Construction of Type-II Heterojunctions in Crystalline Carbon Nitride for Efficient Photocatalytic H2 Evolution.

As an encouraging photocatalyst, crystalline carbon nitride (CCN) exhibits unsatisfactory photocatalytic activity and stability due to its rapid recombination of photo-generative carriers. Herein, high-crystalline g-C3N4 was prepared, including CCN obtained in KCl (K-CCN), LiCl-KCl mixture (Li/K-CCN), and LiCl-NaCl-KCl mixture (Li/Na/K-CCN), via the molten salt strategy using pre-prepared bulk carbon nitride (BCN) as a precursor. The obtained BCN sample was formed by heptazine-based units, which convert into triazine-based units for K-CCN. Heptazine and triazine are two isotypes that co-exist in the Li/K-CCN and Li/Na/K-CCN samples. Compared with BCN and other CCN samples, the as-prepared Li/Na/K-CCN sample exhibited the optimal photocatalytic hydrogen evolution rates (3.38 mmol·g-1·h-1 under simulated sunlight and 2.25 mmol·g-1·h-1 under visible light) and the highest apparent quantum yield (10.97%). The improved photocatalytic performance of the Li/Na/K-CCN sample is mainly attributed to the construction of type-II heterojunction and the institution of the built-in electric field between triazine-based CCN and heptazine-based BCN. This work provides a new strategy for the structural optimization and heterostructure construction of crystalline carbon nitride photocatalysts.

Oxygen Vacancy Induced Atom-Level Interface in Z-Scheme SnO2/SnNb2O6 Heterojunctions for Robust Solar-Driven CO2 Conversion.

The modulation of Z-scheme charge transfer is essential for efficient heterostructure toward photocatalytic CO2 reduction. However, constructing a compact hetero-interface favoring the Z-scheme charge transfer remains a great challenge. In this work, an interfacial Nb-O-Sn bond and built-in electric field-modulated Z-scheme Ov-SnO2/SnNb2O6 heterojunction was prepared for efficient photocatalytic CO2 conversion. Systematic investigations reveal that an atomic-level interface is constructed in the Ov-SnO2/SnNb2O6 heterojunction. Under simulated sunlight irradiation, the obtained Ov-SnO2/SnNb2O6 photocatalyst exhibits a high CO evolution rate of 147.4 µmol h-1 g-1 from CO2 reduction, which is around 3-fold and 3.3-fold of SnO2/SnNb2O6 composite and pristine SnNb2O6, respectively, and favorable cyclability by retaining 95.8% rate retention after five consecutive tests. As determined by electron paramagnetic resonance spectra, in situ Fourier transform infrared spectra, and density functional theory calculations, Nb-O-Sn bonds and built-in electric field induced by the addition of oxygen vacancies jointly accelerate the Z-scheme charge transfer for enhanced photocatalytic performance. This work provides a promising route for consciously modulating Z-scheme charge transfer by atomic-level interface engineering to boost photocatalytic performance.

Weakened Crystalline SnNb2 O6 for Enhanced Performance in Photocatalytic H2 Production and CO2 Reduction.

Low crystalline photocatalysts with unsaturated active sites, such as oxygen vacancy (Ov ), is reported to exhibit enhanced adsorption and activation of oxygen-containing small molecules, such as H2 O and CO2 , thus boosting the activity in photocatalytic H2 evolution and CO2 reduction. However, numerous low-crystalline photocatalysts show unsatisfactory stability due to the easily repaired surface Ov . Herein, three SnNb2 O6 with different crystallinity were prepared by hydrothermal approach with similar precursors. Compared with bulk SnNb2 O6 and ultra-thin layered SnNb2 O6 , low-crystalline SnNb2 O6 (SNA) exhibits optimal visible-light-driven evolution rates of H2 (86.04 µmol g-1 h-1 ) and CO from CO2 (71.97 µmol g-1 h-1 ), which is mainly ascribed to the fast separation of the photogenerated carriers and enhanced photoreduction power caused by the surface Ov . More importantly, the sharp decrease of photocatalytic activity of SNA after seven cycles is well restored by the hydrothermal treatment of recycled SNA, ascribed to the reactivated surface Ov with the recovered low-crystalline structure. These works thus offer a promising strategy for developing low-crystalline and amorphous photocatalysts with high activity and stability.

Cluster-derived TiO2 nanocrystals with multiple carbon coupling for interfacial pseudo-capacitive lithium storage.

TiO2 is one of the most promising anode materials for lithium ion batteries (LIBs) due to its safe working potentials and small volume changes during lithium insertion/extraction. However, its inherently poor electronic and ionic conductivities have restricted its practical applications. Herein, well-defined TiO2 nanocrystals were prepared from an atomically precise titanium-oxo cluster (Ti8Ph) and then coupled with carbon layers and graphene nanosheets. When used as anode materials for LIBs, the TiO2-C-rGO composite delivered a high capacity of 834 mA h g-1 at 0.1 A g-1 after 300 cycles and 398 mA h g-1 at 5.0 A g-1 after 600 cycles, which are far superior to those of the control samples (TiO2-C, TiO2-rGO and TiO2) and most other reported TiO2-based nanostructures. The exposed facets of TiO2 nanocrystals were favorable for lithium diffusion and the carbon coupling was beneficial for the electron transfer. The latter also enhanced the structural robustness and hence the cycling stability of the composite. Moreover, the abundant three-phase interfaces between the carbon species and the TiO2 nanocrystals endowed the material with rich adsorption sites and substantially boosted pseudo-capacitive lithium storage. This work offered an alternative route to rationally design versatile nanostructures from clusters and contributed to the development of high-efficiency energy materials.

Molecular Self-Assembly of Oxygen Deep-Doped Ultrathin C3N4 with a Built-In Electric Field for Efficient Photocatalytic H2 Evolution.

Heteroatom-doped carbon nitride (C3N4) with a built-in electric field can reinforce the carrier separation; however, the stability will be greatly reduced due to the loss of surface-doped atoms. Here, molecule self-assembly, as a facile bottom-up approach, is explored for the synthesis and oxygen doping of C3N4. The obtained C3N4 presents a porous and ultrathin structure and oxygen deep-doping, which generate abundant nitrogen vacancies and a stable built-in electric field. Toward photocatalytic hydrogen evolution, the ultrathin and oxygen deep-doped C3N4 exhibits a 3.5-fold higher activity than bulk C3N4 under simulated sunlight, and 3.6 times higher stability than the oxygen surface-doped counterpart within five cycles. Femtosecond transient absorption spectroscopy indicates the improved carrier separation, and density functional theory (DFT) calculation reveals the promoted H2O adsorption and activation under the built-in electric field, which contribute to the excellent photocatalytic performance of oxygen deep-doped ultrathin C3N4.

Complementary behavior of doping and loading in Ag/C-ZnTa2O6 for efficient visible-light photocatalytic redox towards broad wastewater remediation.

This work reports on the simple fabrication of a silver loaded and carbon doped zinc tantalate (Ag/C-ZnTa2O6) photocatalyst with visible light photocatalytic activity toward broad wastewater remediation, including high photo-reduction of Cr(vi) (98.4% in 210 min), excellent photo-oxidation of tetracycline hydrochloride (94.7% in 210 min), and superior photo-degradation of multiple dyes (>99.0% within 210 min). The optimal photocatalytic performance of Ag/C-ZnTa2O6 is mainly due to the excellent visible light absorption capacity and superior electron-hole separation efficiency, which is ascribed to the complementary behavior between carbon doping and silver loading. Particularly, the generation of defects due to C-doping is greatly inhibited by Ag-loading, and the SPR effect of Ag nanoparticles is enhanced due to the obstruction of Ag+ by C doping.

Assembling Bi2MoO6/Ru/g-C3N4 for Highly Effective Oxygen Generation from Water Splitting under Visible-Light Irradiation.

Water oxidation is a kinetically challenging reaction for photocatalytic overall water splitting. Producing one molecule of O2 will consume four electrons, so it is an extremely difficult obstacle for researchers. Here, a Bi2MoO6/Ru/g-C3N4 composite was obtained by a gentle hydrothermal method, which could oxidize water into O2 highly efficiently. The optimal O2 production reached 328.34 µmol·g-1·h-1 under visible light irradiation. Moreover, the catalyst presented excellent stability, as shown by a still sustentative 91.4% photocatalytic activity and invariant textural structure after seven recycling tests. The ternary material had the smallest resistance, which indicated that it has a good photoelectron conductive tunnel, and a rapid transfer route is proposed through Bi2MoO6 → Ru → g-C3N4 → NaIO3 (electron acceptor). The massive holes (h+) with high oxidative potential are surely enriched due to the quick electron migration, being fit for a large promotion of the multiple-electron water oxidative proceedings. Therefore, the metallic Ru provided a powerful bridge for efficient transfer of the interface electrons which could be beneficial to spatial separation of photoexcited carriers without the loss of the high redox capacity. Finally, it is proposed that the Ru-assisted electron transport and constituent synergy in Bi2MoO6/Ru/g-C3N4 composite play crucial roles to its enhanced light utilization, efficient photoelectric conversion property, and high-producing oxygen capability.

Enhanced photocatalytic activity of Ag/Ag2Ta4O11/g-C3N4 under wide-spectrum-light irradiation: H2 evolution from water reduction without co-catalyst.

Designing a superior and stable catalyst toward H2 evolution under solar light to solve the energy crisis has attracted wide concern. Herein, we have constructed a novel heterojunction photocatalyst Ag/Ag2Ta4O11/g-C3N4 by in situ assembly, which can efficiently split water to generate H2 by utilizing wide-spectrum-light irradiation. Optimal H2 production reaches highly to 253.03 µmol g-1 h-1 under the simulated solar light. Moreover, the catalyst presented well stability by the retained 98% photocatalytic activity and invariable textural structure after five recycling tests. The mechanism of H2 generation over the prepared material was carefully investigated through scanning electron microscope (SEM), transmission electron microscopy (TEM), UV-Vis absorption spectra (UV-Vis), photoluminescence analysis (PL), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance spectra (EPR), and several electrochemical measurements. It is proposed that the carriers are efficiently separated through Ag-mediated Z-scheme route in space, retaining their strong redox ability. Ag particles produced by in situ reduction from the component Ag2Ta4O11 could devote to the quick electron migration as the bridge center, effective solar light harvesting due to their surface plasmon resonance, and excellent stability by inhibiting their agglomeration and elution. This research offers a new idea for constructing full solid Z-scheme photocatalysts under wide-spectrum-light irradiation.

Regulating effect of heterojunctions on electrocatalytic oxidation of methanol for Pt/WO3-NaTaO3 catalysts.

Pt/WO3-NaTaO3 composite catalysts for different W/Ta molar ratios were obtained via a facile hydrothermal method. The WO3-NaTaO3 heterojunction was constituted and could be regulated by the adjustment of the W : Ta ratio, as confirmed by multiple characterizations. Due to the favorable CO anti-poisoning characteristics ascribed to the sufficient surface -OHad provided by both WO3 and NaTaO3, excellent stability of the WO3-NaTaO3 composite in acidic and alkaline environments, and charge transfer from metal oxide to Pt, the as-obtained Pt/WO3-NaTaO3 composite catalyst could exhibit desirably high electrocatalytic performances. As a result, the as-prepared Pt/WO3-NaTaO3 (W : Ta = 3 : 1) and Pt/WO3-NaTaO3 (W : Ta = 0.2 : 1) products exhibited optimal performances in the methanol oxidation reaction (MOR) process in acids and alkalis, respectively, as compared to those of commercial Pt/C, Pt/NaTaO3, and Pt/WO3 catalysts. In particular, in acidic and alkaline environments, the highest electrocatalytic activity of Pt/WO3-NaTaO3 catalyst could reach three times that of commercial Pt/C and its stability could reach more than five times that of commercial Pt/C. Density functional theory calculations further proved the enhancement of WO3 with regard to methanol electrooxidation.

Investigation of the Preferential Doping Site and Regulating on the Visible Light Response and Redox Performance for Fe- and/or La-Doped InNbO4.

The preferential doping site, visible light response, and redox potential of Fe- and/or La-doped InNbO4 (INO) were investigated using first-principles density functional theory. Eight designed doping models, including Fe and/or La doping at In or/and Nb sites of INO are constructed, respectively. It was found that Fe-doping and Fe,La-codoping to substitute In into an INO cell are energetically favorable, confirming that the steric hindrance plays a vital role for the selective doping site than the charge of the dopants. Fe doping always formed two impurity bands between the conduction and valence bands, originated from Fe 3d state, inferring the well visible light response. Furthermore, the presence of La has a specific regulation effects for Fe doping although the energy levels of the single La-doped models were completely similar to those of the undoped INO. The electron exchange between La and Fe dopants results in the significant interaction for codoping INO. Importantly, by doping La into INO cell, the redox potentials of Fe-doped INO could be well-regulated. The band potential moved to the more positive energy level of the models Fe-doped at Nb sites, while it shifted to the more negative level if Fe was doped at In site of La-INO. The present investigation may provide the guidance for the designative dopants to construct the photocatalyst with stable, visible response, and good redox performance.

K4Nb6O17·4.5H2O: a novel dual functional material with quick photoreduction of Cr(VI) and high adsorptive capacity of Cr(III).

A series of orthorhombic phase K4Nb6O17·4.5H2O was synthesized via a hydrothermal approach. When presented in an acidic pH range, K4Nb6O17·4.5H2O showed a strong ability in quick reduction from Cr(VI) to Cr(III). The resulted Cr(III) ions were removed by an effective adsorption through simply adjusting the solution pH from strong acidity to near neutrality, owing to the sample's unique nano-sheet structure with a wide layer spacing. The Cr(III) ions adsorbed onto samples were released again for reusing by eluting with 1molL(-1) HCl solution, and K4Nb6O17·4.5H2O regenerated by immersing in a KOH solution. The reduction efficiency of Cr(VI) was still up to 98% after irradiation for 60min, and the removal efficiency of Cr(III) ions was as high as 83% even after five cycles. Therefore, K4Nb6O17·4.5H2O is clearly demonstrated to be an excellent dual functional material with quick photoreduction of Cr(VI) and high adsorptive capacity of Cr(III). The relevant materials reported herein might be found various environment-related applications.

A novel adsorbent of Na(2)Ta(2)O(6) porous microspheres with F(-) gradient concentration distribution: high cationic selectivity and well-regulated recycling.

Pyrochlore Na2Ta2O6 porous microspheres with F(-) gradient concentration distribution were first prepared, which showed an excellent selectivity toward cationic dyes as an adsorbent. These dyes were regenerated rapidly by adding to NaAc solution. After then, the adsorbent still showed a high adsorption capacity. Optionally, the effective recycling of the adsorbents was achieved by UV light illumination, free of secondary environmental contamination. The rate of adsorption reaction followed the pseudo second-order kinetics, and the sorption isotherm well fitted to the Freundlich isotherm model. Eventually, the adsorption reaction for the absorbents was found to be a spontaneous and endothermic process.

Preparation of nanoscale PbSe particles with different morphologies in diethylene glycol.

Nanoscale PbSe particles with different morphologies including octahedral, tetradecahedral and cubic shapes have been successfully prepared in diethylene glycol (DEG) at 240 degrees C in the presence of PVP-K30: poly(vinyl pyrrolidone), M(W) = 50 000. The formation of PbSe is believed to be an elemental recombination process of corresponding elements reduced from their precursors by the solvent. Experimental results showed that a prominent morphological variation was observed through varying the molar ratios of selenius acid to Pb(2+) when Pb(Ac)(2) was used as lead precursor, while the sizes of the final PbSe products tended to increase along with the increase of the molar ratios of selenius acid to Pb(2+) when Pb(NO(3))(2) was used as lead precursor.