Isopropyl alcohol (IPA) at ppb level is the airborne molecular contamination regarded as a potential pollutant for semiconductor processes. An internal-illuminated monolith photoreactor (IMR) was designed and assembled to transmit and spread light uniformly by optical fibers inside every monolith channels. TiO2 and Ag/TiO2 photocatalysts were synthesized and coated on the surface of the monolith. The coating layer was completely covered the monolith surface and fully characterized by SEM, high-resolution TEM, EDS, BET, XRD, UV-vis, and XPS techniques. The photodegradation of gaseous IPA at ppb level in IMR was then investigated under various operating conditions such as retention time, initial IPA concentration, Ag-decorated contents, and diameter of the optical fiber. The experimental results show that IMR significantly improves the IPA removal efficiency. The enhanced efficiency of light utilization, which can be attributed to the excellent activity performance, is due to unique light distribution by optical fibers and well-coated photocatalyst in every monolith channels. At the optimal operation, 78.6% removal efficiency and 99.5% CO2 selectivity was achieved over Ag/TiO2 photocatalyst. It believes that IMR could be potentially applicable to cleanroom in the semiconductor industry. (C) 2016 Elsevier B.V. All rights reserved.