| The increasingly serious energy crisis and environmental pollution are currently the two mostimportant issues of our time. Photocatalysis is a promising technology to degrade pollutantscompletely and efficiently by utilizing solar energy. During the past few decades, variousphotocatalysts have been developed. TiO2is the most commonly used catalyst in the treatment ofwastewater because of its non-toxicity, reasonable cost, high availability, photochemical stabilityand relatively high photocatalytic activity. However it can only absorb35%of sunlight in theUV region, which limits its application greatly. Therefore it’s still a challenger to find avisible-light responsible photocatalyst to improve sunlight utilization. g-C3N4is an inorganicsemiconductor material with the ability of visible-light responsible. But its main absorption is inthe range of400-450nm, and as a powder catalyst it’s not simple to recycle. Therefore it needsto be modified to meet the application for photocatalytic field.The g-C3N4is prepared by pyrolysing of urea, and a powder catalyst g-C3N4/ZnTcPc withstrong absorption near700nm is obtained by coupling with ZnTcPc, thereby overcoming thedefect of low utilization rate of visible light of g-C3N4. The g-C3N4/ZnTcPc has a lamellarnanostructure, wherein ZnTcPc presents in the form of small molecules, which makes theelectron conduct from ZnTcPc to the g-C3N4better. The decomposition temperature ofg-C3N4/ZnTcPc is above550oC in the air, which shows its good thermal stability. High catalyticactivity is observed in the degradation of Rhodamine B (RhB) and p-chlorophenol (4-CP) overg-C3N4/ZnTcPc, and its catalytic activity is strongly dependent on the amount of ZnTcPc and pH.In the system of degrading RhB, it can be degraded more than90%in the range of pH5to9over g-C3N4/ZnTcPc(0.64%), particularly in the condition of pH9, its activity greatly improvedcompared to g-C3N4. In the system of degradation of4-CP, the catalytic effect ofg-C3N4/ZnTcPc(0.89%) is best. Based on the intermediates detected by ultra performance liquidchromatography-mass spectrometry, N-de-ethylation chromophore cleavage and opening-ringmineralization are the main processes in RhB degradation. The degradation mechanism isdefferent vary with pH. In addition the mechanism of g-C3N4/ZnTcPc is differ from g-C3N4. Inthe system of degrading RhB, h+and O2-play the leading role for both catalysts in the condition of pH5, however, in the condition of pH9, h+is still the dominant oxidizing species,the role of O2-and OH has been enhanced in the g-C3N4/ZnTcPc system compared to theg-C3N4system.The g-C3N4/ZnTcPc/PAN nanofiber catalyst was synthesized by high voltage electrostaticspinning, with the size about300nm. The g-C3N4/ZnTcPc is dispersed uniformly in the PAN,and because of drafting of the electrospinning, the size of g-C3N4/ZnTcPc sheet is furtherreduced. Many dyes such as RhB can be absorbed rapidly into PAN nanofiber and decomposedefficiently in situ simultaneously in the presence of the g-C3N4over a wide pH range undervisible irradiation. Fiber catalyst can be recycled easily, and the catalytic properties ofg-C3N4/ZnTcPc/PAN decreases hardly after repeated use five times. In complex environment ofsodium chloride, urea and other substances g-C3N4/ZnTcPc/PAN still has high visible lightphotocatalytic activity. Mechanism of g-C3N4/ZnTcPc/PAN catalytic degrading RhB varys underdifferent pH. In the condition of pH5, h+and O2-are the dominant catalytic oxidation, whereasin the condition of pH9, the effect of OH is enhanced, and the effect of h+is weakened. It turnout to be a catalytic oxidation system of h+along with O2-and OH contribute to the oxidativedegradation of RhB. |
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