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Sorption of phenol from waters on activated carbon impregnated with iron oxide, aluminum oxide and titanium oxide
MOLLIQ-05079; No of Pages 9 Journal of Molecular Liquids xxx (2015) xxx–xxx
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Sorption of phenol from waters on activated carbon impregnated with iron oxide, aluminum oxide and titanium oxide Basim Abussaud a, Hamza A. Asmaly c, Ihsanullah a, Tawfik A. Saleh b, Vinod Kumar Gupta e,f,g,⁎, Tahar laoui h, Muataz Ali Atieh d,⁎ a
Department of Chemical Engineering, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia Chemistry Department, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia King Abdulaziz City for Science and Technology, Technology Innovation Center on Carbon Capture and Sequestration, King Fahd University of Petroleum and Minerals, Saudi Arabia d Qatar Environment and Energy Research Institute, Hamad bin Khalifa University; College of Science and Engineering, Hamad bin Khalifa University, Qatar Foundation, PO Box 5825, Doha, Qatar e Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India f Center for Environment and Water, The Research Institute, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia g Department of Applied Chemistry, University of Johannesburg, Johannesburg, South Africa h Department of Mechanical Engineering, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia b c
a r t i c l e
i n f o
Article history: Received 28 July 2015 Received in revised form 15 August 2015 Accepted 18 August 2015 Available online xxxx Keywords: Activated carbon Impregnation Phenol Adsorption
a b s t r a c t The efficiency of Fe2O3, Al2O3 and TiO2 nanoparticles-loaded activated carbon (AC) for the adsorption of phenol from waters, was investigated. The raw and doped ACs were characterized by using Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, Thermogravimetric analysis and Brunauer–Emmett–Teller surface analysis. Batch adsorption experiments were performed to evaluate the effects of solution pH, agitation speed, contact time, adsorbent dosage and ionic strength on the phenol removal efficiency. Activated carbon impregnated with Fe2O3, Al2O3 and TiO2 showed higher adsorption capacity compared to raw AC. The maximum removal of phenol was achieved by iron oxide, aluminum Oxide and titanium oxide doped AC under the optimum conditions of 200 mg dosage, at pH 7, 150 rpm agitation speed, 2 ppm initial phenol concentration and contact time of 2 h. While for raw AC, the maximum removal was achieved for an adsorbent dosage of 300 mg under the same treatment conditions. The Langmuir isotherm model best fitted the data of the adsorption of phenol using AC, AC–TiO2, AC–Fe2O3 and AC–Al2O3, with correlation coefficient of 0.971, 0.96, 0.976 and 0.972. Surface characterization of both the impregnated AC showed an improvement in its surface area of the doped AC. The adsorption capacities, as determined by the Langmuir isotherm model were 1.5106, 3.1530, 3.2875 and 3.5461 mg/g for raw AC, AC–TiO2, AC–Fe2O3 and AC–Al2O3. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Environmental laws are given general applicability and their enforcement has developed a growing interest in the treatment of the wastewater. Phenol is the priority organic pollutant due to its harmful nature and potential toxicity to human health. The toxic effect of phenol on human being includes diarrhea, impaired vision and excretion of dark urine [1]. Phenol sources are the wastewater from different chemical industries including pulp and paper, petroleum refinery, dye synthesis, coal gasification and pharmaceutical industries. Therefore, effective removal of phenol from the wastewater and reducing its concentrations to the permitted levels before discharging arechallenging issues [1–3]. The US Environmental Protection Agency (EPA) regulations suggest phenol concentration below 1 ppm for wastewater [4–5]. Various techniques have been developed for the removal of phenol from ⁎ Corresponding authors. E-mail addresses: [email protected] (V.K. Gupta), [email protected] (M.A. Atieh).
wastewater, such as electrochemical oxidation [6], adsorption by carbon fibers or activated carbon [2,7], wet air oxidation [8,9], chemical coagulation [10], solvent extraction [11], membrane separation [12,13], bioremediation [14,15] and photo catalytic degradation [16,17]. Activated sludge has been widely employed for the removal of phenol from wastewater because of relatively low cost and straightforward process [18]. However, this method is not efficient for the treatment of wastewater with high concentration of phenol due to low biodegradability. In addition, the regeneration process of the adsorbent is not only expensive, but also very complex [3,19]. Other process like bioremediation has also been extensively used for phenol and low molecular weight Polycyclic Aromatic Hydrocarbons (PAHs). The process of bioremediation is relatively simple, but has shown limited success for the degradation of high-molecular weight PAHs [13]. Ultraviolet (UV) radiation is another alternate process for mineralization/transformation of these contaminants, but it has the disadvantage of being expensive, particularly on a large scale [19]. Other physical and chemical remediation techniques applied to phenol
http://dx.doi.org/10.1016/j.molliq.2015.08.044 0167-7322/© 2015 Elsevier B.V. All rights reserved.
Please cite this article as: B. Abussaud, et al., Sorption of phenol from waters on activated carbon impregnated with iron oxide, aluminum oxide and titanium oxide, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.044
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B. Abussaud et al. / Journal of Molecular Liquids xxx (2015) xxx–xxx
contaminated water include venting, using solvents and surfactants. The limitation of these techniques is that high solvent concentrations are required for achieving good results [11]. Adsorption is favored by its potential to remove organic and inorganic constituents, even at low concentrations. Adsorption has the advantage of its relative ease of operation both in batch and continuous operation, the absence of sludge formation, potential of regenerative reuse of adsorbent and availability of low cost adsorbent materials [13]. Carbon-based adsorbent materials, which are hydrophobic and non-polar, have good potential for phenol removal in wastewater. Their large surface area, well-developed porosity and tunable surface-containing functional groups are features that enhanced their adsorption efficiency [13–15]. Many researchers [7,20–23] have reported the potential of carbon nanotubes and activated carbon for the removal of phenolic compounds. The large percentage of micropores and high pore volumes and surface area are typical characteristics of activated carbon that are responsible for the enhanced removal of phenols [20]. Although removal of phenol using raw activated carbon is reported by many researchers, however, the potential of modified activated carbon for the removal of phenol compounds is comparatively less reported in the literature [24–27]. Acid treatment of the activated carbon is one of the most effective ways for the enhanced removal of phenols. However, other modification techniques have also been employed to modify the surface of activated carbon [28]. Most of the modification techniques have reported to improve the removal efficiency of AC for the phenolic compounds. Here, the work is to examine adsorption characteristic for phenol on modified AC by nanoparticles of iron oxide, aluminum oxide and titanium oxide. The physicochemical properties of the modified and unmodified AC were determined using SEM, EDS, TGA and BET surface area analysis. The effects of adsorbent dosage, contact time, pH, initial phenol concentration and shaking speed on the removal of phenol were investigated. 2. Material and methods 2.1. Materials Activated carbons (ACs) used in this study were purchased from Calgon Ltd., supplied in 10–30 mesh (0.60–1.0 mm) size. The granular form was milled in a hammer-cutter mill to powder (b0.18 mm in particle diameter) for use in this study.
2.4. Batch adsorption studies Batch adsorption experiments were conducted at room temperature to study the effects of pH, contact time, adsorbent dosage and agitation speed on the phenol adsorption efficiency by the raw and AC impregnated aluminum oxide (Al2O3) and titanium oxide (TiO2). Experiments were performed in volumetric flasks and the concentrations of phenol were measured using UV–VIS spectrophotometer. The adsorption capacity (qe) was calculated using the following equations; Percentage Removal ¼
Ci −Ce 100 Ci
Adsorption Capacity; qe ðmg=gÞ ¼
Ci −Ce V Ms
ð1Þ
ð2Þ
where Ci and Ce are the initial and the equilibrium concentrations of phenol ions in the solution (mg/L), V is the total volume of solution (L), and MS is the adsorbent dosage (g). The parameters considered for the study were adsorbent dosage, contact time, ionic strength of phenol, shaking speed and pH. 2.5. Adsorption isotherm models Langmuir and Freundlich are the two commonly used isotherm models to represent the adsorption data. The Langmuir isotherm model is based on the assumption of monolayer adsorption from the homogenous surface while Freundlich isotherm models assume adsorption from heterogeneous surface, with non-uniform heat distribution on the surface. The Langmuir and Freundlich models can be expressed mathematically by Eqs. (3) and (4) respectively: Ce 1 Ce ¼ þ Q e Q max KL Q max Log Q e ¼ LogK f þ
1 LogðCe Þ n
ð3Þ
ð4Þ
where: Qe (mg/g) = amount adsorbed (mg/g). Ce (mg/L) = equilibrium concentration of phenol in the liquid phase. Qm (mg/g) = maximum adsorption capacity. KL = Langmuir constant. Kf and n are the Freundlich constants. 3. Results and discussions
2.2. Impregnation of activated carbon
3.1. Characterization
Aluminum nitrate was impregnated onto 5 g of the AC in ethanol (98% purity). Firstly, specific amount of AC were dispersed in ethanol, followed by sonication (110 V at 40% amplitude). Aluminum nitrate was also dispersed separately in ethanol and sonicated. Finally, both the solutions (AC and aluminum nitrate) were mixed and sonicated to ensure dispersion of the particles. Ethanol is then evaporated from the mixture and calcinated at 350 °C for 3 h to produce AC–Al2O3. Titanium oxide (TiO2) and iron oxide (Fe2O3) from titanium isopropoxide and iron nitrate were imprinted on AC in a similar way to produce AC– TiO2 and AC–Fe2O3 respectively.
3.1.1. SEM and EDS The SEM images of ACs, AC–Al2O3 and AC–TiO2 are depicted in Fig. 1a & b. The white spots in the SEM images of AC–Al2 O3 and AC–TiO2 show Al2O3 and TiO2 particles, respectively, as confirmed by EDS analysis. The outcome of the analysis is shown as EDS spectrum in Fig. 2. Table 1 indicates the weight percentages of the elements. The peaks of iron, aluminum and titanium can be clearly observed in the spectrum [29].
2.3. Preparation of stock solution The stock solution of phenol with initial concentration of 2 ppm was prepared by serial dilution of 1000 ppm solution. First 1000 mg of phenol was dissolved in 1 L deionized water. Solvents (1.0 M Nitric Acid and 1.0 M Sodium) were used to adjust the pH of the stock solution. The solution pH was maintained constant during the experiments, by means of buffer solutions.
3.1.2. Thermogravimetric analysis (TGA) The thermal analysis results of thermogravimetric analysis (TGA) and derivative thermogravimetric analysis (DTGA) curves obtained from the raw and modified AC with metals at a heating rate (10 °C/min) are shown below in Fig. 3 (a, b, c & d). The TGA thermograms were carried out in the air and it was noted that there was some residual remains of the samples, when it was heated up to 800 °C. The TGA curve for AC–TiO2 (Fig. 3c) shows district behavior from the other three adsorbents. It can be seen that two degradation temperatures exist at 100 °C and 500 °C, respectively. The amount of the sample
Please cite this article as: B. Abussaud, et al., Sorption of phenol from waters on activated carbon impregnated with iron oxide, aluminum oxide and titanium oxide, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.044
B. Abussaud et al. / Journal of Molecular Liquids xxx (2015) xxx–xxx
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Fig. 1. SEM images of (a) raw AC (b) AC–TiO2 (c) AC–Al2O3 (d) AC–Fe2O3 (a) EDS spectrum of AC–Al2O3 (b) EDS spectrum of AC–TiO2 (c) EDS spectrum of AC–Fe2O3.
adsorbents were 7.533, 5.3250, 5.270 and 5.532 mg of AC, AC–Al2O3, AC– TiO2 & AC–Fe2O3, respectively. 3.1.3. Brunauer–Emmett–Teller (BET) surface area analysis Aimed at determining the improvement in surface morphology following aluminum oxide impregnation of the AC, BET surface area analysis was conducted. The analysis was performed using Micrometrics ASAP 2020 and results were interpreted based on the adsorption– desorption of N2 at 77 K for regular and impregnated ACs (Fig. 4). The BET surface area values obtained from the raw AC, iron oxide, titanium oxide and aluminum oxide impregnated ACs were 1127 m2/g, 1039 m2/g, 1081 m2/g and 1884 m2/g. 3.2. Adsorption of phenol from aqueous solution 3.2.1. Effect of pH The role of solution pH is critical in the removal of phenol from water, since it can affect the surface charge of the adsorbent. The extent of dephenolation by ACs, AC–Al2O3 and AC–TiO2 was evaluated in the pH range from 2 to 9, as shown in Fig. 5. All the other parameters including contact time, adsorbent dosage and shacking speed were kept constant at 2 h, 50 mg and 100 rpm respectively. Fig. 5 revealed that the highest removal efficiency of phenol was observed at pH 7, with the percentage removal of 64.8%, 83.7%, 84.2% and 85.3% by AC, AC–TiO2,
AC–Fe2O3 and AC–Al2O3, respectively. However, a decrease in the percentage removal was observed for all the adsorbents at higher pH. The decrease in the percentage removal of phenol at higher pH by raw ACs can be explained on the basis of ionic chemistry of the solution and surface charge of the ACs. Phenol is a weak acid (pKa = 10) and will adsorb to a lesser extent at higher pH. Therefore, at higher pH, the repulsive forces between the negatively charged surface of ACs and phenol are responsible for low adsorption. While at lower pH (below 7), the presence of more positive ions on the surface of ACs, leads to electrostatic interaction with the phenolate ions and enhanced the adsorption. It is also important to note that at higher pH, some other mechanisms like physical adsorption might occur, which can also affect the ion exchange process. It was observed from Fig. 5 that the removal efficiency of phenol by AC–Al2O3 is highest among the three adsorbents for the same pH values. This behavior can be justified due to the highest surface area of ACs after impregnation with Al2O3 which provides more adsorption sites for phenol ions. 3.2.2. Effect of agitation speed Agitation facilitates a proper contact between ions in the solution and adsorbent binding sites and thereby promotes effective diffusion of ions towards the adsorbent surface. The range of agitation speed used in this study was from 50 to 250 rpm, while all the other
Please cite this article as: B. Abussaud, et al., Sorption of phenol from waters on activated carbon impregnated with iron oxide, aluminum oxide and titanium oxide, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.044
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Fig. 2. EDS spectrum of (a) AC–Al2O3, (b) AC–TiO2 and (c) AC–Fe2O3.
parameters including contact time, adsorbent dosage, ionic strength and pH were kept constant at 2 h, 50 mg, 2 ppm and 7 respectively. The effect of shaking speed on the removal efficiency of ACs, AC–TiO2, AC–Fe2O3 and AC–Al2O3 is depicted in Fig. 6. The results showed that the removal efficiency of phenol increases with increase in agitation speed and maximum removal by ACs, AC–TiO2, AC–Fe2O3 and AC–Al2O3 was achieved at 150 rpm. This can be justified by the fact that an effective
transport of phenol ions towards the adsorbent surfaces occurred, due to less resistance to diffusion at higher shaking speed. However, no significant change in removal efficiency was achieved beyond 150 rpm, which might be due to the saturation of adsorption sites. It is worth mentioning that AC–Al2O3 showed the highest removal of 92.1%, while for AC–Fe2O3, AC–TiO2 and raw ACs, removal of 90.5, 89.5 and 73.4% were achieved for the same value of agitation speed.
Please cite this article as: B. Abussaud, et al., Sorption of phenol from waters on activated carbon impregnated with iron oxide, aluminum oxide and titanium oxide, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.044
B. Abussaud et al. / Journal of Molecular Liquids xxx (2015) xxx–xxx Table 1 EDS analysis of ACs, AC–TiO2 and AC–Al2O3. AC sample
Raw ACs
AC–Al2O3
AC–TiO2
Element
Weight %
Weight %
Weight %
Weight %
C O Al Ti Fe Total %
96.6 3.4 – – – 100
74.65 14.01 11.34 – – 100
71.3 12.5 – 16.2 – 100
78.3 10.6 – – 6.1 100
AC–Fe2O3
This observation was attributed to the improved contact between the phenol ions in the solution and the presence of more active adsorption sites on the AC–Al2O3 surface. Some studies have reported similar behavior between carbon based adsorbents and phenol at 200 rpm [30–33]. 3.2.3. Effect of contact time In order to study the effect of contact time on the removal efficiency of phenol and to determine the equilibrium time for maximum uptake of phenol ions by ACs, AC–TiO2, AC–Fe2O3 and AC–Al2O3, experiments were performed under contact times from 0 to 720 min. All the other parameters including agitation speed, adsorbent dosage, ionic strength and pH were kept constant at 150 rpm, 50 mg, 2 ppm and 7 respectively. As can be seen in Fig. 7, a gradual increase in phenol removal efficiency was observed to increase in time till 120 min for all the adsorbents, at which the optimum adsorption was attained. This observation was attributed to the adsorption equilibrium phenomenon, whereby the rate of adsorption was higher than the rate of desorption up to 2 h of contact time, which is the equilibrium adsorption point. The rate of adsorption and desorption were the same and no further removal of phenol from the
5
solution was achieved. Also, a clear desorption of phenol from both the adsorbents was observed after 2 h due to the saturation of the active sites on the surfaces of adsorbents. An increase in adsorption of phenol ions to increase in contact time may also be due to the decrease in boundary layer resistance of the hydrate layer [34]. Furthermore, the phenol removal efficiency of AC–Al2O3 was highest among the three adsorbents at the same contact time. The maximum phenol removal efficiency by AC– Al2O3, AC–Fe2O3, AC–TiO2 and ACs were 93.1, 90.5, 89.5 and 74.4%, respectively, after a contact time of 2 h. 3.2.4. Effect of adsorbent dosage The adsorption effectiveness for treatment of pollutant is usually subjected to the number and availability of active adsorption sites on the adsorbent surface. Generally, increasing the dosage of the adsorbent increases the number of adsorption sites [34]. The doses of adsorbents were varied from 10 to 600 mg, while all the other parameters including shaking speed, contact time, ionic strength and pH were kept constant at 150 rpm, 120 min, 2 ppm and 7 respectively. As depicted in Fig. 8, the percentage removal of phenol was observed to increase with an increase in the adsorbent dosages, with maximum removal at 200 mg for AC–Al2O3, AC-TiO2 and AC-Fe2O3, respectively. While for raw AC, an adsorbent dose of 300 mg was required for achieving the maximum (100%) removal. The higher removal by AC–Al2O3, AC–TiO2 and AC– Fe2O3 is due to increase in surface area after an impregnation and increased number of adsorption sites. 3.2.5. Effect of ionic strength The removal extent of phenol is dependent on the ionic strength. Therefore, the impact of phenol concentration in the aqueous solution on its adsorption by the ACs, AC–TiO2, AC–Fe2O3 and AC–Al2O3 adsorbent was also studied. The ionic strength of phenol in the solution varied from
Fig. 3. TGA curves for (a) AC, (b) AC–Al2O3, (c) AC–TiO2 and (d) AC–Fe2O3.
Please cite this article as: B. Abussaud, et al., Sorption of phenol from waters on activated carbon impregnated with iron oxide, aluminum oxide and titanium oxide, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.044
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Fig. 4. BET surface area for (a) AC, (b) AC–Fe2O3, (c) AC–TiO2 and (d) AC–Al2O3.
2 to 10 ppm, and its effect on the removal efficiency was ascertained. All the other parameters were kept constant during the experiment. From Fig. 9, it was observed that increasing the initial phenol concentration in the solution resulted in a decrease in the removal efficiency of the phenol
Fig. 5. Effect of pH on phenol adsorption.
Fig. 6. Effect of agitation speed on phenol adsorption.
Please cite this article as: B. Abussaud, et al., Sorption of phenol from waters on activated carbon impregnated with iron oxide, aluminum oxide and titanium oxide, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.044
B. Abussaud et al. / Journal of Molecular Liquids xxx (2015) xxx–xxx
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Fig. 9. Effect of ionic strength on phenol adsorption. Fig. 7. Effect of contact time on phenol adsorption.
by raw and doped adsorbents. This observation was attributed to the high amount of phenol ions with limited active adsorption sites on the adsorbent surfaces, which leads to increase the concentration of phenol ions in the bulk solution and thus decreased the removal of phenol. This decrease in phenol uptake with an increase in phenol concentration is logical, because the time required to attain equilibrium was expected to be longer at higher concentrations than at lower concentration. It is interesting to observe that the doped ACs still have higher removal efficiency than the raw ACs for the same value of initial phenol concentration. This can be justified on the basis of availability of more adsorption sites and higher surface area of the doped ACs. Therefore, more ions can be adsorbed on the surface compared to raw ACs at higher phenol concentration and hence higher removal efficiency was observed. 3.2.6. Adsorption isotherm model The experimental results obtained on the adsorption of phenol were analyzed by the Langmuir and Freundlich models. The maximum adsorption capacity determined at optimum set of parameters, were used for these adsorption isotherm models. The linear form of Langmuir isotherm is given by Eq. (3), while a plot of Ce/Qe against Ce is shown in Fig. 10. The maximum adsorption capacity (Qm) and adsorption intensity were determined from the slope and intercept of the straight line [15, 35–38]. It is interesting to note that a good straight line with a high correlation coefficient was obtained for AC, AC–TiO2, AC–Fe2O3 and AC–Al2O3. The data of phenol adsorption were also analyzed by Freundlich model. Based on the Freundlich isotherm model given by the Eq. (4), a plot of log qe against logCe was generated as shown in Fig. 11, which
Fig. 8. Effect of adsorbent dosage on phenol adsorption.
clearly shows the deviation of data from the straight line suggested by the Freundlich model. However, the Freundlich constants, KF and n; were determined from the best-fit line. The adsorption behavior of adsorbent was best described by the Langmuir adsorption model as compared to the Freundlich model, as shown by their correlation coefficient values in Table 2. The adsorption capacities, as determined by the Langmuir isotherm model were 1.5106, 3.1530, 3.2875 and 3.5461 mg/g for raw ACs, AC– TiO2, AC–Fe2O3 and AC–Al2O3 respectively. The highest adsorption capacity of AC–Al2O3 is due to its highest surface area and more adsorption sites than AC–Fe2O3, AC–TiO2 and raw ACs. The above analysis also indicates that phenol ions were strongly adsorbed to the surfaces of the AC–Al2O3 suggesting that impregnation of ACs with Al2O3 have great impact on the adsorption of phenol ions from water. Comparing with some other materials and nanomaterials [39–57], the reported materials showed high capacity with the advantage of being cost-effective. 4. Conclusions The reported AC impregnated with nanoparticles of TiO2, Fe2O3 and Al2O3, were successfully synthesized and used in the removal of phenol from aqueous environments. Tritium oxide, iron oxide and aluminum oxide impregnation has improved its phenol removal efficiency from aqueous solution. Several parameters such as agitation speed, adsorbent dosage, contact time, pH and initial phenol concentration were found to
Fig. 10. Langmuir adsorption model for phenol at pH 7.
Please cite this article as: B. Abussaud, et al., Sorption of phenol from waters on activated carbon impregnated with iron oxide, aluminum oxide and titanium oxide, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.044
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Fig. 11. Freundlich adsorption model for phenol at pH 7.
Table 2 Parameters of Langmuir and Freundlich adsorption isotherm models for phenol removal. Langmuir
Freundlich 2
Adsorbent
Qm (mg/g)
KL (L/mg)
R
n
KF
R2
AC AC–TiO2 AC–Fe2O3 AC–Al2O3
1.5106 3.1530 3.2875 3.5461
33.100 1.3742 2.6658 4.8621
0.971 0.960 0.976 0.972
8.1967 1.535 1.830 2.322
1.3152 2.5823 1.7442 1.5632
0.384 0.933 0.170 0.846
significantly affect the phenol removal efficiency. The optimum removal from the aqueous solution was achieved at pH 7, 150 rpm agitation speed, 200 mg dosage, 2 h contact time and 2 ppm initial phenol concentration. The data from the phenol adsorption behavior of the raw and doped ACs were best fitted by the Langmuir adsorption isotherm model, with correlation coefficients of 0.971, 0.96, 0.976 and 0.972 for AC, AC–TiO2, AC–Fe2O3 and AC–Al2O3. The adsorption capacities, as determined by the Langmuir isotherm model were 1.5106, 3.1530, 3.2875 and 3.5461 mg/g for raw AC, AC–TiO2, AC–Fe2O3 and AC–Al2O3, respectively. The highest adsorption capacity by nanoparticles loaded AC is mainly attributed to additional adsorption sites.
Acknowledgment The authors acknowledge the financial support provided by King Abdulaziz City for Science and Technology (KACST) through the Science and Technology Unit at King Fahd University of Petroleum and Minerals (KFUPM) through project no. AR-30-92.
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Please cite this article as: B. Abussaud, et al., Sorption of phenol from waters on activated carbon impregnated with iron oxide, aluminum oxide and titanium oxide, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.044
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Sorption of phenol from waters on activated carbon impregnated with iron oxide, aluminum oxide and titanium oxide Basim Abussaud a, Hamza A. Asmaly c, Ihsanullah a, Tawfik A. Saleh b, Vinod Kumar Gupta e,f,g,⁎, Tahar laoui h, Muataz Ali Atieh d,⁎ a
Department of Chemical Engineering, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia Chemistry Department, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia King Abdulaziz City for Science and Technology, Technology Innovation Center on Carbon Capture and Sequestration, King Fahd University of Petroleum and Minerals, Saudi Arabia d Qatar Environment and Energy Research Institute, Hamad bin Khalifa University; College of Science and Engineering, Hamad bin Khalifa University, Qatar Foundation, PO Box 5825, Doha, Qatar e Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India f Center for Environment and Water, The Research Institute, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia g Department of Applied Chemistry, University of Johannesburg, Johannesburg, South Africa h Department of Mechanical Engineering, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia b c
a r t i c l e
i n f o
Article history: Received 28 July 2015 Received in revised form 15 August 2015 Accepted 18 August 2015 Available online xxxx Keywords: Activated carbon Impregnation Phenol Adsorption
a b s t r a c t The efficiency of Fe2O3, Al2O3 and TiO2 nanoparticles-loaded activated carbon (AC) for the adsorption of phenol from waters, was investigated. The raw and doped ACs were characterized by using Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, Thermogravimetric analysis and Brunauer–Emmett–Teller surface analysis. Batch adsorption experiments were performed to evaluate the effects of solution pH, agitation speed, contact time, adsorbent dosage and ionic strength on the phenol removal efficiency. Activated carbon impregnated with Fe2O3, Al2O3 and TiO2 showed higher adsorption capacity compared to raw AC. The maximum removal of phenol was achieved by iron oxide, aluminum Oxide and titanium oxide doped AC under the optimum conditions of 200 mg dosage, at pH 7, 150 rpm agitation speed, 2 ppm initial phenol concentration and contact time of 2 h. While for raw AC, the maximum removal was achieved for an adsorbent dosage of 300 mg under the same treatment conditions. The Langmuir isotherm model best fitted the data of the adsorption of phenol using AC, AC–TiO2, AC–Fe2O3 and AC–Al2O3, with correlation coefficient of 0.971, 0.96, 0.976 and 0.972. Surface characterization of both the impregnated AC showed an improvement in its surface area of the doped AC. The adsorption capacities, as determined by the Langmuir isotherm model were 1.5106, 3.1530, 3.2875 and 3.5461 mg/g for raw AC, AC–TiO2, AC–Fe2O3 and AC–Al2O3. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Environmental laws are given general applicability and their enforcement has developed a growing interest in the treatment of the wastewater. Phenol is the priority organic pollutant due to its harmful nature and potential toxicity to human health. The toxic effect of phenol on human being includes diarrhea, impaired vision and excretion of dark urine [1]. Phenol sources are the wastewater from different chemical industries including pulp and paper, petroleum refinery, dye synthesis, coal gasification and pharmaceutical industries. Therefore, effective removal of phenol from the wastewater and reducing its concentrations to the permitted levels before discharging arechallenging issues [1–3]. The US Environmental Protection Agency (EPA) regulations suggest phenol concentration below 1 ppm for wastewater [4–5]. Various techniques have been developed for the removal of phenol from ⁎ Corresponding authors. E-mail addresses: [email protected] (V.K. Gupta), [email protected] (M.A. Atieh).
wastewater, such as electrochemical oxidation [6], adsorption by carbon fibers or activated carbon [2,7], wet air oxidation [8,9], chemical coagulation [10], solvent extraction [11], membrane separation [12,13], bioremediation [14,15] and photo catalytic degradation [16,17]. Activated sludge has been widely employed for the removal of phenol from wastewater because of relatively low cost and straightforward process [18]. However, this method is not efficient for the treatment of wastewater with high concentration of phenol due to low biodegradability. In addition, the regeneration process of the adsorbent is not only expensive, but also very complex [3,19]. Other process like bioremediation has also been extensively used for phenol and low molecular weight Polycyclic Aromatic Hydrocarbons (PAHs). The process of bioremediation is relatively simple, but has shown limited success for the degradation of high-molecular weight PAHs [13]. Ultraviolet (UV) radiation is another alternate process for mineralization/transformation of these contaminants, but it has the disadvantage of being expensive, particularly on a large scale [19]. Other physical and chemical remediation techniques applied to phenol
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Please cite this article as: B. Abussaud, et al., Sorption of phenol from waters on activated carbon impregnated with iron oxide, aluminum oxide and titanium oxide, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.044
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contaminated water include venting, using solvents and surfactants. The limitation of these techniques is that high solvent concentrations are required for achieving good results [11]. Adsorption is favored by its potential to remove organic and inorganic constituents, even at low concentrations. Adsorption has the advantage of its relative ease of operation both in batch and continuous operation, the absence of sludge formation, potential of regenerative reuse of adsorbent and availability of low cost adsorbent materials [13]. Carbon-based adsorbent materials, which are hydrophobic and non-polar, have good potential for phenol removal in wastewater. Their large surface area, well-developed porosity and tunable surface-containing functional groups are features that enhanced their adsorption efficiency [13–15]. Many researchers [7,20–23] have reported the potential of carbon nanotubes and activated carbon for the removal of phenolic compounds. The large percentage of micropores and high pore volumes and surface area are typical characteristics of activated carbon that are responsible for the enhanced removal of phenols [20]. Although removal of phenol using raw activated carbon is reported by many researchers, however, the potential of modified activated carbon for the removal of phenol compounds is comparatively less reported in the literature [24–27]. Acid treatment of the activated carbon is one of the most effective ways for the enhanced removal of phenols. However, other modification techniques have also been employed to modify the surface of activated carbon [28]. Most of the modification techniques have reported to improve the removal efficiency of AC for the phenolic compounds. Here, the work is to examine adsorption characteristic for phenol on modified AC by nanoparticles of iron oxide, aluminum oxide and titanium oxide. The physicochemical properties of the modified and unmodified AC were determined using SEM, EDS, TGA and BET surface area analysis. The effects of adsorbent dosage, contact time, pH, initial phenol concentration and shaking speed on the removal of phenol were investigated. 2. Material and methods 2.1. Materials Activated carbons (ACs) used in this study were purchased from Calgon Ltd., supplied in 10–30 mesh (0.60–1.0 mm) size. The granular form was milled in a hammer-cutter mill to powder (b0.18 mm in particle diameter) for use in this study.
2.4. Batch adsorption studies Batch adsorption experiments were conducted at room temperature to study the effects of pH, contact time, adsorbent dosage and agitation speed on the phenol adsorption efficiency by the raw and AC impregnated aluminum oxide (Al2O3) and titanium oxide (TiO2). Experiments were performed in volumetric flasks and the concentrations of phenol were measured using UV–VIS spectrophotometer. The adsorption capacity (qe) was calculated using the following equations; Percentage Removal ¼
Ci −Ce 100 Ci
Adsorption Capacity; qe ðmg=gÞ ¼
Ci −Ce V Ms
ð1Þ
ð2Þ
where Ci and Ce are the initial and the equilibrium concentrations of phenol ions in the solution (mg/L), V is the total volume of solution (L), and MS is the adsorbent dosage (g). The parameters considered for the study were adsorbent dosage, contact time, ionic strength of phenol, shaking speed and pH. 2.5. Adsorption isotherm models Langmuir and Freundlich are the two commonly used isotherm models to represent the adsorption data. The Langmuir isotherm model is based on the assumption of monolayer adsorption from the homogenous surface while Freundlich isotherm models assume adsorption from heterogeneous surface, with non-uniform heat distribution on the surface. The Langmuir and Freundlich models can be expressed mathematically by Eqs. (3) and (4) respectively: Ce 1 Ce ¼ þ Q e Q max KL Q max Log Q e ¼ LogK f þ
1 LogðCe Þ n
ð3Þ
ð4Þ
where: Qe (mg/g) = amount adsorbed (mg/g). Ce (mg/L) = equilibrium concentration of phenol in the liquid phase. Qm (mg/g) = maximum adsorption capacity. KL = Langmuir constant. Kf and n are the Freundlich constants. 3. Results and discussions
2.2. Impregnation of activated carbon
3.1. Characterization
Aluminum nitrate was impregnated onto 5 g of the AC in ethanol (98% purity). Firstly, specific amount of AC were dispersed in ethanol, followed by sonication (110 V at 40% amplitude). Aluminum nitrate was also dispersed separately in ethanol and sonicated. Finally, both the solutions (AC and aluminum nitrate) were mixed and sonicated to ensure dispersion of the particles. Ethanol is then evaporated from the mixture and calcinated at 350 °C for 3 h to produce AC–Al2O3. Titanium oxide (TiO2) and iron oxide (Fe2O3) from titanium isopropoxide and iron nitrate were imprinted on AC in a similar way to produce AC– TiO2 and AC–Fe2O3 respectively.
3.1.1. SEM and EDS The SEM images of ACs, AC–Al2O3 and AC–TiO2 are depicted in Fig. 1a & b. The white spots in the SEM images of AC–Al2 O3 and AC–TiO2 show Al2O3 and TiO2 particles, respectively, as confirmed by EDS analysis. The outcome of the analysis is shown as EDS spectrum in Fig. 2. Table 1 indicates the weight percentages of the elements. The peaks of iron, aluminum and titanium can be clearly observed in the spectrum [29].
2.3. Preparation of stock solution The stock solution of phenol with initial concentration of 2 ppm was prepared by serial dilution of 1000 ppm solution. First 1000 mg of phenol was dissolved in 1 L deionized water. Solvents (1.0 M Nitric Acid and 1.0 M Sodium) were used to adjust the pH of the stock solution. The solution pH was maintained constant during the experiments, by means of buffer solutions.
3.1.2. Thermogravimetric analysis (TGA) The thermal analysis results of thermogravimetric analysis (TGA) and derivative thermogravimetric analysis (DTGA) curves obtained from the raw and modified AC with metals at a heating rate (10 °C/min) are shown below in Fig. 3 (a, b, c & d). The TGA thermograms were carried out in the air and it was noted that there was some residual remains of the samples, when it was heated up to 800 °C. The TGA curve for AC–TiO2 (Fig. 3c) shows district behavior from the other three adsorbents. It can be seen that two degradation temperatures exist at 100 °C and 500 °C, respectively. The amount of the sample
Please cite this article as: B. Abussaud, et al., Sorption of phenol from waters on activated carbon impregnated with iron oxide, aluminum oxide and titanium oxide, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.044
B. Abussaud et al. / Journal of Molecular Liquids xxx (2015) xxx–xxx
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Fig. 1. SEM images of (a) raw AC (b) AC–TiO2 (c) AC–Al2O3 (d) AC–Fe2O3 (a) EDS spectrum of AC–Al2O3 (b) EDS spectrum of AC–TiO2 (c) EDS spectrum of AC–Fe2O3.
adsorbents were 7.533, 5.3250, 5.270 and 5.532 mg of AC, AC–Al2O3, AC– TiO2 & AC–Fe2O3, respectively. 3.1.3. Brunauer–Emmett–Teller (BET) surface area analysis Aimed at determining the improvement in surface morphology following aluminum oxide impregnation of the AC, BET surface area analysis was conducted. The analysis was performed using Micrometrics ASAP 2020 and results were interpreted based on the adsorption– desorption of N2 at 77 K for regular and impregnated ACs (Fig. 4). The BET surface area values obtained from the raw AC, iron oxide, titanium oxide and aluminum oxide impregnated ACs were 1127 m2/g, 1039 m2/g, 1081 m2/g and 1884 m2/g. 3.2. Adsorption of phenol from aqueous solution 3.2.1. Effect of pH The role of solution pH is critical in the removal of phenol from water, since it can affect the surface charge of the adsorbent. The extent of dephenolation by ACs, AC–Al2O3 and AC–TiO2 was evaluated in the pH range from 2 to 9, as shown in Fig. 5. All the other parameters including contact time, adsorbent dosage and shacking speed were kept constant at 2 h, 50 mg and 100 rpm respectively. Fig. 5 revealed that the highest removal efficiency of phenol was observed at pH 7, with the percentage removal of 64.8%, 83.7%, 84.2% and 85.3% by AC, AC–TiO2,
AC–Fe2O3 and AC–Al2O3, respectively. However, a decrease in the percentage removal was observed for all the adsorbents at higher pH. The decrease in the percentage removal of phenol at higher pH by raw ACs can be explained on the basis of ionic chemistry of the solution and surface charge of the ACs. Phenol is a weak acid (pKa = 10) and will adsorb to a lesser extent at higher pH. Therefore, at higher pH, the repulsive forces between the negatively charged surface of ACs and phenol are responsible for low adsorption. While at lower pH (below 7), the presence of more positive ions on the surface of ACs, leads to electrostatic interaction with the phenolate ions and enhanced the adsorption. It is also important to note that at higher pH, some other mechanisms like physical adsorption might occur, which can also affect the ion exchange process. It was observed from Fig. 5 that the removal efficiency of phenol by AC–Al2O3 is highest among the three adsorbents for the same pH values. This behavior can be justified due to the highest surface area of ACs after impregnation with Al2O3 which provides more adsorption sites for phenol ions. 3.2.2. Effect of agitation speed Agitation facilitates a proper contact between ions in the solution and adsorbent binding sites and thereby promotes effective diffusion of ions towards the adsorbent surface. The range of agitation speed used in this study was from 50 to 250 rpm, while all the other
Please cite this article as: B. Abussaud, et al., Sorption of phenol from waters on activated carbon impregnated with iron oxide, aluminum oxide and titanium oxide, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.044
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Fig. 2. EDS spectrum of (a) AC–Al2O3, (b) AC–TiO2 and (c) AC–Fe2O3.
parameters including contact time, adsorbent dosage, ionic strength and pH were kept constant at 2 h, 50 mg, 2 ppm and 7 respectively. The effect of shaking speed on the removal efficiency of ACs, AC–TiO2, AC–Fe2O3 and AC–Al2O3 is depicted in Fig. 6. The results showed that the removal efficiency of phenol increases with increase in agitation speed and maximum removal by ACs, AC–TiO2, AC–Fe2O3 and AC–Al2O3 was achieved at 150 rpm. This can be justified by the fact that an effective
transport of phenol ions towards the adsorbent surfaces occurred, due to less resistance to diffusion at higher shaking speed. However, no significant change in removal efficiency was achieved beyond 150 rpm, which might be due to the saturation of adsorption sites. It is worth mentioning that AC–Al2O3 showed the highest removal of 92.1%, while for AC–Fe2O3, AC–TiO2 and raw ACs, removal of 90.5, 89.5 and 73.4% were achieved for the same value of agitation speed.
Please cite this article as: B. Abussaud, et al., Sorption of phenol from waters on activated carbon impregnated with iron oxide, aluminum oxide and titanium oxide, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.044
B. Abussaud et al. / Journal of Molecular Liquids xxx (2015) xxx–xxx Table 1 EDS analysis of ACs, AC–TiO2 and AC–Al2O3. AC sample
Raw ACs
AC–Al2O3
AC–TiO2
Element
Weight %
Weight %
Weight %
Weight %
C O Al Ti Fe Total %
96.6 3.4 – – – 100
74.65 14.01 11.34 – – 100
71.3 12.5 – 16.2 – 100
78.3 10.6 – – 6.1 100
AC–Fe2O3
This observation was attributed to the improved contact between the phenol ions in the solution and the presence of more active adsorption sites on the AC–Al2O3 surface. Some studies have reported similar behavior between carbon based adsorbents and phenol at 200 rpm [30–33]. 3.2.3. Effect of contact time In order to study the effect of contact time on the removal efficiency of phenol and to determine the equilibrium time for maximum uptake of phenol ions by ACs, AC–TiO2, AC–Fe2O3 and AC–Al2O3, experiments were performed under contact times from 0 to 720 min. All the other parameters including agitation speed, adsorbent dosage, ionic strength and pH were kept constant at 150 rpm, 50 mg, 2 ppm and 7 respectively. As can be seen in Fig. 7, a gradual increase in phenol removal efficiency was observed to increase in time till 120 min for all the adsorbents, at which the optimum adsorption was attained. This observation was attributed to the adsorption equilibrium phenomenon, whereby the rate of adsorption was higher than the rate of desorption up to 2 h of contact time, which is the equilibrium adsorption point. The rate of adsorption and desorption were the same and no further removal of phenol from the
5
solution was achieved. Also, a clear desorption of phenol from both the adsorbents was observed after 2 h due to the saturation of the active sites on the surfaces of adsorbents. An increase in adsorption of phenol ions to increase in contact time may also be due to the decrease in boundary layer resistance of the hydrate layer [34]. Furthermore, the phenol removal efficiency of AC–Al2O3 was highest among the three adsorbents at the same contact time. The maximum phenol removal efficiency by AC– Al2O3, AC–Fe2O3, AC–TiO2 and ACs were 93.1, 90.5, 89.5 and 74.4%, respectively, after a contact time of 2 h. 3.2.4. Effect of adsorbent dosage The adsorption effectiveness for treatment of pollutant is usually subjected to the number and availability of active adsorption sites on the adsorbent surface. Generally, increasing the dosage of the adsorbent increases the number of adsorption sites [34]. The doses of adsorbents were varied from 10 to 600 mg, while all the other parameters including shaking speed, contact time, ionic strength and pH were kept constant at 150 rpm, 120 min, 2 ppm and 7 respectively. As depicted in Fig. 8, the percentage removal of phenol was observed to increase with an increase in the adsorbent dosages, with maximum removal at 200 mg for AC–Al2O3, AC-TiO2 and AC-Fe2O3, respectively. While for raw AC, an adsorbent dose of 300 mg was required for achieving the maximum (100%) removal. The higher removal by AC–Al2O3, AC–TiO2 and AC– Fe2O3 is due to increase in surface area after an impregnation and increased number of adsorption sites. 3.2.5. Effect of ionic strength The removal extent of phenol is dependent on the ionic strength. Therefore, the impact of phenol concentration in the aqueous solution on its adsorption by the ACs, AC–TiO2, AC–Fe2O3 and AC–Al2O3 adsorbent was also studied. The ionic strength of phenol in the solution varied from
Fig. 3. TGA curves for (a) AC, (b) AC–Al2O3, (c) AC–TiO2 and (d) AC–Fe2O3.
Please cite this article as: B. Abussaud, et al., Sorption of phenol from waters on activated carbon impregnated with iron oxide, aluminum oxide and titanium oxide, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.044
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B. Abussaud et al. / Journal of Molecular Liquids xxx (2015) xxx–xxx
Fig. 4. BET surface area for (a) AC, (b) AC–Fe2O3, (c) AC–TiO2 and (d) AC–Al2O3.
2 to 10 ppm, and its effect on the removal efficiency was ascertained. All the other parameters were kept constant during the experiment. From Fig. 9, it was observed that increasing the initial phenol concentration in the solution resulted in a decrease in the removal efficiency of the phenol
Fig. 5. Effect of pH on phenol adsorption.
Fig. 6. Effect of agitation speed on phenol adsorption.
Please cite this article as: B. Abussaud, et al., Sorption of phenol from waters on activated carbon impregnated with iron oxide, aluminum oxide and titanium oxide, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.044
B. Abussaud et al. / Journal of Molecular Liquids xxx (2015) xxx–xxx
7
Fig. 9. Effect of ionic strength on phenol adsorption. Fig. 7. Effect of contact time on phenol adsorption.
by raw and doped adsorbents. This observation was attributed to the high amount of phenol ions with limited active adsorption sites on the adsorbent surfaces, which leads to increase the concentration of phenol ions in the bulk solution and thus decreased the removal of phenol. This decrease in phenol uptake with an increase in phenol concentration is logical, because the time required to attain equilibrium was expected to be longer at higher concentrations than at lower concentration. It is interesting to observe that the doped ACs still have higher removal efficiency than the raw ACs for the same value of initial phenol concentration. This can be justified on the basis of availability of more adsorption sites and higher surface area of the doped ACs. Therefore, more ions can be adsorbed on the surface compared to raw ACs at higher phenol concentration and hence higher removal efficiency was observed. 3.2.6. Adsorption isotherm model The experimental results obtained on the adsorption of phenol were analyzed by the Langmuir and Freundlich models. The maximum adsorption capacity determined at optimum set of parameters, were used for these adsorption isotherm models. The linear form of Langmuir isotherm is given by Eq. (3), while a plot of Ce/Qe against Ce is shown in Fig. 10. The maximum adsorption capacity (Qm) and adsorption intensity were determined from the slope and intercept of the straight line [15, 35–38]. It is interesting to note that a good straight line with a high correlation coefficient was obtained for AC, AC–TiO2, AC–Fe2O3 and AC–Al2O3. The data of phenol adsorption were also analyzed by Freundlich model. Based on the Freundlich isotherm model given by the Eq. (4), a plot of log qe against logCe was generated as shown in Fig. 11, which
Fig. 8. Effect of adsorbent dosage on phenol adsorption.
clearly shows the deviation of data from the straight line suggested by the Freundlich model. However, the Freundlich constants, KF and n; were determined from the best-fit line. The adsorption behavior of adsorbent was best described by the Langmuir adsorption model as compared to the Freundlich model, as shown by their correlation coefficient values in Table 2. The adsorption capacities, as determined by the Langmuir isotherm model were 1.5106, 3.1530, 3.2875 and 3.5461 mg/g for raw ACs, AC– TiO2, AC–Fe2O3 and AC–Al2O3 respectively. The highest adsorption capacity of AC–Al2O3 is due to its highest surface area and more adsorption sites than AC–Fe2O3, AC–TiO2 and raw ACs. The above analysis also indicates that phenol ions were strongly adsorbed to the surfaces of the AC–Al2O3 suggesting that impregnation of ACs with Al2O3 have great impact on the adsorption of phenol ions from water. Comparing with some other materials and nanomaterials [39–57], the reported materials showed high capacity with the advantage of being cost-effective. 4. Conclusions The reported AC impregnated with nanoparticles of TiO2, Fe2O3 and Al2O3, were successfully synthesized and used in the removal of phenol from aqueous environments. Tritium oxide, iron oxide and aluminum oxide impregnation has improved its phenol removal efficiency from aqueous solution. Several parameters such as agitation speed, adsorbent dosage, contact time, pH and initial phenol concentration were found to
Fig. 10. Langmuir adsorption model for phenol at pH 7.
Please cite this article as: B. Abussaud, et al., Sorption of phenol from waters on activated carbon impregnated with iron oxide, aluminum oxide and titanium oxide, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.044
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B. Abussaud et al. / Journal of Molecular Liquids xxx (2015) xxx–xxx
Fig. 11. Freundlich adsorption model for phenol at pH 7.
Table 2 Parameters of Langmuir and Freundlich adsorption isotherm models for phenol removal. Langmuir
Freundlich 2
Adsorbent
Qm (mg/g)
KL (L/mg)
R
n
KF
R2
AC AC–TiO2 AC–Fe2O3 AC–Al2O3
1.5106 3.1530 3.2875 3.5461
33.100 1.3742 2.6658 4.8621
0.971 0.960 0.976 0.972
8.1967 1.535 1.830 2.322
1.3152 2.5823 1.7442 1.5632
0.384 0.933 0.170 0.846
significantly affect the phenol removal efficiency. The optimum removal from the aqueous solution was achieved at pH 7, 150 rpm agitation speed, 200 mg dosage, 2 h contact time and 2 ppm initial phenol concentration. The data from the phenol adsorption behavior of the raw and doped ACs were best fitted by the Langmuir adsorption isotherm model, with correlation coefficients of 0.971, 0.96, 0.976 and 0.972 for AC, AC–TiO2, AC–Fe2O3 and AC–Al2O3. The adsorption capacities, as determined by the Langmuir isotherm model were 1.5106, 3.1530, 3.2875 and 3.5461 mg/g for raw AC, AC–TiO2, AC–Fe2O3 and AC–Al2O3, respectively. The highest adsorption capacity by nanoparticles loaded AC is mainly attributed to additional adsorption sites.
Acknowledgment The authors acknowledge the financial support provided by King Abdulaziz City for Science and Technology (KACST) through the Science and Technology Unit at King Fahd University of Petroleum and Minerals (KFUPM) through project no. AR-30-92.
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Please cite this article as: B. Abussaud, et al., Sorption of phenol from waters on activated carbon impregnated with iron oxide, aluminum oxide and titanium oxide, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.08.044