Modulation Of Active Sites Of Carbonaceous Catalysts For Degradation Of Organic Pollutants In Water By Activation Of PMS

Refractory organic pollutants containing aromatic ring structure wastewater cannot be removed by conventional processes and damage the ecosystem seriously.Advanced oxidation processes(AOPs)based on persulfate can effectively degrade the organic pollutants in wastewater,attracting more and more attentions.Persulfate contains peroxymonosulfate(PMS)and peroxydisulfate(PDS).PMS is more likely to be activated to produce sulfate radical(SO₄^·-)due to its asymmetrical structure.Compared to hydroxyl radicals(^·OH),SO₄^·-has higher redox potential and a longer half-life period,showing advantages in the degradation of organic pollutants.Carbonous materials have the advantages of easy access,low cost and environmental protection and can be used as catalysts for PMS activation.Carbonaceous materials are typically washed using acid,alkaline or other methods to create active sites,which could generate large amounts of acid and alkali wastewater.Therefore,there is an urgent need to introduce more active sites in carbonaceous catalyst by simple,environmentally friendly and cost-effective methods.The defects in carbon skeleton and the oxygen-containing functional groups on the surface are capable to activate PMS.Besides,N doping and metal loading are two commonly used methods to improve the ability of carbonaceous materials to activate PMS.In this paper,we have used three methods to modulate the active sites on carbon catalysts.In Chapter 2,we collected some waste melon seed shells and prepared melon seed shell biochar(MSBC)using pyrolysis method.Melon seed shells do not contain metal elements.Therefore,acid or alkaline washing was not necessary,avoiding the generation of acid and alkaline wastewater.The melon seed shells contain a large amount of lignin,which can produce more active sites by pyrolysis.We investigated the pyrolysis temperature on the catalytic performance of MSBC.It was found that MSBC-800 pyrolyzed at 800°C showed high efficiency to activate PMS for the degradation of Rh B.The difference in composition and activity between the fresh and used catalysts indicated defects as the main active sites for PMS activation.SO₄^·-?^·OH and ¹O₂ were involved in the degradation process,and ¹O₂ was the main reactive oxygen species.This study offers the prospect of developing non-metallic catalysts with good PMS activation activity.g-C₃N₄ is a polymer semiconductor rich in graphite N.Graphitic N is a key active site for the activation of PMS.However,g-C₃N₄ has poor catalytic activity due to its inherent low specific surface area and poor electrical conductivity.In Chapter 3,to effectively utilize the abundant graphitic nitrogen in g-C₃N₄,we prepared a composite catalyst(g-C₃N₄@PC)by combining g-C₃N₄ with porous carbon(PC)showing good electrical conductivity and large specific surface area.There are synergistic effects between g-C₃N₄ and PC in activating PMS.N doping could modulate electrons of carbonous materials.In order to obtain more active sites,we prepared a new catalyst g-C₃N₄@NPC by calcining urea,g-C₃N₄ and PC together.g-C₃N₄@NPC showed excellent catalytic performance in activating PMS.In the g-C₃N₄@NPC/PMS system.SO₄^·-?^·OH and ¹O₂ contributed to the removal of Rh B,but Rh B was mainly degraded by ¹O₂ and the mediated electron transfer way.Based on the main degradation intermediates identified by LC-MS,possible Rh B degradation pathways were proposed.The results of cycling experiments and Rh B degradation in tap water and river water suggested that the g-C₃N₄@NPC/PMS system has practical prospects for environmental remediation.In Chapter 4,we used a novel approach to introduce trivalent vanadium onto activated carbon.Amine metavanadate and oxalic acid were used as the precursor for vanadium and the reducing agent respectively to synthesize the catalyst(V@AC)using an impregnation method.V@AC showed high efficiency to activate PMS that it was able to degrade high concentration of organic pollutants within 15 min via activated PMS.The conversion between vanadium ions of different valence states could provide electrons to activate PMS,producing strongly oxidizing SO₄^·-?O₂^·-?^·OH and ¹O₂ to degrade Rh B.¹O₂ was identified to be the main reactive oxygen species.This study provides an easy way to prepare supported trivalent vanadium catalyst,which showed high efficiency in PMS activation.