1O2 Production Research Articles

Switching of radical and nonradical pathways through the surface defects of Fe3O4/MoOxSy in a Fenton-like reaction

Coexistence of radical and nonradical reaction pathways during advanced oxidation processes (AOPs) makes it challenging to obtain flexible regulation of high efficiency and selectivity for the requirement of diverse degradation. Herein, a series of Fe3O4/MoOxSy samples coupling peroxymonosulfate (PMS) systems enabled the switching of radical and nonradical pathways through the inclusion of defects and adjustment of Mo4+/Mo6+ ratios. The silicon cladding operation introduced defects by disrupting the original lattice of Fe3O4 and MoOxS. Meanwhile, the abundance of defective electrons increased the amount of Mo4+ on the catalyst surface, promoting PMS decomposition with a maximum k value up to 1.530 min−1 and a maximum free radical contribution of 81.33%. The Mo4+/Mo6+ ratio in the catalyst was similarly altered by different Fe contents, and Mo6+ contributed to the production of 1O2, allowing the whole system to attain a nonradical species–dominated (68.26%) pathway. The radical species-dominated system has a high chemical oxygen demand (COD) removal rate for actual wastewater treatment. Conversely, the nonradical species-dominated system can considerably improve the biodegradability of wastewater (biochemical oxygen demand (BOD)/COD = 0.997). The tunable hybrid reaction pathways will expand the targeted applications of AOPs.

Strong enhancement of the chemiluminescence of cerium (IV)-Na2S system by mono-dispersed N-CDs generated in situ

In this study, nitrogen-doped carbon dots (N-CDs) was observed to strongly amplify the chemiluminescence (CL) intensity of Ce (IV)-Na2S system with an enhancement factor around 55. Possible mechanism was explored and discussed on account of results of free radical scavenger experiments, CL spectra and X-ray photoelectron spectroscopy (XPS), etc. During the CL process, mono-dispersed N-CDs generated in situ catalyzed the production of more 1O2 on its surface and the CL enhancement mainly attributed to the chemiluminescence resonance energy transfer (CRET) between (1O2)2*/Ce (III)* and N-CDs. The new CL system was then developed as a convenient and sensitive platform for H2S detection. The linear range was 20–200 nM and the limit of detection (LOD) was 0.32 nM. The applications in different water samples were proved to have good recovery rate (tap water: 100.46%-109.22%; pool water: 99.91%-102.87%) with satisfactory results.

2D defect-engineered Ag-doped γ-Fe2O3/BiVO4: The effect of noble metal doping and oxygen vacancies on exciton-triggering photocatalysis production of singlet oxygen

The selectivity of singlet oxygen (1O2) holds promising applications in complex environmental systems due to its ability to preferentially oxidize target pollutants. Usually, 1O2 in photocatalytic systems is generated via the electron transfer pathway and •O2− plays an important role as an intermediate, while the exciton-based energy transfer pathway for 1O2 generation has been less studied. Here, a 2D Ag-γ-Fe2O3/BiVO4 with oxygen vacancies was designed which was capable of generating 1O2 by an exciton-based energy transfer-dominated approach, as strongly demonstrated by the results of steady-state fluorescence spectroscopy and phosphorescence spectroscopy. In the Z-type heterojunction photocatalyst system, Ag acted as an electron mediator to promote not only the generation of free carriers but also the generation of singlet excitons, while the appropriate concentration of oxygen vacancies further promotes the exciton-triggering photocatalysis production of 1O2. The Ag-γ-Fe2O3/BiVO4 could degrade 99.4% of sulfadiazine within 90 min, and 1O2 played an important role in the degradation of sulfadiazine, as shown by EPR and active species capture experiments. Ecotoxicity predictions indicated that the main byproducts of sulfadiazine degradation by Ag-γ-Fe2O3/BiVO4 were low in toxicity. The prepared photocatalysts provide a new idea for obtaining 1O2 and designing photocatalysts with selectivity.

Coupling anodic and cathodic reactions using an electrocatalytic dual-membrane system actuates ultra-efficient degradation with regulable mechanisms

The versatile reaction possibilities arising from the interaction between the anodic and cathodic reactions naturally contained in electrocatalytic membrane filtration (EMF) systems are of great valuable in meeting the current complex water treatment requirements. But currently, most studies only focus on half-cell reactions with a single electrocatalytic membrane, which limits the research progress of the EMF technology. Here we report a coupling strategy that utilizes the interaction between the anodic and cathodic reactions to actuate ultra-efficient degradation performance with regulable reaction mechanisms. An electrocatalytic dual-membrane filtration (EDMF) system was established. Six typical configurations of the EDMF system were set up and systematically investigated by adjusting the electrode distance and filtration sequence. Based on the obtained results of degradation performance and mechanisms, a regulation strategy which enabled flexible tuning of direct nonradical oxidation (e.g., h+) and indirect oxidation (e.g., 1O2, ·OH, HO2·, O2·−, etc.) was proposed. In particular, cathodic reactions were found to adversely affect the anodic reactions at the relatively short electrode distance of 0.9 mm. Anodic reactions could inhibit the generation of 1O2 at short distance of 0.9 mm but promote its generation at long distances of 9 and 17 mm. The A–C_0.9 configuration achieved the highest degradation performance, while the C–A_9 configuration was revealed to be much more conducive to 1O2 production. Overall, our findings demonstrate the versatility and tunability of the reaction mechanism and performance of the EDMF system due to the flexible coupling of the anodic and cathodic reactions, which potentially lays a foundation for future development of ultra-efficient mechanism-adjustable electrocatalysis technologies.

Rational design of Multi-model ROS regulation Nano-platform for enhanced Mild-temperature photothermal therapy

The tumor thermotolerance owing to the overexpression of heat shock proteins (HSPs) is the critical challenge in practical application of mild-temperature photothermal therapy (MPTT). Reactive oxygen species (ROS) can not only serve as a powerful weapon to kill cancer cells, but also a regulator to inhibit HSPs, thus improving the thermal sensitivity of tumors. Herein, a multi-model ROS regulation nano-platform based on TCLP nanocomposites consisting of polyacrylic acid encapsulated, chloroperoxidase (CPO) and β-Lapachone (β-Lap) loaded black mesoporous titanium (H-TiO2) has been constructed for the ROS-enhanced MPTT. In this nano-platform, the H-TiO2 acts as the NIR-Ⅱ light triggered photothermal agent and photosensitizer to contribute to deep tissue MPTT and PDT, the β-Lap acts as a H2O2 amplifier to improve the 1O2 production of CPO. The abundant ROS from TCLP NPs can limit the activity as well as the expression of HSPs, ultimately improving the antitumor efficacy of MPTT. Finally, excellent synergistic tumor inhibition based on TCLP NPs has been reached both in vitro and in vivo. This multi- model ROS enhanced MPTT nano-platform with low toxic side effects offers a promising strategy and enlightenments the clinical application of MPTT.

Persulfate activation by sludge-derived biochar for efficient degradation of 2,4-dichlorophenol: performance and mechanism.

Porous sludge biochar (PSDBC) and zero-valent iron (ZVI) supported on porous sludge biochar composite (ZVI@PSDBC) were synthesized using municipal sludge through pyrolysis under N2 atmosphere, which manifested upgraded performance in persulfate (PS) activation for 2,4-dichlorophenol (2,4-DCP) degradation. The 2,4-DCP (50 mg/L) could be almost completely removed within 20 min under relatively low PS dosage (0.5 mmol/L) in both PSDBC/PS and ZVI@PSDBC/PS systems, and the mineralization rate could respectively approach 73.7% and 91.6% in 60 min. Combined with a scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) characterization and electron spin-resonance (ESR) detection, electrochemical analysis, the radical and non-radical pathways in the catalytic systems were discussed. Graphitized structure and superior conductivity made PSDBC and ZVI@PSDBC not only act as electron donors in PS activation to create radicals (mainly SO4·- and ·OH), but also as "mediators" to facilitate the direct electron transfer from 2,4-DCP to the catalysts-PS complexes. The C=O groups of PSDBC and ZVI@PSDBC aided in the production of 1O2. Meanwhile, zero-valent iron nanoparticles promoted the formation of radicals as the reactive sites of PS, resulting in the most effective 2,4-DCP degradation in the ZVI@PSDBC/PS system. The stability and practicability of sludge biochar materials had been demonstrated in reusability and actual wastewater experiments. The findings provided a promising way for the reuse of municipal sludge and effective PS activation in wastewater treatment.

Enhanced degradation of sulfamethoxazole by activation of peroxodisulfate with red mud modified biochar: Synergistic effect between adsorption and nonradical activation

Since the discovery of the potential environmental risk associated with large quantities of red mud, there has been an urgent need to find a rational disposal technology for this waste. In this study, low-cost iron-based biochar catalysts (RM@BC-x) were synthesized by co-pyrolysis of waste red mud and spent coffee grounds after ball milling. RM@BC-800 exhibited remarkable adsorption capacity, reaching 4.70 mg/g in 120 min. The adsorbed SMX was degraded simultaneously after adding peroxodisulfate (PDS), and sulfamethoxazole (SMX) was completely removed from the solution in only 30 min. Correlation analysis and pre-sorption experiment proved that the adsorption of SMX significantly enhanced the oxidation effect. Moreover, the Fe0, defects and CO groups of RM@BC-800 were the main active sites. Singlet oxygen (1O2) played a dominant role in the degradation of SMX rather than the traditional radicals (•OH or SO4•−). In particular, O2•− was shown to be used mainly as a precursor for the production of 1O2 without directly oxidizing SMX. The steady state concentration of 1O2 has been calculated to be hundreds or thousands of times higher than that of other radicals. Five degradation pathways of SMX were proposed (including NS bond cleavage, hydroxylation, and –NH2 oxidation). RM@BC-800 has the advantages of strong anti-interference ability, low iron leaching based on energy calculations and environmental impact assessments. This work provides a new option for the resource utilization of red mud and designs a green material with fast adsorption and efficient catalysis for the practical treatment of antibiotic wastewater.

Rose bengal-decorated rice husk-derived silica nanoparticles enhanced singlet oxygen generation for antimicrobial photodynamic inactivation.

The online version contains supplementary material available at 10.1007/s10853-023-08194-z.

Mechanistic Insights on Salicylic Acid Mediated Enhancement of Photosystem II Function in Oregano Seedlings Subjected to Moderate Drought Stress.

Dramatic climate change has led to an increase in the intensity and frequency of drought episodes and, together with the high light conditions of the Mediterranean area, detrimentally influences crop production. Salicylic acid (SA) has been shown to supress phototoxicity, offering photosystem II (PSII) photoprotection. In the current study, we attempted to reveal the mechanism by which SA is improving PSII efficiency in oregano seedlings under moderate drought stress (MoDS). Foliar application of SA decreased chlorophyll content under normal growth conditions, but under MoDS increased chlorophyll content, compared to H2O-sprayed oregano seedlings. SA improved the PSII efficiency of oregano seedlings under normal growth conditions at high light (HL), and under MoDS, at both low light (LL) and HL. The mechanism by which, under normal growth conditions and HL, SA sprayed oregano seedlings compared to H2O-sprayed exhibited a more efficient PSII photochemistry, was the increased (17%) fraction of open PSII reaction centers (qp), and the increased (7%) efficiency of these open reaction centers (Fv'/Fm'), which resulted in an enhanced (24%) electron transport rate (ETR). SA application under MoDS, by modulating chlorophyll content, resulted in optimized antenna size and enhanced effective quantum yield of PSII photochemistry (ΦPSII) under both LL (7%) and HL (25%), compared to non-SA-sprayed oregano seedlings. This increased effective quantum yield of PSII photochemistry (ΦPSII) was due to the enhanced efficiency of the oxygen evolving complex (OEC), and the increased fraction of open PSII reaction centers (qp), which resulted in an increased electron transport rate (ETR) and a lower amount of singlet oxygen (1O2) production with less excess excitation energy (EXC).

Ultrafast short-range catalytic pathway modified peroxymonosulfate activation over CuO with surface oxygen defects for tetracycline hydrochloride degradation

The presence of antibiotics in water bodies seriously threatens the ecosystem and human health. Advanced oxidation processes (AOPs) based on peroxymonosulfate (PMS), an effective method to remove antibiotics, have a bottleneck problem that the low oxidant utilization is attributed to the hindered electron transfer between metal oxides and peroxides. Here, CuO with rich oxygen vacancies (OVs), MSCuO-300, was synthesized to efficiently degrade tetracycline hydrochloride (TTCH) (k = 0.095 min−1). The dominant role of direct adsorption and activation of OVs and its regulated Cu–O, rather than surface hydroxyl adsorption, mediated a short-range catalytic pathway. The shortened catalytic pathway between active sites and PMS accelerated the charge transfer at the interface, which promoted PMS activation. Compared with CuxO-500 and Commercial CuO, the activation rate of PMS was increased by 11.97, and 12.64 times, respectively. OVs contributed to the production of 1O2 and O2•-, the main active species. In addition, MSCuO-300/PMS showed excellent adaptability to real water parameters, such as pH (3–11), anions, and continuous reactor maintained for 168 h. This study provides a successful case for the purification of antibiotic-containing wastewater in the design of efficient catalysts by oxygen defect strategies.

Photosensitizers Dispersed on Nanosized Triterpenoid Matrix with Deaggregation-Enhanced Singlet Oxygen Production.

Aggregation-caused quenching (ACQ) effects of photosensitizers severely cut down the generation of quantum yield of singlet oxygen (1O2) for effective photodynamic therapy (PDT). Herein, we accomplish a deaggregation-enhanced 1O2 production strategy by the noncovalent coordination of a clinically applied triterpenoid oleanolic acid (OA) and hematoporphyrin (Hp) via one-step self-assembly, forming a nanosensitizer OH, in which Hp is interspersed on the surface of the OA matrix in a face-to-face manner. The scattered arrangement of Hp held by the OA matrix decreases the π-π aggregation in Hp, leading to a 3.7-fold boost in the intracellular 1O2 yield and high phototoxicity in vitro and in vivo. Moreover, the biologically active OA enables OH to display excellent cellular uptake efficiency (increase by 36-fold), deep tumor penetration, and synergistic antitumor outcome at a low dose. Thus, this simple strategy paves the way for the green development of efficient photosensitizers.

Anthracene-Bridged Photosensitizers for Effective and Safe Photodynamic Therapy

Photodynamic therapy (PDT) is a minimally invasive therapeutic modality. However, the residual photosensitizers (PSs) after PDT can still produce toxic singlet oxygen (1O2) under sunlight to damage normal tissues. The PS that can be switched off after PDT is desirable but rare. Herein, we propose a general strategy to design effective and self-degradable PSs by embedding an anthracene bridge into donor–acceptor (D–A) structures. First, the steric anthracene can regulate the orbital distribution for enhancing the 1O2 production capacity. More importantly, the anthracene is responsive to the self-produced 1O2 for self-degradation. Besides, the degradation rate can be fine-tuned by the hydrophilicity of PSs. In this way, the PSs can realize a balance between treatment and suicide to ensure PDT and post-treatment safety. This work provides new insights into the design of degradable PSs with a clear mechanism, aiming to improve the post-safety of PDT.

Insights into the superior singlet oxygen production for BiVO4/Bi4Ti3O12 S-scheme heterojunction catalysts

This study constructed BVO/BTO a S-scheme heterojunction, which constructed oxygen vacancy and facilitated the separation of charge carriers for the promising production of powerful 1O2.

Universal nanosonosensitizer for ROS-mediated reduction of various cancer cells.

Sonodynamic therapy (SDT) has attracted great attention due to its deep tissue penetration, uniform tissue energy distribution, and noninvasiveness features. Additionally, external triggers can precisely focus on the tumor site with good specificity and high controllability. In the past decade, numerous sonosensitizers have been designed and used for SDT. However, the research and development of universal sonosensitizers for many different types of tumors are equally important in clinical treatment. Herein, we synthesized and studied the universality of four MWO4-PEG nanoparticles (NPs). All of the four MWO4-PEG NPs exhibited highly efficient ultrasound (US)-triggered production of 1O2 and ˙OH, enabling effective decreased cell viability, increased cell apoptosis rate, and a destruction of mouse tumors under US stimulation. The US-triggered NPs indicated good sonosensitivity and low toxicity to nine kinds of cancer cells. After accomplishing its therapeutic functions, NiWO4-PEG could be metabolized by the mouse body without any long-term toxicity. The PEGylated MWO4-PEG NPs shown in this study would provide efficient and universal US-triggered cancer therapy with the advantages of a cost-effective, convenient, and noninvasive agent that is promising for noninvasive SDT cancer treatment.

Self-assembled nanoparticles based on cationic mono-/AIE tetra-nuclear Ir(III) complexes: long wavelength absorption/near-infrared emission photosensitizers for photodynamic therapy.

Cyclometalated Ir(III) complexes as photosensitizers (PSs) have attracted widespread attention because of their good photostability and efficient 1O2 production ability. However, their strong absorption in the UV-vis region severely limits their applications in photodynamic therapy (PDT) because the short wavelength illuminating light can be easily absorbed by the skin and subcutaneous adipose tissue causing damage to the patient's normal tissue. Herein, mono- and tetra-nuclear Ir(III) complex-porphyrin conjugates are rationally designed and synthesized, especially [TPP-4Ir]4+ exhibits obvious aggregation-induced emission (AIE) characteristics. PSs comprising Ir(III) complex-porphyrin conjugates self-assembled as nanoparticles (NPs) are successfully achieved. The obtained [TPP-Ir]+ NPs and [TPP-4Ir]4+ NPs exhibit long wavelength absorption (500-700 nm) and near-infrared emission (635-750 nm), successfully overcoming the inherent defects of short wavelength absorption of traditional Ir(III) complexes. Moreover, [TPP-4Ir]4+ NPs exhibit good biocompatibility, high 1O2 generation ability, low half-maximal inhibitory concentration (IC50) (0.47 × 10-6 M), potent cytotoxicity toward cancer cells and superior cellular uptake under white light irradiation. This work extends the scope for transition metal complex PSs with promising clinical applications.

Mo-Based Heterogeneous Interface and Sulfur Vacancy Synergistic Effect Enhances the Fenton-like Catalytic Performance for Organic Pollutant Degradation.

Heterogeneous Fenton-like reactions (HFLRs) based on the in situ electrochemical generation of hydrogen peroxide (H2O2) are one of the green methods to remediate organic pollutants in wastewater. However, the design of Fenton-like catalysts with specific active sites and high pollutant degradation rate is still challenging. Here, MoS2-MoC and MoS2-Mo2N catalytic cathodes with heterojunctions were successfully prepared, and the mechanism by which hydroxyl radicals and singlet oxygen (1O2) were generated cleanly without adding chemical additives other than oxygen was clarified. The composite catalysts contained more sulfur vacancies, and the catalytic cathode achieved a high paracetamol pollutant degradation efficiency with 0.17 kWh g-1 TOC specific energy consumption. And almost 5 times higher activity was achieved compared to a pure MoS2 catalytic cathode. Experimental studies confirmed that the production of 1O2 was based on the transformation of superoxide radicals by Mo6+, and 1O2 accounted for approximately 66% of the total degradation and enhanced the nonradical behavior in the reaction. This work provides a sustainable strategy for pollutant utilization, which is valuable for solving the difficult problems of HFLRs and developing new environmental remediation technologies.

Highly Effective Generation of Singlet Oxygen by an Imidazole-Linked Robust Photosensitizing Covalent Organic Framework.

Developing effective photosensitizers to initiate the generation of singlet oxygen (1O2) is of great significance in both chemistry and physiology. Herein, linking the photoactive porphyrin moieties by in situ-formed robust imidazole groups, a covalent organic framework (COF), PyPor-COF, was successfully designed and synthesized. Detailed characterizations reveal that it not only possesses high crystallinity, permanent porosity, and robust stability but also shows a semiconductive photoresponse activity. As demonstrated by electron paramagnetic resonance experiments, the COF can initiate the generation of 1O2 efficiently under visible-light irradiation, the efficiency of which is higher than that of the pristine porphyrin-based reactant and even higher than some commonly used commercially available photosensitizing agents. Anticancer experiments prove that it can efficiently trigger the production of 1O2 in a physiological environment. This work demonstrates that the imidazole-linked porphyrin-incorporated COF is a highly promising photosensitizer that can even be applied in photodynamic therapy.

An anode fabricated by Co electrodeposition on ZIF-8/CNTs/CF for peroxymonosulfate (PMS) activation

A Co@ZIF-8/CNTs-CF anode for PMS activation was prepared by Co electrodeposition on carbon felt (CF) modified with ZIF-8 and carbon nanotubes (CNTs). The results showed that the fabricated Co@ZIF-8/CNTs-CF anode was an effective peroxymonosulfate (PMS) activator toward tetracycline (TC) removal. Compared with that in reaction system of bare CF anode + PMS, the reaction system of Co@ZIF-8/CNTs-CF anode + PMS exhibited 3.08 times decrease in the activation energy demanded and 4.21 times increase in the reaction rate constant (k), resulting in a kinetic favorable process of PMS activation by the Co@ZIF-8/CNTs-CF anode. The enhanced activation performance of the fabricated anode was ascribed to the high contents of the pyrrolic N and low valence state of Co in the Co@ZIF-8/CNTs-CF anode. Furthermore, the influence factors on the characteristics of transformation among the generated reactive species during the anodic PMS activation process were comprehensively investigated by the quenching experiments and the electron paramagnetic resonance (EPR) tests. The results showed that the SO4•- and reactive oxygen-containing reactive species (O2•- and 1O2) were generated during the activation of PMS by anode and became the major contributors toward TC removal. The production of 1O2 was through the dismutation of O2•-. In addition, the EPR experiments demonstrated that O2•- was generated mainly through the anodic PMS activation but the electrochemically driven molecular oxygen reduction reaction (ORR) process. The fabricated Co@ZIF-8/CNTs-CF anode for PMS activation provided a reference for the wastewater treatment based on the electrochemical advanced oxidation processes (EAOPs).

Basic electrolyzed water coupled with ultrasonic treatment improves the functional properties and digestibility of Antarctic krill proteins

This study firstly constructed a new method of basic electrolyzed water coupled with ultrasonic (USBEW) to creatively modify the Antarctic krill proteins (AKPs), and its effects on amino acid composition, structural and functional properties, as well as in vitro digestibility of AKPs were evaluated. Results showed that BEW inhibited the production of 1O2 and •OH radicals from ultrasonic treatment. In comparison with the deionized water coupled with ultrasonic (USDW) treatment, the USBEW treatment effectively reduced the oxidation of active groups (carbonyl and free sulfhydryl) in the side chain of amino acids of the AKPs, and it also obviously decreased the particle size (18.6 nm), improved the solubility (13.2 %), increased the molecules flexibility and the surface hydrophobicity of AKPs. All these advantageous changes contributed to the improved foam stability, foam capacity and emulsifying properties of AKPs. More importantly, the in vitro digestibility (84.6 %) of AKPs treated by USBEW was significantly higher than that any control samples. Our results prove that the USBEW treatment is a valid and promising method to exploit novel marine protein products with a high nutritional quality.

A cascade FRET photosensitizer that enhances photodynamic therapy for ocular melanoma

Photodynamic therapy (PDT) relies on the generation of cytotoxic singlet oxygen (1O2) from an otherwise nontoxic photosensitizer accumulated in tumor tissue to treat cancer. However, PDT of uveal melanoma, the most common adult intraocular cancer, using potent porphyrin derivatives as photosensitizers has shown limited therapeutic efficacy due to low bioavailability and 1O2 yield. Here, considering the uveal melanoma microenvironment of endogenous melanin, which has a high absorption between 300 nm and 500 nm, we design a carbon dot-based photosensitizer that uses multiple different pathways to generate 1O2. We conjugated gadolinium (Gd)-doped carbon dots (Gd@Cdots) with the porphyrin-derivatives chlorin e6 (Ce6) and verteporfin (Ver). The resulting nanoparticle (Gd@Cdots/Ce6/Ver) generates 1O2 under UV irradiation mainly in cascade FRET from Gd@Cdots to Ce6 and then to Ver; the photoactivated Ver, in turn, transfers its energy to 3O2 to generate 1O2. In human uveal melanoma MUM-2B cells in vitro, Gd@Cdots/Ce6/Ver generated 7.1- and 2.4-fold higher production of hydroxyl radical (·OH) and superoxide anions (O2-·) following UV irradiation than Gd@Cdots, indicating greater induction of tumor cell apoptosis. In an orthotopic mouse model of uveal melanoma, PDT with Gd@Cdots/Ce6/Ver showed the same trend of superior potency in tumor growth inhibition. This photosensitizer design improves the PDT efficacy of uveal melanoma by enhancing the production of 1O2 and should be of broad utility to other PDT.