427 research outputs found
Bifunctional earth-abundant phosphate/phosphide catalysts prepared via atomic layer deposition for electrocatalytic water splitting
The development of active and stable earth-abundant catalysts for hydrogen and oxygen evolution is one of the requirements for successful production of solar fuels. Atomic Layer Deposition (ALD) is a proven technique for conformal coating of structured (photo)electrode surfaces with such electrocatalyst materials. Here, we show that ALD can be used for the deposition of iron and cobalt phosphate electrocatalysts. A PE-ALD process was developed to obtain cobalt phosphate films without the need for a phosphidation step. The cobalt phosphate material acts as a bifunctional catalyst, able to also perform hydrogen evolution after either a thermal or electrochemical reduction step
Atomic Layer Deposition-Based Synthesis of Photoactive TiO2 Nanoparticle Chains by Using Carbon Nanotubes as Sacrificial Templates
Highly ordered and self supported anatase TiO2 nanoparticle chains were
fabricated by calcining conformally TiO2 coated multi-walled carbon nanotubes
(MWCNTs). During annealing, the thin tubular TiO2 coating that was deposited
onto the MWCNTs by atomic layer deposition (ALD) was transformed into chains of
TiO2 nanoparticles (~12 nm diameter) with an ultrahigh surface area (137 cm2
per cm2 of substrate), while at the same time the carbon from the MWCNTs was
removed. Photocatalytic tests on the degradation of acetaldehyde proved that
these forests of TiO2 nanoparticle chains are highly photo active under UV
light because of their well crystallized anatase phase
Synthesis of a 3D network of Pt nanowires by atomic layer deposition on carbonaceous template
The formation of a 3D network composed of free standing and interconnected Pt
nanowires is achieved by a two-step method, consisting of conformal deposition
of Pt by atomic layer deposition (ALD) on a forest of carbon nanotubes and
subsequent removal of the carbonaceous template. Detailed characterization of
this novel 3D nanostructure was carried out by transmission electron microscopy
(TEM) and electrochemical impedance spectroscopy (EIS). These characterizations
showed that this pure 3D nanostructure of platinum is self-supported and offers
an enhancement of the electrochemically active surface area by a factor of 50
Synthesis of Zeolitic-type Adsorbent Materials from Municipal Solid Waste Incinerator Bottom Ash and its Application in Heavy Metal Adsorption
Municipal solid waste incinerator (MSWI) bottom ash (BA) was converted to zeolitic-type adsorbent materials by hydrothermal conversion under strongly alkaline conditions. The conversion product was determined to be a mixture of sodium aluminum silicate hydrate (SASH) (Na2O·Al2O3·1.68SiO2·1.73H2O) and tobermorite (Ca5Si6O16(OH)2·4H2O). The BET specific surface area was 22.1 m2/g, which represented a significant gain compared to the BA (4.6 m2/g) due to the formation of micropores and mesopores. The converted BA demonstrated promising performance for application as a sorbent towards several heavy metals (oxyanions of As(V), and Cd2+, Co2+, Ni2+, Pb2+, and Zn2+). Its performance was found to be generally superior to that of a mainly-clinoptilolite natural zeolite, achieving greater sorption extents and better stabilizing capability of contaminated sediments. At a lower dosage rate (50 mg sorbent per gram sediment) to that of natural zeolite, converted BA achieved greater than 80% reduction of cationic heavy metal concentrations in sediment porewater. These results suggest a promising route for reutilization of MSWI-BA, which can greatly enhance the sustainability of waste incineration technology
PolySilicate Porous Organic Polymers (PSiPOPs), a new family of porous, ordered 3D reticular materials with polysilicate nodes and organic linkers
Spherosilicate, consisting of a double 4-ring cyclosilicate core (D4R;
Si8O20) with every corner functionalized with a dimethylsilyl chloride group
(-SiMe2Cl), was used as node to construct an iso-reticular series of porous
expanded network materials. Interconnecting the nodes with linear, aliphatic
{\alpha},{\omega}-alkanediol linker molecules yields PolySilicate Porous
Organic Polymers (PSiPOPs), a new type of ordered reticular material related to
the well-known metal-organic and covalent organic frameworks (MOFs & COFs). In
the synthesis, sacrificial hydrogen-bonded Si8O20 cyclosilicate crystals are
first converted into silyl chloride terminated spherosilicate. In a second
step, these nodes are linked up by alkanediol units via the intermediate
formation of a Si-N bond with catalytic amines such as pyridine and
dimethylformamide. Overall, the presented synthesis converts D4R cyclosilicate
into an ordered reticular framework with [Si8O20]-[Si(CH3)2-]8 nodes and
O-(CH2)n-O linkers. Example materials with ethylene glycol, 1,5-pentanediol,
and 1,7-heptanediol as linker (n = 2, 5, and 7) were produced and
characterized. On a macroscopic level, the synthesis yields porous frameworks
exhibiting a thermal stability up to 400{\deg}C and a chemical stability
between pH 1 and 12. N2 physisorption revealed a secondary mesopore structure,
indicating future options to produce hierarchical materials using soft
templates. The molecular level structure of these reticular PSiPOP materials
was elucidated using an NMR crystallography approach implementing a combination
of 1D and 2D 1H and 29Si solid-state MAS NMR spectroscopy experiments.
Previously reported reticular COF/POP materials implementing D4R-based nodes,
used Si8 octakis (phenyl) D4R POSS as a node, connecting it to the linker via a
Si-C bond instead of a Si-O-C linkage
Towards Zero-waste Mineral Carbon Sequestration Via Two-way Valorization of Ironmaking Slag
A three-stage process was developed to transform blast furnace slag (BFS) into two valuable products: precipitated calcium carbonate (PCC) and zeolitic materials. The conceptualized process aims to simultaneously achieve sustainable CO2 sequestration and solid waste elimination. Calcium is first selectively extracted by leaching with an organic acid, followed by carbonation of the leachate to precipitate CaCO3. In parallel, the hydrothermal conversion of the extracted solid residues in alkali solution induces the dissolution/precipitation mechanism that leads to the formation of micro- and meso-porous zeolitic materials. Leaching selectivity was identified as a key factor in the valorization potential of both products. Acetic acid satisfactorily limited the leaching of aluminium, required for the subsequent synthesis of zeolites, and carbonation of the acetic acid leachate resulted in the production of PCC of varied mineralogy and morphology, depending on processing conditions. In the hydrothermal conversion stage, the formation of zeolitic phases was observed, and their characteristics were found to vary depending on the calcium extraction efficiency in the previous stage, and the alkali (NaOH) concentration. The zeolitic phases produced, in order of increasing valorization potential, were: tobermorite, sodalite, lazurite, and analcime
Adsorption of Multi-heavy Metals Onto Water Treatment Residuals: Sorption Capacities and Applications
Inherently formed iron-based water treatment residuals (WTRs) were tested as alternative sorbents for multi-heavy metal removal from synthetic solutions, contaminated sediments, and surface waters. The WTRs were mainly composed of iron (hydr)oxides and had a high BET surface area (170.7 m2/g), due to the presence of micro- and mesopores. The sorption capacity of WTRs for As(V), Cd2+, Pb2+ and Zn2+ from synthetic solutions surpassed that of a commercially available goethite by 100-400% for single contaminant tests, and by 240% for total sorption in multi contaminant tests. The maximum sorption capacity of WTRs towards As(V), Pb2+ and Zn2+ was estimated by Langmuir equation fitting to range between 0.5 to 0.6 mmol/g, and their maximum sorption capacity for Cd was 0.19 mmol/g. WTRs performed significantly better than goethite for adsorption of cationic contaminants (Cd, Co, Ni, Pb, Zn) in the sediment tests, independent of the dosage or sediment sample. At the highest WTRs dosage (250 mg/g), concentrations of the cationic contaminants decreased by at least 80%, while approximately 40% removal was obtained with 50 mg/g dosage. Sorbent mixtures composed of WTRs with goethite, and with a clinoptilolite natural zeolite were used to reduce As leaching. The sorbent mixtures delivered the desired performance, with the natural zeolite performing better than the goethite as an amendment to WTRs. In addition, up to 90% removal of surface water contaminants was achieved with both fresh WTRs and the WTRs regenerated using 0.01 M EDTA
- …