Thermodynamically stable alpha-MoO3 nanoplates were synthesized using organic aliphatic acids as structure controlling agents and investigated photocatalytic degradation of methylene blue (MB) and rhodamine blue (Rh-B) in presence of sun light. Three different organic aliphatic acids, citric acid (CA), tartaric acid (TA) and ethylene diamine tetra-acetic acid (EDTA), were employed to control morphologies. CA and TA predominantly produced extended hexagonal plates where EDTA gave nanorods as well as nanoplates. PXRD studies confirmed the formation of alpha-MoO3 nanoparticles. HR-TEM and FE-SEM reveal the formation of plate morphologies with 20-40 nm thickness, 50-100 nm diameter and 600 nm lengths. The different morphologies of alpha-MoO3 nanoparticles lead to the tunable optical band gap between 2.80 and 2.98 eV which was obtained from diffused reflectance spectra (DRS). Interestingly, the synthesized alpha-MoO3 nanoplates exhibited strong photocatalytic degradation of MB and Rh-B up to 99% in presence of sun light without using any oxidizing agents. (C) 2015 Elsevier Ltd. All rights reserved.