The research, led by a team including corresponding author Hongna Li, focused on a class of carbon materials known as biochar, which is produced by heating biomass in oxygen-limited conditions. Biochar has long attracted attention as a low-cost, sustainable sorbent for water treatment, but its catalytic potential has often been limited by a lack of reactive surface sites. The team’s strategy was to dope the sawdust-derived biochar with both nitrogen and boron, two elements that, when embedded in a carbon lattice, can dramatically alter how the material interacts with oxidants. Crucially, the researchers did not simply ask whether adding nitrogen and boron helps. They asked how much of each element, relative to the other, produces the best result.

To answer that question, the team prepared a series of nitrogen and boron co-doped biochars with systematically varying nitrogen-to-boron ratios, abbreviated N:B, and tested each one as an activator of peroxymonosulfate, or PMS, a common oxidant used in advanced oxidation processes for water purification. When PMS is activated on a catalyst surface, it generates reactive species capable of degrading organic pollutants that resist conventional treatment. The performance differences between the doped biochars were striking. Lowering the N:B ratio from 4 down to 0.25 increased the rate constant for sulfamethoxazole degradation from 0.20 to 0.47 per minute, a 2.35-fold improvement achieved purely by changing the dopant proportions.

According to the authors, the lesson is that doping is not a simple additive trick. “Our results show that simply adding nitrogen and boron is not enough. Their relative proportion determines how the biochar interacts with PMS and how efficiently pollutants are degraded,” said Hongna Li. “By adjusting this ratio, we can control the surface structure, active sites and electron-transfer behavior of the material.” In other words, the ratio between two dopant elements acts as a tuning knob that reshapes the entire chemistry of the carbon surface, determining whether the material behaves as a passive sponge or as an active catalyst.

The mechanistic story that emerged from the study is one of the most interesting aspects of the work. At higher N:B ratios, pollutant removal depended primarily on adsorption, meaning sulfamethoxazole molecules were largely captured and held on the biochar surface rather than chemically destroyed. As the ratio dropped, particularly into the range between 1 and 0.25, PMS activation intensified and catalytic degradation became the dominant removal pathway. The material was no longer just storing the pollutant; it was actively converting the oxidant into species capable of breaking the antibiotic apart.

Detailed material characterization explained why the composition shift mattered so much. Lower N:B ratios increased the biochar’s surface area, improved pore accessibility, generated more structural defects in the carbon lattice, and raised the content of graphitic nitrogen, a form of nitrogen integrated directly into the graphitic carbon framework. Together, these features enhanced electron transfer between the biochar and PMS and created favorable sites where the oxidant could be adsorbed and activated. In catalysis, the ability to shuttle electrons efficiently between a surface and an oxidant is often the deciding factor between a mediocre material and an excellent one, and the co-doping strategy appears to optimize exactly this property.

Identifying the actual oxidizing species responsible for degradation was another key achievement of the study. Through experiments using chemical scavengers, which selectively quench particular reactive species, and electron paramagnetic resonance spectroscopy, which directly detects radical intermediates, the researchers pinpointed singlet oxygen as the major oxidant driving sulfamethoxazole destruction. Singlet oxygen is a reactive but nonradical form of oxygen, and it accounted for approximately 73 to 82 percent of degradation across most of the tested systems. Nonradical pathways such as this are increasingly prized in water treatment because they tend to be more selective and less prone to being wasted by reaction with background water constituents such as natural organic matter and chloride ions.

The mechanistic picture was reinforced by density functional theory calculations, a computational method that models electronic interactions at the atomic scale. These calculations showed how defect-rich, nitrogen-containing carbon sites could promote the adsorption and activation of PMS, providing a theoretical foundation for the experimental observations. The combination of spectroscopic evidence, scavenging tests and computational modeling gives the study an unusually complete causal chain, linking the elemental composition of the biochar to specific surface features, and those features to the dominant reaction pathway and ultimately to pollutant destruction.

Perhaps most importantly for practical applications, the optimized material performed well under conditions that approximate real-world water treatment rather than idealized laboratory solutions. The N:B = 0.25 system maintained more than 91.8 percent sulfamethoxazole removal efficiency across a wide pH range from 3 to 9, a significant advantage because real wastewater varies considerably in acidity and alkalinity. The system also achieved over 70 percent removal within 20 minutes when tested in drinking water, river water and secondary effluent, demonstrating robustness in the presence of the competing substances that typically undermine advanced oxidation catalysts. In a continuous-flow reactor, where the biochar was immobilized on a cotton support, the system achieved approximately 99.6 percent sulfamethoxazole removal after 200 minutes of operation at a flow rate of 3 milliliters per minute, showing that the catalyst can function in a flow-through configuration rather than only in batch experiments.

Beyond the immediate performance numbers, the study articulates a broader design principle that could influence how carbon-based water treatment materials are engineered in the future. Rather than treating heteroatom doping as a binary choice of which elements to add, the researchers demonstrate that the ratio between dopants can determine the fundamental behavior of a carbon material, deciding whether it mainly adsorbs contaminants or actively catalyzes their destruction. This reframing turns material design into a compositional optimization problem with a continuous tunable parameter, opening the door to systematic searches for optimal formulations. By converting waste sawdust into a tunable catalyst whose activity can be dialed in through elemental ratios, the findings point toward a class of biochar-based technologies that are inexpensive, derived from renewable waste streams, and capable of removing antibiotic residues and other persistent organic contaminants from water. As concerns about antibiotic resistance driven by environmental pharmaceutical pollution continue to grow, strategies that combine waste valorization with advanced catalytic performance may prove to be exactly the kind of dual-benefit innovation that water treatment needs.

Subject of Research: Nitrogen and boron co-doped sawdust biochar as a tunable peroxymonosulfate activator for antibiotic degradation in water

Article Title: Tuning nitrogen and boron turns waste sawdust biochar into an efficient catalyst for antibiotic removal

Article References: Tuning nitrogen and boron turns waste sawdust biochar into an efficient catalyst for antibiotic removal. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: biochar, sawdust, nitrogen doping, boron doping, peroxymonosulfate, sulfamethoxazole, antibiotic removal, water treatment, singlet oxygen, advanced oxidation, catalysis, wastewater