Indonesian Journal of Chemical Research http://ojs3.unpatti.ac.id/index.php/ijcr Indo. J. Chem. Res., 8(2), 194-201, 2021 The Effectiveness of Magnetite Modified Gallic Acid Synthesized by Sonochemical Method As AuCl4 - Adsorbent-Reductor Maya Rahmayantia,*, Sri Juari Santosab, Sutarnob, Astuti Pawenia a Department of Chemistry, State Islamic University of Sunan Kalijaga, Jl. Marsda Adi Sucipto Yogyakarta, Indonesia b Department of Chemistry, Universitas Gadjah Mada, Jl. Sekip Utara, Yogyakarta 55281, Indonesia *Corresponding Author: maya.rahmayanti@uin-suka.ac.id Received: September 2020 Received in revised: November 2020 Accepted: December 2020 Available online: January 2021 Abstract In recent years gallic acid has been developed as an AuCl4- adsorbent-reducing agent. In this research, gallic acid was modified with magnetite by sonochemical method (GA-Fe3O4), and its effectiveness as an AuCl4 - adsorbent was studied. GA- Fe3O4 was synthesized through one-stage (GA-Fe3O4-SK1) and two-stage (GA- Fe3O4-SK2) methods. The effectiveness of GA-Fe3O4 was studied through optimization studies on pH, time, kinetics, and isotherm adsorption of AuCl4 -. The adsorption method used was the batch method in the pH range 2-7. While the kinetics model used was the Lagergren and Ho kinetics model. The adsorption isotherm model used was the Freundlich and Langmuir isotherm model. The results showed that the optimum pH conditions for adsorption of AuCl4- on GA-Fe3O4 occurred at pH 3. Adsorption of AuCl4 - on GA-Fe3O4-SK1 and GA-Fe3O4-SK2 both followed the Ho kinetic model, while the adsorption isotherm followed the Freundlich isotherm model with values KF were 0.041 and 0.034 mol/g respectively. Keywords: Gallic acid, adsorption, kinetic, isotherm, effectiveness INTRODUCTION Gallic acid is a phenolic compound with a small molecular weight, widely contained in plants as free gallic acid or as part of tannin compounds (Zahrani et al., 2020). Gallic acid has one carboxylic group (- COOH) and three phenolic groups (-OH). Gallic acid is widely developed in the pharmaceutical and chemical industries and is considered promising for developing new drugs. Various studies have reported gallic acid's benefits as an antioxidant, anticancer, antibacterial, and antidiabetic compound (Lone et al., 2017; Sharma et al., 2011). In recent years, gallic acid has been developed as a material applied for the adsorption of AuCl4 - (Rahmayanti et al., 2016a; Rahmayanti et al., 2016b; Santosa et al., 2020; Fitriani, 2020). The active group that plays a role in the adsorption process is the phenolic group. The part of phenolic groups in adsorbing AuCl4 - has also been reported by Rahmayanti et al., 2019 and Rahmayanti et al., 2020). They used humic acid and ascorbic acid as AuCl4 - adsorbents. In this research, the effectiveness of gallic acid modified with magnetite was studied using the sonochemical method (GA-Fe3O4-SK) as an AuCl4 - adsorbent. This research is a preliminary study for the study of gold recovery from electronic waste. The existence of more and more electronic waste and the rapid development of technology is a concern. It is necessary to find an effective method of managing electronic waste by safely recovering the precious metals in electronic waste. The adsorption method using gallic acid is an option. The presence of phenolic groups in gallic acid not only acts as an adsorbent but also as a reducing agent so that Au (III) can be reduced to Au (0) (Rahmayanti et al., 2016a; Rahmayanti et al., 2016b; Santosa et al. ., 2020; Fitriani, 2020; Rahmayanti et al., 2019; Rahmayanti et al., 2020). Gallic acid was modified using magnetite to facilitate the adsorption process and the separation between the adsorbent and the post-adsorption adsorbate. The adsorbent's magnetic properties will facilitate the separation process between the adsorbent and the filtrate, namely only by using an external magnetic field. Likewise, the separation between the post adsorption adsorbent and Au (0) metal was also carried out. The optimum pH conditions and reaction time were also studied in this study. The kinetics and adsorption isotherm studies of AuCl4- on GA-Fe3O4- SK were investigated using two kinetics and isotherm models. DOI: 10.30598//ijcr.2021.8-may 194 Maya Rahmayanti, et al. Indo. J. Chem. Res., 8(2), 194-201, 2021 METHODOLOGY Materials and Instrumentals The research equipment consists of a set of glassware for synthesis and application, sonicator type Leistungsfreq.generator 70VA, hotplate, pH meter Orion 920A, shaker (Osk), magnetic stirrer, BP 110 Sartorius analytical reading, desiccator, vacuum pump, and 4800 oven/furnace. Thermolyn. The research materials' characterization used a Fourier Transform Infrared (FTIR) spectrophotometer, Shimadzu-8201 PC, X-Ray Diffraction (XRD) with the ShimadzuXRD-6000 model, and an optical photomicroscope type Ephitot + Nikon D60. Analysis of the filtrate using Atomic Absorption Spectrometer (AAS). Materials used in the research include iron(II)sulfate heptahydrate (FeSO4.7H2O/Merck), iron(III)chloride hexahydrate (FeCl3.6H2O/Merck), sodium hydroxide (NaOH/Merck), hydrochloric acid (HCl/Merck), and gallic acid (Merck). HAuCl4 solution was prepared by the Laboratory of Analytical Chemistry UGM and Aquabides. Methods Magnetite Modified Gallic Acid Synthesis (GA- Fe3O4-SK) The synthesis of magnetite modified gallic acid was carried out by sonochemical method in one and two stages of reaction. This method refers to the research of Rahmayanti et al. (2015) without modification. One-Stage Sonochemical Method Solutions of Fe3+, Fe2+, and gallic acid (GA) were prepared separately by dissolving FeCl3•6H2O, FeSO4•7H2O, and GA into aquabidest with a molar ratio of 2Fe3+: 1Fe2+: 2GA. The mixture of Fe3+ and Fe2+ was injected into NaOH solution pH 13 under stirring at 60 °C under ultrasonic wave radiation with 200 kHz. After the mixture of Fe3+ and Fe2+ has been injected, the GA solution is added rapidly. The mixture was continuously stirred at 60 °C for 1 hour. The resulting residue was separated from the solution using an external magnetic field, washed with distilled water several times, and then dried at 50 °C for 3 hours. The result of the synthesis is referred to as GA-Fe3O4- SK-1. Two-Stage Sonochemical Method In the first stage, a mixture of Fe3+ and Fe2+ solutions are injected into a NaOH solution pH 13 with stirring at 60 °C for 1 hour under ultrasonic wave radiation with a frequency of 200 kHz. The product obtained was separated by external magnetic decantation, washed with distilled water, and dried at 50 °C for 3 hours to produce magnetite powder (Fe3O4). The second stage was carried out by adding magnetite powder to the GA solution with a molar ratio of 1Fe3O4: 2GA. The mixture was then stirred at 60 °C for 1 hour under ultrasonic wave radiation with a frequency of 200 kHz. The separation, washing, and drying processes are carried out the same as GA-Fe3O4- SK-1. The result of the synthesis is referred to as GA- Fe3O4-SK-2. Effect of pH of Solution on Adsorption of AuCl4- on GA-Fe3O4-SK-1 and GA-Fe3O4-SK-2 A total of 10 mg GA-Fe3O4-SK-1 and GA-Fe3O4- SK-2 were added to each Erlenmeyer, which already contains 10 mL of HAuCl4 25 ppm solution with pH variations 2-7. Mix and shake for 1 hour at room temperature. The mixture is then decanted with the help of an external magnetic field. The filtrate was analyzed for the remaining content of AuCl4 - using AAS. Adsorption Kinetics Study The adsorption kinetics was studied by batch method. A total of 10 mg GA-Fe3O4-SK-1 and GA- Fe3O4-SK-2 were added to the HAuCl4 solution (10 mL, 25 ppm) at optimum pH. The mixture was shaken at 125 rpm for 5, 10, 15, 30, 60, 90, and 120 minutes. The precipitate and the filtrate are separated using an external magnet. The remaining AuCl4 - in each solution was determined using AAS. The adsorption kinetics models of AuCl4 - on GA-Fe3O4-SK-1 and GA- Fe3O4-SK-2 studied in this study were Lagergren's pseudo-first-order kinetics model and Ho's pseudo- second-order kinetics model. Adsorption Isotherm Study The adsorption isotherm was studied by batch method. A total of 10 mg GA-Fe3O4-SK-1 and GA- Fe3O4-SK-2 were added to 10 mL of HAuCl4 solution with various concentrations of 25, 40, 55, 70, 85, and 100 ppm. The reaction was carried out at optimum pH and time with a stirring speed of 125 rpm. The precipitate and the filtrate were separated using an external magnet. The remaining AuCl4 - in each solution was determined using AAS. The AuCl4 - adsorption isotherm model on GA-Fe3O4-SK-1 and GA-Fe3O4-SK-2 studied in this study is the Langmuir and Freundlich isotherm model. DOI: 10.30598//ijcr.2021.8-may 195 Maya Rahmayanti, et al. Indo. J. Chem. Res., 8(2), 194-201, 2021 RESULTS AND DISCUSSION Effect of pH of Solution on Adsorption of AuCl4 - on GA-Fe3O4-SK-1 and GA-Fe3O4-SK-2 The acidity effect (pH) of AuCl4 - on GA-Fe3O4- SK-1 and GA-Fe3O4-SK-2 adsorption process was studied by interacting with AuCl4 - 25 ppm with pH variations 2-7 with GA-Fe3O4-SK-1 and GA-Fe3O4- SK-2. The pH range 2-7 was selected, taking into account changes in the Au species in solution, the adsorbent surface charge, and the pKa value of GA. In this study, adsorption of AuCl4 - on GA-Fe3O4- SK-1 and GA-Fe3O4-SK-2 occurred quite well in the pH range 2-7 (Figure 1). The adsorbed percentage of AuCl4 - is above 90%. The optimum pH is obtained at pH 3. The results of this study can be explained by 1) the GA pKa value, which will affect the surface charge of the GA-Fe3O4 adsorbent, and 2) changes in the Au species in solution. Figure 1. Percent of [AuCl4] - which is absorbed in GA-Fe3O4-SK-1 and GA-Fe3O4-SK-2 in various pH ranges 2-7 GA has a pKa1 price of 4.4 and a pKa2 of 8.5. The -COOH GA group ionized at pH ≥ 4.4, while the -OH GA group ionized at pH ≥ 8.5. At pH <4.4, the surface charge of GA-Fe3O4 is positive because the -COOH and -OH groups are protonated to produce -COOH2 + and -OH2 +. While at pH ≥ 4.4, the -COOH group begins to ionize to become -COO-. Thus, if the interaction between GA-Fe3O4 adsorbent and AuCl4 - through electrostatic interaction, the adsorption occurs very well at pH <4.4. These are relevant results of this study. While above pH 4.4 percent, the adsorption of AuCl4 various pHs of aqueous solutions also affect [AuCl4] - adsorption process on GA-Fe3O4. AuCl4 - species namely [AuCl3(OH)] -, [AuCl2(OH)2] -, [AuCl(OH)3] - increases in solution (Wojnicki et al., 2012; Paclawski et al., 2004). As a result, there is competition between species [AuCl4] - with species [AuCl3(OH)] -, [AuCl2(OH)2] -, [AuCl(OH)3] - to interact with GA- Fe3O4. Thus, the adsorption of AuCl4 - on GA-Fe3O4 decreased above pH 4. Based on this study results, the percent reduction pattern of [AuCl4] - which was absorbed in GA-Fe3O4-SK-1 and GA-Fe3O4-SK-2 was the same. There was also no significant difference from the amount of percent AuCl4 - that was absorbed in GA- Fe3O4-SK-1 and GA-Fe3O4-SK-2. The interaction between GA-Fe3O4-SK-1 and GA-Fe3O4-SK-2 with AuCl4 - is also possible through a redox reaction as reported by Santosa et al. (2011), Fan et al. (2014), Yi et al. (2016), Rahmayanti et al. (2016), Rahmayanti et al. (2019). The explanation regarding the –OH Mag-GA group's role in reducing Au(III) to Au(0) can be proven after characterization of the GA- Fe3O4-SK-1 and GA-Fe3O4-SK-2 adsorbents post- adsorption. Characterization of GA-Fe3O4-SK-1 and GA- Fe3O4-SK-2 Post-adsorption FTIR spectra of GA-Fe3O4-SK-1 and GA-Fe3O4- SK-2 before and after adsorption are presented in Figure 2. Based on Figure 2, the absorption intensity in the 1600 cm-1 area has increased. It might be caused by an oxidation-reduction reaction. The phenolic groups have been oxidized to quinones, and Au(III) has been reduced to Au(0). This statement is reinforced by the XRD diffractogram, which is presented in Figure 3. Figure 2. FTIR Spectra a) GA-Fe3O4-SK-1 and b) GA-Fe3O4-SK-2 before adsorption, c) GA-Fe3O4-SK- 1 and d) GA-Fe3O4-SK-2 post-adsorption The XRD diffractogram shows characteristic peaks for gold metal even though it is low intensity, was still not protonated. The distribution of Au(III) complex ions in - decreased not significantly because the -OH group decrease with increasing pH due to the exchange of -Cl with -OH that results in [AuCl4-n(OH)n]- species DOI: 10.30598//ijcr.2021.8-may 196 Maya Rahmayanti, et al. Indo. J. Chem. Res., 8(2), 194-201, 2021 namely at 2θ = 37.97; 44.16 and 64.44°. That is, the adsorption of AuCl4 - on GA-Fe3O4-SK-1 and GA- Fe3O4-SK-2 is also accompanied by the reduction of Au(III) to Au(0). Figure 3. XRD diffractogram a) GA-Fe3O4-SK-1 and b) GA-Fe3O4-SK-2 before adsorption, c) GA-Fe3O4- SK-1 and d) GA-Fe3O4-SK-2 post-adsorption The illustration of the reaction mechanism between AuCl4-and GA-Fe3O4 is presented in Figure 4. Figure 4 shows that the adsorption of AuCl4 -on GA- Fe3O4 occurs in 2 stages. The first stage is electrostatic interactions followed by the second stage, namely the oxidation of -OH phenolics to quinones and reduction of Au(III) to Au(0). Figure 4. Illustration of the reaction mechanism between AuCl4 - and GA-Fe3O4 Determination of AuCl4 - Adsorption Equilibrium Reaction Time on GA-Fe3O4-SK-1 and GA-Fe3O4- SK-2 Adsorption of AuCl4 - on GA-Fe3O4-SK-1 and GA-Fe3O4-SK-2 at various reaction times is presented in Figure 5. It shows that the adsorption equilibrium was reached in the 60th minute for both GA-Fe3O4-SK- 1 and GA-Fe3O4-SK-2. After equilibrium is obtained, there is no significant increase or decrease in the adsorption process because the surface of either GA- Fe3O4-SK-1 or GA-Fe3O4-SK-2 has been saturated or filled with AuCl4 -. The longer addition time does not show a change in the amount of AuCl4 - which adsorbed significantly. Figure 5. Adsorption of AuCl4 - on GA-Fe3O4-SK-1 and GA-Fe3O4-SK-2 at various reaction times (pH= 3, the concentration of Au(III) = 25 ppm) Adsorption Kinetics Study The parameter used to study the adsorption kinetics is the adsorption rate constant (k). The determination of the adsorption rate constants of AuCl4 - on GA-Fe3O4-SK-1 and GA-Fe3O4-SK-2 was investigated using the kinetics model of Lagergren (Ho, 2004; Ho and McKay, 1999). A linear graph t against ln (qe-qt) was created to study the Lagergren kinetics model. From this graph, you will find the values for k (-slope) and qe (calculated, which is the amount of AuCl4 - absorbed at equilibrium). The pseudo-first-order kinetics graph of the Lagergren model is presented in Figure 6. The pseudo-order kinetics assumes the presence of the adsorption mass action rate, which involves diffusion on the surface layer of the adsorbent as the primary determinant of the adsorption rate. This kinetics model is also limited to adsorption with an initial concentration of adsorbate solution that is more than the availability of the active site on the adsorbent (Santosa et al., 2014). Based on Figure 6, the R2 value of AuCl4 - adsorption on GA-Fe3O4-SK-1 and GA- Fe3O4-SK -2 is below 0.9. It means that the adsorption of AuCl4 - on GA-Fe3O4-SK-1 and GA-Fe3O4-SK-2 did not follow Lagergren's pseudo-first-order kinetics model. The pseudo-second-order adsorption kinetics model proposed by Ho was studied by making a graph between (t/qt) vs. t, so that the value of qe (calculated, which is the amount of AuCl4 - absorbed at equilibrium DOI: 10.30598//ijcr.2021.8-may 197 Maya Rahmayanti, et al. Indo. J. Chem. Res., 8(2), 194-201, 2021 from the formula slope = 1/qe) is obtained. (adsorption rate constant) is obtained from 1/(kqe 2). The initial adsorption rate (h) is determined from the equation h = kqe 2. Figure 6. Lagergren Kinetics Model (box = SK1, round = SK2) Figure 7 obtained the correlation coefficient (R2) of AuCl4 - adsorption on GA-Fe3O4-SK-1 and GA- Fe3O4-SK-2> 0.99. It means that AuCl4 - on GA-Fe3O4- SK-1 and GA-Fe3O4-SK-2 follow Ho's pseudo-second- order kinetics model. Ho's pseudo-second-order kinetics model assumes that the adsorption capacity is proportional to the adsorbent's number of active sites. It means that the adsorption capacity of AuCl4 - on GA- Fe3O4-SK-1 and GA-Fe3O4-SK-2 is proportional to the number of active sites adsorbent GA-Fe3O4-SK-1 and GA-Fe3O4-SK-2 (Ho, 1999). Figure 7. Ho Kinetic Model (box = SK1, round = SK2) Table 1 shows the adsorption rate constants (k) and the initial adsorption rate (h) AuCl4 - on GA-Fe3O4- SK-1 higher than the adsorption rate constants AuCl4 - on GA-Fe3O4-SK-2. However, the amount of AuCl4 - absorbed at equilibrium (qe) in GA-Fe3O4-SK-1 is lower than the amount of AuCl4 - absorbed at equilibrium (qe) GA-Fe3O4-SK-2, but it is not so different. It can be explained as follows: GA-Fe3O4- SK-1 was synthesized through a one-step method; this synthesis occurs in an alkaline environment, where the GA-phenolate group has been ionized to produce -O- so that it does not play a role in the interaction of GA with Fe3O4 (Rahmayanti et al., 2015). Table 1. Parameters of the Ho adsorption kinetics model Adsorben t Ho’s pseudo-second-order model R2 qe (mg.g-1) h (mg.g-1. min-1) k (g.mg-1. min-1) GA-SK1 0.999 27.027 12.500 0.01711 GA-SK2 0.993 27.778 4.202 0.00545 The abundance of the phenolic groups on GA- Fe3O4 increases so that the chance for GA-Fe3O4 to interact with AuCl4 - is getting bigger. As a result, adsorption occurs faster in the initial minutes of adsorption. This result is indicated by the higher k and h values for the adsorption of AuCl4 - on GA-Fe3O4-SK- 1. Meanwhile, GA-Fe3O4-SK-2 synthesized under acidic conditions. In this condition, the GA-phenolic group can play a role in interacting with Fe3O4 so that its abundance is reduced. Adsorption Isotherm Study Adsorption isotherm studies were carried out to study the relationship between AuCl4 - to the weight of GA-Fe3O4 at equilibrium conditions and constant temperature. With the adsorption isotherm, it will be known the ability of GA- Fe3O4 to adsorb AuCl4 - through the value of the adsorption capacity, the adsorption equilibrium constant, and the amount of adsorption free energy of AuCl4 -. The adsorption isotherm model used in this study is the Freundlich and Langmuir isotherm model. The Freundlich isotherm equation is used to describe the non-ideal adsorption process on heterogeneous surfaces. Heterogeneity can be caused by differences in functional groups on the adsorbent surface. The Freundlich isotherm model for adsorption of AuCl4 - on GA-Fe3O4 was determined by graphing log qe (the amount of adsorbate adsorbed at equilibrium versus log Ce (concentration of free ions in solution at equilibrium) (Rahayu et al., 2020; Latupeirissa et al., 2018) as presented in Figure 8. Meanwhile, the Langmuir adsorption isotherm model was determined by making a Ce/qe versus Ce graph (Sekewael et al., 2013), as shown in Figure 9. Figures 8 and 9 show that the correlation coefficient (R2) of the Freundlich isotherm model is higher than for the Langmuir isotherm model of both adsorptions of AuCl4 - on GA-Fe3O4-SK-1 and GA- DOI: 10.30598//ijcr.2021.8-may 198 Maya Rahmayanti, et al. Indo. J. Chem. Res., 8(2), 194-201, 2021 Fe3O4-SK-2. This result means that the adsorption of AuCl4 - on GA- Fe3O4-SK-1 and GA- Fe3O4-SK-2 follows the Freundlich isotherm model. Figure 8. Freundlich Isotherm Model Figure 9. Langmuir Isotherm Model Table 2. Comparison of Freundlich AuCl4 - Adoption Isotherm Model Parameters on GA-Fe3O4 Adsorbate Freundlich Parameter KF (mole/g) n R2 GA-Fe3O4 (sonochemistry , one stage, this research) 0.041 20.83 0.9909 GA-Fe3O4 (sonochemistry , two stage, this research) 0.034 1.62 0.9753 GA-Fe3O4 (conventional, one stage) Rahmayanti et al., 2016 0.019 2.33 0.968 Thus, it can be said that the adsorption of AuCl4 - on GA-Fe3O4-SK-1 and GA-Fe3O4-SK-2 is unlimited with the Ceyang concentration increasing. Besides, it is suspected that there are different types of active groups, GA-Fe3O4-SK-1 and GA-Fe3O4-SK-2, which play a role in the adsorption process of the active groups -COOH and -OH. Table 3. Comparison of Langmuir AuCl4 - Adsorption Isotherm Model Parameters on GA-Fe3O4 Adsorbate Langmuir Parameter qmax (mole/g) KL (L/mole) R2 GA-Fe3O4 (sonochemistry, one stage, this research) 0.000686 14430 0.8295 GA-Fe3O4 (sonochemistry, two stage, this research) 0.000546 12610 0.7524 GA-Fe3O4 (conventional, one stage) Rahmayanti et al., 2016 0.000600 17851 0.944 Compared with previous studies, namely the adsorption of AuCl4 - on GA-Fe3O4 synthesized conventionally/without ultrasonic waves (Rahmayanti et al., 2016), the adsorption isotherm similarly follows the Freundlich isotherm model. However, the KF value generated in this study on GA- Fe3O4-SK-1 and GA- Fe3O4-SK-2 was higher than the KF value of adsorption AuCl4 - on conventional synthesized GA- Fe3O4 (Tables 2 and 3). This result means that the sonochemically synthesized GA-Fe3O4 has a better adsorption ability for AuCl4 - than GA-Fe3O4 synthesized conventionally. CONCLUSION The effectiveness of magnetite-modified gallic acid (GA-Fe3O4) was synthesized by the sonochemical method (one and two steps) as AuCl4 - the adsorbent- reducing agent has been successfully studied through optimization studies of pH, time, kinetics, and adsorption isotherm. The acidity (pH) of the solution affects the ability of GA-Fe3O4 to adsorb AuCl4 -. The higher the pH, the lower the adsorption ability. The reaction time needed to achieve equilibrium in the AuCl4 - adsorption process on GA- Fe3O4-SK-1 and GA-Fe3O4-SK-2 is 60 minutes. Adsorption of AuCl4 - on GA-Fe3O4-SK-1 and GA-Fe3O4-SK-2 followed the pseudo-second-order kinetics model and Freundlich DOI: 10.30598//ijcr.2021.8-may 199 Maya Rahmayanti, et al. Indo. J. Chem. Res., 8(2), 194-201, 2021 isotherm model. Based on the characterization using FTIR and XRD, the predicted interactions that occur between AuCl4 - and GA- Fe3O4 are not only through the adsorption process but also followed by the reduction of Au(III) to Au(0). ACKNOWLEDGMENT The authors would like to thank the Chemical Laboratory of UIN Sunan Kalijaga, UGM Analytical Chemistry Laboratory, and LPPT UGM for the cooperation, services, and facilities. REFERENCES Fan, R., Xie, F., Guan, X., Zhang, Q., dan Luo Z., 2014. Selective Adsorption and Recovery of Au(III) from Three Kinds of Acidic Systems by Persimmon Residual Based bio-sorbent: A Method for Gold Recycling from E-Wastes, Bioresource Technol., 163, 167-171. Fitriani, D., 2020. Synthesis and Characterization of Gallic Acid-immobilized Mg/Al Hydrotalcite and Its Application as Adsorption-reduction of AuCl4 - . Thesis, Universitas Gadjah Mada, Yogyakarta. Ho,Y.S., 2004. Citation Review of Lagergren Kinetic Rate Equation on Adsorption Reactions, Journal Scientometrics, 59,171-177. Ho, Y.S., and McKay, G., 1999. Pseudo-second Order Model for Sorption Processes, Procedia Biochemistry, 34(5), 451-465. Latupeirissa, J., Tanasale, M.F.J.D.P., and Musa S.H., 2018. Kinetika Adsorpsi Zat Warna Metilen Biru Oleh Karbon Aktif Dari Kulit Kemiri (Aleurites moluccana (L) Willd), Indo. J. Chem. Res., 6(1), 12-21. Lone, S.H., Rehman, S.U., and Bhat, K.A., 2017. Synthesis of Gallic-acid-1-phenyl-1h-[1, 2, 3] triazol-4-yl-methyl esters as Effective Antioxidants, Drug Res., 11, 111-118. Paclawski, J., dan Fitzner, K., 2004. Kinetics of gold(III) Chloride Complex Reduction Using Sulfur(IV), Metall. Mater. Trans. B, 35B, 1071– 1085. Rahayu, Tanasale, M.F.J.D.P., and Bandjar, A., 2020. Isoterm Adsorpsi Ion Cr(III) Oleh Kitosan Hasil Isolasi Limbah Kepiting. Rajungan dan Kitosan Komersil. Indo. J. Chem. Res., 8(1), 28-34. Rahmayanti, M., Santosa, S. J., and Sutarno, 2015. Sonochemical Co-precipitation Synthesis of Gallic Acid-modified Magnetite, Adv. Mat. Res., 1101, 286-289. Rahmayanti, M., Santosa, S. J., and Sutarno, 2016. Comparative Study on the Adsorption of [AuCl]- onto Salicylic Acid and Gallic Acid Modified Magnetite Particles, Indones. J. Chem., 16(3), 329-337. Rahmayanti, M., Santosa, S.J., and Sutarno, 2016. Mechanisms of Gold Recovery from Aqueous Solutions using Gallic acid-modified Magnetite Particles Synthesized via Reverse Co- precipitation Method, Int. J. ChemTech Res. 9(4), 446-452. Rahmayanti, M., Abdillah, G., Santosa, S. J., and Sutarno, 2019. Application of Humic Acid Isolated From Kalimatan Peat Soil Modifying Magnetite for Recovery of Gold, Jurnal Bahan Alam Terbarukan, 8 (2):77-83. Rahmayanti, M., 2020. Recovery Emas dalam Sistem Au Tunggal dan Sistem Multilogam (Au/Cu) Menggunakan Adsorben Asam Askorbat Termodifikasi Magnetit, ALCHEMY Jurnal Penelitian Kimia, 16(2), 179-189. Santosa, S.J., Fitriani D., Aprilita, N.H., dan Rusdiarso, B., 2020. Gallic and salicylic acid-functionalized Mg/Al hydrotalcite as highly effective materials for reductive adsorption of AuCl4 -, Appl. Surf. Sci., 507, 145115. Santosa, S.J., Sudiono, S., Siswanta, D., Kunarti, E.S. dan Dewi, S.R., 2011. Mechanism of AuCl4 - Removal from Aqueous Solution by Means of Peat Soil Humin, Ads. Sci.Technol. 29(8), 733- 746. Santosa, S, J., 2014. Sorption Kinetics of Cd (II) Species on Humic Acid-Based Sorbent, Clean Journal Soil Air Water, 42(6), 760-766. Sharma, A., Gautam, S.P., and Gupta, A.K., 2011. Surface Modified Dendrimers: Synthesis and Characterization for Cancer Targeted Drug Delivery, Bioorganic Med. Chem., 19. Sekewael, S.J., Tehubijuluw, H., and Reawaruw, D.R., 2013. Kajian Kinetika dan Isoterm Adsorpsi Logam Pb pada Lempung Asal Desa Ouw Teraktivasi Garam Ammonium Nitrat, Ind.. J. Chem. Res., 1, 38-46. Wojnick, M., Rudnik, E., Luty-Błocho, M., Pacławski, K., and Fitzner, K., 2012. Kinetic Studies of Gold(III) Chloride Complex Reduction and Solid Phase Precipitation in Acidic Aqueous System Using Dimethylamine Borane as Reducing Agent, Hydrometallurgy, 127–128, 43– 53. DOI: 10.30598//ijcr.2021.8-may 200 Maya Rahmayanti, et al. Indo. J. Chem. Res., 8(2), 194-201, 2021 Yi, Q., Fan, R., Xie, F., Min, H., Zhang, Q., and Luo, Z., 2016. Selective Recovery of Au(III) and Pd(II) from Waste PCBs Using Ethylenediamine Modified Persimmon Tannin Adsorbent, Proc. Environ. Sci., 31, 185-194. Zahrani, A.A., El-Shishtawy, R.M., and Asiri, A.M., 2020. Recent Developments of Gallic Acid Derivatives and Their Hybrids in Medicinal Chemistry: A Review, Eur. J. Med. Chem., 204, 112609. DOI: 10.30598//ijcr.2021.8-may 201