Poster Proceedings
APPLICATION OF GRAPHENE QUANTUM DOTS IN HEAVY METALS AND PESTICIDES DETECTION
Slađana Dorontić1, Olivera Marković2, Aurelio Bonasera3, and Svetlana Jovanović1
1“Vinča” Institute of Nuclear Sciences - National Institute of the Republic of Serbia, University of Belgrade P.O. Box 522, 11001 Belgrade, Serbia
2University of Belgrade – Institute of Chemistry, Technology and Metallurgy – National Institute of the Republic of Serbia, Njegoševa 12, 11000, Belgrade, Serbia
3Dept. of Physics and Chemistry-Emilio Segrè; (DiFC) - University of Palermo, Consorzio, Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali (INSTM) - Palermo
Research Unit viale delle Scienze, bdg. 17, rm. 1/B6 90128 Palermo (PA) - Italy e-mail: svetlanajovanovicvucetic@gmail.com
Abstract
Graphene Quantum Dots (GQDs) were produced using electrochemical oxidation of graphite rods. Obtained GQDs were gamma-irradiated in the presence of the N atoms source, ethylenediamine. Both structural and morphological changes were investigated using UV-Vis, X-ray photoelectron and photoluminescence (PL) spectroscopy as well as atomic force microscopy. The ability of both types of dots to change PL intensity in the presence of pesticides such as malathion and glyphosate, as well as copper (II) ions was detected. These preliminary results indicated a high potential of produced GQDs to be applied as non-enzymatic PL sensors for the detection of selected pesticides and metal ions.
Introduction
Graphene quantum dots (GQDs) are round graphene sheets with a diameter below 100 nm and different O-containing functional groups located on the surface and at the edges of dots [1].
Due to a large amount of these functional groups, GQDs are dispersible in water and polar organic solvents. They showed good biocompatibility and low cytotoxicity [2]. Due to the quantum confinement effect and edge sites/defects, GQDs possess stable photoluminescence (PL) and they are resistive to photobleaching [3]. Considering both biocompatibility and photoluminescence, these dots were often investigated for their possible application in the sensing of different ions and molecules [4].
Due to the overuse of pesticides, they are often found in the ground, water, or agricultural products. Pesticides accumulation in the environment leads to their entering into biosystems [5]. Thus, pesticides such as glyphosate and the products of its degradation were detected in human urine in a concentration of 2.63, 1.26, and 0.89 µg/L in samples from Croatia, Belgium, and Malta [6]. Additionally, the pollution of water, air, and ground lead to a high level of heavy metals which are also toxic for animal, humans, and plants [7]. The analytical techniques that are now in-use for pesticides and heavy metal detection request the usage of expensive instruments, highly educated operators, while the analysis often demands time. Thus, there is a need for a new, simple, and affordable method for the detection of these pollutants.
Herein we prepared GQDs using an eco-friendly approach: electrochemical oxidation of graphite electrodes was achieved without the consumption of aggressive and toxic reagents [8].
Dots were purified by dialysis and structurally modified through gamma irradiation. During gamma irradiation, covalent modification of material can be achieved without the consumption of aggressive, toxic reagents. Thus, this method is considered a green tool for modification. By selecting the medium with N-atoms, the incorporation of N-functional groups was achieved.
The effect of the herbicide glyphosate, insecticide malathion, and copper (II) ions on the intensity of photoluminescence of GQDs was investigated.
180 Experimental
GQDs were produced using a previously described procedure [8]. Gamma-irradiation was conducted in a water solution of isopropanol (3 vol%) and ethylenediamine (EDA, 4 vol%) [9].
Before the irradiation, the sample was purged with argon to remove dissolved oxygen. The sample was irradiated at a dose of 50 kGy.
UV-Vis measurements were performed at a Shimadzu UV-2600 UV-Visible spectrophotometer (Shimadzu Corporation, Tokyo, Japan). Spectra were recorded at 20 °C under a normal atmosphere, in the range of 200-800 nm. The concentration of GQD dispersions was 0.25 mg mL-1.
The PL spectra were recorded on Horiba Jobin Yvon Fluoromax-4 spectrometer (Horiba, Kyoto, Japan). GQDs dispersions in methanol (c=0.25 mg mL-1) were placed in a quartz cuvette with 1 cm path length and 4 mL volume. For the excitation, laser wavelengths were 300, 360 and 400 nm. Spectra were collected under room temperature in the air environment.
X-ray Photoelectron Spectroscopy (XPS) was acquired by using a ULVAC-PHI PHI500 VersaProbe II scanning microprobe (ULVAC-PHI, Inc., Chigasaki, Japan), with an Al Kα source (1486.6 eV), 100 μm spot, 25 W power, 15 kV acceleration, and 45° take-off angle. All spectra were collected using a dual neutralization system (both e− and Ar+).
Atomic Force Microscopy (AFM) measurements were performed using Quesant (Agoura Hills, CA, Unites States) microscope operating in tapping mode, in the air, at room temperature. We used the Q-WM300 AFM probe, rotated, monolithic silicon probe for non-contact high-frequency applications. Standard silicon tips (NanoAndMore Gmbh, Wetzlar, Germany) were used, with a force constant of 40 N/m. GQDs were dispersed in MiliQ water in a concentration of 0.25 mg mL-1 and deposited with spin-coated on a mica substrate. Gwyddion 2.53 software was used for image analysis.
Results and discussion
UV-Vis spectroscopy showed that p-GQDs had a peak of absorption centered around 230 nm while after gamma irradiation, this band was narrow, shifted to 205 nm with a shoulder band at 260 nm. The first band was due to π-π* transitions of sp2 C in aromatic bonds, while the second was assigned to π→n transitions of C=O groups. These results indicated the changes in the amount of O functional groups occurred during gamma irradiation. PL spectra showed that after gamma irradiation the highest intensity of emission band was observed with an excitation wavelength of 400 nm (figure 2c) while for p-GQDs, the highest emission was detected at excitation of 300 nm. The excitation-dependent photoluminescent behavior was observed for both samples. AFM analysis (figure 1d and e) showed that irradiation caused the lowering in the average GQDs height, from 1.73 nm as measured for p-GQDs to 1.25 nm. The average diameter was around 18 nm for p-GQDs, and 15 nm for 50γ-GQDs. XPS analysis showed that GQDs had C and O atoms, while 50γ-GQDs had C, O and N atoms in the structure (figure 1f).
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Figure 1. UV-Vis spectra of p-GQDs and 50γ-GQDs (a), PL spectra, and AFM images of p-GQDs (b, d) and 50γ-GQDs (c, e), as well as XPS survey of samples (f).
To investigate the possibility of GQDs application in non-enzymatic PL detection, GQDs were mixed with Cu(II) ions, pesticide malathion and the herbicide glyphosate. After a short incubation time (5 minutes), mixtures of GQDs with analytes were recorded on PL spectroscope and obtained spectra are presented in figure 2. By adding Cu(II) ions, the maximum of the intensity of PL emission spectra was lowered for both p-GQDs and 50γ-GQDs. In the case of malathion which was added in a concentration of 18.1 mM, the PL intensity was increased, while in the case of glyphosate the increase in PL intensity was observed for two concentrations:
10 and 5000 ng mL-1. A higher increase in PL intensity was observed in the case of p-GQDs/malathion while in the case of glyphosate the higher changes were detected for gamma-irradiated GQDs.
Figure 2. PL p-GQDs with Cu (II) ions (a), malathion (b), glyphosate (c) and 50γ-GQDs with the same analytes at (d), (e) and (f), respectively.
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These preliminary results showed that both non-modified and modified GQDs possess the potential for their application in Cu(II) ions, malathion and glyphosate detection. In the case of Cu(II) ions, it was suggested that the lowering in PL intensity was due to the electrostatic destabilization and coagulation of negatively charged GQDs. On the opposite, pesticide malathion and glyphosate induced an increase in PL intensity of GQDs. In future research we will analyze if the increase in pesticide concentration leads to a linear increase of the PL intensity for a wide range of pesticide concentrations.
Conclusion
The potential of GQDs application in the detection of metal ions and pesticides was investigated. GQDs were synthesized in an electrochemical approach and modified by gamma irradiation. This treatment induced the lowering in GQDs height and diameter, and resulted in the incorporation of N atoms in the GQD structure. Both modified and non-modified GQDs were investigated as sensors in PL detection of Cu ions, malathion and glyphosate. A preliminary investigation showed the changes in the PL intensity when these analytes were added: Cu (II) lowered while malathion and glyphosate increased PL intensity.
Acknowledgments
This work was financially supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia (Grant No. 14/2652, 451-03-68/2020-14/200017 and 451-03-68/2020-14/200026). ATeN Center (University
of Palermo; project “Mediterranean Center for Human Health Advanced Biotechnologies (CHAB)” PON R&C 2007–2013) is acknowledged for hospitality and service.
References
[1] S. Jovanovic, Handbook of Graphene Set, 1 (2019) 267.
[2] X. Yuan, Z. Liu, Z. Guo, Y. Ji, M. Jin, X. Wang, Nanoscale Research Letters, 9 (2014) 1.
[3] Z. Gan, H. Xu, Y. Hao, Nanoscale, 8 (2016) 7794.
[4] M. Li, T. Chen, J.J. Gooding, J. Liu, ACS Sensors, 4 (2019) 1732.
[5] R. Mesnage, M.N. Antoniou, Front Public Health, 5 (2017) 316.
[6] L. Niemann, C. Sieke, R. Pfeil, R.J.J.f.V.u.L. Solecki, 10 (2015) 3.
[7] V. Silva, H.G.J. Mol, P. Zomer, M. Tienstra, C.J. Ritsema, V. Geissen, Science of The Total Environment, 653 (2019) 1532.
[8] H.T. Li, X.D. He, Z.H. Kang, H. Huang, Y. Liu, J.L. Liu, S.Y. Lian, C.H.A. Tsang, X.B.
Yang, S.T. Lee, Angew Chem Int Edit, 49 (2010) 4430.
[9] S. Jovanović, S. Dorontić, D. Jovanović, G. Ciasca, M. Budimir, A. Bonasera, M. Scopelliti, O. Marković, B. Todorović Marković, Ceram Int, 46 (2020) 23611.
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ON-LINE CHARACTERIZATION OF NANOPARTICLES BY SINGLE PARTICLE ICP-MS UTILIZING MICROFLUIDIC DEVICES Gyula Kajner1,2, Albert Kéri1,2, Ádám Bélteki1,2, Sándor Valkai3, András Dér3,
Zsolt Geretovszky2,4, Gábor Galbács1,2
1Dept. of Inorg. and Anal. Chem., Univ. of Szeged, H-6720 Szeged, Dóm sq. 7, Hungary
2Dept. of Mater. Sci., Interdiscip. Excel. Cent., Univ. of Szeged, H-6720 Szeged, Dugonics sq. 13, Hungary
3Inst. of Biophys., Biol. Res. Cent., H-6726 Szeged, Temesvári blvd. 62, Hungary
4Dept of Opt. and Quantum Elec., Univ. of Szeged, 6720 Szeged, Dóm sq. 9, Hungary e-mail: galbx@chem.u-szeged.hu
Abstract
In this study, polydimethylsiloxane (PDMS) - glass microfluidic chips (MCs) were designed and fabricated using moulds prepared by a professional 3D printer. The prepared chips were used for the dilution, counting and characterization of nanoparticles (NPs) performing single particle inductively coupled plasma mass spectrometry (spICP-MS) measurements.
Introduction
Single particle inductively coupled plasma mass spectrometry is a novel technique for the rapid characterization of the dispersions of nano- and submicron particles. The technique can provide information on the presence, size and size distribution, number concentration, elemental and isotope composition of nanodispersions [1, 2]. An outstanding advantage of spICP-MS is the low (103-105 mL-1) optimal particle number concentration (PNC), which can be prepared from sub-microgram amounts of sample [3]. This advantage can be best exploited by a sample introduction system capable for the introduction of low-volume samples. The sample preparation procedure of spICP-MS is simple, requiring only the dilution of nanodispersions.
Nevertheless, in case of real-life samples, where the PNC can be hardly estimated accurately, it can be work- and time-consuming to find the right dilution to achieve single particle detection.
MCs are well-established state-of-the-art devices suitable for the handling of low-volume solution and dispersion samples. These tools often serve capillary electrophoresis but are exploited in other fields of analytical separation and sample preparation techniques as well.
Most microfluidic devices are prepared utilizing polydimethylsiloxane (PDMS) and glass/quartz microscope slides as these materials are cost-effective and easy to produce [4].
MCs also bear the possibility for automation which makes them even more attractive.
The aim of our study was to develop microfluidic devices for on-line spICP-MS sample preparation. In this contribution, we present some of our experimental results.
Experimental
An Agilent 7700X inductively coupled plasma mass spectrometer (ICP-MS) was used in all experiments. Sample introduction was performed by utilizing Gilson Minipuls 3 peristaltic pumps (Gilson Inc. Middleton, WI, USA) and a Micro Mist type nebulizer equipped with a Peltier-cooled spray chamber (standard Agilent 7700x accessories). The sample uptake rate was 600 µL/min. The data acquisition software was used in Time Resolved Analysis (TRA) mode.
The integration time was set to 500 ms for the measurement of solution samples and 6 ms for nanodispersions, whereas the acquisition time was set to 60 s. All measurements were repeated three times and the error bars in the following graphs indicate their standard deviation.
The microfluidic chip moulds were fabricated utilizing a Form 3 professional 3D printer using
„High Temp” resin material (Formlabs, Somerville, MA, USA). Utilizing the moulds, the MCs
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were prepared by using Sylgard 184 silicone elastomer and curing agent (Dow Corning, Midland, MI, USA) and sealing the PDMS to a flat glass microscope slide. Detailed description of the preparation of the MCs can be found in one of our earlier publications [5].
Before dilution and also directly before aspiration into the ICP-MS, the dispersions were sonicated in an ultrasonic bath for 5 min (Bransonic 300, Ney, Danbury, CT, USA) in order to minimize particle aggregation.
Co and Ag sample solutions were prepared from 1000 mg/L CertiPUR monoelemental standards (Merck GmbH, Darmstadt, Germany). In spICP-MS measurements, commercially available NP standard dispersions were used. Ultra uniform polyethylene-glycol-capped 47.8 (1.8) nm gold nanospheres were purchased from Nano-Composix (San Diego, California USA), Pelco NanoXact tannic acid-capped 43.4 (3.2) nm silver NPs were obtained from Ted Pella (Redding, California, USA). Trace-quality de-ionized labwater from a MilliPore Elix 10 device equipped with a Synergy polishing unit (Merck GmbH, Darmstadt, Germany) was used for the preparation of all solutions and dispersions. Ismatec S3 E-LFL Tygon tubings (IDEX Health &
Science GmbH, Wertheim, Germany) of 0.27 and 0.48 mm inner diameter were used for the aspiration of liquid samples. To drive the liquid samples to and from the MCs, stainless steel capillaries with 1.2 mm outer diameter, fabricated from medical needles, were placed in the inlet and outlet ports. For the connection of peristaltic tubing, the inlet and outlet needles and the ICP-MS nebulizer, PFA tubing with 0.3 mm inner diameter (part number 5042-0953, Agilent Technologies, Santa Clara, California, USA) and patches prepared from silicone tubing with 1.0 mm inner diameter (Deutsch & Neumann GmbH, Berlin, Germany) were applied.
All data processing was performed within the Agilent MassHunter (Agilent Technologies, Santa Clara, California, USA) and OriginLab Origin (Northampton, Massachusetts, USA) software.
Results and discussion
The design of the MCs (number of inlet ports, the angle between the inlet channels) has a strong impact on flow conditions. Chips with different sample and diluent inlet patterns (presented in Figure 1) were prepared and their performance for the on-line mixing/dilution of solutions was investigated both in computer simulations and in experiments.
In one of the first tests, we investigated how accurately can dilution be performed on the chips.
We pumped Co standard solution and water into the input ports in a calculated microflow ratio and monitored the diminishing of the Co ICP-MS signal. According to our results, presented in Figure 2, the achieved dilution showed a good agreement with the theoretical dilution for “W”
design, while the other two patterns provided less accurate dilution factors. This phenomenon can be probably explained by less favorable flow conditions at the junction when the diluent is introduced in only one channel. Thus, all further spICP-MS experiments were carried out using only the W design. Please also note the small error bars in the graph (and all later graphs), which indicate that the joint action of the chip, nebulizer and spray chamber, the overall mixing of the liquids in the system take place with very good efficiency.
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Figure 1. The various designs of the fabricated microfluidic chips
Figure 2. Investigation of the dilution accuracy of the different microfluidic chip designs A typical task during spICP-MS analysis of unknown dispersions is to find the optimal PNC by performing dilution of the sample. The goal is to find a dilution where the maximum number of particles can be measured to obtain reliable statistical data but individual particle detection is still ensured. In practice this means that several diluted dispersions have to be prepared in relatively large volumes which is a time- and chemical-consuming process. Utilization of MCs for the on-line dilution of nanodispersions can make the process faster and more practical. In order to test this, the online dilution of a gold nanodispersion with 47.8 nm particle size and initial PNC of 1·105 mL-1 was carried out in the dilution range of 1-100 folds. As Figure 3 shows, there is an excellent linearity between the number of detected NP events and the nominal PNC resulted by the on-line dilution in the range of 1·103 and 5·104 mL-1. At the highest measured concentration (1·105 mL-1) the number of detected events falls below expectations, which is a clear indication of the detection of more than one NP during the same integration window.
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Figure 3. On-line dilution of Au nanodispersion with 47.8 nm particle size and initial PNC of 1·105 mL-1 in the 1-100 dilution range
Dissolved analyte content in nanodispersions can originate from either the matrix (presence of precursor residues or impurities of other synthesis reagents), or from the partial dissolution of the NPs. In either case, the dissolved analyte content generates a continuous background signal during the time-resolved spICP-MS measurements, which can bury the signal peaks of small NPs. A practical approach to tackle this interference is to dilute the dispersion, as it does not affect the signal originating from individual NPs, but it effectively diminishes the background signal. Utilization of MCs for this purpose is also favorable. Figure 4 shows our experimental results, which demonstrates the above discussed possibilities. A nanodispersion containing 43.4 nm Ag NPs with 1·105 mL-1 PNC and 1 ppb dissolved Ag was on-line diluted in the range of dilution factors 1 to 10. According to our results, a 5-fold dilution was optimal, as this resulted in a particle peak position that did not shift further to the left with additional dilution. The downside of this technique is that the total measurement time has to be increased in correspondence with the dilution factor in order to maintain the statistical relevance of the collected data.
Figure 4. spICP-MS histograms of on-line diluted nanodispersion originally containing 43.4 nm Ag NPs with 1·105 mL-1 PNC and 1 ppb dissolved Ag
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A particularly challenging situation in spICP-MS is when only a small amount of sample is available for analysis. As MCs are capable for handling of µL liquid samples with ease, they could be applied for the analysis of e.g. precious nanodispersion samples. We tested this concept by the injection of a few ten µL sample volumes and studied if the number of detected events is proportional to the PNC. As our results in Figure 5 indicate, the utilization of the fabricated MCs provided a good correlation with a reasonable standard deviation and accuracy.
Figure 5. The number of detected events of low volume (10-50 µL) Au nanodispersions with 47.8 nm size and initial PNC of 5·105 mL-1 with 10-folds online dilution on the MC Conclusion
PDMS-glass microfluidic chips were successfully applied for the on-line dilution and sample introduction of NPs for spICP-MS analysis. The utilization of the chips provides the prospect of automation (e.g. using electronically actuated microvalves and software control) that makes spICP-MS sample preparation fast and simple. We also demonstrated the feasibility of carrying out spICP-MS measurements on low (only a few tens of µL) sample volumes.
Acknowledgements
The authors gratefully acknowledge the financial support from various sources including the Ministry of Innovation and Technology (No. TUDFO/47138-1/2019-ITM FIKP) and the National Research, Development and Innovation Office (through project No. EFOP-3.6.2-16-2017-00005, GINOP-2.3.3-15-2016-00040 and TKP 2020 Thematic Excellence Program 2020) of Hungary.
References
[1] M.D. Montaño, J.W. Olesik, A.G. Barber, K. Challis, J.F. Ranville, Anal. Bioanal. Chem.
408 (2016) 5053.
[2] D. Mozhayeva, C. Engelhard, J. Anal. At. Spectrom. 35 (2020) 1740.
[3] A. Sápi, A. Kéri, I. Kálomista, D.G. Dobó, Á. Szamosvölgyi, K.L. Juhász, Á. Kukovecz, Z.
Kónya, G. Galbács, J. Anal. At. Spectrom. 32 (2017) 996.
[4] M. He, B. Chen, H. Wang, B. Hu, Appl. Spectrosc. Rev. 54 (2019) 250.
[5] A. Metzinger, A. Nagy, A. Gáspár, Zs. Márton, É. Kovács-Széles, G. Galbács, Spectrochim.
Acta B 126 (2016) 23.
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PHOTOCATALYTIC EFFICIENCY OF ZnFe-MIXED METAL OXIDES IN CORRELATION WITH REACTION PARAMETERS
Milica Hadnadjev-Kostic1, Djurdjica Karanovic1, Tatjana Vulic1
1University of Novi Sad, Faculty of Technology Novi Sad, Bul. cara Lazara 1, 21000 Novi Sad, Serbia.
e-mail: djurdjicakaranovic@uns.ac.rs Abstract
In the last decade, the interest for the photocatalytic phenomena has rapidly grown due to its great potential for the overall environmental decontamination. Photocatalysts based on ZnFe mixed oxides have been considered to be potentially photocatalyticly efficient in wastewater purification. This investigation is focused on the characterization of the synthesized and thermally treated photocatalysts, on their photocatalytic efficiency in the degradation process of organic dye pollutant Rhodamine B (RhB), as well as on the influence of process parameters on the photocatalytic efficiency. The results showed that the obtained mixed oxides are highly efficient in the RhB degradation. In addition, the pH effect of the reaction system on the
In the last decade, the interest for the photocatalytic phenomena has rapidly grown due to its great potential for the overall environmental decontamination. Photocatalysts based on ZnFe mixed oxides have been considered to be potentially photocatalyticly efficient in wastewater purification. This investigation is focused on the characterization of the synthesized and thermally treated photocatalysts, on their photocatalytic efficiency in the degradation process of organic dye pollutant Rhodamine B (RhB), as well as on the influence of process parameters on the photocatalytic efficiency. The results showed that the obtained mixed oxides are highly efficient in the RhB degradation. In addition, the pH effect of the reaction system on the