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SN Applied Sciences

, 1:419 | Cite as

Isotherm and thermodynamic studies of 2,4,6 Tichlorophenol onto newly adsorbents based zeolite as an efficient adsorbents

  • Atyaf Khalid HameedEmail author
  • Mohd Hasbi Ab. Rahim
  • Nugroho Dewayanto
  • Mohd Ridzuan Nordin
Research Article
  • 53 Downloads
Part of the following topical collections:
  1. Chemistry: Nanotechnology and Nanomaterials, Ukraine 2019

Abstract

The aim of this study is to evaluate the adsorption efficiency of using zero valent iron supported on carbon-coated zeolite NZVI/SuZSM and zeolite NZVI/ZSM and as developed adsorbents for the removal of 2,4,6- Trichlorophenol (TCP) from aqueous solution. The characteristic of the adsorbents was conducted via XRD, BET (SBET), TGA, FTIR, FESEM-EDX, and TEM examination. In addition, the impact of different parameters such as contact time, initial concentration, pH and temperature were studied. The experimental data investigated by Langmuir and Freundlich adsorption isotherms and two models for kinetic studies of pseudo-first-order and pseudo-second-order models. The results indicated that the adsorption studies fitted well with Langmuir for the adsorbent NZVI/SuZSM and fitted well with Freundlich for the adsorbent NZVI/ZSM. In addition, both models fitted the data well but pseudo-second-order models more favorable with correlation values of R2 of 0.9995 and 0.9994 more than first order models for the adsorbents NZVI/ZSM and NZVI/SuZSM, respectively. The equilibrium time was achieved after 90 min for both adsorbents. Depending on the Langmuir model, the maximum adsorption capacities were 22.27 mg/g and 30.58 mg/g for NZVI/ZSM and NZVI/SuZSM, respectively at (27 °C ± 2). The thermodynamic parameters indicated that adsorption of TCP onto NZVI/ZSM was an endothermic and non-spontaneous process in temperature of 30 °C, while the adsorption of TCP onto NZVI/SuZSM was an endothermic and spontaneous process. The synthesize adsorbents (NZVI/ZSM and NZVI/SuZSM) could be applied as an efficient adsorbent for the removal of TCP from aqueous solution.

Keywords

Supported nano zero valent iron 2,4,6-Trichlorophenpl adsorption Carbon coated materials Adsorption Kinetic studies Thermodynamic aspect 

1 Introduction

The development of the chemical industry has produced increasing the disposal of pollutants, especially organic pollutant. Wastewater contains chlorophenol pollutants generated from pharmaceuticals, paper, wood, pesticide, solvent, paint, industries, and water disinfecting process [4]. These persistent organic pollutants (POPs) have existed in water and soil because they have three chloride groups linked to the phenol ring. The 2,4,6-Trichlorophenol (TCP) is one of POPs compound and it is harmful to wildlife and human as well as listed as precedence–controlled pollutant by the United States Environmental Protection Agency (USEPA). The TCP compound was toxic, carcinogenic and mutagenic. Also reiterate and long exposures can cause kidney, Liver, bone and neurological marrow disorders and also the loss of anemia, appetite, and weight loss. Thus, TCP presence in water resources even at low concentrations is injurious to aquatic organisms and human health. According to the chemical characteristics and environmental impacts of TCP and the inefficiency of conventional treatment methods for the complete removal of it from the aquatic solution, applying of advanced, quick and effective techniques, is essential.

Several methods have been investigated for the removal of chlorinated phenols, such as chemical, physical and biological treatment by using dead fungus, catalytic wet oxidation, advanced oxidation process (AOP), photocatalytic process, ion-exchange and adsorption techniques performed by Bandstra et al. [5] and Hameed et al. [15]. Most of these methods were expensive and inefficient. Thus, the adsorption of TCP from aqueous solution onto different types of an adsorbent considered as a superior method. Previously, the adsorption of TCP was limited to it is isotherm and kinetic aspect [19].

Zeolite was microporous, aluminosilicate minerals commonly used as adsorbents for several pollutants [20]. Zeolites, in general, were characterized by high specific surface areas and high cation exchange capacities (CECs). Their rigid three-dimensional structures make it free of the shrink/swell behavior. For these reasons, zeolites can offer superior sorption, hydraulic properties and have found use as molecular sieves and sorbents in wastewater treatment [32].

Activated carbon, due to its structure and high surface area, has been proposed as an adsorbent, and a suitable option for the effective removal of organic contaminations. But using of it in large scales (in engineering processes) has been limited because of problems such as filtration, dispersion, create turbidity and high cost of its reduction [3, 19]. Some developments methods in the forming of carbonaceous layer on mesoporous material taken place in order to overcome the above problems. Carbon coated mesoporous materials may be prepared by inundate the coating of mesoporous structure into a carbon source solution, e.g. furfural alcohol and polymer [13, 24]. In addition to the filling, carbon coating was also a very important process not only to enhance the functionality but also to give new functions to porous inorganic materials, as recently reviewed by De la Torre et al. [8]. Therefore, the resulting carbon-coated materials could be applied for the electro-chemical fields such as a porous electrode for super capacitor, fuel cell and biosensor [16].

To illustrate, if the whole surface including the pore walls, zeolite (ZSM-5) was completely and uniformly coated with carbon layer like a single graphene sheet, the coating could endow the mesoporous materials with both good chemical stability and electrical conductivity [25, 31] with keeping their original excellent features such as uniform mesopores, size-controllable pores and high surface area. When once zeolite surface was saliyated with silanol groups, the surface become very active toward the pyrolytic carbon deposition at as low a temperature as 500 °C and thereby uniform carbon deposition could be easily achieved [33] by a simple carbon coated process using carbon precursor.

To the best of our knowledge, utilization of d-glucose as carbon coating precursor on mesoporous materials does not have been investigated so far. The objectives of the present study was to synthesize and characterize a Nano zero valent iron supported on zeolite (NZVI/ZSM) and Nano zero valent iron supported on carbon-coated zeolite (NZVI/SuZSM) adsorbents, assess its efficiency for TCP removal and studding the isotherm, kinetic and thermodynamic aspect of the prepared adsorbents.

2 Methodology

2.1 Materials

Sodium borohydride (NaBH4) 98.5%, iron (III) chloride hex hydrate (FeCl3·6H2O) 99% were obtained from Merck. 2, 4, 6-Trichlorophenol was supplied by the Aldrich Co. with a purity of 99.8%. ZSM-5 (Si/Al = 30) was supplied by Zeolyst International. d-glucose with purity 99% is purchased from Merck. The 2-propanol (chromatography grade), and KBr (IR spectroscopy grade) were purchased from Merck Millipore. Sodium hydroxide (NaOH) and hydrochloric acid (HCl) were obtained from Sigma-Aldrich, while analytical grade absolute ethanol and acetone were obtained from Merck and used directly without purification. Nitrogen for carbon coating step was also supplied by MOX-Linde. Sodium hydroxide (NaOH) and hydrochloric acid (HCl) were obtained from Sigma-Aldrich.

2.2 Preparation and characterization

Modification of ZSM-5 (Zeolyst International) was conducted by impregnation of 4 g ZSM-5 with 100 mL from d-glucose solution (4 g/L) under stirring for 3 h at room temperature (27 °C ± 2). The mixture was centrifuged and decanted to collect the solid and dried in an oven at110 °C for 12 h. The solid was then carbonized in a furnace at a coveted temperature (500 °C) for 2 h in inert condition obtained by flowing N2 gas. Preparation of NZVI/ZSM and NZVI/SuZSM was carried out by introducing one gram and of modified carbon coated zeolite into Fe3+ solution, prepared by dissolving 0.4 g FeCl3·6H2O (from Merck) in 25 mL distilled water. Amount of one gram NaBH4 (Merck) dissolved in 50 mL distilled water adding drop wisely (3 mL/min). The samples were filtered, washed via acetone and dried in an oven at 60 °C for 60 min. The prepared adsorbents were characterized using the N2 physisorption to evaluate the surface area and the porosity at 105 °C prior to the analysis and the adsorption of N2 was measured at − 196 °C by Micrometrics ASAP 2020. The thermal gravimetric analysis (TGA) was carried out by Mettler Toledo TGA/DSC equipped with STAR1 software in order to adjust the weight loss as temperature increases. Nitrogen of flow rate of 50 mL/min was used as cell gas, the X-ray analysis (XRD) was conducted via Rigaku instrument, FTIR analysis was carried out by using Perkin Elmer Spectrometer 100, FESEM equipped with EDX (JEOL) and TEM (Tecnai G2 F20).

Modification of ZSM-5 (Zeolyst International) was conducted by impregnation of 4 g ZSM-5 with 100 mL from d-glucose solution (4 g/L) under stirring for 3 h at room temperature (27 °C ± 2). The mixture was centrifuged and decanted to collect the solid and dried in oven at 110 °C for 12 h. The solid was then carbonized in furnace at coveted temperature (500 °C) for 2 h in inert condition obtained by flowing N2 gas. Preparation of NZVI/ZSM and NZVI/SuZSM was carried out by introducing one gram and of modified carbon coated zeolite into Fe3+ solution, prepared by dissolving 0.4 g FeCl3·6H2O (from Merck) in 25 mL distilled water. Amount of one gram NaBH4 (Merck) dissolved in 50 mL distilled water adding drop wisely (3 mL/min). The samples were filtered, washed via acetone and dried in oven at 60 °C for 60 min. The prepared adsorbents were characterized using the N2 physisorption to evaluate the surface area and the porosity at 105 °C prior to the analysis and the adsorption of N2 was measured at − 196 °C by Micrometrics ASAP 2020. The thermal gravimetric analysis (TGA) was carried out by Mettler Toledo TGA/DSC equipped with STAR1 software in order to adjust the weight loss as temperature increases. Nitrogen of flow rate of 50 mL/min was used as cell gas, the X-ray analysis (XRD) was conducted via Rigaku instrument, FTIR analysis was carried out by using Perkin Elmer Spectrometer 100, FESEM equipped with EDX (JEOL) and TEM (Tecnai G2 F20).

2.3 Adsorption study

The adsorptions of the 2-, 4-, 6-Trichlorophenol (TCP) onto the adsorbents are conducted in a batch experiment. The amount of adsorbent was added into the TCP solution (of certain concentration) in the 250 mL conical flasks. The flasks are placed on the orbital shaker operating at 150 rpm in room temperature (27 ± 2 °C). The initial and final concentrations of TCP was determined by using UV spectrometer (Genesys 10S UV–VIS spectrophotometer) at λmax = 310.

2.4 Isotherm study

The analysis of the pollutant adsorption process could be evaluated by the isotherm studies. The distribution of the molecules between the liquid and the solid phase could be conducted by isotherm studies at the equilibrium rate. However, for the investigation of the sorption isotherm, Langmuir and Freundlich isotherm models are widely used [33].

Monolayer adsorption can be described by the Langmuir isotherm model. The initial of the maximum adsorption capacities corresponds to a saturated homogeneous adsorbent surface with equal energy sites that are equally available for the adsorption and monolayer of solute molecules. The energy of the adsorption process was constant and there is no transmigration of TCP in the plane of the surface [22] Langmuir isotherm model can express as Eq. 1:
$$q_{e} = q_{m} bc_{e} + bc_{e}$$
(1)
where \(q_{e}\) is the adsorbate on the adsorbent (mg/g), \(q_{m}\) is the maximum adsorption capacity of monolayer coverage (mg/g), b is the constant related to the binding site (L/mg), and \(c_{e}\) is the concentration of molecule in the solution at equilibrium (mg/L).Multilayer sorption can be described by the Freundlich model. It is used to analyse the adsorbent capacity in wastewater treatment. The adsorption on a heterogeneous surface is well described by the Freundlich model. In this model, the amount of solute adsorbed onto a given mass of sorbent is not constant at different concentrations [2].The non-linear and linear Freundlich models are expressed in Eqs. 2 and 3, respectively:
$$q_{e} = kc_{e} \frac{1}{n}\quad \left( {{\text{Non-linear}}\;{\text{form}}} \right)$$
(2)
$$\log q_{e} = \log k + \frac{1}{n}\log c_{e} \quad \left( {{\text{Linear}}\;{\text{form}}} \right)$$
(3)
where \(k\), constant value consider as adsorption capacity indicator of the adsorbent (mg/g) in adsorption process. \(\frac{1}{n}\) constant for the intensity of the adsorption. The \(q_{e}\) was the adsorbate on the adsorbent (mg/g), and \(c_{e}\) is the concentration at equilibrium (mg/L). Both n and K and are constants, used to indicate the linearity and the non-linearity between the adsorbate solution concentrations and the uptake values in the adsorption process. The n < 1 indicates poor adsorption. For 2 < n < 10, it indicates good adsorption as reported by Gurses et al. [12].

2.5 Kinetic study

The effect of time on the adsorption capacity can be evaluated by kinetic studies. A number of models was tested to identify the mechanism of the adsorption process such pseudo-first-order kinetic model and pseudo-second-order kinetic model. The first order model equation was the common adsorption model for the sorption of the solid/liquid phase [27] the Eq. 4, could be applied as follows:
$$Ln\left( {q_{e} - q_{t} } \right) = Lnq_{e} - k_{1} t$$
(4)
where t, is the time, \(q_{e}\) is the adsorbate amount at equilibrium time (mg/g), \(q_{t}\) is the adsorbate amount at time t (mg/g), \(k_{1}\) is the rate constant of pseudo first order model (1/min).The kinetic for pseudo-second-order model can be described as Eq. 5:
$${\text{dq}}/{\text{dt}} = k_{2} \left( {q_{e} - q_{t} } \right)^{2}$$
(5)
where \(k_{2}\) is the rate constant of the pseudo second order model, (g mg−1 min−1) which can be calculated from the slop of plot \(t/q_{t}\) versus t, \(q_{e}\) was the adsorbate amount at equilibrium time (mg/g), qt is the TCP amount at time t(mg/g).

2.6 Thermodynamic study

In environmental engineering practice, both energy and entropy factors must be considered in order to determine which process will occur spontaneously [34]. The thermodynamic parameters are calculated for this system by using Eq. 6 [30]:
$$lnk_{d} = \frac{\Delta S^\circ }{R} - \frac{\Delta H^\circ }{RT}$$
(6)
where \(k_{d}\) = distribution coefficient (L/g), \(\Delta H^\circ\) = enthalpy (kJ/mol), \(\Delta S^\circ\) = entropy (J/mol K), T = temperature (K) and R = gas constant (8.314 J/mole K).

3 Result and discussion

3.1 Characterization

3.1.1 TGA analysis

Figure 1a shows the weight loss of ZSM within 90–110 °C. It occurs due to the loss of the hydrate surface water and the condensations of the alumina groups (Al–OH) and the silanol groups (Si–OH) to Al–O–Al and Si–O-Si, respectively. The weight loss occurred within 365–600 °C was due to the decomposition of the ZSM. Figure 1b shows the weight loss of NZVI/ZSM within 100–240 °C. It occurs due to the loss of hydrate surface water and residual ethanol. Also, Fe–OH was transformed into FeO or Fe0. Within 300–500 °C, the weight loss is due to the decomposition of the Fe–O–Al and Fe–O–Si bonds of the adsorbent NZVI/ZSM. Above 500 °C, no significant weight loss is observed. From Fig. 1c, the weight loss pattern of SuZSM is somewhat different from that of ZSM due to the grafting with d-glucose. Within 90–320 °C, weight lose occurs due to the loose of residual water and ethanol. At temperature ranging from 530 to 600 °C, decomposition of the adsorbent SuZSM occurs. Above 600 °C, no significant weight loss is observed. Figure 1d shows the weight loss of NZVI/SuZSM within 100–240 °C which is mainly due to the loss of residual water. Within 390–480 °C, decomposition of adsorbent occurs. Above 500 °C, no significant weight loss appears. The results above show that the stability enhancement of SuZSM was more pronounced than that of ZSM when carbonization via d-glucose is performed.
Fig. 1

TGA and DTA for a ZSM, b NZVI/ZSM, c SuZSM and d NZVI/SuZSM

3.1.2 XRD analysis

The XRD diffractions of NZVI/ZSM and NZVI/SuZSM are illustrated in Fig. 2. The presence of Zero Valent Iron is indicated by a distinct peak at 2θ of 44.45° with detection (1 1 1), which is related to α-Fe (NZVI) as observed in the diffractogram of NZVI/ZSM. It appears that the ZeroValent Iron is successfully loaded into the substrate. As illustrated in Fig. 4, the peaks are observed at 2θ of 8.22°, 9.09°, 23.36°, 24.15°, 24.61° and 30.12° which are related to the crystalline structure of ZSM-5 [6]. The presence of carbon-coated surface on NZVI/SuZSM is indicated by the graphite phase at 2θ of 26.92°, 31.56°. On the other hand, the peak observed at 2θ of 34.50° is related to the ZSM-graphite. The apparent peak at 2θ of 45.47° is related to the ZSM-graphite-α-Fe. These results indicate NZVI is grafted with the carbon layer.
Fig. 2

The XRD diffracton patterns of NZVI/ZSM and NZVI/SuZSM

3.1.3 N2-physisorption analysis

Parameters such as surface area (SBET), pore volume and pore size of adsorbents were summarized in Table 1. The surface areas of NZVI was found to be 40.65 m2/g. Meanwhile, their pore sizes was 152.70 Å. It was clear that the surface area and the pore size of NZVI obtained by this study was larger than that reported by Ling et al. [23], which may be attributed to different experimental conditions. In addition the surface area of the ZSM-5, carbon coated ZSM-5 (SuZSM) and the prepared adsorbents presented in Table 1.
Table 1

The surface area (SBET), pore volume and pore size of the prepared adsorbents

Adsorbent

BET (m2/g)

BJH adsorption pore volume (cm3/g)

BJH adsorption pore size (Å)

NZVI

40.65

0.165

152.70

ZSM

254.33

0.095

63.28

SuZSM

246.48

0.099

75.96

NZVI/ZSM

116.52

0.055

91.22

NZVI/SuZSM

182.65

0.112

85.40

3.1.4 FTIR analysis

The FTIR spectra of NZVI/ZSM and NZVI/SuZSM are shown in Fig. 3. The broad spectrum of adsorption bands at wavenumbers of 3800 cm−1 and 3400 cm−1 were related to the intermolecular OH (Si–OH–Si and Al–OH–Al). Also, they are related to H–O–H stretching [7]. The band at wave numbers of 1648 cm−1 and 1661 cm−1 can be attributed to O–H bending [20]. A combination band of OCH and COH deformations from sugar molecules is indicated by a peak at the wave number of 1408 cm−1 in the NZVI/SuZSM spectrum. The absorption band at the wave number of 1237 cm−1 in both spectra corresponds to the C–H in-plane bending vibrations [29]. Adsorption bands in both spectra at the wave number of 1114 cm−1 are caused by the primary oxygen single bond (–C–O–H) [17], while the bands at wave numbers of 814 cm−1 and 819 cm−1 were attributed to the formation of SiO–Fe bonds [28]. Moreover, the crystalline structure of ZSM-5 was indicated by vibration peak at around 560 cm−1 as observed by Abrishamkar and Izadi [1].
Fig. 3

The FTIR spectra of NZVI/ZSM and NZVI/SuZSM

3.1.5 FESEM analysis

The FESEM micrographs of the prepared adsorbents are presented in Fig. 4a, b, showing the morphologies of NZVI/ZSM and NZVI/SuZSM, respectively. It could be b seen that the modification of ZSM-5 by using impregnation of carbon affects the morphology of the substrate due to the change of the particle shape. As seen from Fig. 4a, the surface morphology of NZVI/ZSM was irregular. On the other hand, the surface morphology of NZVI/SuZSM exhibits more regular cubic shapes as shown in Fig. 4b. Furthermore, Fig. 4a, b shows that the iron nanoparticles were dispersed evenly on the surface and the pore of the substrate. This result agrees with the previous observation whereby the surface area of adsorbent was reduced after impregnation with NZVI. However, the surface area of NZVI on the surface of SuZSM was higher than that on the surface of ZSM.
Fig. 4

The FESEM micrograph of a NZVI/ZSM at ×30,000 magnification and b NZVI/SuZSM at ×45,000 magnification

On the other hand, Table 2 shows the weights and the atomic weights for the elements in ZSM-5 surface, i.e. silicon, and oxygen. The atomic/weight values of Si, O, and Al were found to be 25.47%/37.20%, 73.15%/60.86% and 1.37%/1.93%, respectively.
Table 2

The EDX analysis of ZSM, SuZSM, NZVI/ZSM and NZVI/SuZSM

Adsorbents

Element (%)

Weight (%)

Atomic weight  (%)

ZSM-5

O

60.86

73.15

Si

37.21

25.47

Al

1.93

1.38

SuZSM

C

14.89

21.12

O

59.31

63.18

Al

1.37

0.86

Si

24.44

14.83

NZVI/ZSM

O

75.63

85.69

Si

18.55

11.97

Al

1.29

0.87

Fe

4.53

1.47

NZVI/SuZSM

O

60.59

69.95

Si

24.60

16.18

Al

1.62

1.11

Fe

6.23

2.06

C

6.96

10.71

3.1.6 TEM examination

The morphology and the surface distribution of the novel adsorbent were presented in Fig. 5. The cubic structure of ZSM-5 could be seen from the TEM micrograph (black spots) as shown in Fig. 5a. As shown in Fig. 5b, the center black spot was NZVI and the dark layer was carbon coating. Seemingly, the NZVI was surrounded by the carbon layer. As shown in Fig. 5c, the distribution of NZVI on the surface of ZSM was quite even, thereby increasing the reactivity of the prepared adsorbent. Figure 5d shows the bulk structure of the adsorbent which was related to the graphite layer. It seems that there was no obvious chain structure of NZVI on the surface. Figure 5e shows the spherical particles of NZVI on the surface of the adsorbent. The NZVI particle was surrounded by the carbon layer. Finally, Fig. 5f shows that the spherical particles are surrounded by the carbon layer.
Fig. 5

The TEM examination of NZVI/SuZSM, a the crystalline particals of SuZSM surface at 200 nm, b the black spots for NZVI surrounded with dark layer of carbon coated at 10 nm, c the NZVI loaded on the surface of ZSM and the carbon layer at 100 nm, d the bulk structure of the adsorbent at 200 nm, e the spherical particle of NZVI at 10 nm and f the carbon layer and the dark spots of NZVI at 20 nm

3.2 Adsorption parameters

A stock solution of concentration 1000 mg/L of TCP was prepared by dissolving the required amount of adsorbate in 2-Propanol for the preparation of TCP stock solution. The effect of contact time (2–180 min), temperature (30–50 °C), pH (2–9) and initial concentration (10–40 mg/L) were studied. The adsorption properties of NZVI/ZSM and NZVI/SuZSM were evaluated by sorption of TCP. A stock solution of TCP was prepared via dissolving TCP in alcohol as 2-propanol instead of distilled water. The TCP considered stable compound because the resonance of the aromatic structure in addition to the low solubility in water, Cs ofChlorophenol is 210.8 mol/dm3 as suggested by Kirsanov and Shishkin [21] in addition to the higher acidic strength of chlorine atom.

3.2.1 Contact time

Equilibrium time of adsorption was determined by using 0.1 g of adsorbents (NZVI/ZSM) and (NZVI/SuZSM) in 100 mL of 20 mg/L TCP solutions. The mixture was equilibrated by shaking thoroughly at 150 rpm in orbital shaker. Samples are taken out at different time intervals viz. 2, 4, 8, 15, 30, 60, 90, 120 and 180 min at pH value of 7, in room temperature (27 ± 2 °C). At the end of the shaking period, the solution was sampled by a syringe. The samples were then centrifuged and the supplements are kept for further analysis. The equilibrium time was an important factor to set the adsorption time for each adsorbent and was found to be 90 min for the both tested adsorbents.

3.2.2 Initial concentration

The effect of initial concentration of the TCP on the adsorption performance was carried out through a series of adsorption experiments with different initial TCP concentrations ranging from 10 to 40 mg/L. The experiments were performed by using a 100 mL TCP solution. The adsorbent dosage is 0.1 g/L. The samples used to determine the adsorption performance were available after the batch mixture was stirred for a suitable equilibrium time (90 min) for both adsorbents.

3.2.3 Temperature

To study the temperature effect, the experiment was operating and the thermodynamic parameters such as ΔG°, ΔH°, and ΔS° were then determined. The effects of temperature on the adsorption equilibrium of TCP onto NZVI/ZSM and NZVI/SuZSM were investigated and the results were presented in Fig. 6. Adsorption of TCP increased as temperature increased, indicating the endothermic adsorption process. It was found that the uptake values of NZVI/SuZSM were 16.33 mg/g while the uptake of NZVI/ZSM was 11.93 mg/g.
Fig. 6

Effect of adsorption temperature on TCP adsorption onto NZVI/ZSM and NZVI/SuZSM uptake

3.2.4 pH

Different pH values were considered: 2, 4, 7 and 9. The pH of the solution was measured by the pH meter. The pH-meter was calibrated by using a pH buffer of 4.0, 7.0, and 10 to ensure the accuracy of the pH measurement. The initial pH of the solution was adjusted by using 1 M HCl or 1 M NaOH. Then, the adsorption performance was performed. The effects of pH on the adsorptions of TCP onto NZVI/ZSM and NZVI/SuZSM were illustrated in Fig. 7. The unionized species of halogenated organic compounds were high, which do not favor any repulsion between the adsorbent surface and the molecular species of TCP. Therefore, the electrostatic attractions between the TCP molecules and the adsorption sites increased. Besides, there was competition between the OH ions in the adsorbent surface and the ionic species of TCP, hence reducing the TCP removal. The removal values for the adsorbents NZVI/SuZSM and NZVI/ZSM were found to be 83.40% and 62.78%, respectively.
Fig. 7

Effect of initial pH of TCP solution onto NZVI/ZSM and NZVI/SuZSM uptake

3.3 Adsorption isotherm

The isotherm studies are conducted by a series of batch adsorptions. The initial pollutant concentration is ranging from 10 to 40 mg/L.The Langmuir and Freundlich isotherm models for adsorption of TCP onto NZVI/ZSM and NZVI/SuZSM are presented in Fig. 8a, b respectively. The vertical error bars on the data points indicated the average deviation from triplicate the data collection.The Langmuir and Freundlich constants of adsorption of TCP onto NZVI/ZSM are 0.033 L/mg and 1.21 g/L, respectively, while the Langmuir and Freundlich constants of adsorption of TCP onto NZVI/SuZSM are 0.05 L/mg and 2.16 g/L, respectively. The maximum adsorption capacities of TCP onto NZVI/ZSM and NZVI/SuZSM are 22.27 mg/g and 30.58 mg/g, respectively (from Langmuir isotherm). In general, the Freundlich isotherm characterizes the adsorption process better than the Langmuir isotherm for NZVI/ZSM, while Langmuir isotherm characterizes the adsorption process better than the Freundlich isotherm for NZVI/SuZSM. The 1/n value of the Freundlich isotherm is ~ 1.0 for both NZVI/ZSM and NZVI/SuZSM. Hence, the adsorption of TCP onto NZVI/ZSM can be considered as multilayer adsorption while the adsorption of TCP onto NZVI/SuZSM can be considered as monolayer adsorption. The parameters obtained by fitting the results to the Langmuir and Freundlich isotherm models are summarized in Table 3.
Fig. 8

Adsorption isotherm models of TCP onto NZVI/ZSM and NZVI/SuZSM, a Langmuir and b for Freundlich models

Table 3

Isotherm parameters of the adsorption of TCP onto NZVI/ZSM and NZVI/SuZSM comparison with literature studies in uptake values

Absorbents

Langmuir

Freundlich

References

KL (L/mg)

qmax, (mg/g)

R2

Kf (g/L)

1/N

R2

NZVI/ZSM

0.033

22.27

0.9083

1.21

0.65

0.9933

This study

NZVI/SuZSM

0.05

30.58

0.9946

2.16

0.65

0.9915

This study

Activated carbon/loosestrife

0.15

367.64

0.5222

24.06

0.79

0.9009

Fan et al. [9]

surfactant-modified zeolitic tuff

0.023

12.90

0.9901

   

Naddfi et al. [26]

Activated carbon SKD515

0.40

12.20

0.7800

4.98

0.32

0.9213

Shishkin and Kirsanov [21]

Activated clay

0.022

123.46

0.9300

4.42

0.69

0.9600

Hameed et al. [14]

From the experimental data, it seems that the fitting errors of both Langmuir and Freundlich isotherm models for NZVI/ZSM and NZVI/SuZSM were smaller than one (R2 ~ 1). However, the Langmuir isotherm model gives a smaller fitting error for the adsorbent NZVI/ZSM than the Freundlich isotherm model indicating multilayer adsorption. On the other hand, the correlation coefficients (R2) of Langmuir for the adsorbent NZVI/SuZSM of a high value indicating monolayer adsorption. The correlation coefficients (R2) indicating that the experimental data of the adsorptions for adsorbents as NZVI/ZSM and NZVI/SuZSM are well fitted with both isotherm models. The fitting of the Langmuir and Freundlich isotherm models are summarized in Table 3. Also, the maximum uptake values of all the adsorbents are comparable with other adsorbents reported in Table 3 in monolayer adsorption.

3.4 Kinetic studies

The kinetic studies are conducted by a series of batch adsorptions running at initial pollutant concentration of 20 mg/L. The procedures of kinetic adsorption tests are identical to those of batch equilibration tests. However, the aqueous samples are taken at various time intervals. The result of the kinetic study of TCP adsorption on NZVI/ZSM and NZVI/SuZSM was presented in Fig. 9a, b. It seems that the second order model fits well with the experimental data with a higher R2 value. Thus, it shows that the pseudo-second-order model is more suitable to be applied in the kinetic studies for NZVI/ZSM, and NZVI/SuZSM. The kinetic parameters for the adsorbents such as NZVI/ZSM, and NZVI/SuZSM were summarized in Table 4.
Fig. 9

Linear plot of a pseudo-first kinetic model and b pseudo-second kinetic model of adsorption of TCP onto NZVI/ZSM and NZVI/SuZSM uptake

Table 4

Kinetic parameters of the adsorption of TCP onto, NZVI/ZSM and NZVI/SuZSM were collected in this study

Adsorbents

K1 (min−1)

qe,cal (mg/g)

R2

k2 (g/mg min)

qe,cal (mg/g)

R2

qe (mg/g)

NZVI/ZSM

0.039

5.81

0.9064

0.034

13.73

0.9995

13.63

NZVI/SuZSM

0.040

6.69

0.9408

0.029

16.29

0.9994

16.29

Thus, the experimental data indicates that the pseudo-second-order model is more suitable to be applied in the kinetic studies for NZVI/ZSM, and NZVI/SuZSM and the qe, Cal value near to the qe experimental. The kinetic parameters for the adsorbents NZVI/ZSM and NZVI/SuZSM are summarized in Table 4.

3.5 Thermodynamic studies

Thermodynamic study of adsorption is carried out by equilibrating the TCP solution with an adsorbent at various temperatures ranging from 30 to 50 °C. The thermodynamic studies are conducted by a series of batch adsorptions running at initial pollutant concentration of 20 mg/L. The objectives of this study are to evaluate the changes in enthalpy (ΔH°), entropy (ΔS°) and Gibb’s free energy ΔG°) of adsorption [11].

The values of ΔH°, ΔS°, ΔG° are calculated from Fig. 10 and listed in Table 5. Positive ΔH° value indicates endothermic adsorption. This is supported by the fact that the adsorption of TCP increases as temperature increases. The positive ΔS° reveals that the degree of freedom increases at the solid–liquid interface during adsorption. The ΔG° is negative when adsorption happens on NZVI/SuZSM, reflecting the spontaneity of the process. On the other hand, the adsorption process for NZVI/ZSM is un-spontaneous and difficult to apply in practice in temperature 30 °C and thermodynamically feasible in another temperature.
Fig. 10

Van’t Hoff plot of effect of temperature on adsorption properties of TCP onto NZVI/ZSM and NZVI/SuZSM

Table 5

Thermodynamic parameters for adsorption of TCP onto NZVI/ZSM and NZVI/SuZSM compared with literature review

Adsorbent

ΔH° (kJ/mol)

ΔS° (J/mol K)

ΔG° (J/mol)

References

303 K

313 K

323 K

NZVI/ZSM

23.936

78.066

282.038

− 498.621

− 1279.28

This study

NZVI/SuZSM

44.239

149.59

− 1084.63

− 2580.48

− 4076.33

This study

Montmorillonite

− 28.788

81

− 3392

− 2580

− 1769

Fil et al. [10]

MGC-4

87.200

47.22

− 20850

− 5591.73

6054.6

Wang et al. [33]

Modified malted sorghum mash

38.31

68.16

 

− 21260

− 2200

Oyelude and Appiah-Takyi [27]

Mesoporous silica

55.13

235.8

 

− 17654

− 19651

Kareem et al. [18]

4 Conclusion

In this study, adsorbents such as NZVI/ZSM and NZVI/SuZSM have been successfully synthesized. The prepared adsorbents are characterized by XRD, FTIR, N2-Physisorption, TGA, TEM, and FESEM-EDX. The performances of NZVI are compared in terms of TCP adsorption with the uptake onto ZSM and SuZSM, and adsorbents such as SuZSM show good performance. For the application of d-glucose as a novel additive in the carbon-coating technique, it is found that the optimal activation temperature is 500 °C. In addition, the carbonization performed via d-glucose increases the adsorption capacity of TCP onto the activated inorganic supports such as ZSM. The modification performed with d-glucose via the wet impregnation method followed by the carbonization step can significantly improve the adsorption rate and the adsorption capacity. The spontaneity of the adsorption process is determined from the free energy ΔG°. Meanwhile, ΔH° indicates the process of whether it is endothermic or exothermic. ΔS° signifies the randomness of the system. Carbon-coated technique leads to improving the physical property of the prepared adsorbents. In addition carbon-coated adsorbents provided higher adsorption efficiency due to the synergistic effect, the available active adsorption site of the supporting materials and the stability of the NZVI. The evaluation of the adsorption performance of the prepared adsorbents was proven via the isotherm studies by Langmuir and Freundlich models. In the kinetic study, the pseudo first order and the pseudo-second-order kinetic models are examined. It seems that the pseudo-second-order kinetic model fits well with the experimental data for both adsorbents. As result the both adsorbents are spontaneity and thermodynamically feasible. This study offers solutions to overcome the industrial wastewater problems especially in the field of organic pollutant removal.

Notes

Acknowledgements

The author would like to thanks the ministry of science and technology—Iraq for their Scientific supports.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

This article does not contain any studies with human participants or animals performed by any of the authors.

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Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Atyaf Khalid Hameed
    • 1
    Email author
  • Mohd Hasbi Ab. Rahim
    • 2
  • Nugroho Dewayanto
    • 3
  • Mohd Ridzuan Nordin
    • 4
  1. 1.Environmental and Water Research Technology DirectorateMinistry of Sciences and TechnologyAl-Jadirya, BaghdadIraq
  2. 2.Faculty of Industrial Sciences and TechnologyUniversity Malaysia PahangKuantanMalaysia
  3. 3.University Kuala Lumpur, Malaysian Institute of Chemical and Bioengineering TechnologyAlor GajahMalaysia
  4. 4.Faculty of Technology Management and TechnopreneurshipUniversity Technical Malaysia MelakaDurian TunggalMalaysia

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