Green Process Synth 2017; 6: 565–576 Hai Nguyen Tran, Fu-Chuang Huang, Chung-Kung Lee and Huan-Ping Chao* Activated carbon derived from spherical hydrochar functionalized with triethylenetetramine: synthesis, characterizations, and adsorption application DOI 10.1515/gps-2016-0178 Keywords: activated carbon; dye; glucose; heavy metal; Received October 15, 2016; accepted January 2, 2017; previously hydrochar; triethylenetetramine. published online March 6, 2017 Abstract: This study investigated the adsorption capacities of various contaminants on glucose-derived hydrochar (GH) and glucose-activated carbon (GAC) 1 Introduction functionalized with triethylenetetramine (TETA). The Activated carbon (AC), with its exceptionally large specific two-stage synthesis process consisted of (1) hydrother- surface area, high pore volume, well-developed inter- mal carbonization using various TETA concentrations nal porous structure, and abundant surface functional (1%–5%) to create TETA-functionalized GHs, and (2) groups (polar characters), has been widely applied in chemical activation with NaOH to produce TETA-GACs. various industrial processes. In water treatment, ACs are The basic properties of the adsorbents were examined considered effective adsorbents for the removal of various using Brunauer-Emmett-Teller (BET) surface area analy- organic contaminants. According to an industry market sis, Fourier transform infrared (FTIR) spectrometry, scan- research report [1], the global demand for AC is estimated ning electron microscopy (SEM), and energy dispersive to increase 8.1% per year, and be up to 2.1 million metric X-ray (EDX) spectroscopy. The adsorption characteristics tons by 2018. Nevertheless, the high cost of commercial of the GH and GAC samples toward two heavy metal ions ACs restricts their large-scale use in industries. (Pb2 + and Cu2 +), phenol, methylene green (MG5), and acid Notably, the morphology of AC plays a key role in red 1 (AR1) were also examined. The results indicated that its application; various conformations comprise pow- GAC and GH exhibited excellent adsorption capaci- 1% 1% dered and granular AC, AC fibers, carbon monoliths, ties. Specifically, the maximum adsorption capacities of carbon hollow spheres, carbon nanotubes, and, carbon GAC and GH reached 370 mg/g and 128 mg/g for Pb2 +, 1% 1% spheres [2]. Spherical carbon can be obtained through 208 mg/g and 84 mg/g for Cu2 +, 196 mg/g and 137 mg/g hydrothermal carbonization of diverse organic materials for phenol, 175 mg/g and 67 mg/g for MG5, and 156 mg/g (polyvinylpyrrolidone, sucrose, xylose, fructose, furfural, and 21 mg/g for AR1, respectively. In conclusion, amine glucose, starch, saccharose, and cellulose) in a controlled functionalization on the surface of GHs and GACs effi- temperature autoclave (150–350°C) for 2–48 h at a specific ciently enhances the removal capacities of various con- pressure for producing hydrochar spherical microparti- taminants in water. cles [3–6]. Hydrochars have been commonly tailored for manufacturing ACs with desired characteristics because of the unique attributions of hydrochar – namely a high *Corresponding author: Huan-Ping Chao, Department of density of oxygenated functional groups and a low Environmental Engineering, Chung Yuan Christian University, degree of condensation and impurity [3]. Compared with Chungli 32023, Taiwan, e-mail: [email protected] Hai Nguyen Tran: Department of Civil Engineering, Chung Yuan other ACs, spherical ACs exhibit several enhanced char- Christian University, Chungli 32023, Taiwan; and Department acteristics such as high wear resistance, high mechani- of Environmental Engineering, Chung Yuan Christian University, cal strength, superior adsorption, high purity, low ash Chungli 32023, Taiwan content, smooth surface, low pressure drop, high bulk Fu-Chuang Huang: Department of Environmental Technology and density, high micropore volume, and controllable pore Management, Taoyuan Innovation Institute of Technology, Chung-Li, 32091, Taiwan size distribution [2, 3]. Chung-Kung Lee: Department of Environmental Engineering, Vanung D-glucose (a simple carbohydrate) is the most abun- University, Chung-Li, 32061, Taiwan dant sugar unit in biomass, and it is the major product 566 H. N. Tran et al.: Activated carbon derived from spherical hydrochar functionalized with triethylenetetramine of lignocellulosic biomass acid hydrolysis. There- synthesized through a NaOH chemical activation of the fore, D-glucose is the most used precursor to produce GH samples; GH and GAC samples without TETA modifi- hydrothermal carbonization [4]. A review of the extant cation were also simultaneously prepared. In addition, literature revealed that the adsorption capacity of glu- the basic properties of the adsorbents were examined cose-derived carbon spheres is enhanced by modifying using several techniques (i.e. Brunauer-Emmett-Teller their surfaces with various surfactants. For example, [BET] surface area, Fourier transform infrared [FTIR], Demir-Cakan and others [7] prepared carbonaceous and scanning electron microcopy-energy dispersive materials (hydrochar) through the hydrothermal car- X-ray [SEM-EDX] analyses). Furthermore, the adsorption bonization of glucose in the presence of acrylic acid, behaviors of GHs and GACs with and without a TETA- and they concluded that carboxylate-rich absorbents functionalized surface for two heavy metals (Pb2 + and were successfully employed for the removal of Cd2 + and Cu2 +), phenol, a basic dye (methylene green 5 [MG5]), Pb2 + from water. Wang and coworkers [8] reported on a and an acid dye (acid red 1 [AR1]) were conducted in one-step hydrothermal preparation of amino-function- batch experiments. alized carbon spheres (hydrochar) by mixing a glucose– ammonia solution at low temperature to improve their adsorption performance toward Cr(VI). Various nitrogen sources, derived from nitrogen gas, 2 Materials and methods ammonia, ammonia gas, amines, urea, pyridine, ace- 2.1 Preparation of adsorbents tonitrile, melamine, dimethylformamide, 2-amino-4,6-di- chloro-s-triazine, benzylamine, triethylenetetramine The synthesis processes of carbonaceous adsorbents with and with- (TETA), ethylenediamine, and polyazomethineamide, out surface modification are illustrated in Figure 1. First, a mixture of have been used for synthesizing nitrogen-doped porous glucose and TETA powders (purchased from Merck) was completely carbons [8–13]. Of these, TETA has been widely applied as dissolved in 150 ml of distilled water and then transferred into a 200- an effective cationic surfactant to modify an adsorbent’s ml Teflon-lined autoclave. Mass ratios of glucose and TETA ranging surface; for example the effective adsorption of Cu2 +, Cd2 +, from 1% to 5% were used for the modification. After a 48-h hydrother- mal process at 190°C, the remaining brown precipitate (hydrochar) and Pb2 + from aqueous solutions by both succinylated particles were separated using vacuum filtration, washed repeatedly twice-mercerized sugarcane bagasse and succinylated with a 95% alcohol solution, and then washed in the distilled water mercerized cellulose modified with TETA has been pro- until the pH of the filtrate reached approximately 7.0. The hydrochar posed by [12, 13]. Karnitz and colleagues [10] also com- samples were then collected and dried in an oven at 105°C for 24 h. pared the adsorption capacities of Cu2 +, Cd2 +, and Pb2 + For convenience, the GH samples modified with TETA were labeled from aqueous systems by sugarcane bagasse chemically modified with the polyamines ethylenediamine and TETA. In addition, Barsanescu and colleagues [14] investigated Glucose the effectiveness of using acrylic copolymer prepared Glucose (%)/TETA (%) = from organic matrices with distinct crosslinking degrees, (95/5; 96/4; 97/3; 98/2; 99/1) followed by ethylenediamine and TETA functionalization 2 + Triethylentetramine on the surface to remove Zn ions. However, the char- Water (TETA) acterizations of TETA-modified spherical and activated carbons derived from glucose and the efficiency of these Hydrothermal adsorbents toward the removal of organic and inorganic (190°C, 48 h) contaminants have not been examined and reported Hydrochar Hydrochar (GH , GH , elsewhere. (GH ) 1% 2% 0% GH , GH , GH ) The current study synthesized a TETA-modified 3% 4% 5% adsorbent to determine the adsorption of inorganic and Pyrolysis 5% NaOH organic compounds from aqueous solutions. Glucose- (800°C, 3 h) 5% NaOH derived hydrochar (GH) samples, functionalized with Activated carbon various TETA concentrations (1%–5%), were prepared Activated carbon (GAC1%, GAC2%, GAC3%, (GAC0%) through hydrothermal carbonization of the glucose- GAC4%, GAC5%) TETA mixture, and they were subsequently used as the precursors to produce glucose-AC (GACs). The GAC Figure 1: Schematic illustration of the preparation procedure for the samples with nitrogen groups on their surface were adsorbents. H. N. Tran et al.: Activated carbon derived from spherical hydrochar functionalized with triethylenetetramine 567 GH , GH , GH , GH , and GH , according to the ratio of TETA to 5% 4% 3% 2% 1% 3 Results and discussion glucose. A GH sample without TETA (GH0%) was synthesized under the same conditions. The AC was prepared by first impregnating approximately 10 g of the hydrochar sample with 100 ml of NaOH solution (5%). Next, 3.1 Characterization of adsorbents the mixture of hydrochar and NaOH was dried in an oven at 105°C until the solution completely evaporated. The pyrolysis process was 3.1.1 Textural