Heavy metal content of water exposed to cement lining in the water pipe

Mechanizm wymywania z cementu toksycznych metali ciężkich nie został jeszcze dokładnie rozpoznany. Istnieje wiele czynników mających wpływ na ten proces, jak np. jakość przepływającej wody, a zwłaszcza jej pH, zasadowość, temperatura, zawartość chloru itp. Wpływ mają także skład i mikrostruktura wykładziny cementowej rur wodociągowych. W badaniach modelowych określono zawartość wybranych metali ciężkich (ICP-OES, ICP-MS) w wodzie przed i po 6-miesięcznym czasie eksploatacji rurociągu z żeliwa sferoidalnego z wykładziną cementową. Stwierdzono, że zawartość pierwiastków śladowych (Ba, Fe, K, Ni, Mg, Na, Sr, Zn, V, Cd, Pb, Mn, Cu i As) w wodzie kontaktującej się zarówno z nową wykładziną cementową, jak i po 6-miesięcznej eksploatacji przewodu była niewielka, w większości przypadków poniżej progu detekcji (ICP-OES). Badania strukturalne wykładziny cementowej wykonane za pomocą skaningowej mikroskopii elektronowej wykazały, że cienka warstewka kalcytowa pokrywająca zaczyn cementowy na wewnętrznej powierzchni rury bardzo szybko uległa zniszczeniu, jednakże jej skład chemiczny nie uległ zmianie po 6-miesięcznej eksploatacji układu badawczego. W miejscach zniszczenia wykładziny cementowej stwierdzono obecność znacznej liczby igiełek ettringitu, świadczących o rozpoczynającej się korozji betonu.The mechanism governing the release of toxic heavy metals from cement is still far from being well understood. The process is influenced by a diversity of factors such as the quality of the water flowing in the pipes (especially its pH, alkalinity, temperature and chlorine content), or the composition and microstructure of the internal lining applied. This paper reports on model investigations into the presence of selected heavy metals (determined by ICP-OES and ICP-MS) in the water before and after 6-month service. It has been found that in the majority of instances the trace element content (Ba, Fe, K, Ni, Mg, Na, Sr, Zn, V, Cd, Pb, Mn, Cu and As) was below the detection threshold (ICP-OES), regardless of whether the water was exposed to a fresh lining or after six months of service. Structural examinations of the cement lining by scanning electron microscopy (SEM) have produced the following findings: the thin calcite layer covering the cement paste on the internal surface of the pipe was destroyed within a very short time, the chemical composition of the layer, however, remained unchanged after 6-month service of the pipe being tested. At the points of cement lining destruction a large number of ettringite needles was detected, which is indicative of the onset of concrete corrosion

Steady-state photoinduced absorption of CdSe/CdS octapod shaped nanocrystals

Colloidal branched nanocrystals have been attracting increasing attention due to evidence of an interesting relationship between their complex shape and charge carrier dynamics. Herein, continuous wave photoinduced absorption (CW PIA) measurements of CdSe/CdS octapod-shaped nanocrystals are reported. CW PIA spectra show strong bleaching due to the one-dimensional (1D) CdS pod states (480 nm) and the zero-dimensional (0D) CdSe core states (690 nm). The agreement with previously reported ultrafast pump-probe experiments indicates that this strong bleaching signal may be assigned to state filling. Additional bleaching features at 520 and 560 nm are characterized by a longer lifetime and are thus ascribed to defect states, localized at the pod-core interface of the octapod, showing that some of the initially photogenerated carriers get quickly trapped into these long-lived defect states. However, we remark that a relevant part of electrons remain untrapped: this opens up the opportunity to exploit octapod shaped nanocrystals in photovoltaics applications, as electron acceptor materials, considering that several efficient hole extracting materials are already available for the realization of a composite bulk heterojunction

Plasmon Dynamics in Colloidal Cu(2-x)Se Nanocrystals

The optical response of metallic nanostructures after intense excitation with femtosecond-laser pulses has recently attracted increasing attention: such response is dominated by ultrafast electron-phonon coupling and offers the possibility to achieve optical modulation with unprecedented terahertz bandwidth. In addition to noble metal nanoparticles, efforts have been made in recent years to synthesize heavily doped semiconductor nanocrystals so as to achieve a plasmonic behavior with spectrally tunable features. In this work, we studied the dynamics of the localized plasmon resonance exhibited by colloidal Cu(2-x)Se nanocrystals of 13 nm in diameter and with x around 0.15, upon excitation by ultrafast laser pulses via pump-probe experiments in the near-infrared, with similar to 200 fs resolution time. The experimental results were interpreted according to the two-temperature model and revealed the existence of strong nonlinearities in the plasmonic absorption due to the much lower carrier density of Cu(2-x)Se compared to noble metals, which led to ultrafast control of the probe signal with modulation depth exceeding 40% in transmission

Hierarchical self-assembly of suspended branched colloidal nanocrystals into superlattice structures

Self-assembly of molecular units into complex and functional superstructures is ubiquitous in biology. The number of superstructures realized by self-assembly of man-made nanoscale units is also growing. However, assemblies of colloidal inorganic nanocrystals1, 2, 3 are still at an elementary level, not only because of the simplicity of the shape of the nanocrystal building blocks and their interactions, but also because of the poor control over these parameters in the fabrication of more elaborate nanocrystals. Here, we show how monodisperse colloidal octapod-shaped nanocrystals self-assemble, in a suitable solution environment, on two sequential levels. First, linear chains of interlocked octapods are formed, and subsequently the chains spontaneously self-assemble into three-dimensional superstructures. Remarkably, all the instructions for the hierarchical self-assembly are encoded in the octapod shape. The mechanical strength of these superstructures is improved by welding the constituent nanocrystals togethe

Cryo-EM structure of the native rhodopsin dimer in nanodiscs

Imaging of rod photoreceptor outer-segment disc membranes by atomic force microscopy and cryo-electron tomography has revealed that the visual pigment rhodopsin, a prototypical class A G protein?coupled receptor (GPCR), can organize as rows of dimers. GPCR dimerization and oligomerization offer possibilities for allosteric regulation of GPCR activity, but the detailed structures and mechanism remain elusive. In this investigation, we made use of the high rhodopsin density in the native disc membranes and of a bifunctional cross-linker that preserves the native rhodopsin arrangement by covalently tethering rhodopsins via Lys residue side chains. We purified cross-linked rhodopsin dimers and reconstituted them into nanodiscs for cryo-EM analysis. We present cryo-EM structures of the cross-linked rhodopsin dimer as well as a rhodopsin dimer reconstituted into nanodiscs from purified monomers. We demonstrate the presence of a preferential 2-fold symmetrical dimerization interface mediated by transmembrane helix 1 and the cytoplasmic helix 8 of rhodopsin. We confirmed this dimer interface by double electron?electron resonance measurements of spin-labeled rhodopsin. We propose that this interface and the arrangement of two protomers is a prerequisite for the formation of the observed rows of dimers. We anticipate that the approach outlined here could be extended to other GPCRs or membrane receptors to better understand specific receptor dimerization mechanisms

Staged Self-Assembly of Colloidal Metastructures

We demonstrate sequential assembly of chemically patchy colloids such that their valence differs from stage to stage to produce hierarchical structures. For proof of concept, we employ ACB triblock spheres suspended in water, with the C middle band electrostatically repulsive. In the first assembly stage, only A-A hydrophobic attraction contributes, and discrete clusters form. They can be stored, but subsequently activated to allow B-B attractions, leading to higher-order assembly of clusters with one another. The growth dynamics, observed at a single particle level by fluorescence optical microscopy, obey the kinetics of stepwise polymerization, forming chains, pores, and networks. Between linked clusters, we identify three possible bond geometries, linear, triangular, and square, by an argument that is generalizable to other patchy colloid systems. This staged assembly strategy offers a promising route to fabricate colloidal assemblies bearing multiple levels of structural and functional complexity.close201