Dear Cosmin Jalba

I assume you looked for the data in the literature and couldn't find it. The reason is that FeCl3 reacts with sulfuric acid (at high acid concentrations) to give ferric sulfate and HCl gas. In dilute sulfuric acid the HCl will not evaporate - at least not quickly - but in that case the solubility of the salt should not be very different from its solubility in water.

The solubility of iron chloride in sulfuric acid depends on several factors, such as the temperature, the concentration of the acid, and the oxidation state of the iron. According to one source1, the solubility of iron (III) chloride in 98% sulfuric acid is about 0.1 g/L at 25 °C, and increases to about 0.5 g/L at 100 °C. The solubility of iron (II) chloride in the same acid is much higher, about 100 g/L at 25 °C, and decreases to about 50 g/L at 100 °C. Another source2 states that iron (III) chloride is soluble in concentrated sulfuric acid, forming a brown solution, while iron (II) chloride is insoluble in concentrated sulfuric acid, forming a white precipitate. A third source3 does not provide specific data on the solubility of iron chloride in sulfuric acid, but lists the solubility of various compounds in water at different temperatures.

Here are some references that explain more about the solubility of iron chloride in sulfuric acid:

• Title: Solubility Table of Compounds in Water at Temperature Author: MilliporeSigma Publisher: Sigma-Aldrich Date: N/A URL: 1
• Title: Iron (III) chloride - Wikipedia Author: Wikipedia contributors Publisher: Wikimedia Foundation Date: 2021 URL: 2
• Title: Iron Solubility in Sulfuric Acid Author: Beta Control Publisher: Beta Control Date: N/A URL: 3

The solubility of iron chloride in sulfuric acid depends on several factors, such as the concentration of the acid, the temperature, and the presence of other ions. According to one source1, the solubility of iron (III) chloride in 98% sulfuric acid at 25°C is about 600 g/L, while in 50% sulfuric acid it is about 300 g/L. The solubility decreases as the acid concentration decreases, and also as the temperature increases. The presence of other ions, such as nitrate or sulfate, may also affect the solubility by forming complex ions or precipitates with iron.

The intercalation of FeCl3 in graphite is a process of inserting FeCl3 molecules between the layers of graphite, forming a compound called graphite intercalation compound (GIC). This process can change the physical and chemical properties of graphite, such as its electrical conductivity, thermal stability, and reactivity. One way to intercalate FeCl3 in graphite is to use stage 1 FeCl3-graphite intercalation compounds (GICs) as a precursor and exfoliate them by ultrasonic treatment2. This can produce graphene and FeCl3-intercalated few-layer graphene (FeCl3-FLG) with high yield and large interlayer spacing. The FeCl3-FLG can be used as anode materials for lithium-ion batteries, as it has high capacity and cycling stability2. Another way to intercalate FeCl3 in graphite is to react FeCl3-GICs with intercalants of different strengths, such as nitric acid or tetrahydrofuran (THF)3. This can lead to the formation of different GICs or exfoliated graphite (EG) with iron oxide or iron particles supported on it. The EG can have low bulk density, high ferric oxide content, and magnetic properties3.

References: 1: Iron Solubility in Sulfuric Acid - Beta Control 2: FeCl3 intercalated few-layer graphene for high lithium-ion storage performance - Journal of Materials Chemistry A 3: Interaction of FeCl3-intercalated graphite with intercalants of different strengths | SpringerLink

Learn more:

1. sigmaaldrich.com2. pubs.rsc.org3. link.springer.com4. betacontrol.com5. pubs.rsc.org6. link.springer.com7. en.wikipedia.org8. arxiv.org9. doi.org

Good luck

E.A. Gawad Thank you!

I have a confusion and would like to ask if you have any ideas.

I am doing some experiments on intercalation of graphite with ferric chloride, so called FeCl3-GIC.

I use sulfuric acid (75%), graphite (large flakes) and vary the concentration of ferric chloride (1.4g, 2.7g, 5.6) in the final potassium permanganate (1.8g)

The order of introduction into the reaction is as written above.

I then wash to clean the sample of contaminants

On further analysis (XPS,EDS) I find no trace of the intercalant I want.

The final goal is to obtain graphene films using microwaves after the intercalation step with ferric chloride.

Could it be because of the washing step or what could be another reason?

Emanuel Cooper Thank you for your reply.

I have a confusion and would like to ask if you have any ideas.

I am doing some experiments on intercalation of graphite with ferric chloride, so called FeCl3-GIC.

I use sulfuric acid (75%), graphite (large flakes) and vary the concentration of ferric chloride (1.4g, 2.7g, 5.6) in the final potassium permanganate (1.8g)

The order of introduction into the reaction is as written above.

I then wash to clean the sample of contaminants

On further analysis (XPS,EDS) I find no trace of the intercalant I want.

The final goal is to obtain graphene films using microwaves after the intercalation step with ferric chloride.

Could it be because of the washing step or what could be another reason?

Thanks

Dear Cosmin Jalba

I am not an expert on graphene intercalation compounds, but I skimmed ref. 2 graciously supplied (above) by E.A. Gawad (J. Mater. Chem. A preprint) which is fortunately available in full free of charge.

It seems to me that the key step in the intercalation as described there is:

"FeCl3 and graphite (w/w, 3/1) were mixed and dried at 120 oC for 6 h, and the mixture was then placed in a stainless-steel autoclave (50 ml) under vacuum at 400 oC for 12 h."

Note that there is no acid, and no water, in this step. Furthermore, the reaction occurs above the melting point of FeCl3 (obviously anhydrous!), and where FeCl3 has a large vapor pressure. In other words, FeCl3 molecules in GAS phase intercalate themselves (with obvious difficulty) into graphite. Note that anhydrous FeCl3 has a partially covalent character, similar to anhydrous AlCl3 and GaCl3; like them, it is a strong Lewis acid - hence its affinity to graphite, I guess - but loses much of its Lewis acidity when hydrated.

What you have in 75% H2SO4, on the other hand, is a partially hydrated salt that has no obvious thermodynamic "motivation" to leave the polar liquid phase and intercalate in the graphitic "phase".

Dear Emanuel Cooper

Thanks for your answer. It makes me think a lot in the sense that I am trying different experiments with intercalants to produce graphene films. What I want to point out is that I am doing chemical synthesis for this result, not using autoclave, electrochemical synthesis or other methods..

Briefly, I have done an intercalation with sulphuric acid in graphite (there is data in the literature that it can be done, admittedly not by chemical method, by autoclaving, molten salt etc) and I have had some results in this respect. (See ref*)

Now I am trying to do this intercalation with anhydrous ferric chloride instead of sulphuric acid.

In your opinion, from what I explained earlier, do you have any suggestions to give me?

Am I wrong in the order of the introduction of the reactants?

Should I use oxidizing agents (H2SO4/KMnO4) first in reaction with graphite to split the layers and then introduce ferric chloride?

I wonder where I'm going wrong..

*Synthesis and Characterization of Graphite Intercalation Compounds with Sulfuric Acid - Gintare Rimkute , Mantvydas Gudaitis et al

Dear Cosmin Jalba

Thanks for the opportunity to learn a bit about the technique of intercalating sulfuric acid in graphite. Some comments:

1. Note that Rimkute & al. use 98% H2SO4, and they even add some P2O5 to make sure that the water activity is extremely low. I suspect this is necessary. When people go through a lot of trouble it's not for fun.

2. While it may be possible to use permanganate in 75% sulfuric acid, I think it decomposes in 98% sulfuric acid. Try on a small quantity (1-2 mL) and see. Work in the hood! My recollection is that you will get an unstable purple gas, probably Mn2O7. (HMnO4 is initially formed, and H2SO4 dehydrates it to the volatile oxide.)

3. I think you will not have FeCl3 in concentrated H2SO4, as I already said. Most likely, most of the elemental chlorine will be lost as HCl, except that if you also have a strong oxidant present, like persulfate, some of it will be lost as chlorine gas. (HOOD!) If you're going to end up with ferric sulfate, or more accurately (due to the extremely low pH) with Fe(HSO4)3, maybe it's worth trying to start with anhydrous ferric sulfate and see where it takes you. (Anhydrous ferric bisulfate, Fe(HSO4)3, would be better but I'm not sure it's available.)

4. If you want to intercalate anhydrous FeCl3 instead of sulfuric acid, rather than with sulfuric acid, you have a different kind of problem. Most likely you'll need to go to the gas phase because solid FeCl3 will not do anything in useful time. (Liquid FeCl3 has a very narrow temperature stability range at 1 atm, and I gather you don't want a pressurized system.) Another possibility is to find a solvent that is:

(a) capable of dissolving "enough" anhydrous FeCl3,

(b) a weaker base than graphite surface (not easy) so the FeCl3 can move spontaneously from the solvate complex to the graphite surface, and

(c) compatible with whatever strong oxidant you want to use to generate the charges on the graphite surface.

Not easy to find. On point (b), evaporating the solvent may force the FeCl3 into the graphite; but evaporating an organic solvent that contains a strong oxidant is very risky.

Good luck!

Emanuel Cooper Thank you very much for the fruitful advice, I will try the autoclave experiment in the next period!