Conspectus Catalysts for light-driven water oxidation are a critical component for development of solar fuels technology. The multielectron redox chemistry required for this process has been ...successfully deployed on a global scale in natural photosynthesis by green plants and cyanobacteria using photosystem II (PSII). PSII employs a conserved, cuboidal Mn4CaOX cluster called the O2-evolving complex (OEC) that offers inspiration for artificial O2-evolution catalysts. In this Account, we describe our work on manganese model chemistry relevant to PSII, particularly the functional model MnIII/IV 2(terpy)2(μ-O)2(OH2)2(NO3)3 complex (terpy = 2,2′;6′,2″-terpyridine), a mixed-valent di-μ-oxo Mn dimer with two terminal aqua ligands. In the presence of oxo-donor oxidants such as HSO5 –, this complex evolves O2 by two pathways, one of which incorporates solvent water in an O–O bond-forming reaction. Deactivation pathways of this catalyst include comproportionation to form an inactive MnIVMnIV dimer and also degradation to MnO2, a consequence of ligand loss when the oxidation state of the complex is reduced to labile MnII upon release of O2. The catalyst’s versatility has been shown by its continued catalytic activity after direct binding to the semiconductor titanium dioxide. In addition, after binding to the surface of TiO2 via a chromophoric linker, the catalyst can be oxidized by a photoinduced electron-transfer mechanism, mimicking the natural PSII process. Model oxomanganese complexes have also aided in interpreting biophysical and computational studies on PSII. In particular, the μ-oxo exchange rates of the Mn–terpy dimer have been instrumental in establishing that the time scale for μ-oxo exchange of high-valent oxomanganese complexes with terminal water ligands is slower than O2 evolution in the natural photosynthetic system. Furthermore, computational studies on the Mn–terpy dimer and the OEC point to similar MnIV–oxyl intermediates in the O–O bond-forming mechanism. Comparison between the OEC and the Mn–terpy dimer indicates that challenges remain in the development of synthetic Mn water-oxidation catalysts. These include redox leveling to couple multielectron reactions with one-electron steps, avoiding labile MnII species during the catalytic cycle, and protecting the catalyst active site from undesired side reactions. As the first example of a functional manganese O2-evolution catalyst, the Mn–terpy dimer exemplifies the interrelatedness of biomimetic chemistry with biophysical studies. The design of functional model complexes enriches the study of the natural photosynthetic system, while biology continues to provide inspiration for artificial photosynthetic technologies to meet global energy demand.
Four manganese complexes of pentadentate ligands have been studied for their ability to act as oxygen evolution catalysts in the presence of Oxone or hydrogen peroxide. The complexes ...Mn(PaPy3)(NO3)(ClO4) (1) (PaPy3H = N,N-bis(2-pyridylmethyl)-amine-N-ethyl-2-pyridine-2-carboxamide) and Mn(PaPy3)(μ-O)(PaPy3)Mn(ClO4)2 (2) feature an anionic carboxamido ligand trans to the labile sixth coordination site, while Mn(N4Py)OTf(OTf) (3) (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) and Mn(PY5)(OH2)(ClO4)2 (4) (PY5 = 2,6-bis(bis(2-pyridyl)methoxymethane)-pyridine) have neutral ligands of varying flexibility. 1 and 2 are shown to evolve oxygen in the presence of either Oxone or hydrogen peroxide, but 3 evolves oxygen only in the presence of hydrogen peroxide. 4 is inactive. The activity of 1 and 2 with Oxone suggests that the presence of an anionic N-donor ligand plays a role in stabilizing putative high-valent intermediates. Anionic N-donor ligands may be viewed as alternatives to μ-oxo ligands that are prone to protonation in low-valent Mn species formed during a catalytic cycle, resulting in loss of catalyst structure.
Creating instructional activities and assessments that align with expected learning outcomes can improve student learning. Communicating learning expectations to students may lead to better student ...performance and an increase in student perceptions of the fairness of the assessment tools. One tool for communicating learning outcomes is the distribution of an exam “blueprint”, a document that correlates student learning outcomes with the expected level of performance and the relative weight on the exam. In this study, exam blueprints were prepared and distributed to students in an inorganic chemistry course. Students were surveyed about their use of the blueprints after each exam and interviewed about their perceptions of the congruence between assessments and instruction as well as their use of the blueprints. Students report using the blueprints as both organizational and metacognitive tools by emphasizing heavily weighted objectives. Overall, the blueprints were an effective tool for facilitating instructor–student communication as well as generating positive student attitudes toward exams, even though exam scores did not increase.
Light-driven water oxidation for solar fuels Young, Karin J.; Martini, Lauren A.; Milot, Rebecca L. ...
Coordination chemistry reviews,
November 2012, 2012-11-01, 2012-11-00, 20121101, Letnik:
256, Številka:
21-22
Journal Article
Recenzirano
Odprti dostop
. Display omitted
► Anodes for light-driven water oxidation. ► Design includes semiconductor, light-harvesting molecule, and catalyst. ► Integration of components is greatest challenge.
Light-driven ...water oxidation is an essential step for conversion of sunlight into storable chemical fuels. Fujishima and Honda reported the first example of photoelectrochemical water oxidation in 1972. In their system, TiO2 was irradiated with ultraviolet light, producing oxygen at the anode and hydrogen at a platinum cathode. Inspired by this system, more recent work has focused on functionalizing nanoporous TiO2 or other semiconductor surfaces with molecular adsorbates, including chromophores and catalysts that absorb visible light and generate electricity (i.e., dye-sensitized solar cells) or trigger water oxidation at low overpotentials (i.e., photocatalytic cells). The physics involved in harnessing multiple photochemical events for multi-electron reactions, as required in the four-electron water-oxidation process, has been the subject of much experimental and computational study. In spite of significant advances with regard to individual components, the development of highly efficient photocatalytic cells for solar water splitting remains an outstanding challenge. This article reviews recent progress in the field with emphasis on water-oxidation photoanodes inspired by the design of functionalized thin-film semiconductors of typical dye-sensitized solar cells.
Climate change is a critical scientific and social issue of our time, yet the topic is not frequently discussed by the general public. Additionally, misconceptions about the topic persist. One ...important aspect of climate change is the greenhouse effect. This activity adds a greenhouse gas discussion to an existing module about molecular shape and modeling. The module links the greenhouse effect to climate change. The activity has been used in several introductory chemistry settings. A discussion of student-generated answers and student-reported learning gains is presented.
Late-transition-metal catalysts for polymerization of olefins have drawn a significant amount of attention owing to their ability to tolerate and incorporate polar comonomers. However, a systematic ...way to experimentally quantify the electronic properties of the ligands used in these systems has not been developed. Quantified ligand parameters will allow for the rational design of tailored polymerization catalysts, which would target specific polymer properties. We report a series of platinum complexes bearing bisphosphinemonoxide ligands, which resemble those used in the polymerization catalysts of Nozaki and Chen. Their electronic properties are investigated experimentally, and trends are rationalized by using computed spectral properties. Benchmarking computational data with known experimental parameters further enhances the utility of both methods for determining optimal ligands for catalytic application.
In this laboratory experiment, students evaluated three silver(I) complexes as potential additives for dental adhesives based on bacterial growth inhibition, heat stability, water insolubility, and ...cost-effectiveness. Each student prepared and analyzed a cyanoxime ligand and its corresponding silver(I) complex. Students characterized the antibacterial activity of the silver complexes against E. coli using a Kirby–Bauer disk-diffusion test. Laboratory data were shared among students to compare observed properties to determine which derivative is the most suitable. This multiweek experiment was used in inorganic chemistry laboratory courses to demonstrate the application of inorganic chemistry to biomedicine. The framework of the experiment was developed by a multi-institutional collaboration, and we highlight how the general procedures of the experiment were adapted to meet the needs of varying courses and contexts.
We find that crystallographically resolved Ti17O24(OPr i )20 nanoparticles, functionalized by covalent attachment of 4-nitrophenyl-acetylacetonate or coumarin 343 adsorbates, exhibit hole injection ...into surface states when photoexcited with visible light (λ = 400–680 nm). Our findings are supported by photoelectrochemical measurements, EPR spectroscopy, and quantum dynamics simulations of interfacial charge transfer. The underlying mechanism is consistent with measurements of photocathodic currents generated with visible light for thin layers of functionalized polyoxotitanate nanocrystals deposited on FTO working electrodes. The reported experimental and theoretical analysis demonstrates for the first time the feasibility of p-type sensitization of TiO2 solely based on covalent binding of organic adsorbates.
Connecting chemical concepts with real-world applications has been demonstrated to increase persistence, student attitudes, and performance. In a one-semester general chemistry course, most ...laboratory exercises were designed to have direct implications on real-world issues, and students were asked to consider these implications. Students blogged about an issue related to one of the lab exercises and responded to classmates’ blog postings. Surveys after the implementation of the application-based laboratory curriculum suggest students were able to more clearly connect course material with the societal impact of chemistry.
Interfacial electron transfer (IET) between a chromophore and a semiconductor nanoparticle is one of the key processes in a dye-sensitized solar cell. Theoretical simulations of the electron transfer ...in polyoxotitanate nanoclusters Ti17O24(OPri)20 (Ti 17 ) functionalized with four p-nitrophenyl acetylacetone (NPA-H) adsorbates, of which the atomic structure has been fully established by X-ray diffraction measurements, are presented. Complementary experimental information showing IET has been obtained by EPR spectroscopy. Evolution of the time-dependent photoexcited electron during the initial 5 fs after instantaneous excitation to the NPA LUMO + 1 has been evaluated. Evidence for delocalization of the excitation over multiple chromophores after excitation to the NPA LUMO + 2 state on a 15 fs time scale is also obtained. While chromophores are generally considered electronically isolated with respect to neighboring sensitizers, our calculations show that this is not necessarily the case. The present work is the most comprehensive study to date of a sensitized semiconductor nanoparticle in which the structure of the surface and the mode of molecular adsorption are precisely defined.
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