In a typical experiment, 0.486 g Bi(NO3)3·5H2O (1 mmol) was put into 50 mL round-bottom flask which contained 25 mL 0.5 mol/L mannitol solution. The mixture was stirred and sonicated until Bi(NO3)3·5H2O was dissolved, followed by addition of 5 mL saturated sodium carbonate solution, resulting in the formation of uniform white suspension. Then the mixture was transferred to a Teflon-lined stainless-steel autoclave to perform solvothermal process at 150 °C for 12 h. After cooled down to the room temperature, the solid product was collected by centrifugation and washed with deionized water for five times. The sample was finally dried in a desiccator for few days at room temperature for further characterization (BS2). Other samples were also prepared under identical conditions by changing mannitol concentration, reagents and solvents. The detailed procedure is the same as described above and all the experiment parameters are listed