Study On The Preparation Of Copper-Doped Carbon Nitride Materials And Applied For Pollutants Degradation By Fenton-Like Method

Dyeing and textile wastewater is a typical refractory organic wastewate due to its complex composition,large discharge volume,deep chroma,contains toxic and harmful substances,and poor biodegradability.The traditional water treatment technology can no longer meet the waterquality requirements of these wastewater.Recently,Fenton advanced oxidation processes have been widely applied to remove refractory pollutant from the organic wastewater attributed to its strong oxidizing property,high efficiency,electrophilicity,mild reaction process and low selectivity.However,the classical Fe-based homogeneous Fenton reaction has limited practical applications due to the optimum p H was around 3.00,low hydrogen peroxide utilization,nonrecyclability of the catalyst,and production of a large amount of iron-containing sludge,which causes secondary environmental pollution.To overcome these disadvantages,heterogeneous Fenton-like catalysts has been developed and become a research hotspot.At present,the key factors to promote the practical application of heterogeneous Fenton technology mainly include two aspects:（1）the preparation of heterogeneous catalyst and（2）the expansion of oxidant system.The choice of transition metal and carrier is crucial for heterogeneous catalysts preparation.Among various transition metals,the doping of copper into carriers shows significant advantages in catalytic activation the iron-based Fenton reaction,and it can also be used over a wide p H range.The organic semiconductive polymer carbon nitride are very suitable for transition metal ion doping due to its special structure and electronic properties to improve catalytic performance in Fenton-like reaction.In the study of broadening the oxidant system,sulfate radical(SO₄^·-),as a novel advanced oxidation technology,has become a research hotspot for the removal of refractory organic wastewater treatment due to its advantages,such as SO₄^·-half-life is much longer than that of·OH,stronger selectivity,free radical donor stability and convenient storage.Herein,three kinds of copper-doped carbon nitride composites were prepared by one-step thermal condensation method.The physicochemical of the composites were examined and analyzed by many measures.The performance of the composites were evaluated by catalyst-activated H₂O₂ and PMS to degrade organic pollutant.The specific research contents and conclusions are as follows.（1）The common reactants such as Cu SO₄·5H₂O and melamine were used to synthesize the Cu⁺/g-C₃N₄ composite materials in one-step thermal polycondensation,and Rh B was selected as the target pollutant to evaluate the performance of the catalyst-activated H₂O₂.The physicochemical of Cu⁺/g-C₃N₄（1:4）were characterized by XRD,SEM,BET,FTIR and XPS.The results showed that Cu⁺/g-C₃N₄（1:4）appeared as flakes with abundant mesopores and the BET specific surface area is 20.00 m²/g,increasing 2.5 times that of pure g-C₃N₄,and copper exists in the form of amorphous cuprous.Based on the results of characterization analysis,a possible synthesis path of Cu⁺/g-C₃N₄ was proposed.We mainly investigated the impact of critical factors of the reaction system,such as copper doping ratio,catalyst dosage,H₂O₂ concentration and initial p H,on catalytic performance.The Cu⁺/g-C₃N₄（1:4）samples exhibited the greatest catalytic performance when the dosage of catalyst and H₂O₂ were 0.5g/L and 25 mmol/L,respectively,the degradation of Rh B reached 98.9%in 60 min,which could still reach 97.8%after five cycles.Moreover,the higher catalytic activity of this catalyst can be achieved in a stronger alkaline environment,and the degradation of Rh B more than95.0%in 60 min at initial p H in range of 5.00-12.00.The investigation of the working mechanisms of the catalyst suggested that the Cu atom and g-C₃N₄ were dual active sites,the degradation of pollutants mainly depends on·OH.（2）This part further studied the catalytic performance of pollutant degradation by Cu⁺/g-C₃N₄ activating PMS.We mainly investigated the impact of critical factors of the reaction system,such as sunlight,the ratio of Cu⁺/g-C₃N₄ and PMS,initial p H,and inorganic anions,on catalytic performance.The Cu⁺/g-C₃N₄（1:4）samples exhibited the best PMS activation performance under sunlight when 0.5 g/L catalyst dose and 0.5 mmol/L PMS concentration were used,and the removal rate of Rh B reached 98.8%in 60 min,which could still reach 98.3%after five cycles.Moreover,better catalytic activity of the system can be achieved in the initial p H range of 2.00-10.00.To further studied the stability and recyclability of the catalyst,the XRD and XPS spectra of fresh and used Cu⁺/g-C₃N₄（1:4）were investigated.The degradation of pollutants benefits from the participation of·OH,which are generated by sunlight-assisted heterogeneous activation of PMS,and a possible reaction mechanism was proposed.（3）The poly（triazine imide）（PTI）with intercalation of Cu ion heterogeneous catalysts（Cu/PTI）was synthesized by one-pot thermal condensation of melamine and copper acetate as precursors,and Rh B was selected as the target pollutant to evaluate the performance of the catalyst-activated H₂O₂ and PMS.The microscopic morphology and structural characteristics of Cu/PTI were characterized by XRD,SEM,BET,FTIR,and XPS.The characterization results show that Cu/PTI is a rod structure material with rich mesoporous,and the BET specific surface area is 36.15 m²/g,increasing 4.5 times that of pure g-C₃N₄.The C/N is 0.69,copper mainly exists in the form of amorphous cuprous.The possible formation mechanism of Cu/PTI was proposed.The prepared composite Cu/PTI catalyst was used to activate H₂O₂and PMS to degrade the simulated pollutant Rh B.The Cu/PTI samples exhibited the best H₂O₂ and PMS activation performance under sunlight when the dosage of catalyst was 0.5g/L,the concentration of H₂O₂ and PMS were 15 mmol/L and 0.5 mmol/L,the removal rate of Rh B reached 95.0%and 96.2%in 60 min.The applicable initial p H range of Cu/PTI（1:4）in H₂O₂ system and PMS system is 5.00-10.00 and 3.00-10.00,and the main active species is·OH and O₂^·-,respectively.The mechanism of Cu/PTI Fenton-like reaction to degrade pollutants was proposed.（4）A novel cuprous ion doped nitrogen-rich carbon nitride composites Cu⁺/CN-U was prepared by one-step thermal condensation of urea and intermediate,the intermediate could be obtained by mixing the copper sulfate pentahydrate and melamine thermal polycondensation at 400°C.The Rh B was selected as the target pollutant to evaluate the performance of the catalyst-activated H₂O₂ and PMS.The microscopic morphology and structural characteristics of Cu⁺/CN-U were characterized by XRD,SEM,BET,FTIR,and XPS.The characterization results show that Cu⁺/CN-U is a very fluffy mesoporous sheet material with rich mesoporous,and the BET specific surface area is 89.69 m²/g,increasing11.2 times that of pure g-C₃N₄.The C/N is 0.62,copper mainly exists in the form of amorphous cuprous in composite materials.The possible formation mechanism of Cu/PTI was proposed.The prepared composite Cu⁺/CN-U catalyst was used to activate H₂O₂ and PMS to degrade the simulated pollutant Rh B.For the H₂O₂ system,when the dosage of catalyst and H₂O₂ were 0.25 g/L and 10 mmol/L,respectively,the degradation of Rh B reached 96.5%in 60 min,and the initial p H range is 4.00-10.00.For the PMS system,when0.1 g/L catalyst dose and 0.25 mmol/L PMS concentration were used under sunlight,the removal rate of Rh B reached 98.3%in 60 min,and the initial p H range is 3.00-10.00.The main active species produced by activating H₂O₂ and PMS by Cu⁺/CN-U are ¹O₂ and O₂^·-,respectively.The mechanism of Cu⁺/CN-U Fenton-like reaction to degrade pollutants was proposed.