Muhammad Hassan Agheem

2,3-Pyridine dicarboxylic acid functionalized gold nanoparticles: Insight into experimental conditions for Cr(3+) sensing.

Selectivity of gold nanoparticles (AuNPs) depends upon surface functionality; small changes in structure or concentration bring significant changes in the behavior of AuNPs. In this study, citrate-capped AuNPs were functionalized with ortho-dicarboxylate substituted pyridine (2,3-PDCA) and detailed studies on experimental conditions were carried out to check the stability of AuNPs and response for Cr3+. Stability of PDCA-AuNPs was found sensitive to the pH, ionic strength of buffer and its type. Capping behavior of PDCA on C-AuNPs was examined by FTIR spectroscopy. Surface morphology and size of synthesized AuNPs were confirmed by AFM, XRD, and DLS techniques where particles were found 11nm in size, monodisperse and spherical in shape. Interaction of stabilized AuNPs was tested with various metal ions; where Cr3+ induced the changes in localized surface plasmon band (LSPR) of PDCA-AuNPs which leads to a color change from wine red to violet blue. The phenomenon is explained as cooperative effect of citrate and pyridine nitrogen on surface of AuNPs in contrary to meta-dicarboxylate substituted pyridine derivatives. Further, under optimized and controlled conditions Cr3+ shows linear response with decrease in absorbance at LSPR intensity of AuNPs (518nm). Moreover, to demonstrate the applicability of method, Cr3+ was determined in the presence of Cr (VI) which shows 96% recovery.

Petrographic Studies of the Vihowa Formation, Sulaiman Range, Pakistan: Implications for Provenance

The Vihowa Formation of late to early Miocene is investigated for mineral composition and petrographic characteristics to understand the provenance, diagenesis and depositional environments. Ten representative sandstone samples were collected from various lithological units for petrographic studies. Petrographic results show that the quartz is a major constituent; while the accessory minerals are chlorite, chamosite, palagonite, sphalerite, staurolite, aragonite, hypersthene, glaucophane, monazite, kyanite, epidote, olivine, rutile, ilmenite, hematite, magnetite, zircon, tourmaline and garnet. The tourmaline and rutile showing an igneous source however, the presence of epidote, staurolite and garnet expresses a metamorphic source for studied sandstones. The sandstone is medium to coarse grained having grains dominantly from the meta-sedimentary rocks whereas minor amount of grains from igneous rocks is also observed. Monocrystalline quartz is present in sands derived either from gneiss or granitic rocks, but polycrystalline quartz are from slate and schist. The inclusion of mica and garnet within quartz is observed which indicates a metamorphic source. On the QFL triangular diagram the sandstone of Vihowa Formation is mainly sub-lithic arenite and partly quartz arenite. The Qm-P-K plots indicate that feldspar and quartz are from granitic rocks along with small amount from metamorphic and volcanic rocks. The provenance of sandstone indicates that sediments were mostly deposited by transitional recycled orogeny and mixed magmatic subduction complex.

Petrogenetic evolution of pegmatites of the Shigar Valley, Skardu, Gilgit-Baltistan, Pakistan

Pegmatites of granitic composition intrude the Dassu orthogneiss of the Asian plate in the Shigar Valley of Pakistan. On the basis of field and petrographic studies, these pegmatites are distinguished into evolved and simple pegmatites. The evolved pegmatites are further distinguished as muscovite-tourmaline-beryl-garnet and muscovite-tourmaline pegmatites whereas the simple pegmatites as biotite ± garnet ± muscovite and muscovite-biotite ± garnet pegmatites. In the evolved pegmatites, the predominant minerals are albite and muscovite while in the simple pegmatites orthoclase and biotite are distinctive. Both the pegmatite types seem to be associated genetically to one common magma source and the variation within the mineral constituents are due to fractional crystallization. In spider diagrams, all the pegmatite types illustrate similar negative sloping trends from LILEs to HFSEs with depletion in Ba, Sr, and Ti concentration. In simple pegmatites, P is strongly depleted as compared to the evolved pegmatites. REEs illustrate nearly smooth patterns in all the pegmatite types with contrasting negative Eu anomaly signifying plagioclase fractionation. Both the evolved and simple pegmatites contain aluminous mineral assemblages and show mainly peraluminous geochemistry, which suggest their derivation from pelitic rocks of the Asian continental crust in syn-collision tectonic setting, ensued possibly by the collision of the Indian plate with Asian plate.

Shigar valley gemstones, their chemical composition and origin, Skardu, Gilgit-Baltistan, Pakistan

A variety of gemstones is being mined in the Shigar valley, Skardu, Pakistan. These include beryl (goshenite and aquamarine), tourmaline (schorl), garnet (almandine–spessartine), apatite, topaz, fluorite, zoisite, clinozoisite, and axinite, mostly occurring in complex or zoned pegmatites and metamorphic rocks. These have been analyzed using electron probe micro-analyzer and X-ray diffractometer. The mineral chemistry of each gemstone is similar to its respective typical gemstone variety with homogenous chemical composition. Field and chemical characteristics suggest that beryl, tourmaline, garnet, apatite, topaz, and fluorite are occurring in zoned pegmatites which are largely formed by magmatic hydrothermal fluids in the cavities and vugs within the intermediate zone. However, zoisite, clinozoisite, and axinite may have a metamorphic and/or metasomatic origin.