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Chemical Industry & Chemical Engineering Quarterly

Available on line at Association of the Chemical Engineers of Serbia AChE www.ache.org.rs/CICEQ

Chem. Ind. Chem. Eng. Q. 25 (4) 383−393 (2019) CI&CEQ

383

ABEL ADEKANMI ADEYI1,2

SITI NURUL AIN MD JAMIL3

LUQMAN CHUAH ABDULLAH1,4

THOMAS SHEAN YAW CHOONG1,4

MOHAMMAD ABDULLAH5

KIA LI LAU1 1Department of Chemical and

Environmental Engineering, Faculty of Engineering, Universiti

Putra Malaysia, UPM Serdang, Malaysia

2Department of Chemical and Petroleum Engineering, Afe

Babalola University Ado-Ekiti (ABUAD), Ado-Ekiti, Ekiti State,

Nigeria 3Department of Chemistry, Faculty

of Science, Universiti Putra Malaysia, UPM Serdang, Malaysia

4Institute of Tropical Forestry and Forest Product (INTROP),

Universiti Putra Malaysia, UPM Serdang, Malaysia

5Faculty of Chemical Engineering, Universiti Teknologi Mara Ma sai,

Johor Darul Takzim, Malaysia

SCIENTIFIC PAPER

UDC 66.081.3:678:547.496.3:543.42

ADSORPTION OF MALACHITE GREEN IN A FIXED-BED COLUMN BY THIOUREA- -MODIFIED POLY(ACRYLONITRILE-CO- -ACRYLIC ACID)

Article Highlights • Poly(AN-co-AA) was synthesized via redox polymerization and modified with thiourea • TU-poly(AN-co-AA) possessed multi-functional groups with negative surface charge • MG adsorption onto hydrophilic TU-poly(AN-co-AA) adsorbents was high in a fixed-

-bed column • Column regeneration study indicates the stability and reusability of the polymeric ads-

orbents Abstract

Thiourea-modified poly(acrylonitrile-co-acrylic acid) (TU-poly(AN-co-AA)) poly-meric adsorbent was synthesized and characterized with Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM) and Zeta-sizer. Adsorptive removal of cationic malachite green (MG) dye from aqueous solution in a continuous TU-poly(AN-coAA) packed-bed column was studied. The influences of solution pH (2-9), inlet MG concentration (25-80 mg/L), bed depth (4-8 cm) and linear flow rate (1.5-5.0 mL/min) were investigated via assessment of the column breakthrough curves. Low pH and short bed depth, high MG concentration and flow rate led to early breakthrough of MG. Accord-ing to correlation coefficients (R2) and sum of the squares of the errors (SSE) values, Thomas and Yoon-Nelson dynamic models are more suitable to des-cribe the column experimental data compared to the Bohart-Adams model. TU--poly(AN-co-AA) exhibited effective separation of MG from the liquid phase and displayed high adsorption capacities after five regeneration cycles.

Keywords: adsorption, malachite green, packed-bed column, poly(acryl-onitrile-co-acrylic acid), thiourea.

Dye-bearing wastewaters attract serious con-cern globally due to their adverse effect on human beings and the environment. Significant volumes of colored effluents are been generated by industries such as textile, plastic, leather, printing, cosmetics, pharmaceuticals and agriculture [1–3]. The presence of synthetic dyes in water bodies pollute natural habi-tats and constitute public health problems because of their complex and non-biodegradable nature [2,4].

Correspondence: S.N.A.M. Jamil, Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, UPM Serdang 43400, Malaysia. E-mail: [email protected]; [email protected] Paper received: 23 November, 2018 Paper revised: 12 March, 2019 Paper accepted: 5 May, 2019

https://doi.org/10.2298/CICEQ181123016A

Dyes are also considered toxic, mutagenic and car-cinogenic to aquatic organisms and human life, inflict-ing severe liver, heart, kidney and nervous system malfunctioning [5–7]. For instance, malachite green (MG) is widely used in dyeing (leather, silk, wool, distilleries) and aquaculture (as fungicide and disin-fectant) industries. However, MG was reported carci-nogenic, mutagenic, genotoxic and teratogenic. In addition, MG is non-biodegradable [8,9]. Therefore, it is crucial to eliminate dyestuff from industrial waste-waters for health benefits and safety of the environ-ment. Physical and chemical treatment technologies have been applied to remove dyestuff from colored wastewater. The purification methods are adsorption [10-12], biodegradation [13], chemical precipitation or oxidation [14] and photocatalytic degradation [15]. Amongst all purification methods, adsorption stands

A.A. ADEYI et al.: ADSORPTION OF MALACHITE GREEN IN A FIXED-BED… Chem. Ind. Chem. Eng. Q. 25 (4) 383−393 (2019)

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out as the most effective method for dye removal due to its design simplicity, low cost, adaptability to wide range of dyes and simple operation [4,16-18].

Adsorbents from different materials; chitosan, silica-gel, clay, industrial and agricultural wastes had been applied in industrial wastewater treatment. How-ever, their applications involve deficiencies like sludge generation, poor selectivity, low efficiency, long contact time and non-recyclability. Therefore, preparation of a novel functional adsorbent with a simple preparation route, reasonable cost, high ads-orption capacity and regeneration ability is required. Polymeric adsorbents and its derivatives such as polyurea, polythiophenes and polyacrylonitrile (PAN), poly(acrylonitrile-co-methyl methacylate) [19] have been synthesized and modified for wastewater treat-ments such as in removing industrial dyes, pharma-ceuticals, heavy metals and emerging pollutants.

Recently, many investigations involve function-alization or surface modifications of polymeric mat-erials to enhance its effectiveness and selectivity for specific pollutants. Carboxymethyl cellulose-acrylic acid adsorbent via grafting polymerization [20], poly-dopamine microspheres [21], polyacrylonitrile (PAN) [22], polyacrylamide/chitosan composite [23], amid-oxime polyacrylonitrile chelating nanofibers [24], amidoxime poly(acrylonitrile-co-acrylic acid) [25], amine functionalized mesoporous carbon [26] and thiourea-modified poly(vinyl alcohol), (TU-PVA) [27] were fabricated and applied for industrial wastewater treatment. It was revealed that polymeric adsorbent containing sulphur exhibited a unique affinity for cat-ions, with strong chemical coordination.

To date, a fixed-bed column study by using thio-urea-modified poly(acrylonitrile-co-acrylic acid) (TU-poly(AN-co-AA)) as adsorbent to capture dyes is not -reported elsewhere. Adsorptive potential and reus-ability of TU-poly(AN-co-AA) towards malachite green in a fixed-bed column as well as sorption dynamics were investigated.

EXPERIMENTAL

Materials, reagents and dye

Acrylonitrile (Acros Organics, New Jersey, USA), acrylic acid (Acros Organics, New Jersey, USA), aluminum oxide (MERCK, Darmstadt, Ger-many), potassium persulphate (R&M Chemicals, Essex, UK), and sodium bisulphate (R&M Chemicals, Essex, UK), thiourea (TU) (R&M Chemicals, Essex, UK), hydrochloric acid, sodium hydroxide, nitric acid (R&M Chemicals, Essex, UK), methanol and ethanol were purchased from Systerm ChemAR (Shah Alam,

Malaysia). All chemical reagents were analytical grade, and used without further purification, except acrylonitrile (AN) and acrylic acid (AA) were purified by passing it through AlO3 in a glass column. The cationic dye, malachite green, (MG) (C23H25ClN2) was purchased from Acros Organics (New Jersey, USA). Fine acid-washed sea sand was purchased from Fisher Chemicals (Fisher Scientific, UK).

Synthesis of thiourea modified poly(acrylonitrile-co- -acrylic acid)

Redox polymerizations of AN and AA was per-formed at 60 °C under N2 gas in a three-neck round bottomed flask, fitted with a water condenser. The feed volume ratio of monomers AN:AA was 97:3. The reaction medium, 200 mL deionized water was purged firstly with N2 gas for 0.5 h at 40 °C. Then, 275 mmol of AN and 29 mmol of AA were added into the reaction medium followed by 2.16 g of potassium per-sulphate (KPS) and 2.09 g of sodium bisulphate (SBS). The solution was stirred mechanically at agit-ation speed of 200 rpm by using an egg-shaped mag-netic stirrer. The polymerization reaction was allowed for 2 h. The polymer formed was precipitated in meth-anol for 1 h. The polymer was filtered and washed successively with methanol and DI water. The poly-mer, poly(AN-co-AA) was dried in vacuo at 45 °C until a constant weight was obtained [25].

For modification, 6.0 g of thiourea, and ethanol/ /deionized water (1:2 volume ratio) were mixed and stirred at 200 rpm for 30 min at 70 °C temperature. Then, 5.0 g of poly(AN-co-AA) was added to the sol-ution and the mixture was left for 5 h at 100 °C. Then, the resulting solid TU modified poly(AN-co-AA) was soaked in ethanol/DI water solution, filtered, and dried at 50 °C to constant weight. The synthesis and modi-fication route are represented by Figure 1.

Characterization of TU modified poly(AN-co-AA)

FT-IR spectra of TU modified poly(AN-co-AA) after adsorption of MG was taken using Fourier- -transform infrared spectrometer (Perkin Elmer, 1750X (PerkinElmer Inc., Waltham, MA, USA) by using potassium bromide (KBr) pellets in the reso-lution range of 4000–400 cm-1 at room temperature. Scanning electron microscope (SEM) micrographs were acquired using a Hitachi S-3400N instrument (Hitachi scanning electron microscope (SEM) (Hitachi S3400N High-Technologies Corporation, Minato, Tokyo, Japan). It was operated at 10 to 20 kV to examine the morphology of poly(AN-co-AA) after chemical modification with thiourea. The surface charge of prepared TU-poly(AN-co-AA) polymer was


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measured with Zetasizer Nano Series (ZS Malvern Panalytical Limited, UK).

Fixed-bed column experiments

The efficiency of TU-poly(AN-co-AA) for MG adsorption from the liquid phase was evaluated using a laboratory-scale design continuous fixed-bed column. The fixed-bed adsorption column consist of a cylindrical glass tower (internal diameter 2.5 cm, height 30 cm) packed with TU-poly(AN-co-AA) and coupled to a peristaltic pump (MasterFlex Console Drive, model 77521-47, Cole Parmer Instrument Company, USA). Prior to loading of TU-poly(AN- -coAA) adsorbent, glass wool was fixed at the bottom of the cylinder and then compacted using fine acid-washed sea sand. The glass wool serves as packing to prevent adsorbent loss and provide even flow dis-tribution across the column. TU-poly(AN-co-AA) par-ticles were then added to the column and packed with acid-washed sand. The packed bed was first washed with deionized water to avoid subsequent bed block-ing. The TU-poly(AN-co-AA) was compacted via nat-ural gravity to form a uniform bed and complete expulsion of air bubbles. MG solutions were fed into the column top with downward flow using a peristaltic pump. The effluent aliquots were withdrawn periodic-ally and supernatant MG was scanned and measured at 617 nm wavelength by a UV-spectrometer (Lambda 35, PerkinElmer Life and Analytical Science, Singapore). The initial pH, MG inlet concentration, mass of TU-poly(AN-co-AA) and flow rate were alt-ered respectively, as designed in Table 1 to inves-tigate the effect of column parameters.

Table 1. Column experimental conditions for the MG adsorpt-ion onto TU-poly(AN-co-AA)

Influent pH Initial concentration

(mg/L) Adsorbent mass (g)

Flow rate (mL/min)

2, 5, 9 50 5 3

9 25, 50, 80 5 3

9 50 3, 5, 7 3

9 50 5 1.5, 3.0, 5.0

Column data analysis

Evaluation of the column performance based on the shape of the breakthrough curve was done according to previously published literature [28-32]. The breakthrough curves were obtained from the plot of Ct/Co versus time (t). The breakthrough point or time (tB) and bed saturation/exhaustion time (te) chosen for this research were time when outlet con-centration (Ct) reached 50 and 90% of inlet concen-tration (Co). The total mass of MG adsorbed, qtotal (mg) was calculated from the area under the breakthrough curve using Eq. (1):

total

total ad0

d1000

t

t

Qq C t=

== (1)

where the adsorbed dye concentration and volumetric flow rate are denoted by adC (mg/L) and Q (mL/min). The total mass of MG ( totalW ) added to the column (mg) is calculated by Eq. (2):

o totaltotal 1000

QC tW = (2)

The experimental uptake capacity, Bq (mg/g), is estimated by Eq. (3), where Bt is the breakthrough

Figure 1. Synthesis of poly(acrylonitrile-co-acrylic acid) (poly(AN-co-AA)) (x) and thiourea modification of poly(AN-co-AA) (y).


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time (min) at 50% and adsm represents the weight of TU-modified poly(AN-co-AA) in the column (g):

o BB

ads

QC tqm

= (3)

The total adsorption capacity, eq (mg/g) is cal-culated from Eq. (4), where et is saturation time (min) at 90% [32]:

o ee

ads

QC tqm

= (4)

Eq. (5) is used to calculate the extent of MG uptake, (%)E :

total

total

(%) 100qEW

= × (5)

Dynamic adsorption models

Design of an adsorption column requires precise prediction of the concentration-time profile from the breakthrough curve of discharged effluent from the column. The breakthrough time and curve shape (or slope) are key parameters, determining operations and dynamic response of adsorption in the plug flow system. The following dynamic adsorption models: Thomas, Yoon-Nelson and Bohart-Adams equations were used to analyze the experimental data.

The Thomas model Thomas model assumes that the sorption pro-

cess follows the Langmuir isotherm and pseudo-sec-ond order kinetics of adsorption-desorption without axial dispersion [29,33-35]. The Thomas model is one of the most widely used models for describing the adsorption process in a packed-bed tower. This model is expressed as Eq. (6):

1 expo TH o adsTH o

t

C K q m K C tC Q

= + −

(6)

The linear form of the model is given as:

ln 1o TH o adsTH o

t

C K q m K C tC Q

− = −

(7)

Where Co and Ct are the inlet and outlet MG concen-trations. KTH represents the Thomas kinetic coefficient (mL/mg min), Q and t are volumetric flow rate (mL/ /min) and sampling flow time (min), qo and mads denote adsorption capacity (mg/g) and mass of TU- -poly(AN-co-AA) in the column (g).

The Yoon-Nelson model The adsorption process and breakthrough of

gaseous adsorbate with respect to activated charcoal

was used to derive the Yoon and Nelson model. It is based on the assumption that the decrease in ads-orption rate for each adsorbate molecule is propor-tional to the probability of adsorbate adsorption and adsorbate breakthrough on the adsorbent [10,28,30]. The model is given in Eq. (8):

( )1 expoYN YN

t

C K K tC

τ= + − (8)

The Yoon-Nelson model is linearized for a single component system and expressed as Eq. (9):

ln tYN YN

o t

C K t KC C

τ

= − − (9)

The Yoon-Nelson rate constant is denoted by KYN (min-1), τ is the required time for 50% adsorbate breakthrough (min) and t is the sampling time (min).

The Bohart-Adams model The Bohart and Adams model was derived

based on the surface reaction theory, with the assumption that equilibrium is not instantaneous. Hence, the adsorption rate is proportional to the residual capacity of the adsorbent and concentration of adsorbate. The model was used to described the relationship between Co and t in a plug flow system for the sorption of chlorine on activated charcoal [34]. This model established a correlation between time and bed depth of the column and expressed as Eq. (10):

1 expo AB oAB o

t o

C K N Z K C tC U

= + −

(10)

The linearized form of the Bohart-Adams equat-ion can be written as Eq. (11):

ln AB otAB o

o o

K N ZC K C tC U

= −

(11)

KAB, No, Uo and Z represent the Bohart-Adams kinetic coefficient (L/mg min), saturation concentrat-ion (mg/L), superficial velocity (cm/min) and bed depth (cm), respectively.

The dynamic adsorption model parameters were determined by fitting of the three models with expe-rimental data through linear regression. The superi-ority or suitability of each model was measured via coefficient determination (R2) and analysis of error.

Column regeneration

Experimental study of the possibility of desorb-ing MG ions from TU-poly(AN-co-AA) adsorbent is highly important for potential industrial application.


387

Five regeneration cycles on adsorption-regeneration were performed for adsorbed MG on TU-poly(AN-co- -AA) polymer. The mixed solution of 1.0 M HNO3 and 0.5 M thiourea was used as eluent at 2 mL/min flow rate for 30 min. Post regeneration, TU-poly(AN-co- -AA) polymer was washed with distilled water for an hour and reused in the next cycle of the adsorption study. Efficiency or percentage recovery (η) was calculated using Eq. (12):

Capacity after regeneration100

Capacitybeforeregenerationη = × (12)

RESULTS AND DISCUSSION

Characterization of TU-poly(AN-co-AA)

Identification of functional groups present in the synthesized TU-poly(AN-co-AA) adsorbents was per-formed using FT-IR analysis (Figure 2). The important absorption bands were at 3345, 2935 and 1728 cm-1 which were assigned to stretching vibrations of –NH2 and –OH, -CH and –C=O groups, respectively. Other absorption bands at 1614, 1417, 946 and 729 cm-1, as shown in Figure 1, the peaks were associated with –C=N, -OH bending [36,37], -NH2 bending vibration and –C=S vibration, respectively [27,36,38]. These characteristic absorption bands show that poly(AN- -co-AA) modification with thiourea was successfully synthesized.

The SEM micrograph of TU-poly(AN-co-AA) (Figure 3) revealed the formation of spherical agglo-merated beads. This morphological feature was due to the existence of interparticle bonds between mono-mers, solution viscosity and complex polymerization

nature [39-41]. The polymer diameters and particle size distributions were calculated with ImageJTM soft-ware (version 1.52a) from the SEM image analysis of 100 individual particles. The average particle size of prepared TU-poly(AN-co-AA) is 308 nm. This micro-graph (especially magnified image in Figure 3b) rev-ealed almost uniform spherical morphology and rough surface area that is expected to provide suitable act-ive binding sites for the adsorption of dye.

Figure 3. SEM micrograph of TU-poly(AN-co-AA).

Surface charge of TU-poly(AN-co-AA) prepared was determined using zeta potential Zetasizer Nano series (Zetasizer ZS, Malvern Panalytical Limited, UK). The results are presented in Table 2. TU-poly-(AN-co-AA) was found negatively charged in acidic, neutral and even more negatively charged in alkaline media. Cho et al. and Dalwani group reported nega-tive surface charge of polyacrylonitrile polymer par-ticles and polyacrylonitrile support composite mem-brane, respectively [42,43]. Negative surface charges confirmed the availability of polar functional groups on the modified polymer surface (for instance hydroxyl,

4000 3500 3000 2500 2000 1500 1000 500 0

20

40

60

80

100

Wavenumber (cm-1)

3345 -NH 2 -OH

2395CH-

1728-C=O

1614-C=N

1417-OH

758 -C=S

1094 -NH2

Figure 2. FTIR spectra of TU-poly(AN-co-AA).


388

thioamide and carbonyl groups) that lead to high hyd-rophilic charge density and good adsorption capacity [44-46].

Table 2. Zeta potentials of TU-poly(AN-co-AA) at varied pH

pH 3 5 7 9 11

Zeta potential (mV) -12.5 -13.6 -11.8 -28.4 -15.5

Effect of column parameters on breakthrough curves

The pH of the dye solution has a significant influence on the adsorption process. It affects the interaction of the adsorbent’s surface with dye mole-cules [47,48]. The influence of pH on breakthrough curves at three distinct pH values are shown in Figure 4a. As depicted in Table 3, the adsorption capacity is the lowest at pH 2 and highest at pH 9. This can be attributed to the availability of excess H+ competing with positive MG molecules at lower pH, thereby causing electrostatic repulsion and drastically red-uced the adsorbent capacity. On the other hand, TU-

-poly(AN-co-AA) surface was enhanced with nega-tively charged sites at higher pH (basic conditions) and strong electrostatic attraction exists between cat-ionic MG and adsorbent sites which culminate in higher efficiency. This submission is also confirmed by zeta potential measurement (Table 2) where TU- -poly(AN-co-AA) adsorbent had the highest negative surface charge. Though, the hydrogen bonding inter-actions and influence of electron-donor atoms (N and S) as basic reactive centers might play a role in the sorption process.

The effect of inlet MG concentration is another key process variable with notable impact on the ads-orption process. Breakthrough curves at three differ-ent influent concentrations are presented in Figure 4b. The result reveals that as concentration inc-reased, breakthrough time and exhaustion time dec-reased. Experimental parameters (Table 3) demon-strate that adsorption capacity increased (from 19.20 to 29.28 mg/g) with increasing initial concentration from 25 to 80 mg/L. These results agreed with reports

0 200 400 600 800 1000 1200 1400 0 200 400 600 800 1000 1200 1400 1600 1800 time (min) time (min)

Figure 4. Breakthrough curves of MG adsorption to TU-poly(AN-co-AA) under different conditions: a) pH, b) concentration, c) bed depth and d) flow rate.


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of other researchers that column adsorption capacity increased as inlet dye concentration increased [30,33,49]. This increase in adsorption capacity is associated with higher driving forces towards the TU- -poly(AN-co-AA) adsorbent propelled by higher MG initial concentration, which affects the diffusion of the adsorbate in polymeric adsorbent.

Accumulation of dye molecules in a packed-bed column is directly proportional to the bed depth or amount of solid adsorbent packed. The breakthrough curves generated at three distinct bed depths (4, 6 and 8 cm) with constant inlet concentration of 50 mg/L, pH 9 and 3.0 mL/min flow rate are illustrated in Figure 4c. It shows that breakthrough time and exhaustion time increased with the increasing bed depth. Adsorption capacity increased from 16.50 to 21.43 mg/g as the bed depth increased from 4 to 8 cm (Table 3). Similar trends were reported before where the adsorption capacity significantly increased as bed depth increased [7,11,31,50,51]. This is due to availability of more binding sites and longer residence time in the column.

The breakthrough and exhaustion time for sorp-tion of MG onto TU-poly(AN-co-AA) decreased with increasing the flow rate from 1.5 to 5.0 mL/min (Fig-ure 4d and Table 3). Adhesive forces between MG ions and polymer surface reduced due to the distur-bance of film that surrounded the TU-poly(AN-co-AA) particles at a higher flow rate. These led to poor dis-tributions of MG molecules in the packed-bed, result-ing in inadequate residence time for MG cations and low sorption capacity of the adsorbent. Diffusion of MG cations from the solution to the adsorbent surface is often boosted by the concentration gradient dev-eloped at the interface. Similar observation was rep-orted before by [31,52]. Maximum residence or con-tact time between adsorbate and adsorbent is essen-tial for effective column operation.

According to Table 3, the lowest and highest extent of MG uptake, E (%), in all column operating

conditions were 58.33 and 92.75%, respectively. This demonstrates that the adsorption of cationic MG by TU-poly(AN-co-AA) was effective.

Column dynamic models

The Thomas model Experimental data were fitted with the Thomas

model to determine the rate constant KTH and max-imum adsorption capacity qo. The relatively calculated constant KTH and adsorption capacity qo values using linear regression (OriginPro 9.0) along with statistical parameters are given in Table 4. The values qo cal-culated from the Thomas model were relatively close to qB values in Table 3. The values of R2 range from 0.95 to 0.99 indicating excellent fitness and that the Thomas model was suitable to describe the adsorp-tion of MG in the column study. As the inlet pH inc-reased, the value of qo increased while KTH value decreased. Same trends were observed with influent MG concentration. Furthermore, qo and KTH values increased as the flow rate increased, whereas KTH values decreased as the column bed depth was inc-reased from 4 to 8 cm.

The Yoon-Nelson model The theoretical model developed by Yoon and

Nelson was applied to investigate the breakthrough performance of MG onto TU-poly(AN-co-AA) polymer. The Yoon-Nelson rate constant KYN and 50% break-through time τ values were calculated from the linear plot of Eq. (6) and presented in Table 5. The break-through time τ, calculated from the Yoon-Nelson model agreed with the calculated breakthrough time tB (Table 3) indicating excellent fitness. The value of KYN decreased and τ increased with increasing the initial pH of the MG solution. Gopal and co-workers reported a similar trend with bed depth for column rhodamine B (RhB) adsorption study [54]. The values of R2 range from 0.95 to 0.99 indicating excellent

Table 3. Parameters in fixed-bed column for MG adsorption by TU-poly(AN-co-AA)

pH Co (mg/L) Z (cm) mads (g) Q (mL/min) tB (min) te (min) qB (mg/g) qe (mg/g) E (%)

3 50 6 5 3.0 210 360 6.30 10.80 58.33

6 50 6 5 3.0 440 580 13.20 17.40 75.86

9 50 6 5 3.0 800 980 24.00 29.40 81.63

9 25 6 5 3.0 1280 1380 19.20 20.70 92.75

9 80 6 5 3.0 610 750 29.28 36.00 81.33

9 50 4 3 3.0 330 450 16.50 22.50 73.33

9 50 8 7 3.0 1000 1210 21.43 25.93 82.64

9 50 6 5 1.5 1460 1680 21.90 25.20 86.90

9 50 6 5 5.0 590 820 29.50 41.00 71.95

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Table 4. Thomas model constants and statistical parameters; SSE - sum of the squares of errors

Column variables Thomas

pH Co (mg/L) Z (cm) Q (mL/min) KTH×10-4 (L/(min mg)) qo (mg/g) qB (mg/g) R2 SSE

3 50 6 3.0 4.424 6.60 6.30 0.9887 0.953

6 50 6 3.0 3.688 12.73 13.20 0.9803 1.043

9 50 6 3.0 2.642 23.37 24.00 0.9852 1.656

9 25 6 3.0 7.724 18.95 19.20 0.9713 4.259

9 80 6 3.0 1.843 27.97 29.28 0.9526 4.747

9 50 4 3.0 4.462 15.99 16.50 0.9655 3.238

9 50 8 3.0 2.960 21.08 21.43 0.9901 1.235

9 50 6 1.5 2.616 21.73 21.90 0.9905 1.034

9 50 6 5.0 2.860 29.50 29.50 0.9692 3.652

Table 5. Yoon-Nelson model constants and statistical parameters; SSE - sum of the squares of errors

Column variables Yoon-Nelson

pH Co (mg/L) Z (cm) Q (mL/min) KYN×10-2 (min-1) τ (min) tB (min) R2 SSE

3 50 6 3.0 2.212 220 210 0.9887 0.953

6 50 6 3.0 1.844 424 440 0.9803 1.043

9 50 6 3.0 1.084 816 800 0.9857 2.170

9 25 6 3.0 3.862 1121 1280 0.9713 4.259

9 80 6 3.0 1.474 583 610 0.9526 4.747

9 50 4 3.0 2.231 320 330 0.9655 3.238

9 50 8 3.0 1.480 983 1000 0.9901 1.234

9 50 6 1.5 2.703 1316 1460 0.9828 2.244

9 50 6 5.0 2.864 505 590 0.9692 3.651

fitness of the Yoon-Nelson model to describe the MG adsorption in a packed-bed column.

The Bohart-Adams model Table 6 shows the Bohart-Adams model cons-

tants and statistical parameters that were calculated from the gradient and intercept of model fitting. The results revealed that adsorption capacity No increased with increasing pH, initial MG concentration and flow rate. On the other hand, KAB value decreased with increase in pH, initial MG concentration and flow rate.

This might be due to the domination of external mass in the initial stage of MG removal in packed-bed con-ditions. Similar results were also reported for adsorp-tion of dyes in column mode [53,54]. The values of R2 range from 0.78 to 0.93 indicating relatively good fit-ness of the Bohart-Adams model for the description of MG adsorption in a packed-bed column.

According to R2 values (Tables 4–6), Thomas and Yoon-Nelson models showed higher R2 com-pared to the Bohart-Adams model. Furthermore, con-sidering the sum of the squares of errors (SSE) pre-

Table 6. Bohart-Adams model constants and statistical parameters; SSE - sum of the squares of errors

Column variables Bohart- Adams

pH Co (mg/L) Z (cm) Q (mL/min) KAB×10-4 (L/(min mg)) No (mg/L) qB (mg/g) R2 SSE

3 50 6 3.0 2.218 7.99 6.30 0.8419 3.8845

5 50 6 3.0 1.648 13.70 13.20 0.8338 2.0480

9 50 6 3.0 1.048 25.82 24.00 0.8481 6.2025

9 25 6 3.0 9.812 14.63 19.20 0.9337 4.1120

9 80 6 3.0 1.066 28.36 29.28 0.8155 7.1709

9 50 4 3.0 2.408 15.72 16.50 0.8214 5.6739

9 50 8 3.0 1.568 21.25 21.43 0.8922 4.1573

9 50 6 1.5 3.030 17.38 21.90 0.8338 7.9879

9 50 6 5.0 2.966 24.23 29.50 0.7797 8.6261


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sented, the Bohart-Adams model showed higher SSE than corresponding values of Thomas and Yoon-Nel-son models. These results also confirmed the validity of Thomas and Yoon-Nelson models for application in the adsorption of MG onto TU-poly(AN-co-AA) poly-mer. Baghdadi et al., Guo et al. and Sheng et al. rep-orted that the Thomas model was more appropriate to describe the adsorption of MG and methylene blue (MB), respectively, in a fixed-bed column [31,33,53]. Whereas Thomas, Yoon-Nelson and Bohart-Adams models were reported valid and appropriate to des-cribe adsorption of food azo dyes in a packed-bed column [7,10].

Mechanism of adsorption

The proposed mechanism of malachite green (MG+) adsorption onto TU-poly(AN-co-AA) (MP) poly-mer (Figure 5) under high pH 9 is probably a chemi-sorption and physisorption process attributed to elec-trostatic adsorption and hydrogen bonding interact-ions, based on the column dynamic analysis. In addit-ion, TU-poly(AN-co-AA) adsorbent possesses elec-tron-rich N2 and S atoms which favor the adsorption process as they serve as basic reactive centers for MG uptake, according to [55,56].

Column regeneration

The investigation into the possibility of des-orbing the MG ions adsorbed on TU-poly(AN-co-AA) adsorbents is germane in industry-scale application from economic and technological standpoints. Five cycle runs of adsorption-desorption were conducted for MG on TU-poly(AN-co-AA) using a mixed solution of 1 M nitric acid and 0.5 M thiourea as eluent. The results indicated that the percentage recovery (η) exceeds 90% after five (5) cycles (Figure 6). This shows that the TU-poly(AN-co-AA) exhibited excellent durability and high efficiency for multiple usage.

Figure 6. Recyclability of TU-poly(AN-co-AA) for adsorption

of MG.

CONCLUSION

The study focused on the application of thiourea poly(acrylonitrile-co-acrylic acid) for adsorptive rem-oval of MG dye from aqueous solution in column operation mode. FTIR, SEM and Zetasizer were applied to characterize the physicochemical pro-perties of TU-poly(AN-co-AA) and confirmed the suc-cessful incorporation of thiourea to poly(AN-co-AA). The breakthrough curves were significantly influenced by column operation parameters such as pH, inlet MG concentration, bed depth and flow rate. The maximum TU-poly(AN-co-AA) adsorbent bed capacity was 29.50 mg/g for breakthrough time and saturation time of 590 and 820 min, respectively. The longest break-through time was obtained at pH 9 and low flow rate of 1.5 mL/min. Also, 92.75% uptake of MG dye ions was attained on the column performance using 3.0 mL/min flow rate, 25 mg/L inlet MG concentration and 6 cm bed height. Experimental breakthrough data were well fitted with Thomas and Yoon-Nelson models.

Figure 5. Proposed mechanism of MG adsorption onto TU-poly(AN-co-AA).


392

Column regeneration (recyclability) was feasible and 90% of recovery was demonstrated after five adsorp-tion-elution cycles. The fixed-bed column loaded with TU-poly(AN-co-AA) material is a promising functional adsorbent to treat MG dye-bearing wastewater.

Acknowledgements

The authors acknowledge the Department of Chemical and Environmental Engineering, Faculty of Engineering, and Chemistry Department, Faculty of Science, Universiti Putra Malaysia (UPM), and the Ministry of Education, Malaysia for the financial sup-port via Fundamental Research Grant Scheme (FRGS), FRGS/1/2016/TK05/UPM/02/1.

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ABEL ADEKANMI ADEYI1,2

SITI NURUL AIN MD JAMIL3

LUQMAN CHUAH ABDULLAH1,4

THOMAS SHEAN YAW CHOONG1,4

MOHAMMAD ABDULLAH5

KIA LI LAU1 1Department of Chemical and

Environmental Engineering, Faculty of Engineering, Universiti Putra Malaysia,

UPM Serdang, Malaysia 2Department of Chemical and

Petroleum Engineering, Afe Babalola University Ado-Ekiti (ABUAD), Ado-

Ekiti, Ekiti State, Nigeria 3Department of Chemistry, Faculty of

Science, Universiti Putra Malaysia, UPM Serdang, Malaysia

4Institute of Tropical Forestry and Forest Product (INTROP), Universiti

Putra Malaysia, UPM Serdang, Malaysia

5Faculty of Chemical Engineering, Universiti Teknologi Mara Ma sai,

Johor Darul Takzim, Malaysia

NAUČNI RAD

ADSORPCIJA MALAHITNOG ZELENOG U KOLONI SA NEPOKRETNIM SLOJEM POMOĆU TIOUREOM MODIFIKOVANE POLI(AKRILONITRILNE-KO- -AKRILNE KISELINE)

Polimerni adsorbent na bazi tioureaom-modifikovane poli(akrilonitrilne-ko-akrilne kise-line) (TU-poli(AN-co-AA)) je sintetizovan i karakterisan Fourier infracrvenom (FTIR) spektroskopijom, skenirajućim elektronskim mikroskopom (SEM) i Zetasizer-om. Pro-učavano je uklanjanje boje katjonskog malahitnog zelenog (MG) iz vodenog rastvora adsorpcijom u kontinualnoj koloni sa punjenjem na bazi TU-poli (AN-coAA). Utecaj pH rastvora 2-9), koncentracije ulaznog MG (25-80 mg/l), debljine sloja (4-8 cm) i brzine strujanja (1,5-5,0 ml/min) ispitivani su procenom krive proboja. Nizak pH i mala debljina sloja, visoka koncentracija MG i brzina strujanja doveli su do ranog probija. Prema koefi-cijentima korelacije (R2) i sume kvadrata greške (SSE), dinamički modeli Thomas i Ioon-–Nelson su pogodniji za opisivanje eksperimentalnih podataka u poređenju sa Bohart--Adams modelom. TU-poli(AN-co-AA) je pokazao efektivno odvajanje MG iz tečne faze i visoke adsorpcione kapacitete nakon pet ciklusa regeneracije.

Ključne reči: adsorpcija, malahitno zelena, kolona sa pakovanim slojem, poli-(akrilonitrilna-ko-akrilna kiselina), tiourea.

abel adekanmi adeyi adsorption of malachite green in … no4... · reaction medium followed by 2.16...

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