Marshall,
You are correct, I meant Figure 4.
I did try and learn something about X-ray powder diffraction but was not
successful in the time I have. The numbers (111, 220) refer to planes of
atoms in a crystal. I found the following interesting:
http://prism.mit.edu/xray/BasicsofXRD.ppt
But it appears that you need a computer with a database to search for
the unique diffraction patterns for specific crystals. So I compared the
diffraction patterns in Figure 4 with those in Figure 1. The two planes
(200 and 222) identified in Figure 4 show up in Figure 1(b) at the same
2 theta angles as in Figure 4. So I felt that they did indeed represent
silver chloride.
Similarly Ag(111) in Figure 4 shows up at the 2 theta angle of 40. That
same (111) shows up in Figure 1(a) but not in Figure 1(b). I took this
to indicate Ag in Figure 1(a) but not in Figure 1(b).
There is a (111) in Figure 1(b) but it is at the wrong 2 theta angle for
silver so I assume it is some crystal other than Ag.
Admittedly this is somewhat simplistic but it is the best I can do under
the circumstances.
I am open to other information.
Thanks,
Steve N
-----Original Message-----
From: Marshall Dudley [mailto:mdud...@king-cart.com]
Sent: Thursday, September 30, 2010 1:35 PM
To: silver-list@eskimo.com
Subject: Re: CS>CS and killing of pathogens - Comments on HCl Study
On 9/30/2010 3:03 PM, Norton, Steve wrote:
> The paper specifically states for each test except 5 and 6 in my
> original comments that the silver nitrate derived nanoparticles were
> used so let's skip discussing silver oxide.
>
> 1) Figure 1(a) shows the composition of the silver nitrate derived
> silver nanoparticle solution. Figure 5 identifies the XRD peak at
(111)
> to be Ag.
I presume you mean figure 4, there is no figure 5. Actually they
identify it as Ag(111). Do you know what these number (111, 220) are
referring to? Somehow they do not make sense, for instance in Fig. 1(b)
311 is locatd between 220 and 222, and 222 is located between 311 and
400. Also the 111 peak jumps around depending on where they seem to
want it, moving far left on the 1(b). Somehow this does not seem right
and is inconsistent with other paper's reports of these peaks.
> And Figure 1(a) clearly shows a prominent peak at (111). The
> broadening of peaks in Figure 1(a) is described as indicating the very
> small sizes of Ag crystallites.
The peak at 111 is simply one of many possible forms of Ag crystal,
including 200, 220 and 311.
> Figure 1(b) shows the composition of the silver solution after the
> reaction with HCL. The Ag peak at (111) is greatly diminished.
> Significant peaks at (200) and (220) now show in the XRD pattern.
Figure
> 5 identifies the XRD peaks at (200) and (220) as belonging to silver
> chloride.
Are the peaks at 200 and 220 REALLY silver chloride? Figure 1B of
another paper ( www.springerlink.com/index/710W187LW403T65T.pdf ) says
that this is simply different forms of silver crystals - "Figure 1B .. A
number of strong Bragg reflections can be seen which correspond to the
(111), (200), (220), (311) reflections of cc (cubic crystals of)
silver." If this is accurate, and I believe it is, that completely
blows their theory out of the water since these peaks correspond with
aggregated silver crystals and not silver chloride. Since (111) is I
believe the smallest crystal form, then that it diminishes and the other
forms increase is completely expected when particles aggregate into
larger crystals.
> Now, combine those results with the UV-vis absorption spectra shown in
> Figure 2. The spectra of the silver solution after the reaction with
HCL
> indicates little or no silver particles remaining.
This is true for both of our analysis. They presume that the silver
chloride precipitates out, I presume that the aggregated silver
particles precipitate out. That is that this result supports both
hypothesizes. Actually it is VERY easy to test which is correct. Take
some 20 ppm EIS, and add a pinch of salt to it and let the silver
chloride precipitate out. Then add the HCl and see if you get any
additional silver chloride, if not then I am right, if so then they are.
>
> If the silver chloride resulted from only silver nitrate and not from
a
> reaction of HCl with the silver nanoparticles, I would expect to see
> indications of the silver particles still there.
Not if they aggregate and precipitate out as I have found they do when
the pH is dropped significantly. Colloidal silver is only stable in
water that is very near neutral or pH of 7. I see nothing that they are
doing that would prevent this expected aggregation and precipitation
when they drop the pH significantly.
> I would also expect to
> see smaller XRD peaks at (200) and (220) since little silver chloride
> should be produced by residue silver nitrate. Your conclusions would
> assume a level of incompetence in the researchers that is unimaginable
> to me.
No, they should be larger. First when hydrochloric acid is added to
silver nitrate it produces silver chloride and nitric acid. But that
should not change the peaks at 200 and 220 since those are crystalline
forms of silver (see additional analysis of this below). When the
crystals aggregate then the 111 drops and the higher orders increase.
These lines are NOT silver chloride but simply larger silver particles
as expected. I am not making any assumptions, I am simply analyzing the
data, but I do question their competence somewhat now upon further
research.
If we follow what happens if ANY silver nitrate is present we get the
following actions:
AgNO3 + HCl - > AgCl + HNO3 (nitric acid)
HNO3 + Ag - > AgNO3 + HCl
This means that if you have ANY silver nitrate available, it will take
place in a sequence of actions that will result in the conversion of
silver to silver chloride when HCl is added, but will remain unchanged,
that is it would be an active catalyst. Thus even if silver chloride IS
generated when adding HCl, the results are nullified if there is even a
trace of silver nitrate available since it would be taking place in the
reaction.
> 2) Figure 4 (There is no Figure 5) is for a separate test in which the
> chemical reactivity of Ag nanoparticles in a polymer matrix was also
> been investigated. A separate and unique polyacrylamide (PAM)/Ag
> nanocomposite was prepared and used for the test. I believe that the
> broad peaks in Figure 4 are caused by the PAM material. In any case,
> Figure 4 is not relevant to the Ag/HCl issue.
Except they are erroneously attributing the 200 peak to Silver chloride,
when in fact it is the peak of one of the crystalline forms of silver
particles.
Marshall
> Regards,
> Steve
>
>
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