The primary challenge in materials design and synthesis is achieving the balance between performance and economy for real-world application. This issue is addressed by creating a thiol functionalized porous organic polymer (POP) using simple free radical polymerization techniques to prepare a cost-effective material with a high density of chelating sites designed for mercury capture and therefore environmental remediation. The resulting POP is able to remove aqueous and airborne mercury with uptake capacities of 1216 and 630 mg g , respectively. The material demonstrates rapid kinetics, capable of dropping the mercury concentration from 5 ppm to 1 ppb, lower than the US Environmental Protection Agency's drinking water limit (2 ppb), within 10 min. Furthermore, the material has the added benefits of recyclability, stability in a broad pH range, and selectivity for toxic metals. These results are attributed to the material's physical properties, which include hierarchical porosity, a high density of chelating sites, and the material's robustness, which improve the thiol availability to bind with mercury as determined by X-ray photoelectron spectroscopy and X-ray absorption fine structure studies. The work provides promising results for POPs as an economical material for multiple environmental remediation applications.
A strategy for enhancing the photocatalytic performance of MOF-based systems (MOF: metal−organic framework) is developed through the construction of MOF/ MOF heterojunctions. The combination of MIL-167 with MIL-125-NH 2 leads to the formation of MIL-167/MIL-125-NH 2 heterojunctions with improved optoelectronic properties and efficient charge separation. MIL-167/MIL-125-NH 2 outperforms its single components MIL-167 and MIL-125-NH 2 , in terms of photocatalytic H 2 production (455 versus 0.8 and 51.2 μmol h −1 g −1 , respectively), under visible-light irradiation, without the use of any cocatalysts. This is attributed to the appropriate band alignment of these MOFs, the enhanced visible-light absorption, and long charge separation within MIL-167/MIL-125-NH 2 . Our findings contribute to the discovery of novel MOF-based photocatalytic systems that can harvest solar energy and exhibit high catalytic activities in the absence of cocatalysts.
The light-soaking effect is the observation that under constant illumination the measured power conversion efficiency of certain solar cells changes as a function of time. The theory of the light-soaking in metal halide perovskites is at present incomplete. In this report, we employ steady-state microwave conductivity, a contactless probe of electronic properties of semiconductors, to study the light-soaking effect in metal halide perovskites. By illuminating isolated thin films of two mixed-cation perovskites with AM1.5 solar illumination, we observe a continual increase in photoconductance over a period of many (>12) hours. We can fit the experimentally observed changes in photoconductance to a stretched exponential function, in an analogous manner to bias-stressed thin-film transistors. The information provided in this report should help the community better understand one of the most perplexing open problems in the field of perovskite solar cells and, ultimately, lead to more robust and predictable devices.
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Synthesizing functional materials
from water contributes to a sustainable
energy future. On the atomic level, water drives complex metal hydrolysis/condensation/speciation,
acid–base, ion pairing, and solvation reactions that ultimately
direct material assembly pathways. Here, we demonstrate the importance
of Nb-polyoxometalate (Nb-POM) speciation in enabling deposition of
Nb2O5, LiNbO3, and (Na, K)NbO3 (KNN) from high-concentration solutions, up to 2.5 M Nb for
Nb2O5 and ∼1 M Nb for LiNbO3 and KNN. Deposition of KNN from 1 M Nb concentration represents
a potentially important advancment in lead-free piezoelectrics, an
application that requires thick films. Solution characterization via
small-angle X-ray scattering and Raman spectroscopy described the
speciation for all precursor solutions as the [H
x
Nb24O72](x−24) POM, as did total pair distribution function analyses of X-ray scattering
of amorphous gels prior to conversion to oxides. The tendency of the
Nb24-POM to form extended networks without crystallization
leads to conformal and well-adhered films. The films were characterized
by X-ray diffraction, atomic force microscopy, scanning electron microscopy,
ellipsometry, and X-ray photoelectron spectroscopy. As a strategy
to convert aqueous deposition solutions from {Nb10}-POMs
to {Nb24}-POMs, we devised a general procedure to produce
doped Nb2O5 thin films including Ca, Ag, and
Cu doping.
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