Preparation method of composite hydrogel, composite hydrogel and application of composite hydrogel

The invention discloses a preparation method of composite hydrogel. The preparation method comprises the following steps: A, preparation of amidoximated polyacrylonitrile: dissolving polyacrylonitrile in an organic solvent for amidoxime modification treatment to obtain amidoximated polyacrylonitrile; B, washing the amidoximated polyacrylonitrile obtained in the step A with water, and conducting drying; C, mixing sodium alginate with the amidoximated polyacrylonitrile prepared in the step B, adding water, carrying out uniform mixing under stirring via a stirrer, dropwise adding the formed mixture into a calcium chloride solution, and conducting standing for 8-20 hours to obtain the composite hydrogel; and D, washing the composite hydrogel obtained in the step C with water, and carrying out freeze-drying. The preparation method provided by the invention is simple and convenient and low in cost; and the prepared finished product has the advantages of high uranium adsorption efficiency, strong uranium selective a