Title Science and Technology Indonesia e-ISSN:2580-4391 p-ISSN:2580-4405 Vol. 3, No. 4, October 2018 Research Paper Adsorption of Cobalt (II) on Layered Double Hydroxides (Mg/Al and Ca/Al) In Aqueous Medium : Kinetic and Thermodynamic Aspect Neza Rahayu Palapa1, Tarmizi Taher2, Muhammad Said1, Risfidian Mohadi1, Aldes Lesbani1* 1Magister of Chemistry, Faculty of Mathematic and Natural Sciences, Sriwijaya University, Jl.. Padang Selasa Bukit Besar Palembang 30139 22Department of Enviromental Science, Graduate School, Sriwijaya University, Jl. Padang Selasa No. 524 Ilir Barat 1, Palembang-South Sumatra, Indonesia *Corresponding author: aldeslesbani@pps.unsri.ac.id Abstract Layered double hydroxides Mg/Al and Ca/Al has been synthesized by co-precipitation method with molar ratio M2+:M3+ (3:1) at pH 10. The synthesized materials were characterized by XRD and FTIR. The materials were used as adsorbent for the removal Cobalt (II) in aqueous solution. The adsorption experiments were studied through some variables adsorption such as variation of contact time, variation of temperature and variation of initial concentration. Kinetic parameters was obtained from variation of contact time. Data was analyzed by pseudo-first-order and pseudo-second-order kinetics models in linear analyses. The kinetic studies showed that the adsorption process more fitted by pseudo-second-order than pseudo-first-order based on coefficient correlation. Isotherm parameters was calculated using Langmuir and Freundlich isotherm models. The adsorption process was spontaneous and endothermic. Keywords layered double hydroxides, adsorption, Cobalt (II) Received: 14 September 2018, Accepted: 19 October 2018 https://doi.org/10.26554/sti.2018.3.4.189-194 1. INTRODUCTION Layered material are classi�ed into two groups, cationic clays and anionic clays. Cationic clays are found in nature and an- ionic clays are easily synthesized. Layered double hydroxides (LDH) belong to the anionic clay minerals was consist of sheets of the hydroxides of two metals di�erent valence. The metals hydroxides layeres are positively charged, so neutrality charged requires must be anion intercalated into interlayer. Usually, hydroxil ions was present as anion and this anion can be readily exchanged by others such as carbonate ions (Rosenberg and Armstrong, 2016). LDHs has general formula [M2+(1-x)M3+x(OH)2](An-)x/nH2O, where M2+ and M3+ are di-valent and tri-valent cations such as Mg2+, Fe2+, Co2+, Cu2+, Ni2+, Ca2+ and Al3+, Cr3+, Ga3+, Mn3+ or Fe3+ (Hongo et al., 2017). This layer materials have high �exibility cation exchange and easily synthesized in lab- oratory (Zhao et al., 2011). Layered double hydroxide has many potential aplications for layered double hydroxides in- cluding catalysis, adsorption and �ame retardant composite (Clark et al., 2017). There have been many studies were focusing on the apli- cation of layered double hydroxides as adsorbent Zhao et al. (2011); El-Sayed et al. (2016); Said and Palapa (2017). Lay- ered double hydroxides was used to adsorpted heavy metals Zhao et al. (2011) and stable at pH >5 up to 12 (Costantino et al., 2013). As known, the presence of heavy metals in the environment can be harmful to variety of living species. There- for, the removal of heavy metals from waste water is important to public health. The industrial waste water usually contain- ing cobalt (II) is common. The adsorption of heavy metals in solution can be removed using several technique such as adsorption, precipitation, coagulation, chemical precipitation, ion-exchange, ozonation and membran �ltration (Shou et al., 2015). The adsorption is recognized as an easy, economic and e�ective to removed heavy metals from the waste water (El-Sayed et al., 2016; Taher et al., 2018). In this research, synthesis and characterization of layered double hydroxides was conducted using Frourier Transform Infra Red (FT-IR) and X-Ray Difractometer (XRD). The ad- sorption process of layered double hydroxides is intended to determine the kinetic and thermodynamic parameters by mea- suring residual concentration and adsorbed using Atomic Ad- sorption Spectrophotometer. 2. EXPERIMENTAL SECTION The chemicals used are analytical grade such as magnesium nitrate, alumunium nitrate, calsium nitrate, sodium carbon- https://doi.org/10.26554/sti.2018.3.4.189-194 Palapa et. al. Science and Technology Indonesia, 3 (2018) 189-194 ate, sodium hydroxide and cobalt nitrate. Water was supplied from Integrated Research Lab Graduated School, Sriwijaya University. Analysis instrument were used FT-IR Shimadzu Prestige-21, XRD Shimadzu Lab X-Type 6000 and Atomic Adsorption Spectrophotometer NovAA 350 Analytic Jena. 2.1 Synthesis of Layered Double Hydroxides Synthesis of layered double hydroxides Mg/Al was conducted according to (Palapa and Said, 2016). Synthesis of layered double hydroxides Ca/Al was conducting using 100 mL of a solution containing 0.3 mol Ca(NO3)2 ·H2O and 0.1 mol Al(NO3) ·9H2O under vigorous stirring, while was added drop- wise 2 mol/L of NaOH at pH 11 then stirring until 24 h to form white solid material and dried at room temperature to obtain Ca/Al layered double hydroxides (Rojas, 2014). 2.2 Adsorption Experiment Kinetic Parameter 0.05 g layered double hydroxides Mg/Al and Ca/Al each added into 50 mL of cobalt (II) shaker with variations in contact time varied. The solution of the ad- sorbed cobalt (II) substance was separated by �ltration and then measured its concentration by using Atomic Adsorption Spectrophotometer. Thermodynamic Parameter Thermody- namic adsorption of cobalt (II) using adsorbent 0.05 g layered double hydroxides Mg/Al and Ca/Al each added into 50 mL cobalt (II) by variying the with each adsorption temperature is 30 ºC, 35 ºC, 40 ºC, 45 ºC, 50 ºC. The solution of the adsorbed cobalt (II) substance was separated by �ltration and then measured its concentration by using Atomic Adsorption Spectrophotometer. 3. RESULTS AND DISCUSSION 3.1 Adsorbent Characterization Characterization of layered double hydroxide was carried out using the FT-IR. The FT-IR of the layered double hydrox- ides Mg/Al and Ca/Al is shown in Figure 1. The vibration at wavenumber 3300-3800 cm−1 is assigned as streching of O-H and the bending of O-H at 1635 cm−1. The bending of nitrate is appeared at wavenumber 1381-1388 cm−1. These vibration was unique vibration for layered double hydroxides. The vibrations of Al-O, Ca-O and Mg-O were appreated at 563 cm−1 , 424 cm−1 and 416 cm−1 respectively. The XRD patterns of Mg/Al and Ca/Al material were shown in Figure 2. The unique structure of layered double hy- droxides was identi�ed at di�raction angle. This difraction 100 and 600 indicated that presence of layered materials and the anion on the interlayered. XRD pattern of Ca/Al in Figure2b was shown semiliar to that reported by Hongo et al. (2017) when synthesis of material was carried out at temperature was 27 ºC (room temperature), the peak intensity of calcite was stong, its because layered double hydroxides contained calcite. Figure 1. FT-IR spectrum of layered double hydroxides Mg/Al (a) and layered double hydroxides Ca/Al (b) Figure 2. XRD patterns of layered double hydroxides Mg/Al (a) and layered double hydroxides Ca/Al (b) 3.2 Kinetic Adsorption of Cobalt (II) on Mg/Al and Ca/Al Layered Double Hydorxides In order to establish the equilibrium time for maximum ad- sorption, the adsorption of of cobalt (II) was investigated as the function of contact time. Kinetic adsorption of cobalt (II) on layered double hydroxides Mg/Al and Ca/Al was studied by investigated adsorption time as shown in Figure 3. Figure 3 shows that Mg/Al and C/Al layered double hydrox- ide increased slowly after an hour with percentage adsorp 84% and 78%, respectively. The fast removal adsorption can happen because the adsorbent surfaces have large number of site to ad- sorb Co(II) solution, then the rate of adsorbent was decreased when the surface site full of adsorbate accumulated. To identify the rate kinetics of the adsorption process, two kinetics models, namely the pseudo-�rst-order (PFO) and seudo-second-order (PSO) have been employed to �t the experimental data. The © 2018 The Authors. Page 190 of 194 Palapa et. al. Science and Technology Indonesia, 3 (2018) 189-194 Figure 3. E�ect of contact time on the adsorption of Cobalt (II) onto Mg/Al and Ca/Al LDHs pseudo-�rst-order kinetics model desribes the adsorption of liquid/solid system based on solid capacity. The model can be written as: dqt dt = k1(qe− qt) (1) log(qe− qt)= logqe− k1 2.303 t (2) where qe and qt are the capacity of metal ions adsorbed (mg g−1) at equilibrium and time t (h), respectively, and K1 is the PFO rate constant(h−1). Thus the value of qe and k1 can be determined experimen- tally by plotting log(qe-qt) versus t and extracting information from the least squares analysis of slope and intersept into eq (1). The seudo-second-order adsorption kinetic is expressed as following formulation: dqt dt = k2(qe− qt)2 (3) t qt = 1 k2qe2 + 1 qe t (4) Where k2 (g mg−1 h−1) is the PSO rate constant for the ad- sorption process. Thus values of k2 and qe can be calculated from intercept and the slope of the linear relationship eq (4) between t/qt and t. The calculated values of k1 , k2 , and coe�cient correlation (R2) obtain in Table 1. The result indicated that linear of PFO model did not give reasonable values with regard to the experi- mentals of Co(II). However, the (R2) values are low for linear PFO comparing with (R2) values obtain from PSO. These re- sult suggest that the second order mechanism is predominant, Table 1. Kinetics models for the adsorption of Co (II) kinetics models parameters Adsorbent Mg/Al Ca/Al Pseudo-�rst-order qe exp (mg/g) 17.0769 16.9949 qe calc (mg/g) 18.7013 13.2092 k1 (min-1) 0.0714 0.0359 R2 0.9367 0.9722 Pseudo-Seconds-order qe exp (mg/g) 17.0769 16.9949 qe calc (mg/g) 18.7798 18.3765 k2 (min-1) 0.0053 0.0185 R2 0.992 0.995 in which the adsorption mechanism depends on the adsorbate and adsorbent. The result was shown in Table 1. Table 1 was calculated value of k1 and k2, qe exp, qe calc together with (R2). The value of correlation coe�cient MgAl and Ca/Al (R2) = 0.99 for pseudo-second-order model was better �tted than pseudo-�rst- orde for adsorption Co(II) by MgAl and Ca/Al layered double hydroxides, respectively. The data obtained in Table 1 also showed that the layered double hydroxides Mg/Al has a more reactive than Ca/Al because layered double hydroxides Mg/Al has the adsorption rate (0.0053 (min−1)) lower than layered double hydroxides Ca/Al (min−1). 3.3 Thermodynamic Adsorption of Cobalt (II) on Mg/Al and Ca/Al Layered Double Hydroxides The Thermodinamics parameters was studied by varied of concentration and temperature. Thermodynamics were used two models isotherm for this data Langmuir and Freundlich ishotherm models. The Langmuir assumed that adsorbate was occupied onto monolayer. Its used equation as follows: Ce qe = 1 kLqmax + Ce qmax (5) Where qe is the equilibrium adsorption, Ce is equilibrium concentration, qmax is the maximum adsorption and kL is the equilibrium adsorption constant. Then, the essential features of Langmuir isotherm namely RL (equilibrium parameters). Value RL has indicated the models of isotherm. If irreversible, the RL calculated zero (RL = 0), liniear when RL = 1, and favorable when 0> RL>1 (Kumar et al., 2012). The Freundlich isotherm model identi�ed the heteroge- nous adsorbent surface. The equation is following: Logqe = LogkF +nLogCe (6) Where kF is adsorption capacity when equilibrium. Thermo- dynamic adsorption of cobalt (II) on layered double hydroxides Mg/Al and Ca/Al was studied by variying concentration and temperature. Adsorption data by layered double hydroxides Mg/Al and Ca/Al in Figure 4 and Figure 5. Therefore, both the isotherm models are shown in Table 2. Based on correlation © 2018 The Authors. Page 191 of 194 Palapa et. al. Science and Technology Indonesia, 3 (2018) 189-194 Table 2. Langmuir and Freundlich Isotherm Models Correlation Parameter T= 303 K T= 308 K T= 313 K T= 318 K Langmuir Mg/Al Ca/Al Mg/Al Ca/Al Mg/Al Ca/Al Mg/Al Ca/Al Qmax 18.288 17.453 22.726 18.463 25.773 21.098 36.855 21.318 KL 0.0626 0.071 0.085 0.077 0.080 0.070 0.0557 0.073 RL 0.00068- 0.0054 0.00071- 0.0056 0.00054- 0.0043 0.00067- 0.0054 0.00048- 0.0035 0.00059- 0.0047 0.00033- 0.0027 0.00058- 0.00046 R2 0.996 0.994 0.995 0.994 0.995 0.992 0.994 0.991 Freundlich Mg/Al Ca/Al Mg/Al Ca/Al Mg/Al Ca/Al Mg/Al Ca/Al Kf 1.391 1.933 2.025 2.040 1.969 1.847 2.1433 2.149 n 1.505 1.802 1.476 1.856 1.366 1.537 1.299 1.609 R2 0.894 0.706 0.741 0.718 0.798 0.677 0.848 0.829 Figure 4. Adsorption of cobalt (II) varied concentration and temperature by layered double hydroxides Mg/Al coe�cient of the data, Langmuir isotherm models more �tted than Freundlich isotherm models. Its indicated the adsorp- tion was accour in monolayer adsorption coverage onto LDHs particles and also the homogeneous distribution of active sites adsorbent (Lin et al., 2014). the isotherm was found to be linear studied by good correlation coe�cient (R2 =0.99). The data in Table 2 was showed the monolayer adsorption capacity Cobalt (II) have a higher value at 318 K using Mg/Al LDHs (36.855 mg/g). Thermodynamic investigation plays an indispensable part in the prediction of adsorption mechanisms (i.e., physical or chemical). thermodynamic parameters (∆G°, ∆H°, and ∆S°) can be calculated according to the thermodynamic laws through the following equations: ∆G =−RT lnKc (7) then, the relationship between thermodynamics parameter written by: ∆G =∆H −T∆S (8) Figure 5. Adsorption of cobalt (II) varied concentration and temperature by layered double hydroxides Ca/Al The Van’t Ho� equation was obtain by Equation (7) and (8): lnKc = ∆H R · 1 T + ∆S R (9) The Gibbs energy was calculated by Equation (7), then the enthalpy (∆H) and the entropy (∆S) were obtained from a plot of lnKc versus 1/T, the plot were determined slope and intercept (Equation (9)). In this study the Kc derived from the Langmuir constant (KL) was employed for calculation of the thermodynamic parameters. The thermodynamic parameters for adsorbing Cobalt (II) onto the Mg/Al and Ca/Al LDHs respectively were showed in Table 3. Table 3 were showed the negative values of ∆G were investigated the adsorption was spontaneously. Meanwhile, the positive ∆H re�ects the endothermic nature of the adsorption process and the equilibrium constant (Table 3) at a higher tem- perature. Additionally, the positive ∆S values suggest that an increase in irregularity on the surface with several structural changes both adsorbate and adsorbent. In addition, when the adsorbate is adsorbed on the surface sites, the adsorbate re- places several molecules of water which is its can increasing the entropy. © 2018 The Authors. Page 192 of 194 Palapa et. al. Science and Technology Indonesia, 3 (2018) 189-194 Table 3. Values of Thermodynamic Parameters for The Adsorption of Cobalt (II) By Mg/Al and Ca/Al LDHs T (K) Concentration (mg/L) Mg/Al Ca/Al ∆G ∆S ∆H ∆G ∆S ∆H (kJ/mol) (J/mol.K) (kJ/mol) (kJ/mol) (J/mol.K) (kJ/mol) 303 10 -4.712 85.806 21.286 -1.005 69.614 21.666 308 -6.429 -2.384 313 -8.145 -3.736 318 -8.784 -3.943 303 20 -2.762 111.236 37.480 -0.199 84.261 33.365 308 -5.049 -1.104 313 -7.336 -2.008 318 -8.309 -3.489 303 30 -1.381 114.342 31.883 -0.245 96.094 42.864 308 -4.823 -1.175 313 -8.265 -2.105 318 -8.905 -4.997 303 50 -0.231 138.846 44.383 -0.378 110.654 58.418 308 -0.463 -0.984 313 -3.248 -1.591 318 -4.567 -3.856 303 80 -0.672 172.093 50.761 -0.378 122.035 78.148 308 -2.114 -0.984 313 -3.082 -1.591 318 -3.787 -2.345 4. CONCLUSIONS Adsorption process of cobalt (II) on layered double hydroxides Mg/Al and Ca/Al showed the adsorption rate 0.0053 min−1 and 0.0185 min−1, respectively. Layered double hydroxides Mg/Al more reactive than layered double hydroxides Ca/Al. 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