Heavy metal pollution and the role of inorganic nanomaterials in environmental remediation.

Contamination of water and soil with toxic heavy metals is a major threat to human health. Although extensive work has been performed on reporting heavy metal pollutions globally, there are limited review articles on addressing this pernicious phenomenon. This paper reviews inorganic nanoparticles and provides a framework for their qualities required as good nanoadsorbents for efficient removal of heavy metals from water. Different inorganic nanoparticles including metals, metal oxides and metal sulfides nanoparticles have been applied as nanoadsorbents to successfully treat water with high contaminations of heavy metals at concentrations greater than 100 mg l-1, achieving high adsorption capacities up to 3449 mg g-1. It has been identified that the synthesis method, selectivity, stability, regeneration and reusability, and adsorbent separation from solution are critical parameters in deciding on the quality of inorganic nanoadsorbents. Surface functionalized nanoadsorbents were found to possess high selectivity and capacity for heavy metals removal from water even at a very low adsorbent dosage of less than 2 g l-1, which makes them better than conventional adsorbents in environmental remediation.

Removal of malachite green from aqueous solution using pulverized teak leaf litter: equilibrium, kinetic and thermodynamic studies.

The removal of malachite green (MG) from aqueous solution using teak leaf litter powder (TLLP) was investigated. The process was influenced by initial concentration, pH and temperature of dye solution as well as TLLP dosage. Optimum removal of MG per gram of TLLP occurred at 2 g/L and at pH 6-8. Dubinin-Radushkevich and Freundlich isotherm models fit the batch adsorption data better than Langmuir isotherm. The monolayer capacity of TLLP was 333.33 mg/g at 293-313 K. The mean free energy of 7.07 kJ/mol implied physical adsorption. The pseudo-second order model fit the kinetic data better than the pseudo-first order model. Both intraparticle diffusion and film diffusion mechanisms jointly influenced the adsorption process but the latter was the rate-controlling step. Thermodynamic data indicated that the process was endothermic, spontaneous and feasible. Therefore, TLLP could be an important low-cost adsorbent for removal of MG from aqueous solution.

Equilibrium, Kinetic and Thermodynamic Study of Removal of Eosin Yellow from Aqueous Solution Using Teak Leaf Litter Powder.

Low-cost teak leaf litter powder (TLLP) was prepared as possible substitute for activated carbon. The feasibility of using the adsorbent to remove eosin yellow (EY) dye from aqueous solution was investigated through equilibrium adsorption, kinetic and thermodynamic studies. The removal of dye from aqueous solution was feasible but influenced by temperature, pH, adsorbent dosage and contact time. Variation in the initial concentration of dye did not influence the equilibrium contact time. Optimum adsorption of dye occurred at low adsorbent dosages, alkaline pH and high temperatures. Langmuir isotherm model best fit the equilibrium adsorption data and the maximum monolayer capacity of the adsorbent was 31.64 mg g-1 at 303 K. The adsorption process was best described by pseudo-second order kinetic model at 303 K. Boundary layer diffusion played a key role in the adsorption process. The mechanism of uptake of EY by TLLP was controlled by both liquid film diffusion and intraparticle diffusion. The values of mean adsorption free energy, E (7.91 kJ mol-1), and standard enthalpy, ΔH° (+13.34 kJ mol-1), suggest physical adsorption. The adsorption process was endothermic and spontaneous. Teak leaf litter powder is a promising low-cost adsorbent for treating wastewaters containing eosin yellow.

The effect of alkyl chain length on the structure of lead(ii) xanthates and their decomposition to PbS in melt reactions.

A series of lead(ii) alkylxanthates, [Pb(S2COR)2] (R = ethyl (1), n-propyl (2), n-butyl (3), n-hexyl (4) or n-octyl (5)) have been prepared and explored as single source precursors for use in melt reactions to form lead sulfide. X-ray single crystal structures of (2), (3) and (4) were used along with previously reported structures to investigate the influence of structure and chain length on the materials produced. The complexes were decomposed at 150, 175 or 200 °C forming PbS nanocrystals as confirmed by XRD and TEM. Analysis by SEM shows that the choice of precursor had an influence on nanocrystal size with longer alkyl chains resulting in smaller cubic nanocrystals. In addition to cubes, anisotropic growth was observed from decomposition of compound (5).

Determination of indicator polychlorinated biphenyls (PCBs) by gas chromatography-electron capture detector.

An effective method for determination of indicator polychlorinated biphenyls (PCBs) has been validated using gas chromatography (GC) equipped with electron capture detector (ECD). The GC-ECD method was validated by determining the linear range (working range) for determination of the compounds, minimum detectable quantities (MDQ), the precision and accuracy of the method for the analysis of the compounds. MDQ obtained for the compounds ranges from 0.0005 to 0.002 ng. Indeed the method was found to be more sensitive as the number of chlorine atoms attached to the biphenyl increases. The precision and accuracy of the GC method validated ranges from 2.4% to 14.5% and -7.0% to 14.6% respectively. Coefficient of variation associated with the repeatability of the retention times and corresponding peak areas was found to be 0.0001-0.0007 for the retention times and 0.0014-0.059 for the peak areas. Percentage recoveries for the compounds were in the range of 95.7-101.0%. The validated method was then applied to determine levels of indicator PCBs in sediments sampled from eleven sampling points along the Lake Bosuntwi in Ghana and the highest PCB load of 19.17 ng g(-1) was recorded at Pipie No. 2. PCB 52 and PCB 101 were found to be the most ubiquitous indicator PCBs in the study area, both with 90.91% occurrence.

Single source molecular precursor routes to lead chalcogenides.

The use of single-source molecular precursors for lead chalcogenide thin films by CVD or as nanoparticles by solution methods is reviewed. The potential applications of these materials in solar energy are discussed along with the relative advantages of the various methods.