Photocatalytic air treatment

A photocatalytic reactor 500 comprises: a reaction chamber arranged to receive an airflow comprising or more airborne contaminants, the reaction chamber comprises; a substrate 5003 having a first inner surface 5018A, 5118A, a second inner surface5018B, 51118B, a photo-catalyst 5004 for photocatalytic degradation of one or more of the contaminants disposed upon both the first inner surface and the second inner surface; and a light source 5009, 5010, arranged to illuminate at least a portion of the photo-catalyst disposed on the first inner surface and the second inner surface; wherein the profile of the first inner surface is a mirror image of the profile of the second inner surface, and wherein the first inner surface and the second inner surface are consecutive. The first inner surface and the second inner surface may have cross sections that are curved segments, or they may have parabolic arc shaped profiles. An air treatment device comprising the photocatalytic reactor is also disclosed.