Reusable high performance of calcined Mg/Al hydrotalcite for the removal of Navy

Sri Juari Santosa,Dwi Puji Astuti

Department of Chemistry,Faculty of Mathematics and Natural Sciences,Universitas Gadjah Mada,Bulaksumur,Yogyakarta 55281,Indonesia

Keywords:Adsorption Mg/Al hydrotalcite Navy Blue Yellow F3G Wastewater treatment

ABSTRACT Water pollution with dye chemicals from apparel industries is a serious problem in the world.Since most of dyes are potentially have toxic and carcinogenic effects on human,it is important to remove them before they are discharged to the environment.Among many methods available for dyes removal in water,adsorption is the easiest and economically feasible that has no major obstacle for practical applications.In the present study,we tested calcined Mg/Al hydrotalcite (Mg/Al CHT) prepared by coprecipitation technique as an adsorbent for the removal of Navy Blue (NB) and Yellow F3G (YF3G) dyes.Mg/Al CHT was characterized by using a Fourier transform infrared(FTIR)spectrometer,an X-ray diffractometer(XRD)and a scanning electron microscope(SEM).The results showed that Mg/Al CHT was highly effective as an adsorbent for the removal of NB and YF3G under mild-acidic condition (pH 4) with removal capacities(b)according to Langmuir isotherm model were 7.97×10–4 and 5.80×10–4 mol.g-1,respectively.Kinetics study showed that the adsorption of NB and YF3D on Mg/Al CHT followed pseudosecond order with rate constant(kp2)11.57×103 and 11.75×103 g.mol-1.min-1,respectively.The spent adsorbent can be easily regenerated by simply calcining it at 450 °C for 3 h.Adsorption test on the mixture of NB and YF3G showed that the adsorption capacity of Mg/Al CHT was eightfold higher than that of Mg/Al HT and the value was maintained with repeated use.

1.Introduction

The development of infrared surveillance technology during the Second World War had challenged many countries to develop near-infrared region (NIR,λ=700–1200 nm) compliant colorants for military uniforms to minimize the contrast between the uniforms and the environment over NIR in addition to the visible region [1].Recently,the development of NIR dyes is unnecessarily limited for military purposes but also have been used for scientific interests including solar cells [2],bioimaging [3],cancer imaging[4] and sensors [5].This increasing interest in NIR dyes leads to tremendous environmental problems when the wastewater containing these dyes is not adequately treated.Notably,in the dyeing process of fabrics,about 10%–15%of dyes are generally lost during the process and thus considerably high amounts of dyes are presence in the wastewater,especially when the production is in industrial-scale [6].Because NIR dyes are typically very stable in the environment,they are cannot be degraded by natural means of biodegradation.Therefore,dyes from NIR-textile wastewater must be completely removed before they are discharged to the environment.

The established and currently available technologies for wastewater treatment containing dyes pollutants are including adsorption [7],biological treatment [8–10],ozonation [11,12]and coagulation/flocculation [13,14].Among them,adsorption has been regarded as the cheapest,eco-friendly,easy-handled and the most practical technique for dyes removal from wastewater.Consequently,adsorption has gained considerable attention recently [15,16].

Hydrotalcite (HT) is a layered double hydroxide anionic clay with general structure [M1-x2+Mx3+(OH)2]x+(Axn/n-).mH2O,where M2+and M3+are divalent and trivalent metal ions,respectively,while x is the ratio of M3+to (M2++M3+) with the value varies between 0.2 and 0.33 [17].Recently,HT has been regarded to be one of the most potential materials for adsorbent mainly due to its high adsorption capacity owing to its ability to interact with pollutants in different ways,e.g.,adsorption on the outer layer surface,intercalation by anion exchange and intercalation by utilizing memory effect of the material[18].Memory effect is an effect that allows calcined HT to regain its layered structure by exposing it into an aqueous solution or humid air.For adsorption process,this effect has been reported to be not only useful for increasing the adsorption capacity but also the cyclic use of HT[19].For instance,Orthman et al.reported that the regenerated Mg/Al HT displayed greater adsorption capacity than the fresh ones for the removal of Acid Blue 29 [7].Similarly,Bascialla and Regazzoni [20] also reported that calcined HT is much better than fresh HT by a factor of fifty in removing Acid Blue 113.Although calcined HTs have been used for the removal of some dyes,its application for the removal of NIR colorants,e.g.,Navy Blue (NB) and Yellow F3G(YF3G) dyes,has not yet been reported.

In the present study,we prepared Mg/Al CHT by calcining Mg/Al HT at 450°C and then used it as an adsorbent for the removal of NB and YF3G dyes.The main aim of this study is to investigate the performance of Mg/Al CHT for the removal of NIR colorants,e.g.,NB and YF3G.The adsorption parameters including adsorption kinetics and isotherm as well as the reusability were investigated.In addition,the adsorption mechanism was also elucidated.Eventually,the results showed that Mg/Al CHT was a better adsorbent than that of Mg/Al HT.The XRD diffractogram of Mg/Al CHT before and after adsorption process suggested that structural-memory effect of the layered structure played an important role in the adsorption mechanism of NB and YF3G.The data presented here were partly from the work of a student in our research group,i.e.,Dwi Puji Astuti,for her master thesis [21].

2.Experimental

2.1.Materials

Analytical grade Mg(NO3)2.6H2O,Al(NO3)3.9H2O,NaOH,NB and YF3G were purchased from Merck Co.Inc.(Germany) and used without further purification.Meanwhile,N2gas with purity 99.99% was supplied from CV Perkasa (Indonesia).

2.2.Instrumentation

The apparatuses used in this study were including magnetic stirrer (Nouva),analytical balance (Mettler Toledo AL204),electric pH-meter (Hanna Instrument 211),oven (Fischer Scientific model 655F),siever 0.75 μm,and shaker.For the characterization of the materials,analytical instrumentals,including infra-red spectrometer(Shimadzu FTIR Prestige 21),UV–Vis spectrometer(OPTIMA SP-300),X-ray diffractometer (Shimadzu XRD-6000) and scanning electron microscopy (JEOL JSM-6510) were used.

2.3.Preparation of Mg/Al HT and Mg/Al CHT

Mg/Al HT was prepared by conventional co-precipitation method using NaOH as precipitating agent.Firstly,12.821 g of Mg(NO3)2.6H2O (0.05 mol) and 9.378 g of Al(NO3)3.9H2O(0.025 mol) were dissolved into 100 ml CO2-free distilled water and vigorously stirred under N2atmosphere until homogeneous.Into the mixture,an aqueous solution of NaOH (0.5 mol.L-1) was added dropwise until the pH of the reaction solution reached 10.1 and the stirring was continued for another 30 min.The suspension was then put into an oven and heated at 120 °C for 5 h.The suspension was allowed to stand at room temperature for 24 h to let the solid precipitate at the bottom of the reaction flask.The formed white precipitate was separated from the reaction solution by pouring-out the solution into filtering paper.The solid was washed with CO2-free distilled water until the filtrate reached neutral pH and then dried at 70°C for 48 h to obtain Mg/Al HT.Further,to obtain Mg/Al CHT,the dried Mg/Al HT was calcined at 450 °C,ground with a mortar and sieved using a 0.75 μm of sieve apparatus,respectively.

2.4.Removal of NB and YF3G dyes

2.4.1.Effect of pH

Mg/Al CHT(25 mg)was poured into a series of 12.5 ml of NB or YF3G solution 30 mg.L–1with pH ranging from 3 to 10.The mixture was shaken for 2 h and the filtrate was separated from adsorbent by pouring-out the solution through a 0.45 μm membrane paper.The filtrate was then analyzed by using UV–Vis spectroscopy at 602 and 410 nm for NB and YF3G,respectively.

2.4.2.Adsorption kinetics

Mg/Al CHT (12.5 mg)was poured into a series of 12.5 ml of NB or YF3G solution 25 mg.L–1at optimum pH of the dye adsorption and every mixture was shaken at different contact times ranging from 0 to 180 min.Subsequently,the filtrate was separated by pouring-out the solution through a 0.45 μm membrane paper.The filtrate was then analyzed by using UV–Vis spectroscopy at 602 and 410 nm for NB and YF3G,respectively.

2.4.3.Adsorption isotherms

Mg/Al CHT(12.5 mg)was added into a series of 12.5 ml of NB or YF3G solution at various initial concentrations ranging from 40 to 240 mg.L–1and at optimum pH obtained from the experiment of effect of pH.All mixtures were shaken at equilibrium time obtained from the experiment of adsorption kinetics and followed by separation of filtrates by using a 0.45 μm membrane paper.The filtrate was then analyzed by using UV–Vis spectroscopy at 602 and 410 nm for NB and YF3G,respectively.

2.5.Adsorption of the mixture of NB and YF3G

Mg/Al CHT(12.5 mg)was added into 12.5 ml of a mixture of NB and YF3G at optimum initial concentration and pH from the previous experiment.The mixture was then shaken at optimum time obtained from adsorption kinetics experiment.The filtrate was filtered by using a 0.45 μm membrane paper and analyzed by using UV–Vis spectroscopy at 602 and 410 nm for NB and YF3G,respectively.

2.6.Reusability of Mg/Al CHT

The reusability of Mg/Al CHT for the adsorption of the mixture of NB and YF3G was performed as follows.Firstly,the spent adsorbent from Section 2.5 was collected,dried overnight and regenerated by calcination at 450 °C for 3 h.The regenerated adsorbent was then reused for another adsorption of dyes mixture under optimum conditions.The same experiment was conducted for another reuse.The filtrate of each experiment was filtered by using a 0.45 μm membrane paper and analyzed by using UV–Vis spectroscopy at 602 and 410 nm for NB and YF3G,respectively.After each adsorption,the adsorbent was characterized by using FTIR and XRD.

3.Results and Discussion

3.1.Physical properties of materials

3.1.1.X-ray diffractometer

Fig.1 shows the XRD spectra of as-prepared Mg/Al HT,Mg/Al CHT,Mg/Al CHT after adsorption and regenerated Mg/Al CHT after reused for one time.The typical diffraction lines due to layered double hydroxide structure were observed at 2θ=10.52°,21.89°and 33.93°,ascribed to (0 0 3),(0 0 6) and (0 0 9) planes,respectively (Fig.1a).After Mg/Al HT was calcined into Mg/Al CHT,as shown in Fig.1b,the intensities of(0 0 3),(0 0 6)and(0 0 9)planes were significantly decreased along with slight decreases in their interlayer spacings,from 0.840,0.406 and 0.264 nm to 0.820,0.402 and 0.260 nm,respectively.This demonstrating that the layered structure of HT was partially lost during calcination.The most obvious change was the appearance of two new peaks at 2θ=42.30° and 61.72° attributed to (2 0 0) and (2 2 0) planes,respectively,due to cubic MgO.The diffraction line due to Al2O3,however,cannot be found.These results demonstrated that most of layered structure was broken into cubic MgO but a small portion of the structure was still maintained,presumably due to the presence of NO3–.This will be discussed further in detail later.

Fig.1.XRD patterns of(a)Mg/Al HT,(b)Mg/Al CHT,(c)Mg/Al CHT after adsorption and (d) recalcined Mg/Al CHT after reused for one time.

3.1.2.Scanning electron microscopy (SEM)

SEM analyses of Mg/Al HT,Mg/Al CHT and Mg/Al CHT after adsorption were taken in order to examine their morphological structures.As shown in Fig.2,SEM micrograph of Mg/Al HT indicates a rough irregular structure with cavities(Fig.2a).After calcination (Fig.2b),the cavities were completely diminished and the surface became rougher.Meanwhile,after adsorption of the NB and YF3G mixture,the surface of Mg/Al CHT was deformed and the appearance of cavities as it in Mg/Al HT was observed(Fig.2c).

3.1.3.Fourier transformed infrared (FTIR) spectra

Fig.3 shows the FTIR spectra of the mixture of NB and YF3G,Mg/Al HT,Mg/Al CHT,Mg/Al CHT after adsorption,regenerated Mg/Al CHT,and reused Mg/Al CHT.The mixture of NB and YF3G gave six typical peaks at 3425,2931,2878,1631,1543 and 1170 cm-1assignable to O-H stretching of YF3G,aromatic C-H stretching,saturated C-H stretching,C=O stretching,aromatic C-C stretching,and C-N stretching of NB,respectively (Fig.3a).In the as-prepared Mg/Al HT (Fig.3b),the broad peak at 3464 cm-1was attributed to the O-H stretching from Mg-OH and Al-OH.The weak absorbance at 1635 cm-1was associated with the O-H bending of H2O trapped inside the layer of HT[22].The peak at 1381 cm-1was due to the typical antisymmetric stretching N-O vibration of free[22–25].Meanwhile,the peaks at 671 and 447 cm-1corresponded to the stretching vibration of Al-O and Mg-O,respectively.After Mg/Al HT was calcined at 450 °C,as shown in Fig.3c,the peaks at 3464 and 1635 cm-1were decreased,implying that the surface hydroxyl functional group was oxidized and interlayer H2O was evaporated;leading Mg/Al HT to transform into Mg/Al CHT.This supports the previously mentioned fact that MgO was presence in high crystallinity in XRD spectra (Fig.1b).Meanwhile,the peak corresponded to1381 cm-1was still maintained,suggesting thatwas still presence in the Mg/Al CHT.This is why the weak diffraction lines of the layered structure in Mg/Al CHT in Fig.1b were still observed.

3.2.Removal of NB and YF3G

3.2.1.Effect of pH

In adsorption process,initial pH of the reaction solution plays a key role in the interaction between adsorbent and dyes.This is because the pH may change the surface charges of adsorbent as well as the existing form of adsorbate.The effects of initial pH for the removal of NB and YF3G were evaluated at pH ranging from 3 to 10.As shown in Fig.4,the removals of NB and YF3G were optimum at pH 4.This can be explained as follows.At pH <4,the hydroxyl groups of Mg/Al CHT are protonated.This leads to the break of Mg and/or Al bonds and thus the dissolution of metal cations occurs [26].At pH 4,the protonation of hydroxyl groups significantly decreases and becomes insignificant at higher reaction solution pH.At pH>4,both adsorbent and dyes are negatively charged due to the interaction with hydroxyl anion in the reaction solution,and therefore the repulsive interaction between adsorbent and dyes occurs.Moreover,under basic condition,within interlayer is readily exchanged with OH–[27] which leads to the decrease in length of interlayer spacing of the layered structure and therefore inhibiting the horizontal intercalation of larger NB and/or YF3G (will be discussed further in the reaction mechanism section).This is because OH–has a much smaller effective radius(0.110 nm) than that of the 3D plane height of NB (0.391 nm) and YF3G (0.518 nm).In addition,since the pH after adsorption increased when initial pH was ≤7,but decreased at initial pH >7,it is clear that adsorbent interacts with dyes through electrostatic interaction.

Fig.2.SEM images of (a) Mg/Al HT,(b) Mg/Al CHT and (c) Mg/Al CHT after adsorption.

Fig.3.FTIR spectra of(a)the mixture of NB and YF3G,(b)Mg/Al HT,(c)Mg/Al CHT,(d) Mg/Al CHT after adsorption,(e) recalcined Mg/Al CHT after first use,(f) reused Mg/Al CHT after adsorption.

Fig.4.Effect of medium acidity on the removal of NB and YF3G on Mg/Al CHT.

3.2.2.Removal kinetics

The removal kinetic was performed by examining the effect of contact time on the adsorption of NB and YF3G on Mg/Al CHT.As shown in Fig.5,the adsorption of both NB and YF3G were increased sharply within 15 min and then gradually increased before finally reached equilibrium at 120 min.The adsorption of NB with the time was higher than that of YF3G.The most plausible reason is that the size of NB,as simulated by using Gauss View 4 software (Fig.6),is smaller than that of NB.The smaller the size of adsorbate,the more active sites can participate and thus the higher the adsorption capacity is.

Fig.5.Effect of contact time on the removal of NB and YF3G on Mg/Al CHT.

Fig.6.Geometry of (a) NB and (b) YF3G simulated with Gauss View 4 software.

To gain insight into the adsorption process,pseudo-first order(Eq.(1))[28],pseudo-second order(Eq.(2))[29]and second order(Eq.(3))kinetic models[30]have been used to evaluate the experimental data.The evaluation was based on linearity of the plots of ln(1 -q/qe) versus t from Eq.(1),t/qtversus t from Eq.(2) andversus t from Eq.(3) for the pseudo-first order,pseudo-second order,and second order kinetics models,respectively.

As shown in Table 1,while the pseudo-first order and second order shows relatively the same linearity(R2value)for the adsorption of NB and YF3G,the plot of t/qtversus t from the pseudosecond order gave the highest linearity (R2>995).Moreover,the adsorption capacity of pseudo-second order was also the closest to the experimental data compared to that obtained by pseudofirst order.Therefore,it can be concluded that the adsorption of NB and YF3G followed pseudo-second order.This means that the adsorption process is governed by at least two parameters,presumably the number of active sites of Mg/Al CHT and the concentration of NB or YF3G.The suitability of pseudo-second order on adsorption of dyes on HT and calcined HT have been reported[31,32].

3.2.3.Removal isotherms

In order to evaluate the removal capacity and the surface behavior of Mg/Al CHT in adsorbing NB and YF3G,the classic and widely used Langmuir (Eq.(4)) and Freundlich (Eq.(5)) isotherm models have been applied in this study.For Langmuir isotherm model,the removal capacity (qmax) and equilibrium constant (KL)were estimated from the slope and intercept of plot between Ce/qeand Ce.While,the removal capacity of Freundlich model (B)was determined from the intercept of plot between lg m and lg C.

where m is the amount of removed NB or YF3G onto Mg/Al CHT,b is Langmuir’s removal capacity corresponding to energetically complete monolayer coverage,K is the equilibrium constant,C is the equilibrium concentration of NB or YF3G in solution,B is the Freundlich’s removal capacity,and n is a constant.

As shown in Fig.7,it is obvious that the trends of the experimental data for the removal of NB and YF3G closely follows Langmuir isotherm model.In fact,the R2values of Langmuir model for adsorption of NB and YF3G were much higher than Freundlich model.This means that the bonding sites on NB or YF3G are homogeneous and thus leading to monolayer coverage of adsorbates.The suitability of Langmuir isotherm model in adsorbing dyes by using HT compounds have been reported [7,20,33].Meanwhile,the removal energy calculated from K value from the linear regression of Langmuir model according to the relationship E=RT ln K yielded a value of 28.84 and 29.04 kJ.mol-1for NB and YF3G,respectively (see Table 2).

Table 1Pseudo-first order (k1p),pseudo-second order (k2p),and second order (k2) rate constants for the removal of NB and YF3G by Mg/Al CHT

Table 2Langmuir and Freundlich isotherm models for the removal of NB and YF3G by Mg/Al CHT.

3.3.Reusability of Mg/Al CHT

A good adsorbent is an adsorbent that not only possesses high adsorption capacity but also,for economical reason,can be used repeatedly without significant losses in adsorption capacity.To check the reusability of the adsorbent,the regenerated Mg/Al CHT after the first use was reused for another adsorption of the mixture of NB and YF3G.The same experiment was conducted for the second reuse.The adsorption capacity of the material after the first use and each reuse were then calculated.In addition,the adsorption capacity of Mg/Al HT was also estimated for comparison.

Fig.7.Removal of(a)NB and(b)YF3G on Mg/Al CHT as a function of the remaining NB or YF3G concentration at equilibrium (Ce) as well as the removal profiles modelled according to the Langmuir and Freundlich isotherm models.

As clearly seen in Fig.8,the calcination treatment of Mg/Al HT into Mg/Al CHT significantly increased the adsorption capacity from 11 to 94.5 mg.g-1.The reason for this stark difference in adsorption capacity value will be explained later in the removal mechanism section.From the experiment results,the fact that Mg/Al CHT maintained its adsorption capacity at around 94–95%mg g-1indicating that the regeneration of adsorbent by calcination after the first use and each reuse does not affect the adsorption capacity of the adsorbent.This is a clear indication that Mg/Al CHT is a stable adsorbent that somehow able to maintain the number of its active sites even after recalcined at high temperature,presumably due to structural-memory effect.Therefore,even though the layered structure of Mg/Al HT is broken by calcination,during adsorption process,this structure and the active sites are regained.This experiment shows the important merit of Mg/Al CHT that is the adsorbent could be easily regenerated by burning of the collected species and then reused for other runs in aqueous solution.

3.4.Removal mechanism of NB and YF3G:Influence of memory effect

To gain insight into the removal mechanism when the adsorbent is applied for real wastewater,the adsorption of the mixture of NB and YF3G was conducted under optimum pH,concentration and reaction time,and the spent adsorbent was then characterized by using XRD and FTIR shown in Figs.1 and 3,respectively.After adsorption,as shown in Fig.1c,the intensities of (0 0 3),(0 0 6)and(0 0 9)planes of Mg/Al CHT were significantly increased,while the intensities of the diffraction lines due to MgO were slightlydecreased.Meanwhile,the diffraction angle of (0 0 3) plane was shifted from 10.78°to 10.52°owing to an increase in the interlayer spacing from 0.820 to 0.840 nm.It is noted that the value of interlayer spacing of (0 0 3) plane after adsorption process is the same as that in Mg/Al HT,implying that Mg/Al CHT had restored its layered structure during adsorption process.This is a strong indication that structural-memory effect was occurred.Since naturally the restored structure may allow the adsorbent to be a host for organic species through intercalation [7] and because the heights of geometric structure of NB and YF3G in the 3D plane simulated with Gauss View 4 software (Fig.6) were smaller (0.391 and 0.518 nm,respectively) than that of interlayer spacing of (0 0 3)plane (0.840 nm),it is possible that NB and/or YF3G molecule may be horizontally intercalated into the interlayer spacing of(0 0 3) plane.When Mg/Al CHT after adsorption was recalcined at 450 °C for 3 h,subsequently used for another adsorption and then recalcined again,the diffraction lines due to MgO were increased as the diffraction lines of layered structure were decreased(Fig.1d),indicating that the material is readily regenerated by calcination process.

Fig.8.Reusability of Mg/Al CHT.

From FTIR spectra,ideally due to structural-memory effect,the intensity of O-H after adsorption(Fig.3d)must increases to show the restoration process of layered double hydroxide structure[19].Contrary to that hypothesis,the intensity was decreased,indicating that-OH was lost during adsorption process.The most plausible reason for that is the partial dissolution of MgO due to proton attack (MgO+H+→Mg2++OH–) owing to the medium acidity of the reaction solution which was mild-acidic(pH 4).This supported by the fact that the pH of the reaction solution after adsorption was increased from 4 to 6.In addition,the relative mass percentage of Mg to Al after adsorption process obtained from Energy Dispersive X-ray(EDX)analysis was decreased from 42.37%to 29.97%.Nevertheless,the XRD spectra still indicate that the adsorbent had gained its layered structure during adsorption process (Fig.1c).Meanwhile,the intensity of N-O was significantly decreased,demonstrating the losses of NO3–during adsorption.This is an indication that the intercalation process of layered structure of Mg/Al CHT with NB and/or YF3G may not only be caused by memory effect but also an exchange between NB and/or YF3G and.

Fig.9.Schematic ilustration of the removal mechanism of NB and YF3G on Mg/Al CHT.

In contrast to the first adsorption test,when the recalcined Mg/Al CHT after the first use(Fig.3e)was reused for the mixture of NB and YF3G(Fig.3f),the intensities of O-H and N-O stretching after adsorption were significantly increased and O-H stretching even took a blue shift from 3448 to 3464 cm-1.This clearly demonstrated that layered structure was restored following exposure to reaction solution.

Based on the results above,we proposed two possible adsorption mechanisms for the removal of NB and YF3G on Mg/Al CHT as shown in Fig.9.Firstly,both dyes may be adsorbed on the surface of the outer layer of adsorbent in which NB and YF3G interacts with protonated hydroxyl groups through electrostatic interactions.Secondly,by taking the structural-memory effect of the adsorbent as well as the height of the geometric structure of NB and YF3G which are smaller than the interlayer spacing of (0 0 3)plane into consideration,NB and/or YF3G may be physically or electrostatically intercalated within the interlayer gallery of layered structure of adsorbent.On the other hand,for Mg/Al HT,electrostatic interaction at the outer layer of layered structure is the only mechanism possible and hence the adsorption capacity is much lower (11 mg.g-1) than that of calcined ones (94.5 mg.g-1)(Fig.8).Similar reaction mechanism was reported by Ni et al.[31] for the adsorption of Methyl Orange (MO) on calcined Zn/Al LDH.It was reported that the intercalation of MO within interlayer gallery played a key role for the structural-restoration of the layered structure of Zn/Al LDH.

4.Conclusions

It is concluded that Mg/Al CHT is an effective adsorbent for the removal of NB and YF3G dyes.The characterization by using FTIR and XRD showed that Mg/Al CHT possessed a structural-memory effect which allowed the material to be used for other runs for the adsorption of NB and YF3G.The adsorption test showed that Mg/Al CHT was eightfold more effective than that of Mg/Al HT in removing the mixture of NB and YF3G at pH 4 with removal capacities (b) according to Langmuir isotherm model were 7.97 × 10–4and 5.80 × 10–4mol.g-1,respectively.Kinetics study showed that the adsorption of NB and YF3D on Mg/Al CHT followed pseudoorder second order with rate constant (k) 11.57 × 103and 11.75 × 103g.mol-1.min-1,respectively.In addition,the adsorption capacity of Mg/Al CHT was maintained with repeated use.In short,this study shows the important merit of Mg/Al CHT that the adsorbent could be easily regenerated by burning the collected dyes and then reused for another adsorption in aqueous solution.

Declaration of Competing Interest

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

Acknowledgements

This research initially received financial support from Directorate General of Higher Education,Republic of Indonesia through a research scheme of Penelitian Pascasarjana 2018 with contract number 1783/UN1/DITLIT/DIT-LIT/LT/2018 and continued with a research scheme of World Class Research with contract number 3857/UN1/DITLIT/DIT-LIT/PT/2020.