氯化铜改性石墨相氮化碳吸附剂的脱汞性能
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摘要
针对燃煤电厂汞污染物排放控制的问题,以尿素为前驱体,通过直接热聚合法制得绒毛状石墨相氮化碳(gC_3N_4),并用于低温条件下吸附脱除单质汞(Hg~0)。利用透射电子显微镜(TEM)、X射线衍射(XRD)、氮气吸附-脱附、X射线光电子能谱(XPS)等手段对吸附剂进行表征。结果表明:未改性g-C_3N_4具有良好的低温脱汞活性,在120°C时其脱汞效率可达84.7%;CuCl_2改性可以有效提高g-C_3N_4的脱汞性能,其脱汞效率在40～200°C范围内均可达到97%以上;温度对吸附剂脱汞效率的影响较小。XPS表征测试结果表明,铜离子和共价态氯原子均参与了单质汞的吸附脱除反应,Hg~0被Cu~(2+)离子和共价态Cl原子氧化成了Hg~(2+)离子,再吸附于g-C_3N_4表面而脱除。CO_2、SO_2和水蒸气对吸附剂脱汞效率影响较小,但水蒸气可提高汞吸附量。
To control the mercury emission from the coal-fired power plants,villous graphitic carbon nitride(gC_3N_4)was synthesized via direct thermal polymerization of the precursor of urea,and it was used to adsorption removal of elemental mercury(Hg~0) at low temperature.The sorbents were characterized by transmission electron microscopy(TEM),X-ray diffraction(XRD),nitrogen adsorption-desorption isotherm,and X-ray photoelectron spectroscopy(XPS)techniques.The results showed that pristine g-C_3N_4 performs well toward Hg~0 adsorption with Hg~0 removal efficiency of up to 84.7%at 120°C.CuCl_2 modification could effectively improve the Hg~0 removal performance of g-C_3N_4,and its Hg~0 removal efficiency could approach above 97%at 40～200°C.Temperature had a slight impact on Hg~0 removal efficiency.XPS analysis indicated that both copper ions and covalent chlorine atoms participated in elemental mercury adsorption removal reaction,in which Hg~0 was oxidized into Hg~(2+)by Cu~(2+) ions and covalent Cl atoms,and then Hg~(2+) was adsorbed on g-C_3N_4 surface for removal.CO_2,SO_2and water vapor had slight effects on Hg~0removal efficiency,whereas water vapor could improve mercury adsorption capacity.
To control the mercury emission from the coal-fired power plants,villous graphitic carbon nitride(gC_3N_4)was synthesized via direct thermal polymerization of the precursor of urea,and it was used to adsorption removal of elemental mercury(Hg~0) at low temperature.The sorbents were characterized by transmission electron microscopy(TEM),X-ray diffraction(XRD),nitrogen adsorption-desorption isotherm,and X-ray photoelectron spectroscopy(XPS)techniques.The results showed that pristine g-C_3N_4 performs well toward Hg~0 adsorption with Hg~0 removal efficiency of up to 84.7%at 120°C.CuCl_2 modification could effectively improve the Hg~0 removal performance of g-C_3N_4,and its Hg~0 removal efficiency could approach above 97%at 40～200°C.Temperature had a slight impact on Hg~0 removal efficiency.XPS analysis indicated that both copper ions and covalent chlorine atoms participated in elemental mercury adsorption removal reaction,in which Hg~0 was oxidized into Hg~(2+)by Cu~(2+) ions and covalent Cl atoms,and then Hg~(2+) was adsorbed on g-C_3N_4 surface for removal.CO_2,SO_2and water vapor had slight effects on Hg~0removal efficiency,whereas water vapor could improve mercury adsorption capacity.
引文
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[2]XIE J,QU Z,YAN N,et al.Novel regenerable sorbent based on Zr-Mn binary metal oxides for flue gas mercury retention and recovery[J].Journal of Hazardous Materials 2013,261:206-213.
[3]YAO H,LUO G,XU M,et al.Mercury emission and species during combustion of coal and waste[J].Energy&Fuels,2006,20(5):1946-1950.
[4]LI H,WU C,LI Y,et al.Superior activity of MnOx-CeO2/TiO2catalyst for catalytic oxidation of elemental mercury at low flue gas temperatures[J].Applied Catalysis B:Environmental,2012,111:381-388.
[5]谭增强,牛国平,陈晓文,等.椰壳碳基吸附剂的脱汞特性[J].环境工程学报,2015,12(9):5992-5996.
[6]SUN P,ZHANG B,ZENG X,et al.Deep study on effects of activated carbon’s oxygen functional groups for elemental mercury adsorption using temperature programmed desorption method[J].Fuel,2017,200:100-106.
[7]JAMPAIAH D,IPPOLITO S J,SABRI Y M,et al.Ceria-zirconia modified mnox catalysts for gaseous elemental mercury oxidation and adsorption[J].Catalysis Science&Technology,2016,6(6):1792-1803.
[8]WANG X,BLECHERT S,ANTONIETTI M.Polymeric graphitic carbon nitride for heterogeneous photocatalysis[J].ACS Catalysis,2012,2:1596-1606.
[9]王悦,蒋权,尚介坤,等.介孔氮化碳材料合成的研究进展[J].物理化学学报,2016,32(8):1913-1928.
[10]ZHU J,WEI Y,CHEN W,et al.Graphitic carbon nitride as a metal-free catalyst for NO decomposition[J].Chemical Communications,2010,46:6965-6967.
[11]XIAO J,XIE Y,NAWAZ F,et al.Dramatic coupling of visible light with ozone on honeycomb-like porous g-C3N4towards superior oxidation of water pollutants[J].Applied Catalysis B:Environmental,2016,183:417-425.
[12]DONG F,WU L,SUN Y,et al.Efficient synthesis of polymeric g-C3N4layered materials as novel efficient visible light driven photocatalysts[J].Journal of Materials Chemistry,2011,21:15171-15174.
[13]王幸宜.催化剂表征[M].上海:华东理工大学出版社,2008.
[14]LIU D,LU C,WU J.Elemental mercury adsorption by cupric chloride-modified mesoporous carbon aerogel[J].Colloids and Interfaces,2018,2(4):66.
[15]LIU D,ZHOU W,WU J.Effect of Ce and La on the activity of CuO/ZSM-5 and MnOx/ZSM-5 composites for elemental mercury removal at low temperature[J].Fuel,2017,194(4):115-122.
[16]REN H T,JIA S Y,WU Y,et al.Improved photochemical reactivities of Ag2O/g-C3N4in phenol degradation under UV and visible light[J].Industrial&Engineering Chemistry Research,2014,53:17645-17653.
[17]金瑞瑞,游继光,张倩,等.Fe掺杂g-C3N4的制备及其可见光催化性能[J].物理化学学报,2014,30(9):1706-1712.
[18]DONG F,SUN Y,WU L,et al.Facile transformation of low cost thiourea into nitrogen-rich graphitic carbon nitride nanocatalyst with high visible light photocatalytic performance[J].Catalysis Science&Technology 2012,2:332-1335.
[19]杨丽,石应杰,张辰,等.CuCl2改性材料脱除燃煤烟气中的Hg0[J].环境工程学报,2016,10(11):6598-6602.
[20]ZHANG Q,XU L,NING P,et al.Surface characterization studies of CuO-CeO2-ZrO2catalysts for selective catalytic reduction of NO with NH3[J].Applied Surface Science,2014,317:955-961.
[21]YANG W,SHAN Y,DING S,et al.Gas-phase elemental mercury removal using ammonium chloride impregnated sargassum chars[J].Environmental Technology,2018,1:1-8.
[22]TIAN S,WANG Z,GONG W,et al.Temperature-controlled selectivity of hydrogenation and hydrodeoxygenation in the conversion of biomass molecule by the Ru1/mpg-C3N4Catalyst[J].Journal of the American Chemical Society,2018,140:11161-11164.