## 2 Materials and Methods  
Cockle shells were obtained from a local beach, Pantai Bachok. The collected cockle shells were scrubbed under tap water with a brush to remove dirt and rinsed with double-distilled water (DDW). The cockle shells were finely crushed using a mortar and pestle, and then blended using a blender machine (Premier Super-g, India) into a fine cockle shell powder. The powder was then sieved using a stainless-steel Sieve Shaker AS 200 Control (Retsch GmbH, Haan, Germany) with an aperture size of 63 \(\upmu\)m to obtain micron size (10-63 \(\upmu\)m diameter). Then, 5 g of micron-sized cockle shell powder was dissolved into 20 mL of 5 M hydrochloric acid (HCl) 37%, Emsure(r) (Merck KGaA, Darmstadt, Germany) to form calcium chloride (CaCl\({}_{2}\)). The solution was filtered with filter papers (Filters Fioroni Filter Circles 70 mm, Lab Logistic Group GmbH, Meckenheim, Germany). Contamination products were extracted from the solution using an electric mixer spun at 500 rpm for 1 h at room temperature. The formed CaCl\({}_{2}\) was then diluted with 1 L DDW to form stock solution. Stock solution of K\({}_{2}\)CO\({}_{3}\) was prepared by dissolving 5 g of K\({}_{2}\)CO\({}_{3}\) ACS reagent, \(\geq\)99% (Sigma Aldrich, Steinheim, Germany) in 100 mL of DDW. Different volumes of DDW (0, 10, 20, 50, 60, and 70 mL) were then added to 10 mL of diluted CaCl\({}_{2}\) followed by the addition of 10 mL of diluted K\({}_{2}\)CO\({}_{3}\) at different feeding rates (1, 1.5, 2, and 2.5 h). The procedure was repeated using three different solvents of reaction, namely, methanol, Analytical Reagent Grade, Lot No. 1,352,421 (Sigma Aldrich, Steinheim, Germany); 70% ethanol, ChemPur(r) CAS No. 64-17-5 (Systerm, GmbH, Karlsruhe, Germany); or propanol, Analytical Reagent Grade, Lot No. 1,367,431 (Sigma Aldrich, Steinheim, Germany). The solutions were then left for 24 h to precipitate. Then, the supernatant solution was discarded and the resultant product was centrifuged using Eppendorf Centrifuge 5804 (Eppendorf North America Inc., Enfield, CT, USA) at 7000 rpm for 7 min. The acidity of the resultant solution was then neutralized by washing three times with DDW. The resultant product was either dried using a Memmert oven 100-800 (Memmert, Schwabach, Germany) at 110 \({}^{\circ}\)C for 24 h or by freeze drying; first by putting the resultant product in the Ilshin Europe Biobase DF8517 freezer (Ilshin Lab Co. Ltd., Ede, Netherlands) at \(-\)80 \({}^{\circ}\)C for 3 h and then at \(-\)108 \({}^{\circ}\)C for 48 h in the freeze-drying machine (Scanvac CoolSafe 4.5L, LaboGene ApS, Allerod, Denmark). The CaCO\({}_{3}\) powder derived from cockle shell, obtained using different parameters, was first characterized using a field-emission scanning electron microscope equipped with energy-dispersive X-ray (FESEM-EDX), LEICA EM SCD005, (Leica, Tokyo, Japan) to evaluate its morphology, particle size, and elemental composition. Then, the CaCO\({}_{3}\) powder was characterized with the Brunauer-Emmett-Teller (BET) method using TristarII (Micromerities Instrument Corporation, Norcross, GA, USA) for its average surface area and pore diameter. Once the optimization of CaCO\({}_{3}\) powder was achieved, it was then characterized with an X-ray diffractometer (XRD) using a Shimadzu XRD\(-\)6000 (Shimadzu Corporation, Kyoto, Japan) to study its crystallinity and phases using Cu K\(\alpha\) radiation (\(\uplambda=\) 1.5406 A, 40 kV at 30 mA). Then, the CaCO\({}_{3}\) powder was also characterized with Fourier transform infrared (FTIR) spectroscopy using an FTIR SPECTRUM RX1 (Perkin Elmer Inc. Hopkinton, MA, USA) spectrometer in the range of 600-4000 cm\({}^{-1}\) for determination of the chemical bonding of chemical substances. The thermal stability of CaCO\({}_{3}\) was then investigated with thermogravimetric analysis (TGA), using an SSC/5200 TG/DTA 220 (Seiko Instrument, Tokyo, Japan) with a temperature range of 50-900 \({}^{\circ}\)C and scan rate of 20 \({}^{\circ}\)C/min under N\({}_{2}\) atmosphere.