Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA.
Langmuir. 2011 Dec 20;27(24):14842-8. doi: 10.1021/la2025457. Epub 2011 Nov 23.
The interaction of acetaldehyde with TiO(2) nanorods has been studied under low pressures (acetaldehyde partial pressure range 10(-4)-10(-8) Torr) using chemical ionization mass spectrometry (CIMS). We quantitatively separate irreversible adsorption, reversible adsorption, and an uptake of acetaldehyde assigned to a thermally activated surface reaction. We find that, at room temperature and 1.2 Torr total pressure, 2.1 ± 0.4 molecules/nm(2) adsorb irreversibly, but this value exhibits a sharp decrease as the analyte partial pressure is lowered below 4 × 10(-4) Torr, regardless of exposure time. The number of reversible binding sites at saturation amounts to 0.09 ± 0.02 molecules/nm(2) with a free energy of adsorption of 43.8 ± 0.2 kJ/mol. We complement our measurements with FTIR spectroscopy and identify the thermal dark reaction as a combination of an aldol condensation and an oxidative adsorption that converts acetaldehyde to acetate or formate and CO, at a measured combined initial rate of 7 ± 1 × 10(-4) molecules/nm(2) s. By characterizing binding to different types of sites under dark conditions in the absence of oxygen and gas phase water, we set the stage to analyze site-specific photoefficiencies involved in the light-assisted mineralization of acetaldehyde to CO(2).
采用化学电离质谱（CIMS）技术，在低压条件下（乙醛分压范围为 10（-4）-10（-8）托）研究了乙醛与 TiO2 纳米棒的相互作用。我们定量分离了不可逆吸附、可逆吸附和被归因为热激活表面反应的乙醛吸收。我们发现，在室温下和 1.2 托总压力下，有 2.1 ± 0.4 个分子/纳米 2 不可逆地吸附，但无论暴露时间如何，当分析物分压低于 4 × 10（-4）托时，该值会急剧下降。在饱和时，可逆结合位点的数量达到 0.09 ± 0.02 个分子/纳米 2，吸附自由能为 43.8 ± 0.2 kJ/mol。我们用傅里叶变换红外光谱法（FTIR）对我们的测量进行了补充，并确定热暗反应是一种缩合反应和一种氧化吸附反应的组合，它将乙醛转化为乙酸盐或甲酸盐和 CO，初始测量的总速率为 7 ± 1 × 10（-4）分子/纳米 2 s。通过在没有氧气和气相水的暗条件下对不同类型的位点进行特征分析，我们为分析光辅助将乙醛矿化为 CO2 过程中涉及的特定位点的光效率奠定了基础。
