Cellulose based grafted biosorbents - Journey from lignocellulose biomass to toxic metal ions sorption applications - A review

In the recent past, renewable biobased natural polymers have been explored for their variety of potential applications. Among the various biorenewable polymers, cellulose with ingrained robust characteristics such as biodegradability, nontoxicity, durability, availability, thermal and mechanical stability etc., is extensively studied. These properties can further be improved by different modification techniques, among which the grafting is considered to be the most influencive one. In this comprehensive review article, the general chemistry of the cellulose, different biological, chemical, physical, physio-chemical extraction techniques for its extraction from lignocellulosic biomass, purification and bleaching techniques for extracted cellulose, methods of cellulose grafting, mechanism of free radical grafting initiated by a variety of chemical initiators, are reviewed. Further, recent developments in the field of metal ion sorption applications of grafted cellulosic copolymers, related factors affecting the metal ion sorption efficiencies of these cellulosic biosorbents such as extent of grafting, contact time, temperature, pH, interference of other metal ions, metal ion concentration, biosorbent dose, ionic strength of solution etc. are also reviewed. Various adsorption isotherms models-Langmuir, Freundlich, Temkin, Dubinin–Raduskevich and Redlich–Peterson; adsorption kinetic models-pseudo-first-order, pseudo-second-order, and intra-particle-diffusion models, useful for studying and evaluating the different sorption parameters, mechanism, and rate of sorption of toxic and hazardous heavy metal ions, are also summarized. In the last part of the review, adsorption thermodynamics, desorption and regeneration studies for the grafted cellulosic biosorbents are also reviewed.