bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Photoinduced Charge Transfer Reactions in Chiral, Semiconducting Polymer-Wrapped Single-Walled Carbon Nanotube Superstructures
Authors: Bai Yusong , Bullard George , Olivier Jean-Hubert , Park Jaehong , Glesner Mary G. , Therien Michael J.
Published: February 2020

Highly charged, chiral anionic semiconducting polymers helically wrap single-walled carbon nanontubes (SWNTs) at periodic and constant morphology. These polymers can be used as tools to modulate SWNT electronic properties, provide expansive solubility, or engineer electron acceptor units at rigorously defined intervals along the nanotube backbone. We detail (SWNT)-based nanohybrid compositions based on (6,5) chirality-enriched SWNTs ([(6,5) SWNTs]) and chiral n-type polymers such as (S-PBN(b)-Ph4PDI), that feature a perylenediimide (PDI)-containing repeat unit; S-PBN(b)-Ph4PDI-[(6,5) SWNT] superstructures, for example, feature a PDI electron acceptor unit positioned at 3 nm intervals along the nanotube surface, thus controlling rigorously SWNT–electron acceptor stoichiometry and organization. Potentiometric studies determine driving forces for photoinduced charge separation (CS) and thermal charge recombination (CR) reactions, as well as spectroscopic signatures of SWNT hole polaron and PDI radical anion states. Femtosecond pump-probe transient absorption spectroscopic experiments show that excitation into the SWNT E11 transition of a S-PBN(b)-Ph4PDI-[(6,5) SWNT] superstructure generates SWNT hole polaron [(6,5) SWNT(•+)n] and PDI radical anion (PDI−•) states. Here we describe related compositions that detail reaction driving force- and solvent-dependent photoinduced CS and thermal CR reactions, and provide insights into the factors that govern photoinduced charge transfer reactions at soft matter-hard matter interfaces defined by polymers and SWNTs.

Figure 1
(Invited) Design of Bowl-Shaped Molecules Toward Dielectric Responsive Materials
Authors: Kajitani Takashi , Ishiwari Fumitaka , Shoji Yoshiaki , Sakurai Hidehiro , Akutagawa Tomoyuki , Fukushima Takanori
Published: February 2020

Organic dielectric materials that can respond to electric fields have drawn much attention because of their potential applications to memory and sensing devices. One of the essential requirements for organic dielectric materials is the ability of changing the overall dipole moment in response to external electric fields. In this context, sumanene derivatives featuring a bowl-shaped skeleton are attractive, because they undergo a bowl-to-bowl inversion, which is accompanied by the inversion of the molecular dipole. As the bowl-to-bowl inversion would be facilitated in soft mesophases, liquid-crystalline (LC) sumanenes, for example, are expected to provide an interesting building block for the design of organic dielectric materials. While many examples of crystalline sumanenes have so far been reported, there is no sumanene derivative that can exhibit an LC mesophase. We recently found that sumanene, when carrying six alkyl side chains, successfully shows an LC mesophase over a wide temperature range. Herein, we report the synthesis, assembly structure, and dielectric properties of the new hexa-substituted sumanenes.

Figure 1
(Invited) De-Coupled Electron and Heat Transfer: A Possible Nature’s Strategy for Maximizing Electrocatalysis for CO2 Fixation
Authors: Nakamura Ryuhei
Published: February 2020

How has nature handled electron flow for carbon fixation? We know the mechanism of carbon fixation taking place inside chloroplast. At least, we know the framework of its action and function. Parallelly important, yet relatively unknown processes are carbon fixation taking place in deep-sea hydrothermal environments, which contain low levels or no solar radiation. In such environments, nature has to develop the systems to harvest geochemical and geothermal energy to generate high-energy electrons needed for carbon fixation. Yet, how nature utilizes temperature and chemical gradient fostered by geological settings remains largely unknown. In this talk, based on our findings of electrical current generation across a black smoker hydrothermal vent,[1,2] together with thermoelectrical conversion by deep-sea minerals,[3] I provide the new energetic underpinning of carbon fixation: de-coupled electron and heat transfer at deep-sea hydrothermal vents [4,5]. As catalysis at the deep-sea vent may tightly link with the origin and evolution of life, I provide the perspective to predict the first engine that drives the life emergence and fosters life complexity.

(1) R. Nakamura, et al. Angew. Chem. Int. Ed., 49, 7692 (2010). (2) M. Yamamoto, et al. Angew. Chem. Int. Ed., 52, 10758 (2013). (3) R. Ang, et al. Angew. Chem. Int. Ed., 54, 12909 (2015). (4) A. Yamaguchi, et al. Electrochim. Acta, 141, 311 (2014). (5) A. Yamaguchi, et al. Springer, Chapter 4.3.2. (2016).
(Invited) Formation of One-Dimensional Au-Directed Organometallic Nanostructures with Large Acene Precursor Molecules
Authors: Hayashi Hironobu , Urgel José Ignacio , Deniz Okan , Giovannantonio Marco Di , Dienel Thomas , Ruffieux Pascal , Fasel Roman , Yamada Hiroko
Published: February 2020

Large aromatic molecules such as large acenes and polycyclic aromatic hydrocarbons are regarded as promising materials for organic electronic devices. However, it is normally difficult to synthesize such large aromatic molecules because of the low solubility and stability. On the other hands, we have developed thermal and photochemical precursor methods to overcome these problems. Bicyclo[2.2.2]octadiene(BCOD)-fused acenes can be converted to the corresponding acenes by the thermally induced retro-Diels-Alder reaction, while α-diketone-type precursors can be converted simply by photoirradiation. Specifically, irradiation of a-diketone-type precursors at the n-π* absorption leads to the release of two molecules of CO, and the corresponding acenes can be prepared quantitatively in solutions or in films. Importantly, these precursor molecules are often more soluble and stable than the corresponding one.

Here we report the synthesis of thermally convertible pentacene and photochemically convertible heptacene precursor molecules. Namely, BCOD moieties were introduced in a pentacene aromatic core as thermally removable leaving groups, while α-diketone moieties were introduced in a heptacene aromatic core as photochemically removable leaving groups. In addition, we also report a combined scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM) study to observe the conversion of precursor molecules into the corresponding acenes on a pristine Au(111) substrate under ultrahigh vacuum (UHV) conditions. For example, the STM and nc-AFM images clearly displays that the annealing of pentacene precursor molecule deposited Au(111) substrates at 390 K result in the one-dimensional (1D) Au-directed organometallic nanostructures. Further annealing at 475 K produced the 1D pentacene organometallic nanostructures.

Our result indicates that the precursor method and on-surface synthesis would be a good combination for making novel structure.
Synthesis of Bent and Distorted Expanded Porphyrins
Authors: Kuzuhara Daiki , Xue Songlin , Furukawa Wataru , Aratani Naoki , Yoshimoto Noriyuki , Yamada Hiroko
Published: February 2020

Expanded porphyrins have been widely studied in their specific characteristics of NIR absorption and emission, non-linear optics, versatile electronic states, and multinuclear metal complexes. Generally, porphyrin and related compounds consist of one meso-carbon between pyrrole units, which usually provide the planar and rigid structures. On the other hand, an increase of the numbers of meso-carbons and pyrroles forms flexible frameworks in the formation of bent and distorted structures. Recently, we succeeded to synthesize aromatic rings–fused porphyrin(2.1.2.1) from dipyrrolylbenzene (DPB) [1] and a series of porphyrin(2.1.2.1), hexaphyrin(2.1.2.1.2.1) and octaphyrin(2.1.2.1.2.1) from diphenyldipyrrolylethene (DPDPYE). These porphyrins have unique bent and distorted structures, which are revealed by X-ray crystallography. Porphyrin(2.1.2.1) and hexaphyrin(2.1.2.1.2.1) work as nuclear ligands, which are able to be converted to various metal complexes. The electronic, optical and electrochemical properties and single crystal structures of these expanded porphyrins will be discussed.

Reference

[1] Kuzuhara, D.; Furukawa, W.; Kitashiro, A.; Aratani, N.; Yamada, H. Chem. Eur. J.
2016, 22, 10671.
Facile Synthesis of Cofacial Porphyrin Oligomers Via the Catalyst-Free Aromatic Nucleophilic Substitution Reactions
Authors: Yamashita Ken-ichi
Published: February 2020

Cofacial porphyrin dimers have attracted a considerable attention due to their potential as artificial reaction centers in the photosystem, bimetallic catalysts and function as host molecule. However, their syntheses have required troublesome multi-step reactions. Recently, we have reported a facile and efficient synthetic method for meso-heteroatom-substituted porphyrins from the corresponding meso-bromoporphyrins via the catalyst-free aromatic nucleophilic substitution (SNAr) reactions.1,2,3 In this work, we applied this efficient method to the synthesis of cofacial porphyrin dimers bridged by the dihydroxyarene derivatives. Reaction of resorcinol with an excess of meso-bromoporphyrin in the presence of base afforded the acyclic dimers 1 in good yield. The steric hindrance between porphyrin and substituents on resorcinol determined their formations. For example, 4,6-diethylresorcinol gave cofacial conformation whereas 2-methylresorcinol gave open conformation. Reaction of resorcinol or 2,7-dihydroxynaththalene with meso-dibromoporphyrin afforded cyclic porphyrin dimers 2 and 3 with rigid cofacial conformation in good yield. We will also report the synthesis, structural characterization, and physical properties of the obtained dimer and their metal complexes.

References

(1) K. Yamashita, K. Kataoka, M. S. Asano, K. Sugiura, Org. Lett.
2012, 14, 190–193.

(2) K. Yamashita, S. Sakamoto, A. Suzuki, K. Sugiura, Chem. Asian J.
2016, 11, 1004–1007.

(3) K. Yamashita, K. Kataoka, S. Takeuchi, M. S. Asano, K. Sugiura, J. Org. Chem.
2016, 81, 11176–11184.

Figure 1
Redox Properties of Transition-Metal/Organic Chromophore Arrays: Interplay Between Metal- and Chromophore-Centered Electron-Transfer Processes
Authors: Nemykin Victor V. , Zatsikha Yuriy V. , Kovtun Yuriy P. , Ziegler Christopher J.
Published: February 2020

A large number of ferrocene-containing BODIPYs, azaBODIPYs, and BOPHYs along with several examples of non-innocent transition-metal aza-dipyrromethenes have been prepared and characterized by UV-Vis-NIR, NMR, HRMS, and X-ray crystallography. The redox properties of all target compounds were investigated by electrochemical and spectroelectrochemical methods. The experimental electronic, spectroscopic, and geometric parameters of the organometallic BODIPYs, azaBODIPYs, and BOPHYs as well as transition-metal aza-dipyrromethenes were correlated with DFT and TDDFT calculations.
Electrochemistry of Porphyrazines with Exocyclic Pended Pyridyl and N-Methylpyridyl Rings
Authors: Kadish Karl M , Cong Lei , Sciscione Fabiola , Viola Elisa , Donzello Maria Pia , Ercolani Claudio
Published: February 2020

Two new series of porphyrazines with exocyclic pended 2-pyridyl and 2-N-methylpyridyl rings were investigated as to their electrochemical properties. The structures of the investigated compounds are shown in Chart 1a and represented in one case as [Py8PzM], where M = 2H, MgII(H2O), CoII, CuII or ZnII and in the other as [(2-Mepy)8PzM]8+, where M = MgII(H2O) or ZnII. The redox behavior of these new compounds is then compared to that of earlier synthesized porphyrazines with p-extended systems which are represented as [Py8PyzPzM] (Chart 1b), and [Py8QxPzM] where Qx = quinoxaline. Each porphyrazine undergoes multiple one-electron reductions in DMSO, benzonitrile, pyridine or CH2Cl2 while the two octacationic porphyrazines, [(2-Mepy)8PzM]8+, also exhibit 2 or 3 one electron reductions in water containing 0.1 M NaOAc or 0.1 M KCl as supporting electrolyte. The potentials for each redox reaction were measured by cyclic voltammetry and thin-layer UV-visible spectroelectrochemistry was used to characterize some of the redox reactions. Special emphasis was placed on the cobalt(II) derivative [Py8PzCoII]+, which is oxdized in a single step to give [Py8PzCoIII] or reduced in up to five one-electron transfer steps, with the exact potentials and site of electron transfer depending upon the solvent. Pyridine was shown to strongly coordinate to the metal center of [Py8PzCoII] and [Py8PzCoIII] and binding constants were calculated using standard equations. Finally, comparisons are made between redox behavior of the three types of compounds in Chart 1, [Py8QxPzM] and the well-characterized phthalocyanines, [PcM], having the same central metal ions.

Chart 1. Structures for (a) newly investigated porphyrazines and (b) related porphyrazines with p-extended structures.(In the figure : 1) change formula: [(2-Mepy)8PzM]8+ instead of [(CH3-Py)8PzM] ; 2) change the order of metal centers and put the oxidation state: M = 2H, MgII(H2O), CoII, CuII, ZnII instead of M = Mg(H2O), Cu, Zn, 2H, Co ; 3) put M = MgII(H2O), ZnII instead of M = Mg(H2O), Zn)

Figure 1
Electrochemistry and Protonation of Open-Chain Pentapyrroles and Sapphyrins with Highly Electron-Withdrawing Meso-Substituents
Authors: Shan Wenqian , Naitana Mario L. , Desbois Nicolas , Blondeau-Patissier Virginie , Quesneau Valentin , Gros Claude , Huang Wenhao , Ou Zhongping , Kadish Karl M.
Published: February 2020

A series of open-chain pentapyrroles and sapphyrins with highly electron-withdrawing meso-tetraaryl groups were synthesized and characterized as to their electrochemistry and protonation reactions in nonaqueous media. The chemical conversion of pentapyrroles to sapphyrins upon oxidation in acid media is known but it was not known if sapphyrins could be electrosynthesized from pentapyrroles under the appropriate solution conditions. This was investigated in the present study which compares the redox behavior and acid-base properties of pentapyrroles to that of sapphyrins having the same meso-substituents. The investigated compounds were each characterized by UV−vis and 1H NMR spectroscopy, mass spectrometry and electrochemistry, in addition to spectroelectrochemistry. Structures of the investigated compounds are shown in Chart 1 and are represented as (Ar)4PpyH3 and (Ar)4SapH3.

Cyclic voltammetry was used to measure redox potentials and spectroelectrochemistry was used to monitor the products of each redox reaction. The protonation processes were monitored by UV-vis absorption spectroscopy as protons were added to the investigated compounds in the form of trifluoroacetic acid (TFA). Equilibrium constants were calculated using both the Hill equation and the Mole Ratio method. The electrochemical data, the protonation constants and previous reported mechanisms for reduction and oxidation of pentapyrroles and sapphyrins with other meso-tetraaryl groups were then analyzed as a function of the solvent properties and para-substituents on the four phenyl rings of compounds in the two series.

Figure 1
Synthesis of Oligomeric Benzoporphyrins Via Imidation
Authors: Hu Yi , Jinadasa R. G. Waruna , Wang Hong
Published: February 2020

In recent years, it is known that the porphyrin electronic system is susceptible to conjugative perturbation at the periphery. [1] So, the electronic and optical properties of porphyrin can be rationally tuned. Because of this, a variety of conjugated porphyrin arrays have been constructed over the last two decades. It is one strategy to link electron donors and electron acceptors together using π-conjugated molecular spacers to investigate photoinduced electron transfer processes on a molecular level. [2] The electronic properties of these molecules make them potentially useful in molecular photonics, optoelectronics, nanoscale application and in solar energy conversion. [1]

In this work, we report the synthesis and electronic properties of conjugated porphyrin dimer and monomers. All the porphyrins were synthesized using bromination, palladium catalyzed domino heck reaction followed by electrocyclization/dehydration strategy [3]and then imidation with coupling reagents.

Reference

[1] S. V. Kirner, D. Arteaga, C. Henkel, J. T. Margraf, N. Alegret, K. Ohkubo, B. Insuasty, A. Ortiz, N. Martı´n, L. Echegoyen, S. Fukuzumi, T. Clark and D. M. Guldi, Chem. Sci.,
 
2015, 6, 5994–6007

[2] S. Fukuzumi, K. Ohkubo and T. Suenobu, Acc. Chem. Res., 2014, 47, 1455.

[3] Jinadasa, R. G. W.; Fang, Y.; Kumar, S.; Osinski, A. J.; Jiang, X.; Ziegler, C. J.; Kadish, K. M.; Wang, H. J. Org. Chem., 2015, 80 (24), 12076–12087

Figure 1
Strongly Coupled Bisdonor-BF2 Chelated Azadipyrromethene-Fullerene Tetrads: Synthesis and Charge Separation Studies
Authors: Collini Mellissa , Thomas Michael , Bandi Venugopal , Karr Paul , D'Souza Francis
Published: February 2020

The efficiency and mechanism of electron- and energy transfer events occurring in both in natural and synthetic donor-acceptor systems depend on their distance, relative orientation, and the nature of the surrounding media. Fundamental knowledge gained from model studies is key in building efficient energy harvesting devices. Faster charge separation and slower charge recombination in donor-acceptor systems is often sought out. In our continued effort to build donor-acceptor systems using near-IR sensitizers, in the present study, we report ultrafast charge separation in newly synthesized, strongly coupled, tetrads featuring bisdonor (donor = phenothiazine and ferrocene), BF2-chealted azadipyrromethane (azaBODIPY) and fullerene (C60) entities. The tetrads synthesized using multi-step synthetic procedure revealed strong charge transfer interactions in the ground state involving the donor and azaBODIPY entities. The near-IR emitting azaBODIPY acted as a photosensitizing electron acceptor along with fullerene while the phenothiazine and ferrocene entities acted as electron donors. The control triads (bisdonor-azaBODIPY, 1d and 2d) and tetrads (1 and 2) revealed ultrafast photoinduced charge separation leading to charge separated states as probed by femtosecond transient absorption spectroscopy in both polar and nonpolar solvent media.

Figure 1
Reactions of Adsorbed Porphyrins on Oxides and Metals in Ultrahigh Vacuum and Liquids
Authors: Lytken Ole
Published: February 2020

Adsorption of porphyrins on metal surfaces has been studied extensively in ultrahigh vacuum, but, despite the technological importance of oxides, much less work exists on the adsorption of porphyrins on oxide surfaces. Using X-ray photoelectron spectroscopy (XPS) the adsorption and reactions of 5,10,15,20-tetraphenylporphyrin on MgO(100) and TiO2(110) surfaces in ultrahigh vacuum have been studied and will be compared with reactions on metal surfaces both in ultrahigh vacuum and immersed in aqueous solution. Focus will be on metalation of free-base molecules and metal center exchange of metalloporphyrins where the porphyrin molecules extract metal ions from the oxide surfaces. The behavior on oxide surfaces will be shown to have a lot in common with reactions in the liquid phase, such as ion exchange and protonation.
Comprehensive Structure-Function Studies of Photoactive Ionic π-Conjugated Supermolecular Assemblies
Authors: Mazur Ursula , Hipps K W
Published: February 2020

Organic semiconductors possess unique photon absorption characteristics that result from their highly polarizable π-electronic structures. Although organic semiconductors have become viable alternatives to their well-established inorganic counterparts there is still a continuing need for research in controlling their composition and structure since those factors determine how they function. Consequently, a good fundamental understanding of structure–property relationships is essential in designing and building high performance, stable, and durable molecular materials and is one of the main scientific challenges for advancing organic optoelectronic technology.

The work that we will present is a detailed structure–property study of ionic porphyrin based semiconductors using both experiment and theory. Nano to millimeter size crystalline binary porphyrin structures were synthesized reproducibly from oppositely charged synthons and characterized using XRD, AFM, SEM, DRS, UV-visible, and photoconductivity measurements. The photoconductive properties of the porphyrin materials are linked with their molecular organization and morphology. Electronic band calculations help explain the experimental photoconductivity measurements and provide guidelines for future structure modification to optimize charge transport properties in these π-conjugated systems. These studies are the first to combine structure determination, electronic band calculations, and experiment in a unified approach for these materials.
Coordination to Supported Metalloporphyrins at the Solid-Solution Interface
Authors: Hipps K W , Mazur Ursula
Published: February 2020

Metalloporphyrins play a starring role in the chemistry and physics of biology, photo-electricity, sensing, catalysis, electrochemistry, and other important areas. Because of this, they have been widely studied (both experimentally and theoretically) in the solid state and in solution. Very recently it has become possible to experimentally probe their chemistry at the single molecule level. Of even more relavence to applications, it is now possible to do single molecule studies at the solution-solid interface. Scanning tunneling microscopy (STM) provides images, at the single molecule level, of reactions between surface supported metal porphyrins and molecular species like oxygen, imidazole, and other reactive species. These scanning probe studies clearly demonstrated that the chemistry of the supported porphyrin can be very different than in solution. Density functional theory has allowed us to more fully understand the nature of the substrate-porphyrin-ligand interaction relative to the substrate free case. We find that whenever the porphyrin is supported on a conducting substrate, there is a complex charge exchange process that can significantly modify the axial binding relative to what is observed in solution. In some cases, the interaction is such that even the spin state of the surface supported metal ion differs from that of the same chemical system in solution or gas phase. We will present examples of experimental and computational studies of this new chemistry.
Supramolecular Porphyrin Copolymer Formed Via Competitive Host-Guest Interaction
Authors: Haino Takeharu
Published: February 2020

Polymer properties are directly associated with their primary structures. Control of monomer sequences in polymer sequences is a crucial topic in modern polymer chemistry. Therefore, reorganization of polymer sequences can regulate polymer properties. Sequence reorganization of supramolecular homopolymers to alternating polymers can be realized via competitive guest complexation. We have reported that self-assembly of tetrakisporphyrin 1 produced the supramolecular polymeric assemblies that was dissociated via competitive complexation of trinitrofluorenone (TNF). Employing bis(trinitrofluorenone) 2 instead of TNF as a guest resulted in sequence reorganization of homopolymers (1)n to alternating copolymers (1•2)n. The supramolecular polymerization of (1•2)n was discussed using diffusion-ordered NMR technique, suggesting that large polymeric assemblies were formed with the alternating structures. Solution viscometry of (1)n and (1•2)n demonstrated quite contrastive behaviors. (1•2)n formed entangled solution, whereas (1)n behaved like a rigid rod in solution.

Figure 1
Porphyrinoids Based Hybrid Materials for Chemical Sensor Applications
Authors: Paolesse Roberto , Stefanelli Manuela , Magna Gabriele , Nardis Sara , Pomarico Giuseppe , Di Natale Corrado
Published: February 2020

In the field of chemical sensors, porphyrinoids have been demonstrated to be an excellent sensing materials for target applications in medical diagnosis, food control, and environmental monitoring. These macrocycles offer a wide range of interaction mechanisms that can be exploited to bind host molecules either airborne or in solution and their properties can be finely tuned by synthetic modifications. A further opportunity to improve the performances of porphyrin is represented by their combination with inorganic materials. Porphyrins have been frequently used to functionalize other molecular structures or surfaces. The optical properties of porphyrins prompted the study of functionalized wide band gap semiconductors for solar cell developments. Recently, we have been interested in the exploitation of porphyrin grafted onto ZnO nanoparticles for sensor applications. The results obtained showed that the arrangement of porphyrins onto ZnO greatly affected the sensing properties. In the present work, we summarise our recent results, showing a promising route for chemical sensors applications.
Tailoring the Corrosion Behavior of Biodegradable Mg Alloys By Surface Modification
Authors: Virtanen Sannakaisa
Published: February 2020

The possible use Mg alloys in biodegradable biomedical devices has found tremendously increasing research interest in recent years. However, the corrosion rate should be controlled for the specific applications. There is still need for optimization and further development of biocompatible, biofunctional and biodegradable coatings for Mg alloys. The presentation discusses some recent developments on various surface modification and coating approaches on Mg alloys, including coatings based on natural and synthetic biopolymers. Fabrication routes of coatings will be presented and discussed. Corrosion protection effects, degradation behavior of the coatings, and biocompatibility of the treated surfaces will be discussed.
Deposition of Ultrathin Cellulose Nanofibers Films As Bio-Implant Corrosion Coatings
Authors: Wilson Benjamin Paul , Paukkonen Niina , Yliniemi Kirsi , Hakalahti Minna , Tammelin Tekla , Kontturi Eero , Lundström Mari
Published: February 2020

The wide use of magnesium and magnesium-based alloys for bio-implant materials has so far been restricted due to the rapid corrosion rate of such materials under in-vivo conditions 1,2. Cellulose based coatings have previously been examined as coatings for magnesium materials although the use of TEMPO-oxidised nano-fibrillated cellulose (CNF-TEMPO) coatings has yet to be explored 3,4. The work outlines details of an investigation in to the effect that deposition method has on the coating characteristics. Three different methods were used to deposit CNF-TEMPO coatings including adsorption, spin coating and anodic electrophoretic deposition. The coatings were subsequent analysed using atomic force microscopy (AFM), ellipsometry and quartz crystal microbalance (QCM) to determine differences in nanotopographic surface roughness and hydrophilicity in particular. The ability of the EPD technique to deposit films from relative dilute solutions (0.01 to 0.1 wt-%) was demonstrated. Finally, samples of magnesium were coated and the corrosion properties of the ultrathin films were determined using a number of electrochemical techniques including linear sweep voltammetry, polarization and free corrosion measurements. Overall, the results show that CNF-TEMPO coatings produced using the EPD method offer a potential starting point for the next generation of biobased coatings for implant materials.

References

[1] S. Virtanen, Mater. Sci. Eng. B, 2011, 176, 1600-1608

[2] F. Witte, N. Hort, C. Vogt, S. Cohen, K. U. Kainer, R. Willumeit, F. Feyerabend, Current Opinion in Solid State and Materials Science, 2008, 12, 63-72.

[3] S. Heise, S. Virtanen, A. R. Boccaccini, Journal of Biomedical Materials Research A, 2016 104A, 2628-2641.

[4] K. Yliniemi, B. P. Wilson, F. Singer, S. Höhn, E. Kontturi S. Virtanen, ACS Applied Materials and Interfaces, 2014, 6, 22393-22399.

Figure 1
In-Situ Determination of Hydrogen Evolution Rate on Mg and Mg Alloy during Anodic Dissolution By Gas-Chromatographic Analysis
Authors: Hoshi Yoshinao , Takemiya Rie , Shitanda Isao , Itagaki Masayuki
Published: February 2020

Mg and Mg alloys are expected to be an active material for the negative electrode of air batteries 1) because they dissolve actively in the aqueous solution at less noble potential. However, the hydrogen evolution is occurred on the Mg and Mg alloys during the anodic dissolution in the aqueous solution, which calls the negative difference effect, NDE 2, 3). It may lead to the self-discharge and loss of discharge capacity of air batteries in operation.

In the present study, we determined the hydrogen evolution rate on Mg and Mg alloys during anodic dissolution by gas-chromatographic analysis. Song et al. 4) reported the hydrogen evolution behavior of Mg and Mg alloys. They 4) carried out the gas collection by using a burette vertically mounted over the funnel to estimate the volume of hydrogen gas generated on Mg alloys at different applied current density. Comparing to this, we previously developed an electrochemical cell combined with a gas chromatograph 5) to perform an in-situ determination of hydrogen evolution rate on Mg during anodic dissolution. In this system, the gas generated on the working electrode is directly delivered to a gas chromatograph by a stream of carrier gas 5), namely, the qualitative and quantitative analysis of the gas generated on the working electrode can be carried out. It enables us the analysis of gases involving nitrogen and oxygen during anodic dissolution of Mg and Mg alloys. The details of the developed system and measurement conditions are described in our previous work 5). In the present study, hydrogen evolution rate on various kinds of Mg alloys during anodic dissolution were determined by developed system and the gases evolved on Mg alloys during anodic dissolution were discriminated.

References:

1. R. P. Hamlen, E. C. Jerabek, J. C. Ruzzo and E. G. Siwek, J. Electrochem. Soc., 116, 1588 (1969).

2. G. Song, A. Atrens, D. St John, X. Wu and J. Nairn, Corros. Sci., 39, 1981 (1997).

3. G. S. Frankel, A. Samaniego and N. Birbilis, Corros. Sci., 70, 104 (2013).

4. G. Song, A. Atrens, D. Stjohn, J. Nairn and Y. Li, Corros. Sci., 39, 855 (1997).

5. Y. Hoshi, R. Takemiya, I. Shitanda and M. Itagaki, J. Electrochem. Soc., 163, C303 (2016).
Impedance Measurements to Monitor Concrete Degradation and Rebar Corrosion
Authors: Itagaki Masayuki , Okamoto Tatsuki , Tokieda Hiroyuki , Hoshi Yoshinao , Shitanda Isao , Kato Yoshitaka
Published: February 2020

The degradation of steel-reinforced concrete is serious problem in infrastructures. It is well known that the rebar corrosion in concrete is strongly influenced by the conditions of cover concrete. Figure 1 shows schemes of interface between steel rebar and concrete. Thin water layer is formed at this interface due to water absorption in the concrete which covers the steel rebar. And this water layer is called “transition zone” in the field of civil engineering. The pH of water at transition zone is high when the concrete is good health status, and the passive film is formed on steel rebar. The breakdown of passive film occurs by neutralization and chloride concentration in the water layer with the degradation of concrete. Corrosion resistance of steel rebar is influenced by the water quality in the transition zone. Thus, we can conclude that rebar corrosion in concrete is electrochemical process at metal/water interface. Electrochemical measurements are useful to investigate the corrosion mechanisms. There are some literatures regarding the electrochemical tests, which are mainly measurements of corrosion potential [1] and polarization curves, to evaluate the stability of passive film formed on rebar in concrete. Dawson et al. [2] applied an electrochemical impedance spectroscopy (EIS) to the investigation of rebar corrosion in concrete because the charge transfer resistance at rebar/concrete interface can be determined from the impedance spectrum.

The authors developed an electrode as a sensor probe to monitor concrete degradation and rebar corrosion. A couple of electrodes, which were made of same material as rebar, can be embedded in concrete structure and complex impedance can be measured continuously on the basis of two-electrode method. In this presentation, the authors report the results of three impedance measurements as follows.

(1) Impedance between two electrodes in aqueous solution that simulates the water quality of transition zone (laboratory test).

(2) Impedance between two electrodes embedded in the concrete which was fabricated in the laboratory.

(3) Field test at bridge pier of the highway in coastal marine environment.

References:

[1] ASTM C 876-91 (Reapproved 1999): Standard Test Method for Half-Cell Potentials of Uncoated Reinforcing Steel in Concrete, Annual Book of ASTM standards, Vol. 03.02, pp. 457-462, 1999.

[2] J. L. Dawson, L. M. Callow, K. Hladky and J. A. Richardson, Corrosion/78, No-125 (1978).

Figure 1
A New Reactive-Transport Modeling Framework for Simulating Pore Solution Chemistry at Localized Imperfections Along Steel-Concrete Interface
Authors: Isgor Burkan , Jafari Azad Vahid
Published: February 2020

The variability and uncertainty associated with chloride thresholds for corrosion initiation in reinforced concrete structures can be partly explained by the presence of localized defects and imperfections along steel-concrete interface such as elongated cracks, pores, gaps, crevices, and mill scale. It has been demonstrated in prior research that pore solution in these imperfections might be different from that of the bulk pore solution, and this difference may create the necessary conditions for the breakdown of the passive film. These studies showed that the chemistry of the pore solution, in particular pH and Cl-/OH-, within localized defects provide more favorable conditions for depassivation than the bulk concrete pore solution. Local acidification and increase in Cl-/OH- within these defects were observed, albeit to different degrees. Defect geometry has been found to be a critical parameter affecting local acidification and the increase in Cl-/OH-. However, chemical composition of the pore solution, reactions between corrosion products and the ionic species in the pore solution and changes in transport properties within the defect due to accumulation of solid corrosion product have also been shown to affect the process. Due to these complications, it is challenging to study these effects experimentally, hence numerical investigation techniques are required.

In order to better understand the processes that take place within local defects along the steel-concrete interface a reactive-transport modeling framework is developed. The model incorporates finite element analysis (FEM) with thermodynamic/kinetic modeling of cementitious systems. The FEM module is responsible for modeling multiphysics phenomena such as corrosion, mass transport, heat transfer, phase flow and kinetics, while thermodynamic module is used to model chemically complex reaction computations based on Gibbs Energy Minimization (GEM) theory. A non-iterative operator splitting technique in a time marching scheme is used for uncoupling the multiphysics phenomena from reaction equations. The framework is able to analyze complex chemical systems including processes that take place in cementitious materials and as a result of corrosion reactions.

The presentation will highlight the main components of developed framework and demonstrate its functionality though case studies and hypothetical simulations.
Anodic Oxidation of Bismuth in Halide Containing Electrolytes
Authors: Macak Jan M. , Sopha Hanna
Published: February 2020

The synthesis of highly-ordered nanostructures of valve metal oxides has recently attracted huge scientific and technological interest motivated by their possible use in many applications. The two most established members of this group of materials are nanoporous Al2O3 and TiO2 nanotubes [1,2]. While Al2O3 membranes have been since than widely used as template material of choice for a range of materials [2-4] due to the flexibility of the pore diameter/length and the relative ease of the Al2O3 dissolution, TiO2 nanotubes received high attention because of their applications in e.g. photocatalysis, water splitting, solar cells and biomedical uses [5].

Bismuth oxide is another interesting material and its nanostructures show an enhanced photoelectrochemical performance [6,7]. However, the formation of bismuth nanostructures, such as bismuth oxide nanopores [6,7] or bismuth phosphate nanorods [8], by anodization is not well explored by now. Similar to the formation of nanoporous Al2O3 nanoporous Bi2O3 was produced in acidic, F--free electrolytes.

In this presentation, we demonstrate the anodization of bismuth in halide containing electrolytes similar to the electrolytes classically used for the formation of TiO2 nanotubes.

References

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2. K. Nielsch, F. Müller, A.-P. Li, U. Gösele, Adv. Mater. 12 (2000) 582.

3. H. Asoh et al., J. Electrochem. Soc. 148 (2001) B152.

4. J. Kolar, J. M. Macak, K. Terabe, T. Wagner, J. Mater. Chem. C, 2 (2014) 349.

5. K. Lee, A. Mazare, P. Schmuki, Chem. Rev. 114 (2014) 9385.

6. X. Lv, J. Zhao, X. Wang, X. Xu, L. Bai, B. Wang, J. Solid. Stat Electrochem. 17 (2013) 1215.

7. K.C. Chitrada, K. S. Raja, R. Gakhar, D. Chidambaram, J. Electrochem. Soc. 162 (2015) H380.

8. M. Yang, N. K. Shrestha, R. Hahn, P. Schmuki, Electrochem. Solid-State Lett. 13 (2010) C5.
Influence of CVD Growth Parameters on the Corrosion Resistance of the Resultant Graphene Coating
Authors: R. Anisur M. , Banerjee Parama Chakraborty , Singh Raman R K
Published: February 2020

Graphene coatings have been reported to suppress corrosion of various metal substrates due to their chemical inertness. However, the extent of protection offered depends on the uniformity and defect density of the graphene layers developed on the metallic substrates. Among the various synthesis methods, chemical vapour deposition (CVD) is one of the most promising ones to produce graphene coating on a variety of metal substrates. However, achieving controlled CVD growth of large area, uniform and less defective graphene coating is still challenging. This study investigates the influence of various CVD growth parameters during the graphene synthesis, such as hydrogen flow, carbon precursor flow, growth temperature and cooling rate used on the uniformity of the resultant graphene coating and its corrosion resistance. The barrier properties of graphene-coated Cu substrates were evaluated using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) in 0.1 M NaCl for 1008 h. High graphene growth temperature (1060 ºC) and low hydrocarbon flow rate (1 sccm) in the absence of H2 flow were identified to synthesize a uniform graphene coating, which showed durable barrier performance. During the initial hours of immersion, the graphene coated copper (Cu) specimens showed about one and half order of magnitude improvement in corrosion resistance in 0.1 M NaCl and even after 1008 h, the corrosion resistance provided by the graphene coating was almost five times more than that of bare Cu. The optimized CVD graphene parameters reported here can provide a new direction to achieve long-term durable graphene coating.
Improved Corrosion Resistance of Metastable Beta Ti-X (X = 6Mn, 8Cr, and 36Nb) Binary Alloys As a Function of 10.Wt% Mo Equivalence
Authors: Kim Sinhye , Lee Kwangmin
Published: February 2020

Beta type titanium alloys are developed as metallic biomaterials due to their low elastic modulus compared to well-known Ti-6Al-4V alloy. Since Mo is known to be an efficient beta phase stabilizer, Ti-Mo binary alloy have been extensively studied on their microstructural characteristics, mechanical properties and corrosion resistance. The stability of the beta phase can be expressed using the “molybdenum equivalent” which has minimum critical value of 10-11 .wt%. Niobium is well known to be very good to resist against corrosion in simulated body fluid and presents an excellent biocompatibility. Mn was selected as an alloying element due to its beta stabilizing effect, low cytotoxicity, high availability and lower cost when compared to other popular alloying elements. Cr-induced passive layer has been proven to be strong and solid. Ti-Cr based alloys also have been widely used for dental applications. In this study, the amount of alloying additions were calculated as a function of 10 .wt% Mo equivalence in order to evaluate the corrosion performance of each alloy. Potentiodynamic polarization test and time-based electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion behavior in Ringer’s solution. It was found that the corrosion parameters obtained from potentiodynamic polarization test were not significantly different to those of Ti-10Mo alloy. Substituting Mo to the other studied elements simply shifts the corrosion potential into less-noble zone. However, the overall corrosion current density were lower compared to those of Ti-10Mo alloy. The lowest corrosion current density observed in Ti-6Mn alloy with the value of 7.742 nA/cm2, which 8 times lower than those of Ti-10Mo with the value of 48.81 nA/cm2. Impedance responses increase with increasing immersion time. There is little difference in the profiles in the high- and medium-frequency regions, but at lower frequencies the difference becomes substantial. The solution-film resistance element remains low for different immersion times at lower potentials, while film-substrate resistance increases with time. At higher potentials, both resistance have comparable values, pointing to the increased protectiveness, or less defective structure, of the outer porous layer at higher potentials. This result agrees with XPS evaluation on the passive film which formed on their most stable formation within the working potential range. At OCP, the capacitance values increase with the time. While at higher potentials, the capacitance values remain constant with time.
Corrosion Resistance of Stainless Steel Coated with Hydrogen Silsesquioxane Based Spin-on-Glass Coatings Cured in Oxygen Deprived Atmosphere
Authors: Lampert Felix , Jensen Annemette Hindhede , Din Rameez Ud , Møller Per
Published: February 2020

Thin coatings are applied as a promising surface finish to stainless steel engineering components in highly corrosive environments, where only minor deviations from the component geometry due to coating thickness can be tolerated. In particular silica-based coating systems have gained academic as well as industrial interest due to their outstanding performance in terms of mechanical and electrochemical performance. The aim of this study is to investigate the protective behavior of SiOx coatings from hydrogen silsesquioxane, (HSiO3/2)n, spin-on-glass precursor on AISI 316L 2B substrates in saline environment. The precursor has been deposited on the substrate and thermally cured in oxygen deprived atmosphere at temperatures ranging from 400-800 ˚C. The results showed the formation of highly polymerized SiOx coatings containing various amounts of residual Si-H and silanol moieties. Moreover, the degree of coating polymerization was assessed based on the amount of residual Si-H and an increase in polymerization was found with increasing curing temperature up to 800 ºC. Further, the electrochemical behavior of the coating systems was characterized by linear cyclic polarization and electrochemical impedance spectroscopy. The results showed that the coatings decreased the electrolyte-exposed substrate surface area significantly and possessed enhanced barrier properties with respect to films cured in oxidizing ambient, yielding a minimal corrosion rate in electrochemical tests. Furthermore, the excellent performance of the coating systems in short term electrochemical studies were critically evaluated in comparison to prolonged exposure in accelerated corrosion tests and substrate sensitization due to the deposition process.
Study on the Use of Titania Nanoparticles As Synergy Inhibitor for Steel in Ethanol Fuel Blend
Authors: Nguyen Vu Si Hoai , Pham Hien Van , Nguyen Ngan Oanh Kieu , Phan Binh Minh Quoc , Vu Thu Thi Hanh , Nguyen Nam Dang
Published: February 2020

This study investigated the combination of Aganonerion Polymorphum leaf extraction (APLE) and Titania nanoparticles (TNPs) as main and synergy inhibitor for steel in ethanol fuel blend. APLE has been extracted from soxhlet apparatus, and the APLE components were checked by Fourier transform infrared spectroscopy. TNPs with various sizes were synthesized by sol-gel route from tetraisopropyl orthotitanate precursor. TNPs sizes were calculated by Scherrer’s formula from X-ray diffraction pattern and confirmed by scanning electron microscopy (SEM). Immersion test was taken in simulated fuel environment followed ASTM standards. Electrochemical impedance spectroscopy indicated that APLE established a good adherent protective layer onto the steel surface, which would have been better with TNPs. Tafel fitting from potentiodynamic measurement had a good agreement with EIS data and shown higher corrosion potential and polarization resistance, as well as lower corrosion current density and corrosion rate of the co-inhibiting system. X-ray photoelectron spectroscopy manifested the significant decrease of Fe peaks intensity and the significant increase of C1s and Ti2p peaks from specimens without to one with the inhibitors, that confirmed the inhibiting effectiveness of APLE and TNPs. Finally, SEM images designated smoother surface of specimens submerged in the co-inhibiting system that strengthen those remarks above.

Figure 1
Electrochemical Behavior of Steels in CO2-H2o Systems for Direct Supercritical CO2 Power Cycle Applications
Authors: Repukaiti Richard , Teeter Lucas , Ziomek-Moroz Margaret , Dogan Omer , Tucker Julie
Published: February 2020

In experiments simulating direct supercritical CO2 power cycle conditions, a change in the corrosion behavior of 316 and 347H stainless steels has been observed during the startup and shut down periods. In these exposure tests, the steels experienced environments which are CO2-saturated water systems at elevated temperature and pressure. Due to the electrochemical nature of corrosion processes occurring in these systems, corrosion behavior of ferritic-martensitic P91 steel and austenitic 347H stainless steel was studied in CO2-saturated H2O using potentiodynamic and potentiostatic experiments. The solution was prepared by bubbling CO2 through H2O at constant temperature. The solution preparation and the experiments were carried out at 25 and 50°C.

Potentiodynamic experiments, including cyclic voltammetry, were performed to determine the corrosion behavior of selected materials. Corrosion rates were determined from linear polarization resistance experiments. Optical and scanning electron microscopy of the corroded surfaces were performed after the potentiostatic experiments.