In this research, mercapto-silica coated magnetite (Fe3O4-SiO2-SH) has been prepared in aqueous solution through a simple approach so called a one-pot process. The Fe3O4-SiO2-SH was prepared in nitrogen condition by mixing magnetite, 3-mercaptopropyltrimethoxysilane (MPTMS), and sodium silicate (Na2SiO3) solution extracted from rice hull ash, and adjusting the pH of 7.0 using hydrochloric acid. The residue was washed with deionized water, dried at 150°C and separated with an external magnetic field. In that work, the volume of MPTMS and Na2SiO3 was varied and the total amount of Si represented as silica was kept constant. Characters of the material including the functional group presence, the structure, the porosity, the morphology and stability toward various solvents were identified and evaluated. Results of characterization indicated that mercapto-silica has been coated magnetite particle with a simple one-pot process. Coating mercapto-silica on magnetite increases particle size, surface area, and chemical stability. Additionally, Fe3O4-SiO2-SH also shows high stability toward various organic solvents. The magnetic property of magnetite does not change after coating and the addition of nonmagnetic material still gives high value of maximum saturation magnetization. The presence of mercapto groups effective for interaction with heavy metal ions, the high chemical stability without removing the magnetic property promises the prospective application of Fe3O4-SiO2-SH in the future such as for separation and removal of heavy metal ions from aquatic environments.

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Chrome (VI) has a high level of toxicity. Formaldehyde is potential to be developed as a substitute of chrome tanning agent. The aims of this study are to explain the amount of formaldehyde bound, shrinkage temperature, tensile strength, and tear strength on Mondol stingray (Himantura gerrardi) leather. Pickled mondol stingray has been used as raw material. The study was divided into 4 treatments, that is P.I (formaldehyde 2%), P.II (formaldehyde 4%), P.III (formaldehyde 6%), and P.IV (formaldehyde 8%). The method used is drum tanning. Shrinkage temperatures, tensile strength and tear strength of P.I and P.II are significantly different from P.III and P.IV, but P.I is not significantly different from P.II, whereas P.III is not significantly different from P.IV. P.III is shown to improve the quality of leather stingray more than P.I and P.II, and has fulfilled the requirements of leather stingray according to SNI. 06-6121-1999. It can be concluded that the optimal level of formaldehyde tanning agent that can be used as a chrome tanning agent substitute in tanning Mondol stingray skin is formaldehyde 8% (P.III).

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Two novel materials of 2-aminobenzimidiazole (AB) and 1-(o-tolyl)biguanide (TB) modified silicas coated on the iron sand magnetic material (MM@SiO2/AB and MM@SiO2/TB) have been synthesized and were used to adsorb Au(III) from Au/Cu/Ni solution. Silica layering MM was modified with polyamino compounds via a sol-gel process using a sodium silicate solution, 3-chloropropyltrimethoxysilane (CPTS) and modifier compounds. Adsorption of Au(III) on MM@SiO2/AB and MM@SiO2/TB was investigated in a batch system by varying pH, initial concentration, contact time and the presence of other metal ions (Cu(II) and Ni(II)). The results showed that MM@SiO2/AB and MM@SiO2/TB were successfully synthesized through the sol-gel process using cross-linking agent CPTS. Adsorption of Au(III) on MM@SiO2/AB and MM@SiO2/TB decreased with the increase of pH and followed the Langmuir isotherm models with adsorption capacity of 17.15 and 9.44 mg/g, respectively. The adsorption kinetics fit to pseudo-second-order model with the rate constants of 1.16 × 10-2 and 1.46 × 10-2 g mg-1 min-1, respectively. MM@SiO2/AB and MM@SiO2/TB gave a high selectivity towards Au(III) in a mixture of Cu(II) and Ni(II). The desorption using thiourea 1 M solution in 1 M HCl of metal ions showed that percentage of Au(III) desorbed was higher than that of Cu(II) and Ni(II).