Beneficial aspects of in-situ non-metal-doped carbocatalysts for the removal of contaminants of emerging concern from wastewater

In recent decades, as an adverse effect of global population growth, contaminants of emerging
concern (CECs) are continuously released into the environment, resulting in a huge threat to
human health and aquatic ecosystems. Traditional methods for wastewater treatment are not
adequate enough to tackle the growing complexity of these contaminants found in wastewater
today. As environmental standards become more stringent, the need for innovative, efficient
treatment solutions has never been greater. Advanced oxidation processes (AOPs), especially
sulfate radical-based AOPs, represent a cutting-edge solution designed to avoid secondary
contamination by oxidizing CECs to biodegradable or harmless substances, carbon-dioxide
and water. The addition of a heterogeneous catalyst into the system enables the high
efficiency and easy operation of the process, as well as low energy consumption. In relation to
this, the design of appropriate catalysts for AOPs still remains an important challenge since
their synthesis has to follow the principles of green chemistry implying the replacement of
conventional metal-based catalysts with the metal-free ones. Biomass waste reutilization, as
highly desired in the environmental engineering, can be used for the production of carbon
material – biochar (pyrochar and hydrochar), serving as a green catalyst for persulfatemediated
oxidation of CECs. In this study, one series of non-metal-doped pyrochar-based
catalysts was prepared using a facile one-pot green strategy with urea and boric acid mixed
with pinewood sawdust. The obtained singe- and double-doped (N, (B)-) samples of pyrochar
were used to activate peroxydisulfate (PDS) for the removal of 25 CECs from the water
solution model mixture (30 μg/l concentration of each compound) – 15 pesticides and 10
pharmaceutically active compounds (PhACs). Compared with the pristine pyrochar, the
catalytic activity of all doped samples was significantly higher, resulted from the enhanced
adsorption capacity for all tested CECs. The obtained B-doped catalyst exhibited excellent
capability to boost PDS activation for almost 100% removal of 12 pesticides and 9 PhACs
within 15 min. The introduced boron species, acting as Lewis acid sites, enhanced the surface
affinity towards PDS and modulated the electronic structure of carbon matrix resulting in an
increased electron transfer rate. More importantly, the high stability of boron sites enabled a
superior recyclability of this catalyst for up to four cycles making it a promising candidate for
practical applications in the CECs removal from wastewater.