Correlation between particle size/domain structure and magnetic properties of highly crystalline Fe3O4 nanoparticles

Highly crystalline single-domain magnetite Fe3O4 nanoparticles (NPs) are important, not only for fundamental understanding of magnetic behaviour, but also for their considerable potential applications in biomedicine and industry. Fe3O4 NPs with sizes of 10–300 nm were systematically investigated to reveal the fundamental relationship between the crystal domain structure and the magnetic properties. The examined Fe3O4 NPs were prepared under well-controlled crystal growth conditions using a large-scale liquid precipitation method. The crystallite size of cube-like NPs estimated from X-ray diffraction pattern increased linearly as the particle size (estimated by transmission electron microscopy) increased from 10 to 64.7 nm, which indicates that the NPs have a single-domain structure. This was further confirmed by the uniform lattice fringes. The critical size of approximately 76 nm was obtained by correlating particle size with both crystallite size and magnetic coercivity; this was reported for the first time in this study. The coercivity of cube-like Fe3O4 NPs increased to a maximum of 190 Oe at the critical size, which suggests strong exchange interactions during spin alignment. Compared with cube-like NPs, sphere-like NPs have lower magnetic coercivity and remanence values, which is caused by the different orientations of their polycrystalline structure.This work was supported by JSPS KAKENHI Grant Number 26709061 and 16K13642. This work was partly supported by the Center for Functional Nano Oxide at Hiroshima University. The authors also gratefully acknowledge the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan for providing scholarships (C. W. K.)

Manufacture of a Hydrophobic Silica Nanoparticle Composite Membrane for Oil-Water Emulsion Separation

The superhydrophobic composite membrane was successfully manufactured by a sol-gel method by drying the surrounding pressure. Tetraethylorthosilicate (TEOS) was used as a hydrophobic agent, while waterglass was used as a source of silica. The effect of the water to waterglass ratio (noted at 16:1 and 19:1) was evaluated to study the hydrophobic properties of the silica film coated composite membrane surface. By measuring the water contact angle on the film surface, the highest contact angle was found to occur at the ratio of 19:1, which is 143.86°. The stability of the composite membrane was also investigated by immersing the membrane in water until day 6. The results show that the synthesized composite membrane has good stability until day 6. The hydrophobicity of the surface of the silica film membrane was found to be unaffected by immersion time. Furthermore, the hydrophobicity increased after 6 days due to the interaction of alkyl groups with the humidified environment, and the surface was more stable in hydrophobicity (i.e., the contact angle of water is 153.79°). In addition, hydrophobic properties were obtained, confirming that this film has the potential to be applied to the separation of oil-water emulsions

Fotodegradasi Zat Pewarna Tekstil (Rhodamin B) Menggunakan Adsorben Berbasis Material Komposit Kalsium Titanate (Catio3)

Komposit nanopartikel kalsium titanate (CaTiO3) berhasil disintesis melalui metode solid-state dan proses kalsinasi menggunakan kalsium karbonat (CaCO3) dan titanium oksida (TiO2) anatase. Bahan awal ditetapkan dalam perbandingan molar CaCO3/TiO2 yakni (1:1), (1:5), dan (1:7). Kedua bahan campuran CaCO3 dan TiO2 dilarutkan dan dihomogenkan melalui pengadukan. Campuran larutan yang telah homogen, diendapkan, dikeringkan dan dikalsinasi menggunakan suhu 900oC. Morfologi dan sifat mikro struktural dari bahan CaTiO3 dikarakterisasi menggunakan scanning electron microscopy (SEM) dan analisis energy dispersive X-ray (EDX). Komposit nanopartikel CaTiO3 selanjutnya digunakan untuk fotodegradasi zat pewarna Rhodamine B (RhB) di bawah sinar lampu UV. Hasil investigasi menunjukkan bahwa mekanisme penyerapan (adsorbsi) RhB dan sifat fotokatalitik dari CaTiO3 sangat tergantung pada komposisi bahan awal. Studi kinetika menunjukkan bahwa aktivitas fotokatalitik reaksi CaTiO3 terhadap RhB mengikuti model kinetika orde pertama. Lebih lanjut, 100mg RhB dapat terdegradasi sebesar 97.37% 23.34% pada penggunaan komposisi CaTiO3 sebanyak 0.5 hingga 2.0g dalam waktu 40menit. Hasil penelitian menunjukkan bahwa fotokatalis berbasis komposit CaTiO3 sangat efektif dalam mendegradasi zat pewarna RhB. Hal ini dikaitkan dengan besarnya luas permukaan aktif katalis serta kemampuan menghasilkan ion radikal pendegradasi RhB dari proses pemisahan muatan