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Abstract

Adsorption of paraquat and pirimiphos-methyl in water was performed on four adsorbents including montmorillonite (Mt), organoclay (TDA-Mt) from intercalation of Mt with tetradecylammonium chloride, and mesoporous Mt from intragallery templating method (with and without Ti addition). The adsorbents were characterized by X-ray diffraction, N₂ adsorption–desorption, and transmission electron microscopy. Paraquat adsorption isotherms followed Langmuir model and the adsorption capacity was as follows: TDA-Mt > Mt > mesoporous Ti-Mt > mesoporous Mt. The adsorption mechanism on TDA-Mt and Mt might be via ion exchange. The adsorption on mesoporous samples was on the external surface with negative charge. The presence of Ti enhanced the adsorption capacity. Pirimiphos-methyl adsorbed on negative charge of the external surface of Mt samples. The adsorbed amount increased with the initial concentration due to a strong intermolecular interaction.

Keywords

Paraquat pirimiphos-methyl adsorption montmorillonite organoclay tetradecylammonium chloride mesoporous materials intragallery templating method

Introduction

Herbicides and insecticides are used widely in agricultural activities. Despite the main advantage to increase the product yield, they are considered to be water pollutants when they leach from soil. A herbicide which is widely used in Thailand is paraquat (1,1′-dimethyl-4,4′-bipyridinium dichloride, Figure 1). It is toxic and persistent in the environment (WHO, 1984). An example of insecticide used in Thailand is pirimiphos-methyl (O-2-diethylamino-6-methylpyrimidin-4-yl-O,O-dimethyl phosphorothioate, Figure 1). It is a phosphorothioate which is toxic and hazardous to the aquatic environment (Ngoula et al., 2007). Paraquat and pirimiphos-methyl in water can be removed by adsorption with natural adsorbents such as clay minerals (Eneji et al., 2002; Mithyantha et al., 1975; Patakioutas and Albanis, 2002; Patakioutas et al., 2002; Rytwo et al., 2002).

Figure 1.

Structure of (a) paraquat, (b) pirimiphos-methyl, and (c) tetradecylammonium ion.

Clay minerals are hydrous aluminum phyllosilicates which consist of layers made up of silicon in tetrahedral coordination and aluminum, magnesium, or iron in octahedral coordination. Montmorillonite (Mt) is a member of the smectite family, a 2:1 layer (two tetrahedral and one octahedral sheet) with cationic substitution. Negative charges are generated by substitution of Si by Al in the tetrahedral sheet and the replacement of Al by Mg, Fe, Li, or other small atoms in the octahedral sheet (Rouquerol et al., 1999). The charge distribution and internal surface area may make Mt a suitable adsorbent for cationic herbicides. There are several factors affecting the adsorption ability, for example, surface area, porosity, types of exchangeable cation, interlayer spacing, and the presence of water molecules between the layers (Ganigar et al., 2010; Paul et al., 2010).

The adsorption ability of the clay mineral can be improved by intercalation with cationic surfactant via ion exchange. The produced materials are known as organoclays (Seki and Yurdakoç, 2005). For example, Churchman (2002) modified bentonite using a quaternary ammonium cation to improve toluene removal. Seki and Yurdakoç (2005) modified bentonite (B), also in a smectite family, by nonylammonium chloride (NA, with C₉ chain) and dodecylammonium chloride (DCA, with C₁₂ chain). The modification by both ammonium salts increased the clay interlayer spacing and changed the paraquat adsorption capacity. The adsorption increased on NA-bentonite but decreased in DCA-bentonite. The adsorption ability was related to the exchange ability of ammonium cation with the clay interlayer cation. In addition, the paraquat interaction to the organoclays depended on the thickness of the organic layer and size of paraquat molecules (Seki and Yurdakoç, 2005).

Keawkumay et al. (2012) reported an intercalation of Mt by octadecylammonium chloride (ODA). The modification increased the interlayer spacing (1.38 nm of Mt to 1.62 nm of ODA-Mt), and the obtained material was suitable as a filler of rubber nanocomposite. Such sample may work as an adsorbent for paraquat but the long carbon chain could lower the adsorption capacity (Seki and Yurdakoç, 2005). Therefore, tetradecylammonium chloride (TDA) which has a shorter carbon chain was selected instead for the Mt modification in this work.

Another way to modify the clay was intragallery templating method that surfactant molecules can form micelles in the clay interlayer and pillars are created around the micelle by an addition of silicates. The surfactant molecules can be removed by calcination and mesopores are generated. An example of the intragallery templating method was the modification of Mt using cetyltrimethylammonium bromide (CTAB) with and without an addition of Ti (Mao et al., 2010). Their method was employed in this work and the obtained mesoporous materials were used as adsorbents.

The objectives of this work are to prepare and characterize adsorbents from Mt including organoclay (TDA-Mt) and mesoporous materials from Mt and use as adsorbents for paraquat and pirimiphos-methyl. In this study, the new organoclay TDA-Mt was prepared from modification of Mt with TDA. Thus, it was the first time that TDA-Mt and mesoporous Mt and Ti-Mt were used as adsorbents for paraquat and pirimiphos-methyl.

Experimental

Mt with cation exchange capacity (CEC) of 80 meq/100 g was purchased from Thai Nippon Co., Ltd. The contents by weight percentage in oxide form on the product label were as follows: Al₂O₃, 6.59; SiO₂, 68.24; CaO, 3.39; K₂O, 3.36; Fe₂O₃, 11.52; and TiO₂, 2.40. It was modified by TDA with a method adapted from Keawkumay et al. (2012). The content of TDA was equivalent to the CEC. Briefly, Mt (10 g) was dispersed in 200 mL hot deionized water (70℃) with continuous stirring. Tetradecylamine (1.71 g, Acros) in 100 mL hot deionized water was protonated by concentrate hydrochloric acid (1 mL) and added to the clay–water dispersion. The mixture was stirred vigorously for 2 h, filtered, washed repeatedly with hot deionized water, vacuum-filtered, and dried at 70℃. The obtained organoclay was notated as TDA-Mt.

Mesoporous Ti-Mt was synthesized by intragallery templating method (Mao et al., 2010). Mt (10 g) was dispersed in 30 mL water and stirred for 10 min. CTAB (10.23 g) (Unilab) was dissolved in 65 mL of ethanol, added with a mixture from 63 mL tetraethoxy silane (TEOS, Fluka) and 4.8 mL tetrabutyl titanate (Ti(OBu)₄), Aldrich), and stirred for 30 min to produce a clear solution. The solution was dropped slowly to the clay dispersion and stirred at room temperature for 1 h. The pH of the obtained gel was adjusted to 10 by an ammonia solution (25%, Fischer Chemical). The mixture was stirred for 2 h, filtered, dried at 90℃, and calcined at 600℃ for 6 h with heating rate of 2℃/min. This sample was referred to as mesoporous Ti-Mt. In addition, mesoporous Mt without the addition of Ti(OBu)₄ was synthesized with the same procedure.

All adsorbents from Mt were characterized by X-ray diffractometer (XRD, Bruker D8 ADVANCE) with a Cu K_α radiation (λ = 1.5418 Å) operated at a voltage of 40 kV. The XRD patterns were recorded with a step size of 0.02 and a scan speed of 0.2°/min. The interlayer spacing of Mt was calculated from the XRD peak position using Bragg’s law. N₂ adsorption–desorption isotherms were obtained from a Micromeritics ASAP 2010 instrument. Each sample was degassed at 300℃ for 8 h before the measurement except TDA-Mt, which was degassed at 150℃ to preserve the organic content. The specific surface area (S_BET) was calculated using the Brunauer–Emmett–Teller (BET) equation. The morphologies of all adsorbents were observed by a transmission electron microscope (TEM) (TECNAI G²). The samples were dispersed in ethanol and dropped onto a copper mesh grid.

The adsorption of paraquat and pirimiphos-methyl was performed using a commercial paraquat solution (27.6% w/v in water) and pirimiphos-methyl solution (50.0% w/v EC) purchased from a local agro store. The exact concentration was determined from a calibration curve constructed from the chemical grade reagents. The adsorption was performed by adding 0.10 g of the adsorbent to a conical flask containing 25 mL of paraquat or pirimiphos-methyl solution with various concentrations. The mixture was agitated using a magnetic stirrer at the speed of 400 r/min for 60 min. Then 10 mL of the samples in each flask was collected and immediately filtered using a 0.45-µm syringe filter. The amount of remaining paraquat in the solution was determined using a UV–Vis spectrophotometer (Varian CARY 300) at a wavelength corresponding to the maximum absorbance, λ_max at 247 and 257 nm for pirimiphos-methyl and paraquat, respectively. The amount of paraquat or pirimiphos-methyl adsorbed at equilibrium (q_e) was calculated by equation (1) (Boparai et al., 2011; Tan and Xiao, 2009).

q_{e} = \frac{(C_{0} - C_{e}) \times V}{w}

(1) C₀ and C_e are the initial and equilibrium concentration of paraquat or pirimiphos-methyl (mg/L), respectively. V is the volume of paraquat or pirimiphos-methyl solution (L) and w is the amount of adsorbent (g).

The Langmuir isotherm assumes that the adsorbate forms monolayer on the adsorbent with uniform sites and the maximum adsorption could be determined by equation (2) (Boparai et al., 2011; Singh, 2009; Tan and Xiao, 2009; Thomas and Crittenden, 1998).

\frac{C_{e}}{q_{e}} = \frac{1}{K_{L} q_{m}} + \frac{C_{e}}{q_{m}}

(2) where K_L is the Langmuir constant related to the affinity of binding site (L/mg) and q_m is the maximum adsorption capacity (mg/g). Both K_L and q_m can be determined from the linear plot of C_e/q_e versus C_e.

The effect of pH was performed by adding 0.10 g of the adsorbents to a polypropylene (PP) bottle containing 20 mL of 500 mg/g of paraquat or pirimiphos-methyl solutions with various pH (1.5, 3.5, 5.5 (as-prepared), 7.5, and 9.5 for paraquat; 1.0, 3.0, 4.9 (as-prepared), 7.0, and 9.0 for pirimiphos-methyl). The mixture was agitated using a magnetic stirrer at the speed of 400 r/min for 60 min before sampling and analysis by the UV–Vis spectrophotometer.

Results and discussion

XRD patterns of Mt and TDA-Mt are shown in Figure 2(a) and those of mesoporous Mt and Ti-Mt shown in Figure 3. The XRD peaks of Mt occurred at 5.7° and 8.9°. The first peak corresponded to the plane 001 and the interlayer spacing of 1.54 nm. The major XRD peak of TDA-Mt at 5.2° corresponds to an interlayer spacing of 1.73 nm. The increase spacing from that of Mt corresponded to intercalation of TDA into the interlayers (de Paiva et al., 2008). The change depended on the chain length of surfactant. For example, the larger increase from 1.22 nm of Na-Mt to 3.92 and 2.14 nm of Mt functionalized with a zwitterionic surfactant (3-(N,N-dimethylhexadecylammonio)propanesulfonate, DHAPS) (Gu et al., 2015). The expansion from 0.97 nm of untreated Na-Mt to 1.40 nm in an organoclay from Na-Mt and benzyl decyltrimethyl ammonium was also reported (Guégan et al., 2015). An increase of interlayer spacing was also reported on bentonite modified with NA and DCA (Seki and Yurdakoç, 2005).

Figure 2.

XRD patterns of (a) Mt and TDA-Mt, and (b) Mt- and TDA-Mt–containing paraquat.

Figure 3.

XRD patterns of mesoporous Mt and mesoporous Ti-Mt.

The XRD patterns of mesoporous Mt and mesoporous Ti-Mt show a broad peak corresponding to a plane (001) in an ordered lamellar clay material (Mao et al., 2010; Yang et al., 2013). The peak from mesoporous Ti-Mt had higher intensity than that from mesoporous Mt suggesting a more uniform structure. Both samples did not show peaks corresponding to hexagonal mesoporous silica (Brigante and Avena, 2014).

N₂ adsorption–desorption isotherm of Mt and TDA-Mt are shown in Figure 4(a). The adsorption isotherm (filled symbols) of Mt and TDA-Mt were type II according to the IUPAC classification (Sing, 1982). The samples were nonporous or macroporous. The adsorbed volume to form monolayer was low and the multilayer adsorption began afterward. TDA-Mt had a lower adsorbed volume than Mt (Table 1) due to the presence of the surfactant within the interlayer. The decrease of surface area was also reported when Na-Mt contained a zwitterionic surfactant (Gu et al., 2015). The desorption isotherm (empty symbols) of Mt did not overlap with the adsorption forming a H3 hysteresis loop in the P/P₀ range 0.45–1.0. The H3 loop is a characteristic of aggregates of plate-like particles possessing nonrigid slit-shaped pores (Rouquerol et al., 1999; Sing, 1982). The term “pseudo type II” or “type IIb” were also used to classify the isotherm of natural montmorillonite (Rouquerol et al., 1999). Similar hysteresis loops were reported by Gu et al. (2015).

Figure 4.

N₂ adsorption–desorption isotherm of (a) Mt and TDA-Mt and (b) mesoporous Mt and mesoporous Ti-Mt.

Table 1.

Surface area, total pore volume, average pore diameter, and Langmuir parameters for paraquat adsorption on Mt and modified Mt.

Adsorbent	S_BET (m² g⁻¹)	Total pore volume (cm³ g⁻¹)	Average pore diameter (nm)	Langmuir parameter for paraquat
Adsorbent	S_BET (m² g⁻¹)	Total pore volume (cm³ g⁻¹)	Average pore diameter (nm)	q_m (mg g⁻¹)	K_L (L mg⁻¹)	R ²
Mt	49	0.1078	8.72	38	0.211	0.9908
TDA–Mt	26	0.1355	20.77	52	0.374	0.9950
Mesoporous Mt	379	0.2846	3.00	18	0.132	0.9959
Mesoporous Ti–Mt	716	0.5871	3.28	25	0.348	0.9975

Mt: montmorillonite; TDA: tetradecylammonium chloride.

The isotherm of mesoporous Mt and Ti-Mt are shown in Figure 4(b). Both samples had type IV adsorption isotherm according to the IUPAC classification with a hysteresis loop type H3 (Rouquerol et al., 1999; Sing, 1982). The adsorbed volume from mesoporous Ti-Mt was higher than that without Ti indicating a larger surface area (Table 1).

The morphologies of the Mt and modified Mt samples from TEM are shown in Figure 5. Mt showed aggregation of several layers with varied sizes and orientations. TDA-Mt exhibited the intercalation of TDA into the clay layers and the particles may be exfoliated. In the images of mesoporous Mt and mesoporous Ti-Mt, the clay layers were discernible as solid dark lines. The pores appear in lighter contrast between the layers which consists of uniform layered structure. Furthermore, the uniform gallery pores can be observed between the dark layers (Gao et al., 2012; Mao et al., 2009, 2014, 2015; Yang et al., 2013).

Figure 5.

TEM images of Mt, TDA-Mt, mesoporous Mt, and mesoporous Ti-Mt.

Amount of paraquat and pirimiphos-methyl adsorbed on all adsorbents at various equilibrium concentrations are shown in Figure 6(a) and (b). The amount of paraquat adsorbed on all adsorbents increased sharply at very low equilibrium concentrations, implying that paraquat adsorption on these adsorbents was chemisorption. The isotherms of paraquat adsorbed on Mt samples based on Giles classification (Giles et al., 1960) was class H (high affinity) in subgroup 2 which is a strong adsorption. The adsorption curve tended to be a plateau indicating a formation of paraquat monolayer on the adsorbent surface. The similar adsorption behavior was reported on montmorillonite-zirconium(IV) cross-linked compound (González-Pradas et al., 2000), Algerian bentonite (Ait Sidhoum et al., 2013), and DHAPS-Mt (Gu et al., 2015).

Figure 6.

Adsorption isotherm plots of (a) paraquat and (b) pirimiphos-methyl adsorbed on all adsorbents at various equilibrium paraquat concentrations.

The adsorption of paraquat on Mt samples followed Langmuir isotherm indicating a monolayer adsorption. The Langmuir parameters are summarized in Table 1. The adsorption of paraquat on TDA-Mt had the highest K_L values indicated that the highest affinity of paraquat molecules to the binding sites (Giles et al., 1960). The maximum adsorption capacity (q_m) of the adsorbents on TDA-Mt was the highest (52 mg/g adsorbent) followed by Mt, mesoporous Ti-Mt, and mesoporous Mt. Although TDA-Mt had the lowest surface area, it had the highest adsorption capacity. Paraquat dication could exchange with TDA and cations in the clay layers of TDA-Mt and Mt, respectively.

To confirm the exchange hypothesis, the Mt and TDA-Mt samples containing paraquat were characterized by XRD and the results are shown in Figure 2(b). The XRD pattern of Mt-containing paraquat (Mt-PQ) shows the main peak at 7.0° corresponding to the interspacing layer 1.26 nm. The decrease of the interlayer spacing indicated ion exchange between hydrated cations and paraquat dication. Similar behavior was also reported on ion exchange of hydrated Na⁺ from Na-Mt by alkyl ammonium, glycine ethylester, and ethylenediammonium (Bala et al., 2000; Khan et al., 2009, 2012; Laura and Cloos, 1975). The XRD pattern of TDA-Mt–containing paraquat (TDA-Mt-PQ) shows the main peak at 7.0° corresponding to the interlayer spacing 1.27 nm. The spacing was similar to that of paraquat adsorbed on untreated Mt indicating that paraquat exchanged with TDA.

The influence of pH on the adsorption of paraquat is shown in Figure 7(a). The lower amount adsorbed at the lower pH indicated a competition between proton and paraquat to the adsorption sites. A similar effect was reported on adsorption of paraquat on silica (Brigante and Avena, 2014).

Figure 7.

Adsorption of (a) paraquat and (b) pirimiphos-methyl on all adsorbents at various pH values.

Table 2 compares paraquat adsorption capacities between this work and literature. The adsorption capacities of Mt from different studies seemed to depend on composition and treatment method. From other works, Mt modified with cationic or non-ionic surfactant had lower capacities than the unmodified ones due to the difficulty to exchange (Gu et al., 2015; Guégan et al., 2015). Zwitterion surfactants could improve the adsorption capacity because their anionic group on one side interacted strongly with paraquat dication (Gu et al., 2015).

Table 2.

Maximum adsorption capacities of Mt, organoclay (based Mt), and mesoporous Mt.

Adsorbent	Type of surfactant in organoclay	q_max (mg g⁻¹)	Reference
Mt		38	This work
TDA-Mt	Cationic	52	This work
Na-Mt		134	Guégan et al. (2015)
BDTA-Mt	Cationic	–	Guégan et al. (2015)
C₁₀E₃-Mt	Non-ionic	39	Guégan et al. (2015)
Na-Mt		Low	Gu et al. (2015)
CTAB-Mt	Cationic	6.4 and 6.9	Gu et al. (2015)
DHAPS-Mt	Zwitterionic	70.8 and 75.5	Gu et al. (2015)
SDS-Mt	Zwitterionic	85.2 and 90.9	Gu et al. (2015)
Mesoporous Mt		18	This work
Mesoporous Ti-Mt		25	This work
MCM-41		21.3	Rongchapo et al. (2013)
Al-MCM-41		66.4	Rongchapo et al. (2015)
Mesoporous silica		107	Brigante and Avena (2014)

BDTA: benzyl decyltrimethyl ammonium; C₁₀E_3: triethylene glycol mono n-decyl ether; CTAB: cetyltrimethylammonium bromide; DHAPS: (3-(N,N-dimethylhexadecylammonio)propanesulfonate; SDS: sodium dodecyl sulfonate; TDA: tetradecylammonium.

In the case of mesoporous Ti-Mt and mesoporous Mt, the adsorption capacity was low despite the large surface area. The results indicated that adsorption occurred on the external surface. The presence of Ti-generated negative charge surface and enhanced the adsorption. With the similar reason, the presence of Al in mesoporous MCM-41 led to higher adsorption capacities (Rongchapo et al., 2013, 2015). Moreover, the higher adsorption capacity was reported on mesoporous silica with uniform particle size prepared with a mixed surfactant (Brigante and Avena, 2014).

The adsorption isotherms of pirimiphos-methyl on Mt samples, also based on Giles classification (Giles et al., 1960) were class L in subgroup 1. The equilibrium concentration increased with the initial concentration and did not reach a plateau. The pirimiphos-methyl molecules might adsorb with end-on orientation on the surface with a strong intermolecular attraction leading to high adsorption capacity. The amount adsorbed did not relate to the surface area.

The influence of pH on the adsorption of pirimiphos-methyl is shown in Figure 7(b). The amount adsorbed increased with the pH indicating that adsorption occurred on the surface with negative charge. At low pH, the external surface was protonated and not available for the adsorption. However, the amount adsorbed was high on all samples indicating a strong intermolecular interaction.

Conclusions

Mt was modified by TDA to produce TDA-Mt. The intercalation of TDA resulted in the increase of interlayer spacing and decrease in the surface area. Moreover, Mt was modified by intragallery templating to produce mesoporous Mt and mesoporous Ti-Mt. Both samples had lamellar structure with significantly higher surface area than the parent Mt due to the presence of mesopores. The paraquat adsorption capacity was as follows: TDA-Mt > Mt > mesoporous Ti-Mt > mesoporous Mt. The adsorption isotherm fitted with Langmuir model. The adsorption on TDA-Mt and Mt was ion exchange. For mesoporous materials, the adsorption occurred on external surface and the presence of Ti increased the adsorption capacity. The adsorption decreased in acidic conditions.

The adsorption of pirimiphos-methyl on Mt samples occurred on external surface area with negative charge. The adsorbed amount increased with the initail concentration and did not form a plateau indicating a strong intermolecular interaction.

Footnotes

Declaration of Conflicting Interests

The author(s) declared no potential conflict of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Keawkumay is supported by SUT-PhD scholarship from Suranaree University of Technology (SUT-PhD/11/2554). Rakmae and Rongchapo are supported by Royal Golden Jubilee PhD program from the Thailand Research Fund (TRF) and SUT (PHD/0173/2553 and PHD/0163/2552, respectively).

References

Ait Sidhoum

Socias-Viciana

Urena-Amate

(2013) Removal of paraquat from water by an Algerian bentonite. Applied Clay Science 83–84: 441–448.

Bala

Samantaray

Srivastava

(2000) Synthesis and characterization of Na-montmorillonitealkylammonium intercalation compounds. Materials Research Bulletin 35: 1717–1724.

Boparai

Joseph

O’Carroll

(2011) Kinetics and thermodynamics of cadmium ion removal by adsorption onto nanozerovalent iron particles. Journal of Hazardous Materials 186: 458–465.

Brigante

Avena

(2014) Synthesis, characterization and application of a hexagonal mesoporous silica for pesticide removal from aqueous solution. Microporous and Mesoporous Materials 191: 1–9.

Churchman

(2002) Formation of complexes between bentonite and different cationic polyelectrolytes and their use as sorbents for non-ionic and anionic pollutants. Applied Clay Science 21: 177–189.

de Paiva

Morales

Diaz

FRV

(2008) Organoclays: Properties, preparation and applications. Applied Clay Science 42: 8–24.

Eneji

Buncel

Vanloon

(2002) Degradation and sorption of pirimiphos-methyl in two Nigerian soils. Journal of Agricultural and Food Chemistry 50: 5634–5639.

Ganigar

Rytwo

Gonen

(2010) Polymer–clay nanocomposites for the removal of trichlorophenol and trinitrophenol from water. Applied Clay Science 49: 311–316.

Gao

Mao

(2012) Facile synthesis route to NiO-SiO₂ intercalated clay with ordered porous structure: Intragallery interfacially controlled functionalization using nickel–ammonia complex for deep desulfurization. Microporous and Mesoporous Materials 148: 25–33.

10.

Giles

Macewan

Nakhwa

(1960) Study in adsorption Part XI. A system of classification of solution adsorption isotherm, and its use in diagnosis of adsorption mechanism and in measurement of specific surface areas of solids. Journal of the Chemical Society 4: 3973–3993.

11.

González-Pradas

Villafranca-Sanchez

Rey-Bueno

(2000) Removal of paraquat and atrazine from water by montmorillonite-(Ce or Zr) phosphate cross-linked compounds. Pest Management Science 56: 565–570.

12.

Gao

(2015) Montmorillonite functionalized with zwitterionic surfactant as a highly efficient adsorbent for herbicides. Industrial and Engineering Chemistry Research 54: 4947–4955.

13.

Guégan

Giovanela

Warmont

(2015) Nonionic organoclay: A ‘Swiss Army knife’ for the adsorption of organic micro-pollutants? Journal of Colloid and Interface Science 437: 71–79.

14.

Keawkumay

Jarukumjorn

Wittayakun

(2012) Influences of surfactant content and type on physical properties of natural rubber/organoclay nanocomposites. Journal of Polymer Research 19: 9917..

15.

Khan

Bala

Nurnabi

(2012) Investigations on microstructural and layer disorder parameters of Na-montmorillonite glycine intercalation compounds. Dhaka University Journal of Science 60(1): 25–29.

16.

Khan

Nurnabi

Bala

(2009) Studies on thermal transformation of Na-montmorillonite-glycine intercalation compounds. Journal of Thermal Analysis and Calorimetry 96: 929–935.

17.

Laura

Cloos

(1975) Adsorption of ethylenediamine (EDA) on montmorillonite saturated with different cations; III, Na-, K- and Li-montmorillonite; ion-exchange, protonation, co-ordination and hydrogen-bonding. Clays Clay Minerals 23: 61–69.

18.

Mao

(2009) Mesoporous nickel (or cobolt)-doped silica-pillared clay: Synthesis and characterization studies. Materials Research Bulletin 47: 1569–1575.

19.

Mao

(2010) Facile synthesis and catalytic properties of titanium containing silica-pillared clay derivatives with ordered mesoporous structure through a novel intra-gallery templating method. Microporous and Mesoporous Materials 130: 314–321.

20.

Mao

Zhu

(2014) Document synthesis of titania modified silica-pillared clay (SPC) with highly ordered interlayered mesoporous structure for removing toxic metal ion Cr(VI) from aqueous state. Applied Surface Science 292: 1009–1019.

21.

Mao

Zhu

(2015) Restructuring of silica-pillared clay (SPC) through posthydrothermal treatment and application as phosphotungstic acid supports for cyclohexene oxidation. Journal of Colloid and Interface Science 446: 141–149.

22.

Mithyantha

Rao

(1975) Paraquat adsorption on clay minerals. Bulletin of the Indian National Science Academy 50: 293–298.

23.

Ngoula

Watcho

Dongmo

M-C

(2007) Effects of pirimiphos-methyl (an organophosphate insecticide) on the fertility of adult male rats. African Health Sciences 7: 1–8.

24.

Patakioutas

Albanis

(2002) Adsorption–desorption studies of alachlor, metolachlor, EPTC, chlorothalonil and pirimiphos-methyl in contrasting soils. Pest Management Science 58: 352–362.

25.

Patakioutas

Karras

Hela

(2002) Pirimiphos-methyl and benalaxyl losses in surface runoff from plots cultivated with potatoes. Pest Management Science 58: 1194–1204.

26.

Paul

Yang

(2010) Adsorption of the herbicide simazine on moderately acid-activated beidellite. Applied Clay Science 49: 80–83.

27.

Rongchapo

Deekamwong

Loiha

(2015) Paraquat adsorption on NaX and Al-MCM-41. Water Science and Technology 71: 1347–1353.

28.

Rongchapo

Sophiphun

Rintramee

(2013) Paraquat adsorption on porous materials synthesized from rice husk silica. Water Science and Technology 68: 863–869.

29.

Rouquerol F, Rouquerol J and Sing K (1999) Assessment of surface area. Adsorption by Powders and Porous Solids: Principles, Methodology and Applications. London: Academic Press.

30.

Rytwo

Tropp

Serban

(2002) Adsorption of diquat, paraquat and methyl green on sepiolite: Experimental results and model calculations. Applied Clay Science 20: 273–282.

31.

Seki

Yurdakoç

(2005) Paraquat adsorption onto clays and organoclays from aqueous solution. Journal of Colloid and Interface Science 287: 1–5.

32.

Sing

KSW

(1982) Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity. Pure & Applied Chemistry 54: 2201–22l8.

33.

Singh

(2009) Adsorption of herbicides on coal fly ash from aqueous solutions. Journal of Hazardous Materials 168: 233–237.

34.

Tan

Xiao

(2009) Adsorption of cadmium ion from aqueous solution by ground wheat stems. Journal of Hazardous Materials 164: 1359–1363.

35.

Thomas WJ and Crittenden B (1998) Adsorption Technology and Design. Boston: Butterwort-Heinemann.

36.

WHO (1984) Paraquat and diquat. In: Environment health criteria, Geneva, Switzerland, p. 39. Available at: http://www.who.int/iris/handle/10665/37301 (accessed March 2016).

37.

Yang

Liang

(2013) Synthesis of TiO₂ pillared montmorillonite with ordered interlayer mesoporous structure and high photocatalytic activity by an intra-gallery templating method. Materials Research Bulletin 48: 3948–3954.

Adsorption of paraquat and pirimiphos-methyl by montmorillonite modified with tetradecylammonium chloride and intragallery templating method

Abstract

Keywords

Introduction

Experimental

Results and discussion

Conclusions

Footnotes

Declaration of Conflicting Interests

Funding

References