Abstract
Hazardous chemicals like toxic organic dyes are very harmful to the environment and their removal is quite challenging. Therefore there is a necessity to develop techniques, which are environment friendly, cost-effective and easily available in nature for water purification and remediation. The present research work is focused on the development` and characterization of the ecofriendly semi-interpenetrating polymer network (semi-IPN) nanocomposite hydrogels composed of polyvinyl alcohol (PVA) and alginate (Alg) hydrogel beads incorporating natural bentonite (Bent) clay as a beneficial adsorbent for the removal of toxic methylene blue (MB) from aqueous solution. PVA−Alg/Bent nanocomposite hydrogel beads with different Bent content (0, 10, 20, and 30 wt%) were synthesized via external ionic gelation method. The designed porous and steady structure beads were characterized by the use of Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX), and scanning electron microscopy (SEM). The performance of the beads as MB adsorbents was investigated by treating aqueous solutions in batch mode. The experimental results indicated that the incorporation of Bent (30 wt%) in the nanocomposite formulation sustained the porous structure, preserved water uptake, and increased MB removal efficiency by 230% compared to empty beads. Designed beads possessed higher affinity to MB at high pH 8, 30 °C, and fitted well to pseudo-second-order kinetic model with a high correlation coefficient. Moreover, the designed beads had good stability and reusability as they exhibited excellent removal efficiency (90%) after six consecutive adsorption-desorption cycles. The adsorption process was found be combination of both monolayer adsorption on homogeneous surface and multilayer adsorption on heterogeneous surface. The maximum adsorption capacity of the designed beads system as calculated by Langmuir isotherm was found to be 51.34 mg/g, which is in good agreement with the reported clay-related adsorbents. The designed semi-IPN PVA−Alg/Bent nanocomposite hydrogel beads demonstrated good adsorbent properties and could be potentially used for MB removal from polluted water.
Highlights
Methylene blue (MB) is a well-known cationic phenothiazine dye, with versatile industrial applications in the textile, leather, plastics, paper and cosmetics industry and used as a biological stain and photosensitizer in photodynamic therapy [1–7]
Numerous different adsorbents have been synthesized such as activated carbons [21,22], porous ceramics [23,24], metal oxides [25], and polymeric hydrogels [26–30] for the remediation of contaminated water
The chemical composition of the Bent, polyvinyl alcohol (PVA)-Alg control hydrogel and PVA-Alg/Bent nanocomposite hydrogel were analyzed by Fourier transform infrared spectroscopy (FTIR) spectroscopy using a Spectrum Two FT-IR spectrometer (Perkin-Elmer, Waltham, MA, USA)
Summary
Methylene blue (MB) is a well-known cationic phenothiazine dye, with versatile industrial applications in the textile, leather, plastics, paper and cosmetics industry and used as a biological stain and photosensitizer in photodynamic therapy [1–7]. Various conventional physicochemical techniques have been proposed and introduced for the purification of toxic dyes from water from including photocatalysis, chemical oxidation, ozonation, membrane filtration, coagulation and flocculation, as well as adsorption [13–17]. Among all of these techniques, the adsorption method is employed, fast and highly efficient [18–20]. Numerous different adsorbents have been synthesized such as activated carbons [21,22], porous ceramics [23,24], metal oxides [25], and polymeric hydrogels [26–30] for the remediation of contaminated water From both an environmental and industrial point of view, an ideal adsorbent should have large surface area, porous structure, available active functional sites, high mechanical stability and strength, as well as low cost and be eco-friendly [31,32]
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