A study is performed of the adsorption of glyphosate on carbon-containing materials obtained from pyrolysis products of sugar cane waste and commercial coconut activated carbon. The adsorption capacity of the materials with respect to glyphosate was determined using a variety of experimental model

Greish, A. A.

Nguyen Dinh Chien

Sokolovskiy, P. V.

Vezentsev, A. I.

DSpace at Belgorod State University

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2021, Vol. 95, No. 6, pp. 1212–1215. © Pleiades Publishing, Ltd., 2021.Russian Text © The Author(s), 2021, published in Zhurnal Fizicheskoi Khimii, 2021, Vol. 95, No. 6, pp. 928–932.PHYSICAL CHEMISTRY OF SURFACE PHENOMENAAdsorption of Glyphosate on Carbon-Containing MaterialsD. C. Nguyena,b,*, A. I. Vezentseva,**, P. V. Sokolovskiyc,***, and A. A. Greishc,****a Belgorod State University, Belgorod, 308015 Russiab Institute of Environmental Technology, Vietnam Academy of Science and Technology, Hanoi, 650000 Vietnamc Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, 119991 Russia*e-mail: ngudichi@yandex.ru**e-mail: vesentsev@bsu.edu.ru***e-mail: carbsorb@gmail.com****e-mail: greish@ioc.ac.ruReceived July 15, 2020; revised July 15, 2020; accepted August 11, 2020Abstract—A study is performed of the adsorption of glyphosate on carbon-containing materials obtainedfrom pyrolysis products of sugar cane waste and commercial coconut activated carbon. The adsorptioncapacity of the materials with respect to glyphosate was determined using a variety of experimental models.The obtained data indicate the adsorption of glyphosate on the samples occurs due to chemical interactionwith the adsorbent surfaces.Keywords: adsorption, glyphosate, herbicide, pesticide, water purification, activated carbon, sugar cane wasteDOI: 10.1134/S0036024421060194INTRODUCTIONThe use of pesticides and herbicides in insect andweed control is a conventional way of increasing cropyields. The demand for herbicides and pesticides inagriculture grows every year. At the same time, thenegative effect of modern chemicals for protectingplants should be reduced during their development.An ideal herbicide must meet several requirements: itshould be effective in relatively low doses, have a quickeffect on weeds, and eventually decompose into rela-tively simple chemical compounds. Many herbicides(including glyphosate), however, do not meet thisstandard, so their regular use can contaminate soilsand adjacent environments.Glyphosate is one of the most common and widelyused herbicides. Glyphosate (N-(phosphonomethyl)-glycine, C3H8NO5P) is a derivative of a phosphonicacid and is soluble in water (10.5 g/L). Glyphosateenters water through careless transportation in opencontainers or improper storage and use. This has alarge negative effect on aquatic biota, phytoplankton,and periphyton [1–3]. Glyphosate is a carcinogeniccompound (hazard category 2A), according to datafrom the World Health Organization’s InternationalAgency for Research on Cancer (IARC) [4]. Glypho-sate products thus require special care and attention.Ways of removing glyphosate from water can beconditionally divided into physical (straining, settling,filtration (centrifugal and otherwise), and ultraviolettreatment); chemical (neutralization, oxidation, andreduction); physicochemical (f lotation, sorption,extraction, ion exchange, electrodialysis, reverseosmosis, and thermal); and biological (biologicalponds, filtration fields, biofilters, aeration tanks (oxy-tanks), and digesters). Each way of removing glyphos-phate traces from aqueous media includes many spe-cific options in the purification process and the designof its hardware. It should be noted that water purifica-tion is considered a complex process with fundamen-tally different ways of achieving maximum efficiencyto remove harmful compounds. It is known that herbi-cide can bond with organic matter in the soil or its clayfraction. This lowers the concentration of the herbi-cide in the soil and thus its toxicity. It is known thatglyphosate can lose its herbicidal properties due toadsorption on mineral or organic compounds when itenters the soil. Glyphosate bounds most strongly tothe inorganic components of the soil (i.e., clay parti-cles and aluminum and iron oxides) [5–9].Some studies show that the adsorption of an herbi-cide correlates negatively with soil pH. This is becausean increase in pH can raise the negative charge of boththe surface of the soil particles and glyphosate mole-cule, which weakens adsorption [10, 11].Despite the vital role of the soil’s mineral compo-nents, the organic part is also of great importance inthe adsorption of glyphosate. Studies of the sorption ofglyphosate on seven purified fractions of soil humusshowed that their aromatic components (presumablyphenolic groups) have a strong effect. The organic part1212ADSORPTION OF GLYPHOSATE 1213Fig. 1. Reaction between glyphosate and ninhydrin in the presence of sodium molybdate. OOOHOHHOHN POOOHHO+OOOH Na2MoO4POCOOHHO OH H2OOONCOOHPOOOHOONCOOHPOOOHOOHNCOOHPOOOHNinhydrin GlyphosateMagenta 3 Magenta 2 Magenta 1plays a more important role in the sorption of glypho-sate in sandy soils than in clayey sediments. Thedesorption of glyphosate from humus, however, pro-ceeds faster than from amorphous iron and aluminumoxides [12]. The preservation of crop residues in a fieldalso reduces the mobility of glyphosate and increasesits half-life [13].Describing in detail the adsorption of a herbicide inwater and soil is a necessary stage of studying itsbehavior in the environment, since the bonding of aherbicide largely determines its ability to spread anddecompose. Experiments are performed in which acertain mass of an adsorbent is in equilibrium with aknown volume of a solution with a certain concentra-tion of adsorbate. The equilibrium concentration ofadsorbate thus describes the adsorption process. Thetime required to attain equilibration can be from 2 to48 h. The soil (adsorbent)–solution ratio is usually1 : 0.3 to 1 : 20. Such studies are performed on 4–6 dif-ferent initial herbicide concentrations.Numerous studies indicate that the degradation ofglyphosate in the soil can be described with a two-phase model of first-order kinetics [14–17]. Theamount of the substance adsorbed in the soil is foundfrom the difference between the initial and equilib-rium concentrations. The experimental results arerepresented in the form of an adsorption isothermshowing the ratio between the amount of the sub-stance adsorbed per unit mass of the adsorbent and theequilibrium concentration of the adsorbate.There are several types of adsorption isotherms. AnS-type is observed when the molecules of a solute aremonofunctional, and there is competition between theadsorbent and the solvent for the bonding sites. An L-type isotherm corresponds to sorption in the form of amonomolecular layer, and sorption becomes moredifficult as the sorption sites are filled. The H-typecorresponds to strong affinity of a sorbent for a sor-RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A  Vobate, and the solute is almost completely sorbed fromthe solution. Finally, the C-type characterizes a linearor near linear adsorption isotherm and is observedwhen the substance easily penetrates into the sorbent.L- and C-type isotherms are often observed duringthe adsorption of herbicides. The Langmuir equationis used to describe isotherms in the first case; the Fre-undlich one, in the second.The bonding of glyphosate to clay soil has beenthoroughly studied. The adsorption of glyphosate inan aqueous environment, however, requires additionalstudies for the development of new adsorbents andmore modern procedures. In this work, we developcarbon-containing materials obtained via the pyrolysisof sugar cane waste, and study the adsorption of gly-phosate in a model aqueous solution. The pyrolysis ofsugar cane was described thoroughly in [18]. Sugarcane bagasse carbonizate (BC) and chemically acti-vated (ABC) samples obtained under identical condi-tions are used to study the adsorption characteristics.The waste was impregnated earlier with a 1 M potas-sium hydroxide solution. Commercial coconut acti-vated carbon CAC-A (CAC) was used as a standard.EXPERIMENTALThe sorption capacity of experimental materialswith respect to glyphosate was found using modelmonocomponent solutions. The initial concentrationof glyphosate was 2–16 mmol/L (0.338–2.704 g/L).The concentration of glyphosate was determined viaspectrophotometry with a ninhydrin solution at wave-length λ = 570 nm [19–23]. Figure 1 shows the reac-tion between glyphosate and ninhydrin in the presenceof sodium molybdate.l. 95  No. 6  20211214 NGUYEN et al.Fig. 2. Dependences of the residual concentration of gly-phosate in a solution (C) and the contact time (τ) for BC,ABC, and CAC adsorbents. 0.940.960.981.001.020 10 20 30 40C, mmol/L, hBCABCCACRESULTS AND DISCUSSIONFigure 2 shows the ratios between the residual con-centration of glyphosate in the solutions and the con-tact time for three sorbents: BC, ABC, and CAC.The data show that the equilibrium in the adsor-bent–adsorbate–solvent system was reached within6 h for all of the experimental samples. The parametersof the adsorption for the resulting sugar cane bagassecarbonizate are comparable to those of commercialcoconut activated carbon CAC-A (0.942 mmol/L).When it was impregnated with a 1 M potassium hydrox-ide solution, adsorption reached 0.956 mmol/L.Figure 3 shows the isotherms of glyphosate adsorp-tion on the test materials. The shape of the isothermsRUSSIAN JOURNAL OFig. 3. Adsorption isotherms of glyphosate on experimental mateand Ceq is the equilibrium concentration. 00.10.20.30 2 4 6A, mmol/gsuggests that the sorption of glyphosate on these sam-ples was limited to the formation of a monolayer.Table 1 shows the isotherm parameters obtainedupon approximation of the experimental data with theLangmuir, Freundlich, and Dubinin–Radushkevichmodels.The correlation coefficients (Table 1) show that theadsorption of glyphosate on the samples is bestdescribed by the Langmuir equation (the correlationcoefficients are the highest) and (to a lesser extent) theDubinin–Radushkevich model. The empirical Freun-dlich equation is the least applicable to describe theexperimental adsorption data (the correlation coeffi-cients are the lowest).The results agree with one another comparativelywell, despite the ambiguous description of experimen-tal data by the different models of adsorption. TheLangmuir model data show that the CAC sample(0.2714 mmol/g) had the greatest sorption capacitywith respect to glyphosate (QL), while the BC sample(0.2330 mmol/g) had the poorest one. The same sorp-tion capacities were obtained using the Dubinin–Radushkevich equation (QDR value). We obtained thesame result with the Freundlich equation: the acti-vated carbon CAC-A had the greatest sorption capac-ity, and BC had the poorest.The Langmuir and Freundlich models are widelyused to describe processes of adsorption. At the sametime, however, they have a considerable shortcoming:they lack any data on a mechanism of the adsorptionprocess. On the other hand, the KDR parameter isintroduced in the Dubinin–Radushkevich model(equation), allowing us to study the forces of sorbent–sorbate interaction, since constant KDR and the energyof adsorption are associated by the equationF PHYSICAL CHEMISTRY A  Vol. 95  No. 6  2021rials: (1) BC, (2) BC-CA, and (3) CAC. A is a specific adsorption8 10 12 14BCBC-CACACCeq, mmol/gADSORPTION OF GLYPHOSATE 1215Table 1. Parameters of Langmuir, Freundlich, and Dubinin–Radushkevich adsorption equationsKL in L/mmol; QL in mmol/g; KF in mmol1−1/nL1/n/g; KDR in mol2/J2; QDR in mmol/g; and Ead in kJ/mol.SampleLangmuir model Freundlich model Dubinin–Radushkevich modelKL QL R2 KF 1/n R2 KDR QDR Ead R2BC 0.7504 0.2330 0.9829 0.0904 0.4056 0.7891 6 × 10–9 0.4891 9.13 0.8423ABC 1.0278 0.2453 0.9904 0.1102 0.3577 0.7629 5 × 10–9 0.4978 10.0 0.8133CAC 0.9531 0.2714 0.9917 0.1179 0.3739 0.7942 5 × 10–9 0.5514 10.0 0.8464(1)If the energy of adsorption is 8–16 kJ/mol, we mustassume that adsorption proceeds via chemical interac-tion with the adsorbent (chemisorption). If the energyis less than 8 kJ/mol, we may assume that adsorptionis predominantly physical [24]. The adsorption ener-gies Ead calculated for the Dubinin–Radushkevichmodel (Table 1) are more than 9 kJ/mol. We may con-clude that the adsorption of glyphosate on the carbon-containing materials was due to chemical interactionwith the adsorbent.CONCLUSIONSStudies show that carbon-containing materialsobtained from plant raw materials have comparativelyhigh adsorption capacity with respect to glyphosate.The material obtained via joint pyrolysis of sugar canebagasse waste with crushed clay appears to be a fairlyeffective adsorbent of glyphosate from water. Whenthe carbonizate is impregnated with a 1 M potassiumhydroxide solution, we can achieve adsorption charac-teristics (0.956 mmol/L) comparable to that of com-mercial coconut activated carbon CAC-A(0.942 mmol/L). According to our data, the timerequired to reach equilibrium in the glyphosate–sol-vent–adsorbent system is no more than 6 h.FUNDINGThis work was supported by the Russian Foundation forBasic Research; and by the Government of Belgorod oblastas part of scientific project no. 18-43-310012.REFERENCES1. F. Botta, G. Lavison, G. Couturier, et al., Chemo-sphere 77, 133 (2009).2. S. M. Bradberry, A. T. Proudfoot, and J. A. Vale,Toxicol. Rev. 23, 159 (2004).3. G. L. Perez, A. Orremorell, H. Mugni, et al., Ecol.Appl. 17, 2310 (2007).4. K. Z. Guyton, D. Loomis, Y. Grosse, et al., LancetOncol. 16, 490 (2015).5. A. Skinner, K. A. Lewis, K. S. Bardon, et al., HumanEcol. Risk Assessm., No. 7039, 1050 (2016).6. A. L. Gimsing, O. K. Borgard, and M. Bang, Eur. J.Soil Sci. 55, 183 (2004).7. L. Mamy and E. Barriuso, Chemosphere 61, 844(2005).8. R. C. Pessagno, R. M. Torres Sanchez, and M. SantosAfonso, Environ. Pollut. 153, 53 (2008).9. H. Vereecken, Pest Manage. Sci. 61, 1139 (2005).10. C. N. Albers, G. T. Banta, O. S. Jacobsen, et al., Envi-ron. Pollut. 157, 2865 (2009).11. E. Okada, J. L. Costa, and F. Bedmar, Geoderma 263,78 (2016).12. C. N. Albers, O. Pantos, T. C. Morgan, et al., Environ.Pollut. 157, 2865 (2009).13. M. A. Castillo, N. Felis, P. Aragón, et al., Int. Biodete-rior. Biodegrad. 58, 196 (2006).14. J. Doublet, L. Mamy, and E. Barriuso, Chemosphere77, 582 (2009).15. A. L. Gimsing, O. K. Borggaard, and M. Bang, Eur. J.Soil Sci. 55, 183 (2004).16. D. Landry, S. Dousset, J. C. Fournier, et al., Environ.Pollut. 138, 191 (2005).17. M. Stenrod, M.-P. Charnay, P. Benoit, et al., Soil Biol.Biochem. 38, 962 (2006).18. D. C. Nguyen, A. I. Vezentsev, L. F. Peristaya, et al.,Vestn. Tekhnol. Univ. 22 (7), 61 (2019).19. R. T. A. Carneiro, T. B. Taketa, R. J. G. Neto, et al.,J. Environ. Manage. 151, 353 (2015).20. M. A. Heitkamp, W. J. Adams, and L. E. Hallas, Can.J. Microbiol. 38, 921 (1992).21. M. R. Assalin, S. G. de Moraes, A. C. N. Queiroz,et al., J. Environ. Sci. Health, Part B 45, 89 (2009).22. B. L. Bhaskara and P. Nagaraja, Helv. Chim. Acta 89,2686 (2006).23. L. Rissouli, M. Benicha, T. Chafik, et al., J. Mater. En-viron. Sci. 8, 4544 (2017).24. V. I. Zelentsov and T. Ya. Datsko, Elektron. Obrab.Mater. 48 (6), 65 (2012).Translated by A. Tulyabaev−= 0.5ad DR( ) .2Е KRUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A  Vol. 95  No. 6  2021

Adsorption of glyphosate on carbon-containing materials

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Adsorption of glyphosate on carbon-containing materials

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