Nowadays, the valorization of organic wastes using various carbon-capturing technologies is a prime research area. The anaerobic digestion (AD) technology is gaining much consideration in this regard that simultaneously deals with waste valorization and bioenergy production sustainably. Biochar, a well-recognized carbonaceous pyrogenic material and possessing a broad range of inherent physical and chemical properties, has diverse applications in the fields of agriculture, health-care, sensing, catalysis, carbon capture, the environment and energy. The nano-biochar-amended anaerobic digestion approach has intensively been explored for the past few years. However, an inclusive study of multi-functional roles of biochar and the mechanism involved for enhancing the biogas production via the AD process still need to be evaluated. The present review inspects the significant role of biochar addition and the kinetics involved, further focusing on the limitations, perspectives, and challenges of the technology. Additionally, the techno-economic analysis and life-cycle assessment of biochar-aided AD process for the closed-loop integration of biochar and AD and possible improvement practices are discussed.

In recent decades, several studies have been conducted on sustainability progress with high efficiency of renewable energies by utilizing advanced nano-module catalysts. Some collaborative studies advocate the unique characteristics of unconventional materials, including carbon nanotubes, nanosheets, nanoparticles, conducting polymers, integrated nano polymers, nano enzymes, and zero-dimensional nanomaterials/carbon dots (CDs) at the atomic and molecular level to generate efficient energy from various biomass substrates. Nanotechnology-based catalysts are considered a crucial tool for revolutionizing various energy-related applications. This review article addresses the sustainable and scarce biomass resources to synthesize CDs, properties, mechanisms, and insights with the advancement of research on CDs as nanocatalysts in the field of energy applications. These materials possess exceptional and rapidly expanding features such as being non-toxic, biocompatible, having excellent electrocatalytic activity and photoluminescence, and being highly dispersible in water. Because of these advantages, they are appealing for use in energy conversion and as storage material. Moreover, the emphasis is placed on the function of CDs as nanocatalysts for energy storage devices, and relevant instances are provided to clarify the concepts. These advanced strategies of nanotechnology for energy storage and conversion are expected to play a vital role in promoting sustainability.