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Carbon Nanotubes Composite for Liquid-Phase Adsorption
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ScienceDirect Materials Today: Proceedings 11 (2019) 398–403
www.materialstoday.com/proceedings
ICMTMTE_2018
Development of a Bentonite Clay/Carbon Nanotubes Composite for Liquid-Phase Adsorption Dmitriy Kurnosov, Alexandr Burakov, Irina Burakova* Tambov State Technical University, 106 Sovetskaya Str., Tambov, 392000, Russia
Abstract
The paper describes a technology developed for obtaining an efficient adsorption composite based on a bentonite clay (Al2[Si4O10](ОH)2•nH2О) modified with multilayered carbon nanotubes (MWCNTs) consisting of cylindrical graphene layers. The method for producing the composite material lied in impregnating the original clay with a catalyst solution having the following metal ratio: Co:Mo:Mg:Al = 1.4: 0.14: 1.6: 0.5 (atomic), followed by heat treatment. To synthesize the MWCNTs on the catalyst oxide particles formed, chemical vapor deposition (CVD) of carbon was used under pilot production conditions. The resulting material was studied by the methods of scanning electron microscopy, Raman spectroscopy, and thermogravimetry. The results of the diagnosis analyses confirmed the availability of the MWCNTs on the surface and in the granule structure of the bentonite clay. The adsorption activity of the composite with respect to heavy metal ions was determined in comparison with the reference original clay. The nanomodified material exhibited 1.5-1.8-fold increase in the adsorption capacity and 4-fold increase in the absorption rate. The degree of heavy metal removal for the synthesized composite was found to vary in the following sequence: Cu2+ ˃ Cr3+ ˃ Zn2+. © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Modern Trends in Manufacturing Technologies and Equipment 2018: Materials Science. Keywords:nanomodification; bentonite clay; carbon nanotubes; chemical vapor deposition; adsorption; heavy metal ions
* Corresponding author. Tel.: +7-953-703-37-13; fax: +7-4752-63-55-22. E-mail address:[email protected] 2214-7853© 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Modern Trends in Manufacturing Technologies and Equipment 2018: Materials Science.
D. Kurnosov et al. / Materials Today: Proceedings 11 (2019) 398–403
399
1. Introduction The variety of chemical industries and the huge number of chemical products (original, intermediate, and final) used and formed in technological processes cause the generation of inorganic- and organic-substance-contaminated wastewater strongly differing in composition and volume [1]. Heavy metal ions are common contaminants of wastewater coming from many industrial enterprises. To purify heavy-metal-containing wastewater, physical and chemical techniques, such as reagent, membrane, electrochemical, biochemical and adsorption, are used. Adsorption removal of metals from wastewater has become quite widespread due to its high efficiency and the absence of secondary contamination. Adsorption materials extract metals from aqueous solutions practically down to zero residual concentrations [1]. It is widely known to use zeolites for the purification of aquatic media from heavy metal ions [2-4]. The adsorption of Fe3+ ions from solutions was studied using natural adsorbents - bentonite clays. Chemically modified forms of bentonite were obtained and investigated. It was found that the modification of bentonite with triethanolamine significantly improves its adsorption characteristics [3]. Besides, the adsorption of copper, cobalt and manganese ions from chloride and nitrate solutions by natural and acid-modified clinoptilolite was studied [5]. At the same time, a huge number of literary sources contain information on high efficiency of using multilayered carbon nanotubes (MWCNTs) and their modified forms to remove heavy metals from aqueous solutions [6-9]. As an example, in [7], the adsorption of Cr6+ on untreated and oxidized MWCNTs prepared through CVD over Ni-Fe catalyst particles was investigated. In [8], MWCNTs were modified with 8-hydroxyquinoline and used to remove Cu2+, Pb2+, Cd2+ and Zn2+ from aqueous solutions. In [9], the individual and competitive adsorption capacity of nitric-acid-treated MWCNTs for Cu2+, Pb2+ and Cd2 ions were also studied. Considering the aforementioned, in the present work, the expediency of obtaining a MWCNT-modified bentonite clay composite and using it as adsorbent of heavy metal ions is discussed. The physical, chemical and functional properties of this new material were determined in comparison with the original (reference) clay sample. 2. Materials and methods 2.1. Adsorption materials A bentonite (chemical formula: Al2[Si4O10](ОH)2•nH2О) produced by Bento Group Minerals (Moscow, Russia) according to Technical Specifications of the Russian Federation No. 9199-001-86571025-13was used as original carrier material. The technology of the carrier material nanomodification consisted of several steps: a) The carrier material was dried in a UT-4610 drying oven (ULAB, St. Petersburg, Russia) at 100-150 °C for 3 h; b) 10 g of the dried bentonite sample were treated with 60 mL of a 0.05 % solution of a Co-Mo-Mg-Al catalyst mixture (atomic Co:Mo:Mg:Al ratio: 1.4:0.14:1.6:0.5). The catalyst was prepared as follows: 4.944 g of ammonium molybdate and 8 mL of water were added a beaker. The mixture was stirred at room temperature until the ammonium molybdate was completely dissolved (15-20 min). After this, 22.514 g (± 1 g) of citric acid monohydrate, 11.64 g of cobalt nitrate, 11.717 g of magnesium nitrate and 5.364 g of aluminum nitrate were added. After the addition of each component following the cobalt nitrate, the mixture was stirred for 2-3 min. To completely dissolve all the constituents and obtain a clear solution, the reaction mixture was heated at 60 °C for 4060 min under continuous stirring; c) The impregnated sample was subjected to stepwise temperature treatment in air at 120 °C for 3 h to reduce the nitrate groups by organics, and then - at 500-550 °C for 1 h to generate an oxide form of the catalyst on the bentonite carrier; d) To grow MWCNTs on the carrier, catalytic pyrolysis of hydrocarbons was carried out in a pilot-industrial reactor (NanoTechCenter Ltd., Tambov, Russia). The process consisted of the following main stages: reduction of the metal oxides with hydrogen to the crystalline form of nanoparticles, and diffusion of carbon (propane-butane
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D. Kurnosov et al. / Materials Today: Proceedings 11 (2019) 398–403
mixture, feed rate: 40 cm3 min-1) through the bulk of the catalyst particle to form carbide compounds and subsequently grow MWCNTs. The process temperature was 650 °C, and the synthesis time was 40 min. 2.2. Material characterization To determine the parameters of the structure formed, a DXR ™ Raman microscope (Thermo Fisher Scientific Inc., Waltham, MA, USA) was used. In particular, it allows estimation of the carbon structure orderliness by identifying peaks in Raman spectra. Thermogravimetry (TG) and differential scanning calorimetry (DSC) measurements were performed using an STA 449 F3 Jupiter thermal analyzer (NETZSCH-Feinmahltechnik GmbH, Selb, Germany). Results of this type of analysis provide information concerning the thermal stability of the material and temperature transitions arising during destructuring. Temperature programming included heating to 800-900 °C (depending on the sample) at a rate of 10 °C min-1. The morphology of the studied material surface was estimated by scanning electron microscopy (SEM) on a MERLIN field emission electron microscope (CARL ZEISS, Jena, Germany) at the “Analytical Microscopy” Interdisciplinary Center of Kazan (Volga) Federal University (Kazan, Russia). 2.3. Adsorption experiment In the present research, the following model nitrate solutions were used as contaminant simulators to be adsorbed by the nanocomposite: Cu(NO3)2•3H2O, Zn(NO3)2•6H2O, and Cr(NO3)3. The conditions for carrying out the comparative kinetic experiment were as follows: solution volume - 0.03 L, sample weight - 0.15 g, initial metal concentration - 100 mg L-1, pH 6 under normal conditions. 3. Results and discussion 3.1. Material Structure The obtained SEM images of the nanomodified clay make it possible to confirm the availability of the MWCNT structure on the caly granule surface. The lower magnification image (Fig. 1a) allows verification of the uniformity of the MWCNT layer growth. Fig. 1b demonstrates the MWCNT layer (15-40 nm in diameter), with no apparent amorphous carbon content, and with the presence of the catalyst particles (size: 10-30 nm).
Fig. 1. SEM images of the nanomodified bentonite clay at two different magnifications.
D. Kurnosov et al. / Materials Today: Proceedings 11 (2019) 398–403
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The TG analysis of the original bentonite clay (Fig. 2a) shows its stability in the program heating range (up to 800 °C). The process is mainly exothermic, with the exception of the initial period of removal of bound water from the material structure. Further weight changes are monotonous and insignificant, which is most likely due to the removal of organic impurities from the aluminosilicate framework. The residual weight of the sample is 92.1 %. The TG analysis of the nanomodified clay (Fig. 2b) demonstrates a slight monotonous weight change primarily associated with the removal of structured water and organic impurities available in the aluminosilicate matrix. The endo-effect at ~ 645 °C presumably suggests high-temperature oxidation of unreacted particles of the catalyst system. The residual weight of the nanomodified sample is 97.33 %.
a
b
c
d
Fig. 2. Results of the studies on the original and nanomodified clays: a – TG and DSC curves constructed for the original clay; b – TG and DSC curves constructed for the nanomodified clay; c – Raman spectra recorded for the original clay; d – spectra recorded for the nanomodified clay.
The Raman spectra recorded for the original bentonite clay (Fig. 2c) presents a rather pronounced intensity peak at an ordered set of characteristic frequencies (1,646.49, 1,533.63, 1,522.17, 1,402.17, and 1,089.83 cm-1). They presumably correspond to the vibrations of the atoms of the silicic acid structure and the octahedral alumohydroxyl crystals. Due to the long distance, they are weakly linked, which is theoretically confirmed by insignificant intensity of the peaks. The presence of isomorphous substitutions and weak interaction between the crystalline structures cause a considerable adsorption capacity of the material under study. The spectral pattern of the nanomodified clay (Fig. 2d) allows identification of the clearly pronounced G and D peaks at ~ 1,590 and ~ 1,340 cm-1, respectively. The intensity of the characteristic peak at ~ 2,950 cm-1 indicates the degree of interaction between the carbon layers. Compared with the original clay spectra, in this case, it is possible to observe the absence of characteristic vibrations of the aluminosilicate matrix related to the overlapping with more intense vibrations of the С-С bonds in the carbon structure.
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D. Kurnosov et al. / Materials Today: Proceedings 11 (2019) 398–403
3.2. Kinetic study Kinetic studying is very important for the elucidation of mechanisms controlling the adsorption of the target contaminant by the nanocomposite developed, as well as for the determination of the limiting step and the rate of this process. Fig. 3 shows the experimental kinetic dependencies obtained for the reference (pristine, or original) clay and MWCNTs/clay composite samples.
а)
b)
c)
d)
Fig. 3. Kinetic dependencies obtained for the heavy metal adsorption on the MWCNTs/clay composite developed and the reference (pristine) clay: а –Zn2+ ions; b – Cu2+ions; с – Cr3+ions; d – comparison between the dependencies for removing the metal ions using the MWCNTs/clay composite.
The obtained results show a 1.5-1.8-fold increase in the adsorption capacity and 4-fold increase in the absorption rate during the removal of all the test contaminants. Besides, the process of metal ion removal using the composite is much more intensive in the initial period of time; the nanoadsorbent is saturated within 100-300 min, whereas the reference adsorbent is saturated within 400-1200 min. Furthermore, the relationships presented in Fig. 3d demonstrate the sequence of the adsorption affinity of the nanomaterial to the target metal ions: Cu2+˃ Cr3+ ˃ Zn2+. Thus, it was established that the modification of the aluminosilicate structure of the bentonite clay with the MWCNT not only makes it possible to increase the adsorption capacity for the heavy metals, but also to reduce the time to achieve equilibrium by several times
D. Kurnosov et al. / Materials Today: Proceedings 11 (2019) 398–403
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4. Conclusion The technology of synthesizing the efficient adsorption composite based on the MWCNTs-modified bentonite clay was described herein. The material can be developed by the CVD of carbon on clay samples containing an impregnated and treated Co-Mo-Mg-Al catalyst. As a result, a homogeneous (uniform) MWCNT structure with controlled qualitative parameters is formed on the carrier. The resulting composite was examined by scanning electron microscopy, Raman spectroscopy, and thermogravimetry. To study the adsorption characteristics typical for the material developed, a kinetic study on the removal of Cu2+, Cr3+ and Zn2+ ions from model aqueous solutions was carried out. It was shown that the carbon nanomodification of the aluminosilicate structure of the bentonite clay significantly improves the efficiency of the liquid-phase adsorption of inorganic contaminants such as heavy metals, and also considerably reduces the adsorbent saturation time. Acknowledgements This work was supported by the Ministry of Education and Science of the Russian Federation (Project No. 16.1384.2017/PCh). References [1] E.S. Klimov, M.V. Buzaeva, Natural Sorbents and Complexones in Wastewater Treatment. Ulyanovsk State Technical University Publishers, Ulyanovsk, 2011. (in Russian) [2] V.M. Mukhin, I.V. Burakova, A.E. Burakov, Adv. Mater. Technol. 2 (2017) 50-56. [3] E.Erdem, N.Karapinar, R.Donat, J.Colloid Interface Sci. 280(2004) 309–314. [4] A.K. Adryshev, N.A. Strunnikova, M.K. Karibayeva, Ekologiya (Ecology). 2 (2008) 102-109. (in Russian) [5] T.L. Rakitskaya, L.A. Raskola, T.A. Kiose, A.N. Zakharia, V.V. Kitayskaya, Odesa National University Herald. 15 (3) (2010) 85-91. (in English) [6] R.V. Popov, S.I. Lazarev, S.V. Kovalev, A.A. Arzamastsev, V.М. Dmitriev, Transactions of the TSTU (Vestnik TGTU) 23(2) (2017) 288294 [in Russian] [7] J. Hu, S.W. Wang, D.D. Shao, Y.H. Dong, J.X. Li, X.K. Wang,Open Environ. Pollut. Toxicol. J. 1 (2009) 66-73. [8] S.A. Kosaa, G. Al-Zhrania, M.A. Salama, Chem. Eng. J. 181-182 (2012) 159-168. [9] Y.H. Li , J. Ding , Z. Luan , Z. Di , Y. Zhu , C. Xu, D. Wu , B. Wei, Carbon 41 (2003) 2787–2792.
ScienceDirect Materials Today: Proceedings 11 (2019) 398–403
www.materialstoday.com/proceedings
ICMTMTE_2018
Development of a Bentonite Clay/Carbon Nanotubes Composite for Liquid-Phase Adsorption Dmitriy Kurnosov, Alexandr Burakov, Irina Burakova* Tambov State Technical University, 106 Sovetskaya Str., Tambov, 392000, Russia
Abstract
The paper describes a technology developed for obtaining an efficient adsorption composite based on a bentonite clay (Al2[Si4O10](ОH)2•nH2О) modified with multilayered carbon nanotubes (MWCNTs) consisting of cylindrical graphene layers. The method for producing the composite material lied in impregnating the original clay with a catalyst solution having the following metal ratio: Co:Mo:Mg:Al = 1.4: 0.14: 1.6: 0.5 (atomic), followed by heat treatment. To synthesize the MWCNTs on the catalyst oxide particles formed, chemical vapor deposition (CVD) of carbon was used under pilot production conditions. The resulting material was studied by the methods of scanning electron microscopy, Raman spectroscopy, and thermogravimetry. The results of the diagnosis analyses confirmed the availability of the MWCNTs on the surface and in the granule structure of the bentonite clay. The adsorption activity of the composite with respect to heavy metal ions was determined in comparison with the reference original clay. The nanomodified material exhibited 1.5-1.8-fold increase in the adsorption capacity and 4-fold increase in the absorption rate. The degree of heavy metal removal for the synthesized composite was found to vary in the following sequence: Cu2+ ˃ Cr3+ ˃ Zn2+. © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Modern Trends in Manufacturing Technologies and Equipment 2018: Materials Science. Keywords:nanomodification; bentonite clay; carbon nanotubes; chemical vapor deposition; adsorption; heavy metal ions
* Corresponding author. Tel.: +7-953-703-37-13; fax: +7-4752-63-55-22. E-mail address:[email protected] 2214-7853© 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Modern Trends in Manufacturing Technologies and Equipment 2018: Materials Science.
D. Kurnosov et al. / Materials Today: Proceedings 11 (2019) 398–403
399
1. Introduction The variety of chemical industries and the huge number of chemical products (original, intermediate, and final) used and formed in technological processes cause the generation of inorganic- and organic-substance-contaminated wastewater strongly differing in composition and volume [1]. Heavy metal ions are common contaminants of wastewater coming from many industrial enterprises. To purify heavy-metal-containing wastewater, physical and chemical techniques, such as reagent, membrane, electrochemical, biochemical and adsorption, are used. Adsorption removal of metals from wastewater has become quite widespread due to its high efficiency and the absence of secondary contamination. Adsorption materials extract metals from aqueous solutions practically down to zero residual concentrations [1]. It is widely known to use zeolites for the purification of aquatic media from heavy metal ions [2-4]. The adsorption of Fe3+ ions from solutions was studied using natural adsorbents - bentonite clays. Chemically modified forms of bentonite were obtained and investigated. It was found that the modification of bentonite with triethanolamine significantly improves its adsorption characteristics [3]. Besides, the adsorption of copper, cobalt and manganese ions from chloride and nitrate solutions by natural and acid-modified clinoptilolite was studied [5]. At the same time, a huge number of literary sources contain information on high efficiency of using multilayered carbon nanotubes (MWCNTs) and their modified forms to remove heavy metals from aqueous solutions [6-9]. As an example, in [7], the adsorption of Cr6+ on untreated and oxidized MWCNTs prepared through CVD over Ni-Fe catalyst particles was investigated. In [8], MWCNTs were modified with 8-hydroxyquinoline and used to remove Cu2+, Pb2+, Cd2+ and Zn2+ from aqueous solutions. In [9], the individual and competitive adsorption capacity of nitric-acid-treated MWCNTs for Cu2+, Pb2+ and Cd2 ions were also studied. Considering the aforementioned, in the present work, the expediency of obtaining a MWCNT-modified bentonite clay composite and using it as adsorbent of heavy metal ions is discussed. The physical, chemical and functional properties of this new material were determined in comparison with the original (reference) clay sample. 2. Materials and methods 2.1. Adsorption materials A bentonite (chemical formula: Al2[Si4O10](ОH)2•nH2О) produced by Bento Group Minerals (Moscow, Russia) according to Technical Specifications of the Russian Federation No. 9199-001-86571025-13was used as original carrier material. The technology of the carrier material nanomodification consisted of several steps: a) The carrier material was dried in a UT-4610 drying oven (ULAB, St. Petersburg, Russia) at 100-150 °C for 3 h; b) 10 g of the dried bentonite sample were treated with 60 mL of a 0.05 % solution of a Co-Mo-Mg-Al catalyst mixture (atomic Co:Mo:Mg:Al ratio: 1.4:0.14:1.6:0.5). The catalyst was prepared as follows: 4.944 g of ammonium molybdate and 8 mL of water were added a beaker. The mixture was stirred at room temperature until the ammonium molybdate was completely dissolved (15-20 min). After this, 22.514 g (± 1 g) of citric acid monohydrate, 11.64 g of cobalt nitrate, 11.717 g of magnesium nitrate and 5.364 g of aluminum nitrate were added. After the addition of each component following the cobalt nitrate, the mixture was stirred for 2-3 min. To completely dissolve all the constituents and obtain a clear solution, the reaction mixture was heated at 60 °C for 4060 min under continuous stirring; c) The impregnated sample was subjected to stepwise temperature treatment in air at 120 °C for 3 h to reduce the nitrate groups by organics, and then - at 500-550 °C for 1 h to generate an oxide form of the catalyst on the bentonite carrier; d) To grow MWCNTs on the carrier, catalytic pyrolysis of hydrocarbons was carried out in a pilot-industrial reactor (NanoTechCenter Ltd., Tambov, Russia). The process consisted of the following main stages: reduction of the metal oxides with hydrogen to the crystalline form of nanoparticles, and diffusion of carbon (propane-butane
400
D. Kurnosov et al. / Materials Today: Proceedings 11 (2019) 398–403
mixture, feed rate: 40 cm3 min-1) through the bulk of the catalyst particle to form carbide compounds and subsequently grow MWCNTs. The process temperature was 650 °C, and the synthesis time was 40 min. 2.2. Material characterization To determine the parameters of the structure formed, a DXR ™ Raman microscope (Thermo Fisher Scientific Inc., Waltham, MA, USA) was used. In particular, it allows estimation of the carbon structure orderliness by identifying peaks in Raman spectra. Thermogravimetry (TG) and differential scanning calorimetry (DSC) measurements were performed using an STA 449 F3 Jupiter thermal analyzer (NETZSCH-Feinmahltechnik GmbH, Selb, Germany). Results of this type of analysis provide information concerning the thermal stability of the material and temperature transitions arising during destructuring. Temperature programming included heating to 800-900 °C (depending on the sample) at a rate of 10 °C min-1. The morphology of the studied material surface was estimated by scanning electron microscopy (SEM) on a MERLIN field emission electron microscope (CARL ZEISS, Jena, Germany) at the “Analytical Microscopy” Interdisciplinary Center of Kazan (Volga) Federal University (Kazan, Russia). 2.3. Adsorption experiment In the present research, the following model nitrate solutions were used as contaminant simulators to be adsorbed by the nanocomposite: Cu(NO3)2•3H2O, Zn(NO3)2•6H2O, and Cr(NO3)3. The conditions for carrying out the comparative kinetic experiment were as follows: solution volume - 0.03 L, sample weight - 0.15 g, initial metal concentration - 100 mg L-1, pH 6 under normal conditions. 3. Results and discussion 3.1. Material Structure The obtained SEM images of the nanomodified clay make it possible to confirm the availability of the MWCNT structure on the caly granule surface. The lower magnification image (Fig. 1a) allows verification of the uniformity of the MWCNT layer growth. Fig. 1b demonstrates the MWCNT layer (15-40 nm in diameter), with no apparent amorphous carbon content, and with the presence of the catalyst particles (size: 10-30 nm).
Fig. 1. SEM images of the nanomodified bentonite clay at two different magnifications.
D. Kurnosov et al. / Materials Today: Proceedings 11 (2019) 398–403
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The TG analysis of the original bentonite clay (Fig. 2a) shows its stability in the program heating range (up to 800 °C). The process is mainly exothermic, with the exception of the initial period of removal of bound water from the material structure. Further weight changes are monotonous and insignificant, which is most likely due to the removal of organic impurities from the aluminosilicate framework. The residual weight of the sample is 92.1 %. The TG analysis of the nanomodified clay (Fig. 2b) demonstrates a slight monotonous weight change primarily associated with the removal of structured water and organic impurities available in the aluminosilicate matrix. The endo-effect at ~ 645 °C presumably suggests high-temperature oxidation of unreacted particles of the catalyst system. The residual weight of the nanomodified sample is 97.33 %.
a
b
c
d
Fig. 2. Results of the studies on the original and nanomodified clays: a – TG and DSC curves constructed for the original clay; b – TG and DSC curves constructed for the nanomodified clay; c – Raman spectra recorded for the original clay; d – spectra recorded for the nanomodified clay.
The Raman spectra recorded for the original bentonite clay (Fig. 2c) presents a rather pronounced intensity peak at an ordered set of characteristic frequencies (1,646.49, 1,533.63, 1,522.17, 1,402.17, and 1,089.83 cm-1). They presumably correspond to the vibrations of the atoms of the silicic acid structure and the octahedral alumohydroxyl crystals. Due to the long distance, they are weakly linked, which is theoretically confirmed by insignificant intensity of the peaks. The presence of isomorphous substitutions and weak interaction between the crystalline structures cause a considerable adsorption capacity of the material under study. The spectral pattern of the nanomodified clay (Fig. 2d) allows identification of the clearly pronounced G and D peaks at ~ 1,590 and ~ 1,340 cm-1, respectively. The intensity of the characteristic peak at ~ 2,950 cm-1 indicates the degree of interaction between the carbon layers. Compared with the original clay spectra, in this case, it is possible to observe the absence of characteristic vibrations of the aluminosilicate matrix related to the overlapping with more intense vibrations of the С-С bonds in the carbon structure.
402
D. Kurnosov et al. / Materials Today: Proceedings 11 (2019) 398–403
3.2. Kinetic study Kinetic studying is very important for the elucidation of mechanisms controlling the adsorption of the target contaminant by the nanocomposite developed, as well as for the determination of the limiting step and the rate of this process. Fig. 3 shows the experimental kinetic dependencies obtained for the reference (pristine, or original) clay and MWCNTs/clay composite samples.
а)
b)
c)
d)
Fig. 3. Kinetic dependencies obtained for the heavy metal adsorption on the MWCNTs/clay composite developed and the reference (pristine) clay: а –Zn2+ ions; b – Cu2+ions; с – Cr3+ions; d – comparison between the dependencies for removing the metal ions using the MWCNTs/clay composite.
The obtained results show a 1.5-1.8-fold increase in the adsorption capacity and 4-fold increase in the absorption rate during the removal of all the test contaminants. Besides, the process of metal ion removal using the composite is much more intensive in the initial period of time; the nanoadsorbent is saturated within 100-300 min, whereas the reference adsorbent is saturated within 400-1200 min. Furthermore, the relationships presented in Fig. 3d demonstrate the sequence of the adsorption affinity of the nanomaterial to the target metal ions: Cu2+˃ Cr3+ ˃ Zn2+. Thus, it was established that the modification of the aluminosilicate structure of the bentonite clay with the MWCNT not only makes it possible to increase the adsorption capacity for the heavy metals, but also to reduce the time to achieve equilibrium by several times
D. Kurnosov et al. / Materials Today: Proceedings 11 (2019) 398–403
403
4. Conclusion The technology of synthesizing the efficient adsorption composite based on the MWCNTs-modified bentonite clay was described herein. The material can be developed by the CVD of carbon on clay samples containing an impregnated and treated Co-Mo-Mg-Al catalyst. As a result, a homogeneous (uniform) MWCNT structure with controlled qualitative parameters is formed on the carrier. The resulting composite was examined by scanning electron microscopy, Raman spectroscopy, and thermogravimetry. To study the adsorption characteristics typical for the material developed, a kinetic study on the removal of Cu2+, Cr3+ and Zn2+ ions from model aqueous solutions was carried out. It was shown that the carbon nanomodification of the aluminosilicate structure of the bentonite clay significantly improves the efficiency of the liquid-phase adsorption of inorganic contaminants such as heavy metals, and also considerably reduces the adsorbent saturation time. Acknowledgements This work was supported by the Ministry of Education and Science of the Russian Federation (Project No. 16.1384.2017/PCh). References [1] E.S. Klimov, M.V. Buzaeva, Natural Sorbents and Complexones in Wastewater Treatment. Ulyanovsk State Technical University Publishers, Ulyanovsk, 2011. (in Russian) [2] V.M. Mukhin, I.V. Burakova, A.E. Burakov, Adv. Mater. Technol. 2 (2017) 50-56. [3] E.Erdem, N.Karapinar, R.Donat, J.Colloid Interface Sci. 280(2004) 309–314. [4] A.K. Adryshev, N.A. Strunnikova, M.K. Karibayeva, Ekologiya (Ecology). 2 (2008) 102-109. (in Russian) [5] T.L. Rakitskaya, L.A. Raskola, T.A. Kiose, A.N. Zakharia, V.V. Kitayskaya, Odesa National University Herald. 15 (3) (2010) 85-91. (in English) [6] R.V. Popov, S.I. Lazarev, S.V. Kovalev, A.A. Arzamastsev, V.М. Dmitriev, Transactions of the TSTU (Vestnik TGTU) 23(2) (2017) 288294 [in Russian] [7] J. Hu, S.W. Wang, D.D. Shao, Y.H. Dong, J.X. Li, X.K. Wang,Open Environ. Pollut. Toxicol. J. 1 (2009) 66-73. [8] S.A. Kosaa, G. Al-Zhrania, M.A. Salama, Chem. Eng. J. 181-182 (2012) 159-168. [9] Y.H. Li , J. Ding , Z. Luan , Z. Di , Y. Zhu , C. Xu, D. Wu , B. Wei, Carbon 41 (2003) 2787–2792.