@article{AntoniouPashalidisGessneretal.2011, author = {Antoniou, Stella and Pashalidis, I. and Gessner, Andre and Kumke, Michael Uwe}, title = {The effect of humic acid on the formation and solubility of secondary solid phases (Nd(OH)CO3 and Sm(OH)CO3)}, series = {Radiochimica acta : international journal for chemical aspects of nuclear science and technology}, volume = {99}, journal = {Radiochimica acta : international journal for chemical aspects of nuclear science and technology}, number = {4}, publisher = {De Gruyter}, address = {Berlin}, issn = {0033-8230}, doi = {10.1524/ract.2011.1812}, pages = {217 -- 223}, year = {2011}, abstract = {The formation of secondary Ln(III) solid phases (e.g. Nd(OH)CO3 and Sm(OH)CO3) has been studied as a function of the humic acid (HA) concentration in 0.1 M NaClO4 aqueous solution and their solubility has been investigated in the neutral pH range (6.5-8) under normal atmospheric conditions. Nd(III) and Sm(III) were selected as analogues for trivalent lanthanide and actinide ions. The solid phases under investigation have been prepared by alkaline precipitation and characterized by TGA, ATR-FTIR, XRD, TRLFS, DR-UV-Vis and Raman spectroscopy, and solubility measurements. The spectroscopic data obtained indicate that Nd(OH)CO3 and Sm(OH)CO3 are stable and remain the solubility limiting solid phases even in the presence of increased HA concentration (0.5 g/L) in solution. Upon base addition in the Ln(III)-HA system decomplexation of the previously formed Ln(III)-humate complexes and precipitation of two distinct phases occurs, the inorganic (Ln(OH)CO3) and the organic phase (HA), which is adsorbed on the particle surface of the former. Nevertheless, HA affects the particle size of the solid phases. Increasing HA concentration results in decreasing crystallite size of the Nd(OH)CO3 and increasing crystallite size of the Sm(OH)CO3 solid phase, and affects inversely the solubility of the solid phases. However, this impact on the solid phase properties is expected to be of minor relevance regarding the chemical behavior and migration of trivalent lanthanides and actinides in the geosphere.}, language = {en} } @article{AntoniouPashalidisGessneretal.2011, author = {Antoniou, Stella and Pashalidis, Ioannis and Gessner, Andre and Kumke, Michael Uwe}, title = {Spectroscopic investigations on the effect of humic acid on the formation and solubility of secondary solid phases of Ln(2)(CO3)(3)}, series = {Journal of rare earths}, volume = {29}, journal = {Journal of rare earths}, number = {6}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1002-0721}, doi = {10.1016/S1002-0721(10)60490-5}, pages = {516 -- 521}, year = {2011}, abstract = {The formation of secondary Ln(III) solid phases (e.g., Nd-2(CO3)(3) and Sm-2(CO3)(3)) was studied as a function of the humic acid concentration in 0.1 mol/L NaClO4 aqueous solution in the neutral pH range (5-6.5). The solid phases under investigation were prepared by alkaline precipitation under 100\% CO2 atmosphere and characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), time-resolved laser fluorescence spectroscopy (TRLFS), diffuse reflectance ultraviolet-visible (DR-UV-Vis), Raman spectroscopy, and solubility measurements. The spectroscopic data obtained indicated that Nd-2(CO3)(3) and Sm-2(CO3)(3) were stable and remained the solubility limiting solid phases even in the presence of increased humic acid concentration (0.5 g/L) in solution. Upon base addition in the Ln(III)-HA system, decomplexation of the previously formed Ln(III)-humate complexes and precipitation of two distinct phases occurred, the inorganic (Ln(2)(CO3)(3)) and the organic phase (HA), which was adsorbed on the particle surface of the former. Nevertheless, humic acid affected the particle size of the solid phases. Increasing humic acid concentration resulted in decreasing crystallite size of the Nd-2(CO3)(3) and increasing crystallite size of the Sm-2(CO3)(3) solid phase, and affected inversely the solubility of the solid phases. However, this impact on the solid phase properties was expected to be of minor relevance regarding the chemical behavior and migration of trivalent lanthanides and actinides in the geosphere.}, language = {en} } @article{RadziukSkirtachGessneretal.2011, author = {Radziuk, Darya and Skirtach, Andre and Gessner, Andre and Kumke, Michael Uwe and Zhang, Wei and M{\"o}hwald, Helmuth and Shchukin, Dmitry}, title = {Ultrasonic Approach for Formation of Erbium Oxide Nanoparticles with Variable Geometries}, series = {Langmuir}, volume = {27}, journal = {Langmuir}, number = {23}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/la203622u}, pages = {14472 -- 14480}, year = {2011}, abstract = {Ultrasound (20 kHz, 29 W. cm(-2)) is employed to form three types of erbium oxide nanoparticles in the presence of multiwalled carbon nanotubes as a template material in water. The nanoparticles are (i) erbium carboxioxide nanoparticles deposited on the external walls of multiwalled carbon nanotubes and Er(2)O(3) in the bulk with (ii) hexagonal and (iii) spherical geometries. Each type of ultrasonically formed nanoparticle reveals Er(3+) photoluminescence from crystal lattice. The main advantage of the erbium carboxioxide nanoparticles on the carbon nanotubes is the electromagnetic emission in the visible region, which is new and not examined up to the present date. On the other hand, the photoluminescence of hexagonal erbium oxide nanoparticles is long-lived (mu s) and enables the higher energy transition ((4)S(3/2)-(4)I(15/2)), which is not observed for spherical nanoparticles. Our work is unique because it combines for the first time spectroscopy of Er(3+) electronic transitions in the host crystal lattices of nanoparticles with the geometry established by ultrasound in aqueous solution of carbon nanotubes employed as a template material. The work can be of great interest for "green" chemistry synthesis of photoluminescent nanoparticles in water.}, language = {en} }