Title Science and Technology Indonesia e-ISSN:2580-4391 p-ISSN:2580-4405 Vol. 7, No. 4, October 2022 Research Paper Hydrochar and Humic Acid as Template of ZnAl Layered Double Hydroxide for Adsorption of Phenol Muhammad Badaruddin1, Nur Ahmad2, Erni Salasia Fitri3, Aldes Lesbani2,4, Risfidian Mohadi1,4* 1Magister Programme Graduate School of Mathematics and Natural Sciences, Sriwijaya University, Palembang, South Sumatera, 30139, Indonesia2Graduate School of Mathematics and Natural Sciences, Faculty of Mathematics and Natural Sciences, Sriwijaya University, Palembang, South Sumatera, 30139, Indonesia3Magister Programme in Environment Management, Sriwijaya University, Palembang, South Sumatera, 30139, Indonesia4Research Center of Inorganic Materials and Coordination Complexes, Faculty of Mathematics and Natural Sciences, Sriwijaya University, Palembang, South Sumatera, 30139, Indonesia *Corresponding author: risfidian.mohadi@unsri.ac.id AbstractThe adsorbents potential ZnAl-LDH, ZnAl-Hydrochar, and ZnAl-Humic acid were prepared using the coprecipitation method. Theadsorbents were characterization by XRD, FTIR, and BET analysis. XRD peaks of ZnAl-LDH at 10.29°, 20.07°, 29.59°, 32.12°, 34.02°,48.06°, and 60.16°. The FTIR absorption peak was observed at 3400-3500 cm−1, 1600-1700 cm−1, 1381 cm−1, 1000 cm−1,500-700 cm−1. All adsorbents exhibited N2 adsorption-desorption isotherms type IV classified as a mesoporous structure (poresize= 2-50 nm). The surface areas of composites were higher than LDH and following order: ZnAl-Hydrochar > ZnAl-Humic acid >ZnAl-LDH. The kinetic parameter showed the pseudo-second-order kinetics model. The maximum adsorption capacity of ZnAl-LDH,ZnAl-Hydrochar, and ZnAl-Humic acid were 48.077 mg/g, 90.090 mg/g, 94.340 mg/g, respectively; with Freundlich isothermmodel. Reusability after 5 times of ZnAl-LDH, ZnAl-Hydrochar, and ZnAl-Humic acid in the range 49.81-0.890%, 95.92-9.84%, and70.02-5.72%, respectively. The adsorbent can be used up to 3 times. KeywordsHydrochar, Humic Acid, LDH, Adsorption, Phenol, Regeneration Received: 21 July 2022, Accepted: 8 October 2022 https://doi.org/10.26554/sti.2022.7.4.492-499 1. INTRODUCTION Water is a basic human need to carry out activities. Drink- ing water used must meet physical, chemical, and biological requirements. Recently, rivers as water sources have been pol- luted by various kinds of waste, ranging from household and industrial to domestic waste (Selvanathan et al., 2017). The waste is not handled correctly, so the water becomes polluted (Chaari et al., 2020). One of the most dangerous wastes for the aquatic environment is phenol waste. Several industries that have the potential to produce phenol waste include the petroleum rening, textile, gas, pharmaceutical, and petro- chemical industries, coal processing, pharmaceuticals, polymer resins, pesticides, and household industries that produce liquid phenol waste (Desmiarti et al., 2019; Zhang et al., 2021). Phenol is a dangerous organic compound with a high level of toxicity, which can cause harm to humans and biota (De la Luz-Asunción et al., 2015; Dehbi et al., 2020; Dehmani et al., 2021; Girish and Ramachandra Murty, 2014) and accumu- lates in the environment. The limit of phenol concentration is 1.0 mg/L in water (Xie et al., 2020). Thus, developing an eective treatment to removal of phenol is necessary before being discharged to environment. Various methods have been proposed for phenol wastewater treatment, including oxidation, membrane separation, biodegradation, ion exchange, and ad- sorption (Tshemese et al., 2021). Adsorption is one technique for removal of phenol because it is fast, cost-eective, easy han- dling, regeneration, high selectivity, and high eciency(Badhai et al., 2020; Ho and Adnan, 2021). One of the materials used forwater treatment in the adsorp- tion process is layered double hydroxide (LDH). This material has become a material that has been widely developed because of its uniqueness and good absorption. Its application in wa- ter treatment as an adsorbent has excellent potential due to its low cost, exchangeable anionic features, and large surface area (Bouteraa et al., 2020; Zubair et al., 2021). According to Vithanage et al. (2020), LDH is adsorbent in water treatment applications to remove organic, inorganic species, dyestus, and toxic metal contaminants. Rathee et al. (2019) reported thatLDH,whichwasappliedasanadsorbent, had limitations in https://crossmark.crossref.org/dialog/?doi=10.26554/sti.2022.7.4.492-499&domain=pdf https://doi.org/10.26554/sti.2022.7.4.492-499 Badaruddin et. al. Science and Technology Indonesia, 7 (2022) 492-499 the regeneration process. Therefore, the double-layerhydroxyl needs to be modied with a carbon-based support material to form a composite. Layered double hydroxide NiAl, ZnAl, and MgAl compos- ited with carbon-based materials such as chitosan were eec- tively to remove congo red, and the ability of the composite to be used repeatedly was stable until the seventh cycle in the regeneration process (Siregar et al., 2021). Based on the liter- ature, it can be concluded that carbon-based supporting ma- terials to form composites, such as hydrochar and humic acid, are suitable for use in layered double hydroxide. According to Zubair et al. (2021), layered double hydroxide modied with carbon-based support material showed signicant results, namely an increase in physicochemical characteristics such as surface area, structural stability, functional groups, and the resulting adsorption characteristics. In this study, the synthesis of ZnAl-LDH using the copre- cipitation method and the preparation of ZnAl composites with hydrochar and humic acid were carried out. The synthe- sized and prepared materials were characterized using X-Ray Diraction (XRD), Fourier Transform Infra-Red (FTIR), and Brunauer Emmet Teller (BET). Furthermore, the material will beappliedasanadsorbent toadsorbphenolbystudyingvarious parameters including pH, contact time, temperatures, initial concentration, and regeneration. 2. EXPERIMENTAL SECTION 2.1 Chemicals and Instrumentation The chemicals were used, including zinc nitrate hexahydrate (Zn(NO3)2.6H2O),aluminumnitratenonahydrate (Al(NO3)3. 9H2O), sodium carbonate (Na2CO3), humic acid, hydrochar, hydrogenchloride (HCl), distilledwater(H2O),sodiumhydrox- ide(NaOH),phenol (C6H5OH),4-aminoantipyrine(C11H13N3 O), potassium hexacyanoferrate(III) (K3[Fe(CN)6]), and ac- etate buer solution (CH3COONa) pH 10. Instrumentation was used in this study, including X-Ray Diraction (XRD), Brunauer Emmet Teller (BET), and Fourier Transform Infra- Red (FTIR). 2.2 Synthesis of ZnAl-LDH ZnAl-LDH synthesis was carried out with 100 mL Zn(NO3)2. 6H2O 0.75 M mixed with 100 mL Al(NO3)3.9H2O 0.25 M, then dripped into 50 mL NaOH 2 M solution (Mohadi et al., 2022). The mixture was adjusted to pH 10, then stirred for 20 h at 353 K. After stirring, the precipitate was ltered and rinsed using distilled water to remove impurities. The precipitate was dried using an oven. 2.3 Preparation of ZnAl-Hidrochar and ZnAl-Humic Acid ZnAlcompositeswerepreparedusingthecoprecipitationmethod with constant pH. A total of 15 mL of 0.75 M Zn solution and 15 mL of 0.25 M Al solution were mixed, and the pH was adjusted to pH 10. The mixture was stirred for 1 h un- til homogeneous, and a gel was formed, then 3 g of humic acid/hydrochar was added. The solution was kept at 353 K for 3 days. The precipitate from the preparation was ltered and dried using an oven. 2.4 Adsorption of Phenol Phenol is a colorless solution, so it must be complexed before being measured using a UV-Vis spectrophotometer (Xie et al., 2020). 1 mL of phenol solution was put in a beaker, then 0.1 mL of 4-aminoantipyrine 2% was added, 0.1 mL of potassium hexacyanoferrate (III) 8%, 1 mL of pH 10 buer solution, and 3 mL of distilled water were added. Then homogenized and allowed to stand for 5 min. The maximum wavelength of phenol after complexing is 510 nm. 2.5 Eect of pH Adsorbent (0.05 g) was put into a 100 mL beaker lled with 50 mL of phenol solution, each at a concentration of 20 mg/L with a variation of pH 2-11 with stirring for 2 h. 2.6 Eect of Contact Time Adsorbent (0.05 g) was added to 50 mL of 20 mg/L phenol solution, then stirred with variations contact time (0-180 min). The adsorbent was separated from the phenol solution. 2.7 Eect of Initial Concentration and Temperatures Adsorbent (0.05 g) was added 50 mL of phenol solution with various initial concentrations (10 mg/L, 20 mg/L, 30 mg/L, 40 mg/L and 50 mg/L and various temperatures (303 K, 313 K, 323 K, and 333 K). The solution was stirred for 2 h. 2.8 Reusability of Adsorbents The adsorption process for phenol is carried out before being used repeatedly as an adsorbent. After that, the desorption of phenol solution using an ultrasonic device. The regeneration process is carried out by adding 50 mg/L of 50 mL phenol solution to adsorbent that has gone through the desorption process. 3. RESULT AND DISCUSSSION Figure 1. XRD Diractogram of Adsorbents © 2022 The Authors. Page 493 of 499 Badaruddin et. al. Science and Technology Indonesia, 7 (2022) 492-499 XRD patterns of ZnAl-LDH, ZnAl-Hydrochar, and ZnAl- Humic acid is displayed in Figure 1. ZnAl-LDH peaks at 10.29°, 20.07°, 29.59°, 32.12°, 34.02°, 48.06°, and 60.16° were indexed to (003), (006), (101), (012), (015), (107), and (110) corresponding to JCPDS No 05-0669 (Elhalil et al., 2017). The peaks at 10.29° and 60.16° indicated the anion in the interlayer of layered double hydroxide. After ZnAl-LDH was composited with hydrochar and humic acid, the peak at 20.3° indicated the humic acid, while the diraction peaks of hydrochar at peaks 18.0°. The characteristic peaks of the constituents ZnAl-LDH, hydrochar, and humic acid indicated that the preparation of the composite has been successful. Figure 2. FTIR Spectra of Adsorbents Figure 2 shows the FTIR spectra of ZnAl-LDH, ZnAl- Hydrochar, and ZnAl-Humic acid. The absorption peak was observed at 3400-3500 cm−1 assigned to O-H vibration from water in LDH (Li et al., 2020). The peak at 1600-1700 cm−1 indicated vibration of -OH and carbonyl (COO) (Rashid et al., 2017). The peak at 1381 cm−1 corresponds to N-O from ni- trate (Palapa et al., 2021). The new peak around 1000 cm−1 at ZnAl-Hydrochar and ZnAl-Humic acid indicated C-O stretch- ing from hydrocharand humic acid (Lu et al., 2019; Shao et al., 2022). The peak at 500-700 cm−1 assigns to metal-oxide in LDH (Ahmad et al., 2022b). Textural properties of ZnAl-LDH, ZnAl-Hydrochar, and ZnAl-Humic acid give in Figure 3. All adsorbents exhibited N2 adsorption-desorption isotherms type IV classied as a meso- porous structure (pore size = 2-50 nm) (Cao et al., 2022). In line with the data in Table 1, the pore size of adsorbent is 4-27 nm. The surface areas of composites were higher than LDH and were in the following order: ZnAl-Hydrochar > ZnAl-Humic acid > ZnAl-LDH. The pore volume of ZnAl- Hydrochar was higher than ZnAl-Humic acid and ZnAl-LDH. Thus, the surface area is directly proportional to the pore vol- ume. The eect of pH in adsorption phenol was displayed in Figure 4. pH is one of the key parameters in adsorption. pH Figure 3. N2 Adsorption-desorption Isotherms Figure 4. Eect of pH optimum of ZnAl-LDH, ZnAl-Hydrochar, and ZnAl-Humic acid was at pH 4, 2, and 2, respectively. Under acidic condi- tions, phenol adsorption is better because the phenol molecules do not dissociate, thereby reducing electrostatic repulsion and hydrogenbondingbeing theprimaryinteraction (Asnaouietal., 2022). Kinetic parameters adsorption of phenol is shown in Figure 5. The pseudo-rst-order (PFO) and pseudo-second-order (PSO) kinetic models were determined through the highest linear regression value. Based on Table 2, ZnAl-LDH, ZnAl- Hydrochar, and ZnAl-Humic acid followed the PSO kinetics model (R2 closer to 1). PSO model assumes that the active site of the adsorbent is available more than the possible bond between the adsorbent and the adsorbate that occurs (de Farias et al., 2022). Determination isotherm model seen the linear regression value (R2) which is closer to 1. ZnAl-LDH, ZnAl-Hydrochar, and ZnAl-Humic acid tend to follow the Freundlich isotherm model because the R2 value is closer to 1 compared to the © 2022 The Authors. Page 494 of 499 Badaruddin et. al. Science and Technology Indonesia, 7 (2022) 492-499 Figure 5. Eect of Contact Time Table 1. BET Analysis of Adsorbents Adsorbents Surface Area Pore Size Pore Volume (m2/g) (nm), BJH (cm3/g), BJH ZnAl-LDH 1.968 27.687 0.006 ZnAl-Hydrochar 29.874 24.420 0.042 ZnAl-Humic Acid 16.425 4.811 0.039 Table 2. Kinetics Parameters the Adsorption Process Kinetic Parameters Adsorbents Parameter ZnAl-LDH ZnAl- Hydrochar ZnAl-Humic Acid PFO Qeexp (mg/g) 46.845 52.228 48.627 Qecalc (mg/g) 48.228 44.627 41.295 k1 (min−1) 0.033 0.034 0.034 R2 0.965 0.989 0.969 PSO Qeexp (mg/g) 46.845 52.228 48.627 Qecalc (mg/g) 56.644 59.524 56.497 k2 (min−1) 0.001 0.001 0.001 R2 0.993 0.993 0.986 © 2022 The Authors. Page 495 of 499 Badaruddin et. al. Science and Technology Indonesia, 7 (2022) 492-499 Table 3. Isotherm Parameters the Adsorption Process Adsorbents Langmuir Freundlich T (K) Qmax kL R2 n kF R2 ZnAl-LDH 303 20.492 0.167 0.974 5.149 15.765 0.994 313 48.077 0.063 0.844 1.866 5.338 0.847 323 43.487 0.140 0.930 2.482 9.643 0.822 333 42.553 0.332 0.984 3.221 15.191 0.855 ZnAl-Hydrochar 303 27.027 0.019 0.961 1.989 6.703 0.947 313 85.470 0.012 0.956 1.164 2.078 0.957 323 75.188 0.038 0.7984 1.473 4.248 0.954 333 90.090 0.071 0.8516 1.900 7.579 0.943 ZnAl-Humic Acid 303 26.882 0.078 0.969 3.837 12.552 0.989 313 44.444 0.053 0.944 1.678 4.281 0.975 323 64.935 0.049 0.900 1.616 5.018 0.962 333 94.340 0.077 0.911 1.987 8.468 0.968 Table 4. Several Adsorbents to Adsorption of Phenol Adsorbent Qmax (mg/g) References Lignite 6.216 (Liu et al., 2021) Tea waste biomass 7.62 (Gupta and Balomajumder, 2015) MAG-CTAB-KH550 56.13 (Ge et al., 2018) Bentonite 23.64 (Ahmadi and Igwegbe, 2018) Fe-Biochar 39.23 (Dong et al., 2021) ZnCl2-BFAC 17.02 (Sathya Priya and Sureshkumar, 2020) Claried sludge from basic oxygen furnace 1.052 (Mandal and Das, 2019) 𝛼-Fe2O3 21.93 (Dehmani and Abouarnadasse, 2020) Activated carbon 75.81 (da Silva et al., 2022) ZnAl-LDH 48.077 This study ZnAl-Hydrochar 90.090 This study ZnAl-Humic Acid 94.340 This study Table 5. Adsorption Thermodynamic Parameter Adsorbents ΔH (kJ/mol) ΔS (J/K.mol) ΔG (kJ/mol) R2 303 K 313 K 323 K 333 K ZnAl-LDH 51.180 0.171 -0.586 -2.294 -4.003 -5.711 0.985 ZnAl-Hydrochar 33.152 0.110 -0.224 -1.326 -2.427 -3.529 0.993 ZnAl-Humic Acid 33.821 0.133 -0.488 -1.620 -2.752 -3.885 0.988 © 2022 The Authors. Page 496 of 499 Badaruddin et. al. Science and Technology Indonesia, 7 (2022) 492-499 Langmuir isotherm model (See Table 3). Freundlich isotherm assumes that the adsorption process is physisorption and occurs in multilayers (Jain et al., 2022). The maximum adsorption ca- pacity of ZnAl-LDH, ZnAl-Hydrochar, and ZnAl-Humic acid were 48.077 mg/g, 90.090 mg/g, 94.340 mg/g, respectively. The comparison of adsorption capacity with other adsorbents can be seen in Table 4. The thermodynamic parameters determined in the adsorp- tion includeenthalpy(ΔH),entropy(ΔS),andGibbs freeenergy (ΔG) as presented in Table 5. The enthalpy (ΔH) is positive in the range of 31-51 kJ/mol, this indicates that the reaction that occurs is endothermic (Dehmani et al., 2020). The entropy (ΔS) is positive in the range of 0.110 - 0.171 J/mol.K, this indicates that the degree of disorder is small during the adsorp- tion process (Zhang et al., 2022). The Gibbs free energy (ΔG) is negative, indicating that adsorption of phenol is spontaneous (Ahmad et al., 2022a). Figure 6. Reusability of Adsorbents Reusabilityofadsorbent is therepeateduseof theadsorbent byremovingtheadsorbatefromtheadsorbent (Quetal.,2022). Based on Figure 6, reusability after 5 times of ZnAl-LDH, ZnAl-Hydrochar, and ZnAl-Humic acid in the range 49.81- 0.890%, 95.92-9.84%, and 70.02-5.72%, respectively. The percentageofreusabilitydecreaseswith thefrequentadsorption process. The adsorbent can be used up to 3 times. 4. CONCLUSION In summary, ZnAl-LDH, ZnAl-Hydrochar, and ZnAl-Humic acid were successfully prepared. The adsorbents were charac- terization by XRD, FTIR, and BET analysis. The maximum adsorption capacity is 94.340 mg/g on ZnAl-Humic acid. Pa- rameters such as pH, contact time, concentration, temperature, and regeneration aected to adsorption process. 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Page 499 of 499 INTRODUCTION EXPERIMENTAL SECTION Chemicals and Instrumentation Synthesis of ZnAl-LDH Preparation of ZnAl-Hidrochar and ZnAl-Humic Acid Adsorption of Phenol Effect of pH Effect of Contact Time Effect of Initial Concentration and Temperatures Reusability of Adsorbents RESULT AND DISCUSSSION CONCLUSION ACKNOWLEDGMENT