Disclosed are various combinations of three different metal-oxide photocatalysts with three different bandgaps that can be used to harvest multiple wavelengths of incident solar radiation and to thus efficiently degrade recalcitrant contaminants. The photocatalysts are from the class of transition metal oxides and are non-toxic compounds based on earth-abundant materials. In some embodiments, particles of the photocatalysts are formed to be greater in diameter than about 0.1 μm in order to make them easier to filter out after treating the contaminant. In some embodiments, the metal-oxide photocatalysts are zinc oxide which is ultraviolet active, hematite which is active in the visible spectrum, and copper oxide which is active in the near infrared spectrum. Various combinations in various embodiments achieve measured contaminant degradation rates greater than the sum of the degradation rates of the individual photocatalysts that make up the combination.