Himani Medhi

Bio: Himani Medhi is an academic researcher from Gauhati University. The author has contributed to research in topics: Adsorption & Ecosystem. The author has an hindex of 5, co-authored 16 publications receiving 64 citations. Previous affiliations of Himani Medhi include Jawaharlal Nehru Centre for Advanced Scientific Research.

Kinetic and mechanistic studies on adsorption of Cu(II) in aqueous medium onto montmorillonite K10 and its modified derivative

Abstract: Copper is a widely used metal and known as a micronutrient; however, it is poisonous to the living organisms and has a permissible concentration of 1.3 mg L−1 in aqueous solutions. Thus, it is necessary to provide a suitable, environmentally friendly, and cost-effective copper removal process to save the world. The adsorption technique has been found to be an effective method for the treatment and removal of copper from aqueous solutions. Clays and clay minerals are naturally abundant adsorbents used in this field from very early days. The commercially available montmorillonite K10 clay mineral is modified via intercalation with tetramethylammonium cations to enhance its characteristic properties. The materials are characterized via CEC, FTIR, XRD, TGA-DTG, BET N2-adsorption, and SEM-EDX measurements, and their adsorption capacities for Cu(II) removal from a water system are investigated. Cu(II) adsorption study shows an increase in adsorption capacity from 41.71 to 96.31 mg g−1 after modification of Mt, and at pH 7.0, the Cu(II) removal capacity reaches up to 99.40%. The kinetics study and statistical analysis shows pseudo-second order kinetics as the best fit model for Cu(II) adsorption controlled by more than one mechanism. Thermodynamic study shows the endothermic and spontaneous nature of Cu(II) adsorption with higher affinity towards the TMA-Mt surface. The isotherm study shows the Langmuir maximum adsorption capacity of Mt and TMA-Mt to be 450.45 and 925.93 mg g−1, respectively, for Cu(II) removal from a water system.

Kinetics of Aqueous Cu(II) Biosorption onto Thevetia peruviana Leaf Powder.

Abstract: Copper is an essential micronutrient; however, as a result of its increasing demand, subsequent mining followed by its direct discharge into the environment has led to the contamination of our ecosystem. Thevetia peruviana (TP) is an ornamental herb of medicinal interest and is extensively used as an antipyretic and anticancer agent due to the presence of cardiac glycosides. In this work, we have explored the TP leaf powder as a biosorbent for Cu(II) removal from aqueous media and observed that it yields better results in comparison to other reported biosorbents for the removal of Cu(II). This work also emphasizes on the biosorption kinetics along with its plausible mechanism of interactions. The leaf powder characterized by FT-IR spectroscopy confirmed the diverse surface functionalities including hydroxyl, carbonyl, glycosides, etc. The morphology and elemental composition of the plant material have been investigated using SEM-EDAX analysis that confirms the heterogeneity and porosity of the biosorbent surface. The encouraging results revealed that the TP leaf powder could be used as a cost-effective biosorbent with an adsorption capacity of 187.51 mg g-1 for Cu(II) in aqueous media at pH ∼ 5 and a temperature of 303 K. The complex functionality of the TP surface most likely played a significant role in attaining fast equilibrium within 60 min by following pseudo-second-order kinetics, having a rate constant of 2 × 103 mg g-1 min-1 that has been confirmed with statistical tools such as regression coefficient, chi-squared, and sum of error square tests. The adsorption mechanism is controlled by diffusion of Cu(II) from the liquid phase to the solid phase of the TP biosorbent followed by the chemical interaction between the biosorbent and the adsorbate with slow intraparticle diffusion on the biosorbent surface. The adsorption of Cu(II) on TP has been observed to rise from 59.29 to 197.63 mg g-1 with the rise in the pH of the medium from 2 to 7. The adsorption of Cu(II) has been found to increase from 176.80 to 191.33 mg g-1 with increasing temperature from 293-308 K, confirming the endothermic nature of the adsorption process. The thermodynamic study revealed the adsorption process to be spontaneous with negative ΔG (-10.43 to -13.74 kJ mol-1) and that it has an endothermic nature with positive ΔH (54.24 kJ mol-1). The isotherm study for Cu(II) on TP followed the Langmuir adsorption isotherm model with the maximum monolayer adsorption capacity of 303.03 mg g-1 rather than Freundlich and Temkin isotherm models, which confirmed the chemical interaction between the sorbent and sorbate. FT-IR and SEM-EDAX analyses have also been used to confirm the adsorption of Cu(II) onto the TP surface. The present study revealed 99.7% Cu(II) desorption using 0.8 N HCl as the desorbent accompanied by a 69.71% regeneration efficiency of the TP biosorbent. After desorption of Cu(II), the regenerated TP could be disposed of in soil. The encouraging results revealed that TP could be used as an alternative and low-cost biosorbent for the removal of heavy metals from aqueous solutions.

Dynamics of chemical bond: general discussion

Abstract: Kunal Dhoke, Martin Zanni, Upendra Harbola, Ravi Kumar Venkatraman, Elangannan Arunan, King-Chuen Lin, Artur Nenov, Jonathan Skelton, R J Dwayne Miller, Jonathan D. Hirst, Vincenzo Aquilanti, John R. Helliwell, Srihari Keshavamurthy, Sai Ramesh, Mike Ashfold, Anuradha Pallipurath, Priyadarshi Roy Chowdhury, Sanghamitra Mukhopadhyay, Jemmis E D, Himani Medhi, Debabrata Goswami, Prasenjit Halder, Wolfgang Junge, Mahesh Hariharan, Santosh Kumar Singh, Siva Umapathy, Adithya Lakshmannam, Martin Meedom Nielsen, Sankarampadi Aravamudhan, Volker Deckert, Kenneth Ghiggino, Keisuke Tominaga and Alison Edwards

Hydrolysis of Hemicellulose and Derivatives-A Review of Recent Advances in the Production of Furfural.

Abstract: Biobased production of furfural has been known for decades. Nevertheless, bioeconomy and circular economy concepts is much more recent and has motivated a regain of interest of dedicated research to improve production modes and expand potential uses. Accordingly, this review paper aims essentially at outlining recent breakthroughs obtained in the field of furfural production from sugars and polysaccharides feedstocks. The review discusses advances obtained in major production pathways recently explored splitting in the following categories: (i) non-catalytic routes like use of critical solvents or hot water pretreatment, (ii) use of various homogeneous catalysts like mineral or organic acids, metal salts or ionic liquids, (iii) feedstock dehydration making use of various solid acid catalysts; (iv) feedstock dehydration making use of supported catalysts, (v) other heterogeneous catalytic routes. The paper also briefly overviews current understanding of furfural chemical synthesis and its underpinning mechanism as well as safety issues pertaining to the substance. Eventually, some remaining research topics are put in perspective for further optimization of biobased furfural production.

Recyclable photocatalyst composites based on Ag 3 VO 4 and Ag 2 WO 4 @MOF@cotton for effective discoloration of dye in visible light

Abstract: Photocatalysts are highly applicable in treatment of the water pollution. However, most of the applied photocatalysts suffer from the inapplicability and non-recyclability which limited their application. Herein, applicable and recyclable effective photocatalyst composites of Ag2WO4@MIL-125-NH2@cotton and Ag3VO4@MIL-125-NH2@cotton successfully prepared by direct synthesis of MIL-125-NH2 and Ag2WO4 or Ag3VO4 within the cotton fabric as supported template, sequentially. Agglomerated rock structure of Ag2WO4@MIL-125-NH2 and smaller particles of Ag3VO4@MIL-125-NH2 formed onto the cotton. The prepared composites applied as photocatalysts in the degradation of Methylene Blue (MB) and Rhodamine B (RhB) dyes in the visible light. The highest photodegradtion of dyes observed for Ag2WO4@MIL-125-NH2@cotton and Ag3VO4@MIL-125-NH2@cotton composites because of their low optical band gaps (2.36 eV and 1.87 eV) and their quenching in luminescent spectrum which helped in the ease transfer of photoexcited electrons. The rate constant (k2) for the photodegradation of MB (RhB) dye reduced significantly from 1.78 × 10–3 (2.8 × 10–3) L/mg min to 0.43 × 10–3 (1.04 × 10–3) L/mg min and 0.29 × 10–3 (0.79 × 10–3) L/mg min, when Ag2WO4 and Ag3VO4 incorporated in MIL-125-NH2@cotton composite, respectively. After 4 recycling process, the photodegradation activity of the applied composites diminished from 86–92% (68–80%) to 58–65% (47–54%). The obtained results declared the topmost photocatalytic activity in daylight of the recyclable prepared tri-component composites, reflecting their promising potentials in environmental applications.

Biosorption: A Review of the Latest Advances

Abstract: Biosorption is a variant of sorption techniques in which the sorbent is a material of biological origin. This technique is considered to be low cost and environmentally friendly, and it can be used to remove pollutants from aqueous solutions. The objective of this review is to report on the most significant recent works and most recent advances that have occurred in the last couple of years (2019–2020) in the field of biosorption. Biosorption of metals and organic compounds (dyes, antibiotics and other emerging contaminants) is considered in this review. In addition, the use and possibilities of different forms of biomass (live or dead, modified or immobilized) are also considered.