These values corresponded to Fe3+ ions on tetrahedral A-sites

and Fe2.5+-like average signals from octahedral B-sites, respectively, and were identified as magnetite (Fe3O4). The SX2_U spectral component with hyperfine parameters of B hf = 51.6 T, δ = 0.45 mm/s; ΔE Q = −0.13 mm/s was attributed to hematite (Fe2O3). The latter iron oxide was also detected by XRD. For the as-received sample, the hyperfine parameters determined Metformin clinical trial for D1_U and D2_U were δ = 0.45 mm/s; ΔE Q = 0.95 mm/s and δ = 0.79 mm/s; ΔE Q = 2.33 mm/s characteristic of ferric and ferrous ions, respectively. The quadrupole split doublets were attributed to silicates. Figure 10 Room-temperature 57 Fe Mössbauer spectra for (a) as-received and (b) acetylene-treated coal fly ash sample at 700°C. Table 2 Room-temperature Mössbauer parameters for as-received and acetylene-treated coal fly ash samples   Values As-received SX1_U SX2_U SX3_U D1_U D2_U   B hf (T) 49.0 51.6 44.2 – -  δ (mm/s) 0.40 0.45 0.59 0.45 0.79  ΔE Q (mm/s) −0.02 −0.13 −0.01 0.95 2.33  Area (%) 21 18 27 23 11 Treated SX1_T D1_T D2_T       B hf (t) 20.5 – -      δ (mm/s) 0.29 0.43 1.02      ΔE Q (mm/s) CH5424802 datasheet −0.003 0.41 2.15      Area (%) 49 21 30     The as-received sample showed that the total population of the oxides is 66% and 34% is attributed to silicates. After treatment, a

decrease in the area fraction of 17% was observed for the oxides with a corresponding increase in the silicates. After exposure to acetylene, only one sextet, SX1_T, with a reduced magnetic field was observed in the spectrum with hyperfine parameters of B hf = 20.5 T, δ = 0.29 mm/s; ΔE Q = −0.003 mm/s which has been identified as nanocrystalline iron

carbide (Fe3C). The hyperfine parameters of δ = 0.43 mm/s; ΔE Q = 0.41 mm/s and δ = 1.02 mm/s; ΔE Q = 2.15 mm/s obtained for D1_T and D2_T, respectively, were very similar to those obtained for the as-received PLEKHM2 sample except for the quadrupole splitting of D1_T which was lower and indicated some structural relaxation. For the as-received fly ash sample, the total population of the oxides was 66% with the remaining fraction of 34% attributed to silicates. After exposure to acetylene, a decrease in the area fraction of 17% was observed for the oxides with a corresponding increase in the silicates. The abundance of the Fe2+ state before treatment was approximately 11% but showed an increase of approximately 19% after acetylene treatment due to the reduced magnetic field. These results indicate a reduction in the oxidation state of iron (with decreasing oxide content), as a new phase of iron (Fe3C) and silica emerged. This suggestion is in agreement with He et al., who have studied Mössbauer spectroscopy of CNT formation from acetylene which reacted over iron-supported zeolite catalysts and who have found that the +3 oxidation state of iron was reduced to +2 by H2, which they concluded was the active phase for their synthesis [48]. Dunens et al.