Sciencemadness Discussion Board

NH4NO3 from N2, water and light

Whathappensif - 13-7-2020 at 20:37

https://spj.sciencemag.org/journals/research/2020/3750314/
Quote:

In this work, ultrathin W18O49 nanowires with distorted surface structures containing abundant surface oxygen vacancies were synthesized using a simple solvothermal method and are intended as a prototype for studying the wavelength-controlled N2 fixation in the presence of surface defects. The as-synthesized sample showed photocatalytic activity for N2 fixation to NH4+ and NO3- in pure water from ultraviolet up to near the end of visible light (730 nm) and exhibited high performance under simulated solar light (AM 1.5G) irradiation. The quantum efficiency (QE) reached about 9% at 365 nm through the simultaneous generation of both NH4+ and NO3-




Quantities synthesized are very small but it is an interesting start for a mostly passive process. Any thoughts on how to increase the yield?

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Refinery - 13-7-2020 at 23:22

Just wait till EU hears that you can make nitrates from air, water and carbon.

Next thing is to decide which one will be banned.

(No even) pun intended, but this sounds most interesting. Carbon related structures seem to offer a whole new array of methods from structural, catalysis, batteries to separation applications.

violet sin - 14-7-2020 at 00:12

W18O49 probably tungsten oxide ... It would appear so, I found something somewhat related.

Synthesis of W18O49 Nanorod via Ammonium Tungsten Oxide and Its Interesting Optical Properties
https://pubs.acs.org/doi/abs/10.1021/la202513q#

mackolol - 14-7-2020 at 04:35

Quote: Originally posted by Refinery  
Just wait till EU hears that you can make nitrates from air, water and carbon.

Next thing is to decide which one will be banned.

There is nothing that stops a good chemist. Even sulfuric acid ban, It's just a matter of more effort to put into the hobby :D

Mateo_swe - 14-7-2020 at 12:55

It sounds interesting, but you probably need very specialized equipment to make those nano wire surfaces needed for this to work.
But eventually even complex nano structures can be made at home with some new nano-3D printers.
That would be cool.
Unless they put a ban on those new nano-3D printers too, in fear of ordinary people could make real chemicals at home.

Draeger - 14-7-2020 at 13:01

Quote: Originally posted by Mateo_swe  
It sounds interesting, but you probably need very specialized equipment to make those nano wire surfaces needed for this to work.
But eventually even complex nano structures can be made at home with some new nano-3D printers.
That would be cool.
Unless they put a ban on those new nano-3D printers too, in fear of ordinary people could make real chemicals at home.

How expensive are those nano 3d printers?

Whathappensif - 14-7-2020 at 20:17

Well, if we make two simplifying assumptions that:
1. We don't need W18O49 and can instead do with more common tungsten oxides
2. The nanowire structures the researchers used is also unnecessary, and any morphology of tungsten oxide would do as long as it increases surface area*

*I think the reason why they went for nanowires is because with a mesh-like structure, you get diffusion of N2 onto the substrate and light can also arrive at the substrate.

Then the question really comes down to how we can make tungsten oxide nanopowders. I think the easiest may be electrical wire explosion of tungsten wire in an oxygen atmosphere.

My main caution about working with tungsten is that it is a suspected carcinogen, and the cancers that it causes in rats are very aggressive.
https://pubmed.ncbi.nlm.nih.gov/15929896/

So anyone who decides to try please be careful.

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violet sin - 14-7-2020 at 20:23

Selected bits from the linked paper in op.

"It is an established understanding that the ratedetermining step for N2 fixation is the activation and dissociation ofthe extremely stable N≡N triple bond (bond strength of ~941 kJ mol-1) [14, 16, 17]. A key step for effective photocatalytic N2 fixation is to efficiently transfer the energetic photoexcited electrons to the rather inert N2 molecule [8]. The N≡N triple bond can be weakened and activated when electrons are injected from the solid-state catalysts into the empty antibonding π∗-orbitals of the nitrogen molecule [8, 18]. For this purpose, abundant active sites with localized electrons should be created so that the N2 molecule can be chemisorbed for facile electron access. Such sites serve as the effective bridge between the energetic photoelectrons and the nitrogen molecule [14]. Surface vacancies with rich localized electrons due to the charge-transfer phenomenon [19] can effectively activate and weaken the N≡N triple bond by inducing chemisorption and electron injection [2, 20, 21]. Diversified surface vacancies, including oxygen [8, 9, 12, 14, 18], sulfur [22, 23], and nitrogen [24–26], have been proven to promote the photocatalytic N2 fixation efficiency"

"It is an established understanding that the ratedetermining step for N2 fixation is the activation and dissociation ofthe extremely stable N≡N triple bond (bond strength of ~941 kJ mol-1) [14, 16, 17]. A key step for effective photocatalytic N2 fixation is to efficiently transfer the energetic photoexcited electrons to the rather inert N2 molecule [8]. The N≡N triple bond can be weakened and activated when electrons are injected from the solid-state catalysts into the empty antibonding π∗-orbitals of the nitrogen molecule [8, 18]. For this purpose, abundant active sites with localized electrons should be created so that the N2 molecule can be chemisorbed for facile electron access. Such sites serve as the effective bridge between the energetic photoelectrons and the nitrogen molecule [14]. Surface vacancies with rich localized electrons due to the charge-transfer phenomenon [19] can effectively activate and weaken the N≡N triple bond by inducing chemisorption and electron injection [2, 20, 21]. Diversified surface vacancies, including oxygen [8, 9, 12, 14, 18], sulfur [22, 23], and nitrogen [24–26], have been proven to promote the photocatalytic N2 fixation efficiency. On the other hand, the appropriate anion vacancies in the bulk and on the surfaces ofsemiconductor photocatalysts can facilitate the separation and migration ofthe photogenerated electrons and holes [27], which is also crucial for photocatalytic reacPrevious work has indicated that N2 can also be oxidized to NO3
reasonable that NO3
neously, with N2 fixation proceeding through the following reactions:
tions [9, 12, 18]. The defects and disordered surfaces of a semiconductor alter the electronic structures by forming midgap states or band tail states [28–30], thus extending the light absorption spectrum and resulting in enhanced light absorption capability. In this work, ultrathin W18O49 nanowires with distorted
surface structures containing abundant surface oxygen vacancies were synthesized using a simple solvothermal method and are intended as a prototype for studying the wavelength-controlled N2 fixation in the presence of surface defects. The as-synthesized sample showed photocatalytic activity for N2 fixation to NH4
+ and NO3 - in pure water from
ultraviolet up to near the end of visible light (730 nm) and exhibited high performance under simulated solar light (AM 1.5G) irradiation. The quantum efficiency (QE) reached about 9% at 365nm through the simultaneous generation of both NH4
+ and NO3 -. Both experimental and theoretical
results suggested that surface oxygen vacancies serve as catalytic sites and are essential for the high efficiency of N2 fixation."

"W18O49 nanowires were prepared using a solvothermal method, and a reference sample was prepared by subsequently annealing the as-synthesized W18O49 nanowires at 300°C in air for 30min to eliminate oxygen vacancies from the surface. The crystal structure and phase purity of the as-synthesized blue velvet-like product (Figure 1(a)) were revealed by X-ray diffraction (XRD) to be consistent with the standard monoclinic W18O49 (P2/m) (PDF 05-0392)"

****************************
Something found by using search terms from above. I've no idea if they share authors or not, always surfing on my phone and it's a real pain to dig too deep ... But I hope it's helpful


https://doi.org/10.1111/j.1551-2916.2005.00341.x
Solvothermal Synthesis of Tungsten Oxide Nanorod/Nanowire/Nanosheet

Abstract
A simple process enables to synthesize tungsten oxide with various nanomorphologies, i.e. nanorods, nanowires, and nanosheets. The tungsten hexachloride (WCl6) was used as a raw material and the tungsten oxide nanoparticles were obtained by solvothermal treatment with solvents, i.e., ethanol, mixed solvent (ethanol+water), and water, at 200°C for 10 h. The various crystalline phases of tungsten oxide, such as monoclinic W18O49 nanorods, hexagonal WO3 platelets, and monoclinic WO3 nanosheets, were synthesized by simply changing the composition of the solvent. The oxygen, which was contained in water, played an important role in the final tungsten oxide phase. Especially, W18O49 nanorods grew to nanowires as the concentration of WCl6 was decreased. Using this simple process, it will be possible to control the crystalline phase and morphologies of nanostructured tungsten oxide system