Application of South African heulandite (HEU) zeolite for the adsorption and removal of Pb2+ and Cd2+ ions from aqueous water solution: Experimental and computational study.

The capacity of South African Heulandite (HEU) zeolite to remove Pb2+ and Cd2+ ions from aqueous solution was investigated using batch experiments and molecular simulations studies. The effect of different factors on the adsorption of these ions onto the zeolite was investigated; contact time, initial metal ion concentration and the amount of HEU adsorbent. Molecular simulations was done using Monte Carlo and density functional theory. Experimental results obtained indicate that the maximum adsorption for the two ions occur at pH 5 and after 240 min of contact time. The percent removal based on contact time of Pb2+ and Cd2+ ions from water by the heulandite zeolite were 99.7 and 76.7 %, respectively. The adsorption of two metal ions onto the HEU zeolite follows the Langmuir adsorption isotherm. From the molecular simulation findings, the adsorption of Pb2+ ions onto the HEU window is equidistant from the two adjacent oxygen atoms within the HEU structure while the Cd2+ ion is adsorbed in the upper left side of the 8-ring HEU window. It was observed that the performance of the zeolite can significantly be improved by doping with germanium, aluminum, thallium indium, and sodium cations. These results indicate that the application of HEU zeolite as an adsorbent holds a great promise in heavy metal removal from aqueous solutions.

Controlling the reactivity of [Pd(II)(N

Four [(N^N^N)Pd(II)Cl]+ complexes [chloride-(2,2':6',2''-terpyridine)Pd(II)]Cl (PdL1), [chlorido(2,6-bis(N-pyrazol-2-yl)pyridine)Pd(II)]Cl (PdL2), [chlorido(2,6-bis(3,5-dimethyl-N-pyrazol-2-yl)pyridine)Pd(II)]Cl (PdL3) and [chlorido(2,6-bis(3,5-dimethyl-N-pyrazol-2-ylmethyl)pyridine)Pd(II)]BF4 (PdL4) were synthesized and characterized. The rates of substitution of these Pd(II) complexes with thiourea nucleophiles viz; thiourea (Tu), N,N'-dimethylthiourea (Dmtu) and N,N,N',N'-tetramethylthiourea (Tmtu) was investigated under pseudo first-order conditions as a function of nucleophile concentration [Nu] and temperature using the stopped-flow technique. The observed rate constants vary linearly with [Nu]; kobs = k2[Nu] and decreased in the order: PdL1 > PdL2 > PdL3 â‰« PdL4. The lower π-acceptability of the cis-coordinated N-pyrazol-2-yl groups (which coordinates via pyrazollic-N π-donor atoms) of the PdL2-4 significantly decelerates the reactivity relative to PdL1. Furthermore, the six-membered chelates having methylene bridge in PdL4 do not allow π-extension in the ligand and introduces steric hindrance further lowering the reactivity. Trends in DFT calculated data supported the observed reactivity trend. Spectrophotometric titration data of complexes with calf thymus DNA (CT-DNA) and viscosity measurements of the resultant mixtures suggested that associative interactions occur between the complexes and CT-DNA, likely through groove binding with high binding constants (Kb = 104 M-1). In vitro MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] cytotoxic activity data showed that PdL1 was the most potent complex against MCF7 breast cancer cells; its IC50 value is lower than that of cisplatin. The results demonstrate how modification of a spectator ligand can be used to slow down the reactivity of Pd(II) complexes. This is of special importance in controlling drug toxicity in both pharmaceutical and biomedical applications.