C. Rajagopal

Competitive Sorption of Cu(II), Pb(II) and Hg(II) Ions from Aqueous Solution Using Coconut Shell-based Activated Carbon

Many adsorbents have been studied for their adsorption properties towards one-component metal ion solutions. However, if these materials are to be used for treating wastewater, their performance has to be determined in multi-component solutions. In the present work, multi-component metal sorption by coconut shell-based activated carbon has been studied using single, binary and ternary systems composed of Cu(II), Pb(II) and Hg(II) ions. The influence of solution pH was also demonstrated. A set of desorption studies was also performed for the same metal ions with the aim of investigating the mechanism involved. It was found that chemisorption, surface chelation and complexation might be a possible metal ion removal mechanism. Scanning electron micrographs (SEM) and the EDAX spectrum of the activated carbon surface before and after equilibration of the adsorbent with the metal ion solution clearly showed the presence of Cu(II), Pb(II) and Hg(II) ions. An attempt was made to quantify the interaction behaviour of the metal ion on the adsorbent and to correlate such observations with the chemical and physical properties of the metal ions. The ability of isotherm models such as those of Freundlich and Langmuir to predict the equilibrium uptake of Cu(II), Pb(II) and Hg(II) ions from one-component, binary and ternary systems was also tested. Both the Langmuir and Freundlich models were found to fit the experimental data well. The applicability of the extended Langmuir model was also evaluated for multi-component systems.

Mercury (II) removal from water by coconut shell based activated carbon: Batch and column studies

Abstract This study was undertaken to investigate adsorption behavior of Hg (II) from aqueous systems on activated carbon in static and dynamic mode by varying initial Hg (II) concentration, adsorbent dose and pH. Langmuir and Freundlich adsorption isotherm were applied to model the adsorption data. Removal of mercury obeyed the Langmuir and Freundlich adsorption isotherm models. The extent of removal of Hg (II) was found to be dependent on sorbent dose, pH and initial Hg (II) concentration. Mercury uptake increased from 72 to 100 percent with increasing pH from 2 to 10. A set of desorption studies was also performed for the metal ions with the aim of investigating the mechanism involved. Moreover, the competing effects of various ions like Pb (II) and Cu (II) is also described. The column capacity for a column diameter of 20 mm, bed height of 0.4 m, hydraulic loading rate of 7.5 m3h‐1m‐2 and a feed concentration of 3 mg I‐1 were found to be 3.02 mg g‐1. Breakthrough curves were plotted for the adsorption of mercury on the adsorbent using continuous‐flow column operation by varying different operating parameters like hydraulic loading rate (3–10.5 m3h‐1m‐2), bed height (0.3–0.5 m), and feed concentrations (2–6 mg I‐1). The aim was to assess the effect of bed height, hydraulic loading rate and initial feed concentration on breakthrough time and adsorption capacity, which helped in ascertaining the practical applicability of the adsorbent. At the end an attempt has been made to develop empirical relationship from the data generated from column studies for designing the adsorption column, based on the Bohart ‐Adams model.

Curing kinetics of self-healing epoxy thermosets

The curing kinetics of self-healing epoxy compositions was investigated by non-isothermal differential scanning calorimetric (DSC) studies. Cycloaliphatic epoxy resin was encapsulated in urea–formaldehyde (UF) using emulsion polymerisation technique to prepare epoxy-loaded UF microcapsules. Triethylene tetramine (TETA) hardener was immobilised on a mesoporous siliceous substrate (SBA 15) and both these additives were dispersed into an epoxy resin, which was subsequently cured using TETA. DSC studies revealed the autocatalytic nature of epoxy curing, which remained unaltered due to addition of the above-mentioned fillers, responsible for introducing self-healing functionality. The kinetic parameters of the curing process were determined using both Friedman and Kissinger–Akahira–Sunose (KAS) method. The activation energy at different degrees of conversion (Eα) was found to decrease with increasing degree of cure (α). Although UF resins possess secondary amine functionalities, which have the potential to react with the epoxy groups, no significant differences in the curing kinetics of the base resin were observed. Kinetic parameters were used to predict the curing behaviour of compositions at higher heating rates using KAS method. As expected, the onset curing temperature (Tonset) and peak exotherm temperature (Tp) of epoxy shifted towards higher temperatures with increased heating rate; however, introduction of fillers does not affect these characteristic temperatures significantly. Also, the overall order of reaction does not vary significantly which supports the autocatalytic nature of curing reaction. The results suggests that although 2° amino groups are available with the UF resin, these do not directly participate in the curing reaction, as the primary amino groups in TETA are more easily accessible.

Core–shell polysiloxane–MOF 5 microspheres as a stationary phase for gas–solid chromatographic separation

Core–shell poly(dimethylsiloxane) (PDMS)–MOF 5 microspheres were prepared by directed crystallization of MOF 5 on thermally stable PDMS beads. The microspheres were evaluated for their potential use as a stationary phase for gas-chromatographic separation of permanent gases and liquids, where the issues associated with pressure drop were circumvented. The successful demonstration of this simple and versatile methodology widens the scope for large-scale application of Metal–Organic Frameworks (MOFs) in chromatographic separation.

Investigating the Degradation Behavior of LDPE-grafted Maleic Anhydride for Use as Compatibilizer in Environmentally Degradable Compositions

In this paper, we report the degradation behavior of a LDPE-grafted Maleic anhydride polymer prepared using a reactive extrusion technique. 70 ± 5 µm blown films were exposed to oxidative environments, and the degradation was followed by monitoring physico-chemical and morphological changes. The studies indicated that grafting with Maleic anhydride does not affect the degradation characteristics of the base polymer. Kinetic parameters of degradation, as estimated using non-isothermal TGA, were used to estimate the theoretical lifetime of the polymers, which remained unaltered due to grafting. The results, however, indicated that cobalt stearate, a typical pro-oxidant, led to massive degradation during thermal processing.

A pilot scale evaluation for adsorptive removal of lead (II) using treated granular activated carbon.

Wastewaters discharged from the defence serviceable industries pose a serious environmental hazard due to their heavy metal load. The present study focused on optimizing the operational variables viz, hydraulic loading rate, bed height and feed concentration through bench scale study and using that for assessing the efficiency of pilot scale system with sulphur loaded carbon (AC-S) as the adsorbent in the removal of Pb (II). Static mode adsorption studies were also carried out for Pb (II) removal using treated (AC-S) and untreated carbon (AC). AC-S shows about 35 percent increase in maximum adsorption capacity over that on AC. The maximum adsorption capacity in the column mode for Pb (II) at the optimized conditions: bed height of 0.4 m, hydraulic loading rate of 7.5 m3h−1m−2 and the feed concentration of 6 mg l−1 for achieving 50 % breakthrough concentration was found to be 2.89 mg g−1. Adsorption mechanism involved during Pb (II) in the column has also been explored. Bohart - Adams model was used for modeling the bench scale data and predicting the adsorption behavior at pilot scale level.