In this study, a series of CuS/Bi4Ti3O12 p-n heterojunction materials were synthesized by a two-step process. Initially, the Aurivillius phase Bi4Ti3O12 (BT) was synthesized by a facile combustion route using urea as a fuel. The Bi4Ti3O12 was subsequently modified by deposition of CuS (5-20 wt%) using a hydrothermal route to prepare the heterojunction materials. The methods of synthesis and calcination temperature were important factors which influenced the morphology, particle size and phase purity of Bi4Ti3O12 material. Phase pure BT nanoplates with planar dimension of 150-200 nm and thickness between 50 and 70 nm were obtained at a calcination temperature of 600 degrees C. Pure CuS prepared by hydrothermal method, contained hierarchical microspheres with diameter in the range of 1.2-1.6 mu m. The heterostructure materials exhibited hierarchical flower like structure consisting of ultrathin CuS nanosheets and BT-nanoflakes. HRTEM and microstructural study revealed microscopic close interaction between the two phases. The optical and electrical measurement study suggested significant improvement in visible light absorption (400-800 nm) and charge carrier separation due to heterojunction formation. The CuS/Bi4Ti3O12 materials showed excellent photocatalytic activity for aqueous phase degradation of 2-methyl-4-chlorophenoxyacetic acid (MCPA) herbicide under visible light (> 95% degradation in 3 h). The rate constant for CuS/Bi4Ti3O12 materials was 4.5 times higher than the pure BT material towards MCPA degradation. The center dot OH and O-2(center dot-) radicals have been identified as the reactive species, the formation of which was confirmed by spectrometric method using terephthalic acid and nitroblue tetrazolium as molecular probes. The mechanism of MCPA degradation over the photocatalyst surface IShas also been elucidated using LC-ESI-MS, TOC and scavenger experiments.