Pyrolysis reaction of squaric acid: A one-step method for producing expanded foam of mesoporous carbon Mélody Leclère a,b,e , Michaël Lejeune c , Loïc Dupont a,e , Anne-Lise Barrès d,e , Stéven Renault a,b,e,1 , Franck Dolhem b,e , Philippe Poizot a,d,e,n a Laboratoire de Réactivité et Chimie des Solides (LRCS), UMR CNRS 7314, 33 rue Saint-Leu, 80039 Amiens Cedex, France b Laboratoire de Glycochimie, des Antimicrobiens et des Agroressources (LG2A), FRE CNRS 3517, 33 rue Saint-Leu, 80039 Amiens Cedex, France c Laboratoire de Physique de la Matière Condensée (LPMC), EA 2081, 80039 Amiens Cedex, France d Institut des Matériaux Jean Rouxel (IMN), UMR CNRS 6502, 2 rue de la Houssinière, B.P. 32229, 44322 Nantes Cedex 3, France e Réseau sur le Stockage Electrochimique de l'Energie (RS2E), France article info Article history: Received 28 June 2014 Accepted 28 August 2014 Available online 6 September 2014 Keywords: Squaric acid Carbon materials Porous materials Mesoporous carbon Oxocarbon pyrolysis abstract A template-free approach is described for the synthesis of expanded foams of mesoporous carbon exhibiting high surface areas ranging from 550 to 1100 m 2 g À1 . The procedure is based on the exceptional carbonization reaction that occurs with squaric acid (H 2 C 4 O 4 ), a strained four-membered carbocycle belonging to the oxocarbon acids. Indeed the pyrolysis reaction proceeds just above 300 1C through an amazing one-step and sharp exothermic phenomenon coupled with a weight loss of 90%, thereby promoting a porous structure. This massive gas release behaves also as a “fluid” template during the carbon production, which explains the formation of expanded foams. This particular thermal behaviour seems related to the phase transition that occurs in H 2 C 4 O 4 crystals at T c ¼121 1C. Below T c the planar squaric acid molecules exhibit a fully ordered structure in a monoclinic system whereas for T 4T c the structure undergoes a disordered tetragonal structure where all C–O bonds of squaric acid become statistically equivalent in a perfect square, making a discrete thermal decomposition reaction possible. & 2014 Elsevier B.V. All rights reserved. 1. Introduction The pyrolytic decomposition of organic precursors constitutes a common synthesis route for producing a large variety of carbona- ceous materials with various structures and morphologies depend- ing on the used experimental conditions. In particular numerous mesoporous carbon materials can be prepared in this way, which are usually characterized by high surface areas and high pore volumes [1]. Basically, the mesostructure is the result of a templating effect that often involves the use of pre-synthesized inorganic or organic templates of various degrees of complexity. With organic precursors, many other original strategies are also known [1,2] such as the elegant concept of the polymer blend carbonization method proposed by Ozaki et al. in 1997 [3]. In the latter case, two polymers of appropriate mutual affinity but with different degrees of thermal stability (one of them tends to carbonize at high temperatures while the other decomposes into gaseous products) are first intimately mixed. The as-obtained nanostructured precursor phase serves then as a template of the target mesoporous carbon material, which is obtained by pyrolysis accompanied by volatilization of the sacrificial polymer. Herein, we report in fact a variation of this former approach. However, in the present case, both carbon source and gas pre- cursors (sacrificial atoms) are directly included at the molecular level within a single compound. Revisiting the chemistry of cyclic oxocarbons for the past few years [4,5], we realized indeed that the simple pyrolysis reaction of squaric acid (H 2 C 4 O 4 , 3,4-dihy- droxycyclobut-3-ene-1,2-dione) for T 4300 1C induces the spon- taneous production of expanded foam of mesoporous carbon [6]. The specific feature of this carbonization process as well as morphological/structural properties of the as-obtained carbona- ceous materials is presented and discussed herein based on four relevant pyrolysis temperatures (400, 600, 800 and 965 1C). 2. Results and discussion In a typical procedure, 0.5 g of squaric acid was placed into a quartz tubular furnace under Ar or N 2 . The pyrolysis program Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/matlet Materials Letters http://dx.doi.org/10.1016/j.matlet.2014.08.148 0167-577X/& 2014 Elsevier B.V. All rights reserved. n Corresponding author at: Institut des Matériaux Jean Rouxel (IMN), UMR CNRS 6502, 2 rue de la Houssinière, B.P. 32229, 44322 Nantes Cedex 3, France. Tel.: þ33 2 40 37 39 41; fax: þ33 2 40 37 39 95. E-mail address: Philippe.Poizot@cnrs-imn.fr (P. Poizot). 1 S. R. is currently at Uppsala University (Department of Chemistry - Ångström Laboratory, Structural Chemistry) – Sweden. Materials Letters 137 (2014) 233–236