Rice Waste-Derived Carbon Nanomaterials: A Sustainable Approach to Nanotechnology

Rice is one of the excessive productions in India which comes with a large amount of agricultural waste (i.e., rice husks/rice straws/rice husk ash) that is frequently wasted or disposed of in environmentally detrimental ways. Thus, rice wastes serve as a sustainable/renewable feedstock for producing advanced carbon-based nanoscale materials, such as graphene or graphene-like nanosheets, carbon nanotubes, carbon quantum dots, activated porous carbon, and more. Emphasis is placed on green and low-cost synthesis routes such as pyrolysis, hydrothermal carbonization, chemical activation, and catalytic chemical vapor deposition, highlighting how process conditions govern material structure, surface chemistry, porosity, and functional performance. Rice waste contains an abundance of lignocellulosic-silica materials that allow the production of carbon-silica structures with hierarchical architectures, high surface areas, tunable pore networks, and abundant functional groups on their surfaces. These materials also provide good thermal, optical, electrical, and mechanical properties. The paper reviews the various physical and chemical properties associated with the production of carbon nanomaterials from rice waste and makes connections to their various applications, including their use as environmentally friendly solutions through water and air purification and the removal of harmful substances such as heavy metals and dyes; their application as energy storage devices (supercapacitors, batteries, and fuel cells); their use in detection and measurement (sensory technology); and their contribution to health and well-being (bioimaging). Valorization of waste from rice is beneficial to local economies by producing high-value carbon nanomaterials from low-value agricultural waste via a circular economy. By creating high value from rice waste, it provides alternatives to open burning or burying rice waste and is thereby a significant contributor to assisting local agriculture with increased economic advantages. Information is provided within this paper regarding current challenges toward commercializing carbon nanomaterials, including but not limited to scalability issues, substantial energy requirements, feedstock pretreatment issues, and impacts associated with the life cycle of carbon nanomaterials. Furthermore, the paper includes a list of proposed areas for future study to develop cleaner, more efficient, and commercially viable green nanotechnology alternatives.