Title Science and Technology Indonesia e-ISSN:2580-4391 p-ISSN:2580-4405 Vol. 5, No. 2, April 2020 Research Paper Malachite Green Removal by Zn/Al-citrate LDHs in Aqueous Solution Nurlisa Hidayati1*, Risfidian Mohadi1, Elfita1, Aldes Lesbani1 1Chemistry Department, Faculty of Mathematics and Natural Science, University of Sriwijaya, Indralaya, South Sumatera, Indonesia *Corresponding author: hidayatinurlisa@yahoo.com Abstract Zn/Al-citrate LDHs was synthesized using co precipitation method at basic condition and the material were applied as adsorbent of malachite green (MG) dye in aqueous medium using batch system. Adsorption of MG onto Zn/Al-citrate was investigated through kinetic, isotherm adsorption and thermodynamic studies. Kinetic model was fi�ed PSO than PFO for MG adsorption. The rate of adsorption k2 for Zn/Al LDHs was 0.000692 g.mg−1 min−1 and 0.000371 g for Zn/Al-citrate LDHs.mg−1 min−1. Adsorption of malachite green onto Zn/Al LDHs and Zn/Al citrate LDHs was investigated and following Langmuir adsorption isotherm model shows chemical adsorption process. The adsorption capacity maximum of Zn/Al-citrate is 333 mg/g from Zn/Al LDHs is only 111 mg/g. Thermodynamic parameters of Zn/Al-citrate confirmed adsorption process was endothermic and spontaneous. Keywords LDHs, citric acid, intercalation, adsorption, malachite green Received: 17 March 2020, Accepted: 09 April 2020 https://doi.org/10.26554/sti.2020.5.2.59-61 1. INTRODUCTION Various industries are widely applied dyes to colour their product. Disposal of dye wastewater from the dyestu� manufacturing, printing, dyeing and textile industry represent a serious problem all over the world, because in wastewater dyes undergo chemical changes and destroy aquatic life and they even endangers human health (Song et al., 2013). Cationic reactive dyes are widely used in the tannery, paper, textile industries, distilleries, food beverage etc. Malachite green is a cationic base dye used in manufacturing of paints and printing inks. It also most commonly used for dyeing silk, cotton, paper and leather (Hameed and El-Khaiary, 2008). Malachite green has reported to a�ect the immune and reproductive system of animal due to its carcinogenic properties (Song et al., 2020). Malachite green also represents adverse e�ect on reproductive and immune system (Yildirim and Bulut, 2020). Therefore an increased interest has been focused on removing of such dyes from wastewater. Many methods have been used to decolorize dye wastewater including adsorption, membrane �ltration, coagulation, elec- trochemical methods, oxidation and biological technology. Of these techniques due to its e�ective and economical, adsorp- tion is a common method for dye removal (Palapa et al., 2019). Layered double hydroxide (LDH) is a type of anionic clay hav- ing a hydrotalcite crystal structure, that are formed by two kinds of metal ions, usually a divalent and trivalent one, to- gether with hydroxyl group, an interlayer anion and water molecules (Pan et al., 2020). The general formula of LDH is [M1−x+2Mx+3(OH)2]+3[Ax/n].mH2O, where x is the molar ratio M+3/ (M+2 + M+3) ranging from 0.20 to 0.30 in order to avoid the formation of undesirable phase (Lesbani et al., 2020). To improve of LDH sorption properties some researchers conducted inter- calation in the layer space using anion such as hexacyanoferrat (II) anion (Puzyrnaya et al., 2016) and ethylendiamintetraacetic acid (Kameda et al., 2013). The aim of this study was to examine the feasibility of using Zn/Al-citrate for the removal of MG dyes from aqueous solution. The e�ect of di�erent parameters including contact time, dye concentration and temperature were studied to optimize the sorption process. Descriptions of the adsorption process were explored through kinetic parameter, adsorption isotherm and thermodynamic parameter. 2. EXPERIMENTAL SECTION 2.1 Material and instrumentation All the chemical used in this study were of analytical grade (p.a) Zn(NO3)2.6H2O, Al(NO3)2.9H2O, N2 gas, NaOH, malachite green and aquadest. The instrument spectrophotometer UV-Vis (EMC- 61-PC Spektrofotometer) used for measuring concentration of MG. https://doi.org/10.26554/sti.2020.5.2.59-61 Hidayati et. al. Science and Technology Indonesia, 5 (2020) 59-61 2.2 Methods 2.2.1 Synthesis of Zn/Al-citrate Zn/Al LDHs was synthesized by coprecipitation method accord- ing to Palapa et al. (2019). As much as the solution contain- ing Zn(NO3)2.6H2O 0.3M and Al(NO3)2.9H2O 0.1M with molar ratio Zn/Al 3:1 was added one drop at a time to a vigorously stirred solution of NaOH and 1 M at a constant solution pH of 10. The resulting precipitate dried hydrothermally at 80oC for 18 h. Preparation of Zn/Al-citrate was conducted under nitrogen atmosphere, 2 gs of Zn/Al LDH gel was diluted by 50 mL deion- ized water whereas in another beaker 10 gs of citric acid was diluted by 50 mL deionized water. The solution of LDH added dropwise into citric acid with continoues strirring for 24 hours. Wash and dried obtained materials in room temperature. 2.2.2 Adsorption experiments MG adsorption were determined using e�ect of contact time, initial concentrationa and temparature adsorption. As much as 0.02 g Zn/Al LDHs and Zn/Al-citrate LDHs were contacted with 25 mL of 100 mg/L MG solution for e�ect of adsorption time contact experiments by varying time ranging 5 to 180 minutes. The e�ect of initial concentration and temperature were deter- mined by 140 and 190 mg/L for Zn/Al LDHs and Zn/Al-citrate LDHs, respectively, and the various temperature from 30 − 60oC after each adsorption experiment completed, samples were �l- trated to separate supernatant and precipitate. Supernatants were analyzed using spectrophotometer at 617 nm. 3. RESULTS AND DISCUSSION 3.1 Kinetic Models Successful application of malachite green removal by LDHs, can be achieved through high adsorption for malachite green in a short time. Fig 1 shows malachite green adsorption on LDHs as function of contact time. The rate of malachite Green removal by LDHs was sharp at initial time followed by a long slow de- cline. The adsorption equilibrium was fully established after 120 minutes for both of LDHs. The result show that adsorption of Zn/Al-citrate LDHs was higher than Zn/Al LDH. The adsorption rate constant (k) and malachite green ad- sorbed at equilibrium time were determined from the slope and intercept of linear plot of pseudo �rst order and pseudo second order according to Song et al. (2020). Table 1 showed mathemat- ical form and parameter of both models. Based on Table 1, both material were �tted in pseudo second order than pseudo �rst order according to coe�cient correlation was closed to one. this phenomena were supported by adsorption rate of Zn/Al-citrate for was bigger than pristine. The adsorption capacity of both material indicated that the experimental adsorp- tion capacity in pseudo second order better �tted by calculation adsorption capacity. 3.2 Isotherm Adsorption The adsorption isotherms were obtained according Freundlich and Langmuir isotherm. The isotherm model parameters were listed in Table 2. Table 2 shows the values of the constants Figure 1. E�ect of time contact on malachite green adsorption onto Zn/Al LDHs Table 1. Kinetics parameter for MG adsorption onto Zn/Al and Zn/Al-citrate Kinetic Model Parameters Zn/Al LDH Zn/Al-citrate PFO qeexp (mg/g−1) 36.181 119.636 qecalc (mg/g−1) 31.9154 130.617 k1 (min − 1) 0.021 0.03915 R2 0.992 0.935 PSO qeexp (mg/g-1) 36.181 119.636 qecalc (mg/g−1) 43.4783 142.657 k2 (g/mgmin) 0.000692 0.000371 R2 0.997 0.998 obtained for the two models. Adsorption isoterm data using Fre- undlich and Langmuir adsorption isotherm of malachite green on Zn/Al LDHs showed that Langmuir isotherm adjusted best the experimental isotherm with R2 value 0.897-0.9935. It indi- cated homogeneity of adsorbent and formation monolayer of dye covering the surface of the adsorbent (dos Santos et al., 2017). Table 2 also showed that the qmax of Zn/Al-citrate is bet- ter at lower temperature which amount of adsorption capacity maximum is 333 mg/g from Zn/Al LDHs is only 111 mg/g. This phenom indicated the intercalation process of Zn/Al LDHs was better adsorbed than pristine. However, the favorable of MG adsorption onto Zn/Al-citrate also denotes by KL which is the value ranging 0