Solid-state Voltammetry Research Articles

Solid state electrochemical behaviour of porphine in aqueous media

The electrochemical behaviour of porphine was studied by cyclic, differential pulse and square-wave voltammetry, in aqueous media, in the pH range between 3.4 and 9.2. The studies were carried out by solid state voltammetry with the insoluble porphine mechanically transferred onto the glassy carbon electrode. The porphine redox mechanism was established by comparison with the redox behaviour of pyrrole, 1,4-dimethylpyridinium p-toluenesulfonate, and two meso-substituted porphyrins, 5,10,15,20-tetraphenyl-21H,23H-porphine (TPP) and 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (TPyP). The porphine oxidation is a two-step, irreversible and pH-dependent process, each oxidation step involving the loss of one electron from the lone pairs in the nitrogen atoms. The porphine reduction is a one-step, irreversible and pH-dependent process, involving the acceptance of one electron and one proton. A second reduction step at more negative potentials is probable, but cannot be detected due to the limitation of the GCE potential range. The presence of phenyl and pyridyl substituents at meso position disturbs the electron density and the planarity of the porphine ring, which results in a shift of the porphine redox potentials to more positive values, consistent with a more difficult oxidation and a facilitated reduction, as observed for TPP and TPyP.

Regulation of flavonoid biosynthesis pathway by a single or dual short-term CO2 treatment in black table grapes stored at low temperature

The application of one or two short-term treatments with high levels of CO2 during 3 days at 0 °C maintained the quality of Autumn Royal table grapes (Vitis vinifera) during storage at 0 °C. We have analyzed how the application of a 3-day gaseous treatment, for one or two times at 0 °C, influences on common (VviPAL, VviCHS, VviCHI, VviF3′H, VviF3′5′H, VviF3H and VviLDOX) and branch-specific (VviFLS1, VviLAR1, VviLAR2, VviANR and VviUFGT) flavonoid gene expression in the skin of Autumn Royal table grapes. Likewise, the content of flavonols, flavan-3-ols and anthocyanins were identified with Q-TOF equipment and quantified by HPLC-quadrupole together with the total phenolic content and the antioxidant capacity by the ABTS and FRAP methods. Moreover, we have also used a solid-state voltammetry methodology to compare the effect of the application of one or two gaseous treatments in the skin of table grapes stored at 0 °C. Results revealed that the application of one or two gaseous treatments modulated the expression of flavonoid gene expression and the levels of catechin, in the case of one application, or quercetin-3-glucoside and five anthocyanins in fruit treated twice, maintaining their levels after 28 days of storage at 0 °C similar to those recorded in freshly harvested fruit. Satisfactorily, the electrochemical approach was useful to distinguish between treated and non-treated samples not only in the first stage of storage but also after 16 days.

Potential availability of trace metals in sediments in southeastern and southern Brazilian shipyard areas using the DGT technique and chemical extraction methods

Speciation and partitioning of trace metals, from solid to solution phases of sediments, control their bioavailability and thus their potential ecological risk to organisms. Therefore, in order to obtain a broad evaluation of their risk, it is necessary to couple methodologies that are able to assess metal mobility in sediment. In this study, the Diffusive Gradients in Thin Films (DGT) technique and the application of 0.1 M HCl acid extraction methods, together with solid-state voltammetric sensors, were used with the objective of assessing mobility and potential availability of Cr, Cu, Ni, Pb, V and Zn in sediment porewaters and solid sediments in southeastern and southern Brazilian shipyard areas. The highest labile metal concentrations were found in shipyards with the longest histories of operations. Trace metal distributions in porewater and in the solid phase of sediments (labile metals) and significant correlations among metals enabled to distinguish the contribution of anti-fouling paint components. The diffusive flux of every metal measured at the surface of the sediment indicated that CuDGT had the highest flux (3.66E−03 mmol·m−2 d−1) in the shipyard with the longest operating time. Therefore, enrichment was observed for Cu, Pb and Zn in sediments, indicating a possible ecological risk level of ‘Effects Range Median’ to ‘Apparent Effects Threshold’ for oyster larvae (Mollusca) (Cu), bivalves (Pb) and the infaunal community (Zn). Probable Effect Concentrations (PEC) to sediment-dwelling biota can be expected as well, related to high concentrations of Cu and Zn in sediment. This study allowed a comprehensive evaluation of potential bioavailability and ecological risk of trace metals in aquatic systems where there is continuous and specific input of these elements. The use of the DGT technique with solid-state voltammetry in the sediment of distinct Brazilian estuarine systems demonstrated its potential to be applied in future environmental network programs.

Effect of high levels of CO2on the electrochemical behavior and the enzymatic and non‐enzymatic antioxidant systems in black and white table grapes stored at 0 °C

In this study, we analyzed the effect of the application of high levels of CO2 (20 kPa CO2 + 20 kPa O2 + 60 kPa N2 ) for 3 days at low temperature on a white table-grape cultivar (Superior Seedless) in comparison with a black one (cv. Autumn Royal) in terms of quality parameters. We also used a solid-state voltammetry methodology to analyze the effect of the 3-day gaseous treatment in berry tissues from both cultivars in the first stage of storage. We determined the role of the non-enzymatic (total phenols, total anthocyanins, and antioxidant activity) and the enzymatic antioxidant (catalase (GCAT), ascorbate peroxidase (VcAPX) gene expression) systems in the behaviors of both cultivars. Our results indicate that the application of a 3-day gaseous treatment was effective in maintaining the quality of black and white table grapes for up to 28 days of storage at 0 °C. The electrochemical methodology applied was useful for differentiating between skin and pulp samples, and between black and white table grape cultivars. Some molecular mechanisms were modulated in the skin of both cultivars to overcome oxidative stress, which was not manifested with the same intensity in grapes treated with CO2 for 3 days. However, some differences were observed in relation to the non-enzymatic system. The 3-day gaseous treatment was useful to maintain black and white table grape quality at 0 °C. The voltammetry analysis indicated that CO2 -treated samples from the skin and pulp showed more similarity to freshly harvested ones. © 2019 Society of Chemical Industry.

Microelectrode Based Devices for Diagnosis of Electron Transport and Electrochemical Behavior of Redox-Conducting Materials

We are going to address practical issues related to the principles and analytical aspects of electrochemical studies (typically done at room temperature) of solid, rigid or semi-rigid (nonfluid) systems in the absence of a liquid solution phase. Representative examples include redox and conducting organic polymers, melts and solid solutions of redox centers in solid ionic conductors, mixed-valence polynuclear inorganic materials, transition metal salts, oxides, and zeolites. The emphasis is on the elements of dynamics for the efficient delivery of charge and on reactivity of the ‘redox conducting’ materials. The effective (apparent) diffusional mechanism is critical to the success of most analytical measurements in solid-state. Historically, electrochemistry in the absence of a bulk liquid phase has focused on the problems of energy storage and production. Recently, it has become possible to apply conventional electrochemical methods to characterize solid-state type redox electrolytes with respect to analytical characterization of materials, measurement of electron transfer rates, and determination of analytes using amperometric sensing. The characterization of materials by solid-state voltammetry primarily has focused on mixed-valence, ionically conducting compounds and on diverse organic ionomers hosting identifiable molecular (redox) sites. Potential materials for solid-state electrochemical measurements are expected to contain three-dimensionally distributed highly concentrated redox centers between which fast electron self-exchange (hopping) is feasible. Among inorganic systems, single crystals of heteropolyacids of molybdenum and tungsten, as well thin films of Prussian Blue type metal hexacyanoferrates will be considered. These redox centers are fixed and, although they may have short range mobility about an equilibrium position, they classically are macroscopically immobile. The applicable materials also must host mobile counter-ions that are capable of providing charge balance during electron transfers, thereby serving the same purpose as the supporting electrolytes in conventional electrochemistry. The population of these ions must be sufficient to support diffusive mass transport of electrons and to minimize ohmic effects. We will describe typical electrochemical cells and experimental tactics to overcome the relatively slow dynamics of transport in solid (non-fluid) systems. Application of microdimensional electrodes leads to an improvement in the quality of solid-state electrochemical data and provides new diagnostic and analytical possibilities. Basic concepts of mechanistic studies, which are relevant to the development of novel analytical methods, together with trends towards possible future applications will also be addressed.

Versatile titanium dioxide nanoparticles prepared by surface-grown polymerization of polyethylenimine for photodegradation and catalytic C[sbnd]C bond forming reactions

Crystalline TiO2 anatase nanoparticles have been synthesized by a sol-gel procedure with a certain ratio of brookite phase due to low calcination temperature. TiO2 NPs have been successfully functionalized with hyperbranched polyethylenimine polymer (PEI) by the surface polymerization of aziridine or with N1-(3-trimethoxysilylpropyl)-diethylenetriamine (DT) by surface silanization to form catalyst with notable basic and photocatalytic properties. The TiO2 NPs have been characterized by X-ray diffraction (XRD), adsorption-desorption isotherms, fourier-transform infrared spectroscopy (FT-IR), diffuse reflectance UV–vis spectroscopy (DRUV-vis), elemental analysis, thermogravimetric analysis, transmission electron microscopy (TEM), photoluminiscence spectroscopy (PL) and solid-state voltammetry. Functionalized TiO2 NPs have revealed to be efficient in the photodegradation of methylene blue in water and as basic heterogeneous catalysts carbon-carbon forming reactions as Knoevenagel condensation, multicomponent reactions and Biginelli reaction. PEI-TiO2 with mesoporous structure and narrow size pore distribution, fulfill the requirements imposed to an eco-friendly and cost-effective catalyst since it is easily synthesized and recyclable.

Independent Quantification of Electron and Ion Diffusion in Metallocene-Doped Metal-Organic Frameworks Thin Films.

The chronoamperometric response (I vs t) of three metallocene-doped metal-organic frameworks (MOFs) thin films (M-NU-1000, M = Fe, Ru, Os) in two different electrolytes (tetrabutylammonium hexafluorophosphate [TBAPF6] and tetrabutylammonium tetrakis(pentafluorophenyl)borate [TBATFAB]) was utilized to elucidate the diffusion coefficients of electrons and ions (De and Di, respectively) through the structure in response to an oxidizing applied bias. The application of a theoretical model for solid state voltammetry to the experimental data revealed that the diffusion of ions is the rate-determining step at the three different time stages of the electrochemical transformation: an initial stage characterized by rapid electron diffusion along the crystal-solution boundary (stage A), a second stage that represents the diffusion of electrons and ions into the bulk of the MOF crystallite (stage B), and a final period of the conversion dominated only by the diffusion of ions (stage C). Remarkably, electron diffusion (De) increased in the order of Fe < Ru < Os using PF61- as the counteranion in all the stages of the voltammogram, demonstrating the strategy to modulate the rate of electron transport through the incorporation of rapidly self-exchanging molecular moieties into the MOF structure. The De values obtained with larger TFAB1- counteranion were generally in agreement with the previous trend but were on average lower than those obtained with PF61-. Similarly, the ion diffusion coefficient (Di) was generally higher for TFAB1- than for PF61- as the ions diffuse into the crystal bulk, due to the high degree of ion-pair association between PF61- and the metallocenium ion, resulting in a faster penetration of the weakly associated TFAB1- anion through the MOF pores. These structure-function relationships provide a foundation for the future design, control, and optimization of electron and ion transport properties in MOF thin films.

Assessment of Noni (Morinda citrifolia L.) Product Authenticity by Solid State Voltammetry

Assessment of Noni (Morinda citrifolia L.) Product Authenticity by Solid State Voltammetry

Charge Propagation in Redox-Conducting Materials: Diagnosis of Mechanisms and Dynamics with Microelectrochemical Devices

Historically, electrochemistry in the absence of a bulk liquid phase has focused on the problems of energy storage and production. Recently, it has become possible to apply conventional electrochemical methods to characterize solid-state type redox electrolytes with respect to analytical characterization of materials, measurement of electron transfer rates, and determination of analytes using amperometric sensing. The characterization of materials by solid-state voltammetry primarily has focused on mixed-valence, ionically conducting compounds and on diverse organic ionomers hosting identifiable molecular (redox) sites. We are going to address practical issues related to the principles and analytical aspects of electrochemical studies (typically done at room temperature) of solid, rigid or semi-rigid (nonfluid) systems in the absence of a liquid solution phase. Representative examples include redox and conducting organic polymers, melts and solid solutions of redox centers in solid ionic conductors, mixed-valence polynuclear inorganic materials, transition metal salts, oxides, and zeolites. The emphasis is on the elements of dynamics for the efficient delivery of charge and on reactivity of the ‘redox conducting’ materials. The effective (apparent) diffusional mechanism is critical to the success of most analytical measurements in solid-state. The potential materials for solid-state electrochemical measurements are expected to contain three-dimensionally distributed highly concentrated redox centers between which fast electron self-exchange (hopping) is feasible. These redox centers are fixed and, although they may have short range mobility about an equilibrium position, they classically are macroscopically immobile. The applicable materials also must host mobile counter-ions that are capable of providing charge balance during electron transfers, thereby serving the same purpose as the supporting electrolytes in conventional electrochemistry. The population of these ions must be sufficient to support diffusive mass transport of electrons and to minimize ohmic effects. We will describe typical electrochemical cells and experimental tactics to overcome the relatively slow dynamics of transport in solid (non-fluid) systems. Application of microdimensional electrodes leads to an improvement in the quality of solid-state electrochemical data and provides new diagnostic and analytical possibilities. Basic concepts of mechanistic studies, which are relevant to the development of novel analytical methods, together with trends towards possible future applications will also be addressed.

Evaluation of aging processes of petroleum asphalt cements by solid state electrochemical monitoring

The changes in the chemistry of organosulfur compounds from asphalt cements during aging are studied using solid state voltammetry of immobilized microparticles. Five Brazilian asphalt cements were evaluated after three forced aging processes: Rolling Thin Film Oven Test (RTFOT), Pressure Aging Vessel (PAV) and SUNTEST. It was possible to identify the presence of thiophenes, sulfides and sulfoxides in the different samples and the reactional changes during the aging processes were proposed. Voltammetric data, supported by ATR-FTIR spectroscopy, indicate that aging asphalts involve the increase of the proportion of sulfoxide and thiophene components and that polythiophene compounds were formed mainly in the SUNTEST aging due the involvement of radical species.

Mesoporous SBA-15 modified with titanocene complexes and ionic liquids: interactions with DNA and other molecules of biological interest studied by solid state electrochemical techniques.

The immobilization of two titanocene complexes on SBA-15 has been accomplished following post-synthetic procedures. The ionic liquid, 1-methyl-3-[(triethoxysilyl)propyl]imidazolium chloride, has also been incorporated into the titanium containing materials to determine its influence on the interaction with molecules of biological interest. Cyclic voltammetry has been used to study the influence of the ionic liquid on the mechanism of reduction of titanocene derivatives. The interaction of titanocene and titanocene/ionic liquid-containing mesoporous silica SBA-15 materials, with molecules of biological interest associated with important processes of metallodrug action against cancer cells, has been studied. Thus, we have carried out hydrolysis experiments on the materials functionalized with titanocene derivatives in physiological media to determine their stability and the interaction with serum/transport proteins such as transferrin and BSA and with target molecules such as guanosine, single-stranded DNA and double-stranded DNA by means of solid state voltammetry techniques. A qualitative analysis of the data based on peak current and reduction potential value changes of the couple Ti(iv)/Ti(iii) in the presence of biomolecules at physiological pH, has revealed that grafted titanocene complexes show higher affinity for serum/transport proteins than for nucleic acids, indicating that the transport steps to the cells may be easier than the subsequent attack on DNA.

Electrochemical identification of toxigenic fungal species using solid-state voltammetry strategies

An electrochemical methodology for the characterization of mycotoxin-producing fungal species from the genera Aspergillus and Fusarium using solid-state voltammetry is described. Upon attachment of fungal colony microsamples to glassy carbon electrodes in contact with aqueous acetate buffer, characteristic voltammetric signals mainly associated to the oxidation of polyphenolic metabolites are recorded. The possibility of fungi-localized electrochemical processes was assessed by means of electron microscopy and field emission scanning electrochemical microscopy coupled to the application of oxidative potential inputs. Using pattern recognition methods, the determined voltammetric profiles were able to discriminate between mycotoxin-producing fungi from different sections and to identify selected toxigenic species of the Aspergillus and Fusarium genera isolated from grapes and cereals.

Archaeometric analysis of Roman bronze coins from the Magna Mater temple using solid-state voltammetry and electrochemical impedance spectroscopy

Voltammetry of microparticles (VMP) and electrochemical impedance spectroscopy (EIS) techniques, complemented by SEM-EDX and Raman spectroscopy, were applied to a set of 15 Roman bronze coins and one Tessera from the temple of Magna Mater (Rome, Italy). The archaeological site, dated back between the second half and the end of the 4th century A.D., presented a complicated stratigraphic context. Characteristic voltammetric patterns for cuprite and tenorite for sub-microsamples of the corrosion layers of the coins deposited onto graphite electrodes in contact with 0.10 M HClO4 aqueous solution yielded a grouping of the coins into three main groups. This grouping was confirmed and refined using EIS experiments of the coins immersed in air-saturated mineral water using the reduction of dissolved oxygen as a redox probe. The electrochemical grouping of coins corroborated the complex stratigraphy of the archaeological site and, above all, the reuse of the coins during the later periods due to the economic issues related to the fall of the Roman Empire.

Titanium alkoxides immobilized on magnetic mesoporous silica nanoparticles and their characterization by solid state voltammetry techniques: Application in ring opening polymerization

In this paper, we present the synthesis of mesoporous silica coated Fe3O4 core–shell nanoparticles or magnetic mesoporous silica nanoparticles (MMSNs) via a surfactant templated sol–gel method using magnetite nanoparticles (MNPs) stabilized with tartrate as nucleation seeds. The synthetic parameters have been carefully controlled in order to scale up the synthetic procedure to obtain more than 1 g of stable, high quality core–shell and biocompatible MMSNs per synthesis. MMSNs have been used as support to prepare heterogeneous titanium catalysts for ring opening polymerization (ROP) of ε-caprolactone. The prepared materials have been fully characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF) N2 adsorption-desorption, transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TG-DTG), UV–vis and DRUV-vis techniques. In addition, extensive solid state electrochemical studies have been carried out in aqueous and organic medium demonstrating the coating of MNPs with a layer of mesoporous silica and the immobilization of titanium as electroactive species.

Controlled Synthesis of Silver Nanoparticles Using Double Reductants and Its Voltammetric Characteristics Study

Constructing robust silver nanoparticles (AgNPs) with good shape and dispersibility is of particular interest in analytical applications. Herein, monodispersibility AgNPs with the average size of 20 nm have been successfully prepared via one-pot method using sodium borohydride and trisodium citrate as co-reductants. The introduction of sodium borohydride greatly accelerated the rate of nucleation, which can effectively solve the problem of broad size distribution. Both shape and dispersibility of AgNPs can be effectively adjusted by simple control of refluxing time or concentrations of the sodium borohydride. We also studied the voltammetric characteristics of the AgNPs using Ag/AgCl solid-state voltammetry. An intense and stable current peak at a low potential could be obtained, which could provide a unique advantage in analytical applications.

Study of the Interaction Between Graphene Oxide and Surface-confined Biomolecules to Develop New Kind of Biosensors

In this work, we have studied the interaction between graphene oxide (GO) and the biomolecules immobilized on an electrode surface, which has been further employed to develop new kind of biosensors by fabricating gammaglutamyltransferase (γ-GGT) sensor as an example. Specifically, glutathione (GSH) is firstly immobilized on the surface of a gold electrode, and GO nanosheet is introduced to recognize the charge change of GSH caused by the catalysis of γ-GGT. Then, the introduction of reductant and Ag+ induces silver deposition and partial reduction of GO, forming GOAgNPs complex for electrochemical readout. Since this complex may have excellent electric conductivity and the solidstate voltammetry of Ag/AgCl can provide a well-defined symmetrically sharp silver stripping peak, a sensitive electrochemical biosensor for the detection of γ-GGT is thus developed. Moreover, the experimental results obtained in this work indicate that GO itself can serve as a general recognition element for biosensor fabrication and GO-AgNPs can be a promising material in a general sensing platform, so such kind of more biosensors can be developed in the future. Keywords: Electrochemical assay, gamma-glutamyltransferase, graphene oxide, in situ reduction, silver nanoparticles, solidstate voltammetry.

Enhancement of Charge Transport Rates By Incorporation of Platinum Nanoparticles to Iodine/Iodide Ionic Liquid Redox-Conducting Electrolytes

The iodine/iodide redox system has so far been the most commonly and most successfully used as a charge relay (mediator) in Dye Sensitized Solar Cells (DSSCs)[1]. The semi-liquid or semi-solid iodine/iodide-based systems have probably led the most promising results so far in the area of practical DSSCs. More recently, the iodide/iodine redox couple has been considered together with ionic liquids. The resulting redox-conducting electrolytes have several advantages: high conductivity, low vapor pressure, high iodide/iodine concentration and good electrochemical stability. Among disadvantages is their high viscosity that certainly contributes to the low diffusion coefficient of the oxidized form of the redox couple, iodine or triiodide, if the charge transport mechanism is truly physical. If charge transport involves electron hoping between I- and I, which seems to be operative as well, its effectiveness would require fast dissociation of iodine (I2), or triiodide (I3 -), molecule. Indeed, both interfacial and bulk (self-exchange) electron transfers involving the iodine/iodide redox system are somewhat complicated and appear slower than one would expect. There is a need to develop means of inducing the I-I bond breaking in the I3 - or I2 molecule. It has also been established that platinum (e.g. when deposited on the counter electrode of DSSC) catalyzes interfacial electron transfers in the iodine/iodide redox system. Surface chemistry data provide clear evidence that iodine (or iodides) chemisorb readily on platinum as monoatomic iodine. Strong interactions of Pt with iodine were reported and described; further, formation of the monolayer type coverages of strongly adsorbed monoatomic iodine together with weakly bound electroactive iodine/iodide was also postulated. In the present work, we explore the concept of three-dimensional distribution of nanostructured platinum within the electrolyte phase) to enhance dynamics of iodine/iodide electron transfers (electron self-exchange) as an attempt to develop a new generation of charge iodine-based relays for DSSC. The diagnostic experiments have been performed using the electroanalytical methodology developed for solid-state electrochemical measurements in the absence of external liquid supporting electrolyte. They have included measurements using the planar three-electrode cell utilizing an ultramicrodisk electrode and two-electrode type sandwich configuration [2,3]. In the present case of theiodine/iodide system dispersed together with Pt nanoparticles within ionic liquid phase, mutual compensations between physical and effective (electron self-exchange type) diffusion mechanisms are postulated. Regardless the mechanism, the charge propagation rates expressed in diffusional terms have been found on 10-6 cm2 s-1 level.[1] M. Graetzel, Acc. Chem. Res., 42 (2009) 1788[2] P.J. Kulesza, M.A. Malik in Wieckowski A (ed.), Interfacial Electrochemistry - Theory, Experiment and Applications, Solid-State Voltammetry 673, Marcel Dekker, New York (1999)[3] P.J. Kulesza, J.A. Cox, Electroanalysis 10 (1998) 73

Discovery of indigoid-containing clay pellets from La Blanca: significance with regard to the preparation and use of Maya Blue

Analytical studies using extraction/liquid chromatography, pyrolysis–silylation gas chromatography–mass spectrometry, visible and infrared spectroscopies, solid state voltammetry and electron microscopy on a set of spherical greenish pellets discovered in the Structure 4H1 of the ancient Maya site of La Blanca (Peten Department, Guatemala), dated in the Terminal Classic period, confirm the presence of indigoids (dehydroindigo, indigo) associated to palygorskite. The appearance of such pieces, whose origin and function is uncertain, but most likely correspond to residuals of a decorative plaster, can be considered as indicative of the use of Maya Blue in a quotidian context, thus suggesting that the materials used for Maya Blue preparation where used not only in ritual contexts. This would be consistent with the idea that the Mayas could make a versatile use of such materials and that their symbolic value could vary with time during the evolution of Maya culture.

Redox Tuning and Species Distribution in Maya Blue-Type Materials: A Reassessment

Maya Blue-type specimens prepared from indigo (1 wt %) plus kaolinite, montmorillonite, palygorskite, sepiolite, and silicalite are studied. Liquid chromatography with diode array detection, ultra-performance liquid chromatography coupled with mass spectrometry, and pyrolysis-silylation gas chromatography-mass spectrometry analyses of the extracts from these specimens combined with spectral and solid-state voltammetry, electrochemical impedance spectroscopy, and scanning electrochemical microscopy techniques provide evidence for the presence of a significant amount of dehydroindigo and isatin accompanying indigo and other minority organic compounds in all samples. Solid-state electrochemistry data permits the estimatation of indigo loading in archeological Maya Blue, which is in the range of 0.2 to 1.5 wt %. These results support a view of 'genuine' Maya Blue-type materials as complex polyfunctional organic-inorganic hybrids.

Structurally stressed PT09SBA: A close look at the properties of large pore photoluminescent, redox active mesoporous hybrid silica

A thien-2-yl substituted, electron-rich phenothiazine has been converted over several steps into a redox active sol–gel precursor. Following a fluoride-catalyzed synthesis, a phenothiazine-based mesoporous hybrid organosilica was obtained. The electrochemical behavior and the luminescence properties of the immobilized chromophore have been studied using solid state fluorescence spectroscopy, electron paramagnetic resonance spectroscopy (EPR) and solid state voltammetry (CV and DPV). The influence of both the presence of fluoride anions and the acidic pH during the material synthesis were explored by means of scanning and transmission electron microscopy (SEM and TEM), X-ray powder diffraction (XRD) and nitrogen physisorption measurements. While a combination of acidic pH and fluoride was found necessary for the material formation, partial cleavage of the precursor was observed. Data obtained from both the chemical as well as the electrochemical oxidation/reduction of the immobilized PT dye indicates the formation of an organic layer containing several species inside the pore channels.