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Journal Archives

I had no idea that Trump had British relatives, and that these relatives visited New Zealand.

Tourists From Hell Visit New Zealand And The Whole Country Unites Against Them

Two nice boys playing Cello.

Government for the people, BY the people, FOR the people, OF the people, HAS vanished.

What we can say about James Buchanan, who was generally considered the worst President in US history, was a least the crisis that he failed miserably to address, the horror of human slavery, existed before he took office.

There had been many threats to break up the Union because Southern racists hated and exploited African Americans with more enthusiasm than they loved their country, just as Trump today hates Mexicans more than he loves Americans. (He loves nothing, save his withered self.)

It was fortunate that the United States has a man like Lincoln - from whose famous Gettysburg address the title here, of course, is modified - to succeed Buchanan.

Lincoln of course, cared what history would think of him, and Lincoln had something missing today in the party he helped found, intelligence and integrity and patriotism.

The two new candidates for succeed Buchanan in the minds of future historians, should historians exist, Trump and Bush Jr, manufactured crises, Bush in Iraq, Trump, even more mindlessly, at the Mexican border.

When Trump is done, I should not be surprised if the Mexican army could kick down the walls, take back Texas, New Mexico, Arizona and California, he is so weak, so ignorant, so vicious.

He is destroying this government, with the complicity of many of those in it. It is interesting that the same general area responsible for the Civil War, is also responsible for the destruction of the American Government 150 years after the fact.

Carbon Dioxide, Oxygen Depletion, and the Mass Extinction in the Permian Era.

The paper I'll discuss in this post is this one: Temperature-dependent hypoxia explains biogeography and severity of end-Permian marine mass extinction (Penn et al, Science, (2018) Vol. 362, Issue 6419, eaat1327).

This paper is the source material for a news article which came to my attention by a post here: Stanford Study: We Will Be 20% Of The Way To Permian Extinction 2.0 By 2100 With Business As Usual

From the introduction:

Volcanic greenhouse gas release is widely hypothesized to have been the geological trigger for the largestmass extinction event in Earth’s history at the end of the Permian Period [~252 million years (Ma) ago] (1, 2). At least two-thirds of marine animal genera and a comparable proportion of their terrestrial counterparts were eliminated, but the mechanisms connecting environmental change to biodiversity collapse remain strongly debated. Geological and geochemical evidence points to high temperatures in the shallow tropical ocean (3, 4), an expansion of anoxic waters (5–8), ocean acidification (9–12), changes in primary productivity (13, 14), and metal (15) or sulfide (16, 17) poisoning as potential culprits. However, a quantitative, mechanistic framework connecting climate stressors to biological tolerance is needed to assess and differentiate among proposed proximal causes.

In this study, we tested whether rapid greenhouse warming and the accompanying loss of ocean O2—the two best-supported aspects of end- Permian environmental change—can together account for the magnitude and biogeographic selectivity of end-Permianmass extinction in the oceans. Specifically, we simulated global warming across the Permian/Triassic (P/Tr) transition using a model of Earth’s climate and coupled biogeochemical cycles, validated with geochemical data.

This is an in silico evaluation, since the experimental loading of the entire atmosphere with excess carbon dioxide, while well underway, has not been completed, although some preliminary intermediate results are currently being observed. The experimental portion of the work described herein - other than burning all of the world's fossil fuels and dumping the waste in the atmosphere just described - is limited to viewing the metabolic effects of oxygen depletion on extant species. (Trilobites were not available for testing.) The in silico data is also compared with the fossil record, including oxygen isotope ratios in fossil conodonts, eel like animals that lived in those time, generally known from fossils of their teeth.

The following graphic from the paper touches on that point:


The caption:

• Fig. 1 Permian/Triassic ocean temperature and O2.
(A) Map of near-surface (0 to 70 m) ocean warming across the Permian/Triassic (P/Tr) transition simulated in the Community Earth System Model. The region in gray represents the supercontinent Pangaea. (B) Simulated near-surface ocean temperatures (red circles) in the eastern Paleo-Tethys (5°S to 20°N) and reconstructed from conodont δ18O apatite measurements (black circles) (4). The time scale of the δ18O apatite data (circles) has been shifted by 700,000 years to align it with δ18Oapatite calibrated by U-Pb zircon dates (open triangles) (1), which also define the extinction interval (gray band). Error bars are 1°C. (C) Simulated zonal mean ocean warming (°C) across the P/Tr transition. (D) Map of seafloor oxygen levels in the Triassic simulation. Hatching indicates anoxic regions (O2 < 5 mmol/m^3). (E) Simulated seafloor anoxic fraction ƒanox (red circles). Simulated values are used to drive a published one-box ocean model of the ocean’s uranium cycle (8) and are compared to δ238U isotope measurements of marine carbonates formed in the Paleo-Tethys (black circles). Error bars are 0.1‰. (F) Same as in (C) but for simulated changes in O2 concentrations (mmol/m^3).

The test animal used to perhaps model metabolism is the common crab found along the East Coast of North America Cancer irroratus. Crustaceans, like the trilobites, which inhabited the oceans for 280 million years before their extinction in this event, are members of the phylum Euarthropoda (Arthropods) and like the trilobites, feature an exoskeleton that probably was fairly acid sensitive. It is not clear that the extinction of the trilobites was a function of increased acidity owing to the carbon dioxide content of the oceans, or whether it derived from oxygen depletion or perhaps both. The authors discuss this briefly in the discussion, but in a rather general and somewhat speculative way.

With this editor and the type of text used by Science I cannot produce the equation for the "metabolic index" used here, but for those with a modicum of a science back ground, this index is proportional to the partial pressure of oxygen divided by a term that looks very much like an Arrhenius term, an exponential operator on the negative value of energy (here measured in electron-volts), divided by the Boltzman constant (R/No) times the difference between reciprocal temperatures. The proportionality constant has units of inverse pressure and therefore the metabolic index, Φ, is dimensionless. This metabolic index (which differs from what your fitbit might put out or what you can see on a "lose your fat and look good" website) is described here: Climate change tightens a metabolic constraint on marine habitats, which seems to be along the same lines as the paper under discussion.

A graphic about the metabolic index:


The caption:

• Fig. 2 Physiological and ecological traits of the Metabolic Index (Φ ) and its end-Permian distribution.
(A) The critical O2 pressure (pO2crit) needed to sustain resting metabolic rates in laboratory experiments (red circles, Cancer irroratus) vary with temperature with a slope proportional to Eo from a value of 1/Ao at a reference temperature (Tref), as estimated by linear regression when Φ = 1 (19). Energetic demands for ecological activity increase hypoxic thresholds by a factor Φcrit above the resting state, a value estimated from the Metabolic Index at a species’ observed habitat range limit. (B) Zonal mean distribution of Φ in the Permian simulation for ecophysiotypes with average 1/Ao and Eo (~4.5 kPa and 0.4 eV, respectively). (C and D) Variations in Φ for an ecophysiotype with weak (C) and strong (D) temperature sensitivities (Eo = 0 eV and 1.0 eV, respectively), both with 1/Ao ~ 4.5 kPa. Example values of Φcrit (black lines) outline different distributions of available aerobic habitat for a given combination of 1/Ao and Eo.

Text touching on the metabolic index is this paper:

pO2 and T are the O2 partial pressure and temperature of ambient water, respectively; kB is Boltzmann’s constant; and the parameters Ao (kPa^(−1)) and Eo (eV) represent fundamental physiological traits of a species. The inverse of Ao (i.e., 1/Ao, in kPa) is the minimum pO2 that can sustain the resting metabolic rate (i.e., the “hypoxic threshold”) at a reference temperature (Tref), and Eo is the temperature sensitivity of that threshold (Fig. 2A). The Metabolic Index measures the capacity of an environment to support aerobic activity by a factor of F above an organism’sminimumrequirement in a complete resting state (F = 1). For both marine and terrestrial animals, the energy required for sustained activity (e.g., feeding, reproduction, defense) is elevated by a factor of ~1.5 to 7 above resting metabolic demand (18, 25) and represents an ecological trait, termedFcrit. If climate warming and O2 loss reduce the Metabolic Index for an organism below its species-specific Fcrit, the environment would no longer have the capacity to support active aerobic metabolism and, by extension, long-term population persistence.

The graphic immediately following the one above:


The caption:

• Fig. 3 Aerobic habitat during the end-Permian and its change under warming and O2 loss.
(A) Percentage of ocean volume in the upper 1000 m that is viable aerobic habitat (Φ ≥ Φcrit) in the Permian for ecophysiotypes with different hypoxic threshold parameters 1/Ao and temperature sensitivities Eo. (B) Relative (percent) change in Permian aerobic habitat volume (ΔVi, where i is an index of ecophysiotype) under Triassic warming and O2 loss. Colored contours are for ecophysiotypes with Φcrit = 3. Measured values of 1/Ao and Eo in modern species are shown as black symbols, but in (B) these are colored according to habitat changes at a species’ specific Φcrit where an estimate of this parameter is available. The gray region at upper left indicates trait combinations for which no habitat is available in the Permian simulation.

Some information about the distribution of oxygen depletion in the oceans:


Fig. 4. Global and regional extinction at the end of the Permian. (A) Global extinction versus latitude, as predicted for model ecophysiotypes and observed in marine genera from end-Permian fossil occurrences in the Paleobiology Database (PBDB). Model extinction is calculated from the simulated changes in Permian global aerobic habitat volume (DVi) under Triassic warming and O2 loss (19). The maximum depth of initial habitat and fractional loss of habitat resulting in extinction (Vcrit) are varied from 500 to 4000 m (colors) and from 40 to 95% (right-axis labels), respectively.The observed extinction of genera combines occurrences from all phyla in the PBDB (points). Error bars are the range of genera extinction across two taxonomic groupings: phyla multiply sampled in the modern physiology data (arthropods, chordates, and mollusks) and all other phyla. Latitude bands with fewer than five Permian fossil collections are excluded. The average range is used for latitude bands missing extinction estimates from both taxonomic groupings (i.e., 80°S, 30°S, and 40°N). The main latitudinal trend—increased extinction away from the tropics—is found when including all data together and when restricting to the best-sampled latitude bands (fig. S14). In all panels, model values are averaged across longitude and above 500 m. (B) Average hypoxic threshold and Fcrit across ecophysiotypes versus latitude in the Permian. In (B) to (D), shading represents the 1s standard deviation at each latitude. (C) Regional extinction (i.e., extirpation) versus latitude for model ecophysiotypes, with individual contributions from warming and the loss of seawater O2 concentration. Extirpation occurs in locations where the Metabolic Index meets the active demand of an ecophysiotype in the Permian (F ≥ Fcrit) but falls below this threshold in the Triassic (F < Fcrit). (D) Same as (C) but including globally extinct ecophysiotypes (using a maximum habitat depth of 1000 m and Vcrit = 80%), and as observed in marine genera from end-Permian and early Triassic fossil occurrences of all phyla in the PBDB. Observed extirpation magnitudes are averaged across tropical and extratropical latitude bands (red points and horizontal lines). Regional 1s standard deviations are shown as vertical lines.

The authors conclude with somewhat obvious remarks on the relevance of this study to the present times:

The end-Permian mass extinction resulted in the largest loss of animal diversity in Earth’s history, and its proposed geologic trigger—volcanic greenhouse gas release—is analogous to anthropogenic climate forcing. Predicted patterns of future ocean O2 loss under climate change (30, 31) are broadly similar to those simulated here for the P/Tr boundary. Moreover, greenhouse gas emission scenarios projected for the coming centuries (32) predict a magnitude of upper ocean warming by 2300 CE that is ~35 to 50% of that required to account for most of the end-Permian extinction intensity. Given the fundamental nature of metabolic constraints from temperature-dependent hypoxia in marine biota, these projections highlight the potential for a future mass extinction arising from depletion of the ocean’s aerobic capacity that is already under way.

But you already knew that, didn't you?

To be clear, this paper refers to oxygen in the oceans, and not the atmosphere. Almost all of the oxygen now on earth originates in the oceans, but it's not clear how it partitions between the oceans and the air. In general, gases are less soluble in hot water than in cold water, as is clear to anyone who's messed around with carbonated beverages, but I'm not aware in any quantitative sense of how these solubility relations relate to oxygen as compared with carbon dioxide. (The latter is controlled, in water, by the equilibrium between solvated CO2, its water adduct, carbonic acid, bicarbonate and carbonate, all of which are present.) It is quite possible that the warm surface layers, rich with algae or other photosynthetic species, cranked out lots of oxygen after the Permian extinction, but that it all went into the air and did not remain in the ocean.

(From the text of the paper, one factor seems to have been the circulation patterns of oceanic water, which were arrested by the heating.)

I didn't mean to divert your attention from all the hoopla surrounding the orange fool, but frankly, he doesn't matter and has never mattered, and his ultimate significance will prove to be that of Caligula, so much as Caligula matters today - he doesn't - except for the amusing historical fact that Caligula put a horse in the Senate and the orange idiot has a turtle in the Senate.

Same difference.

Have a nice day tomorrow.

Metal Free Thermochemical Water Splitting at Unusually Mild Conditions.

The paper I'll discuss in this post is this one: Phosphorus-Doped Graphene as a Metal-Free Material for Thermochemical Water Reforming at Unusually Mild Conditions (Garcia et al ACS Sustainable Chem. Eng., 2019, 7 (1), pp 838–846.

Recently in this space I discussed the thermochemical splitting of carbon dioxide (into CO and O2 gases) using a cerium oxide based catalyst in which the oxygen evolution reaction took place at 1400C, showing that there is - as currently operated using "simulated solar energy" - not enough cerium on earth to split one billion tons of carbon dioxide, using either solar thermal or nuclear energy (although nuclear is considerably less onerous in terms of putative cerium demands). One billion tons of carbon dioxide about 3% of what we currently dump each year into the planetary atmosphere.

Here's that post: Cerium Requirements to Split One Billion Tons of Carbon Dioxide, the Nuclear v Solar Thermal cases

From my perspective, the thermochemical splitting of either carbon dioxide or water is probably the only serious manner in which climate change can be reversed, and even if taken seriously - there are few people on this planet left or right who are serious about addressing climate change - it would still be a long shot, but, as the only shot with a modicum of probable success, one worth taking.

Scientists however, continue to work on the problem.

I have spent many years considering thermochemical cycles for splitting either water or carbon dioxide using nuclear energy (or less seriously solar thermal energy), and most, with a few exceptions, involve metals - the main exception being the famous sulfur iodine cycle (which has metal based modifications however) - my personal favorite being the zinc oxide cycle for reasons I won't go into here. The one I'll discuss here - it's really a half reaction, not a full cyclic reaction - is new to me, I must admit. It clearly is not scalable or even worthy of consideration of scale, but the research is extremely interesting and certainly comes under the rubric of "a good lead," particularly since the required temperatures for hydrogen evolution are unusually low, about 900 C.

This involves an interesting material, graphene, which has been the subject of huge amounts of research in materials science.

From the introduction:

Among the most general ways to obtain graphene-related materials, the one starting with graphite that is submitted to deep chemical oxidation to graphite oxide, followed by subsequent exfoliation to graphene oxide (GO), and final chemical reduction provides a graphene material denoted as reduced graphene oxide (r-GO). r-GO is among the most widely studied graphene materials because it can be prepared in a reliable way in gram scale (Scheme 1).(1,2)


Scheme 1. Process of Preparation of r-GO from Graphite Involving Oxidation to Graphite Oxide and Exfoliation to GOa

a(i) Chemical oxidation, (ii) exfoliation, and (iii) chemical reduction.

The above process to perform graphite exfoliation by conversion of graphene (G) into GO is based on the possibility of carrying out the oxidation and reduction of G/GO, increasing the oxygen content to above 50 wt % from G to GO, with a certain degree of control, and then, subsequently decreasing this oxygen content from 50 to about 10 wt %, which is characteristic of r-GO. This ability to increase and decrease the oxygen content on G sheets is reminiscent of the so-called Mars van Krevelen oxidation/reduction of nonstoichiometric transition metal oxides, in where the oxygen content of the inorganic oxide can be varied to a certain extent, generally much lower than the one commented in the case of G/GO/r-GO.(3) This Mars van Krevelen mechanism has been, however, advantageously used to promote catalytic oxidations/reductions, and more related to the present work, this swing between the two related materials with different oxygen contents is at the base of the thermochemical cycles for water splitting or steam reforming.

In steam reforming, a substrate (S) promotes the reduction of water, resulting in the generation of hydrogen (eq 1) and substrate oxidation. If the oxidized form of the substrate, most frequently inorganic oxides (for instance ceria, perovskites, or spinel ferrites) due to the required thermal stability (T = 1300–1500 °C), can subsequently be thermally reduced by oxygen evolution (eq 2), then the two steps can serve to perform cyclically the overall water splitting.(4,5) It has been reported, that one of the main challenges in thermochemical water reforming is the development of materials able to promote efficiently thermochemical transformations at low temperatures (<1100 °C), especially for large scale production.(5−7)

Graphene is a form of carbon in which all of the carbon atoms are bonded together in a plane, which is also characteristic of graphite, but unlike graphite, the graphene is exactly one atom thick. The layers are not connected.

What is interesting here is that the carbon source for the graphene is biomass, as opposed to a dangerous fossil fuel source, meaning that it is possible that this approach is sustainable, at least on a moderate scale.

One source is alginic acid, which is obtained from brown algae, many species of which are believed to be excellent tools for carbon capture from the atmosphere. The other is phytic acid, which is per-phosphorylated inositol, which is found in beans, and notably in manure, where it is responsible for the environmentally problematic concentration of phosphorous.

Graphene in the presence of steam is reformed normally, yielding carbon dioxide and hydrogen - and the reforming of biomass is probably an excellent approach to carbon capture as well as thermochemical splitting - however there are certain mineral considerations that represent significant hurdles.

In order to prevent the reformation of graphene, the authors here have phosphorylated graphene oxide.

Some pictures from the paper, first the synthesis of the graphene (and its oxide):

The caption:

Scheme 1. Process of Preparation of r-GO from Graphite Involving Oxidation to Graphite Oxide and Exfoliation to GO

(i) Chemical oxidation, (ii) exfoliation, and (iii) chemical reduction.

Next, the xray photoelectron spectrum (XPS) of the graphene:

The caption:

Figure 1. XPS survey spectrum (a) and C 1s (b), O 1s (c), and P 2p (d) high-resolution peaks recorded for Phy-G and their corresponding best deconvolution fits.

The chemical nature of the phosphorous attached to the graphene can be discerned from nuclear magnetic resonance spectrometry (NMR) since the only isotope of phosphorous that occurs naturally, 31P, is magnetically active. The 31P spectrum:

The caption:

Figure 2. Solid state 31P NMR spectrum of Phy-G, with indication of the assignment based on the literature.(31−34)

"Phy-G" is phosphorous doped graphene.

High resolution tunneling electron microscope images:

Atomic force microscope images:

The caption:

Figure 4. AFM images of Phy-G samples. (a) General wide-field image of Phy-G samples showing a 2D sheet on which smaller particles are supported. (b) 3D image of a wide-field region of the same Phy-G sample. (c) Image corresponding to a part of a 2D sheet, where the blue, green, and red lines indicate the height measurements. (d) Height measurement along the lines indicated with the same colors in image (c).

The hydrogen evolution over 21 cycles:

The caption:

Figure 6. H2 evolution upon 21 consecutive activation-oxidation cycles (red). The temperature cycles have been included in blue.

The authors do some in silico calculations. Here's some fun details of their approach:

The potential energy calculations were performed using spin polarized DFT with the VASP 5.4.1 code (Vienna ab inito simulation program) developed at the Fakultät für Physik of the Universität Wien.(20) We used the projector augmented wave (PAW) scheme(21) with the Perdew–Burke–Ernzerhof (PBE)(22) exchange and correlation (xc)-functional and a plane-wave energy cutoff of 400 eV. The system was modeled by a hexagonal 5 × 5 unit cell containing 50 atoms with a P atom substituting a C atom (2% doping),(23) with an optimized C–C bond separation of 1.429 Å and a 14 Å separation between graphene sheets. Γ-point sampling of the reciprocal space was used in the optimizations and the nudged elastic band (NEB)(24) method calculations.

Here's what they found:

The caption:

Figure 8. (a) Calculated PBE free energy profile (kcal/mol) at 650 °C for the stepwise thermochemical water splitting reaction on P-doped graphene (2%). The approximate transition structures TS1 and TS2 are the highest points on the NEB profiles (see Computational Details section). The structures include the most significant bond lengths in Å and angles in °. (b) Calculated PBE free energy in kcal/mol (relative to the R structure) for the intermediates formed in three successive hydrolysis steps (addition of a H2O molecule and cleavage of a P–C bond at every step) resulting in formation of phosphoric acid. Note that, in both figures, only the carbon atoms of the unit cell in the vicinity of the catalytic center are displayed.

Of course the main problem with this system is that oxygen is not evolved, the reduction of water to hydrogen is first accomplished by the oxidation of phosphorous, and finally, after a number of cycles, to the oxidation of the graphene, that is, ultimate reformation.

The authors write:

Lack of O2 Evolution
It is worth noting, that evolution of O2 was not detected in any step in these experiments, either using Phy-G or G, indicating that eq 2 does not take place. However, since H2 evolves in the hydrolysis steps, it is clear that the O atoms present in H2O must remain attached in the Phy-G catalyst or could promote some decomposition. In order to address the nature of the oxygenated groups being formed on Phy-G, Raman spectroscopy and XPS analysis of the Phy-G catalyst after extensive use in the thermochemical H2O reactions were carried out.

The XPS P 2p peaks of Phy-G, after its use in steam reforming and its best deconvolution fit, are presented as Figure 7, which also provides a comparison with the P 2p peak of the fresh sample. The first information provided by XPS was a decrease in the proportion of P quantified by the decrease of the P/C atomic ratio from the initial 0.072 value for the fresh Phy-G material to the 0.021 ratio determined for the Phy-G sample after its use in the thermochemical H2 generation from H2O. Comparison of P 2p spectra of fresh and used Phy-G confirms a shift in the P 2p peak of the used Phy-G toward higher binding energies, indicating the increasing presence of oxidized P in the catalyst composition. In addition, as it can be observed in Figure 7, the P 2p peak of Phy-G after the reaction presents only two main components instead of three. In this case, the component at 132 eV, related to the P–C bond, is no longer present, while components at 134 and 136 eV in relative percentages of 74.5 and 25.5%, respectively, are related to the formation of the P–O bonds...

...The solid-state 31P NMR spectra of fresh and used Phy-G have been similarly recorded, and they are compared in Figure S7. As it can be seen there, the contribution of peaks corresponding to triphenylphosphine and triphenylphosphine oxide has considerably decreased, while the peaks attributed to phosphate and other P oxide groups have undergone a notable increase in good agreement with the information provided by XP and Raman spectroscopies. Therefore, the incorporation of O atoms in P-doped G as phosphate groups is confirmed by three different techniques, and thus, the lack of O2 gas in the stream can be attributed to the oxophilic nature of P and also, to some degree, of graphenic C oxidation during reaction. Observation of CH4 and CO in the thermochemical cycles clearly indicates this gradual oxidation of G, since it is the most likely origin of CH4 is methanation of CO2.

Nevertheless, a cool paper, and quite interesting for the development of future catalytic systems.

An excerpt of the paper's conclusion:

It has been found experimentally that defective G obtained from biomass pyrolysis undergoes steam reforming at temperatures above 400 °C forming H2 and CO2. Grafting of P atoms on the G sheet increases considerably its stability under conditions of steam reforming. A graphenic material doped with P was obtained by pyrolysis of phytic acid. Characterization of this material shows that together with the expected P-doped G, the other nanoparticulated component is also present in much lesser proportions. Although the stability of Phy-G is notably higher than that of G, and H2 evolution is observed, no oxygen evolution could be achieved under the conditions tested. It seems that oxygen becomes too strongly attached to P atoms and also some degree of oxidation of the graphenic material to CO and CO2 (converted to CH4) is occurring...

Have a nice day tomorrow.

Reaching the end of a job interview, the Human Resources Manager asked the young engineer...

...fresh out of the university, , "And what starting salary were you looking for?"

The engineer said, "In the neighborhood of $100,000 a year, depending on the benefit's package."

The HR Manager said, "Well, what would you say to a package of $200,000 a year, 5 weeks vacation, 14 paid holidays, full medical and dental, company matching retirement fund to 50% of salary, and a company car leased every 2 years - say, a red Mercedes?"

The engineer sat up straight and said, "Wow!!! Are you joking?"

And the HR Manager said, "Of course, ...but you started it."

You know what happened to the relationship between Lise Meitner and Otto Hahn?

If you get right down to the nucleus of their relationship, well, they split.

A string theorist's husband walks in on his wife in bed with another man.

She yells, "I can explain everything!"

Polymers of Cerium and Plutonium.

The paper I'll discuss in this post is this one: Monomers, Dimers, and Helices: Complexities of Cerium and Plutonium Phenanthrolinecarboxylates (Albrecht-Schmitt*† et al Inorg. Chem., 2016, 55 (9), pp 4373–4380)

Recently in this space, I discussed, based on my knowledge of plutonium chemistry, that polymers of cerium also exist, since cerium is often utilized in the lab as a plutonium analogue: Cerium Requirements to Split One Billion Tons of Carbon Dioxide, the Nuclear v Solar Thermal cases.

As the year wound down, I decided to burn up the remaining unused "free" literature downloads connected with my ACS membership - we get 50 free papers per year with our membership - since all the major libraries were closed for the holidays. My search term was to search for recent papers in ACS journals with "plutonium" in the title.

And low and behold, I came across a paper on cerium polymers investigated along with plutonium polymers, a paper focusing on the validity of the "close analogue" association connected with the two elements.

From the introduction:

Cerium provides a useful, nonradioactive analogue of plutonium owing to their similar ionic radii when in the 4+ oxidation state, and as a result, several families of coordination complexes and materials form isomorphous series.(1-4) Examples of this include a variety of phosphonates such as M[C6H4(PO3H)(PO3H2)][C6H4(PO3H)(PO3)]3·2H2O (M = Ce, Pu),(5, 6) the cationic framework tellurites, [M2Te4O11]Cl2 (M = Ce, Pu),(7) and a large collection of sulfates.(8) However, there are notable deviations in the oxidation state, reactivity, and coordination chemistry between cerium and plutonium, as documented in the PuIV maltol complex, Pu(C6H5O3)4,(9) the mixed-valent molybdate, CsPu3Mo6O24(H2O),(10) and the hydroxypyridonate, Pu{5LIO(Me-3,2-HOPO)}2.(2) In Pu(C6H5O3)4 and Pu{5LIO(Me-3,2-HOPO)}2, the differences are subtle and lie in divergence in the point symmetry of the local coordination environments without a change in the coordination number.(2, 9)...

...To further understand the convergence and divergence in the reaction chemistry between cerium and plutonium complexes and better characterize the viability of using CeIV as a nonreactive analogue of PuIV, the mixed N- and O-donor 1,10-phenanthroline-2,9-dicarboxylic acid (PDA) was chosen as a complexant. The tetradentate PDA ligand is exceptionally suited for comparative studies with f elements. For example, many lanthanide- and actinide-containing PDA complexes have been prepared that demonstrate the ability of PDA to provide a suitable coordination environment for large, trivalent, oxophilic ions.(16-22) PDA has also provided a platform to interrogate f-element electronic structure and bonding in EuIII and TbIII complexes through sensitization studies of EuIII luminescence(18) and to evaluate the differences in the thermodynamics of complexation with the early actinides ThIV,(19) UVI,(19) and NpV.(20) This ligand is additionally attractive given that it, as well as its derivatives, are being investigated for use in the separation of americium and curium from lanthanides in advanced nuclear fuel cycles.

Apparently the plutonium in the complexes is in the +4 oxidation state, also accessible to cerium:

The complexity of the redox chemistry of plutonium is unparalleled by any other element. This makes the oxidation state assignment challenging, particularly from visual coloration alone. There are, for instance, blue compounds containing PuIV,(24, 25) although this color is normally indicative of PuIII. Likewise, PuIV complexes yield a variety of colors, with red and green being most common.(4-6) Mixtures of oxidation states are more common than not for plutonium in solution but quite rare in the solid state because crystallization is always under solubility control and may or may not reflect the dominant species in solution.(26, 27) Fortunately, the fingerprint spectra of intra-f transitions for plutonium in different oxidation states have been well established for decades, and identification of the formal charge from electronic absorption spectra is relatively straightforward, particularly in solids.(4-6) The reaction of PuIII with PDA results in the formation of a solid with a golden color that is not clearly indicative of any particular oxidation state. However, both the absorption spectrum and structural data are consistent with PuIV (vide infra), and the compound has the straightforward formulation of 3.

Plutonium is, by the way, unparalleled by any other element and in my less than humble opinion, is the key element for saving the world, despite a lot of tripe about how unacceptably "dangerous" it is.

A photograph of crystals of plutonium and cerium complexes described in this paper:

The caption:

Figure 1. Photographs of single crystals of (a) 1, (b) 2, and (c) 3.

"3" is the plutonium PDA complex, Pu(PDA)2 the other two are cerium complexes. (PDA = 1,10-phenanthroline-2,9-dicarboxylic acid)

Some other graphics from the text:

The caption:

Figure 2. View of a portion of the 1D chain in 1 formed via linking of the CeIII centers by carboxylate moieties. The local coordination environment around the cerium centers is formed via chelation by the tetradentate PDA2– anions, two water molecules, and a chloride anion. The ninth site is occupied by the oxygen atom from a carboxylate group of a crystallographically equivalent [Ce(PDA)(H2O)2Cl] structural building unit.

The caption:

Figure 3. Depictions of the two distinct substructures in 2. (a) View of helical [Ce(PDAH)(PDA)]1∞ chains formed via the bridging of [Ce(PDAH)(PDA)] units by carboxylate groups. (b) Illustration of dimers created from [Ce(PDAH)(PDA)] monomers that are again linked by carboxylate moieties. The CeIII centers are 9-coordinate within the dimers and 10-coordinate within the chains.

The caption:

Figure 4. View of the molecular structure 3 formed via the chelation of a PuIV cation by two tetradentate PDA2– anions, creating an 8-coordinate, cross-shaped geometry where the PDA2– ligands are roughly orthogonal to each other. These molecule form short π···π contacts with an intermolecular distance of 3.285(4) Å.

In their discussion the authors show that the assumption of identity in the chemistry of cerium and plutonium often does not hold. Here is the UV/Vis spectra of the analogues:

The caption:

Figure 5. Absorption spectrum acquired from a single crystal of 3 showing characteristic f–f transitions indicative of PuIV.

The caption:

Figure 6. Absorption spectrum acquired from a single crystal of 2. The intense transition at ca. 400 nm is a combination MLCT and IVCT transitions (i.e., π–π*) of the PDAHx ligands.

The caption:

Figure 7. Absorption spectrum measured from a single crystal of 1.

Some magnetic and thermal properties:

The caption:

Figure 10. Summary of the magnetic properties and heat capacity for 2 showing behavior that is consistent with that of an insulating trivalent cerium compound. (a) Inverse magnet susceptibility χ–1 = (M/H)−1 versus temperature T collected in a magnetic field H = 5 kOe. (b) Magnetization M versus H at T = 2 K. (c) Heat capacity divided by temperature C/T versus T. (d) C/T versus T2 for low T.

The conclusion of the paper:

The challenges, both real and perceived, in working with radioactive elements like plutonium necessitate the use of less nonradioactive analogues for a variety of reasons. Among the acceptable reasons for conducting chemistry with analogues of radionuclides is actually to discern differences between elements that share common physicochemical features. Cerium and plutonium both possess stable 3+ oxidation states, and both can be oxidized to 4+. CeIV and PuIV have negligibly different ionic radii, and their structural chemistry can be quite similar (vide supra). Normally, if differences occur, the plutonium system is more complex because plutonium undergoes more facile redox chemistry than cerium and readily oxidizes to states well beyond 4+. While PuIII does oxidize to PuIV when complexed by PDA, this results in a simple, molecular bis-chelate, 3, where both the structure and oxidation state assignment are straightforward. In contrast, CeIII does not undergo oxidation under these conditions, but the large size of the CeIII ion relative to PuIV results in increased coordination numbers that yield complex dimeric and polymeric structures. In addition, MLCT in the cerium compounds creates intricacies that required both extensive spectroscopic and physical property interrogation to remove ambiguity in the oxidation state assignment. These results add to the growing body of knowledge that indicates that, while analogues of radionuclides are useful guides, they should not be treated as true surrogates, particularly with plutonium.

This may all seem very esoteric, and in my previous post I argued that cerium based carbon dioxide splitting can never address the bulk of the climate change problem should future generations need to clean up our mess to simply survive, but I personally believe that thermochemical splitting can participate in the clean up.

The existence of cerium polymers, particularly as organics that can be grafted easily onto supports may serve in greatly improving the mass efficiency of cerium for this purpose, should it ever become feasible to so use cerium.

I wish you the happiest and healthiest New Year.

During the French revolution a priest, a drunk and an engineer are sent to the guillotine.

They ask the priest if he wants to face up or down when he meets his fate. The priest says he would like to face up so he will be looking towards heaven when he dies. They raise the blade of the guillotine and release it. It comes speeding down and suddenly stops just inches from his neck. The authorities take this as divine intervention and release the priest.

The drunkard comes to the guillotine next. He also decides to die face up, hoping that he will be as fortunate as the priest. They raise the blade of the guillotine and release it. It comes speeding down and suddenly stops just inches from his neck. Again, the authorities take this as a sign of divine intervention, and they release the drunkard as well.

Next is the engineer. He, too, decides to die facing up. As they slowly raise the blade of the guillotine, the engineer suddenly says, "Hey, I see what your problem is ..."
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