Design of ZIF(Co & Zn)@wool composite for efficient removal of pharmaceutical intermediate from wastewater

Journal of Colloid and Interface Science 552 (2019) 494–505

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Regular Article

Design of ZIF(Co & Zn)@wool composite for efficient removal of pharmaceutical intermediate from wastewater Reda M. Abdelhameed a,⇑, Hossam E. Emam b,⇑ a

Applied Organic Chemistry Department, Chemical Industries Research Division, National Research Centre, Scopus affiliation ID 60014618, 33 EL Buhouth St., Dokki, Giza 12622, Egypt Department of Pretreatment and Finishing of Cellulosic based Textiles, Textile Industries Research Division, National Research Centre, Scopus affiliation ID 60014618, 33 EL Buhouth St., Dokki, Giza 12622, Egypt b

g r a p h i c a l a b s t r a c t

a r t i c l e

i n f o

Article history: Received 10 March 2019 Revised 21 May 2019 Accepted 24 May 2019 Available online 25 May 2019 Keywords: 2-naphthol Wool ZIF-8 ZIF-67 Adsorption Recycling

a b s t r a c t Removal of naphthols, as one of the most common pharmaceutical intermediates which released in the wastewater, is in the top priority for the time being. In the current study, zeolitic imidazole frameworks (ZIF-8, Zn & ZIF-67, Co) were directly prepared within the matrix of wool fabric to remove 2-naphthol from water. The ZIF@wool fabric composite was firstly prepared and then characterized by X-ray diffraction, infrared spectroscopy, electronic microscope and energy dispersive X-ray. The material contents within wool were measured to be 118.3–128.8 mg/g for ZIF and 31.5–33.0 mg/g for M+2 (Zn & Co). The as-prepared composites were applied in the removal of 2-naphthol from water. Adsorption of 2-naphthol onto composites was followed to pseudo-first order kinetic model and the rate of adsorption was speeded up two times after incorporation of ZIF inside wool. Adsorption data were fully obeyed to Langmuir isotherm and the maximum adsorption capacity was extremely enlarged from 197.1 mg/g for wool to 371.2–391.1 mg/g for ZIF@wool composite, attributing to the increment in active binding sites. By regeneration for 4 cycles, the adsorption capacities of composites was reduced by only 8–9%. It is hypothesized that, the as-synthesized ZIF@wool fabric composite is a highly applicable adsorbent composite and could be safely applied in removing of 2-naphthol with the capability for the recycling. Ó 2019 Elsevier Inc. All rights reserved.

1. Introduction ⇑ Corresponding authors. E-mail addresses: [email protected] (R.M. Abdelhameed), hossamelemam@ yahoo.com (H.E. Emam). https://doi.org/10.1016/j.jcis.2019.05.077 0021-9797/Ó 2019 Elsevier Inc. All rights reserved.

One of the global environmental problem faced human is the water pollution, especially in the developing countries and the most polluted water results from the presence of the toxic

R.M. Abdelhameed, H.E. Emam / Journal of Colloid and Interface Science 552 (2019) 494–505

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 of 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 [1–6]. 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 of pollutants in general from environment because of several advantages presented in simplicity, energy saving, costeffectiveness and the 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 literature for adsorption of organic pollutants from contaminated wastewater [1,6,15,17–32].

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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 [17,21]. 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 application of the applied adsorbents and to incrbease the adsorption capacity. To achieve the effective adsorption, adsorbents based on porous materials were widely used [42,43]. One from the highly porous materials is 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

Fig. 1. Formation mechanism of ZIF(Zn & Co) within wool fabric.

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materials [6,15,46–48]. However, using of such MOFs in removal of naphthols from water was not largely studied. In accordance to our information, a few works were published for removal of 1naphthol from wastewater by using zeolitic imidazole frameworks (ZIF-67) as MOF [38]. While, no studies were considered for employment of MOF based materials in elimination of 2naphthol. Moreover, the applicability of MOFs as adsorbent are still limited and hence 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 [6,15,16,46]. Consequently, the current study concerns with 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 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

(NO3)2
6H2O were individually dissolved in 50 mL of methanol to prepare solution (A) and (B), respectively. In solution (C), a 1.623 g of 2-methylimidazole 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 EMPYREAN system. The diffraction angle was measured in the range of 3.5–50° with scanning rate of 1 s and 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)

[a]

2.1. Chemicals and materials ZIF-8@Wool

Intensity (a.u.)

Co(NO3)2
6H2O (98%, from Merck) , Zn(NO3)2
6H2O (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-Mehalla El-Kobra – Egypt. To remove the impurities, wool fabrics were washed with a solution containing 2 g/L nonionic detergent (Hostapal CV, Clariant) for 30 min at 50 °C using 1:50 material to liquor ratio. Afterwards, fabrics were rinsed with tap water and then dried on air at RT.

Wool

ZIF-8 5

10

15

20

25

30

35

40

45

50

2 Theta degree

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)2
6H2O (4 mmol) and Co(NO3)2
6H2O (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 & ZIF67; Co) were prepared by direct formation of ZIFs within wool fabrics matrix. Typically, three different solutions (A, B, C) were separately prepared. A 0.758 g Zn(NO3)2
6H2O and 0.733 g of Co

[b]

ZIF-67@Wool

Intensity (a.u.)

2.2. Preparation methods

Wool

ZIF-67 5

10

15

20

25

30

35

40

45

50

2 Theta degree Fig. 2. X-ray diffraction patterns for ZIF, wool fabric and ZIF@wool fabric composites; [a] ZIF-8 and [b] ZIF-67.

R.M. Abdelhameed, H.E. Emam / Journal of Colloid and Interface Science 552 (2019) 494–505

and the spectra were measured in the wavenumber range of 4000– 400 cm 1. 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 the 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° observer 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 tab water and then dried in vacuum. The differences in fabrics’ weight between before and after dissolution process were

497

recorded and the losses in weight of fabrics were indicated to the content of ZIF. By knowing the chemical formula (C8H10N4Zn; C8H10N4Co) 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 2naphthol in deionized water, and the required concentration was obtained by further dilution. The adsorption experiments were performed using a static adsorption method to avoid the introducing oxygen into the solution during the measurement of samples. In 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 analysed. 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 wavelength of 292 nm. To investigate the reusability, the composite after adsorption step was soaked in ethanol/acetic acid (99/1, v/v) solution for 48 h in the desorption process. Afterwards, the composite was collected by filtration and dried at 75 °C prior to be applied in the higher regeneration cycles.

Fig. 3. FTIR spectrum for ZIF, wool fabric and ZIF@wool fabric composites; [a] ZIF-8 and [b] ZIF-67. The magnified spectra inserted in the right side.

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Fig. 4. Microscopic images and EDX analysis for ZIF@wool fabric composites; [a] ZIF-8 and [b] ZIF-67.

Table 1 Contents of materials (metals & ZIF) and colorimetric data for untreated wool and ZIF@wool fabric composites. Fabric

ZIF Content (mg/g)

Zn Content (mg/g)

Co Content (mg/g)

L*

a*

b*

K/S (580 nm)

Abs (580 nm)

Wool ZIF-8@Wool ZIF-67@Wool

0.00 128.8 ± 12.5 118.3 ± 14.5

0.00 33.0 ± 3.6 –

0.00 – 31.5 ± 3.9

81.51 ± 0.21 82.51 ± 0.31 50.15 ± 0.07

1.04 ± 0.06 1.66 ± 0.02 21.97 ± 0.51

7.23 ± 0.01 7.13 ± 0.2 47.21 ± 0.17

0.13 ± 0.01 0.12 ± 0.01 7.35 ± 0.37

0.22 ± 0.01 0.21 ± 0.01 1.22 ± 0.01

R.M. Abdelhameed, H.E. Emam / Journal of Colloid and Interface Science 552 (2019) 494–505

3. Results and discussion 3.1. ZIF(Zn & Co)@wool fabric composites Two ZIFs containing different metal centers (Zn & Co) were directly grown within wool fabric matrix to prepare two different composites namely; ZIF-8@wool fabric and ZIF-67@wool fabric, respectively. Composites of ZIF@wool fabrics were synthesized by mixing the metal salts and organic ligand of 2-methyl imidazole in the presence of wool fabrics which exhibit various functional groups for potential interactions with metal ions (Zn & Co) and 2-methyl imidazole. As displayed in Fig. 1, the negative groups of wool fabrics (OH, SH and NH) act as active sites for binding with metal ions (Zn & Co) via electrostatic/coordination bond and with 2-methyl imidazole via hydrogen bonding [6,15,16,45,46]. Owing to its several binding sites, wool fabric can serve as a mixed linker and participate in the interaction with metal ions (Zn & Co) instead of 2-methyl imidazole [6,15,16,45,46]. Metal ions can bind with NH of imidazole from a side and with the functional groups of wool from the other side. The prepared composites were characterized by using X-ray diffraction (XRD), infrared (FTIR) and scanning electron microscope (SEM). The diffraction of X-ray was applied for ZIF powder, wool fabrics and ZIF@wool fabric composites, and the diffraction data were presented in Fig. 2. For ZIF powder, four diffraction patterns were

499

appeared at 2h = 7.4°, 10.4°, 12.8° and 18.1°. These diffraction peaks are characteristic for ZIF (8 & 67) and matched with the previous published data [49,50]. Two broad diffraction peaks were recorded for wool fabric at 2h = 9.2° and 20.2° [15]. In case of composites (ZIF@wool fabric), all diffraction peaks of ZIF were notably recorded which confirmed the formation of ZIF within the matrix of wool fabric. The function groups as well as the interaction between ZIF and wool were further emphasized by using FTIR spectra. The FTIR absorbance spectra of wool fabric, ZIF and ZIF@wool fabric composites were presented in Fig. 3. For untreated wool, absorption peaks of NH stretching vibration and NH deformation were appeared at 3276 and 1450 cm 1, respectively. Absorption peaks at 1639, 1533 and 1228 cm 1 were assigned to amide I, II and III, respectively. While absorption peaks at 2958 cm 1 and 1170 cm 1 were corresponding to the aliphatic CAH asymmetric stretching and the aliphatic CAC stretching, respectively [15]. For ZIF ZIFs, the appeared absorption bands at 418, 759–1457, 2908, 2985 and 3679 were associated with Zn-N stretch, entire vibration of imidazole ring, aliphatic CAH, aromatic CAH and bending NAH, respectively [52–54]. In case of ZIF@wool fabric composites, besides the absorption peaks of wool, peaks of M+2–N stretch and entire vibration of imidazole ring were obviously observed at 418, 759–1457. These data are supported the XRD data and further proved the formation of ZIFs inside the wool building units.

Fig. 5. FTIR spectrum for 2-naphthol, ZIF@wool fabric composites and 2-naphthol@ZIF@wool fabric composites; [a] ZIF-8 and [b] ZIF-67. The magnified spectra inserted in the right side.

500

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(C8H10N4Zn for ZIF-8 and C8H10N4Co for ZIF-67), metal contents (Zn and Co) were calculated based on ZIF contents to be 33.0 mg/ g for Zn and 31.5 mg/g for Co. However, ZIF-8@wool fabric composite showed slightly higher contents (ZIF/M+2) compared to that of ZIF-67@wool fabric composite, the differences could be neglected due to its small value by including the standard deviation values. Colorimetric parameters (L*, a*, b*, K/S and Abs) for wool fabrics and composites were summarized in Table 1. The data displayed that, the color of wool fabrics was not changed by incorporation of ZIF-8 attributing to the white color of this type of ZIF. Meanwhile, the direct insertion of ZIF-67 was accompanied by the changing in color from creamy-white to reddish-blue (violet color). The violet was the typical color of ZIF-67 as seen for the powder form of ZIF and this color confirmed the formation of ZIF inside the building units of wool fabrics.

The morphological features and surface structures for ZIF@wool fabric composites were investigated by electron microscope and the micrographs were shown in Fig. 4. It was observed that deposits were diffused on the whole surface of wool fabrics. EDX analyses displayed separated signals for Zn (Fig. 4a) and Co (Fig. 4b) elements besides signals of C, O and S elements for wool structure. These indicate that the deposits onto fabrics were both of ZIF-8 and ZIF-67 which consequently confirmed the immediate formation of ZIFs within wool fabric structure. From micrographs, the wool fibrils were densely enveloped with ZIFs and the shape of ZIF was depended on metal type. Particles like shape was observed for ZIF-8 (Fig. 4a) and ZIF-67 with hexagonal crystalline structure (Fig. 4b) was clearly seen onto wool fabrics. The morphological structure of ZIF (8 & 67) showed on the surface of wool was similar to that reported in literature for their corresponding ZIF [49,50], which is considered as another evidence for successful formation of ZIFs within fabrics. The amounts of metals (Zn & Co) and ZIFs onto the wool fabrics were measured and collected in Table 1. The estimated amounts of ZIFs in the composites were 128.8 and 118.3 mg/g for ZIF-8 and ZIF67, respectively. Considering the chemical formula of ZIFs

[a]

3.2. Removal of 2-naphthol from water The prepared ZIF-8@wool fabric and ZIF-67@wool fabric composites were applied in the removing of 2-naphthol as a pharmaceutical intermediate from water. The untreated wool fabric was used as reference to compare the efficiency of composites. The adsorption of 2-naphthol onto wool fabric and ZIF@wool fabric composites was firstly confirmed by measuring the infrared spectra as presented in Fig. 5. The IR spectrum of 2-naphthol showed various important absorption peaks at 3245, 3050, 1633–1577, 1467, 1371, 742 and 516 cm 1 which are referred to the OAH stretching, aromatic CAH stretching, aromatic C@C, CAH in-plane bending, CAO stretching, CAC in-plane bending, OAH out-ofplane deformation and CAC in-plane deformation, respectively, as assigned in literature [24]. After adsorption of 2-naphthol, all the aforementioned absorption peaks for OAH, CAH, C@C and CAC of 2-naphthol molecule were clearly recorded, confirming the adsorption of 2-naphthol onto wool fabric and ZIF@wool fabric composites.

400 350

Qt (mg/g*h)

300 250 200 150 100

Wool ZIF-8@Wool ZIF-67@Wool

50 0 0

[b]

10

20

30

40

50

3.3. Kinetics of 2-naphthol adsorption

60

Time (hours)

The effect of contact time onto the removal amounts of 2naphthol (Qt, mg/g) from water was studied up to 60 hrs and the results were presented in Fig. 6. For all experiments, the adsorption of 2-naphthol was very fast in the first 10 hrs, followed by forming a plateau shape until reached the equilibrium after 48 hrs. Similar profiles were observed for wool and ZIF@wool composites, but, the composites exhibited considerable higher adsorption contents than wool fabric. The higher affinity of composites is referred to the several binding sites including binding sites of wool and ZIF. After 24 hrs, the adsorbed amounts of 2-naphthol onto ZIF@wool composites were (338.3–356.0 mg/g; 84.6–89.0%) double of that on the wool (172 mg/g; 43.0%). In comparison with ZIF-67@wool fabric composite, relatively higher adsorption capacity was observed for ZIF-8@wool fabrics composites (356 mg/g) which may be related to the higher ZIF content. This further explained the assumption of increment in adsorption capacity by increasing the binding sites within composites. Kinetics for adsorption of 2-naphthol onto wool fabric and ZIF@wool fabric composites were investigated by applying

400 350

Qt (mg/g*h)

300 250 200 150 100

Wool ZIF-8@Wool ZIF-67@Wool

50 0 0

10

20

30

40

50

60

Time (hours) Fig. 6. Effect of contact time on the adsorbed amounts of 2-naphthol.

Table 2 Parameters of Kinetics for adsorption of 2-naphthol onto untreated wool and ZIF@wool fabric composites. Samples

Wool ZIF-8@Wool ZIF-67@Wool

Experimental qe (mg/g)

172.0 ± 6.6 356.0 ± 7.2 338.4 ± 6.3

Pseudo-first order

Pseudo-second order 3

qe (mg/g)

K1  10

189.2 ± 2.8 356.6 ± 3.8 343.1 ± 2.3

47.5 ± 1.6 94.7 ± 2.8 79.5 ± 1.4

(mg/g h)

R2

Chi-square (x2)

qe (mg/g)

K2  10

3

0.99 0.99 0.99

6.6 38.8 12.1

261.5 ± 8.1 431.8 ± 8.3 428.7 ± 8.1

14.3 ± 1.1 23.4 ± 2.3 18.2 ± 1.4

(mg/g h)

R2

Chi-square (x2)

0.99 0.99 0.99

12.7 61.5 41.6

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was enlarged from 47.5  10 3 (mg/g h) for wool fabric to 94.7  10 3 (mg/g h) for ZIF-8@wool fabric composite. This reflects the acceleration of 2-naphthol adsorption by insertion of ZIF. The relevant assumption of pseudo-first order kinetic is that, the main rate determining step of the 2-naphthol adsorption onto wool fabric and composites is physisorption [56]. Such postulation describes that, the chemical interaction is happened between two main reactants (2-naphthol and composites), however, the adsorption rate is originally depending on only the concentration of composites. In adsorption process, the formation of actual bonds such as covalent or ionic between reactants is characterized for chemisorption, while the physisorption adsorption included weak interactions (e.g. hydrophobic bonding, van der Waals interactions ion-dipole, dipole-dipole interactions, hydrogen bonding and coordination bonding) [5,57,58]. Consequently, the adsorption of 2naphthol is basically depended on the active sites in composites which is more relevant to ZIF content and hence increasing the ZIF contents within wool fabrics could be resulted in much higher 2-naphthol uptake. The lower rate constant (79.5  10 3 mg/g h) for ZIF-67@wool composite than that for ZIF-8@wool composite is attributed to the lower ZIF content and subsequently, is further supported such hypothesis.

pseudo-first and pseudo-second order models. Parameters of kinetics including, adsorption capacities at equilibrium (qe), rate constants (K1 & K2) and correlation coefficients (R2) are all collected in Table 2. For further confirmation, the suitability of kinetic model, Chi-square data (v2) as statistical test [55], were exported from the fitting figure and the values were introduced in Table 2. From the data in Table 2, adsorption of 2-naphthol onto wool and composites was fully fitted to pseudo-first order model rather than pseudo-second order model, however similar (R2 = 0.99) was recorded for both models. This fitting is confirmed by two things; chi-square values and calculated adsorption capacities at equilibrium. Chi-square values are quite smaller in case of pseudo-first order model compared to that of pseudo-second order model. Values of the calculated qe are much closer to that of the experimental qe for pseudo-first order model. For pseudo-first order, the rate constant (K1) was increased by factor of 2 after incorporation of ZIF within wool fabrics, and it

400

300

qe (mg/g)

3.4. Isotherm 200

The uptake values (qe, mg/g) of 2-naphthol onto wool and composites were plotted with the initial concentration of 2-naphthol (mg/L) in Fig. 7. For the three adsorbent materials (wool fabric, ZIF-8@wool fabric and ZIF-67@wool fabric), plateau shape profiles were observed. The adsorption values of 2-naphthol were gradually grown with its initial concentration up to the optimal concentration (1 g/L) and further increment in the initial concentration over this limit was not accompanied by a notable changing in the adsorption values. The adsorption capacities were followed the order of ZIF-8@wool fabric > ZIF-67@wool fabric >> wool fabric. This explained the fundamental role of ZIF in the adsorption of 2naphthol onto wool fabrics. The linear fitting of 2-naphthol adsorption onto wool and composites were applied for both isotherm models; Langmuir

100

Wool ZIF-8@Wool ZIF-67@Wool

0

0

1000

2000

3000

4000

Ce (mg/L)

Fig. 7. Effect of 2-naphthol concentration on the adsorption capacity of wool fabric and ZIF@wool fabric composites.

Table 3 Parameters of adsorption isotherm for 2-naphthol onto untreated wool and ZIF@wool fabric composites. Samples

Wool ZIF-8@Wool ZIF-67@Wool

Experimental qe (mg/g)

172.0 ± 6.6 356.0 ± 7.2 338.4 ± 6.3

Langmuir isotherm

Freundlich isotherm 3

Qmax (mg/g)

kL  10

197.1 ± 2.4 391.1 ± 4.2 371.2 ± 5.1

6.1 ± 0.4 44.1 ± 1.0 24.1 ± 0.6

(L/mg)

R2

Chi-square (x2)

kF (mg1

0.99 0.99 0.99

13.2 626.5 706.3

40.7 ± 3.7 137.5 ± 7.3 112.2 ± 5.3

n

Ln/g)

n

R2

Chi-square (x2)

5.1 ± 0.7 7.1 ± 1.5 6.3 ± 1.1

0.96 0.90 0.93

152.5 2015.2 1314.4

Table 4 Maximum adsorption capacities of naphthol for several adsorbents used in literature. Adsorbate

Adsorbent

Maximum capacity (q max, mg/g)

Reference

2-naphthol

ZIF-8@wool fabric composite ZIF-67@wool fabric composite

356.0 338.4

Present work Present work

2-naphthol

Carbon nanotube- based composite Bamboo hydrochars Anion-cation organopalygorskite Montmorillonite modified with gemini surfactant Cross-linked poly(styrene-co-divinyl benzene) resin

0.12 12.2 33.7 193.8 – 223.7 210.0

40 37 35 23, 36 34

1-naphthol

Modified diatomite Graphene oxide/Fe3O4@polyaniline b-cyclodextrin modified graphene oxide nanosheets Sulfonated graphene na nosheets ZIF-67

1.5 13.2 290.8 331.6 339.0

60 39 61 33 38

R.M. Abdelhameed, H.E. Emam / Journal of Colloid and Interface Science 552 (2019) 494–505

[a]

400 ZIF-8@Wool ZIF-67@Wool

350 300 250

qe (mg/g)

and Freundlich, and the fitting graphs were presented in supplementary data (Fig. S1). Parameters of isotherm (qmax, kL, kF, n and R2) and Chi-square (v2) values for both models were calculated and recorded in Table 3. The presented data confirmed that, the 2-naphthol adsorption was well adapted to Langmuir model via realizing best linearization (R2 = 0.99) and smaller v2 values. The calculated maximum uptake capacities (qmax) were significantly increased from 197.1 mg/g for wool fabric to 371.2–391.1 mg/g for ZIF@wool fabric composites and the ZIF-8 exhibited much higher capacity compared to that of ZIF-76. By incorporation of 12.9% ZIF, the uptake capacity of wool fabric against 2-napthol was enlarged by 50%. Such isotherm of Langmuir is characterized by the formation of monolayer from adsorbate (2-naphthol) on the homogeneous surface of adsorbents (wool & ZIF@wool composites) [59]. Molecules of 2-naphthol are supposed to be adsorbed onto wool or composites through their active binding sites and each active site occupied with only one molecule. Therefore, the adsorption of 2-naphthol is governed by the availability of active sites onto wool/composites and forming one adsorption layer. The maximum capacities for removal of 1- and 2-naphthol from water by using different adsorbent materials were summarized in Table 4 for comparing with that reported in the current study (338.4–356.0 mg/g). Very low adsorption capacities (0.12– 33.7 mg/g) were observed for carbon nanotube-based composite, bamboo hydrochars and anion-cation organopalygroskite [35,37,40]. The application of montmorillonite modified with surfactant, cross-linked poly(styrene-co-divinyl benzene) resin and sawdust results in acceptable adsorption of 2-naphthol (193.8 – 272.2) [23,34,36]. Modified diatomite, graphene oxide/Fe3O4@polyaniline and b-cyclodextrin/graphene oxide nanosheets were used in removing 1-naphthol with lower capacity [60,61]. According to our knowledge, the highest recorded adsorption capacities in literature was 331.6–339.0 mg/g for 1-naphthol by using sulfonated graphene nanosheets and ZIF-67 [33,38], which are much lower than that obtained in the current work. Taking in account the aforementioned data, using of the so-prepared ZIF@wool fabric composite exhibited the best removal results of 2-naphthol from water. Moreover, the prepared composite is considered as an easily applicable compared to the other mentioned adsorbents.

200 150 100 50 0 1

3

4

[b] ZIF-67@Wool

ZIF-8@Wool

Wool 5

10

15

20

25

30

35

40

45

50

2 Theta degree

[c] Regenerated ZIF-67@Wool

Regenerated ZIF-8@Wool

3.5. Regeneration of ZIF@wool fabric composites The regeneration of composites towards the adsorption of 2naphthol was studied in order to check the reusing efficacy of composites in the removal of 2-naphthol. The regeneration of composites was performed through repetitive cycles of adsorption/ desorption up to 4 cycles. The adsorption capacities of 2naphthol onto the regenerated ZIF@wool composites were shown in Fig. 8a. The regenerated composites showed good efficiency in 2-naphthol adsorption and the adsorption capacities were marginally affected by the regeneration process. After 4 regenerated cycles, the adsorption capacity of the composites (311.2– 324.0 mg/g) was reduced by only 8–9%. XRD and FTIR absorbance spectra were measured for the regenerated composites as shown in Fig. 8b and c. These data declared that; ZIF are still existed inside composites after 4 regeneration cycles and hence the composites show good stability against repetitive wash. From XRD patterns, the amount of ZIF onto composites was reduced by regeneration process due to its leaching out into the environment during the different processes (adsorption & desorption). However, diminishing in ZIF contents is explained the lowering of adsorption capacities for the regenerated composites, the adsorption efficiency of ZIF@wool composites was substantial good after regeneration process. As a conclusion, the data suggested that; further enlargement in the adsorption of 2-napthol and higher regeneration cycles could

2

Number of cycles

Intensity (a.u.)

502

Wool

4000

3500

3000

2500

2000

1500

1000

500

Wavenumber (cm-1) Fig. 8. Reusability study for ZIF@wool fabric composites in removal of 2-naphthol; [a] adsorption capacity, [b] XRD for ZIF@wool fabric composites after regeneration and [c] FTIR spectra for ZIF@wool fabric composites after regeneration.

be both obtained by incorporation of higher contents from ZIF within wool fabrics.

3.6. Adsorption chemistry The adsorption mechanism of 2-naphthol onto ZIF@wool fabric composites were suggested based on the data of kinetics and isotherm, as presented in Fig. 9, in consideration with the chemical structure and the nature of reactants. 2-naphthol has an aromatic structure and composites have several active sites. The

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R H N

HN O

O

H N

N H

O M

S

R

H N O

N M N

N

O

R

N H (CH2)4 H NH N MN

H N O

O

N M N

N

M N

N M

n

ZIF@Wool Composite O H

O H R H N

HN O S

O

H N

N H

O M

R

N

H N O

N M N O H

O

R

N H (CH2)4 H NH N MN

H N O

O

N M N O H

N

M N

N M

n

2-naphthol@ZIF@Wool Composite Fig. 9. Adsorption mechanism of 2-naphthol onto ZIF@wool fabric composite.

physisoprtion nature of adsorption reflects that the adsorption of 2-naphthol onto composites is dominantly carried out through weak interactions represented in van der Waals interactions, hydrophobic bonding, ion-dipole interactions, dipole-dipole interactions, hydrogen bonding and coordination bonding [5,57,58]. The weak interactions are formed between the functional groups of the whole composites (OH, NH, SH) and OH in the 2-naphthol. Moreover, interaction between the two aromatic rings (phenyl in 2-naphthol and imidazolium ring in composite) could be expressed as p - p interaction [38,62]. The considerable enlargement in 2-naphthol adsorption by incorporation of ZIF within wool fabrics is corresponding to the several functional groups of ZIF characterized for composites which subsequently increases the availability of interaction formation between composites and 2-naphthol. Additionally, the physical deposition or trapping of 2-naphthol molecules onto pores and/or intermolecular spaces of composites can’t be ignored [6,15,16].

4. Conclusion Removal of 2-naphthol as a pharmaceutical intermediate from water by using the prepared ZIF (Zn & Co)@wool fabric composites,

was systematically studied. The preparation process of ZIF@wool composites was confirmed by XRD, FTIR, SEM and EDX. Material contents (ZIF/M+2) as well as colorimetric data were measured for the as-prepared composites. The application of ZIF@wool composites was performed for removal of 2-naphthol. Adsorption of 2naphthol onto the prepared composites was well complied with pseudo-first order kinetic model and Langmuir isotherm profile. The data showed that, adsorption of 2-naphthol is physisorption and carried out through weak interaction with the functional groups of ZIF@wool composites. The adsorption reaction rate was accelerated by factor of two, due to the incorporation of ZIF within wool fabrics. The adsorption capacities were enlarged from 172.0 mg/g for wool to 338.3 – 356.0 mg/g for composites within 48 hrs contact time. The regeneration and reusing study reflected the good constancy of composites as the adsorption capacity was lessen by 8–9% only after regeneration for 4 cycles. As a conclusion, data presented in the current study showed significant findings in the removal of 2-naphthol from water using applicable adsorptive composite based on ZIF and wool fabric. Comparable with conventional techniques for removal of 2-naphthol, the current work exhibited valuable advantages represented in applicability, simplicity, cost effectiveness and regeneration of composites. Additionally, controlling in the

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