Reduction Of MV2 Research Articles

Systematic homogenization of heterogenous biomass batches – Industrial-scale production of solid biofuels in two case studies

Biomass is a heterogeneous material with respect to its chemical composition due to different plant species and components as well as the potential content of impurities. Especially in the production of large fuel batches heterogeneous chemical compositions are a challenge with respect to the required compliance with fuel standards and emission thresholds during utilization. This can be avoided by fuel pre-treatment and systematic homogenization during fuel production. For this reason, the study analyses the effects of biomass leaching in combination with homogenization of biomass batches on industrial-scale. Within two case studies, low-quality herbaceous biomasses, i.e. foliage and wheat straw were pretreated and homogenized in quantities ranging from 8 to 51 tons. In the first case study, foliage was first leached, then mixed with sawdust and homogenized by separating batch parts with high ash content, followed by systematic recombination of the batches. In the second case study, homogenization of straw pellets (untreated and leached) was attempted by a layering approach during bagging. Both case studies (i) confirm earlier findings that critical fuel components can be substantially reduced by leaching (i.e. reduction of ash content MV by 45 w-%) but indicate that material agitation during leaching is necessary; (ii) underscore that systematic homogenization is necessary for fuel batches consisting of materials from different origins and reduce i.e.-the ash content RSD by 48%, and (iii) demonstrate that even low-quality fuels from herbaceous biomass assortments can comply with the requirements of fuel standards if dedicated fuel pretreatment is employed.

Two-electron transfer photoreduction of methyl viologen and perfluorooctanoic acid mediated by flavin mononucleotide at colloidal titanium dioxide interfaces

Environmentally friendly catalyst consisting of a flavin mononucleotide and titanium dioxide nanoparticles for MV2+ and poly-fluorinated octanoic acid reduction.

Closed Bipolar Electrode-Enabled Electrochromic Sensing of Multiple Metabolites in Whole Blood.

We report a closed bipolar electrode (CBE)-based sensing platform for the detection of diagnostic metabolites in undiluted whole human blood. The sensor is enabled by electrode chemistry based on: (1) a mixed layer of blood-compatible adsorption-resistant phosphorylcholine (PPC) and phenylbutyric acid (PBA), (2) ferrocene (Fc) redox mediators, and (3) immobilized redox-active enzymes. This scheme is designed to overcome nonspecific protein adsorption and amplify sensing currents in whole human fluids. The scheme also incorporates a diffusing mediator to increase electronic communication between the immobilized redox enzyme and the working electrode. The use of both bound and freely diffusing mediators is synergistic in producing the electrochemical response. The sensor is realized by linking the analyte cell, containing the specific electrode surface architecture, through a CBE to a reporter cell containing the electrochromic reporter, methyl viologen (MV). The colorless-to-purple color change accompanying the 1e- reduction of MV2+ is captured using a smartphone camera. Subsequent red-green-blue analysis is performed on the acquired images to determine cholesterol, glucose, and lactate concentrations in whole blood. The CBE blood metabolite sensor produces a linear color change at clinically relevant concentration ranges for all metabolites with good reproducibility (∼5% or better) and with limits of detection of 79 μM for cholesterol, 59 μM for glucose, and 86 μM for lactate. Finally, metabolite concentration measurements from the CBE blood metabolite sensor are compared with results from commercially available FDA-approved blood cholesterol, glucose, and lactate meters, with an average difference of ∼3.5% across all three metabolites in the ranges studied.

Stabilization of p-GaAs electrode surfaces in organic solvent by bi-phenyl rings for spin dependent electron transfer studies

Biphenyl-4-thiol (B4t) functionalised p-GaAs photocathodes were compared to non-functionalised p-GaAs ones in the presence of methyl viologen cation radical (MV+) as a redox mediator. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) studies revealed that at bare p-GaAs photocathodes the radical interacts strongly with the electrode surface, displaying unwanted surface states (SS) mediated electron transfer (ET) even in the dark. Functionalising the electrode with B4t passivated the interface against this unwanted process, while ensuring that the conduction band (CB) electrons still facilitated faradaic reduction of MV+ to MV0 with unhindered efficiency.

Photoinduced electron transfer in semiconductor–clay binary nanosheet colloids controlled by clay particles as a turnout switch

Although semiconductor photocatalysis has been investigated actively for a long time, control of dark processes successive to electron transfer from photocatalysts is almost unexplored compared with designing photocatalysts themselves. The present study proposes employment of clay particles as for controlling the dark processes independently of semiconductor photocatalyst particles. We employed niobate–clay binary nanosheet colloids, where colloidal niobate and clay nanosheets are spatially separated at a micrometer level. Niobate nanosheets worked as the semiconductor photocatalyst that released electrons upon UV excitation, and clay nanosheets worked as the turnout switch of the released electrons to determine their destination. When methylviologen (MV2+) molecules that accept the electrons released from niobate were adsorbed on clay nanosheets, reduction of MV2+ predominantly occurred, and hydrogen was little evolved from the colloid. When Pt nanoparticles were deposited on clay nanosheets, photocatalytic hydrogen evolution occurred because Pt loaded on the clay nanoparticles played a role of cocatalyst. When MV2+ and Pt were co-loaded on clay nanosheets, both of MV2+ reduction and hydrogen evolution occurred competitively. The photocatalytic hydrogen evolution carried out by stirring the colloid sample was worse than that conducted without stirring, which indicated positive contribution of the spatial separation of photocatalytic niobate and cocatalytic clay nanosheets.

Surface-Bound Cucurbit[8]uril Catenanes on Magnetic Nanoparticles Exhibiting Molecular Recognition.

We demonstrate the preparation of surface-bound cucurbit[8]uril (CB[8]) catenanes on silica nanoparticles (NPs), where CB[8] was employed as a tethered supramolecular "handcuff" to selectively capture target guest molecules. In this catenane, CB[8] was threaded onto a methyl viologen (MV(2+) ) axle and immobilized onto silica NPs. The formation of CB[8] catenanes on NPs were confirmed by UV/Vis titration experiments and lithographic characterization, demonstrating a high density of CB[8] on the silica NPs surface, 0.56 nm(-2) . This CB[8] catenane system exhibits specific molecular recognition towards certain aromatic molecules such as perylene bis(diimide), naphthol and aromatic amino acids, and thus it can act as a nanoscale molecular receptor for target guests. Furthermore, we also demonstrate its use as an efficient and recyclable nano-platform for peptide separation. By embedding magnetic NPs inside silica NPs, separation could be achieved by simply applying an external magnetic field. Moreover, the peptides captured by the catenanes could be released by reversible single-electron reduction of MV(2+) . The entire process demonstrated high recoverability.

Effect of Liposomes on the Kinetics and Mechanism of the Photocatalytic Reduction of Methyl Viologen.

Liposomes are interesting scaffolds for photocatalysis. In particular, charged liposomes were shown to increase the quantum efficiency of photocatalytic reactions involving charged porphyrin photosensitizers and charged electron acceptors. In this work, the effects of adding positively charged liposomes (DMPC/eDMPCCl 1:1) on the mechanism of the photocatalytic reduction of methyl viologen (MV(2+)) by cysteine in the presence of sodium meso-tetra-(4-sulfonato)porphyrinatozinc (Na41) were probed by modeling UV-vis spectroscopy data using a steady-state approximation. By varying the concentration of methyl viologen, we found that the liposomes not only prevent the formation of a 1:1 complex between ground-state photosensitizer 1(4-) and MV(2+) but also that they increase the cage-escape yield in the excited state. Furthermore, the electrostatic repulsion between the liposomes and MV(2+) diminishes by 1 order of magnitude the rate of oxidative quenching of the photosensitizer triplet excited state ((T)1(4-)) by MV(2+). By varying the amount of sacrificial electron donor (cysteine), the effect of liposome addition on the charge recombination reactions could also be studied. Because of the positive charge borne by the photoproduct MV(•+), it was also repelled from the membrane, which significantly slows charge recombination at the surface of the liposome. Overall, compared to a liposome-free solution, the rates of most elementary steps of the photocatalytic reduction of MV(2+) by cysteine are strongly modified when the negative photosensitizer is adsorbed on a positively charged liposome surface. These results not only explain the much higher efficiency of the liposome-containing system but also illustrate the power of supramolecular chemistry for the tuning of photocatalysis.

Electroreduction of Selenium Oxyanions in the Presence of Methyl Viologen

INTRODUCTION It has been recently claimed [1] that the electroreduction of selenate on glassy carbon electrodes in neutral and acidic aqueous electrolytes can be accelerated by the presence of solution phase methyl viologen, MV2+(aq), at room temperature. This contribution will present evidence that the effects described in that report are due to the reduction of selenite, a common impurity found in commercial selenate salts. Also to be discussed are the results of our detailed studies involving the MV2+(aq)-mediated reduction of selenite, from which the onset for the overall process was found to occur at potentials far more positive than those associated with the reduction of MV2+(aq). EXPERIMENTAL Commercially available Na2SeO4 (Alfa Aesar, 99.9%) was purified by the method described by Gruebel et al. [2] which involved adsorption of SeO3 2- on high area TiO2 at low pH. A glassy carbon (GC) rotating disk electrode (RDE) was used as a working electrode, and a carbon rod and a Ag/AgCl as counter and reference electrodes, respectively. Cyclic voltammetric experiments were performed in aqueous 0.2 M sodium acetate buffer (pH 4.02), or 0.1 M sodium phosphate buffer (pH 7) in the presence of 1 mM MVCl2 (Sigma-Aldrich, 98%), 30 mM Na2SeO4, or 1 mM Na2SeO3 (ACROS organics, 44- 46% Se) or mixtures thereof prepared with ultrapure water (18.3 MΩ, Barnstead water purifier) using a bipotentiostat (Pine Instruments, RDE3). RESULTS AND DISCUSSION In marked contrast with the literature report [1], no changes were detected in the cyclic voltammogram of GC recorded at a scan rate of 100 mV/s under stagnant conditions after addition of 30 mM ultrapure Na2SeO4 into 0.2 M sodium acetate (pH 4.02) containing 1 mM MV2+ (see black and red lines, respectively in Fig. 1). However, a large increase in the negative current was observed after addition of 1 mM Na2SeO3. It may thus be concluded on this basis, that selenate does not undergo reduction on GC under the conditions of these experiments, and that the results reported earlier are consistent with the presence of selenite as an impurity in the commercial selenate. Interestingly, the onset for the reduction of SeO3 2- in the presence of MV2+, as found in dynamic polarization curves recorded at a scan rate of 10 mV/s with the GC RDE rotating at 900 rpm (blue line, Figure 2) was far more positive, ca. -0.2 V vs Ag/AgCl, than the onset of the reduction of either of SeO3 2- (black line, Fig. 2) or MV2+ (magenta line, Fig. 2) individually in the same buffered solution (ca. -0.55 V). One possible explanation for this phenomenon may be found in the formation of an adduct between the two reactive species for which the redox potential would be more positive than for either one of the constituents. However, no such species has been detected in our initial measurements involving solution phase NMR and UV-vis spectroscopies. Yet another plausible explanation involves the adsorption of either one of the species on GC which might lead to a change in its redox properties which might facilitate reduction of the other. These are currently being explored in our laboratory and will be reported in due course. REFERENCES 1. Fumiya, Koshikumo., Wakana Murata., Akiyuki, Ooya; Shin-ichiro, Imabayashi. Electrochemistry. 81(2013), 350- 352. 2. Gruebel, K. A.; Davis, J. A.; Leckie, J. O. Environ. Sci. Tech. 29(1995), 586-594. ACKNOWLEDGEMENTS This work was supported by a Grant from NSF. Figure 1

Interaction study of methyl violet 2B with DNA and voltammetric determination of DNA in aqueous solutions

Differential pulse voltammetry, cyclic voltammetry, and chronocoulometry at a hanging mercury drop electrode were used for the study of the interaction of methyl violet 2B (MV) with double-stranded DNA in 0.1 mol dm−3 acetate buffer pH 4.0. The mechanism of the electrochemical reduction of MV was also investigated, using cyclic voltammetry at a hanging mercury drop electrode. UV–Vis spectrophotometry was used for the investigation of the interaction as well. The kinetic parameters of the reduction of MV and the DNA–MV complex and the thermodynamic parameters of the formed DNA–MV complex were calculated. Moreover, the calibration dependence of the peak current of MV on the concentration of DNA in acetate buffer was constructed to be used for the indirect determination of DNA based on the decreasing peak current of MV with increasing concentration of DNA in the measured solution.

Electrochemical behavior of N-methyl-N′-carboxydecyl-4,4′-bipyridinium probed by surface-enhanced Raman spectroscopy

Interfacial structure determines the activity and selectivity of a sensor and plays important roles in interfacial electrochemistry, electroanalysis, biosensing, etc. In situ electrochemical Raman spectroscopy appears to be a powerful tool to probe the electrochemical interface and surface process by providing the molecular fingerprint information. Herein, the electrochemical behaviors of N-methyl-N′-carboxydecyl-4,4′-bipyridinium (derivatives of methyl viologens, MV2+) with different alkyl chain lengths (n=2 and 10) on roughened Au electrodes were systematically investigated by the electrochemical surface-enhanced Raman spectroscopy (SERS). Three systems with different interfacial structures were constructed. One is to anchor the MV2+ molecules via esterification with the 2-mercaptoethanol molecule pre-assembled on the Au surface. The second system is similar to the first one but without esterification. The third system is the direct adsorption of MV2+ molecules on the bare roughened Au surfaces. The three systems gave different spectral response upon the change of the electrode potential. A drastically increased relative Raman intensity of 19a/8a modes of the MV2+ molecules was observed at negative potentials. The phenomenon is attributed to the formation of the reduced form of MV2+ molecules, which produces resonant Raman effect to enhanced the signal of 19a mode. The third system showed the highest electrochemical reduction activity towards the reduction of MV2+ molecules, followed by the first and second systems. The result indicates that the interfacial structure can sensitively influence electrochemical activity of the electrode.

Photoinduced Electron Transfer between Ruthenium-bipyridyl Complex and Methylviologen in Suspensions of Smectite Clays

We examined photoinduced electron transfer (PET) in multicomponent aqueous suspensions composed of tris(2,2′-bipyridine)ruthenium(II) (Ru(bpy)32+, photocatalyst), methylviologen (1,1′-dimethyl-4,4′-bipyridinium dication, MV2+, electron acceptor), and ethylenediamine tetraacetate (EDTA, sacrificial electron donor) together with particles of smectite-type clays although previous studies indicated inhibition of the electron transfer from Ru(bpy)32+ to MV2+ in the presence of clay particles. Clays with different lateral particle sizes were compared: hectorite (Hect) and saponite (Sapo) with small particle sizes (∼30 nm) and fluorohectorite (FH) and montmorillonite (Mont) with large particle sizes (>0.1 μm). Clay particles were flocculated and were settled in many cases after the addition of Ru(bpy)32+, MV2+, and EDTA species, and the Ru(bpy)32+ and MV2+ cations were almost all adsorbed on the clay particles. When Hect and Sapo were used, reduction of MV2+ was observed on the aggregated clay particles upon visible light irradiation indicating the occurrence of PET from Ru(bpy)32+ to MV2+. However, the reaction was not observed for the samples where the clay particles were not settled. When FH and Mont were used, PET was not observed irrespective of the flocculation of clay particles. These results demonstrated that PET from Ru(bpy)32+ to MV2+ in the presence of clay particles is possible when the clay particles with small sizes are appropriately aggregated to allow interparticle electron hopping.

PHOTOINDUCED ELECTRON ACCUMULATION OF TITANIUM DIOXIDE NANOPARTICLES MODIFIED ELECTRODES

Titanium dioxide ( TiO 2) nanoparticles (Nps) were prepared by the hydrolysis of titanium tetraisopropoxide ( TTIP ) in 2-propanol with different water contents (0.5 vol% to 7.2 vol%) at 45 °C. The diameter of the Nps was estimated to be 1.5±0.5 nm ( L - TiO 2) and 3.0±0.6 nm ( S - TiO 2) from the onset wavelength in the absorption spectra and by transmission electron microscopy (TEM). A modified Pt electrode with a three-layered sandwich structure was prepared; the outermost and innermost layers were composed of S - TiO 2 and L - TiO 2, respectively, and the middle layer contained 1, 1'-dimethyl-4,4'-bipyridyl ( MV 2+)/Nafion®. Irradiation by a 500 W superhigh-pressure mercury lamp produced electrons in the conduction band of TiO 2. An anodic current was observed after turning off the light. The mechanism by which anodic current is generated after turning off the radiation involves the reduction of MV 2+ to MV +. by photogenerated electrons on the Nps and the diffusion of MV +. in the middle layer. After turning off the irradiation, MV +. transferred an electron to the Pt electrode via holes in the innermost layer or the conduction band of S - TiO 2 coincidentally localized on the Pt electrode, resulting in the generation of the anodic current. The generation of MV +. was confirmed by the absorption spectra of MV +.. As a sacrificial reagent, 2-propanol (0.1 M) was used.

Determination of dissolved oxygen based on photoinduced electron transfer from quantum dots to methyl viologen

A rapid colorimetric methodology based on photoinduced electron transfer from excited CdS quantum dots (CdS QDs) to methyl viologen (MV2+) has been developed for the sensitive determination of dissolved oxygen (DO) content. The reduction of MV2+ is initiated by light excitation of CdS QDs, which induces the electron transfer from sacrificial donor glutathione (GSH) to the photogenerated hole of CdS QDs. Due to the presence of oxygen, the reduced radical-cation of methyl viologen (MV+˙) could be rapidly reoxidized, thus turning into the original methyl viologen dication (MV2+). The existence of MV+˙ is confirmed by electron paramagnetic resonance technique. This proposed colorimetric methodology has been applied to quantify the concentration of DO in real water samples. The result is consistent with the value obtained while adopting the traditional standard Winkler's methodology. A linear response of the absorbance of CdS QDs-GSH-MV system to the different concentrations of DO is obtained in the range of 0.75∼7.95 ppm, with a detection limit of 0.23 ppm in pH 7.5.

Electron energy factors in photocatalytic methylviologen reduction in the presence of semiconductor nanocrystals

A linear relationship between the conduction band potential of a number of semiconductor nanocrystals (Cd x Zn 1− x S, CdSe, CdTe, ZnO) and the quantum efficiency of the photocatalytic methylviologen (MV 2+) reduction was found. It reflects dependence between the rate of photoinduced electron transfer from a semiconductor nanophotocatalyst to methylviologen and the overpotential of this process and is not affected by variations in chemical composition of the photocatalytic system. Cadmium selenide nanocrystals were found to have photocatalytic properties in the MV 2+ reduction by sodium sulfite. Differences in the photoprocess kinetics observed for CdSe and Cd x Zn 1− x S nanocrystals indicate that simultaneous photocatalytic reduction of MV + to MV 0 takes place in the case of cadmium selenide. Low efficiency of this process for Cd x Zn 1− x S nanocrystals was interpreted as a result of lowering of the energy of photogenerated electrons due to the surface trapping. The results presented show that the availability, nature, and depth of surface charge traps of a nanophotocatalyst should be taken into consideration when interpreting the kinetics of photocatalytic processes with the participation of semiconductor nanocrystals.

Photocatalytic H2 evolution from water based on cyclometalated platinum(II) complex

Abstract Cyclometalated platinum(II) complex, [ClPt(C^N^NPhMe)] ( 1 ) (HC^N^NPhMe = 4-( p -tolyl)-6-phenyl-2,2′-bipyridine) was found to be an efficient photosensitizer for photocatalytic hydrogen evolution from water, 98 turnovers of hydrogen were obtained after 10 h irradiation of solution containing MV 2+ (4,4′-dimethyl-2,2′-bipyridinium), triethanolamine (TEOA), photosensitizer and colloidal Pt, which is far effective than that of platinum(II) terpyridyl complex [ClPt(N^N^NPhMe)]ClO 4 ( 2 ) (N^N^NPhMe = 4′-( p -tolyl)-2,2′:6′,2″-terpyridine). Net photocatalytic reduction of MV 2+ by the complexes in the presence of TEOA in CH 3 CN/H 2 O solvents were observed and compared upon irradiation ( λ > 400 nm).

Characterization of photoelectrochemical active intercalation compound of K 4Nb 6O 17 with methylviologen

Intercalation compound of methylviologen into layered niobate K 4Nb 6O 17 · 3H 2O was achieved by ion-exchange method. The MV 2+-K 4Nb 6O 17 composite material was characterized using SEM, AFM, XRD, IR and element analysis. The photochemical and electrochemical behaviors of the MV 2+-K 4Nb 6O 17 hybrid thin film were investigated. The photo excitation of oxygen-present MV 2+-K 4Nb 6O 17 thin film with UV light indicated the electron transfer from the niobate layer to MV 2+ to form MV + radical cation and (MV) 2 2 + spin-paired radical cation dimer. The cyclic voltammogram of the MV 2+-K 4Nb 6O 17 hybrid thin film exhibited a surface-restricted process of MV 2+/MV + redox reaction and reduction of MV + to MV 0, together with a comproportionation reaction of MV 0 which forms (MV) 2 2 + dimer.

Transient and Stable Silver Clusters Induced by Radiolysis in Methanol

The optical absorption spectra of Ag0, Ag2+, transient oligomers, and stable clusters were studied in deaerated methanol by pulse and γ-radiolysis methods and compared with data obtained from studies using other solvents. From the decay of e-solv at 620 nm, the formation rate constant of Ag0 was determined to be k(e-solv + Ag+) = (2.6 ± 0.6) × 1010 M -1 s-1. The coalescence rate of transient oligomers is particularly slow and the growth process is not completed within 2 s after the pulse. The surface plasmon band of stable clusters obtained by γ-radiolysis in methanol is intense and sharp (ε385 nm = 1.8 × 104 M-1 cm-1). The clusters are readily oxidized by oxygen. By adding methyl viologen MV2+ to the solution containing stable silver clusters, the blue color of MV+• is transitorily observed, and the small clusters are developed into larger ones. Similarly, by pulse radiolysis of a mixture of silver cations and MV2+, silver atoms and MV+• are formed immediately through solvated electron scavenging, but subsequently additional MV+• are produced by reduction of MV2+ by Ag0 and small oligomers. In a further step, MV+• radicals reduce Ag+ cations adsorbed on large clusters and let them develop eventually to larger sizes. The general mechanism of the methanol radiolysis is revisited on the basis of electron and radical scavenging by Ag+ and silver clusters, and values of the yields of methanol radiolysis species are discussed in detail.

Polycyano–polycadmate host clathrates including a methylviologen dication. Syntheses, crystal structures and photo-induced reduction of methylviologen dication

A series of polycyano–polycadmate host clathrates including a methylviologen dication (MV2+), which is a strong electron acceptor, and an organic molecule, such as alcohols, haloalkanes, ethers and small aromatics, and two complexes built of a polycyano–polycadmate and MV2+ have been synthesized. Single crystal X-ray diffraction experiments on ten clathrates and the two complexes revealed their 3-D network polycyano–polycadmate structures constructed with Cd2+ ions and CN− bridges. The network structures are classified into five structure types. Type I, II and III were found in the clathrates, and Type IV and V were found in the two complexes. Type I and II have cage-like cavities and each of the cavities includes one guest, MV2+ or an organic molecule. Type III has a channel-like cavity where MV2+ ions and organic molecules are included. Type IV and V have 3-D cavities, the shape of which is neither cage-like nor channel-like, for embracing MV2+. Although all compounds were colorless and the formation of a charge transfer complex between MV2+ and a neutral guest in the clathrates was not confirmed from the crystal structure data and diffuse reflectance spectra, some of them showed a color change from colorless to blue on UV irradiation, which arose from the reduction of MV2+ to a methylviologen radical cation MV+˙.

Catalysis of the sodium sulfide reduction of methylviologene by cus nanoparticles

Feasibility was demonstrated for the catalysis of the sodium sulfide reduction of methylviologene (MV2+) in aqueous solution using cupric sulfide nanoparticles. The catalytic activity of the nanoparticles depends on their size. The basic features were found for the formation of the MV+· radical–cation in the reduction of MV2+ by HS− anions in the presence of CuS nanoparticles as the catalyst. This is an equilibrium reaction.

Photocatalytic reduction of dioxygen by colloidal semiconductors and macrocyclic cobalt(III) complexes in Nafion and cellulose matrices

The colloidal semiconductors TiO 2 and CdS are used for the photosensitized reduction of MV 2+ and Co(III) complexes. Photoinduced electron transfer reactions are carried out using the semiconductors in colloidal state, adsorbed and intercalated into Nafion and cellulose matrices. The back electron transfer reaction between h vb +(TiO 2 or CdS) and MV + · or Co(II) complex is prevented by the reaction of the hole with an electron donor triethanolamine (TEA). Hydrogen peroxide (H 2O 2) is produced by the reaction of the photoproduced MV + · or Co(II) complex with dissolved molecular oxygen (O 2). The photosensitized reaction mechanisms of the formation of MV + · and Co(II) complex and the photocatalytic reduction of O 2 to yield H 2O 2 in the semiconductor modified systems are explained.