Pore Engineering in γ-Fe₂O₃ Nanoparticles: Hierarchical Pores by Controlled Lixiviation Using Citrate Ligands

Porous magnetic nanomaterials are attracting increasing attention due to their potential applications in environmental remediation, catalysis, biomedical fields, and magnetic storage media. This paper presents a leaching-based pore engineering approach for the synthesis of porous γ-Fe2O3. This environmentally benign approach uses a citrate buffer for the leaching process. The citrate ligands play a role by binding to surface/interface ions and leaching them into the solution, affecting micropore widths. Concurrently, the citrate ligands also lixiviate smaller-sized particles in the size distribution, resulting in a 6% increase in the average mesopore size. A two-level hierarchical pore size regime is created. The smaller size regime results in a 33% increase in adsorption capacity, and the bigger size regime leads to a 36% enhancement in the mass transport rate of methylene blue (MB) in γ-Fe2O3 nanoparticles leached for 6 days. During ultrasonication for MB adsorption studies, a dynamic pore evolution is observed, leading to a remarkable 183% increase in the MB adsorption capacity for sixth-day leached samples after 60 min. Changes in the pore width influence interparticle magnetic interactions. The blocking temperature decreases from 126 K in the as-prepared sample to 116 K in the sixth-day sample. This study highlights the potential of the citrate leaching process for pore engineering.