Coal-based carbon dot for oil field tracer agent and preparation method of coal-based carbon dot

The invention discloses a preparation method of coal-based carbon dots for an oil field tracer agent. The preparation method comprises the following steps: 1, carrying out ultrasonic treatment on coal powder and a hydrogen peroxide solution at room temperature to obtain a reaction solution A; 2, the reaction liquid A is neutralized to be neutral and then poured into a filtering device to be subjected to reduced-pressure suction filtration, and filtrate obtained after filtration is taken as reaction liquid B; 3, carrying out size separation on the reaction liquid B; 4, drying the separated components below 1kD, carrying out heat treatment, carrying out reduced pressure suction filtration, and carrying out vacuum freeze drying to obtain corresponding coal-based carbon dots; and carrying out vacuum freeze drying on the separated components of more than 1kD to obtain the corresponding coal-based carbon dots. The prepared coal-based carbon dots can emit various fluorescence which is blue, cyan, green and yellow re