Application of photocatalysts that strongly absorb within the visible range is a common strategy to improve the efficiency of photoelectrochemical (PEC) systems; this may translate to high ...photocurrents, but it is not always the case. Here, we show that nitrogen doping enhances visible light absorption of TiO
2
; however, it does not necessarily result in improved PEC performance. Depending on the applied external potential, N-doping can improve, or degrade, PEC performance either under water oxidation conditions or
via
hole scavenging (Na
2
S/Na
2
SO
3
). In this work, we developed a holistic approach to evaluate the true impact of N doping in TiO
2
on PEC performance. Interstitial and substitutional N doping are experimentally explored for the first time through a simple and novel PEC approach which complemented X-ray photoelectron analyses. Using this approach, we show that interstitial N doping of anatase TiO
2
dominates up to 400 °C and substitutional doping up to
ca.
600 °C, without rutile formation. This reveals that the bottleneck for doping higher N-concentrations in TiO
2
is the direct transformation to thermodynamically favorable N-rich phases, such as TiN/Ti
2
N at 700 °C, inhibiting the formation of rutile phase. Transmission electron microscopy revealed that N doping proceeds mainly from the inner to the outer tube walls
via
nitridation and follows a preferential pathway from interstitial to substitutional doping. Direct PEC experimental evidence on visible light activation of N doped TiO
2
, and the location of interband states, showed acceptor levels of 1.0 eV for substitutional and 0.7 eV for interstitial doping above the TiO
2
valence band maximum. In addition, due to O vacancies and Ti
3+
species, donor levels below the conduction band minimum were also created. These levels act as trapping/recombination centers for charge carriers and, therefore, the gain in the visible range due to N doping does not translate to an improved PEC performance by these structural defects. Ultimately, we show that whilst there is a benefit of visible light absorption through N doping in TiO
2,
the PEC performance of the samples only surpasses pristine TiO
2
at relatively high biasing (>0.3 V
vs.
Ag/AgCl).
A holistic approach to fully characterize the physical-chemical properties of N doped TiO
2
and evaluate its true impact on photoelectrochemical applications.
We report the design and preparation of multifunctional hybrid nanomaterials through the stabilization of gold nanoparticles with thiol‐functionalised hybrid organic–inorganic polyoxometalates ...(POMs). The covalent attachment of the hybrid POM forms new nanocomposites that are stable at temperatures and pH values which destroy analogous electrostatically functionalised nanocomposites. Photoelectrochemical analysis revealed the unique photochemical and redox properties of these systems.
Handy hybrids: A material based on gold nanoparticles stabilized by organic–inorganic hybrid polyoxometalates is described (see picture). The new nanomaterial exhibits unprecedented stability and photoactivity under visible light and can be reversibly reduced and oxidized at electrode surfaces, making it very promising for future photonic and electrochemical systems.
Carbon nitride (C 3 N 4 ) possesses both a band gap in the visible range and a low-lying conduction band potential, suitable for water splitting and CO 2 reduction reactions (CO 2 RR). Yet, bulk C 3 ...N 4 (b-C 3 N 4 ) suffers from structural disorder leading to sluggish reaction kinetics. This can be improved by graphitisation; however, current processes in the literature, lead to a variety of graphitised C 3 N 4 (g-C 3 N 4 ), making it difficult to link the degrees of graphitisation with the functional properties. Herein, we employ complementary analyses, including electrochemical impedance, photoluminescence, and photocurrent, to elucidate structure–property–function relationships. Guided by the descriptors, we developed a facile two-step annealing method that yields nanocrystalline carbon nitride (nc-C 3 N 4 ), comprising nanoscale graphitic domains within an amorphous matrix. The nanocrystalline grains of nc-C 3 N 4 allow effective immobilisation of Cu atoms and stabilisation of low oxidation states (Cu( i )). Electron microscopy and energy-dispersive X-ray spectroscopy demonstrate that Cu is atomically dispersed. Importantly, the addition of only 0.11 wt% of copper to nc-C 3 N 4 drastically decreases the charge recombination and resistance to change transfer. The synergy of the Cu single-atom catalyst and nanocrystalline domains in carbon nitride (Cu/nc-C 3 N 4 ) leads to a remarkable 99% selectivity towards methanol production with a rate of 316 μmol g cat −1 h −1 during the photocatalytic CO 2 RR, which is absent in Cu/b-C 3 N 4 .
Carbon nitride (C
3
N
4
) possesses both a band gap in the visible range and a low-lying conduction band potential, suitable for water splitting and CO
2
reduction reactions (CO
2
RR). Yet, bulk C
3
...N
4
(b-C
3
N
4
) suffers from structural disorder leading to sluggish reaction kinetics. This can be improved by graphitisation; however, current processes in the literature, lead to a variety of graphitised C
3
N
4
(g-C
3
N
4
), making it difficult to link the degrees of graphitisation with the functional properties. Herein, we employ complementary analyses, including electrochemical impedance, photoluminescence, and photocurrent, to elucidate structure-property-function relationships. Guided by the descriptors, we developed a facile two-step annealing method that yields nanocrystalline carbon nitride (nc-C
3
N
4
), comprising nanoscale graphitic domains within an amorphous matrix. The nanocrystalline grains of nc-C
3
N
4
allow effective immobilisation of Cu atoms and stabilisation of low oxidation states (Cu(
i
)). Electron microscopy and energy-dispersive X-ray spectroscopy demonstrate that Cu is atomically dispersed. Importantly, the addition of only 0.11 wt% of copper to nc-C
3
N
4
drastically decreases the charge recombination and resistance to change transfer. The synergy of the Cu single-atom catalyst and nanocrystalline domains in carbon nitride (Cu/nc-C
3
N
4
) leads to a remarkable 99% selectivity towards methanol production with a rate of 316 μmol g
cat
−1
h
−1
during the photocatalytic CO
2
RR, which is absent in Cu/b-C
3
N
4
.
Synergistic magic: copper single atom and nanocrystalline carbon nitride for selective CO
2
to methanol conversion.
Generally, anatase is the most desirable TiO 2 polymorphic phase for photovoltaic and photocatalytic applications due to its higher photoconductivity and lower recombination rates compared to the ...rutile phase. However, in applications where temperatures above 500 °C are required, growing pure anatase phase nanoparticles is still a challenge, as above this temperature TiO 2 crystallite sizes are larger than 35 nm which thermodynamically favors the growth of rutile crystallites. In this work, we show strong evidence, for the first time, that achieving a specific fraction (50%) of the {112} facets on the TiO 2 surface is the key limiting step for anatase-to-rutile phase transition, rather than the crystallite size. By using a fluorinated ionic liquid (IL) we have obtained pure anatase phase crystallites at temperatures up to 800 °C, even after the crystallites have grown beyond their thermodynamic size limit of ca. 35 nm. While fluorination by the IL did not affect {001} growth, it stabilized the pure anatase TiO 2 by suppressing the formation of {112} facets on anatase particles. By suppressing the {112} facets, using specific concentrations of fluorinated ionic liquid in the TiO 2 synthesis, we controlled the anatase-to-rutile phase transition over a wide range of temperatures. This information shall help synthetic researchers to determine the appropriate material conditions for specific applications.
Generally, anatase is the most desirable TiO
2
polymorphic phase for photovoltaic and photocatalytic applications due to its higher photoconductivity and lower recombination rates compared to the ...rutile phase. However, in applications where temperatures above 500 °C are required, growing pure anatase phase nanoparticles is still a challenge, as above this temperature TiO
2
crystallite sizes are larger than 35 nm which thermodynamically favors the growth of rutile crystallites. In this work, we show strong evidence, for the first time, that achieving a specific fraction (50%) of the {112} facets on the TiO
2
surface is the key limiting step for anatase-to-rutile phase transition, rather than the crystallite size. By using a fluorinated ionic liquid (IL) we have obtained pure anatase phase crystallites at temperatures up to 800 °C, even after the crystallites have grown beyond their thermodynamic size limit of
ca.
35 nm. While fluorination by the IL did not affect {001} growth, it stabilized the pure anatase TiO
2
by suppressing the formation of {112} facets on anatase particles. By suppressing the {112} facets, using specific concentrations of fluorinated ionic liquid in the TiO
2
synthesis, we controlled the anatase-to-rutile phase transition over a wide range of temperatures. This information shall help synthetic researchers to determine the appropriate material conditions for specific applications.
Fluorinated ionic liquids are used to finely control the exposure of {112} facets on the TiO
2
surface enabling an exquisite temperature control of the anatase-to-rutile phase transition.
A method of pore fabrication in the walls of carbon nanotubes has been developed, leading to porous nanotubes that have been filled with catalysts and utilized in liquid- and gas-phase reactions. ...Chromium oxide nanoparticles have been utilized as highly effective etchants of carbon nanotube sidewalls. Tuning the thermal profile and loading of this nanoscale oxidant, both of which influence the localized oxidation of the carbon, have allowed the controlled formation of defects and holes with openings of 40–60 nm, penetrating through several layers of the graphitic carbon nanotube sidewall, resulting in templated nanopore propagation. The porous carbon nanotubes have been demonstrated as catalytic nanoreactors, effectively stabilizing catalytic nanoparticles against agglomeration and modulating the reaction environment around active centers. CO2 sorption on ruthenium nanoparticles (RuNPs) inside nanoreactors led to distinctive surface-bound intermediates (such as carbonate species), compared to RuNPs on amorphous carbon. Introducing pores in nanoreactors modulates the strength of absorption of these intermediates, as they bond more strongly on RuNPs in porous nanoreactors as compared to the nanoreactors without pores. In the liquid-phase hydrosilylation of phenylacetylene, the confinement of Rh4(CO)12 catalyst centers within the porous nanoreactors changes the distribution of the products relative to those observed in the absence of the additional pores. These changes have been attributed to the enhanced local concentration of phenylacetylene and the environment in which the catalytic centers reside within the porous carbon host.
A method of pore fabrication in the walls of carbon nanotubes has been developed, leading to porous nanotubes that have been filled with catalysts and utilized in liquid- and gas-phase reactions. ...Chromium oxide nanoparticles have been utilized as highly effective etchants of carbon nanotube sidewalls. Tuning the thermal profile and loading of this nanoscale oxidant, both of which influence the localized oxidation of the carbon, have allowed the controlled formation of defects and holes with openings of 40-60 nm, penetrating through several layers of the graphitic carbon nanotube sidewall, resulting in templated nanopore propagation. The porous carbon nanotubes have been demonstrated as catalytic nanoreactors, effectively stabilizing catalytic nanoparticles against agglomeration and modulating the reaction environment around active centers. CO
sorption on ruthenium nanoparticles (RuNPs) inside nanoreactors led to distinctive surface-bound intermediates (such as carbonate species), compared to RuNPs on amorphous carbon. Introducing pores in nanoreactors modulates the strength of absorption of these intermediates, as they bond more strongly on RuNPs in porous nanoreactors as compared to the nanoreactors without pores. In the liquid-phase hydrosilylation of phenylacetylene, the confinement of Rh
(CO)
catalyst centers within the porous nanoreactors changes the distribution of the products relative to those observed in the absence of the additional pores. These changes have been attributed to the enhanced local concentration of phenylacetylene and the environment in which the catalytic centers reside within the porous carbon host.
Correction for 'Highly modulated supported triazolium-based ionic liquids: direct control of the electronic environment on Cu nanoparticles' by Cristián Valdebenito
et al.
,
Nanoscale Adv.
, 2020,
2
..., 1325-1332. DOI:
10.1039/d0na00055h
.
Photodegradation of PLA/PE, PLA/PE/TiO
2
nanospheres and PLA/PE/TiO
2
nanotubes was obtained under simulated sunlight. The nanocomposites were analyzed by infrared spectroscopy, scanning electron ...microscopy and tensile-deformation measurements. TiO
2
nanospheres and TiO
2
nanotubes were found to present different effects on the crystallinity of PLA and a straight correlation between structural organization and photostability was observed. According to the results, TiO
2
promotes the degradation of PLA and PE, affecting the organizational level of the polymers. By adding TiO
2
nanoparticles to the PLA/PE films, vibration modes characteristic of degradation products were promptly observed and the lifetime of the polymer decreased when compared to the PLA/PE without TiO
2
nanoparticles. Mechanical measurements showed an improvement of the mechanical properties when adding the TiO
2
nanoparticles.
PDF
