nanomaterials
Article
Ultrasound-Assisted Synthesis of Luminescent Micro- and
Nanocrystalline Eu-Based MOFs as Luminescent Probes for
Heavy Metal Ions
Stefaniia S. Kolesnik
1
, Viktor G. Nosov
1
, Ilya E. Kolesnikov
1
, Evgenia M. Khairullina
1
, Ilya I. Tumkin
1
,
Aleksandra A. Vidyakina
1
, Alevtina A. Sysoeva
2
, Mikhail N. Ryazantsev
1,3
, Maxim S. Panov
1
,
Vasiliy D. Khripun
1
, Nikita A. Bogachev
1
, Mikhail Yu. Skripkin
1
and Andrey S. Mereshchenko
1,2,
*
Citation: Kolesnik, S.S.; Nosov,V.G.;
Kolesnikov, I.E.; Khairullina, E.M.;
Tumkin, I.I.; Vidyakina, A.A.;
Sysoeva, A.A.; Ryazantsev, M.N.;
Panov, M.S.; Khripun, V.D.; et al.
Ultrasound-Assisted Synthesis of
Luminescent Micro- and
Nanocrystalline Eu-Based MOFs as
Luminescent Probes for Heavy Metal
Ions. Nanomaterials 2021, 11, 2448.
https://doi.org/10.3390/nano11092448
Academic Editors: Marcin Runowski
and Guoping Dong
Received: 26 July 2021
Accepted: 16 September 2021
Published: 20 September 2021
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Attribution (CC BY) license (https://
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4.0/).
1
Saint-Petersburg State University, 7/9 Universitetskaya emb., 199034 St. Petersburg, Russia;
staphylinuscaesareus@gmail.com (S.S.K.); nosoff.vitia2018@yandex.ru (V.G.N.);
ilya.kolesnikov@spbu.ru (I.E.K.); iskint@mail.ru (E.M.K.); i.i.tumkin@spbu.ru (I.I.T.);
vidyakina.aleksandra@mail.ru (A.A.V.); mikhail.n.ryazantsev@gmail.com (M.N.R.);
m.s.panov@spbu.ru (M.S.P.); v.khripun@spbu.ru (V.D.K.); allanfrack@yandex.ru (N.A.B.);
skripkin1965@yandex.ru (M.Y.S.)
2
Sirius University of Science and Technology, 1 Olympic Ave, 354340 Sochi, Russia; sysoevaaa_04@mail.ru
3
Laboratory of Nanobiotechnology, Saint Petersburg Academic University, ul. Khlopina 8/3,
194021 St. Petersburg, Russia
* Correspondence: a.mereshchenko@spbu.ru; Tel.: +7-951-677-5465
Abstract: The luminescent coarse-, micro- and nanocrystalline europium(III) terephthalate tetrahy-
drate (Eu
2
bdc
3
·4H
2
O) metal-organic frameworks were synthesized by the ultrasound-assisted wet-
chemical method. Electron micrographs show that the europium(III) terephthalate microparticles are
7 μm long leaf-like plates. According to the dynamic light scattering technique, the average size of
the Eu
2
bdc
3
·4H
2
O nanoparticles is equal to about 8 ± 2 nm. Thereby, the reported Eu
2
bdc
3
·4H
2
O
nanoparticles are the smallest nanosized rare-earth-based MOF crystals, to the best of our knowl-
edge. The synthesized materials demonstrate red emission due to the
5
D
0
–
7
F
J
transitions of Eu
3+
upon 250 nm excitation into
1
ππ* state of the terephthalate ion. Size reduction results in broadened
emission bands, an increase in the non-radiative rate constants and a decrease in both the quantum
efficiency of the
5
D
0
level and Eu
3+
and the luminescence quantum yields. Cu
2+
, Cr
3+
, and Fe
3+
ions
efficiently and selectively quench the luminescence of nanocrystalline europium(III) terephthalate,
which makes it a prospective material for luminescent probes to monitor these ions in waste and
drinking water.
Keywords: metal-organic framework; luminescence; rare earth; europium; nanoparticle; luminescent probe
1. Introduction
Rare-earth-based metal-organic frameworks (MOFs) are actively used in various fields
of science and technology as luminescent sensors [1–11], LED components [12], luminescent
probes for bioimaging [13,14], and luminescent thermometers [15,16]. Small-sized crystals
of the rare-earth-based MOFs are especially interesting due to their unique properties. Such
materials have a large specific surface area, and as a result, they can effectively adsorb
other ions and molecules, which is necessary for the development of sensitive luminescent
sensors [17–19]. The presence of heavy metals in drinking water can cause numerous
disorders and diseases of humans and animals [20,21]. Therefore, one must develop new
sensors for such pollutants. MOFs are actively used as luminescent and electrochemical
sensors for heavy metal ion detection in drinking and wastewater [1–3,6,7,10]. Nanosized
luminescent MOFs are able to penetrate the cell membrane and are therefore used in
bioimaging as luminescent probes [13,14]. The nano-sized rare-earth-based MOFs can
be synthesized by several synthetic routes [13,14,22–25] such as solvothermal, reverse
Nanomaterials 2021, 11, 2448. https://doi.org/10.3390/nano11092448 https://www.mdpi.com/journal/nanomaterials