Mechanothermal Approach for N-, S-, P-, and B-Doping of Carbon Nanotubes: Methodology and Catalytic Performance in Wet Air Oxidation

Abstract

The texture and the surface chemistry of carbon nanotubes (CNTs) were modified using a solvent-free methodology involving a ball-milling mechanical treatment and thermal treatment under nitrogen in the presence of adequate precursors (melamine, sodium thiosulfate, sodium dihydrogen phosphate, and boric acid) of different heteroatoms (N, S, P, and B, respectively). The incorporation of these heteroatoms promotes significant changes in the pristine textural and chemical properties. This easy post-doping method allows the introduction of large concentrations of heteroatoms. Their effect on the catalytic activity of the materials was evaluated in the oxidation of oxalic acid by catalytic wet air oxidation (CWAO), as an alternative to the noble metal and rare earth oxide catalysts traditionally used in this process. Improved catalytic activities were obtained using the N-, P-, and B-doped CNTs in oxalic acid oxidation, while the S-doped CNT sample underperformed in comparison to the pristine material.

Preparation of Granulated Biomass Carbon Catalysts—Structure Tailoring, Characterization, and Use in Catalytic Wet Air Oxidation of Bisphenol A

“…The atomic abundance for boron was 8.9-13.0% and that for silicon was 1.8-2.5%. The B1s spectrum peaked at 192.5 eV, a typical binding energy attributed to boron oxide (B2O3) [44,45]. The peak detected at 103.5 eV corresponds to the Si 2p binding energy, which is assigned to silicon dioxide [46], supporting the XRD results ( Figure 1).…”

“…Boron intrinsically accepts electrons, and this may lead to high affinity towards oxygen, thus improving the adsorption of oxygen and the formation of oxygen reactive species, which again may enhance the oxidation of organic compounds [71]. Similar results for phenol removal using phosphorus-, boron-, and nitrogen-doped carbon blacks in catalytic wet peroxide oxidation have been presented elsewhere [44]. In this study, the kinetic rate constants of hydrogen peroxide degradation were up to eight times larger when doped carbons were used than when non-modified carbons were utilized.…”

Processing Methods Used in the Fabrication of Macrostructures Containing 1D Carbon Nanomaterials for Catalysis

“…The introduction of oxygen-containing functionalities has been demonstrated in carbon nanofibers, and their effect on their activity as catalyst or as catalyst support has been tested in several reactions, including ozonation [24] and catalytic wet air oxidation [25] of water contaminants, in fuel cell electrodes [26,27], nitrate [28], nitrobenzene [29,30], naphthalene [31], cinnamaldehyde [32,33], phenylacetylene [34] hydrogenation, nitrous oxide reduction [35], electrocatalytic oxygen reduction [35], methanol oxidation [36], Fischer-Tropsch reaction [27], and others [5]. Similar studies have been carried out when using other elements as dopants, such as nitrogen [37][38][39][40][41][42][43][44][45][46][47], boron [38,45,48], potassium [27,38,49], fluorine [50,51], phosphorous [45], or sulfur [52][53][54]. Nevertheless, the various morphologies of the 1D carbon nanofibers illustrated in Figure 2 may offer particular characteristics of interest to specific catalytic applications, in particular the potential presence of a large number of defects on the carbon lattice of the carbon nanofibers when compared with carbon nanotubes (Figure…”

Insights into the Kinetics Degradation of Bisphenol A by Catalytic Wet Air Oxidation with Metals Supported onto Carbon Nanospheres

“…The selection of the catalytic material for the CWAO process is of significant importance. In recent decades, different materials have been studied to act as support for the catalyst: zeolites [20], clays [21], resins [22], and carbon-based materials [23]. From this classification, carbon support has attracted attention, carbon nanospheres being optimal support for this process.…”