The efficiency, stability, identity, and specific applicability of materials are most commonly altered during the synthesis stage. The most common phases of iron oxides, namely hematite, maghemite, and magnetite, and their synthesis approaches done so far were reviewed in this study. These three common phases of iron oxides are reported applicable in waste monitoring; in medicine as antimicrobial, anti-cancer, drug delivery, and MRI contrast agents; in agriculture as growth stimulants, antioxidants, and drought stress reducers; and in energy for hydrogen production, batteries, and energy storage. For the synthesis of these materials, different synthesis methods such as hydrothermal, solvothermal, sol-gel, co-precipitation, thermal decomposition, chemical vapor deposition, microemulsion, and the green approach were critically reviewed. Most of the methods are time-, cost-, energy-, and reagent-consuming methods. In this review, the issues of starting materials, calcination, reagents, and their consequences were discussed in detail. Finally, we indicated the existing synthesis challenges and outlined future research direction for advancing the synthesis methods.
A novel glutaraldehyde-functionalized urea-modified Fe₃O₄@TMU-16-NH₂ sorbent was synthesized and used for the magnetic solid-phase extraction (MSPE) of linuron and imidacloprid prior to high-performance liquid chromatography with ultraviolet detection (HPLC-UV). Various parameters affecting the MSPE efficiency were systematically screened and optimized using Plackett–Burman design (PBD) and Box–Behnken design (BBD), respectively, to achieve optimal analytical performance. Under the optimized condition, the proposed method exhibited good linearity (R2 > 0.9940) over the concentration range of 0.50–200.00 μg L−1, with LODs and LOQs of 0.12–0.14 and 0.41–0.46 μg L−1, for selected analytes, respectively. The method exhibited acceptable precision with relative standard deviations (%RSDs) ranging from 2.10 to 5.50%. The method achieved enrichment factors (EFs) of 128–135 and absolute recoveries (ARs) of 64.00–67.50%. The applicability of the developed method was successfully demonstrated through the determination of the target analytes in celery, soil, tomato, cucumber, and carrot samples. The obtained relative recoveries (RRs) were higher than 90%, confirming the reliability of the proposed method for the determination of linuron and imidacloprid in complicated matrices. The sorbent retained its extraction performance over nine consecutive reuse cycles, with no observable change in extraction performance. The greenness and practical applicability of the proposed method were also evaluated using the AGREEprep and BAGI metrics, yielding scores of 0.75 and 80, respectively. The proposed MSPE-HPLC-UV method enables the sensitive and reliable determination of linuron and imidacloprid at trace levels in complex matrices.
