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Surfaces and Interfaces

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Insights into the modeling, characterization and adsorption performance ofmesoporous activated carbon from corn cob residue via microwave-assistedH3PO4 activationAli H. Jawada,⁎, Mondira Bardhanb, Md. Atikul Islamb, Md. Azharul Islamc,Syed Shatir A. Syed-Hassand, S.N. Suripa, Zeid A. ALOthmane, Mohammad Rizwan Khanea Faculty of Applied Sciences, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysiab Environmental Science Discipline, Khulna University, Bangladeshc Forestry and Wood Technology Discipline, Khulna University, Bangladeshd Faculty of Chemical Engineering, University Teknologi MARA, 40450 Shah Alam, Selangor, Malaysiae Chemistry Department, College of Science, King Saud University, Riyadh 11451, Saudi Arabia

A R T I C L E I N F O

Keywords:Corn cobActivated carbonMicrowave activationAdsorptionOptimizationBox-Behnken design

A B S T R A C T

Microwave-assisted H3PO4 chemical activation was applied to convert corn (Zea mays) cob (CC) residue intomesoporous corn cob activated carbon (CC-AC) as a desirable adsorbent for cationic dye (methylene blue; MB)removal. The activation process was carried out by impregnating CC with phosphoric acid (H3PO4) (1:2 Wt.%mixing ratio) before being placed inside a microwave oven with activation power of 600 W for 20 min for CC-ACproduction. A Box-Behnken design (BBD) was applied to develop response model followed by numerical opti-mization in order to optimize the input adsorption variables (CC-AC dose, solution pH, temperature, and contacttime) towards MB dye removal by CC-AC. The best numerical option for MB dye removal (99.7%) was recordedat following operation conditions: CC-AC dosage 0.1 g, solution pH 9.4, temperature 39.9 °C, and contact time34.1 min. The adsorption results at these optimum conditions indicated the capability of CC-AC for uptaking183.3 mg/g MB dye at equilibrium as determined by Langmuir isotherm. The consequence of this study sug-gested the feasibility of producing a high quality of mesoporous activated carbon for cationic dye removal by arelatively fast microwave process.

1. Introduction

Water is polluted due to discharge of untreated industrial, agri-cultural, and domestic effluents which causes the environment pollu-tion. Among these sectors, textile and dye industries generate seriouswater pollution by discharging different synthetic dyes, acidic and basicdyes [1]. Therefore, it is very much crucial to treat these dyes properlybefore discharging them into the ecosystem [2]. Various physico-chemical treatment methods such as precipitation [3], coagulation-flocculation [4], membrane filtration [5], ionic exchange [6], electro-chemical destruction [7], photodegradation [8], and adsorption [9]have been applied for the removal of dyes. Among these treatmentmethods, adsorption is substantially efficient method due to its sim-plicity in design, does not generate toxic byproducts, and high se-lectivity [10]. It is remarkably auspicious to combat such environ-mental degradation and increases the production resulting to economic

development as well as ensure environmental sustainability [11].Among various adsorbents, activated carbon (AC) has been ex-

tensively used as an efficient, environment friendly, cost-effective, andrenewable adsorbent material due to its desirable surface property suchas rich in various oxygen-functional groups, porous structure, largesurface area, and high adsorption capacity [12]. In this point of view,naturally available agricultural residues and/or byproducts might beconsidered as a promising alternative precursor for producing highquality AC with remarkable adsorptive property. Recently, severalbiomass materials have been utilized to prepare AC for dye removal, forinstance, waste fibrous biomass or flux [13], palm kernel shell [14], ricestraw [15], coffee grounds [16], oil palm waste [17], watermelon rind[18], palm shell [19], coconut shell [20], macadamia nut endocarp[21], waste tea [22] and so on. Based on governmental policy of agri-cultural cultivation, corn cob is considered as one of the importantMalaysian economic sources of lignocellulose product, which is also

https://doi.org/10.1016/j.surfin.2020.100688Received 12 May 2020; Received in revised form 24 August 2020; Accepted 5 September 2020

⁎ Corresponding author.E-mail addresses: ali288@uitm.edu.my, ahjm72@gmail.com (A.H. Jawad).

Surfaces and Interfaces 21 (2020) 100688

Available online 10 September 20202468-0230/ © 2020 Elsevier B.V. All rights reserved.

T

considered feasible and renewable low-cost precursor for AC produc-tion [23].

The extraordinary physicochemical properties of AC such as abun-dant oxygen-containing functional groups, tunable surface areas, andcontrollable porous structures are mainly depend on the nature ofprecursor, activation technique, and type of chemical activator [12].Among various activation method, microwave radiation is the mostpreferable one over other conventional heating methods because of itsmany desirable properties such as high yield of target product, less timeconsuming, uniform heating process, minimal production and emissionof hazardous by-products [24,25]. Among various chemical activationagents, H3PO4 presents itself as low-cost and environment friendlydehydrating catalyst that offers the decomposition of the lignocellulosicprecursor at relatively low activation temperatures with less corrosionto the activation equipment [20].

Thus, the main focus of this research work is to convert corn cob asan agricultural residue into mesoporous activated carbon (CC-AC) viamicrowave-assisted H3PO4 activation. The physicochemical propertyand adsorptive performance of CC-AC for MB dye removal from aqu-eous environment were investigated. The MB dye removal was max-imized in relatively short time, less labors, and less chemicals con-sumption by numerical optimization for main the input adsorptionvariables via Box-Behnken design (BBD) in response surface metho-dology (RSM). The physicochemical characterizations of CC-AC, andadsorption kinetic, isotherm, thermodynamic, and mechanism werediscussed.

2. Experimental part

2.1. Preparation of CC-AC

The corn cob (CC) an agricultural residue was collected from foodproduction mill, located at Pontian, Johor, Malaysia. CC was primarilywashed with boiled water for several times before being dried inside anoven at 100 °C for 24 h to remove the moisture content. After that, thedried CC crashed into powder form with constant particle size(<2 mm). The chemical activation process was carried out by im-pregnating CC with phosphoric acid (H3PO4) with optimum mixingratio (1:2 CC / H3PO4%) (pre-determined as the best mixing ratio),followed by drying process inside an oven for 24 h at 100 °C. After ovendrying, the impregnated CCeH3PO4 material was placed inside amodified microwave oven (SAMSUNG Solo 20 L Microwave OvenME711K). The microwave irradiation process was operated at 600 Wfor 20 min under nitrogen condition (pre-determined as the best acti-vation conditions). The final product of corn cob activated carbon (CC-AC) rinsed rapidly with boiled distilled water until the neutral solutionpH was obtained. The CC-AC sample was placed in an oven for 24 h at100 °C to remove moisture content. After that, the dried CC-AC wassieved into a constant particle size (≥250 µm) before being stored inthe sealed container for further application.

2.2. Characterization of CC-AC

The surface property and porosity of CC-AC was investigated byusing a Micromeritics ASAP 2060 analyzer. The morphological struc-ture of CC-AC was determined by using scanning electron microscope(SEM, Zeiss Supra 40 VP). The crystalline structure of CC-AC was de-termined using X-ray diffractometer (XRD, X'Pert PRO, PAnalytical).The point of zero charge (pHpzc) of the CC-AC was determined based onmethod described elsewhere [26]. Functional groups of the CC-AC wereidentified by FT-IR spectrophotometer (Perkin-Elmer, Spectrum RX I)with working range 4000 cm−1–500 cm−1. In this analysis, 0.02 g ofthe CC-AC sample was mixed with 0.1 g of KBr in a mortar for preparingthe transparent pellet. Then the mixture was connected to piston of thehydraulic pump for a compression pressure to obtain a transparent andthin solid disk that was transferred to FTIR analyzer. The same

procedure was repeated for the CC-AC after MB dye adsorption. Theelemental composition of CC-AC was estimated using a Flash 2000,Organic Elemental Analyzer, Thermo-scientific, Netherlands. The io-dine number test was performed in order to estimate the surface areaand porosity of CC-AC. In this test, 0.3 g of CC-AC is transferred into250 mL of Erlenmeyer flask containing 10 mL of 5% of hydrochloricacid (HCl) and swirl continuously to be wetted of CC-AC properly. Themixture was boiled on the hot plate for one minute and then was al-lowed to cool at the room temperature. After that, 100 mL of 0.1 Niodine solution was added into the mixture and immediate shaking wascarried out vigorously for 30 s. The solution was filtered and collected25 mL of the filtrate sample was titrated with 0.1 N sodium thiosulphatesolution until the yellow color became colorless. The volume of sodiumthiosulphate solution used was recorded. The experiment was repeatedagain for activated carbon sample mass of 0.6 g and 0.9 g accordingly.The iodine number was calculated by using the following Eq. (1):

=× × × × ×+{ }( )

The adsorbed iodine amount per gram of carbon

N V N V

M

( 126.93 ) ( 126.93)V VV Na S O Na S O

c

1 1HCl

F1

2 2 2 2 2 2

(1)

where, N1and V1 are the iodine solution normality and the added vo-lume of iodine solution, VHCl is the added volume of 5% HCl, VF is thefiltrate volume used in titration, NNa2S2O3 is the sodium thiosulfatesolution normality, VNa2S2O3 is the consumed volume of sodium thio-sulfate solution and Mc is the mass of activated carbon.

The bulk density, ash content, and moisture content were analyzedto determine the physical characteristics of CC-AC. For bulk densityanalysis, a 5 mL clean measuring cylinder was weighed. The CC-ACsample was filled into the measuring cylinder and again was weighted.Then it was calculated by Eq. (2):

=Bulk density gmL

W WV

2 1

1 (2)

where, W1 and W2 are the weight of void and filled cylinder respec-tively where V1 demonstrate the volume of container.

Ash content was determined by using muffle furnace. 1 g of CC-ACwas transferred into an ignited crucible and placed it in the furnacecontaining the temperature up to 650 °C. This process was taken for 3 to16 h until getting constant weight. The ash content, Ac (%) was de-termined by Eq. (3):

= ×Ash content A F GB G

, (%) 100c (3)

where, F = mass of crucible plus ashes sample (g), G = mass of emptycrucible (g) and B = mass of crucible plus dried sample (g).

1 g of CC-AC was placed into an oven at temperature 150 °C for 3 hand then being weighted in case of determining the moisture content.The calculation of moisture content is given in Eq. (4):

= ×Moisture content W WW

(%) 1001 2

1 (4)

Where, W1 is the weight of original sample before drying and W2 isthe weight of dried sample.

2.3. MB dye removal and adsorption study

The experiments for the MB dye removal and adsorption study werecarried out by adding a specified quantity of CC-AC adsorbent to a set ofErlenmeyer flasks (250 mL) containing 100 mL of 100 mg/L MB dyesolution. The flasks were placed in a water bath shaker. The MB dyeconcentration was determined by UV–Vis spectroscopy (HACH DR2800) at the maximum absorbing wavelength (λmax) of 661 nm. TheMB dye removal (DR%) was calculated by Eq. (5):

A.H. Jawad, et al. Surfaces and Interfaces 21 (2020) 100688

2

= ×DR C CC

% ( ) 100 %o e

o (5)

Where Co (mg/L) and Ce (mg/L) represent the initial and equili-brium MB dye concentration, respectively.

The adsorption of MB dye by CC-AC was performed in batch modeat the optimum adsorption conditions as determined by BBD. The ad-sorption capacity of CC-AC for MB dye uptake at equilibrium, qe (mg/g)was estimated by Eq. (6):

=q C C VW

( )e

o e(6)

V (L) represents the volume of dye solution, while W (g) is the ad-sorbent weight.

All the experiments were conducted in dark condition by usingcovered water bath thermostat shaker in order to avoid any possiblephotolysis of MB dye by ambient light. Moreover, a control experimentwas made in order to count the color leached by the adsorbent. In thisexperiment, 0.1 g of the adsorbent was placed in 250 mL Erlenmeyerflask contains 100 mL of ultrapure water. The same procedure wasrepeated by adding 100 mL of 100 mg/L MB dye in 250 mL Erlenmeyerflask without any adsorbent in order to control any possible adsorptionof MB dye by glass material of the Erlenmeyer flask container. All theadsorption experiments were carried out in duplicate under identicaloperational conditions and the results were recorded as an averagevalue.

3. Results and discussion

3.1. Physicochemical properties of CC-AC

The elemental composition, bulk density, moisture content, and ashcontent of CC-AC are summarized in Table 1. The amount of carboncontent was found 61.79% that makes CC-AC as a potential adsorbent.Low bulk density (0.49 g/mL) theoretically indicates high porosity ofthe obtained product [27]. Additionally, low moisture content (0.15%)acts as a favorable property of AC. The adsorption nature of AC could beobsessed by ash content as it reveals the impeding or facilitating effectson adsorption nature of adsorbent in case of different organic chemicals[28]. Basically, it is directly linked to the pore structure of AC [29]. CC-AC with low ash content (13.2%) indicates low amount of mineral orinorganic residue remained after activation process and as a resultpreferable adsorptive performance of CC-AC can be obtained.

The obtained BET surface area, and total pore volume with its meanpore diameter are summarized in Fig. 1 and Table 1. The average widthof pore was found 3.35 nm authenticating the mesoporous character-istic of CC-AC in accordance with the IUPAC definition [30]. Moreover,similar mesoporous activated carbon was obtained by activating var-ious lignocelluloses materials with H3PO4 such as eucalyptus residue[31], tabah bamboo [32], and S. psammophila [33]. Further confirm

was made by iodine number test which provides an enumeration of thesurface area and porosity of proposed adsorbent and it is well-definedparameter for activated carbon testing due to its simplicity and fastassessment of adsorbent quality [34]. The high iodine number meanshigh level of activity for activated carbon due to high degree of acti-vation, therefore iodine number ranging from 500 to 1200 mg/g isdemanded for activated carbon materials that utilized as adsorbents inwastewater treatment methods [35]. In this study, the result for iodinenumber is 693.9 mg/g, which indicates that the CC-AC could be po-tentially applied as a promising adsorbent for treatment of con-taminated water.

The XRD analysis was carried out in order to investigate the natureof CC-AC surface whether it's amorphous or crystalline in nature. TheXRD profile of CC-AS is depicted in Fig. 2. As can be seen, the existenceof broad shoulders in XRD pattern without appearance of sharp anddistinguished peaks reveal the amorphous in nature of CC-AC [36].

The surface morphology of CC-AC is given in Fig. 3a which displaysporous structure of the CC-AC surface with well-developed visiblecavities. Moreover, the cavities sizes in the CC-AC surface are shown tobe generally circular and ellipse shaped. In fact, adsorption is a surfacephenomenon, and it mainly relies on the CC-AC surface property.Therefore, rich pores/cavities surface of CC-AC will definitely offerpreferable adsorptive property towards MB dye molecules. This as-sumption was confirmed by observing the SEM image of CC-AC afterMB dye adsorption (Fig. 3b). The pores/cavities are completely blockedand the surface morphology of CC-AC converted to be compact andregular surface, which indicates an even distribution of MB dye

Table 1Physicochemical properties of CC-AC.

Properties/ Characteristics Values

Bulk Density (g/mL) 0.49Ash Content (wt%) 13.1Moisture Content (wt.%) 0.15Elemental analysis (wt.%)Carbon, C 61.8Hydrogen, H 4.08Nitrogen, N 0.72Oxygen, O (by difference) 33.4Textural propertiesVolume in pores (cm³/g) 95.4Total volume in pores (cm³/g) 0.35Mean pore diameter (nm) 3.35BET surface area (m²/g) 415.2

Fig. 1. Isotherms of N2 adsorption–desorption for CC-AC.

Fig. 2. XRD spectrum of CC-AC.

A.H. Jawad, et al. Surfaces and Interfaces 21 (2020) 100688

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molecules onto CC-AC surface.The FT-IR spectral analysis was used for determining the possible

engagement of CC-AC functional groups with the MB dye molecules asshown in Fig. 4. Various IR peaks are presented in FTIR spectrum of CC-AC before adsorption (Fig. 4a). The peak at 3500–3250 cm−1

(overlapping stretching vibration of N–H and O–H), the peak at1600–1500 cm−1 (C=C vibrations in aromatic rings), the peaks at1000–1250 cm−1 (stretching vibration of C–O and/or C–O–C in acids,phenols, alcohols, ethers, and/or esters groups) [18,23]. From Fig. 4a, itcan be concluded that the CC-AC surface is rich with various oxyge-nated and acidic functional groups, which are highly demanded in theadoption process for cationic dyes such as MB dye [20]. These dis-tinguished functional groups are responsible for promoting the elec-trostatic interaction towards cationic dye species of MB dye [10]. In thisregard, Hu et al., [12] reported the ability of organic water pollutants toform hydrogen bonds with the various oxygen-functional groups suchas hydroxyl (–OH), carboxyl (–COOH), epoxy (–O–) and carbonyl(–C=O) groups that available on graphene oxide. The FTIR spectrum ofCC-AC after MB dye adsorption is given in Fig. 4b, which indicates notmuch difference in spectrum compare to spectrum of CC-AC before MBdye adsorption (Fig. 4a), except slight shifting in some peaks locationswhich can be assigned to loading of MB dye molecules on the CC-ACsurface after adsorption process.

3.2. BBD-RSM design

The Design Expert, version 12.0 (Stat-Ease, Minneapolis, USA)software was employed to design the adsorption experiments and sta-tistical analysis of the experimental data. Table 2 displays the levels ofindependent adsorption parameters along with their coded values. Therange of these independent parameters was determined based on pre-liminary experiments. A quadratic equation was employed to predictthe dye removal efficiency and analyze the experimental data as follows(7):

= + + +Y X X X Xi i ii i ij i j02

(7)

Y is the predicted response for MB dye removal (%); Xi and Xj are codedthe independent variables; β0 is the constant; βi, βii and βij are coeffi-cients of linear, quadratic, and interactive coefficient of input in-dependent variables, respectively. According to the BBD, 29 experi-ments (runs) with three levels, three factors and five center points (forerror calculation) were implemented to optimize and investigate theeffects of the adsorption parameters given in Table 2. The BBD matrixand the response results of MB dye removal (%) are presented inTable 3. The adequacy of the model was justified through analysis ofvariance (ANOVA) and lack of fit test (LOF). From the ANOVA analysis(Table 4), it can be concluded that the model regression co-efficient ofdetermination of (R2) of 0.9634 for MB dye removal% was in a goodagreement with the experimental outputs, indicating 96.34% of thevariability can be revealed by the model, leaving 3.66% residualvariability for response (MB dye removal%). Moreover, non-significantLOF related to pure error indicating good response to the model by theexperimental data. Thus, it may be concluded that the BBD was ade-quate to predict the MB dye removal% on the adsorbent CC-AC withinthe range of variables studied. The final predicted process models interms of actual significant factors for MB dye removal% are recorded inEq. (8):

= + + + + +MB removal(%) 84.48 16.66A 24.43 B 9.90 AB 11.35AD 9.90 BC 12.11 A 25.60

B2

2 (8)

Fig. 3. Morphological structure of (a) CC-AC, and (b) CC-AC after MB dyeadsorption, at magnification power 1000x.

Fig. 4. FTIR spectra of (a) CC-AC, and (b) CC-AC after MB dye adsorption.

Table 2Codes and ranges of independent variables at their respective levels.

Codes Variables Level 1 (−1) Level 2 (0) Level 3 (+1)

A CC-AC dose (g) 0.04 0.07 0.1B Solution pH 3 6.5 10C Temperature ( °C) 30 40 50D Time (min) 10 35 60

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From Eq. (8), it can be concluded that the adsorbent dose (A) andsolution pH (B) had an individual positive significant effect on MB dyeremoval% by CC-AC.

From ANOVA analysis (Table 4), the interaction effect of adsorbentdose (A) and solution pH (B) is statistically significant (p-value < 0.0131) and had positive impact on removal% of MB dye byCC-AC (Fig. 5a). It was observed from Fig. 5a, the MB dye removal%was increased by increasing the CC-AC dose and solution pH from 4 to10 (the other independent variables were kept constant; temp. 40 °Cand time 35 min). As the adsorbent dose increased, the MB dye removal% increased as well. This can be attributed to the more adsorption sitesand greater surface area will be offered for MB dye molecules for

binding on the CC-AC surface. Regarding solution pH effect, the pHpzcof the CC-AC was found to be 4.2 as shown in Fig. 5b, which indicatesthat the CC-AC surface can acquire positive charge at pH < pHpzc. Bycontrast, the surface charge of CC-AC surface can adopt negative chargeat solution pH above pHpzc 4.2, indicating the capability of cationicdye adsorption onto CC-AC surface. As a result, strong electrostaticattraction can be achieved between negatively charged surface func-tional groups of CC-AC surface with cationic species of MB dye mole-cules as presented in Eq. (9):

+ …+ +CC AC O MB CC AC O MB (9)

On the other hand, the interaction effect between the CC-AC dosage(A) and contact time (D) is statistically significant (p-value < 0.0058)and had positive impact on removal% of MB dye by CC-AC (Fig. 5c).Meanwhile, the other input parameters (solution pH 6.5 and tempera-ture 40 °C) were kept constant. The 3D response surface plot of the ADinteraction is illustrated in Fig. 5c. The MB dye removal% increased byincreasing the CC-AC dose. This can be attributed to greater number ofactive adsorption sites and/or better surface area of CC-AC will be of-fered to the MB dye molecules in the bulk solution of MB dye. Fur-thermore, Fig. 5c shows non-significant effect on MB dye removal%with rising the contact time from10 min to 60 min, indicating diffusionprocess of MB dye molecules into porous surface of CC-AC is fast withrapid penetration, and as a result can be occurred within a short periodof time.

Another statistically significant interaction (p-value < 0.0131) isbetween solution pH (B) and temperature (C) on the MB dye removal%,meanwhile the other input parameters (CC-AC dose 0.07 g (A), andcontact time 35 min (D)) were kept constant. It was found that the MBdye removal% increased by increasing the solution pH towards basicenvironment (this effect is discussed previously). Moreover, it can bealso observed from Fig. 5d that the MB dye removal% increased gra-dually by increasing MB solution temperature from 30 °C to 50 °C. Thisobservation may indicate that the MB dye adsorption process on CC-ACsurface is an endothermic in nature.

3.3. Confirmation experiment

The optimization process is pursued by using numerical modelingoptimization process in order to find the specific point of the inputparameters which are responsible for maximizing the response (MBremoval%), the detailed procedure was described elsewhere [37]. Themaximum MB dye removal (99.75%) by CC-AC was recorded at CC-ACdose of 0.1 g, solution pH 9.4, temperature of 39.9 °C, and contact time34.1 min as depicted in Fig. 6. In order to verify the validity of thesecond-order response surface model of BB, three additional runs wereperformed based on the suggested numerical solutions by RSM. Thesuggested experimental conditions by numerical solutions and theirpredicted and actual responses are recorded in Table 5. As given inTable 5, the actual values of MB dye removal (%) were closed to thepredicted values given be numerical solution of BBD. This observationindicates that the second-order response model of BBD was very ap-propriate for optimizing the operational conditions for the removal ofMB dye by removal by CC-AC. Therefore, the optimal operational ad-sorption conditions were adopted in further investigations of this study.

3.4. Adsorption performance

The uptake of MB dye by CC-AC was performed in batch mode. Theoptimum adsorption conditions were obtained from confirmation ex-periment (Section 3.3) to be CC-AC dose of 0.1 g, solution pH 9.4, andtemperature of 39.9 °C. At these optimum adsorption conditions, theadsorption performance of CC-AC over MB dye was conducted toevaluate the equilibrium adsorption capacity (qe) at 8 different initialMB concentrations (50, 100, 150, 200, 250, 300, 350 and 400 mg/L)versus various contact times as shown in Fig. 7. As can be seen from

Table 3Box-Behnken design matrix for MB dye removal by CC-AC.

Run A:Dose (g) B:pH C:Temp. (°C) D:Time (min) MB removal (%)

1 0.04 3 40 35 19.92 0.1 3 40 35 27.23 0.04 10 40 35 42.44 0.1 10 40 35 89.35 0.07 6.5 30 10 84.26 0.07 6.5 50 10 88.67 0.07 6.5 30 60 90.88 0.07 6.5 50 60 94.89 0.04 6.5 40 10 85.410 0.1 6.5 40 10 95.411 0.04 6.5 40 60 43.812 0.1 6.5 40 60 99.213 0.07 3 30 35 21.914 0.07 10 30 35 93.015 0.07 3 50 35 53.516 0.07 10 50 35 85.017 0.04 6.5 30 35 46.918 0.1 6.5 30 35 92.319 0.04 6.5 50 35 59.020 0.1 6.5 50 35 93.921 0.07 3 40 10 33.422 0.07 10 40 10 95.323 0.07 3 40 60 40.924 0.07 10 40 60 85.025 0.07 6.5 40 35 80.126 0.07 6.5 40 35 87.227 0.07 6.5 40 35 81.528 0.07 6.5 40 35 84.829 0.07 6.5 40 35 88.8

Table 4Analysis of variance (ANOVA) of the response surface quadratic model for MBdye removal.

Source Sum ofSquares

df MeanSquare

F-value p-value

Model 17,930.34 14 1280.74 26.34 < 0.0001 SignificantA-Dose 3330.00 1 3330.00 68.48 < 0.0001B-pH 7163.85 1 7163.85 147.33 < 0.0001C-Temp. 174.04 1 174.04 3.58 0.0794D-Time 64.40 1 64.40 1.32 0.2691AB 392.04 1 392.04 8.06 0.0131AC 27.56 1 27.56 0.5668 0.4640AD 515.29 1 515.29 10.60 0.0058BC 392.04 1 392.04 8.06 0.0131BD 79.21 1 79.21 1.63 0.2226CD 0.0400 1 0.0400 0.0008 0.9775A² 952.04 1 952.04 19.58 0.0006B² 4251.81 1 4251.81 87.44 < 0.0001C² 15.28 1 15.28 0.3143 0.5839D² 206.88 1 206.88 4.25 0.0582Residual 680.75 14 48.63Lack of Fit 626.52 10 62.65 4.62 0.0767 not significantPure Error 54.23 4 13.56Cor Total 18,611.09 28

R2 = 0.9634; Adjusted R² = 0.9268.

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Fig. 7, at low concentration of MB dye (50 and 100 mg/L), the equili-brium was reached within 60 min, whereas almost 180 min was re-quired to obtain equilibrium in case of high MB concentration levels(150 – 300 mg/L). Similarly, at high concentration MB levels (350 and400 mg/L) require up to 300 min for reaching the equilibrium. Initiallya swift escalation is noticed because of various workable sites for ad-sorption. Only a minute number of sites remained barren with timeswhich were saturated gently by competing adsorbate. Any prominentchange of the extended adsorption curve was not appeared afterreaching a stable like condition (Fig. 7). The experimental data disputesthat the MB dye uptake at equilibrium point increase from 39.7 mg/L to199.4 mg/L by increasing the initial concentration of MB dye from 50to 400 mg/L. High driving force of MB dye molecules for shifting to theadsorption sites was opined as a reason [38]. The time to reach equi-librium was also increased with increases in the initial MB dye con-centration as well. The possible reason might be the collision of ad-sorbate substances impeding the adsorption rate in higher dyeconcentrations [39].

3.5. Adsorption kinetic study

Kinetic study was conducted for disputing the rate as well as me-chanism of adsorption process. In this work, non-linear pseudo-first-order (PFO) and pseudo-second-order (PSO) parameters were used toanalyze the kinetic studies. PFO kinetic model was recommended byLagergren [40], mathematically expressed the non-linear form as givenin Eq. (10):

=q q exp(1 )t ekit (10)

where, qt and qe are the adsorbed amounts (mg/g) of MB dye on CC-ACsurface at time t (min) and equilibrium time, respectively, and k1 (1/min) is the adsorption rate constant of PFO kinetic model. The non-linear form of PSO kinetic model was proposed by Ho and McKay [41],numerically articulated as in Eq. (11):

=+

qq k t

q k t1te

e

22

2 (11)

where, k2 (g/mg⋅min) is the rate constant of PSO adsorption. Betweenthese two models, best-fitted one was attained by calculating the

Fig. 5. (a) 3D response surface for adsorbent dose (A) and solution pH (B) significant interaction on MB dye removal, (b) pHPZC of CC-AC, (c) 3D response surface foradsorbent dose (A) and time (D) significant interaction on MB dye removal, and (d) 3D response surface for solution pH (B) and temperature (C) significantinteraction on MB dye removal.

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coefficient of determination (R2) by Eq. (12):

= =

=R

q qq q

1( )( )¯

nn

e exp e mod

nn

e exp e mod

2 1 . .2

1 . .2

(12)

where, qt.exp (mg/g) and qt.mod (mg/g) are the experimental and model-predicted adsorption capacity of MB dye at time t, respectively, and n isthe number of observations. High R2 value demonstrates best-fittedmodel.

The calculated rate constant (k1), PSO rate constant (k2), correlationcoefficient (R2) and the adsorption capacities from non-linear plot ofPFO and PSO (Figure not shown) are summarized in Table 6. The best-fitted kinetic model was identified by comparing the calculated valuesof qe with the experimental one and the high R2 values. From Table 5,the calculate qe of PSO model is closer to the experimental qe ratherthan PFO. Moreover, the R2 values of PSO are higher than other re-corded by PFO. This finding supports the dominancy of PSO kineticmodel. A properly fitted PSO model suggests that the chemisorptionrather than boundary layer resistance is the possible rate determiningstep that limits the adsorption process. It means that the MB dye ad-sorption rate is corresponding to the total number of workable activesites of CC-AC.

3.6. Adsorption isotherm study

The interaction and distribution between adsorbent and adsorbatemolecules, dynamic equilibrium of sorption process and maximumadsorption capacity of adsorbent material can be identified by ad-sorption isotherm model [42]. In this content, two isotherm modelsnamely Langmuir isotherm model [43] and Freundlich isotherm model[44] were tested. Langmuir model can describe the monolayer ad-sorption, deducing that the selected surface sites allow only one solutemolecule limiting its adsorption capacity [45]. The mathematical ex-pressions of non-linear and linear Langmuir isotherm models are givenin Eqs. (13) and (14) respectively:

=+

qq K C

K CNonlinear Langmuir isotherm:

1em a e

a e (13)

= +Cq

Cq K q

Linear form of this equation is: 1e

e

e

m L m (14)

where, qe (mg/g) and Ce (mg/L) is the experimental amount of MBadsorbed and dye concentration respectively under equilibrium condi-tions. qm (mg/g) is the maximum monolayer adsorption capacity, Ka (l/mg) is the Langmuir constant and KL (L/mg) is a constant related to thefree energy of adsorption.

Fig. 6. Desirability ramps for the optimization of important adsorption input parameters for MB dye removal% by CC-AC.

Table 5Predicted and actual values for MB dye removal (%) form numerical solutions.

Run Doge (g) pH Temp. ˚C Time (min) Predicted (%) Actual (%) Desirability

1 0.097 8.41 43.56 40.19 99.47 97.82 12 0.095 8.03 46.74 51.79 99.69 96.24 13 0.094 9.09 42.74 55.24 99.32 96.12 1

A.H. Jawad, et al. Surfaces and Interfaces 21 (2020) 100688

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Differently, Freundlich isotherm model can be used to discuss themultilayer adsorption process between the adsorbed molecules. Themathematical expressions of non-linear and linear Freundlich isothermmodels are given in Eqs. (15) and (16) respectively.

=q K CNonlinear Freundlich isotherm: e F en1/ (15)

= +q Kn

CLinear form of this equation is: ln ln 1 lne F e (16)

where, KF (mg/g (l/mg)1/n) is the Freundlich constant that representsthe adsorption capacity and 1/n is the adsorption intensity and curva-ture.

Moreover, the best fitted isotherm model between these two modelswas determined by the coefficient of determination (R2) and confirmedby the residual root-mean square error (RMSE). The numerical ex-pressions are as given in Eqs. (17) and (18) respectively:

=Rq qq q

1( )( )

nn

e meas e cal

nn

e meas e cal

2 1 . .2

1 . .2 (17)

=RMSEn

q q11

( )n

n

e meas e cal1

. .2

(18)

where qe.meas(mg/g) and qe.cal(mg/g) are the experimental and model-predicted adsorption capacity at equilibrium respectively and n is thenumber of observations.

The calculated non-linear isotherm values such as adsorption ca-pacity (qe), coefficient of determination (R2), and root mean squareerror (RMSE) are summarized in Table 7. The high R2 value and lowRMSE are the determination parameter of the best fitted isotherm

model. The present study confirms the high R2 (0.99) and low RMSE(1.87) values in case of Langmuir isotherm model rather than Freun-dlich model as shown in Table 7. This finding authenticates thehomogenous adsorption model as better fitted isotherm model for MBdye adsorption on CC-AC surface. The Fig. 8 represents the non-linearplotting of MB dye concentrations (Ce) verses adsorption capacity (qe)for both isotherm models. Moreover, the value of adsorption intensityand curvature (1/n) has a noticeable role in understanding the sorptionbehavior. According to Tharaneedha et al. [46], the 1/n = 0.1 to 0.5indicates the adsorption process of MB dye is significant, 1/n= 0.5 to 1indicates the MB dye is easy to adsorb, and 1/n = >1 revels the MBdye is hardly adsorbed. From Table 7, the 1/n value (0.18) is close tozero which reveals the adsorption process was favorable for the MB dyeremoval at present studied conditions. Furthermore, the highest ad-sorption capacity (qm = 183.3 mg/g) of CC-AC on MB dye adsorptionwas obtained by Langmuir isotherm model at 40 °C. Table 8 records the

Fig. 7. Performance of the CC-AC adsorbent for uptaking MB dye at various concentrations (CC-AC dose 0.1 g, solution pH 9.4, Temp. = 39.9 °C, V = 100 mL).

Table 6Non-linear kinetic parameters for adsorption of MB dye by CC-AC at different initial concentrations.

Parameters Co (mg/L)50 100 150 200 250 300 350 400

qe exp (mg/g) 39.7 70.4 119.6 143.1 156.3 169.2 193.3 199.4Pseudo-first-orderqe (mg/g) 36.7 60.2 61.0 149.1 151.1 179.9 179.9 185.1k1 × 10−2 (1/min) 0.03 0.03 9.40 1.40 2.90 3.40 5.0 7.90R2 0.83 0.85 0.86 0.90 0.93 0.87 0.89 0.93Pseudo-second-orderqe (mg/g) 38.8 69.6 117.2 139.9 152.1 167.1 187.1 195.9k2 × 10−3(g/mg min) 0.04 0.05 0.06 0.07 0.07 0.10 0.20 0.24R2 0.93 0.93 0.81 0.77 0.95 0.84 0.97 0.79

Table 7Isotherm parameters for adsorption of MB dye by CC-AC at 39.9 °C.

Model Parameter Values

Langmuir qm (mg/g) 183.3Ka (L/mg) 0.28R2 0.99RMSE 1.87

Freundlich KF (mg/g (L/mg)1/n) 77.81/n 0.18R2 0.99RMSE 3.46

A.H. Jawad, et al. Surfaces and Interfaces 21 (2020) 100688

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comparison of qm of MB dye by various activated carbon materialsprepared by H3PO4 activation. Form Table 8, CC-AC shows reasonableadsorption capacity (qm) which enables CC-AC to be a promising ad-sorbent for treating cationic dye such as MB dye.

3.7. Adsorption thermodynamic study

Adsorption thermodynamic parameters comprise Gibbs free energychange (ΔG˚), enthalpy change (ΔH˚), and entropy change (ΔS˚) that areimportant for determining the nature of various adsorption process, assuch endothermicity or exothermicity, randomness or spontaneity. Thethermodynamic parameters are calculated by the following Eqs.(19)–(21) [56]:

=k sR

HRT

ln d (19)

=G RT kln d (20)

where R is the universal gas constant (8.314 J/mol K), and T is theabsolute temperature (K), kd represents the adsorption distributionconstant (l/mg) that can be analyzed by,

=K CCd

Ae

e (21)

where CAe is the amount of dye adsorbed on the adsorbent at equili-brium (mg/L) and Ce is the MB concentration at equilibrium(mg/L).

In the present study, the ΔG˚, ΔS˚ and ΔH˚ were determined at fourdifferent temperatures (303, 313, 323 and 333 K). The values of the ΔS˚and ΔH˚ were computed from the slope and intercept of the ln kd verses1/T plotting (Eq. (19)), whereas the ΔG˚ value was calculated fromEq. (20), and all the obtained results are summarized in Table 9. The

negative value of ΔG° as recorded in Table 9 confirms the feasibility andspontaneous character of adsorption process. The negativity decreaseswith increasing temperatures which implies that the adsorption processwas favored with temperature raising. This result in line with the resultof BBD analysis that signifies the MB dye removal% increased by in-creasing the temperature up to 50 °C as shown in Fig. 5d. Moreover, thepositive sign of ΔH° affirms the endothermic nature of the adsorptionprocess. Besides, the randomness of adsorption process is verified by thepositive ΔS° value that authenticates a better interaction between ad-sorbate and adsorbent.

3.8. Adsorption mechanism

The adsorption mechanism of MB dye onto CC-AC surface can beproposed based on the available functional groups such as (-OH),(CeO), and (CeO-C) as identified by FTIR spectral analysis. Therefore,there are several possible interactions between the surface functionalgroups of CC-AC and MB dye molecules as illustrated in Fig. 9. Thefavorable electrostatic interaction can be generated between the nega-tive (oxygenated) surface functional groups of CC-AC with the cationicspecies in the MB dye molecules. Similar observation was reported inthe literature for the adsorption of paracetamol onto activated carbonsurface [57]. Another possible interaction was hydrogen bonding in-teraction as shown in Fig. 9. It was reported in the literatures that theexistence of the oxygen-functional groups such as hydroxyl (–OH),epoxy (–O–) and carbonyl (–C=O) groups in the graphene oxidestructure, which are highly sensitive to form hydrogen bonds with or-ganic compounds [12]. Furthermore, π–π electron donor–acceptor in-teractions (cf. Fig. 9). The occurrence of π–π interactions was reportedon the adsorption of MB dye by activated carbon materials developedfrom low-rank coal [10], and bamboo chip [58].

4. Conclusion

Corn cob was successfully converted into mesoporous activatedcarbon via microwave-assisted H3PO4 activation to be a renewable andpromising adsorbent for MB dye removal from aqueous environment.The physicochemical properties of the CC-AC was studies by using FTIRand pHpzc, iodine test, ash content, bulk density and moisture content.The value of ash content, moisture content and bulk density result are13.15%, 0.153% and 0.49 mg/mL while the value of iodine test is693.87 mg/g. FTIR analysis reveals the availability of various acidicfunctional groups on the surface of CC-AC. The point of zero charge(pHpzc) for ACeCC was identified to be pH = 4.2. BBD determined theoptimum adsorption conditions of ACeCC for MB removal to be 0.1 gadsorbent dosage, solution adjusted pH 9.4, and temperature 39.9 °C.The Langmuir isotherm model fitted better than Freundlich modelwhereas kinetic data supported the pseudo second order model. Thethermodynamics experiment revealed the spontaneity and an en-dothermic in nature of adsorption process by CC-AC with maximumadsorption capacity of 183.3 mg/g.

CRediT authorship contribution statement

Ali H. Jawad: Conceptualization, Methodology, Software, Writing -review & editing, Supervision, Project administration, Funding

Fig. 8. Adsorption isotherm curve of the Langmuir and Freundlich models forMB dye adsorption at 40 °C.

Table 8Comparative of adsorption capacities for MB dye onto different activatedcarbon materials prepared by H3PO4 activation.

Activated carbon SBET (m2/g) qm (mg/g) References

Corn cob (CC-AC) 415.2 183.3 This studyShrimp shell waste 560.6 826 [47]Rice husks 2028 578 [48]Cotton 1370 476 [49]Coffee grounds 1440 370.4 [50]Date palm pits 725 345 [51]Peach stone shells 1153 306 [52]Mushroom roots 994 306 [53]Cotton stalks 594 180 [54]Soyabean hulls 631 171 [55]

Table 9Thermodynamic parameters values for the adsorption of MB dye by CC-AC.

Temperatures ΔG° (kJ/mol) ΔH°(kJ/mol) ΔS°(kJ/mol.K)

303 −6.66 56.5 208.6313 −8.75323 −10.8333 −12.9

A.H. Jawad, et al. Surfaces and Interfaces 21 (2020) 100688

9

acquisition. Mondira Bardhan: Formal analysis, Writing - originaldraft. Md. Atikul Islam: Formal analysis, Writing - original draft,Writing - review & editing. Md. Azharul Islam: Formal analysis,Writing - original draft, Writing - review & editing. Syed Shatir A.Syed-Hassan: Investigation, Resources. S.N. Surip: Resources. Zeid A.ALOthman: Funding acquisition. Mohammad Rizwan Khan: Fundingacquisition.

Declaration of Competing Interest

The authors declare that they have no known competing financialinterests or personal relationships that could have appeared to influ-ence the work reported in this paper.

Acknowledgements

This work was funded by the Researchers Supporting ProjectNumber (RSP-2020/138) King Saud University, Riyadh, Saudi Arabia.

References

[1] R.A. Rashid, M.A.M. Ishak, K.M. Hello, Adsorptive removal of methylene blue bycommercial coconut shell activated carbon, Sci. Lett. 12 (1) (2018) 77–101.

[2] A.H. Jawad, A.S. Abdulhameed, Mesoporous Iraqi red kaolin clay as an efficientadsorbent for methylene blue dye: adsorption kinetic, isotherm and mechanismstudy, Surf. Interfac. 18 (2020) 100422.

[3] C. Cao, L. Xiao, C. Chen, X. Shi, Q. Cao, L. Gao, In situ preparation of magneticFe3O4/ chitosan nanoparticles via a novel reduction–precipitation method and theirapplication in adsorption of reactive azo dye, Powder Technol. 260 (2014) 90–97.

[4] S. Kuppusamy, K. Venkateswarlu, P. Thavamani, Y.B. Lee, R. Naidu, M. Megharaj,Quercusrobur a corn peel as a novel coagulating adsorbent for cationic dye removalfrom aquatic ecosystems, Ecol. Eng. 101 (2017) 3–8.

[5] V.R. Pereira, A.M. Isloor, U.K. Bhat, A.F. Ismail, A. Obaid, H.-.K. Fun, Preparationand performance studies of polysulfone-sulfated nano-titania (S-TiO2) nanofiltra-tion membranes for dye removal, RSC Adv. 5 (2015) 53874–53885.

[6] M. Greluk, Z. Hubicki, Efficient removal of Acid Orange 7 dye from water using thestrongly basic anion exchange resin Amberlite IRA-958, Desalination 278 (2011)

219–226.[7] E. Brillas, C.A. Martinez-Huitle, Decontamination of wastewaters containing syn-

thetic organic dyes by electrochemical methods. An updated review, Appl. Catal. BEnviron. 166–167 (2015) 603–643.

[8] A.H. Jawad, N.S.A. Mubarak, M.A.M. Ishak, K. Ismail, W.I. Nawawi, Kinetics ofphotocatalytic decolourization of cationic dye using porous TiO2 film, J. TaibahUniv. Sci. 10 (3) (2016) 352–362.

[9] A.S. Abdulhameed, A.T. Mohammad, A.H. Jawad, Statistical optimization for dyeremoval from aqueous solution by cross-linked chitosan composite, Sci. Lett. 14 (2)(2020) 1–14.

[10] A.H. Jawad, K. Ismail, M.A.M. Ishak, L.D. Wilson, Conversion of Malaysian low-rank coal to mesoporous activated carbon: structure characterization and adsorp-tion properties, Chin. J. Chem. Eng. 27 (7) (2019) 1716–1727.

[11] C. Chen, S. Zhang, Y. Liu, N.S. Alharbi, S.O. Rabah, S. Wang, X. Wang, Synthesis andfabrication of g-C3N4-based materials and their application in elimination of pol-lutants, Sci. Total Environ. 731 (2020) 139054.

[12] B. Hu, Y. Ai, J. Jin, T. Hayat, A. Alsaedi, L. Zhuang, X. Wang, Efficient eliminationof organic and inorganic pollutants by biochar and biochar-based materials, Biochar26 (26) (2020) 1–8.

[13] J.M. Illingworth, B. Rand, P.T. Williams, Non-woven fabric activated carbon pro-duced from fibrous waste biomass for sulphur dioxide control, Process Saf. Environ.Protect. 122 (2019) 209–220.

[14] R.K. Liew, M.Y. Chong, O.U. Osazuwa, W.L. Nam, X.Y. Phang, M.H. Su, C.K. Cheng,C.T. Chong, S.S. Lam, Production of activated carbon as catalyst support by mi-crowave pyrolysis of palm kernel shell: a comparative study of chemical versusphysical activation, Res. Chem. Intermediat. 44 (2018) 3849–3865.

[15] S. Sangon, A.J. Hunt, T.M. Attard, P. Mengchang, Y. Ngernyen, N. Supanchaiyamat,Valorisation of waste rice straw for the production of highly effective carbon basedadsorbents for dyes removal, J. Clean. Prod. 172 (2018) 1128–1139.

[16] S. Rattanapan, J. Srikram, P. Kongsune, Adsorption of methyl orange on coffeegrounds activated carbon, Energy Procedia 138 (2017) 949–954.

[17] N.A. Rashidi, S. Yusup, A review on recent technological advancement in the ac-tivated carbon production from oil palm wastes, Chem. Eng. J. 314 (2017)277–290.

[18] A.H. Jawad, R. Razuan, J.N. Appaturi, L.D. Wilson, Adsorption and mechanismstudy for methylene blue dye removal with carbonized watermelon (Citrullus la-natus) rind prepared via one-step liquid phase H2SO4 activation, Surf. Interfac. 16(2019) 76–84.

[19] K.T. Wong, N.C. Eu, S. Ibrahim, H. Kim, Y. Yoon, M. Jang, Recyclable magnetiteloaded palm shell-waste based activated carbon for the effective removal of me-thylene blue from aqueous solution, J. Clean. Prod. 115 (2016) 337–342.

[20] A.H. Jawad, S. Sabar, M.A. Ishak, L.D. Wilson, S.S. Ahmad Norrahma, M.K. Talari,A.M. Farhan, Microwave-assisted preparation of mesoporous-activated carbon fromcoconut (Cocos nucifera) leaf by H3PO4 activation for methylene blue adsorption,

Fig. 9. Illustration of the possible interaction between CC-AC and MB dye including electrostatic attraction, H-bonding interaction, and π-π interactions.

A.H. Jawad, et al. Surfaces and Interfaces 21 (2020) 100688

10

Chem. Eng. Commun. 204 (10) (2017) 1143–1156.[21] O.P. Junior, A.L. Cazetta, R.C. Gomes, E.O. Barizão, I.P.A.F. Souza, A.C. Martins,

T. Asefa, V.C. Almeida, Synthesis of ZnCl2-activated carbon from macadamia nutendocarp (Macadamia integrifolia) by microwave-assisted pyrolysis: optimizationusing RSM and methylene blue adsorption, J. Anal. Appl. Pyrolysis. 105 (2014)166–176.

[22] Y. Gokce, Z. Aktas, Nitric acid modification of activated carbon produced fromwaste tea and adsorption of methylene blue and phenol, Appl. Surf. Sci. 313 (2014)352–359.

[23] A.H. Jawad, S.A. Mohammed, M.S. Mastuli, M.F. Abdullah, Carbonization of corn(Zea mays) cob agricultural residue by one-step activation with sulfuric acid formethylene blue adsorption, Desalin. Water Treat. 118 (2018) 342–351.

[24] S. Ren, H. Lei, L. Wang, Q. Bu, S. Chen, J. Wu, J. Julson, R. Ruan, Biofuel productionand kinetics analysis for microwave pyrolysis of Douglas fir sawdust pellet, J. Anal.Appl. Pyrol. 94 (2012) 163–169.

[25] A.H. Jawad, M.A.M. Ishak, A.M. Farhan, K. Ismail, Response surface methodologyapproach for optimization of color removal and COD reduction of methylene blueusing microwave-induced NaOH activated carbon from biomass waste, Desalin.Water Treat. 62 (2017) 208–220.

[26] A. Dalvand, R. Nabizadeh, M.R. Ganjali, M. Khoobi, S. Nazmara, A.H. Mahvi,Modeling of Reactive Blue 19 azo dye removal from colored textile wastewaterusing L-arginine-functionalized Fe3O4 nanoparticles: Optimization, reusability, ki-netic and equilibrium studies, J. Magn. Magn. Mater. 404 (2016) 179–189.

[27] M. Xiaohui, H. Xiaoxia, D. Haiyan, L. Hanyu, Anunoriented three dimension fra-mework (network) of fibrous porous ceramics prepared by freeze casting, J. Eur.Ceram. Soc. 36 (2016) 797–803.

[28] C. Wang, W. Chen, L. Yang, R. Wei, J. Ni, Y. Yang, Insights into the roles of themorphological carbon structure and ash in the sorption of aromatic compounds towood-derived biochars, Sci. Total Environ. 693 (2019) 133455.

[29] S.M. Anisuzzaman, D. Krishnaiah, S. Abang, G.M. Labadin, Adsorptive deni-trogenation of fuel by oil palm shells as low cost adsorbents, J. Appl. Sci. 14 (2014)3156–3161.

[30] K.S. Sing, Reporting physisorption data for gas/solid systems with special referenceto the determination of surface area and porosity (Recommendations 1984), PureAppl. Chem. 57 (4) (1985) 603–619.

[31] Q. Han, J. Wang, B.A. Goodman, J. Xie, Z. Liu, High adsorption of methylene blueby activated carbon prepared from phosphoric acid treated eucalyptus residue,Powder Technol 366 (2020) 239–248.

[32] D.N.K.P. Negara, T.G.T. Nindhia, I.W. Surata, F. Hidajat, M. Sucipta, Nanoporestructures, surface morphology, and adsorption capacity of tabah bamboo-activatedcarbons, Surf. Interface. 16 (2019) 22–28.

[33] X. Zhu, Y. Liu, F. Qian, C. Zhou, S. Zhang, J. Chen, Preparation of magnetic porouscarbon from waste hydrochar by simultaneous activation and magnetization fortetracycline removal, Bioresour. Technol. 154 (2014) 209–214.

[34] B. Bestani, N. Benderdouche, B. Benstaali, A. Addou, Adsorption of methylene blueand iodine from aqueous solutions by a desert Salsolavermiculata species,Bioresour. Technol. 99 (2008) 8441–8444.

[35] C. Saka, TG–DTG BET, S.E.M. FT-IR, iodine number analysis and preparation ofactivated carbon from acorn shell by chemical activation with ZnCl2, J. Anal. Appl.Pyrolysis 95 (2012) 21–24.

[36] S. Sujatha, R. Sivarethinamohan, Investigation of detoxification nature of activatedcarbons developed from Manilkara zapota and de oiled soya, Mater. Today Proce.21 (2020) 663–668.

[37] M.A. Islam, V. Sakkas, T.A. Albanis, Application of statistical design of experimentwith desirability function for the removal of organophosphorus pesticide fromaqueous solution by low-cost material, J. Hazard. Mater. 170 (1) (2009) 230–238.

[38] N.N.A. Malek, A.H. Jawad, A.S. Abdulhameed, K. Ismail, B.H. Hameed, Newmagnetic Schiff’s base-chitosan-glyoxal/fly ash/Fe3O4 biocomposite for the removalof anionic azo dye: an optimized process, Int. J. Biol. Macromol. 146 (2020)530–539.

[39] A.H. Jawad, Z.S. Mehdi, M.A.M. Ishak, K. Ismail, Large surface area activated

carbon from low-rank coal via microwave-assisted KOH activation for methyleneblue adsorption, Desalin. Water Treat. 110 (2018) 239–249.

[40] S. Lagergren, Zur theorie der sogenannten adsorption geloster stoffe, Vet. Akad.Handl. 24 (1898) 1–39.

[41] Y.S. Ho, G. McKay, Sorption of dye from aqueous solution by peat, Chem. Eng. J. 70(1998) 115–124.

[42] V.O. Njoku, K.Y. Foo, M. Asif, B.H. Hameed, Preparation of activated carbons fromrambutan (Nepheliumlappaceum) peel by microwave-induced KOH activation foracid yellow 17 dye adsorption, Chem. Eng. J. 250 (2014) 198–204.

[43] I. Langmuir, The adsorption of gases on plane surfaces of glass, mica and platinum,J. Am. Chem. Soc. 40 (1918) 1361–1403.

[44] H.M.F. Frenudlich, Over the adsorption in solution, J. Phys. Chem. 57 (1906)385–471.

[45] N. Barka, K. Ouzaouit, M. Abdennouri, M. El Makhfouk, S. Qourzal, A. Assabbane,Y. Ait-Ichou, A. Nounah, Kinetics and equilibrium of cadmium removal from aqu-eous solutions by sorption onto synthesized hydroxyapatite, Desalin. Water Treat.43 (2012) 8–16.

[46] V. Tharaneedhar, P.S. Kumar, A. Saravanan, C. Ravikumar, V. Jaikumar, Predictionand interpretation of adsorption parameters for the sequestration of methylene bluedye from aqueous solution using microwave assisted corncob activated carbon,Sustain. Mater. Technol. 11 (2017) 1–11.

[47] X. Liu, C. He, X. Yu, Y. Bai, L. Ye, B. Wang, L. Zhang, Net-like porous activatedcarbon materials from shrimp shell by solution-processed carbonization and H3PO4activation for methylene blue adsorption, Powder Technol. 326 (2018) 181–189.

[48] Y. Chen, S.R. Zhai, N. Liu, Y. Song, Q.D. An, X.W. Song, Dye removal of activatedcarbons prepared from NaOH-pretreated rice husks by low-temperature solution-processed carbonization and H3PO4 activation, Bioresour. Technol. 144 (2013)401–409.

[49] X. Duan, C. Srinivasakannan, X. Wang, F. Wang, X. Liu, Synthesis of activatedcarbon fibers from cotton by microwave induced H3PO4 activation, J. Taiwan Inst.Chem. Eng. 70 (2017) 374–381.

[50] A. Reffas, V. Bernardet, B. David, L. Reinert, M.B. Lehocine, M. Dubois, L. Duclaux,Carbons prepared from coffee grounds by H3PO4 activation: characterization andadsorption of methylene blue and Nylosan Red N-2RBL, J. Hazard. Mater. 175 (1–3)(2010) 779–788.

[51] K.S.K. Reddy, A. Al Shoaibi, C. Srinivasakannan, A comparison of microstructureand adsorption characteristics of activated carbons by CO2 and H3PO4 activationfrom date palm pits, New Carbon Mater 27 (5) (2012) 344–351.

[52] B.S. Girgis, A.A. Attia, N.A. Fathy, Modification in adsorption characteristics ofactivated carbon produced by H3PO4 under flowing gases, Colloids Surf. APhysicochem. Eng. Asp. 299 (1–3) (2007) 79–87.

[53] C. Cheng, J. Zhang, Y. Mu, J. Gao, Y. Feng, H. Liu, C. Zhang, Preparation andevaluation of activated carbon with different polycondensed phosphorus oxyacids(H3PO4, H4P2O7, H6P4O13 and C6H18O24P6) activation employing mushroom rootsas precursor, J. Anal. Appl. Pyrol. 108 (2014) 41–46.

[54] B.S. Girgis, E. Smith, M.M. Louis, A.N.A. El-Hendawy, Pilot production of activatedcarbon from cotton stalks using H3PO4, J. Anal. Appl. Pyrol. 86 (1) (2009) 180–184.

[55] B.S. Girgis, A.M. Soliman, N.A. Fathy, Development of micro-mesoporous carbonsfrom several seed hulls under varying conditions of activation, Micropor. Mesopor.Mater. 142 (2–3) (2011) 518–525.

[56] A.H. Jawad, A.S. Abdulhameed, M.S. Mastuli, Mesoporous crosslinked chitosan-activated charcoal composite for the removal of thionine cationic dye: compre-hensive adsorption and mechanism study, J. Polym. Environ. 28 (2020) 1095–1105.

[57] L. Spessato, K.C. Bedin, A.L. Cazetta, I.P. Souza, V.A. Duarte, L.H. Crespo,V.C. Almeida, KOH-super activated carbon from biomass waste: insights into theparacetamol adsorption mechanism and thermal regeneration cycles, J. Hazard.Mater. 371 (2019) 499–505.

[58] A.H. Jawad, A.S. Abdulhameed, Statistical modeling of methylene blue dye ad-sorption by high surface area mesoporous activated carbon from bamboo chip usingKOH-assisted thermal activation, Energ. Ecol. Environ. (2020). doi 10.1007/s40974-020-00177-z.

A.H. Jawad, et al. Surfaces and Interfaces 21 (2020) 100688

11