4 research outputs found
Adsorption Mechanisms of Typical Carbonyl-Containing Volatile Organic Compounds on Anatase TiO<sub>2</sub> (001) Surface: A DFT Investigation
The
carbonyl-containing compounds (CCs) are typical volatile organic
compounds (VOCs) and ubiquitously present in the environment. Therefore,
the adsorption structures and properties of typical CCs on the anatase
TiO<sub>2</sub> (001) surface were investigated systematically with
density functional theory (DFT) to understand their further catalytic
degradation mechanisms. The adsorption mechanisms show that three
selected typical CCs, acetaldehyde, acetone, and methyl acetate, can
easily be trapped on the anatase TiO<sub>2</sub> (001) surface via
the interaction between the carbonyl group with Ti<sub>5c</sub> sites
of catalyst surface. Especially for acetaldehyde with the bare carbonyl
group and the strongest adsorption energy, it is the most stable on
the surface, because the bare carbonyl group can interact with not
only the Ti<sub>5c</sub> atom, but also the O<sub>2c</sub> atom of
the surface. The substituent effect of different CCs has less impact
on its adsorption models in this studied system and the bare carbonyl
group is the key functional group within studied CCs. The Ti<sub>5c</sub> atoms of anatase TiO<sub>2</sub> (001) surface are active sites
to trap CCs. Our theoretical results are expected to provide insight
into the adsorption mechanisms of these carbonyl-containing VOCs on
TiO<sub>2</sub> catalyst and also to help understand the further catalytic
degradation mechanisms of air pollutants at the molecular level
Microwave-assisted Synthesis of Mesoporous Co<sub>3</sub>O<sub>4</sub> Nanoflakes for Applications in Lithium Ion Batteries and Oxygen Evolution Reactions
Mesoporous Co<sub>3</sub>O<sub>4</sub> nanoflakes with an interconnected architecture
were successfully synthesized using a microwave-assisted hydrothermal
and low-temperature conversion method, which exhibited excellent electrochemical
performances as anode materials in lithium ion batteries and as catalysts
in the oxygen evolution reaction (OER). Field-emission scanning electron
microscopy (FESEM) and transmission electron microscopy (TEM) observations
showed the unique interconnected and mesoporous structure. When employed
as anode materials for lithium ion batteries, mesoporous Co<sub>3</sub>O<sub>4</sub> nanoflakes delivered a high specific capacity of 883
mAh/g at 0.1C current rate and stable cycling performances even at
higher current rates. Post-mortem analysis of <i>ex situ</i> FESEM images revealed that the mesoporous and interconnected structure
had been well maintained after long-term cycling. The mesoporous Co<sub>3</sub>O<sub>4</sub> nanoflakes also showed both OER active properties
and good catalytic stability. This could be attributed to both the
stability of unique mesoporous structure and highly reactive facets
Nitrogen-Doped Graphene for Generation and Evolution of Reactive Radicals by Metal-Free Catalysis
N-Doped
graphene (NG) nanomaterials were synthesized by directly
annealing graphene oxide (GO) with a novel nitrogen precursor of melamine.
A high N-doping level, 8–11 at. %, was achieved at a moderate
temperature. The sample of NG-700, obtained at a calcination temperature
of 700 °C, showed the highest efficiency in degradation of phenol
solutions by metal-free catalytic activation of peroxymonosulfate
(PMS). The catalytic activity of the N-doped rGO (NG-700) was about
80 times higher than that of undoped rGO in phenol degradation. Moreover,
the activity of NG-700 was 18.5 times higher than that of the most
popular metal-based catalyst of nanocrystalline Co<sub>3</sub>O<sub>4</sub> in PMS activation. Theoretical calculations using spin–unrestricted
density functional theory (DFT) were carried out to probe the active
sites for PMS activation on N-doped graphene. In addition, experimental
detection of generated radicals using electron paramagnetic resonance
(EPR) and competitive radical reactions was performed to reveal the
PMS activation processes and pathways of phenol degradation on nanocarbons.
It was observed that both <sup>•</sup>OH and SO<sub>4</sub><sup>•–</sup> existed in the oxidation processes and
played critical roles for phenol oxidation
Few-Layered Trigonal WS<sub>2</sub> Nanosheet-Coated Graphite Foam as an Efficient Free-Standing Electrode for a Hydrogen Evolution Reaction
Few-layered
tungsten disulfide (WS<sub>2</sub>) with a controlled-phase ratio
(the highest trigonal-phase ratio being 67%) was exfoliated via lithium
insertion. The exfoliated WS<sub>2</sub> nanosheets were then anchored
onto three-dimensional (3D) graphite foam (GF) to fabricate free-standing
binder-free electrodes. The 3D GF can increase the interfacial contact
between the WS<sub>2</sub> nanosheets and the electrolyte and facilitate
ion transfer. Without the nonconductive binder, an intimate contact
between the WS<sub>2</sub> and GF interface can be created, leading
to the improvement of electrical conductivity. In comparison to the
pure WS<sub>2</sub> nanosheets, the overpotential for a hydrogen evolution
reaction is significantly decreased from 350 mV to 190 mV at 10 mA/cm<sup>2</sup>, and no deactivation occurs after 1000 cycles. The density
functional theory computations reveal that the efficient catalytic
activity of the trigonal-phase WS<sub>2</sub>/GF electrode is attributed
to the lower Gibbs free energy for H* adsorption and higher electrical
conductivity