This study describes the preparation of clay/polymer composites using Bijoypur clay (kaolinite) and copolymer poly(hydroxyethylacrylamide-co-3-methacryloxypropyltrimethoxysilane) (poly(HEAA-co-MAPTS)) for the removal of organic dyes from industrial wastewater. The copolymer was prepared by free-radical polymerization of hydroxyethylacrylamide (HEAA) and 3-methacryloxypropyltrimethoxysilane (MAPTS). The clay was activated and purified followed by modification with dodecylamine. FT-IR analysis confirmed successful modification of clay and incorporation of polymer and organoclay in the composites. TG analysis showed that the composite exhibited better thermal properties with increasing polymer percentage. X-ray diffraction analysis revealed that the crystalline size of the composites increased from 23.79 to 60.43 nm with the increasing percentage (1–4%) of polymer. SEM analysis of the composite with higher polymer percentage showed uniform porous structure. Adsorption study was carried out using methylene blue (MB) and acid black-172 (AB) dyes. The composites with higher polymer concentration showed better adsorption capacity for both MB (5.288 mg/g) and AB (6.696 mg/g) dyes in aqueous solution, at initial concentration of 25 ppm, 50 mg of dose, and pH of 10.1 for MB and 4 for AB. The developed composites exhibited adsorption capability for both cationic and anionic dyes which gives a scope to their universal application in dye removal from industrial wastewater.

  • Clay/polymer composites (kaolinite/poly(HEAA-co-MAPTS)) were prepared.

  • Locally available Bijoypur clay was used as one of the raw materials.

  • The composites were characterized by FT-IR, TGA, XRD, and SEM analysis.

  • Methylene blue (cationic) and acid black-172 (anionic) were chosen as the organic dyes.

  • The composites with higher polymer percentage showed developed adsorption capacity.

Water is a fundamental resource for thriving and developing countries. The main worldwide request for usable water has been expanding at a rate of around 1% per year due to rapid growth of the world population, financial advancement, and changing consumption patterns, and it will proceed to develop essentially over the following decades. However, the availability of usable water is being decreasing because of fast industrialization, various anthropogenic activities and inappropriate waste disposal (Akter et al. 2021). Millions of occupants are at the hazard of unfeigned health expressions due to pollutants generated from diverse industries approaching to the habitants (Paul et al. 2013).

Recently, different sorts of dyes have been consolidated into the color list within the leather industries and textile industries. Due to the low biodegradability of dyes, the release of colored wastewater from these industries had caused numerous critical inconveniences within the environment. The volume of dye-containing effluent discharged into water bodies is alarming; both from a toxicological and esthetic perspective, and subsequently, the treatment of these effluents earlier to their release are vital (Özcan & Özcan 2004; Sakkayawong et al. 2005). Currently, a number of dyes especially methylene blue (MB) and acid black-172 (AB) are forbidden due to possible health risks and carcinogenicity (Smith 1920). The main strategies that have been used for dye removal from effluents are adsorption, ion exchange, precipitation, reverse osmosis, heterogeneous photo catalysis and membrane filtration (Zhao et al. 2021). Among all these techniques, adsorption is considered to be most convenient one due to its flexibility, compatibility, low cost, and regeneration ability, and is commonly used to remove nondegradable organic compounds from industrial effluents (Biswas et al. 2017; Rahman et al. 2022).

Composite materials based on synthetic polymer and clay have attracted considerable interest due to their several distinct properties which is because they can forgather both the physical and chemical properties of inorganic and organic materials (Biswas et al. 2017, 2020, 2021; Mukhopadhyay et al. 2020; Faizan et al. 2022). These composites play a vital role in removal of dye molecules from industrial wastewater by physically and chemically entrapping molecules of interest. Clay is a readily available, cheap and hydrous aluminosilicate making up the colloid fraction of soils, rock, and sediments (Gu et al. 2019). It has exchangeable cations and anions on its surface that can be utilized for adsorption, ion exchange, or both, to remove pollutants. Because of its large surface area, layered structure, mechanical stability, and environmental friendliness, clay is a desirable option for composite materials (Ebrahimi et al. 2018). Bijoypur clay, a type of locally available kaolinite clay, is readily used for the fabrication of polymer-clay composite. It has high content of SiO2 (70.08%), significant amount of Al2O3 (27.24%) and relatively low amount of Fe2O3 (1.03%) and TiO2 (1.65%) (Mousharraf et al. 2011).

In this study, composite was prepared from Bijoypur clay (kaolinite) and a copolymer, poly(hydroxyethylacrylamide-co-3-methacryloxypropyltrimethoxysilane (poly(HEAA-co-MAPTS)), where clay was exfoliated in a solvent in which the polymer is soluble and is expected to exhibit good dye adsorption capacity in aqueous solution due to their structure. 3-Methacryloxypropyltrimethoxysilane (MAPTS) is mainly used as a coupling agent because it has dual functional groups so it can improve the adhesion capacity of the polymer with clay (Pantoja et al. 2009; Jiang et al. 2017). A critical property of the clay is that the layers are adversely charged and they are regularly adjusted by hydrated cations set within the interlayer spaces. On the other hand, having negatively charged moieties in their structure, the polymeric molecules of the composite are capable of adsorbing cationic molecules. In this regard, both cationic and anionic dye particles have high affinity towards kaolinite/poly(HEAA-co-MAPTS) composite and are readily adsorbed on the composite surfaces (Margulies et al. 1988; Bujdák & Komadel 1997; Pantoja et al. 2009). The detailed characteristics of the composite were performed and the adsorption performance was evaluated for a cationic dye, MB and an anionic dye, AB.

Materials

Bijoypur clay was collected from Bijoypur area, Netrokona, Bangladesh (supplied by Bangladesh Insulator and Sanitaryware Factory (BISF), Dhaka, Bangladesh). Hydroxyethylacrylamide (HEAA) and MAPTS, dodecylamine, dichloromethane (DCM) were obtained from Sigma Aldrich, Japan. Hydrochloric acid (36 wt%), MB and AB were obtained from Merck, Germany. Methanol was collected from Loba Chemie Pvt. Ltd, India and AIBN (Initiator) from TCI chemicals, Japan. Deionized water was used throughout the experiment. All the chemicals were of analytical grade.

Methods

Activation and purification of bijoypur clay

Activation of clay was carried out to progress the surface properties of clay by following the modified method of Biswas et al. (Biswas et al. 2017). At first, clay (Supplementary material, Figure S1(A)) was crushed by a milling machine and was screened with 180 meshes to evacuate the lump and large particles. After that, the fine particles of clay were subjected to acid treatment. 100 g of screened clay was scattered in a 3 M HCl solution for treatment. The clay slurry was mixed by a mechanical stirrer at 2,000 rpm for 5 h and after that it was centrifuged by a centrifuge machine at 4,000 rpm for 15 min. It was done eight times to remove acid from the clay so that the pH was brought to neutral. At that point, the clay was oven-dried at 60 °C and it was once more grinded and screened with 180 meshes so that fine particles are obtained (Supplementary material, Figure S1(B)).

Modification of bijoypur clay

Fifty grams (50 g) of purified clay was scattered in 250 mL of water and was stirred in a mechanical stirrer at 80 °C to create homogenous slurry. Four and a half grams (4.5 g) of dodecylamine was taken into another beaker and 100 mL of water was added to this and it was warmed to form liquid dodecylamine (Biswas et al. 2017). Then, 6 M of HCl was added and the solution was heated for 30 min at 80 °C. The previously prepared clay scattering was added in the dodecylamine solution and was blended for 2 h and after that, centrifuging, drying, grinding and screening processes were repeated to get modified clay (Supplementary material, Figure S1(C)) (Islam et al. 2017).

Preparation of poly(HEAA-co-MAPTS)

Poly(HEAA-co-MAPTS) was prepared by free-radical polymerization method reported by Shahruzzaman et al. (Hossain et al. 2021). In this process, HEAA and MAPTS were mixed together using methanol solvent, and then the mixture was kept in an inert atmosphere (N2) for 30 min. AIBN was used as the initiator. The reaction was continued for 6 h. After that, the reaction mixture was dissolved in DCM and precipitated in diethyl ether and dried to get poly(HEAA-co-MAPTS) (Supplementary material, Figure S1(D)).

Fabrication of biocomposites (kaolinite/poly(HEAA-co-MAPTS))

First, different amount of polymers were added in water and were stirred at 300 rpm for 2 h at room temperature to prepare the polymer solution (1, 2 and 4 wt%). Then the desired amounts of modified clay dispersed solutions were prepared at 40 rpm for 2 h. After stirring, the clay solution was sonicated for 30 min for proper dispersion. The dispersed clay and the polymer solution was mixed and blended at 500 rpm for 4 h at 90 °C. The blended solution was casted by solution casting method and kept in a deep freezer at −22 °C for 24 h to get the composites (PC1, PC2 and PC3) (Table 1, Supplementary material, Figure S2) (Yang et al. 2014). The reaction scheme is shown in Figure 1.
Table 1

Preparation of composites with varying polymer percentages

Name of compositesVariation in weight
Polymer (wt. %)Clay (wt. %)
PC1 1% 1% 
PC2 2% 1% 
PC3 4% 1% 
Name of compositesVariation in weight
Polymer (wt. %)Clay (wt. %)
PC1 1% 1% 
PC2 2% 1% 
PC3 4% 1% 
Figure 1

Schematic representation of the preparation of (kaolinite/poly(HEAA-co-MAPTS) composite.

Figure 1

Schematic representation of the preparation of (kaolinite/poly(HEAA-co-MAPTS) composite.

Close modal

Characterization techniques

To investigate the successful modification of the clay and the interaction between polymer and modified clay, which helps to develop the composite structure, the Fourier Transform Infrared (FT-IR) spectroscopic analysis of polymer, raw clay, modified clay, and composites were obtained using the IR spectrophotometer (IR prestige-21, Shimadzu Corporation, Kyoto, Japan) in the range of 4,000–400 cm−1. The spectra were acquired in a transmission mode with a resolution of 4 cm−1 and accumulated 32 scans.

To analyze the thermal behaviour, thermogravimetric analysis (TGA) of the samples were carried out by a thermogravimetric analyzer (TG-00260 Serial NO.C300346, SHIMADZU, Japan) in a nitrogen purging environment at a flow rate of 20 mLmin−1, in aluminium cell with a heating rate of 10 °C/min from room temperature to 800 °C.

To observe the surface morphology of the composite, scanning electron microscope (JSM-7610F, Japan) was used. Before scanning with an auto fine coater (JEOL, JEC-3000FC, Japan) linked to a pump (ULVAC, G-100DB, Japan), completely dried specimens were sputter coated with platinum to increase the surface conductivity. The samples of fibres that will be evaluated were placed on an aluminium plate to observe the samples at magnification levels ranging from 100 to 50,000 times with an accelerating voltage of 5 kV.

X-ray diffraction (XRD) was used to identify the crystalline or amorphous properties of composite and to investigate the degree of crystallization imparted by both the raw materials on composites. For XRD, an X-ray diffractometer (BRUKER AXS Diffract Meter D8, Germany) was utilized. The XRD patterns of the samples were measured in the continuous scanning mode with the scan speed of 30/min and in the scan range of 10°–70°. The Bragg's law and Scherrer equation were applied to determine d-spacing and crystalline size, respectively. Bragg's Law –

Here, n is the order of diffraction and its value is 1, λ is the wavelength of incident X-ray and it is 1.5406 Å, Ѳ is the peak position in radians, and d is the inter planer spacing/d-spacing.
where n is the Scherrer constant and its value is 0.9, λ is the wavelength of incident X-ray and it is 0.15406 nm, β and Ѳ are the FWHM and peak position, respectively, in radians, and D is the crystalline size.

Adsorption studies

Two different dyes, one cationic (MB) and the other anionic (AB) were used to figure out the adsorption capacity of raw clay, modified clay, polymer and polymer-clay composites. The stock solutions of 100 ppm of both the dyes (MB and AB) were prepared by dissolving roughly 0.01 g of dye in 100 mL of deionized water and the test solutions were acquired by subsequent dilution of the dye stock solutions to exact extents to create the desired concentration of 5 to 50 ppm. The concentration of MB and AB within the aqueous solution were decided at λmax of 663 and 570 nm, respectively, employing a UV-visible spectrophotometer (UV-1700 Pharmaspec (Shimadzu, Kyoto, Japan)) (Pantoja et al. 2009; El-Wakil et al. 2015). Adsorption capacity was determined by following equation:
where, q = adsorption capacity (mg/g), Ci = initial concentration of dye (mg/L), Ce = equilibrium concentration of dye (mg/L), V = volume of the dye solution (L), m = amount of adsorbent (g).

Statistical evaluation

Microsoft Excel was used to determine the variance and correlation among the data reported in this study. The one-way Analysis of Variance (ANOVA) test's significance threshold was set at p < 0.05, and the standard deviation and standard error mean were calculated for replicates.

FT-IR spectroscopic analysis

Figure 2(a) shows the FT-IR spectra of poly(HEAA-co-MAPTS). The peak at 3,340 cm−1 is attributed to the –OH group and 3,317 cm−1 is due to N–H stretching from the polymer (Zhao et al. 2012). Peak shown at 2,943 cm−1 is due to the C–H asymmetric extending vibration of the methyl group. Moving on the peak at 1,635 cm−1 is attributed to the vibration of the C = O groups. The peak at 1,421 cm−1 appears for C–H twisting within the polymer, 1,238 cm−1 is due to H–C–H turning most likely in alkane chain, and 1,049 cm−1 due to the extending vibration of C–O group. The major peaks of the polymer have been indicated which give clear evidence of the polymerization.
Figure 2

FT-IR analysis of (a) poly(HEAA-co-MAPTS), (b) raw clay (a) and modified clay (b), (c) and composites PC3 (a), PC2 (b), PC1 (c).

Figure 2

FT-IR analysis of (a) poly(HEAA-co-MAPTS), (b) raw clay (a) and modified clay (b), (c) and composites PC3 (a), PC2 (b), PC1 (c).

Close modal

FT-IR of clay and modified clay was carried out to investigate the effective association of dodecylamine into the clay. In Figure 2(b), the presence of primary amine from the dodecylamine used for modification gives band at 3,633 cm−1 and twelve carbon-containing dodecyl groups show a peak at 2,904 cm−1. The peak at 918 cm−1 is due to the Al–Al–OH bonds. The peak at 779 cm−1 is for free silica and/or quartz and a few other peaks that observed within the unique mark covered are at 702 cm−1 for Si–O–Si, 628 cm−1 for Si–O out-of-plane twisting, 540 cm−1 for Si–O–Al twisting, 455 cm−1 for Si–O–Si in-plane bowing and 424 cm−1 for Si–O bonds. In the FT-IR spectrum of modified clay, all the important peaks are present and they are more or less unaltered as anticipated, however, the presence of alkane peak at 2,904 cm−1 clearly shown the incorporation of dodecyl group into the clay (Biswas et al. 2017; Biswas et al. 2020).

The FT-IR spectrum of different compositions of the composite is shown in Figure 2(c) and it is of vital significance to have major peaks comparing to both clay and polymer within the composite material. It is obvious that for composites, peaks from both clay and polymer are available. Major peaks just like the alkane peak due to the dodecyl group gather within the adjusted clay can be found at 2,939 cm−1 and 1,045 cm−1 is due to extending vibration of C–O presents in polymer can be observed in composite. These peaks are prevailing in composites PC2 and PC3 as peaks from both clay and polymer have covered compare to the composite PC1, which indicates the strong interaction of clay and polymer in the composite (Biswas et al. 2017).

Thermogravimetric analysis

Figure 3(a) shows the TGA curve of poly(HEAA-co-MAPTS). The weight loss was observed in three fundamental stages. First, within the temperature range of 23–192 °C, all absorbed moisture were eliminated (5.6%). The weight loss was due to the evacuation of the water ingested on the surface of silica particles. Furthermore, within the range of 257–502 °C, the weight loss was around 50%, due to the condensation of CO2 and Si–OH. Finally, within the temperature range of 630–799 °C, the ultimate weight loss was 98.5% due to the thermal degradation of the polymer.
Figure 3

TGA curve of (a) poly(HEAA-co-MAPTS), (b) raw clay (a) and modified clay (b), (c) and biocomposites PC1 (a), PC2 (b) and PC3 (c).

Figure 3

TGA curve of (a) poly(HEAA-co-MAPTS), (b) raw clay (a) and modified clay (b), (c) and biocomposites PC1 (a), PC2 (b) and PC3 (c).

Close modal

TGA curve of modified clay was appeared (Figure 3(b)) with three steps of weight loss from the encompassing temperature up to 100 °C with a weight loss of 0.2% and it was due to water loss. The next weight loss was found within the temperature range of 221–414 °C coming about in a weight loss of 0.5% due to elimination of volatile elements. The ultimate weight loss was at 485–799.1 °C due to the deterioration of alkyl amine intercalated within the clay. The raw clay was more vulnerable to the moisture and for this reason, the weight loss of up to 225 °C was found to be higher for raw clay than the modified clay. From TGA curve, modified clay appeared a weight loss of around 1.6%, whereas for raw clay it was found to be 6.9% (Biswas et al. 2017).

TGA was performed on the clay–polymer composites of different compositions as an essential degree of their thermal stability (Figure 3(c)). Previous studies showed that clay increases thermal stability of clay polymer composites; at higher loads of clay the decomposition temperature increased (Biswas et al. 2017). Hence, within the temperature upto 284 °C, the weight loss was found to be around 20%. As the percentage of polymer increase, the weight loss was increased and it was found to be 71.1, 85.5 and 87.5% for the composites, PC1, PC2 and PC3, respectively. However, the tendency of the weight loss percentage from PC2 to PC3 (85.5 to 87.5%) is very lower (2%) compared to the weight loss (14.4%) from PC1 to PC2 (71.1 to 85.5%). So, PC3 appeared more thermal stable compared to other composites.

XRD pattern analysis

From the XRD analysis of polymer (Figure 4(a)), it might be said that the polymer was fundamentally amorphous in nature because there was no sharp peak found within the XRD curve. The major peak was found at 22.36° for 2 theta which was exceptionally wide for its amorphous nature and another minor peak was watched at 11.64°. The quantitative examination by XRD)of both Bijoypur raw clay and modified clay appeared well at 2Ѳ of 26.27° (Figure 4(b)). Here the sharp and well inter-planar spacing peak was obtained. The peak intensity of the modified clay was found higher than raw clay which influenced the crystalline character of the clay (Biswas et al. 2017; Islam et al. 2017). The average crystalline size of the raw clay and modified clay was found to be 44.76 and 41.65 nm, respectively.
Figure 4

XRD analysis of (a) poly(HEAA-co-MAPTS), (b) raw clay (a) and modified clay (b), and (c) composites PC1 (a), PC2 (b), PC3 (c).

Figure 4

XRD analysis of (a) poly(HEAA-co-MAPTS), (b) raw clay (a) and modified clay (b), and (c) composites PC1 (a), PC2 (b), PC3 (c).

Close modal

The major XRD peak of composite (Figure 4(c)) appeared at 2Ѳ of 26.75° which was additionally found in clay. The intensity of peak at PC1 was found sharper among the three composites. The higher the concentration of peak, the lower the crystalline nature (Cornides 1982). It is evident that the crystalline size of PC3 was higher than others and it was 60.43 nm. The crystalline size of PC1 and PC2 were found 23.79 and 57.44 nm, respectively. The higher percentage of polymer is responsible for larger crystal size of the PC3.

Scanning electron microscopic analysis

The surface morphology of the polymer-clay composite was studied by scanning electron microscopic (SEM) analysis. Figure 5 shows the electron micrograph for the surface of kaolinite/poly(HEAA-co-MAPTS) composite with 2% (PC2) and 4% (PC3) polymer content. It can be seen that the composite with higher polymer percentage had better three-dimensional porous structure. Higher porosity of the composites results in larger surface area which ultimately improve the dye adsorption capacity of the composite. The pores could be the regions of water permeation and interaction site of the water and dye molecules.
Figure 5

SEM images of kaoline/poly(HEAA-co-MAPTS), composites (a) PC2 and (b) PC3.

Figure 5

SEM images of kaoline/poly(HEAA-co-MAPTS), composites (a) PC2 and (b) PC3.

Close modal

Adsorption study

Calibration curve of MB and AB- dye

The UV-visible spectra of MB and AB dyes exhibited the λmax as 663 and 570 nm, respectively. To establish the calibration curve, dye solutions of different concentrations, such as 5, 10, 15, 20, 25, 30, 35, 40, 45, and 50 ppm were prepared. Then the absorbance of these solutions was measured. By plotting these corresponding absorbance values of the successive concentrations, calibration curves were obtained which are shown in Figure 6.
Figure 6

Calibration curve of MB and AB. All data presented are means calculated from triplicate measurements.

Figure 6

Calibration curve of MB and AB. All data presented are means calculated from triplicate measurements.

Close modal

Optimization of the adsorption conditions

Removal of toxic dyes from aqueous solution by using an adsorbent generally depends on the initial concentration of the dye, amount of the adsorbent, temperature, pH of the solution, added salt, and the contact time of adsorption. The optimum conditions of various parameter of adsorption of MB and AB are shown in Table 2.

Table 2

Optimum conditions of adsorption for MB and AB-dyes

ParameterValue
MBAB
Temperature 27 °C 27 °C 
Time 2 h 2 h 
pH 10.1 4.0 
Dose 50 mg 50 mg 
Concentration 25 ppm 25 ppm 
Volume 20 mL 20 mL 
ParameterValue
MBAB
Temperature 27 °C 27 °C 
Time 2 h 2 h 
pH 10.1 4.0 
Dose 50 mg 50 mg 
Concentration 25 ppm 25 ppm 
Volume 20 mL 20 mL 

Adsorption study of MB and AB

Raw clay, modified clay, polymer and composites of different compositions (PC1, PC2, and PC3) were utilized for the adsorption of MB and AB dyes. The adsorption results are shown in Table 3 and Figure 7.
Table 3

Adsorption results from UV-vis spectrum for MB and AB adsorption

SampleMB
AB
Conc. (ppm)AbsorbanceConc. (ppm)Absorbance
Initial/stock solution 24.77 0.3688 25.23 0.2082 
Polymer 15.38 0.2290 11.98 0.0988 
PC1 15.93 0.2372 11.60 0.0957 
PC2 13.98 0.2081 9.16 0.0756 
PC3 11.55 0.1720 8.49 0.0701 
Raw clay 17.89 0.2663 20.76 0.1713 
Modified clay 14.48 0.2156 16.27 0.1342 
SampleMB
AB
Conc. (ppm)AbsorbanceConc. (ppm)Absorbance
Initial/stock solution 24.77 0.3688 25.23 0.2082 
Polymer 15.38 0.2290 11.98 0.0988 
PC1 15.93 0.2372 11.60 0.0957 
PC2 13.98 0.2081 9.16 0.0756 
PC3 11.55 0.1720 8.49 0.0701 
Raw clay 17.89 0.2663 20.76 0.1713 
Modified clay 14.48 0.2156 16.27 0.1342 

Absorbance data by means of triplicate measurements.

Figure 7

Comparative studies of adsorption capacities of MB and AB dyes by raw clay, modified clay, polymer and composites of different compositions PC1, PC2, and PC3. All data presented are means calculated from triplicate measurements.

Figure 7

Comparative studies of adsorption capacities of MB and AB dyes by raw clay, modified clay, polymer and composites of different compositions PC1, PC2, and PC3. All data presented are means calculated from triplicate measurements.

Close modal

From Figure 7, it is clearly evident that the most elevated adsorption capacity was obtained for both MB and AB dyes by PC3 composite using the settled parameters. The clay–polymer composites especially PC3 showed great adsorption capacity (5.288 mg/g for MB and 6.696 mg/g for AB) because of the higher porosity and available adsorption sites in the composite structure. For both the dyes, PC3 composite demonstrated significantly higher adsorption capacity compared to raw clay, modified clay, and polymer control. Table 4 compares the MB adsorption efficiency of recently reported polymer-clay based composites. Most of the adsorbents listed in the table show higher adsorption capacity than kaolinite/poly(HEAA-co-MAPTS) composite. However, the values from previous work represent maximum adsorption capacity at optimized conditions. We believe, the adsorption capacity of kaolinite/poly(HEAA-co-MAPTS) composite can be significantly improved upon optimization of process parameters. We did not find any previous study on application of polymer-clay composites for removal of AB dye.

Table 4

Comparison of the MB adsorption capacity/removal percentage of composites with other clay-based composites

DyeAdsorbentsMaximum adsorption capacity (Qmax) (mg/g)Removal percentage (%)Reference
MB Chitosan-kaoline-rich-modified clay beads 2.4 40.60 Biswas et al. (2017)  
Poly(acrylic acid) exfoliated clay composite 162.3 – Rahman et al. (2022)  
Bio-clay-ceramic hybrid composites 43.7 – Sathiyajothi et al. (2024
Bentonite/polydimethylsiloxane composite – 85 Tsekpo et al. (2023)  
Magnetite nanoparticles/bentonite/polydimethylsiloxane composite – 91 Tsekpo et al. (2023)  
Purified bentonite clay 1,383  Ouaddari et al. (2024)  
Kaolin clay/cellulose composite 291.5  Reghioua et al. (2024)  
Kaolinite/poly(HEAA-co-MAPTS) composite 5.3  Present study 
DyeAdsorbentsMaximum adsorption capacity (Qmax) (mg/g)Removal percentage (%)Reference
MB Chitosan-kaoline-rich-modified clay beads 2.4 40.60 Biswas et al. (2017)  
Poly(acrylic acid) exfoliated clay composite 162.3 – Rahman et al. (2022)  
Bio-clay-ceramic hybrid composites 43.7 – Sathiyajothi et al. (2024
Bentonite/polydimethylsiloxane composite – 85 Tsekpo et al. (2023)  
Magnetite nanoparticles/bentonite/polydimethylsiloxane composite – 91 Tsekpo et al. (2023)  
Purified bentonite clay 1,383  Ouaddari et al. (2024)  
Kaolin clay/cellulose composite 291.5  Reghioua et al. (2024)  
Kaolinite/poly(HEAA-co-MAPTS) composite 5.3  Present study 

Possible adsorption mechanism of composite and dye molecules

The proposed adsorption mechanism of MB and AB by kaolinite/poly(HEAA-co-MAPTS) composite has several kinds of interactions (Figure 8). MB is a cationic dye and composite PC3 showed the better adsorption capacity (5.228 mg/g) compare to other composites (PC1 = 3.56 mg/g, PC2 = 4.316 mg/g). The adsorption capacity steadily increased by increasing polymer percentage and the MB exists within the arrangement as a positive cation. At pH 10.1, hydroxyl groups of clay become deprotonated and create clay –O ion and alkoxysilane is used to go for self-condensation by siloxane bond formation (Aljeboree & Alkaim 2024). However, free silanol has hydroxyl groups on it that can also form SiO ion at high pH. Thus, the positive ions of the cationic dyes are pulled towards the anionic layer of the clay and silane –O whereas polymer draws MB on its –OH groups. So, an increase in adsorption was noted as the rate of polymer increased within the composite. On the other hand, AB is an anionic dye and composite PC3 showed the better adsorption capacity (6.696 mg/g) compare to other composites (PC1 = 5.45 mg/g, PC2 = 6.42 mg/g). At pH 4.0, amine groups of the modified clay become protonated and create clay–, which reacts with the negative ions () of the anionic dye, AB. Moreover, the hydrogen bonding dipole-dipole interactions were present among free hydrogen of the composite with nitrogen in the structure of AB. Finally, in case of both dyes, n-π interaction occurs among the electron donating groups of the composite surface and the π system in the aromatic ring of MB and AB dyes.
Figure 8

Possible adsorption mechanism of kaolinite/poly(HEAA-co-MAPTS) with MB and AB dye molecules.

Figure 8

Possible adsorption mechanism of kaolinite/poly(HEAA-co-MAPTS) with MB and AB dye molecules.

Close modal

Bijoypur clay and polymer can be successfully utilized to fabricate polymer-clay based composites. FT-IR, TGA, XRD and SEM analyses confirmed the successful formation of the composites. The composite material demonstrated enhanced properties compared to its component materials. Higher percentage of polymer in the composite materials enable them to exhibit better morphological and adsorption properties. The composites were applied as adsorbent for the removal of hazardous dyes such as MB and AB. Among raw clay, modified clay, polymer and all the prepared composites, the composite with higher polymer percentage (4 wt%) showed higher porosity and hence, exhibited maximum adsorption capacity of 5.288 mg/g for MB (cationic dye) and 6.696 mg/g for AB (anionic dye), respectively. The inorganic-organic combination and moieties of components of the composite enabled the successful adsorption of both cationic dyes and anionic dyes from the aqueous medium. As most of the industrial effluents contain different types of dyes at the same time, development of this composite opens up great opportunity for the removal of different dye molecules from the industrial effluent, especially when both cationic and anionic dyes are present in the effluent. For better understanding of detailed adsorption performance and efficacy of the composite, further investigations on (i) optimization of the process parameters, (ii) adsorption isotherm and kinetics, (iii) removal efficiency from a mixture of both the dyes, (iv) dye removal from real industrial wastewater, (v) recyclability of the composite, and (vi) computational approach on the composite to quantify the structure–activity relationship are crucial.

The research work receives no funding from any source.

The authors have no conflict of interest.

All relevant data are included in the paper or its Supplementary Information.

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