Organic radicals: formation, classification, and environmental application

Over the past two centuries, as our industries have boomed and our economies have thrived, air pollution has increasingly troubled us, tugging at our collective conscience. The rise of industries and the combustion of fossil fuels, such as coal, oil, and natural gas, have released various pollutants into the atmosphere; therefore air pollution is a central concern, particularly in industrial processes. The emission of airborne pollutants, including particulate matter (PM), ground-level ozone, nitrogen oxides (NOx), sulfur dioxide (SO2), volatile organic compounds (VOCs), dioxins, polycyclic aromatic hydrocarbons (PAHs), carbon monoxide, and heavy metals such as lead, poses serious health hazard. As these pollutants can result in a range of ailments, such as respiratory diseases (e.g., asthma, COPD), cardiovascular issues, neurological disorders, and cancer, it is crucial to prioritize the management of gaseous pollutants. This is critical not only for safeguarding human health but also for preserving air quality, protecting the environment, and addressing the broader concern of climate change. In the context of environmental remediation, numerous technological advancements have been introduced to mitigate the emissions of pollutants originating from different sources, such as industrial and transportation systems. These technologies encompass various approaches, including physical techniques such as adsorption and membrane technology. Additionally, chemical redox processes have been employed to transform pollutants into less hazardous or nontoxic substances via chemical reactions. One of the extensively researched chemical approaches in the realm of air pollution mitigation is the employment of advanced oxidation processes (AOPs). It is noteworthy to mention that AOPs also have a well-established history in the field of water and wastewater treatment. This methodology utilizes highly reactive radical species, such as hydroxy radicals (•OH), superoxide radicals (•O2−), and singlet oxygen (1O2), among others. Recently, scientific investigations have shifted their focus toward reactive organic-based radicals, both in the context of water treatment and the removal of air pollutants. This shift is primarily attributed to the enhanced selectivity demonstrated by these specific radical species. This chapter will provide an overview of air pollutants and their removal technologies. Following that, the advanced oxidation processes will be discussed, and their applications in both reactive and stable organic radicals in air pollutant removal will be explored.