ABSTRACT
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.
HIGHLIGHTS
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.
INTRODUCTION
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.
EXPERIMENTAL
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))
Preparation of composites with varying polymer percentages
Name of composites . | Variation in weight . | |
---|---|---|
Polymer (wt. %) . | Clay (wt. %) . | |
PC1 | 1% | 1% |
PC2 | 2% | 1% |
PC3 | 4% | 1% |
Name of composites . | Variation in weight . | |
---|---|---|
Polymer (wt. %) . | Clay (wt. %) . | |
PC1 | 1% | 1% |
PC2 | 2% | 1% |
PC3 | 4% | 1% |
Schematic representation of the preparation of (kaolinite/poly(HEAA-co-MAPTS) composite.
Schematic representation of the preparation of (kaolinite/poly(HEAA-co-MAPTS) composite.
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 –
Adsorption studies
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.
RESULTS AND DISCUSSION
FT-IR spectroscopic analysis
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).
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).
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
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).
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).
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
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).
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).
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
SEM images of kaoline/poly(HEAA-co-MAPTS), composites (a) PC2 and (b) PC3.
Adsorption study
Calibration curve of MB and AB- dye
Calibration curve of MB and AB. All data presented are means calculated from triplicate measurements.
Calibration curve of MB and AB. All data presented are means calculated from triplicate measurements.
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.
Optimum conditions of adsorption for MB and AB-dyes
Parameter . | Value . | |
---|---|---|
MB . | AB . | |
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 |
Parameter . | Value . | |
---|---|---|
MB . | AB . | |
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
Adsorption results from UV-vis spectrum for MB and AB adsorption
Sample . | MB . | AB . | ||
---|---|---|---|---|
Conc. (ppm) . | Absorbance . | Conc. (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 |
Sample . | MB . | AB . | ||
---|---|---|---|---|
Conc. (ppm) . | Absorbance . | Conc. (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.
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.
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.
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.
Comparison of the MB adsorption capacity/removal percentage of composites with other clay-based composites
Dye . | Adsorbents . | Maximum 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 |
Dye . | Adsorbents . | Maximum 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


Possible adsorption mechanism of kaolinite/poly(HEAA-co-MAPTS) with MB and AB dye molecules.
Possible adsorption mechanism of kaolinite/poly(HEAA-co-MAPTS) with MB and AB dye molecules.
CONCLUSIONS
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.
FUNDING DECLARATION
The research work receives no funding from any source.
CONFLICT OF INTEREST
The authors have no conflict of interest.
DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.