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Charge carrier separation is considered as a key factor in enhancing the photocatalytic process and can be maximized by mitigating surface recombination. Following this idea, the surface of zinc oxide (ZnO) was modified by thermal treatment and nickel oxide (NiO) deposition. The influence of the ZnO thermal treatment and NiO deposition conditions on the ZnO surface chemistry and heterostructure interface properties were investigated by in situ X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) and correlated to the dye photodegradation efficiency. The XPS analysis confirmed a change of doping of ZnO after thermal treatment, which mainly influenced the developed band bending, and has led to an improved photocatalytic activity. For the same reason, the heterostructures based on the surface cleaned ZnO surface had higher photocatalytic efficiency than the ones based on non-cleaned ZnO. The temperature input during NiO deposition had negligible effect on the heterostructure interface properties. The photocatalytic efficiency did not follow the band bending evolution because of a dominant contribution of charge recombination across the NiO layer as indicated by PL analysis.