Thermochemical Study of Photoinduced Processes at TiO2 -Nanoparticles in Aqueous Suspension Containing Br- or Cl-. Photodeaggregation and Subsequent Processes
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- 作者：Ronald Pagel ; Jü ; rgen K. Dohrmann
- 刊名：Journal of Physical Chemistry C
- 出版年：2007
- 出版时间：March 22, 2007
- 年：2007
- 卷：111
- 期：11
- 页码：4458 - 4464
- 全文大小：269K
- 年卷期：v.111,no.11(March 22, 2007)
- ISSN：1932-7455
文摘
Laser pulse-induced optoacoustic calorimetry (LIOAC) was applied to determine enthalpy changes in aeratedaqueous suspensions of TiO2 nanoparticles (2.4 nm mean diameter) at pH = 1 in the absence and presenceof the halide ions X- = Br- or Cl-. LIOAC demonstrates that in the system TiO2
H2O, O2 10% of theabsorbed optical energy are stored for at least a few 
s, which can be assigned to the decomposition of water.In the systems containing the X-, the overall photoprocess was exothermic although the oxidation of X- to
k/111/i11/eqn/jp067297te10001.gif">- and the concurrent decomposition of water are endothermic. As an explanation we suggest a model inwhich the photodeaggregation of TiO2 nanoparticle aggregates produces additional photocatalyst surface area.The subsequent establishment of the thermodynamic equilibria on the additional surface comprises protonationof the TiO2 particles, halide adsorption, and formation of the electrochemical double layer. All these processesare exothermic. Adsorption of X- is best described by a Temkin-isotherm with k/111/i11/eqn/jp067297te10002.gif"> in the range -5 to -20kJ mol-1 for the transfer of X- from the outer to the inner Helmholtz plane on the TiO2 particles. The enthalpyof deaggregation is ca. + 30 kJ mol-1 as was calculated on the basis of energy conservation considerations.
H2O, O2 10% of theabsorbed optical energy are stored for at least a few s, which can be assigned to the decomposition of water.In the systems containing the X-, the overall photoprocess was exothermic although the oxidation of X- to