Nano Adsorbents for Oil Pollution Removal in the Caspian Sea: A Comprehensive Review of Advances, Mechanisms, and Challenges

Abstract

The Caspian Sea, the world's largest enclosed inland water body, faces chronic and acute oil pollution due to intensive hydrocarbon extraction, transportation, natural seeps, and riverine inputs. Its enclosed nature, moderate to high salinity (12–13.5 g/L), seasonal low temperatures, and ongoing sea-level decline pose significant challenges to conventional remediation methods. Nano adsorbents have emerged as a promising advanced solution, offering superior sorption capacities (up to 48.2 g oil/g for graphene/chitosan aerogel tested with Sardar-e-Jangal crude), rapid kinetics (minutes to hours), excellent selectivity in saline and cold conditions, and high recyclability (up to 11–20 cycles). Materials such as graphene-based hybrids, chitosan composites, magnetic nanoparticles, and emerging types (CNTs, silica aerogels, smart hybrids) outperform traditional sorbents by 5–20 times in capacity and speed while effectively handling emulsified light crudes. However, high production costs, potential ecotoxicity, aggregation in brackish water, and scalability barriers remain key limitations. This review synthesizes the types, mechanisms, performance, and Caspian-specific applications of nano adsorbents, recommending greener synthesis, field-scale pilots, life-cycle assessments, and international regulatory frameworks to enable sustainable deployment and protect this ecologically and economically vital ecosystem.