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The structural role of manganese ions in soil active silicate–phosphate glasses
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx
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The structural role of manganese ions in soil active silicate–phosphate glasses q Magdalena Szumera ⇑ Faculty of Materials Science and Ceramics, Dep. of Ceramics and Refractories, AGH University of Science and Technology, Krakow, Poland
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Glasses from the
SiO2AP2O5AK2OACaOAMgOAMnO2 system were prepared and analyzed. Glasses were characterized by spectroscopic methods. The relation between the structure and chemical activity of glasses was found.
a r t i c l e
i n f o
Article history: Received 25 October 2013 Received in revised form 7 March 2014 Accepted 22 March 2014 Available online xxxx Keywords: Silicate–phosphate glasses Manganese ions Glass structure FTIR and Raman spectroscopies Chemical activity
a b s t r a c t Silicate–phosphate glasses of SiO2AP2O5AK2OAMgOACaO system containing manganese ions were synthesized by the melt-quenching technique and were investigated to obtain information about the influence of Mn-cations on the glass structure and their chemical activity. Structural properties were studied using X-ray method, FTIR and Raman spectroscopies. The chemical activity of analyzed glasses in the 2 wt.% citric acid solution was measured by chemical analysis (ICP-AES, EDS) and SEM observations. It has been found that increasing amount of MnO2 in the structure of investigated glasses causes their gradual depolymerization. This process is more apparent in the case of the silico-oxygen subnetwork than phospho-oxygen one. This is related to increasing amounts of SiO4 tetrahedra containing two nonbridging oxygen atoms in silico-oxygen subnetwork. It has been also found that the presence of ‘‘weaker’’ chemical bonds of SiAOAMn type in comparison to SiAOACa and SiAOAMg bonds is responsible for the increase in solubility of the analyzed silicate–phosphate glasses in conditions simulating natural soil environment. Ó 2014 Elsevier B.V. All rights reserved.
Introduction It is known that oxide glasses, mainly those of polymeric structure, like silicate, borate and phosphate, and mixed network glasses, like alumino-silicate, boro-silicate and phospho-silicate
q Selected paper presented at XIIth International Conference on Molecular spectroscopy, Kraków – Białka Tatrzan´ska, Poland, September 8–12, 2013. ⇑ Tel.: +48 6172480; fax: +48 6334630. E-mail address: [email protected]
glasses or other three or more network-formers containing glasses have a unique ability to include into their structure a wide range of chemical compounds which can coexist together in an oxide glass structure [1]. The development of inorganic silicate and phosphate glasses has attracted both academic and industrial interest in recent years [2]. In literature, several authors [2–5] have shown that technologically interesting products can be obtained by multicomponent network formation and also by doping transition metal ions in these competitive networks [2,6]. One of the interesting glass structure modifier is manganese ion. It is known that the
http://dx.doi.org/10.1016/j.saa.2014.03.102 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: M. Szumera, The structural role of manganese ions in soil active silicate–phosphate glasses, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.03.102
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introduction of manganese ions in a glass composition leads to changes in their structure and confers interesting properties, e.g. electrical, optical and magnetic [7–10]. It is also known that both Mn2+ and Mn3+ ions are well-known paramagnetic ions. Mn3+ ion has a large magnetic anisotropy due to its strong spin–orbit interaction of the 3d orbital whereas such anisotropy energy of Mn2+ ion is small because its orbital angular momentum is zero [11]. Because of its paramagnetic properties it is often referred to as a luminescent activator [12]. Manganese ions exist in different valence states with different coordination in glass matrices. Mn3+ ions exist in borate glasses with octahedral coordination, whereas in silicate and germinate glasses as Mn2+ with both tetrahedral and octahedral environment [11,13]. Introduction of the MnO into the structure of silicate glasses when its concentration is around 1.0 mol% [14] and up to 20 mol% in phosphate glasses [7], indicates that manganese ions mostly exist in Mn2+ state, occupy network forming positions with MnO4 structural units or play the role of vitreous network modifier in the phosphate glasses, but when its concentration, in both silicate and phosphate glasses, is higher these ions seem to exist mostly in the Mn3+ state and occupy only modifying position. The FTIR studies conducted by Pascuta and others [7] show that the controlled addition of MnO in the MnOAP2O5AZnO system generates several rearrangements in the network structure at the short-range order level. The authors suggested that it may be due to the formation of the PAOAMn bonds at the expense of the rest of the PAOAP linkages. The formation of bridging oxygen (PAOAMn) would increase the cross-link density of the glass network improving the chemical durability of the glass. The authors concluded that with increasing content of MnO in the phosphate, glass structure increases, confirming the role of manganese ions as glass modifiers. These results are also confirmed by other scientists [2,15–17]. Simultaneously, Soliman et al. [14], Mohan et al. [18] and Durga and Veeraiah [13] maintain that in the case of silicate glasses the number of silicon ions associate with one or more nonbridging oxygens increases, because of the excess of manganese ions which are able to associate with silicon. This leads to a decrease in the polymerization of the silicate network and expands the structure of the glass structure and in turn, leads to an increase in the molar volume. Also a decrease in density beyond 0.4 mol% MnO2 supported that the network weakened as manganese oxide is accommodated in the glass including a rearrangement of the network. Until now, extensive studies are conducted mostly on the structure of Mn-doped silicate or phosphate glasses, but not silicate– phosphate glasses. Therefore, the author has undertaken detailed studies using XRD, FTIR and Raman techniques as analytical methods in order to examine the effect of MnO2 addition into the structure of model silicate–phosphate glasses from SiO2AP2O5A K2OACaOAMgO system acting as ecological fertilizers providing a controlled release rate of the nutrients for plants. In these glasses manganese plays a role of a micronutrient necessary for the proper development of plants [19]. Manganese influences plants’ growth
process by regulation of ox-redox reactions and activation of some enzymes in the metabolic processes of plants. Additionally, the author has determined the relation between the structure of analyzed MnO2-doped silicate–phosphate glasses and their chemical activity under conditions simulating the biological soil environment. Experimental procedure Preparation of the glasses Silicate–phosphate glasses from SiO2AP2O5AK2OACaOAMgO system modified by MnO2 addition were prepared. In all glasses, constant quantities of P2O5, K2O, and SiO2 were kept, and the increasing amount of MnO2 was introduced at the cost of the decreasing amount of MgO and CaO, with the constant MgO/CaO ratio. The silicate–phosphate glasses were produced by traditional melting of raw materials mixture, i.e., SiO2, H3PO4, K2CO3, MgO, CaCO3, and MnO2 in platinum crucibles at 1300–1450 °C. Then the obtained amorphous material was fritted in water. All glasses were ground to grain size of 0.1–0.3 mm. X-ray fluorescence spectroscopy The chemical composition of glasses was controlled by X-ray fluorescence spectroscopy using ARL Advant ‘XP spectrometer. Chemical composition of the examined glasses was presented in Table 1. Amorphous state of the analyzed silicate–phosphate glasses was confirmed by X-ray diffraction method. FTIR spectroscopy Middle infrared (MIR) spectroscopic measurements of the glasses were made with a Bruker Vertex 70v spectrometer. Transmission technique, samples as KBr pellets. Spectra were collected after 124 scans at 4 cm 1 resolution. The position of bands on the MIR spectra was defined automatically in Win-IR. Spectra decomposition has been carried out according to the mathematical self-deconvolution method using the minimization of the number of the bands rule, proposed by Handke et al. [20]. Raman spectroscopy Raman studies were caried out using Horriba Yvon Jobin LabRAM HR micro-Raman spectrometer equipped with a CCD detector. Excitation wavelength of 532 nm was used and beam intensity was about 10 mW. Acquisition time was set to 30 s. The position of bands on the Raman spectra was defined automatically in Win-IR. Due to the high level of noise, for better legibility of the spectra, it was necessary to conduct Fourier smoothing of the Raman spectra.
Table 1 The chemical composition of silicate–phosphate glasses studied in the present work. No
0 Mn 1.7 Mn 3.3 Mn 6.8 Mn 12.8 Mn 25.7 Mn 40.2 Mn
Chemical composition of silicate–phosphate glasses/mol% SiO2
P2O5
K2O
MgO
CaO
MnO2
42.59 43.60 44.17 43.39 43.78 43.79 43.82
6.47 6.17 6.71 6.68 6.52 6.83 6.88
6.74 7.06 7.06 7.00 7.05 7.11 7.06
21.22 19.82 18.44 16.97 14.05 7.79 0.95
22.98 21.65 20.35 19.20 15.76 8.79 1.08
0.00 1.71 3.26 6.77 12.84 25.7 40.21
Please cite this article in press as: M. Szumera, The structural role of manganese ions in soil active silicate–phosphate glasses, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.03.102
M. Szumera / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx
Inductively-coupled plasma atomic emission spectroscopy Chemical activity of analyzed glasses was determined using the test applied in agricultural chemistry, based on their dissolving in the 2 wt.% citric acid solution; the weight ratio of glass to solution was 1:100. The solutions were mixed for 0.5 h (300–350 rot./min) at 25 °C, after which they were filtered. The above conditions simulate physico-chemical state similar to the natural environment between plants and the surrounding soil [21]. The contents of the chemical components of solutions were measured using ICPAES method (Perkin–Elmer Corp. – Plasma 40 Sequential ICP-AES spectrometer).
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middle infrared range (Fig. 2). The spectroscopic data available from these measurements provide important information concerning the local structure. FTIR spectra interpretation has been carried out according to the assumption that the glass structure consists of silicon–oxide bonds existing in amorphous SiO2 and phosphorus– oxide bonds existing in amorphous P2O5 [22]. FTIR spectra of the examined glasses are characterized by three main absorption bands at: 900–1200, 700–820 and 450–620 cm 1.
Scanning electron microscope & energy dispersive spectrometer Surface analyses, chemical analysis and imaging on a variety of materials were performed using a The Nova NanoSEM™ scanning electron microscope (SEM) – FEI Europe Company. The SEM microscope is equipped with an energy dispersive spectrometer (EDS) of EDAX. Results and discussion Powder X-ray diffraction studies It is known that in the case of amorphous materials X-rays will be scattered in many directions leading to a large bump distributed in a wide range (2 Theta) instead of high intensity narrower peaks. All analyzed MnO2-doped glasses show one broad peak and this observation led to the conclusion that in an amorphous material there is no long-range order. All samples only exhibit short-range order (Fig. 1). It has been found that increasing content of MnO2 in the structure of analyzed silicate–phosphate glasses causes a gradual decrease in the intensity of the registered increase in the background. This behavior suggests the presence of changes in the short arrangement of the amorphous structure of the investigated silicate–phosphate glasses. This issue is currently under detailed study. Analysis of FTIR spectra The effect of MnO2 addition on the structure of analyzed silicate–phosphate glasses is illustrated by the FTIR spectra in the
Fig. 2. FTIR spectra of silicate–phosphate glasses from the SiO2AP2O5AK2 OACaOAMnO2 system.
Fig. 1. XRD patterns of analyzed silicate–phosphate glasses.
Please cite this article in press as: M. Szumera, The structural role of manganese ions in soil active silicate–phosphate glasses, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.03.102
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Due to the complex and broad character of absorption spectra of the investigated glasses their decomposition process into separate bands was carried out (Fig. 3). The FTIR bands originating from the vibrations of [SiO4]4 and [PO4]3 in the mixed silicate–phosphate glass overlap and thus the bands at 1030 cm 1 appearing for 0Mn sample can be assigned to SiAO(Si), PAO and SiAO(P) vibrations [23]. In the spectra of analyzed glasses after decomposition of the band there appeared additional absorption bands (Fig. 3) situated in the range at about 850–1000 cm 1 and 1000–1170 cm 1. The first of these bands can be originated from a combination of stretching vibrations of PAO groups in PAOAP bridges and/or to the SiAO vibrations [23–26]. Simultaneously, bands lying within the range of higher frequencies can be attributed to stretching vibrations of double Si@O bonds [27]. Introduction of MnO2 up to 40 mol% to the structure of glasses causes a shift of the bands toward lower wavenumbers
(1030 ? 998 cm 1) (Fig. 2), showing a strong depolymerization effect of manganese ions on the silicate–phosphate glass network. This behavior may suggest the formation of SiAOAMn bonds [22,23,28]. It should be also noted that in the analyzed range P@O bond at 1300 cm 1 did not appear in any group of examined glass. Bands at about 772 cm 1 can be attributed to a combination of vibrations of SiAOASi, SiAOAP and PAOAP bridges [22] and with higher content of MnO2, no detectable changes in the position of these bands are observed. The next group of bands at about 650– 560 cm 1 was assigned to the OAPAO bending vibrations [28]. The position of this broad band changes in two ways. The decomposition process of the FTIR spectra allowed to determine the presence of some additional component bands. All spectra of glasses modified with the addition of MnO2 showed the presence of a band at about 620 cm 1 (Fig. 3b), which could be attributed
Fig. 3. The decomposition of MIR spectra of silicate–phosphate glasses from the SiO2AP2O5AK2OACaOAMnO2 system containing: (a) 0 mol% MnO2 and (b) 40.2 mol% MnO2.
Please cite this article in press as: M. Szumera, The structural role of manganese ions in soil active silicate–phosphate glasses, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.03.102
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to the MnAO bond produced upon gradual addition of MnO2 into the silicate–phosphate matrix [29–31]. No detectable changes in the position of these bands are observed. Additionally, remaining bands were found at about 500–570 cm 1 which are characteristic for OAPAO bending vibrations [24,32]. Simultaneously, the presence of the bands at about 470 cm 1 shifted towards higher wavenumbers (476 ? 491 cm 1) and they are assigned to the combination of bending vibrations of OASiAO and OAPAO bonds [23–25]. The FTIR data show that the controlled addition of MnO2 in the structure of analyzed silicate–phosphate glasses generates several rearrangements in the network structure at the short-range order level. From the obtained spectra it follows that the increasing content of MnO2 in the structure of silicate–phosphate glasses causes the breaking the oxygen bridges, i.e. SiAOASi, SiAOAP and PAOAP and the formation of SiAOAMn and/or PAOAMn oxygen bridges. It is responsible for the increasing degree of depolymerization of the structure formed of silicate and phosphate tetrahedral. This means and confirms the role of manganese ions as a glass modifier. Analysis of Raman spectra The Raman spectra of the analyzed glassy samples listed in Table 1 are shown in Fig. 4. The spectra of the silicate–phosphate glasses exhibited similar spectral features. There are a dominant three bands at about 958, 630 and 440 cm 1. The first of these bands is characterized by the presence of shoulder at its higher frequency side i.e. 1060 cm 1. Along the order of the glasses whose MnO2 – content increases, the intensity of the peaks at about 958 cm 1 increased but the intensity of the 440 cm 1 band decreased. Simultaneously, the position of 958 and the shoulders at 440 cm 1 band does not change. In the case of the position of bands at about 640 cm 1 its becomes shifted towards lower wavenumbers. According to the literature [33–36] on silicate glasses, bands at 800–1200 cm 1 range have been assigned to the asymmetric vibration of SiO4 tetrahedra, where precise peak wavenumber depends on the number of non-bridging oxygens constituting the tetrahedra. These bands can be assigned to the SiAO stretching vibrations in Q3 (at 1050 cm 1) and Q2 (at 958 cm 1) units in the silico-oxygen subnetwork [23], resulting from the presence of network-modifying cations. The spectra of 0Mn glass is characterized by the presence of small shoulder at lower frequency side at about 870 cm 1. Accordingly, the observed bands near 870 cm 1 have been assigned to the stretching vibrations of monomer SiO44 unit (Q0) [33,37]. The existence of Q0 units in the glass network is witnessed by the bands registered between 550 and 750 cm 1. A second interpretation has assigned them to vibrations in SiAO stretching vibrations in silicate tetrahedral units with three non-bridging oxygens (Q1) [23]. Bands at about 630 cm 1 can be assigned to SiAOASi bending vibrations in the Q2 silico-oxygen units [38]. The increasing content of MnO2 in the structure of the glasses caused gradually increase of its intensity and it can be attributed to a higher number of Q2 units in the silico-oxygen subnetwork. Simulatneously, it becomes shifted towards lower wavenumbers (640 ? 630 cm 1). Such behavior suggests the increasing degree of silico-oxygen sub-network depolymerization and confirms results obtained using FTIR spectroscopy. The next group of bands at about 440 cm 1 are associated with the vibrations in OAPAO bending modes of the orthophosphate PO34 unit (Q0) [33,39], with higher content of MnO2, no detectable changes in the position of these bands are observed. In summary, the Raman spectroscopy results suggest that increasing content of MnO2 in the structure of the analyzed
Fig. 4. Raman spectra of the silicate–phosphate glasses from the SiO2AP2O5AK2 OACaOAMnO2 system.
silicate–phosphate glasses has noticeable influence especially on silico-oxygen sub-network. It was found that in silico-oxygen sub-network occurs both Q3, Q2 and Q1 or Q0 units. This behavior is rather expected because increasing amount of MnO2 in the silicate–phosphate glass structure causes a decrease of the total number of the SiAO bond in Q3 units with simultaneous increase number of SiAO in Q0 units which may suggests gradual depolymerization process of silico-oxygen subnetwork and formation of SiAOAMn bonds.
Analysis of chemical activity Results of the investigations of the solubility of glasses from SiO2AP2O5AK2OAMgOACaOAMnO2 system in citric acid solution indicate that about 25–70 wt.% of their components are released (Fig. 5). The introduction of even small quantity of MnO2, in comparison to the 0Mn glass, into the glass structure increases the solubility of all elements that are contained in them. Under citric acid solution action about 40 wt.% of their main components i.e. CaO, K2O, MnO2 are released from the glass containing 2 mol% MnO2, while glasses containing 40 mol% MnO2 releases 70 wt.% of CaO and K2O and 50–60 wt.% of P2O5 and MnO2. It is worth emphasizing very low solubility of SiO2, reaching only 8 mol%. Generally, increase of MnO2 content in the glass structure up to 40 mol% increases their solubility. It was found that chemical activity of silicate–phosphate glasses modified by the addition of MnO2 change with the chemical composition of the glasses. This phenomena can be explained on the basis of crystal-chemical factors connected with the strength of the chemical bonds between the oxygen atoms and framework-forming components and modifiers. This refers to the
Please cite this article in press as: M. Szumera, The structural role of manganese ions in soil active silicate–phosphate glasses, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.03.102
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Fig. 5. Solubility of the chemical selected components of analyzed silicate–phosphate glasses, in citric acid solution.
Görlich’s ionicity (iG) of the chemical bonds between different ions, as a cation–oxygen bonds [40]. The oxygen bridges formed as a result of introducing into the silicate–phosphate structure modifiers in the form of calcium, magnesium, manganese and potassium ions are characterized by some strength of bonds with oxygen atoms. As a measure of the strength of oxygen bonds it is proposed to accept the difference in the value of ionicity of the bonds (iG) with the oxygen of the cations joined by this oxygen (DiG) [41,42] (Table 2). The smaller the difference in the ionicity of these bonds, the lower is the strength of the oxygen bridges, and hence the easier breaking of the bonds between them as a result of their chemical activity (dissolution process). This suggests that the ionic character of bonds in the oxygen bridges occurring in the structure of the glasses contributes to their chemical activity, and the succession of washing out the particular
components from the silicate–phosphate glasses which is as follows: Ca > K > Mg/Mn > P > Si, and it is in agreement with the strength of the oxygen bridges, combining the released compounds (Table 2). It was found that the introduction of increasing amounts of MnO2 to the structure of the studied silicate–phosphate glasses at the cost of decreasing content of MgO and CaO is associated with an increasing number of Mn3+AOASi and/or Mn2+AOASi type of oxygen bridges. The lower strength of these oxygen bridges (e.g. DiG Mn2+AOASi = 0.235) in comparison to the strength of the CaAOASi (DiG = 0.279) and MgAOASi (DiG = 0.242) is responsible for the increasing solubility of these glasses. The same applies to Mn3+AOAP and/or Mn2+AOAP oxygen bridges. The lower values of DiG Mn2+AOAP = 0.349) in comparison to DiG CaAOAP = 0.393 and DiG MgAOAP = 0.303 is also responsible for the increasing solubility of analyzed silicate–phosphate glasses.
Table 2 Characteristics of chemical bonds occurring in structure of the analyzed silicate–phosphate glasses. The type of chemical bonds
Ionicity of bonds iG by Görlich [40]
Oxygen bridges
Difference of ionicity of the bonds DiG
Oxygen bridges
Difference of ionicity of the bonds DiG
Mn3+AO Mn2+AO MgAO CaAO
0.505 0.663 0.670 0.707
PAOAMn3+ PAOAMn2+ PAOAMg PAOACa
0.191 0.349 0.303 0.393
SiAOAMn3+ SiAOAMn2+ SiAOAMg SiAOACa
0.077 0.235 0.242 0.279
Please cite this article in press as: M. Szumera, The structural role of manganese ions in soil active silicate–phosphate glasses, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.03.102
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Fig. 6. FTIR spectra of silicate–phosphate glasses from the SiO2AP2O5AK2OACaOAMnO2 system before and after dissolution process.
Fig. 7. SEM micrograph and EDS data of 12.8 Mn silicate–phosphate glass surface after dissolution process in 2 wt.% citric acid solution.
Thermal studies presented earlier [43] confirm that manganese ions in the examined glasses replace SiAOASi and/or SiAOAP bonds by SiAOAMn3+ and/or SiAOAMn2+ bonds. The presence of these type of bonds was confirmed by the formation of manganese silicates such as Mn7O8SiO4, being the glass crystallization products, which contains in its structure manganese ions. This suggests that the formation of these type of bonds causes gradual increase in glass solubility in conditions simulating the soil environment.
Additionally, in order to verify effect of the solubility on the structure of the glasses, the Author has done additional FTIR (Fig. 6) analysis of selected glasses also after their dissolution process in 2 wt.% citric acid solution. In comparison of the FTIR spectra of selected glasses before and after their dissolution process there are differences between them. It was found that in the case of FTIR, spectra after dissolution process main bands which can be assigned to SiAO(Si), PAO and/or
Please cite this article in press as: M. Szumera, The structural role of manganese ions in soil active silicate–phosphate glasses, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.03.102
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SiAO(P) vibrations, are shifted towards higher wavenumbers and show the presence of a shoulder at about 940 cm 1 characteristic for terminal SiAO bonds [23,25]. All of these effects may be due to the fact that during the dissolution process of silicate–phosphate glasses in 2 wt.% citric acid solution, there takes place leaching of their modifying ions i.e. Mg2+, Ca2+, Mn3+, Mn2+ and K+. The interaction of citric acid and the analyzed glasses induces the occurrence on their surface a corrosion layer enriched with SiO2, retaining in its composition potassium, magnesium, manganese as well as calcium and phosphorus (Fig. 7). Their content in the silica gel decreases with the dissolution time, as they diffuse gradually towards the inside of the solution and in this connection their solubility increases, which can be explained by their depolymerizing influence on the framework [44]. Conclusion Based on X-ray diffraction analysis, FTIR and Raman spectroscopies the influence of MnO2 on the structure and chemical activity of model silicate–phosphate glasses was evaluated. Glasses of these systems can play a role of carriers of a wide range of macro(K, Mg, Ca, P) and microelement in the form of manganese ions. It was found that increasing amount of MnO2 in the structure of glasses from SiO2AP2O5AK2OAMgOACaO system causes their gradual depolymerization. This process is more apparent in the case of the silico-oxygen subnetwork than phospho-oxygen one. This is related to increasing amounts of SiO4 tetrahedra containing two nonbridging oxygen atoms in silico-oxygen subnetwork. It was also found that the presence of ‘‘weaker’’ chemical bonds of SiAOAMn type in comparison to SiAOACa and SiAOAMg bonds is responsible for the increase in solubility of the analyzed silicate–phosphate glasses in conditions simulating natural soil environment. Acknowledgments The author want to express their thanks for help in FTIR and Raman spectroscopies studies to Prof. Irena Wacławska and Prof. Maciej Sitarz of Faculty of Materials Science and Ceramics, AGH University of Science and Technology in Cracow. Additionally, the author want to thank in spectra decomposition process to M.Sc. Piotr Jelen´. The work was supported by Faculty of Materials Science and Ceramics AGH – University of Science and Technology (2013) No 11.11.160.603-1.
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Please cite this article in press as: M. Szumera, The structural role of manganese ions in soil active silicate–phosphate glasses, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.03.102
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The structural role of manganese ions in soil active silicate–phosphate glasses q Magdalena Szumera ⇑ Faculty of Materials Science and Ceramics, Dep. of Ceramics and Refractories, AGH University of Science and Technology, Krakow, Poland
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Glasses from the
SiO2AP2O5AK2OACaOAMgOAMnO2 system were prepared and analyzed. Glasses were characterized by spectroscopic methods. The relation between the structure and chemical activity of glasses was found.
a r t i c l e
i n f o
Article history: Received 25 October 2013 Received in revised form 7 March 2014 Accepted 22 March 2014 Available online xxxx Keywords: Silicate–phosphate glasses Manganese ions Glass structure FTIR and Raman spectroscopies Chemical activity
a b s t r a c t Silicate–phosphate glasses of SiO2AP2O5AK2OAMgOACaO system containing manganese ions were synthesized by the melt-quenching technique and were investigated to obtain information about the influence of Mn-cations on the glass structure and their chemical activity. Structural properties were studied using X-ray method, FTIR and Raman spectroscopies. The chemical activity of analyzed glasses in the 2 wt.% citric acid solution was measured by chemical analysis (ICP-AES, EDS) and SEM observations. It has been found that increasing amount of MnO2 in the structure of investigated glasses causes their gradual depolymerization. This process is more apparent in the case of the silico-oxygen subnetwork than phospho-oxygen one. This is related to increasing amounts of SiO4 tetrahedra containing two nonbridging oxygen atoms in silico-oxygen subnetwork. It has been also found that the presence of ‘‘weaker’’ chemical bonds of SiAOAMn type in comparison to SiAOACa and SiAOAMg bonds is responsible for the increase in solubility of the analyzed silicate–phosphate glasses in conditions simulating natural soil environment. Ó 2014 Elsevier B.V. All rights reserved.
Introduction It is known that oxide glasses, mainly those of polymeric structure, like silicate, borate and phosphate, and mixed network glasses, like alumino-silicate, boro-silicate and phospho-silicate
q Selected paper presented at XIIth International Conference on Molecular spectroscopy, Kraków – Białka Tatrzan´ska, Poland, September 8–12, 2013. ⇑ Tel.: +48 6172480; fax: +48 6334630. E-mail address: [email protected]
glasses or other three or more network-formers containing glasses have a unique ability to include into their structure a wide range of chemical compounds which can coexist together in an oxide glass structure [1]. The development of inorganic silicate and phosphate glasses has attracted both academic and industrial interest in recent years [2]. In literature, several authors [2–5] have shown that technologically interesting products can be obtained by multicomponent network formation and also by doping transition metal ions in these competitive networks [2,6]. One of the interesting glass structure modifier is manganese ion. It is known that the
http://dx.doi.org/10.1016/j.saa.2014.03.102 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: M. Szumera, The structural role of manganese ions in soil active silicate–phosphate glasses, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.03.102
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introduction of manganese ions in a glass composition leads to changes in their structure and confers interesting properties, e.g. electrical, optical and magnetic [7–10]. It is also known that both Mn2+ and Mn3+ ions are well-known paramagnetic ions. Mn3+ ion has a large magnetic anisotropy due to its strong spin–orbit interaction of the 3d orbital whereas such anisotropy energy of Mn2+ ion is small because its orbital angular momentum is zero [11]. Because of its paramagnetic properties it is often referred to as a luminescent activator [12]. Manganese ions exist in different valence states with different coordination in glass matrices. Mn3+ ions exist in borate glasses with octahedral coordination, whereas in silicate and germinate glasses as Mn2+ with both tetrahedral and octahedral environment [11,13]. Introduction of the MnO into the structure of silicate glasses when its concentration is around 1.0 mol% [14] and up to 20 mol% in phosphate glasses [7], indicates that manganese ions mostly exist in Mn2+ state, occupy network forming positions with MnO4 structural units or play the role of vitreous network modifier in the phosphate glasses, but when its concentration, in both silicate and phosphate glasses, is higher these ions seem to exist mostly in the Mn3+ state and occupy only modifying position. The FTIR studies conducted by Pascuta and others [7] show that the controlled addition of MnO in the MnOAP2O5AZnO system generates several rearrangements in the network structure at the short-range order level. The authors suggested that it may be due to the formation of the PAOAMn bonds at the expense of the rest of the PAOAP linkages. The formation of bridging oxygen (PAOAMn) would increase the cross-link density of the glass network improving the chemical durability of the glass. The authors concluded that with increasing content of MnO in the phosphate, glass structure increases, confirming the role of manganese ions as glass modifiers. These results are also confirmed by other scientists [2,15–17]. Simultaneously, Soliman et al. [14], Mohan et al. [18] and Durga and Veeraiah [13] maintain that in the case of silicate glasses the number of silicon ions associate with one or more nonbridging oxygens increases, because of the excess of manganese ions which are able to associate with silicon. This leads to a decrease in the polymerization of the silicate network and expands the structure of the glass structure and in turn, leads to an increase in the molar volume. Also a decrease in density beyond 0.4 mol% MnO2 supported that the network weakened as manganese oxide is accommodated in the glass including a rearrangement of the network. Until now, extensive studies are conducted mostly on the structure of Mn-doped silicate or phosphate glasses, but not silicate– phosphate glasses. Therefore, the author has undertaken detailed studies using XRD, FTIR and Raman techniques as analytical methods in order to examine the effect of MnO2 addition into the structure of model silicate–phosphate glasses from SiO2AP2O5A K2OACaOAMgO system acting as ecological fertilizers providing a controlled release rate of the nutrients for plants. In these glasses manganese plays a role of a micronutrient necessary for the proper development of plants [19]. Manganese influences plants’ growth
process by regulation of ox-redox reactions and activation of some enzymes in the metabolic processes of plants. Additionally, the author has determined the relation between the structure of analyzed MnO2-doped silicate–phosphate glasses and their chemical activity under conditions simulating the biological soil environment. Experimental procedure Preparation of the glasses Silicate–phosphate glasses from SiO2AP2O5AK2OACaOAMgO system modified by MnO2 addition were prepared. In all glasses, constant quantities of P2O5, K2O, and SiO2 were kept, and the increasing amount of MnO2 was introduced at the cost of the decreasing amount of MgO and CaO, with the constant MgO/CaO ratio. The silicate–phosphate glasses were produced by traditional melting of raw materials mixture, i.e., SiO2, H3PO4, K2CO3, MgO, CaCO3, and MnO2 in platinum crucibles at 1300–1450 °C. Then the obtained amorphous material was fritted in water. All glasses were ground to grain size of 0.1–0.3 mm. X-ray fluorescence spectroscopy The chemical composition of glasses was controlled by X-ray fluorescence spectroscopy using ARL Advant ‘XP spectrometer. Chemical composition of the examined glasses was presented in Table 1. Amorphous state of the analyzed silicate–phosphate glasses was confirmed by X-ray diffraction method. FTIR spectroscopy Middle infrared (MIR) spectroscopic measurements of the glasses were made with a Bruker Vertex 70v spectrometer. Transmission technique, samples as KBr pellets. Spectra were collected after 124 scans at 4 cm 1 resolution. The position of bands on the MIR spectra was defined automatically in Win-IR. Spectra decomposition has been carried out according to the mathematical self-deconvolution method using the minimization of the number of the bands rule, proposed by Handke et al. [20]. Raman spectroscopy Raman studies were caried out using Horriba Yvon Jobin LabRAM HR micro-Raman spectrometer equipped with a CCD detector. Excitation wavelength of 532 nm was used and beam intensity was about 10 mW. Acquisition time was set to 30 s. The position of bands on the Raman spectra was defined automatically in Win-IR. Due to the high level of noise, for better legibility of the spectra, it was necessary to conduct Fourier smoothing of the Raman spectra.
Table 1 The chemical composition of silicate–phosphate glasses studied in the present work. No
0 Mn 1.7 Mn 3.3 Mn 6.8 Mn 12.8 Mn 25.7 Mn 40.2 Mn
Chemical composition of silicate–phosphate glasses/mol% SiO2
P2O5
K2O
MgO
CaO
MnO2
42.59 43.60 44.17 43.39 43.78 43.79 43.82
6.47 6.17 6.71 6.68 6.52 6.83 6.88
6.74 7.06 7.06 7.00 7.05 7.11 7.06
21.22 19.82 18.44 16.97 14.05 7.79 0.95
22.98 21.65 20.35 19.20 15.76 8.79 1.08
0.00 1.71 3.26 6.77 12.84 25.7 40.21
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Inductively-coupled plasma atomic emission spectroscopy Chemical activity of analyzed glasses was determined using the test applied in agricultural chemistry, based on their dissolving in the 2 wt.% citric acid solution; the weight ratio of glass to solution was 1:100. The solutions were mixed for 0.5 h (300–350 rot./min) at 25 °C, after which they were filtered. The above conditions simulate physico-chemical state similar to the natural environment between plants and the surrounding soil [21]. The contents of the chemical components of solutions were measured using ICPAES method (Perkin–Elmer Corp. – Plasma 40 Sequential ICP-AES spectrometer).
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middle infrared range (Fig. 2). The spectroscopic data available from these measurements provide important information concerning the local structure. FTIR spectra interpretation has been carried out according to the assumption that the glass structure consists of silicon–oxide bonds existing in amorphous SiO2 and phosphorus– oxide bonds existing in amorphous P2O5 [22]. FTIR spectra of the examined glasses are characterized by three main absorption bands at: 900–1200, 700–820 and 450–620 cm 1.
Scanning electron microscope & energy dispersive spectrometer Surface analyses, chemical analysis and imaging on a variety of materials were performed using a The Nova NanoSEM™ scanning electron microscope (SEM) – FEI Europe Company. The SEM microscope is equipped with an energy dispersive spectrometer (EDS) of EDAX. Results and discussion Powder X-ray diffraction studies It is known that in the case of amorphous materials X-rays will be scattered in many directions leading to a large bump distributed in a wide range (2 Theta) instead of high intensity narrower peaks. All analyzed MnO2-doped glasses show one broad peak and this observation led to the conclusion that in an amorphous material there is no long-range order. All samples only exhibit short-range order (Fig. 1). It has been found that increasing content of MnO2 in the structure of analyzed silicate–phosphate glasses causes a gradual decrease in the intensity of the registered increase in the background. This behavior suggests the presence of changes in the short arrangement of the amorphous structure of the investigated silicate–phosphate glasses. This issue is currently under detailed study. Analysis of FTIR spectra The effect of MnO2 addition on the structure of analyzed silicate–phosphate glasses is illustrated by the FTIR spectra in the
Fig. 2. FTIR spectra of silicate–phosphate glasses from the SiO2AP2O5AK2 OACaOAMnO2 system.
Fig. 1. XRD patterns of analyzed silicate–phosphate glasses.
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Due to the complex and broad character of absorption spectra of the investigated glasses their decomposition process into separate bands was carried out (Fig. 3). The FTIR bands originating from the vibrations of [SiO4]4 and [PO4]3 in the mixed silicate–phosphate glass overlap and thus the bands at 1030 cm 1 appearing for 0Mn sample can be assigned to SiAO(Si), PAO and SiAO(P) vibrations [23]. In the spectra of analyzed glasses after decomposition of the band there appeared additional absorption bands (Fig. 3) situated in the range at about 850–1000 cm 1 and 1000–1170 cm 1. The first of these bands can be originated from a combination of stretching vibrations of PAO groups in PAOAP bridges and/or to the SiAO vibrations [23–26]. Simultaneously, bands lying within the range of higher frequencies can be attributed to stretching vibrations of double Si@O bonds [27]. Introduction of MnO2 up to 40 mol% to the structure of glasses causes a shift of the bands toward lower wavenumbers
(1030 ? 998 cm 1) (Fig. 2), showing a strong depolymerization effect of manganese ions on the silicate–phosphate glass network. This behavior may suggest the formation of SiAOAMn bonds [22,23,28]. It should be also noted that in the analyzed range P@O bond at 1300 cm 1 did not appear in any group of examined glass. Bands at about 772 cm 1 can be attributed to a combination of vibrations of SiAOASi, SiAOAP and PAOAP bridges [22] and with higher content of MnO2, no detectable changes in the position of these bands are observed. The next group of bands at about 650– 560 cm 1 was assigned to the OAPAO bending vibrations [28]. The position of this broad band changes in two ways. The decomposition process of the FTIR spectra allowed to determine the presence of some additional component bands. All spectra of glasses modified with the addition of MnO2 showed the presence of a band at about 620 cm 1 (Fig. 3b), which could be attributed
Fig. 3. The decomposition of MIR spectra of silicate–phosphate glasses from the SiO2AP2O5AK2OACaOAMnO2 system containing: (a) 0 mol% MnO2 and (b) 40.2 mol% MnO2.
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to the MnAO bond produced upon gradual addition of MnO2 into the silicate–phosphate matrix [29–31]. No detectable changes in the position of these bands are observed. Additionally, remaining bands were found at about 500–570 cm 1 which are characteristic for OAPAO bending vibrations [24,32]. Simultaneously, the presence of the bands at about 470 cm 1 shifted towards higher wavenumbers (476 ? 491 cm 1) and they are assigned to the combination of bending vibrations of OASiAO and OAPAO bonds [23–25]. The FTIR data show that the controlled addition of MnO2 in the structure of analyzed silicate–phosphate glasses generates several rearrangements in the network structure at the short-range order level. From the obtained spectra it follows that the increasing content of MnO2 in the structure of silicate–phosphate glasses causes the breaking the oxygen bridges, i.e. SiAOASi, SiAOAP and PAOAP and the formation of SiAOAMn and/or PAOAMn oxygen bridges. It is responsible for the increasing degree of depolymerization of the structure formed of silicate and phosphate tetrahedral. This means and confirms the role of manganese ions as a glass modifier. Analysis of Raman spectra The Raman spectra of the analyzed glassy samples listed in Table 1 are shown in Fig. 4. The spectra of the silicate–phosphate glasses exhibited similar spectral features. There are a dominant three bands at about 958, 630 and 440 cm 1. The first of these bands is characterized by the presence of shoulder at its higher frequency side i.e. 1060 cm 1. Along the order of the glasses whose MnO2 – content increases, the intensity of the peaks at about 958 cm 1 increased but the intensity of the 440 cm 1 band decreased. Simultaneously, the position of 958 and the shoulders at 440 cm 1 band does not change. In the case of the position of bands at about 640 cm 1 its becomes shifted towards lower wavenumbers. According to the literature [33–36] on silicate glasses, bands at 800–1200 cm 1 range have been assigned to the asymmetric vibration of SiO4 tetrahedra, where precise peak wavenumber depends on the number of non-bridging oxygens constituting the tetrahedra. These bands can be assigned to the SiAO stretching vibrations in Q3 (at 1050 cm 1) and Q2 (at 958 cm 1) units in the silico-oxygen subnetwork [23], resulting from the presence of network-modifying cations. The spectra of 0Mn glass is characterized by the presence of small shoulder at lower frequency side at about 870 cm 1. Accordingly, the observed bands near 870 cm 1 have been assigned to the stretching vibrations of monomer SiO44 unit (Q0) [33,37]. The existence of Q0 units in the glass network is witnessed by the bands registered between 550 and 750 cm 1. A second interpretation has assigned them to vibrations in SiAO stretching vibrations in silicate tetrahedral units with three non-bridging oxygens (Q1) [23]. Bands at about 630 cm 1 can be assigned to SiAOASi bending vibrations in the Q2 silico-oxygen units [38]. The increasing content of MnO2 in the structure of the glasses caused gradually increase of its intensity and it can be attributed to a higher number of Q2 units in the silico-oxygen subnetwork. Simulatneously, it becomes shifted towards lower wavenumbers (640 ? 630 cm 1). Such behavior suggests the increasing degree of silico-oxygen sub-network depolymerization and confirms results obtained using FTIR spectroscopy. The next group of bands at about 440 cm 1 are associated with the vibrations in OAPAO bending modes of the orthophosphate PO34 unit (Q0) [33,39], with higher content of MnO2, no detectable changes in the position of these bands are observed. In summary, the Raman spectroscopy results suggest that increasing content of MnO2 in the structure of the analyzed
Fig. 4. Raman spectra of the silicate–phosphate glasses from the SiO2AP2O5AK2 OACaOAMnO2 system.
silicate–phosphate glasses has noticeable influence especially on silico-oxygen sub-network. It was found that in silico-oxygen sub-network occurs both Q3, Q2 and Q1 or Q0 units. This behavior is rather expected because increasing amount of MnO2 in the silicate–phosphate glass structure causes a decrease of the total number of the SiAO bond in Q3 units with simultaneous increase number of SiAO in Q0 units which may suggests gradual depolymerization process of silico-oxygen subnetwork and formation of SiAOAMn bonds.
Analysis of chemical activity Results of the investigations of the solubility of glasses from SiO2AP2O5AK2OAMgOACaOAMnO2 system in citric acid solution indicate that about 25–70 wt.% of their components are released (Fig. 5). The introduction of even small quantity of MnO2, in comparison to the 0Mn glass, into the glass structure increases the solubility of all elements that are contained in them. Under citric acid solution action about 40 wt.% of their main components i.e. CaO, K2O, MnO2 are released from the glass containing 2 mol% MnO2, while glasses containing 40 mol% MnO2 releases 70 wt.% of CaO and K2O and 50–60 wt.% of P2O5 and MnO2. It is worth emphasizing very low solubility of SiO2, reaching only 8 mol%. Generally, increase of MnO2 content in the glass structure up to 40 mol% increases their solubility. It was found that chemical activity of silicate–phosphate glasses modified by the addition of MnO2 change with the chemical composition of the glasses. This phenomena can be explained on the basis of crystal-chemical factors connected with the strength of the chemical bonds between the oxygen atoms and framework-forming components and modifiers. This refers to the
Please cite this article in press as: M. Szumera, The structural role of manganese ions in soil active silicate–phosphate glasses, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.03.102
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Fig. 5. Solubility of the chemical selected components of analyzed silicate–phosphate glasses, in citric acid solution.
Görlich’s ionicity (iG) of the chemical bonds between different ions, as a cation–oxygen bonds [40]. The oxygen bridges formed as a result of introducing into the silicate–phosphate structure modifiers in the form of calcium, magnesium, manganese and potassium ions are characterized by some strength of bonds with oxygen atoms. As a measure of the strength of oxygen bonds it is proposed to accept the difference in the value of ionicity of the bonds (iG) with the oxygen of the cations joined by this oxygen (DiG) [41,42] (Table 2). The smaller the difference in the ionicity of these bonds, the lower is the strength of the oxygen bridges, and hence the easier breaking of the bonds between them as a result of their chemical activity (dissolution process). This suggests that the ionic character of bonds in the oxygen bridges occurring in the structure of the glasses contributes to their chemical activity, and the succession of washing out the particular
components from the silicate–phosphate glasses which is as follows: Ca > K > Mg/Mn > P > Si, and it is in agreement with the strength of the oxygen bridges, combining the released compounds (Table 2). It was found that the introduction of increasing amounts of MnO2 to the structure of the studied silicate–phosphate glasses at the cost of decreasing content of MgO and CaO is associated with an increasing number of Mn3+AOASi and/or Mn2+AOASi type of oxygen bridges. The lower strength of these oxygen bridges (e.g. DiG Mn2+AOASi = 0.235) in comparison to the strength of the CaAOASi (DiG = 0.279) and MgAOASi (DiG = 0.242) is responsible for the increasing solubility of these glasses. The same applies to Mn3+AOAP and/or Mn2+AOAP oxygen bridges. The lower values of DiG Mn2+AOAP = 0.349) in comparison to DiG CaAOAP = 0.393 and DiG MgAOAP = 0.303 is also responsible for the increasing solubility of analyzed silicate–phosphate glasses.
Table 2 Characteristics of chemical bonds occurring in structure of the analyzed silicate–phosphate glasses. The type of chemical bonds
Ionicity of bonds iG by Görlich [40]
Oxygen bridges
Difference of ionicity of the bonds DiG
Oxygen bridges
Difference of ionicity of the bonds DiG
Mn3+AO Mn2+AO MgAO CaAO
0.505 0.663 0.670 0.707
PAOAMn3+ PAOAMn2+ PAOAMg PAOACa
0.191 0.349 0.303 0.393
SiAOAMn3+ SiAOAMn2+ SiAOAMg SiAOACa
0.077 0.235 0.242 0.279
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Fig. 6. FTIR spectra of silicate–phosphate glasses from the SiO2AP2O5AK2OACaOAMnO2 system before and after dissolution process.
Fig. 7. SEM micrograph and EDS data of 12.8 Mn silicate–phosphate glass surface after dissolution process in 2 wt.% citric acid solution.
Thermal studies presented earlier [43] confirm that manganese ions in the examined glasses replace SiAOASi and/or SiAOAP bonds by SiAOAMn3+ and/or SiAOAMn2+ bonds. The presence of these type of bonds was confirmed by the formation of manganese silicates such as Mn7O8SiO4, being the glass crystallization products, which contains in its structure manganese ions. This suggests that the formation of these type of bonds causes gradual increase in glass solubility in conditions simulating the soil environment.
Additionally, in order to verify effect of the solubility on the structure of the glasses, the Author has done additional FTIR (Fig. 6) analysis of selected glasses also after their dissolution process in 2 wt.% citric acid solution. In comparison of the FTIR spectra of selected glasses before and after their dissolution process there are differences between them. It was found that in the case of FTIR, spectra after dissolution process main bands which can be assigned to SiAO(Si), PAO and/or
Please cite this article in press as: M. Szumera, The structural role of manganese ions in soil active silicate–phosphate glasses, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.03.102
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M. Szumera / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx
SiAO(P) vibrations, are shifted towards higher wavenumbers and show the presence of a shoulder at about 940 cm 1 characteristic for terminal SiAO bonds [23,25]. All of these effects may be due to the fact that during the dissolution process of silicate–phosphate glasses in 2 wt.% citric acid solution, there takes place leaching of their modifying ions i.e. Mg2+, Ca2+, Mn3+, Mn2+ and K+. The interaction of citric acid and the analyzed glasses induces the occurrence on their surface a corrosion layer enriched with SiO2, retaining in its composition potassium, magnesium, manganese as well as calcium and phosphorus (Fig. 7). Their content in the silica gel decreases with the dissolution time, as they diffuse gradually towards the inside of the solution and in this connection their solubility increases, which can be explained by their depolymerizing influence on the framework [44]. Conclusion Based on X-ray diffraction analysis, FTIR and Raman spectroscopies the influence of MnO2 on the structure and chemical activity of model silicate–phosphate glasses was evaluated. Glasses of these systems can play a role of carriers of a wide range of macro(K, Mg, Ca, P) and microelement in the form of manganese ions. It was found that increasing amount of MnO2 in the structure of glasses from SiO2AP2O5AK2OAMgOACaO system causes their gradual depolymerization. This process is more apparent in the case of the silico-oxygen subnetwork than phospho-oxygen one. This is related to increasing amounts of SiO4 tetrahedra containing two nonbridging oxygen atoms in silico-oxygen subnetwork. It was also found that the presence of ‘‘weaker’’ chemical bonds of SiAOAMn type in comparison to SiAOACa and SiAOAMg bonds is responsible for the increase in solubility of the analyzed silicate–phosphate glasses in conditions simulating natural soil environment. Acknowledgments The author want to express their thanks for help in FTIR and Raman spectroscopies studies to Prof. Irena Wacławska and Prof. Maciej Sitarz of Faculty of Materials Science and Ceramics, AGH University of Science and Technology in Cracow. Additionally, the author want to thank in spectra decomposition process to M.Sc. Piotr Jelen´. The work was supported by Faculty of Materials Science and Ceramics AGH – University of Science and Technology (2013) No 11.11.160.603-1.
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Please cite this article in press as: M. Szumera, The structural role of manganese ions in soil active silicate–phosphate glasses, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.03.102