A novel photoanode architecture of dye-sensitized solar cells based on TiO2 hollow sphere/nanorod array double-layer film

A novel TiO(2) double-layer (DL) film consisting of TiO(2) hollow spheres (HSs) as overlayer and single-crystalline TiO(2) nanorod arrays (RAs) as underlayer was designed as the photoanode of dye-sensitized solar cells (DSSCs). This new-typed TiO(2) HS/RA DL film could significantly improve the efficiency of DSSCs owing to its synergic effects, i.e. the relatively large specific surface area of TiO(2) HSs for effective dye adsorption, enhanced light harvesting capability originated from TiO(2) RA film, and rapid interfacial electron transport in one-dimensional TiO(2) nanorod arrays. The overall energy-conversion efficiency of 4.57% was achieved by the formation of TiO(2) DL film, which is 16% higher than that formed by TiO(2) HS film and far larger than that formed by TiO(2) RA film (η=0.99%). The light absorption and interfacial electron transport, which play important roles in the efficiency of DSSCs, were investigated by UV-vis absorption spectra and electrochemical impedance spectra.     

TiO2纳米棒载Pd催化剂的制备及其对甲酸的电催化氧化

利用水热合成和无机溶胶法,分别制备了具有棒状(TiO2-R)和无规则结构(TiO2-I)的锐钛矿相TiO2,并以之为载体制备得到Pd/TiO2电催化剂.循环伏安测试显示,与无规则TiO2相比,具有棒状结构的TiO2载Pd催化剂对甲酸氧化的电催化性能提高了70%;计时电流测试显示,运行3000 s后,甲酸在棒状TiO2载Pd催化剂上的氧化电流是无规则TiO2载Pd催化剂的16倍.其原因可能与TiO2纳米棒拥有更好的电子传导性且表面拥有较多的活性含氧基团有关,从而能够有效提高催化剂对甲酸氧化的电催化活性和抗毒化性能.     

Preparation of nanoporous MgO-coated TiO2 nanoparticles and their application to the electrode of dye-sensitized solar cells

Sol-gel-derived Mg(OH)(2) gel was coated onto TiO(2) nanoparticles, and the subsequent thermal topotactic decomposition of the gel formed a highly nanoporous MgO crystalline coating. The specific surface area of the electrode that was prepared from the core-shell-structured TiO(2) nanoparticles significantly increased compared with that of the uncoated TiO(2) electrode. The increase in the specific surface area of the MgO-coated TiO(2) electrode was attributed to the highly nanoporous MgO coating layer that resulted from the topotactic reaction. Dye adsorption behavior and solar cell performance were significantly enhanced by employing the MgO-coated TiO(2) electrode. Optimized coating of a MgO layer on TiO(2) nanoparticles enhanced the energy conversion efficiency as much as 45% compared to that of the uncoated TiO(2) electrode. This indicates that controlling the extrinsic parameters such as the specific surface area is very important to improve the energy conversion efficiency of TiO(2)-based solar cells.     

CdS修饰TiO2纳米带制备及光催化降解有毒有机污染物

以硫酸钛为原料,在210℃低温下,水热制备TiO₂纳米带.通过沉淀法用CdS修饰TiO₂纳米带表面,制得TiO₂@CdS复合光催化剂,采用XRD、TEM和反射紫外对其结构及光化学特性进行初步表征.以可见光(λ≥450 nm)光催化降解罗丹明B(Rhodamine B,RhB)、水杨酸(Salicylic Acid,SA)及2,4-二氯苯酚(2,4-Dichlorophenol,2,4-DCP)为探针反应,研究反应温度、介质和负载CdS对TiO₂@CdS结构性能的影响.结果表明,所制备的TiO₂纳米带分散性好.复合粉末由锐钛矿相TiO₂和立方相CdS组成.常温25℃中性介质中用CdS修饰的TiO₂的活性,在可见光照射下,为单纯TiO₂纳米带的29倍.同时,TiO₂也促进了CdS可见光光催化活性的提高.通过跟踪降解体系紫外-可见光谱(UV-vis)、红外光谱(FTIR)和总有机碳(TOC)测定,结果发现TiO₂@CdS/vis体系在pH 7.0时,对SA的降解率较TiO₂纳米带有显著地提高,反应15 h和21 h后,RhB和2,4-DCP的矿化率分别可达到47.8%和30.8%.     

Quantum dot solar cells. harvesting light energy with CdSe nanocrystals molecularly linked to mesoscopic TiO2 films

By using bifunctional surface modifiers (SH-R-COOH), CdSe quantum dots (QDs) have been assembled onto mesoscopic TiO(2) films. Upon visible light excitation, CdSe QDs inject electrons into TiO(2) nanocrystallites. Femtosecond transient absorption as well as emission quenching experiments confirm the injection from the excited state of CdSe QDs into TiO(2) nanoparticles. Electron transfer from the thermally relaxed s-state occurs over a wide range of rate constant values between 7.3 x 10(9) and 1.95 x 10(11) s(-1). The injected charge carriers in a CdSe-modified TiO(2) film can be collected at a conducting electrode to generate a photocurrent. The TiO(2)-CdSe composite, when employed as a photoanode in a photoelectrochemical cell, exhibits a photon-to-charge carrier generation efficiency of 12%. Significant loss of electrons occurs due to scattering as well as charge recombination at TiO(2)/CdSe interfaces and internal TiO(2) grain boundaries.     

Photocatalytic reactivity of surface platinized TiO2: substrate specificity and the effect of Pt oxidation state

Surface platinized TiO(2) (Pt/TiO(2)) has been frequently studied, but its photocatalytic reactivities reported in the literature are not consistent in some cases. To understand the discrepancies, the effects of Pt speciation on TiO(2) on the photocatalytic degradation (PCD) of a few chlorinated organic compounds (trichloroethylene (TCE), perchloroethylene (PCE), dichloroacetate, etc.) were investigated with several Pt/TiO(2) samples that were prepared differently. The oxidation state of Pt deposits was analyzed by X-ray photoelectron spectroscopy and was found to be the most important factor in determining the initial PCD rates of chlorinated organic compounds. TiO(2) with oxidized Pt species (Pt(ox)/TiO(2)) was less reactive than TiO(2) with metallic Pt (Pt(0)/TiO(2)) for all substrates tested. In particular, Pt(ox)/TiO(2) strongly inhibited the PCD of TCE and PCE whereas it was more reactive than pure TiO(2) for the PCD of other compounds. The photocurrents obtained with the Pt(ox)/TiO(2) electrode were lower than those with the Pt(0)/TiO(2) electrode, which was ascribed to the role of Pt(ox) species as a recombination center. It is proposed that TCE adsorbed on Pt(ox) chemically mediates the charge recombination through the redox cycle of TCE. The Pt effects in photocatalysis are highly substrate-specific and depend on the Pt-substrate interaction as well as the properties of Pt deposits.     

Exfoliated and reorganized graphite oxide on titania nanoparticles as an auxiliary co-catalyst for photocatalytic solar conversion

The hybrid of graphite oxide (GO)/TiO(2) was prepared through the spontaneous exfoliation of bulky graphite oxide and reorganization with TiO(2) nanoparticles as a solar conversion and hydrogen-generating photocatalyst. GO/TiO(2) showed enhanced activities for both photocurrent generation (in an electrode form) and hydrogen production (in a slurry form) than those of bare TiO(2) under UV light irradiation. The enhanced photocatalytic activity of GO/TiO(2) is ascribed to the ability of graphitic layers in accepting and transporting electrons from excited TiO(2), promoting the charge separation. When GO was hybridized with platinized TiO(2) (Pt/TiO(2)), it showed a marked synergistic effect for the photocatalytic hydrogen production compared with GO/TiO(2) and Pt/TiO(2). This indicates that the cheap and abundant carbon material can be a good candidate for an electron attracting reservoir and an auxiliary co-catalyst for the photocatalytic hydrogen production.     

Drying and nondrying layer-by-layer assembly for the fabrication of sodium silicate/TiO2 nanoparticle composite films

Influences of drying and nondrying steps on structures of layer-by-layer (LbL) assembled sodium silicate/TiO(2) nanoparticles films (donated as silicate/TiO(2) films) have been systematically investigated. The nondrying LbL assembly produces highly porous silicate/TiO(2) films with large thickness. In contrast, the silicate/TiO(2) films fabricated with a drying step after each layer deposition are flat and thin without porous structures. In situ atomic force microscopy (AFM) measurements confirm that the sodium silicate and TiO(2) nanoparticles are deposited in their aggregated forms. A N(2) drying step can disintegrate the aggregated silicate and TiO(2) nanoparticles to produce thin silicate/TiO(2) films with compact structures. Without the drying steps, the aggregated silicate and TiO(2) nanoparticles are well retained, and their LbL assembly produces highly porous silicate/TiO(2) films of large thickness. The highly porous silicate/TiO(2) films are demonstrated to be useful as reusable film adsorbents for dye removal from wastewater because they can adsorb a large amount of cationic organic dyes and decompose them under UV irradiation. The present study is meaningful for exploring drying/nondrying steps for tailoring structure and functions of LbL assembled films.     

Density functional theory study on the structural and electronic properties of low index rutile surfaces for TiO2/SnO2/TiO2 and SnO2/TiO2/SnO2 composite systems

The present study is concerned with the structural and electronic properties of the TiO2/SnO2/TiO2 and SnO2/TiO2/SnO2 composite systems. Periodic quantum mechanical method with density functional theory at the B3LYP level has been carried out. Relaxed surface energies, structural characteristics and electronic properties of the (110), (010), (101) and (00) low-index rutile surfaces for TiO2/SnO2/TiO2 and SnO2/TiO2/SnO2 models are studied. For comparison purposes, the bare rutile TiO2 and SnO2 structures are also analyzed and compared with previous theoretical and experimental data. The calculated surface energy for both rutile TiO2 and SnO2 surfaces follows the sequence (110) < (010) < (101) < (001) and the energy increases as (010) < (101) < (110) < (001) and (010) approximately = (110) < (101) < (001) for SnO2/TiO2/SnO2 and TiO2/SnO2/TiO2 composite systems, respectively. SnO2/TiO2/SnO2 presents larger values of surface energy than the individual SnO2 and TiO2 metal oxides and the TiO2/SnO2/TiO2 system renders surface energy values of the same order that the TiO2 and lower than the SnO2. An analysis of the electronic structure of the TiO2/SnO2/TiO2 and SnO2/TiO2/SnO2 systems shows that the main characteristics of the upper part of the valence bands for all the studied surfaces are dominated by the external layers, i.e., by the TiO2 and the SnO2, respectively, and the topology of the lower part of the conduction bands looks like the core layers. There is an energy stabilization of both valence band top and conduction band bottom for (110) and (010) surfaces of the SnO2/TiO2/SnO2 composite system in relation to their core TiO2, whereas an opposite trend is found for the same surfaces of the TiO2/SnO2/TiO2 composite system in relation to the bare SnO2. The present theoretical results may explain the growth of TiO2@SnO2 bimorph composite nanotape.     

Titanium dioxide anatase as matrix for matrix-assisted laser desorption/ionization analysis of small molecules

The use of inorganic species as assisting materials in matrix-assisted laser desorption/ionization (MALDI) analysis is an alternative approach to avoid interfering matrix ions in the low-mass region of the mass spectra. Reports of the application of inorganic species as matrices in MALDI analysis of small molecules are, however, scarce. Nevertheless, titanium dioxide (TiO(2)) powder has been reported to be a promising matrix medium. In this study we further explore the use of TiO(2) as a matrix for the MALDI analysis of low molecular weight compounds. We present results showing that nanosized TiO(2) anatase and TiO(2) rutile perform better as MALDI matrices than a commercial TiO(2) anatase/rutile mixture. Moreover, when using nanosized TiO(2) anatase as a matrix, high-quality mass spectra can be obtained with strong analyte signals and weak or non-existing matrix interference ions. Furthermore, our results show that the phase type plays an important role in the application of TiO(2) as a MALDI matrix.     

Comparison of electrode structures and photovoltaic properties of porphyrin-sensitized solar cells with TiO2 and Nb, Ge, Zr-added TiO2 composite electrodes

Electrode structures and photovoltaic properties of porphyrin-sensitized solar cells with TiO2 and Nb-, Ge-, and Zr-added TiO2 composite electrodes were examined to disclose the effects of partial substitution of Ti atom by the other metals in the composite electrodes. The TiO2 and Nb-, Ge-, and Zr-added TiO2 composite electrodes were prepared by sol-gel process using laurylamine hydrochloride as a template for the formation of micellar precursors yielding well-defined mesoporous nanocrystalline structures, as in the cases of the formation of silica and titania tubules and nanoparticles by the templating mechanism. The TiO2 and Nb-, Ge-, and Zr-added TiO2 composite electrodes were characterized by transmission electron microscopy, BET surface area analysis, X-ray diffraction analysis, Raman spectroscopy, and impedance measurements. The TiO2 anatase nanocrystalline structure is retained after doping a small amount (5 mol %) of Nb, Ge, or Zr into the TiO2 structure, suggesting the homogeneous distribution of the doped metals with replacing Ti atom by the doped metal. The power conversion efficiency of the porphyrin-sensitized solar cells increases in the order Zr-added TiO2 (0.8%) < Nb-added TiO2 (1.2%) < TiO2 (2.0%) < Ge-added TiO2 cells (2.4%) under the same conditions. The improvement of cell performance of the Ge-added TiO2 cell results from the negative shift of the conduction band of the Ge-added TiO2 electrode. The Ge-added TiO2 cell exhibited a maximum power conversion efficiency of 3.5% when the porphyrin was adsorbed onto the surface of the Ge-added TiO2 electrode with a thickness of 4 microm in MeOH for 1 h.     

Synthesis of dendrimer-protected TiO2 nanoparticles and photodegradation of organic molecules in an aqueous nanoparticle suspension

Dendrimer-protected TiO2 nanoparticles were synthesized by hydrolysis of TiCl4 in solutions of poly(amido amine) dendrimers (64 terminals) under cooling. The morphology of dendrimers surrounding TiO2 nanoparticles depended on the terminal groups (amine, carboxyl, hydroxy) of dendrimers. The size (4.4-6.7 nm) of dendrimer-protected TiO2 nanoparticles was slightly smaller than that (7.5 nm) of bare TiO2 nanoparticles. The photodegradation of 2,4-dichlorophenoxyacetic acid revealed that dendrimer-protected TiO2 nanoparticles are more active as a photocatalyst than TiO2 nanoparticles without protectors. This suggests that the dendrimer acts as a reservoir of photoreacting reagents besides acting as a protector of nanoparticles.     

Enhanced photocatalytic degradation of C.I. Basic Violet 2 using TiO2-SiO2 composite nanoparticles

In this report, TiO(2) -SiO(2) composite nanoparticles were prepared by the thermal hydrolysis method using titanium tetrachloride and tetraethylorthosilicate as TiO(2) and SiO(2) precursors, respectively. The prepared nanoparticles were characterized by X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), nitrogen adsorption/desorption and UV-Vis diffuse reflectance spectroscopy (DRS). The results indicated that, in comparison with pure TiO(2), TiO(2)-SiO(2) composite nanoparticles had a higher thermal stability, which prevents phase transformation from anatase to rutile. In addition, the TiO(2)-SiO(2) nanoparticles had a higher specific surface area, larger pore volume, greater band gap energy and smaller crystallite size. Thus, the surface area of TiO(2)-40% SiO(2) composite nanoparticles was about 17 times higher than that of pure TiO(2) nanoparticles. The photocatalytic activity of TiO(2)-SiO(2) composite nanoparticles in the photodegradation of C.I. Basic Violet 2 was investigated. The photodegradation rate of Basic Violet 2 using TiO(2)-40% SiO(2) nanoparticles calcined at 600°C was much faster than that using pure TiO(2) and Degussa P25 TiO(2) by 10.9 and 4.3 times, respectively. The higher photoactivity of the TiO(2)-SiO(2) composite nanoparticles was attributed to their higher surface area, larger pore volume, greater band-gap energy and smaller crystallite size compared with pure TiO(2).     

Matrix infrared spectra and density functional calculations of TiO3 and TiO5 in solid argon

The reaction of titanium monoxide molecules and O2 was studied by using matrix isolation infrared spectroscopy as well as theoretical calculations. The titanium monoxide molecule reacts with O2 to form TiO 3 spontaneously on annealing. The TiO3 molecule is characterized to be a side-on bonded peroxo titanium monoxide complex, (eta(2)-O2)TiO, which has a nonplanar Cs symmetry with a 1A' ground state. The (eta(2)-O2)TiO complex can further coordinate another dioxygen to give TiO 5, a disuperoxo titanium monoxide complex, (eta(2)-O2)(2)TiO, which possesses a 3A' ground state and a nonplanar Cs geometry.     

Enhanced photocatalytic activity of bimodal mesoporous titania powders by C60 modification

In this work, fullerene modified TiO(2) nanocomposites (denoted as C(60)/TiO(2)) with low C(60) loadings (0-1.5 wt.%) have been prepared by a simple hydrothermal method using tetrabutylorthotitanate (TBOT, Ti(OC(4)H(9))(4)) as the titanium precursor. The as-prepared C(60)/TiO(2) nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, UV-visible spectrophotometry, nitrogen adsorption, and X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy. The formation of hydroxyl radicals (˙OH) on the surface of UV-illuminated TiO(2) is probed by photoluminescence using terephthalic acid as a probe molecule. Our results have demonstrated that C(60) molecules can be dispersed as a monolayer onto bimodal mesoporous TiO(2)via covalent bonding. The photocatalytic oxidation rate of gas-phase acetone over C(60)/TiO(2) nanocomposites is greater than that over pure TiO(2), commercial Degussa P25 (P25) and C(60)-TiO(2) counterparts prepared by simple impregnating mixing. In particular, 0.5 wt.% C(60)/TiO(2) nanocomposites show the greatest photocatalytic activity with the rate constant k exceeding that of P25 by a factor of 3.3. Based on the results of the current study, we propose that C(60) molecules doped onto TiO(2) act as "electron acceptors" responsible for the efficient separation of photogenerated charge carriers and the enhancement of photocatalytic activity. The proposed mechanism for the observed photocatalytic performance of C(60)/TiO(2) nanocomposites is further corroborated by experiments on hydroxyl radical and transient photocurrent response.     

Wet chemical synthesis of Cu/TiO2 nanocomposites with integrated nano-current-collectors as high-rate anode materials in lithium-ion batteries

Using a soft-template assisted method, well-organized Cu/TiO(2) nanoarchitectured electrode materials with copper nanowires as their own current collectors are synthesized by controlled hydrolysis of tetrabutyl titanate in the presence of Cu-based nanowires, and investigated by SEM, TEM, XRD, Raman spectroscopy and electrochemical tests towards lithium storage. Two types of Cu/TiO(2) nanocomposites with different TiO(2) grain sizes are obtained by using different thermal treatments. The two types of Cu/TiO(2) nanocomposites show much enhanced rate performances compared with bare TiO(2). A high-rate capability (reversible capacity at 7500 mA g(-1) still accounts for 58% of its initial capacity at 50 mA g(-1)) is observed for the Cu/TiO(2) nanocomposite with smaller TiO(2) grain size. The improvements can be attributed to the integrated Cu nanowires as mechanical supports and efficient current collectors. A cell made from the Cu/TiO(2) nanoarchitectured electrodes exhibits promise as an energy storage device with both high energy and high power densities.     

Highly active TiO2N photocatalysts prepared by treating TiO2 precursors in NH3/ethanol fluid under supercritical conditions

N-doped TiO2 photocatalysts were prepared by pretreating the TiO2 precursor in NH3/ethanol fluid under supercritical conditions, denoted as TiO2N(SC). In contrast to the TiO2N(DC), obtained via direct calcination in which the N dopants were mainly present in the form of surface adsorbed NH3 molecules, most N dopants in the TiO2N(SC) were present in O-Ti-N and N-Ti-N nitrides, as confirmed by either the X-ray photoelectron spectroscopy (XPS) and or the Fourier transform infrared (FTIR) spectra. During liquid-phase oxidative degradation of phenol under irradiation with UV light characteristic of 365 nm, the TiO2N(SC) exhibited much higher activity than either the TiO2N(DC) or the TiO2(SC), i.e., the undoped TiO2 obtained under SCs. According to various characterizations including X-ray diffraction, transmission electron microscopy, FTIR, Brunauer-Emmett-Teller, XPS, and UV-vis diffuse reflectance spectra, the higher activity of the TiO2N(SC) could be attributed to its higher surface area, larger pore volume, well-crystallized anatase, and stronger absorbance of light with longer wavelength. Meanwhile, the OH species resulted from the nitridation of TiO2 could supply more HO* radicals, which were considered as powerful oxidants during phenol degradation. Furthermore, the electron-deficient nitrogen atoms in O-Ti-N nitrides could also account for the higher activity since it could inhibit the recombination between the photoinduced electrons and holes by capturing the photoinduced electrons. The activity of the TiO2N(SC) first increased and then decreased with the increase of the N-content. The TiO2N(SC)-1 with N/Ti molar ratio of 1.73% exhibited maximum activity, which was even much higher than P-25.     

A theoretical investigation on photocatalytic oxidation on the TiO2 surface

The TiO(2) photocatalytic oxidation mechanism was theoretically investigated by using long-range corrected time-dependent density functional theory (LC-TDDFT) with a cluster model of the anatase TiO(2)(001) surface. We found that LC-TDDFT with the cluster model quantitatively reproduces the photoexcitations of the TiO(2) surface by calculating the electronic spectra of a clean TiO(2) surface and one with oxygen defects. We calculated the electronic spectra of a molecularly adsorbed TiO(2) surface for the adsorptions of phenol, methanol, and methane molecules as typical organic molecules. We obtained the surprising result that the main peak of the phenol-adsorbed TiO(2) surface, which overlaps with the main peak of the clean TiO(2) surface, corresponds to charge transfers from the phenol molecule to the TiO(2) surface. This indicates that the TiO(2) photocatalytic oxidation proceeds through direct charge transfer excitation from the substrate molecules to the TiO(2) surface. In contrast, we found slight and no charge transfer for methanol and methane adsorption, respectively, in agreement with the experimental findings for their reactivities. In light of these results, we propose a new mechanism for heterogeneous TiO(2) photocatalytic oxidations.     

二氧化钛纳米粒子-氧化石墨烯/聚酰亚胺混合基质膜的原位聚合及气体渗透性能

以钛酸四丁酯为前驱体,采用浸渍-沉淀法制备二氧化钛纳米粒子-氧化石墨烯(TiO_2-GO)复合物,再将TiO_2-GO复合物与4,4'-(六氟异亚丙基)邻苯二甲酸酐和4,4'-二氨基二苯醚通过原位聚合构建TiO_2-GO/TiO_2-GO/PI(聚酰亚胺)混合基质膜,用于CO_2的渗透脱除.采用傅里叶变换红外光谱(FTIR)、拉曼光谱(Raman)、透射电子显微镜(TEM)、扫描电子显微镜(SEM)、热失重(TG)和Zeta电位等表征了TiO_2-GO复合物和TiO_2-GO/PI混合基质膜的形貌与结构;探讨了TiO_2掺杂量对TiO_2-GO复合物及TiO_2-GO/PI混合基质膜的结构和气体渗透性能的影响.结果表明,TiO_2-GO复合物中TiO_2纳米粒子较均匀地沉积在GO片层上,TiO_2纳米粒子在形成的同时破坏了GO的结构,使其无序度增加.TiO_2的掺杂对TiO_2-GO/PI混合基质膜的形貌与结构影响较小,但提升了TiO_2-GO/PI混合基质膜的CO_2和N2渗透性能.但过量的掺杂使TiO_2粒子在GO片层上团聚,从而导致TiO_2-GO复合物在混合基质膜中的分散性变差,CO_2渗透性及CO_2/N2渗透选择性降低.当TiO_2掺杂质量分数为30%时,TiO_2-GO/PI混合基质膜的CO_2渗透性为360 Barrer[1 Barrer=10~(-10)cm~3(STP)·cm/(cm~2·s·cm Hg)=7.5×10~(-14)cm~3(STP)·cm/(cm~2·s·Pa)],CO_2/N_2的渗透选择性可达31.     

Redox processes in mesoporous oxide membranes: layered TiO2 phytate and TiO2 flavin adenine dinucleotide films

Thin films of TiO2 (anatase) nanoparticles are assembled at an electrode surface via a layer-by-layer deposition process employing phytic acid, pyromellitic acid, or flavin adenine dinucleotide (FAD) as molecular binders. With all three types of binders, layers of typically 30 nm thickness are formed each deposition cycle. FAD as an electrochemically active component immobilized at the surface of the TiO2 particles is reduced to FADH2 and reoxidized in a chemically reversible two electron-two proton redox process. Two distinct voltammetric signals are observed for the immobilized FAD redox system associated with (i) hopping of electrons at the TiO2 surface (reversible) and (ii) conduction of electrons through the TiO2 assembly (irreversible). The conduction of electrons through the TiO2 assembly is possible by diffusion over considerable distances as well as through a "spacer" layer of TiO2 phytate. An order of magnitude (upper limit) estimate for the diffusion coefficient of electrons through TiO2 phytate, D(electron) approximately 10(-6) m(2) s(-1), is obtained from voltammetric data. Finally, it is demonstrated that the calcination of TiO2 assemblies causes dramatic changes in the electron transfer kinetics for the immobilized FAD/FADH2 redox system.