Comparative Adsorption Behavior of Ibuprofen and Clofibric Acid onto

Article pubs.acs.org/IECR

Comparative Adsorption Behavior of Ibuprofen and Clofibric Acid onto Microwave Assisted Activated Bamboo Waste Ruhul Amin Reza,† M. Ahmaruzzaman,† Asim K. Sil,† and Vinod Kumar Gupta*,‡ †

Department of Chemistry, National Institute of Technology Silchar, Silchar-788010, Assam India Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee-247667 (U.K.), India

‡

S Supporting Information *

ABSTRACT: The adsorption behavior of two representative pharmaceutically active compounds and widespread used drugs (ibuprofen and clofibric acid) were evaluated using a relatively abundant and inexpensive material, bamboo waste, as adsorbent prepared via ZnCl2 activation process followed by microwave heating. The Langmuir, Freundlich, Dubunin−Raushkevich, and Temkin models were applied to describe the adsorption isotherm for the two systems. The goodness of curve fitting in the various models was done in accordance with linear regression coefficients and various error functions. The Langmuir isotherm model was applicable for describing the binding data for both ibuprofen (IBP) and clofibric acid (CA) onto activated bamboo waste (ABW) with the following order of adsorption capacity: IBP (278.55 mg·g−1) > CA (229.35 mg·g−1). The Gibbs free energy of −6.15 and −5.56 kJ mol−1 estimated for IBP and CA onto ABW unravelled the spontaneous nature of this adsorbent toward these adsorbates. Both pH and temperature exhibited a remarkable effect on the adsorption of IBP and CA. Adsorption kinetic data for IBP and CA showed that the processes obeyed pseudo-second-order kinetic expression and diffusion in micropore and mesopore was the potential rate-controlling step. The desorption of IBP using methanol was very effective with more than 96% of IBP desorbed from ABW within 10 min to allow the reusability of the adsorbents. In contrast, methanol was less effective for CA as only 60% desorption was possible with the solvent. Certain physicochemical and spectroscopic characterization, viz., macro- and microanalysis, Bohem titration, pHpZC, Drift method, SEM-EDS, surface area, porosity, and FTIR were analyzed in an attempt to better understand the adsorption process.

1. INTRODUCTION

depression, respiratory problems, and acute renal failure are well recognized by ibuprofen overdose patients.12,13 Clofibric acid [(2-(4-chlorophenoxy)-2-methylpropanoic acid)] is the active metabolite of the lipid regulators clofibrate, etofibrate, and etofyllinclofibrate and is also considered as a potential endocrine disruptor, since it interferes with the synthesis of cholesterol.14 This drug should not be underestimated due to resemblance in its structure with the phenoxy acid herbicides, such as Mecoprop.15 Activated carbons are the most widely used adsorbents for the removal of pollutants from wastewater due to their extended surface area, microporous structure, high adsorption capacity, and high degree of surface reactivity.16,17 These studies were mainly focused on the adsorption of metals, dyes, and phenolic compounds. However, concerning with the removal of PPCPs by activated carbons, only a few studies were reported.18,19 The conventional heating method using electrical furnace is usually adopted by many researchers for the preparation of activated carbons. In recent times microwave (MW) heating methods are in practice to produce activated carbons due to their rapid and uniform heating.20−22 The present work explores the potential of bamboo waste as a precursor material for the preparation of activated carbon, developed by ZnCl2

Pharmaceuticals and personal care products (PPCPs) are indispensible components of human life in the modern era. These emergent pollutants are kinds of chemical contaminants that come up extensively from human excretions in unmodified or partially metabolized form and veterinary applications of a variety of products, such as medicines, fungicides, and disinfectants used for industrial, domestic, and agricultural purposes.1 Due to the advancement of analytical techniques, these emergent contaminants have been detected in nanogram per liter level in the effluents of wastewater treatment plant, lake, river, and occasionally in groundwater.2,3 To meet the customer’s demand, the usage of PPCPs is increasing day by day along with rapid growth of population in the world, and hence it is one of the persistent contaminants in the environment even after these products have been used up.4−6 The widespread occurrence of these contaminants is of concern due to their adverse effect, such as antagonizing hormone actions, causing development and reproductive problems, hindering metabolic processes, etc., when consumed by human and aquatic species.7,8 Hence, the removal of these emerging contaminants from potable water and aquatic systems is a challenging issue for the worldwide researchers.4,6,9 Ibuprofen is a nonsteroidal anti-inflammatory drug used for treatment of rheumatic disorders, pain, and fever and having annual production of several kilotons.10 The normal therapeutic concentration of ibuprofen above 250 mg·L−1 in blood is toxic.11 The gastrointestinal effects, central nervous system © 2014 American Chemical Society

Received: Revised: Accepted: Published: 9331

December 10, 2013 April 20, 2014 April 20, 2014 April 21, 2014 dx.doi.org/10.1021/ie404162p | Ind. Eng. Chem. Res. 2014, 53, 9331−9339

Industrial & Engineering Chemistry Research

Article

(EDS) analysis was performed using a field emission scanning electron microscope (Sigma, Zeiss, Germany). The physical and chemical analysis of ABW was conducted according to ASTM standards (American Standard for Testing and Materials). Ultimate analysis or microanalysis includes the determination (wt %) of carbon, hydrogen, and nitrogen content and was carried out by PerkinElmer 2400 Elemental Analyzer. The point of zero charge (PZC) and amounts of surface functional groups of the sample were measured by pH drift method and Boehm titration, respectively. 2.4. Liquid Phase Adsorption and Data Analysis. Batch equilibrium studies were carried out to find the optimum pH, contact time, adsorbent dose, and equilibrium isotherm. A total of 20 mL of each of the IBP and CA having individual concentration of 100 mg·L−1 (containing the ABW in varying weight from 10 to 45 mg) was taken in different well-capped 100 mL Erlenmeyer flasks. These flasks were kept in a constant temperature-cum shaker incubator (Alfa Instrument) and stirred at 160 rpm for 6 h at specific temperatures maintained at 298, 303, and 313 K. Upon attainment of equilibrium, the liquids were separated from adsorbent by centrifugation (at 2500 rpm for 5 min). To study the effect of solution pH on the adsorption, experiments were carried out at initial concentration of 50 mg·L−1 and a temperature of 298 K. The pH of the solution before adsorption was adjusted using 0.1 N HCl and 0.1 N NaOH with the help of a sensIon 3 Laboratory pH meter (Hatch company). The residual concentration of ibuprofen and clofibric acid in the supernatant solution were analyzed with the aid of an UV− vis spectrophotometer (Thermo SCIENTIFIC; Model: GENESYS 10S) at maximum wavelengths of 221 and 227 nm, respectively. The percentage adsorption and adsorption capacity at equilibrium and time t (qe (mg·g−1) and qt (mg· g−1)) of IBP and CA onto ABW were computed using the following mass−balance relationships

activation followed by MW irradiation for the removal of IBP and CA from aqueous phase. To the best knowledge of the authors, this precursor has not been utilized for the removal of IBP and CA by adsorption process via MW irradiation. The experiments were designed in order to optimize the influence of operating factors (adsorbent dose, concentration, pH, and temperature). Isotherm modeling, kinetics, and thermodynamics of the adsorption process are also evaluated.

2. EXPERIMENTAL SECTION 2.1. Reagents and Target Adsorbates. All the chemicals and reagents used in the experimental study were of analytical reagent (AR) grade. ZnCl2, NaOH, HCl, NaCl, Na2CO3, and NaHCO3 used in the present study were obtained from Merck India Ltd. The target compounds, ibuprofen (IBP) and clofibric acid (CA), used in the present investigation were purchased from Sigma-Aldrich. The physicochemical properties and the molecular structures of these compounds are listed in Table S1 in the Supporting Information. The stock solution of IBP and CA was prepared with ultrapure water from a Millipore water purification system (Model: ELIX 3S KIT (IL), France). 2.2. Effect of Activating Agent and Preparation of Adsorbent. The influence of the activating agent, such as H3PO4, KOH, NaOH, HCl, and ZnCl2, was studied to choose the best activating agent. The activating agents, like H3PO4, KOH, NaOH, and HCl, were found to be less prone to volatile loss and low adsorption capacity. But ZnCl2 activation develops porosity and increases the surface area of the adsorbent. Among all agents ZnCl2 is a widely used activating agent as it leads to larger surface area and higher yields.23 The raw material used in the current study was bamboo waste (BW), which is very cheap and inexpensive and obtained from Cachar Paper Mill, Assam, India. Before any treatment, the raw precursor was cleaned with pure water and dried in an oven at 383 K for 24 h and was then impregnated with an adequate amount of 5 M ZnCl2 solution in the hot plate for 1 h at 333 K, and the mixture was kept overnight. Then the sample was kept in a crucible and placed on the rotating plate of a microwave oven for heating the sample uniformly. The microwave equipment (Model No. MG-5578) had an input power of 3 kW and frequency of 2450 MHz. The different power levels (180, 360, 540, 720, 900 W) of the oven can be controlled by a power controller, and there is a timer for various exposure times at a preset microwave power level. Based on the preliminary runs, an input power of 720 W and irradiation time of 15 min were selected as the heating period for activation. The resultant activated carbon was washed repeatedly with deionized water until the pH of washing solution became 6−7. The activated carbon obtained was ground into fine powder and kept in the desiccator until use. 2.3. Instrumentation and Characterization. The pore structural analysis was characterized by nitrogen adsorption− desorption at 77.71 K using a Micromeritics, A SAP 2010 Surface Area Analyzer. The specific surface area (SBET) was calculated by the Brunauer−Emmett−Teller (BET) equation; the surface morphology image was taken using a scanning electron microscope (SEM Leo 1430 VP). Chemical characterization of functional groups was detected using spectroscopic grade potassium bromide (KBr) pellets containing 5% of carbon sample by FTIR spectrometer (3000 Hyperion Microscope with Vertex 80 FTIR System, Bruker, Germany). To determine the weight/atomic percentage composition of the candidate, adsorbent energy dispersive X-ray spectrometer

%removal =

(Co − Ce)100 m

(1)

qe =

(Co − Ce)V m

(2)

qt =

(Co − Ct )V m

(3)

where Co, Ct, and Ce are liquid phase initial, at time t, and equilibrium concentrations (mg·L−1), V is the volume (L) of IBP and CA, and m is the weight (g) of the dry adsorbent. 2.5. Desorption Studies. Desorption and regenerations are the most significant aspects to establish the feasibility of adsorption process. Different eluents, such as water, HCl, H2SO4, CH3COOH, CH3OH, and C2H5OH, were tested for desorption of IBP and CA from loaded adsorbent. Desorption efficiencies were calculated using the following relationship %desorption =

Cd − Vd × 100 qe × w

(4)

where Cd is desorbed adsorbate concentration (mg·L−1), Vd is volume of desorption solution (L), w is the mass of the preadsorbed adsorbent (g), and qe is the amount of adsorbate preadsorbed on the adsorbent (mg·g−1). 9332

dx.doi.org/10.1021/ie404162p | Ind. Eng. Chem. Res. 2014, 53, 9331−9339


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3. RESULTS AND DISCUSSION 3.1. Characterization of the Adsorbent. The textural characteristics, surface area, and pore size distribution of ABW is reported in Table S2 in the Supporting Information. According to International Union of Pure and Applied Chemistry (IUPAC) classifications, the nitrogen adsorption/ desorption isotherm of ABW exhibited a type-II isotherm, a typical signature of material consisting of both mesopores and micropores. It indicates that ABW have a very narrow pore size distribution. The fraction of pores opened at both ends was found to be nil. The hysteresis loop observed at relatively low pressure in the N2 adsorption/desorption isotherm plot (Figure 1) of ABW indicates small pore size in the mesoporous range

(most of them near to micropore range as average pore diameter is around 2.9 nm). The Barrett−Joyner−Halenda (BJH) adsorption pore distribution plot (Figure 2) illustrates the maximum concentration of the pores in the diameter range of 1−20 nm with an average diameter of 3.3 nm. This figure also shows that the largest contribution to the total pore volume is contributed by the mesopores followed by a certain number of micropores. The surface topography of ABW with SEM and surface chemistry play an important role in determining adsorption properties. Highly heterogeneous surface and porous structure was ascertained by SEM micrograph of ABW (Figure 3). The roughness of the surface indicates high surface area for adhering adsorbate molecules, thus favoring adsorption of IBP and CA onto adsorbent surface. Figure 4a shows the FTIR spectra of ABW for pre- and postadsorption of IBP. The absorption bands at 3423, 1845, and 1160 cm−1, represent OH, Ar−CO, and C−O stretching vibrations, respectively. The peak at 3423 cm−1 has become less intense and shifted to 3390 cm−1 after adsorption of IBP. It can be inferred that the alkane groups do not play any significant role in adsorption as their peak positions at 2920 and 2841 cm−1 remain unchanged after adsorption. The shift in peak position and change in intensity clearly indicated the participation of −OH group in the adsorption of IBP. The shifting of the peak position from 3423 to 3438 cm−1 (Figure 4b) after the adsorption of CA can explicate involvement of the H bonded OH stretching in the adsorption of clofibric acid. The new peak position appearing at 1716 cm−1 is due to CO of carboxylic group which also confirms adsorption of clofibric acid onto ABW. The carboxylate peak (1587 cm−1) shows significant decrease in intensity and shifting of peak position to 1569 and 1579 cm−1, which reveals possible participation of this group in the adsorption of both the adsorbate IBP and CA. The presence of C−Cl bond of clofibric acid also confirmed by the appearance of a new peak at 731 cm−1 after adsorption and indicates the adsorption of CA onto ABW. The results of physical characterization and elemental composition of the adsorbent are shown in Table S1 in the

Figure 1. N2 adsorption/desorption isotherm of ABW at 77.71 K.

Figure 2. Pore size distribution of ABW. 9333



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Figure 3. SEM micrograph (2000×) of ABW.

value (Table S1) of CA (2.84), it exists in molecular form25 and its binding onto adsorbent surface may be due to H-bonding at low pH. At pH greater than pHPZC (5.2), the surface would be more negatively charged and above the pKa value clofibric acid is in anionic form25 which results in high electrostatic repulsions, leading to no significant adsorption. 3.2.2. Effect of Adsorbent Load. The dependence of adsorbent dosages on the adsorption of IBP and CA was carried out by using different adsorbent dosages which are varied from 10 to 50 mg/20 mL at 298 K temperature and fixed adsorbate concentration (100 mg·L−1). It has been observed that percentage of IBP removal increases from 73.45% to 97.00% with increase in adsorbent dose from 10 to 40 mg/20 mL where as for CA the removal percentage increase from 68.70% to almost 99% for adsorbent load of 45 mg/20 mL. It can be attributed to the increase in surface area and greater availability of the active sites at the higher adsorbent dosage. 3.2.3. Effect of Contact Time. The experiments were carried out with adsorbent dosage of 40 mg/20 mL for each of IBP and CA at 298 K, at concentration of 80 mg. L−1 for different periods of contact time with maximum reaching up to 2 h. The removal of IBP and CA increases with time, and saturation is attained in about 60 min. The equilibrium contact time needed for IBP and CA adsorption was found to be nearly 40 and 60 min, respectively. The adsorption was rapid within the first 1 h and became almost asymptotic after 1.2 h. This is due to the bulk diffusion from the solution to the surface of the adsorbent; it slows down after first 1 h due to change in adsorption mechanism and finally attains plateau indicating the attainment of equilibrium. 3.3. Adsorption Isotherm and Modeling. Modeling of equilibrium data has been studied using four isotherm equations, viz., Freundlich, Langmuir, Temkin, and Dubunin−Radushkevich.26 The estimated model parameters and regression coefficient values of the different equilibrium isotherm models for adsorption of IBP and CA onto ABW

Supporting Information. The ultimate analysis of ABW shows high carbon (80.62%) and low moisture content (2.10%) which appeared to be very suitable material for use in the adsorption process. The high carbon and oxygen content (80.52 and 19.48%) were also estimated by EDS. Experiment was carried out to evaluate adsorption capacity using preactivated bamboo waste. The adsorption capacity of candidate adsorbent was found to be 14.97 and 11.90 mg·g−1 for IBP and CA, respectively, and hence further study was not extended. The result clearly indicates that effect of activating agent followed by MW irradiation leads to increased surface area and porosity and more adsorption capacity. 3.2. Effect of Operational Parameters on IBP and CA Adsorption. 3.2.1. Effect of Solution pH and Point of Zero Charge (PZC). The presence of several functional groups leads to acidic/basic character to the adsorbent surface and causes the surface properties of ABW to depend on the pH of the solution. Adsorption of acidic pharmaceuticals such as IBP and CA are strongly dependent on initial pH of the solution. From Figure 5 it is evident that the maximum adsorption for IBP takes place at around pH 2−5 (85.66−97.02%). This can be explained by considering the nature of the surface functional groups on the adsorbent at different pH values and also the ionic state of IBP at these pH values. The pH values higher than the pKa value (Table S1) of the IBP (4.91) molecule will be deprotonated.24 Consequently as the pH increases for values higher than 5, the adsorption of IBP will be less favorable due to electrostatic repulsion between the anionic IBP and the surface of activated carbon that gradually becomes more negatively charged. Considering the pH effect of clofibric acid, removal efficiency decreases with an increase in alkalinity of the medium. The adsorption of clofibric acid on ABW surface gradually decreases from 94.25% (at about pH 3) to 90.07% (at about pH 4−5) (Figure 5), and thereafter it drops suddenly with increase in pH. It may be linked with the fact that at pH below the pKa 9334



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are computed given in Table S3(a−d) in the Supporting Information. It is important to establish the most appropriate correlation with experimental data to design the adsorption system. The detailed error analysis was also undertaken to investigate the best fit adsorption isotherm which describes the adsorption process. The five different error functions that were studied are listed in Table S4 in the Supporting Information. The Langmuir isotherm model is one of the most common adsorption models, and it assumes monolayer coverage of adsorbate over a homogeneous adsorbent surface. The Langmuir parameters and theoretical monolayer adsorption capacity computed from slopes and intercepts were 278.55 and 229.35 mg·g−1 for IBP and CA respectively. The experimental data are well explained by Langmuir model for both the targeted drugs having linear regression coefficient of 0.99807− 0.9982 for IBP and 0.9873−0.9949 for CA at all studied temperatures. The essential characteristics and feasibility of the Langmuir isotherm is described by dimensionless constant separation factor, RL, which is defined as RL =

1 1 + bCo

(5)

For favorable adsorption RL should lie between 0 and 1, and greater than 1 indicates unfavorable adsorption. RL values turn out to be 0.02 and 0.16 for IBP and CA, respectively, which in the defined range represents favorable adsorption. The linearized plot of Langmuir, Freundlich, Temkin, and Dubunin−Radushkevich models is compared with the experimental adsorption data shown in Figure 6a, b for both systems. The computed model parameters, linear regression coefficient R2, and error functions values reflect a good fitting of experimental data for the Langmuir model. On the basis of the lowest value of various error functions estimated and from the linear regression coefficient R2 value, the fitting of the entire studied isotherm is of the followng order: Dubunin− Radushkevich < Temkin < Freundlich < Langmuir for both the drugs.

Figure 4. FTIR spectra of pre- and postadsorption onto ABW (a) IBP and (b) CA.

Figure 5. Effect of pH media on the adsorption of IBP and CA. 9335



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Figure 6. Validity of adsorption isotherms for both PPCPs toward different adsorption models at 298 K: (a) IBP and (b) CA; Co = 100 mg·L−1.

Figure 7. Pseudo-second-order kinetic fit for both PPCPs at 298 K: (a) IBP and (b) CA.

3.4. Adsorption Kinetics. The estimated parameters and linear regression coefficient R2 of the four kinetic models for both IBP and CA adsorption onto ABW are listed in Table S5(a, b) in the Supporting Information. The linear regression coefficient (R2) values and standard deviation (Δq %) are in the range 0.9990−0.9999 and 1.05, 0.90, 1.64, and 2.65 for IBP and 0.9929−0.9999 and 3.13, 0.95, 0.78, and 0.53 for CA. The pseudo-second-order kinetic model better described the experimental data in the studied cases and conditions than the pseudo-first-order kinetic model as shown in Figure 7a, b. All the experimental evidence indicated that the adsorption of IBP and CA onto ABW followed a pseudo-second-order kinetic model. If the adsorption process is controlled by intraparticle diffusion, then the Weber−Morris27 plot of qe versus t1/2 gives a straight line. The plot of qe versus t1/2 (Figure 8) for IBP and CA adsorption from aqueous phase onto ABW at 298 K reveals that the adsorption of IBP and CA onto ABW is controlled by external mass transfer. External mass transfer is followed by a gradual adsorption stage with intraparticle diffusion model. It can be inferred from the Weber−Morris plot of ABW that the diffusion from the bulk phase to the external surface of the adsorbent is the fastest. This behavior can be attributed to fast utilization of ready available adsorbing sites on the adsorbent surface. The first sharp portion indicates external surface

adsorption by mesopore diffusion. The second portion is the gradual adsorption stage where intraparticle diffusion into micropores is the rate-limiting step. The equilibrium stage is achieved when the concentrations of the drugs are extremely low and the curve attains the linear shape. The plots of ln(1 − qt/qe) versus t for liquid film diffusion are nonlinear, and R2 values are obtained in the range of 0.7174− 0.9340 for IBP and 0.9184−0.9530 for CA. These put forward that the liquid film diffusion model is not appropriate for relating the experimental data for both the drugs. 3.5. Adsorption Thermodynamics and Effect of Temperature. The effect of temperature on the equilibrium adsorption of IBP and CA on ABW was carried out, and it has been observed that adsorption capacity decreases as the temperature increases from 298 to 313 K for both IBP and CA. This indicated the exothermic nature of adsorption. The thermodynamics parameters ΔG°, ΔH°, and ΔS° for adsorption of IBP and CA onto ABW are computed from the plots, and values are presented in Table 1. All ΔG° values are found to be negative with temperature which indicates that the adsorption of IBP and CA onto ABW are spontaneous and confirming the affinity of ABW for both the targeted drugs. The value of ΔG° in between 0 to −20 kJ mol−1 is consistent with electrostatic interaction between adsorption sites while a more negative value ranging from −80 to −400 kJ mol−1 indicates 9336



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Figure 8. Weber−Morris plot for IBP and CA single system onto ABW at 298 K.

Table 1. Thermodynamic Parameters for Uptake of IBP and CA onto ABW adsorbate IBP

CA

T (K) 298 303 313 323 333 298 303 313 323 333

ΔG° (kJ mol−1) −6.15 −5.89 −5.39 −4.88 −4.38 −5.56 −5.50 −5.38 −5.27 −5.15

ΔH° (kJ mol−1)

ΔS° (J mol−1.K−1)

Table 2. % Desorption of IBP and CA by Different Eluents % desorption

R2

−21.20

−50.05

0.9800

−8.97

−11.45

0.9700

eluents

IBP

CA

H2O HCl NaOH C2H5OH CH3OH CH3COOH

0 1.30 3.30 69.06 96.87 0

6.18 3.50 1.67 25.87 60.00 0

of the adsorbent used for treatment process, regeneration, and recovery of solvents. The efficiency of commercial activated carbon (CAC) in the treatment of contaminated water is wellknown but the expensive nature of CAC demands the need for developing activated carbons which are prepared from abundant and inexpensive material giving reasonable adsorption capacity over and above its economic feasibility. The breakup of cost for the preparation, regeneration of ABW, and recovery of solvents in laboratory scale is found to be USD 27.38 per kg as shown in Table 3. The adsorption of IBP and CA onto ABW was compared with other adsorbents reported in the literature1,29−31 and is presented in Table 4. It has been observed that ABW compares well with the other adsorbents reported. Therefore, ABW is effective for the removal of IBP and CA from aqueous phase since it has relatively high adsorption capacity and is also economical. 3.7. Future Aspects of the ABW. The real wastewater contains many other components along with targeted drugs. To carry out the application of this material for industrial use, extensive column study is required with real wastewater by varying the bed height, flow rate, etc.32 The main future objective of the research work is to move the water treatment via adsorption process to an industrial scale. It is relatively easy to demonstrate it on a laboratory scale, but it is a more challenging to express it on a pilot scale, and to really scale it up to a industrial scale would be require significant financial and technological effort. This mismatch between scientific progress

that adsorption involves charge sharing or transferring from the adsorbent surface to the adsorbing ion to form coordinate bond (Chemisorption).28 The magnitude of evaluated values of ΔG° (−6.15 to −4.38 kJ mol−1 for IBP and −5.56 to −5.15 kJ mol−1 for CA) for these adsorption systems are under the physical adsorption range. The negative value of ΔH° (−21.20 and −8.97 kJ mol−1) for IBP and CA, respectively, indicates that adsorption is physical in nature involving weak attracting forces and is exothermic. This implies that the adsorption process is energetically stable. The negative values of ΔS° suggest decrease in randomness of the adsorbed species at the solid− solution interface. 3.6. Desorption Studies and Economical Aspects. The desorption efficiencies of various eluents are reported in Table 2. The desorption efficiency of IBP and CA adhered on ABW was more rapid at room temperature by methanol than other eluents and was found to be 96.87% and 60%, respectively. The regenerated adsorbent tested for its adsorption efficiency two times and showed that decrease in adsorption capacity of the ABW per cycle was found to be negligible. Cost analysis is an important parameter in determining the criteria for applicability of the adsorbent and selection of the treatment process for environmental cleaning purposes. The cost of the adsorption process is mainly dependent on the cost 9337



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Table 3. Cost Estimation for Preparation, Regeneration, and Recovery per kg of ABW breakup of cost

amount (g or L)

unit cost/(g or L) (USD)

duration (h)

power rating (kW)

power unit (kWh)

price/unit of power (USD)

price (USD)

− − − − 340.77

− −. − − 0.0129

24 1 16.6 2 − −. − 6.6

. 1.2 0.72 1.5 − − − 0.075

36 1.2 11.952 3 − − − 0.049

0.0655 0.0655 0.0655 0.0655 − − − 0.0655

2.358 0.079 0.783 0.197 4.396

drying in oven impregnation in hot plate activation at MW oven final drying at oven ZnCl2 used methanol used for regeneration recovery of methanol net cost overhead cost (10% of net cost) total cost

3.5 −

4.87 −.

exothermic in nature. The methanol is found to be the best desorbing agent for both the PPCPs. The results demonstrated that activated bamboo waste as an adsorbent may be a good alternative for the adsorptive removal of PPCPs from wastewater for environment clean up purpose.

Table 4. Adsorption Capacities of Different Activated Carbon adsorbent

adsorbate

adsorption capacity (mg· g−1)

ref

cork based AC PET waste based AC coal based AC wood based PAC bamboo waste based AC MIL-101 commercial activated carbon cork based activated carbon coconut shell based AC wood based AC bamboo waste based AC

IBP IBP IBP IBP IBP CA CA

139.20 378.10 69.30 86.70 278.55 312.00 244.00

1 29 29 29 this study 30 30

CA

92.60

31

CA CA CA

255 181 229.35

31 29 this study

17.045 0.032 24.890 2.489 27.38

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ASSOCIATED CONTENT

S Supporting Information *

Physicochemical properties of the target compounds (Table S1), physical characteristics and elemental composition of developed ABW (Table S2), Langmuir, Freundlich, Temkin, and Dubunin−RadushkevichiIsotherm parameters and their respective error functions for adsorption of IBP and CA onto ABW (Table S3(a, b, c, d)), expression of different error functions (Table S4), kinetic models parameters for adsorption of IBP onto ABW Table S5(a), and kinetic models parameters for adsorption of CA onto ABW Table S5(b). This material is available free of charge via the Internet at http://pubs.acs.org/.

■

in adsorption research and stagnation in industrial technology innovation needs to be corrected through translational research and technology transfer with a push for commercialization of research.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]; [email protected]. Phone: +911332285801. Fax: +911332273560. Notes

4. CONCLUSION The present study reported the suitability of microwave assisted activated bamboo waste for adsorptive removal of two selected PPCPs, vis , ibuprofen and clofibric acid. The main advantage of MW irradiation is that it shortens the activation time considerably. The investigations may be quite useful in developing the appropriate design for wastewater treatment plant laden with PPCPs. The ABW is proven to be a promising material for the removal of PPCPs such as ibuprofen and clofibric acid from wastewater. The physical parameters such as pH, contact time, adsorbent dose, and temperature furnishing highest adsorption efficiency were estimated at 2−3, 40 min, 2 g·L−1, 298 K for IBP and 2−5, 60 min, 2.25 g·L−1, 298 K for CA, respectively. Comparatively Langmuir isotherm explains the experimental data better than the other models. The adsorption isotherm displayed that the adsorption capacity of IBP onto ABW is higher than that of CA. The adsorptions of IBP and CA were found to be more favorable at lower temperature, and the optimum temperature was at 298 K under the experimental condition investigated. The rate of adsorption conformed to pseudo-second-order kinetics, and a significant correlation was obtained for this model for the PPCPs− adsorbent system. Thermodynamic studies predict that the adsorption is spontaneous, thermodynamically favorable, and

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are thankful to Sophisticated Analytical Instrumental Facility, Indian Institute of Technology Bombay for providing the analysis result in due time and are also grateful to the Director, NIT Silchar, for providing us the necessary facilities for carrying out the research work.

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ABBREVIATIONS AND ACRONYMS ABW = activated bamboo waste BET = Brunauer−Emmett−Teller BJH = Barrett−Joyner−Halenda CA = clofibric acid Ce = equillibrium concentration in mg·L−1 EDS = energy dispersive spectroscopy FTIR = Fourier transform infrared spectroscopy IBP = ibuprofen MW = microwave PPCPs = pharmaceutical and personnel care products qe = adsorption capacity at equilibrium (mg·g−1) qt = adsorption capacity at time t (mg·g−1) PZC = point of zero charge dx.doi.org/10.1021/ie404162p | Ind. Eng. Chem. Res. 2014, 53, 9331−9339


Article

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SEM = scanning electron microscopy t = time in minute

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Comparative Adsorption Behavior of Ibuprofen and Clofibric Acid onto

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