50 ◦ C for about 30 min while the gel was continually mixed. The
mixture was held at this temperature for another 60 min. The tem- perature of the mixture was increased to 96 ◦ C for 30 min, and held for a further 60 min. The ultimate mixture was neutralized with sodium hydroxide solution and cooled down to 25 ◦ C, after which the produced particles were isolated from the water, washed to remove divalent ions, filtered, and dried with a frizzed dryer.