Photocatalytic Of Rhodamine B With Graphite Phase Carbonization Nitrogen Under Visible Light

Rhodamine B is a basic dye which has been used a lot as food additive. Due to itsproved carcinogenicity, it has been banned for the food industry afterwards. WhereasRhB is still widely used in papermaking, textile dyeing, leather manufacturing, coloredglass color, cell fluorescence dye manufacturing and fireworks manufacturing andother industries. Large quantities of RhB dye wastewater was produced in theseindustries, if not properly disposed, it will pose great damage on human health andecological environment. Therefore, it is of importance to seek an efficient andeconomical wastewater treatment method represented by RhB dye. On the basis ofpredecessors, in this study, preparation methods of graphite phase carbonizationnitrogen were improved and RhB was used as the target pollutant, influencing factorscatalytic degradation of RhB by g-C3N4under visible light were studied, the optimumreaction conditions were obtained, and the handling situation of actual printing anddyeing wastewater using g-C3N4prepared by microwave assisted sintering process wasinvestigated. Understanding and the main achievements are as follows:(1) Melamine was completely decomposed by samples prepared inMicrowave-assisted sintering method, in the XRD analysis, the decompositionproducts has a typical diffraction peaks at2θ of27.5°, corresponding lattice spacingis that of d=0.326nm. The peak is corresponding with (002) crystal facecharacteristic peak of g-C3N4that of d002=0.322nm, indicating that the sample has astacked type ABAB. The XRD spectrum the sample of microwave assisted sinteringmethod is basically the same as for that of the traditional solid state sintering method,suggesting the sample powder of g-C3N4is essentially has a kind of graphite layerstructure in microwave sintering method. Sample S by Microwave-assisted sinteringmethod and S0by conventional solid state sintering method were both generated with agraphite-like layered structure, and S has a smaller layer spacing and larger specificsurface area when compared with S0, which will provide more active sites forphotocatalytic reaction, and the layer distance and morphology of S did not changeobviously after the reaction, and S stayed stable, which are conducive to the opticalcatalyst. (2) The sample S of microwave-assisted sintering process has obvious effect onRhB’s degradation by photocatalytic under visible light, the decolorization rate reachesat96.5%after240min, which is higher than that of the sample S0of79.5%. Recyclingof the catalyst for5times, it was found that sample S was relatively stable, and changedlittle in its catalytic activity, decolorization rate for the five recycling experiments wasrespectively97.8%,95.9%,93.9%,89.9%and86%. This stable photocatalyticproperty is very important for its applicable use in actual dye wastewater treatment.(3) Triphenylmethane dye RhB could be degraded by graphite phase carbonizationnitrogen through photocatalytic way, with the dye concentration decreased, the rate ofphotocatalytic reaction went down. When the catalyst dosage changed in1g/L~2.5g/L,decolorization rate of RhB increased as the dosage increased, however, when it came to3g/L, decolorization rate became lessened on the contrary. This in one hand is becausesuch excessive dosing of the catalyst made the amount of adsorbed RhB increased,which desorbed slowly during the reaction, inducing an increase of degradation time,and in other hand since the catalyst dosage used is too large, the suspended catalystparticles seemed to be a barrier to reduce the utilization efficiency of light photons.Under acidic environment, smaller pH value resulted in the faster degradation ofRhB,when pH is at1,2,3,4, decolorization rate of RhB by g-C3N4has reached95%after150min, while at pH of5,6,7the decolorization rate of RhB was respectively97.2%,91.9%,81.8%. In an alkaline environment, pH went up, the slower the rate ofdegradation of RhB would be. When pH is of7,8,9,10,11, the decolorization rate ofRhB was respectively53.1%,45.4%,39.4%,37%,30.9%after90min reaction. And atpH of13, the decolorization rate increased dramatically, probably due to reaction ofRhB with a base. Effect of temperature on degradation of RhB was not large, threetemperature levels degradation curves of temperature10℃,20℃,30℃were closed.For the30℃group, decolorization rate did not change significantly at the beginningof the irradation, which was likely that when temperature became higher, it wouldaffect the amount of adsorption of RhB carbonation graphite phase nitrogen, resultingthe solution of RhB desorption phenomenon. It can be seen in the rear of the curve thattemperature became higher led increased decolorization rate, but this increase was notobvious. Increase the distance between xenon lamp and liquid interface from10cm to30cm, the speed of RhB solution decolorization tended to become smaller, but thechange was not obvious, the decolorization rate of three experiments are more than95%after270min.(4) Orthogonal experiments show that the impact effect of factors on the photocatalytic degradation of RhB by g-C3N4under visible light can be identified ascatalyst dosing quantity> initial pH> initial concentration. Within a certain range,increasing the dosage of catalyst on the catalytic reaction can significantly promote thedegradation process. The lower the pH value, the better effect photocatalyticdegradation of RhB by g-C3N4was obtained. The optimum conditions of photocatalyticdegradation of RhB by g-C3N4under visible light obtained through orthogonal testwere: initial concentration of1mg/L, initial pH of5, catalyst dosage of0.25g/L.(5) When the sunlight was used as the light source, g-C3N4has certain effect on theactual dye wastewater. The COD decolorization rate reached up to26.8%after threehours reaction. When decoloring rates were arranged from high to low, thecorresponding light source condition were: sunny noon, sunny evening, sunny morningand cloudy day. The optimal catalyst dosage was3g/L when g-C3N4treated on theactual wastewater. The removal rate of COD was28.6%at the time. This optimumcatalyst dosage is slightly higher than the best catalyst dosage which was found by asingle factor experiment under laboratory conditions. When g-C3N4was used todealing with the waste water in actual production, the best reaction solution pH was3,and the COD removal efficiency was38.6%. Compared with activated carbonadsorption (costs about20yuan/ton), graphite carbide nitrogen photocatalytictechnology has obvious price advantage. Compared with biological treatmenttechnology (cost about1.5-2yuan/ton), the cost of graphite carbide nitrogenphotocatalytic technology is still on the high side, but in terms of treatment efficiencyand pollutant removal efficiency, graphite carbide nitrogen photocatalytic technologyhas obvious advantages over the biological technology.The results of this study suggested that the graphite phase nitrogen carbonationwhich used melamine as precursors and was synthesis by microwave assisted sinteringmethod has a good ability for photocatalytic degradation of RhB wastewater undervisible light. The decolorizing reaction was rapid, and produced no secondary pollution.Compared with other processing technology, this photocatalytic method has largeapplication space for its low cost, stable performance and convenient operation.