The role of O- and S-containing surface groups on carbon nanotubes for the elimination of organic pollutants by catalytic wet air oxidation

Tuning CNT Properties for Metal-Free Environmental Catalytic Applications

“…After treatment at 600˝C (CNT-HNO 3 -600), the surface only contains phenol and carbonyl/quinone groups, and a small amount of lactones. Almost all the oxygen-containing surface groups are removed at 900˝C [26,38] (Figure 4). This approach has the advantage that the thermal treatments do not promote significant additional changes on the specific surface area of the CNTs [38], as can be seen in Table 1.…”

“…After treatment at 600 °C (CNT-HNO3-600), the surface only contains phenol and carbonyl/quinone groups, and a small amount of lactones. Almost all the oxygen-containing surface groups are removed at 900 °C [26,38] (Figure 4). This approach has the advantage that the thermal treatments do Comparing with the traditional oxidation (in 7 M solution of HNO 3 at boiling temperature) the hydrothermal functionalization of CNTs using a 0.3 M solution of HNO 3 at 200˝C can achieve a similar degree of functionalization, with the amount of oxygen-containing surface groups being even higher when compared with the traditional refluxing with HNO 3 [32] (Table 1).…”

“…Comparing with the traditional oxidation (in 7 M solution of HNO3 at boiling temperature) the hydrothermal functionalization of CNTs using a 0.3 M solution of HNO3 at 200 °C can achieve a similar degree of functionalization, with the amount of oxygen-containing surface groups being even higher when compared with the traditional refluxing with HNO3 [32] (Table 1). Oxidative treatments in the liquid-phase with hydrogen peroxide (H2O2) or ozone (O3) have also been reported, but the degree of functionalization is lower [38]. While treatments with HNO3 originate materials with large amounts of surface acidic groups, mainly carboxylic acids and, to a smaller extent, lactones, anhydrides, and phenol groups [15], H2O2 oxidation generates less acidic materials [39] (Table 1), whereas ozone treated CNTs in the liquid phase revealed slight functionalization [38].…”

“…Oxidative treatments in the liquid-phase with hydrogen peroxide (H2O2) or ozone (O3) have also been reported, but the degree of functionalization is lower [38]. While treatments with HNO3 originate materials with large amounts of surface acidic groups, mainly carboxylic acids and, to a smaller extent, lactones, anhydrides, and phenol groups [15], H2O2 oxidation generates less acidic materials [39] (Table 1), whereas ozone treated CNTs in the liquid phase revealed slight functionalization [38]. In order to introduce mainly basic and neutral oxygenated groups on the surface (mainly phenol and carbonyl/quinone groups), CNTs can be oxidized in the gas phase with diluted oxygen (5% O2 in N2) at high temperatures (500 °C).…”

An overview on the advanced oxidation processes applied for the treatment of water pollutants defined in the recently launched Directive 2013/39/EU

“…More recently, metal-free carbon materials as catalysts on their own have gained increasing attention due to actual concerns with metal scarcity and catalyst deactivation by metal leaching. Some exam-ples are activated carbons (Morales-Torres et al, 2010), carbon xerogels (Apolinário et al, 2008;Gomes et al, 2008), carbon nanotubes Rocha et al, 2011Rocha et al, , 2014, carbon foams and fibers (Sousa et al, 2010) and graphite (Domínguez et al, 2014). Fig.…”