# What is the crystal structure of bismuth oxyhydroxyphosphate (BOHP)?

The recent Chemical & Engineering News article Photocatalyst shreds drinking water contaminant PFOA report the following:

Cates and his colleagues made an accidental breakthrough while testing the photocatalyst bismuth phosphate. After finding that it could break down PFOA as effectively as a previously reported photocatalyst, gallium oxide, they tried to improve its performance by varying the pH of the reaction used to make the catalyst particles. The researchers had hoped this would change the particles’ size and shape, but the process inadvertently produced bismuth oxyhydroxyphosphate (BOHP). This new catalyst has the highest photocatalytic activity for PFOA degradation ever reported.

In lab tests under UV light, BOHP degraded all the PFOA in a 130 μM solution in about an hour, roughly 15 times faster than did bismuth phosphate or gallium oxide. BOHP performed almost as well over five repetitions of the experiment, suggesting it can be reused. To simulate PFOA-contaminated groundwater, the researchers then tested a more dilute solution of 1.2 μM PFOA accompanied by 500 μg dissolved organic carbon/L. In this case, the photocatalyst also degraded all the PFOA, though it took two hours. Strathmann calls it a “promising development” that advances the application of photocatalytic treatment of PFOA.

It also includes this SEM image of microcrystals of the "inadvertently produced bismuth oxyhydroxyphosphate (BOHP)."

The accidentally synthesized BOHP (shown) can break down the toxic industrial contaminant PFOA faster than any other photocatalyst. Credit: Environ. Sci. Technol. Lett.

A quick check with google doesn't send me to the materials Wikipedia page, and I'm wondering if that is because this is an unusual substance or the crystal structure hasn't been solved yet.

Question: What is the crystal structure of bismuth oxyhydroxyphosphate (BOHP)?

• Another quick google leads to this paper : pubs.acs.org/doi/abs/10.1021/… that mentions 'Petitjeanite' which is mindat.org/min-3329.html Apr 9 '19 at 10:29
• @gilleain That's great, thank you! I won't be able to read the paper one until I get to the library, but the page for Petitjeanite, triclinic, α = 88.28°, β = 115.27°, γ = 110.7° is a great start! Hopefully someone can find a diagram of what the unit cell looks like as in these questions 1, 2, 3
– uhoh
Apr 9 '19 at 11:59
• @gilleain for comparison, I've asked about the mineral here: What does the unit cell of petitjeanite look like?.
– uhoh
Apr 9 '19 at 12:11

What is the crystal structure of bismuth oxyhydroxyphosphate (BOHP)?

Not exactly sure what an answer looks like so here is everything.

First off looking at the diffraction pattern from the paper, bismuth oxyhydroxyphosphate matches that of petitjeanite so that is definately the prototype structure.

Using the information about diffraction, from the ICDD Databse (pdf 01-082-8058)we find that petitjeanite is a triclinic system of the $$\mathrm P\bar 1$$ space group (#2). with lattice parameters of:

$$\require{mediawiki-texvc}$$ $$a = 9.798\AA; ~ b = 7.250\AA; ~ c= 6.866 \AA; \qquad \alpha = 88.280^\circ \beta = 115.270^\circ ~ \gamma = 110.700^\circ$$

and atomic positions of: $$\begin{array}{c|lll} \text{Atom}&x&y&z\\ \hline \ce{Bi}&~~~0.52327&~~~0.41421&~~~0.7523\\ \ce{Bi}&~~~0.29838&~~~0.74044&~~~0.55549\\ \ce{Bi}&~~~0.07735&~~~0.1609&~~~0.28045\\ \ce{P}&~~~0.6952&~~~0.0172&~~~0.9215\\ \ce{P}&~~~0.0961&~~~0.372&~~~0.7862\\ \ce{O}&~~~0.3777&~~~0.5382&~~~0.4759\\ \ce{O}&~~~0.3066&~~~0.1549&~~~0.5579\\ \ce{O}&~~~0.859&~~~0.0275&~~~0.8943\\ \ce{O}&~~~0.5569&-0.2084&~~~0.8602\\ \ce{O}&~~~0.621&~~~0.1596&~~~0.7526\\ \ce{O}&~~~0.7684&~~~0.1052&~~~1.1811\\ \ce{O}&~~~0.2584&~~~0.5101&~~~0.7497\\ \ce{O}&-0.0468&~~~0.4637&~~~0.6902\\ \ce{O}&~~~0.0209&~~~0.1498&~~~0.6362\\ \ce{O}&~~~0.1695&~~~0.3727&~~~1.0506\\ \end{array}$$

and last but not least this renders to an image of:

Purple: Bi
Orange: P
Red: O

• Oh this is excellent! You've answered from the points of view of several disciplines, how lovely! The last but not least image of the unit cell is what I was hoping for but the list of atom coordinates is helpful too if I want to stay indoors this weekend and make more space-filling models. Visualization is hard for me, I can't figure out the four disembodied (apparently unbonded) orange oxygens(?) not connect to anything, nor why I can't see an outside-the-box oxygen corresponding to 0.7684 0.1052 1.1811 with z>1, but those are challenges for me ;-) Thank you!
– uhoh
Apr 12 '19 at 23:36
• @uhoh those are phosphorous. I have ammended a legend. If my crystal maker skills were better there would be more images.
– A.K.
Apr 13 '19 at 0:46