Preparation of Exfoliated Ag-Laponite Nanocomposites Through a Freeze-Drying of Laponite Sols

Experimental

Analytically pure AgNO3 (Sigma-Aldrich, 99+%), NaBH4 (Aldrich, 99%), NaOH (Daejung, 98%), and redistilled deionized water were used for all sample preparations. Laponite RD (Rockwood) was used without further puri-fication and was considered as an anionic material with a negative charge (cationic exchange capacity) of about 50 mmol/100 g. Laponite RD (1.00 g, 0.50 mmol of negative charge) in 1000 mL water was set at pH 10 using NaOH (1 M, 5.5 mL) to avoid degradation.19 The solution was vigorously stirred for 12 h using a mechanical stirrer and filtered through 0.45 μm pore size Millipore filters. Excess NaBH4 (9.55 mg, 0.25 mmol) was added into the laponite solution and stirred for 5-10 more minutes. Separately, analytically pure AgNO3 (8.58 mg, 0.05 mmol) in 100 mL water was prepared and Ag colloids in laponite sol were generated by slowly dropping silver nitrate solution in water into the laponite solution containing NaBH4. The same pro-cedure was conducted for the preparation of other concentrations of colloidal Ag nanoparticles. Ag-laponite nano-composites were obtained with a freeze-drying process using a Samwon deep freezer (SFDSM24L). Ag-laponite nano-composites were washed with distilled water three times and dried at room temperature. The morphology and size of the resulting products were analyzed by a transmission electron microscope (TEM; JEOL JEM-3010) operating at 300 kV. The absorption spectra of the nanoparticles were recorded on a UV2201 Shimadzu UV-vis spectrophotometer using optical quartz cells. The solid state characterization of nano-particles in laponite was done by XRD (Rigaku, Ultima IV).