Direct Synthesis of Cobalt Incorporated Mesoporous Silica SBA-15: Effects of the Source and Adding Sequence of Cobalt Salts

Aysen Yilmaz^1*, Ebubekir Sen¹, Semih Seyyidoglu¹, Jie Fan²

¹Department of Chemistry, Middle East Technical University, 06531, Turkey.

²Department of Chemistry and Biochemistry, University of California, Santa Barbara, 93106, USA

Abstract

Highly ordered cobalt incorporated mesoporous silica SBA-15 (CoSBA-15) has been synthesized by single-step direct synthesis method. The degree of cobalt incorporation can be adjusted by variation of Si/Co molar ratio in initial synthesis gels. Mesoporous CoSBA-15 samples were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), N₂ sorption, infrared spectroscopy (FT-IR), and Inductively coupling plasma with optical emission spectroscopy (ICP-OES) elemental analyses. The effect of cobalt salt adding sequence with respect to the addition of triblock copolymers and siliceous sources was firstly investigated in this study. It is found that most Co ions exist as isolated framework species at low cobalt concentration in synthesis solution (Si/Co > 5). At high cobalt concentration (Si/Co ≤ 3), XRD data reveal that there is cobalt oxide nanocrystals exits either within the inorganic walls or within the SBA-15 channels. Cobalt species prefer to grow within the channels and formed nanoparticles with length of 50 ~ 100 nm when cobalt salts are added after addition of siliceous sources. Whereas, cobalt oxides grows within silica walls when cobalt salts are added before addition of siliceous sources. Controlled cobalt loading was possible to a maximum of 7.74 wt% by changing the cobalt source from chlorides to nitrates. No bulk cobalt oxide was detected outside the SBA-15 mesoporous silica particles.

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