Mukesh Sharma

Dissolution of α-chitin in deep eutectic solvents

Deep eutectic solvents (DESs) consisting of mixtures of choline halide (chloride/bromide)–urea, choline chloride–thiourea, chlorocholine chloride–urea and betaine hydrochloride–urea were demonstrated to be effective solvent systems for α-chitin. The dissolution of the biopolymer in the DESs was carried out by conventional heating, heating under microwave irradiation and heating assisted by ultrasonication under an inert atmosphere. Microwave and ultrasonication helped to reduce the time and temperature required for dissolution. Maximum dissolution of the biopolymer (9% w/w) was observed in the DES consisting of choline chloride–thiourea. The absence of insoluble particles in the solutions was confirmed by optical light microscope. No remarkable degradation of chitin during the dissolution process was observed upon investigations using FT-IR, XRD, 1H NMR, TGA, viscometry and rheology.

Rapid dissolution of DNA in a novel bio-based ionic liquid with long-term structural and chemical stability: successful recycling of the ionic liquid for reuse in the process

DNA from salmon testes was solubilised in two bio-based ionic liquids up to 3.5% w/w in 6 h. No structural degradation of the molecule was observed for the sample solubilised in choline-indole-3-acetate (chol-IAA). However, the molecule was found to be denatured in choline-indole-3-butyrate (chol-IBA). The structural and chemical stability of the DNA molecules after six months of storage in the former was established. Further recyclability of the ionic liquid with very high yield (90-95%) for consecutive reuse in the redissolution of DNA was demonstrated.

Deep eutectic solvents as efficient solvent system for the extraction of κ-carrageenan from Kappaphycus alvarezii.

Three different deep eutectic solvents (DESs) prepared by the complexation of choline chloride with urea, ethylene glycol and glycerol along with their hydrated counterparts were used for the selective extraction of κ-carrageenan from Kappaphycus alvarezii. Upon comparison of the quality of the polysaccharide with the one obtained using water as extraction media as well as the one extracted using widely practiced conventional method, it was found that, the physicochemical as well as rheological properties of κ-carrageenan obtained using DESs as solvents was at par to the one obtained using conventional method and was superior in quality when compared to κ-carrageenan obtained using water as solvent. Considering the tedious nature of the extraction method employed in conventional extraction process, the DESs can be considered as suitable alternative solvents for the facile extraction of the polysaccharide directly from the seaweed. However, among the hydrated and non-hydrated DESs, the hydrated ones were found to be more effective in comparison to their non-hydrated counterparts.

Choline chloride-thiourea, a deep eutectic solvent for the production of chitin nanofibers.

Deep eutectic solvents (DESs) consisting of the mixtures of choline halide (chloride/bromide)-urea and choline chloride-thiourea were used as solvents to prepare α-chitin nanofibers (CNFs). CNFs of diameter 20-30 nm could be obtained using the DESs comprising of the mixture of choline chloride and thiourea (CCT 1:2); however, NFs could not be obtained using the DESs having urea (CCU 1:2) as hydrogen bond donor. The physicochemical properties of thus obtained NFs were compared with those obtained using a couple of imidazolium based ionic liquids namely, 1-butyl-3-methylimidazolium hydrogen sulphate [(Bmim)HSO4] and 1-methylimidazolium hydrogen sulphate [(Hmim)HSO4] as well as choline based bio-ILs namely, choline hydrogen sulphate [(Chol)HSO4] and choline acrylate. The CNFs obtained using the DES as a solvent were used to prepare calcium alginate bio-nanocomposite gel beads having enhanced elasticity in comparison to Ca-alginate beads. The bio-nanocomposite gel beads thus obtained were used to study slow release of 5-fluorouracil, an anticancer drug.

Preparation of tamarind gum based soft ion gels having thixotropic properties

Tamarind gum was used to prepare ion gels using both synthetic ionic liquids (ILs) namely 1-butyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium bromide and bio-based ionic liquids (Bio-ILs) namely choline acrylate, choline caproate and choline caprylate by heating cooling process. The gels were found to have good thermal stability and exhibited thixotropic behaviour. Upon relaxation after applied breaking strain, the recovery of gel structures after ten consecutive cycles was observed. The hydrogel of the gum prepared using ethanol aqueous solution had much inferior quality in terms of viscosity, viscoelasticity, thermal stability and thixotropicity when compared with the ion gels. The ion gels also showed very good adherence to human finger muscles and skin. The ion gels thus prepared may find application in electrochemistry, sensors, actuators and the gels prepared with Bio-ILs could even be useful in biomedical applications.

Fuel intermediates, agricultural nutrients and pure water from Kappaphycus alvarezii seaweed

The present work reports a standalone integrated scheme for the production of 5-hydroxymethyl furfural (HMF) and potassium sulphate (K2SO4) from granular biomass rich in the sulphated polysaccharide, κ-carrageenan. Fresh Kappaphycus alvarezii seaweed was crushed to expel the juice rich in KCl (0.7 m3 t−1 of fresh seaweed) and granular biomass (0.04 t dry weight per t of fresh seaweed). The latter yielded κ-carrageenan through seawater extraction. HMF was derived from this phycocolloid through reaction with Mg(HSO4)2 acid catalyst and isolated in pure form. Galactose was a co-product which remained in the aqueous phase. The aqueous phase was recycled up to 10 times by maintaining a constant acid strength, and utilized thereafter for the recovery of K2SO4. Selective crystallization of K2SO4 was guided by the phase diagram and use was made of a part of the seaweed juice in this process. The spent aqueous phase rich in galactose was subjected to further reaction with HCl obtainable through bipolar electro-dialysis (ED) of seaweed juice. The reaction yielded levulinic acid (LA) and formic acid (FA) in nearly equal proportions. The processing of 1 t of granular biomass was computed to require 30.15 GJ of energy and would yield 0.18 t HMF, 0.056 t LA, 0.020 t FA, 0.27 t K2SO4, and 5.77 m3 pure water. The process energy requirement for the scheme can be met from additional supplies of granule (3.35 t). Combustion/gasification of this biomass would yield additionally 0.74 t glaserite fertilizer and the required amount of H2SO4 for Mg(HSO4)2 preparation.

Deep eutectic solvent promoted one step sustainable conversion of fresh seaweed biomass to functionalized graphene as a potential electrocatalyst

Herein we report a facile method for the scalable production of Fe3O4/Fe doped graphene nanosheets (Fe3O4/Fe–GN) from a naturally abundant seaweed resource. The granules that remained after the recovery of liquid juice from a fresh brown seaweed, Sargassum tenerrimum, were utilized as a raw material and a deep eutectic solvent (DES) generated by the complexation of choline chloride and FeCl3 (ChoCl–FeCl3) was employed as a template as well as a catalyst for the production of graphene nanosheets. Pyrolysis of a mixture of seaweed granules and DES at 700–900 °C under a 95% N2 and 5% H2 atmosphere resulted in the formation of Fe3O4/Fe–GN with a high surface area (220 m2 g−1) and high electrical conductivity (2384.6 mS m−1). The synthesized nanosheets were then tested for their electrocatalytic activity in the oxygen reduction reaction (ORR) in an alkaline fuel cell. The electrocatalyst demonstrated a positive onset potential, high cathodic current density, low hydrogen peroxide formation ( 80% activity of the catalyst, making the functionalized graphene sheets derived from Sargassum tenerrimum a sustainable replacement for existing precious metal-based ORR catalysts.

Self-healing guar gum and guar gum-multiwalled carbon nanotubes nanocomposite gels prepared in an ionic liquid

Guar gum is a galactomannan extracted from the seed of the leguminous shrub Cyamopsis tetragonoloba. It was found to form a soft viscoelastic gel in 1-butyl-3-methylimidazolium chloride, an ionic liquid at an optimized concentration of 10%w/v. A nanocomposite gel of the gum with enhanced strength could be prepared with 0.2%w/v of multiwalled carbon nanotubes (MWCNTs) in the ionic liquid. When the gels thus prepared were subjected to surface fractures or bisected completely, they found to self-heal at room temperature without any external interventions. The self-healing process could be repeated several times. These viscoelastic gel systems showed thixotropic nature and recovery of the storage modulus with time for several cycles was observed upon rheological investigations. The interaction took place between ionic liquid, guar gum and MWCNT was studied by SEM, TEM, FT-IR, powder XRD and rheometry. The results suggested that, upon standing at room temperature development of electrostatic interactions and the van der Waals interactions among the ionic liquid molecules facilitated the formation of reversible noncovalent bonds and eventually activated the self-healing in the gel systems through appropriate chain entanglements.

A green and sustainable approach to utilize bio-ionic liquids for the selective precipitation of high purity agarose from an agarophyte extract

A few choline based bio-ionic liquids (bio-ILs) were employed for the first time for the selective precipitation of agarose from the hot seaweed extract of Gracilaria dura (an agarophyte) under ambient conditions. The method thus developed is much “greener” and economical in comparison with the methods widely practiced for agarose production. Among the bio-ILs, choline laurate was found to be the most effective for the isolation of agarose with a lower usage level (4.0%, w/w) with the yield of 14.0 ± 0.5% w/w. Agarose obtained by this process had the desired properties required for molecular biological applications and gel electrophoresis. Furthermore the bio-ILs were recycled and reused for subsequent batches of agarose isolation without compromising the yield and quality of biopolymers.

Simultaneous dehydration of biomass-derived sugars to 5-hydroxymethyl furfural (HMF) and reduction of graphene oxide in ethyl lactate: one pot dual chemistry

Low yield of chemicals is often identified as a major obstacle for the complete utilization of bioresources as a source of important chemicals and thereby limits their application in industries. The issue of low yield can be partially compensated by integrated processes, i.e., production of two or more chemicals from the same biomass using single or multistep processes. Herein, a simple pathway for simultaneous production of 5-hydroxymethyl furfural (HMF) from biomass-derived sugars by dehydration of fructose (molar yield 76.3%) using graphene oxide (GO) as acid catalyst and choline chloride (ChoCl) as additive in ethyl lactate is demonstrated. Moreover, during the course of reaction GO was reduced to produce six-layered graphene nanosheets (96% recovery). Furthermore, the solvent was recycled after recovery of both products and successfully reused for subsequent production of the two chemicals with high purity.