PDMAEMA grafted microspheres as an efficient adsorbent for the removal of Sunset yellow from pharmaceutical preparations, beverages and waste water

Highlights

• A novel adsorbent is proposed as a support for Sunset yellow (SY) removal.

• An efficient extraction of SY with a high adsorption capacity.

• The adsorption data best fitted with Langmuir and pseudo-second order models.

• The polymer was applied for the removal of SY dye in beverages and pharmaceutical preparations.

• The absorbent is of great reusability and can be reused by at least five times.

Abstract

Sunset yellow (SY) dye removal in the beverages, waters and pharmaceutical preparations is of great importance due to its negative side effects. In this context, a new and efficient adsorbent, PDMAEMA grafted PS-DVB-VBC microspheres were synthesized and applied for the adsorption of SY dye. The morphology, chemical and physical properties of the proposed adsorbent was fully characterized using scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), elemental and Brunauer–Emmett–Teller (BET) surface area analysis. The adsorption performance of the adsorbent was investigated systematically, including the influence of pH, contact time, adsorbent dose, adsorption isotherms, adsorption kinetics, and reusability. The optimized conditions of the SY towards the sorbent were as follows: pH of 2.0, contact time of 40.0 min, adsorbent dose of 0.4 g L⁻¹ at 25 °C. The equilibrium adsorption process followed the Langmuir isotherm model with a maximum adsorption capacity of 312.5 mg g⁻¹. Pseudo-second-order kinetic model was found to be most appropriate to define the adsorption of SY dye onto the adsorbent. The quantitative results (96.3–103%) obtained for the real samples (beverages, pharmaceutical preparation and synthetic waste water) confirmed the high performance, feasibility and efficacy of the novel method. The uptake of SY dye was high (>90%) even after recycling five times indicating that the adsorbent could be regenerated and reused in practical applications.

Introduction

Contamination caused by synthetic dyes is an important problem that should be considered by the human beings [1], [2], [3]. Sunset yellow (Yellow 6, E 110 or SY) is a food dye providing a yellow-orange color that is added to the fruit juices, candies, jelly sweets, dairy products, pharmaceuticals and beverages to improve the texture of foods [4]. It is especially added to beverages to improve and preserve color during the storage or/and production of the soft drinks. Moreover, the addition of SY provides several improvements such as color uniformity, high stability to oxygen, light and pH, relatively lower production costs and low microbiological contamination in the beverages, food or pharmaceutical preparations [5]. Nevertheless, the excessive intake of SY may cause several side effects, including nasal congestion, kidney tumors, abdominal pain, chromosomal damage, hyperactivity, diarrhea, severe weight loss and allergies [6]. The acceptable daily intake (ADI) value of SY in non-alcoholic beverages was reported to be between 0 and 2.5 mg kg⁻¹ [7]. As SY is a mono-azo disulfonated hydroxyl dye and possesses aromatic ring and azo (N = N) functional group, the presence of SY in the industrial effluents, food, beverages and pharmaceutical preparations must be controlled [8].

Many technologies, including flocculation, liquid-liquid extraction, (bio)adsorption, and membrane filtration have been utilized for the removal of SY from food samples, effluents, pharmaceutical preparations and beverages [9], [10], [11], [12], [13]. Among these techniques, adsorption was stated to be superior to other techniques due to its high versatility, efficiency, relatively high cost, effectiveness with no secondary pollution [14], [15], [16], [17]. The preparation of an effective adsorbent for SY removal is a challenging demand to protect both environment and human health. For this purpose, several materials were applied such as polyurethane foam, activated carbon, modified silica, and chitosan etc. [18], [19], [20], [21] Polymers are reported to be excellent adsorbents in terms of remarkable adsorption ability, flexibility, simplicity in design and ease of use [22], [23], [24].

In the present study, an effective adsorbent was synthesized in two steps. First, chloro methyl functional dense crosslinked PS-DVB-VBC (polystyrene-co-divinyl benzene-co-vinyl benzyl chloride) microbeads were synthesized by suspension polymerization. After, chloromethyl group substitution of morpholine dithiocarbamate group PDMAEMA (polydimethyl aminoethyl methacrylate) hairy brushes were tethered to the surface of the microbeads via surface initiating polymerization (SIP) method. It is known that the functionalization of the adsorbents with the amine groups is an attractive choice extending the potential application of the polymers in the adsorption studies [25]. From this point of view, it was aimed to synthesize a powerful and efficient adsorbent owing tertiary amine groups and apply for the adsorption of SY dye in the beverages, waste water and pharmaceutical preparations. The novelty of this work premises on the coexistence of many properties on one material as an adsorbent through the design of PDMAEMA grafted crosslinked microspheres. In this perspective, crosslinked nature of the material yields easy handling during the whole process. The whole chemicals used for obtaining the microbeads with poly(DMAEMA) hairy brushes are cheap and commercially available. The applied suspension polymerization technique for creating the microbeads are industrial processes and have lots of advantages such as easy heat transfer and capable of large scale production. Next, the dense crosslinked microspheres have strong and inert structure which provides long-life. Last, poly(DMAEMA) hairy brushes on the microspheres provide flexibility and pseudo-homogeneous behavior of the active tertiary amine groups and compatibility with the aqueous environment. The microbeads with poly(DMAEMA) hairy brushes were successively utilized for the removal of Sunset yellow (SY) dye with high adsorption capacity. All these features and the dye binding results, make the microsphere a commercial recyclable and long-life candidate for binding anionic dyes with a good competitive price-to-performance ratio.

The physicochemical properties of the adsorbent (elemental composition, microstructure, surface morphology etc.) were examined in detail with various techniques viz., scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), elemental and Brunauer–Emmett–Teller (BET) surface area analysis to control the success of polymerization process. The affinity of the proposed adsorbent towards Sunset yellow dye was investigated in aqueous solutions and the dependency of the adsorption process on pH, contact time and adsorbent dosage were determined. The adsorption kinetics and isotherms were examined to evaluate the mechanism of the adsorption process and understand relationship between the adsorbate/adsorbent at equilibrium.