Thermogravimetric analysis of wheatleyite Na2Cu2+(C2O4)2·2H2O

Abstract

Evidence for the existence of primitive life forms such as lichens and fungi can be based upon the formation of oxalates. These oxalates form as a film like deposit on rocks and other host matrices. The anhydrous oxalate mineral moolooite CuC 2 O 4 as the natural copper (II) oxalate mineral is a classic example. Another example of a natural oxalate is the mineral wheatleyite Na 2 Cu 2+ (C 2 O 4 ) 2 .2H 2 O. High resolution thermogravimetry coupled to evolved gas mass spectrometry shows decomposition of wheatleyite at 255°C. Two higher temperature mass losses are observed at 324 and 349°C. Higher temperature mass losses are observed at 819, 833 and 857°C. These mass losses as confirmed by mass spectrometry are attributed to the decomposition of tennerite CuO. In comparison the thermal decomposition of moolooite takes place at 260 °C. Evolved gas mass spectrometry for moolooite shows the gas lost at this temperature is carbon dioxide. No water evolution was observed, thus indicating the moolooite is the anhydrous copper (II) oxalate as compared to the synthetic compound which is the dihydrate.Keywords: oxalate, wheatleyite, moolooite, copper(II) oxalate, Raman spectroscopy, high resolution thermogravimetry, evolved gas mass spectrometry IntroductionThe presence of oxalates is widespread in nature. These minerals form as the result of expulsion of heavy metals from fungi, lichens and plants [1][2][3]. The production of simple organic acids such as oxalic and citric acids has profound implications for metal speciation in biogeochemical cycles [4]. The metal complexing properties of the acids are essential to the nutrition of fungi and lichens and affects the metal stability and mobility in the environment [4]. Lichens and fungi produce the oxalates of heavy metals as a mechanism for the removal of heavy metals from the plant [5].Thermal analysis has been used for a long time for the analysis of oxalates [6][7][8][9][10][11][12][13][14][15]. Many of these analyses were undertaken many years ago [16][17][18][19][20][21]. The development of technology in thermal analysis has meant that high resolution studies with evolved gas mass spectrometry can now be undertaken to study both synthetic and natural oxalates [22][23][24][25][26][27]. A mineral commonly found in the drier parts of Australia is the mineral moolooite which is the anhydrous copper(II) oxalate. The mineral has been formed through the expulsion of copper from primitive plant forms. These primitive plant forms have been found on host rocks which contain copper. The presence of• Author to whom correspondence should be addressed (r.frost@qut.edu.au) 2 oxalates is widespread in nature, not only in plants but also as naturally occurring minerals. Among these minerals is the sodium copper oxalate mineral wheatlyite [28].The thermal stability of minerals such as the natural oxalates is important to test for life on Mars.. Thermal analysis has been used extensively for testing the stability of minerals [29][30][31][32][33][34][35][36][37][38][39][40][41][42...

Thermogravimetric analysis and hot-stage Raman spectroscopy of cubic indium hydroxide

“…Therefore the aim of this research is to demonstrate the use of thermal analysis and hot stage Raman spectroscopy to assess the thermal stability of indium hydroxide, and to determine the changes in the molecular structure of the material as the indium hydroxide is thermally treated. Such research compliments the thermal analysis and differential thermogravimetric analysis of materials [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. It is reported that many factors, such as disorder, size and shape distribution, can all influence the thermoanalytical properties and vibrational properties.…”

A Novel Copper Oxalate, Na2Cu(C2O4)2

“…Bond Valence Sum (BVS) calculation reveals the valence for Cu and Na is +2.118 and +1.016, respectively. These values agree well with other similar compounds …”

“…These values agree well with other similar compounds. [14][15][16][17][18][19] It is worth to point out that the stacking pattern of [Cu(C 2 O 4 ) 2 ] 2units in this compound is quite different from the known copper oxalates. Figure 3 displays [20] and Rb 2 Cu(C 2 O 4 ) 2 ·2H 2 O [21] the same as in K 2 Cu(C 2 O 4 ) 2 ·2H 2 O, thus not displayed in Figure 3.…”

“…In the sodium‐copper‐oxalate system, only one phase has been reported so far, viz. Na 2 Cu(C 2 O 4 ) 2 · 2H 2 O …”

“…Na 2 Cu(C 2 O 4 ) 2 ·2H 2 O. [16][17][18][19] As part of a current interest in the exploration of novel transition metal-oxalate compounds in our group, herein we report the synthesis and novel crystal structure of anhydrous sodium copper oxalate, namely Na 2 Cu(C 2 O 4 ) 2 . The compound was obtained together with the known phase Na 2 Cu(C 2 O 4 ) 2 ·2H 2 O through hydrothermal synthesis, but displayed a very different crystallization habit.…”