Tailoring the Surface Chemistry of Activated Carbon by Nitric Acid: Study Using Response Surface Method

Abstract

Tailoring the surface chemistry of adsorbents, especially activated carbons, make them suitable to specific applications. Many times oxidation is the first step and greatly affects the next steps of tailoring. We modified the surface chemistry of a microporous activated carbon (AC) by nitric acid solutions at different conditions of acid concentration, time, and oxidation temperature. The oxidized AC samples were inspected with the aid of physical adsorptiondesorption of nitrogen at 77°C and temperature-programmed desorption (TPD). It was shown that oxidation by nitric acid lowers surface area of the studied AC even at mild severity. Moreover, different instrumental analysis pointed out creation of a considerable amount of oxygen-containing functional groups, especially acidic ones on the surface. Central composite design (CCD) was applied to evaluate the individual and interactive effects of oxidation parameters and to provide a compromise between the amount of oxygen groups and BET surface area as two of studied responses. The significant factors and interactions on each response were recognized by Analysis of Variance (ANOVA). A linear model and a two factor interaction (2FI) model were developed to correlate the oxidation conditions to BET surface area and the amount of oxygen surface groups. In addition, optimized oxidation conditions were established.

Oxidation of Different Microporous Carbons by Chemical and Electrochemical Methods

“…These results indicate that the chemical oxidation may be faster at the beginning, so that its rate decreases with time (Figure 2A). Such a kinetic behavior can be observed also in other ACs reported in literature (Moreno-Castilla et al, 1997;Houshmand et al, 2011; Figure 2A) and was associated to the uncontrollability of chemical oxidation (Berenguer et al, 2012). The main consequence is that significantly long times are needed to reach significant oxidation degrees, so that further functionalization of this material by this method and conditions becomes complex and restricted.…”

“…The effect of multiple different oxidation methods and conditions on their properties and applications was analyzed (Shen et al, 2008;Daud and Houshamnd, 2010;Jaramillo et al, 2010;Rivera-Utrilla et al, 2011;Thakur and Thakur, 2016). So far, liquid-phase chemical oxidation by using H 2 O 2 , HNO 3 or (NH 4 ) 2 S 2 O 8 has been the most studied oxidative method (Otake and Jenkins, 1993;Moreno-Castilla et al, 1995, 1998De la Puente et al, 1997;Gil et al, 1997;Mangun et al, 1999;Pradhan and Sandle, 1999;El-Sayed and Bandosz, 2001;Shim et al, 2001;Strelko and Malik, 2002;El-Hendawy, 2003;Li et al, 2003Li et al, , 2011Houshmand et al, 2011;Ternero-Hidalgo et al, 2016). It has been claimed that the oxidation degree of microporous ACs can be easily controlled by adjusting the oxidation parameters, i.e., treatment time, concentration, and temperature of common oxidants (HNO 3 or (NH 4 ) 2 S 2 O 8 ) (Moreno-Castilla et al, 1997;Houshmand et al, 2011).…”

“…These treatments generally cause a decrease in specific surface area and micropore volume, which becomes more significant with an increasing degree of activation in the oxidized material (Moreno-Castilla et al, 1995. While some authors suggest that the decrease in textural properties is due to a blockage by SOGs at the entry of the micropores (Moreno-Castilla et al, 1995Pradhan and Sandle, 1999;Li et al, 2003;Maroto-Valer et al, 2004;Szymanski et al, 2004;Houshmand et al, 2011), others claim their destruction by the oxidation reaction (Moreno-Castilla et al, 1995, 1998Pradhan and Sandle, 1999;Li et al, 2003). These disparities have been attributed to the distinct oxidation method and differences in the micropore texture, thickness of micropore walls, etc.…”

“…It can be deduced from literature, hence, that not only the oxidative method but also the micropore structure of the oxidized material seem to play an important role on the reactivity and effects of the oxidation processes. Among the vast literature, however, few investigations compare the effect of different oxidation methods on a given carbon material (Otake and Jenkins, 1993;Figueiredo et al, 1999;Li et al, 2003;Houshmand et al, 2011;Berenguer et al, 2012Berenguer et al, , 2013a and very few deal with the influence of the different micropore structure of the material when oxidized by a specific method (Moreno-Castilla et al, 1997;El-Sayed and Bandosz, 2001). To the knowledge of the authors, there are no investigations analyzing both effects at the same time.…”

A Comparative Study on a Cationic Dye Removal through Homogeneous and Heterogeneous Fenton Oxidation Systems

“…], 0.5-1.5 g/L for catalysts concentration and oxidation reaction time of 300 min were chosen based on the preliminary studies and the literatures. [21][22][23] A total of 11 experiments were performed for each hetero-catalyst in which three of them were at the center point: (A) = 0.2, (B) = 1. The following second order polynomial equation (Eq.…”