| Nowadays,due to continuous population growth and industrial production,a large number of toxic and harmful pollutants are discharged,which has become a serious environmental problem in many countries.With the rapid development of the printing and dyeing industry,dye wastewater has become one of the most important pollution sources in water.At present,the world’s annual output of dyes is about（8-9）×105t.Plenty of textiles have been produced in our country,the export value of textiles of which has ranked first in the world for many years,and the annual dye production volume is as high as 1.5×105t.A large amount of residual dyes are inevitably discharged into water,seriously polluting river water,sea water,ground water and even drinking water.Wastewater treatment of dyes and intermediates has always been a problem in environmental remediation.Some of the more stable dyes such as gentian violet are difficult to be degraded by simple physical and chemical methods or biological methods.In order to effectively solve the environmental problems caused by dyes in wastewater,photocatalytic technology has become a research hotspot in the field of environmental remediation due to its environmental protection and efficient degradation advantages.Among them,g-C3N4has been widely used due to its simple synthesis method,abundant raw materials,and high catalytic activity.This study is based on g-C3N4and modified it by constructing a heterojunction by combining with NH2-MIL-125（Ti）.Therefore,the specific work of this research is as followsOn one hand,thiourea is used as the precursor,and g-C3N4flakes are obtained through high-temperature calcination twice,then g-C3N4flakes are functionalized with benzoic acid to obtain CNB,and then CNB is added to NH2-MIL-125（Ti）during the synthesis process,a series of CNB/NH2-MIL-125（Ti）（CNBM）Z-type heterojunction photocatalysts were obtained.In order to evaluate the photocatalytic performance of the synthesized composite,a study was conducted with gentian violet as the target pollutant.The results showed that the photocatalytic degradation ability of CNBM was significantly higher than that of CNB and NH2-MIL-125（Ti）,among them,10wt%CNBM obtained the highest photocatalytic activity,and the removal efficiency of gentian violet reached 98.5%within 1 hour.At the same time,using the first-order kinetic model to conduct a more in-depth study of the photocatalytic oxidation process,it was found that the first-order rate constant of10wt%CNBM was 0.04567min-1,which was 30.05 and 21.54 times of CNB and NH2-MIL-125（Ti）,respectively.In addition,we also used free radical capture experiments to study which active species played a major role in the entire experiment.The results showed that superoxide free radicals played a major role in the process of gentian violet being degraded.On the other hand,X-ray diffraction（XRD）,fourier transform infrared spectroscopy（FT-IR）,X-ray photoelectron spectroscopy（XPS）,photoluminescence Spectroscopy（PL）and other series of characterization methods are used to further reveal the photocatalytic mechanism of CNBM composites.The analysis results show that NH2-MIL-125（Ti）has a large specific surface area and the CNB particles in composite are dispersed on the surface of NH2-MIL-125（Ti）,both of which are beneficial to improve the surface characteristics of the CNBM composite.In addition,compared with the two monomers of CNB and NH2-MIL-125（Ti）,the maximum absorption wavelength of 10wt%CNBM has a red shift,and the composite shows the lowest fluorescence intensity,indicating that the prepared composite photocatalysts enhance the absorption capacity of visible light,and at the same time enhances the separation ability of photogenerated carriers.Finally,based on the energy band theory,the valence and conduction bands of CNB and NH2-MIL-125（Ti）are calculated,and a series of characterization analysis and radical capture experiments are combined to propose a reasonable photocatalytic degradation pathway. |
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