-ray Diffractometry, Transmission Electronic Microscopy, Thermogravimetric Analysis, N2 adsorption/desorption and dye loading. Further the nanoparticles (0.2 % w/w) were incorporated into cotton fabrics by exhaustion methodology. The antibacterial textiles were characterized by ATR-FTIR, Diffuse Reflectance, Fluorescence Microscopy, Scanning Electronic Microscopy, Fluorescence Lifetime, and singlet oxygen generation. The results showed that silica nanoparticles prevent the premature leakage of dyes from the fibers and retaining their photophysical properties, specifically their singlet oxygen production. The efficiency of antibacterial textiles was proven by the inactivation of Staphylococcus aureus and Escherichia coli. The developed materials showed antibacterial activity even in the dark, but enhanced in the light in some cases. Therefore, both systems have great potential as smart textiles for use in hospital clothing or wound dressings.

Zr‐MOF nanosheets featuring benzothiadiazoles enable efficient visible light driven photooxidation of sulfides and amines

Ultrathin zirconium‐based metal–organic framework (MOF) nanosheets, embedded with photochromic units, are expected to be highly efficient heterogeneous photocatalysts, thanks to their rich catalytic sites, short diffusion paths, and effective separation of photogenerated charge carriers. Herein, we reported the synthesis of novel Zr‐MOF nanosheets (Zr‐BTDB) through a solvothermal synthesis that integrates benzothiadiazole (BTz) as a photochromic moiety within the framework of MOF. The Zr‐BTDB nanosheets processes a [Zr12(μ3‐O)8(μ3‐OH)8(μ2‐OH)6] cluster with hcp topology. Importantly, Zr‐BTDB nanosheets exhibit excellent photocatalytic activity for the photooxidation of sulfides and amines at room temperature under blue light irradiation. Notably, these nanosheets maintain their photocatalytic activity and selectivity for up to five cycles without significant loss of activity and crystallinity. Systematical catalytic reactions revealed that the Zr‐BTDB nanosheets enable the generation of singlet oxygen (1O2) and superoxide radical (O2•–) under visible light irradiation, which is critical reactive oxygen species for the photooxidation of sulfides and benzylamines. Our work represents a straightforward route for the preparation of ultrathin, water stable, and visible‐light‐activated Zr‐MOF nanosheets, offering new potentials for the selective photooxidation of sulfides and amines in an eco‐friendly way.

Can Porphyrin-Triphenylphosphonium Conjugates Enhance the Photosensitizer Performance Toward Bacterial Strains?

Antimicrobial photodynamic treatment (aPDT) offers an alternative option for combating microbial pathogens, and in this way, addressing the challenges of growing antimicrobial resistance. In this promising and effective approach, cationic porphyrins and related macrocycles have emerged as leading photosensitizers (PS) for aPDT. In general, their preparation occurs via N-alkylation of nitrogen-based moieties with alkyl halides, which limits the ability to fine-tune the features of porphyrin-based PS. Herein, is reported that the conjugation of porphyrin macrocycles with triphenylphosphonium units created a series of effective cationic porphyrin-based PS for aPDT. The presence of positive charges at both the porphyrin macrocycle and triphenylphosphonium moieties significantly enhances the photodynamic activity of porphyrin-based PS against both Gram-positive and Gram-negative bacterial strains. Moreover, bacterial photoinactivation is achieved with a notable reduction in irradiation time, exceeding 50%, compared to 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin (TMPyP), used as the reference and known as good PS. The improved capability of the porphyrin macrocycle to generate singlet oxygen combined with the enhanced membrane interaction promoted by the presence of triphenylphosphonium moieties represents a promising approach to developing porphyrin-based PS with enhanced photosensitizing activity.

Self-Reporting Conjugated Polymer Nanoparticles for Superoxide Generation and Detection.

Conjugated polymer nanoparticles (CPNs or Pdots) have become increasingly popular fluorophores for multimodal applications that combine imaging with phototherapeutic effects. Reports of CPNs in photodynamic therapy applications typically focus on their ability to generate singlet oxygen. Alternatively, CPN excited states can interact with oxygen to form superoxide radical anion and a CPN-based hole polaron, both of which can have deleterious effects on fluorescence properties. Here, we demonstrate that CPNs prepared from the common conjugated polymer poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo-{2,1',3}-thiadiazole)] (PFBT, also known as F8BT) generate superoxide upon irradiation. We use the same CPNs to detect superoxide by doping them with a superoxide-responsive hydrocyanine dye developed by Murthy and co-workers. Superoxide induces off-to-on fluorescence switching by converting quenching hydrocyanine dyes to fluorescent cyanine dyes that act as fluorescence resonance energy transfer (FRET) acceptors for PFBT chromophores. Amplified FRET from the multichromophoric CPNs yields fluorescence signal intensities that are nearly 50 times greater than when the dye is excited directly or over 100 times greater when signal readout is from the CPN channel. The dye loading level governs the maximum amount of superoxide that induces a change in fluorescence properties and also influences the rate of superoxide generation by furnishing competitive excited state deactivation pathways. These results suggest that CPNs can be used to deliver superoxide in applications in which it is desirable and provide a caution for fluorescence-based CPN applications in which superoxide can damage fluorophores.

Carbon defects-enriched NBC-C3N5@CoMn with ultrafast modulation of redox couples for efficient degradation of contaminant

The inefficiency of catalysts in sulfate radical-based advanced oxidation processes (SR-AOPs) is primarily attributed to the sluggish circulation of redox couples. Herein, a carbon defects-enriched NBC-C3N5@CoMn (NCC) was synthesized through a self-assembly approach. The carbon defects within the NCC induce the electron trap effect, thereby facilitating the efficient cycling of redox couples in photo-Fenton-like processes during contaminant degradation. This effect enables the self-regeneration of the NCC catalyst. The reductive redox couples (Co (II) and Mn (II)) are continuously regenerated following the degradation process. Within the NCC, CoMn layered double hydroxides (LDHs) act as primary active sites, promoting the generation of hydroxyl radicals (•OH), sulfate radicals (SO4•-) and singlet oxygen (1O2) through continuous electron gain and loss. Additionally, the internal electric field established within the NCC further accelerates electron transfer. Density Functional Theory (DFT) calculations confirm that the carbon defects-enriched NCC exhibits lower adsorption energies and higher electron transfer efficiencies than carbon defect-deficient NCC. This study introduces a novel photocatalyst with self-regenerating capabilities, presenting an innovative approach to regulate redox couples in SR-AOPs for sustainable degradation.

Efficient generation of singlet oxygen for photocatalytic degradation of antibiotics: Synergistic effects of Fe spin state reduction and energy transfer

Singlet oxygen (1O2) exhibits excellent degradation performance and stability in removing antibiotics from an aqueous environment. However, its production is limited by free radical competition. This study proposed a photocatalytic method employing ferrihydrite (Fh) as the base, coated with K-doped g-C3N4 and modified by AgCl (Ag/AgCl), leading to the KC3N4/AgCl/Fh composite for efficient 1O2 production. Compared with Fh, the loading of KC3N4 reduced Fe (III) spin, facilitating the rapid conversion of H2O2 to 1O2. The addition of Ag promoted the intersystem crossing process, decreasing the singlet-triplet energy gap from 0.0708 to 0.0458 eV, thereby effectively generating more triplet excitons to convert O2 into 1O2 in a targeted manner. The KC3N4/AgCl/Fh achieved a degradation rate of 98.10 % for enrofloxacin in 30 min, showing high effectiveness and stability. This work suggests a new way to create Fh-based photocatalysts for the efficient production of 1O2.