Global copper slag (CS) emissions reached 57.2 million tons in 2021. Despite the increasing reuse of CS, the treatment of CS is still dominated by landfill so far, which not only occupies land ...resources but also causes damage to the environment. The application of CS to cement-based materials (CBMs) is one of the main approaches to its comprehensive utilization and has important economic and social implications. This article reviews the physicochemical properties, activity excitation, and heavy metal leaching properties of CS and summarizes the effect of CS on the working properties, mechanical properties, and durability of CBMs. At the end of the article, the existing problems in the research are analyzed, and the development trend is proposed, which provides technical guidance and reference for further research and application of CS in CBMs in the future.
The development of environmental catalysts is an urgent subject to be tackled by scientists and engineers all over the world due to the borderless nature of environmental pollution. We named the ...catalyst enabling the decomposition of the pollutants by effectively utilizing the solar energy from ultraviolet to infrared as “solar environmental catalysts”. This Feature Article reviews the recent studies on a novel class of solar environmental catalysts consisting of TiO2 and molecular scale oxides of 3d metals and for comparison d10 (Sn) on the surface (MOs/TiO2). The TiO2 surface modification with MO clusters by the chemisorption–calcination cycle (CCC) technique presents novel band engineering for finely tuning the top of the valence band, while the unique physicochemical and electronic properties of MOs/TiO2 give rise to the outstanding photo- and thermocatalytic activities for the decomposition of organic pollutants. In the first part following the Introduction, the CCC technique for forming extremely small MO clusters on TiO2, the structures, physicochemical properties, and electronic structures of MOs/TiO2 are described. The second part deals with their thermo- and photocatalytic activities for the degradation of model organic pollutants and the essential action mechanisms of the MO clusters. The combination of experiments and first-principles density functional theory simulations shows that Co2O3/TiO2 can be a prototype of the solar environmental catalyst with high levels of photo(UV and visible)- and thermocatalytic activities.
Fe(acac)3 is chemisorbed on the surfaces of anatase TiO2 via partial ligand exchange between the acetylacetonate and surface Ti−OH groups Fe(acac)2/TiO2. The postheating at 773 K in air forms iron ...oxide species on the TiO2 surface in a highly dispersed state at a molecular level ((FeO x ) m /TiO2). As a result of the iron oxide surface modification, the band gap of TiO2 decreases, while the absorption due to the d−d transition clearly observed for the usual impregnation samples is very weak. (FeO x ) m /TiO2 gives rise to a noticeable visible light activity concomitantly with a significant increase in UV light activity, whereas Fe(acac)2/TiO2 hardly responds to visible light. Valence-band X-ray photoelectron spectra of (FeO x ) m /TiO2 showed that the band gap narrowing results from the rise in the valence band top with surface modification. Also, photoluminescence spectroscopy indicated that the surface iron oxide species rapidly capture the excited electrons in the conduction band of TiO2 to suppress recombination via surface oxygen vacancy levels. Furthermore, the surface iron oxide species act as excellent mediators for electron transfer from TiO2 to O2.
Cu(acac)2 is chemisorbed on TiO2 particles P-25 (anatase/rutile = 4/1 w/w), Degussa via coordination by surface Ti–OH groups without elimination of the acac ligand. Post-heating of the ...Cu(acac)2-adsorbed TiO2 at 773 K yields molecular scale copper(II) oxide clusters on the surface (CuO/TiO2). The copper loading amount (Γ/Cu ions nm–2) is controlled in a wide range by the Cu(acac)2 concentration and the chemisorption–calcination cycle number. Valence band (VB) X-ray photoelectron and photoluminescence spectroscopy indicated that the VB maximum of TiO2 rises up with increasing Γ, while vacant midgap levels are generated. The surface modification gives rise to visible-light activity and concomitant significant increase in UV-light activity for the degradation of 2-naphthol and p-cresol. Prolonging irradiation time leads to the decomposition to CO2, which increases in proportion to irradiation time. The photocatalytic activity strongly depends on the loading, Γ, with an optimum value of Γ for the photocatalytic activity. Electrochemical measurements suggest that the surface CuO clusters promote the reduction of adsorbed O2. First principles density functional theory simulations clearly show that, at Γ < 1, unoccupied Cu 3d levels are generated in the midgap region, and at Γ > 1, the VB maximum rises and the unoccupied Cu 3d levels move to the conduction band minimum of TiO2. These results suggest that visible-light excitation of CuO/TiO2 causes the bulk-to-surface interfacial electron transfer at low coverage and the surface-to-bulk interfacial electron transfer at high coverage. We conclude that the surface CuO clusters enhance the separation of photogenerated charge carriers by the interfacial electron transfer and the subsequent reduction of adsorbed O2 to achieve the compatibility of high levels of visible and UV-light activities.
A number of NiO clusters have been formed on TiO2 (anatase/rutile = 4/1 w/w, P-25, Degussa) in a highly dispersed state (NiO/TiO2) by the chemisorption–calcination cycle technique. The NiO/TiO2 ...causes high visible-light activities for the degradations of 2-naphthol and p-cresol exceeding those of FeO x /TiO2 ( Tada Angew. Chem., Int. Ed. 2011, 50, 3501−3505 ). The main purpose of this study is to clarify the origin at an electronic level by the density functional simulation for NiO, Ni2O2, Ni3O3, and Ni4O4 clusters supported on TiO2 rutile (110) and anatase (001) surfaces. The clusters adsorb strongly on both rutile and anatase with adsorption energies ranging from −3.18 to −6.15 eV, creating new interfacial bonds between the clusters and both surfaces. On rutile, intermetallic Ni–Ti bonds facilitate stronger binding compared with anatase. The electronic structure shows that the top of the valence bands (VBs) of rutile and anatase arises from electronic states on the NiO cluster. On the other hand, the conduction band of rutile is from the Ti 3d states, whereas NiO cluster levels are generated near the conduction band minimum of anatase. This is in contrast to the SnO2/rutile TiO2 system, where the density of states near the conduction band minimum increases with the VB unmodified. In the NiO/TiO2 system, the band gaps of both rutile and anatase are narrowed by up to 0.8 eV compared with pristine TiO2, which pushes the photoactivity into the visible region. In view of the calculated electronic structure, we have attributed the enhanced photocataltyic activity both to the charge separation due to the excitation from the Ni 3d surface sub-band to the TiO2 conduction band and the action of the NiO species as a mediator for the electron transfer from the TiO2 conduction band to O2.
Why is an optimum size present? Titanium dioxide‐supported gold nanoparticles (Au/TiO2) show catalytic activity for H2O2 decomposition (kobs) with a maximum at the mean size of 4.6 nm (see graph) as ...a result of the balance of the active site numbers and the Fermi energy of Au NPs. The H2O2–Au/TiO2 system enables the chemoselective oxidation of cinnamyl alcohol to cinnamaldehyde, for which the selectivity parallels kobs.
This study first presents a "TiO2-based eco-catalyst" working in the dark and under visible-light irradiation for the degradation of environmental organic pollutants. Molecular scale cobalt(III) ...oxide clusters are formed on the surface of highly active anatase TiO2 nanoparticles (Co2O3-TiO2) by the chemisorption-calcination cycle method. Co2O3-TiO2 exhibits very high visible-light activities for the degradation of 2-naphthol and formic acid used as model organic pollutants. Unprecedented thermocatalytic activity is concomitantly endowed on TiO2 by the surface modification. Prolonging reaction time in the Co2O3-TiO2 photo- and thermo-catalyzed reactions leads to the decomposition of 2-naphthol and formic acid to CO2. The essential action mechanisms of the Co2O3 clusters in the photocatalysis and thermocatalysis of Co2O3-TiO2 were discussed on the basis of spectroscopic and electrochemical data.
Sn(acac)
2
Cl
2
is chemisorbed on the surfaces of anatase TiO
2
via
ion-exchange between the complex ions and H
+
released from the surface TiOH groups without liberation of the acetylacetonate ...ligand (Sn(acac)
2
/TiO
2
). The post-heating at 873 K in air forms tin oxide species on the TiO
2
surface in a highly dispersed state on a molecular scale ((SnO
2
)
m
/TiO
2
). A low level of this p block metal oxide surface modification (0.007 Sn ions nm
2
) accelerates the UV-light-activities for the liquid- and gas-phase reactions, whereas in contrast to the surface modification with d block metal oxides such as FeO
x
and NiO, no visible-light response is induced. Electrochemical measurements and first principles density functional theory (DFT) calculations for (SnO
2
)
m
/TiO
2
model clusters (
m
= 1, 2) indicate that the bulk (TiO
2
)-to-surface interfacial electron transfer (BS-IET) enhances charge separation and the following electron transfer to O
2
to increase the photocatalytic activity.
The SnO
2
-surface modification of anatase TiO
2
increases its UV-light-activities for both liquid- and gas-phase reactions.
Surface modification of rutile TiO2 with extremely small SnO2 clusters gives rise to a great increase in its UV light activity for degradation of model organic water pollutants, while the effect is ...much smaller for anatase TiO2. This crystal form sensitivity is rationalized in terms of the difference in the electronic modification of TiO2 through the interfacial Sn–O–Ti bonds. The increase in the density of states near the conduction band minimum of rutile by hybridization with the SnO2 cluster levels intensifies the light absorption, but this is not seen with modified anatase. The electronic transition from the valence band to the conduction band causes the bulk-to-surface interfacial electron transfer to enhance charge separation. Further, electrons relaxed to the conduction minimum are smoothly transferred to O2 due to the action of the SnO2 species as an electron transfer promoter.
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