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Journal of Cleaner Production 253 (2020) 119989

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Journal of Cleaner Production

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Preparation and evaluation of an effective activated carbon fromwhitesugar for the adsorption of rhodamine B dye

Wei Xiao a, Zaharaddeen N. Garba a, Shichang Sun a, Ibrahim Lawan a, Liwei Wang b, **,Ming Lin a, ***, Zhanhui Yuan a, *

a College of Materials Engineering, Fujian Agriculture and Forestry University, Fuzhou, 350002, Chinab Ocean College, Minjiang University, Fuzhou, 350108, China

a r t i c l e i n f o

Article history:Received 19 September 2019Received in revised form10 December 2019Accepted 3 January 2020Available online 7 January 2020

Handling Editor: Panos Seferlis

Keywords:Activated sugar-based carbonAdsorptionHigh porosityRegeneration

* Corresponding author.** Corresponding author.*** Corresponding author.

E-mail addresses: wlw@mju.edu.cn (L. Wang),zhanhuiyuan@fafu.edu.cn (Z. Yuan).

https://doi.org/10.1016/j.jclepro.2020.1199890959-6526/© 2020 Elsevier Ltd. All rights reserved.

a b s t r a c t

Activated carbon (AC) has been widely used in wastewater treatment for a long time. However, theapplications of the AC are limited by the difficulties associated with their regeneration process afterusage. Fortunately, the samples in this study could not only be regenerated for many times, but alsomaintained its adsorption efficiency. Herein, highly porous carbon has been prepared from white sugarusing acid dehydration method. The prepared carbon was activated in a nitrogen environment whichresulted in the formation of the activated sugar-based carbon (ASC). The ASC was characterized usingsome classical characterization techniques such as (Brunauer-Emmett-Teller (BET), scanning electronmicroscopy (SEM), X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR), X-ray photoelectronspectroscopy (XPS)). The obtained findings reveal that the pore parameters of the ASC were consideredadequate for adsorption, for instance 1144.77 m2/g, 0.53 cm3/g and 2.17 nmwere recorded for the surfacearea, pore volume and pore size respectively. Furthermore, the ASC was used for the adsorption with therhodamine B (Rhd B) solution and maximum adsorption efficiency of about 98.28% and adsorption ca-pacity of 123.46 mg/g were achieved within the 12th minutes contact time. More interestingly, the ASCwas found to be regenerated up to 7-times and the data related to the equilibrium and kinetic of the RhdB adsorption onto ASC obeyed Langmuir isotherm and pseudo-second order models, respectively.

© 2020 Elsevier Ltd. All rights reserved.

1. Introduction

Environmental pollution is becomingmore andmore prominentwith increase in the activities of industries. Textile, cosmetic, paper,leather, and food processing industries produces a lot of waste-water that is polluted with significantly high amount of syntheticdyes (Brillas and Martínez-Huitle, 2015). Most of these syntheticdyes are chemically and thermally stable, non-biodegradable andquite toxic (Le�on et al., 2018; Yagub et al., 2014). The dye-pollutedwastewater not only damages the environment but also endan-gers human’s health with diseases such as carcinogenic anddysfunction of the kidneys. These are the reasons why the removalof organic dyes from wastewater remains an environment

fjlm403@163.com (M. Lin),

challenge that attracts attention of the research community (Liet al., 2016).

Recently, various methods that includes: photodegradationbased on quantum dots (Rajabi et al., 2018, 2016a; 2016b; Roushaniet al., 2017), ion-exchange, oxidation, membrane separation, andadsorption were reported to efficiently remove dyes from waste-water (Brillas and Martínez-Huitle, 2015; Gupta and Suhas, 2009;Labanda et al., 2009). Adsorption has been reported to be themost widely used method perhaps due to its effectiveness andsustainability (Abo El Naga et al., 2018; Garba et al., 2019). Variousadsorbents such as active carbon nanoparticles (Do et al., 2011),chitosan (Wang and Wang, 2008), carboxymethyl cellulose (Yanet al., 2011) and perovskite-type oxides (Deng et al., 2019) havebeen reported by many studies. Among the large number of ad-sorbents, activated carbon exhibited advantages over other adsor-bents for it’s higher adsorption capacity when used on wastewaterwith different dye molecules (Dong et al., 2011; Li et al., 2016). It’swell known that activated carbon materials have porous structureand high surface area. The porosity, size of the specific surface area

W. Xiao et al. / Journal of Cleaner Production 253 (2020) 1199892

and chemical properties of the activated carbon are the main fac-tors that determined the adsorption process of organic dyes (Liet al., 2016; Pereira et al., 2003). Most of the activated carbon ma-terials used for adsorption research come from fruit peel (Ma et al.,2017), rubber tires (Al-Saadi et al., 2013) and so on. Although theseactivated carbon materials have good adsorption properties, only afew studies has reported regeneration of their activated carbon,where relatively low regeneration efficiencies were established.

Sugar has been regarded as an available and sustainable sourceof carbon. It has a short-chain and soluble carbohydrates which canbe extracted from the most plants, especially sugarcane. Generally,white sugar is obtained from raw sugar through purifying processto remove the molasses (Oyedotun et al., 2019). Some researchersreported the electrochemical behaviour of sugar-based carbonmaterial. For instance, Ma et al. confirmed production of an carbonfromwhite sugar and its combinationwith graphene oxide resultedin formation of composite with high electrical conductivity (Maet al., 2014). However, considering the open and subscribed re-ports, there has never been any effort towards investigating thesugar-based carbon for the adsorption of dye.

Herein, sugar-based carbon was produced from white sugarusing acidic dehydration method and it was activated with highcalcination temperature under nitrogen to obtain the highly porousactivated sugar-based carbon (ASC). The prepared ASC was char-acterized using some classical characterization methods andrhodamine B (Rhd B) was selected as a model dye and used inevaluating the ASC adsorption performance in aqueous solutions. Inthe results obtained from adsorption process, it takes a little time toreach the adsorption equilibrium and achieves a good adsorptionefficiency. In addition, the ASC can be reused for many times underrecycle activation. Furthermore, adsorption isotherms, kinetics,mechanism, and regeneration of the ASC were established. Thus,the study provides important information that could provide basisfor an in-depth research on the adsorption of dyes by sugar-basedcarbon materials or its composites.

2. Experimental

2.1. Reagents

White sugar, H2SO4 (98%) and NaOH (AR) were procured fromGuangdongmaojiazhuang Food Co.,Ltd. and Xilong Scientific Co.,Ltd. respectively.

Commercial activated carbon (AR) was purchased fromShanghai Titan Scientific Co., Ltd.

2.2. Preparation of ASC

In preparing the ASC, method reported in the literature withslight modification was used (Oyedotun et al., 2019). A stoichio-metric amount and volume of the white sugar and H2SO4 wererespectively put into a glass beaker and then stirred quickly with aglass rod for 30 s at 25 �C. The reaction was highly exothermic andresulted in the formation of dehydrated sugar-based carbon (DSC)after few minutes. The obtained DSC materials were dissolved in acertain amount of deionized water, and the solution pH wasadjusted to neutral via the addition of a certain concentration ofNaOH before being filtrated. The residue was washed with distilledwater several times before drying it in an electric oven at temper-ature of 60 �C for 10 h. Afterwards, 1 g of the recovered carbon wasthoroughly mixed with 2 g of NaOH and before putting it in anatmospheric pressure chemical vapour deposition device andcalcined for 2 h at 700 �C under nitrogen environment (Fig. 1). Thecarbon sample obtained was dissolved in 10% HCl (v/v) and the pHwas adjusted to be neutral before washing it thoroughly using the

deionized water and which was later dried at 60 �C for 4 h. Thatresulted in the formation of the activated sugar-based carbon (ASC).Equations (1) and (2) presented below describes the chemical re-actions involved in the formation of the ASC.

C12H22O11ðSÞ þH2SO4ðaqÞ/12CðSÞ þ 11H3OþðaqÞ þ 11HSO�

4ðaqÞ(1)

6NaOHþ2C42Naþ 3H2 þ 2Na2CO3 (2)

2.3. Characterization of the adsorbents

The specific surface and porosity of the samples were analyzedusingMicrometrics ASAP 2020 equipment. The surfacemorphologyof the samples were studied by means of Scanning Electron Mi-croscope (SEM, JSM-5900LV). The crystal morphology of the sam-ples was analyzed by the patterns of the X-ray diffraction (XRD),which were recorded on a MiniFlex 600 diffractometer (15 kV,50 mA) using filtered Cu Ka radiation. Diffraction data werecollected in the 2q range of 10e90�. The function groups on thesamples were analyzed by FT-IR spectra, which were recorded us-ing KBr with the 1% of the sample at room temperature with aresolution setting of 4 cm�1 and 400 to 4000 cm�1 range on aThermo Nicolet iS5 spectrometer. The surface complexes on sam-ples were studied via XPS, and the XPS was conducted on a *1/AXISUltra DLD X-ray photoelectron spectrometer equipped with amonochromatic Al Ka X-ray source (hc ¼ 1486.6 eV). The bindingenergy of all elements was calibrated according to the C 1s peak ofadventitious carbon (the binding energy of C 1s used for calibrationwas 284.8 eV).

The pH of the point of zero charge (pHpzc) is an importantproperty of activated carbons. Herein, the solide additional methodwas used to determined the value of pHpzc (Tran et al., 2016). Aseries of 0.1 M NaCl solutions with a pH of 2e11 were prepared byadjusting with 1 M HCl and 1 M NaOH, and recorded as pHi. Take50ml of each solution into a 125ml jar and add 0.1 g of ASC powder.Shake it at 180 rpm and 30 �C for 4 h. Take the supernatant tomeasure the pH and record it as pHf. Use pHi as the abscissa andDpH ¼ pHi-pHf as the ordinate to make a graph. The intersection ofthe graph and the abscissa is the value of pHpzc.

2.4. Adsorption experiments

The adsorption experiments were carried out by mixing acertain amounts of ASC samples with 100 ml Rhd B solutions in125 ml glass jars using incubator shaker (IS-RSD3) at a constantconditions (180 rpm, 293 K) for a certain time. The effect severaladsorption parameters such as the absorbent dosage (0.02 ge0.1 g),dye solution pH (2.4e11.4), contact time (2 mine14 min), initialRhd B concentration (25 mg/L-100 mg/L) and temperature(15 �Ce45 �C) were studied. Then the best conditions were selectedfor the next experiments. In addition to the batch experiment thatthe effect of the initial concentration of the dye was measured, allother batch experiments maintains the initial Rhd B concentrationof 50 mg/L.

The concentration of Rhd B was obtained by UVevis spectro-photometry (Shimadzu UV-2600), applying a scan in the rangefrom 190 to 800 nm. According to the curve obtained, the dye wasexamined at 554 nm wavelength to ascertain its maximumadsorption capacity. For the kinetic study, the ASC was mixed witha series of Rhd B solutions and then shaked for different designedtime. In the whole adsorption experiment, the absorbance of the

Fig. 1. Technical route followed in obtaining the ASC samples.

Fig. 2. N2 adsorption-desorption isotherms of ASC samples. (Inset: the pore size dis-tributions of ASC analyzed by BJH method from the adsorption branch of theisotherms.)

W. Xiao et al. / Journal of Cleaner Production 253 (2020) 119989 3

supernatant at 554 nm was analyzed also by Shimadzu UV-2600after the adsorption of each group, so as to determine the dyeconcentration and built the calibration curves with known dyeconcentration as reported in other studies (Deng et al., 2019;Essandoh and Garcia, 2018).

Both removal efficiency (E) and adsorption capacity (qt) are thetwo important parameters to evaluate the adsorption ability of ASC,which were defined by equations (3) and (4) respectively.

E¼C0 � CtC0

� 100% (3)

Where C0 (mg/L) denote the initial dye concentration; Ct (mg/L)represents the residual dye concentration at time t.

qt ¼VðC0 � CtÞm

(4)

Where qt (mg�g�1) represents the adsorption capacity at time t; V(L) denote the volume of dye solution; m (g) denote the weight ofthe adsorbent.

After the adsorption test, the recovered ASC powder was re-generated at 700 �C under nitrogen conditions. Then the regener-ated powder was used to repeat the same steps of adsorptionexperiment.

3. Results and discussion

3.1. Characterization of the adsorbents

Table 1 showsthe pore parameters of the prepared materials. Itcould be observed that the BET surface area (SBET) of ASC(1144.77 m2/g) was found to be significantly higher as compared tothat of the DSC (3.88 m2/g). Similarly, the average pore volumes(Vm) of DSC and ASC were found to be 0.0016 and 0.53 cm3/g,respectively. While pore sizes of 2.17 and 1.13 nm for the ASC andDSC were obtained respectively. Fig. 2 shows a type I adsorption-desorption isotherm of ASC with a non-obvious type H4 hystere-sis loop, indicating a micropore structure. The pore size areconcentrated between 0.5 and 2.5 nm, as characterized using theBJH method (Fig. 2). These relatively high pore parameters estab-lished with the ASC could effect the adsorption process with theaqueous solution. Interestingly, comparing the pore parameters ofthe ASC with that reported in literatures reveals that the ASC is

Table 1Textural parameters of the samples.

Samples SBET (m2/g) Vm (cm3/g) Pore size (nm)

DSC 3.88 0.0016 1.13ASC 1144.77 0.53 2.17Regenerated ASC 1104.39 0.53 2.24

having similar pore parameters of the activated carbons preparedusing the well-established methods (Ahmad et al., 2012; Wanget al., 2011; Yener et al., 2008).The indirect NaOH activation ofthe sugar at elevated activation temperature have contributedpositively to the adsorption experiments since compounds fromgroup I elements (K and Na) were proven to be among the bestchemical activating agents (Garba and Rahim, 2014).

Fig. 3 shows the SEM images of DSC and ASC samples. It can beobserved that there are almost no pores on the surface of DSC.While on the contrary, the surface of the ASC exhibited a rough andbumpy surface with restively larger pores. This means that theactivation of the DSC with sodium hydroxide under the nitrogencondition has significantly improved the porosity of the adsorbent.The formation mechanism of pores is the gasification of carbon,which was accomplished in two ways. One is that the Na2CO3 canbe decomposed to produce CO2 in calcination at high temperature,which reactedwith DSC to active the dormant pores and release theexisting micropores. The second is that Na2CO3 can be reduced bycarbon to metallic sodium (Na) and produced CO2, thus, leading tothe pores formation (Oyedotun et al., 2019). This result has alsoshown that effective activation process using the NaOH under thenitrogen condition has resulted in the formation of the well-developed pores at surfaced of the ASC. Other researchersrevealed similar results in their work when they produced acti-vated carbons from a bio-based material (Garba and Rahim, 2016),orange peel (K€oseoʇlu and Akmil-Basar, 2015) and palm date seed(Islam et al., 2015).

Fig. 4 shows the XRD patterns for DSC and ASC. From the patternexhibited by the ASC, it is obvious that it is amorphous in natureevident by two broad diffraction peaks centered at 22.89� and

Fig. 3. SEM images for (a,b,c) DSC, (d,e,f) ASC.

Fig. 4. XRD patterns for DSC and ASC.

Fig. 5. FTIR spectra for DSC, ASC, ASC/Rhd B, Regenerated ASC, Rhd B.

W. Xiao et al. / Journal of Cleaner Production 253 (2020) 1199894

42.23� which is attributed to the typical (002) and (101) planes ofgraphitic carbon (JCPDS no. 41e1487).

Fig. 5 shows the FTIR spectra of the DSC, ASC, ASC/Rhd B(samples after adsorption of Rhd B), regenerated ASC and Rhd B.Comparing the spectra of DSC and ASC (before and after adsorptionof Rhd B), it can be seen that they have similar characteristic peaksexcept for the bands at 2945 cm�1 and 1050 cm�1, which areassigned to stretching vibrations of saturated CeH and unsaturatedCeH, respectively. The broad band at 3446 cm�1 and 3454 cm�1 forASC and DSC are attributed to stretching vibrations of OeH forhydroxyl groups. The peaks at 2086 cm�1 and 1384 cm�1 areassigned to stretching vibrations of C]O and CeO, respectively. Thepeak at 1600 cm�1 attributed to the stretching vibration of C]Cgroup belonging to the aromatic ring. These observations are inagreement with the finding of other researchers when they re-ported the adsorption of Rhd B onto Palm Shell-Based activatedcarbon (Mohammadi et al., 2010), attributing it to hydrogenbonding and van derWaals interactions between the dyemolecules

Table 2XPS parameters of ASC, ASC/Rhd B and regenerated ASC.

Component Elemental Content (at %)

C 1s O 1s

ASC 91.07 8.93ASC/Rhd B 86.22 13.10Regenerated ASC 92.37 6.98

W. Xiao et al. / Journal of Cleaner Production 253 (2020) 119989 5

and activated carbon(Das et al., 2006).Fig. 6(a) shows the two main peaks identified and labeled as C

1s, O 1s for the ASC, ASC/Rhd B and regenerated ASC. And of course,there was contained N element in the ASC/Rhd B. It was attributedto the nitrogen-containing groups in Rhd B. After adsorption anddesorption of the Rhd B, there was an increase and subsequentdecrease in the contents of C and O (Table 2). This finding could beattributed to the addition and removal of oxygen groups in Rhd B.Also, Fig. 6(bed) shows there are four peaks at 531.35, 532.54,534.04, 536.37 eV produced in the deconvolution of O 1s plot forthe ASC; these peaks represented O]C, OeC, R-O-C]O, andCeOOH, respectively (Ge et al., 2015; Yu et al., 2013). During theprocess of chemical activation, oxygen functional groups wereformed on the surface of ASC (Yu et al., 2013). The number of ox-ygen functional groups varied with the adsorption and desorptionof Rhd B. It could be attributed to the oxygen-containing groups inRhd B molecules were the same as that in ASC.

Fig. 7 shows the curve obtained using the pH drift method. It canbe seen from the figure that as initial pH increases, the curve firstdecreases and then increases. At about pH ¼ 7.3, the curve in-tersects the abscissa. Therefore, pH ¼ 7.3 is considered as the zerocharge of the adsorbent.

Fig. 7. Point of zero charge of ASC.

3.2. Batch adsorption studies

3.2.1. Effect of the solution pH on adsorption of Rhd BFig. 8 shows the relationship between solution pH and removal

efficiency of Rhd B. According to the results, it can be seen that anincrease in solution pH from 2.4 to 11.4 does not change much inthe percentage removal of Rhd B using the ASC. When plotted witha small scale (Fig. 8, inset), the curve shows a trend of first increaseand then decrease, which is similar to the reported adsorptionbehavior of Rhd B by LFO-ACFs (Deng et al., 2019). This can beattributed to the electrostatic interaction between the Rhd B mol-ecules and the ASC. On one hand, when the solution pH is abovepHpzc, the acidic oxygen groups on the surface of the adsorbent aredeprotonated, making the surface negatively charged. On the otherhand, Rhd B exists as cations and zwitterions in polar solvents.When the solution pH above 3.7 (pKa of Rhd B), the deprotonation

Fig. 6. Wide and deconvolution of the core level O 1s spectra: (a)

occurs on the carboxyl group of the Rhd B, which lead to thecationic converts into zwitterionic form (Mohammadi et al., 2010).This resulted in electrostatic repulsion between Rhd B and thenegatively charged ASC. The electrostatic interaction betweenxanthine and the carboxyl group of Rhd B monomer causes Rhd Bpolymerization to form dimer, which prevents dye molecules fromadsorbing into the pores (Deng et al., 2019; Mohammadi et al.,2010). When the solution pH<pHpzc, the surface of the ASC willbe protonated, which will cause the surface to be positively chargedand form an electrostatic repulsionwith the cationic dye. Thus, this

survey spectra, (b) ASC, (c) ASC/Rhd B, (d) Regenerated ASC.

Fig. 8. The relationship between solution pH and removal efficiency of Rhd B. (Inset:Curve drawn on a small scale.)

Fig. 10. The relationship between temperature and removal efficiency and of Rhd Busing ASC.

W. Xiao et al. / Journal of Cleaner Production 253 (2020) 1199896

results in reduced dye removal efficiency in acidic or basic solutions(Xie et al., 2017). However, the overall removal efficiency varieswithin 1%, which is also within the tolerance range of the error bar.Therefore, we believe that although the electrostatic effect exists, itdoes not dominate the entire adsorption process.

3.2.2. Effect of adsorbent dosage on adsorption of Rhd BThe effect of adsorbent dosage was investigated by carefully

observing the batch adsorption experiments using 50 mg/L as thedye initial concentration and the results are depicted on Fig. 9. Fromthe results presented, it could be seen that with increasing amountsof ASC from 20 mg to 100 mg, the removal efficiency of the dye wasincreased from about 35% to 98%. The increase in the removal ef-ficiency could be attributed to the number of reactive sites availableof the reaction which caused more dyes to be adsorbed. However,increasing the amount of adsorbent to 80 mg, the requiredadsorption sites reached saturation, as such the adsorbent can notlonger have much impact on the adsorption efficiency. Therefore,the optimal amounts of the adsorbent dosage is 80 mg.

3.2.3. Effect of temperature on adsorption of Rhd BFig. 10 shows the effects of temperature and Rhd B removal ef-

ficiency using the ASC. The result obtained reveals that the removal

Fig. 9. The relationship between adsorbent dosage and removal efficiency of Rhd Busing ASC.

efficiency of ASC remained the same at different temperatures.Thus, for the sake of controlling conditions and saving energy, 25 �Cwas choosen as the reaction temperature in the subsequentexperiments.

3.2.4. Effect of contact time and initial dye concentration onadsorption of Rhd B

Fig. 11 shows the relationship between contact time andremoval efficiency at different initial concentrations of Rhd B so-lution. Results obtained reveals that there was increase in theremoval efficiency with increase of both the contact time and initialconcentration. However, after the 12th min, the removal efficiencybecame almost constant. Therefore, 12 min is considered as theoptimum adsorption time. Similarly, the ASC exhibited higherremoval efficiency with the least dye concentration.

Similarly, Fig. 12 has also presented the relationship betweencontact time and adsorption capacity at different initial concen-trations of Rhd B solution, and it could be observed that within thelimits of experimental factors used, an increase in the adsorptioncapacity with increase in the contact timewas established, with thehighest adsorption capacity achieved and with the highest initialdye concentration. However, the adsorption capacity of the ASCbecomes almost constant after the 12th minutes.

Fig. 11. The relationship between contact time and removal efficiency at differentinitial concentrations.

Fig. 12. The relationship between contact time and adsorption capacity at differentinitial concentrations.

W. Xiao et al. / Journal of Cleaner Production 253 (2020) 119989 7

It could be seen that both the removal efficiency and adsorptioncapacity exhibited similar characteristic, where there were rapidand significant increase in both the removal efficiency andadsorption capacity at the beginning and later insignificant in-crease before subsequently reaching equilibrium. This trend of re-sults could perhaps be the effects of the higher vacant sites presenton the carbon at the initial stage, however, later, the vacant sitesremaining becomes affected by the repulsive forces that existedbetween the molecules on the surface of the carbon (Tan et al.,2009). Also, close observations on Fig. 11 will reveal that longercontact time is required for the solutions with higher initial con-centrations to attain equilibrium. Interestingly, this trend was alsoearlier on established in the adsorption process of Rhd B fromaqueous solutions using a hierarchical SnS2 nanostructure asadsorbent (Wang et al., 2017). These results gave further proof thatthe diffusion of Rhd B dye molecule can be improved efficiently byoffering better transport paths, with large surface area providingabundant adsorption sites.

3.2.5. Compare with commercial activated carbonFig. 13 shows the removal efficiency of Rhd B dyes by DSC,

Commercial activated carbon and ASC. Results obtained reveals

Fig. 13. Comparison of removal efficiency of rhodamine B dyes by DSC, Commercial ACand ASC under optimal conditions.

that the adsorption efficiency of the DSC on the Rhd B dye is muchlower than that of commercial activated carbon. In contrast, theactivated sugar-based carbon (ASC) has significantly improved dyeremoval efficiency and is much better than commercial activatedcarbon.

3.3. Kinetic and isotherm adsorption

3.3.1. Adsorption kineticIn order to investigating the adsorption mechanism, various

kinetic models were be used in the literature (Tavakkoli andYazdanbakhsh, 2013). In this paper, the adsorption kinetics of RhdB dye onto ASC was studied by pseudo-first order and pseudo-second order kinetic models (Lopes et al., 2003). The parametersfor pseudo-first order and pseudo-second order were calculated byequations (5) and (6) respectively.

lnðqe � qtÞ¼ lnqe � k1t (5)

tqt

¼ 1k2q2e

þ tqe

(6)

Where qe (mg�g�1) represents the adsorption capacity at equilib-rium; k1 (min�1) and k2 (g�mg�1min�1) are the adsorption rateconstant for pseudo-first order and pseudo-second order respec-tively; t (min) is the contact time.

The parameters of the two kinetic models obtained from non-linear regression of the experimental values are described inTable 3. The results revealed that the pseudo-second order modelhas best fitted to the experimental data obtained, considering thevalue of coefficients (R2 ¼ 0.9982) achieved was relatively closer to1. Comparing the two models, the pseudo-second order modelpresented significantly higher rate constants and adequately pre-dicts reactions that occurred with the higher rates (Santos et al.,2018).

3.3.2. Adsorption isotherm modelsThe interactive behavior between solute and adsorbent in so-

lution is usually described by equilibrium adsorption isotherms.The nonlinear equilibrium relationship between the solute adsor-bed onto the adsorbent and that left in the solution can beexplained by Isothermmodels (Tavakkoli and Yazdanbakhsh, 2013).Herein, the adsorption data was studied by Langmuir and Freund-lich isotherm models.

Equations (7) and (8) are express the linear of Langmuirisotherm and Freundlich isotherm respectively.

Ceqe

¼ 1bqmax

þ Ceqmax

(7)

logqe ¼ logKF þ1nlogCe (8)

Where Ce (mg/L) means the residual concentration of dye in thesolution at equilibrium; qmax (mg/g) is the maximum value of qeand it varies with Ce; b is the adsorption equilibrium constant ofLangmuir isotherm; KF and n are the adsorption equilibrium con-stants of Freundlich isotherm.

In addition, equation (9) defines the dimensionless constantseparation factor RL, which can express the feasibility of the Lang-muir isotherm (Le�on et al., 2018; Tavakkoli and Yazdanbakhsh,2013).

Table 3Kinetic models parameters for adsorption of Rhd B on ASC.

Pseudo-first order Pseudo-second order

R2 k1 (min�1) qe (mg/g) R2 k2 (g/mgmin) qe (mg/g)0.9679 0.3919 61.12 0.9982 7.08 � 10�3 71.94

Table 4Isotherm models parameters for adsorption of Rhd B on ASC.

Langmuir Isotherm Freundlich Isotherm

qmax (mg/g) b (L/mg) RL R2 KF (mg1�n/g Ln) n R2

Rhd B 123.46 0.7163 0.0272 0.9796 50.62 2.74 0.6416

W. Xiao et al. / Journal of Cleaner Production 253 (2020) 1199898

RL ¼1

1þ bC0(9)

Where RL demonstrates the shape of the isotherm, when RL ¼ 0,means irreversible; 0<RL < 1, means the adsorption is favorable;RL ¼ 1, means linear; RL > 1, means unfavorable.

Table 4 summarizes all the parameters from these two iso-therms. It could be seen that the R2 value of the Langmuir isothermwas 0.9796, its closer to 1 than that of the Freundlich isotherm(0.6416). This suggested that the adsorption process was betterdescribed by the Langmuir isothermmodel. And furthermeans thatthe adsorption was characterized by being monolayer on a ho-mogenous surface. RL ¼ 0.0272 (between 0 and 1) also confirmedthe adsorption was favorable. According to the Langmuir modelresults obtained, the maximum adsorption capacity is 123.46 mg/g.

Table 5 presented the comparison of maximum adsorption ca-pacity (qmax) of Rhd B dye achieved with some reported activatedcarbons synthesized from different sources.

It could be seen that the ASC adsorbent obtained in the currentwork present very good performance. In particular, ASC has sig-nificant advantages over other carbon-based adsorbents in terms ofequilibrium time and adsorption capacity. It is clear that ASC is anexcellent adsorbent material with fast and high yield in Rhd B dyewastewater treatment.

3.4. Adsorption mechanisms

The adsorption mechanisms could be analyzed by FTIR and XPSspectra of the ASC and ASC/Rhd B samples (Figs. 5 and 6). From FTIRspectra, the peak of ASC, at 3446 cm�1 attributing to stretchingvibration of OeH for hydroxyl groups, produced a slight shift to3450 cm�1 for ASC/Rhd B, meaning the existence of hydrogenbonding between the ASC and Rhd B molecules (Liu et al., 2019).Besides, the peak at 1600 cm�1 attributing to the stretching vi-bration of C]C groups belonging to the aromatic ring, migrated to1617 cm�1 for ASC/Rhd B, which might be ascribed to the p-pinteraction (Tran et al., 2017). From XPS spectra, the Binding Energy

Table 5Comparison of maximum Rhd B dye adsorption capacities of various active carbon adso

Adsorbent Adsorbent dosage (g) Dye concentration

Palm shell-based activated carbon 1.00 62.6 mmol/LPSC-600 0.01 45 mg/LC-carnauba-CaCl2 2.00 65 mg/La-CNT 0.05 4.7902 mg/LFNC 0.01 47.8 mg/LNi/C nanoparticles 2.00 5 mg/LASC 0.08 50 mg/L

PSC-600: Purified sludge carbon at 600 �C, a-CNT: Amorphous carbon nanotubes, FNC: F

(BE) of the same oxygen group was different in ASC, ASC/Rhd B andregenerated ASC. This is suggested to hydrogen bonding betweenadsorbent and dye molecules. When adsorbing or desorbing dyes,hydrogen bonding occurs or disappears between nitrogen or oxy-gen in the dyes and hydrogen in the oxygen-containing groups onthe surface of the adsorbent, which is suggested to be affected theBE of oxygen-containing groups. The possible adsorption mecha-nisms of Rhd B on ASC were shown in Fig. 14.

3.5. Regeneration

Disposal of waste adsorbents may cause environmental pollu-tion and significant increase in economic costs. Therefore, it’scrucial to treat the used adsorbent and re-use it to reduce itsdisposal and at same time reduce economic costs which could inturn increase its sustainability (Saleh et al., 2018). In this work, theadsorbent was regenerated after the adsorption experiment asdescribed previously in 2.4 subsection. From the results achieved(Fig. 15), it could be seen that the adsorption efficiency of the re-generated sample remained almost the same with the originalsample even after 7 cycles, meaning there is no significant changein the percentage removal of Rhd B (Fig. 15). It has also beenestablished that the regeneration methodology adopted hasresulted to the removal of dye molecules from the surface of theASC completely, this made the used ASC to almost completelyregained it efficiency. Table 1 shows that the values of SBET, Vm andpore size for the regenerated ASC are almost the same as that of thefresh ASC sample, which demonstrated that the efficacy of theadsorbent has almost completely regained after the regenerationtreatment. In addition, From Fig. 5, the spectra shows that thesamples ASC/Rhd B and Rhd B have the same characteristic peaks at1180 cm�1 and 1258 cm�1, which could be attributed to thestretching vibrations of CeN and CeOeC of the Rhd B molecules,respectively. But ASC and regenerated ASC do not have those twopeaks, confirming that the adsorbent completely regained its effi-cacy after the regeneration treatment.

4. Conclusion

From the results presented and the discussion made, it could beconcluded that sugar-based activated carbon materials was suc-cessfully prepared by a simple method and the resulting adsorbent(ASC) possess adequate porosity which signifies it is suitable forusage as an efficient adsorbents. Results achieved reveals that theASC could remove Rhd B in aqueous solutions in a very short time(12mins), with adsorption efficiency of ~98%. Furthermore,comparing the ASC with other adsorbents shows that the ASC evenachieves the adsorption process in a shorter time. Also, the datarecorded has fitted into the Langmuir and pseudo-second ordermodel which describes the equilibrium and kinetic experimentaldata respectively. Overall, the finding of this study has demon-strated suitability and high regeneration efficiency of the novel ASC

rbents.

Equilibrium time (mins) qmax (mg/g) Reference

360 29.98 Mohammadi et al. (2010)60 30.63 Zou et al. (2013)120 39.22 da Silva Lacerda et al. (2015)45 25.66 Banerjee et al. (2017)120 140.4 Xie et al. (2017)5 5.269 Kim et al. (2018)12 123.46 This study

ibrous N-doped porous carbon.

Fig. 14. Possible adsorption mechanism of Rhd B on ASC.

Fig. 15. Reusability of ASC for Rhd B removal.

W. Xiao et al. / Journal of Cleaner Production 253 (2020) 119989 9

adsorbent, which signifies that the ASC adsorbent has great po-tentials in wastewater treatment particularly the removal of Rhd Bdye, thus further study could be carried out to improve on itsefficacy.

Author statement

Wei Xiao: Investigation, Data curation, Writing- Original draftpreparation, Formal analysis. Zaharaddeen N. Garba: Conceptual-ization, Methodology, Software, Investigation, Validation. ShichangSun: Software, Validation. Ibrahim Lawan: Writing- Reviewingand Editing. Liwei Wang: Supervision, Funding acquisition, Projectadministration. Ming Lin: Funding acquisition, Project adminis-tration, Supervision. Zhanhui Yuan: Resources, Funding acquisi-tion, Project administration, Supervision, Writing- Reviewing andEditing.

Declaration of competing interest

The authors declare that they have no known competingfinancial interests or personal relationships that could haveappeared to influence the work reported in this paper.

Acknowledgements

The authors will like to acknowledge support from the openproject Program of Fujian Key Laboratory of Novel Functional

Textile Fibers and Materials (No. FKLTFM1708), the Fujian Engi-neering Research Center of New Chinese lacquer Material (NO.323030010301) both provided by Minjiang University. Also, theinternational funding (No. KXB16001A) provided by Fujian Agri-culture and Forestry University and the funding provided (No.2017H6003) by the Department of Science and Technology ofFujian Province are humbly appreciated.

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