Composite coating for eliminating pollution by heavy metal chromium and VOCs from source and preparation method

A composite coating for eliminating pollution by chromium and VOCs from a source, comprising a conversion film layer and a coating surface layer, wherein:

• the conversion film layer is made from a surface pretreatment liquid, and the surface pretreatment liquid comprises the following components:
• an organic compound A having an aromatic ring and at least two phenolic hydroxyl groups in the molecule thereof or a hydrate of the organic compound A;
• an ionic compound B containing an element of zirconium and/or titanium and fluorine;
• a mixed solution C containing manganese fluoride;
• and
• an inorganic salt D containing potassium ions or sodium ions,
• wherein the coating surface layer is a FEVE-type fluorocarbon powder coating layer,
• wherein a molecular structure of the at least two phenolic hydroxyl groups in the molecule of the organic compound A is:
• wherein R2, R3, R4, R5, and R6 are selected from H or OH, and at least two of R2, R3, R4, R5, and R6 are OH, and
• R1 is selected from an amide group, a carboxyl group, or an aldehyde group.