Further, using equation ( ), the decrease in 'ε' over time was utilized to find the variation in the rate constant (k) of photocatalytic degradation. After completion of 4.0 hours, the total degradation of the dye under the same condition but with different photocatalysts was found to be clearly different. This showed from equation (5) only 14.6% degradation of the dye under dark conditions by FePM catalyst. Under light conditions, the highest degradation was 86.1% by FeAH, followed by 76.9% by FePM catalyst. However, the lowest of 29.3 by the FeBH catalyst was also observed (Fig. ). Moreover, the 14.6% degradation of the dye with the FePM catalyst under dark conditions, along with 10.2% without any catalyst under the same condition could be ascribed to difference may stem from the various sequential stages in photocatalysis. These are namely the efficiency of light absorption, generation of charge carriers (e -/h + ) and their lifetime (τ), migration of the charge (diffusion length, LD) to the surface or catalyst active sites, and then finally, the efficiency of the charge transfer (Fig. ) at the catalyst-dye interface. However, in most cases, the interfacial charge transfer step is a rate-determining step (k) in this process. Interestingly, in this experiment, the (k) appears to be intricately related to the morphology and interface structure of the catalyst systems. nanoparticles. However, on the contrary, the sphere-like FeAH, being α-Fe2O3 form, tops the list in terms of photocatalytic activity and thus underlines the inevitable role of the interface structure beyond the morphology. Thus, the highest activity by FeAH cannot be explained due to the possible effect of shape anisotropy alone. This may, however, involve the interfacial parameters like ESCA per unit mass, the number of active sites, (ø), and the (Rct) across the dye catalyst. Also, the observed first-order rate constant in this process suggests a heterogeneous catalysis regime, which generally has an interfacial charge transfer step as the rate-determining step.