Heated aluminum oxide particles (HAOPs): From synthesis and mechanisms to applications and environmental aspects

Heated Aluminum Oxide Particles (HAOPs) have emerged as a promising class of engineered adsorbents with unique physicochemical properties suited for water purification. Their ability to effectively remove a range of contaminants positions them as valuable materials in advancing water treatment technologies. This review summarizes current research on HAOPs covering their synthesis, chemistry, adsorption mechanisms, applications, comparative analysis, environmental aspects, and future research directions. The HAOPs were synthesized by neutralizing aluminum sulfate hydrate with sodium hydroxide to form aluminum hydroxide precipitates, which were then heated at 110°C for 24 hours. They have a well-organized microcrystalline structure with abundant surface hydroxyl groups, contributing to high adsorption efficiency, and demonstrate significant potential in removing natural organic matter, phosphorus, and uranium from water sources. Compared to other adsorbents such as powdered activated carbon and iron oxide particles, HAOPs offer improved contaminant removal and fouling mitigation. Environmentally, their moderate-temperature synthesis reduces energy consumption and production costs. Effective regeneration extends material life and reduces waste, but proper disposal and management of spent HAOPs are crucial to avoid secondary pollution. Comprehensive life-cycle cost assessments and advanced regeneration methods are needed to improve economic feasibility and sustainability. Future research should focus on developing HAOP composites and exploring sustainable disposal and regeneration options to optimize their application in water treatment systems.