Dr. Billah focuses on the development of semiconductor metal oxides in the form of nanomaterials, thin films, and membranes for a wide range of multifunctional applications. These materials are explored for their potential in photocatalytic degradation of persistent organic pollutants (POPs), antibiotic removal from wastewater, heavy metal removal, water splitting, capacitive energy storage, Li-ion batteries, and antimicrobial activity. A significant part of the research is dedicated to understanding how synthesis routes, process parameters, and doping, particularly with non-metallic and rare-earth elements, influence the structure and properties of these materials. The materials systems include ZnO, CuO, TiO2, MnO2, BiVO4, and more. Additionally, Dr. Billah investigates conducting polymers like Polyaniline for multifunctional applications, as well as polymer matrix composites reinforced with semiconductor metal oxides for diverse applications, including food packaging. The research also extends to the development of thermal interface materials, which are vital for improving heat transfer efficiency in electronic devices, as well as investigating their electromigration failure behavior. Dr. Billah also works on surface modification of carbon nanotubes and other nanoparticles, along with carbon nanotube-reinforced metal matrix composites for advanced material solutions. He is actively involved in collaborations with faculties from both home and abroad, particularly in validating experimental results using first-principle approaches.