A Review on Nano Ti-Based Oxides for Dark and Photocatalysis: From Photoinduced Processes to Bioimplant Applications

Catalysis on TiO2 nanomaterials in the presence of H2O and oxygen plays a crucial role in the advancement of many different fields, such as clean energy technologies, catalysis, disinfection, and bioimplants. Photocatalysis on TiO2 nanomaterials is well-established and has advanced in the last decades in terms of the understanding of its underlying principles and improvement of its efficiency. Meanwhile, the increasing complexity of modern scientific challenges in disinfection and bioimplants requires a profound mechanistic understanding of both residual and dark catalysis. Here, an overview of the progress made in TiO2 catalysis is given both in the presence and absence of light. It begins with the mechanisms involving reactive oxygen species (ROS) in TiO2 photocatalysis. This is followed by improvements in their photocatalytic efficiency due to their nanomorphology and states by enhancing charge separation and increasing light harvesting. A subsection on black TiO2 nanomaterials and their interesting properties and physics is also included. Progress in residual catalysis and dark catalysis on TiO2 are then presented. Safety, microbicidal effect, and studies on Ti-oxides for bioimplants are also presented. Finally, conclusions and future perspectives in light of disinfection and bioimplant application are given

Thiophen-basierte konjugierte acetylenische Polymere mit dualen aktiven Zentren für effiziente Cokatalysator-freie photoelektrochemische Wasserreduktion im alkalischen Medium

AbstractKonjugierte Polymere sind attraktive Materialien für die photoelektrochemische Wasserstoffentwicklungsreaktion (PEC‐HER) unter neutralen oder sauren Bedingungen. Jedoch zeigen sie im alkalischen Medium immer noch eine geringe PEC‐HER‐Leistung aufgrund des Fehlens von Wasserdissoziations‐Zentren. Hier zeigen wir, dass durch Anpassung des konjugierten acetylenischen Polymers (CAPs) von Poly(diethinylthieno[3,2‐b]thiophen) (pDET) zu Poly(2,6‐diethinylbenzo[1,2‐b:4,5‐b′]dithiophen (pBDT) und Poly(diethinyldithieno[3,2‐b:2′,3′‐d]thiophen) (pDTT) hocheffiziente aktive Wasserdissoziations‐Zentren in CAPs eingeführt werden können. Infolgedessen zeigen auf Cu‐Substrat gewachsene pDTT und pBDT Benchmark‐Photostromdichten von 170 μA cm−2 und 120 μA cm−2 (bei 0,3 V vs. RHE; pH 13), die 4,2‐ bzw. 3‐mal höher sind als die von pDET. DFT‐Rechnungen und elektrochemische Operando‐Resonanz‐Raman‐Spektroskopie zeigen, dass die elektronenangereicherten Cβ der äußeren Thiophenringe von pDTT die aktiven Zentren für die Wasserdissoziation sind, während die ‐C≡C‐Bindungen als aktive Zentren für die Wasserstoffentwicklung fungieren

Donor-Acceptor Conjugated Acetylenic Polymers for High- Performance Bifunctional Photoelectrodes

Due to the drastic required thermodynamical requirements, a photoelectrode material that can function as both a photocathode and a photoanode remains elusive. In this work, we demonstrate for the first time that, under simulated solar light and without co-catalysts, donor-acceptor conjugated acetylenic polymers (CAPs) exhibit both impressive oxygen evolution (OER) and hydrogen evolution (HER) photocurrents in alkaline and neutral medium, respectively. In particular, poly(2,4,6-tris(4-ethynylphenyl)-1,3,5-triazine) (pTET) provides a benchmark OER photocurrent density of ~200 μA cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE) at pH 13 and a remarkable HER photocurrent density of ~190 μA cm−2 at 0.3 V vs. RHE at pH 6.8. By combining theoretical investigations and electrochemical-operando Resonance Raman spectroscopy, we show that the OER proceeds with two different mechanisms, with the electron-depleted triple bonds acting as single-site OER in combination with the C4-C5 atoms of the phenyl rings as dual sites. The HER, instead, occurs via an electron transfer from the tri-acetylenic linkages to the triazine rings, which act as the HER active sites. This work represents a novel application of organic-based materials and contributes to the development of high-performance photoelectrochemical catalysts for the solar fuels’ generation

Thiophene-Based Conjugated Acetylenic Polymers with Dual Active Sites for Efficient Co-Catalyst-Free Photoelectrochemical Water Reduction in Alkaline Medium

Although being attractive materials for photoelectrochemical hydrogen evolution reaction (PEC HER) under neutral or acidic conditions, conjugated polymers still show poor PEC HER performance in alkaline medium due to the lack of water dissociation sites. Herein, we demonstrate that tailoring the polymer skeleton from poly(diethynylthieno[3,2-b]thiophene) (pDET) to poly(2,6-diethynylbenzo[1,2-b:4,5-b′]dithiophene (pBDT) and poly(diethynyldithieno[3,2-b:2′,3′-d]thiophene) (pDTT) in conjugated acetylenic polymers (CAPs) introduces highly efficient active sites for water dissociation. As a result, pDTT and pBDT, grown on Cu substrate, demonstrate benchmark photocurrent densities of 170 μA cm−2 and 120 μA cm−2 (at 0.3 V vs. RHE; pH 13), which are 4.2 and 3 times higher than that of pDET, respectively. Moreover, by combining DFT calculations and electrochemical operando resonance Raman spectroscopy, we propose that the electron-enriched Cβ of the outer thiophene rings of pDTT are the water dissociation active sites, while the −C≡C− bonds function as the active sites for hydrogen evolution. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH Gmb

Interfacial Covalent Bonds Regulated Electron-Deficient 2D Black Phosphorus for Electrocatalytic Oxygen Reactions

Developing resource-abundant and sustainable metal-free bifunctional oxygen electrocatalysts is essential for the practical application of zinc–air batteries (ZABs). 2D black phosphorus (BP) with fully exposed atoms and active lone pair electrons can be promising for oxygen electrocatalysts, which, however, suffers from low catalytic activity and poor electrochemical stability. Herein, guided by density functional theory (DFT) calculations, an efficient metal-free electrocatalyst is demonstrated via covalently bonding BP nanosheets with graphitic carbon nitride (denoted BP-CN-c). The polarized P-N covalent bonds in BP-CN-c can efficiently regulate the electron transfer from BP to graphitic carbon nitride and significantly promote the OOH* adsorption on phosphorus atoms. Impressively, the oxygen evolution reaction performance of BP-CN-c (overpotential of 350 mV at 10 mA cm−2, 90% retention after 10 h operation) represents the state-of-the-art among the reported BP-based metal-free catalysts. Additionally, BP-CN-c exhibits a small half-wave overpotential of 390 mV for oxygen reduction reaction, representing the first bifunctional BP-based metal-free oxygen catalyst. Moreover, ZABs are assembled incorporating BP-CN-c cathodes, delivering a substantially higher peak power density (168.3 mW cm−2) than the Pt/C+RuO2-based ZABs (101.3 mW cm−2). The acquired insights into interfacial covalent bonds pave the way for the rational design of new and affordable metal-free catalysts. © 2021 The Authors. Advanced Materials published by Wiley-VCH Gmb

Kombinierte Schwingungsspektroskopie und Elektrochemie zur Untersuchung biologischer und materieller Systeme

In this thesis, combined vibrational spectroscopy and electrochemistry is applied to investigate two different projects in biological and materials sciences. In the biological project on the putative hemoprotein redox sensor MsmS(-sGAF2) from M. acetivorans, resonance Raman (RR) spectroscopy reveals that a six-coordinated low spin (6cLS) and a five-coordinated high spin (5cHS) state is the prevailing configuration in the oxidized and reduced state, respectively. Comparative studies on engineered variants showed that H702 is most likely the proximal axial ligand which serves as a potent hydrogen-bond donor to a nearby amino acid residue. This conclusion is based on the relatively low frequency and the H/D sensitivity of the ν4 mode of the 5cHS ferrous heme, as well as the upshift of the ν4 mode of the 5cHS form in the reduced state of the H702 mutant variants (H702G, K661G/H702G, and H702/708G). The findings are consistent to those for the analogous protein MA0863 for which similar effects on the ν4 mode have been observed. An increased amount of heme groups in the 5cHS configuration was noted when polar amino acid residues of MsmS-sGAF2 in the distal region were mutated (Y665F and H646A). Temperature-dependent RR spectroscopy revealed that the 6th ligand acts as a strong ligand as reflected by the gradual decrease in the 5cHS/6cLS ratio with increasing temperatures. An energy-minimized structural model confirmed that the distal pocket region with its polar residues can accommodate a small polar molecule. These studies suggest that the second-coordination sphere plays an important role for MsmS’s ligand-binding function, which could influence the heme redox state. Using surface-enhanced resonance Raman (SERR) spectroscopy and infrared absorption spectroscopic techniques, MsmS-sGAF2 was found to display redox reversibility accompanied by reversible conformational changes. SERR spectroscopic redox titration of MsmS-sGAF2 immobilized on 8-aminooctanethiolate|roughened silver yielded midpoint potentials (Emidpt) for the Fe3+/2+ transition of -0.28 V (vs. Ag/AgCl, 3 M KCl) and -0.29 V for the redox transitions of 5cHS and 6cLS species for the aerobic BL21(DE3) E. coli preparation, respectively, as well as -0.32 V and -0.20 V for the 5cHS and 6cLS species for the anaerobic Nissle 1917 E. coli preparation, respectively. The average values (5cHS+6cLS) are similar to that obtained from cyclic voltammetry of the anaerobic preparation, Emidpt = -0.297 V. In the materials system, anodized titania nanotubes (TiO2-NTs) with inherently different localized electric field (EF) enhancement properties (TiO2-NT|low and TiO2-NT|high for low and high EF enhancements, respectively; TiO2-NT|high|BD-PATP or TiO2-NT|low|BD-PATP for the electrodes deposited with the dye, benzidine-p-aminothiophenolate (BD-PATP)) were used as substrate for the laser-induced photocatalytic degradation of BD-PATP, which was resolved using time-dependent SERR spectroscopy. The degradation rate constant for TiO2-NT|high|BD-PATP, 5.1 (1.4) s-1, is ~70 % higher than the one measured for TiO2-NT|low|BD-PATP, 3.0 (0.6) s-1. Applying an external potential of +0.4 V, resulted in a significantly higher (~2.5 times) rate constant for the decay of TiO2-NT|high|BD-PATP, 25.5 (5) s-1, vs. of TiO2-NT|low|BD-PATP, 10.1 (3) s-1 indicating an improved performance of TiO2-NT|high vs. TiO2-NT|low. Degradation was found to depend on the excitation at 413 nm indicating a degradation pathway involving the excited state of the dye and no contributions from the charges of the TiO2-NTs. Low-frequency Raman measurements at 488 nm show that the Eg mode of the TiO2-NT|high is downshifted compared to that of TiO2-NT|low (145.5 cm-1 vs. 147.3 cm-1) indicative of possible size-dependent charge-transfer surface enhancement of the Raman signals. The high capacitance values from electrochemical impedance spectroscopy data obtained at negative potentials reveal the poor electron-acceptor character of TiO2-NTs at these potentials possibly due to proton/cation intercalation, which increases the injected electron-oxidized dye recombination rate. On the other hand, the lower capacities of TiO2-NTs at positive potentials and of TiO2-NT|high relative to TiO2-NT|low, reveal their improved electron-accepting capabilities at higher potentials, necessary for efficient surface-to-bulk electron transport. Based on this, the higher decay rate for TiO2-NT|high at +0.4 V can be justified by a combined effect of better electron-accepting property and photon-capturing ability of the material.In dieser Arbeit wird kombinierte Schwingungsspektroskopie und Elektrochemie verwendet, um biologische und materialwissenschaftliche Fragenstellungen zu untersuchen. In dem biologischen Projekt über MsmS (-sGAF2) von M. acetivorans, welches vermutlich ein Hämoprotein-Redox-Sensor ist, zeigen die Resonanz-Raman (RR) spektroskopische Untersuchungen, dass ein sechsfach koordinierter low-spin (6cLS) und ein fünffach koordinierter high-spin (5cHS) Zustand die vorherrschende Konfiguration im oxidierten bzw. reduzierten Zustand der Häm-Gruppe ist. Vergleichsstudien mit Mutanten zeigten, dass H702 höchstwahrscheinlich der proximale axiale Ligand ist, welche darüber hinaus eine Wasserstoffbrücke zu einem nahegelegenem Aminosäurerest aufweist. Diese Schlussfolgerung basiert auf der relativ niedrigen Frequenz und der H/D-Empfindlichkeit des ν4-Mode des reduzierten 5cHS- Häms sowie auf dem Hochverschiebung der ν4-Mode des reduzierten 5cHS-Häms der H702-Mutant (H702G, K661G/H702G und H702/708G). Die Ergebnisse stimmen mit denen für das analoge Protein MA0863 überein, für das ähnliche Effekte für die ν4-Mode beobachtet wurden. Eine erhöhte Menge an Häm-Gruppen in der 5cHS-Konfiguration wurde festgestellt, wenn polare Aminosäurereste von MsmS-sGAF2 im distalen Bereich mutiert wurden (Y665F und H646A). Temperaturabhängige RR-Messungen zeigten, dass der sechste Ligand ein starker Ligand ist, was sich in einer allmählichen Abnahme des 5cHS/6cLS-Verhältnisses mit steigender Temperatur widerspiegelt. Ein energieminimiertes Strukturmodell bestätigte, dass im distalen Taschenbereich mit polaren Resten ein kleines polares Molekül aufnehmen kann. Diese Studien legen nahe, dass die zweite Koordinationssphäre eine wichtige Rolle für die Ligandenbindungsfunktion von MsmS spielt, die den Häm-Redoxzustand beeinflussen könnte. Oberflächenverstärkte Resonanz-Raman (SERR) und Infrarotspektroskopie zeigten, dass MsmS-sGAF2 reversible Redox- und Konformationübergänge aufweist. SERR-spektroskopische Redoxtitration von MsmS-sGAF2 immobilisiert auf 8-Aminooctanthiolat-immobilisiertem Silberelektroden ergab ein Redoxpotential für den Fe2+/3+-Übergang (Emidpt) von -0,28 V (gegenüber Ag/AgCl, 3 M KCl) bzw. -0,29 V für die Redoxübergänge der 5cHS- und 6cLS-Spezies für das aerobe BL21 (DE3) E. coli-Präparat, sowie -0,32 V bzw. -0,20 V für die 5cHS- und 6cLS-Spezies für das anaerobe Nissle 1917 E. coli-Präparat. Die Durchschnittswerte (5cHS+6cLS) sind ähnlich zu den elektrochemisch bestimmten Emidpt = -0,297 V) für die anaerobe Präparation. Im materialwissenschaftlichen Projekt wurden mittels zeitaufgelöster SERR-Spektroskopie die Anwendbarkeit von anodisierte Titanoxid-Nanoröhren (TiO2-NTs) mit inhärent unterschiedlichen Eigenschaften für die Verstärkung von lokalisierten elektrischen Feldern (TiO2-NT|low und TiO2-NT|high für niedrige bzw. hohe Feldverstärkung; TiO2-NT|high|BD-PATP oder TiO2-NT|low|BD-PATP für die Elektroden abgeschiedenen mit dem Farbstoff Benzidin-p-Aminothiophenolat (BD-PATP)) als Substrat für laserinduzierte photokatalytischen Abbau des Farbstoffs Benzidin-p-aminothiophenolat (BD-PATP) untersucht. Die für TiO2-NT|high|BD-PATP, 5,1 (1,4) s-1, gemessene Konstante der Abbaurate ist ~70 % höher als die für TiO2-NT|low|BD-PATP, 3,0 (0,6) s-1. Anlegen eines externen Potentials von +0,4 V führte zu einer signifikant höheren (2,5-fachen) Geschwindigkeitskonstanten für TiO2-NT|high|BD-PATP, 25,5 (5) s-1, gegenüber TiO2-NT|low|BD-PATP, 10,1 (3) s-1 und zeigt die verbesserte photokatalytische in Anwesenheit von elektromagnetischer Feldverstärkung nahe der Reaktionsoberfläche. Die photokatalytische Aktivität war auf eine elektronische Anregung bei 413 nm beschränkt, was auf einen Abbauweg hindeutet, der den angeregten Zustand des Farbstoffs und keine Beiträge von Ladungen der TiO2-NTs beinhaltet. Niederfrequente Raman-Messungen bei 488 nm zeigen, dass die Eg-Mode von TiO2-NT|high im Vergleich zu TiO2-NT|low heruntergeschaltet ist (145,5 cm-1 vs. 147,3 cm-1), was auf eine mögliche größenabhängige, ladungsübertragende Oberflächenverstärkung der Raman-Signale hindeutet. Die bei negativen Potentialen gemessenen hohen Kapazitätswerte mittels Impedanzspektroskopie zeigten den schlechten Elektronenakzeptorcharakter von TiO2-NTs bei diesen Potentialen. Möglicherweise ist dies auf Proton/Kation-Interkalationseffekt zurückzuführen, was die Rekombinationsrate von injiziertem Elektron und oxidiertem Farbstoff erhöht. Andererseits wiesen die niedrigeren Kapazitäten von TiO2-NT bei positiven Potentialen und von TiO2-NT|high im Vergleich zu TiO2-NT|low auf verbesserten Elektronenakzeptor-Charakter bei höheren Potentialen hin, welcher besonders förderlich für einen effizienten Weitertransport der Elektronen von der Oberfläche zum Inneren hin ist. Auf dieser Grundlage kann die höhere Zerfallsrate für TiO2-NT|high bei +0,4 V durch einen kombinierten Effekt aus besseren Elektronenakzeptoreigenschaften und der Fähigkeit des Materials, Photonen einzufangen, gerechtfertigt werden

Porous Inorganic Nanomaterials: Their Evolution towards Hierarchical Porous Nanostructures

The advancement of both porous materials and nanomaterials has brought about porous nanomaterials. These new materials present advantages both due to their porosity and nano-size: small size apt for micro/nano device integration or in vivo transport, large surface area for guest/target molecule adsorption and interaction, porous channels providing accessibility to active/surface sites, and exposed reactive surface/active sites induced by uncoordinated bonds. These properties prove useful for the development of different porous composition types (metal oxides, silica, zeolites, amorphous oxides, nanoarrays, precious metals, non-precious metals, MOFs, carbon nanostructures, MXenes, and others) through different synthetic procedures—templating, colloidal synthesis, hydrothermal approach, sol-gel route, self-assembly, dealloying, galvanostatic replacement, and so—for different applications, such as catalysis (water-splitting, etc.), biosensing, energy storage (batteries, supercapacitors), actuators, SERS, and bio applications. Here, these are presented according to different material types showing the evolution of the structure design and development towards the formation of hierarchical porous structures, emphasizing that the formation of porous nanostructures came about out of the desire and need to form hierarchical porous nanostructures. Common trends observed across these different composition types include similar (aforementioned) applications and the use of porous nanomaterials as templates/precursors to create novel ones. Towards the end, a discussion on the link between technological advancements and the development of porous nanomaterials paves the way to present future perspectives on these nanomaterials and their hierarchical porous architectures. Together with a summary, these are given in the conclusion

Electromagnetic Field Enhancement of Nanostructured TiN Electrodes Probed with Surface-Enhanced Raman Spectroscopy

We present a facile approach for the determination of the electromagnetic field enhancement of nanostructured TiN electrodes. As model system, TiN with partially collapsed nanotube structure obtained from nitridation of TiO2 nanotube arrays was used. Using surface-enhanced Raman scattering (SERS) spectroscopy, the electromagnetic field enhancement factors (EFs) of the substrate across the optical region were determined. The non-surface binding SERS reporter group azidobenzene was chosen, for which contributions from the chemical enhancement effect can be minimized. Derived EFs correlated with the electronic absorption profile and reached 3.9 at 786 nm excitation. Near-field enhancement and far-field absorption simulated with rigorous coupled wave analysis showed good agreement with the experimental observations. The major optical activity of TiN was concluded to originate from collective localized plasmonic modes at ca. 700 nm arising from the specific nanostructure

Functionalized graphene with iodine and the investigation of its effect in DSSCs

Covalent modification of graphene offers an alternative approach to tailor its electronic properties. In this study, a modified Hunsdiecker reaction is used to covalently attach iodine to the graphene structure. The product was characterized using Raman Spectroscopy. Raman spectra showed a modification in the graphene structure based on changes in the D and G band relative intensities. The product was further tested in the dye-sensitized solar cell (DSC) as replacement for the common electrolyte I-/I3-. Without the presence of the iodine-based electrolyte, and using only the modified graphene, the DSSC registered photoactivity but at very low photovoltage

Thiophene-Based Conjugated Acetylenic Polymers with Dual Active Sites for Efficient Co-Catalyst-Free Photoelectrochemical Water Reduction in Alkaline Medium

Although being attractive materials for photoelectrochemical hydrogen evolution reaction (PEC HER) under neutral or acidic conditions, conjugated polymers still show poor PEC HER performance in alkaline medium due to the lack of water dissociation sites. Herein, we demonstrate that tailoring the polymer skeleton from poly(diethynylthieno[3,2-b]thiophene) (pDET) to poly(2,6-diethynylbenzo[1,2-b:4,5-b′]dithiophene (pBDT) and poly(diethynyldithieno[3,2-b:2′,3′-d]thiophene) (pDTT) in conjugated acetylenic polymers (CAPs) introduces highly efficient active sites for water dissociation. As a result, pDTT and pBDT, grown on Cu substrate, demonstrate benchmark photocurrent densities of 170 μA cm−2 and 120 μA cm−2 (at 0.3 V vs. RHE; pH 13), which are 4.2 and 3 times higher than that of pDET, respectively. Moreover, by combining DFT calculations and electrochemical operando resonance Raman spectroscopy, we propose that the electron-enriched Cβ of the outer thiophene rings of pDTT are the water dissociation active sites, while the −C≡C− bonds function as the active sites for hydrogen evolution