Journal of Colloid and Interface Science 324 (2008) 150–155 Contents lists available at ScienceDirect Journal of Colloid and Interface Science www.elsevier.com/locate/jcis Tuning of texture and surface chemistry of carbon xerogels N. Mahata a , M.F.R. Pereira a , F. Suárez-García b , A. Martínez-Alonso b , J.M.D. Tascón b , J.L. Figueiredo a,∗ a Laboratório de Catálise e Materiais (LCM), Laboratório Associado LSRE/LCM, Departamento de Engenharia Química, Faculdade de Engenharia, Universidade do Porto, 4200-465 Porto, Portugal b Instituto Nacional del Carbón, CSIC, Apartado 73, 33080 Oviedo, Spain article info abstract Article history: Received 1 April 2008 Accepted 4 May 2008 Available online 10 May 2008 Keywords: Carbon xerogel Surface activation Oxygen plasma Catalyst support The inﬂuence of different activation processes on the textural and surface chemical properties of carbon xerogels was studied. Carbon xerogels were prepared by the conventional sol–gel approach using resorci- nol and formaldehyde; two different pHs of sol–gel processing led to carbon materials with distinct pore size distributions. The materials were subjected to controlled activation by three different methods: acti- vation by oxygen plasma, activation by HNO 3 , and activation by diluted air. Treatments with HNO 3 and diluted air created oxygen groups on the external surface as well as inside the pore channels, whereas plasma is more suitable for introducing oxygen groups selectively on the external surface. Nevertheless, it was shown that samples with wider pores can be oxidized to some extent on the pore interiors by plasma. Signiﬁcant changes in total surface area by air activation were observed.  2008 Elsevier Inc. All rights reserved. 1. Introduction Carbon materials are widely used as adsorbents and cata- lyst supports. Especially for liquid phase catalytic reactions, they present some advantages over conventional inorganic supports, such as higher stability in acidic and basic media. Conventional inorganic supports such as alumina and silica are dissolved at high pHs and the former is also attacked even at very low pHs [1]. Recently, carbon xerogels have attracted a great deal of interest, since they can be produced with mesoporous and macroporous textures combined with large pore volume, which is more ade- quate for liquid phase applications. Also, carbon xerogels possess excellent characteristics as catalyst supports, such as high surface area, high porosity, open pore network, controllable pore size, and can be prepared in the desired form (monolith, thin ﬁlm, or pow- der). Another important advantage of carbon xerogels is that the composition of the carbon is controlled and fully reproducible, which is not the case for activated carbons. The composition of the carbon may play a major role in processes like impregnation (for catalysts manufacture) or during reactions, adsorption, etc. The use of supported precious metal catalysts in the ﬁne chem- icals area is very common. In terms of economy, a very important point is the recovery, reﬁning, and recycling of precious metals, es- pecially when catalysts with high metal loading are used. The use of carbon supports makes this quite simple, because the spent cat- alyst can be burnt off, and the resulting highly concentrated ashes make the recovery of precious metals economical. The process pro- * Corresponding author. Fax: +351 22 5081449. E-mail address: jlﬁg@fe.up.pt (J.L. Figueiredo). duces smaller amounts of solid waste and hence it is effective from an ecological point of view too. A very important issue in supported catalysts is the maximum availability of the active phase. A well-dispersed active phase is beneﬁcial for obtaining the maximum activity of a catalyst. The textural and surface chemical properties of a support play a crucial role in dispersing the active phase. Open pore networks and the presence of suitable anchoring sites for the precursor are beneﬁcial in this regard. Carbon materials are superior in this context, since their texture and surface chemistry can be modiﬁed in a controlled way by appropriate methodologies [2]. In the present work, synthesis of carbon xerogels and modi- ﬁcation of their surface chemistry by various methodologies are reported. Carbon xerogels (CX) were synthesized by the conven- tional sol–gel approach using formaldehyde and resorcinol, using two different solution pH values. The wet gels were directly dried and then carbonized, leading to carbon xerogels with different tex- tural properties. The xerogels were subjected to subsequent oxida- tion treatment with oxygen plasma, nitric acid, and diluted air. The inﬂuence of the different treatments on the textural and surface chemical properties is discussed. 2. Experimental 2.1. Preparation of carbon xerogels Two types of mesoporous carbon xerogels were prepared by sol–gel condensation of resorcinol and formaldehyde at two dif- ferent pHs of sol–gel processing and subsequent carbonization of the dried gels. The detailed procedure is described elsewhere [3]. In brief, sol–gel processing was performed with a formalde- 0021-9797/$ – see front matter  2008 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2008.05.006