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Using density-functional theory (DFT) calculations within the generalized gradient corrected approximation, the models that nonmetallic impurities X (X = C, N, S, F) substituted for O or Ti sites in anatase TiO 2 were investigated. By calculating the formation energy of X-monodoped TiO 2 with X substituted for O, we suggested that X dopants existed as C 4− , N 3− , S 2− and F − ions, respectively. Meanwhile, the X dopants existed as C 4+ , N 3+ , and S 6+ for X-monodoped (X = C, N, S) TiO 2 with X substituted for Ti. The conclusion of the valence states of nonmetallic impurities X substituted for O or Ti sites in TiO 2 is also supported by the results of optimized cell parameters and the local structures. Furthermore, an effective nonmetallic passivated codoping approach to modify the band edges of TiO 2 is proposed. Based on the first-principle calculations, we suggested that nonmetallic passivated groups such as (S 2− + C 4+ ) and (C 4− + S 6+ ) could reduce the band gap largely and make less perturbation in conduction band minima (CBM), thus lead to an ideal visible-light absorption region without affecting the reducing power. This work provides some new results and is anticipated to give some inspiration and guidance for design visible-light-driven TiO 2 photocatalyst with high efficiency. [ABSTRACT FROM AUTHOR]

[Display omitted] • A dual p-n heterojunction composed of NiCo 2 O 4 /NiO/Al: SrTiO 3 was fabricated. • The dual p-n heterojunction was constructed with electrostatic adsorption force. • MOF-derived NiCo 2 O 4 /NiO was used as the O 2 -producing co-catalyst for water splitting. • The property of dual p-n heterojunction is superior to the single p-n heterojunction. • The built-in electric field contributes to the enhanced photocatalytic performance. In this study, NiCo 2 O 4 /NiO/Al: SrTiO 3 (labeled as NCO/NO/ASTO) with dual p-n heterojunction structure was devised and in-situ fabricated for the first time, in which metal–organic framework (MOF)-derived NiCo 2 O 4 /NiO (NCO/NO) was utilized as the O 2 -producing co-catalyst. This dual p-n heterojunction with the matching built-in electric field made it possible to separate and transfer charge carriers in a manner that was substantially more effective than the use of a single p-n heterojunction. The NCO/NO/ASTO-1 exhibits an excellent overall water splitting performance of 1.74 (H 2)/0.85 (O 2) mmol g−1h−1 when exposed to UV radiation, which is 1.3 and 2.6 times that of NiCo 2 O 4 /Al: SrTiO 3 (NCO/ASTO) and NiO/Al: SrTiO 3 (NO/ASTO) with single p-n heterojunction structure, respectively. The electrostatic adsorption force and matching built-in electric field between ASTO and NCO/NO have been demonstrated, ensuring the presence as well as the stability of the dual p-n junction and accelerating the migration of photogenerated carriers. Moreover, density functional theory (DFT) was used to offer theoretical evidence of the driving force for the interfacial charge transfer in the NCO/NO/ASTO dual p-n heterojunction, which could be attributed to the difference in the work functions (Φ) of the components of NO, NCO, and ASTO. [ABSTRACT FROM AUTHOR]

[Display omitted] • An all-organic S-scheme heterojunction has been successfully developed. • The heterojunction contains a D-A type conjugated polymer and C 3 N 4 nanosheets. • The interfacial heterojunction was fabricated via a π-π conjugated interaction. • DFT calculations indicated the formed built-in electric field drove charge transfer. • The optimal P 2 CNNS exhibits photocatalytic H 2 evolution rate of 50.2 mmol·g−1 h−1. Designing an excellent photocatalyst with high space separation efficiency of photogenerated carriers to boost the rate of photocatalytic hydrogen (H 2) generation remains a challenge. In this work, the S-scheme heterojunction containing a donor–acceptor (D-A) type conjugated polymer of PyDTDO-3 and a two-dimensional (2D)-layered conjugated polymer of C 3 N 4 nanosheets with conjugated heptazine units (denoted as PCNNS) was prepared for photocatalytic H 2 production. It is found that the recombination rate of photogenerated electron-hole pairs is decreased by the S-scheme heterojunction structure through establishing an intimate π–π conjugated heterointerface between PyDTDO-3 and C 3 N 4 NS. To clarify the potential photocatalytic mechanism, diversified characterization techniques were employed and the density functional theory (DFT) calculations were conducted. As a result of the difference in the work function, a Fermi level gap is formed between PyDTDO-3 and C 3 N 4 , which eventually leads to the band edge bent upward/downward and the presence of the built-in electric field causing the spontaneous interfacial charge transfer from C 3 N 4 NS to PyDTDO-3 at the π–π conjugated interface. Owing to its unique structure and optical properties, the optimal P 2 CNNS heterojunction photocatalyst shows excellent photocatalytic H 2 generation performance, which reaches a maximum of 50.2 mmol g−1 h−1 under visible illumination. [ABSTRACT FROM AUTHOR]

[Display omitted] • [Mo 3 S 13 ]2− nanoclusters are highly dispersed into the micropores of TpPa-1-COF. • The size and micro-environment of micropores play a central role in anchoring MS-c. • The photocatalytic H 2 evolution rate of MS-c@TpPa-1 is increased by 4.7 times. • The coordinated Mo − N groups between MS-c and TpPa-1-COF result in enhanced stability. • The favorable electron–proton transfer to form H* occurs on the S instead of N sites. Non-noble-metal-based [Mo 3 S 13 ]2− nanoclusters (MS-c) as a co-catalyst face the problems of instability and inevitable aggregation, which limit its photocatalytic applications. Herein, β-ketoenamine-linked covalent organic framework (COF), namely TpPa-1-COF, was utilized to embed MS-c. The micropores of TpPa-1-COF could not only limit the growth of MS-c to achieve its high dispersion but also play a central role in anchoring MS-c. Moreover, the structural stability of MS-c is highly enhanced due to the confinement effect of TpPa-1-COF, and the visible-light-driven photocatalytic H 2 evolution rate of 528 μmol g−1h−1 for MS-c@TpPa-1 (0.3: 1), which is increased by 4.7 times as compared with that of TpPa-1-COF. The density functional theory (DFT) calculations indicate that the electrons transfer from TpPa-1 to MS-c occurs at the interface of MS-c@TpPa-1 in the ground state based on the charge density difference analysis. With the irradiation of visible light, the photoexcited electrons derived from the π-conjugated TpPa-1-COF backbone could be delivered to the embedding MS-c through the coordinated Mo − N groups, and the favorable electron–proton transfer to form H* and efficient desorption of H 2 occurs on the S sites instead of N sites in MS-c@TpPa-1, resulting in the enhanced photocatalytic H 2 evolution rate. Overall, this work provides a novel approach for embedding the unstable MS-c with low cost into the micropores of COF via coordination bonds to improve the structural stability and photocatalytic activity. [ABSTRACT FROM AUTHOR]

[Display omitted] • [Mo 3 S 13 ]2− nanoclusters are highly dispersed into the micropores of TpPa-1-COF. • The size and micro-environment of micropores play a central role in anchoring MS-c. • The photocatalytic H 2 evolution rate of MS-c@TpPa-1 is increased by 4.7 times. • The coordinated Mo − N groups between MS-c and TpPa-1-COF result in enhanced stability. • The favorable electron–proton transfer to form H* occurs on the S instead of N sites. Non-noble-metal-based [Mo 3 S 13 ]2− nanoclusters (MS-c) as a co-catalyst face the problems of instability and inevitable aggregation, which limit its photocatalytic applications. Herein, β-ketoenamine-linked covalent organic framework (COF), namely TpPa-1-COF, was utilized to embed MS-c. The micropores of TpPa-1-COF could not only limit the growth of MS-c to achieve its high dispersion but also play a central role in anchoring MS-c. Moreover, the structural stability of MS-c is highly enhanced due to the confinement effect of TpPa-1-COF, and the visible-light-driven photocatalytic H 2 evolution rate of 528 μmol g−1h−1 for MS-c@TpPa-1 (0.3: 1), which is increased by 4.7 times as compared with that of TpPa-1-COF. The density functional theory (DFT) calculations indicate that the electrons transfer from TpPa-1 to MS-c occurs at the interface of MS-c@TpPa-1 in the ground state based on the charge density difference analysis. With the irradiation of visible light, the photoexcited electrons derived from the π-conjugated TpPa-1-COF backbone could be delivered to the embedding MS-c through the coordinated Mo − N groups, and the favorable electron–proton transfer to form H* and efficient desorption of H 2 occurs on the S sites instead of N sites in MS-c@TpPa-1, resulting in the enhanced photocatalytic H 2 evolution rate. Overall, this work provides a novel approach for embedding the unstable MS-c with low cost into the micropores of COF via coordination bonds to improve the structural stability and photocatalytic activity. [ABSTRACT FROM AUTHOR]

It is still challenging to fabricate photocatalysts via loaded metal cocatalysts with good dispersion onto the conjugated polymers (CPs). Herein, a donor-acceptor (D–A) structural CP of PyDTDO-3 was employed to host platinum (Pt) nanoparticles (NPs) using N , N ′-dimethylformamide (DMF) as a protectant, stabilizer, and reducing agent, which not only promotes Pt NPs to have excellent dispersion property on the surface of PyDTDO-3 but also endows Pt NPs to maintain metallic Pt0 species. As a result, the PyDTDO-3 loaded with Pt NPs exhibits remarkable hydrogen (H 2) evolution activity with a rate of 39.9 mmol g−1 h−1 under visible light irradiation, and the fair stability of optimal 7% Pt/PyDTDO-3 is expressed in the rate of H 2 generation upon 30 h cycling. Based on density functional theory (DFT) calculations, it has been demonstrated that Pt NPs are selectively loaded onto the acceptor (A) unit of PyDTDO-3 that has the lowest adsorption energies (E ads) and the closest bond lengths between the Pt NPs and PyDTDO-3. Moreover, there are much more electrons filling at the Fermi level (E f), indicating the optimal 7% Pt/PyDTDO-3 with high electroconductivity timely captured and removed the photoinduced electrons and thus realized the space separation efficiency of electron-hole pairs. Overall, our findings offer a rational way to load metal cocatalysts onto CPs with good dispersion for efficient photocatalytic H 2 evolution. [Display omitted] • Well-dispersed Pt NPs are fabricated onto the conjugated D-A type polymers. • DMF was used as a protectant, stabilizer, and reducing agent to obtain metallic Pt0. • Pt (111) plane is selectively loaded onto the acceptor (A) unit of PyDTDO-3. • The photoinduced electrons transfer from D to A unit of PyDTDO-3 and then to Pt NPs. • The optimal 7% Pt/PyDTDO-3 exhibits photocatalytic H 2 rate of 39.9 mmol g−1 h−1. [ABSTRACT FROM AUTHOR]