2011 下半年讲课 氮吸附 孔分析
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© 2003, Quantachrome Instruments
吸附理论
被吸附物 吸附剂
© C©op2y0r0ig3h,t Quuaannttaacchhrormome CeoIrnpsotrrautimonen20ts00. All rights reserved.
/alp/plasma/history.html
Vm N Axs
22,414
0-1 0-2 0-3
P/Po
Where, N = Avogadro’s number Axs= cross-sectional area of adsorbate molecule
© C©op2y0r0ig3h,t Quuaannttaacchhrormome CeoIrnpsotrrautimonen20ts00. All rights reserved.
© C©op2y0r0ig3h,t Quuaannttaacchhrormome CeoIrnpsotrrautimonen20ts00. All rights reserved.
在MONOSORB中对单点BET的校正
© 2003, Quantachrome Instruments
样品准备---- 必须让吸附质”看到”表面
Sample preparation
The adsorbate has to “see” the real surface.
• ቤተ መጻሕፍቲ ባይዱ时发生的微量潮气吸附并不影响单分子层能力,但会 影响吸附的强度, 所以与在一个清洁表面上比较,单分子 层的形成压力会发生改变.
Whilst a little pre-adsorbed moisture wouldn't affect the monolayer capacity, it would affect the strength with which it is adsorbed, so the monolayer would be formed at a different pressure than on a clean surface.
liquidargontemperature比表面分析微孔介孔和大孔的孔径分析可在较高的相对压力下105103获得微孔数据031nm也可用液氮但不能用于大于12nm的孔因为773k比氩的三相点还低65k所以在较大孔内不能凝聚poresizeanalysisthinmicromesoporousfilmsthommesetal2004005与025之间nova不能用coporesizeanalysis15nmparticularlymicroporouscarbons2003quantachromeinstruments常用的比表面和孔径分析吸附质so15901commonlyusedadsorptivesporesizeanalysis沸石分子筛炭分子筛等微孔材料的孔径和孔体积进行分析是很困难的因为填充孔径在051nm的孔要在相对压力在107至105间才会发生此时扩散速度和吸附平衡都很慢
表面脱气Outgassing of Surface
在适宜的加热温度下,样品通过真空的应用或干燥惰性 气体的流动除去吸附污染物的过程,主要是水汽.
Sample is cleaned of adsorbed contaminants, mainly moisture, by the application of vacuum or flow of dry inert gas and preferably some heat.
© 2003, Quantachrome Instruments
Langmuirian behavior
Confining adsorption to a monolayer, the Langmuir equation can be written
V = KP Vm 1 + KP where V is the volume of gas adsorbed at pressure P, Vm is the monolayer capacity (i.e. θ=1) expressed as the volume of gas at STP and K is a constant for any given gas-solid pair. Rearranging in the form of a straight line (y=ab+x) gives P= 1 + P V KVm Vm
加热到多高温度?
How much heat?
© 2003, Quantachrome Instruments
表面脱气Outgassing of Surface
如何选择样品的脱气温度?
What is the proper temperature for sample preparation?
• 在不改变样品表面特性的前提下,应选择足够高的温度以快速除去表 面吸附物质.Should be high enough to promote rapid removal of surface
• 孔道因毛细作用极易被潮气阻塞.
Pores can be easily blocked by moisture. Water undergoes capillary condensation at humidities well below bulk saturation in the confines of the pore (just as nitrogen does as we will see later).
BET 理论
V
P (P −
P0 )
=
1 VmC
+
(C − 1) VmC
⎜⎜⎝⎛
P P0
⎟⎟⎠⎞
吸附剂
© C©op2y0r0ig3h,t Quuaannttaacchhrormome CeoIrnpsotrrautimonen20ts00. All rights reserved.
比表面积测定原理--BET法
• 微孔能完全被填满,不再是阻塞!
Micropores can be completely filled, not just blocked!
• 我们始终提供的是单位干重的表面积.
We always quote surface area per unit of dry mass. © 2003, Quantachrome Instruments
adsorbed species without changing the surface texture.
•不能高于固体的熔点或玻璃的相变点,Tg .Obviously not high enough to melt the
solid, nor hot enough to exceed the glass transition point, Tg. Estimate Tg as melting pt × 0.7 in kelvin (allow safety margin).
• 建议不要超过熔点温度的一半. Or no more than melting point × 0.5
(kelvin) – Tammann temperature.
• 举例:硬脂酸镁: 40 °C (for 2 hours)
Example: Magnesium Stearate monograph: 40 °C (for 2 hours)
193123 T-InhveeNntoebdetlhPergizaes ifnillCedh,ecmoilsetdrytu"nfogrstheins dfiilsacmoevenrtiienscandeisncveenstilgaamtipo.ns in surface chemistry"
1919 to 1921, his interest turned to an examination of atomic theory, and he published his "concentric theory of atomic structure" . In it he proposed that all atoms try to complete an outer electron shell of eight electrons
© 2003, Quantachrome Instruments
含有微孔样品的BET计算
• 活性炭样品举例:
• BET计算范围为0.050.1 (P/P0)
• 多数符合Langmiur 方程
• 务必使C值大于0 • 保持回归系数优于
0.9999
© 2003, Quantachrome Instruments
比表面积= Vm N0σ/22400W
N0为阿佛加得罗常数, σ为一个吸附分子截面积
© 2003, Quantachrome Instruments
比表面积计算
B.E.T. 图表
斜率 (s) = C-1 Vm C
截距 (i) = 1 Vm C
1 w[(Po/P)-1]
Vm = 1 s+i
Stotal =
Irving Langmuir (1881-1957)
G19r2a7duCaoteidneads tahemuestaelloufrtghiecatleremng"inpelaesrmfrao"mfothrean iSocnhiozoedl ogfaMs. ines at Columbia University in 1903
BET公式:只能用于类型II,IV
• 常数“C”与吸附能量有关
– C ∝（E吸附-E蒸发）/RT – 必须为正值 – 低值为弱吸附，低表面的固体
• “C”值范围
– C=2-50,有机物,高分子与金属 – C=50-200, 氧化物,氧化硅 – C=>200 活性碳,分子筛
以微孔为主的样品的比表面计算应该用Langmuir 方程, 但是……
含有微孔样品的BET计算
--- ERM-FD107 (标准值610.6 ±13.8m2/g)
© 2003, Quantachrome Instruments
单点与多点的比较
相对误差
C 常数 1
10 50 100 1000 ∞
相对误差 0 .7 0 0 .1 9 0 .0 4 0 .0 2
0 .0 0 2 0
190335-190367 MW.iAth. aKnadthPehr.iDne. iBnl1o9d0g6etftrsotmudGieödtthiningefnil.ms.
190468-190593 IWnsitrhuVctionrcienntCShcehmaiesfteryr daitsScotevveerneds that the iInntsrtoitduutectoiofnToefchdnryoliocgeya,nHdoiboodkideen,inNtoewa sJuerfsfiecyi.ently m19o0i9st–c1lo9u5d0 oGfelnoewratleEmlpecetrraitcuCreocmopualdnyinadtuce pSrcehceinpeitcattaiodyn.where he eventually became Associate Director
• 对于上述五种等温线有许多种解释，其中最成功的是 BRUMAUER-EMMETT-TELLER三人在1938年提出的
多分子层吸附理论
• 由该理论得到的方程式称为BET公式
P
1
C -1 P
V（P0-P）= VmC
+
*
VmC P0
• 在P/ P0为0.05-0.35范围内可得一直线, 通过斜率和截距 可求得Vm(单层饱和吸附量)
© 2003, Quantachrome Instruments
朗格缪尔理论 P = 1 + 1 (P)
W KWm Wm
被吸附物
吸附剂
© C©op2y0r0ig3h,t Quuaannttaacchhrormome CeoIrnpsotrrautimonen20ts00. All rights reserved.
© 2003, Quantachrome Instruments
真空脱气还是流动脱气?
Vacuum or flow
• 流动脱气对于除去表面大量弱结合的吸 附水是非常好的, 但对孔中吸附的水,只有 经长时间吹扫使之扩散至表面,才能被带 出.
A flow is good at removing large quantities of weakly bonded “wet” water by displacement of the vapor from external surfaces. However in the depths of a pore, water must diffuse out… and in doing so must battle past a much higher concentration of purge gas. Only when it is out of the pore will it be physically swept away.
吸附理论
被吸附物 吸附剂
© C©op2y0r0ig3h,t Quuaannttaacchhrormome CeoIrnpsotrrautimonen20ts00. All rights reserved.
/alp/plasma/history.html
Vm N Axs
22,414
0-1 0-2 0-3
P/Po
Where, N = Avogadro’s number Axs= cross-sectional area of adsorbate molecule
© C©op2y0r0ig3h,t Quuaannttaacchhrormome CeoIrnpsotrrautimonen20ts00. All rights reserved.
© C©op2y0r0ig3h,t Quuaannttaacchhrormome CeoIrnpsotrrautimonen20ts00. All rights reserved.
在MONOSORB中对单点BET的校正
© 2003, Quantachrome Instruments
样品准备---- 必须让吸附质”看到”表面
Sample preparation
The adsorbate has to “see” the real surface.
• ቤተ መጻሕፍቲ ባይዱ时发生的微量潮气吸附并不影响单分子层能力,但会 影响吸附的强度, 所以与在一个清洁表面上比较,单分子 层的形成压力会发生改变.
Whilst a little pre-adsorbed moisture wouldn't affect the monolayer capacity, it would affect the strength with which it is adsorbed, so the monolayer would be formed at a different pressure than on a clean surface.
liquidargontemperature比表面分析微孔介孔和大孔的孔径分析可在较高的相对压力下105103获得微孔数据031nm也可用液氮但不能用于大于12nm的孔因为773k比氩的三相点还低65k所以在较大孔内不能凝聚poresizeanalysisthinmicromesoporousfilmsthommesetal2004005与025之间nova不能用coporesizeanalysis15nmparticularlymicroporouscarbons2003quantachromeinstruments常用的比表面和孔径分析吸附质so15901commonlyusedadsorptivesporesizeanalysis沸石分子筛炭分子筛等微孔材料的孔径和孔体积进行分析是很困难的因为填充孔径在051nm的孔要在相对压力在107至105间才会发生此时扩散速度和吸附平衡都很慢
表面脱气Outgassing of Surface
在适宜的加热温度下,样品通过真空的应用或干燥惰性 气体的流动除去吸附污染物的过程,主要是水汽.
Sample is cleaned of adsorbed contaminants, mainly moisture, by the application of vacuum or flow of dry inert gas and preferably some heat.
© 2003, Quantachrome Instruments
Langmuirian behavior
Confining adsorption to a monolayer, the Langmuir equation can be written
V = KP Vm 1 + KP where V is the volume of gas adsorbed at pressure P, Vm is the monolayer capacity (i.e. θ=1) expressed as the volume of gas at STP and K is a constant for any given gas-solid pair. Rearranging in the form of a straight line (y=ab+x) gives P= 1 + P V KVm Vm
加热到多高温度?
How much heat?
© 2003, Quantachrome Instruments
表面脱气Outgassing of Surface
如何选择样品的脱气温度?
What is the proper temperature for sample preparation?
• 在不改变样品表面特性的前提下,应选择足够高的温度以快速除去表 面吸附物质.Should be high enough to promote rapid removal of surface
• 孔道因毛细作用极易被潮气阻塞.
Pores can be easily blocked by moisture. Water undergoes capillary condensation at humidities well below bulk saturation in the confines of the pore (just as nitrogen does as we will see later).
BET 理论
V
P (P −
P0 )
=
1 VmC
+
(C − 1) VmC
⎜⎜⎝⎛
P P0
⎟⎟⎠⎞
吸附剂
© C©op2y0r0ig3h,t Quuaannttaacchhrormome CeoIrnpsotrrautimonen20ts00. All rights reserved.
比表面积测定原理--BET法
• 微孔能完全被填满,不再是阻塞!
Micropores can be completely filled, not just blocked!
• 我们始终提供的是单位干重的表面积.
We always quote surface area per unit of dry mass. © 2003, Quantachrome Instruments
adsorbed species without changing the surface texture.
•不能高于固体的熔点或玻璃的相变点,Tg .Obviously not high enough to melt the
solid, nor hot enough to exceed the glass transition point, Tg. Estimate Tg as melting pt × 0.7 in kelvin (allow safety margin).
• 建议不要超过熔点温度的一半. Or no more than melting point × 0.5
(kelvin) – Tammann temperature.
• 举例:硬脂酸镁: 40 °C (for 2 hours)
Example: Magnesium Stearate monograph: 40 °C (for 2 hours)
193123 T-InhveeNntoebdetlhPergizaes ifnillCedh,ecmoilsetdrytu"nfogrstheins dfiilsacmoevenrtiienscandeisncveenstilgaamtipo.ns in surface chemistry"
1919 to 1921, his interest turned to an examination of atomic theory, and he published his "concentric theory of atomic structure" . In it he proposed that all atoms try to complete an outer electron shell of eight electrons
© 2003, Quantachrome Instruments
含有微孔样品的BET计算
• 活性炭样品举例:
• BET计算范围为0.050.1 (P/P0)
• 多数符合Langmiur 方程
• 务必使C值大于0 • 保持回归系数优于
0.9999
© 2003, Quantachrome Instruments
比表面积= Vm N0σ/22400W
N0为阿佛加得罗常数, σ为一个吸附分子截面积
© 2003, Quantachrome Instruments
比表面积计算
B.E.T. 图表
斜率 (s) = C-1 Vm C
截距 (i) = 1 Vm C
1 w[(Po/P)-1]
Vm = 1 s+i
Stotal =
Irving Langmuir (1881-1957)
G19r2a7duCaoteidneads tahemuestaelloufrtghiecatleremng"inpelaesrmfrao"mfothrean iSocnhiozoedl ogfaMs. ines at Columbia University in 1903
BET公式:只能用于类型II,IV
• 常数“C”与吸附能量有关
– C ∝（E吸附-E蒸发）/RT – 必须为正值 – 低值为弱吸附，低表面的固体
• “C”值范围
– C=2-50,有机物,高分子与金属 – C=50-200, 氧化物,氧化硅 – C=>200 活性碳,分子筛
以微孔为主的样品的比表面计算应该用Langmuir 方程, 但是……
含有微孔样品的BET计算
--- ERM-FD107 (标准值610.6 ±13.8m2/g)
© 2003, Quantachrome Instruments
单点与多点的比较
相对误差
C 常数 1
10 50 100 1000 ∞
相对误差 0 .7 0 0 .1 9 0 .0 4 0 .0 2
0 .0 0 2 0
190335-190367 MW.iAth. aKnadthPehr.iDne. iBnl1o9d0g6etftrsotmudGieödtthiningefnil.ms.
190468-190593 IWnsitrhuVctionrcienntCShcehmaiesfteryr daitsScotevveerneds that the iInntsrtoitduutectoiofnToefchdnryoliocgeya,nHdoiboodkideen,inNtoewa sJuerfsfiecyi.ently m19o0i9st–c1lo9u5d0 oGfelnoewratleEmlpecetrraitcuCreocmopualdnyinadtuce pSrcehceinpeitcattaiodyn.where he eventually became Associate Director
• 对于上述五种等温线有许多种解释，其中最成功的是 BRUMAUER-EMMETT-TELLER三人在1938年提出的
多分子层吸附理论
• 由该理论得到的方程式称为BET公式
P
1
C -1 P
V（P0-P）= VmC
+
*
VmC P0
• 在P/ P0为0.05-0.35范围内可得一直线, 通过斜率和截距 可求得Vm(单层饱和吸附量)
© 2003, Quantachrome Instruments
朗格缪尔理论 P = 1 + 1 (P)
W KWm Wm
被吸附物
吸附剂
© C©op2y0r0ig3h,t Quuaannttaacchhrormome CeoIrnpsotrrautimonen20ts00. All rights reserved.
© 2003, Quantachrome Instruments
真空脱气还是流动脱气?
Vacuum or flow
• 流动脱气对于除去表面大量弱结合的吸 附水是非常好的, 但对孔中吸附的水,只有 经长时间吹扫使之扩散至表面,才能被带 出.
A flow is good at removing large quantities of weakly bonded “wet” water by displacement of the vapor from external surfaces. However in the depths of a pore, water must diffuse out… and in doing so must battle past a much higher concentration of purge gas. Only when it is out of the pore will it be physically swept away.