Advances in production & activation of marine macroalgae-derived biochar catalyst for sustainable biodiesel production

[Display omitted] •Synthesis and activation of biochar derived catalyst is critically examined.•Activation of biochar catalyst has significant impact for biofuel production.•Challenge and way forward is presented by highlighting research gaps. Biodiesel is considered as a promising sustainable biofuel from renewable resources with lower pollutant emissions. However, high production cost, difficulty in recovering catalyst, and an expensive separation process associated with the use of homogeneous catalysts are still critical challenges. Heterogeneous catalysts derived from biomass are considered as viable options. Marine macroalgae-derived biochar owing to its vast surface area, diverse functional groups, presence of inorganics, and high porosity, could be considered as a suitable heterogeneous catalyst or as a supported catalyst for biodiesel synthesis. Thermochemical conversion processes, such as hydrothermal carbonization and pyrolysis, convert marine macroalgae biomass into biochar, which primarily composed of carbon, oxygen, and inorganics (Ca, K, Mg, Fe, etc.). The activation of macroalgae-derived biochar either physically or chemically played a vital role towards biofuel production. The catalytic activity and the performance of the macroalgae-derived biochar catalyst are influenced by its physicochemical properties (–SO3H group density, porosity, overall surface area, functional groups, and so on). Biodiesel production over marine macroalgae-derived biochar catalyst represents a more sustainable solution to current energy demands and develops economically beneficial biodiesel technology. This article provides a critical assessment of the marine macroalgae-derived biochar catalysts for the production of biodiesel. Initially, macroalgal biochar is produced through different thermochemical conversion technologies, including hydrothermal carbonization and pyrolysis, and its yield and physicochemical characteristics are discussed. After that, various techniques for the activation of macroalgae-derived biochar are discussed.