Preparation And Properties Of Polymeric Metal Phthalocyanine/graphitic Carbon Nitride Composite Photocatalysts

The economic and social development has simultaneously led to the intensification of the global energy crisis and the deterioration of the natural environment.In recent years,the massive use and discharge of pharmaceuticals and personal care products（PPCPs）have been recognized as emerging contaminants prevalent in the aquatic environment.These emerging pollutants are difficult to be completely removed by conventional water treatment technologies due to their complex and stable structures,which seriously endanger the ecological environment,human health and sustainable development of society.Photocatalytic oxidation technology,as one of the advanced oxidation processes（AOPs）,which is a kind of water treatment technology with mild reaction conditions and environmental friendliness.Among them,photocatalytic oxidation technology based on potassium peroxymonosulfate（PMS）activation has received more and more attention because of its excellent oxidation capacity and less usage constraints.Photocatalysts are the core of photocatalysis technology,and the preparation of photocatalytic materials with high activity,selectivity and stability is beneficial to solve the bottleneck problems of photocatalysis technology in practical applications.Graphitic carbon nitride（g-C₃N₄）is a visible light-responsive two-dimensional（2D）sheet semiconductor material with good thermal and chemical stability.However,its photocatalytic efficiency is low due to its low visible light utilization rate and high photogenerated electron-hole pair complexation rate.Polymeric metal phthalocyanine（MPPc）is a class of polymeric organic semiconductor materials with highπ-electron conjugated structure.MPPc has the dual properties of metal phthalocyanine and polymer,excellent visible light response range,unique electron donor and acceptor properties,which also has some potential in the field of photocatalysis.Therefore,in this paper,we tried to compound MPPc（M=Co,Fe）with g-C₃N₄ to obtain photocatalysts with excellent performance and degrade emerging pollutants in water by activating PMS..The g-C₃N₄ and MPPc（M=Co,Fe）were prepared by solid-phase synthesis method.The above two 2D lamellar materials were exfoliated by mechanical force to prepare the thin-layer structure using high-energy ball milling,which achieved the recombination between the two materials while weakening the internal interlayer buildup of the two-dimensional materials.The two composite photocatalysts were prepared and named as Co PPc/g-C₃N₄ and Fe PPc/g-C₃N₄,respectively.The results of scanning electron microscope（SEM）,fourier transform infrared spectroscopy（FTIR）and X-ray diffraction（XRD）showed that MPPc（M=Co,Fe）was mechanically exfoliated by ball milling and dispersed on g-C₃N₄ successfully.The UV-vis diffuse reflectance spectroscopy（DRS）spectra indicated that the introduction of MPPc（M=Co,Fe）significantly broadened the visible light absorption range of g-C₃N₄,resulting in a strong light response at 600-800 nm of composite catalyst.The photocatalytic degradation activities of two composite catalysts were investigated using carbamazepine（CBZ）with a better conjugated structure as the contaminating substrate and PMS as the oxidizing agent.The results showed that both composite photocatalysts have the ability to degrade CBZ efficiently.The influence factor experiments and the degradation experiments with different substrates were designed,which indicated that the both composite catalysts still had excellent photocatalytic performance under a wide p H environment,and also could degrade a variety of sulfonamide antibiotics.However,the photocatalytic performance of the Co PPc/g-C₃N₄ catalytic system was significantly inhibited in the presence of large amounts of chloride ions（Cl^-）,while the Fe PPc/g-C₃N₄ catalytic system was not affected by the anion influence experiment.Above results indicated that Fe PPc/g-C₃N₄ had better environmental suitability than Co PPc/g-C₃N₄.The high photogenerated electron-hole separation efficiency of the two composite catalysts was demonstrated by photoluminescence spectra（PL）,electrochemical impedance spectroscopy（EIS）and photocurrent response tests.Theπ-πconjugate stacking interaction between MPPc（M=Co,Fe）and g-C₃N₄ may promote electron transfer.The mechanism was analyzed through trapping agent experiments and electron paramagnetic resonance tests,which concluded that the active species generated by the photocatalytic activation of PMS in the MPPc/g-C₃N₄ composite catalytic system are hydroxyl radicals（·OH）,sulfate radicals（SO₄·^-）,superoxide radicals（O₂·^-）and singlet oxygen radicals（¹O₂）.Furthermore,the degradation pathway of CBZ was analyzed according to ultra-performance liquid chromatography and high-definition mass spectrometry.The aromatic ring structures of CBZ were destroyed and the chemical bonds were broken by the various active species,which were eventually mineralized to carbon dioxide and water.In order to solve the problems of limited light area,easy agglomeration and difficult recovery of the powder catalyst in the actual water treatment process,the Fe PPc/g-C₃N₄ composite catalyst with excellent performance,which was prepared by the greener raw material,was selected and spun into nylon 6（PA6）fibers.The Fe PPc/g-C₃N₄@PA6 catalytic fiber with good hydrophilicity were prepared by centrifugal-electrostatic spinning technique.SEM,FTIR and XRD displayed that the powder catalyst could be firmly and uniformly loaded into the fiber.The DRS results indicated that the supported photocatalytic fiber could maintain the excellent visible light response of the powder catalyst.The photocatalytic degradation of CBZ experiments confirmed that the Fe PPc/g-C₃N₄@PA6 catalytic fiber has excellent photocatalytic performance and excellent cycle stability.Experiments on influencing factors showed that the catalytic fiber could achieve catalytic degradation of organic pollutants in the presence of a wide p H range and a large number of inorganic anions.The mechanistic investigation illustrated that the mechanism of CBZ degradation in Fe PPc/g-C₃N₄@PA6 photocatalytic fiber system was still due to the combined action of·OH,SO₄·^-,O₂·^-and ¹O₂.CBZ could be deeply oxidized into non-toxic and harmless small molecules.In this paper,MPPc/g-C₃N₄ composite catalysts with excellent catalytic degradation performance for pharmaceutical organic pollutants were prepared,and the loaded fibers were also prepared and used to solve the problems of difficult recovery and poor reusability of powder catalysts,which has good application potential in practical pharmaceutical wastewater treatment.