Pengaruh doping kobalt (Co) dan penambahan surfaktan sodium dodecyl sulfate (SDS) terhadap sifat fisis, sifat optis, dan aktivitas fotokatalitik nanokristal Zno = Influence of cobalt (Co) doping and surfactant sodium dodecyl sulfate (SDS) on the physical properties optical properties and photocatalytic activity of Zno nanocrystalline