Industrial discharges are a significant source of water contamination, introducing recalcitrant organic pollutants like dyes into water bodies. To address this, advanced oxidation processes (AOPs) are being developed to degrade these pollutants without generating secondary contamination. A recent study by Puthiya Veetil Nidheesh and Sakshi, published in Environmental Science and Pollution Research, investigates the use of biochar-activated peroxymonosulfate (PMS) for the degradation of Rhodamine B (RhB) dye.

The study specifically examined the impact of pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More temperature and solution pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More on the effectiveness of biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More in activating PMS for dye degradation. Biochar, a carbonaceous material produced from biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More through pyrolysis, is known for its environmental benefits, including enhancing soil fertility and mitigating CO2 emissions. Its unique physicochemical properties, such as high surface area, porosityPorosity of biochar is a key factor in its effectiveness as a soil amendment and its ability to retain water and nutrients. Biochar’s porosity is influenced by feedstock type and pyrolysis temperature, and it plays a crucial role in microbial activity and overall soil health. Biochar More, and the presence of functional groups and persistent free radicals (PFRs), make it an effective catalyst for activating PMS.

The researchers used biochar produced from coir pith at three different pyrolysis temperatures: 350∘C, 500∘C, and 650∘C. These biochar samples were then used to degrade Rhodamine B dye at various pH levels (3, 6, and 9). The results were impressive: complete removal (100%) of Rhodamine B was observed across all tested pH conditions and within 60 minutes of reaction time. For biochar produced at 350∘C, 500∘C, and 650∘C, the dye removal efficiencies reached up to 100%, 98%, and 99%, respectively.

A key finding of the study was that singlet oxygen was the predominant oxidant generated during the activation of PMS by biochar via the electron acceptor pathway. This non-radical pathway contributed significantly, accounting for 59% of the dye degradation. This is particularly important because, unlike traditional methods that rely on highly reactive but less selective hydroxyl and sulfate radicals, a singlet oxygen-dominated process can offer more targeted degradation with potentially fewer undesirable byproducts. The study also revealed that even though the dye removal efficiency was similar for biochar produced at different pyrolysis temperatures and solution pH, singlet oxygen generation was notably higher at pH 9 and with biochar produced at 500∘C.

The activation of PMS by biochar primarily occurred via the electron acceptor pathway, driven by the presence of C=0 groups and oxygen-centered persistent free radicals on the biochar’s surface. The research suggests that the higher singlet oxygen production at pH 9 may be due to enhanced deprotonation of intermediates under alkaline conditions. Furthermore, the enhanced singlet oxygen by biochar produced at 500∘C is due to other functional groups in addition to ketone groups , and the amount of persistent free radicals is significantly higher for biochar produced at 500∘C.

This research highlights the significant potential of biochar-activated PMS as a sustainable and effective method for treating dye-contaminated wastewater. The findings underscore that this non-radical degradation pathway offers a promising solution to reduce the environmental impact of dye pollution, aligning with global efforts towards cleaner water and sanitation.

Source: Nidheesh, P. V., & Sakshi. (2025). Impact of pyrolysis temperature and solution pH on singlet oxygen dominated dye degradation in biochar activated peroxymonosulfate process. Environmental Science and Pollution Research.