Valorisation of nuts biowaste: Prospects in sustainable bio (nano) catalysts and environmental applications
The nutrient resources make up a significant portion of wastes from all around the world. According to several recent studies, nuts and their residues are regarded as valuable natural resources for a nutrition and the other applications. The presence of waste nut residues in nature may lead to the environmental problems. The use of this waste for various applications is a very important issue. Nuts contain precious chemicals, which may be advantageous for preparing (nano)materials for the catalytic purposes. Different parts of nuts such as shell, kernel, extracts, etc. have valuable components, which can be used directly to make a variety of heterogeneous catalysts or as stabilising and reducing agents for nanoparticles. For example, the shell of some nuts is rich in lignin, cellulose and hemicellulose, which can be used as an effective and environmentally friendly supports for the heterogeneous catalysts. The design and application of safer and cheaper catalytic systems for different applications including organic synthesis, hydrogen evolution reactions, oxidation reactions, hydrolysis, degradation of pollutants, etc., are an extreme necessity in which nuts and their wastes can play a significant part due to their excellent chemical properties. Cheaper catalysts comprise of natural compounds such as biopolymers, aluminosilicates, kernel shells, zeolites, diatomites, agricultural wastes (such as bagasse pith, rice husk, smaise cob, coconut shell), nut wastes, etc. These compounds are of natural origin and therefore do not harm the environment. Since they are considered a type of waste, they are also cheap and economical. This review for the first time summarises the preparation of (nano)materials from nuts as an environmentally benign resources and their catalytic applications and highlights the industrial benefits and potential applications of these economically sustainable green resources to convert waste to wealth. The recent developments in the synthesis and applications of bio(nano)catalysts in catalytic and environmental areas have been discussed. In this review, the application of nuts as an efficient supports and green reducing agents for the synthesis of nanomaterials has been discussed. Due to the beneficial compounds, which they contain, activated carbon can be extracted from them and used to make heterogeneous catalysts. These bio(nano)catalysts are applied for organic synthesis, hydrogen evaluation reaction (HER), oxidation reactions and hydrolysis for an environmental applications in reduction and degradation of nitro compounds and organic dyes.