Variations of Chemical Composition and Band Gap Energies in Hectorite and Montmorillonite Clay Minerals on Sub-Micron Length Scales

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1 Mission Kearney Foundation of Soil Science: Understanding and Managing Soil-Ecosystem Functions Across Spatial and Temporal Scales Final Report: , 1/1/ /31/2011 Variations of Chemical Composition and Band Gap Energies in Hectorite and Montmorillonite Clay Minerals on Sub-Micron Length Scales William Horwath*, Yan Ling Liang The relevance of clay minerals to humanity cannot be underestimated. Clays contribute to a plethora of soil processes and are believed to have played a role in the origin of life on earth (Porter et. al. 2000). In modern times clays are used for environmental remediation, catalytic reactions, industrial processes and chemical filtering. In the natural environment clay minerals can comprise a significant mass of soils, providing physical support and nutrients for plants, fauna and microbial life (Dixon and Weed 1989). A complete knowledge of the chemical, physical and electronic characteristics of clays is indispensible for understanding these natural and industrial processes. Due to the ubiquitous nature of clays minerals, any additional knowledge gained about the subject matter would be beneficial at many scales from soil microaggregates to soil pedons to large scale industrial and environmental systems. Our research focuses on the electronic properties of clay minerals, specifically the band gap energy of clay minerals on a spatially resolved sub-micron scale. Band gap energies are the energies required to promote an electron from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO). We are interested in this property because it has been shown to relate with many physical and chemical properties of molecules. For instance, band gap energies have been shown to play a part in determining optical properties of a material, determining the insulating/conducting properties, determining the stability of a product relative to its transition state and reactants, determining the degree of covalent/ionic bond nature between two atoms, determining the enthalpy of a reaction and determining a correlation to magic numbers in metal clusters [Pearson 1997, Pearson 1967]. To gain a more thorough understanding of clay mineral band gaps and the type of variability that can occur in natural environments based on band gap properties; we explored various methods of calculating and measuring band gap information. Three different methods were explored: theoretical modeling, a more commonly used method DR UV-Vis spectroscopy and a more novel method TEM-EELS. Results from the three methods are presented below. Department of Land, Air and Water Resources, University of California Davis * Principal Investigator For more information contact Dr. William Horwath (wrhorwath@ucdavis.edu)

2 Project Objectives Objective: Correlate the degree of isomorphic substitution (chemical composition) in Hectorite and Montmorillonite clays to the magnitude of the band gap measured on a sub-micron spatially resolved scale. o Hypothesis: We suspect that spatial areas of higher isomorphic substitution will have a smaller band gap, indicating higher reactivity of the area (lower electronic stability). Objective: Study the variation of chemical composition on the sub-micron spatially resolved scale for Hectorite and Montmorillonite clay minerals. Approach and Procedures Clay preparation o Clays were homogenized by ball milling until average particle size was 2 µm. After particle size homogenization, clays were saturated with Ca by multiple washing with 0.1 M Ca(NO 3 ) 2. Saturated clays were washed with DI water to remove excess nitrates and Ca precipitation products until no further Ca could be detected using UV-Vis spectroscopy. Particle-size analysis was performed with a Beckman Coulter LS-230 Particle Size Analyzer. Theoretical Modeling o Theoretical modeling was performed using Materials Studio, CASTEP model. o Hectorite and Montmorillonite crystal structure models were obtained from American Mineralogist Crystal Structure database. Diffuse Reflectance Ultraviolet-Visible Spectroscopy (DR UV-Vis Spec) o Instrumentation: Thermo Scientific Evolution 220 UV-Vis Spectrometer with Thermo INSIGHT software. Scan: nm, bandwidth: 1nm, integration time: 0.1 s, data interval: 1 nm, scan speed: 600 nm/min. Transmission Electron Microscopy-Electron Energy Loss Spectroscopy/Energy Dispersive Spectroscopy (TEM-EELS/EDS) o Instrumentation: JEOL 2500 TEM equipped with Fischione detector Clays were drop casted on holey carbon grids, decontaminated by exposure to incandescent light and stored under vacuum to minimize carbon contamination. TEM was aligned using basic alignment procedures, and then subsequently aligned in STEM mode. GIF tuning performed to maximize energy resolution in EELS. Data processed in Digital Micrograph software. EELS analysis (Digital Micrograph) includes Zero Loss Peak (ZLP) removal, then multiple scattering deconvolution. EDS quantification (Digital Micrograph) method used is a standardless k-factor method. 2

3 Results Theoretical Modeling Results and Diffuse Reflectance UV-Vis Spectroscopy Results Figures 1 and 2 show the density of states results modeled using CASTEP, the x axis is the energy of the electron state in ev and y axis is the Density of States (DOS). DOS indicates the probability of a particular electronic state at any energy level. According to the model, Hectorite theoretically has a band gap of approximately 4 ev (Figure 1). The theoretical band gap for Montmorillonite is 0 ev (Figure 2). A 4 ev band gap designates the material as an insulator, while 0 ev band gap indicates the material is a conductor. Figure 3 shows a DR UV-Vis spectrum where the x axis is energy in ev and y axis is arbitrary Abs units. The blue flat line is the Teflon blank (Figure 3). There is little noise in the measurements and the spectrum becomes noisier only at energies less than 2 ev and greater than 6 ev, which can be observed also in the sample spectrums (red and green curves in Figure 3). The red and green curves are Hectorite and Montmorillonite spectrums respectively. Hectorite has a larger range of band gaps from 1.5 ev to 6.5 ev compared to that of Montmorillonite which starts at 2 ev extending to 6.5 ev. Both clays have the majority of its band gaps residing at 4.75 ev. Figure 1. CASTEP theoretical modeling results for Hectorite clay mineral. 3

4 Figure 2. CASTEP theoretical modeling results for Montmorillonite clay mineral. Figure 3. Diffuse Reflectance UV-Vis data for Hectorite, Montmorillonite and Teflon blank. X axis is energy in ev, y axis is arbitrary Abs units. 4

5 TEM-EELS and TEM-EDS Results Table 1 summarizes the band gaps and elemental composition of Hectorite clay particle H1 shown in Image 1. The box #s in Table 1 correspond to the appropriately labeled colored boxes in Image 1. O, Si, Mg and Ca atom % does not add up to 100%, the remaining element not included in the tables is C, which accounts for the remaining atoms %. The band gap measured by TEM-EELS ranges from 3.25 to 3.6 ev, giving a range of 0.35 ev. The average band gap value is 3.4 ev. The overall atom % can fluctuate greatly for each individual element (the signals of O, Si, and Mg) depending on the atom % of carbon contributing to the EDS (Table 1). Despite the large variation that can occur with the raw elemental EDS signals, the ratios of these raw elements Si/Mg, Si/O and Mg/O remain relatively stable (Table 1). The Si/Mg ratio ranges from 1.16 to 1.31, giving a range of The Si/O ratio ranges from 0.32 to 0.41, range is The Mg/O ratio ranges from 0.24 to 0.31, range is This seems to indicate that the degree of isomorphic substitution in this particular Hectorite particle is fairly evenly distributed. Calcium atom % was too low to contribute to the EDS signal, which is a sign of a very low level of calcium coverage either on the surface and/or in the interlayers of the clay particle. In order to determine if a linear correlation of band gap energies with raw elemental atom % or the calculated ratios, the band gap value for each box # was plotted against each element O, Si, Mg and ratios Si/Mg, Si/O and Mg/O for the corresponding box #. The R 2 values, slopes and intercepts are summarized in Table 1. Si/Mg and Mg/O ratios gave the best linear correlations with band gap values, while the other elements and ratio gave significantly poorer linear correlation (less than 0.4). Table 2 summarizes the band gaps and elemental composition of Hectorite clay particle H2 shown in Image 2. The box #s in Table 2 correspond to the appropriately labeled colored boxes in Image 2. O, Si, Mg and Ca atom % do not add up to 100% in Table 2, the remaining element not included in the tables is C, which accounts for the remaining of the atoms %. The band gap measured by TEM- EELS ranges from 3.15 to 3.7 ev, giving a range of 0.55 ev. Box 14 (Table 2) gives a band gap of 5.05 ev, this is considerably larger than the other measured values from the same sample (Boxes 1-13). It is suspected that the EELS signal from the surrounding carbon grid overwhelms the EELS signal from the Hectorite particle, resulting in an inaccurate band gap which also includes a significant amount the carbon grid. Essentially, the band gap measured for box 14 (Table 2) is a mixed signal band gap of the carbon grid and H2 particle. The average band gap (disregarding box 14) is 3.4 ev. The atom % for O, Si and Mg can vary up to 10%, the element ratios appear to be more stable. The Si/Mg ratio ranges from 1.33 to 1.62, range is The Si/O ratio ranges from 0.36 to 0.54, range is The Mg/O ratio ranges from 0.27 to 0.39, range is Calcium atom % was too low to contribute to the EDS signal (Table 2), low levels of calcium surface coverage and/or interlayer coverage is suspected for particle H2. The R 2, slope and y-intercept values for the linear plots of band gaps against each element O, Si, Mg and ratios Si/Mg, Si/O and Mg/O are summarized in Table 2. The best correlation was found to be with oxygen, while the rest of the elements and ratios gave very poor correlations. 5

6 H1 Atom % Ratios Box # Band gap (ev) O ±O Si ±Si Mg ±Mg Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A O Si Mg Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca R^2 = Slope = Intercept = Table 1. TEM EELS and EDS data for Hectorite particle H1. Box #s correspond to box numbers in Image 1 below with respective EELS band gap information and EDS chemical composition information. R 2, slope and intercept values from linear fit of atom % and ratios against band gap values included. N/A results from the denominator being 0 atom %, rendering the ratios uninformative. 6

7 Image 1. Hectorite particle H1 images and box numbers. Corresponds to Table 1. Spectrum Image 0.5 µm 7

8 H2 Atom % Ratios Box # Band gap (ev) O ±O Si ±Si Mg ±Mg Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A O Si Mg Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca R^2 = Slope = Intercept = Table 2. TEM EELS and EDS data for Hectorite particle H2. Box #s correspond to box numbers in Image 2 below with respective EELS band gap information and EDS chemical composition information. R 2, slope and intercept values from linear fit of atom % and ratios against band gap values included. 8

9 Spectrum Image 1 µm Image 2. Hectorite particle H2 images and box numbers. Corresponds to Table 2. Table 3 below summarizes the band gaps and elemental composition of Hectorite clay particle H3 shown in Image 3. O, Si, Mg and Ca atom % does not add up to 100% in Table 3, the remaining element not included in the tables is C, which accounts for the remaining of the atoms % as previously mentioned. The band gap measured by TEM-EELS ranges from 1.65 to 7.2 ev, giving a range of 5.55 ev. This could suggest that particle H3 has a very large spatial variation in isomorphic substitution from one area to the next. The average band gap is approximately 4.5 ev. Si/Mg ratios range from 1.98 to 3.35, range is Si/Ca ratio range from 2.3 to 12.57, range is Mg/Ca ratios range from 1.14 to 5.2, range is Si/O ratios range from 0.68 to 1.1, range is Mg/O ratios range from 0.2 to 0.45, range is O/Ca ratios range from 3.37 to 16.21, range is The R 2, slope and y-intercept values from linear correlation of band gaps to element atom % (O, Si, Mg and Ca) and ratios (Si/Mg, Si/Ca, Mg/Ca, Si/O, Mg/O and O/Ca) for particle H3 are summarized in Table 3. The greatest linear correlation with band gaps was for Si/Mg ratios. The rest of the elements had linear correlations that were much poorer. Calcium concentration on particle H3 is significantly higher, averaging about 3.2 atom %. Possibly the high degree of spatial variation in isomorphic substitution contributed to such high calcium surface and interlayer coverage. Unfortunately, it cannot be distinguished where the calcium is on the surface, but since EDS signals arise from mainly surface elements, there is a good probability a major portion of the calcium signal is from surface sorbed Ca ions. 9

10 H3 Atom % Ratios Box # Band gap (ev) O ±O Si ±Si Mg ±Mg Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca O Si Mg Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca R^2 = E Slope = Intercept = Table 3. TEM EELS and EDS data for Hectorite particle H3. Box #s correspond to box numbers in Image 3 below with respective EELS band gap information and EDS chemical composition information. R 2, slope and intercept values from linear fit of atom % and ratios against band gap values included. 10

11 Spectrum Image 1 µm Image 3. Hectorite particle H3 images and box numbers. Corresponds to Table 3. H4 Atom % Ratios Box # Band gap (ev) O ±O Si ±Si Mg ±Mg Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca N/A N/A N/A O Si Mg Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca R^2 = Slope = Intercept = Table 4. TEM EELS and EDS data for Hectorite particle H4. Box #s correspond to box numbers in Image 4 below with respective EELS band gap information and EDS chemical composition information. R 2, slope and intercept values from linear fit of atom % and ratios against band gap values included. 11

12 Table 4 summarizes the band gaps and elemental composition of Hectorite clay particle H4 shown in Image 4. O, Si, Mg and Ca atom % does not add up to 100% in Table 4, the remaining element not included in the table is C, which accounts for the remaining atoms %. The band gap measured by TEM-EELS ranges from 4.0 to 4.55 ev, giving a range of 0.55 ev. The small number of boxes taken resulted from the particle being too small and the EDS signal being too low, larger areas had to be summed for an acceptable signal for quantification. The average band gap is 4.25 ev. Si/Mg ratios range from 1.71 to 2.63, range is Si/Ca ratios range from to 79.18, range is Mg/Ca ratios range from to 42.18, range is Si/O ratio ranges from 0.71 to 0.99, range is Mg/O ratios range from 0.36 to 0.41, range is O/Ca ratios range from to , range is Ratios where calcium is the dominator tend on the larger side due to the small Ca atom %. The R 2, slope and y-intercept values from linear correlation of band gaps to element atom % and ratios for particle H4 are summarized in Table 4. The best linear correlation was given by Si/O ratio, while Ca and Si atom % also gave nearly as good quality linear fits as Si/O ratio. Calcium sorption on particle H4 accounts for an average of 0.4 atom %, though there is a large standard deviation associated, giving a possibly calcium coverage range of 0.15 to 0.9 atom %. Image 4. Hectorite particles H4 and H5 images and box numbers. Corresponds to Tables 4 & 5. 12

13 Table 5 below summarizes the band gaps and elemental composition of Hectorite clay particle H5 shown in Image 4. O, Si, Mg and Ca atom % does not add up to 100% in Table 5, the remaining element not included in the tables is C, which accounts for the remaining of the atoms %. The band gap measured by TEM-EELS ranges from 3.65 to 4.6 ev, giving a range of 0.95 ev. The average band gap is 4.2 ev. Si/Mg ratios range from 1.76 to 2.6, range is Si/Ca ratios range from to 95.17, range is Mg/Ca ratios range from to 54.03, range is Si/O ratios range from 0.72 to 0.97, range is Mg/O ratios range from 0.34 to 0.47, range is O/Ca ratios range from to , range is Ratios where calcium is the dominator is one or more magnitude greater than other ratios due to the small Ca atom %. The best linear correlation with band gap values (Table 5) was given by Si/O ratio, with Si and Ca atom % giving also a good linear fit. Calcium surface/interlayer coverage accounted for an average of 0.6 atom %. Table 6 summarizes the band gaps and elemental composition of Hectorite clay particle H6 shown in Image 5. O, Si, Mg and Ca atom % does not add up to 100% in Table 6, the remaining element not included in the tables is C, which accounts for the remaining of the atoms %. The band gap measured by TEM-EELS ranges from 4.05 to 4.4 ev, giving a range of 0.35 ev. The average band gap is 4.2 ev. O, Si, Mg and Ca atom % does not add up to 100% in Table 6, the remaining element not included in the tables is C which accounts for the remaining of the atoms %. Box 1 (Table 6) gave an extremely high level of calcium (5.64 atom %), the EDS signal used for this quantification was sufficiently high and there does not appear to be any reason to disregard this value. Si/Mg ratios range from 1.69 to 2.01, range is Si/Ca ratios range from 4.11 to 45.45, range is Mg/Ca ratios range from 2.29 to 24.24, range is Si/O ratios range from 0.72 to 0.85, range is Mg/O ratios range from 0.4 to 0.48, range is O/Ca ratios range from 5.59 to 57.82, range is The best linear correlation (Table 6) was given by Ca atom %, with Si/O ratio being nearly equally well fitted with the band gaps. The average calcium % coverage is 2.5 atom %, this is skewed by the large calcium coverage found in box 1. The most common coverage is 0.75 atom. 13

14 H5 Atom % Ratios Box # Band gap (ev) O ±O Si ±Si Mg ±Mg Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca O Si Mg Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca R^2 = Slope = Intercept = Table 5. TEM EELS and EDS data for Hectorite particle H5. Box #s correspond to box numbers in Image 4 above with respective EELS band gap information and EDS chemical composition information. 14

15 H6 Atom % Ratios Box # Band gap (ev) O ±O Si ±Si Mg ±Mg Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca O Si Mg Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca R^2 = Slope = Intercept = Table 6. TEM EELS and EDS data for Hectorite particle H6. Box #s correspond to box numbers in Image 5 below with respective EELS band gap information and EDS chemical composition information. R 2, slope and intercept values from linear fit of atom % and ratios against band gap values included. 15

16 Spectrum Image 0.5 µm Image 5. Hectorite particle H6 images and box numbers. Corresponds to Table 6. Table 7 summarizes the band gaps and elemental composition of Hectorite clay particle H7 shown in Image 6. O, Si, Mg and Ca atom % does not add up to 100% in Table 7, the remaining element not included in the tables is C, which accounts for the remaining of the atoms %. The band gap measured by TEM-EELS ranges from 3.5 to 3.65 ev, giving a range of 0.15 ev. The average band gap is 3.55 ev. Si/Mg ratios range from 1.75 to 1.98, range is Si/Ca ratios range from to 84.0, range is Mg/Ca ratios range from to 43.03, range is Si/O ratios range from 0.94 to 1.02, range is Mg/O ratios range from 0.47 to 0.56, range is O/Ca ratios range from to 82.18, range is The best linear correlation (Table 7) was given by O atom %, with Si/Ca and Mg/Ca ratios being nearly equally well fitted with the band gaps. The average calcium coverage is 0.55 atom %. 16

17 H7 Atom % Ratios Box # Band gap (ev) O ±O Si ±Si Mg ±Mg Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca O Si Mg Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca R^2 = Slope = Intercept = Table 7. TEM EELS and EDS data for Hectorite particle H7. Box #s correspond to box numbers in Image 6 below with respective EELS band gap information and EDS chemical composition information. R 2, slope and intercept values from linear fit of atom % and ratios against band gap values included. 17

18 H8 Atom % Ratios Box # Band gap (ev) O ±O Si ±Si Mg ±Mg Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca O Si Mg Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca R^2 = E Slope = Intercept = Table 8. TEM EELS and EDS data for Hectorite particle H8. Box #s correspond to box numbers in Image 6 below with respective EELS band gap information and EDS chemical composition information. R 2, slope and intercept values from linear fit of atom % and ratios against band gap values included. 18

19 H9 Atom % Ratios Box # Band gap (ev) O ±O Si ±Si Mg ±Mg Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca O Si Mg Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca R^2 = Slope = Intercept = Table 9. TEM EELS and EDS data for Hectorite particle H9. Box #s correspond to box numbers in Image 6 below with respective EELS band gap information and EDS chemical composition information. R 2, slope and intercept values from linear fit of atom % and ratios against band gap values included. H10 Atom % Ratios Box # Band gap (ev) O ±O Si ±Si Mg ±Mg Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca N/A N/A N/A Table 10. TEM EELS and EDS data for Hectorite particle H10. Box #s correspond to box numbers in Image 6 below with respective EELS band gap information and EDS chemical composition information. 19

20 H11 Atom % Ratios Box # Band gap (ev) O ±O Si ±Si Mg ±Mg Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca Table 11. TEM EELS and EDS data for Hectorite particle H11. Box #s correspond to box numbers in Image 6 below with respective EELS band gap information and EDS chemical composition information. Image 6. Hectorite particles H7, H8, H9, H10 and H11 images and box numbers. Corresponds to Tables 7, 8, 9, 10 and

21 Table 8 summarizes the band gaps and elemental composition of Hectorite clay particle H8 shown in Image 6. O, Si, Mg and Ca atom % does not add up to 100% in Table 8, the remaining element not included in the tables is C, which accounts for the remaining of the atoms %. The band gap measured by TEM-EELS ranges from 3.85 to 4.35 ev, giving a range of 0.5 ev. The average band gap is 4.1 ev. Si/Mg ratios range from 2.88 to 3.55, range is Si/Ca ratios range from 10.5 to 79.18, range is Mg/Ca ratios range from 4.5 to 42.18, range is Si/O ratios range from 0.37 to 1.38, range is Mg/O ratios range from 0.29 to 0.62, range is O/Ca ratios range from to , range is The best linear correlation (Table 8) was given by O atom %, with Si and Ca atom % being nearly equally well fitted with the band gaps. The average calcium coverage is 0.65 atom %. Table 9 summarizes the band gaps and elemental composition of Hectorite clay particle H9 shown in Image 6. The band gap measured by TEM-EELS ranges from 3.85 to 4.8 ev, giving a range of 0.95 ev. The average band gap is 4.3 ev. Si/Mg ratios range from 2.08 to 2.31, range is Si/Ca ratios range from to 77.42, range is Mg/Ca ratios range from to 37.23, range is Si/O ratios range from 1.29 to 1.53, range is Mg/O ratios range from 0.62 to 0.66, range is O/Ca ratios range from to 59.92, range is The best linear correlation with the band gap (Table 9) was given by Si atom %. No other element atom % or ratio seems to give a reasonably close linear fit with the band gap as Si. The average calcium coverage is 0.7 atom %. Tables 10 and 11 summarize the band gaps and elemental composition of Hectorite clay particles H10 and H11 respectively. The corresponding image to Tables 10 and 11 is Image 6. Due to their low EDS signals, these two particles were only able to be measured as a whole particle, they were not divided into various boxes. No linear correlation with the band gap was made for H10 and H11. Particle H10 did not have any measurable Ca EDS signal, while H11 has an average Ca coverage of.69 atom %. Table 12 below is a summary of the average band gap values, elemental atomic % and ratios from each observe Hectorite particle (H1 through H11). O, Si, Mg and Ca atom % does not add up to 100% in Table 12, the remaining element not included in the tables is C, which accounts for the remaining of the atoms %. All elemental atom % when comparing one Hectorite particle to the next have roughly the same variation range as did the variation ranges within the same Hectorite particle. Si/Mg ratios range from 1.28 to 3.13, range is This interparticle range (Table 12) is larger than any range observed within the same Hectorite particle, which has a maximum range of 1.37 (Table 13a). Inter-particle Si/Ca ratios range from 10.5 to 79.18, range is 68.68, which places this value in the larger variation range compared to values found in Table 13a, but is not the largest. Inter-particle Mg/Ca ratios range from 4.5 to 42.18, giving range of 37.68, also on the larger end of range values shown in Table 13a. Inter-particle Si/O ratios range from 0.37 to 1.38, giving a range of 1.01, not larger than the values shown in Table 13a but comparable. Inter-particle Mg/O ratios range from 0.29 to 0.63, giving range of 0.34, this is only slightly higher than the values in Table 13a. Inter-particle O/Ca ratios range from to , giving range of 94.54, not the largest variation when comparing to Table 13a (intra-particle variations) but is comparable to the larger values. The best linear correlation with the band gap (Table 12) was given by the Si/O ratio, with Si atom percent being almost as good a linear fit. 21

22 H# Band gap (ev) O ±O Si ±Si Mg ±Mg Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca N/A N/A N/A N/A N/A N/A N/A N/A N/A Ratios O Si Mg Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca R^2 = E E Slope = Intercept = Table 12. TEM EELS and EDS data for Hectorite particles H1-H11, average values. R2, slope and intercept values from linear fit of atom % and ratios against band gap values included. Table 13 is a summary of the R 2 values that correspond to Table 12. The orange highlighted cells are the elemental atom % or ratio which gave the greatest linear correlation with band gap values, while the purple highlighted cells are those that gave comparable linear correlations to the orange cells. O atom %, Si atom %, Si/Mg and Si/O ratios (Table 13) seemed to correlate well with the band gap values more often when compared to other atom % or ratios. No one single element or ratio gave the best linear correlations consistently. About 50% of the highlighted R 2 values were under 0.5, which indicates a poor linear relationship despite it being the best correlation when compared to other elements and ratios with the same H#. 22

23 H# O Si Mg Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca 1 R^2 = N/A N/A N/A N/A 2 R^2 = N/A N/A N/A N/A 3 R^2 = R^2 = R^2 = R^2 = R^2 = R^2 = R^2 = Table 13. Summary of R 2 values for particles H1-H9 averages, R 2 values corresponds to Table 12 values. Particle Min. Band Gap (ev) Max. Band Gap (ev) Band Gap Range (ev) Ca atom % Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca H N/A N/A N/A H N/A N/A N/A H H H H H H H H10 N/A N/A #VALUE! N/A N/A N/A N/A N/A N/A N/A H11 N/A N/A #VALUE! N/A N/A N/A N/A N/A N/A N/A 23 Ranges Ca atom % Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca R^2 = Slope = Intercept = Table 13a. Summary of the minimum band gap values, maximum band gap values, band gap ranges, average Ca atom %, and Si/Mg, Si/Ca, Mg/Ca, Si/O, Mg/O and O/Ca ranges for particles from Tables 1-11.

24 Table 13a is a summary of the minimum band gap values, maximum band gap values, band gap ranges, average Ca atom %, and Si/Mg, Si/Ca, Mg/Ca, Si/O, Mg/O and O/Ca ranges for particles from Tables In order to calculate the R 2, slope and y-intercept values band gap ranges were plotted against Ca atom %, Si/Mg, Si/Ca, Mg/Ca, Si/O, Mg/O and O/Ca ranges. The highest correlation found was between band gap ranges and Ca atom % (table 13a). Variation range of Si/Mg ratio also gave a decent linear correlation with band gap ranges. M1 Atom % Ratios Box # Band gap (ev) O ±O Si ±Si Mg ±Mg Al ±Al Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca Si/Al Al/Mg O/Al N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A 9.52 N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A O Si Mg Al Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca Si/Al Al/Mg O/Al R^2 = Slope = Intercept = Table 14. TEM EELS and EDS data for Montmorillonite particle M1. Box #s correspond to box numbers in Image 7 below with respective EELS band gap information and EDS chemical composition information. R2, slope and intercept values from linear fit of atom % and ratios against band gap values included. 24

25 Table 14 above summarizes the band gaps and elemental composition of Montmorillonite clay particle M1 shown in Image 7. The band gap measured by TEM-EELS ranges from 3.6 to 5.7 ev, giving a range of 2.1 ev. The average band gap is 4.6 ev. O, Si, Mg, Al and Ca atom % does not add up to 100% in Table 14, the remaining element not included in the table is C which accounts for the remaining of the atoms %. Si/Mg ratios range from to , range is Si/O ratios range from 0.85 to 1.46, range is Mg/O ratios range from 0.01 to 0.06, range is Si/Al ratios range from 9.52 to 31.45, range is Al/Mg ratios range from 1.19 to 8.54, range is O/Al ratios range from 9.29 to 29.89, range is The best linear correlation with band gaps (Table 14) was given by Si atom %. The majority of the boxes (Table 14, Image 7) resulted in a calcium signal that was too low to be quantified, however summing over a larger area (box # 12, Table 14) gave an average calcium coverage is 0.19 atom %. The degree of isomorphic substitution (based on Mg atom %) is random and low and was only measurable in boxes 5, 7 and 9 (Image 7, Table 14). Spectrum Image 0.2 µm Image 7. Montmorillonite particle M1 images and box numbers. Corresponds to Table 14. Table 15 summarizes the band gaps and elemental composition of Montmorillonite clay particle M2 shown in Image 8. The band gap measured by TEM-EELS ranges from 3.8 to 4.55 ev, giving a range of 0.75 ev. The average band gap is 4.3 ev. Same as with other tables O, Si, Mg, Al and Ca atom % does not add up to 100% in Table 15, the remaining element not included in the table is C, which accounts for the remaining of the atoms %. Si/Mg ratios range from to , range is Si/Ca ratios range from to , range is Mg/Ca ratios range from 0 to 5.0, range is 5. Si/O ratios range from 0.92 to 1.55, range is Mg/O ratios range from 0 to 0.07, range is O/Ca ratios range from to 143.0, range is Si/Al ratios range from 3.11 to 18.22, range is Al/Mg ratios range from 3.64 to 10.5, range is O/Al ratios range from 2.8 to 13.35, range is The best linear correlation with band gaps (Table 15) was given by Si/Al ratios, with O/Al ratios being nearly as well fitted to the band gaps. The average calcium coverage is 0.35 atom %. Isomorphic substitution of Mg for Al is more evenly distributed and prominent in M2 compared with M1. Mg atom % can range from 0 % to 2.65 %, 2.65 % being an area with higher isomorphic substitution. 25

26 M2 Atom % Ratios Box # Band gap (ev) O ±O Si ±Si Mg ±Mg Al ±Al Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca Si/Al Al/Mg O/Al N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A O Si Mg Al Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca Si/Al Al/Mg O/Al R^2 = Slope = Intercept = Table 15. TEM EELS and EDS data for Montmorillonite particle M2. Box #s correspond to box numbers in Image 8 below with respective EELS band gap information and EDS chemical composition information. R2, slope and intercept values from linear fit of atom % and ratios against band gap values included. 26

27 Table 16 summarizes the band gaps and elemental composition of Montmorillonite clay particle M3 shown in Image 9. The band gap measured by TEM-EELS ranges from 3.5 to 4.0 ev, giving a range of 0.5 ev. The average band gap is 3.75 ev. Si/Mg ratios range from to , range is Si/O ratios range from 0.92 to 1.39, range is Si/Al ratios range from 9.68 to 29.85, range is Al/Mg ratios range from 5.42 to 10.88, range is O/Al ratios range from 6.94 to 28.65, range is The best linear correlation with band gaps (Table 16) was given by Si/Al ratios, with Si/O ratios being nearly as well fitted to the band gaps. There is no detectable calcium coverage on particle M3. Based on Mg atom %, particle M3 has an isomorphic substitution of 0.16 atom % where Mg is substituting for Al. Spectrum Image 0.5 µm Image 8. Montmorillonite particle M2 images and box numbers. Corresponds to Table

28 Spectrum Image 0.2 µm Image 9. Montmorillonite particle M3 images and box numbers. Corresponds to Table

29 M3 Atom % Ratios Box # Band gap (ev) O ±O Si ±Si Mg ±Mg Al ±Al Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca Si/Al Al/Mg O/Al N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A 9.68 N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A O Si Mg Al Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca Si/Al Al/Mg O/Al R^2 = Slope = Intercept = Table 16. TEM EELS and EDS data for Montmorillonite particle M3. Box #s correspond to box numbers in Image 9 above with respective EELS band gap information and EDS chemical composition information. R2, slope and intercept values from linear fit of atom % and ratios against band gap values included. 29

30 M4 Atom % Ratios Box # Band gap (ev) O ±O Si ±Si Mg ±Mg Al ±Al Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca Si/Al Al/Mg O/Al N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A 7.52 N/A N/A N/A N/A N/A 8.88 N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A 7.32 N/A N/A N/A N/A N/A N/A N/A O Si Mg Al Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca Si/Al Al/Mg O/Al R^2 = Slope = Intercept = E Table 17. TEM EELS and EDS data for Montmorillonite particle M4. Box #s correspond to box numbers in Image 10 below with respective EELS band gap information and EDS chemical composition information. R2, slope and intercept values from linear fit of atom % and ratios against band gap values included. 30

31 Spectrum Image 0.5 µm Image 10. Montmorillonite particle M4 images and box numbers. Corresponds to Table

32 M5 Atom % Ratios Box # Band gap (ev) O ±O Si ±Si Mg ±Mg Al ±Al Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca Si/Al Al/Mg O/Al N/A N/A N/A N/A 6.38 N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A 6.48 N/A O Si Mg Al Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca Si/Al Al/Mg O/Al R^2 = Slope = Intercept = Table 18. TEM EELS and EDS data for Montmorillonite particle M5. Box #s correspond to box numbers in Image 11 below with respective EELS band gap information and EDS chemical composition information. R2, slope and intercept values from linear fit of atom % and ratios against band gap values included. Table 17 summarizes the band gaps and elemental composition of Montmorillonite clay particle M4 shown in Image 10. The band gap measured by TEM-EELS ranges from 3.55 to 4.5 ev, giving a range of 0.95 ev. The average band gap is 4.0 ev. Si/Mg ratios range from to 63.8, range is Si/O ratios range from 0.86 to 1.11, range is Mg/O ratios range from 0 to 0.03, range is Si/Al ratios range from 7.09 to 19.04, range is Al/Mg ratios range from 2.74 to 7.74, range is 5. O/Al ratios range from 6.69 to 18.09, range is The best linear correlation with band gaps (Table 17) was given by Si/O ratios. There is no detectable calcium coverage on particle M4. The isomorphic substitution of Mg for Al in particle M4 is fairly evenly distributed. Isomorphic ranges from 0 to 0.86 atom % (Table 17). Table 18 above summarizes the band gaps and elemental composition of Montmorillonite clay particle M5 shown in Image 11. The band gap measured by TEM-EELS ranges from 2.45 to 2.85 ev, giving a range of 0.4 ev. The average band gap is 2.65 ev. Si/O ratios range from 0.46 to 0.58, range is Si/Al ratios range from 6.38 to 6.48, range is 0.1. O/Al ratios range from to 13.73, range is The best linear correlation with band gaps (Table 18) was given by O atom %, with Si/O ratios being nearly equally well fitted. There is no detectable calcium coverage on particle M5. Isomorphic substitution on particle M5 was not detectable (Table 18). 32

33 Spectrum Image 0.5 µm Image 11. Montmorillonite particle M5 images and box numbers. Corresponds to Table 18. Table 19 below summarizes the band gaps and elemental composition of Montmorillonite clay particle M6 shown in Image 12. The band gap measured by TEM-EELS ranges from 6.6 to 8.9 ev, giving a range of 2.3 ev. The average band gap is 7.75 ev. Si/O ratios range from 0.34 to 0.56, range is Si/Al ratios range from 7.53 to 7.76, range is The best linear correlation with band gaps (Table 19) was given by O atom %, with Si/O ratios and Si atom % being nearly equally well fitted. There is no detectable calcium coverage on particle M6. Isomorphic substitution on particle M6 was not detectable (Table 19). 33

34 M6 Atom % Ratios Box # Band gap (ev) O ±O Si ±Si Mg ±Mg Al ±Al Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca Si/Al Al/Mg O/Al N/A N/A N/A N/A 7.53 N/A N/A N/A N/A N/A 7.76 N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A O Si Mg Al Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca Si/Al Al/Mg O/Al R^2 = Slope = Intercept = Table 19. TEM EELS and EDS data for Montmorillonite particle M6. Box #s correspond to box numbers in Image 12 below with respective EELS band gap information and EDS chemical composition information. R2, slope and intercept values from linear fit of atom % and ratios against band gap values included. Spectrum Image 0.5 µm Image 12. Montmorillonite particle M6 images and box numbers. Corresponds to Table

35 Table 20 below summarizes the band gaps and elemental composition of Montmorillonite clay particle M7 shown in Image 13. The band gap measured by TEM-EELS ranges from 3.1 to 5.7 ev, giving a range of 2.6 ev. The average band gap is 4.4 ev. Si/Mg ratios range from to 57.83, range is Si/Ca ratios range from 84.1 to , range is Mg/Ca ratios range from 1.82 to 6.1, range is Si/O ratios range from 0.9 to 1.22, range is Mg/O ratios range from 0 to 0.04, range is O/Ca ratios range from to , range is Si/Al ratios range from 9.66 to 12.26, range is Al/Mg ratios range from 3.93 to 8.19, range is O/Al ratios range from 5.33 to 16.05, range is The best linear correlation with band gaps (Table 20) was given by Ca atom %. Ca coverage ranged from 0 to 0.49 atom %, the distribution of Ca atoms appears to be evenly distributed on a 0.25 µm scale. Isomorphic substitution on particle M7 does seem to be consistently distributed. Mg atom % values and Al/Mg ratios do not indicate an unusually high level of isomorphic substitution than other Montmorillonite particles observed. 35

36 M7 Atom % Ratios Box # Band gap (ev) O ±O Si ±Si Mg ±Mg Al ±Al Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca Si/Al Al/Mg O/Al N/A N/A N/A N/A N/A N/A N/A 9.44 N/A N/A N/A N/A N/A N/A N/A N/A 7.46 N/A 6.69 Table 20. TEM EELS and EDS data for Montmorillonite particle M7. Box #s correspond to box numbers in Image 13 below with respective EELS band gap information and EDS chemical composition information. R2, slope and intercept values from linear fit of atom % and ratios against band gap values included. 36

37 M7 Atom % Ratios Box # Band gap (ev) O ±O Si ±Si Mg ±Mg Al ±Al Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca Si/Al Al/Mg O/Al N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A O Si Mg Al Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca Si/Al Al/Mg O/Al R^2 = Slope = Intercept = Table 20 cont. TEM EELS and EDS data for Montmorillonite particle M7. Box #s correspond to box numbers in Image 13 below with respective EELS band gap information and EDS chemical composition information. R2, slope and intercept values from linear fit of atom % and ratios against band gap values included. 37

38 Spectrum Image 1 µm Image 13. Montmorillonite particle M7 images and box numbers. Corresponds to Table 20. Table 21 below summarizes the band gaps and elemental composition of Montmorillonite clay particle M9 shown in Image 14. The band gap measured by TEM-EELS ranges from 4.45 to 6.5 ev, giving a range of 2.05 ev. The average band gap is 5.5 ev. Si/Mg ratios range from to 111.6, range is Si/Ca ratios range from to , range is Si/O ratios range from 1.03 to 1.2, range is Mg/O ratios range from 0 to 0.02, range is O/Ca ratios range from to , range is Si/Al ratios range from to 16.91, range is Al/Mg ratios range from 5.59 to 7.81, range is O/Al ratios range from 8.92 to 15.22, range is 6.3. The best linear correlation with band gaps (Table 21) was given by Si/Al ratios, O/Al ratios also give nearly as good linear fits. Ca coverage ranged from 0 to 0.49 atom % and the distribution of Ca atoms appears to be random. On average, there appear to be little detectable Ca ion coverage. Isomorphic substitution on particle M9 does not seem to be consistently distributed; there are areas where no calcium is detected and other areas (box 4 & 6, Table 21) where there is detected calcium coverage. The calcium coverage did not correlate with areas where Mg isomorphic substitution occurred. Mg atom % values and Al/Mg ratios are comparable to other Montmorillonite particles observed. 38

39 M9 Atom % Ratios Box # Band gap (ev) O ±O Si ±Si Mg ±Mg Al ±Al Ca ±Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca Si/Al Al/Mg O/Al N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A O Si Mg Al Ca Si/Mg Si/Ca Mg/Ca Si/O Mg/O O/Ca Si/Al Al/Mg O/Al R^2 = Slope = Intercept = Table 21. TEM EELS and EDS data for Montmorillonite particle M9. Box #s correspond to box numbers in Image 14 below with respective EELS band gap information and EDS chemical composition information. R2, slope and intercept values from linear fit of atom % and ratios against band gap values included. Table 22 summarizes the band gaps and elemental composition of Montmorillonite clay particle M10 shown in Image 14. The band gap measured by TEM-EELS ranges from 3.45 to 5.6 ev, giving a range of 2.15 ev. The average band gap is 4.5 ev. Si/Mg ratios range from to , range is Si/Ca ratios range from to 253.1, range is Mg/Ca ratios range from 0 to 3.09, range is Si/O ratios range from 0.93 to 1.23, range is 0.3. Mg/O ratios range from 0 to 0.02, range is O/Ca ratios range from to 208.0, range is Si/Al ratios range from 9.03 to 20.21, range is Al/Mg ratios range from 4.4 to 8.63, range is O/Al ratios range from 8.39 to 18.27, range is The best linear correlation with band gaps (Table 22) was given by Si/Mg ratios, O atom % and Al/Mg ratios also give nearly as good linear fits. Ca coverage ranged from 0 to 0.27 atom % and the distribution of Ca atoms appears to be random. On average Ca ion coverage accounts for 0.25 atom %. Isomorphic substitution by Mg on particle M10 seem to be fairly equally distributed. Mg atom % values are comparable to other Montmorillonite particles observed. Al/Mg ratios are on the higher end indicating a lower degree of isomorphic substitution but still within the range of other particles observed. 39

40 Chemical Hardness Quantification of Clay Minerals Using Hard-Soft Acid-Base Principle Horwath Image 14. Montmorillonite particle M9-M13 images and box numbers. Corresponds to Tables Table 23 summarizes the band gap and elemental composition of Montmorillonite clay particle M11 shown in Image 14. Due to the small size and low EDS signal from this particle, the entire particle had to be summed to produce sufficient signal for quantification. Average Ca coverage is 0.51 atom %. Isomorphic substitution based on Al/Mg ratio 4.39 is within the range of observed degree of substitution, this ratio indicates an average degree of substitution compared to other observed Montmorillonite particles. 40