We have synthesized iron oxide doped carbon nitride with 0.5 to 2 wt.% iron oxide and characterized by XPS, TGA, FTIR, SEM, photoluminescence spectroscopy and photoelectrochemical measurements. A herbicide, dicamba was employed as model organic pollutant for degradation in presence with the catalyst and hydrogen peroxide. A 3D printed photon concentrator with two chips on board (COB) LEDs with visible light spectra and two complex parabolic mirror surfaces was used as photo-reactor. The findings revealed that both photocurrent and degradation of dicamba were functions of light intensity and concentrator geometry. The rapid degradation of dicamba can be attributed to the holistic and individual actions of structural components of the photocatalyst. Four distinct phenomena, including photocatalytic activity of carbon nitride, quenching of electron/hole pairs and generation of additional reactive hydroxyl radicals by hydrogen peroxide, Fenton and photo-Fenton activity of iron oxide component of carbon nitride in presence of hydrogen peroxide and photocatalytic activity of iron oxide alone in conjuncture with carbon nitride can contribute to the overall photocatalytic activity of the system. Liquid Chromatography-Mass spectrometry (LCMS) analysis of the degradation products showed loss of chlorine from the aromatic ring and evidence of free radical addition reactions in the course of photocatalysis.