Method of using gold/zinc/graphene oxide photocatalyst nanocomposite for water treatment

A method for making a gold/zinc/graphene oxide photocatalyst nanocomposite and treating a dye-contaminated aqueous composition comprising:

• preparing a date seed extract suspension by grinding a date seed and heating the ground date seed in water at a temperature in the range of 60 to 100° C. for a time in the range of 1 to 5 hours to form an extract suspension mixture,
• separating solids from the extract suspension mixture to form an extract mixture, then
• evaporating water from the extract mixture to obtain crystals of the date seed extract,
• preparing an aqueous suspension of zinc acetate, chloroauric acid, and graphene oxide, wherein the zinc acetate and chloroauric acid are present in an equimolar ratio;
• mixing the aqueous suspension with the date seed extract to form a mixture, and
• heating the mixture at temperature in the range of 100-200° C. for a time in the range of 10 to 20 hours to form the gold/zinc/graphene oxide photocatalyst nanocomposite;
• wherein the gold/zinc/graphene oxide photocatalyst nanocomposite comprises Au nanoparticles, hexagonal wurtzite ZnO, and reduced graphene oxide (rGO):
• wherein the Au nanoparticles are present in an amount of 2 mol. % to 10 mol. % based on the molar amount of the ZnO nanoparticles and the rGO is present in an amount of 48 wt. % to 52 wt. % of the total weight of the gold/zinc/graphene oxide photocatalyst nanocomposite,
• wherein the Au nanoparticles have a diameter in the range of 15 to 20 nm and are homogeneously distributed on the ZnO nanoparticles and on the rGO:
• the ZnO nanoparticles have a diameter in the range of 30 to 40 nm and are present on the rGO;
• then
• mixing the gold/zinc/graphene oxide photocatalyst nanocomposite with the dye-contaminated aqueous composition to form a treatment mixture;
• and
• exposing the treatment mixture to sunlight to photodecompose the dye and form purified water.