不同取代基对乙酰丙酮在水溶液中的光化学行为影响
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摘要
乙酰丙酮(AA)作为光活化剂在水中可高效转化染料、硝酸盐、亚砷酸等污染物,但光反应发生的具体机理尚不清楚.本文选取AA及AA中心碳上的氢被不同基团取代的4种衍生物(AAs)为研究对象,初步探究AAs在水溶液中的光化学性质,包括:未经光照时和光照过程中的紫外吸收光谱,并选择3种不同类型的染料进行光反应实验,从取代基效应的角度出发比较不同取代基的存在对自身性质及其光化学活性的影响.实验结果表明,取代基的存在对物质在水中的稳定性、自身的紫外吸收光谱以及转化染料的光化学活性产生影响.吸电子基的存在对AA光化学转化染料的活性无明显的影响.推电子基的存在则会促进AAs的自身光降解,取代基的推电子能力越强,在水中越不稳定,转化染料的光活性越高.研究结果为选取合适的AAs用于光化学脱色提供了理论依据.
Acetylacetone( AA) can act as a photoactivator to enhance the transformation of pollutants,such as dyes,nitrate,and arsenate. However,the underlying mechanisms behind these reactions are unclear yet. In this work,structure-activity relationship in the UV/AA process was investigated by employing a series of α-substituted AA derivatives( AAs). In order to figure out the inductive effects,one of the two hydrogen atoms at the central carbon in AA was replaced with—CH3,—CH2 CH3,and —Cl groups,respectively. It is well known that —Cl is an electron withdrawing group,whereas —CH3 and —CH2 CH3 are electron donating groups. As a consequence,the electron density on the central carbon and the electron cloud distribution of these compounds were varied due to inductive effect. In AA-( CH3)2,the two hydrogen atoms at the central carbon were both replaced with —CH3. Three different types of dyes were selected as model compounds to check the photoactivities of the AAs. The effects of the substituting groups on the efficiency of the UV/AA process for decolorization were evaluated through parallel experiments. Under identical conditions,the k1 of the UV/AA—( CH3)2 process was close to that of UV/AA,indicating that the enol form of AA might not be of vital importance as previously proposed. The presence of —Cl had negligible effect on the efficiency of decolorization,whereas the presence of —CH3 and —CH2 CH3 significantly accelerated both the self-photodegradation of AAs and the degradation of the three dyes.The results here provide a criterion for the selection of proper AAs for the photodegradation of dyes.
Acetylacetone( AA) can act as a photoactivator to enhance the transformation of pollutants,such as dyes,nitrate,and arsenate. However,the underlying mechanisms behind these reactions are unclear yet. In this work,structure-activity relationship in the UV/AA process was investigated by employing a series of α-substituted AA derivatives( AAs). In order to figure out the inductive effects,one of the two hydrogen atoms at the central carbon in AA was replaced with—CH3,—CH2 CH3,and —Cl groups,respectively. It is well known that —Cl is an electron withdrawing group,whereas —CH3 and —CH2 CH3 are electron donating groups. As a consequence,the electron density on the central carbon and the electron cloud distribution of these compounds were varied due to inductive effect. In AA-( CH3)2,the two hydrogen atoms at the central carbon were both replaced with —CH3. Three different types of dyes were selected as model compounds to check the photoactivities of the AAs. The effects of the substituting groups on the efficiency of the UV/AA process for decolorization were evaluated through parallel experiments. Under identical conditions,the k1 of the UV/AA—( CH3)2 process was close to that of UV/AA,indicating that the enol form of AA might not be of vital importance as previously proposed. The presence of —Cl had negligible effect on the efficiency of decolorization,whereas the presence of —CH3 and —CH2 CH3 significantly accelerated both the self-photodegradation of AAs and the degradation of the three dyes.The results here provide a criterion for the selection of proper AAs for the photodegradation of dyes.
引文
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[12] LIU X T,SONG X J,ZHANG S J,et al. Non-hydroxyl radical mediated photochemical processes for dye degradation[J]. PhysicalChemistry Chemical Physics,2014,16(16):7571-7577.
[13] SUN H F,HUANG W G,YANG H,et al. Co-immobilization of laccase and mediator through a self-initiated one-pot process for enhancedconversion of malachite green[J]. Journal of Colloid and Interface Science,2016,471:20-28.
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[2] WANG M S,LIU X T,PAN B C,et al. Photodegradation of acid orange 7 in a UV/Acetylacetone process[J]. Chemosphere,2013,93(11):2877-2882.
[3] CHEN Z H,SONG X J,ZHANG S J,et al. Acetylacetone as an efficient electron shuttle for concerted redox conversion of arsenite andnitrate in the opposite direction[J]. Water Research,2017,124:331-340.
[4] SONG X J,WU B D,ZHANG S J. Decoloration of alizarin red(an anthraquinone dye)with the UV/Acetylacetone process[J]. ActaChimica Sinica,2014,72(4):461-466.
[5] MOFADDEL N,BAR N,VILLEMIN D,et al. Determination of acidity constants of enolisable compounds by capillary electrophoresis[J].Analytical&Bioanalytical Chemistry,2004,380(4):664-668.
[6] ERIC V A,DENNIS A D.现代物理有机化学[M].北京:高等教育出版社,2009:421-424.ERIC V A,DENNIS A D. Modern physical organic chemistry[M]. Beijing:Higher Education Press,2009:421-424(in Chinese).
[7]韩春霞,塔娜,李城镐.染料降解产物鉴定方法及降解机理研究进展[J].环境化学,2017,36(5):1156-1165.HAN C X,TA N,LI C H. Research progress on identification methods and degradation mechanism of dye degradation products[J].Environmental Chemistry,2017,36(5):1156-1165(in Chinese).
[8]陈晔,陈刚,陈亮,等.菌株Enterobactor sp. S8对不同结构偶氮染料脱色性能的影响[J].环境化学,2011,30(4):838-842.CHEN Y,CHEN G,CHEN L,et al. Decolorization of azo dyes with different molecular structure by Enterobactor sp. S8[J].Environmental Chemistry,2011,30(4):838-842(in Chinese).
[9]邢其毅,裴伟伟,徐瑞秋,等.基础有机化学[M].北京:高等教育出版社,2005:243-244.XING Q Y,PEI W W,XU R Q,et al. Basic organic chemistry[M]. Beijing:Higher Education Press,2005:243-244(in Chinese).
[10] ELOVITZ M S,FISH W. Redox interactions of Cr(Ⅵ)and substituted phenols:Kinetic investigation[J]. Environmental Science&Technology,1994,28(12):2161-2169.
[11] ELOVITZ M S,FISH W. Redox interactions of Cr(Ⅵ)and substituted phenols:Products and mechanism[J]. Environmental Science&Technology,1995,29(8):1933-1943.
[12] LIU X T,SONG X J,ZHANG S J,et al. Non-hydroxyl radical mediated photochemical processes for dye degradation[J]. PhysicalChemistry Chemical Physics,2014,16(16):7571-7577.
[13] SUN H F,HUANG W G,YANG H,et al. Co-immobilization of laccase and mediator through a self-initiated one-pot process for enhancedconversion of malachite green[J]. Journal of Colloid and Interface Science,2016,471:20-28.
[14] POCKER Y,SPYRIDIS G T. Modulation of tautomeric equilibria by ionic clusters. Acetylacetone in solutions of lithium perchlorate-diethylether[J]. Journal of the American Chemical Society,2002,124(35):10373-10380.
[15] WU B D,ZHANG G Y,ZHANG S J. Fate and implication of acetylacetone in photochemical processes for water treatment[J]. WaterResearch,2016,101:233-240.
[16] ZEPP R G,SCHLOTZHAUER P F,SINK R M. Photosensitized transformations involving electronic energy transfer in natural waters:Roleof humic substances[J]. Environmental Science&Technology,1985,19(1):74-81.
[17] MILLER P L,CHIN Y P. Photoinduced degradation of carbaryl in a wetland surface water[J]. Journal of Agricultural&Food Chemistry,2002,50(23):6758-6765.
[18] HU C,MULLER-KARGER F E,ZEPP R G. Absorbance,absorption coefficient and apparent quantum yield:A comment on commonambiguity in the use of these optical concepts[J]. Limnology&Oceanography,2002,47(4):1261-1267.
[19] GRANDBOIS M,LATCH D E,MCNEILL K. Microheterogeneous concentrations of singlet oxygen in natural organic matter isolate solutions[J]. Environmental Science&Technology,2008,42(24):9184-9190.
[20] BORDWELL F G,MCCOLLUM G J. Carbon acids. 10. Resonance saturation of substituent effects in the fluorene series[J]. The Journal ofOrganic Chemistry,1976,41(14):2391-2397.
[21] HANSCH C,LEO A,TAFT R W. A survey of Hammett substituent constants and resonance and field parameters[J]. Cheminform,1991,22(39):165-172.