Abstract: Disclosed is a method of photochemically oxidizing gaseous halogenated organic compounds, an apparatus for photochemically oxidizing gaseous halogenated organic compounds, a lining insert for an apparatus for photochemically oxidizing gaseous halogenated organic compounds, and a method for producing such a lining. The principal method comprises: a) exposing gaseous halogenated organic compounds to ultraviolet light to oxidize the gaseous halogenated organic compounds into gaseous oxidation products; and b) reacting the gaseous oxidation products with an internal surface of a reaction chamber, the internal surface comprising a dry porous cementitious and chemically sorbent material which is chemically reactive with the gaseous oxidation products, with the gaseous oxidation products being reacted with the dry porous cementitious material to produce solid reaction products incorporated in sidewalls of the chamber.