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Current environmental concerns have encouraged researchers to search for a facile, environmentally-friendly and efficient method for sewage treatment. Cellulose aerogels (CAs) with high porosities, large specific surfaces and sustainability are promising candidates as catalytic carriers to solve many environment problems. However, pure CAs often lack mechanical strength and are prone to collapse under a small force, especially in water. Here, blended polyester fibers (B-PET) were used to support a CA containing nanosheet graphitic carbon nitride (g-C3N4), which greatly enhanced the tensile strength of the pure CA. Moreover, the composited aerogel, g-C3N4@CA/B-PET, showed high impact resistance in the water impact experiment and maintained its robust structure after 24 h of water shock. The g-C3N4@CA/B-PET exhibited a favorable photocatalytic activity towards the removal of hexavalent chromium and antibiotics simultaneously, which could challenge freestanding g-C3N4. The as-prepared composite material could be reused easily and maintained its excellent photocatalytic performance in cycling tests. Finally, the possible pathway for the degradation of sulfaquinoxaline and the mechanism in this photocatalytic system were proposed, where the superoxide radicals ( O2−) were the dominant active species, resulting in the oxidation of antibiotics. In addition, the photoelectrons could reduce the toxic hexavalent chromium to harmless trivalent chromium.

Utilizing peroxymonosulfate (PMS)-based advanced oxidation processes to remove emerging contaminants in water has received widespread attention. In this study, g-C3N4-IMA-FePcCl16 that was fabricated by axial coordination was applied to activate PMS for carbamazepine (CBZ) degradation. The introduction of imidazole-based ligand (IMA) and iron hexadecachlorophthalocyanine (FePcCl16) facilitates the photogenerated electron-hole pairs separation of g-C3N4 and broadens the visible-light response range. The coordination structure was characterized by X-ray diffraction and X-ray photoelectron spectroscopy. Photocatalytic experiments demonstrated that g-C3N4-IMA-FePcCl16 can highly effective eliminate CBZ with a removal of ∼95% within 25 min in the presence of PMS. The effects of various experimental parameters on the CBZ degradation were investigated, such as the loading amount of FePcCl16, pH, PMS dosage and anions. It is noteworthy that Cl− has a positive effect on the degradation of CBZ. Another interesting finding is that the degradation of CBZ is attributed to the synergistic effect of multiple active species, which is confirmed by gas chromatography-mass spectrometry, electron paramagnetic resonance and radical quenching tests. Superoxide radicals (O2 −) and singlet oxygen (1O2) are the dominated active species. This work offers a novel idea for the rational design of high-efficiency photocatalysts for wastewater remediation.

Developing efficient and environmentally friendly catalytic system is significant for the removal of sulfide in fuel. O-bridged diiron perfluorophthalocyanine/4-mercaptopyridine (FePcF16-O-FePcF16/4-Mpy) as a novel composite catalyst was designed and prepared by axial coordination. The catalyst characterization was conducted through ultraviolet-visible spectroscopy, fourier transform infrared spectroscopy, X-ray diffractometry, electrospray ionization–mass spectrometry and density-functional theory technology. A high-efficient extraction oxidative desulfurization system is composed of hydrogen peroxide (H2O2), the mixture of ethanol and water and FePcF16-O-FePcF16/4-Mpy. Notably, the coordination of 4-Mpy greatly enhanced the catalytic activity of FePcF16-O-FePcF16, 99.4% of the desulfurization rate was achieved in 20 min at 30 °C. The catalyst system was cycled 8 times without significantly reducing the removal of dibenzothiophene. Electron paramagnetic resonance and gas chromatography–mass spectroscopy proved the high-valent iron-oxo intermediates were the main active substances in the FePcF16-O-FePcF16/4-Mpy/H2O2 system, and the pathway of catalytic oxidation DBT was proposed. This work provided useful insights to select suitable ligands to improve the activity of metal phthalocyanine, and offered a novel idea for the construction of efficient oxidative desulfurization system.

Single-atom catalysts (SACs) have become an attractive concept in heterogeneous catalysis because of its high activity, selectivity and maximized utilization efficiency. However, constructing a high-loading SACs through conventional pyrolysis methods remains a challenge, because metal precursors usually have low thermal stability and the decrease of particle size will lead to an increase of surface energy. Herein, we used dicyandiamide to tailor the metatungstate and fix the W atoms during the thermal polymerization process, finally obtained a new kind of W-SAC (single W atoms anchored on graphitic carbon nitride, named as W-CN) with a high-loading of 11.16 wt% and a unique O, N coordination. The electrospray ionization high-definition mass spectrometry (ESI-HDMS) revealed that single W atoms were introduced into graphitic carbon nitride via the polycondense of W-containing dicyandiamide intermediate. The unique atomically dispersed N-W-O3 moieties, which promoted the separation efficiency of photogenerated electron-hole pairs, were identified by Aberration-corrected scanning transmission electron microscopy (AC-TEM), X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure spectroscopy (XAFS) and Density functional theory (DFT) calculation. Moreover, compared to pure CN, the W-CN exhibited an enhanced catalytic performance for the oxidation of carbamazepine (CBZ) under solar light irradiation. The experiment results revealed that photogenerated holes (h+), superoxide radicals (•O2−), and singlet oxygen (1O2) were the predominant active species and played an important role in eliminating emerging contaminants. This work paves a facile and efficient path toward high-loading SAC, and opens new insight into tracking SAC structure evolution.

The treatment of river course pollution via photocatalysis has recently received significant attention. However, the problem of catalyst immobilization is hindering the popularization of powder catalysts in practical application. In this paper, graphitic carbon nitride (g-C3N4) was embedded on the surface of the sheath-core composite polyester fibers (LMPET) by a hot-melt adhesive process to construct a robust three-dimensional nonwoven catalytic platform (g-C3N4@LMPET). The results of field-emission scanning electron microscopy and digital microscopy showed that the scattered fibers were assembled in an irregular interpenetrating network system and the presence of the semi-coated inlaid g-C3N4 on LMPET structure was confirmed. This system showed a favorable photocatalytic activity towards the decomposition of antibiotics, such as sulfadiazine (SDZ) and sulfamerazine. Additionally, electron paramagnetic resonance spectra and ultra-performance liquid chromatography coupled with high-definition mass spectrometry analysis indicated that O2− is the predominant radical involved in the degradation of antibiotics in neutral solutions, avoiding the corrosion of polyester carriers during the pollutant elimination process. The superior performance of g-C3N4@LMPET, in terms of tensile strength and regenerability, was confirmed through mechanical tests and cycling experiments. Furthermore, the consequence of SDZ photocatalytic degradation in different water media exhibited an intriguing practical application performance of g-C3N4@LMPET. This work offers distinctive insight on the immobilization and large-scale application of powder materials.

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.

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.

Self-purification of an aquatic environment occurs through the enzymatic functioning of microorganisms; however, nowadays, pollutant release has exceeded the self-purification capacity in the aquatic environment, and some antibiotics, such as sulfonamides, can inhibit microorganism reproduction. Therefore, to enhance the self-purification capacity in an aquatic environment, we developed a biomimetic catalytic system by mimicking the catalytic mechanism of enzymes. This system is based on iron phthalocyanine coordinates on poly (4-vinylpyridine)/polyacrylonitrile nanofibers. The resulting coordination structure was characterized by digital microscopy, X-ray photoelectron spectroscopy etc. The catalytic system was highly active and stable for sulfonamide degradation, even in the presence of inorganic salts at neutral pH. Gas chromatography–mass spectroscopy and high-definition electrospray ionization mass spectrometry proved the heterolytic cleavage of the peroxide O O bond to generate high-valency iron-oxo species instead of homolytic cleavage to generate OH in a catalytic system. Detailed density functional theory calculations, ultra-performance liquid chromatography and high-definition mass spectrometry showed that the aromatic compounds were degraded to small acids by the electrophilic attack of iron-oxo active species.

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.

Developing efficient photocatalytic materials for the elimination of emerging contaminants is of great significance for wastewater treatment. However, photocatalysts in powder form usually suffer from the problems of easy agglomeration and difficult recycle in water. Herein, graphitic carbon nitride/polylactic acid (g-C3N4/PLA) fiber composites with highly hierarchical macro/mesoporous structure were constructed by a simple and efficient methods of centrifugal-electrostatic spinning and alkali treatment. The porous structure of fiber could provide abundant space to immobilize g-C3N4 nanosheets, avoiding the wrapping of g-C3N4 inside the fiber and creating more active sites for photocatalytic reaction. Importantly, the carbamazepine (CBZ) removal rate by porous g-C3N4/PLA fiber composites under solar irradiation was as high as 99% in 2 h. The reaction mechanisms and CBZ degradation pathways were identified. Superoxide radical (•O2−), singlet oxygen (1O2) and hole (h+) were regarded as dominant active species in porous g-C3N4/PLA photocatalytic system for photocatalytic degradation of CBZ. The porous fiber composites not only possessed superior photocatalytic activity, repeatability and stability, but also could be biodegraded in natural environment without secondary pollution. This work proposed a promising way for developing efficient, stable and environmental-friendly photocatalytic materials for the removal of CBZ and other emerging contaminants in wastewater.

Due to their excellent flexibility and high sensitivity, conductive hydrogel flexible sensors have got more and more attention in the wearable electronic devices field. However, for conductive hydrogel flexible sensors, the integration of conductive hydrogels key features (strength, stretchability, anti-freezing, antibacterial properties and large linear sensing range) is very necessary for their practical application. In this work, we creatively used soft 1D silk nanofibers (SNFs) and hard 2D graphitic carbon nitride (g-C3N4) nanosheets to co-reinforce polyvinyl alcohol (PVA) organohydrogel. Surprisingly, the addition of only 0.1% silk nanofibers and little g-C3N4 nanosheets greatly improved the tensile strength (~3.2 times) and toughness (~7.7 times) of organohydrogel. By using a binary solvent system composed of water and ethylene glycol, the organohydrogel had anti-freezing function. Even at −18 °C, it could well maintain the flexibility and conductivity of the organohydrogel. Due to the addition of Al3+, the bactericidal rate of conductive polyvinyl alcohol - silk nanofibers - graphitic carbon nitride nanosheets (PVA/SNF/CN) organohydrogel against E. coli and S. aureus was 99.527% and 99.41%, respectively. A sandwich-like flexible strain sensor based on PVA/SNF/CN organohydrogel had a large linear sensing range (0%–100%), fast response (276 ms) and superb antifatigue property (1000 cycles). It could not only successfully detect human motions (wrist bending, knee joint bending) and facial expression (smiling and frowning), but also still maintain the accuracy of the output signal for up to 20 days of use. The PVA/SNF/CN organohydrogel has shown enormous potential in flexible sensors.

The development of coordination complexes to activate hydrogen peroxide (H2O2) selectively is a goal that has long been pursued. As highly reactive intermediates, the high-valent metal-oxo species play important roles in many biological and industrial catalytic oxidation processes. To improve the catalytic efficiency of metal complexes, the peroxide OO bond should be cleaved heterolytically to decrease the decomposition of H2O2 into O2 and H2O. In this work, we provide a simple method to obtain coordination complex catalysts based on iminodiacetic acid (IDA), copper(II) ions and pyridine derivatives. Catalytic activity tests showed that the introduction of 4-aminopyridine ligands resulted in an enhanced catalytic activity of the IDA/Cu(II)/4-ampy complex. A series of designed experiments proved that high-valent copper-oxo species ([OCuIII(IDA)(4-ampy)2] species) were formed in the IDA/Cu(II)/4-ampy complex system in the presence of hydrogen peroxide. The [OCuIII(IDA)(4-ampy)2] species were detected by in-situ high-definition electrospray ionization mass spectrometry, and has been considered as the possible active species during H2O2 activation catalyzed by the IDA/Cu(II)/4-ampy complex (with the molar ratio of IDA/Cu(II)/4-ampy being greater than 1:1:2). A mechanism has been proposed based on the results of electron paramagnetic resonance and density functional theory calculations.

The development of advanced oxidation processes to generate reactive oxygen species (ROS) has been one of the most important and great challenging goals in environmental catalysis field. Herein, a representative of persistent free radicals (PFRs), activated carbon fibers (ACFs), was innovatively employed to construct a novel and outstanding catalytic system, Cit-Fe@ACFs/AA/H2O2, in which PFRs act as an electron sink to release electrons to Cit-Fe (“discharging”), thus accelerating the reaction rate-determining step of Cit-FeIII to Cit-FeII. Meanwhile, ascorbic acid (AA) serves as an electron donor provides electrons to ACFs to supply the consumed PFRs (“charging”). Previously, AA was mainly reported to be a ROS scavenger instead. Remarkably, in our system, the PFRs coupled with AA enabled unblocked electron transfer, strongly improving the generation of ROS (OH), allowing for an extreme rate enhancement in oxidative decomposition of organic contaminants by hundreds of times compared with that of the sole Cit-Fe/H2O2 system.

Peroxymonosulfate (PMS) activation with the generation of strongly oxidizing hydroxyl radicals (•OH) and sulfate radicals (SO4•−) has attracted widespread attention for the elimination of organic contaminants. However, the design of an eco-friendly catalytic system with high mineralization rate and high stability remains a challenge. Here, an iron-based photocatalyst (β-FeOOH@g-C3N4) for the activation of PMS was prepared by a cyclic microwave-assisted reaction, whereby Fe3+ was introduced at the nitrogen sites of g-C3N4, resulting in in situ growth and a uniform distribution of nano-β-FeOOH thereon. β-FeOOH@g-C3N4 maintained high catalytic activity after acid treatment or repeated tests, demonstrating excellent stability and reusability. Moreover, compared with the catalytic systems with β-FeOOH or g-C3N4 alone, the catalytic activity of β-FeOOH@g-C3N4 was increased 5–10 times for the catalytic oxidation of carbamazepine (CBZ) and other emerging contaminants under solar irradiation. Importantly, the CBZ mineralization rate with the β-FeOOH@g-C3N4/PMS system under solar irradiation was as high as 92%. From the results of electron paramagnetic resonance spectroscopy and radical trapping experiments, large amounts of O2•−, 1O2, and FeV = O are present at the beginning of the reaction, which contribute to the rapid oxidative removal of CBZ, while SO4•− and •OH contribute to the deep oxidation, leading to a significantly enhanced total organic carbon (TOC) removal efficiency. This work provides an alternative method for the design of a highly efficient and stable catalyst for PMS activation to eliminate emerging contaminants.

The development of an efficient and green catalytic system for recalcitrant pollutant removal is an attractive yet challenging research topic in the field of environmental catalysis. In the present work, the use of activated carbon fibers (ACFs) as a novel and excellent metal-free catalyst is proposed for peracetic acid (PAA) activation, constructing a pro-environmental and efficient catalytic system for the removal of organic pollutants. In this system, ACFs could effectively activate PAA to remove the dye Reactive Brilliant Red X-3B (RR X-3B) over a wide pH range (3–11), exhibiting a remarkable pH-tolerant performance. Moreover, the ACFs also displayed excellent sustained catalytic ability and regeneration capability, avoiding secondary contamination. A hybrid method that combines various radical scavengers with electron paramagnetic resonance (EPR) technology has been used to confirm that both hydroxyl radicals (HO ) and alkoxyl radicals (CH3C(O)O ) were generated in the ACFs/PAA catalytic system. Furthermore, a combination of EPR with density functional theory calculations has been employed to evaluate the role of ACFs in the ACFs/PAA system. The results suggested that the introduction of ACFs facilitated homolytic cleavage of the O–OH bond, resulting in the generation of HO and CH3C(O)O for the effective removal of organic dyes. Based on these results and analyses, a possible mechanism is proposed.

Peroxymonosulfate (PMS) activation has received increasing attention owing to the generation of powerful radicals for the removal of organic pollutants in the environmental catalysis field, although the development of highly efficient and environmentally benign oxidation processes has proven to be a significant challenge. In this work, an effective and stable catalyst (Fe@ACFs) has been tested for the first time for the heterogeneous activation of PMS for the removal of organic pollutants. The experimental results revealed that Fe@ACFs displayed sustained catalytic ability, and compared with the most commonly used oxidant, H 2 O 2 , the introduction of PMS contributed specifically to the activity enhancement of the catalytic system. Meanwhile, electron paramagnetic resonance (EPR) combined with two kinds of radical scavengers (methanol and tert -butyl alcohol) has been employed to confirm that hydroxyl radicals ( OH) and sulfate radicals (SO 4 − ) serve as the active species in the reaction process. Importantly, the negative effect of NaCl normally observed in hydrogen peroxide activation was turned into a positive effect at high NaCl concentrations. Furthermore, the catalyst also displayed excellent stability and reusability in these experiments, avoiding secondary contamination and being conducive to green catalysis. This work provides a new process to solve the dichotomy between efficiency and environmental benignity in PMS activation, which may find practical application for the treatment of organic pollutants in water.

We report herein three commercial activated carbon fibers (ACFs) with different adsorption capacities for use as Fe-supports in developing a series of heterogeneous Fenton catalysts (Fe@ACFs) for water purification via a simple impregnation method. Studies relating to the characteristics of the Fe@ACFs and their adsorptive or catalytic performance have been performed and these data revealed that high adsorption capacity led to greatly enhanced catalytic activity. HPLC, EPR, DTG and FT-IR were used to differentiate between adsorptive and catalytic behavior. These results demonstrated that the catalytic process leads to extensive multi-step oxidation due to the production of hydroxyl radicals. The effects of various factors such as the initial concentration of substrate, the dosage of catalyst and the addition of H 2 O 2 were evaluated. The use of H 2 O 2 to oxidize pollutants appeared to be optimum at a high concentration of pollutants and low concentration of H 2 O 2 . These findings may provide a viable method toward facile improvement in the properties of the Fenton catalyst via control of the support from a new perspective.

This paper presents the fabrication of colored photocatalytic fibers by individually combining white TiO2 with red α-Fe2O3, green copper perchlorophthalocyanine (CuPcCl16), and blue copper phthalocyanine (CuPc), followed by immobilization of three as-prepared nanocomposites (i.e., Fe2O3/TiO2, CuPcCl16/TiO2, and CuPc/TiO2) onto the low melting point sheath-core composite polyester fibers (LMPET). The spectroscopic and surface measurements of colored fabrics show uniform distribution of the composites on LMPET fibers. Compared with TiO2-based white fabric, the prepared colored catalytic fabrics have better performance in photocatalytic degradation of formaldehyde (HCHO), a pollutant in water and indoor air. In addition, the prepared fibers could be recycled or reused without any appreciable decrease in their effectiveness. The investigation of antibacterial activity of colored fabrics shows 6-log inactivation of both Escherichia coli and Staphylococcus aureus. The enhancement in the photocatalytic activity of colored fabric is attributed to a broadening photo-absorption region and also a decrease in the recombination of electron-hole pairs. In the photocatalytic process, an increase in photocurrent response suggests the increase in charge separation. Additionally, hydroxyl radicals ( OH) as the major reactive species in photocatalytic activity of colored fabrics are confirmed by the electron paramagnetic resonance technique. This study suggests that the developed colored photocatalysts can be applied in textiles to clean water and air.

The development of a pH-tolerant Fenton-like catalyst is an active and challenging project in water treatment. In this study, activated carbon fibers (ACFs) supported 8-hydroxyquinoline ferric (QuFe) has been reported as a heterogeneous Fenton-like catalyst (QuFe@ACFs) for efficient removal of dyes. The catalyst possessed remarkable catalytic performance across a wide range of pH values (3–9). Moreover, it also presented excellent sustained catalytic ability and regeneration capability in the experiments, causing reducing secondary contamination. Importantly, with the introduction of ACFs, QuFe@ACFs exhibited a greatly enhanced catalytic activity in comparison with bare QuFe. The hydroxyl radicals (OH) are confirmed as the active species in QuFe@ACFs/H2O2 system by the use of electron paramagnetic resonance (EPR) and fluorescence spectra. In addition, the central composite design (CCD) matrix and response surface methodology (RSM) were applied in designing the experiments for evaluating the interactive effects of temperature, pH, initial dye concentration and catalyst dosage. This study not only opens a novel avenue for designing pH-tolerant heterogeneous Fenton-like catalyst, but also provides a viable process for efficient elimination of dyes effluent.