Optimizing of malachite green extraction from aqueous solutions using hydrophilic and hydrophobic nanoparticles

Highlights

• The SiO₂ hydrophobic nanoparticle caused to improved stability of the SLM system.

• Optimum values of parameters include pH, feed concentration and carrier was determined.

• Hydrophilic TiO₂ and hydrophobic SiO₂ nanoparticles in liquid membrane were evaluated.

Abstract

In this study, malachite green (MG) dye extraction was investigated using the supported liquid membrane (SLM) from the aqueous solution. Response surface methodology (RSM) based on the central composite design (CCD) was performed for determining the optimum of operating parameters include pH, feed concentration, and carrier. Extraction percentage of MG after 10 h in optimum condition, feed phase pH of 6, feed concentration of 135.1 mg/ml, and carrier of 21.91%v/v is 93.15%. Influence of presence hydrophilic TiO₂ and hydrophobic SiO₂ nanoparticles were investigated on extraction percentage and stability of the system. The hydrophilic TiO₂ nanoparticles have a negative effect on the SLM and decreased extraction percentage of MG dye and stability of the SLM. The SiO₂ hydrophobic nanoparticle caused to improved stability of the SLM system and increased the MG dye extraction percentage. Under optimal operating conditions, loading of the SiO₂ hydrophobic nanoparticles to 5 mg/ml, the stability of the system, and MG dye extraction efficiency were obtained 99.07% and 70 h, respectively.

Introduction

In the past decades, dyes are used in various parts of the industry, such as textile, cosmetics, dyeing, paper, plastic, and food crafts, since the wastewater of these industries contains a large amount of dye pollutants [1]. The presence of dye in water sources prevents the penetration of light. So it prevents biological processes and damages aquatic communities on the ecosystem [2,3]. Dyes are divided into three groups based on their charge in solutions, which include cationic, anionic, and non-ionic [4,5]. MG is a cationic dye and mainly has been used in order to dyeing the wool, silk, and leather in the textile industries, dyeing the Food and food additives in the food industries and as an antiseptic in the medical and fish breeding industries [6]. However, there are reports that the fish treated with the MG dye have been adverse effects on the immune system and reproductive system for consumers [7]. MG is a toxic substance due to its genetic, mutagenic, and carcinogenic properties, which have undesirable effects on the liver, nervous, intestine, gonads, and pituitary gonadotropic cells [8]. There are various methods for separating dyes from an aqueous solution that is generally divided into three groups, physical, chemical, and biological groups. The physical methods include adsorption, membrane processes, liquid-liquid extraction, ion exchange, electro synthetic coagulation and irradiation, chemical methods including Fenton, photochemical, electrochemical degradation, and zonation and biological methods including aerobic decomposition and anaerobic degradation [[9], [10], [11], [12]].

In recent years, membrane processes as a valuable technology have attracted the attention of many different industries. SLM has been highly regarded for its features, such as low cost and easy maintenance, low energy consumption, single-stage mass transfer, high selectivity, and easy use [13]. According to reports, generally in the liquid membranes, solvents such as alcohols, alkanes, ketones, which due to their toxicity caused environmental problems, has been used. Therefore, natural oil has been studied for its benefits such as cheap, non-toxic, and environmentally friendly. Studies have shown that sunflower oil, coconut oil, and palm oil can be used as solvents for dye separation [[14], [15], [16]]. G. Muthuraman et al. for the removal of Rhodamine B from aqueous solutions with the use of the SLM have been used natural oils (sunflower, coconut, and palm) as solvent [17]. They found that palm oil had better results. In another research, Kazemi et al. for methylene blue removal were used of mixture D2EHPA/M2EHPA as the carrier and sesame oil as the diluent in the SLM process [18]. Hajarabeevi et al. studied transfer cationic dyes using carrier D2EHPA and coconut oil as liquid membranes [19]. To investigate the effect of diluent for removal cationic dye, G.muthuraman et al. have been used toluene, kerosene, and coconut oil as the diluent, and they observed that coconut oil has more permeable [20].

Although the SLM has been extensively investigated on a laboratory scale, its industrial application is finite due to the instability of the membrane. Possible reasons of the membrane instability include blockage of the pores, wetting of the pores, pressure difference in the membrane, reduction in diluent and carrier concentration, dissolution the organic phase of the membrane in the feed or strip phases, emulsifier of membrane phase due to shearing force and osmotic pressure in the interface membrane [13,21]. Kumar et al. performed different techniques for improving the SLM stability in the removal of phenol. These techniques include adding the electrolyte or surfactant in the liquid membrane and covering an extra layer gel of polymeric to decrease the emulsification [22]. Kazemi et al. reported that in the SLM system for phenol extraction, the stability increases with salt concentration enhancement in the feed phase, and the stability decreased by increasing of carrier and NaOH in phase strip [23].

Another problem that SLM systems face is the wetting of the pores of the membranes in contact with the aqueous solution, which can be resolved by the creation of superhydrophobic surfaces. [24]. Recently, nanotechnology has been widely used in various processes. Scientists are thoroughly studying the physical properties and applications of various forms of nano-sized materials [25,26]. In some studies, they have investigated the effect of the presence of nanoparticles on liquid-liquid extraction [27,28]. Tehrani and Rahbar-Kelishami were performed hydrophobic and hydrophobic effects using SLM extraction of gadolinium (III) with TiO₂ and SiO₂ nanoparticles and reported that the hydrophobic SiO₂ nanoparticles increased the rate of mass transfer [29]. Mahdavi et al. studied the effect of loading of the TiO₂, hydrophilic ZnO, Fe₃O_4, and hydrophobic ZIF-8 nanoparticles in the liquid membrane for removal of Rhodamine B and methylene blue dyes by SLM. They reported that the hydrophobic ZIF-8 and Fe₃O₄ nanoparticles increase the extraction of dyes. Also, the separation of the dyes was performed further by ZIF-8 nanoparticles due to their more porous structure. [30].

In this study, using the SLM process, and the mixture of vegetable oil and D2EHPA/M2EHPA as a liquid membrane, removal of MG dye from aqueous solution was investigated. RSM determined the optimum conditions for dye extraction. In the following, the presence of hydrophobic and hydrophobic nanoparticles at different concentrations of the liquid membrane on the stability of the SLM system and percentage of dye extraction were investigated.