Detailed molecular structural information of the living state is of enormous
significance to the medical and biological communities. Since hydrated biologically
active structures are small delicate complex three-dimensional (3D) entities,
it is essential to have molecular scale spatial resolution, high contrast,
distortionless, direct 3D modalities of visualization of naturally functioning
specimens in order to faithfully reveal their full molecular architectures. An
x-ray holographic microscope equipped with an x-ray laser as the illuminator
would be uniquely capable of providing these images. A quantitative interlocking
concordance of physical evidence, that includes (a) the observation of
strong enhancement of selected spectral components of several Xeq+ hollow-atom
transition arrays (q = 31,
32, 34, 35, 36, 37) radiated axially from confined plasma channels, (b)
the measurement of line narrowing that is spectrally correlated with the
amplified transitions, (c) evidence for spectral hole-burning in the
spontaneous emission, a manifestation of saturated amplification, that
corresponds spectrally with the amplified lines, and (d) the detection of
an intense narrow (δθx ∼ 0.2 mrad)
directed beam of radiation, (1) experimentally demonstrates
in the λ ∼ = 2.71–2.93 Å
range (ℏωx ∼ = 4230–4570 eV)
the operation of a new concept capable of producing the ideal conditions for
amplification of multikilovolt x-rays and (2) proves the feasibility of a
compact x-ray illuminator that can cost-effectively achieve the mission
of biological x-ray microholography. The measurements also (α) establish the
property of tunability in the quantum energy over a substantial fraction of the spectral
region exhibiting amplification (Δℏωx ∼ 345 eV) and
(β)
demonstrate the coherence of the x-ray output through the observation of a
canonical spatial mode pattern. An analysis of the physical scaling revealed by
these results indicates that the capability of the x-ray source potentially includes
single-molecule microimaging, the key for the in situ structural analysis of
membrane proteins, a cardinal class of drug targets. An estimate of the peak
brightness achieved in these initial experiments gives a value of ∼1031–1032 photons s−1 mm−2 mrad−2/(0.1% bandwidth),
a magnitude that is ∼107–108-fold
higher than presently available synchrotron technology.
Single-pulse measurements of spectral hole burning of Xe(L) 3d → 2p hollow atom transition arrays observed from a self-trapped plasma channel provide new information on the dynamics of saturated amplification in the λ ∼ 2.8-2.9 Å region. The spectral hole burning on transitions in the Xe 34+ and Xe 35+ arrays reaches full suppression of the spontaneous emission and presents a corresponding width hω x ∼ = 60 eV, a value adequate for efficient amplification of multikilovolt x-ray pulses down to a limiting length τ x ∼ 30 as. The depth of the suppression at 2.86 Å indicates that the gain-to-loss ratio is 10. An independent determination of the x-ray pulse energy from damage produced on the surface of a Ti foil in the far field of the source gives a pulse energy of 20-30 µJ, a range that correlates well with the observation of the spectral hole burning and indicates an overall extraction efficiency of ∼10%.
Arsenic pollution
in waters has become a worldwide issue, constituting a severe hazard
to whole ecosystems and public health worldwide. Accordingly, it is
highly desirable to design
high-performance adsorbents for arsenic decontamination. Herein, a
feasible strategy is developed for in situ growth of β-FeOOH
nanorods (NRs) on a three-dimensional (3D) carbon foam (CF) skeleton
via a simple calcination process and subsequent hydrothermal treatment.
The as-fabricated 3D β-FeOOH NRs/CF monolith can be innovatively
utilized for arsenic remediation from contaminated aqueous systems,
accompanied by remarkably high uptake capacity of 103.4 mg/g for arsenite
and 172.9 mg/g for arsenate. The superior arsenic uptake performance
can be ascribed to abundant active sites and hydroxyl functional groups
available as well as efficient mass transfer associated with interconnected
hierarchical porous networks. In addition, the as-obtained material
exhibits exceptional sorption selectivity toward arsenic over other
coexisting anions at high levels, which can be ascribed to strong
affinity between active sites and arsenic. More importantly, the free-standing
3D porous monolith not only makes it easy for separation and collection
after treatment but also efficiently prevents the undesirable potential
release of nanoparticles into aquatic environments while maintaining
the outstanding properties of nanometer-scale building blocks. Furthermore,
the monolith absorbent is able to be effectively regenerated and reused
for five cycles with negligible decrease in arsenic removal. In view
of extremely high adsorption capacities, preferable sorption selectivity,
satisfactory recyclability, as well as facile separation nature, the
obtained 3D β-FeOOH NRs/CF monolith holds a great potential
for arsenic decontamination in practical applications.
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