Electron Paramagnetic Resonance Spin Trapping Research Articles

Aqueous photochemistry of fullerol revisited: Energy transfer vs. electron transfer processes probed by Rhodamine B degradation

Singlet oxygen, superoxide radicals and hydroxyl radicals generated by fullerol under irradiation were unambiguously identified by spin-trapping electron paramagnetic resonance technology. Comparing the photodegradation of a chemical probe of Rhodamine B by fullerol, Rose Bengal, and Fenton reaction systems demonstrated that different reactive oxygen species led to two competitive processes: cleavage of the dye skeleton by hydroxyl radicals and N-de-ethylation of the dye by singlet oxygen, which indicates that the degradation pathways of organics by irradiated fullerol depend on the competitive energy transfer and electron transfer processes.

First unequivocal identification of the critical acyl radicals from the anti-tuberculosis drug isoniazid and its hydrazide analogs by complementary applications of ESR spin-trapping and HPLC/MS methods

The carbon-centered isonicotinic acyl radical of isoniazid (INH), a widely-used frontline anti-tuberculosis drug, has been considered to play a critical role in inhibiting Mycobacterium tuberculosis, but not fully identified. Here we show that this radical intermediate can be unequivocally characterized by complementary applications of ESR spin-trapping and HPLC/MS methods by employing N-tert-butyl-α-phenylnitrone (PBN) as the suitable spin-trapping agent, which can form the most stable radical adduct. More importantly, for the first time, analogous carbon-centered acyl radicals and their respective NAD+ adducts have also been detected and identified from its two isomers (nicotinic acid hydrazide and 2-pyridinecarbohydrazide) and benzhydrazide which are structurally-related to INH, but not by 2-chloroisonicotinohydrazide. This study represents the first unequivocal identification of the carbon-centered acyl radicals of INH and other hydrazide analogs by both ESR spin-trapping and HPLC/MS methods, which may have broad biomedical and toxicological significance for future research for more efficient hydrazide anti-tuberculosis drugs.

Production of Reactive Oxygen Species by the Reaction of Periodate and Hydroxylamine for Rapid Removal of Organic Pollutants and Waterborne Bacteria.

Periodate (PI, IO4-) can be activated by hydroxylamine (HA), resulting in the rapid removal of organic pollutants within seconds. While the previous studies on PI-based advanced oxidation processes (AOPs) have proposed iodate radical (•IO3) as the major reactive species, no evidence of •IO3 production was found in the present PI/HA system. Reactive oxygen species (ROS) including •OH, HO2•, and 1O2 are proposed to be the main oxidants of the PI/HA system, which is supported by various tests employing the scavengers, chemical probes, and spin-trapping electron paramagnetic resonance (EPR) technique. To minimize the risk of toxic iodinated byproduct formation caused by reactive iodine species such as HOI and I2, the molar ratio of HA/PI was optimized at 0.6 to achieve the stoichiometric conversion of IO4- to iodate (IO3-), a preferred nontoxic sink of iodine species. The PI/HA system also efficiently inactivated both Gram-positive and -negative bacteria with producing 1O2 as the dominant disinfectant. The mechanism of ROS production was also investigated and is discussed in detail. This work offers a simple and highly efficient option for PI activation and ROS production which might find useful applications where urgent and rapid removal of toxic pollutants is needed.

Development of Flow-Injection Spin-Trapping ESR Methods for Kinetic Study of the O2−• Radical Scavenging Reaction with Mixtures of Phenolic Antioxidants

AbstractThe apparent second-order rate constants (aks) of the reaction between the O2−• radical and mixed solutions (aAox) of caffeic acid (CA) and 4-hydroxy-coumaric acid (4CA) were estimated in this study; this was achieved by a flow-injection spin-trapping ESR (FI-ESR) method that employed 5,5-dimethyl-pyrroline-N-oxide (DMPO) as the spin-trapping reagent. The aAox solutions were prepared by varying the mixing molar ratio of CA (a = [CA]/([CA] + [4CA])). The FI-ESR signal intensities of the DMPO spin-adduct of the O2−• radical (DMPO/O2) were monitored in the absence (I0) and presence (I) of aAox to estimate the inhibition ratio Y (%) (Y = 100 × I/I0), and 50% inhibitory dose of aAox (aID50). Further, the aks values of aAox were evaluated using these aID50 values through a competitive reaction kinetics treatment, which was conducted by using the second-order rate constant of the spin-trapping reaction (k1). The value obtained for the aks of aAox showed excellent agreement with the calculated values (akscal) that were estimated from the molar ratio (a) weighted mean of the ks values of CA (CAks) and 4CA (4CAks): akscal = aCAks + (1 − a)4CAks. These results demonstrate that CA and 4CA contribute independently to the O2−• radical scavenging reactions, and that the aks values of aAox completely satisfy the additive property depending on the mixing molar ratio (a). The O2−• radical scavenging capacities of aAox were also evaluated as equivalent concentrations of CA (Y[CA]eq.) using the observed inhibition ratio Y (%), and the 50% inhibitory dose of CA (CAID50): Y[CA]eq. = CAID50 × (100 − Y)/Y. The estimated Y[CA]eq. values of aAox agreed with the calculated equivalent concentrations of CA (k[CA]eq.) that were obtained on the basis of the additive property established for aAox and aks: k[CA]eq. = [CA] + (4CAks/CAks) × [4CA].

Near-Complete Suppression of Oxygen Evolution for Photoelectrochemical H2O Oxidative H2O2 Synthesis.

Solar energy-assisted water oxidative hydrogen peroxide (H2O2) production on an anode combined with H2 production on a cathode increases the value of solar water splitting, but the challenge of the dominant oxidative product, O2, needs to be overcome. Here, we report a SnO2-x overlayer coated BiVO4 photoanode, which demonstrates the great ability to near-completely suppress O2 evolution for photoelectrochemical (PEC) H2O oxidative H2O2 evolution. Based on the surface hole accumulation measured by surface photovoltage, downward quasi-hole Fermi energy at the photoanode/electrolyte interface and thermodynamic Gibbs free energy between 2-electron and 4-electron competitive reactions, we are able to consider the photoinduced holes of BiVO4 that migrate to the SnO2-x overlayer kinetically favor H2O2 evolution with great selectivity by reduced band bending. The formation of H2O2 may be mediated by the formation of hydroxyl radicals (OH·), from 1-electron water oxidation reactions, as evidenced by spin-trapping electron paramagnetic resonance (EPR) studies conducted herein. In addition to the H2O oxidative H2O2 evolution from PEC water splitting, the SnO2-x/BiVO4 photoanode can also inhibit H2O2 decomposition into O2 under either electrocatalysis or photocatalysis conditions for continuous H2O2 accumulation. Overall, the SnO2-x/BiVO4 photoanode achieves a Faraday efficiency (FE) of over 86% for H2O2 generation in a wide potential region (0.6-2.1 V vs reversible hydrogen electrode (RHE)) and an H2O2 evolution rate averaging 0.825 μmol/min/cm2 at 1.23 V vs RHE under AM 1.5 illumination, corresponding to a solar to H2O2 efficiency of ∼5.6%; this performance surpasses almost all previous solar energy-assisted H2O2 evolution performances. Because of the simultaneous production of H2O2 and H2 by solar water splitting in the PEC cells, our results highlight a potentially greener and more cost-effective approach for "solar-to-fuel" conversion.

Naphthoquinone derivatives: Naturally derived molecules as blue-light-sensitive photoinitiators of photopolymerization

Two naphthoquinone derivatives, i.e. 5-hydroxy-1,4-naphthoquinone (5HNQ) and 2-hydroxy-1,4-naphthoquinone (2HNQ), combined with different additives such as diphenyliodonium hexafluorophosphate (Iod), N-vinylcarbazole (NVK), phenacyl bromide (R-Br), N-phenyl glycine (NPG) and ethyl 4-dimethylamino benzoate (EDB), are investigated as photoinitiating systems (PISs) for free radical polymerization of trimethylolpropane triacrylate (TMPTA) and cationic polymerization of triethyleneglycol divinyl ether (DVE-3). The photopolymerization of the thiol-ene system trimethylolpropane tris(3-mercaptopropionate) (Trithiol)/DVE-3 with 5HNQ or 2HNQ based PISs are also investigated. 5HNQ shows maximum absorption in visible light region (blue light) which thus has the potential to perform under the irradiation of blue LED light. For the free radical polymerization of TMPTA, 5HNQ/Iod/NPG shows the highest photoinitiating ability among all the naphthoquinone derivative-based PISs, while 2HNQ-based systems are inefficient. The addition of Trithiol to TMPTA can significantly increase the double bond conversion of TMPTA during the photopolymerization. For the cationic photopolymerization of DVE-3, 2HNQ/Iod shows the highest photoinitiating ability among all the naphthoquinone derivative-based photoinitiating systems. 5HNQ-based systems also demonstrate good photoinitiation ability for DVE-3, but with slower polymerization rate compared to 2HNQ-based systems. In thiol-ene photopolymerization, 5HNQ PISs shows better photoinitiation ability than 2HNQ PIs systems. The results illustrate that the position of hydroxyl group in 1,4-naphthoquinone molecules plays an important role on photoinitiation ability of naphthoquinone derivatives. Steady state photolysis and electron spin resonance trapping experiments are also carried out to evaluate the relevant photochemical mechanism.

Photoinactivation of Salmonella enterica (serovar Typhimurium) by tetra-cationic porphyrins containing peripheral [Ru(bpy)2Cl]+ units

In the last years, antimicrobial photodynamic therapy (aPDT) has been considered as one important alternative to be used in antimicrobial treatments. In the present work we report the first photoinactivation of Salmonella enterica serovar Typhimurium (Salmonella Typhimurium) by cationic free-base meso-tetra-(phenyl)porphyrin and its Zn(II) complex containing peripheral Ru(II)-bipyridyl complexes. Bacterial inoculum (107 CFU mL-1) was incubated with the porphyrins (25 μM) with an irradiation system containing a halogen lamp with fluence values of 0, 180, 360, 720 and 1080 J cm-2. Both porphyrins demonstrate phototoxicity against bacteria, but higher efficiency was observed by Zn(II) complex. It was demonstrated that RuTPyP and ZnRuTPyP phototoxicity is due to their photodynamic activity associated with the formation of singlet oxygen, anion superoxide and hydroxyl radical at their irradiation by visible light. The formation of these reactive species was confirmed using flash-photolysis technique and spin-trap electron paramagnetic resonance (EPR) spectroscopy. The singlet oxygen quantum yield was determined by indirect method using the uric acid as singlet oxygen scavenger. Besides the characterization of optical absorption and fluorescence RuTPyP and ZnRuTPyP properties were realized using optical absorption and fluorescence spectroscopies. It was observed that complexation with Zn(II) ion increases the quantum yields of porphyrin fluorescence and singlet oxygen formation.

2-Hydroxy-4-methoxybenzophenone Enhances the Suppression of Superoxide Anion Radicals Generated via UVA-induced Photosensitizing by t-Butyl Methoxydibenzoylmethane.

4-tert-Butyl-4'-methoxydibenzoylmethane (BMDM) is widely used throughout the world as a highly effective UVA absorber that can prevent the progression of photoaging in skin. However, due to its low photostability, BMDM is also known for the disadvantage of having a reduced capability to absorb UVA during prolonged exposure to sunlight. Although many studies have been carried out to overcome this disadvantage of BMDM, little attention has been paid to how the radicals generated from BMDM during UV exposure influence the skin. Therefore, the purpose of this study was twofold: One goal was to clarify the influence of radicals on human skin using cytotoxicity as a parameter. The second was to propose a solution that could reduce the radical formation while taking photostability into consideration. Using ESR spin trapping and superoxide dismutase (SOD) treatment, the radicals produced by the UV exposure of BMDM were shown to be superoxide anion radicals (•O2-). HaCaT keratinocytes exposed to UVA in the presence of BMDM showed a significant reduction in cell viability, indicating that the radicals produced from BMDM have a harmful influence on the skin. UVA exposure coincidently led to a reduction of UVA absorbance by BMDM. Interestingly, 2-hydroxy-4-methoxybenzophenone (Benzophenone-3; BP3) reduced both the radical formation and the cytotoxicity resulting from the UVA-exposure of BMDM, while also restoring its UVA absorbance. In conclusion, the results show that BMDM and BP3 is an effective combination to reduce the influence of UVA-exposed BMDM on the skin and to prevent the loss of UVA absorbance by BMDM during UV exposure.

Correlation Between Reactive Oxygen Species Scavenging Ability by ESR Spin Trap Method and Brightness of Miso

Correlation Between Reactive Oxygen Species Scavenging Ability by ESR Spin Trap Method and Brightness of Miso

One-step preparation of sulfur-doped porous g-C3N4 for enhanced visible light photocatalytic performance.

Nonmetal doping is a convenient method to adjust the visible light photocatalytic activity of graphitic carbon nitride (g-C3N4). Herein, highly active sulfur-doped porous g-C3N4 (C3N4-S) was successfully prepared by one-step calcination using thiourea and melamine as the precursors. C3N4-S exhibited excellent photocatalytic performance for the degradation of Rhodamine B (RhB) under visible light irradiation. C3N4-S not only promoted the separation of photogenerated electron-hole pairs, but also enhanced electron transfer, resulting in a great improvement in the photocatalytic efficiency. Based on capture experiments and DMPO spin-trapping ESR spectra, the superoxide radical (˙O2-) was proved to be the predominant active species and the possible photocatalytic mechanism of C3N4-S was proposed. The photocatalytic mechanism of RhB degradation over C3N4-S was further explored using high-resolution mass spectra (HRMS).

How g-C3N4 Works and Is Different from TiO2 as an Environmental Photocatalyst: Mechanistic View.

Graphitic carbon nitride (CN) as a popular visible light photocatalyst needs to be better understood for environmental applications. The behaviors of CN as an environmental photocatalyst were systematically studied in comparison with a well-known TiO2 photocatalyst. The two photocatalysts exhibit different photocatalytic oxidation (PCO) behaviors and dependences on the experimental conditions (e.g., pH, Pt loading, and the kind of organic substrate and scavenger). The PCO of organic substrates was significantly enhanced by loading Pt on TiO2 under UV light (λ > 320 nm), whereas Pt-CN exhibited a lower PCO activity than bare CN under visible light (λ > 420 nm). While the presence of Pt enhances the charge separation in both TiO2/UV and CN/visible light systems (confirmed by transient IR absorption spectroscopic analysis), the opposite effects of Pt are ascribed to the different mechanisms of •OH generation in the two photocatalytic systems. The negative effect of Pt on CN is ascribed to the fact that Pt catalytically decomposes in situ-generated H2O2 (a main precursor of OH radical), which hinders •OH production. The production of OH radicals on CN is favored only at acidic pH but 1O2 generation is dominant in alkaline pH. The pH-dependent behaviors of reactive oxygen species generation on CN were confirmed by electron paramagnetic resonance spin trap measurements.

Activation of artemisinin and heme degradation in Leishmania tarentolae promastigotes: A possible link

Endoperoxides (EPs) appear to be promising drug candidates against protozoal diseases, including malaria and leishmaniasis. Previous studies have shown that these drugs need an intracellular activation to exert their pharmacological potential. The efficiency of these drugs is linked to the extensive iron demand of these intracellular protozoal parasites. An essential step of the activation mechanism of these drugs is the formation of radicals in Leishmania. Iron is a known trigger for intracellular radical formation. However, the activation of EPs by low molecular iron or by heme iron may strongly depend on the structure of the EPs themselves. In this study, we focused on the activation of artemisinin (Art) in Leishmania tarentolae promastigotes (LtP) in comparison to reference compounds. Viability assays in different media in the presence of different iron sources (hemin/fetal calf serum) showed that IC50 values of Art in LtP were modulated by assay conditions, but overall were within the low micromolar range. Low temperature electron paramagnetic resonance (EPR) spectroscopy of LtP showed that Art shifted the redox state of the labile iron pool less than the EP ascaridole questioning its role as a major activator of Art in LtP. Based on the high reactivity of Art with hemin in previous biomimetic experiments, we focused on putative heme-metabolizing enzymes in Leishmania, which were so far not well described. Inhibitors of mammalian heme oxygenase (HO; tin and chromium mesoporphyrin) acted antagonistically to Art in LtP and boosted its IC50 value for several magnitudes. By inductively coupled plasma methods (ICP-OES, ICP-MS) we showed that these inhibitors do not block iron (heme) accumulation, but are taken up and act within LtP. These inhibitors blocked the conversion of hemin to bilirubin in LtP homogenates, suggesting that an HO-like enzyme activity in LtP exists. NADPH-dependent degradation of Art and hemin was highest in the small granule and microsomal fractions of LtP. Photometric measurements in the model Art/hemin demonstrated that hemin requires reduction to heme and that subsequently an Art/heme complex (λmax 474 nm) is formed. EPR spin-trapping in the system Art/hemin revealed that NADPH, ascorbate and cysteine are suitable reductants and finally activate Art to acyl-carbon centered radicals. These findings suggest that heme is a major activator of Art in LtP either via HO-like enzyme activities and/or chemical interaction of heme with Art.

Drugs Repurposed as Antiferroptosis Agents Suppress Organ Damage, Including AKI, by Functioning as Lipid Peroxyl Radical Scavengers.

Ferroptosis, nonapoptotic cell death mediated by free radical reactions and driven by the oxidative degradation of lipids, is a therapeutic target because of its role in organ damage, including AKI. Ferroptosis-causing radicals that are targeted by ferroptosis suppressors have not been unequivocally identified. Because certain cytochrome P450 substrate drugs can prevent lipid peroxidation via obscure mechanisms, we evaluated their antiferroptotic potential and used them to identify ferroptosis-causing radicals. Using a cell-based assay, we screened cytochrome P450 substrate compounds to identify drugs with antiferroptotic activity and investigated the underlying mechanism. To evaluate radical-scavenging activity, we used electron paramagnetic resonance-spin trapping methods and a fluorescence probe for lipid radicals, NBD-Pen, that we had developed. We then assessed the therapeutic potency of these drugs in mouse models of cisplatin-induced AKI and LPS/galactosamine-induced liver injury. We identified various US Food and Drug Administration-approved drugs and hormones that have antiferroptotic properties, including rifampicin, promethazine, omeprazole, indole-3-carbinol, carvedilol, propranolol, estradiol, and thyroid hormones. The antiferroptotic drug effects were closely associated with the scavenging of lipid peroxyl radicals but not significantly related to interactions with other radicals. The elevated lipid peroxyl radical levels were associated with ferroptosis onset, and known ferroptosis suppressors, such as ferrostatin-1, also functioned as lipid peroxyl radical scavengers. The drugs exerted antiferroptotic activities in various cell types, including tubules, podocytes, and renal fibroblasts. Moreover, in mice, the drugs ameliorated AKI and liver injury, with suppression of tissue lipid peroxidation and decreased cell death. Although elevated lipid peroxyl radical levels can trigger ferroptosis onset, some drugs that scavenge lipid peroxyl radicals can help control ferroptosis-related disorders, including AKI.

γ-Radiolysis of Room-Temperature Ionic Liquids: An EPR Spin-Trapping Study.

The radiolytic stability of a series of room-temperature ionic liquids (ILs) composed of bis(trifluoromethylsulfonyl)imide anion (Tf2N-) and triethylammonium, 1-butyl-1-methylpyrrolidinium, trihexyl(tetradecyl)phosphonium, 1-hexyl-3-methylpyridinium, and 1-hexyl-3-methylimidazolium (hmim) cations was studied using spin-trap electron paramagnetic resonance (EPR) spectroscopy with a spin-trap α-(4-pyridyl N-oxide)-N-tert-butylnitrone (POBN). The trapped radical yields were measured as a function of POBN concentration and as a function of radiation dose by double integration of the broad unresolved lines. Well-resolved motionally narrowed EPR spectra for the trapped radicals were obtained by dilution of the ILs with CH2Cl2 after irradiation. The trapped radicals were identified as mainly carbon-centered alkyl and •CF3, and their ratio varies greatly across the series of ILs. Expected nitrogen-centered radicals derived from Tf2N- were not observed. The hmim liquid proved most interesting because a large part of the trapped radical yield (entirely carbon-centered) grew in over several hours after irradiation. We also discovered a complicated narrow-line stable radical signal in this neat IL with no spin trap added, which grows in over several hours after irradiation and decays over several weeks.

Investigation into the Direct Photolysis Process of Photo-Induced RAFT Polymerization by ESR Spin Trapping.

The direct photolysis of reversible addition fragmentation chain transfer (RAFT) agents under visible light was demonstrated by electron spin resonance (ESR) using 5,5-dimethyl-1-pyrroline N-oxide as a typical spin trap. The hyperfine coupling lines obtained by ESR spectroscopy showed the successful capture of the carbon-centered and the sulfur-centered radical. Photo-polymerization of vinyl acetate under different wavelengths was performed to verify the effects of wavelength on the process. The effect of the R group of RAFT agents on the photolysis was investigated by spin-trapping experiments using poly (butyl acrylate) and poly (vinyl acetate) as macroRAFT agents. The quantitative experiment showed the yield of photolysis of a xanthate to be only 0.023% under λ > 440 nm.

Cu(II) Complexes with FomA Protein Fragments of Fusobacterium Nucleatum Increase Oxidative Stress and Malondialdehyde Level

An explanation of carcinogenesis processes may certainly contribute to the prevention and development of novel methods for cancer treatment. In this paper, we considered the probable relationship between the presence of Fusobacterium nucleatum in the colon and its possible influence on the development of colorectal cancer. For this purpose, intracellular and/or extracellular generation of reactive oxygen species (ROS) by mouse colon carcinoma cells (CT26) was stimulated by two fragments of FomA adhesin from F. nucleatum and their complexes with copper(II): Cu(II)-Ac-KGHGNG-NH2 (1Cu) and Cu(II)-Ac-PTVHNE-NH2 (2Cu). Incubation of the cells with copper complexes was followed with ICP-MS technique. The overall generation of ROS was shown by means of fluorescence spectroscopy with two proper probes, whereas identification of ROS was achieved by the spin trapping technique and electron paramagnetic resonance measurements. As a result, an abundant production of the hydroxyl radicals, both inside and outside the cells, was observed upon the stimulation of the CT26 cells with the copper complexes. Clearly both compounds induced strong oxidation stress which triggered a radicals' cascade that finally resulted in the pronounced lipid peroxidation. The latter was evidenced with the measured level of malondialdehyde, a biomarker of the peroxidation process. By applying N-acetylcysteine antioxidant to the studied system, the free radical mechanism of the lipid peroxidation process was confirmed. Hypothetically this mechanism can lead to colon cell damage and further cancerogenesis processes.

Fabricated Ag dots/flower-like MoS2/rGO multidimensional photocatalyst for enhanced photocatalytic activity

Abstract Ag dots/flower-like MoS2/rGO multidimensional photocatalysts were successfully prepared via one-pot hydrothermal method. The characterizations of morphology and structure showed that the as-prepared photocatalysts with zero dimensional Ag dots, three dimensional flower-like MoS2 and two dimensional rGO composite structures have been clearly formed in composite multidimensional photocatalysts. Moreover, the photoelectronic performances exhibited that the composite multidimensional structure could efficiently enhance the transfer rate of charges. Especially the intensity of photocurrent was obviously improved after the Ag dots modified MoS2/rGO. The Ag/MoS2/rGO showed excellent photocatalytic activity of degradation tetracycline (TC), the removed rate of TC could reach 85.5% in 90 min. The species trapping experiments and electron spin resonance spin-trap tests clearly revealed that the h+ and ·O2− active species play the key roles during the photocatalytic degradation processes of TC. Overall, the composite multidimensional photocatalysts with zero, three and two dimensional in this work show a promising way to remove the TC wastewater, which suggested one strategy fabricate high active photocatalyst, and the photocatalytic mechanism was also discussed.

An urchin-like Ag3PO4/Pd/LaPO4 photocatalyst with Z-scheme heterojunction for enhanced hydrogen evolution

An urchin-like LaPO4-based nanocomposite integrating Ag3PO4 and Pd has been initially synthesized via a controllable self-assembly route, with enhanced photocatalysis and ultrastable structure for the synergistic hydrogen (H2) evolution under sunlight. Citric acid was employed as a structure-mediated agent to guide the oriented growth of LaPO4 along [101] facet at room temperature, showing the urchin-like 3D structure. Furthermore, Pd and Ag3PO4 were coated in turn resulting in the Ag3PO4/Pd/LaPO4 nanocomposite, in which Pd and Ag3PO4 could act as the functions of electron receptor and electron donor in the photocatalysis, respectively. It was discovered that the as-developed nanocomposite could present the robust photocatalysis and stable morphology after consecutive uses. Based on the band structure analysis, a Z-scheme system of Ag3PO4/Pd/LaPO4 was thereby proposed for the sunlight photocatalysis, as testified by DMPO spin trapping ESR spectra. Also, the photoluminescence and electrochemical impedance of nanocomposites were conducted, indicating that the improved carriers properties should be responsible mainly for the dramatically enhanced photocatalytic activities. Moreover, the outstanding photocatalytic performances of Ag3PO4/Pd/LaPO4 were demonstrated in H2 evolution (1084.3 μmol·g−1·h−1) under sunlight. Importantly, such a citric acid-controlled self-assembly route may pave the way toward the fabrication of multi-component photocatalyst tailored for the wide photocatalytic applications.

Fabrication of Z-scheme γ-Bi2MoO6/Bi12GeO20 heterostructure for visible-light-driven photocatalytic degradation of organic pollutants

In this study, an efficient and durable photocatalyst composed of Bi12GeO20 and γ-Bi2MoO6 through like Z-scheme mechanism was successfully obtained by heat treatment. The as-prepared Z-scheme 40γ-Bi2MoO6/Bi12GeO20 heterostructure presents the superior photocatalytic performance for degrading MBT, which is nearly 46 and 4.95 times higher than that of the pure Bi12GeO20 (kapp = 0.0007 min−1) and Bi2MoO6 (kapp = 0.0065 min−1), respectively. Meanwhile, the 40γ-Bi2MoO6/Bi12GeO20 heterostructure also shows the quite high photocatalytic performance for degrading TC, which is approximately 5.48 and 1.89 times higher than that of the pure Bi12GeO20 (kapp = 0.0021 min−1) and Bi2MoO6 (kapp = 0.0061 min−1), respectively. The enhancement of photocatalytic performance originates from not only the strong interface between Bi12GeO20 and γ-Bi2MoO6, but also the unique Z-scheme system which can effectively promote the separation of photogenerated electron-hole pairs and sufficiently utilize the photogenerated carriers for generating more active radicals. In addition, based on the active species trapping experiments and electron spin resonance (ESR) spin-trap technique, the photocatalytic mechanism over the Z-scheme γ-Bi2MoO6/Bi12GeO20 heterostructure is discussed in detail. The research may provide theoretical basis and significant guiding for future development of fabricating other Z-scheme heterostructure with superior photocatalytic performance and high stability.

Enhanced photoelectric conversion efficiency: A novel h-BN based self-powered photoelectrochemical aptasensor for ultrasensitive detection of diazinon

This work presents a novel hexagonal boron nitride (h-BN) based self-powered photoelectrochemical (PEC) aptasensor for ultrasensitive detection of diazinon (DZN) with excellent photoelectric conversion efficiency. It was the first time that h-BN based materials were applied to PEC aptasensor, in which the construction of Z-scheme heterojunction of h-BN and graphitic carbon nitride (CN) via doping sulfur into h-BN was innovatively proposed. Meanwhile, Au nanoparticles (AuNPs) were utilized for the surface plasmon resonance (SPR) effect and the formation of new recombination centers. The charge transfer mechanism was expounded and verified by the electron spin resonance (ESR) spin-trap technique. The proposed PEC aptasensor for determination of DZN exhibited a wide linear range from 0.01 to 10000 nM and a low detection limit of 6.8 pM with superb selectivity and remarkable stability. Moreover, the constructed PEC aptasensor performed well with excellent recoveries in three different real samples. This work illustrated that PEC aptasensor is a promising alternative to conventional analytical technologies for the detection of DZN and other organophosphorus (OP) pesticides. The designing ideas of the proposed h-BN based material can provide a foothold for the innovative construction of photoactive materials for PEC bioanalysis.