A. Santhana Krishna Kumar

Graphene oxide–aluminium oxyhydroxide interaction and its application for the effective adsorption of fluoride

A novel aluminium oxy hydroxide [Al–O(OH)] modified graphene oxide was prepared by a chemical precipitation method wherein Al3+ ions could interact effectively with the different functional groups of graphene oxide (GO). The prepared (GO–Al–O(OH) adsorbent was tested for the effective defluoridation of water. The Al3+ modified graphene oxide adsorbent was characterized using FT-IR, FT-Raman, SEM-EDS, XRD and XPS studies. The thermodynamically feasible adsorption is supported by the pseudo second order kinetics and a high Langmuir maximum adsorption capacity (51.42 mg g−1) for the GO–Al–O(OH) adsorbent. Furthermore, we could treat 2.0 L of 5.0 mg L−1 fluoride ion solution to bring the level within the permissible limits and the regeneration of the adsorbent was done using ammonium hydroxide.

A novel ultrasonication method in the preparation of zirconium impregnated cellulose for effective fluoride adsorption.

In the present work, we propose for the first time a novel ultrasound assisted methodology involving the impregnation of zirconium in a cellulose matrix. Fluoride from aqueous solution interacts with the cellulose hydroxyl groups and the cationic zirconium hydroxide. Ultrasonication ensures a green and quick alternative to the conventional time intensive method of preparation. The effectiveness of this process was confirmed by comprehensive characterization of zirconium impregnated cellulose (ZrIC) adsorbent using Fourier transform infrared spectroscopy (FT-IR), energy dispersive X-ray spectrometry (EDX) and X-ray diffraction (XRD) studies. The study of various adsorption isotherm models, kinetics and thermodynamics of the interaction validated the method.

Effective adsorption of hexavalent chromium through a three center (3c) co-operative interaction with an ionic liquid and biopolymer

Biopolymers as well as ionic liquids are known for their potential applications. In this work, we report the utility of chitosan as an excellent platform for impregnating the ionic liquid, tetraoctylammonium bromide by ultrasonication and its subsequent adsorption for chromium(VI). The effective mass transfer due to sonication coupled with the hydrogen bonding interaction between chitosan-ionic liquid and the electrostatic interaction involving the amino groups in chitosan and hexavalent chromium governs this three center (3c) co-operative mechanism. The adsorption followed a pseudo second order kinetics with a Langmuir adsorption capacity of 63.69 mg g(-1). Various isotherm models were used to correlate the experimental data and the adsorption process is exothermic with a decreased randomness at the solid-solution interface. The thermodynamics of the spontaneous adsorption process could be explained through a positive co-operative effect between the host (chitosan) and the guest (ionic liquid). The adsorbed chromium(VI) could be converted to ammonium chromate using ammonium hydroxide, thereby regenerating the adsorbent. The method could be translated into action in the form of practical application to a real sample containing chromium.

Exploring the interesting interaction between graphene oxide, Aliquat-336 (a room temperature ionic liquid) and chromium(VI) for wastewater treatment

We report an interesting interaction between exfoliated graphene oxide (EGO), ionic liquid (IL) Aliquat-336 and hexavalent chromium. Graphene oxide was impregnated with the ionic liquid and the interaction primarily involves electrostatic affinity between the quaternary ammonium cation and surface hydroxyl groups in EGO. The IL-EGO combination functions as an effective adsorbent for hexavalent chromium. The IL-EGO adsorbent acts as a good host in welcoming the incoming guest, hydrochromate anion and several interesting interactions such as cation–π, electrostatic as well as anion–π could be conceptualized in this process. The adsorbent features are ably supported by various physico-chemical characterization techniques and the effect of various analytical parameters affecting the adsorption is examined in detail. A high Langmuir adsorption capacity of 285.71 mg g−1 is augmented by the thermodynamically favourable adsorption process. Kinetic studies confirm the pseudo second order model and furthermore, the process could be upgraded by column study to a sample volume of 1200 mL. Effective regeneration of the adsorbent could be accomplished with ammonium hydroxide and the potential of this novel adsorbent material has been examined in the total removal of chromium from a tannery effluent sample.

An efficient ultrasound assisted approach for the impregnation of room temperature ionic liquid onto Dowex 1×8 resin matrix and its application toward the enhanced adsorption of chromium (VI).

The work discussed in this paper is based on the utilization of ultrasound in conjunction with an ionic liquid (Aliquat 336) impregnated Dowex 1×8 resin for the effective adsorption of chromium. Ionic liquids are known for their selectivity toward metal extraction and ultrasonic medium offers efficient energy transfer for impregnating the ionic liquid in the resin matrix. The molecular interaction between the ionic liquid impregnated resin and chromium was studied through various physicochemical and spectroscopic techniques. The influence of various analytical parameters on the adsorption of Cr(VI) such as pH, adsorbent dosage, temperature and interference of foreign ions was studied in detail. Chromium (VI) was quantitatively adsorbed in the pH range of 3.5-4, with a high adsorption capacity of 230.9 mg g(-1) in conformity with the Langmuir isotherm model. The study of thermodynamic parameters showed that the adsorption process is exothermic and spontaneous. The adsorbent could be regenerated using 1 mol L(-1) HCl-0.28 mol L(-1) ascorbic acid mixture. Chromium could be effectively detoxified from an industrial effluent and finally the developed method was validated with the analysis of a certified reference material (BCR-715). The obtained results indicated that the ultrasonic assisted impregnation of the room temperature ionic liquid significantly enhances and improves the removal efficiency of Cr(VI).

Microwave assisted preparation of n-butylacrylate grafted chitosan and its application for Cr(VI) adsorption.

Biopolymers such as chitosan possess excellent properties suited for varied applications. In this work, we describe a novel microwave assisted method for the preparation of n-butylacrylate grafted chitosan adsorbent and its utility for the adsorption of chromium(VI). A 3 min irradiation time was enough to prepare the adsorbent, and techniques such as FT-IR, powder XRD, SEM and EDS were used for comprehensive characterization. The adsorption was effective at pH 3.5 with 25 mL of 20 ppm Cr(VI) solution. Langmuir, Freundlich, Dubinin-Radushkevich, Temkin, Elovich and Redlich isotherms were studied in detail. The ΔG, ΔH and ΔS parameters were evaluated to understand the adsorption thermodynamics. The adsorption involves the interaction of Cr(VI) with the hydroxyl and amino groups in chitosan.

Comprehending the interaction between chitosan and ionic liquid for the adsorption of palladium.

Biopolymers and ionic liquids are of prime importance in numerous applications. Recovery of industrially important noble metals such as palladium is of paramount significance considering their diverse applications. The main idea behind this work was to develop an effective strategy involving the impregnation of Aliquat-336 (ionic liquid) onto chitosan as a novel adsorbent for the adsorption of Pd(II). The analytical characterization was systematically done through FT-IR, XRD, SEM and EDX analysis. The interaction of the amino and hydroxyl functional groups in chitosan with the cationic nitrogen in the ionic liquid could be established through the above characterization. Several key parameters such as pH influence, amount of adsorbent, isotherms, kinetics and thermodynamic studies were also studied in detail for the adsorption of palladium. The effectiveness of adsorption was observed between pH 3.5-4.0 with 50 mL of 120 mg L(-1) Pd(II) solution giving a commendable monolayer adsorption capacity of 187.61 mg g(-1).

Microwave assisted solvent free green preparation and physicochemical characterization of surfactant-anchored cellulose and its relevance toward the effective adsorption of chromium.

The molecular interaction between tetrabutylammonium iodide (TBAI) and cellulose and its potential application for the adsorption of chromium is discussed in this paper. The biosorbent was prepared under solvent free conditions using microwave irradiation. A subtle balance between electrostatic and the hydrophobic effects governs the interaction of biopolymer with the surfactant. The interaction between the biosorbent and chromium was comprehensively studied using spectroscopic, thermal and surface analysis techniques. The various analytical parameters that influence the adsorption were optimized, and the maximum adsorption capacity of Cr(VI) obtained from the Langmuir isotherm model was found to be 16.67 mg g(-1). The sorption thermodynamics indicated the spontaneity and exothermic nature of adsorption. The biosorbent could be effectively regenerated using NaOH, which imparts greener aspect to the overall process.

A perspective on diverse adsorbent materials to recover precious palladium and the way forward

The removal and recovery of precious noble metals is noteworthy in a variety of applications. The need to recover these precious metals is associated with their high cost and other environmental impacts. The Nobel Prize conferred to Suzuki, Heck and Negishi in 2010 has underlined the remarkable significance of palladium as a catalyst in several important transformations. Palladium is one such platinum group noble metal that finds diverse applications in the automobile industry, electronics, jewelry, pharmaceutics, catalysis, etc. Therefore, the recovery of palladium has acquired importance. Methods such as liquid–liquid extraction and adsorption using biopolymers, polymeric resins, carbonaceous materials and silica based materials are discussed based on their removal efficiency, adsorption capacities, regeneration and other parameters. The review looks at a perspective based on the applicability of certain important adsorbents employed in recent years pertaining to the removal of palladium from aqueous solution, spent catalysts and industrial wastes.

An Integrated Use of Biopolymer-Ceramic Composites Towards Capacitor and Environmental Application

Biopolymer composite films comprising strontium titanate crystallites in [(100 - x) Cellulose - xSrTiO3] (0 ≤ x ≤ 90, in wt %) system were fabricated via solution casting technique. The X-ray diffraction (XRD) and scanning electron microscopic (SEM) studies were carried out on these composite films for structural and microstructural analyses. The dielectric constant of these composites increased with the concentration of strontium titanate crystallites dispersed in the cellulose matrix. Different dielectric mixture formulae were employed to rationalize the dielectric properties of the biopolymer composite systems. The composite films also showed promising application towards the removal of toxic chromium(VI).