Emerging nanotechnologies for paint wastewater treatment: Trends, challenges, and sustainable solutions

The paint industry generates complex wastewater streams filled with recalcitrant organic compounds, heavy metals, pigments, surfactants, and volatile organic compounds (VOCs), which are acute threats to aquatic environments and human health. Conventional treatment technologies, such as coagulation, flocculation, sedimentation, and biological treatment, are generally not effective in removing contaminants completely, particularly at trace levels or when pollutants are chemically stable. Nanotechnology has emerged as a revolutionary technology for treating paint wastewater with outstanding advantages over the last few decades, owing to its high surface area, enhanced reactivity, tunability in surface chemistry, and multifunctionality. This review critically evaluates recent advances in nanomaterials, including metal and metal oxide nanoparticles, carbon-based nanostructures, nanocomposites, and photocatalysts, with a focus on their removal mechanisms, efficiencies, and application trends. Prospects such as hybrid nanomaterial systems, membrane-nanotechnology integration, and green synthesis techniques are discussed, along with their scaling-up potential. Challenges such as nanoparticle recovery, toxicity, environmental persistence, cost, and regulatory loopholes are also addressed. Finally, solutions and future research directions are proposed for scaling up the safe, efficient, and sustainable application of nanotechnology to treat paint wastewater. This merging aims to guide researchers, engineers, and policymakers to innovative and sustainable wastewater treatment approaches that facilitate global sustainability goals.