Research article Fast and efficient adsorption of methylene green 5 on activated carbon prepared from new chemical activation method Hai Nguyen Tran a, b, * , Sheng-Jie You b, * , Huan-Ping Chao b, * a Department of Civil Engineering, Chung Yuan Christian University, Chungli 320, Taiwan b Department of Environmental Engineering, Chung Yuan Christian University, Chungli 320, Taiwan article info Article history: Received 20 September 2016 Received in revised form 1 December 2016 Accepted 3 December 2016 Keywords: Activated carbon Golden shower Chemical activation Methylene green 5 Adsorption mechanism Oxygenation method abstract Activated carbon (AC) was synthesized from golden shower (GS) through a new chemical activation process. The three-stage process comprised (1) hydrothermal carbonization of GS to produce hydrochar, (2) pyrolysis of hydrochar to produce biochar, and (3) subsequent chemical activation of biochar with K 2 CO 3 to obtain GSHBAC. The traditional synthesis processes (i.e., one-stage and two-stage) were also examined for comparison. In the one-stage process, GS that was impregnated with K 2 CO 3 was directly pyrolyzed (GSAC), and the two-stage process consisted of (1) pyrolytic or hydrothermal carbonization to produce biochar or hydrochar and (2) subsequent chemical activation was defined as GSBAC and GSHAC, respectively. The synthesized ACs were characterized by scanning electron microscope, Brunauer eEmmetteTeller (BET) surface area analysis, Fourier transform infrared spectrometry, point zero charge, and Boehm titration. The adsorption results demonstrated that the MG5 adsorption process was not remarkably affected by neither the solution pH (2.0e10) nor ionic strength (0e0.5 M NaCl). Kinetic studies showed that the adsorption equilibrium was quickly established, with a low activation energy required for adsorption (Ea; 3.30e27.8 kJ/mol), and the ACs removed 50e73% of the MG5 concentration from solution within 01 min. Desorption studies confirmed the adsorption was irreversible. Thermo- dynamic experiments suggested that the MG5 adsorption was spontaneous (DG  ) and endothermic (þDH  ), and increased the randomness (þDS  ) in the system. Although the specific surface areas of the ACs followed the order GSAC (1,413) > GSHAC (1,238) > GSHBAC (903) > GSBAC (812 m 2 /g), the maximum adsorption capacities determined from the Langmuir model (Q o max ) at 30  C exhibited the following order: GSHBAC (531) > GSAC (344) > GSHAC (332) > GSBAC (253 mg/g). Oxygenation of the ACs' surface through a hydrothermal process with acrylic acid resulted in a decrease in MG5 adsorption and identified the importance of p-p interactions to the adsorption process. The primary interactions in MG5 adsorption were p-p interactions and pore filling, while hydrogen bonding and n-p interactions were minor contributors. The three-stage process can be regarded as the effective preparation method of AC with a high adsorption capacity toward the cationic dye. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Activated carbon (AC) with exceptionally large specific surface area, high pore volume, well-developed internal porous structure, relative chemical stability, high thermal stability, and abundant surface functional groups, has been widely applied in various in- dustrial processes. In water treatment, ACs can be considered as effective adsorbents for the removal of various organic and inor- ganic contaminants. According to an industry market research report (Freedonia, 2014), world demand for AC is estimated to in- crease 8.1 percent per year to 2.1 million metric tons in 2018. ACs can be synthesized through two well-known processes: physical and chemical activation. The chemical activation process can be conducted using one or two stage process. One-stage pro- cess is the most common method in which the raw materials are directly mixed with certain activating reagents and then the resulting mixture is pyrolyzed. By contrast, the two-stage process comprises (1) a precarbonization process (i.e., pyrolysis or * Corresponding authors. Department of Environmental Engineering, Chung Yuan Christian University, Chungli 320, Taiwan. E-mail addresses: trannguyenhai2512@gmail.com (H.N. Tran), sjyou@cycu.edu.tw (S.-J. You), hpchao@cycu.edu.tw (H.-P. Chao). Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman http://dx.doi.org/10.1016/j.jenvman.2016.12.003 0301-4797/© 2016 Elsevier Ltd. All rights reserved. Journal of Environmental Management 188 (2017) 322e336