Following several years of contracted spectroscopy-based research on clay deposit exploration and mineral processing, know-how and funding were re-invested in curiosity-driven fundamental research. The themes of this research include the development of spectroscopic tools for the compositional/structural investigation of clays, the complementarity of vibrational spectroscopy with other established techniques, mainly XRD, the non-invasive study of water as a structural proxy of solid surfaces, as well as the spontaneous formation of clay-based hybrids by self-assembly.

Research Highlights

The fascinating chemistry of Maya blue

The clay mineral palygorskite and the common dye known as indigo form spontaneously upon mild heating a very resistant hybrid pigment with a vivid blue color.  Near-infrared spectroscopy (NIR), turned out to be the ideal tool for studying the structure of the hybrid, which is relevant to the famous meso-American pigment known as Maya blue. Palygorskite particles are lath-like. They have a chessboard cross-section of alternating aluminosilicate ribbons and hydrated channels, as well as abundant hydrophilic silanol groups on their outer surface.  At the reaction temperature (up to 130 ^oC) both the tunnels and the surface SiOH dehydrate, thereby inducing well-defined spectral changes in the NIR, which are reversible upon cooling at ambient temperature and relative humidity.  How can the binding site of indigo be identified?  Why indigo, among many organics, is so unique in forming a stable complex with palygorskite at loadings up to 10 wt%?  Is the formation of the complex limited to the (nearly ideal) variety found in Yucatan, Mexico? Answers to these (and other) questions can be found in Tsiantos et al., 2014, Tsiantos et al., 2012, Sanchez del Rio et al., 2009.

 

 

Folding sepiolite and palygorskite

Sepiolite and palygorskite, the two members of a clay group with a discontinuous octahedral sheet and modulated layer structure, undergo structural "folding", i.e. the collapse of their tunnels over a narrow temperature range. Locally, folding is induced by the removal of half of the coordinated H₂O molecules lining the "side walls" of the tunnels. On a crystallite scale, a huge number of these individual dehydration events must correlate along the length of several tunnels to produce a cooperative effect:  all tunnels in the cross-section of the crystallite must fold simultaneously.  As these minerals are in the form of laths or fibers, cooperative folding necessitates both, the 1D diffusion of H₂O out of extremely long tunnels, as well as the integrity of the chemical bonds ("hinges") keeping the structural modules together throughout the process.  Tsampodimou et al., 2015 studied and discussed sepiolite folding as a cooperative structural transformation based on complementary NIR and TGA experiments.

 

Synchronous NIR and ATR spectral acquisition

Attenuated total reflectance (ATR) spectroscopy in the mid-infrared, as well as diffuse reflectance via optical fibers in the near-infrared (NIR) are the least invasive vibrational spectroscopic techniques for the study of clay minerals.  Combining these two spectroscopic techniques in real-time and on the same sample is an extremely powerful method for the structural study of processes involving clays.  Due to the different extinction coefficients of the fundamental and higher order vibrations, the two techniques operate ideally on different sample scales.  Bukas et al. 2013 developed a simple environmental cell allowing for the independent synchronous collection of the NIR and ATR spectra under optimum sampling conditions and demonstrated its potential with the study of sepiolite upon drying from the H- and D-form.  Additional designs for non-invasive infrared sampling are reviewed by Chryssikos, 2017.

 

 

 

A new method for measuring the layer charge of smectites

Smectites are expandable phyllosilicates owing to the negative charge of their layers which is compensated by hydrated cations in the interlayer.  The layer charge, a key determinant of the technological properties of smectite, is extremely difficult to measure by the standard structural formula and alkylammonium exchange methods.  In collaboration with the Institute of Geological Sciences of the Polish Academy of Sciences in Cracow, we have developed and calibrated a new infrared-based methodology for the determination of layer charge. The so-called O-D method exploits the spectroscopic properties of interlayer H₂O which presents “dangling” O-H bonds protruding towards and weakly interacting with the charged siloxane layer. The interlayer is H₂O is exchanged by D₂O in situ (to avoid spectral interference with the structural OH of the mineral) and the exact wavenumber of “dangling” O-D bonds is linearly correlated to layer charge.  The new method is based on an intensive property measurement of an intrinsic interlayer and requires less than 5 mg of sample with essentially no preparation.  It is fast, accurate, precise and requires a modest single-reflection ATR cell with an environmental cup for performing   layer charge measurements on a routine basis. Its use and merits can be appreciated in several recent publications (e.g. Tsiantos et al. 2018, Christidis et al. 2018, Kuligiewicz et al. 2018, Kaufhold et al. 2019 etc.).  A critical assessment of the various methods for measuring the layer charge of smectites can be found here.

 

 

Layer charge measurements by the O-D method are provided by the Applied Spectroscopy Laboratory of TPCI/NHRF in the context of academic partnerships or industrial service collaborations.

 

Multivariate analysis of large spectral datasets

High through-put vibrational spectroscopic techniques, such as NIR diffuse reflectance spectroscopy, are able to generate large "hyperspectral" datasets which can capture the compositional variability of very large samples, e.g. a deposits. Multivariate techniques can interrogate these datasets and extract different kinds of information from them. For a recent review on multivariate analysis of clays, see Chryssikos and Gates 2017. They can produce unsupervised hierarchical classification schemes, identify the minimum number of latent key players needed to describe meaningfully the variability of the spectra, and they can be trained to correlate the spectra with independently collected data to produce quantitative chemometric tools. Published examples of chemometric algorithms developed in our laboratory can be found here, here, and here.

 

 

Multivariate and chemometric methodologies for the clay deposit management and processing are provided as services to the relevant industry by the Applied Spectroscopy Laboratory of TPCI/NHRF.

 

Re-interpreting the sigmoidal kinetics of intercalation in kaolinite

We use NIR spectroscopy to study the well-known sigmoidal kinetics of the intercalation of kaolinite at the level of chemical bonding and compare with XRD.  NIR allows for the convenient real-time monitoring of the heterogeneous reaction which takes place in a closed reactor as a function of temperature and in the presence of excess amide.  The results were surprising.  NIR recorded exactly the same sigmoidal kinetics as XRD despite the different scale of the two techniques.  The shape of the sigmoidal depended on kaolinite but not on temperature.  At each temperature, a single environment of intercalated amide was observed regardless of reaction progress and type of kaolinite studied.  This meant that the interlayers are observed either empty or fully intercalated.  Instead of the true intercalation reaction, the sigmoidals represent the temporal distribution of instantaneous intercalation events following exposure to the amide and can be fitted as such, e.g. by a cumulative log-normal function.  New, intriguing aspects of kaolinite intercalation can be found in the recent papers by Andreou et al. (2021) and (2022).

Current Members

Dr. Georgios D. Chryssikos, Research Director
Dr. Eirini Siranidi

Past Members

Ms. Aikaterini Kouseri
Dr. Vassilis Gionis, Senior Researcher
Ms. Fevronia T. Andreou, MSc.
Mr. Costas Tsiantos, MSc.
Mrs. Maria Tsampodimou, MSc.
Dr. Vanessa-Jane Bukas
Dr. Elizabeth T. Stathopoulou
Dr. Eugenia Dessypri

Dr. Steven Hillier
The James Hutton Institute, Aberdeen, Scotland

Dr. Arkadiusz Derkowski
Polish Academy of Sciences, Cracow, Poland

Dr. Marek Szczerba
Polish Academy of Sciences, Cracow, Poland

Dr. Stephan Kaufhold
BRG, Hannover, Germany

George Kacandes
Geohellas S.A., Athens, Greece

Prof. George Christidis
Technical University of Crete, Chania, Greece

Dr. M. Sanchez del Río
ESRF, Grenoble, France

Prof. Mercedes Suárez
U. Salamanca, Spain

Prof. Emilia García-Romero
Complutense U., Madrid, Spain

Seamless funding for this activity is coming from the income of the Applied Spectroscopy Laboratory at TPCI which provides spectroscopy-based services to the industry. Among these services, there were contracts of significant duration and budget with Geohellas S.A. and S&B Industrial Minerals S.A. 

Additional important funding was received via the two KRHPIS projects of TPCI: “Advanced materials and devices” (MIS 5002409) and Polynano (MIS 447963) which were co-financed by Greece (GSRT) and the European Union (European Regional Development Fund).

A. Articles

• G.E. Christidis, G.D. Chryssikos, A. Derkowski, R. Dohrman, D.D. Eberl, E. Joussein, S. Kaufhold, Methods for determination of the layer charge of smectites: A critical assessment of existing approaches.  Clays Clay Min., 2023.
  DOI: 10.1007/s42860-023-00234-8
• Andreou, E. Siranidi, A. Derkowski, G.D. Chryssikos, On the unusual temperature dependence of kaolinite intercalation capacity for N-methylformamide. Clays Clay Min., 2022, 70, 796-807.
  DOI: 10.1007/s42860-023-00217-9
• F. Andreou, B. Barylska, Z. Ciesielsca, M. Szczerba, A. Derkowski, V. Gionis, E. Siranidi, G. D. Chryssikos, "Intercalation of N-methylformamide in kaolinite: In situ monitoring by near-infrared spectroscopy and X-ray diffraction", Appl. Clay Sci., 2021, 212, 106209.
  DOI: 10.1016/j.clay.2021.106209
• S. Kaufhold, G. D. Chryssikos, G. Kacandes, V. Gionis, K. Ufer, R. Dohrmann, "Geochemical and mineralogical characterization of smectites from the Ventzia basin, western Macedonia, Greece", Clay Miner., 2019, 54, 95-107.
  DOI: 10.1180/clm.2019.8
• A. Kuligiewicz, A. Derkowski, J. Środoń, V. Gionis, G. D. Chryssikos, "The charge of wettable illite-smectite surfaces measured with the OD method", Appl. Clay Sci., 2018, 161, 354-363.
  DOI: 10.1016/j.clay.2018.05.003
• G. E. Christidis, C. Aldana, G. D. Chryssikos, V. Gionis, H. Kalo, M. Stoter, J. Breu, J.-L. Robert, "The nature of laponite: pure hectorite or a mixture of different trioctahedral phases?", Minerals, 2018, 8, 314.
  DOI: 10.3390/min8080314
• C. Tsiantos, V. Gionis, G. D. Chryssikos, "Smectite in bentonite: near infrared systematics and estimation of layer charge", Appl. Clay Sci., 2018, 160, 81-87.
  DOI: 10.1016/j.clay.2018.01.022
• M. Szczerba, A.Kuligiewicz, A. Derkowski, V. Gionis, G. D. Chryssikos, A. G. Kalinichev, "Structure and dynamics of water-smectite interfaces: Hydrogen bonding and the origin of the sharp O-Dw/O-Hw infrared band from molecular simulations", Clays and Clay Miner., 2016, 64, 452-471.
  DOI: 10.1346/CCMN.2016.0640409
• M. Tsampodimou, V.-J. Bukas, E. T. Stathopoulou, V. Gionis, G. D. Chryssikos, "Near-infrared investigation of folding sepiolite", Amer. Mineral. 2015, 100, 195-202.
  DOI:  10.2138/am-2015-4988
• A. Kuligiewicz, A. Derkowski, M. Sczerba, V. Gionis, G. D. Chryssikos, "Revisiting the infrared spectrum of the water-smectite interface", Clays and Clay Miner. 2015, 63, 15-29. 
  DOI: 10.1346/CCMN.2015.0630102
• A. Kuligiewicz, A. Derkowski, K. Emmerich, G.E. Christidis, C. Tsiantos, V. Gionis, G. D. Chryssikos, "Measuring the layer charge of dioctahedral smectites by O-D vibrational spectroscopy", Clays and Clay Miner. 2015, 63, 443-456.
  DOI: 10.1346/CCMN.2015.0630603
• C. Tsiantos, M. Tsampodimou, G. H. Kacandes, M. Sanchez del Rio, V. Gionis, G. D. Chryssikos, "Comment to the paper: Identification of indigoid compounds present in archaeological Maya blue by pyrolysis-silylation-gas chromatography-mass spectrometry (M.T. Domenech-Carbo, L. Osete-Cortina, A. Domenech-Carbo, M.L. Vazquez de Agredos-Pascual and C. Vidal-Lorenzo, J. Anal. Appl. Pyrol. 105, 355-362)",  J. Anal. Appl. Pyrol. 2014, 108, 327-328.
  DOI: 10.1016/j.jaap.2014.04.004
• V. J. Bukas, M. Tsampodimou, V. Gionis, G. D. Chryssikos, "Synchronous ATR infrared and NIR-spectroscopy investigation of sepiolite upon drying", Vibr. Spectr., 2013, 68, 51-60.
  DOI:  10.1016/j.vibspec.2013.05.009
• E. N. Skoubris, G. D. Chryssikos, G. E. Christidis, V. Gionis, " Structural characterization of reduced-charge montmorillonites. Evidence based on FTIR spectroscopy, thermal behavior, and layer-charge systematics", Clays Clay Miner., 2013, 61, 83-97.
  DOI: 10.1346/CCMN.2013.0610207
• C. Tsiantos, M. Tsampodimou, G. H. Kacandes, M. Sanchez del Rio, V. Gionis, G. D. Chryssikos, "Vibrational investigation of indigo-palygorskite association(s) in synthetic Maya blue", J. Mater. Sci., 2012, 47, 3415-3428.
  DOI: 10.1007/s10853-011-6189-x
• E.T. Stathopoulou, M. Suarez, E. Garcia-Romero, M. Sanchez del Rio, G. H. Kacandes, V. Gionis, G. D. Chryssikos, "Trioctahedral entities in palygorskite: Near-infrared evidence for sepiolite-palygorskite polysomatism", Eur. J. Mineral., 2011, 23, 567-576.
  DOI: 10.1127/0935-1221/2011/0023-2112
• M. Sanchez del Rio, E. Boccaleri, M. Milanesio, G. Croce, W. van Beek, C. Tsiantos, G. D. Chryssikos, V. Gionis, G. H. Kacandes, M. Suarez, E. Garcia-Romero, "A combined synchrotron powder diffraction and vibrational study of the thermal treatment of palygorskite-indigo to produce Maya blue", J. Mater. Sci., 2009, 44, 5524-5536.
  DOI: 10.1007/s10853-009-3772-5
• G. D. Chryssikos, V. Gionis, G. H. Kacandes, E. T. Stathopoulou, M. Suarez, E. Garcia-Romero, M. Sanchez Del Rio, "Octahedral cation distribution in palygorskite", Amer. Mineral. 2009, 94, 200-203.
  DOI: 10.2138/am.2009.3063
• E. T. Stathopoulou, V. Psycharis, G. D. Chryssikos, V. Gionis, G. Theodorou, "Bone diagenesis: New data from infrared spectroscopy and X-ray diffraction", Palaeo3, 2008, 266, 168-174. 
  DOI: 10.1016/j.palaeo.2008.03.022  
• V. Gionis, G. H. Kacandes, I. D. Kastritis, G. D. Chryssikos, "Combined near-infrared and X-ray diffraction investigation of the octahedral sheet composition of palygorskite", Clays Clay Miner., 2007, 55, 543-553.
  DOI: 10.1346/CCMN.2007.0550601  
• V. Gionis, G. H. Kacandes, I. D. Kastritis, G. D. Chryssikos, "On the structure of palygorskite by mid-and near-infrared spectroscopy", Amer. Mineral., 2006, 91, 1125-1133.
  DOI: 10.2138/am.2006.2023

B. Book Chapters

• G.D. Chryssikos, W.P. Gates, "Spectral manipulation and Introduction to multivariate analysis", Developments in Clay Science, Elsevier, 2017, vol. 8, Ch. 4, 64-106.
  DOI: 10.1016/B978-0-08-100355-8.00004-7
• G. D. Chryssikos, "Modern Infrared and Raman Instrumentation and Sampling Methods", Developments in Clay Science, Elsevier, 2017, vol. 8, Ch. 3, 34-63.
  DOI:  10.1016/B978-0-08-100355-8.00003-5