Comparison between endogenous and exogenous nitrogen of nitrogen-doped carbon catalyst in the process of activating PMS

Abstract

Background

Advanced oxidation processes (AOPs) based on sulfate radicals (SO₄^•–) have proven to be highly effective in degrading organics in wastewater. Carbon-based materials have emerged as promising catalysts for activating persulfate, which generates environmentally friendly sulfate radicals (SO₄^•–), for remediation purposes. The nitrogen doping technique is an effective method for site-specific regulation and can significantly enhance the performance of carbon-based catalysts, which could promote the application of carbon-based catalysts in the future. Endogenous and exogenous nitrogen sources can provide nitrogen sources for N doping. However, there are few reports on the comparison of the structure and catalytic mechanism of these two types of N-doped biochar. It is also of great significance to reveal the mechanisms of constructing catalytic sites using endogenous and exogenous nitrogen.

Methods

Herein, the preparation of endogenous nitrogen-doped biochar (BC) was achieved by using soybean as the precursor material, which is rich in natural nitrogen-containing components of proteins. Subsequently, the BC was doped by mixing it with urea and pyrolysis, resulting in the preparation of exogenous nitrogen-doped biochar (NBC).

Significant findings

The characterization of XRD and HRTEM showed that g-C₃N₄ formed in NBC. The results of catalytic degradation and quenching experiments demonstrate that the exogenous nitrogen-doped catalysts have a better performance than endogenous nitrogen-doped catalysts. The OFL removal rate in BC/PMS was higher than that in the BC/PMS system (71.68% vs. 61.83 %). The k_obs in NBC/PMS are also higher than that in BC/PMS (0.00943 min⁻¹ vs. 0.01369 min⁻¹). The NBC could be a promising catalyst for PMS activation in practical application. DFT results showed that the g-C₃N₄ generated from exogenous nitrogen can improve PMS activation performance in the g-C₃N₄/graphene bilayer structure. The influence on the charge distribution of surrounding carbon materials makes endogenous nitrogen doping a good choice for optimizing the local performance of the material in the absence of natural nitrogen components.