Abstract

Acid catalysis is quite prevalent and probably one of the most routine operations in both industrial processes and research laboratories worldwide. Recently, “graphene”, a two dimensional single-layer carbon sheet with hexagonal packed lattice structure, imitative of nanomaterials, has shown great potential as alternative and eco-friendly solid carbocatalyst for a variety of acid-catalyzed reactions. Owing to their exceptional physical, chemical, and mechanical properties, graphene-based nanomaterials (G-NMs) offer highly stable Brønsted acidic sites, high mass transfer, relatively large surface areas, water tolerant character, and convenient recoverability as well as recyclability, whilst retaining high activity in acid-catalyzed chemical reactions. This comprehensive review focuses on the chemistry of G-NMs, including their synthesis, characterization, properties, functionalization, and up-to-date applications in heterogeneous acid catalysis. In line with this, in certain instances readers may find herein some criticisms that should be taken as constructive and would be of value in understanding the scope and limitations of current approaches utilizing graphene and its derivatives for the same.

Highlights

  • The prime source of energy on Earth for the present and foreseeable future is found in chemical bonds

  • Catalysis affords the means of changing the rates at which chemical bonds are formed and broken making it possible to elicit a desirable product over an undesired one, the phenomenon of chemical specificity

  • The current state-of-the-art in graphene-based acid catalysis (G-AC) can be largely categorized into graphite/graphene oxide (GO). Their sulfated (-O-SO3H) or sulfonated (-SO3H) derivatives. Whereas the former are obtained by chemical oxidation of natural graphite and/or subsequent exfoliation, the latter rely on the fundamental idea of surface functionalization of Graphene Oxide (GO) with sulfonating agents

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Summary

Introduction

The prime source of energy on Earth for the present and foreseeable future is found in chemical bonds. The unique spatial separation (similar to that of enzymes) as well as the self-similarity of structures between the active sites in these homogeneous molecular acids allow consistent energetic interactions between each active site and reaction substrate (even at ambient conditions) and make them responsive to most spectroscopic characterization techniques. Their sulfated (-O-SO3H) or sulfonated (-SO3H) derivatives Whereas the former are obtained by chemical oxidation of natural graphite and/or subsequent exfoliation, the latter rely on the fundamental idea of surface functionalization of GO with sulfonating agents. Both classes exhibit unique acid activity and hold great promise in replacing traditional homogeneous and heterogeneous acid catalysts in an environmentally benign manner (Table 1). It should be noted that in some applications, both GO and its sulfonated counterparts have been examined together and the organization of this review should be regarded as a flexible guide to the classification of these applications

Synthesis and Structure
Acidic Properties of Graphite Oxide and GO
Reduction of GO
Sulfonation of rGO and GO
Fuming Sulfuric Acid
Chlorosulfonic Acid
Sulfuric Acid
Applications of G-NMs in Heterogeneous Acid Catalysis
Michael-Type Friedel-Crafts Addition
Polymerization
Synthesis of Dipyrromethanes
Hydration of Alkynes
Aza-Michael Addition
Ring Opening of Epoxides and Acetalization of Aldehydes
Sulfonated Graphene and GO as Acid Catalysts Prepared by Diazonium Salt
Sulfated Graphene as Acid Catalyst Prepared by ClSO3H
Sulfated rGO as Acid Catalyst Prepared by H2SO4
Findings
Conclusions
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