Surface complexation onto LaF3 nanocrystals
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 8, August, 2011
1577
ethylenediaminetetraacetic acid (EDTA) disodium salt, were at
least of the reagent grade and were used as is. The acetate buffer
solution was prepared by mixing AcOH and NaOH solutions.
The borate buffer solution was prepared by dissolving sodium
tetraborate in degassed water. The pH value was controlled with
the use of HCl and NaOH solutions.
The Xꢀray powder diffraction study of the samples was perꢀ
formed at room temperature on a DRONꢀ3M diffractometer
(CoꢀKα radiation, λ = 0.179021 nm) over the scanning range
2θ = 20—70°. The average crystallite size was determined acꢀ
cording to the Scherrer equation
Adsorption kinetics. A borate buffer, pH 9.18 (2 mL), and
a solution of 1 (2.5 mL, 6.7•10–5 mol L–1) were added to LaF3
(0.01 g). Then the reaction mixture was vigorously stirred at
20 °C. At specified intervals of time, LaF3 was precipitated on
a centrifuge, and the absorption spectrum of the solution was
recorded in the visible region. Then the solution and the precipꢀ
itate were again stirred.
The adsorption kinetics of 2 was studied in the same way
using an acetate buffer solution, pH 5.1 (3 mL), and a solution of
2 (0.75 mL, 9.3•10–4 mol L–1).
Results and Discussion
D = kλ/(β•cosθ),
(1)
where k = 0.89 and β is the halfꢀwidth at halfꢀheight of the
reflection.
The synthesis of LaF3 was performed using the douꢀ
bleꢀdrop method,17,18 which enables the production of
preparative amounts of nanoparticles having a narrow size
distribution. According to the Xꢀray powder diffraction
patterns, the resulting sample corresponded to the hexaꢀ
gonal structure of LaF3 (JCPDS 32ꢀ0483, the space group
P3–c1). Reflections belonging to other phases were abꢀ
sent in the Xꢀray diffraction pattern, which is indicative of
the purity of the synthesized LaF3 sample. The average
crystallite size estimated from the Scherrer equation (1)
was 16 nm.
The micrographs of the samples were recorded with
a LEO912 AB OMEGA transmission electron microscope. The
specific surface (Ssp) was measured on an ASAP 2010 analyzer
(Micromeritics) by the Brunauer—Emmett—Teller (BET) method
using lowꢀtemperature nitrogen adsorption.
The absorption spectra of solutions were recorded on a Jenꢀ
way 6310 spectrophotometer. The diffuse reflectance spectra of
modified samples of LaF3 were measured on a Spektrotron specꢀ
trocolorimeter. The Kubelka—Munk function was calculated
from the measured intensities of reflections according to the
equation:
According to the transmission electron microscopy
data (Fig. 1), the resulting nanoparticles had a nearly hexaꢀ
gonal platelet shape with a diameter of 13—18 nm and
a thickness of 2—4 nm. The specific surface Ssp of the
F(R) = (1 – R)2/2R,
where R is the diffuse reflection coefficient of the substance.
Synthesis of LaF3 nanoparticles. A 0.51 M LaAc3 solution
(10 mL) and a 0.51 M NaF solution (30 mL) were added dropꢀ
wise with continuous stirring to water (30 mL) at 20 °C, the
addition of one drop of the LaAc3 solution being followed by the
addition of three drops of the NaF solution. When the addition
of the reagents was completed, the reaction mixture was stirred
for 30 min. The final product was isolated on a centrifuge at 8000 rpm
for 15 min, washed several times with water, and dried in air.
Sorption measurements. In all experiments, the complexꢀ
ation was monitored based on the change in the concentration of
the free ligand in solution at 20 °C. The concentration was deꢀ
termined from the calibration curve based on the absorption of
compounds 1 and 2 at 410—415 and 430—440 nm, respectively.
The La3+ complexes with 1 and 2 did not interfere with the
determination because their absorption is observed at 510—515
(see Refs 13—15) and 570—576 nm,11,16 respectively.
powder was 120 m2 g–1
.
The treatment of LaF3 with aqueous solutions of 1 or 2
led to the appearance of the intense color of the sample,
which is indicative of adsorption of the ligand on the surꢀ
face of LaF3. The diffuse reflectance spectrum of 1@LaF3
The amount of the adsorbed ligand was calculated from the
difference between the introduced (n0/mol) and remainder
amounts (n1/mol) of the free ligand in the solution. The degree
of extraction was calculated from the equation
S(%) = 100(n0 – n1)/n0.
The surface density (ρ/molecule nm–2) of the ligands was
determined from the equation
ρ = (n0 – n1)NA•1018/(Sspm),
100 nm
where NA is the Avogadro constant, Ssp is the specific surface
area of the LaF3 powder (m2 g–1), and m is the weight of the
LaF3 sample (g).
Fig. 1. Micrograph of the synthesized LaF3 recorded by transꢀ
mission electron microscopy.