The sublethal content of antibiotics in the environment brings added urgency to degrade antibiotics to prevent the growth of antibiotic resistance and the accompanying public health crisis. Herein, we adopted a rational and intriguing strategy for constructing a porous, supported photocatalyst. A solution containing graphitic carbon nitride (g-C3N4), polyethylene glycol (PEG), and polyethylene terephthalate (PET) was electrospun, and followed by a postprocessing to remove the PEG, porous nanofibers (g-C3N4@PET) were obtained. Meanwhile, the g-C3N4@PET morphology and composition were determined by a series of analysis techniques. The g-C3N4/PET exhibits several favorable characteristics, namely, (i) it is easy to create more active sites due to the formation of pores throughout the nanofibers and the successful embedding of g-C3N4, (ii) the interconnected channel is beneficial for catalyst–antibiotics contact and light absorption, and (iii) it possesses high photocatalytic performance and reusability, avoiding the reunion and sedimentation of pure g-C3N4. This approach has an enormous potential for loading powder catalysts in real applications.

Photocatalytic H2 evolution is usually from pure water or water with sacrificial agents. Surprisingly, it has been found that the presence of poisonous macrolide antibiotics in an aqueous medium for catalytic H2 evolution enhances the H2 yield while itself being degraded, using Pt/graphitic carbon nitride (Pt/g-C3N4) under visible light (λ > 420 nm). Hence, a promising method that addresses the issues of energy shortage and environmental pollution is proposed. Among macrolide antibiotics, Roxithromycin (Rox) is so effective in facilitating the decomposition of water that it can be acted as a model in this paper to explain phenomenon as mentioned above. Furthermore, the mechanism of the reaction is also explored and 13 intermediates of Rox are identified by ultraperformance liquid chromatography and high-resolution mass spectrometry. The degradation pathway of Rox is proposed on the basis of the identified intermediates. In the whole process, both energy generation and pollutant control can be achieved simultaneously. Thereby, this represents a surprising waste-to-energy conversion process.Keywords: Graphitic carbon nitride; Hydrogen; Macrolide antibiotics; Photocatalysis; Water splitting;

The ligands and protein surroundings are important in peroxidase processes with iron porphyrins as catalysts. Similarly, two bioinspired composite catalysts made from iron phthalocyanine with axial ligands, 4-aminopyridine and 2-aminoethanethiol, were anchored on multiwalled carbon nanotubes to degrade some pollutants to the water environment, such as 4-chlorophenol, dyes, and so on. The effect of pH and sustained catalytic stability were investigated in the presence of two catalysts. Different axial ligands and carbon nanotubes that synergistically donated electrons to the central iron of iron phthalocyanine significantly improved the catalytic activity and stability during hydrogen peroxide activation. Electron paramagnetic resonance spin-trapping experiments indicated that catalytic oxidation is dominated by hydroxyl radicals in both catalytic systems, which is different from the high-valent metal-oxo generated in common biomimetic catalytic systems with iron porphyrins in the presence of the fifth ligands. The high catalytic activity and strong durability are distinct from traditional peroxide-activating catalysts of metal complexes dominated by hydroxyl radicals, where catalysts have poor stability and are self-destructive in repetitive cyclic oxidation. In our catalytic system, the axial ligand and carbon nanotubes together affect the electronic structure of the central iron in which electron-donor substituents shift the FeIII/II potential to more negative values, which make the activation process of hydrogen peroxide occur at neutral pH, and increase the rate of the step from FeIII to FeII. However, the reaction takes place under acidic conditions, and FeIII/FeII cycling occurs slowly in the traditional Fenton system with hydrogen peroxide.

Molecular hydrogen is one of the essential reactants in the chemical industry, and its generation from renewable sources such as biomass materials and water is of great benefit to the future society. Generally, molecular oxygen should be pre-eliminated in the hydrogen evolution reactions (HERs) in order to avoid the reverse hydrogen oxidation reaction (HOR). Here, we report a highly efficient HER from a formaldehyde/water mixture using MgO supported Ag nanoparticles (AgNPs/MgO) as the catalyst and molecular oxygen as a promoter. The HER rate depends almost linearly on the oxygen partial pressure, and the optimal turnover frequency (TOF) of the silver catalyst exceeds 6,600 h–1. Based on the experimental and theoretical results, a surface stabilized MgO/Ag–•OOH complex is suggested to be the main catalytically active species for the HER.Keywords: Ag; formaldehyde; hydrogen evolution reaction; MgO; oxygen promotion;

•A biomimetic catalytic system for oxidative desulfurization was proposed.•FePcCl16 exhibited remarkable catalytic activity for sulfides oxidation at 30 °C.•FePcCl16 catalyst could be recycled for more than 23 times.•High-valent iron(IV)-oxo species were the active species in the catalytic process.A biomimetic catalytic system composed of iron hexadecachlorophthalocyanine (FePcCl16), hydrogen peroxide (H2O2), H2O and pyridine exhibited high activity for ultra-deep removal of dibenzothiophene (DBT) in model oil containing n-octane. The conversion of DBT was up to 100% after 60 min operation at room temperature. In addition, the FePcCl16 catalyst could be recycled for more than 23 times without noticeable decrease on the conversion of DBT. Moreover, the activation energy evaluated through Arrhenius’ equation was found to be equal to 25.5 kJ/mol. Nitrogen-containing compounds such as pyridine, quinoline, and acridine, naturally existing in many kinds of fuel oil, had previously been considered to inhibit the oxidative desulfurization (ODS) process. Surprisingly, these organonitrogen compounds could actually accelerate the conversion rate of DBT in this catalytic system. Mechanistic studies revealed that the high-valent iron(IV)-oxo species were the main active intermediate via the heterolytic O–O bond cleavage of the putative iron(II)-hydroperoxo species. Pyridine binding to iron(II)-hydroperoxo complexes was demonstrated to facilitate the generation of high-valent iron(IV)-oxo species and enhance the reactivity of high-valent iron(IV)-oxo species in ODS.Download high-res image (105KB)Download full-size image

The non-heme oxamate anionic cobalt(III) complexes [CoIII(opbaX)]− (opbaX = 4-X-o-phenylenebis(oxamate), X = H, NO2, CH3) with different substituents were synthesized and applied to targeted micropollutant degradation. Typical radical scavengers (isopropanol and chlorine anions) have no negative effect on the catalytic oxidation of substrates, and no DMPO–˙OH or DMPO–˙OOH (DMPO = 5,5-dimethyl-pyrroline-oxide) signal was detected by electron paramagnetic resonance spin-trap technique in [CoIII(opbaX)]−/H2O2 system, suggesting that the non-hydroxyl radical biomimetic catalytic mechanism was dominant in the oxidation process. The results of high-definition ESI-MS pronounced the presence of cobalt-oxo intermediates which played a key role in the catalytic oxidation of substrates. Furthermore, density functional theory calculations were used to evaluate the viability of such cobalt-oxo species and it demonstrated an optimizing electromer with a formulation of [CoIVO˙]− or [CoIII–OH]˙. The calculations explained that the catalytic activity of [CoIII(opbaX)]− was significantly enhanced by introducing an electron-withdrawing substituent which could change the coordination environment of cobalt to generate more electron-deficient cobalt-oxo species with stronger oxidizing power. This paper made a progress in verifying bio-mimic high oxidation state species and applied it to water purification, which provided deep insight into the properties of transition-metal centers in aqueous catalysis.

•The system is a combination of photocatalysis and biomimetic catalysis.•The catalytic activity of g-C3N4 and the stability of hemin were enhanced under solar irradiation.•High-valent iron (Fe(IV) = O) species could be detected by ESI–MS and GC–MS.•The final products of 4-CP were small molecule acids which were biodegradable.•O2−, Fe(IV) = O, OOH species played the main role in g-C3N4-IMD-hemin/H2O2 system.In nature, metalloporphyrins, such as chlorophyll, cytochrome P450 and so forth, are key materials in maintaining the ecological cycles, especially the carbon cycle, and play an important role in both photosynthesis and the catalytic oxidation of organisms. Inspired by these factors, we skillfully combined photocatalysis and biomimetic catalysis using imidazole (IMD)-functionalized modification of g-C3N4 and axial coordination with hemin. Compared with pure hemin, g-C3N4 and a mixture of the two, our novel catalytic system (g-C3N4-IMD-hemin/H2O2) showed high photocatalytic oxidation activity for the degradation of 4-chlorophenol (4-CP), and the stability of hemin was enhanced under solar irradiation. Furthermore, the effect of pH and the sustained photocatalytic oxidation stability of g-C3N4-IMD-hemin for degrading 4-CP were investigated. The results indicated that g-C3N4-IMD-hemin presents a high photocatalytic oxidation activity over a wide pH range and exhibits good recyclability. A series of designed experiments showed that superoxide radicals (O2−), high-valent iron (Fe(IV) = O) species, peroxy radicals (OOH) and few hydroxyl radicals (OH) were generated in the g-C3N4-IMD-hemin/H2O2 system. This synergistic photocatalytic and biomimetic process offers new insight for the utilization of solar energy and offers a new perspective for the exploration of catalysts for environmental remediation.Download high-res image (171KB)Download full-size image

•Pyridine-based ligand INA served as a “bridge” connecting g-C3N4 and FePcCl16.•Fe (IV) = O, OH and SO4− species played the main role in CBZ degradation.•Fe (IV) = O originated from *FePcCl16 differs from traditional PMS activation system.Recently, peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) have received increasing attention because of their capability and adaptability in decontamination. The couple of solar light and PMS activation is an environmentally friendly and efficient strategy for environmental remediation. Herein, the iron hexadecachlorophthalocyanine (FePcCl16) was used to coordinate with graphitic carbon nitride (g-C3N4), which was functionalized by pyridine-based ligand isonicotinic acid (INA) to prepare a distinctive catalyst, g-C3N4-INA-FePcCl16. The experimental results revealed that g-C3N4-INA-FePcCl16 can activate PMS efficiently for the elimination of carbamazepine (CBZ) under visible light irradiation over a wide pH range. Upon irradiation with visible light, CBZ was destroyed by the solider g-C3N4 with generated sulfate (SO4−) and hydroxyl (OH) radicals, on the other hand, high-valent iron (Fe (IV) = O) species accompanied by SO4− and OH radicals were produced by excited-state FePcCl16 (*FePcCl16) during oxidation, which is different from a traditional PMS activation system. The axial pyridine-based ligand was protected under the FePcCl16 macrocyclic structure shield. Noteworthy, in the absence of visible light, g-C3N4-INA-FePcCl16 showed a higher catalytic performance than pure g-C3N4, FePcCl16 and a mechanical mixture of the two. This study allows for the construction of an effective and environmental catalytic system, which can be applied to purify water that contains refractory pollutants.Download high-res image (263KB)Download full-size image

•g-C3N4-IMD-FePcCl16 were prepared by axial coordination between g-C3N4 and FePcCl16.•The generation of anchored species under visible-light irradiation.•The fabrication converts the mechanism based on OH into anchored species.•Transformation products of CBZ were finally transformed to small molecules.As highly active species, in theory, hydroxyl radicals (OH) can move freely and destroy almost all organic compounds, including catalysts with a conjugate structure. Therefore, a system that can generate oxidative species with a high activity, but where the active species is anchored to avoid autooxidation, is urgently required. In this work, we fabricated a novel visible-light-assisted advanced oxidation process based on high-valent iron species (Fe(IV)O) over graphitic carbon nitride (g-C3N4) that was coordinated to iron hexadecachlorophthalocyanine (FePcCl16) through imidazole ligands (IMD). Under visible-light excitation, the phthalocyanine ring of the g-C3N4-IMD-FePcCl16/hydrogen peroxide (H2O2) can be motivated to an excited state FePcCl16∗, in which active H2O2 and the generation of anchored Fe(IV)O species are used for the degradation of carbamazepine (CBZ). Because the molecular movement of transient Fe(IV)O species is restricted, the possibility of oxidative collision is minimized, which provides good stability. An analysis of the electron paramagnetic resonance, gas chromatography/mass spectrometry, photoluminescence spectra, periodic on/off photocurrent density response and the photo-assisted catalytic active experiments, indicates that the rapid generation of Fe(IV)O species occurs as the catalyst contacts the H2O2, which inhibits the conduction-band electrons of the g-C3N4 from reacting with H2O2 and generating OH. This study provides insight into the construction of suitable structures that will enhance visible-light-assisted catalytic oxidation activity and allow for the fabrication of an anchored highly active species.Download high-res image (136KB)Download full-size image

For powder catalysts to be recycled easily and to be applied in practical wastewater treatment, it is imperative to search suitable carriers that can be applied to support catalytic particles. Herein, we highlight a facile route to synthesize an easily recycled photocatalyst using polyethylene terephthalate (PET) to disperse graphitic carbon nitride (g-C3N4) via electrospinning and subsequent hydrothermal treatment. The resultant nanofiber is labeled T-g-C3N4/PET. The design concept is to expose the g-C3N4 on the PET surface and convert it from inactivation to re-emergence. g-C3N4 is embedded into the PET, which avoids the reunion and unrecyclable deficiencies of powder catalysts. T-g-C3N4/PET was characterized by field-emission scanning electronic microscopy, transmission electron microscopy, UV–vis diffuse reflectance spectra, two-dimensional X-ray diffraction, Fourier-transform infrared spectroscopy, and thermogravimetric analysis technologies. T-g-C3N4/PET showed a high photocatalytic activity for the degradation of antibiotics such as sulfaquinoxaline and sulfadiazine under solar irradiation, and the activity was almost unaffected in a high background. The as-obtained catalysts could be reused several times with no loss in performance in cycling photodegradation tests. Finally, a possible pathway and mechanism for degrading sulfaquinoxaline with T-g-C3N4/PET was proposed, respectively, in which holes and the superoxide radical were the predominant active species, and resulted in the oxidative degradation of antibiotics. These results demonstrate that the preparation method may provide a novel idea for supporting nanoscale catalysts for reuse.Keywords: g-C3N4; nanofiber; PET; photocatalytic antibiotics degradation; solar irradiation

The rapid diffusional mass transfer process (DMTP) always results in a highly efficient reaction. Herein, cobalt phthalocyanine (CoPc) was covalently anchored on to multiwall carbon nanotubes (MWCNTs) by an easy and moderate one-step deamination method to obtain the catalyst MWCNT-immobilized CoPc (CoPc-MWCNT). The interfacial peroxidase-like catalytic activity of CoPc-MWCNTs is described for controllable H2O2 activation. According to the experimental results and density functional theory calculations, we can be confident that high-valent cobalt-oxo intermediates are formed during the H2O2 activation. Such active species are anchored and exposed on the surface of MWCNTs, shortening the DMTP and enhancing the resistance of CoPc-MWCNTs to oxidative decay. The introduction of linear alkylbenzene sulphonates (LAS) facilitates the catalytic H2O2 activation by CoPc-MWCNTs, and at the same time, CoPc-MWCNTs could maintain a high and sustained catalytic activity because of the specific hydrophobic interactions between the long-chain alkyl group of LAS and the π-conjugated surface of the MWCNTs.

A visible-light responsive photocatalyst, polyacrylonitrile-dispersed graphitic carbon nitride nanofibers (g-C3N4/PAN nanofibers), was synthesized by electrospinning. The g-C3N4 is dispersed uniformly in the nanofibers, which helps it overcome the defects of easy aggregation and difficult recycling of powder catalysts. The model substrate, rhodamine B (RhB), could be adsorbed rapidly into the PAN nanofibers and decomposed efficiently in situ simultaneously in the presence of the g-C3N4 over a wide pH range under visible light irradiation. As a fibrous catalyst, the g-C3N4/PAN nanofibers were quite simple to recycle, and the catalytic activity maintained a high level without obvious decline after being reused several times. In addition, based on the intermediates detected by ultra performance liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry, N-de-ethylation chromophore cleavage and ring-opening mineralization are the main processes in RhB degradation. Finally, a possible mechanism was proposed, in which the hole along with the superoxide radical mainly contribute to the oxidative degradation of RhB.

The chemistry of enzymes presents a key to understanding the catalysis in the world. In the pursuit of controllable catalytic oxidation, researchers make extensive efforts to discover and develop functional materials that exhibit various properties intrinsic to enzymes. Here we describe a bioinspired catalytic system using ordered-mesoporous-carbon (OMC)-bonded cobalt tetraaminophthalocyanine (CoTAPc-OMC) as a catalyst that could mimic the space environment and reactive processes of metalloporphyrin-based heme enzymes and employing linear dodecylbenzenesulfonate as the fifth ligands to control the activation of H2O2 toward the peroxidase-like oxidation. The generation of nonselective free hydroxyl radicals was obviously inhibited. In addition, functional modification of OMC has been achieved by a moderate method, which can reduce excessive damage to the structure of OMC. Because of its favorable and tunable pore texture, CoTAPc-OMC provides a suitable interface and environment for the accessibility and oxidation of C.I. Acid Red 1, the model compound, and exhibits significantly enhanced catalytic activity and sufficient stability for H2O2 activation. The high-valent cobalt oxo intermediates with high oxidizing ability have been predicted as the acceptable active species, which have been corroborated by the results from the semiempirical quantum-chemical PM6 calculations.Keywords: bioinspired catalysis; cobalt phthalocyanine; hydrogen peroxide activation; ordered mesoporous carbon;

The development of a pH-tolerant Fenton-like catalyst is an active and challenging research front in the area of environmental engineering. In the present work, a novel catalyst iron−γ-aminopyridine ligand (FeAPy) was prepared and immobilized on activated carbon fibers (ACFs) by a covalent bond to obtain a heterogeneous FeAPy-ACFs. FeAPy-ACFs present a pH-tolerant microenvironment for the Fenton-like oxidation process, which exhibits remarkable catalytic ability across a wide pH range from acidic to alkaline. At neutral pH, employing hydrogen peroxide as an oxidant, the FeAPy-ACFs showed enhanced catalytic ability to degrade hazardous environmental pollutants Acid Red 1 (AR1) dyes and avoid secondary pollution with regard to FeAPy. FeAPy-ACFs are stable and remain efficient in repetitive test cycles with no obvious decrease of catalytic activity. Moreover, in comparison to most reported supports for Fenton-like catalyst, the introduction of ACFs contributed specifically to the activity improvement of FeAPy. Probe studies combined with electron paramagnetic resonance experiments were conducted to ascertain the role of several reactive species (•OH, HO2•, and FeIV═O) on dye decolorization.

•A novel heterogeneous catalyst system (FeCit@ACFs/H2O2) has been elucidated.•The higher adsorption capacity of FeCit@ACFs brings more excellent performance.•Exhibiting remarkable catalytic activity across a wider pH rang of 2–10.Activated carbon fibers supported ferric citrate (FeCit@ACFs) as a heterogeneous catalyst for the rapid removal of dyes under visible light irradiation is reported. The FeCit@ACFs/H2O2 system exhibited remarkable catalytic activity across a wide pH range (2–10). Moreover, the catalyst presented excellent sustained catalytic ability in these experiments. The effects of catalyst dosage, and H2O2 concentration were also evaluated. Electron paramagnetic resonance (EPR) spectroscopy confirmed the hydroxyl radicals (OH) involved as the active species in the catalytic system. Moreover, the superoxide radical (O2-) was not detected by EPR, suggesting better use of H2O2 for removal of dyes. According to the observed effects of the scavengers n-butanol and KI, hydroxyl radicals, especially the surface-bounded OH, had a dominant role in the oxidation of dyes. More importantly, the high adsorption capacity of ACFs could efficiently enhance the removal rate of dyes by the surface-bounded OH. This paper discusses a possible catalytic oxidation mechanism in the FeCit@ACFs/H2O2 system, which provides a feasible approach for the elimination of widely existing pollutants.Graphical abstract

Fe-doped BiOBr hollow microspheres were successfully prepared by a simple solvothermal method. The as-prepared samples exhibit excellent photocatalytic activity and electrochemical behaviour, attributed to the unique hollow structure and Fe doping, which is favorable for transfer of photogenerated carriers and enhancement of photoadsorption.

Cobalt tetra(2,4-dichloro-1,3,5-triazine)aminophthalocyanine (CoPc) was immobilized covalently on activated carbon fiber (ACF) felt to obtain CoPc-modified ACF (CoPc-ACF) catalyst, and an electrocatalytic oxidation system using CoPc-ACF as the anode was constructed. The electrocatalytic oxidation of Acid Red 1 (AR1) was investigated in aqueous solution by an UV-vis spectrophotometer and UPLC. The results indicated that AR1 could be eliminated efficiently in this electrocatalytic oxidation system. In addition, the results of FTIR, TOC and GC-MS suggested that the electrocatalytic oxidation experienced the decoloration achieved by destroying the azo linkage and the further mineralization due to the cleavages of benzene ring and naphthalene ring. The intermediates were mainly small molecular compounds such as maleic acid and succinic acid, etc. Repetitive tests showed that CoPc-ACF can maintain high electrocatalytic activity over several cycles. The further EPR spin-trap experiments indicated that the hydroxyl radicals did not dominate the reaction in this electrocatalytic system, which was completely different from the traditional electro-Fenton system. Based on the non-radical reaction mechanism, the CoPc-modified ACF electrocatalyst has potential application in treating actual dyestuffs wastewaters, which are accompanied with high concentration of hydroxyl radical scavengers such as chlorine ions and additives in the textile printing and dyeing industry.

Employing a commercial semiconductor with a positive conduction band level, we investigated a new plasmonic photocatalyst, Pt/Bi2O3, with high photocatalytic activity for decomposition of environmental organic pollutants under visible light.

Fe-doped BiOBr hollow microspheres were successfully prepared by a simple solvothermal method. The as-prepared samples exhibit excellent photocatalytic activity and electrochemical behaviour, attributed to the unique hollow structure and Fe doping, which is favorable for transfer of photogenerated carriers and enhancement of photoadsorption.