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Research Article | DOI: https://doi.org/10.31579/2578-8957/003
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Citation:
Copyright: © an AL-KHATIB. Kinetic and Adsorption Removal Study of Malachite Green Dye on Carbon Nanotubes Immobilized Biomass (CNTIB). J. Pollution and Public Health, DOI: 10.31579/2578-8957/003
Received: 30 November -0001 | Accepted: 27 February 2018 | Published: 05 March 2018
Keywords: MG, CNTIB, Biosorbent, Kinetics
The adsorption of Malachite green (MG) onto Carbon Nanotubes Immobilized Biomass (CNTIB) was carried out in this research. The interactive effects of experimental variables such as Biosorbent loading, MG dye concentration and pH were investigated. Optimized conditions for adsorption studies were achieved by employing the Response Surface Methodology (RSM) of Design expert 7 software using the Faced Centered Central Composite Design (FCCD). MG adsorption uptake was found to increase with an increase in biosorbent loading. Isotherm studies showed that the experimental data better fitted with the Langmuir isotherm for CNTIB when compared to Freundlich isotherm. Adsorption kinetics was found to follow the pseudo-second order kinetic model which suggests that chemisorption is the process through which adsorption took place. The biosorbent was produced by immobilization technique. Optimized conditions of parameters for biosorption studies (initial dye concentration, biosorbent loading and pH) as well as response were determined. 111.0mg/L of dye was removed out of an initial dye concentration of 112.5mg/L. Acidic pH was favourable for the adsorption of MG. Coefficient of determination (R2) for biosorption model was 0.989. The biosorbent produced was characterized using SEM to determine its morphology and available functional groups which would further enhance its biosorption ability.
Highlights
Textile industry consumes a large quantity of water and therefore generates a huge amount of wastewater (Hai et al., 2007). Normally, a number of sophisticated dyes and auxiliary chemicals are used in the textile industries to obtain a good quality product. Continuous usage of these chemicals have brought about an environmental concern (Coulibaly et al., 2004).Dye wastewater dischargedby textile and dyestuff industries therefore need to be well treated before being released into the environment. Physical, chemical and some biological methods have been used in dye removal. However, these methods are characterized by some major setbacks such as low efficiency and high cost amongst others. Several researchers have shown that biosorption (adsorption) can be a better substitute to the physico-chemical, microbial and or enzymatic biodegradation methods (Khan et al., 2013).
CNTs have been investigated as the best adsorbent for industrial pollutants even from dilute solutions. This is due to their large specific surface area and nano structure, outstanding thermal and chemical stability, excellent adsorption efficiency, environmental friendly nature, high reactivity, porosity, surface functional groups, binding strength, high affinity between sites and the particular pollutant of interest, high adsorptive capacities etc. (Chen et al., 2009).
The last three decades have also witnessed an extensive study of biomass being a perfect replacement for activated carbon. A wide diversity of microorganisms has been studied and results have shown that they were able to decolorize a wide variety of dyes. Among the various types of biomass, the fungal biomass has proved to be particularly suitable. Fungal biomass is highly effective yet very cheap. Considering the nature of CNTs and fungi biomass as excellent adsorbents in the removal of textile dye contaminants from industrial wastewaters, this research therefore comes up with a novel biomaterial such as a combination of non-living fungal biomass and CNTs in the treatment of dye wastewater. This new biosorbent will be referred to Carbon Nanotubes Immobilized biomass (CNTIB).
A basic understanding of the adsorption equilibrium and kinetics is very paramount for adsorption studies on dye wastewater. The equilibrium studies highlights a relationship between the concentration in the majority of the fluid phase and the material adsorbed at a constant temperature. The adsorption isotherms are used to express the amounts of dye adsorbed per unit mass. Moreover, it gives adequate information about the adsorption process. In this study, the Langmuir and the Freundlich isotherm models were used to describe the equilibrium adsorption characteristics of Malachite green using CNTIB by varying dye concentrations. Its validity assumes that a monolayer sorption of malachite green dye on a surface containing a finite number of sites took place in the studied system.
1.Materials And Methods
The materials and chemicals used in this research were CNTs (from sigma), Methanol (CH3OH), malt extract, distilled water, hydrochloric acid (HCl), Sodium hydroxide (NaOH), fungal strains (collected from Environmental Biotechnology lab of IIUM) , other consumables and Malachite Green dye (MG) of analytical chemical grade. About 200 mg/L of MG was prepared as stock solution by dissolving 200 mg of MG dye in 1000 mL distilled water. The stock solution was then diluted with distilled water to different concentrations desired for the experiment. The supernatant fluids were then filtered off with whattman filter paper. The chemical formula, molecular weight and maximum wavelength and chemical structure of MG dye have been summarized in Table 1 and figure 1 respectively.
Malachite green
Basic green, aniline green, fast green, etc
N-[4-[[4-(dimethylamino)phenyl]phenylmethylene]-2,5- cyclohexadien-1-ylidene]-N- methylmathanaminium chloride
Figure1: Malachite green structure
2.2 Instrumentation
The structure of the carbon nanotubes immobilized biomass (CNTIB) was examined using the scanning electronmicroscope (SEM) (model: JEOL JSM-6300F) under a voltage of 18 Kv and resolution of 5.0 nm. All pH measurements were made with a pH meter. The sample was dried in a drier and agitation of the system was done on a shaker. The residual MG concentration in the aqueous solution was ascertained by using UV/Vis spectrophotometer. The structure of the carbon nanotubes immobilized biomass (CNTIB) was examined using the scanning electron.
(A)Aspergillus niger biomass only
(B) Carbon nanotubes only
Figure 2 a, b and c shows the SEM images of Carbon nanotubes alone, fungal biomass only and carbon nanotubes immobilized biomass (CNTIB). From figures 2 a and b, the SEM images showed no existence for any matrix on their surfaces. However, from c, the results for the carbon nanotubes immobilized biomass of Aspergillus niger showed the attachment of fungal mycelia attached to carbon nanotubes. Furthermore, Figure 2c showed that there was an obvious entrapment after immobilization of Aspergillus niger on carbon nanotubes forming a matrix. It is clearly indicated that the powered carbon nanotubes were significantly attached to Aspergillus niger which is well disposed for adsorption of dye molecules. As shown, the branches of microbial biomass got a significant structural change as compared to the structures without entrapment.
3.2 Statistical analysis for dye removal
Using the experimental design software version 7, batch runs were conducted according to Face Centered Central Composite Design (FCCCD) (model design experiments) to visualize the effect of independent variables on the response along with the experimental conditions.
The analysis demonstrated that the model was highly significant with a model F-value of 8.32 and Prob> F value of 0.0009. In general, Prob > F values of less than 0.0500 indicate the model is significant (Design Expert Software, 2007). The adequate precision ratio of the model was 8.85 which show an adequate signal for the model. It also implies that the model can be used to navigate the design space.
As discussed earlier, an experimental design (FCCCD) coupled with RSM was used to evaluate the effects of three process variables on the dye removal process.
3.2.1.1 Effect of dosages (Biosorbent loading) and pH on biosorption
In Figure 4.15 and 4.16, the contour and 3D-surface plots were developed as a function of dosages and pH, while the dye concentration was at 112.5 mg/L. As shown from the Figures, the maximum amount of dye removed was about 111.0 mg/L. The amount of dye removed from the initial amount of malachite green dye increased with increase in biosorbent dosages. The lowest amount of synthetic dye removed (64.65 mg/L) was obtained at a pH of about 8.75, while the dosage was around 4.75 mg/L. Based on ANOVA results obtained, both pH and biosorbent loading (dosages) were found to have significant effects on dye removal from dye solution.
Amount of dye removed (mg/L) |
Figure 3b: 3D-surface plot for dye removal as a function of Dosages (Biosorbent loading) and pH (contact time 6 hours)
3.2.1.2 Effect of dye concentration and dosages (biosorbent loading)
To investigate the interactive effect of dye concentration and biosorbent loading on dye removal, surface contour and 3D plots were drawn and studied. The plots are shown in Figure 4a and b. It was observed that the interactive effect of the two process variables seemed to be same as compared to that of previous interaction. The lowest residual concentration of dye (64.65 mg/L) was obtained at a dosage of about 6.5 g/L. An increase in biosorbent loading also resulted in further increase in the amount of dye removed.
Biosorbent loading, C (g/L)
Actual amount of dye removed (mg/L)
Table 3: Validation of experimental model for dye biosorption
The Langmuir and Freundlich models were employed to describe the equilibrium adsorption. The Langmuir model assumes that adsorption occurs on homogenous surfaces for a known number of sites. The linear expression of the Langmuir model as described by (Periasamy, management, 1995).
(4)
Where qe is the amount of solute adsorbed per unit weight of adsorbent (mg/g), qmax is the maximum adsorption capacity corresponding to the site saturation, Ce is the solute concentration at equilibrium (mg/L) and Ka is the Langmuir equilibrium constant (L/mg).
Furthermore, the essential characteristics of the Langmuir isotherm can be expressed by the separation factor or equilibrium parameter which is a dimensionless constant RL as defined by Weber & Chakravorti (1974)
(5)
Where Ka is the Langmuir equilibrium constant (L/mg) and Ce is the highest initial dye concentration (mg/L). The parameter RL indicates the nature of the adsorption process. On the other hand, the Freundlich model is an empirical relation between the solute concentrations on an adsorbent surface to the concentration of the solute in the liquid it is in contact with. The non-linear freundlich isotherm model is given as:
(6)
The non-linear equation may also be linearized and represented by the following equation:
(7)
Where qe is the amount of solute adsorbed per unit weight of adsorbent (mg/g), Ce is the solute concentration at equilibrium (mg/L), while Kf and n are Freundlich constants, which can be determined by plotting loge versus log Ce. The value of n gives an indication of how favorable the adsorption process and KF represents the adsorption capacity of the adsorbent (Tan & Ahmad 2008).
The pseudo-first-order kinetic model has been widely used to predict sorption kinetics. Simonin (2016)definedthemodelas:
(8)
where qeand qt are the amounts of adsorbate adsorbed at equilibrium and at any time, t (min), respectively ( mg/g) and k1 is the adsorption rate constant (1/min). The plot of log (qe-qt) versus t gives the slope of k1 and intercept of log qe. At the concentration range of 20 mg/L to 60 mg/L, the linearized pseudo first-order and pseudo second-order kinetics model were plotted.
Figure7: kinetics graphs for biosorption of MG at different concentrations (a) Pseudo-first order and (b) Pseudo-second order (Conditions-dosage-3.5g/L, room temperature, and contact time of 3hr).
Linear regression of the pseudo-first order and pseudo-second order models was used to decide the corresponding kinetic parameters as presented in table 5.
At all the concentrations studied, comparing all R2 values, those of the pseudo second-order kinetics were found to be more than 0.90. According to (Wang & Chen, 2008) and (Ahalya, 2003), pseudo-second order kinetic model assumed that the rate limiting step was biosorption in which sharing or exchange of electrons between the biosorbent and the biosorbate must exist. The figure therefore provides a very similar correlation data.
Table 1: Dye used for the present study
Table 2: Analysis of variance (ANOVA) for Response Surface Model for dye biosorption
3.2.1 Effect of interactive experimental variables
Figure 3 a: Surface plot for dye removal from synthetic dye water as a function of Dosages (Biosorbent loading) and pH (Dye Conc. of 112.5mg/L)
To validate the robustness and applicability of the biosorption process, the initial values of process parameters were determined by the software for low and high levels. The actual values of biosorption parameters and the predicted values were presented in Table 3. The result showed that predicted values by the software and experimental values were close and this suggests that the model was validated.
amount of dye removed (mg/L)
Langmuir isotherm model
Freundlich isotherm model
qmax
(mg/g)
20 mg/L 1.89
K1
40 mg/L 1.95
60 mg/L 3.48
Table 4: Coefficients of Langmuir and Freundlich isotherms
Pseudo-second order
Table 5: Pseudo-first order and pseudo-second order kinetic model parameters for the biosorption of MG onto CNTIB at different concentrations
For both model plots, with respect to the correlation coefficient values, R2, the biosorption of Malachite green dye on CNTIB was described best by the pseudo second order model.
This study investigated the equilibrium and adsorption of Malachite green on CNTIB at various concentrations. The results of biosorption evaluation using the active biosorbent for dye removal showed that the dye was decolorized with a dye uptake of 98% at a dye concentration of 60mg/L as shown in table 5. Isotherm studies showed that the experimental data better fitted with the Langmuir isotherm for CNTIB when compared to Freundlich isotherm. The kinetic study however indicated that the biosorption followed the pseudo-second order kinetic model which suggests that chemisorption is most likely the process through which biosorption took place.
The authors would like to acknowledge the generous support from the research supported from Ministry of High Education Malaysia under FRGS 15-198-0439, as well we acknowledge the technical support from department of Biochemical
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