Application of Magnetically Activated Carbon for the Separation of

Article pubs.acs.org/jced

Application of Magnetically Activated Carbon for the Separation of Nicotinic Acid from Aqueous Solution Dipaloy Datta,* Sanjana Sah, Nikita Rawat, and Rajat Kumar Department of Chemical Engineering, Malaviya National Institute of Technology (MNIT), Jaipur, Rajasthan, India

ABSTRACT: The adsorption of nicotinic acid molecules from their solution in the aqueous phase was studied in batch mode by using magnetically activated carbon (M-AC) as the adsorbent. Activated carbon was magnetized by a coprecipitation method. The effects of the amount of adsorbent (0.25 to 5 g·L−1), initial acid concentration (2.46 to 14.77 g·L−1 or 0.02 to 0.12 mol·L−1), contact time (0 to 120 min), and temperature (298 to 333 K) on the percentage removal were investigated. Theoretically (from the Langmuir isotherm), an adsorption capacity of 23.28 g·g−1 was obtained by M-AC for acid removal. Equilibrium isotherms such as the Langmuir, the Freundlich, and the Temkin were applied to determine equilibrium parameters and to fit the equilibrium data, out of which the Langmuir gave the best match to the results. Nicotinic acid adsorption kinetics was modeled with pseudo-first order, pseudo-second order, and intraparticle diffusion models. The kinetic data was best described by the pseudo-second-order model. Thermodynamic parameters such as ΔHo, ΔSo, and ΔGo were calculated, and their values pointed out that the adsorption of acid molecules onto M-AC was exothermic and the process was spontaneous.

1. INTRODUCTION The use of activated carbon (granular and powdered) as the adsorbent has become popular because of the accessibility of the large surface area per unit volume and the presence of networks of submicroscopic pores where adsorption takes place. This material can be obtained from different carbonaceous sources such as coal, peat, coconuts, wood, lignite, nutshells, and so forth and has several applications in the pollution control of air and water.1 It is also used as the catalytic support in various petrochemical industries2 because of its extremely good physical and chemical properties such as a high specific surface area (varies from 200 to 2000 m2·g−1 and depends upon the method of preparation), high thermal stability, porosity, and chemical inertness.3 To enhance the rate of adsorption, powdered activated carbon with a small particle size is usually used. Compared to filtration, separation by using magnetic particles is considered to be a rapid and effective method, and this technique is widely used in many areas of biochemistry, cell biology, microbiology, mining ores, and environmental technology4 in recent days. Magnetic particles have been used extensively for cleaning up oil spills5 and speeding up the coagulation process in sewage,6 and powder MnO-Fe2O3 nanocomposite has been used for the removal of organic dyes containing wastewater.7 These materials have very narrow © 2017 American Chemical Society

application ranges, and also the applicable range of pH was very narrow.8 Therefore, to get rid of these limitations of powdered activated carbon and magnetic particles, preparation methods such as ball milling,9 impregnation, and chemical coprecipitation10 have been applied to produce these magnetic composites, which can easily and conveniently get separated by a magnetic field. The chemical coprecipitation method is the most widely used preparation method as it is easy and does not require special chemicals and procedures. Nicotinic acid, which is also known as niacin or vitamin B3, is soluble in water and used as a necessary micronutrient in animal food or diets. It is also used in a wide variety of applications in the chemical, biochemical, and therapeutic fields. The acid helps in the reduction of the total cholesterol level in the human body. Nicotinic acid is a biologically active molecule and hence finds growing application as a food additive, fodder, in cosmetics, and several areas of science and technology.11 The acid is also widely used in the treatment of dyslipidemia and is considered to be a very important hypolipidemic drug that helps to control and lower high cholesterol levels.12 The annual worldwide output of Received: September 5, 2016 Accepted: January 11, 2017 Published: January 20, 2017 712

DOI: 10.1021/acs.jced.6b00784 J. Chem. Eng. Data 2017, 62, 712−719

Journal of Chemical & Engineering Data

Article

nicotinic acid is approximately 35 000 tons.13 The pharmaceutical industry producing this acid discharges high doses of partially treated or untreated wastewater into the environment. These industrial effluents may contain traces of nicotinic acid, which has many harmful effects. When ingested, it is found that a high dosage of nicotinic acid may cause health problems. It can result in a vasodilatory response, which is the dilation of blood vessels causing a decrease in blood pressure.12 Other harmful effects of nicotinic acid are skin flushing and itching, dry skin, a skin rash such as acanthosis nigricans, eczema exacerbation, birth defects, hyperuricemia, blood sugar elevation, and maculopathy in animals and humans. Because of these harmful effects of nicotinic acid on the environment and subsequent side effects on human health, the effluents containing nicotinic acid should be treated.14 Among the several methods used in the treatment of wastewater, adsorption is proposed to be the most economic, easy, and widely used techniques. Therefore, in the present study attempts have been made to remove nicotinic acid from its aqueous solution by adsorption onto the surface of magnetically activated carbon.

adsorbent and the removal efficiency as a percentage were determined by using the experimental data and following eqs 1 and 2, respectively. qe =

(C0 − Ce)V m

removal % =

(C0 − Ce) × 100 C0

(1)

(2)

The initial and equilibrium concentrations of acid in the aqueous solution are denoted by C0 and Ce (both in g·L−1), respectively. V (mL) and m (mg) are the volume of the aqueous solution and the amount of adsorbent, respectively. Standard uncertainties in temperature and pH and the standard relative uncertainty in the concentration measurement are 0.58 K, 0.006, and 0.10, respectively. The reproducibility is checked for selected data points and found to be within the ±5% limit. The magnetic carbon particles were dispersed in water, and their interaction between the magnet and magnetically activated carbon dispersed in the aqueous phase is shown in Figure 1. After each experiment, the dispersed magnetic nanoparticles were separated from the aqueous phase by using a magnet within a short time.

2. MATERIALS AND METHODS 2.1. Materials. Activated carbon (powder, 300 mesh particle size) was obtained from CDH, India. Sodium hydroxide (98%) was purchased from Merck Specialties Pvt. Ltd., India, and ferric chloride (anhydrous, 96%) was procured from Qualigens Fine Chemicals, India. Iron sulfate heptahydrate (98%) from Ranbaxy Fine Chemicals Ltd., India, and nitric acid (69−72%, CDH) and nicotinic acid (>99%) were obtained from Spectrochem Pvt. Ltd., India. 2.2. Method. 2.2.1. Preparation of the Magnetically Activated Carbon (M-AC) Composite. M-AC was synthesized by the coprecipitation method. At first, 10 g of raw activated carbon (AC) was washed with 20 mL of HNO3 at 343 K for 2 h in a magnetic stirrer. Then, this treated AC was washed many times with distilled water to bring the pH to neutral and then dried for 4 h in an oven at 383 K. A solution containing 0.1 M ferric chloride anhydrous (FeCl3) and 0.05 M iron sulfate heptahydrate (FeSO4·7H2O) with a molar ratio of 1:2 was prepared. The treated AC was suspended in this solution (100 mL) for 2 h at 343 K under constant stirring maintained at a pH of 10−11 by adding 5 M NaOH solution (dropwise) so that the precipitation of iron oxides occurs. This mixture was further aged for 1 h under stirring at 343 K. At the end of the precipitation reaction, the suspension was cooled, and then the prepared magnetically activated carbon was separated using a magnet. The magnetically activated carbon was then washed with distilled water and ethanol, respectively, and dried at 383 K for 2 h in an oven. 2.2.2. Adsorption Experiments. Experiments on adsorption were performed using the batch equilibrium technique in an incubator shaker. The effect of the M-AC amount was determined by changing its concentration in the water phase between 0.25 and 5 g·L−1 in 20 mL of aqueous solution of 14.77 g·L−1 nicotinic acid. To get the isotherm data, the concentration range of nicotinic acid was chosen to be 2.46 to 14.77 g·L−1 with 1 g·L−1 M-AC adsorbent. For the kinetic study, a 14.77 g·L−1 initial concentration of nicotinic acid solution was taken with 1 g· L−1 adsorbent, and samples were taken at a specific time between 0 and 120 min. The temperature effect on adsorption was studied at 298, 313, 323, and 333 K with 14.77 g·L−1 nicotinic acid and 1 g·L−1 M-AC. The concentrations of nicotinic acid in the water phase after adsorption were determined by titration against 0.04 M NaOH solution. The adsorption capacity (qe in g·g−1) of

Figure 1. (a) M-AC dispersed in the aqueous phase. (b) Interaction between dispersed M-AC and the magnet.

3. RESULTS AND DISCUSSION 3.1. Effect of Contact Time (t, min). The dynamic behavior of the adsorbent particles for the effective removal of acid molecules onto M-AC is shown in Figure 2. A faster removal rate of adsorption of acid molecules from the water phase was observed in the initial stages. This is because sufficient numbers of vacant sites on the M-AC surface were present for the easy mass transfer of solute molecules from the liquid water to the solid M-AC phase. With an increase in the time of adsorption, the remaining vacant sites on the M-AC surface were not easily occupied by the acid molecules as there prevails a repulsive force between the solute molecules present on the M-AC phase and in the bulk aqueous phase. The removal efficiency of acid molecules reaches a fixed value of 55.67% with 1 g·L−1 M-AC and 14.77 g· L−1 acid after 90 min. Hence, a steady-state approximation may be considered, and a quasi-equilibrium situation may be assumed at t = 90 min. Therefore, 90 min was chosen as the appropriate time to perform further equilibrium experiments with M-AC. 713



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Figure 2. Kinetic data for the removal of nicotinic acid (14.77 g·L−1 or 0.12 mol·L−1) by magnetically activated carbon (1 g·L−1) at a temperature of T = 298 K. Symbols: ■, experimental data; solid line, ⎛ q −q ⎞ exp cal 100 N ⎟, N = number of data points, % PFO (% APE = N ∑i = 1 ⎜⎜ q ⎟ exp ⎝ ⎠ APE = 20.57%); ---, PSO, % APE = 3.43%);..., IPD, % APE = 3.35%).

Figure 4. Equilibrium isotherms for the removal of nicotinic acid (2.46 to 14.77 g·L−1) by magnetically activated carbon (1 g·L−1) at a temperature of T = 298 K. Symbols: ■, experimental data; solid line, ⎛ q −q ⎞ exp cal 100 N ⎟, N = number of data points, Langmuir (% APE = N ∑i = 1 ⎜⎜ q ⎟ exp ⎝ ⎠ % APE = 2.99%); ---, Freundlich (% APE = 2.97%);...., Temkin (% APE = 15.30%).

of 2.46, 4.92, 9.85, and 14.77 g·L−1 to generate equilibrium results and to analyze the influence of the initial acid concentration on the adsorption characteristics of M-AC. The equilibrium isotherms between nicotinic acid concentrations in the solid phase and the aqueous phase are shown in Figure 4. It can be observed from Figure 4 that with an increase in the initial acid concentration in the aqueous solution the transfer of nicotinic acid molecules onto the surface of M-AC was also increased from 1.58 to 8.22 g·g−1. The percentage removal (defined as the ratio of the number of acid molecules adsorbed on M-AC to the initial concentration of acid molecules in the water phase) had decreased from 64 to 55.67% with a 1 g·L−1 MAC concentration when the initial concentration of acid was increased at 298 K. This happens because the possible adsorption sites on the solid surface of M-AC get saturated with the solute (acid) molecules. 3.4. Equilibrium and Kinetic Adsorption Models. The equilibrium data of adsorption were investigated with the Langmuir, the Freundlich, and the Temkin isotherms, and the kinetic data with pseudo-first order (PFO), pseudo-second order (PSO), and intraparticle diffusion (IPD) models as shown in Table 1. The equilibrium results on the adsorption of nicotinic acid molecules using M-AC as the adsorbent were fitted, and the parameters of these isotherms were determined by fitting a straight line to the experimental values of 1 versus 1 for the

Figure 3. Effect of amount of adsorbent (0.25 to 5 g·L−1) on the percentage removal (■) and adsorption capacity (●) of nicotinic acid (14.77 g·L−1) by magnetically activated carbon at a temperature of T = 298 K.

3.2. Effect of Adsorbent Amount. To explore the effect of the amount of adsorbent, its concentration in the aqueous solution was varied between 0.25 and 5 g·L−1 for a 20 mL aqueous solution of 14.77 g·L−1 nicotinic acid. The effect of variation in the M-AC amount was seen in terms of the adsorption capacity (qe) and the percentage removal of nicotinic acid (Figure 3). A decrease in the adsorption capacity (31.12 to 1.92 g·g−1) and an increase in the removal (52.67 to 65%) were observed with the increase in the amount of adsorbent. The maximum adsorption capacity (= 31.12 g·g−1) was achieved with a 0.25 g·L−1 concentration of M-AC in the aqueous phase of nicotinic acid (14.77 g·L−1). 3.3. Effect of Initial Nicotinic Acid Concentration (C0, g· L−1). Aqueous solutions of acid were prepared at concentrations

qe

Ce

Langmuir (Figure 5a), ln qe versus ln Ce for the Freundlich (Figure 5b), and qe versus ln Ce for the Temkin (Figure 5c). The model parameters are presented in Table 2. In Figure 5, it is obvious that the experimental adsorption data follow the Langmuir and the Freundlich isotherms more closely than they follow the Temkin model. The values of the coefficient of determination of fitting also indicate the better fit of the Langmuir and the Freundlich isotherms (R2 = 0.9981 for the 714



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Table 1. Equilibrium and Kinetic Models sl no

1

models

equations

ref

Equilibrium 1 1 1 = + qe (KLq )Ce qm

Langmuir

15

m

1 ln Ce n

2

Freundlich

ln qe = ln KF +

3

Temkin

qe = qm ln K T + qm ln Ce

( )

Kinetic ⎛ q ⎞ ln⎜⎜1 − t ⎟⎟ = − k1t qm ⎠ ⎝

16

( )

17

4

pseudo-first order (PFO)

5

pseudo-second order (PSO)

t 1 1 = + qt qmt k 2qm 2

19, 20

6.

intraparticle diffusion

qt = k int 0.5 + c

21, 22

18, 19

Figure 5. Determination of (a) the Langmuir, (b) the Freundlich, and (c) the Temkin model parameters for nicotinic acid (2.46 to 14.77 g·L−1) adsorption by using magnetically activated carbon (1 g·L−1) at a temperature of T = 298 K.

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Table 2. Equilibrium and Kinetic Model Parameters for the Adsorption of Nicotinic Acid with M-AC at a Temperature T of 298 K Equilibrium Model Parameters Langmuir

Freundlich

parameter

value

qm (g·g−1) KL (L·g−1) R2 SD

23.28 0.081 0.9981 0.0124

PFO parameter −1

qm (g·g ) k1 (min−1) R2 SD

Temkin

parameter KF [(g·g−1) (L·g−1)1/n] n R2 SD Kinetic Model Parameters

value

parameter

value

1.76 1.19 0.9968 0.0508

qm (g·g−1) KT (L·g−1) R2 SD

3.35 1.57 0.9656 0.6753

value

parameter

value

8.33 0.088 0.9997 0.0734

kin c R2 SD

0.234 6.321 0.8870 0.2584

PSO value 8.38 0.089 0.8593 1.098

IPD

parameter −1

qm (g·g ) k2 (g·g−1·min−1) R2 SD

Figure 6. Determination of (a) pseudo-first order, (b) pseudo-second order, and (c) intraparticle diffusion model parameters for nicotinic acid (14.77 g· L−1) adsorption by using magnetically activated carbon (1 g·L−1) at a temperature of T = 298 K.

found to be 23.28 g·g−1. The predicted values of adsorption capacity (qe) with these three models are plotted in Figure 4.

Langmuir isotherm and 0.9968 for the Freundlich isotherm). The maximum monolayer adsorption capacity of the M-AC was 716



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pH = 4,T = 300 K, t = 24 h, w = 0.7 g·L−1 pH = 2, w = 1 g·L−1 pH = 4,T = 298 K, t = 10 h, w = 1 g·L−1 pH = 5, T = 313 K, t = 20 min, w = 2 g·L−1 pH = 6.5, T = 293 K, t = 5 h, w = 1 g·L−1 pH = 7.5, T = 298 K, t = 24 h, w = 1 to 1.15 g·L−1

present study 24 25 26 27 28 29 pseudo-first and -second order and intra particle diffusion pseudo-first and -second order pseudo-first and -second order pseudo-first and -second order pseudo-first and -second order pseudo-first and -second order pseudo-first and -second order

t*, equilibrium time; w#, adsorbent dosage.

arsenic chromium(VI) Congo red malachite green aniline cyanide 2 3 4 5 6 7

a

nicotinic acid 1

2 50 to 100 20 to 70 100 50 to 300 500 to 1000

4.16 57.37 62.94 89.29 90.91 67.82

Langmuir, Freundlich, and Temkin Langmuir and Freundlich Langmuir and Freundlich Langmuir and Freundlich Langmuir and Freundlich Langmuir and Freundlich Langmuir and Freundlich 23.28

kinetic model isotherm model max adsorption capacity (mg·g−1)

0 L

which describes the necessary characteristics of the Langmuir model, were calculated. These values indicate the characteristics and the nature of the adsorption process. The values of RL also imply the feasibility of the isotherm (RL > 1, unfavorable; RL = 1, linear; 0 < RL < 1, favorable; and RL = 0, irreversible). The values of RL were calculated and found to be in the range of 0.653 to 0.933, showing that the removal of acid on the adsorbent (MAC) was favorable. The time dependency of the adsorption process was demonstrated by using three kinetic models, namely, the pseudo-first order (PFO), pseudo-second order (PSO), and intraparticle diffusion (IPD) models. In the PFO model, a graph between the experimental values of (1 − qt/qm) vs t (as shown in Figure 6a) was plotted and fitted linearly to provide the value of the rate constant, k1. A value of the PFO rate constant, k1, was found from the slope to be 0.089 min−1. However, the PFO did not give a suitable result because a low value of R2 (= 0.8593) was achieved. The model parameters of PSO, k2 and qm, were determined from the plot of t/qt vs t (as shown in Figure 6b) and

concentration (mg·L−1)

1

Also, the values of the equilibrium parameter, RL (= 1 + C K ),23

solute

Figure 8. Gibbs’ free energy versus temperature plot for the adsorption of nicotinic acid (14.77 g·L−1) using M-AC (1 g·L−1), the coefficient of determination R2 = 0.9638, and the standard deviation SD = 54.0352.

sl no

Table 3. Comparison of Maximum Adsorption Capacity (qm) and Processing Conditions of Activated Carbona

Figure 7. Effect of solution temperature on the percentage removal (■) and adsorption capacity (●) of nicotinic acid (14.77 g·L−1) using M-AC (1 g·L−1) at a temperature of T = 298 K.

2.46 to 14.77

process condition

#

pH = 6, T = 298 K, t* = 90 min, w = 0.25 g·L

−1

ref

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Article

fitting it linearly. The values were obtained to be 0.0883 g·g−1· min−1 and 8.33 g·g−1, respectively. It can be seen from Figure 6 that the PSO graph yielded a perfect linear fit to the adsorption data of nicotinic acid onto M-AC, showing that the rate of adsorption could be approximated by the PSO kinetic model. The value of the correlation coefficient (R2 = 0.9997) found in the linear fit in Figure 6b also showed that the model is acceptable. A straight-line fit to the graph of qt vs t0.5 (Figure 6c) gave the values of kin and c (IPD model parameters) as 0.234 g· g−1·min−0.5 and 6.321 g·g−1, respectively. A reasonable fit was not obtained for IPD as suggested from the R2 value (= 0.8870). The values of kinetic model parameters determined are shown in Table 2. To show the rate of adsorption on the bare surface of MAC, the initial adsorption rate was calculated by the PSO model (r0 = k2qm2), and a value of 6.13 g·g−1·min−1 was obtained. The predicted values of the adsorption capacity with time by these three models for the M-AC adsorbent are plotted in Figure 2. 3.5. Effect of Temperature on the Adsorption. In Figure 7, the variation of temperature with the percentage removal and adsorption capacity of M-AC (1 g·L−1) for the separation of nicotinic acid (14.77 g·L−1) is shown. An increase in the temperature (from 298 to 333 K) caused a similar increase in the removal of nicotinic acid (from 55.67 to 60%). The amplification of the adsorption rate with temperature could be assigned to the increased number of active sites that are accessible for adsorption on the solid adsorbent surface and also an improvement in the porosity and the overall cubage of the pores of M-AC. The intensity of the adsorption also depends on the thickness of the boundary layer, which surrounds the adsorbent and offers resistance to mass transfer. With the increase in temperature there is a decrease in the boundary layer thickness, which may increase the mass transfer and decrease the mass transfer resistance. Because of the temperature increase, there also may be the possibility that the mobility of acid molecules increased with an increase in their kinetic energy and with increased diffusion speed inside the particles of the adsorbent. 3.6. Adsorption Thermodynamics: Gibbs’ Free Energy Model. A change in the standard Gibbs’ free energy (ΔG°) at different temperatures can be determined by using eq 3. ⎛q ⎞ ΔGo = −RT ln Kd = −RT ln⎜ e ⎟ ⎝ Ce ⎠

4. CONCLUSIONS Fe3O4-impregnated activated carbon was synthesized using the coprecipitation method and used for the separation of nicotinic acid from the water phase. The equilibrium and kinetics of adsorption were analyzed by studying the effect of the amount of adsorbent, the nicotinic acid concentration, the temperature, and the time of adsorption. The percentage removal increased as the contact time increased, and it became constant after some time. The equilibration time obtained was about 90 min. The maximum adsorption capacities obtained at 298 K for M-AC (8.22 g·g−1) and at 333 K for M-AC (8.56 g·g−1) showed that the temperature had little effect on the adsorption capacity. The adsorption capacity increased from 1.576 to 8.22 g·g−1 as the initial concentration of nicotinic acid increased from 2.46 to 14.77 g·L−1. As the adsorbent dosage increased from 0.25 to 5 g· L−1, the quantity removed increased from 52.67 to 65%. The adsorption equilibrium and kinetics were best fitted by the pseudo-second order and Langmuir isotherm models. Therefore, it may be proposed that the impregnation of iron particles in the powdered form of activated carbon would provide an easy separation of powdered activated carbon after its use in the purification of nicotinic acid containing industrial wastewater streams.

■

Corresponding Author

*E-mail: [email protected]. ORCID

Dipaloy Datta: 0000-0002-2048-9064 Notes

The authors declare no competing financial interest.

■

REFERENCES

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(3)

and

ΔGo = ΔH o − T ΔS o

AUTHOR INFORMATION

(4)

R is the universal gas constant (8.314 J mol−1 K−1), and T is the temperature in K. Then, to determine the values of standard enthalpy (ΔH°) and entropy (ΔS°), a graph between ΔG° and temperature (T) (as shown in Figure 8) was drawn using eq 4. This plot was fit by a straight line, and from the values of the intercept and slope, the changes in enthalpy (ΔH° = −4000.86 J·mol−1) and entropy (ΔS° = 15.25 J·mol−1·K−1), respectively, were estimated. A negative value of ΔH° indicated that the adsorption process is exothermic in nature, and the positive value of ΔS° showed that there is an increase in randomness in the adsorption system. The prepared M-AC is compared to other activated carbon for the removal of different pollutants from aqueous solution in terms of the maximum adsorption capacity and processing condition as shown in Table 3. 718



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Application of Magnetically Activated Carbon for the Separation of

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