Binder-free production of 3D N-doped porous carbon cubes for efficient Pb 2þ removal through batch and fixed bed adsorption Sandesh Y. Sawant a , Radheshyam R. Pawar b , Seung-Mok Lee b, ** , Moo Hwan Cho a, * a School of Chemical Engineering, Yeungnam University, Gyeongsan-si, Gyeongbuk 712-749, Republic of Korea b Department of Energy and Environment Convergence Technology, Catholic Kwandong University, Gangneung, 210701, Republic of Korea article info Article history: Received 30 April 2017 Received in revised form 7 August 2017 Accepted 24 August 2017 Available online 4 September 2017 Keywords: 3D adsorbent Water treatment Pb 2þ adsorption N-doped carbon Carbon cubes abstract N-doped carbon cubes (NCCs) with varying nitrogen contents and different densities were fabricated using a simple and binder-free method that involved the curing of resorcinol-formaldehyde (RF) gel with different RF contents in the framework of a melamine sponge. In addition to the robust structure and nitrogen doping, the porosity of the NCCs could be tailored easily within the mesopores and ultra- micropores with a unique combination of macro, meso, and micropores. The prepared NCCs exhibited excellent uptake capacity, ranging from 32.1 to 39.3 mg/g Pb 2þ ions, owing to their high surface area (up to 675 m 2 /g) and nitrogen doping (max. 4.9 wt. %). The Pb 2þ adsorption property of NCC-10 was also compared with that of widely used commercial 3D carbon adsorbents. The weight and surface area- normalized Pb 2þ adsorption capacity of NCC-10 was found to be 3.7 and 6.6 times higher, respectively than the commercial activated carbon granules. The continuous mode model data fitted with experi- mental fixed-bed results well, and showed 8.95 mg/g loading capacity, proving that NCC-10 is an effective 3D adsorbent. The prepared NCCs could be used as a practical adsorbent for the removal of Pb 2þ ions because of their high adsorption capacity, easy regeneration, and exceptional stability maintained after longer reuse. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction Water pollution originating from Pb 2þ ion contamination is a major global concern because of its serious consequences for human's health. Acute exposure to Pb 2þ may cause gastrointestinal disturbances, hepatic and renal damage, hypertension, and neurological effects which may lead to convulsions and death (J€ arup, 2003). In addition to occupational exposure, Pb 2þ -contam- inated food, dust, and drinking water are the major sources of Pb 2þ exposure. According to the Institute for Health Metrics and Evalu- ation, more than half million deaths per year are caused by the Pb 2þ exposure which has prompted research into the removal Pb 2þ from water. Among the different methods of Pb 2þ -contaminated water treatment, including precipitation-coagulation, electrodialysis, and membrane separation, adsorption is considered the easiest, economical and effective technique for Pb 2þ removal (Kurniawan et al., 2006; Pawar et al., 2016a). Different choices of adsorbent, such as clays, activated carbon, metal hydroxides, zeolites, resins, and bio-sorbents, are available for the effective removal of Pb 2þ (Fu and Wang, 2011; Madadrang et al., 2012). Carbon-based adsorbents have the several advantages, such as chemical stability, low cost, and high adsorption capacity compared to other adsorbents (Radovic et al., 2001; Sawant et al., 2017). In addition to the superior porosity, carbon-based adsorbents offer a robust surface texture that can be tailored easily with different surface functional groups for enhanced Pb 2þ adsorption (Bhatnagar et al., 2013). N-doping/ functionalization has been found to be an effective way to enhance the Pb 2þ adsorption capacity of adsorbents (Yang et al., 2015). Recently, nanomaterial-based adsorbents have also been demon- strated for Pb 2þ removal but their practical applicability is still debatable because of their high cost and biocompatibility (Guo and Mei, 2014). A literature survey reported that the development of Pb 2þ removal adsorbents was performed mostly on the powdered adsorbents (Bailey et al., 1999; Hua et al., 2012). The direct appli- cation of powder adsorbents for water treatment is inconvenient and it has a disadvantage in a column experiment due to cracking in the bed and back pressure due to blockage in the column. These * Corresponding author. ** Corresponding author. E-mail addresses: leesm@cku.ac.kr (S.-M. Lee), mhcho@ynu.ac.kr (M.H. Cho). Contents lists available at ScienceDirect Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro http://dx.doi.org/10.1016/j.jclepro.2017.08.229 0959-6526/© 2017 Elsevier Ltd. All rights reserved. Journal of Cleaner Production 168 (2017) 290e301