Heavy Metals Contamination: Environmental Threats and Removal Using g-C₃N₄ Nanosheets

Developing countries have experienced rapid growth in their human populations, as well as a sharp increase in energy demand and consumption, emerging as a significant driving force for environmental degradation. In addition, urbanization, intensive mining operations, the growth of industrial hubs, infrastructure development, and the overuse of chemical fertilizers, pesticides, and herbicides in agricultural activities have all contributed to the acceleration of ecosystem degradation in an attempt to sustain an expanding population and raise living standards. Inadequate waste management techniques in several expanding towns in India have become a major source of heavy metal leakage into aquatic ecosystems in recent times, severely degrading the environment. Heavy metals with high density and weight have been identified as environmental pollutants due to their high toxicity level and ability to cause serious health issues if accumulated in the human body. Heavy metals (Cd, Cr, Pb, Hg, As, and Zn) pose significant risks to human health and ecological balance when present in excess, as they are not biodegradable, persist in the environment for extended periods, and accumulate through the food chain, unlike organic contaminants. Excessive amounts of heavy metals in the human body can cause major health problems, such as neurological system damage, anemia, liver and kidney problems, memory loss, cardiovascular disorders, and even cancer. In this sense, humans can be exposed to heavy metals in various ways, including drinking contaminated water, consuming food contaminated with heavy metals, inhaling dust containing heavy metal particles, and coming into contact with contaminated soil or water through their skin.

The development of an effective and sustainable method for removing heavy metals from contaminated water bodies is urgently needed to protect aquatic ecosystems, conserve natural water supplies, and mitigate environmental degradation. The development of effective and affordable wastewater treatment technologies remains a top research priority, despite the availability of numerous techniques for removing heavy metals. This is because traditional methods often have drawbacks, including incomplete removal, high operating costs, secondary pollution, and low selectivity at trace metal concentrations.

                           Highly effective functional materials with excellent chemical stability, outstanding adsorption capability, and environmental compatibility have garnered significant attention in recent years for sustainable heavy metal remediation. Functionalized nanomaterials, such as metal and metal-oxide nanoparticles, carbon-based nanomaterials, polymer nanocomposites, and newly developed two-dimensional materials, have demonstrated exceptional adsorption capacities and rapid kinetics in the search for highly effective nanomaterials for heavy-metal removal. Because of their strong affinity for metal ions through electrostatic interactions, coordination bonding, and surface complexation, as well as their tunable electronic properties, excellent thermal and chemical stability, and low toxicity, graphitic carbon nitride (g-C₃N₄) nanosheets have emerged as promising metal-free nanomaterials for heavy-metal removal. To improve adsorption and heavy metal removal performances, the two-dimensional layered structure of g-C₃N₄ nanosheets offers easily accessible active sites that can be further manipulated through exfoliation, doping, and nanocomposite creation. According to reports, heavy metals can be effectively removed from contaminated water using nanocomposites of g-C₃N₄ nanosheets coupled with cellulose nanofibers or plasmonic metals. By adjusting the calcination temperature and regulating the kind and concentration of dopant ions, the adsorption performance of this 2D nanomaterial (g-C₃N₄) can be improved. Furthermore, due to their porous character, these g-C₃N₄ nanosheets are expected to serve as a sustainable and adaptable substrate for next-generation CO₂ adsorbing nanomaterials.