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NNadir

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Gender: Male
Current location: New Jersey
Member since: 2002
Number of posts: 25,745

Journal Archives

Eleanor Rigby.

Another Casualty of Trumpism: The Credibility of the FDA.

There have been some actions of the FDA with which I have disagreed, but overall, the FDA is a critical, absolutely critical regulatory agency, driven by high scientific integrity, for the maintenance of safe medications.

The FDA saves lives, and all around the world, until now, regulatory agencies all around the world have aspired to meeting its example of integrity, standards, and guidance.

Well, the orange racist unintelligent corrupt thug as greatly damaged the reputation of this important American infrastructure:

From Fierce Pharma:

Critics are slamming the FDA and Commissioner Stephen Hahn for authorizing COVID-19 plasma treatment prematurely, but the issue is much broader than one emergency use authorization. The agency's reputation is on the line. And if it falls, the pharma industry will pay a hefty price.

Since Hahn stood beside President Trump Sunday to announce the plasma authorization, critics of all kinds have lit up social media—commenting that they can’t trust the FDA, or won’t take drugs it approves or, perhaps most notably, won’t get a COVID-19 vaccine even if stamped with the agency's approval.

And there's some basis for the concerns that FDA decisionmaking has been politicized. Recently, the White House strategized about pushing AstraZeneca's vaccine to market before the election, ahead of full data from its 30,000-patient late-stage trial, according to reports. President Trump himself has repeatedly promised to have a vaccine by October. Indeed, in a controversial tweet that helped spark the plasma controversy, the president accused the agency of being part of a "deep state" effort to slow-walk vaccines until the election.

While AstraZeneca refuted reports of a fast track for its shot, telling FiercePharma it has not discussed any emergency authorization with the U.S. government, the constant swirl of rumors around vaccine approval, along with the FDA's most recent actions, have experts worried about the effects on the agency's independence and public confidence in its decisions, particularly during the pandemic.

“FDA's credibility has never been more important and more threatened simultaneously,” said Mark Senak, a public relations professional and Eye on FDA blogger, especially as phase 3 data on COVID-19 drugs and vaccines begin to come in and the need for public trust increases.

RELATED: FDA's emergency nod for convalescent plasma sparks questions of whether it's bowing to Trump

Senak has written about the problem of a politicized FDA since December, saying Monday that “if there were concerns then, it is only compounded now in the midst of a pandemic.”

Some press releases from the FDA, for instance, have made the FDA sound like cheerleaders for the Trump administration, Senak said, including the plasma release which is absolutely “cheerleader language.” The title? “FDA Issues Emergency Use Authorization for Convalescent Plasma as Potential Promising COVID–19 Treatment, Another Achievement in Administration’s Fight Against Pandemic.”

Data from The Harris Poll, which has tracked public sentiment around the coronavirus since March, shows that among trusted resources for COVID-19 information, 78% of American say scientists are trustworthy, while only 49% say the same of the White House and president.



FDA faces a reputation crisis amid Trump pressure for fast COVID action—and that's bad news for pharma

This stupid evil man doesn't care what or who he kills to satisfy his childish ego.

Don the Con with his Friends the Falwells.



Jerry Falwell Blames His Fall From Grace On His Wife.

I certainly would not wish to be a fly on the wall in a room with these sybaritic heathens.

Shelia's Party, there's a case in point; the right wing hooey sure stunk up the joint.



In honor of the national hate festival for corrupt stupid people.

Phosphate Immobilization in Wastewater Using MgO-Modified Industrial Hemp-Stem-Driven Biochar.

The paper I'll discuss in this post is this one: Strong Immobilization of Phosphate in Wastewater onto the Surface of MgO-Modified Industrial Hemp-Stem-Driven Biochar by Flowerlike Crystallization

One almost cannot be a member of my generation without having a generalized knowledge of the effects of marijuana use, which I oppose. Before everyone jumps down my throat - this happens quite a bit - this does not mean that I support criminal sanctions against marijuana, but I oppose its use, and to be frank, its open sale in the equivalent of liquor stores.

Over the years, of course, I've heard all kinds of arguments about why marijuana is good for this or that, some arguments being quite tortured frankly, but one hears them anyway. I generally don't buy them; and I've generally been dismissive of all of them.

One of the more tortured arguments I've heard - thankfully far less so recently - since I spend a lot of time thinking about climate change, is that hemp is the key to removing carbon dioxide from the air, more hemp, less climate change.

Sigh...

The world's "bad boy and bad girl" fascination with marijuana of course, has indeed, despite my distaste for the subject, resulted in some very good science however. Notably, this is true of the elucidation of the cannabanoid receptor system, which has implications far beyond their psychological effects.

For a nice brief discussion of areas of interest in this receptor system, there is in a paper about a privileged structure acting upon it, an introduction giving an overview. It's this paper: Polycyclic Maleimide-based Scaffold as New Privileged Structure for Navigating the Cannabinoid System Opportunities (Alessandra Bisi*Alessandra Bisi , Alì Mokhtar Mahmoud, Marco Allará, Marina Naldi, Federica Belluti, Silvia Gobbi, Alessia Ligresti*, and Angela Rampa* ACS Med. Chem. Lett. 2019, 10, 4, 596–600) The introduction discussing the cannabanoid systems "opportunities" is this:

The presence of an endogenous cannabinoid system (ECS) was discovered while attempting to understand the effects induced in humans by the use of Cannabis Sativa.(1) It has now become clear that ECS dysregulation is connected to pathological conditions, and thus, its modulation has gained enormous potential for intervention in multiple areas of human health. ECS is a neuromodulatory system found both in the brain and in the periphery. It consists of two G protein-coupled receptors, known as the cannabinoid type 1 (CB1) and type 2 (CB2) receptors, endogenous ligands, of which anandamide (N-arachidonoyl-ethanolamine, AEA) and 2-arachidonoylglycerol (2-AG) are the best characterized, and the enzymes that regulate their production and degradation.(1) The CB1 receptors (CB1Rs) are primarily located in the central nervous system (CNS) and represent a therapeutic target that may impact pathways that mediate pain, hunger, neurodegenerative disorders, and drug-seeking behavior, even if detrimental side effects, including psychoactivity, depression, and suicidal thoughts, could be observed. On the contrary, the CB2 receptors (CB2Rs) are mainly distributed in peripheral tissues and immune cells, and therefore, they play significant roles in pathologies involving an inflammatory component (such as pain, inflammatory bowel disease, atherosclerosis, osteoporosis, and cancer).(2) In particular, with respect to cancer, pharmacological activation of the CB2R has been shown to produce antitumor effects in different cancer types. Changes in the expression of this receptor were reported in human cancers and a correlation between its expression, histologic grade, and prognosis has been demonstrated in breast cancer,(3) glioma, hepatocellular carcinoma, pancreatic cancer, endometrial carcinoma, and leukemia.(4−6)

However, the presence of CB2-positive cells in the brain during injury and in inflammatory neurodegenerative disorders might provide a novel strategy for cannabinoid-mediated intervention against stroke-induced neurodegeneration, without the unwanted psychoactive effects related to CB1R stimulation.(7) CB2Rs are also detected in glial cells, and in particular, they are overexpressed in Aβ plaque-associated microglia, suggesting a crucial role in Alzheimer’s disease (AD).(8) Indeed, several studies have shown that Aβ-mediated activation of microglia induces the production of various proinflammatory mediators that cause neuronal dysfunction and cell death, suggesting its involvement in AD.(9)...


God bless the memory of Jerry Garcia, I guess...

The paper under discussion here - NNadir should be made to eat his words as often as is possible according to some people (to whom, regrettably, I can't listen owing to the expansion of my wonderful "ignore list" here - is about how hemp can participate in addressing a problem that really, really, really troubles me, the implications of the phosphorous cycle, a cycle which is decidedly not closed, but will need to be so in a sustainable world. It's a very serious matter.

P (phosphate) is a nonrenewable resource, which is also one of the necessary nutrients for the growth of organisms in an aquatic environment. However, excessive phosphorus in surface water will cause water eutrophication and other environmental problems, which have a huge negative impact on the aquatic ecosystem.(1) Therefore, the development of an effective and environmentally friendly method to remove and recycle phosphate from aquatic ecosystems will not only protect the water body but provide a new method for the sustainable development of phosphorus.(2)
Biological,(3) chemical,(4) ion exchange, and adsorption(5) treatment methods have commonly been used for phosphate removal. Biological processes, including activated sludge(6) and biofilm(7) techniques, are widely adopted in many countries. However, due to the sensitivity of microorganisms to water qualities,(8) including temperature and pH, this method shows limited phosphate adsorption efficiency within ∼30%. Chemical precipitation and flocculation(9) are common physical–chemical processes, which have an outstanding capacity for phosphorus removal. However, large amounts of chemical sludge and byproducts have also been produced simultaneously. The ion-exchange method applies a strong anion-exchange effect to the selective removal of phosphate, but resin is often easy to poison.(10) Compared with these methods, adsorption has been considered a promising technique, because it provides higher treatment efficiency and a faster removal rate.(11) The common adsorbents, such as biomass,(12) zeolite,(13) hydrotalcite,(14) hydrogel,(15) and montmorillonite,(16) have been used in experiments. Nowadays, biochar is an eco-friendly potential adsorbent due to various beneficial properties, low cost, abundance, lower pollution, and the possibility of regeneration.(17)

Biochar is a carbon-rich solid formed by pyrolysis of biomass wastes at relatively low temperatures under limited oxygen. A large specific surface area, abundant pore structure, and considerable functional groups are the basis of biochar as a potential adsorbent for pollutant remediation. Unfortunately, the surface of biochar with permanent electronegativity has limited phosphate adsorption capacity, so it is of great significance to modify the biochar for enhancing its adsorption efficiency. Recently, various modification methods have been investigated, such as cationic surfactant modification, metal ion surface modification (magnesium,(18) aluminum,(19) calcium,(20) and so on), and rare-earth metal modification (lanthanum,(21) zirconium(22)). However, compared with those of the other two modification methods, metal ion surface modification has a stronger adsorption ability and larger adsorption capacity. Yao et al. obtained MgO nanoparticles derived from anaerobically digested sugar beet tailings, which showed that the maximum adsorption capacity was 133 mg/g.(23) Ming Zhang et al. used porous MgO/biochar nanocomposites to remove phosphate and used Langmuir adsorption capacities as high as 835 mg/g for phosphate...(24)

...However, the phosphate is easily separated from the adsorbent surface due to the unstable structure after adsorption. Therefore, it will be of great importance for the stable immobilization of PO43– in wastewater.

In this work, the MgPO4)y·zH2O crystallization effect has been used for stably anchoring the adsorbed P onto the biochar surface, which has been paid little attention, as before. Specifically, the biochar was driven from an industrial hemp plant waste by pyrolysis at relatively mild conditions...


The following cartoon shows how the authors make their MgO impregnated hemp stem biochar:



The caption:

Figure 1. Preparation process of MgO/biochar.


Different conditions utilized and the effect on phosphate uptake efficiency are shown in the following table:



The MgO impregnated biochar was characterized by TEM (transmission electron microscopy), XRD(X-Ray Diffraction) , IR (Infrared Spcectroscopy, BET (the Brunauer–Emmett–Teller method for surface area using N2 gas), and SEM (Scanning Electron Microscopy.)

XRD and IR of two samples:



The caption:

Figure 2. (a) XRD of A-C-1 and A-C-2 and (b) FTIR of A-C-1 and A-C-2.


The effect of pH on absorption:



The caption:

Figure 3. (a) Effect of initial pH on the removal of phosphate (C0 = 300 mg/L, at dosage = 1 g L–1, time = 12 h). (b) Equilibrium pH after adsorption of phosphate.

Adsorption science is generally viewed, in a number of applications, by certain kinds of plots, one of which, that Langmuir parameter having earned Irving Langmuir the Nobel Prize. These plots are called "isotherms":



The caption:

Figure 4. Isotherm sorption models for phosphate at different temperatures: (a) Langmuir isotherm and (b) Freundlich isotherm.


Kinetics:



The caption:

Figure 5. Adsorption kinetics for 300 mg/L phosphate on MgO/biochar at different temperatures: (a) pseudo-first-order kinetics model, (b) pseudo-second-order kinetics model, and (c) intraparticle diffusion model.


Some images:



The caption:

Figure 6. (a) SEM of MgO/biochar. (b, c) TEM of MgO/biochar. (d) SAED of MgO/biochar. (e–g) Mapping of Mg, O, and C. (h) EDS of MgO/biochar.




The caption:

Figure 7. (a, d) SEM of MgO/biochar after adsorption. (b, c, f, i, l) Mapping of MgO/biochar after adsorption. (e, g, h, k) TEM of MgO/biochar after adsorption. (j) EDS of MgO/biochar after adsorption.


Changes after adsorption of phosphate:



The caption:

Figure 8. (a) XRD and (b) FTIR of MgO/biochar before and the after adsorption.


A cartoon about how the process works.



Figure 9. Mechanism of phosphate immobilization and the formation process of the flowerlike crystalline compound.


Some remarks from the conclusion:

MgO-modified industrial hemp-stem-driven nanocomposites produced by in situ precipitation have the superior ability to immobilize phosphate from wastewater under a range of pH values and competitive ion conditions. Different carbonization conditions can affect the specific surface area of biochar and the crystallinity of the MgO crystal, and this further affected the phosphate adsorption capacity. Biochar with the large specific surface area provided a good carrier for MgO, which was more conducive to phosphate immobilization by forming the MgPO4)y·zH2O crystal. The maximum phosphate adsorption capacity was 233 mg/g with the Langmuir model at 25 °C, which outperformed many other adsorbents. Phosphate adsorption was feasible and spontaneous through the study of thermodynamics and kinetics. MgO/biochar had a good reusability, and there was still a 90 mg/g absorption capacity after five cycles. Phosphate removal was mainly controlled by electrostatic adsorption, crystallization, and the inner-sphere surface complex. In conclusion, MgO/biochar was a promising adsorbent for phosphate removal, with a high adsorption capacity and the cost of hemp, as an agricultural waste, being low.


OK, OK, OK...After many decades of hearing about the wonders of pot/hemp/weed/whatever, this potentially represents an important use for the stuff.

I still don't recommend smoking the stuff. It's not good for you.

Biochars, by the way, represent sequestered carbon, perhaps trivial in this application, but it is carbon removed from air.

I trust you're having a safe and enjoyable Sunday afternoon.

A nice little table of the technologies utilizing the lanthanide elements.

I am not going to fully cover the paper from which this graphic comes, because it is on the subject of recovering elements from flowback water from the "fracking" industry in China.

The paper is this one: Rare Earth Elements Occurrence and Economical Recovery Strategy from Shale Gas Wastewater in the Sichuan Basin, China (Liu et al., ACS Sustainable Chem. Eng. 2020, 8, 32, 11914–11920)

As I have made clear, many times, I oppose all dangerous fossil fuels, the mining of all dangerous fossil fuels, and frankly, any technology which attempts to claim to mitigate the tragedy, because all of these attempts have and will prove trivial as compared to dangerous fossil fuels.

One of the huge waste profiles of dangerous natural gas - which many people who believe that so called "renewable energy" ignore based on their toxic fantasy that dangerous natural gas is "transitional" - is flow back water, the chemical and mineral laced water that is used to hydraulically shatter rocks permanently in the earth's crust so our generation can work to get the last molecule of methane burned and its waste, carbon dioxide, dumped into the planetary atmosphere, this at the expense of all future generations.

Many putative "green" technologies actually depend heavily on lanthanide elements, the overwhelming majority of which are mined and processed in China, often under decidedly dirty conditions that are hardly "green."

These elements, once thought as laboratory curiosities - I don't think we spent more than 5 minutes discussing them in my high school chemistry class when I was a child - are now key to many technologies.

This graphic from the paper shows how things have changed in my (long) lifetime, and how many technologies rely on access and purification of these elements which are, in general, not "renewable."



The caption:

Figure 1. (a) Range of applications for REEs in many fields. (b) Water samples collected from different sites in Sichuan Basin, China.


With the exception of scandium (Sc) (which could in theory be made via the neutron irradiation of calcium) all of the elements listed in this table up to (and more or less including) gadolinium (Gd) are present in used nuclear fuels, although some of them would require fairly long cooling before being available for non-nuclear applications and/or applications in closed systems. (Some closed system applications would be improved by using the radioactive forms of these elements rather than the stable form, but that's not current practice.) Others, such as yttrium, lanthanum, praseodymium, neodymium, would require very short (or no) cooling times, cerium only moderate cooling times. However the same energy to mass ratio that makes nuclear fuels superior in a purely environmental sense to all other forms of energy, means that the amounts available would more or less be trivial when compared to those available from the ores we are working so hard to deplete.

One of the elements listed, promethium, does not occur on earth except in minuscule amounts, from spontaneous fission in uranium ores. It has no stable, non-radioactive isotopes. Pm-147 can, and has been isolated from used nuclear fuels, but its use in signage, lighting and batteries has been limited because regrettably, nuclear fuel recycling has been limited.

I knew of most of these applications, but it was nice to see them all in one place, and I thought I'd post it.

I hope you're having a wonderful weekend.

Covalent surface modifications and superconductivity of two-dimensional metal carbide MXenes

The paper I will discuss in this post is this one: Covalent surface modifications and superconductivity of two-dimensional metal carbide MXenes (Vladislav Kamysbayev, Alexander S. Filatov, Huicheng Hu, Xue Rui, Francisco Lagunas, Di Wang, Robert F. Klie, Dmitri V. Talapin, Science 21 Aug 2020: Vol. 369, Issue 6506, pp. 979-983)

My son decided that he wanted to go into materials science while still in high school, and as such, we visited the Materials Science Departments of the various universities during the touring process. I attended the majority of them, but my wife took my son to Drexel University where, I learned afterward, the great Egyptian-American scientist Michel Barsoum actually came to speak to the prospective students, this, ironically on the very day I had acquired access to his book, MAX Phases: Properties of Machinable Ternary Carbides and Nitrides



Of course, if I had attended, any effort on my part to have engaged Dr. Barsoum would have distracted from his mission, which was to convince promising students to come to Drexel where, according to my wife, he promised, if they worked hard, even freshman undergraduates could be invited to work in his lab.

Drexel made my son a decent offer but the university he ultimately attended made him a great offer, and anyway, my son really found the idea of attending a university located right in a major metropolitan area distasteful, which is why he refused to even look at NYU, Columbia or MIT, not that any of these universities would have made him an offer we could have afforded to accept, or for that matter, even admitted him. So he didn't go to Drexel, and he didn't get to work with Michel Barsoum, even though his father had been discussing the MAX phases with him for some time.

In my opinion, however, Dr. Barsoum is one of the most important scientists of our time. He did not discover the MAX Phases, but he recognized them for what they were, greatly expanded on the knowledge of their chemistry and properties, and as published with scientists all over the world on the subject.

The MAX phases (which Dr. Barsoum named) have many of the important features of ceramics, resistance to high temperatures, resistance to harsh chemicals, while possessing some of the important properties of metals, specifically, machinability, as they lack the brittle nature of ceramics. I came across them in connection with my interest in high temperature materials and chemical resistance given my interest in nuclear reactors as well as in thermochemical carbon dioxide and water splitting using them in order to make for a sustainable world, something that we are no closer to doing than when I was a child; in fact we are living in a less sustainable world than the one into which I was born. (History will not forgive my generation, nor should it.) In any case, structurally, MAX phases consist of layers of atoms in a fairly precise arrangement, and this, as Dr. Barsoum and others have taught the world, leaves them capable of offering new opportunities in materials science in many areas.

One area in which Dr. Barsoum has further pioneered the applicability of these materials is in their use in preparing "MAXenes" which are two dimensional layered materials having a single molecule thickness. Although the MAX phases are notable for their chemical resistance, there are some which do react with chemicals. The most famous MAX phase - there are many, but the most famous - is Ti3SiC2. If this phase is treated with hydrofluoric acid, the silicon in them can be dissolved, leaving a two dimensional series of layers of Titanium carbide. The invention of the FFC Cambridge process should make titanium metal readily available in the future at reasonable prices, and the properties of its carbides (and indeed, the already widely used nitride) are very, very, very, exciting.

Much of what is written today on the subject of two dimensional materials these days relates to graphene and graphene nitride. MAXenes open up a much larger segment of the periodic table to these types materials.

Modification to MAXene titanium carbides is the subject of the paper under discussion and it extends the elements of the period table to two dimensional materials to the halides.

From the introduction to the paper:

Two-dimensional (2D) transition-metal carbides and nitrides (MXenes) (1) have been actively studied for applications in supercapacitors (2), batteries (3), electromagnetic interference shielding (4), composites (5, 6), and catalysts (7). MXenes are typically synthesized from the corresponding MAX phases (Fig. 1A), where M stands for the transition metal (e.g., Ti, Nb, Mo, V, W, etc.) and X stands for C or N, by selectively etching the main group element A (e.g., Al, Ga, Si, etc.). The etching is usually performed in aqueous hydrofluoric (HF) solutions, rendering MXenes terminated with a mixture of F, O, and OH functional groups, commonly denoted as Tx. These functional groups can be chemically modified, unlike the surfaces of other 2D materials such as graphene and transition-metal dichalcogenides. Recent theoretical studies predict that selective terminations of MXenes with different surface groups can lead to remarkable properties, such as opening or closing bandgap (8), room-temperature electron mobility exceeding 104 cm2/V⋅s (9), widely tunable work functions (10), half-metallicity, and 2D ferromagnetism (11). Covalent functionalization of MXene surfaces is expected to uncover new directions for rational engineering of 2D functional materials

The surface of MXene sheets is defined during MAX phase etching. Electrochemical and hydrothermal methods have been recently applied for etching MAX phases without resorting to HF solutions, but the use of aqueous solutions introduces a mixture of Cl, O, and OH surface groups (12, 13). The etching of Ti3AlC2 MAX phase in molten ZnCl2 and several other Lewis acidic molten salts above 500°C results in Ti3C2Cl2 MXene with a pure Cl termination (14, 15). Because etching of MAX phases in molten salts eliminates unwanted oxidation and hydrolysis, we used a variation of this method for synthesis of Ti3C2Cl2, Ti2CCl2, and Nb2CCl2 MXenes in CdCl2 molten salt (figs. S1 to S5). Moreover, the use of Lewis acidic CdBr2 allowed us to extend the molten salt etching route beyond chlorides to prepare the first Br-terminated Ti3C2Br2 and Ti2CBr2 MXenes (Fig. 1, B and C, and figs. S6 and S7)...


Figure 1:



The caption:

Fig. 1 Surface reactions of MXenes in molten inorganic salts.
(A) Schematics for etching of MAX phases in Lewis acidic molten salts. (B) Atomic-resolution high-angle annular dark-field (HAADF) image of Ti3C2Br2 MXene sheets synthesized by etching Ti3AlC2 MAX phase in CdBr2 molten salt. The electron beam is parallel to the [21¯1¯0] zone axis. (C) Energy-dispersive x-ray elemental analysis (line scan) of Ti3C2Br2 MXene sheets. a.u., arbitrary units. HAADF images of (D) Ti3C2Te and (E) Ti3C2S MXenes obtained by substituting Br for Te and S surface groups, respectively. (F) HAADF image of Ti3C2⬜⬜2 MXene (⬜ stands for the vacancy) obtained by reductive elimination of Br surface groups.


Here is a excerpted brief discussion of the chemical processing of these phases:

The transition-metal atoms from the outer layers of MXene sheets (Ti, Mo, Nb, and V) form relatively weak M-Cl and M-Br bonds, in comparison to M-F and M-OH bonds typical for MXenes with Tx surface groups. This point can be demonstrated by the enthalpies of formation for TiBr4 (−617 kJ mol−1) and TiCl4 (−804 kJ mol−1) versus TiF4 (−1649 kJ mol−1), as well as by direct comparison of the bond energies (table S1). Strong Ti-F and Ti-O bonds make it difficult to perform any postsynthetic covalent surface modifications of MXenes (16). In contrast, Cl- and Br-terminated MXenes with labile surface bonding act as versatile synthons for further chemical transformations.

MXene surface exchange reactions typically require temperatures of 300° to 600°C, which are difficult to achieve using traditional solvents. We instead used molten alkali metal halides as solvents with unmatched high-temperature stability, high solubility of various ionic compounds, and wide electrochemical windows (17–19). For example, Ti3C2Br2 MXene (Fig. 1B) dispersed in CsBr-KBr-LiBr eutectic (melting point: 236°C) reacted with Li2Te and Li2S to form Ti3C2Te (Fig. 1D and figs. S8 to S10) and Ti3C2S (Fig. 1E and fig. S11) MXenes, respectively. The reactions of Ti3C2Cl2 and Ti3C2Br2 with Li2Se, Li2O, and NaNH2 yielded Ti3C2Se, Ti3C2O, and Ti3C2(NH) MXenes, respectively (figs. S12 to S16). The multilayers of Ti3C2Tn MXenes (T = Cl, S, NH) were further treated with n-butyl lithium (n-BuLi) resulting in Li+ intercalated sheets (fig. S17) with a negative surface charge (Fig. 2A and fig. S18)


A graphic on delamination of the MAXenes:



The caption:

Fig. 2 Delamination of multilayer Ti3C2Tn MXenes.

(A) Schematic of delamination process. (B) Photographs of stable colloidal solutions of Ti3C2Tn MXenes (T = Cl, S, NH) in NMF exhibiting Tyndall effect. (C) TEM image of Ti3C2Cl2 MXene flakes deposited from a colloidal solution. (Inset) Fast Fourier transform of the circled region, showing crystallinity and hexagonal symmetry of the individual flake. (D) XRD patterns of multilayer MXene and delaminated flakes in a film spin coated on a glass substrate.


There is considerable discussion in the paper of various means and results of characterization, including a discussion of the electrical properties of these materials.

The above examples show that the composition and structure of MXenes can be engineered with previously unattainable versatility. Chemical functionalization of MXene surfaces is expected to affect nearly every property of these materials, and we found that the surface groups defined the nature of electronic transport in Nb2CTn MXenes. Figure 4, A and B, shows temperature-dependent four-probe resistivity (ρ measured on cold-pressed pellets of Nb2CTn (T = ⬜, Cl, O, S, Se) MXenes (fig. S41), all synthesized by the procedures described above. Figure 4A also compares the conductivity of the parent Nb2AlC MAX phase with that of Nb2CCl2 MXene. Above 30 K, both MAX phase and MXene samples showed similar specific resistivity, which decreased when the sample was cooled. This temperature dependence is often associated with metallic conductivity. The ultraviolet photoelectron spectroscopy (UPS) confirmed nonzero density of electronic states at the Fermi energy EF (fig. S42), which is also consistent with a metallic state.


Figure 4:



The caption:

Fig. 4 Electronic transport and superconductivity in Nb2CTn MXenes.
(A) Temperature-dependent resistivity for the cold-pressed pellets of Nb2AlC MAX phase and Nb2CCl2 MXene. (Inset) Magnetic susceptibility (i.e., ratio of magnetization to magnetizing field strength) of Nb2CCl2 MXene as a function of temperature. FC and ZFC correspond to the field cooled and zero-field cooled measurements, respectively. emu, electromagnetic unit. (B) Temperature-dependent resistivity for the cold-pressed pellets of Nb2CTn MXenes. (Inset) Resistance as a function of temperature at different applied magnetic fields (0 to 8 T) for the cold-pressed pellets of Nb2CS2 MXene.


I never get too excited about applications of niobium, since niobium is a monoisotopic (A = 93) element that is subject to depletion of resources and which cannot be obtained from used nuclear fuel owing to the long half-life of its parent, Zr-93.

In any case, the authors continue:

However, when the Nb2CCl2 MXene was cooled below 30 K, the resistivity started increasing, possibly indicating the onset of localization. A sharp drop of resistivity by several orders of magnitude occurred at a critical temperature Tc ~ 6.0 K (Fig. 4A), which is reminiscent of a superconductive transition. The magnetic susceptibility measurements showed the development of a strong diamagnetism below 6.3 K that we interpreted as the Meissner effect (Fig. 4A). From the magnitude of zero-field cooled data at 1.8 K, we estimated the lower bound for the superconducting volume fraction of Nb2CCl2 MXene as ~35%. Consistent with superconductivity, the transition broadened, and Tc shifted to lower temperatures with the application of an external magnetic field (Fig. 4B and fig. S43). In contrast, the parent Nb2AlC MAX phase exhibited normal metal behavior down to the lowest measured temperature (1.8 K), which is consistent with a previously reported Tc ~ 0.44 K for Nb2AlC (28). For reference, Nb2CTx MXene with mixed O, OH, and F termination prepared by the traditional aqueous HF etching route shows two orders of magnitude higher resistivity and no superconductivity (fig. S44) (29).


In the conclusion the authors suggest a breakthrough in MAXene processing:

The MXene exchange reactions represent an exciting counterexample to the traditional perception of solids as entities that are difficult to postsynthetically modify. We showed that chemical bonds inside an extended MXene stack can be rationally designed in a way that is more typical for molecular compounds. Other MXene structures could be enabled by the combinations of etching and substitution reactions using Lewis acidic and Lewis basic molten salts, respectively.


It's a cool paper on what I regard as an important area in the future of materials science.

I trust you are having a pleasant weekend and enjoying the excitement over our outstanding virtual Democratic Party and are filled, as I am, with feelings of hope.














Five charts that will change everything you know about mud

The current issue of Science, has a number of articles, and a cover, devoted to mud.

Special Issue: A World of Mud



They are news items, not research papers.

One is called, as the title here indicates: Five charts that will change everything you know about mud (By David Malakoff, Nirja Desai, Xing Liu, Science, August 21, 2020.)

(One may need a subscription to open the paper, I'm not sure.)

An excerpt from the introduction:

Glop. Mire. Ooze. Cohesive sediment. Call it what you want, mud—a mixture of fine sediment and water—is one of the most common and consequential substances on Earth. Not quite a solid, not quite a liquid, mud coats the bottoms of our lakes, rivers, and seas. It helps form massive floodplains, river deltas, and tidal flats that store vast quantities of carbon and nutrients, and support vibrant communities of people, flora, and fauna. But mud is also a killer: Mudslides bury thousands of people each year.

Earth has been a muddy planet for 4 billion years, ever since water became abundant. But how it forms and moves have changed dramatically. About 500 million years ago, the arrival of land plants boosted the breakdown of rock into fine particles, slowed runoff, and stabilized sediments, enabling thick layers of mud to pile up in river valleys. Tectonic shifts that gave rise to mountains, as well as climate changes that enhanced precipitation, accelerated erosion, and helped blanket sea floors with mud hundreds of meters thick. Over time, many mud deposits hardened into mudrock, the most abundant rock in the geologic record, accounting for roughly half of all sedimentary formations.

Now, humans are a dominant force in the world of mud. Starting about 5000 years ago, erosion rates shot up in many parts of the world as our ancestors began to clear forests and plant crops. Even more sediment filled rivers and valleys, altering landscapes beyond recognition. In some places dams and dykes trapped that mud, preventing fresh sediment from nourishing floodplains, deltas, and tidal flats and causing them to shrink (see graphic below). And industrial processes began to produce massive quantities of new forms of mud—mine and factory waste—that is laden with toxic compounds and often stored behind dams that can fail, unleashing deadly torrents...


A few of the five charts:







An interesting read, these news items.

Something about my EKG is freaking medical people out.

Twenty-seven years ago, after an EKG, and echocardiogram, a stress echocardiogram, and finally an angiogram, my cardiologist at the time - not the most pleasant guy in the world, truth be told - told me that every time someone took my EKG, they were going to freak out and send me for all kinds of tests, if not hospitalize me. (This actually took place after two hospitalizations, one involving a stay in an ICU.)

So I just went through my third or fourth - I can't remember how many more - stress echo.

Now I just tell this story with every EKG freak out, and nobody gets excited, but they do get "concerned," with far more class than Susan Collins could ever muster.

However in the most recent freak-out my general physician did tell me that I'm older now, fatter now, with (managed) high blood pressure (why, oh why, do I ever post in E&E here) and that my EKG had "changed," and I should get it checked out.

So I went again.

A good time was had by all; wonderful nice techs, a very friendly and warm cardiologist. I got to get injected with a lipid formulation of the greenhouse gas SF6 as a contrast agent, got to talk a little about the chemistry of the gas.

"Looks good," the cardiologist told me. (Usually they don't tell you on the spot, but this is the first one where a cardiologist was in the room.)

I do have - I learned about 3 or 4 years ago when I'd developed a murmur - a mild mitral prelapse, this from a "normal" (non-stress) echocardiogram but no big deal.

I should lose weight, and I probably should stop talking about energy, engineering and climate change, especially in E&E.

But a good time was had by all.

Life is wonderful and then you die.

I will die - as my angiogram physician told me in a deadpan example of bad bedside manner, adding, after a pause, "but almost certainly not from heart disease."

Again...

A good time was had by all.

Life is wonderful and then you die.

He's on fire. Period, a President who can actually speak in complete sentences. Go Joe!!! n/t.

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