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Detection of copper ions from aqueous solutions using layered double hydroxides thin films deposited by PLD
Accepted Manuscript Title: Detection of copper ions from aqueous solutions using layered double hydroxides thin films deposited by PLD Author: A. Vlad R. Birjega A. Matei C. Luculescu A. Nedelcea M. Dinescu R. Zavoianu O.D. Pavel PII: DOI: Reference:
S0169-4332(15)00523-1 http://dx.doi.org/doi:10.1016/j.apsusc.2015.02.192 APSUSC 29875
To appear in:
APSUSC
Received date: Revised date: Accepted date:
15-11-2014 20-2-2015 27-2-2015
Please cite this article as: A. Vlad, R. Birjega, A. Matei, C. Luculescu, A. Nedelcea, M. Dinescu, R. Zavoianu, O.D. Pavel, Detection of copper ions from aqueous solutions using layered double hydroxides thin films deposited by PLD, Applied Surface Science (2015), http://dx.doi.org/10.1016/j.apsusc.2015.02.192 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Detection of copper ions from aqueous solutions using layered double hydroxides thin films deposited by PLD A. Vlad*, R. Birjega, A. Matei, C. Luculescu, A. Nedelcea, M. Dinescu,
Bucharest-Magurele, Romania
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R. Zavoianu, O.D. Pavel
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National Institute for Lasers, Plasma and Radiation Physics, 409 Atomistilor Str., 76900
University of Bucharest, Faculty of Chemistry, Department of Chemical Technology and
us
Catalysis, 4-12 Regina Elisabeta Bd., Bucharest, Romania
an
Abstract
Layered double hydroxides (LDHs) thin films with Mg-Al were deposited using
M
pulsed laser deposition (PLD) technique. We studied the ability of our films to detect copper ions in aqueous solutions. Copper is known to be a common pollutant in water, originating
d
from urban and industrial waste. Clay minerals, including layered double hydroxides (LDHs),
te
can reduce the toxicity of such wastes by adsorbing copper. We report on the uptake of copper ions from aqueous solution on LDH thin films obtained via PLD.
Ac ce p
The obtained thin films were characterized using X-Ray Diffraction, Atomic Force
Microscopy, and Scanning Electron Microscopy with Energy Dispersive X-ray analysis. The results in this study indicate that LDHs thin films obtained by PLD have potential as an efficient adsorbent for removing copper from aqueous solution.
Keywords: LDH thin films, pulsed laser deposition, copper metals uptake *
Author for correspondence: Angela Vlad Tel: +40 21 457 44 14; Fax: +40 21 457 42 43; E-mail: [email protected];
Page 1 of 17
1. Introduction Clay minerals possess a high specific surface area and good adsorptive/exchange capacity, which makes them very useful for a wide range of applications. Layered double hydroxides
ip t
(LDHs), also known as hydrotalcite-type (HT) compounds, display similar properties to those
cr
of clay minerals [1, 2]. Removal of heavy metal ions (Cu2+, Cd2+, Pb2+, Ni2+, Co2+) from aqueous solutions or contaminated water is an important environmental issue [3].
us
The general formula of LDHs is: [M2+1-xM3+x(OH)2]x+(An-x/n) · mH2O, where M2+ and M3+ are divalent (Mg2+, Ni2+, Zn2+, or Co2+) and trivalent (Al3+, Cr3+, Fe3+, or Ga3+) cations,
an
respectively. An- is an interlayer anion of charge n and x is equal to the ratio M3+/(M2+ + M3+) [4]. Papers about the uptake of heavy metals onto LDHs thin films from water are scarce,
M
probably because layered double hydroxides have only recently been considered for
and environment [10].
d
industrial/health applications [5-9]. Some of the heavy metals pose serious hazards to health
te
Studies on uptake of metal ions from an aqueous solution by Mg-Al or Zn-Al LDHs were
Ac ce p
done using intercalated suitable chelating resins like ethylenediaminetetraacetate (edta) [11, 12], citrate, malate [13]. In these cases the anions act as scavengers and can remove heavy metals from water by forming complexes of chelate bonded heavy metals. For example, the team of Perez et al. [14] observed that uptake of Cu2+ was higher than that of Pb2+ or Cd2+ when using edta intercalated ZnAl LDHs. Komarneni’s group [15] reported that the “diadochy” process is the main mechanism of metal uptake from wastewater. The process allows selective cation uptake that takes place via substitution of Mg2+ ions in the Mg-Al LDH structure. Our research group reported a new way to obtain LDHs thin films by pulsed laser deposition (PLD) and matrix assisted pulsed laser evaporation (MAPLE) [16-18]. We also reported on the ability of LDH thin films deposited via laser techniques to retain Ni or Co from aqueous
Page 2 of 17
solutions [17, 18]. We have described the mechanism of adsorption of these heavy metals through the already cited “diadochy” process [15], in competition with a reconstruction process. All the divalent metals, from Mg2+ to Mn2+, form LDH, except for Cu2+ which forms pure LDH if other bivalent cations, such as Zn, Cr, Co, Mg, and Mn, are present. In most
ip t
cases Cu-LDHs are always mixed with other phases, such as malachite [Cu (OH)2CuCO3] and
cr
gerhardite [Cu (OH)3NO3], due to the Jahn-Teller effect of the Cu2+ ion [19,20]. This work is an investigation on the capacity of copper to be adsorbed on oriented Mg-Al LDHs thin films
us
obtained by pulsed laser deposition (PLD), as compared to other heavy metals not exhibiting a Jahn-Teller effect. The Mg-Al LDHs thin films were obtained by pulsed laser deposition
an
technique at three different wavelengths. We investigate the influence of their roughness, thickness and the presence of some amorphous or delaminated material on the copper uptake.
M
2. Experimental 2.1 Materials preparation
d
Mg-Al LHD powder was prepared by co-precipitation at supersaturation at pH=10 using
te
aqueous solutions of Mg and Al nitrates, sodium hydroxide and carbonate. The Mg/Al molar
Ac ce p
ratio was adjusted to 2. The obtained gel have been dried at 850C for 24 hours under controlled nitrogen flow pressure and then dried and pressed as pellets in order to be used as targets in pulsed laser deposition experiments. In this report the as prepared powder and the corresponding target will be referred to as 'Mg2Al' 2.2 Films preparation
We deposited Mg-Al LDH thin films on Si (100) substrates using a pulsed Nd:YAG laser working at three different wavelengths (λ=266, 532 and 1064 nm, τL~5 ns), at a pulse repetition rate of 10 Hz. The films were deposited at room temperature in a parallel configuration. The laser fluence was 2 J/cm2. The number of pulses irradiating the target was set at 12000, and the resulting thin films had thicknesses between 250 to 350 nm. After deposition the films were immersed
Page 3 of 17
in aqueous solution of CuSO4 (1g/L), in a volume is 5 ml at ambient temperature at different contact times 30s, 30 min, 1h and 3 days, respectively. 1 h is considered the representative contact time. The uptake of copper was evaluated by energy dispersive X-ray spectroscopy (EDX). The thickness of the films, prior and after the immersion was determined by
ip t
profilometry. The crystalline structure of the films was studied by X-ray diffraction at grazing
cr
incidence (GI-XRD) using a CuKα (λ=1.5418 Ǻ) radiation. 3. Results and discussion
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3.1 EDX results
The energy dispersive (EDX) results are presented in Table 1. High Cu/Al ratios accompanied
an
by a significant decrease of the Mg/Al ratios are observed. Also, the presence of sulfur (S) was evidenced. The Cu/Al ratio values are higher for films deposited at 532 nm and 1064 nm,
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probably in correlation with their higher thickness, while the S/Cu ratio is lower and almost constant for all three ablation wavelengths after 1 h immersion time.
d
3.2 SEM and AFM investigations
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SEM and AFM analyses of films morphology reveal rough surfaces, with big grains deposited
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onto the film surface, especially at 266 nm (Fig. 1). Fine, oriented layered structures are observed in the SEM images of films after 1 hour immersion in CuSO4, which indicates that a reconstruction process has occurred. We observed the same aspect denoting a reconstruction process in our previous reports on Ni and Co uptakes [17, 18]. 3.3 XRD results
The hydrotalcites exhibit an R3m rhombohedral symmetry and were Miller indexed in a hexagonal lattice. The lattice parameters of the Mg2Al powder and Mg2Al target are the same, and comparable to standard hydrotalcite values having the same Mg/Al molar ratio (JCPDS no.04-011-5899). In the XRD patterns of the as-deposited thin films only the basal spacings (00l) are detectable, which is indicative of the oriented nature of the formed films (Fig.2). After a one hour immersion in aqueous solution of CuSO4 (1g/L) at room temperature
Page 4 of 17
the XRD patterns of the thin films exposed only the basal spacing which are considerable shifted towards lower angles in comparison with the as deposited films. This important increase of the c-parameter is higher in comparison with our reported previous observations on Co and Ni absorption effect. The structural data are included in Table 2. The interlayer
ip t
distance is calculated by subtraction of 4.8 Å, corresponding to the hydrotalcite-layer
solution could be explained by considering the following effects:
Intercalation of (SO4)2- in the interlayer spacing, as supported by the EDX results. The
us
-
cr
thickness from d003 [21]. The interlayer distance increase following 1h immersion in copper
an
values of the basal d003 given by Miyata [22] and cited by Rives [23] are slightly larger for SO4-bearing LDHs, which means that CO32- combined with small amounts of SO42-
M
are intercalated in these films. The cointercalation of both CO32- and SO42- leads also to a disorder effect on the stocking arrangement of the layers. The result is endorsed by the
The used CuSO4 solution (1g/L) is pale-blue due to the presence of [Cu(H2O)6]2+
te
-
d
broadness of the basal reflections.
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complex ions. [Cu(H2O)6]2+ is a Jahn-Teller ion exhibiting plasticity and adopting different geometries, an octahedral structure in most cases, with a first or even a second hydration sphere [24], which lead to larger ions to be intercalated. The pH of the solution in which the films were immersed is dominated by the acid character of [Cu(H2O)6]2+. The pH of the CuSO4 (1g/L) solution we used was 4.9 during the 1 hour immersion time, which favored the coprecipitation of Cu2+ with dissolved Al3+ to form
Cu-Al LDH [11]. Mg2+ does not precipitate at this pH value. Therefore, the reconstruction occurred with the formation of a Cu rich layered double hydroxide. These assumptions are consistent with the EDX results, after 1 h immersion time, i.e. high Cu/Al and low Mg/Al atomic ratio values, the increase of thickness of the films upon
Page 5 of 17
copper uptake, as well with the SEM images exposing the formation of fine layered structures after immersion. The possibility of “diadochy”, isomorphic substitution of Mg2+ of Cu2+ is uncertain due to the
ip t
Jahn-Teller distortion. The lack of the (110) reflection connected to the layer parameter does not allow to state on this aspect. Komarneni et al. introducing the “diadochy” function for
cr
LDH, the uptake of transitional metals, Ni2+, Co2+, Zn2+, Cu2+ through the isomorphous substitution of Mg2+ reported also the precipitation of Cu in the presence of LDHs but not for
us
the other cations [15].
an
Therefore we explain the larger amount of Cu uptake mainly by coprecipitation of Cu2+ with
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dissolved Al3+ to form Cu-Al LDH backed by the Mg2+ dissolution. We aimed also to collect experimental observation on the influence of the deposition
d
conditions, namely of the laser wavelengths on the LDH thin films formation and
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consequently, on the films behavior after immersion in a CuSO4 solution (1g/L). The film deposited at a shorter laser wavelength, 266 nm, exhibits a smoother morphology and poor
Ac ce p
crystallinity (Figs 1 and 2 and tables 1 and 2). The result is overall explained by shorter penetration depths and ablation plumes containing a higher fraction of ionized, high kinetic energy material [25,26] leading to thinner and smoother films. The plasma temperatures in the early phase of expansion is highest in the case of 1064 nm at the same value of laser irradiance leading to an increase of micro and nano-sized droplets, clusters or conglomerates ejected from the target which explain the thickness and roughness of the film [24,25]. The deposition at 532 nm appears to be closer to the 1064 nm deposition. The slight difference in the morphological and structural aspects are preserved after immersion in a CuSO4 solution (1g/L) for 1 hour implying that the film deposited at 266 nm due to its thickness and presence of amorphous material are less efficient in the detection of copper from aqueous solutions.
Page 6 of 17
Removal efficiency appears to be the highest around 1 hour. Similar to the uptake of Ni and Co studies, previously reported [18], at 30 s the detection of Cu is possible due to the hydrophilicity of the LDH surface which retains drops of CuSO4 solution on top of the film surface, the reconstruction of a layered structure occurring during the evaporation process.
ip t
The SEM images and XRD patterns after 30 s and 30 min immersion time respectively (Fig.3)
cr
along with the elemental data obtained from the EDX analyses (Table 1) show no significant change while an important increase occurred for the films after 1 hour immersion time. After
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3 days immersion the increase of the Cu uptake is significantly (Table 2). Besides the formation of a LDH phase, an additional Cu2.5SO4(OH)3.2H2O phase (JCPDS no. 51-0321)
an
are formed alongside (see Fig.3). Fig. 4 exhibits the comparative evolution of the heavy metals uptake. The data for Ni and Co uptake are taken from our previous work [18]. The
M
solutions we used were at the same concentration, 1g/L as CuSO4 and, the LDH films derived from a Mg2Al target deposited at 1064 nm. The proportion of Cu uptake after 1hour
d
immersion is significantly higher backing for a different mechanism then “diadochy” process
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occurring as dominant process for Ni or Co uptake [17,18]. Due to the Jahn-Teller effect
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which impeded the Cu substitution in the brucite layered while the Cu interlayer intercalation along with coprecipitation dissolved Al3+ to form a Cu, Al-LDH film are favored.
4. Conclusions
In this study, the uptake of copper ions from aqueous solution was carried out by using thin films of Mg-Al based LDH deposited by PLD. The uptake studies were performed for different contact times. The 1 h immersion time was found to be sufficient to reach detectable copper and sulfate values. The film deposited at 266 nm due to their thickness and roughness are less efficient in Cu detection while the films deposited at 1064 and 532 nm respectively exhibit similar behavior. The results suggest that Mg-Al LDH thin films obtained in this work could be suitable for the detection of copper in aqueous solutions. The copper uptake is Page 7 of 17
explained mainly by the co-precipitation of Cu2+ with dissolved Al3+ to form Cu-Al LDH. The ability to form Cu-Al LDHs is backed by the Mg2+ dissolution. Uptake of Cu2+ was possible without a preliminary functionalization step which makes the method and the procedure
ip t
promising.
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Acknowledgments
This work was supported by a grant of the Romanian National Authority for Scientific
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Research, CNCS – UEFISCDI, project number PD15/2011 and PCCA 137/2012.
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References:
[1] C. Del Hoyo, Appl Clay Sci 36 (2007) 103-121
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[2] P. Nalawade, B. Aware, V.J. Kadam, R.S. Hirlekar, J. Sci&Ind. Res 68 (2009) 267-272 [3] J. O. Nriagu, J. M. Pacyna, Nature 333 (1988) 134-139
d
[4] F. Cavani, F. Trifiro, A. Vaccari, Catal. Today 11 (1991) 173–301
te
[5] F. Basile, A. Vaccari, V. Rives (Ed.), Layered Double Hydroxides: Present and Future,
Ac ce p
Nova Science Publishers, Inc., New York (2001) 323–365 [6] S. Mandal, S. Mayadevi, Appl. Clay Sci. 40 (2008) 54–62 [7] D. Shan, W. Yao, H. Xue, Biosens. Bioelectron. 23 (2007) 432–437. [8] G. Di Francia, V. La Ferrara, S. Manzo, S. Chiavarini, Biosens. Bioelectron. 21 (2005) 661–665.
[9] C. Mousty, Anal Bioanal Chem.396 (2010) 315-325 [10] J. L. Dorne, G. E. Kass, L.R. Bordajandi, B. Amzal, U. Bertelsen, A.F. Castoldi, C. Heppner, M. Eskola, S. Fabiansson, P. Ferrari, E. Scaravelli, E. Dogliotti, P. Fuerst, A. R. Boobis, P. Verger, Met ions Life sci 8 (2011) 27-60. [11] T. Kameda, S. Saito, Y. Umetsu, Sep. Purif. Technol. 47 (2005) 20-26 [12] T. Kameda, K. Hoshi, T. Yoshioka, Solid State Sci. 17 (2013) 28-34
Page 8 of 17
[13] T. Kameda, H. Takeuchi, T. Yoshioka, Colloids Surf. A 355 (2010) 172–177 [14] M. R. Perez, I. Pavlovic, C. Barriga, J. Cornejo, M.C. Hermosin, M. A. Ulibarri, Appl. Clay Sci. 32 (2006) 245-251 [15] S.Komaneni, N. Kozai, R. Roy, J. Mater. Chem 8, (1998), 1329.
ip t
[16] A. Matei. R. Birjega, A. Nedelcea, A. Vlad, D. Colceag, M. D. Ionita, C. Luculescu, M.
cr
Dinescu, R. Zavoainu, O. D. Pavel, Appl. Surf. Sci., 257 (2011) 5308-5311
[17] A. Matei. R. Birjega, A. Vlad, M. Filipescu, A. Nedelcea, C. Luculescu, R. Zavoainu, O.
us
D. Pavel, M. Dinescu, Appl. Surf. Sci., 258 (2012) 9466-9470
Pavel, Appl. Surf. Sci., 302 (2014) 99-104
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[18] A. Vlad, R. Birjega, A. Matei, C. Luculescu, B. Mitu, M. Dinescu, R. Zavoainu, O. D.
[19] A. Alejandre, F. Medina, X. Rodriguez, P. Salagre and J. E. Sueiras, J. Catal., 188 (1999)
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311-324
[20] R. Manivannan, A. Pandurangan, Appl. Clay Sci , 44 (2009) 137-143
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[21] S. Miyata, Clays Clay Miner. 23 (1975) 369-375
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[22] S. Miyata, Clays Clay Miner. 31 (1983) 305-311
Ac ce p
[23] V. Rives (ed.) Layered Double Hydroxides, Present and Future, Nova Sci. Pub,Inc., New York (2010). [24] T. Kameda, H.Takeuchi, T.Yoshioka, Sep. Purif. Technol. 62 (2008) 330-336 [25] R. Delmdahl, R. Pätzel, Appl. Phys. A, 93 (2008) 611-615 [26] M.N.R. Ashfold, F. Claeyssens, G. M. Fuge, S. J. Henley, Chem.Soc.Rev., 33, 2004, 2331
Page 9 of 17
Figures caption Table 1. Atomic ratios of Mg/Al, Cu/Al, S/Al (before and after hydration, respectively), and
Mg/Al (molar ratio)
Cu/Al (molar ratio)
Powder/target Mg2Al
1.93
-
λ(nm) 266 532 1064
2.08 2.01 1.98
-
266 532 1064
1.48 1.33 1.42
0.58 0.70 0.74
0.39 0.44 0.47
2.06 2.03 2.16
266 532 1064
1.42 1.26 1.29
0.57 0.84 0.99
0.38 0.41 0.42
1.99 2.10 2.28
266 532 1064
1.13 1.25 0.74
1.63 2.72 3.03
0.14 0.14 0.15
2.76 3.97 3.77
266 532 1064
1.02 0.11 0.56
1.90 6.68 5.88
0.71 0.82 0.96
2.92 6.79 6.44
(Mg+Cu)/Al (molar ratio)
cr us
an
M
te
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Mg2Al thin films as deposited via PLD After 30sec immersion in aqueous sol CuSO4 (1g/L) After 30 min immersion in aqueous sol CuSO4 (1g/L) After 1 hour immersion in aqueous sol CuSO4 (1g/L) After 3 days immersion in aqueous sol CuSO4 (1g/L)
S/Cu (molar ratio)
ip t
Samples
d
(Mg+Cu)/Al immersed in aqueous solution of CuSO4 (1g/L) (EDX).
Page 10 of 17
Table 2. The structural data of as deposited Mg2Al thin films before and after one hour immersion in aqueous solution of CuSO4 and their corresponding target. The roughness and the thickness of the obtained films are presented.
22.698
2.67
-
23.09 22.85 22.97 31.09 26.67 27.78
2.90 2.82 2.86 5.56 4.09 4.46
ip t
us
3.028
an
λ(nm) 266 532 1064 266 532 1064
Morphological data Roughness Thickness (5x5 µm) (nm)
42 nm 109 nm 21 nm 35 nm 89 nm 20 nm
265 nm 341 nm 365 nm 301 nm 388 nm 396 nm
Ac ce p
te
d
After 1 hour immersion 1g/L sol CuSO4 (1g/L)
IFS (Å) 3.04535 22.7010 2.77
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Mg0.67 Al0.33 ( CO3)0.165 (OH)2(H2O)0.48 (JCPDS-04-011-5899) Mg2Al powder target thin films Mg2Al thin films as deposited via PLD
Structural data a (Å) c (Å)
cr
Samples
Page 11 of 17
Figures caption Fig. 1 AFM and SEM images for Mg2Al thin films grown by PLD on silicon substrates from an Mg2Al target using three ablation wavelengths (266 nm, 532 nm and 1064 nm. The SEM images of the thin films after 1 hour immersion in a CuSO4 aqueous solution (1g/L) are
ip t
labeled with Mg2Al&Cu.
cr
Fig. 2 The XRD pattern of Mg2Al films grown by PLD on silicon substrates at three ablation wavelengths (266 nm, 532 nm and 1064 nm), before and after 1 h immersion in aqueous
us
solution of CuSO4 (1g/L).
Fig. 3 SEM images and corresponding XRD patterns of the LDHs films deposited at 1064
an
nm after 30s, 30 min, 1 h and 3 days, respectively immersion in CuSO4 solution (1g/L). (o) are labeled the reflections of a Cu2.5SO4(OH)3.2H2O phase byproduct (JCPDS no.051-0321).
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Fig.4 The evolution of the Me=Cu, Ni or Co after immersion in 1g/L solutions at different contact times. The data for Ni and Co are reported in [18]. The time scale is logarithmic. With
Ac ce p
te
d
(o) are indicated peaks assigned to Cu2.5SO4(OH)32H2O phase .
Page 12 of 17
Ac ce p
te
d
M
an
us
cr
ip t
Fig.1
Page 13 of 17
Ac ce p
te
d
M
an
us
cr
ip t
Fig. 2
Page 14 of 17
Ac ce p
te
d
M
an
us
cr
ip t
Fig. 3.
Page 15 of 17
Ac ce p
te
d
M
an
us
cr
ip t
Fig. 4
Page 16 of 17
Ac ce p
te
d
M
an
us
cr
ip t
PLD was successfully used to produce Mg2Al thin films from Mg-Al LDH target (Mg/Al=2). Well oriented LDH films were obtained for all three wavelengths of a Nd:YAG laser: 266 nm, 352 nm, 1064 nm. Mg-Al LDH thin films obtained in this work could be suitable as adsorbent material for the detection of copper in aqueous solutions.
Page 17 of 17
S0169-4332(15)00523-1 http://dx.doi.org/doi:10.1016/j.apsusc.2015.02.192 APSUSC 29875
To appear in:
APSUSC
Received date: Revised date: Accepted date:
15-11-2014 20-2-2015 27-2-2015
Please cite this article as: A. Vlad, R. Birjega, A. Matei, C. Luculescu, A. Nedelcea, M. Dinescu, R. Zavoianu, O.D. Pavel, Detection of copper ions from aqueous solutions using layered double hydroxides thin films deposited by PLD, Applied Surface Science (2015), http://dx.doi.org/10.1016/j.apsusc.2015.02.192 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Detection of copper ions from aqueous solutions using layered double hydroxides thin films deposited by PLD A. Vlad*, R. Birjega, A. Matei, C. Luculescu, A. Nedelcea, M. Dinescu,
Bucharest-Magurele, Romania
cr
R. Zavoianu, O.D. Pavel
ip t
National Institute for Lasers, Plasma and Radiation Physics, 409 Atomistilor Str., 76900
University of Bucharest, Faculty of Chemistry, Department of Chemical Technology and
us
Catalysis, 4-12 Regina Elisabeta Bd., Bucharest, Romania
an
Abstract
Layered double hydroxides (LDHs) thin films with Mg-Al were deposited using
M
pulsed laser deposition (PLD) technique. We studied the ability of our films to detect copper ions in aqueous solutions. Copper is known to be a common pollutant in water, originating
d
from urban and industrial waste. Clay minerals, including layered double hydroxides (LDHs),
te
can reduce the toxicity of such wastes by adsorbing copper. We report on the uptake of copper ions from aqueous solution on LDH thin films obtained via PLD.
Ac ce p
The obtained thin films were characterized using X-Ray Diffraction, Atomic Force
Microscopy, and Scanning Electron Microscopy with Energy Dispersive X-ray analysis. The results in this study indicate that LDHs thin films obtained by PLD have potential as an efficient adsorbent for removing copper from aqueous solution.
Keywords: LDH thin films, pulsed laser deposition, copper metals uptake *
Author for correspondence: Angela Vlad Tel: +40 21 457 44 14; Fax: +40 21 457 42 43; E-mail: [email protected];
Page 1 of 17
1. Introduction Clay minerals possess a high specific surface area and good adsorptive/exchange capacity, which makes them very useful for a wide range of applications. Layered double hydroxides
ip t
(LDHs), also known as hydrotalcite-type (HT) compounds, display similar properties to those
cr
of clay minerals [1, 2]. Removal of heavy metal ions (Cu2+, Cd2+, Pb2+, Ni2+, Co2+) from aqueous solutions or contaminated water is an important environmental issue [3].
us
The general formula of LDHs is: [M2+1-xM3+x(OH)2]x+(An-x/n) · mH2O, where M2+ and M3+ are divalent (Mg2+, Ni2+, Zn2+, or Co2+) and trivalent (Al3+, Cr3+, Fe3+, or Ga3+) cations,
an
respectively. An- is an interlayer anion of charge n and x is equal to the ratio M3+/(M2+ + M3+) [4]. Papers about the uptake of heavy metals onto LDHs thin films from water are scarce,
M
probably because layered double hydroxides have only recently been considered for
and environment [10].
d
industrial/health applications [5-9]. Some of the heavy metals pose serious hazards to health
te
Studies on uptake of metal ions from an aqueous solution by Mg-Al or Zn-Al LDHs were
Ac ce p
done using intercalated suitable chelating resins like ethylenediaminetetraacetate (edta) [11, 12], citrate, malate [13]. In these cases the anions act as scavengers and can remove heavy metals from water by forming complexes of chelate bonded heavy metals. For example, the team of Perez et al. [14] observed that uptake of Cu2+ was higher than that of Pb2+ or Cd2+ when using edta intercalated ZnAl LDHs. Komarneni’s group [15] reported that the “diadochy” process is the main mechanism of metal uptake from wastewater. The process allows selective cation uptake that takes place via substitution of Mg2+ ions in the Mg-Al LDH structure. Our research group reported a new way to obtain LDHs thin films by pulsed laser deposition (PLD) and matrix assisted pulsed laser evaporation (MAPLE) [16-18]. We also reported on the ability of LDH thin films deposited via laser techniques to retain Ni or Co from aqueous
Page 2 of 17
solutions [17, 18]. We have described the mechanism of adsorption of these heavy metals through the already cited “diadochy” process [15], in competition with a reconstruction process. All the divalent metals, from Mg2+ to Mn2+, form LDH, except for Cu2+ which forms pure LDH if other bivalent cations, such as Zn, Cr, Co, Mg, and Mn, are present. In most
ip t
cases Cu-LDHs are always mixed with other phases, such as malachite [Cu (OH)2CuCO3] and
cr
gerhardite [Cu (OH)3NO3], due to the Jahn-Teller effect of the Cu2+ ion [19,20]. This work is an investigation on the capacity of copper to be adsorbed on oriented Mg-Al LDHs thin films
us
obtained by pulsed laser deposition (PLD), as compared to other heavy metals not exhibiting a Jahn-Teller effect. The Mg-Al LDHs thin films were obtained by pulsed laser deposition
an
technique at three different wavelengths. We investigate the influence of their roughness, thickness and the presence of some amorphous or delaminated material on the copper uptake.
M
2. Experimental 2.1 Materials preparation
d
Mg-Al LHD powder was prepared by co-precipitation at supersaturation at pH=10 using
te
aqueous solutions of Mg and Al nitrates, sodium hydroxide and carbonate. The Mg/Al molar
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ratio was adjusted to 2. The obtained gel have been dried at 850C for 24 hours under controlled nitrogen flow pressure and then dried and pressed as pellets in order to be used as targets in pulsed laser deposition experiments. In this report the as prepared powder and the corresponding target will be referred to as 'Mg2Al' 2.2 Films preparation
We deposited Mg-Al LDH thin films on Si (100) substrates using a pulsed Nd:YAG laser working at three different wavelengths (λ=266, 532 and 1064 nm, τL~5 ns), at a pulse repetition rate of 10 Hz. The films were deposited at room temperature in a parallel configuration. The laser fluence was 2 J/cm2. The number of pulses irradiating the target was set at 12000, and the resulting thin films had thicknesses between 250 to 350 nm. After deposition the films were immersed
Page 3 of 17
in aqueous solution of CuSO4 (1g/L), in a volume is 5 ml at ambient temperature at different contact times 30s, 30 min, 1h and 3 days, respectively. 1 h is considered the representative contact time. The uptake of copper was evaluated by energy dispersive X-ray spectroscopy (EDX). The thickness of the films, prior and after the immersion was determined by
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profilometry. The crystalline structure of the films was studied by X-ray diffraction at grazing
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incidence (GI-XRD) using a CuKα (λ=1.5418 Ǻ) radiation. 3. Results and discussion
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3.1 EDX results
The energy dispersive (EDX) results are presented in Table 1. High Cu/Al ratios accompanied
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by a significant decrease of the Mg/Al ratios are observed. Also, the presence of sulfur (S) was evidenced. The Cu/Al ratio values are higher for films deposited at 532 nm and 1064 nm,
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probably in correlation with their higher thickness, while the S/Cu ratio is lower and almost constant for all three ablation wavelengths after 1 h immersion time.
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3.2 SEM and AFM investigations
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SEM and AFM analyses of films morphology reveal rough surfaces, with big grains deposited
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onto the film surface, especially at 266 nm (Fig. 1). Fine, oriented layered structures are observed in the SEM images of films after 1 hour immersion in CuSO4, which indicates that a reconstruction process has occurred. We observed the same aspect denoting a reconstruction process in our previous reports on Ni and Co uptakes [17, 18]. 3.3 XRD results
The hydrotalcites exhibit an R3m rhombohedral symmetry and were Miller indexed in a hexagonal lattice. The lattice parameters of the Mg2Al powder and Mg2Al target are the same, and comparable to standard hydrotalcite values having the same Mg/Al molar ratio (JCPDS no.04-011-5899). In the XRD patterns of the as-deposited thin films only the basal spacings (00l) are detectable, which is indicative of the oriented nature of the formed films (Fig.2). After a one hour immersion in aqueous solution of CuSO4 (1g/L) at room temperature
Page 4 of 17
the XRD patterns of the thin films exposed only the basal spacing which are considerable shifted towards lower angles in comparison with the as deposited films. This important increase of the c-parameter is higher in comparison with our reported previous observations on Co and Ni absorption effect. The structural data are included in Table 2. The interlayer
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distance is calculated by subtraction of 4.8 Å, corresponding to the hydrotalcite-layer
solution could be explained by considering the following effects:
Intercalation of (SO4)2- in the interlayer spacing, as supported by the EDX results. The
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-
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thickness from d003 [21]. The interlayer distance increase following 1h immersion in copper
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values of the basal d003 given by Miyata [22] and cited by Rives [23] are slightly larger for SO4-bearing LDHs, which means that CO32- combined with small amounts of SO42-
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are intercalated in these films. The cointercalation of both CO32- and SO42- leads also to a disorder effect on the stocking arrangement of the layers. The result is endorsed by the
The used CuSO4 solution (1g/L) is pale-blue due to the presence of [Cu(H2O)6]2+
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-
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broadness of the basal reflections.
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complex ions. [Cu(H2O)6]2+ is a Jahn-Teller ion exhibiting plasticity and adopting different geometries, an octahedral structure in most cases, with a first or even a second hydration sphere [24], which lead to larger ions to be intercalated. The pH of the solution in which the films were immersed is dominated by the acid character of [Cu(H2O)6]2+. The pH of the CuSO4 (1g/L) solution we used was 4.9 during the 1 hour immersion time, which favored the coprecipitation of Cu2+ with dissolved Al3+ to form
Cu-Al LDH [11]. Mg2+ does not precipitate at this pH value. Therefore, the reconstruction occurred with the formation of a Cu rich layered double hydroxide. These assumptions are consistent with the EDX results, after 1 h immersion time, i.e. high Cu/Al and low Mg/Al atomic ratio values, the increase of thickness of the films upon
Page 5 of 17
copper uptake, as well with the SEM images exposing the formation of fine layered structures after immersion. The possibility of “diadochy”, isomorphic substitution of Mg2+ of Cu2+ is uncertain due to the
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Jahn-Teller distortion. The lack of the (110) reflection connected to the layer parameter does not allow to state on this aspect. Komarneni et al. introducing the “diadochy” function for
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LDH, the uptake of transitional metals, Ni2+, Co2+, Zn2+, Cu2+ through the isomorphous substitution of Mg2+ reported also the precipitation of Cu in the presence of LDHs but not for
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the other cations [15].
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Therefore we explain the larger amount of Cu uptake mainly by coprecipitation of Cu2+ with
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dissolved Al3+ to form Cu-Al LDH backed by the Mg2+ dissolution. We aimed also to collect experimental observation on the influence of the deposition
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conditions, namely of the laser wavelengths on the LDH thin films formation and
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consequently, on the films behavior after immersion in a CuSO4 solution (1g/L). The film deposited at a shorter laser wavelength, 266 nm, exhibits a smoother morphology and poor
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crystallinity (Figs 1 and 2 and tables 1 and 2). The result is overall explained by shorter penetration depths and ablation plumes containing a higher fraction of ionized, high kinetic energy material [25,26] leading to thinner and smoother films. The plasma temperatures in the early phase of expansion is highest in the case of 1064 nm at the same value of laser irradiance leading to an increase of micro and nano-sized droplets, clusters or conglomerates ejected from the target which explain the thickness and roughness of the film [24,25]. The deposition at 532 nm appears to be closer to the 1064 nm deposition. The slight difference in the morphological and structural aspects are preserved after immersion in a CuSO4 solution (1g/L) for 1 hour implying that the film deposited at 266 nm due to its thickness and presence of amorphous material are less efficient in the detection of copper from aqueous solutions.
Page 6 of 17
Removal efficiency appears to be the highest around 1 hour. Similar to the uptake of Ni and Co studies, previously reported [18], at 30 s the detection of Cu is possible due to the hydrophilicity of the LDH surface which retains drops of CuSO4 solution on top of the film surface, the reconstruction of a layered structure occurring during the evaporation process.
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The SEM images and XRD patterns after 30 s and 30 min immersion time respectively (Fig.3)
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along with the elemental data obtained from the EDX analyses (Table 1) show no significant change while an important increase occurred for the films after 1 hour immersion time. After
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3 days immersion the increase of the Cu uptake is significantly (Table 2). Besides the formation of a LDH phase, an additional Cu2.5SO4(OH)3.2H2O phase (JCPDS no. 51-0321)
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are formed alongside (see Fig.3). Fig. 4 exhibits the comparative evolution of the heavy metals uptake. The data for Ni and Co uptake are taken from our previous work [18]. The
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solutions we used were at the same concentration, 1g/L as CuSO4 and, the LDH films derived from a Mg2Al target deposited at 1064 nm. The proportion of Cu uptake after 1hour
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immersion is significantly higher backing for a different mechanism then “diadochy” process
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occurring as dominant process for Ni or Co uptake [17,18]. Due to the Jahn-Teller effect
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which impeded the Cu substitution in the brucite layered while the Cu interlayer intercalation along with coprecipitation dissolved Al3+ to form a Cu, Al-LDH film are favored.
4. Conclusions
In this study, the uptake of copper ions from aqueous solution was carried out by using thin films of Mg-Al based LDH deposited by PLD. The uptake studies were performed for different contact times. The 1 h immersion time was found to be sufficient to reach detectable copper and sulfate values. The film deposited at 266 nm due to their thickness and roughness are less efficient in Cu detection while the films deposited at 1064 and 532 nm respectively exhibit similar behavior. The results suggest that Mg-Al LDH thin films obtained in this work could be suitable for the detection of copper in aqueous solutions. The copper uptake is Page 7 of 17
explained mainly by the co-precipitation of Cu2+ with dissolved Al3+ to form Cu-Al LDH. The ability to form Cu-Al LDHs is backed by the Mg2+ dissolution. Uptake of Cu2+ was possible without a preliminary functionalization step which makes the method and the procedure
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promising.
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Acknowledgments
This work was supported by a grant of the Romanian National Authority for Scientific
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Research, CNCS – UEFISCDI, project number PD15/2011 and PCCA 137/2012.
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References:
[1] C. Del Hoyo, Appl Clay Sci 36 (2007) 103-121
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[2] P. Nalawade, B. Aware, V.J. Kadam, R.S. Hirlekar, J. Sci&Ind. Res 68 (2009) 267-272 [3] J. O. Nriagu, J. M. Pacyna, Nature 333 (1988) 134-139
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[4] F. Cavani, F. Trifiro, A. Vaccari, Catal. Today 11 (1991) 173–301
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[5] F. Basile, A. Vaccari, V. Rives (Ed.), Layered Double Hydroxides: Present and Future,
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Nova Science Publishers, Inc., New York (2001) 323–365 [6] S. Mandal, S. Mayadevi, Appl. Clay Sci. 40 (2008) 54–62 [7] D. Shan, W. Yao, H. Xue, Biosens. Bioelectron. 23 (2007) 432–437. [8] G. Di Francia, V. La Ferrara, S. Manzo, S. Chiavarini, Biosens. Bioelectron. 21 (2005) 661–665.
[9] C. Mousty, Anal Bioanal Chem.396 (2010) 315-325 [10] J. L. Dorne, G. E. Kass, L.R. Bordajandi, B. Amzal, U. Bertelsen, A.F. Castoldi, C. Heppner, M. Eskola, S. Fabiansson, P. Ferrari, E. Scaravelli, E. Dogliotti, P. Fuerst, A. R. Boobis, P. Verger, Met ions Life sci 8 (2011) 27-60. [11] T. Kameda, S. Saito, Y. Umetsu, Sep. Purif. Technol. 47 (2005) 20-26 [12] T. Kameda, K. Hoshi, T. Yoshioka, Solid State Sci. 17 (2013) 28-34
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[13] T. Kameda, H. Takeuchi, T. Yoshioka, Colloids Surf. A 355 (2010) 172–177 [14] M. R. Perez, I. Pavlovic, C. Barriga, J. Cornejo, M.C. Hermosin, M. A. Ulibarri, Appl. Clay Sci. 32 (2006) 245-251 [15] S.Komaneni, N. Kozai, R. Roy, J. Mater. Chem 8, (1998), 1329.
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[16] A. Matei. R. Birjega, A. Nedelcea, A. Vlad, D. Colceag, M. D. Ionita, C. Luculescu, M.
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Dinescu, R. Zavoainu, O. D. Pavel, Appl. Surf. Sci., 257 (2011) 5308-5311
[17] A. Matei. R. Birjega, A. Vlad, M. Filipescu, A. Nedelcea, C. Luculescu, R. Zavoainu, O.
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D. Pavel, M. Dinescu, Appl. Surf. Sci., 258 (2012) 9466-9470
Pavel, Appl. Surf. Sci., 302 (2014) 99-104
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[18] A. Vlad, R. Birjega, A. Matei, C. Luculescu, B. Mitu, M. Dinescu, R. Zavoainu, O. D.
[19] A. Alejandre, F. Medina, X. Rodriguez, P. Salagre and J. E. Sueiras, J. Catal., 188 (1999)
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311-324
[20] R. Manivannan, A. Pandurangan, Appl. Clay Sci , 44 (2009) 137-143
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[21] S. Miyata, Clays Clay Miner. 23 (1975) 369-375
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[22] S. Miyata, Clays Clay Miner. 31 (1983) 305-311
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[23] V. Rives (ed.) Layered Double Hydroxides, Present and Future, Nova Sci. Pub,Inc., New York (2010). [24] T. Kameda, H.Takeuchi, T.Yoshioka, Sep. Purif. Technol. 62 (2008) 330-336 [25] R. Delmdahl, R. Pätzel, Appl. Phys. A, 93 (2008) 611-615 [26] M.N.R. Ashfold, F. Claeyssens, G. M. Fuge, S. J. Henley, Chem.Soc.Rev., 33, 2004, 2331
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Figures caption Table 1. Atomic ratios of Mg/Al, Cu/Al, S/Al (before and after hydration, respectively), and
Mg/Al (molar ratio)
Cu/Al (molar ratio)
Powder/target Mg2Al
1.93
-
λ(nm) 266 532 1064
2.08 2.01 1.98
-
266 532 1064
1.48 1.33 1.42
0.58 0.70 0.74
0.39 0.44 0.47
2.06 2.03 2.16
266 532 1064
1.42 1.26 1.29
0.57 0.84 0.99
0.38 0.41 0.42
1.99 2.10 2.28
266 532 1064
1.13 1.25 0.74
1.63 2.72 3.03
0.14 0.14 0.15
2.76 3.97 3.77
266 532 1064
1.02 0.11 0.56
1.90 6.68 5.88
0.71 0.82 0.96
2.92 6.79 6.44
(Mg+Cu)/Al (molar ratio)
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Mg2Al thin films as deposited via PLD After 30sec immersion in aqueous sol CuSO4 (1g/L) After 30 min immersion in aqueous sol CuSO4 (1g/L) After 1 hour immersion in aqueous sol CuSO4 (1g/L) After 3 days immersion in aqueous sol CuSO4 (1g/L)
S/Cu (molar ratio)
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Samples
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(Mg+Cu)/Al immersed in aqueous solution of CuSO4 (1g/L) (EDX).
Page 10 of 17
Table 2. The structural data of as deposited Mg2Al thin films before and after one hour immersion in aqueous solution of CuSO4 and their corresponding target. The roughness and the thickness of the obtained films are presented.
22.698
2.67
-
23.09 22.85 22.97 31.09 26.67 27.78
2.90 2.82 2.86 5.56 4.09 4.46
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3.028
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λ(nm) 266 532 1064 266 532 1064
Morphological data Roughness Thickness (5x5 µm) (nm)
42 nm 109 nm 21 nm 35 nm 89 nm 20 nm
265 nm 341 nm 365 nm 301 nm 388 nm 396 nm
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te
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After 1 hour immersion 1g/L sol CuSO4 (1g/L)
IFS (Å) 3.04535 22.7010 2.77
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Mg0.67 Al0.33 ( CO3)0.165 (OH)2(H2O)0.48 (JCPDS-04-011-5899) Mg2Al powder target thin films Mg2Al thin films as deposited via PLD
Structural data a (Å) c (Å)
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Samples
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Figures caption Fig. 1 AFM and SEM images for Mg2Al thin films grown by PLD on silicon substrates from an Mg2Al target using three ablation wavelengths (266 nm, 532 nm and 1064 nm. The SEM images of the thin films after 1 hour immersion in a CuSO4 aqueous solution (1g/L) are
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labeled with Mg2Al&Cu.
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Fig. 2 The XRD pattern of Mg2Al films grown by PLD on silicon substrates at three ablation wavelengths (266 nm, 532 nm and 1064 nm), before and after 1 h immersion in aqueous
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solution of CuSO4 (1g/L).
Fig. 3 SEM images and corresponding XRD patterns of the LDHs films deposited at 1064
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nm after 30s, 30 min, 1 h and 3 days, respectively immersion in CuSO4 solution (1g/L). (o) are labeled the reflections of a Cu2.5SO4(OH)3.2H2O phase byproduct (JCPDS no.051-0321).
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Fig.4 The evolution of the Me=Cu, Ni or Co after immersion in 1g/L solutions at different contact times. The data for Ni and Co are reported in [18]. The time scale is logarithmic. With
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te
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(o) are indicated peaks assigned to Cu2.5SO4(OH)32H2O phase .
Page 12 of 17
Ac ce p
te
d
M
an
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cr
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Fig.1
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Ac ce p
te
d
M
an
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cr
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Fig. 2
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Ac ce p
te
d
M
an
us
cr
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Fig. 3.
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Ac ce p
te
d
M
an
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cr
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Fig. 4
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Ac ce p
te
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M
an
us
cr
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PLD was successfully used to produce Mg2Al thin films from Mg-Al LDH target (Mg/Al=2). Well oriented LDH films were obtained for all three wavelengths of a Nd:YAG laser: 266 nm, 352 nm, 1064 nm. Mg-Al LDH thin films obtained in this work could be suitable as adsorbent material for the detection of copper in aqueous solutions.
Page 17 of 17