Staniszewski Aaron, Morris Amanda J, Ito Tamae, Meyer Gerald J
Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA.
J Phys Chem B. 2007 Jun 21;111(24):6822-8. doi: 10.1021/jp070413n. Epub 2007 Apr 20.
Mesoporous thin films comprised of interconnected nanocrystalline (anatase, 20 nm) TiO2 particles were functionalized with Ru(bpy)2(deebq)2, where bpy is 2,2'-bipyridine and deebq is 4,4'-diethylester-2,2'-biquinoline, or iron(III) protoporphyrin IX chloride (hemin). These compounds bind to TiO2 with saturation surface coverages of 8 (+/-2)x10(-8) mol/cm2. Electrochemical measurements show that the compounds first reduction occurs prior to or commensurate with the reduction of the TiO2 electrode. Apparent diffusion constants, Dapp, abstracted from chronoabsorption data measured in acetonitrile were found to be dependent on the applied potential and the electrolyte used. The Dapp values for reduction of Ru(dcbq)(bpy)2/TiO2, where dcbq is 4,4'-(COO-)2-2,2'-biquinoline, increased with decreasing surface coverage. At near saturation surface coverage, the apparent diffusion constant was 9.0 x 10(-12) m2/s after a potential step from -0.61 to -1.31 vs Fc+/0. The Dapp varied by over a factor of six with applied potential for the oxidation of [Ru(dcbq-)(bpy)2]-/TiO2 to Ru(dcbq)(bpy)2/TiO2. Complete reduction of hemin/TiO2 to heme/TiO2 was observed under conditions where the heme surface coverage was about 1/100 of that expected for monolayer surface coverage. The hemin reduction rates were strongly dependent on the final applied potential. The rates for heme to hemin oxidation were less than or equal to the hemin to heme rates in the presence and absence of pyridine. This behavior was opposite to that observed with Ru(dcbq)(bpy)2/TiO2 where reduction was slower than oxidation. A Gerischer-type model was proposed to rationalize the rectifying properties of the interface.
由相互连接的纳米晶体（锐钛矿，20纳米）二氧化钛颗粒组成的介孔薄膜用Ru(bpy)2(deebq)2进行功能化处理，其中bpy是2,2'-联吡啶，deebq是4,4'-二乙酯基-2,2'-联喹啉，或者用氯化铁(III)原卟啉IX（血红素）。这些化合物以8(±2)×10(-8) mol/cm2的饱和表面覆盖率与二氧化钛结合。电化学测量表明，这些化合物的首次还原发生在二氧化钛电极还原之前或与之同时发生。从在乙腈中测量的计时吸收数据提取的表观扩散常数Dapp被发现取决于施加的电势和所使用的电解质。Ru(dcbq)(bpy)2/TiO2（其中dcbq是4,4'-(COO-)2-2,2'-联喹啉）还原的Dapp值随着表面覆盖率的降低而增加。在接近饱和表面覆盖率时，相对于Fc+/0，从-0.61到-1.31的电势阶跃后，表观扩散常数为9.0×10(-12) m2/s。对于[Ru(dcbq-)(bpy)2]-/TiO2氧化为Ru(dcbq)(bpy)2/TiO2，Dapp随施加的电势变化超过六倍。在血红素表面覆盖率约为单层表面覆盖率预期值的1/100的条件下，观察到血红素/TiO2完全还原为血红素/TiO2。血红素的还原速率强烈依赖于最终施加的电势。在有和没有吡啶的情况下，血红素氧化为血红素的速率小于或等于血红素还原为血红素的速率。这种行为与Ru(dcbq)(bpy)2/TiO2观察到的相反，在Ru(dcbq)(bpy)2/TiO2中还原比氧化慢。提出了一个Gerischer型模型来合理化界面的整流特性。
