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Herein, we first design a model of reversible redox-switching metal-organic framework single-unit-cell sheets, where the abundant metal single sites benefit for highly selective CO

Here, noble-metal-doped two-dimensional metal oxide nanosheets are designed to realize selective CO

Two-dimensional (2D) ultrathin mesoporous anatase TiO2 nanosheets with engineered surface defects (SDUATNs) are prepared by evaporation-induced self-assembly, solvothermal and surface hydrogenation reduction strategies. The as-prepared SDUATNs possess a comparatively large specific surface area of 100.4 m2 g−1, a main pore size of 9.7 nm, and a pore volume of 0.36 cm3 g−1. After surface hydrogenation, the narrowed bandgap of 2.97 eV expands the photoresponse from the ultraviolet to the visible-light region as a result of efficient surface defect engineering. The SDUATNs exhibit excellent photocatalytic hydrogen production performance (3.73 mmol h−1 g−1), which is about 3-fold higher than that of pristine ultrathin mesoporous anatase TiO2 nanosheets (1.31 mmol h−1 g−1) under AM 1.5G irradiation. The improvement of the hydrogen evolution performance is attributed to the efficient engineered surface defects and the special 2D ultrathin structure reducing the bandgap, increasing sunlight utilization, providing adequate surface active sites, shortening the migration distance of charge carriers and thus favoring the spatial separation of photogenerated electron–hole pairs. The high stability also favors practical applications. This work presents new insight to enhance the photocatalytic performance and may provide valuable ideas to fabricate other high-performance 2D photocatalysts.

Defective WO3 ultrathin surface-engineered nanosheets are fabricated by a solvothermal and low-temperature surface hydrogenation reduction strategy. The obtained defective WO3 ultrathin nanosheets with thicknesses of ∼4 nm possess a relatively large surface area of ∼25 m2 g−1. After surface engineering, the bandgap is narrowed to ∼2.48 eV due to the presence of surface oxygen vacancies, which further enhance the visible light absorption. The defective WO3 ultrathin nanosheets exhibit excellent solar-driven photocatalytic degradation performance for the complete degradation of the highly-toxic metribuzin herbicide (∼100%). The first-order rate constant (k) of the defective WO3 ultrathin nanosheets is ∼3 times higher than that of the pristine one. This can be ascribed to the formation of suitable surface-oxygen vacancy defects that promote the separation of photogenerated electron-hole pairs, and the two-dimensional ultrathin structure facilitating the surface engineering as well as furnishing a large number of surface active sites. Moreover, the defective WO3 ultrathin nanosheets exhibit high stability because the photocatalytic activity remains almost unchanged after 10 cycles, making them favorable for practical applications. This work offers new insights into the fabrication of other high-performance ultrathin nanosheet oxide photocatalysts for environmental applications.

Electrochemical activation strategy is very effective to improve the intrinsic catalytic activity of metal phosphate toward the sluggish oxygen evolution reaction (OER) for water electrolysis. However, it is still challenging to operando trace the activated reconstruction and corresponding electrocatalytic dynamic mechanisms. Herein, a constant voltage activation strategy is adopted to in situ activate Ni

It is still a challenge to evolve visible light photocatalysts that possess both efficient oxidation and reduction capabilities. In this paper, phosphorus-doped tubular carbon nitride@UiO-66-NH2 (p-TCN@U6-X) composites were prepared by in-situ load of UiO-66-NH2 on the surface of p-TCN based on solvothermal method, which exhibit excellent photocatalytic oxidation and reduction ability. As a result, under visible light irradiation (λ > 420 nm), the photocatalytic H2 production performance of p-TCN@U6-3 reached 2628 μmol g−1h−l, which was 8.19 and 5.36 times higher than that of p-TCN and UiO-66-NH2, respectively. Meanwhile, p-TCN@U6-3 also exhibited well selectivity rate (99%) and conversion rate (98%) for oxidative coupling of amine compounds. The high photocatalytic activities can be assigned to the improved visible light adsorption resulted from the tubular structure of p-TCN and enhanced electrical conductivity because of the phosphorus doping in p-TCN. Furthermore, UiO-66-NH2 plays the role of co-catalyst and active centers in the photocatalytic system to synergistically catalyze the reactions. Transient photocurrent spectra, steady-state photoluminescence (PL) and time-resolved photoluminescence (TRPL) further prove the more effective charge separation and transfer happened in the p-TCN@U6-X system compared with sole p-TCN and UiO-66-NH2, respectively. This work provides an effective method for creating novel carbon nitride-based photocatalytic systems with efficient capability for photocatalytic oxidation and reduction.

Herein, Pt-decorated TiO2 nanocube hierarchy structure (Pt-TNCB) was fabricated by a facile solvothermal synthesis and in-situ photodeposition strategy. The Pt-TNCB exhibits an excellent solar-driven photocatalytic hydrogen evolution rate (337.84 μmol h-1 ), which is about 37 times higher than that of TNCB (9.19 μmol h-1 ). Interestingly, its photocatalytic property is still superior to TNCB with post modification Pt (1 wt %) (208.11 μmol h-1 ). The introduction of Pt efficiently extends the photoresponse of the composite material from UV to visible light region, simultaneously boosting their solar-driven photocatalytic performance, which attribute to the porous structure, the sub size TNCB, the SPR effect of Pt NPs and strong interaction of two components. In fact, Pt NPs can enhance collective oscillations on delocalized electrons, which is conducive to capture electrons and hinder the recombination of photogenerated electron-hole pairs, leading to the longer lifetime of photogenerated charges. The fabrication of Pt-TNCB photocatalyst with SPR effect may provide a promising method to improve visible-light photocatalytic activities for traditional photocatalysts.

Using solar energy to achieve seawater desalination and sewage disposal has received tremendous attention for its potential possibility to produce clean freshwater. However, the low solar-thermal conversion efficiency for solar absorber materials obstacles their practical applications. Herein, Ag nanoparticles modified floating carbon cloth (ANCC) are first synthesized via wet impregnation, photoreduction, and low-temperature drying strategy, which could float on the water and absorb the solar energy efficiently. It is worth noting that vaporization rate of ANCC with a high wide-spectrum absorption (92.39%) for the entire range of optical spectrum (200-2500 nm) is up to 1.36 kg h-1 m-2 under AM 1.5, which corresponds to solar-thermal conversion efficiency of ∼92.82% with superior seawater desalination and sewage disposal performance. Plasmon Ag promotes the conversion efficiency obviously compared to the pristine carbon cloth because the surface plasmon resonance effect could increase the local temperature greatly. After the desalination, the ion concentrations (Mg2+, K+, Ca2+, and Na+ ions) in water are far below the limit of drinking water. Such high-performance floating ANCC material may offer a feasible and paradigm strategy to manage the global water contamination and freshwater shortage problem.

Defect-engineered magnetic γ-Fe2O3 ultrathin nanosheets/mesoporous black TiO2 hollow sphere heterojunctions (γ-Fe2O3/b-TiO2) are fabricated by a metal-ion intervened hydrothermal technique and high-temperature hydrogenation, which exhibit wide-spectrum response and magnetic separation. The specific surface area, pore size and pore volume of the resultant γ-Fe2O3/b-TiO2 with hollow structure are ∼63 m2 g−1, 10.5 nm and 0.14 cm3 g−1, respectively. After surface hydrogenation, α-Fe2O3 nanosheets are converted to γ-Fe2O3 ultrathin nanosheets (∼6 nm) combined with the formation of surface defects. The ultrathin nanosheet structure facilitates the surface engineering and also favors the diffusion and transportation of photogenerated charge carriers. The apparent rate constant (k) of defect-engineered γ-Fe2O3/b-TiO2 photocatalytic degradation biotoxic tetracycline is ∼3 times higher than that of α-Fe2O3/b-TiO2 under AM 1.5 irradiation. The enhancement is attributed to the introduction of narrow bandgap unit-cell-thick γ-Fe2O3 nanosheets, the hollow structure and the defect engineering, which are beneficial to solar-light-harvesting and rapid electron transport, and spatial separation of photogenerated charge carriers. The photocatalytic degradation mechanism is also proposed. The novel magnetic γ-Fe2O3/b-TiO2 heterojunction is a promising photocatalyst for recovering the domestic sewage in environment.

It is desirable to develop an efficient visible-light-driven photocatalyst for practical application to degrade highly-noxious pollutants. Herein, the hydrogenation hierarchical flower-like Bi2MoO6 hollow spheres (H-BMO-X, where X represents the different hydrogen calcination temperatures) have been successfully fabricated by a solvothermal-surface hydrogenation process. The as-prepared nano-photocatalyst H-BMO-300 clearly exhibits a photocatalytic reaction apparent rate constant k for high-noxious pollutants by ∼3-times higher than pristine Bi2MoO6. Moreover, the resultant H-BMO-300 sample with a narrow bandgap of ∼2.70 eV possesses surface oxygen vacancy defects. Based on the scanning Kelvin probe and surface photovoltage spectroscopy, it is deduced that the photocatalytic activities are attributed to the surface oxygen vacancy of H-BMO-X favoring the electron-hole pair’s separation. The enhanced photocatalytic performance can be ascribed to the synergistic effect of surface defects favoring efficient electron-hole separation and the hollow hierarchical structure benefiting the utilization of visible light, which provides more surface-active sites. This work provides a viable route to perceptibly enhance the photocatalytic activities of H-BMO-300 for environmental remediation with good mineralization properties.

Atomically two-dimensional semiconductor nanomaterials have drawn tremendous attention in photocatalytic applications due to their unique and remarkable properties. Herein, the assembly of TiO2 ultrathin nanosheets was fabricated from the titanate sheets using a gas-assisted liquid exfoliation method combined with hydrogenation treatment strategy. The hydrogenation treatment can introduce more surface point defects such as oxygen vacancies without damaging the ultrathin two-dimensional structure. The ultrathin two-dimensional assembly has high percentages of low-coordinated surface atoms and large specific surface areas (340 m2/g), which could increase the absorption of photon and accelerate the photocatalytic reaction process. Meanwhile, homogeneous oxygen vacancies and large fraction of low-coordinated surface atoms in TiO2 nanosheets can cause surface lattice distortion, which leads to a reduction in band gap and an upshift of conduction band minimum. The assembly possesses strong solar-light absorption, efficient charge transfer, and more surface-reactive sites for photocatalytic reactions. As a result, the assembly exhibits fast photocatalytic hydrogen evolution rate of 540.7 μmol h−1 (30 mg catalyst) and good cycling stability under simulated solar irradiation. This work may provide perspectives for designing two-dimensional semiconductor materials besides TiO2 ultrathin nanosheets as photocatalysts.

Ag/mesoporous black TiO2 nanotubes heterojunctions (Ag-MBTHs) were fabricated through a surface hydrogenation, wet-impregnation and photoreduction strategy. The as-prepared Ag-MBTHs possess a relatively high specific surface area of ≈85 m2 g-1 and an average pore size of ≈13.2 nm. The Ag-MBTHs with a narrow band gap of ≈2.63 eV extend the photoresponse from UV to the visible-light and near-infrared (NIR) region. They exhibit excellent visible-NIR-driven photothermal catalytic and photocatalytic performance for complete conversion of nitro aromatic compounds (100 %) and mineralization of highly toxic phenol (100 %). The enhancement can be attributed to the mesoporous hollow structures increasing the light multi-refraction, the Ti3+ in frameworks and the surface plasmon resonance (SPR) effect of plasmonic Ag nanoparticles favoring light-harvesting and spatial separation of photogenerated electron-hole pairs, which is confirmed by transient fluorescence. The fabrication of this SPR-enhanced visible-NIR-driven Ag-MBTHs catalyst may provide new insights for designing other high-performance heterojunctions as photocatalytic and photothermal catalytic nanomaterials.

Oxygen vacancy (VO) plays a vital role in semiconductor photocatalysis. Rutile TiO2 nanomaterials with controllable contents of VO (0–2.18%) are fabricated via an in-situ solid-state chemical reduction strategy, with color from white to black. The bandgap of the resultant rutile TiO2 is reduced from 3.0 to 2.56 eV, indicating the enhanced visible light absorption. The resultant rutile TiO2 with optimal contents of VO (~2.07%) exhibits a high solar-driven photocatalytic hydrogen production rate of 734 μmol h−1, which is about four times as high as that of the pristine one (185 μmol h−1). The presence of VO elevates the apparent Fermi level of rutile TiO2 and promotes the efficient electron-hole separation obviously, which favor the escape of photogenerated electrons and prolong the life-time (7.6×103 ns) of photogenerated charge carriers, confirmed by scanning Kelvin probe microscopy, surface photovoltage spectroscopy and transient-state fluorescence. VO-mediated efficient photogenerated electron-hole separation strategy may provide new insight for fabricating other high-performance semiconductor oxide photocatalysts.

The solar-light-harvesting and separation of nanostructured photocatalysts in slurry systems are key issues in fields of photocatalysis. Herein, magnetic Fe2O3/mesoporous black TiO2 hollow sphere heterojunctions (M-Fe2O3/b-TiO2) are fabricated through wet-impregnation and surface hydrogenation strategy, which show wide-spectrum response and magnetic separation. The decreased specific surfaces, pore sizes and pore volumes from ∼80 to 67 m2 g−1, ∼12 to 10.3 nm, and ∼0.20 to 0.16 cm3 g−1, respectively, all confirm the efficient loading of magnetic Fe2O3. The M-Fe2O3/b-TiO2 with narrow bandgap of ∼2.41 eV extends the photoresponse from UV to near infrared region and exhibits excellent solar-driven photocatalytic degradation performance and long-term stability for complete mineralization methyl orange and high-toxic herbicide metribuzin. The photocatalytic reaction apparent rate constant k for metribuzin is ∼ 9 times higher than that of pristine TiO2 under AM 1.5 irradiation. Especially for single-wavelength of 950 nm, the degradation ratio is up to 4%. The enhancement is attributed to Ti3+ and magnetic Fe2O3 with narrow bandgap facilitating solar-light-harvesting, the hollow structure benefiting mass transport, and the heterojunctions favoring the spatial separation of photogenerated electron-hole pairs. The magnetic separation is conducive to recycle of photocatalysts, which favors practical applications in environment.

Ti3+ self-doped black TiO2 nanotubes (TDBTNs) with mesoporous nanosheet architecture have been successfully synthesized by solvothermal method combined with ethylenediamine encircling strategy to protect mesoporous frameworks, then calcined at 600 °C under hydrogen atmosphere. In this case, ethylenediamine molecules play important roles on maintaining the mesoporous networks and inhibiting the phase transformation from anatase-torutile effectively. The as-prepared TDBTNs with mesoporous nanosheet architecture possess a relatively high specific surface area of ∼95 m2 g–1 and an average pore size of ∼15.6 nm. The reduced bandgap of ∼2.87 eV extends the photoresponse from ultroviolet to visible light region due to the Ti3+ self-doping. The solar-driven photocatalytic hydrogen evolution rate for TDBTNs is approximately 3.95 mmol h–1 g–1, which is much better (about four times) than that of the pristine one (∼0.94 mmol h–1 g–1). This improvement is attributed to the reduced bandgap increasing the utilization r...

A novel mesoporous Pt/NiS/black TiO2 hollow nanotubes (P-NBTNs) is assembled by a facile synthesize route based on hollow black TiO2 nanotubes with 2D mesoporous TiO2 nanosheets. This unique structure increases the specific surface area of the material, exposes more photocatalytic reaction active sites, and reduces the bandgap to about 2.87 eV, thereby improving its light absorption capacity in the visible light region. At the same time, the surface plasmon resonance effect of the noble metal Pt is employed to further improve the absorption and utilization of visible light. The strong electron-withdrawing ability of Pt nanoparticles and the synergistic catalytic between NiS and Pt, and the formation of built-in electric field at the interface all promote the separation and transmission of photo-generated charge carriers, leading to significant improvement of photocatalytic performance. Under AM 1.5 G irradiation, the hydrogen production rate of P-NBTNs is up to 4.70 mmol h−1g−1, which is more than 4 times higher than that of pristine TiO2 nanotubes (TNs) (~0.94 mmol h−1g−1). The photocatalytic performance nearly keeps constant after more than 10 cycles, indicating the high stability of P-NBTNs, which favors the practical applications.

NiS nanoparticles modified black TiO

Ag/mesoporous black TiO

Photocatalytic hydrogen production using semiconductors is identified as one of the most promising routes for sustainable energy; however, it is challenging to harvest the full solar spectrum in a particulate photocatalyst for high activity. Herein, a hierarchical hollow black TiO2 /MoS2 /CdS tandem heterojunction photocatalyst, which allows broad-spectrum absorption, thus delivering enhanced hydrogen evolution performance is designed and synthesized. The MoS2 nanosheets not only function as a cost-effective cocatalyst but also act as a bridge to connect two light-harvesting semiconductors into a tandem heterojunction where the CdS nanoparticles and black TiO2 spheres absorb UV and visible light on both sides efficiently, coupling with the MoS2 cocatalyst into a particulate photocatalyst system. Consequently, the photocatalytic hydrogen rate of the black TiO2 /MoS2 /CdS tandem heterojunction is as high as 179 µmol h-1 per 20 mg photocatalyst under visible-light irradiation, which is almost 3 times higher than that of black TiO2 /MoS2 heterojunctions (57.2 µmol h-1 ). Most importantly, the stability of CdS nanoparticles in the black TiO2 /MoS2 /CdS tandem heterojunction is greatly improved compared to MoS2 /CdS because of the formation of tandem heterojunctions and the strong UV-absorbing effect of black TiO2 . Such a tandem architectural design provides new ways for synthesizing particulate photocatalysts with high efficiencies.

Porous defective ZnO cellular hexagonal plates with surface oxygen vacancies (OVZCHPs) are fabricated by hydrothermal and high-temperature NaBH4 reduction methods. The prepared OVZCHPs with a hexagonal structure have a relatively large specific surface area compared to that of pristine ZnO (ZCHPs), and the pore diameter is ~53.5 nm. After reduction, the defective OVZCHPs with a narrow band gap of ~2.95 eV extends the photoresponse to visible light region. Additionally, the surface oxygen vacancy defects are formed during the NaBH4 reduction procedure, which is confirmed by X-ray photoelectron spectroscopy, and favor the electron-hole separation. The solar-driven photocatalytic degradation rate of tetracycline for the OVZCHPs is up to ~99.9%, which is approximately three-times higher than that of the ZCHPs. This enhancement can be attributed to the hexagonal porous structure offering more surface active sites and the surface oxygen vacancy defects favoring the electron-hole separation and visible-light absorption. The novel OVZCHPs are promising photocatalysts for wastewater purification, and the fabrication strategy may provide new insights for designing other high-performance porous photocatalytic materials.

NiS nanoparticles modified black TiO2 hollow nanotubes (NBTNs) are successfully synthesized via surface hydrogenation and the facile solvothermal method. The unique structure with intensified surface and interface characteristics endow NBTNs with more catalytic sites, and increase charge carrier separation efficiency with an extended charge lifetime, overwhelmingly promoting its photocatalytic performance. The resultant NBTNs possess a relatively high surface area and pore size of ∼89 m2 g-1 and ∼9.8 nm, respectively. The resultant NBTNs exhibit an excellent solar-driven photocatalytic hydrogen rate (3.17 mmol h-1 g-1), which is almost as high as that of Pt as cocatalyst, in which the apparent quantum yield of 5.4% (420 nm) is recorded for the NBTNs sample. Moreover, the turnover number can be up to 116 000 within 48 h and the turnover frequency is 2400 for NiS. This novel strategy could provide a better understanding of cocatalyst photocatalytic mechanisms, and a scheme simultaneously regulating the morphology and structure of photocatalysts for promoting H2 generation.