Chemistry

Abstract

Electrochemical production of fuels from solar energy, commonly referred to as solar-fuel production, is a key technology for converting abundant yet intermittent solar energy into a stable energy source. Typically, this process employs an electrolyzer coupled with photovoltaic (PV) cells through an electronic maximum power point tracking (MPPT) system. Here, we propose a chemical MPPT system, integrated directly into the electrolyzer, to enable stand-alone and unmanned liquid solar-fuel production with stabilized concentration changes from sunrise to sunset. The working principle of the MPPT system is derived from the impedance and heat-transfer properties of the electrolyzer, which incorporates a solid-state electrolyte exhibiting ionic resistivity with a negative temperature coefficient. Application of the mathematical model to a real electrolyzer energized by a commercially-available monocrystalline-Si PV panel for producing pure aqueous formic-acid solution demonstrated a high utilization factor (85%) of PV energy and a 2% external solar-to-formic-acid (eSTF) energy efficiency for 0.1 kg of formic acid from pure water and carbon dioxide (CO2) during daytime operation, all without the use of a conventional electronic MPPT system.

cross-posted from: https://lemmy.world/post/47979979

Paywall removed

I have a soft wet wood support beam, as described here. I bought some wood hardener. Instructions say to not apply to wet wood, only dry. I just wonder how that makes sense. I need the hardener liquid to penetrate the wood as much as possible. Water will creep along a wet surface better than a dry surface. I believe the wicking action of a wet surface will get the harder deeper into the wood. OTOH, they must have a reason for the guidance. Is it that the hardener would trap the water inside the wood fibers and be unable to escape?

If I use a hair dryer or something to dry the wood out as much as possible, is there anything I can do to improve the penetration of the hardener? I suppose I could make holes but of course that’s probably a bad idea in this case.

I should also mention that the hardener is water-based, which adds to my bafflement. The PDF says “Substrates must be cohesive, clean, sound and dry.” But the 2nd bullet on the webpage says “Adheres to damp wood”. Webpage also says “Surfaces: Can be applied to any types of woods, absorbent wood, dry or damp, including exotic species, chipboard and plywood sanded or stripped beforehand. ... Directions for use: Do not apply to soggy wood.”

It’s confusing but all their statements together seem to suggest it’s okay to apply to wet wood, but not ideal or optimal. Though my intuition would be to favor slightly damp wood to get wicking effects.

Dr Thomas de Prinse undertakes the fourth and fifth steps of his large-scale cubane synthesis, the Diels-Alder and the double deprotection.

Previous episode

Recent Veritasium video on per- and polyfluoroalkyl substances.

cross-posted from: https://mander.xyz/post/31227704

This weekend I did some experiments with turmeric powder. Here are some images of the results, and the description of how to create these microscopic chemical landscapes is given below.

Turmeric powder is a fantastic material to play with. The powder has a high concentration of colored and fluorescent curcuminoids and volatile turmerone oils.

When you use a polar solvent to extract these compounds, what you get is a kind of fluorescent oily resin called a turmeric 'oleoresin'.

The curcuminoids are yellow at acidic and neutral pH, but they become bright red at high pH due to keto-enol tautomerization. There is a lot of cool things you can do with the curcuminoids in terms of photo/electrochemistry.

I have been playing with very simple chemistry under the microscope, and I have noticed that you can create some cool-looking micro-landscapes. During this process you can also see different types of physico-chemical processes happening in real time.

Procedure to do this:

• Place a few grams of turmeric powder into a glass container
• Add enough isopropanol to cover the material, and a bit more
• Mix
• Wait for the solids to settle
• Collect a bit of the isopropanol liquid from the top and place on a glass coverslip
• Wait for the isopropanol to evaporate.

At this time, you can see under the microscope that golden oil droplets have been deposited, and that the surroundings are also yellow. The drops are oleoresins, which consist of curcuminoids suspended in turmerones and other oily compounds. Thin curcuminoid films might also be forming in between these droplets.

• Add a sprinkle of baking soda crystals (sodium bicarbonate) on top of the coverslip. You can blow on the coverslip if you accidentally add too much.

• Add a small drop of water, and wait a bit.

At this time you can see that the crystals are dissolving under the microscope, but the colors are not changing. The water and oils are not mixing, and so you get this film of alkaline water surrounding the oil droplets, but nothing is yet really changing.

• After waiting a few minutes, add a drop of isopropanol.

Now the isopropanol will re-dissolve the oleoresin and mix with the alkaline water. The carbonate ions are now able to react with the curcuminoids, and when they do, they go into the ketone form and instantly turn red. Under the microscope you can see quite dramatic movements of yellow and rad streaking as well as turbulent movements of the baking soda crystals.

• Wait some time for the liquids to evaporate again

• You will end up with a landscape that combines yellow resins, red resins, sodium bicarbonate crystals, and several different patterns.

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You can vary the parameters - the amount of sodium bicarbonate, the position and size of the drops, you can pre-mix the water and isopropanol, etc. Small changes can drastically affect the resulting landscape.

From the description:

We're at GSI in Germany where rare samples of enriched isotopes are fashioned into targets for their epic accelerator.

Featuring Sir Martyn Poliakoff speaking with Dr Bettina Lommel in the Target Lab.

Check it out.

Dr Thomas de Prinse undertakes the third step of his large-scale cubane synthesis, the bromination of the ethylene ketal of cyclopentanone to its tribromocyclopentanone derivative.

Previous episode

A humorous look at FOOF by the inimitable Derek Lowe

This is not some sort of fancy new development, but it's such a classical experiment that it's always worth sharing IMO. Plus it's fun.

When you initially mix both solutions, nothing seems to happen. But once you wait a wee bit, the colour suddenly changes, from transparent to a dark blue.

There are a bunch of variations of this reaction, but they all boil down to the same things:

• iodide - at the start of the reaction, it'll flip back and forth between iodide (I⁻) and triiodide ([I₃]⁻)
• starch - it forms a complex with triiodide, with the dark blue colour you see in the video. But only with triiodide; iodide is left alone. So it's effectively an indicator for the triiodide here.
• some reducing agent - NileRed used vitamin C (aka ascorbic acid; C₆H₈O₆), but it could be something like thiosulphate (S₂O₃²⁻) instead. The job of the reducing agent is to oxidise the triiodide back to iodide.
• some oxidiser - here it's the hydrogen peroxide (H₂O₂) but it could be something like chlorate (ClO₃⁻) instead. Its main job is to oxidise the iodide to triiodide. You need more than enough oxidiser to be able to fully oxidise the reducing agent, plus a leftover.

"Wait a minute, why are there a reducing agent and an oxidiser, doing opposite things? They should cancel each other out!" - well, yes! However this does not happen instantaneously. And eventually the reducing agent will run dry (as long as there's enough oxidiser), the triiodide will pile up, react with the starch and you'll get the blue colour.

Here are simplified versions of the main reactions:

1. 3I⁻ + H₂O₂ → [I₃]⁻ + 2OH⁻
2. [I₃]⁻ + C₆H₈O₆ + 2H₂O → 3I⁻ + C₆H₆O₆ + 2H₃O⁺

(C₆H₆O₆ = dehydroascorbic acid) Eventually #2 stops happening because all vitamin C was consumed, so the triiodide piles up, reacts with the starch, and suddenly blue:

Dr Thomas de Prinse makes yttrium oxide doped with erbium and ytterbium.

Upconversion: Material absorbs two infrared photons, emits one visible photon.

A chemist told me rust does not spread. The top of my refrigerator gives me some doubt. It’s covered in these spots. The center of every spot is a small break in the paint, but the rust all around those spots is on top of the paint.

cross-posted from: https://lemmy.ca/post/39143995

The authors of the academic study, published in the Journal of the American Chemical Society on Thursday, had to get the smell from inside the sarcophagus without interfering with the mummy inside.

The researchers, from UCL and the University of Ljubljana in Slovenia, did so by inserting a tiny tube so they were able measure the scent without taking any physical samples.

If you want to smell the smell too

They say recreating the composition of the smells chemically will allow others to experience a mummy's whiff - and help to tell when the bodies inside may be starting to rot.

"We want to share the experience we had smelling the mummified bodies, so we're reconstructing the smell to be presented in the Egyptian Museum in Cairo," Cecilia Bembibre, one of the researchers, told BBC Radio 4's Today programme.