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Hybrid magnetic nanoparticles (mgNP) with a magnetite core diameter of 10 ± 1 nm surface functionalized with oligo(ω-pentadecalactone) (OPDL) oligomers with Mn between 1300 and 3300 g mol-1 could be successfully prepared having OPDL grafted from 200 mg g-1 to 2170 mg g-1. The particles are dispersible in chloroform resulting in stable suspensions. Magnetic response against an external magnetic field proved the superparamagnetic nature of the particles with a low coercivity (Bc) value of 297 µT. The combination of the advantageous superparamagnetism of the mgNP with the exceptional stability of OPDL makes these novel hybrid mgNP promising candidates as multifunctional building blocks for magnetic nanocomposites with tunable physical properties.
Agglomerated superparamagnetic iron
oxide nanoparticles can easily and in large scale be
precipitated from iron salt solutions. Although the
process is well known, it is ambiguously either assumed
that magnetite or maghemite is obtained. The first part
of our study clarifies this question using X-ray absorption
spectroscopy. For further processing of the nanoparticles,
i.e., for giving them a surface functionality or
incorporating them into composites, it is important to
break the agglomerates and individualize the particles
at first. This can effectively be done with nitric acid
treatment. The influence of this process on the particles
chemistry and structure was analyzed in great detail
using X-ray diffraction, X-ray absorption, and smallangle
X-ray scattering. In contrast to our expectation,
no oxidation from magnetite (Fe3O4) to maghemite (γ-
Fe2O3) was found; the formal valence of the particles in
any case is magnetite (Fe3O4). Instead, an increase in
the particles' surface disorder was discovered from
X-ray absorption analyses and high-resolution transmission
electron microscopy. The acid treatment
roughens and distorts the surface of the nanoparticles
which is connected with an increased spin disorder.
Well-defined and facetted bimetallic gold–palladium nanoalloys have been synthesized and anchored in spherical polyelectrolyte brushes (SPB) as composite particles (AuPd@SPB). These particles are better catalysts in aqueous phase than the pure metals. The atomistic arrangement of these nanoalloys has been analysed by extended X-ray absorption fine structure (EXAFS) spectroscopy at the Au–L3 and the Pd–K absorption edge. The samples with high amounts of gold appear as almost statistically mixed random alloys. Alloy compositions with less gold show slight enrichment of Pd at the surface of the particle. In addition, signals of non-metallic palladium appear at the Pd–K edge which indicate the presence of the Pd2+ species in addition to metallic palladium. The relation of these structural features to the catalytic activity is discussed.
With the increase in the awareness of the public in the environmental impact of oil shale utilization, it is of interest to reveal the mobility of potentially toxic trace elements in spent oil shale. Therefore, the Cr and As oxidation state in a representative Jordanian oil shale sample from the El-Lajjoun area were investigated upon different lab-scale furnace treatments. The anaerobic pyrolysis was performed in a retort flushed by nitrogen gas at temperatures in between 600 and 800 °C (pyrolytic oil shale, POS). The aerobic combustion was simply performed in porcelain cups heated in a muffle furnace for 4 h at temperatures in between 700 and 1000 °C (burned oil shale, BOS). The high loss-on-ignition in the BOS samples of up to 370 g kg–1 results from both calcium carbonate and organic carbon degradation. The LOI leads to enrichment in the Cr concentrations from 480 mg kg–1 in the original oil shale up to 675 mg kg–1 in the ≥850 °C BOS samples. Arsenic concentrations were not much elevated beyond that in the average shale standard (13 mg kg–1). Synchrotron-based X-ray absorption near-edge structure (XANES) analysis revealed that within the original oil shale the oxidation states of Cr and As were lower than after its aerobic combustion. Cr(VI) increased from 0% in the untreated or pyrolyzed oil shale up to 60% in the BOS ash combusted at 850 °C, while As(V) increased from 64% in the original oil shale up to 100% in the BOS ash at 700 °C. No Cr was released from original oil shale and POS products by the European compliance leaching test CEN/TC 292 EN 12457-1 (1:2 solid/water ratio, 24 h shaking), whereas leachates from BOS samples showed Cr release in the order of one mmol L–1. The leachable Cr content is dominated by chromate as revealed by catalytic adsorptive stripping voltammetry (CAdSV) which could cause harmful contamination of surface and groundwater in the semiarid environment of Jordan.