Andre Gessner

The effect of humic acid on the formation and solubility of secondary solid phases (Nd(OH)CO3 and Sm(OH)CO3)

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.

Photoluminescence study of terbium-exchanged ultrastable Y zeolites: Number of species, photoluminescence decays, and decay-associated spectra

Terbium-exchanged ultrastable Y (USY) zeolites were investigated by using time-resolved photoluminescence spectroscopy techniques and methods. To determine the distribution of terbium species in USY zeolites together with their photoluminescence properties, several analysis methods for the time-resolved luminescence spectra were used such as the area normalization of time-resolved photoluminescence spectra, singular value decomposition, global nonlinear least squares, and the maximum entropy. Except for a questionable long lifetime, small contribution of a terbium species with lifetime of 1.9–2.1 ms, all the experimental and analysis results converged to a two terbium species distribution with lifetimes varying between 410–440 and 1000–1100 μs. The effects of the silylation of terbium-exchanged USY zeolites with phenyl-, vinyl-, and hexadecyltrimethoxysilanes on the lanthanide’s photoluminescence properties were also described.

Europium(3+) : An Efficient Luminescence Probe for the Si to Al Ratio and Silylation Effects in the Microporous-Mesoporous Zeogrid Materials

The optical response of europium ions in the parent (non-silylated) and silylated microporous-mesoporous Zeogrid materials was investigated in detail in relation to Zeogrid structure. All materials were characterized using nitrogen adsorption isotherms, powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry, and time-resolved photoluminescence spectroscopy. A two europium species distribution with distinct luminescence spectra and lifetimes was found for both parent and silylated Zeogrid. In the parent Zeogrid, the short-lived europium species is characterized by the intensity ratio R=I(5D0-(7)F2)/I(5D0-(7)F1) or asymmetry values of approximately 0.4-0.7 and photoluminescence (PL) lifetimes of 110-125 micros and therefore is assigned to an almost fully hydrated europium species. In the silylated Zeogrid, the short-lived europium species is characterized by asymmetry values of 1.0-2.4 and lifetimes of 160-180 micros suggesting a relatively distorted europium environment. The long-lived europium species exhibits similar asymmetry ratios in the parent and silylated Zeogrid, which vary between 5.0 and 6.2 with increasing Si to Al ratio from 25 to 150 and slightly different PL lifetimes. The mechanism responsible for the intensity of the electric and magnetic forbidden 5D0-(7)F0 transition was determined to be J-mixing of the 7F2 into the 7F0 state through the axial second-order crystal-field potential. The comparison between the photoluminescence properties of europium in the parent and silylated Zeogrid demonstrates that the effects of rehydration were strongly suppressed following silylation.

Spectroscopic investigations on the effect of humic acid on the formation and solubility of secondary solid phases of Ln2(CO3)3

Abstract The formation of secondary Ln(III) solid phases (e.g., Nd2(CO3)3 and Sm2(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 Nd2(CO3)3 and Sm2(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 (Ln2(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 Nd2(CO3)3 and increasing crystallite size of the Sm2(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.