Photocatalyst nanocomposite

A photocatalyst nanocomposite, comprising:

• Au nanoparticles, hexagonal wurtzite ZnO nanoparticles, and reduced graphene oxide (rGO),
• wherein the photocatalyst nanocomposite is made by the method of
• preparing an aqueous suspension of zinc acetate, chloroauric acid, and graphene oxide;
• mixing the aqueous suspension with a date seed extract to form a mixture;
• and
• heating the mixture at a temperature in the range of 100-200° C. for a time in the range of 10 to 20 hours to form the photocatalyst nanocomposite;
• wherein the date seed extract is prepared 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 and separating solids to form the date seed extract in the form of a liquid,
• wherein the photocatalyst nanocomposite comprises rGO in an amount in the range of 40 wt. % to 60 wt. % of the total weight of the 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;
• and the Au nanoparticles are present in an amount in the range of 2 mol. % to 10 mol. % based on the molar amount of the ZnO nanoparticles, and
• wherein the photocatalyst nanocomposite catalyzes the photodecomposition of methyl orange in an aqueous solution at a faster rate than a photocatalyst nanocomposite prepared by a substantially similar method but with NaOH instead of a date seed extract.