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Oxygen vacancy-mediated sandwich-structural TiO2−x /ultrathin g-C3N4/TiO2−x direct Z-scheme heterojunction visible-light-driven photocatalyst for efficient removal of high toxic tetracycline antibiotics
“…These pioneering studies clearly proved that heteroatoms doping could simultaneously induce the formation of defects, and the synergistic effect of doping and defects could dramatically boost the photocatalytic performance. Considering the benefits of Z-scheme heterojunctions, some photocatalysts with rich OVs, including BiOCl, BiOCl x I 1– x , and TiO 2– x , have been coupled with g-C 3 N 4 to form Z-scheme heterojunction photocatalysts. ,,− Our group also reported a double defect-mediated Z-scheme g-C 3 N 4 /TiO 2 system, showing a superior PHE rate of approximately ∼651.79 μmol/h …”
Exploring
novel 2D heterojunction photocatalysts with a wide spectral
response and high active site exposure has been a huge challenge.
A small-sized catalyst with high dispersibility has been considered
an ideal model for maximizing active sites and increasing atomic efficiency.
Herein, the 0D/2D Z-scheme heterojunction was designed by in situ
solvothermal and subsequent calcination in air by integrating dopant
and defect doubly modified CeO2 nanodots and g-C3N4 nanosheets (CNNS). Ultrafine cobalt-doped CeO2 nanodots (≈4 to 5 nm) with enriched oxygen vacancies (Co-CeO2–OVs) were uniformly and tightly anchored on the surface
of CNNS to form a heterojunction. The density functional theory (DFT)
calculations confirmed that cobalt dopants and oxygen vacancies form
impurity energy states at the top of a valence band, thus narrowing
the band gap. The optimized 0D/2D heterojunction showed a remarkable
hydrogen production rate of ∼203.6 μmol/h, which was
approximately 4.9- and 30.8-fold higher than that of CNNS (∼41.2
μmol/h) and CeO2 (∼6.6 μmol/h), respectively.
Moreover, a large quantum yield of ∼8.94% was achieved at 420
nm. The 0D/2D heterojunction with a larger intimate area provided
abundant reactive active sites and strong electron interactions to
excite photogenerated carrier dynamics, and the doping and defect
engineering could expand the light response range by regulating the
electronic band structure. Strong evidence provided by experimental
results and DFT calculations proved the Z-scheme charge transfer pathway.
This work not only provided a novel approach to integrate 0D nanodots
and 2D nanosheets for the formation of intimate Z-scheme heterointerfaces
but also deepened the understanding of the dopant–defect synergistic
modification to optimize the band structure and electronic structures
for high-efficient solar energy capture and conversion.
“…These pioneering studies clearly proved that heteroatoms doping could simultaneously induce the formation of defects, and the synergistic effect of doping and defects could dramatically boost the photocatalytic performance. Considering the benefits of Z-scheme heterojunctions, some photocatalysts with rich OVs, including BiOCl, BiOCl x I 1– x , and TiO 2– x , have been coupled with g-C 3 N 4 to form Z-scheme heterojunction photocatalysts. ,,− Our group also reported a double defect-mediated Z-scheme g-C 3 N 4 /TiO 2 system, showing a superior PHE rate of approximately ∼651.79 μmol/h …”
Exploring
novel 2D heterojunction photocatalysts with a wide spectral
response and high active site exposure has been a huge challenge.
A small-sized catalyst with high dispersibility has been considered
an ideal model for maximizing active sites and increasing atomic efficiency.
Herein, the 0D/2D Z-scheme heterojunction was designed by in situ
solvothermal and subsequent calcination in air by integrating dopant
and defect doubly modified CeO2 nanodots and g-C3N4 nanosheets (CNNS). Ultrafine cobalt-doped CeO2 nanodots (≈4 to 5 nm) with enriched oxygen vacancies (Co-CeO2–OVs) were uniformly and tightly anchored on the surface
of CNNS to form a heterojunction. The density functional theory (DFT)
calculations confirmed that cobalt dopants and oxygen vacancies form
impurity energy states at the top of a valence band, thus narrowing
the band gap. The optimized 0D/2D heterojunction showed a remarkable
hydrogen production rate of ∼203.6 μmol/h, which was
approximately 4.9- and 30.8-fold higher than that of CNNS (∼41.2
μmol/h) and CeO2 (∼6.6 μmol/h), respectively.
Moreover, a large quantum yield of ∼8.94% was achieved at 420
nm. The 0D/2D heterojunction with a larger intimate area provided
abundant reactive active sites and strong electron interactions to
excite photogenerated carrier dynamics, and the doping and defect
engineering could expand the light response range by regulating the
electronic band structure. Strong evidence provided by experimental
results and DFT calculations proved the Z-scheme charge transfer pathway.
This work not only provided a novel approach to integrate 0D nanodots
and 2D nanosheets for the formation of intimate Z-scheme heterointerfaces
but also deepened the understanding of the dopant–defect synergistic
modification to optimize the band structure and electronic structures
for high-efficient solar energy capture and conversion.
“…Some studies have indicated that the separation mechanisms of charge carriers in ternary and quaternary heterojunction following that of binary heterojunction systems. Ni et al ( 2020 ) successfully synthesized a ternary sandwich-like TiO 2-x /ultrathin g-C 3 N 4 /TiO 2-x for efficient degradation of tetracycline under visible light and found that direct Z-scheme system was introduced to this ternary heterojunction (Fig. 12 ).…”
Section: Mechanisms Of Semiconductor Heterojunction Photocatalysis and The Separation Of Electron–hole Pairsmentioning
confidence: 99%
“…12 a Formation route of TiO 2-x /ultrathin g-C 3 N 4 /TiO 2-x : planetary grinding method. b Possible photocatalytic mechanism diagram of TiO 2-x /ultrathin g-C 3 N 4 /TiO 2-x : direct Z-scheme heterojunction model (Reprinted with permission of Elsevier from Ni et al 2020 ). TCH, tetracycline hydrochloride; O 2 · − , superoxide radical; ·OH hydroxyl radical; UCN, ultrathin g-C 3 N 4 ; S-TUCN, sandwich-like TiO 2 /ultrathin g-C 3 N 4 /TiO 2 ; S-TUCNov, ov-mediated sandwich-like TiO 2 /ultrathin g-C 3 N 4 /TiO 2 Fig.…”
Section: Mechanisms Of Semiconductor Heterojunction Photocatalysis and The Separation Of Electron–hole Pairsmentioning
Antibiotic pollution is a major health issue inducing antibiotic resistance and the inefficiency of actual drugs, thus calling for improved methods to clean water and wastewater. Here we review the recent development of heterojunction photocatalysis and application in degrading tetracycline. We discuss mechanisms for separating photogenerated electron–hole pairs in different heterojunction systems such as traditional, p–n, direct Z-scheme, step-scheme, Schottky, and surface heterojunction. Degradation pathways of tetracycline during photocatalysis are presented. We compare the efficiency of tetracycline removal by various heterojunctions using quantum efficiency, space time yield, and figures of merit. Implications for the treatment of antibiotic-contaminated wastewater are discussed.
“…Heterojunction engineering is observed to be a very encouraging technique for suppression of charge recombination as well as for obtaining applicable conduction and valance band edge positions for enhanced photocatalytic activity [ 124 , 125 ]. Particularly, the Z-scheme approach, encouraged with the natural photosynthesis process, promotes excellent redox facilities that would be advantageous for holes and radicals generation and propagation [ 124 , 126 , 127 ]. Fabricating Z-scheme between TiO 2 and other semiconductors having higher potential of the conduction band is considered to be a challenging task for CO 2 .…”
Section: Tio
2
Z-scheme Heterojunction Composites ...mentioning
Photocatalytic CO2 reduction is a most promising technique to capture CO2 and reduce it to non-fossil fuel and other valuable compounds. Today, we are facing serious environmental issues due to the usage of excessive amounts of non-renewable energy resources. In this aspect, photocatalytic CO2 reduction will provide us with energy-enriched compounds and help to keep our environment clean and healthy. For this purpose, various photocatalysts have been designed to obtain selective products and improve efficiency of the system. Semiconductor materials have received great attention and have showed good performances for CO2 reduction. Titanium dioxide has been widely explored as a photocatalyst for CO2 reduction among the semiconductors due to its suitable electronic/optical properties, availability at low cost, thermal stability, low toxicity, and high photoactivity. Inspired by natural photosynthesis, the artificial Z-scheme of photocatalyst is constructed to provide an easy method to enhance efficiency of CO2 reduction. This review covers literature in this field, particularly the studies about the photocatalytic system, TiO2 Z-scheme heterojunction composites, and use of transition metals for CO2 photoreduction. Lastly, challenges and opportunities are described to open a new era in engineering and attain good performances with semiconductor materials for photocatalytic CO2 reduction.
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