金属有机框架MIL-53(Fe)可见光催化还原水中U(Ⅵ)
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摘要
U(Ⅵ)是放射性废液中铀的主要存在形式.将可溶的U(Ⅵ)还原为难溶的U(Ⅳ)是治理铀污染的有效方法.以溶剂热法合成了铁基金属有机框架材料MIL-53(Fe).在表征了材料的结构及光响应特性基础上,开展了MIL-53(Fe)在可见光下催化还原水中U(Ⅵ)的研究.探究了空穴捕获剂种类、空穴捕获剂浓度、反应体系pH及催化剂用量等对U(Ⅵ)光催化还原的影响.结果表明,空穴捕获剂甲酸的加入可有效提高光催化反应的电荷分离效率.当甲酸浓度为1 mmol·L~(-1)时,400 mg·L~(-1)的MIL-53(Fe)在可见光下,2 h内对初始浓度为50 mg·L~(-1)的U(Ⅵ)去除率达到80%;光电子能谱检测结果显示反应中有U(Ⅳ)生成,推测其主要反应机制是甲酸与MIL-53(Fe)的光生空穴反应产生强还原性的·COO-,将U(Ⅵ)还原为U(Ⅳ),从而实现对水中U(Ⅵ)的光催化去除.
Uranium typically occurs in the hexavalent form U( Ⅵ) as the mobile,aqueous uranyl ion in radioactive wastewater. The reduction of soluble U( Ⅵ) to insoluble U( Ⅳ) oxide is an effective approach to eliminate uranium pollution. Herein,the metal organic framework material MIL-53( Fe) was successfully synthesized by a solvothermal method,and its application as photocatalyst in the reduction of U( Ⅵ) under visible light was studied in detail using various types and concentrations of hole trapping agents,solution pH values,and catalyst dosages. The results show that the use of formic acid as the hole trapping agent greatly accelerates the catalytic reaction rate by improving the charge separation efficiency. When 1 mmol·L~(-1) formic acid was used and the initial concentration of U( Ⅵ) was 50 mg·L~(-1),MIL-53( Fe) achieved a high reduction rate of 80% after 2 hours of visible light exposure. Photoelectron spectroscopy( XPS) clearly suggested that U( Ⅳ) was generated during the reaction process. A possible mechanism is that formic acid reacted with the photogenerated hole,resulting in the formation of ·COO-,which can reduce U( Ⅵ) to U( Ⅳ). Accordingly,the elimination of the uranium pollution from wastewater was achieved.
Uranium typically occurs in the hexavalent form U( Ⅵ) as the mobile,aqueous uranyl ion in radioactive wastewater. The reduction of soluble U( Ⅵ) to insoluble U( Ⅳ) oxide is an effective approach to eliminate uranium pollution. Herein,the metal organic framework material MIL-53( Fe) was successfully synthesized by a solvothermal method,and its application as photocatalyst in the reduction of U( Ⅵ) under visible light was studied in detail using various types and concentrations of hole trapping agents,solution pH values,and catalyst dosages. The results show that the use of formic acid as the hole trapping agent greatly accelerates the catalytic reaction rate by improving the charge separation efficiency. When 1 mmol·L~(-1) formic acid was used and the initial concentration of U( Ⅵ) was 50 mg·L~(-1),MIL-53( Fe) achieved a high reduction rate of 80% after 2 hours of visible light exposure. Photoelectron spectroscopy( XPS) clearly suggested that U( Ⅳ) was generated during the reaction process. A possible mechanism is that formic acid reacted with the photogenerated hole,resulting in the formation of ·COO-,which can reduce U( Ⅵ) to U( Ⅳ). Accordingly,the elimination of the uranium pollution from wastewater was achieved.
引文
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[17] Araya T,Jia M K,Yang J,et al. Resin modified MIL-53(Fe)MOF for improvement of photocatalytic performance[J]. Applied Catalysis B:Environmental,2017,203:768-777.
[18] Huang W Y,Liu N,Zhang X D,et al. Metal organic framework g-C3N4/MIL-53(Fe)heterojunctions with enhanced photocatalytic activity for Cr(Ⅵ)reduction under visible light[J]. Applied Surface Science,2017,425:107-116.
[19] Yang Z W,Xu X Q,Liang X X,et al. MIL-53(Fe)-graphene nanocomposites:efficient visible-light photocatalysts for the selective oxidation of alcohols[J]. Applied Catalysis B:Environmental,2016,198:112-123.
[20] Horcajada P,Serre C,Maurin G,et al. Flexible porous metalorganic frameworks for a controlled drug delivery[J]. Journal of the American Chemical Society,2008,130(21):6774-6780.
[21]吴晓朦,刘洪雪,王锐,等.硝酸铀酰溶液初始浓度与pH值对其水解反应的影响[J].辽宁石油化工大学学报,2015,35(5):18-21.Wu X M, Liu H X, Wang R, et al. The effect of initial concentration and pH value of the uranyl nitrate solution on the its hydrolysis reaction[J]. Journal of Liaoning Shihua University,2015,35(5):18-21.
[22]罗昭培,董发勤,何辉超,等. P25半导体矿物光催化还原U(Ⅵ)[J].核化学与放射化学,2017,39(1):30-35.Luo Z P,Dong F Q,He H C,et al. Photocatalytic reduction of U(Ⅵ)by P25 semiconductor mineral[J]. Journal of Nuclear and Radiochemistry,2017,39(1):30-35.
[23] Salomone V N, Meichtry J M, Litter M I. Heterogeneous photocatalytic removal of U(Ⅵ)in the presence of formic acid:U(III)formation[J]. Chemical Engineering Journal,2015,270:28-35.
[24]习海玲,韩世同,左言军,等. Ti O2光催化降解乙酰甲胺磷[J].环境化学,2008,27(5):559-564.Xi H L,Han S T,Zuo Y J,et al. Photocatalytic degradation of O,S-dimethyl acetyl phosphoramidothioate[J]. Environmental Chemistry,2008,27(5):559-564.
[25] Wang G H, Zhen J, Zhou L M, et al. Adsorption and photocatalytic reduction of U(Ⅵ)in aqueous Ti O2suspensions enhanced with sodium formate[J]. Journal of Radioanalytical and Nuclear Chemistry,2015,304(2):579-585.
[26] Allen G C,Tucker P M,Tyler J W. Oxidation of uranium dioxide at 298 K studied by using X-ray photoelectron spectroscopy[J]. The Journal of Physical Chemistry,1982,86(2):224-228.
[27] Konstantinou I K,Albanis T A. Ti O2-assisted photocatalytic degradation of azo dyes in aqueous solution:kinetic and mechanistic investigations:a review[J]. Applied Catalysis B:Environmental,2004,49(1):1-14.
[28] Yamazaki S,Iwai S,Yano J,et al. Kinetic studies of reductive deposition of copper(Ⅱ)ions photoassisted by titanium dioxide[J]. The Journal of Physical Chemistry A,2001,105(50):11285-11290.
[29] Nguyen V N H,Amal R,Beydoun D. Effect of formate and methanol on photoreduction/removal of toxic cadmium ions using Ti O2semiconductor as photocatalyst[J]. Chemical Engineering Science,2003,58(19):4429-4439.
[2]陈保冬,陈梅梅,白刃.丛枝菌根在治理铀污染环境中的潜在作用[J].环境科学,2011,32(3):809-816.Chen B D,Chen M M,Bai R. Potential role of arbuscular mycorrhiza in bioremediation of uranium contaminated environments[J]. Environmental Science,2011,32(3):809-816.
[3] Katz S A. The chemistry and toxicology of depleted uranium[J].Toxics,2014,2(1):50-78.
[4]谢水波,王水云,张浩江,等.硫酸盐还原菌还原U(Ⅵ)的影响因素与机制[J].环境科学,2009,30(7):1962-1967.Xie S B, Wang S Y, Zhang H J, et al. Efficiency and mechanism on reduction of U(Ⅵ)by sulfate reducing bacteria[J]. Environmental Science,2009,30(7):1962-1967.
[5] Fu F L,Dionysiou D D,Liu H. The use of zero-valent iron for groundwater remediation and wastewater treatment:a review[J].Journal of Hazardous Materials,2014,267:194-205.
[6] Li P,Zhun B,Wang X G,et al. Highly efficient interception and precipitation of uranium(Ⅳ)from aqueous solution by ironelectrocoagulation combined with cooperative chelation by organic ligands[J]. Environmental Science&Technology,2017,51(24):14368-14378.
[7] Lu C H,Zhang P,Jiang S J,et al. Photocatalytic reduction elimination of UO22+pollutant under visible light with metal-free sulfur doped g-C3N4photocatalyst[J]. Applied Catalysis B:Environmental,2017,200:378-385.
[8] Guo Y D,Guo Y Q,Wang X G,et al. Enhanced photocatalytic reduction activity of uranium(VI)from aqueous solution using the Fe2O3-graphene oxide nanocomposite[J]. Dalton Transactions,2017,46(43):14762-14770.
[9] Li Z J,Huang Z W,Guo W L,et al. Enhanced photocatalytic removal of uranium(VI)from aqueous solution by magnetic Ti O2/Fe3O4and its graphene composite[J]. Environmental Science&Technology,2017,51(10):5666-5674.
[10] Jiang X H, Xing Q J, Luo X B, et al. Simultaneous photoreduction of uranium(VI)and photooxidation of arsenic(III)in aqueous solution over g-C3N4/Ti O2heterostructured catalysts under simulated sunlight irradiation[J]. Applied Catalysis B:Environmental,2018,228:29-38.
[11] Xamena F X L I,Corma A,Garcia H. Applications for metalorganic frameworks(MOFs)as quantum dot semiconductors[J].The Journal of Physical Chemistry C,2007,111(1):80-85.
[12] Shen L J,Liang S J,Wu W M,et al. CdS-decorated Ui O-66(NH2)nanocomposites fabricated by a facile photodeposition process:an efficient and stable visible-light-driven photocatalyst for selective oxidation of alcohols[J]. Journal of Materials Chemistry A,2013,1(37):11473-11482.
[13] Laurier K G M,Vermoortele F,Ameloot R,et al. Iron(Ⅲ)-based metal-organic frameworks as visible light photocatalysts[J]. Journal of the American Chemical Society,2013,135(39):14488-14491.
[14] Liang R W,Jing F F,Shen L J,et al. MIL-53(Fe)as a highly efficient bifunctional photocatalyst for the simultaneous reduction of Cr(Ⅵ)and oxidation of dyes[J]. Journal of Hazardous Materials,2015,287:364-372.
[15] Whitfield T R,Wang X Q,Liu L M,et al. Metal-organic frameworks based on iron oxide octahedral chains connected by benzenedicarboxylate dianions[J]. Solid State Sciences,2005,7(9):1096-1103.
[16] Du J J,Yuan Y P,Sun J X,et al. New photocatalysts based on MIL-53 metal-organic frameworks for the decolorization of methylene blue dye[J]. Journal of Hazardous Materials,2011,190(1-3):945-951.
[17] Araya T,Jia M K,Yang J,et al. Resin modified MIL-53(Fe)MOF for improvement of photocatalytic performance[J]. Applied Catalysis B:Environmental,2017,203:768-777.
[18] Huang W Y,Liu N,Zhang X D,et al. Metal organic framework g-C3N4/MIL-53(Fe)heterojunctions with enhanced photocatalytic activity for Cr(Ⅵ)reduction under visible light[J]. Applied Surface Science,2017,425:107-116.
[19] Yang Z W,Xu X Q,Liang X X,et al. MIL-53(Fe)-graphene nanocomposites:efficient visible-light photocatalysts for the selective oxidation of alcohols[J]. Applied Catalysis B:Environmental,2016,198:112-123.
[20] Horcajada P,Serre C,Maurin G,et al. Flexible porous metalorganic frameworks for a controlled drug delivery[J]. Journal of the American Chemical Society,2008,130(21):6774-6780.
[21]吴晓朦,刘洪雪,王锐,等.硝酸铀酰溶液初始浓度与pH值对其水解反应的影响[J].辽宁石油化工大学学报,2015,35(5):18-21.Wu X M, Liu H X, Wang R, et al. The effect of initial concentration and pH value of the uranyl nitrate solution on the its hydrolysis reaction[J]. Journal of Liaoning Shihua University,2015,35(5):18-21.
[22]罗昭培,董发勤,何辉超,等. P25半导体矿物光催化还原U(Ⅵ)[J].核化学与放射化学,2017,39(1):30-35.Luo Z P,Dong F Q,He H C,et al. Photocatalytic reduction of U(Ⅵ)by P25 semiconductor mineral[J]. Journal of Nuclear and Radiochemistry,2017,39(1):30-35.
[23] Salomone V N, Meichtry J M, Litter M I. Heterogeneous photocatalytic removal of U(Ⅵ)in the presence of formic acid:U(III)formation[J]. Chemical Engineering Journal,2015,270:28-35.
[24]习海玲,韩世同,左言军,等. Ti O2光催化降解乙酰甲胺磷[J].环境化学,2008,27(5):559-564.Xi H L,Han S T,Zuo Y J,et al. Photocatalytic degradation of O,S-dimethyl acetyl phosphoramidothioate[J]. Environmental Chemistry,2008,27(5):559-564.
[25] Wang G H, Zhen J, Zhou L M, et al. Adsorption and photocatalytic reduction of U(Ⅵ)in aqueous Ti O2suspensions enhanced with sodium formate[J]. Journal of Radioanalytical and Nuclear Chemistry,2015,304(2):579-585.
[26] Allen G C,Tucker P M,Tyler J W. Oxidation of uranium dioxide at 298 K studied by using X-ray photoelectron spectroscopy[J]. The Journal of Physical Chemistry,1982,86(2):224-228.
[27] Konstantinou I K,Albanis T A. Ti O2-assisted photocatalytic degradation of azo dyes in aqueous solution:kinetic and mechanistic investigations:a review[J]. Applied Catalysis B:Environmental,2004,49(1):1-14.
[28] Yamazaki S,Iwai S,Yano J,et al. Kinetic studies of reductive deposition of copper(Ⅱ)ions photoassisted by titanium dioxide[J]. The Journal of Physical Chemistry A,2001,105(50):11285-11290.
[29] Nguyen V N H,Amal R,Beydoun D. Effect of formate and methanol on photoreduction/removal of toxic cadmium ions using Ti O2semiconductor as photocatalyst[J]. Chemical Engineering Science,2003,58(19):4429-4439.