Preparation of porous carbons from phenol–formaldehyde resins with chemical and physical activation

Designing Nanostructured Carbon Xerogels

“…(Czzakel et al, 2005;Dingcai & Rouwen, 2006;Long et al, 2008aLong et al, , 2008bPekala et al, 1995 ;Scherdel & Reichenauer, 2009). Amongst all the possible variations, probably the most commonly synthesized carbon gels are those based on resorcinol and formaldehyde, although in order to reduce the cost of the materials involved in the synthesis process, some less expensive precursors, such as phenol (Mukai et al, 2005a;Scherdel & Reichenauer, 2009;Teng & Wang, 2000) or cellulose (Gryzb et al, 2010), have attracted interest in recent years. Another important parameter for the preparation of carbon gels is the reaction media because there are several available solvents such as deionised water (Job et al, 2004;Pekala, 1989;Zhu et al, 2007), acetone (Berthon et al, 2001) or methanol (Zubizarreta et al, 2008a).…”

“…One of the main disadvantages of this type of activation, apart from the higher cost of the activating agents (KOH, H 3 PO 4 vs. CO 2 and steam water, for instance), is the washing stage since, in addition to lengthen the process, sometimes it is extremely difficult to completely remove all the traces of the residual activating agent. Despite these drawbacks, chemical activation has several advantages compared to physical activation including the lower temperature and activation time, higher yield and higher development of porosity achieved (Lozano-Castelló, 2002;Molina-Sabio et al, 2004;Teng & Wang, 2000). Physical activation consists of (i) thermal treatment of the precursor in an inert atmosphere and the successively controlled gasification of the carbonaceous material or (ii), the direct activation of the raw material in the presence of the activating gas.…”

“…Most of published works on carbon gels used in catalysis field are focused on heterogeneous processes and the great interest of carbon gels in this field research is due to their attractive features such as: tailored pore texture, possibility of enriching their surface chemistry by different processes, high packing density, high durability under harsh conditions, etc. (Cotet et al, 2006;Job et al, 2005;Moreno-Castilla et al, 1999;Teng & Wang, 2000). The major challenge in catalysis, together with the reduction of costs is to increase their activity and selectivity.…”

“…Basically, an organic gel is a solid nanostructure comprised of nano-sized pores and interlinked primary particles obtained by means of polymerization reactions between hydroxylated benzenes and aldehydes, and then subjected to a drying process. The most commonly used monomers are resorcinol and formaldehyde (Al-Mutasheb & Ritter, 2003;Czzakel et al, 2005;Job et al, 2004;Tian et al, 2011a;Zhang et al, 2007;Zhu et al, 2007;Zubizarreta et al, 2008a) but, there are other potential combinations such as phenol/formaldehyde (Mukai et al, 2005a;Scherdel & Reichenauer, 2009;Teng & Wang, www.intechopen.com Nanomaterials 188 2000), phenol/furfural (Dingcai & Ruowen, 2006;Long et al, 2008a;Pekala et al, 1995), phenol/melamine/formaldehyde (Long et al, 2008b), cresol/formaldehyde (Li et al, 2001;Zhu et al, 2006), etc. As shown in Figure 1, the formation of organic gels involves the following stages: (i) formation of a three-dimensional polymer in a solvent, known as gelation step, (ii) curing period where the crosslinking of previously formed polymer clusters (particles) takes place and, finally, (iii) drying step, that can be performed under subcritical, supercritical or freezing conditions, resulting in xerogels, aerogels and cryogels, respectively (Al-Mutasheb & Ritter, 2003;Czzakel et al, 2005;Job et al, 2004;Zubizarreta et al, 2008a).…”

Microporous activated carbon spheres prepared from resole‐type crosslinked phenolic beads by physical activation

“…32 Teng and Wang 33 prepared activated carbons with a specific BET surface area up to 2220 m 2 /g at a higher burnoff of 78% and with a carbon yield of 12.0% by a physical and chemical etching method from phenolformaldehyde resins, which were grounded and sieved. Lin and Teng 34 reported that cured resins carbonized in N 2 at 700 C, and this was followed by gasification of the resulting char in steam at the same temperature for different extents of burn-off.…”