A challenging problem to create an efficient photocatalyst suitable for industrial water remediation, aiming to remove cyclic organic compounds attracts increasing attention. The current study aimed to clarify a few “dark spots” in the field, namely to find out if it is possible to make an efficient photocatalyst activated with visible light by using a simple and cheap strategy and what are the key factor impacting its efficiency. In this work, a new procedure to obtain spherical nanoparticles with the same average size but different amounts of oxygen vacancies and defects and dopant concentrations was developed. The approach based on hydrothermal treatment was suggested to obtain rod-shaped nanoparticles. The systematic study of photocatalytic behavior on the example of oxytetracycline and methylene blue degradation under visible light of widely available LED lamp was performed. Based on chemical and computational experiments the main factor affecting the process efficiency was determined.