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To answer your first question, I believe that the ammonium oleate already being a relatively soluble salt allows its deprotonation such that the resulting oleate ions are able to bond to the magnetite in suspension (both by electrostatic attraction and hydrophobic interactions). Subsequent heating is done simply to remove dissociated $\ce{NH4Cl}$ from the water in the form of $\ce{NH3}$ and $\ce{HCl}$ gas. Might be worth noting that your initial addition of aqueous $\ce{NH3}$ (aka $\ce{NH4OH}$) for the co-precipitation is in excess. A video by NileRed suggests neutralising this excess ammonium (hydroxide) instead with the use of hydrochloric acid, instead of using high heat which would expel a large amount of nasty fumes. Cleaning of the magnetite can then be done with deionised water to remove the dissolved salts.

To answer your second question, no, adding oleic acid post-decanting would not work. Using the logic I've stated, adding pure oleic acid (in a non-aqueous form) would not yet coat the magnetite particles because the oleic acid is not yet deprotonated, and so the oleate anion cannot bond to the magnetite until water is added.

Even if you were to add aqueous oleic acid, doing so post-decanting doesn't seem logical; normally, surfactants are added as soon as the magnetite has fully precipitated, without stopping the stirring, because you'd want the surfactants to coat the magnetite nano/microparticles (MNPs) while they are still dispersed (before they begin aggregating). In your case, having the intermediate decanting step will definitely introduce excessive, irreversible magnetite aggregation and the resulting MNPs will not be of high quality. Anyways, as previously mentioned, the decanting step is not necessary because the ammonium chloride salt will not contaminate your final magnetite sample, considering that it can be easily washed with deionised water, and even short-chain alcohols to remove excess oleic acid.

To summarise, your last paragraph is correct in saying that ammonium chloride can be rinsed more easily from the magnetite sample than removed through evaporation. Using an acid might be a good way to do it as proposed by NileRed.

To answer your first question, I believe that the ammonium oleate already being a relatively soluble salt allows its deprotonation such that the resulting oleate ions are able to bond to the magnetite in suspension (both by electrostatic attraction and hydrophobic interactions). Subsequent heating is done simply to remove dissociated $\ce{NH4Cl}$ from the water in the form of $\ce{NH3}$ and $\ce{HCl}$ gas. Might be worth noting that your initial addition of aqueous $\ce{NH3}$ (aka $\ce{NH4OH}$) for the co-precipitation is in excess. A video by NileRed suggests neutralising this excess ammonium (hydroxide) instead with the use of hydrochloric acid, instead of using high heat which would expel a large amount of nasty fumes. Cleaning of the magnetite can then be done with deionised water to remove the dissolved salts.

To answer your second question, no, adding oleic acid post-decanting would not work. Using the logic I've stated, adding pure oleic acid would not coat the magnetite particles, as oleic acid by itself will not deprotonate in water until it has reacted with ammonia to form the ammonium oleate soap.

Even if you were to add aqueous ammonium oleate, doing so post-decanting doesn't seem logical; normally, surfactants are added as soon as the magnetite has fully precipitated, without stopping the stirring, because you'd want the surfactants to coat the magnetite nano/microparticles (MNPs) while they are still dispersed (before they begin aggregating). In your case, having the intermediate decanting step will definitely introduce excessive, irreversible magnetite aggregation and the resulting MNPs will not be of high quality. Anyways, as previously mentioned, the decanting step is not necessary because the ammonium chloride salt will not contaminate your final magnetite sample, considering that it can be easily washed with deionised water, and even short-chain alcohols to remove excess oleic acid.

To summarise, your last paragraph is correct in saying that ammonium chloride can be rinsed more easily from the magnetite sample than removed through evaporation. Using an acid might be a good way to do it as proposed by NileRed.

To answer your first question, I believe that the ammonium oleate already being a relatively soluble salt allows its constituent ions to dissociate such that the oleate ions are able to bond to the magnetite in suspension (both by electrostatic attraction and hydrophobic interactions). Subsequent heating is done simply to remove dissociated $\ce{NH4Cl}$ from the water in the form of ammonia and hydrogen chloride gas. Might be worth noting that your initial addition of aqueous $\ce{NH3}$ (aka $\ce{NH4OH}$) for the co-precipitation is in excess. A video by NileRed suggests neutralising this excess ammonium (hydroxide) instead with the use of hydrochloric acid, instead of using high heat which would expel a large amount of ammonia gas into the surroundings. Cleaning of the magnetite can then be done with deionised water to remove the dissolved salts.

To answer your second question, no, adding oleic acid post-decanting would not work. Using the logic I've stated, adding pure oleic acid (in a non-aqueous form) would not yet coat the magnetite particles because the $\ce{H^\oplus}$ proton and oleate anions are not yet dissociated, and in so doing cannot bond to the magnetite electrostatically until water is added.

Even if you were to add aqueous oleic acid, doing so post-decanting doesn't seem logical; normally, surfactants are added as soon as the magnetite has fully precipitated, without stopping the stirring, because you want the surfactants to coat the magnetite nano/microparticles (MNPs) while they are still dispersed (before they begin aggregating). In your case, having the intermediate decanting step will definitely introduce excessive, irreversible magnetite aggregation and the resulting MNPs will not be of high quality. Anyways, as previously mentioned, the decanting step is not necessary because the ammonium chloride salt will not contaminate your final magnetite sample, considering that it can be easily washed with deionised water, and even short-chain alcohols to remove excess oleic acid.

To summarise, your last paragraph is correct in saying that ammonium chloride can be rinsed more easily from the magnetite sample than removed through evaporation. Using an acid might be a good way to do it as proposed by NileRed.

To answer your first question, I believe that the ammonium oleate already being a relatively soluble salt allows its deprotonation such that the resulting oleate ions are able to bond to the magnetite in suspension (both by electrostatic attraction and hydrophobic interactions). Subsequent heating is done simply to remove dissociated $\ce{NH4Cl}$ from the water in the form of $\ce{NH3}$ and $\ce{HCl}$ gas. Might be worth noting that your initial addition of aqueous $\ce{NH3}$ (aka $\ce{NH4OH}$) for the co-precipitation is in excess. A video by NileRed suggests neutralising this excess ammonium (hydroxide) instead with the use of hydrochloric acid, instead of using high heat which would expel a large amount of nasty fumes. Cleaning of the magnetite can then be done with deionised water to remove the dissolved salts.

To answer your second question, no, adding oleic acid post-decanting would not work. Using the logic I've stated, adding pure oleic acid (in a non-aqueous form) would not yet coat the magnetite particles because the oleic acid is not yet deprotonated, and so the oleate anion cannot bond to the magnetite until water is added.

Even if you were to add aqueous oleic acid, doing so post-decanting doesn't seem logical; normally, surfactants are added as soon as the magnetite has fully precipitated, without stopping the stirring, because you'd want the surfactants to coat the magnetite nano/microparticles (MNPs) while they are still dispersed (before they begin aggregating). In your case, having the intermediate decanting step will definitely introduce excessive, irreversible magnetite aggregation and the resulting MNPs will not be of high quality. Anyways, as previously mentioned, the decanting step is not necessary because the ammonium chloride salt will not contaminate your final magnetite sample, considering that it can be easily washed with deionised water, and even short-chain alcohols to remove excess oleic acid.

To summarise, your last paragraph is correct in saying that ammonium chloride can be rinsed more easily from the magnetite sample than removed through evaporation. Using an acid might be a good way to do it as proposed by NileRed.

To answer your first question, I believe that the ammonium oleate already being a relatively soluble salt allows its constituent ions to dissociate such that the oleate ions are able to bond to the magnetite in suspension (both by electrostatic attraction and hydrophobic interactions). Subsequent heating is done simply to remove dissociated $\ce{NH4Cl}$ from the water in the form of ammonia and hydrogen chloride gas. Might be worth noting that your initial addition of aqueous $\ce{NH3}$ (aka $\ce{NH4OH}$) for the co-precipitation is in excess. A video by NileRed suggests neutralizing this excess ammonium (hydroxide) instead with the use of hydrochloric acid, instead of using high heat which would expel a large amount of ammonia gas into the surroundings. Cleaning of the magnetite can then be done with deionised water to remove the dissolved salts.

To answer your second question, no, adding oleic acid post-decanting would not work. Using the logic I've stated, adding pure oleic acid (in a non-aqueous form) would not yet coat the magnetite particles because the $\ce{H^\oplus}$ proton and oleate anions are not yet dissociated, and in so doing cannot bond to the magnetite electrostatically until water is added.

Even if you were to add aqueous oleic acid, doing so post-decanting doesn't seem logical; normally, surfactants are added as soon as the magnetite has fully precipitated, without stopping the stirring, because you want the surfactants to coat the magnetite nano/microparticles (MNPs) while they are still dispersed (before they begin aggregating). In your case, having the intermediate decanting step will definitely introduce excessive, irreversible magnetite aggregation and the resulting MNPs will not be of high quality. Anyways, as previously mentioned, the decanting step is not necessary because the ammonium chloride salt will not contaminate your final magnetite sample, considering that it can be easily washed with deionised water, and even short-chain alcohols to remove excess oleic acid.

To summarise, your last paragraph is correct in saying that ammonium chloride can be rinsed more easily from the magnetite sample than removed through evaporation. Using an acid might be a good way to do it as proposed by NileRed.

To answer your first question, I believe that the ammonium oleate already being a relatively soluble salt allows its constituent ions to dissociate such that the oleate ions are able to bond to the magnetite in suspension (both by electrostatic attraction and hydrophobic interactions). Subsequent heating is done simply to remove dissociated $\ce{NH4Cl}$ from the water in the form of ammonia and hydrogen chloride gas. Might be worth noting that your initial addition of aqueous $\ce{NH3}$ (aka $\ce{NH4OH}$) for the co-precipitation is in excess. A video by NileRed suggests neutralising this excess ammonium (hydroxide) instead with the use of hydrochloric acid, instead of using high heat which would expel a large amount of ammonia gas into the surroundings. Cleaning of the magnetite can then be done with deionised water to remove the dissolved salts.

To answer your second question, no, adding oleic acid post-decanting would not work. Using the logic I've stated, adding pure oleic acid (in a non-aqueous form) would not yet coat the magnetite particles because the $\ce{H^\oplus}$ proton and oleate anions are not yet dissociated, and in so doing cannot bond to the magnetite electrostatically until water is added.

Even if you were to add aqueous oleic acid, doing so post-decanting doesn't seem logical; normally, surfactants are added as soon as the magnetite has fully precipitated, without stopping the stirring, because you want the surfactants to coat the magnetite nano/microparticles (MNPs) while they are still dispersed (before they begin aggregating). In your case, having the intermediate decanting step will definitely introduce excessive, irreversible magnetite aggregation and the resulting MNPs will not be of high quality. Anyways, as previously mentioned, the decanting step is not necessary because the ammonium chloride salt will not contaminate your final magnetite sample, considering that it can be easily washed with deionised water, and even short-chain alcohols to remove excess oleic acid.

To summarise, your last paragraph is correct in saying that ammonium chloride can be rinsed more easily from the magnetite sample than removed through evaporation. Using an acid might be a good way to do it as proposed by NileRed.