| Biochar was widely used for wastewater treatment and soil remediation.Its degradation efficiency and pathway of degradation had been sufficiently studied.The high degradation efficiency of biochar towards organic contaminants was generally regarded to be related with the environmental persistent free radicals（EPFRs）produced from the thermolysis of raw material.However,it was still lack of research that the comparison of the reactivity of EPFRs,the degradation quantity attributed to EPFRs and the way to show the reacivity of EPFRs.In this study,tobacco waste was pyrolyzed to produce biochar at 300,500,700°C respectively.These two kinds of biochar was used to react with p-nitrophenol（PNP）to figure out the reactivity of the EPFRs of tobacco waste biochar pyrolyzed at different temperatures.In order to further explore the reactivity of EPFRs of biochar,different kinds of free radical scavengers were selected to react with rice straw biochar pyrolyzed at 350°C which was place until its intensity of EPFRs remained steady.The intensity,kind and other parameters before and after reaction was compared to analyze the possible pathway to show the reactivity of EPFRs.The results showed that,the ability of PNP removal of these two kinds of biochar increased first and then declined with the increase of pyrolysis temperature.Among all,the removal rates of biochar pyrolyzed at 500°C were the lowest.The removal rates were 56.70%and 71.30%respectively.When the pyrolysis temperature rose to700°C,the PNP removal rate of both two kinds of biochar were above 90%.The removal of PNP was on one hand attributed to adsorption.The adsorption quantity of tobacco leaf stalk biochar（YE）increased first and then declined while the adsorption of tobacco stem biochar increased first and then remained unchanged with the increase of pyrolysis temperature.The reason to this situation is biochar pyrolyzed at relatively low temperature contained insufficiently pyrolyzed organic matter which could promote the adsorption capacity of biochar.At 500°C,fine porous structure and internal surface of biochar was not sufficiently developed leading to a suppress of adsorption quantity.At 700°C,fine visible pore was already formed on biochar’s surface,leading to an increase of internal surface for adsorption,providing more adsorption sites causing an increase in adsorption quantity.On the other hand,the removal of PNP was attributed to degradation.With the increasing of pyeolysis temperature,the degradation rate of tobacco leaf stalk biochar was 31.89%,31.16%and 14.64%respectively.While the situation of YA was quite different.With the rose of pyrolyzed temperature,the degradation rate of biochar gradually increased from8.06%,31.23%to 54.33%.Compared to the intensity of EPFRs of biochar,the reactivity of EPFRs was not only related to intensity of EPFRs.When it comes to biochar pyrolyzed at low temperature,The degradation towards PNP was attributed to EPFRs whose center was oxygen atom could transfer its unpaired electron to the dissolved oxygen to produce reactive oxygen.While during the process of biochar pyrolyzed at middle/high temperatures react with PNP,EPFRs formed ROS degraded PNP producing new free radicals formed and stabilized on biochar,leading to an increase in intensity and a decline in reactivity.In order to further explore the way to show EPFRs reactivity,different kinds of free radical scavenger was selected to react with biochar The result of free radical scavenging research showed that,the reactivity of EPFRs of biochar mainly showed by transferring unpaired electron to H2O2to form reactive oxygen.The electron vacants contributed to the intensity of EPFRs,however the reactivity of them still remained unknown.In this study,the degradation reactivity of EPFRs of biochar was clarified,providing a new insight to research the degradation of biochar towards organic contaminants and a theoretical basis about organic contaminants removed by biochar. |
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