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

Emerging pollutants are an increasing problem in wastewater globally. Bisphenol A (BPA) is one compound belonging to this group. This work proposes the study of the employment of several metal-supported (2 wt. %) carbon nanospheres (CNS) for BPA degradation by catalytic wet-air oxidation. Several techniques were used for the catalyst characterization: thermogravimetry, X-ray diffractometry (XRD), Fourier transformed infrared spectrometry (FTIR), determination of isoelectric point, elemental analysis, X-ray fluorescence (XRF), scanning electron microscopy (SEM), and N2 adsorption–desorption isotherms. Different loads of Ru in the catalyst were also tested for BPA degradation (1, 2, 5, 7, and 10%), being the first minimum value to achieve a conversion above 97% in 90 min 2 wt. % of Ru in the CNS-Ru catalyst. In the stability test with CNS-Ru and CNS-Pt, CNS-Pt demonstrated less activity and stability. Two potential models were proposed to adjust experimental data with CNS-Ru(2%) at different conditions of BPA initial concentration, catalyst mass, temperature, and pressure of the reaction. Both models showed a high determination coefficient (R2 > 0.98). Finally, the efficiency of CNS-Ru and CNS-Pt was tested in a real hospital wastewater matrix obtaining better results the CNS-Pt(2%) catalyst.

Heteroatom (N, S) Co-Doped CNTs in the Phenol Oxidation by Catalytic Wet Air Oxidation

The N, S-co-doping of commercial carbon nanotubes (CNTs) was performed by a solvent-free mechanothermal approach using thiourea. CNTs were mixed with the N, S-dual precursor in a ball-milling apparatus, and further thermally treated under inert atmosphere between 600 and 1000 °C. The influence of the temperature applied during the thermal procedure was investigated. Textural properties of the materials were not significantly affected either by the mechanical step or by the heating phase. Concerning surface chemistry, the developed methodology allowed the incorporation of N (up to 1.43%) and S (up to 1.3%), distributed by pyridinic (N6), pyrrolic (N5), and quaternary N (NQ) groups, and C–S–, C–S–O, and sulphate functionalities. Catalytic activities of the N, S-doped CNTs were evaluated for the catalytic wet air oxidation (CWAO) of phenol in a batch mode. Although the samples revealed a similar catalytic activity for phenol degradation, a higher total organic carbon removal (60%) was observed using the sample thermally treated at 900 °C. The improved catalytic activity of this sample was attributed to the presence of N6, NQ, and thiophenic groups. This sample was further tested in the oxidation of phenol under a continuous mode, at around 30% of conversion being achieved in the steady-state.