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JOURNAL OF NANO- AND ELECTRONIC P Vol. 5 No 4, 04031(3pp) (2013)

HYSICS

Short Communication

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5 4, 04031(3cc) (2013)

Mechanisms of Ions Adsorption by Nanodiamonds in Aqueous Suspensions K.A. Laptinskiy1, S.A. Burikov1, T.V. Laptinskaya1, J.M. Rosenholm2, O.A. Shenderova3, I.I. Vlasov4, T.A. Dolenko1
2

Physical Department, Moscow State University, 1/2, Leninskie gory, 119991 Moscow, Russia Center of Functional Materials, Laboratory of Physical Chemistry, Department of Natural Sciences, Abo Akadmi University, 20500 Turku, Finland 3 International Technology Center, Raleigh, North Carolina 27617, United States 4 General Physics Institute, Russian Academy of Sciences, 119991 Moscow, Russia
1

(Received 30 September 2013; published online 10 December 2013) This work is devoted to the study of adsorption properties and adsorption mechanisms of the orig inal (I6), modified (I6COOH) nanodiamonds and charcoal dispersed in water, with respect to dissolved ions (Cu2 +, Pb2 +, NO3 ­, CH3COO ­) using optical spectroscopy methods: Raman and IR spectroscopies, absor ption, dynamic light scattering. Mechanisms of anions and cations adsorption were studied. Keywords: Nanodiamonds, Adsorption mechanisms, Dynamic light scattering, Raman spectroscopy, IR spectroscopy. PACS numbers: 68.43. ­ h, 78.30. ­ j

1. INTRODUCTION New efficient sorbents of inorganic and organic ions are very important for impurities removal from liquids and gases, for production of high-purity materials and drugs, and for biomedicine. It was shown that due to large specific surface, multi-functionality of surface groups, possibility of targeted modification of the su rface, adsorption properties of nanodiamond (ND) particles exceed adsorption capacity of many carbon sorbents. Adsorption properties of powdered detonation nanodiamonds are described in many papers [1, 2, 3]. It is obvious that in many applied problems (especially in biomedicine) it is advisable to use NDs dispersed in water. It is very important to understand mechanisms of adsorption in order to make targeted modifications of ND surface for increasing its adsorption efficiency. This work presents the results of a study of adsorption properties and adsorption mechanisms of the ori ginal and modified NDs dispersed in aqueous solutions, with respect to dissolved ions Cu2 +, Pb2 +, NO3 ­, CH3COO ­ using several complementary spectroscopic methods ­ photon correlation, absorption, Raman and IR spectroscopies. Parallel experiments were carried out with charcoal in order to compare efficiency of a dsorbents. 2. OBJECTS AND METHODS Adsorption properties of initial (I6) and modified (I6OOH) nanodiamonds in aqueous solutions of Cu(NO3)2, Pb(NO3)2, Cu(CH3COO)2 and Pb(CH3COO)2 were investigated. Characterization of the ND samples is presented in [4, 5, 6] and in the Table 1. Initial solutions of copper and lead salts with concentrations 0.5 and 0.75 M (for nitrates), 0.2 and 0.4 M (for acetates) and initial suspensions of NDs with co ncentration 0.5 mg/ml were prepared in deionized bidistilled water. The aqua NDs suspensions were

treated in ultrasonic bath during 3 hours. The obtained solutions and suspensions were characterized by diffe rent methods (titration, dynamic light scattering (DLS), electron microscopy (Table 1, Fig. 1). Measured parameters have shown stability of aqua suspensions of NDs. Then NDs suspensions and salts solutions were mixed and were characterized by the same methods. Concentrations of ions before and after adsorption by NDs were estimated by absorption spectroscopy. The second approach is based on concentration dependence of the own Raman lines intensity of NO3 ­ (1045 cm ­ 1) and CH3COO ­ (898 cm ­ 1, 2950 cm ­ 1) [7]. Results of absorption spectroscopy and Raman spectroscopy are in good accordance. Adsorption efficiency of ND is determined by the amount of ions adsorbed on the surface unit area of ND. In this work it is assumed that ions concentration in solution changes due to sorption by NDs only, and the efficiency was calculated from the ratio of ions co ncentration in initial solution and in supernatant. . Calculations demonstrated that ratio of areas of the total adsorbing surface of the aggregates was SI6/SI6COOH ~ 3, thus explaining 3 times higher adsorption efficiency of

Fig. 1 ­ HRTEM image of I6 (International Technological Center, USA)

The article was reported at the International Conference «Physics and Technology of Nanomaterials and Structures», Kursk, 21-22 November, 2013

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2013 Sumy State University


K.A. LAP

TINSKIY

, S.A. BURI

KOV

, T.V. LAP

TINSKAYA, ET. AL

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. PHYS. 5, 04031 (2013)

I6COOH relative to I6 (under approximately the equal change of Cu2+ and of the both anions concentrations). Ions Pb2 + are adsorbed by the modified ND slightly better than Cu2 + yielding 4 times higher sorption efficiency of I6COOH for Pb2 +. In compare with charcoal, NDs adsorption efficiency didn't show essential advantage (Fig. 2). Despite of this fact, the study of NDs adsorption properties is very important to solve the problem of elaboration of a multifunctional biose nsor on the base of NDs. Such biosensors can be used as sorbent, drug delivery and fluorescent marker simultaneously.

Fig. 3 ­ IR absorption spectra of nanodiamonds I6 and I6 with adsorbed ions

Fig. 2 ­ Adsorption activity of I6, I6COOH and charcoal: 1 ­ Cu2 + in Cu(CH3COO)2, 2 ­ CH3COO ­ in Cu(CH3COO)2, 3 ­ CH3COO ­ in Pb(CH3COO)2)

In order to clarify mechanisms of ion adsorption on ND surfaces, IR spectra of powders I6, I6COOH and powders, extracted from the aqueous mixturessuspensions (adsorbent + adsorbate) were obtained (Fig. 3, 4) using confocal FTIR spectrometer (Perkin Elmer Spectrum One). Presence of great amount of OH groups in IR absorption spectrum of powders (adsorbent + adsorbate) extracted from the aqueous mixtures-suspensions and absence of the valence band of Cu-O (640 cm ­ 1) show that a physical adsorption of Cu2 + ions plays a dominant role. A cation forms a solid hydration shell in water, and it moves in the solution together with this shell. We suppose that adsorption of copper cations on the sur Table 1 ­ Characterization of aqueous suspensions of NDs

Fig. 4 ­ IR absorption spectra of nanodiamonds I6COOH with adsorbed ions

face of NDs occurs without destruction of their hydration shells (Fig. 5). As both NDs have many oxygen containing surface functional groups, both NDs actively adsorb copper on their surface by hydrogen bonding. I6COOH (its surface was modified by oxygencontaining groups) adsorbs copper more actively in comparison with I6. Appearance of vibrational lines of N-O and NO bounds in compare with IR spectra of initial NDs shows formation of the new bonds between nitrates anions and NDs surface.

Sample

Methods of synthesis and treatment of studied samples Wet synthesis; CrO3 in H2SO4; NaOH + H2O2; fractionated Sample I6 treated in air at 420 °C

Size of crystallites*, [nm] 6-10 nm

-potential [mV] @pH 5.7, sizes of ND dispersions#, [nm] 19.6 3.4 mV 64.5 nm ­ 27.6 17 mV 190 nm

Production value 5.57 Chelyabinsk (Russi a) The modification was performed in the International Technology Centre, Raleigh (USA) Russia

I6

I6COOH

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3.5

Chacoal
*

75nm, 385 nm
#

Size was determined by Small Angle X-ray Scattering (SAXS),

Size was determined by DLS measurements.

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Fig. 5 ­ Scheme of adsorption of copper ions on ND surface

That means that chemical adsorption of nitrates anions plays a dominant role. Observed changes of IR spectrum of all powders (adsorbent + adsorbate) extracted from the aqueous mixtures-suspensions of Cu(CH3COO)2 allow to say that chemical adsorption is the main mechanism of acetate ions adsorption by NDs.
3. CONCLUSIONS

ions and metal cations, and the adsorption efficiency of modified ND is about 3 times higher than that of I6 in respect to the ions. In acetates salts solutions both NDs and charcoal don't adsorb Cu2 + and adsorb acetate ions weekly. The adsorption efficiency of I6, I6COOH and charcoal in respect to all ions in acetate salt solutions is practically equal. On the basis of the IR and Raman spectroscopy results, we propose a hypothesis about adsorption mechanisms of nitrate and acetates anions and cooper cations on the surface of the NDs. According to this hypothesis the main mechanism of adsorption of Cu2 + cations is a physical adsorption, and the main mechanism of nitrates and acetates anions is a chemical adsorption. ACKNOWLEDGEMENTS Authors of this paper thank A.A. Shiryaev from Institute of Geology of Ore Deposits, Petrography, Mi neralogy and Geochemistry, RAS (Moscow, Russia) for IR spectra registration. This work was supported in part by RFBR grants no.12-01-31523-mol_a, CBP.EAP.CLG. 984276, the grant of RAS program no. 24, the grant of President of the Russian Federation for leading scientific schools no 3076.2012.

In this research it was found that in nitrates salts solutions both NDs and charcoal actively adsorb nitrate

REFERENCES
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