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.

•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

•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

•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

•ESI-MS assisted by pyridine ligands was used to identify FePcF16-O-FePcF16.•DFT analysis indicated the HOMO and LUMO energy levels of FePcF16-O-FePcF16 and Fe(IV)O.•The main active species in CBZ degradation were Fe(IV)O.•CBZ degradation products were finally transformed to four small molecule acids.Phthalocyanine has been used widely as an oxidation catalyst, e.g., in wastewater treatment. It has become important and necessary to study phthalocyanine derivatives, to understand the potential effect they may have. Despite the fact that phthalocyanine dimers are easy to generate, such complexes have been ignored as catalysts. We prepared O-bridged iron perfluorophthalocyanine dimers (FePcF16-O-FePcF16). Ultraviolet–visible, X-ray diffractometry, X-ray photoelectron spectroscopy, density-functional theory analysis and electrospray ionization–mass spectrometry technology assisted by pyridine ligands have been used to identify the structure of FePcF16-O-FePcF16. Carbamazepine selected as a model pollutant could be effectively oxidized in the system with FePcF16-O-FePcF16 and H2O2. Electron paramagnetic resonance data indicated an active center that was different from OH in the Fenton reaction. Electrospray ionization–mass spectrometry detected the generation of high-valent diiron-oxo species, which implies that carbamazepine degradation was accomplished by the attack of FeIVOFeIVO in the FePcF16-O-FePcF16/H2O2 system. Thus, we identified an O-bridge iron perfluorophthalocyanine dimer and proposed a catalytic mechanism. These results may provide a novel explanation for the oxidative mechanism.Download high-res image (78KB)Download full-size image

•PMS generated anchored species for contaminant degradation with highly reactive activity under sunlight irradiation.•The photodegradation pathway of CBZ was proposed based on intermediates identified by UPLC Synapt G2-S HDMS.•Reaction mechanism and the stability of FePcCl16/PMS/Sunlight were studied in detail.In the field of environmental catalysis, the construction of highly efficient and stable catalytic oxidation processes has raised considerable attention. In this study, a novel solar-initiated photocatalytic oxidation system, FePcCl16/PMS/Sunlight, was established by iron hexadecachlorophthalocyanine (FePcCl16) with peroxymonosulfate (PMS) in the presence of sunlight excitation. Under sunlight irradiation, the phthalocyanine ring of the FePcCl16 is motivated to FePcCl16∗ in the excited state, which activates PMS to generate free radicals or high–valent iron(IV)-oxo intermediates (Fe(IV) = O) to oxidize carbamazepine (CBZ). The system could degrade CBZ effectively and total-organic-carbon removal from solution reached nearly 80% within 90 min. FePcCl16 catalytic activity was almost without loss and without iron leaching after twenty recycles, indicating that the FePcCl16/PMS/Sunlight was a stable and efficient photocatalytic oxidation system. Electron paramagnetic resonance, gas chromatography-mass spectrometry and photocatalytic-activity-experiment analysis shows that Fe(IV) = O species, singlet oxygen (1O2), hydroxyl and sulfate radicals (OH, SO4−) are the main active species in the catalytic oxidation of CBZ. Density functional theory (DFT) calculations exhibits that the electronic cloud for excited state FePcCl16∗ is transferred from the porphyrazine ring and peripheral substituents to the central Fe atom and its axial position. The main degradation intermediates and possible degradation pathway of CBZ were proposed by ultra-performance liquid chromatography and high-resolution mass spectrometry (UPLC Synapt G2-S HDMS). This study provides efficient catalytic oxidation support for wastewater treatment.Download high-res image (64KB)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

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 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.

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;

Iron tetranitrophthalocyanine (FePc) was modified and immobilized on carbon fiber (FePc(NO2)3–CF) by covalent bond to obtain a supported heterogeneous catalyst for the removal of dibenzothiophene (DBT) in tridecane. In the supported catalytic system, the catalyst exhibited an excellent catalytic performance without any sacrificial agents, and the conversion of DBT could reach 92 % at 130 °C and 0.2 MPa of initial dioxygen pressure for 3 h. Compared to unsupported FePc, the introduction of carbon fiber dramatically improved the catalytic activity of FePc and facilitated the reuse of catalysts. The amount of FePc(NO2)3–CF, temperature and the initial pressure of molecular oxygen were also studied in detail to optimize the reaction conditions. The removal of DBT significantly increased with the increasing of concentration of DBT in model oil. Finally, a mechanism involving high-valent iron oxo species was proposed for the oxygenation. This study provides new insights into industrial desulfurization systems using carbon fiber as catalyst carrier.

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.