▎ 摘　　要

NOVELTY - Composite hydrogel comprises polyvinyl alcohol, chitosan, graphene oxide and sodium alginate, where weight ratio of the polyvinyl alcohol and chitosan is 5:95-95:5. USE - The composite hydrogel is useful for adsorption of heavy metal ions and heavy metals in industrial sewage treatment (all claimed). ADVANTAGE - The composite hydrogel enables efficient adsorption of the heavy metal ions and has wider application prospects. The graphene oxide dispersion has good uniformity and stability, and does not produce agglomeration, and hence properties of the graphene oxide are improved. The preparation method is simple and recyclable, has strong operability and stable performance, and does not cause secondary pollution. DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for preparation method of the above-mentioned composite hydrogel, which involves (a) adding polyvinyl alcohol, sodium alginate and deionized water to three-neck flask, heating obtained solution in boiling water bath, and stirring the solution by mechanical stirrer for 1-4 hours for complete and uniform mixing of the solution, (b) heating the solution in water bath at 60-100 degrees C, adding chitosan to the solution, and stirring the solution uniformly for 2-10 hours, (c) cooling obtained solution to room temperature, adding graphene oxide to the solution, subjecting the solution to ultrasonication for 0.2-2 hours and stirring the solution for 0.2-2 hours for uniformly dispersing the graphene oxide in the solution, and (d) dropping obtained uniformly dispersed solution by syringe into 3% saturated solution of calcium chloride and boric acid to obtain chemically cross-linked and spherical hydrogel particles having particle diameter of 0.5-5 mm, allowing the hydrogel particles to remain soaked in the saturated solution for 12-36 hours and finally rinsing the particles with deionized water for 2-6 times.