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To develop high-quality film device with good reliability, it is often essential to be able to evaluate the parameters such as stress, the biaxial elastic modulus, and coefficient of thermal expansion (CTE) of film. Based on the stress measurement in situ during the thermal cycle by laser scanning method, two techniques were used to measure the biaxial elastic modulus and CTE of BaTiO3 films deposited on substrate. The value of the biaxial elastic modulus and CTE for BaTiO3 films determined from two methods is close, in which the biaxial elastic modulus of BaTiO3 films is higher than that of corresponding bulk while the CTE of BaTiO3 films is a little smaller than that of bulk material. [ABSTRACT FROM AUTHOR]

Charge kinetics plays a vital role in determining the quantum efficiency of solar-to-chemical conversion in photocatalysis. For most layered compounds, the photocatalytic performance is largely hindered by its sluggish charge transfer kinetics. Herein, we propose a novel strategy—heteroatom-mediated spatial charge separation and transfer—to accelerate photogenerated charge kinetics for boosting the photocatalytic performance of graphitic carbon nitride (CN). Both the experimental results and first-principle calculations show that out-of-plane charge transport and in-plane charge separation within CN nanosheets can be accelerated via F intercalation and B intralayer modification. The B implantation could realize in-plane charge-separation by spatial separation of HOMO and LUMO to promote efficient exciton dissociation, and the F heteroatom, as interlayer electron channel, accelerates the out-of-plane oriented charge transport. The visible-light photocatalytic activity of codoped CN nanosheets is greatly boosted via modulating the charge kinetics, which can be demonstrated by degrading methyl orange and colorless phenol as models. Moreover, the samples exhibit excellent photo-electrocatalysis OER activity, outperforming the metal CoSe2 catalyst. The enhanced catalytic activities are attributed to synergistically utilizing 2D ultrathin structural advantage and accelerating charge kinetics. This work proposes a novel strategy to tune charge carrier separations and migrations in functionalized 2D layered materials for environmental catalysis and advanced energy. Highlights A novel heteroatom-mediated spatial charge separation and transfer strategy is proposed in B/F codoped CN nanosheets. Both the experimental results and first-principle calculations show that photogenerated charge kinetics can be accelerated within B/F codoped CN nanosheets. The B implantation could realize in-plane charge-separation by spatial separation of HOMO and LUMO to promote efficient exciton dissociation. The F heteroatom, as interlayer electron channel, accelerates the out-of-plane oriented charge transport. The optimized B/F codoped CN nanosheets have highly efficient catalytic activity for degrading organic pollutant and OER activity. [ABSTRACT FROM AUTHOR]

Graphite carbon nitride (g-C3N4) is a promising candidate as an efficient, affordable, and sustainable alternative photocatalyst owing to its unique physical and chemical properties. However, the photocatalytic activity of pristine g-C3N4 is still far below what is expected, because of its insufficient active site and high electron–hole recombination rates. Herein, we develop a novel strategy—a one-step hydroxy-carbonate-assisted route—to try to overcome these disadvantages in g-C3N4 nanosheets by creating substantial pores ranging from mesoporous to macropore, which are mainly caused by the partial breaking of hydrogen bonds and removing of magnesium oxide. Luxuriant pores in g-C3N4 not only serve as a reaction center by providing a large number of active sites at pore edges, but also effectively improve the photogenerated carrier separation by shortening their transfer lengths. The highly efficient visible-light photocatalytic activity of porous g-C3N4 nanosheets are demonstrated by degrading methyl blue (MB) and gentian violet (GV) as models, which its degradation rate constant is respectively more than 109 times and 12 times higher than those of pristine g-C3N4. Meanwhile, the high porous g-C3N4 has robust stability. The simple and effective strategy proposed here provides a direct route to highly functionalized g-C3N4 nanosheets and other layered semiconductors for various applications. Highlights: 1. A novel one-step hydroxy-carbonate-assisted route to prepare well-developed porous g-C3N4 nanosheets is proposed for the first time. 2. The porous structure not only provides abundant active sites, but also accelerate the transfer of electrons to reach the lateral surface of the pores. 3. The high porous g-C3N4 have highly efficient and stability for photocatalytic application. 4. This work provides a simple and effective strategy to design highly functionalized g-C3N4 nanosheets and other layered semiconductors for various applications. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (g-C3N4) has attracted increasing interest in recent years as a metal-free polymeric photocatalyst for water splitting and degradation of organic pollutants. However, the relatively low photocatalytic activity and serious aggregation of g-C3N4 nanosheets substantially limit its applications. Herein, we propose a generalized and facile bottom-up approach to self-assembly synthesis of isotype heterojunction g-C3N4/g-C3N4 nanosheets/0D metal oxide nanoparticles hierarchical architectures, in which the highly dispersed 0D metal oxide (CeO2 and ZnO as representatives) nanoparticles are anchored on 2D flexible g-C3N4/g-C3N4 heterojunction nanosheets, and the former can be spatially separated by the latter as well. The pyrolysis-induced gases play a critical role in the construction of unique 0D metal oxide/2D g-C3N4/g-C3N4 (metal oxide/CN-UT) hierarchical architectures, which possess improved light harvesting and pollutant adsorption capacity, as well as enhanced separation of photoinduced charge carriers via the three-level electron–hole transfer process owing to the intimate contact between constituents and band alignment among them. As a result, the obtained metal oxide/CN-UT exhibits extraordinary photocatalytic performance under natural sunlight and indoor light illumination. This work demonstrates a generalized bottom-up synthetic method to design efficient composite photocatalysts by adopting integrative nanostructure engineering and a cocatalyst strategy and highlights the promising applications in the field of energy and environment. [ABSTRACT FROM AUTHOR]

All-carbon heterostructures consisting of carbon allotropes have attracted considerable attention because of their intriguing properties. However, understanding is still lacking of the interactions at the interface, as well as the connection between such interactions and their performance. Herein, we systematically explore the interfacial interaction in all-carbon penta-graphene (PG)/C20 (C60) heterostructures, and its effect on structural and electronic properties. Based on first-principles calculations, we report that the all-carbon PG/C20 (C60) heterostructures show two types of interfacial interactions: dispersive and covalent. The PG/C20 van der Waals (vdWs) heterostructure is less stable than its covalent one. By contrast, the PG/C60 vdWs heterostructure is the more stable. In the covalent heterostructures, either two or four C–C bonds can be formed between PG and C20, whereas only two can be formed between PG and C60. The near-gap electronic structures depend on the interfacial interactions, and the levels near the Fermi level are mainly composed of C20 (C60) states, giving rise to a small band gap of heterostructure, making them promising for visible light absorption. All the differences in these PG/C20 (C60) heterostructures can be well understood in terms of the different topology of fullerene. This finding indicates that all-carbon PG/fullerene heterostructures are promising candidates for photocatalysis, photodetectors, and solar energy harvesting and conversion. [ABSTRACT FROM AUTHOR]

Designing a mediator-free direct Z-scheme heterojunction photocatalyst is a highly effective strategy for environmental purification and hydrogen generation from water. Herein, hierarchical g-C3N4/CeO2 Z-scheme heterojunctions are successfully prepared via a facile calcination method without using any templates. This feasible strategy combines the morphology control with the formation of direct Z-scheme heterojunction. The resultant hierarchical g-C3N4/CeO2 heterojunction is much more active than the commercial Degussa P25 under visible light irradiation, validated by the high methylene blue degradation rate of 0.246 h−1, which is about 4.8, 8.8 and 30.8 times higher than that of commercial Degussa P25 (0.051 h−1), bulk g-C3N4 (0.028 h−1) and hierarchical CeO2 (0.008 h−1), respectively. The Z-scheme charge transfer mechanism across the heterojunction is verified by the active species trapping and producing experiments, as well as ab initio calculations. The hierarchical structures with large exposure surface, more efficient light harvesting, and a direct Z-scheme heterojunction for efficient photoinduced charge carriers transfer and separation across the interfacial domain of g-C3N4/CeO2 heterostructures, are the key to attractive photocatalytic performance. This work provides a promising approach to design high-efficient mediator-free direct Z-scheme photocatalysts by morphology control and heterojunction engineering. [ABSTRACT FROM AUTHOR]

Hierarchical carbon/g-C3N4 composites consisting of nanosheets are synthesized by a direct thermal diffusion and exfoliation approach with glucose acting as the intercalator and carbon source. This facile protocol not only renders nanosheets with a large surface area, but also carbon intercalation into the interlayer of g-C3N4. Therefore, the synthesized carbon/g-C3N4 composites exhibit superior photocatalytic performance for degrading representative methylene blue (MB) under visible light irradiatuon. Carbon/g-C3N4 composites with an optimal glucose mass ratio of 0.25% show the apparent reaction rate constant of 0.253 h−1, which is 9 times higher than that over bluk g-C3N4. The superior photocatalytic performance of carbon/g-C3N4 hierarchical architectures can be attributed to the synergic effects of large reactive sites, effective visible light adsorption and faster charge transfer owing to the superior electron transfer ability of carbon as verified by the PL and photoelectrochemical measurements. The main reactive species responsible for the photocatalytic degradation are photoinduced holes and ·OH radicals under visible light irradiation. This work provides a facile way to fabricate effecient g-C3N4-based photocatalysts for the potential application in dealing with environmental and energy shortage issues using solar energy. [ABSTRACT FROM AUTHOR]

High photocatalytic activity and photostability are the pursuit of the goal for designing promising photocatalysts. Herein, using ZnO to encapsulate ZnS nanoparticles is proposed as an effective strategy to enhance photocatalytic activity and anti-photocorrosion. The ZnS/ZnO core/shell heterostructures are obtained via an annealing treatment of ZnS nanoparticles produced by a facile wet chemical approach. Due to its small size, the nascent cubic sphalerite ZnS (s-ZnS) converts into a hexagonal wurtzite ZnS (w-ZnS)/ZnO core/shell structure after annealing treatment. In situ oxidation leads to increasing ZnO, simultaneously decreasing the w-ZnS content in the resultant w-ZnS/ZnO with thermal annealing time. The w-ZnS/ZnO core/shell heterostructures show high photocatalytic activity, demonstrated by the photodegradation rate of methylene blue being up to ten-fold and seven-fold higher than that of s-ZnS under UV and visible light irradiation, respectively, and the high capability of degrading rhodamine B. The enhanced photocatalytic activity may be attributed to the large specific surface and improved charge carrier separation at the core/shell interface. Moreover, it displays high photostability owing to the protection of the ZnO shell, greatly inhibiting the photocorrosion of ZnS. This facile in situ oxidation is effective and easily scalable, providing opportunities for developing novel core/shell structure photocatalysts with high activity and photostability. [ABSTRACT FROM AUTHOR]

For the first time, novel β-C3N4/CuO composites with superior photocatalytic activity are successfully fabricated via a facile reflux method followed by a thermal process. The morphologies, particle size and microstructure of the synthesized β-C3N4/CuO composites largely depended upon copper chloride and the volume ratio of Vwater:Vethanol in the mixed precursors. The fabricated β-C3N4/CuO nanoflakes exhibited obviously enhanced visible light photocatalytic activity for the degradation of methylene blue (MB) with an  ∼3.4 and 1.9 fold increase in efficiency over that of pure g-C3N4 and commercial P25, respectively. The β-C3N4/CuO composite photocatalyst also showed photocatalytic activity for the degradation of methyl orange (MO). Moreover, the β-C3N4/CuO nanoflakes showed almost no loss of photocatalytic activity after three recycles of the degradation of the MB. A multiple synergetic mechanism in β-C3N4/CuO nanoflakes, which is featured by the highly reactive {0 0 2} facets, exposed many active sites of nanoflakes and the efficient charge separation are proposed to account for the distinguished photocatalytic activity. This work provides a facile and cost-effective strategy for designing novel β-C3N4/CuO photocatalysts for application in environmental purification. [ABSTRACT FROM AUTHOR]

Using the density functional theory (DFT), we systematically study the interfacial interaction in monolayer MX2 (M = Mo, W; X = S, Se)/CeO2 heterostructures and its effects on electronic and optical properties. The interfacial interaction in the MX2/CeO2 heterostructures depends largely on chalcogens, and its strength determines the band gap variation and important electronic states at the band edges of the heterostructures. The MX2/CeO2 heterostructures with the same chalcogen have similar absorption spectra, from ultraviolet to near-infrared regions. These results suggest that chalcogens importantly determine the properties of MX2/metal oxide heterostructures. [ABSTRACT FROM AUTHOR]

The photocatalytic performance of semiconductors can be improved by coupling two-dimensional (2D) layered materials. Understanding the underlying mechanism of this phenomenon at the electronic level is important for the development of photocatalysts with a high efficiency. Here, we first present a theoretical elucidation of the dual functions of 2D layered material as a sensitizer and a co-catalyst by performing density functional theory calculations, taking WS2 and a lateral heterogeneous WS2–MoS2 monolayer as examples to couple with a promising photocatalyst Ag3PO4. The band alignment of a staggered type-II is formed between Ag3PO4 and the 2D monolayer with the latter possessing the higher electron affinity, resulting in the robust separation of photoexcited charge carriers between them, and indicating that the 2D monolayer is an effective sensitizer. Interestingly, the W (Mo) atoms, which are catalytically inert in the isolated 2D monolayer, turn into catalytic active sites, making the 2D monolayer a highly active co-catalyst in hybrids. A better photocatalytic performance in the coupled lateral heterogeneous WS2–MoS2 monolayer and Ag3PO4 can be expected. The calculated results can be rationalized by available experiments. These findings provide theoretical evidence supporting the experimental reports and may be used as a foundation for developing highly efficient 2D layered materials-based photocatalysts. [ABSTRACT FROM AUTHOR]

Selectively exposing surfaces with high reactivity is an effective strategy to enhance the photocatalytic activity of semiconductor photocatalysts. We report the facile synthesis of hexagonal flake-like Bi2S3/ZnS composites with a large percentage of reactive exposed {2 2 1} facets by tuning only the molar ratios of Bi to Zn. The samples exhibit enhanced optical absorption and red shift of absorption edge. The Bi2S3/ZnS composites with hexagon morphology display superior photocatalytic degradation of methylene blue (MB), faster than that with pure Bi2S3 and pure ZnS by a factor of 7.1 and 3.6, respectively. The enhanced photocatalytic activity can be attributed to the highly reactive {2 2 1} exposed facets and the more efficient separation of photogenerated electron–hole pairs is due to the interface of the hetero-junction. Furthermore, a tentative mechanism for photodegradation of MB over Bi2S3/ZnS composites has been proposed involving the photogenerated holes and ⋅OH radicals as the main active species, which is confirmed by using different scavengers. The novel constructed Bi2S3/ZnS composite is expected to be an attractive candidate as a photocatalyst for environmental purification and energy conversion. [ABSTRACT FROM AUTHOR]