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Chromium is a potentially poisonous and carcinogenic species, which originates from human activities and various industries such as leather, steel, iron, and electroplating industries. Chromium is present in various oxidation states, among which hexavalent chromium (Cr(VI)) is highly toxic as a natural contaminant. Therefore, chromium, particularly Cr(VI), must be eliminated from the environment, soil, and water to overcome significant problems due to its accumulation in the environment. There are different approaches such as adsorption, ion exchange, photocatalytic reduction, etc. for removing Cr(VI) from the environment. By converting Cr(VI) to Cr(III), its toxicity is reduced. Cr(III) is essential for the human diet, even in small amounts. Today, biopolymers such as alginate, cellulose, gum, pectin, starch, chitin, and chitosan have received much attention for the removal of environmental pollutants. Biopolymers, particularly polysaccharides, are very useful compounds due to their OH and NH 2 functional groups and some advantages such as biodegradability, biocompatibility, and accessibility. Therefore, they can be widely applied in catalytic applications and as efficient adsorbents for the removal of toxic compounds from the environment. This review briefly investigates the application of polysaccharide-based (nano)materials for efficient Cr(VI) removal from the environment using adsorption/reduction, photocatalytic, and chemical reduction mechanisms. [Display omitted] • Polysaccharide-based (nano)materials show remarkable potential for the removal of Cr(VI). • Recent studies on the preparation of polysaccharide-based (nano)materials have been reviewed. • Catalytic removal of Cr(VI) has been presented. • Future challenges for the removal of Cr(VI) using polysaccharide-based (nano)materials have been discussed. [ABSTRACT FROM AUTHOR]

Heck cross-coupling reaction (HCR) is one of the few transition metal catalyzed C C bond-forming reactions, which has been considered as the most effective, direct, and atom economical synthetic method using various catalytic systems. Heck reaction is widely employed in numerous syntheses including preparation of pharmaceutical and biologically active compounds, agrochemicals, natural products, fine chemicals, etc. Commonly, Pd-based catalysts have been used in HCR. In recent decades, the application of biopolymers as natural and effective supports has received attention due to their being cost effective, abundance, and non-toxicity. In fact, recent studies demonstrated that biopolymer-based catalysts had high sorption capacities, chelating activities, versatility, and stability, which make them potentially applicable as green materials (supports) in HCR. These catalytic systems present high stability and recyclability after several cycles of reaction. This review aims at providing an overview of the current progresses made towards the application of various polysaccharide and gelatin-supported metal catalysts in HCR in recent years. Natural polymers such as starch, gum, pectin, chitin, chitosan, cellulose, alginate and gelatin have been used as natural supports for metal-based catalysts in HCR. Diverse aspects of the reactions, different methods of preparation and application of polysaccharide and gelatin-based catalysts and their reusability have been reviewed. Current trends, challenges and future prospects exploiting the sustainable applications of chitin, chitosan, starch, cellulose, pectin, alginate, gelatin and gum based (nano)catalysts for the Heck coupling reactions, are highlighted. [Display omitted] • Advances in Heck coupling reactions by biopolymer-based catalysts are described. • Synthetic methods for attaining biopolymer-based catalysts are highlighted. • Catalytic activity of chitin, chitosan, starch, cellulose, pectin, alginate, gelatin and gum based catalysts are presented. • Mechanistic details are provided for Heck coupling reactions using biopolymer-based catalysts. • Future challenges pertaining to Heck coupling reactions using biopolymer-based catalysts are discussed. [ABSTRACT FROM AUTHOR]

• Advances in oxidation reactions by polysaccharide derived (nano)catalysts, are described. • Summary of synthetic methods for attaining polysaccharide derived (nano)catalysts. • Catalytic oxidation of alcohols, phenols, etc , are presented. • Future challenges on oxidation reactions using polysaccharide derived (nano)catalysts are discussed. Exploitation of polymers as effective starting materials to produce various valuable catalysts is attracting the attention of industrial and academic researchers. Moreover, among all polymers, natural polysaccharides such as cellulose, starch, alginate, gum, pectin, chitin and chitosan have drawn the most attention in recent years due to their unique structural features and important potential applications. A lot of studies have been performed on the synthesis of polysaccharide based (nano)catalysts and their application in chemical transformations. The present review provides recent developments on polysaccharides as green resources for the production of (nano)catalysts. Herein, the application of polysaccharide based (nano)catalysts derived from different organisms, plants or animals in oxidative transformations has been reviewed. These compounds can be used as economical and recyclable catalytic materials for various oxidation reactions including oxidation of alcohols, phenols, sulfides etc. The challenges in the application of polysaccharide based (nano)catalysts have also been discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Advances in catalytic and environmental applications of biopolymer-based ionic liquids are described. • Synthetic methods are highlighted for obtaining polysaccharide and lignin-based ionic liquids. • Catalytic activity of alginate, cellulose, lignin, chitosan and starch based ionic liquids have been reviewed. Today, the use of heterogeneous catalysts for various chemical and environmental transformations is of great interest. For this aim, researchers have applied different natural or synthetic supports for the heterogeneity of catalysts. The most widely used catalyst supports are perlite, bentonite, diatomite, and synthetic and natural polymers. Natural polymers (biopolymers) are one of the most promising compounds, which are widely applied as efficient and green supports. Among biopolymers, polysaccharides are highly regarded as catalyst supports by researchers. Many studies have been performed on improvements in the synthesis, characterization, and applications of biopolymers such as alginate, cellulose, lignin, chitin/chitosan and starch based catalysts. These polymers have some advantages such as biodegradability, biocompatibility, non-toxicity, and unique structures. This review paper describes the applications of alginate, cellulose, chitosan, starch and lignin supported ionic liquids (ILs) as catalysts for many catalytic and environmental applications. These catalysts are applied in reactions such as acetalization, hydrogenation, condensation, reduction, oxidation, epoxidation, and synthesis of 1,2,3-triazoles, dichlorophenylphosphine, diaryl ether, etc. As green resources, polysaccharides and lignin-based catalysts have many merits such as low cost, availability, good stability, recyclability, etc. [ABSTRACT FROM AUTHOR]