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Home > Design of ZIF(Co & Zn)@wool composite for efficient removal of pharmaceutical intermediate from wastewater
Design of ZIF(Co & Zn)@wool composite for efficient removal of pharmaceutical intermediate from wastewater
Reda M. Abdelhameed, Hossam E. Emam
1. Introduction
One of the global environmental problems faced human is water pollution, especially in developing countries and the most polluted water results from the presence of toxic synthetic organic compounds. Pollution of water by organic contaminants are particularly happened by discharging of such contaminants during the industrial production processes or as a result of spraying crops with pesticides [1]. Both human health and ecosystem are directly affected by the toxic and deleterious impacts of such organic pollutants. Therefore, there has been in recent a growing interest to find effective solutions and techniques for treating the contaminated water or chemical wastewater.
Many published researches have been interested in the elimination of organic pollutants from the wastewater using different remediation techniques [6–14]. Among the used techniques, sorption is the most promising and extensively applied technique for removing pollutants in general from the environment because of several advantages presented in simplicity, energy-saving, cost-effectiveness and efficiency [5,6,15,16]. Many adsorbents including fly ash, carbon nanotubes, bentonite, clay, charcoal, activated carbon, agricultural wastes, composites, and grafted polymer, are reported in the literature for adsorption of organic pollutants from contaminated wastewater.
Owing to the exceedingly existence in the industrial wastewater and drinking water, naphthols (1-naphthol & 2-naphthol) are considered as one type of the contaminants which have the top priority to be eliminated from the environmental water [1,17,21]. Naphthols as ionized aromatic compounds are more reactive than phenol and they are very toxic to aquatic organisms and human beings.
Several published studies have been concerned with removing naphthols from wastewater [1,17,18,21,23–25,33–41] and some of them are interested in 2-naphthol adsorption. But the way still open for further working in the 2-naphthol removing using new materials and extensive works in such area are needed to overcome the difficulties in the application of the applied adsorbents and to increase
the adsorption capacity.
To achieve the effective adsorption, adsorbents based on porous materials were widely used [42,43]. One from the highly porous
materials are metal-organic frameworks (MOFs) which are consisted of metal ions as inorganic species and organic linkers [44–46].
Therefore, MOFs were excessively applied in environmental applications which interested in separation and adsorption of organic materials [6,15,46–48]. However, using such MOFs in the removal of naphthols from water was not largely studied. In accordance with our
information, a few works were published for the removal of 1-naphthol from wastewater by using zeolitic imidazole frameworks (ZIF-67) as MOF [38]. While no studies were considered for the employment of MOF based materials in the elimination of 2-naphthol. Moreover, the applicability of MOFs as adsorbent is still limited and hence the incorporation of MOFs inside applicable material such like fabric is quite interesting in order to combine the high adsorption properties and applicability together in a single product.
Consequently, the current study concerns the preparation of zeolitic imidazole frameworks (ZIF)@wool fabric as an easily applicable composites in order to the effective removal of 2-naphthol from wastewater. The ZIF@wool fabric composites were prepared by direct formation of different ZIFs (ZIF-8 and ZIF-67) within wool fabric networks. The produced composites were well characterized using X-ray diffraction, infrared spectroscopy, scanning electron microscope, and energy dispersive X-ray. The colorimetric data and materials contents (ZIF/M+2) were both measured for ZIF@wool fabric composites. After confirmation of the successful preparation, composites were applied in the removal of 2-naphthol from water. The adsorption process was systematically evaluated by studying the adsorption kinetics and isotherm. As an important indicator for the applicability, the regeneration and reusing of the ZIF@wool fabric composites were tested.
2. Experimental
2.1. Chemicals and materials
Co(NO3)26H2O (98%, from Merck), Zn(NO3)26H2O (99%, from Merck), 2-naphthol (98%, from Aldrich), methanol (absolute, from Fluka), 2-methylimidazole (99%, from Merck) and ethanol (absolute, from Fluka) were obtained from Aldrich and were all used without any purification. Pure Australian merino scoured woven 100% wool fabrics (210 g/m2), were provided by Misr Company for Spinning and Weaving, El-Mahalla El-Kobra – Egypt. To remove the impurities, wool fabrics were washed with a solution containing 2 g/L non-ionic detergent (Hostapal CV, Clariant) for 30 min at 50 C using 1:50 material to liquor ratio. Afterward, fabrics were rinsed with tap water and then dried on-air at RT.
2.2. Preparation methods
2.2.1. Synthesis of ZIF(Zn & Co)
Zeolitic imidazole framework-8 (ZIF-8) and Zeolitic imidazole framework-67 (ZIF-67) were prepared according to the reported procedure with a little modification [49,50]. ZIF-8 and ZIF-67 were both prepared by individual addition of Zn(NO3)26H2O (4 mmol) and Co(NO3)26H2O (4 mmol), respectively to 100 mL methanol containing 16 mmol of 2-methylimidazole. Mixtures were vigorously stirred at room temperature for 24 h. The formed solids (white for ZIF-8 and purple for ZIF-67) were separated by centrifugation and washed several times with methanol and ethanol, respectively. Then the solids were dried on oven overnight at 75 C prior to analysis and characterization.
2.2.2. Preparation of ZIF(Zn & Co)@wool composites
Two different composites based on type of ZIFs (ZIF-8; Zn & ZIF-67; Co) were prepared by direct formation of ZIFs within the wool fabrics matrix. Typically, three different solutions (A, B, C) were separately prepared. A 0.758 g Zn(NO3)26H2O and 0.733 g of Co (NO3)26H2O were individually dissolved in 50 mL of methanol to prepare a solution (A) and (B), respectively. In solution (C), a 1.623 g of 2 methyl imidazole was dissolved in 50 mL methanol.
Specimens of wool fabric (2 cm 2 cm) were separately submerged in solution (A) and (B) and stirred for 1 h at room temperature. Solution (C) was then rapidly poured on the mixtures (A) and (B) containing fabrics and under continuous stirring for 8 h. The treated wool fabrics were removed, washed three times with methanol and then dried under vacuum at 60 C for 12 h prior to characterization and application. The prepared samples were named as ZIF-8@wool fabric and ZIF-67@wool fabric composites for samples merged in solution (A) and (B), respectively.
2.3. Characterization
The XRD pattern for wool, ZIF and ZIF@wool fabric composites
were recorded at room temperature by a PANalytical diffractometer (Reflection, Spinner mode, Cu Ka radiation, 45 kV, 40 mA, and
k = 1.5406 Å) using the EMPYREAN system. The diffraction angle was measured in the range of 3.5–50 with a scanning rate of 1 s and a step
size of 0.03.
The attenuated total reflection – Fourier transform infrared spectroscopy (ATR-FTIR) was applied to investigate wool, ZIF, ZIF@
wool fabric composites, 2-naphthol, and 2-naphthol@ZIF@wool fabric composites by using the absorption mode. Samples were conducted to ATR-FTIR spectroscopy (Mattson 5000 FTIR spectrometer) and the spectra were measured in the wavenumber range of 4000–400 cm1.
The surface structure of ZIF@wool fabric composites were examined by using a scanning electron microscope (SEM, Hitachi
SU-70) operated at an accelerating voltage of 200 kV at room temperature. The elemental analysis was detected by an energy dispersive X-ray spectrometer (EDX) equipped with a microscope.
The color measurements data represented in color coordinates(L, a*, b*), color strength (K/S) and absorbance, were recorded for wool and ZIF@wool fabric composites with a spectrophotometer with pulsed xenon lamps as light source (UltraScan Pro, Hunter Lab, USA). The equipment was adjusted using 10 observers with D65 illuminant, d/2 viewing geometry, and 2 mm measurement area. Color coordinates L*, a*, and b* are refereed to lightness from black to white (0–100), the ratio of red (+)/green () and the ratio of yellow (+)/blue () [45,51]. Three measurements were recorded for each sample at three independent areas and the average values were considered.
The contents of ZIF (Zn & Co) within wool fabrics were measured through the isolation of ZIF from fabrics by ammonia using the method reported in literature [45,46]. Specific weight from composites was submerged in 30 mL of ammonia solution (2.3 M) and stirred for 15 min causing of a complete dissolution of ZIF. Fabric samples were removed, washed three times with tap water and then dried in vacuum. The differences in fabrics’weight between before and after the dissolution process was recorded and the losses in weight of fabrics were indicated to the content of ZIF. By knowing the chemical formula (C8H10N4Zn; C8- H10N4Co) of ZIF, the metal contents (Zn & Co) were estimated.
2.4. Adsorption experiments of 2-naphthol
Stock solution (5000 mg/L) was prepared by dissolving 2-naphthol in deionized water and the required concentration was obtained by further dilution. The adsorption experiments were performed using a static adsorption method to avoid introducing oxygen into the solution during the measurement of samples.
In the experiment of kinetics, 12–15 copies of glass tube contained 250 mg of composite in 50 mL of 2-naphthol solution (100 mg)
were placed in a shaker water bath with a pre-adjusted temperature at 30 C. At a given time point (0.5–60 h), one of the glass tube
was opened and the pure solution was carefully taken by syringe to be analyzed. Isotherm study was performed for 2-naphthol concentrations ranged in 0–5000 mg/L. The residual concentration of 2-naphthol was determined by an ultraviolet-visible (UV–Vis)
spectroscopy (TU-1810, Persee Co., China) at the wavelength of 292 nm.
To investigate the reusability, the composite after the adsorption step was soaked in ethanol/acetic acid (99/1, v/v) solution for
48 h in the desorption process. Afterward, the composite was collected by filtration and dried at 75 C prior to be applied in the
higher regeneration cycles.
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