N,P-co-doped carbocatalyst from olive pomace obtained by catalytic hydrothermal carbonization for efficient dye degradation via persulfate-based advanced oxidation process

The strategy of doping carbocatalysts with heteroatoms has proven its effectiveness in degrading organic pollutants by persulfate-based advanced oxidation processes. However, research on the effect of doping phosphorus atoms on the degradation performance remains very limited. In this work, a new N, P-doped carbocatalyst (N,P-HC) is designed by hydrothermal carbonization (HTC) followed by pyrolysis at 700°C using a biowaste (olive pomace) as a carbon source to degrade organic pollutants in the presence of peroxydisulfate (PDS). The experimental results showed that N,P-HC, with its large specific surface area (871.73 m2.g-1), high N-pyridine and N-pyrrolic content as well as the existence of P-O-C and O-P-C bonds, provides high degradation performance (98% degradation of Rhodamine B (RhB) in 40 min with a an apparent rate constant (kapp) of 0.055 min-1 and an excellent turnover frequency (TOF) of 0.275 min-1. The quenching study revealed that singlet oxygen generation (1O2) and direct electron transfer were the main reaction ways for the non-radical pathway in the degradation of RhB. The improved catalytic efficiency can be attributed to the synergistic effect created between N and P atoms in the graphitic structure of the carbocatalyst. On the other hand, a heat treatment at 500°C of the used N,P-HC carbocatalyst allows recovery efficiently their performance. Overall, this study provided a facile and clean method for efficiently synthesizing a high-performance N,P co-doped olive pomace-based carbocatalyst for water depollution in presence of PDS.