Andersen Lars Klembt, Frei Heinz
Physical Biosciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720, USA.
J Phys Chem B. 2006 Nov 16;110(45):22601-7. doi: 10.1021/jp0640326.
Carbon monoxide molecules generated in the channels of mesoporous MCM-41 silica sieve from a precursor (diphenyl cyclopropenone) by photodissociation with a nanosecond laser pulse were monitored by time-resolved Fourier transform infrared (FTIR) spectroscopy using the step-scan and rapid-scan methods. A very broad absorption of CO is observed in the region 2200-2080 cm(-1) at room temperature that decays in a biphasic mode. Two-thirds of the band intensity decays on the hundreds of microsecond scale (lifetime 344 +/- 70 micros). The process represents the escape of the molecules through the mesopores into the surrounding gas phase, and a diffusion constant of 1.5 x 10(-9) m(2)/s is derived (assuming control by intra-MCM-41 particle diffusion). The broad profile of the absorption is attributed to contact of the random hopping CO with siloxane and silanol groups of the pore surface. Measurements using MCM-41 with the silanols partially capped by trimethyl silyl groups gave further insight into the nature of the IR band profile. These are the first observations on the diffusion behavior of carbon monoxide in a mesoporous material at room temperature. The residual carbon monoxide remains much longer in the pores and features distinct peaks at 2167 and 2105 cm(-1) characteristic for CO adsorbed on SiOH groups C end on and O end on, respectively. The bands decrease with time constants of 113 +/- 3 ms (2167 cm(-1)) and 155 +/- 15 ms (2105 cm(-1)) suggesting that CO in these sites is additionally trapped by surrounding diphenyl acetylene coproduct and/or precursor molecules.
通过纳秒激光脉冲光解离，由前驱体（二苯基环丙烯酮）在介孔MCM - 41硅分子筛通道中生成的一氧化碳分子，采用步进扫描和快速扫描方法，通过时间分辨傅里叶变换红外（FTIR）光谱进行监测。在室温下，在2200 - 2080 cm⁻¹区域观察到非常宽的CO吸收峰，其衰减呈双相模式。三分之二的谱带强度在数百微秒尺度上衰减（寿命为344 ± 70微秒）。该过程代表分子通过介孔逃逸到周围气相中，并推导出扩散常数为1.5×10⁻⁹ m²/s（假设受MCM - 41颗粒内扩散控制）。吸收峰的宽谱归因于随机跳跃的CO与孔表面的硅氧烷和硅醇基团的接触。使用硅醇部分被三甲基硅烷基封端的MCM - 41进行测量，进一步深入了解了红外谱带轮廓的性质。这些是关于室温下一氧化碳在介孔材料中扩散行为的首次观察。残留的一氧化碳在孔中停留的时间长得多，并且分别在2167和2105 cm⁻¹处具有明显的峰，这分别是CO以C端和O端吸附在SiOH基团上的特征峰。这些谱带以113 ± 3 ms（2167 cm⁻¹）和155 ± 15 ms（2105 cm⁻¹）的时间常数下降，表明这些位点的CO还被周围的二苯基乙炔副产物和/或前驱体分子捕获。
