Doped Carbon Gels

One area of major interest in carbon gel research is the incorporation of metal species into the carbon framework, taking advantage of the pore texmre of these gels to achieve good dispersion and stability of the metal nanoparticles in the 

Source Reproduced with permission from Elsevier. 

Three main strategies have been nsed to introduce metal species into the carbon framework  

Dissolving the metal precnrsor in the initial resorcinol-formaldehyde mix-tnre 

Introdncing a functionalized moiety with binding sites for the metal ions into the initial mixture or in the organic gel 

---

In other Pt-doped monolithic carbon aerogels, prepared by adding the Pt pre-cnrsor to the initial R/F mixture [41], the Pt particle size determined by H2 chemisorption was mnch higher than that determined by high-resolution transmission electron microscopy (HRTEM). This indicates that some Pt particles were encapsnlated by the carbon matrix and were consequently inaccessible to H2. This can be the main problem of this preparation method when the metal-doped carbon gel is to be used as catalyst, because part of the metal will not be accessible to the reactant molecules. 

CATALYTIC REACTIONS OF METAL-DOPED CARBON GELS... 

Environmental applications of metal-doped carbon gels can be divided between reactions carried out in the gas and aqueous phases. The former group includes volatile organic compound (VOC) oxidation (e.g., toluene and xylene oxidation) and NO reduction. The latter group includes the catalytic wet air oxidation (CWAO) of aniline solutions and advanced oxidation processes (AOPs) (e.g., catalytic ozonation and photooxidation of pollutants). 

Metal-doped carbon gels have been used as catalysts in several reactions, including the removal of pollutants in either gas or aqueous phase, ORR and methanol electrooxidation for fuel cell applications, C=C double-bond hydrogenations, skeletal isomerization and hydrodechlorination reactions, and other organic syntheses. The activity and/or selectivity of metal-doped carbon gels was better than that of other, more widely used supported catalysts in many of the... 

An important feature of these materials is that metal-doped monolithic carbon gels can readily be prepared (see below). These are emergent materials in the field of heterogeneous catalysis, and their use will grow in the near future, due... 

Nanocomposited carbon aerogels represent a different approach because of the organic nature of the precursory gel and the pyrolysis step [11]. In this case, high metal content can be achieved (up to 46% in the case of Pd-doped carbon aerogel)... 

Figure 21.9. Pt-doped carbon aerogel derived via copolymerization of a metal complex with the gel precursors image reprinted from [3], p. 2339, with permission from Elsevier.

Wang J, Pamidi PVA, Nascimento VB, Angnes L (1997) Dimethylglyoxime doped sol-gel carbon composite voltam-metric sensor for trace nickel. Electroanalysis 9 689-692... 

Dansby-Sparks RN, Jin J, Mechery SJ et al (2010) Fluorescent-dye-doped sol—gel sensor for highly sensitive carbon dioxide gas detection below atmospheric concentrations. Anal Chem 82 593-600... 

Yang, M. H., Y. H. Yang, Y. L. Liu, G. L. Shen, and R. Q. Yu, 2006. Platinum nano-particles-doped sol-gel/carbon nanotubes composite electrochemical sensors and biosensors. Biosens Bioactuat 21 1125-1131. 

Metal nanoparticle-doped sol-gel silica nanocomposites do not possess the required conductivity to fabricate bulk or screen-printed electrodes. Inspired by the well-known resorcinol/formaldehyde sol-gel process, which can be pyro-lyzed to get a conductive amorphous carbon matrix, we have synthesized a nanocomposite material made of a carbon xerogel doped with bismuth nanoparticles and fabricated a carbon paste electrode for heavy metal analysis (Figure 46.11) [24]. The resulting sensor is very sensitive to several heavy metals. Extremely low detection limits for Pb " and Cd of around 0.5 ppb were achieved using a nanocomposite paste electrode containing 6 wt. % of bismuth. 

---