Krishna G. Bhattacharyya

Adsorption of methylene blue on kaolinite

Abstract Methylene blue was adsorbed on kaolin from a local deposit. The raw kaolin itself was a relatively good adsorbent. The adsorption capacity was improved by purification and by treatment with NaOH solution. Calcination of the kaolin reduced the adsorption capacity. The adsorption data could be fitted by the Freundlich and Langmuir equations. Also, the thermodynamic parameters such as ΔH0, ΔS0 and ΔG0 were determined.

Kinetics of adsorption of metal ions on inorganic materials: A review

It is necessary to establish the rate law of adsorbate-adsorbent interactions to understand the mechanism by which the solute accumulates on the surface of a solid and gets adsorbed to the surface. A number of theoretical models and equations are available for the purpose and the best fit of the experimental data to any of these models is interpreted as giving the appropriate kinetics for the adsorption process. There is a spate of publications during the last few years on adsorption of various metals and other contaminants on conventional and non-conventional adsorbents, and many have tried to work out the kinetics. This has resulted from the wide interest generated on using adsorption as a practical method for treating contaminated water. In this review, an attempt has been made to discuss the kinetics of adsorption of metal ions on inorganic solids on the basis of published reports. A variety of materials like clays and clay minerals, zeolites, silica gel, soil, activated alumina, inorganic polymer, inorganic oxides, fly ash, etc. have been considered as the adsorbents and cations and anions of As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, and Zn as adsorbate have been covered in this review. The majority of the interactions have been divided into either pseudo first order or second order kinetics on the basis of the best fit obtained by various groups of workers, although second order kinetics has been found to be the most predominant one. The discussion under each category is carried out with respect to each type of metal ion separately. Application of models as given by the Elovich equation, intra-particle diffusion and liquid film diffusion has also been shown by many authors and these have also been reviewed. The time taken for attaining equilibrium in each case has been considered as a significant parameter and is discussed almost in all the cases. The values of the kinetic rate coefficients indicate the speed at which the metal ions adsorb on the materials and these are discussed in all available cases. The review aims to give a comprehensive picture on the studies of kinetics of adsorption during the last few years.

Adsorption characteristics of the dye, Brilliant Green, on Neem leaf powder

A novel adsorbent was developed from mature leaves of natural Neem trees for removing dyes from water. The adsorbent, in the form of fine powder, was found to be very effective in removing the dye, Brilliant Green, from aqueous solution. The adsorption process was carried out in a batch process with different concentrations of the aqueous dye solution as well as with different adsorbent doses, at a range of pH values and temperature. The suitability of the adsorbent was tested by fitting the adsorption data with Langmuir and Freundlich isotherms and by computing equilibrium thermodynamic and kinetic parameters, the values of which showed the Neem leaf powder as a promising adsorbent for dyes in aqueous solution.

Adsorption of Cr(VI) in layered double hydroxides

Abstract Adsorption of Cr(VI) by various uncalcined and calcined layered double hydroxides (LDH) of Mg–Al, Ni–Al and Zn–Cr types was investigated. Adsorption of Cr 2 O 7 2− through ion exchange in uncalcined LDH is slower in rate and smaller in amount than in calcined one where the adsorption occurs via rehydration. The nature and content of bi- and trivalent metal ions in LDH influence the adsorption. Calcined Mg–Al LDH with higher Al 3+ content in the precursor structure shows higher adsorption capacity. Adsorption is higher in the Mg–Al LDH than in Ni–Al and Zn–Cr LDH. A two-step first-order rate kinetics was observed for the adsorption process which follows the Freundlich-type adsorption isotherm. The explanation of adsorption phenomenon has been supported by X-ray diffraction patterns. The pH of initial Cr 2 O 7 2− solution has no affect on adsorption by calcined LDH. Release of Cr 2 O 7 2− from the adsorbed product depends upon the type of anion in the aqueous phase and CO 3 2− being the most effective ion. Calcination of the Cr 2 O 7 2− adsorbed product up to 1250°C has not resulted in the formation of Cr-immobilized phases.

Adsorption of heavy metals on kaolinite and montmorillonite: a review

The process of adsorption is considered to be one of the best water treatment technologies around the world. Different heavy metals, due to their toxic and hazardous nature, are possibly the most widespread groundwater contaminants imposing a serious threat to human health. In this review, an attempt has been made to discuss the use of two common clay materials, namely kaolinite and montmorillonite, along with their modified forms for heavy metal removal on the basis of published reports (2008 onwards). The modifications of clays have been attempted by the process of pillaring, intercalation, acid/base activation, functionalization, etc. The adsorption of toxic metals, viz., As, Cd, Cr, Co, Cu, Fe, Pb, Mn, Ni, Zn, etc., has been studied predominantly. Montmorillonite and its modified forms have much higher metal adsorption capacity compared to that of kaolinite as well as modified-kaolinite. The modification often boosted the adsorption capacities of the clays, however, reverse trends are also reported in some cases.

Adsorption of metal ions by clays and inorganic solids

This review deals with adsorption of metal ions, particularly those considered as hazardous, on clays and some inorganic solids and covers the publication years 2000–2013 describing and quantifying the use of isotherms to obtain the adsorption capacities of the solids. The inorganic solids in the review include clays and clay minerals, their modified forms (obtained by treatment with acids and alkalis, organic functionalization, etc.), zeolites, silica gel, soil, river sediment, activated alumina, inorganic polymers, red mud, inorganic oxides, fly ash, etc. The use of two parameter and three parameter linear isotherms are only discussed with a view to obtain quantitative description of adsorptive accumulation and separation of metal ions from aqueous solution on the solids. The extensively used isotherms are those of Freundlich, Langmuir, Dubinin–Radushkevich and Redlich–Peterson. How these isotherms are being used to obtain the adsorption capacities along with their interpretations form the bulk of the review. The review is divided into sections, each describing the use of a particular isotherm. The metal cations receiving immense importance in adsorption studies are As(III)/As(V), Cd(II), Cr(III)/Cr(VI), Cu(II), Co(II), Pb(II), Ni(II), Hg(II), and Zn(II), and the review covers both the cationic and the anionic metal ions. A few other cations such as Mn(II), Fe(III), Se(V), which have not received much attention, are also covered.

HZSM-5 catalysed conversion of aqueous ethanol to hydrocarbons

Abstract The conversion of aqueous ethanol to hydrocarbons, over HZSM-5 of silica-alumina ratio 206 and 40, is described. The effect of temperature (673–773 K) on product distribution reveals definite trends. The yield and distribution of the products were influenced by catalyst-binder (alumina) composition, dilution of feed and the silica-alumina ratio of the catalyst. It is seen that light olefins can be obtained in good yield at high temperature, in absence of a binder, with dilution of the feed and with higher silica-alumina ratio.

Adsorption of Crystal violet on raw and acid-treated montmorillonite, K10, in aqueous suspension.

Crystal violet is used as a dye in cotton and silk textiles, paints and printing ink. The dye is hazardous and exposure to it may cause permanent injury to the cornea and conjunctiva including permanent blindness, and in severe cases, may lead to respiratory and kidney failure. The present work describes removal of Crystal violet from aqueous solution by adsorption on raw and acid-treated montmorillonite, K10. The clay mineral was treated with 0.25 and 0.50 M sulfuric acid and the resulting materials were characterized by XRD, zeta potential, SEM, FTIR, cation exchange capacity, BET surface area and pore volume measurements. The influences of pH, interaction time, adsorbent amount, and temperature on adsorption were monitored and explained on the basis of physico-chemical characteristics of the materials. Basic pH generally favors adsorption but considerable removal was possible even under neutral conditions. Adsorption was very rapid and equilibrium could be attained in 180 min. The kinetics conformed to second order model. Langmuir monolayer adsorption capacity of raw montmorillonite K10 was 370.37 mg g(-1) whereas 0.25 M and 0.50 M acid treated montmorillonite K10 had capacities of 384.62 and 400.0 mg g(-1) respectively at 303 K. Adsorption was exothermic and decreased in the temperature range of 293-323 K. Thermodynamically, the process was spontaneous with Gibbs energy decreasing with rise in temperature. The results suggest that montmorillonite K10 and its acid treated forms would be suitable for removing Crystal violet from aqueous solution.

Adsorption of Co(II) from Aqueous Medium on Natural and Acid Activated Kaolinite and Montmorillonite

Abstract Hazardous metal cations enter water through the natural geochemical route or from the industrial wastes. Their separation and removal can be achieved by adsorptive accumulation of the cations on a suitable adsorbent. In the present work, toxic Co(II) ions are removed from water by accumulating them on the surface of clay minerals. Clay adsorbents are obtained from kaolinite, montmorillonite, and their acid activated forms, and are characterized with the measurement of XRD patterns, specific surface area, and cation exchange capacity. The adsorption experiments are carried out in a batch process in environments of different pH, initial Co(II) concentration, amount of clay, interaction time, and temperature. Adsorption of Co(II) on the clays increases continuously from pH 1.0 to 8.0 after which adsorption could not be carried out due to the decreasing solubility of Co(II). Under appropriate conditions, the adsorption of Co(II) is very fast at low coverage approaching equilibrium within 240 min and the interactions are best described by second order kinetics. Langmuir monolayer capacity has been computed in the range of 11.2 to 29.7 mg/g and Co(II) accumulation has the order of acid‐activated montmorillonite>montmorillonite>acid activated kaolinite>kaolinite. Adsorption of Co(II) on kaolinite and acid‐activated kaolinite is endothermic driven by entropy increase but the same process follows exothermically on montmorillonite and acid‐activated montmorillonite supported by entropy decrease. In both cases, spontaneous adsorptive accumulation is ensured by favorable Gibbs energy decrease. It is found that acid activation enhances the adsorption capacity of kaolinite and montmorillonite.

XPS study of mica surfaces

Abstract Muscovite mica surfaces were studied with X-ray photoelectron spectroscopy. The air-cleaved mica surfaces showed a large C1s peak in the range 285.3–285.9 eV indicating the presence of carbon species other than the adventitious. Normal emission and grazing emission spectra were utilised to calculate bulk and surface elemental ratios respectively for air-cleaved as well as vacuum-cleaved mica surfaces. Preferential attenuation of some peaks has been proposed for a few abnormal elemental ratios. Apparent shifts in binding energy due to sample charging were investigated for differently treated mica surfaces. Changes in the apparent shift are shown to be due to the existence of strong dipole fields at the surface resulting in a potential drop of as much as 3.6 V across the dipole layer.