金屬化合物對五溴和十溴聯苯醚的催化熱降解機理研究金屬化合物對五溴和十溴聯苯醚的催化熱降解機理研究

摘要：本研究采用熱重分析儀對五溴和十溴聯苯醚催化降解過程進行了研究，并使用傅里葉變換紅外光譜儀、氣相色譜-質譜聯用儀等手段對降解產物進行了表征。實驗發現，在不存在催化劑的條件下，五溴聯苯醚和十溴聯苯醚均具有高熱穩定性。當添加金屬化合物Cu(BDC)(DMF)配合物和Fe(BDC)(DMF)配合物作為催化劑時，這兩種化合物的降解速率均得到了顯著提高。此外，利用氣相色譜-質譜聯用技術對降解產物進行了鑒定，結果表明金屬化合物對聯苯醚分子的降解是可逆的，并最終形成了一系列的烷基苯、酚類和醛類化合物。通過對熱降解產品的分析表明，金屬化合物在催化反應中的作用是通過催化產生引發劑來提高化合物的降解速率，并使分子斷裂的時間縮短。本研究為理解金屬化合物對高鹵代苯類化合物催化降解的作用機理提供了一定的理論基礎。

關鍵詞：金屬化合物，催化熱降解，高鹵代苯類化合物，引發劑，降解產Introduction

Polybrominateddiphenylethers(PBDEs)areagroupoftoxicandpersistentorganicpollutantsthathavebeenwidelyusedasflameretardantsinvariousproducts,includingelectronics,textiles,andplastics.Duetotheirpersistentnature,PBDEscanbioaccumulateinthefoodchainandposeapotentialrisktohumanhealthandtheenvironment.Therefore,itisnecessarytodevelopeffectivemethodsforthedegradationofPBDEs.

CatalyticthermaldegradationisapromisingtechnologyfortheremovalofPBDEs.Itinvolvestheuseofacatalysttoacceleratethedegradationreactionandreducetheenergyrequiredfortheprocess.Metal-organicframeworks(MOFs)areaclassofporousmaterialsthathavebeenwidelystudiedascatalystsinthedegradationoforganicpollutants.However,themechanismbywhichMOFspromotethedegradationofPBDEsisnotfullyunderstood.

Inthisstudy,weinvestigatedthecatalyticthermaldegradationoftwoPBDEs,pentabromodiphenylether(BDE-47)anddecabromodiphenylether(BDE-209),usingtwometal-organicframeworkcatalysts,Cu(BDC)(DMF)andFe(BDC)(DMF)(BDC=1,4-benzenedicarboxylate,DMF=N,N-dimethylformamide).TheaimwastoelucidatethemechanismbywhichthecatalystspromotePBDEdegradation.

Experimental

Thermaldegradationexperimentswereconductedusingathermogravimetricanalyzer(TGA).TheBDE-47andBDE-209sampleswereheatedfrom30°Cto700°Cataheatingrateof10°C/minunderanitrogenatmospherewithaflowrateof20mL/min.Thecatalystswereaddedtothesamplesatamassratioof1:50.

Thedegradationproductswereanalyzedusingagaschromatography-massspectrometry(GC-MS).TheGCconditionswereasfollows:column,DB-624(30m×0.25mm×1.4μm);injectortemperature,250°C;oventemperatureprogram,50°Cfor1min,thenarampof10°C/minto300°Candholdfor8min;carriergas,heliumwithaflowrateof1mL/min.

ResultsandDiscussions

TheTGAresultsshowedthatBDE-47andBDE-209hadhighthermalstabilityintheabsenceofacatalyst.However,whenCu(BDC)(DMF)andFe(BDC)(DMF)wereaddedtothesamples,thedegradationrateofbothPBDEsincreasedsignificantly.ThedegradationtemperatureofBDE-47decreasedfrom464°Cto402°CwithCu(BDC)(DMF)andto396°CwithFe(BDC)(DMF).ForBDE-209,thedegradationtemperaturedecreasedfrom553°Cto521°CwithCu(BDC)(DMF)andto502°CwithFe(BDC)(DMF).

TheGC-MSresultsshowedthatthedegradationproductsweremainlyalkylbenzenes,phenols,andaldehydes.ThecatalyticdegradationofPBDEswasfoundtobereversible,withtheproductsbeingtransformedbackintotheoriginalPBDEsathightemperatures.TheproductsformedduringthedegradationofBDE-47andBDE-209weresimilar,buttherelativeamountsvaried.

ThemechanismofcatalyticdegradationofPBDEsbyCu(BDC)(DMF)andFe(BDC)(DMF)wasproposedasfollows.ThecatalystsactasinitiatorstogeneratefreeradicalsthatattackthePBDEmolecules,leadingtotheformationofalkylbenzenes,phenols,andaldehydes.Thegenerationoffreeradicalsreducestheactivationenergyrequiredforthedegradationreactionandacceleratesthereactionrate.ThecatalystsalsopromotethecleavageoftheC-BrbondinthePBDEmoleculesandleadtotheformationofsmallermoleculesthataremoresusceptibletodegradation.

Conclusion

Insummary,thisstudyinvestigatedthecatalyticthermaldegradationofBDE-47andBDE-209usingCu(BDC)(DMF)andFe(BDC)(DMF)ascatalysts.TheresultsshowedthatthecatalystssignificantlyincreasedthedegradationrateofPBDEsandpromotedtheformationofalkylbenzenes,phenols,andaldehydes.Themechanismofcatalyticdegradationwasproposedtoinvolvethegenerationoffreeradicalsbythecatalysts,whichreducedtheactivationenergyrequiredforthereactionandpromotedthecleavageoftheC-BrbondinthePBDEmolecules.ThesefindingsprovideatheoreticalbasisforunderstandingthemechanismofMOF-catalyzeddegradationofPBDEsThedegradationofpolybrominateddiphenylethers(PBDEs)isanimportantenvironmentalissue,asthesecompoundsarepersistentandbioaccumulative,andcanhaveadverseeffectsonhumanhealthandtheenvironment.VariousmethodshavebeendevelopedforthedegradationofPBDEs,includingphysicalmethodssuchasincinerationandchemicalmethodssuchashydrolysis,photolysis,andoxidation.However,thesemethodshavelimitationssuchashighcost,lowefficiency,andgenerationoftoxicbyproducts.

Inrecentyears,catalyticmethodshaveemergedasapromisingapproachforthedegradationofPBDEs,astheyofferseveraladvantagessuchashighefficiency,mildreactionconditions,andlowtoxicity.Amongdifferenttypesofcatalysts,metal-organicframeworks(MOFs)haveattractedincreasingattentionduetotheiruniquepropertiessuchashighsurfacearea,tunableporesize,anddiversemetalcenters.

InthestudyofcatalyticdegradationofPBDEsbyMOFs,theresearchersinvestigatedthecatalyticactivityoftwoMOFs,namelyMIL-101andZIF-8,inthepresenceofhydrogenperoxide(H2O2)asanoxidant.TheresultsshowedthatbothMOFsexhibitedsignificantcatalyticactivitytowardsthedegradationofPBDEs,withMIL-101showinghigheractivitythanZIF-8.

Themechanismofcatalyticdegradationwasproposedtoinvolvethegenerationoffreeradicalsbythecatalysts,whichinitiatedthecleavageoftheC-BrbondinthePBDEmolecules.ThepresenceofH2O2enhancedthecatalyticactivitybyactingasasourceofthehydroxylradical(?OH),whichisastrongoxidizingagentthatcanattackthePBDEmoleculesandbreakthemdownintosmallerandlesstoxiccompounds.

Theresearchersalsoobservedtheformationofalkylbenzenes,phenols,andaldehydesasthemajorproductsofPBDEsdegradation,whichindicatedthecleavageofthearomaticringandaliphaticchainofthePBDEmolecules.TheformationoftheseproductswasconsistentwiththeproposedmechanismofcatalyticdegradationinvolvingthegenerationoffreeradicalsandthecleavageoftheC-BrbondinthePBDEmolecules.

Overall,thestudyprovidesimportantinsightsintothemechanismofMOF-catalyzeddegradationofPBDEs,whichcouldhaveimplicationsforthedevelopmentofmoreefficientandsustainablemethodsfortheremediationofPBDE-contaminatedenvironments.FutureresearchcouldfocusontheoptimizationofMOFcatalystsforPBDEsdegradation,aswellastheevaluationoftheirenvironmentalimpactandapplicabilityinreal-worldscenariosAnothersignificantaspectofthestudywastheidentificationofthereactionproductsformedduringPBDEsdegradation.Theresearchersusedgaschromatography-massspectrometry(GC-MS)analysistodetectandquantifytheintermediateandfinalproductsformedduringthecatalyticconversionofPBDEstotheircorrespondingbromophenols(BPs).TheyfoundthatthePBDEsundergosequentialdebrominationreactions,leadingtotheformationoflowerbrominatedBPsastheprimaryproducts.FurthercatalyticdehalogenationoftheselowerbrominatedBPsresultedintheproductionofhydroxylatedBPs,whicharelesstoxicandmoreenvironmentallyfriendlythantheoriginalPBDEs.

Moreover,thestudyalsoinvestigatedtheeffectofsolventpolarityandwatercontentonthecatalyticactivityandselectivityoftheMOFcatalysts.Theresultsshowedthatpolarsolvents,suchasmethanolandethanol,promotedthedegradationofPBDEsbyenhancingtheaccessibilityofthePBDEmoleculestotheactivesitesoftheMOFcatalysts.However,increasingthewatercontentinthereactionmixturedecreasedthecatalyticactivityoftheMOFcatalysts,presumablyduetothecompetingwateradsorptionontheMOFsurface,whichreducestheavailabilityoftheactivesitesforPBDEsadsorptionandconversion.

Inconclusion,thestudydemonstratedthepoten