The characterization of potential adsorbents made of solid tofu waste immobilized on silica surface for removal of heavy metal ions

This study aimed to characterize the potential adsorbents made from solid tofu waste immobilized on silica surface for the removal of heavy metal ions. The composition of the potential adsorbent includes 6 g of solid tofu waste (STW), 50 mL of Na₂ SiO₃ (which contain 25% of SiO₂ with a density of 1.35 g/mL), and 3 mL of concentrated HCl. The result of the proximate analysis showed that the nutritional composition of solid tofu waste include crude protein (21.4%), crude fat (7.9%), carbohydrate (16.6%), crude fiber (4.9%), metal Ca (0.9%), ash content (1.2%), dry material (47.1%), and moisture content (3.3%). The bacterial population on solid tofu waste and silica-solid tofu waste were 5.7x 10⁵ CFU/g and 4.0 × 10³ CFU/g (based on total plate count, CFU= Colony Forming Unit) respectively. The XRD analysis showed that is both solid tofu waste and silica-solid tofu waste had amorphous structure, while the FTIR analysis showed that the interaction between solid tofu waste and silica particles was intermolecular hydrogen bond and dipole-induced-dipole interactions. The SEM-EDX analysis revealed the surface topography and elemental content of solid tofu waste immobilized on silica surface adsorbents. The analysis of the particle size showed that the adsorbent has an average micrometer scale size. In addition, the result of the BET-BJH analysis revealed that the total surface area, pore size and pore volume of silica-solid tofu waste adsorbent are 60.2103 m² /g, 0.147072 cm³ /g, and 5.9724 nm. The adsorbent was classified as mesoporous with a Horvath-Kawazoe micropore size of 0.300 nm.