Vacancy Associates Promoting Solar-Driven Photocatalytic Activity of Ultrathin Bismuth Oxychloride Nanosheets

Durability, inactivation and regeneration of silver tetratantalate in photocatalytic H2 evolution

The prepared Ag₂Ta₄O₁₁ photocatalyst exhibits durable activity for H₂ production from water, which can achieve the dual recovery of the photocatalyst and activity.

Enhanced visible light photocatalytic activity in BiOCl/SnO2: heterojunction of two wide band-gap semiconductors

A series of BiOCl/SnO₂ heterojunctions exhibiting exceptional visible light photocatalytic performance has been successfully prepared using a two-step solution route.

Surface chemical-modification for engineering the intrinsic physical properties of inorganic two-dimensional nanomaterials

This tutorial review summarizes the recent advances in engineering the intrinsic physical properties of inorganic two-dimensional nanomaterials by surface chemical modification.

Well-defined BiOCl colloidal ultrathin nanosheets: synthesis, characterization, and application in photocatalytic aerobic oxidation of secondary amines

Well-defined BiOCl ultrathin nanosheets were prepared by a facile colloidal route, and exhibit high photocatalytic performance toward the oxidation of secondary amines to corresponding imines under visible irradiation.

We demonstrate the first colloidal synthesis of single-crystalline BiOCl ultrathin nanosheets (UTNSs) that feature a well-defined square morphology. Unlike BiOCl nanomaterials prepared by hydrothermal routes, our colloidal BiOCl UTNSs exhibit hydrophobic surface properties and high activity and selectivity toward the photocatalytic aerobic oxidation of secondary amines to corresponding imines at room temperature. Hence, the application of BiOCl nanomaterials has been successfully extended from the widely studied photodecomposition of pollutants in aqueous solution to the synthesis of fine chemicals in organic solvent using a green approach.

A dye-sensitized visible light photocatalyst-Bi24O31Cl10

The p-block semiconductors are regarded as a new family of visible-light photocatalysts because of their dispersive and anisotropic band structures as well as high chemical stability. The bismuth oxide halides belong to this family and have band structures and dispersion relations that can be engineered by modulating the stoichiometry of the halogen elements. Herein, we have developed a new visible-light photocatalyst Bi₂₄O₃₁Cl₁₀ by band engineering, which shows high dye-sensitized photocatalytic activity. Density functional theory calculations reveal that the p-block elements determine the nature of the dispersive electronic structures and narrow band gap in Bi₂₄O₃₁Cl₁₀. Bi₂₄O₃₁Cl₁₀ exhibits excellent visible-light photocatalytic activity towards the degradation of Rhodamine B, which is promoted by dye sensitization due to compatible energy levels and high electronic mobility. In addition, Bi₂₄O₃₁Cl₁₀ is also a suitable photoanode material for dye-sensitized solar cells and shows power conversion efficiency of 1.5%.

Construction of teethlike homojunction BiOCl (001) nanosheets by selective etching and its high photocatalytic activity

Teethlike homojunctions BiOCl (001) nanosheets with tunable photoresponse were constructed by selective etching with triethanolamine and allowed fast charge separation across the interfaces to facilitate photocatalysis. The unique microstructure exhibits a superior photocatalytic activity that can be ascribed to the combined interaction of the high UV/vis light harvest, high photogenerated charge separation efficiency, and the fast interfacial charge-transfer rate based on the unique homogeneous topotactic structure. We believe that the creation of this new model junction may be a great aid in the design and preparation of efficient semiconductor based photocatalysts and a new understanding of the essential relation between the junction and the photocatalytic activity.

Sustainable molecular oxygen activation with oxygen vacancies on the {001} facets of BiOCl nanosheets under solar light

We demonstrate that oxygen vacancies on the {001} facets of BiOCl nanosheets can more sustainably activate molecular oxygen for organic pollutant removal under solar light than the TiO₂ counterparts. The oxygen vacancies on the {001} facets of BiOCl nanosheets are effectively refreshed by UV light, and are also responsible for the efficient utilization of visible light to activate molecular oxygen, accounting for their long term stability and high efficiency.

Low overpotential in vacancy-rich ultrathin CoSe2 nanosheets for water oxidation

According to Yang Shao-Horn's principle, CoSe2 is a promising candidate as an efficient, affordable, and sustainable alternative electrocatalyst for the oxygen evolution reaction, owing to its well-suited electronic configuration of Co ions. However, the catalytic efficiency of pure CoSe2 is still far below what is expected, because of its poor active site exposure yield. Herein, we successfully overcome the disadvantage of insufficient active sites in bulk CoSe2 by reducing its thickness into the atomic scale rather than any additional modification (such as doping or hybridizing with graphene or noble metals). The positron annihilation spectrometry and XAFS spectra provide clear evidence that a large number of VCo″ vacancies formed in the ultrathin nanosheets. The first-principles calculations reveal that these VCo″ vacancies can serve as active sites to efficiently catalyze the oxygen evolution reaction, manifesting an OER overpotential as low as 0.32 V at 10 mA cm(-2) in pH 13 medium, which is superior to the values for its bulk counterparts as well as those for the most reported Co-based electrocatalysts. Considering the outstanding performance of the simple, unmodified ultrathin CoSe2 nanosheets as the only catalyst, further improvement of the catalytic activity is expected when various strategies of doping or hybridizing are used. These results not only demonstrate the potential of a notable, affordable, and earth-abundant water oxidation electrocatalyst based on ultrathin CoSe2 nanosheets but also open up a promising avenue into the exploration of excellent active and durable catalysts toward replacing noble metals for oxygen electrocatalysis.

Novel Cu₂O quantum dots coupled flower-like BiOBr for enhanced photocatalytic degradation of organic contaminant

Here we report a highly efficient novel photocatalyst consisting of Cu2O quantum dots (QDs) incorporated into three-dimensional (3D) flower-like hierarchical BiOBr (hereafter designated QDs-Cu2O/BiOBr), which were synthesized via a simple reductive solution chemistry route and applied to decontaminate the hazardous wastewater containing phenol and organic dyes. The deposition of Cu2O QDs onto the surface of the BiOBr was confirmed by structure and composition characterizations. The QDs-Cu2O/BiOBr composites exhibited superior activity for organic contaminant degradation under visible light and 3 wt% QDs-Cu2O/BiOBr composite showed the highest degrade rate for phenol and methylene blue (MB), which was 11.8 times and 1.4 times than that of pure BiOBr, indicated the QDs-Cu2O/BiOBr composite has the great potential application in purifying hazardous organic contaminant. The incorporated Cu2O QDs played an important role in improving the photocatalytic performance, due to the enhancement of visible light absorption efficiency as well as the efficient separation of the photogenerated charge carriers originating from the intimately contacted interface and the well-aligned band-structures, which was confirmed by the results of PL, photocurrent and EIS measurements. The possible photocatalytic mechanism was proposed based on the experiments and theoretical results.

Adsorption and enhanced photocatalytic activity of the {0 0 0 1} faceted Sm-doped ZnIn2S4 microspheres

In this study, the doping effect of samarium on the structure, morphology, adsorption and photocatalytic performance of hexagonal ZnIn2S4 microspheres was studied. The photocatalytic activity of Sm-doped ZnIn2S4 microspheres was evaluated for the photodegradation of Rhodamine B (RhB) and methyl orange (MO) under visible light irradiation. The samples were characterized by XRD, SEM, XPS, UV-vis, TEM, and N2 adsorption-desorption analysis. The results show that the hexagonal ZnIn2S4 microspheres are composed of nanoplates growing along c-axis with the predominant negative-charged S plane. Compared with the photodegadation of MO dye, the negative-charged {0 0 0 1} facets not only are beneficial for the adsorption of RhB by -N(Et)2 groups but also can accumulate the separation of photogenerated electrons and holes, enhancing photodegradation efficiency by direct-hole photocatalysis. Moreover, Sm is partially substituted for In in the crystal lattice for forming the doping energy level which promotes the separation of photoinduced electron-hole pairs and enhances absorption of visible light. Hexagonal 2% Sm-doped ZnIn2S4 microspheres with exposed {0 0 0 1} facets resulted in higher photodegradation efficiency of RhB under visible light irradiation.

W18O49 nanowire alignments with a BiOCl shell as an efficient photocatalyst

Top-down nanostructure engineering and band engineering are promising methods for fabricating efficient photocatalysts with enhanced optical and electronic properties; however, composites with simultaneously engineered structure and band are very rare. Herein, we constructed a unique architecture composed of a W18O49 nanowire alignment core and porous BiOCl shell (WA@BiOCl), which combined the advantages of both an assembly structure and a type II core-shell heterojunction. The W18O49 alignments (WA) were synthesized using a "one-pot" solvothermal treatment of WCl6/NaNO3via NO3(-)-mediated assembly, whereas the W18O49 nanowires with BiOCl shell (W@BiOCl) were obtained using WCl6/BiCl3. Then, WA@BiOCl, in contrast to W@BiOCl alignments, were fabricated when WCl6 and Bi(NO3)3 were present in the starting mixture. Optical absorption, photoelectrochemical measurements and photoluminescence characterizations show that either the alignments or the core-shell heterojunctions can enhance light harvesting, photo-charge transfer and collection. As a synergetic result, the WA@BiOCl architecture exhibited very high photoactivity and photostability. Under UV-vis (or vis) irradiation, WA@BiOCl is 2.43 (1.93), 3.93 (2.73) and 5.34 (3.44)-fold more active than W@BiOCl, WA and W18O49, respectively. The results demonstrate that the simultaneous nanostructure and band engineering can produce a more efficient photocatalyst than a single strategy alone, which suggests a potential method for the fabrication of photocatalysts in the fields of environment and energy.

Bismuth oxyhalide nanomaterials: layered structures meet photocatalysis

In recent years, layered bismuth oxyhalide nanomaterials have received more and more interest as promising photocatalysts because their unique layered structures endow them with fascinating physicochemical properties; thus, they have great potential photocatalytic applications for environment remediation and energy harvesting. In this article, we explore the synthesis strategies and growth mechanisms of layered bismuth oxyhalide nanomaterials, and propose design principles of tailoring a layered configuration to control the nanoarchitectures for high efficient photocatalysis. Subsequently, we focus on their layered structure dependent properties, including pH-related crystal facet exposure and phase transformation, facet-dependent photoactivity and molecular oxygen activation pathways, so as to clarify the origin of the layered structure dependent photoreactivity. Furthermore, we summarize various strategies for modulating the composition and arrangement of layered structures to enhance the photoactivity of nanostructured bismuth oxyhalides via internal electric field tuning, dehalogenation effect, surface functionalization, doping, plasmon modification, and heterojunction construction, which may offer efficient guidance for the design and construction of high-performance bismuth oxyhalide-based photocatalysis systems. Finally, we highlight some crucial issues in engineering the layered-structure mediated properties of bismuth oxyhalide photocatalysts and provide tentative suggestions for future research on increasing their photocatalytic performance.

An efficient dye-sensitized BiOCl photocatalyst for air and water purification under visible light irradiation

A photosensitized BiOCl catalyst was found to be effective for photocatalytic water purification and air remediation under visible light irradiation (λ > 420 nm). Prepared by a solvothermal method, the BiOCl crystals possessed a 3D hierarchical spherical structure with the highly active facets exposed. When sensitized by Rhodamine B (RhB), the photocatalyst system was more active than N-doped TiO2 for breaking down 4-chlorophenol (4-CP, 200 ppm) and nitric monoxide (NO, 500 ppb). The high activity could be attributed to the hierarchical structure (supplying feasible reaction tunnels for adsorption and transition of reactants or products) and the efficient exposure of the {001} facets. The former provides an enriched oxygen atom density that promotes adsorption of cationic dye RhB, and creates an oxygen vacancy state. The HO˙ and ˙O2(-) radicals produced from the injected electrons from the excited dye molecule (RhB*) into the conduction band of BiOCl were responsible for the excellent photocatalytic performance of the RhB-BiOCl system.

Spatial location engineering of oxygen vacancies for optimized photocatalytic H2 evolution activity

Enhanced H2 evolution efficiency is achieved via manipulating the spatial location of oxygen vacancies in niobates. The ultrathin K4 Nb6O17 nanosheets which are rich in surface oxygen vacancies show enhanced optical absorption and band gap narrowing. Meanwhile, the fast charge separation effectively reduces the probability of hole-electron recombination, enabling 20 times hydrogen evolution rate compared with the defect-free bulk counterpart.

Atomically-thick two-dimensional crystals: electronic structure regulation and energy device construction

Atomically-thick two-dimensional crystals can provide promising opportunities to satisfy people's requirement of next-generation flexible and transparent nanodevices. However, the characterization of these low-dimensional structures and the understanding of their clear structure-property relationship encounter many great difficulties, owing to the lack of long-range order in the third dimensionality. In this review, we survey the recent progress in fine structure characterization by X-ray absorption fine structure spectroscopy and also overview electronic structure modulation by density-functional calculations in the ultrathin two-dimensional crystals. In addition, we highlight their structure-property relationship, transparent and flexible device construction as well as wide applications in photoelectrochemical water splitting, photodetectors, thermoelectric conversion, touchless moisture sensing, supercapacitors and lithium ion batteries. Finally, we outline the major challenges and opportunities that face the atomically-thick two-dimensional crystals. It is anticipated that the present review will deepen people's understanding of this field and hence contribute to guide the future design of high-efficiency energy-related devices.

Synthesis of a highly efficient BiOCl single-crystal nanodisk photocatalyst with exposing {001} facets

BiOCl is known as a highly efficient photocatalyst for degradation of pollutants. However, effective methods for fabricating BiOCl nanomaterials with well-defined facets are still lacking. In this work, a facile synthetic method was developed for the fabrication of BiOCl nanodisks with exposed {001} facets. The central feature of this approach was the use of water as the hydrolysis agent and ethylene glycol as the crystal growth inhibitor agent to tune the growth of BiOCl nanomaterial. With this approach, the size and shape of BiOCl nanostructures could be effectively tuned through adjusting the volume ratio of ethylene glycol/H2O. In addition, the mechanism of the crystal growth in this fabrication process was elucidated. The as-prepared BiOCl nanodisks with exposed {001} facets exhibited an excellent photocatalytic activity towards Rhodamine B degradation under both ultraviolet and visible light irradiations. These findings shed light on the deep understanding of formation mechanisms of BiOCl nanodisks and provide an efficient and facile method for the synthesis of high active photocatalyst.

Engineering BiOX (X = Cl, Br, I) nanostructures for highly efficient photocatalytic applications

Heterogeneous photocatalysis that employs photo-excited semiconductor materials to reduce water and oxidize toxic pollutants upon solar light irradiation holds great prospects for renewable energy substitutes and environmental protection. To utilize solar light effectively, the quest for highly active photocatalysts working under visible light has always been the research focus. Layered BiOX (X = Cl, Br, I) are a kind of newly exploited efficient photocatalysts, and their light response can be tuned from UV to visible light range. The properties of semiconductors are dependent on their morphologies and compositions as well as structures, and this also offers the guidelines for design of highly-efficient photocatalysts. In this review, recent advances and emerging strategies in tailoring BiOX (X = Cl, Br, I) nanostructures to boost their photocatalytic properties are surveyed.

Advanced chemical compositions and nanoarchitectures of bismuth based complex oxides for solar photocatalytic application

Bismuth based complex oxide photocatalysts with high activity and stability could be obtained by engineering chemical compositions, morphologies, and microstructures.

A new family of sunlight-driven bifunctional photocatalysts based on TiO₂ nanoribbon frameworks and bismuth oxohalide nanoplates

By taking advantage of the structural affinity between bismuth oxohalide and TiO₂, we successfully prepare a family of hybrid frameworks via the designated growth of bismuth oxohalide nanoplates on TiO₂ nanoribbons, and propose them as sunlight-driven bifunctional photocatalysts for all-weather removal of pollutants. The structural variability of bismuth oxohalide allows the optical absorption of the hybrid framework to be monotonically tuneable across the visible spectrum. Meanwhile, the hybridization greatly increases the surface roughness of the frameworks and enables the frameworks to harvest more photons to participate in photocatalytic reactions. Furthermore, the hybridization establishes two potential gradients to promote the separation of photo-induced electron-hole pairs: the internal electrical field perpendicular to the wide surfaces of bismuth oxohalide nanoplates and across the semiconductor-semiconductor heterojunction. Owing to the synergetic effects of the permeable mesoporous architecture, the intense visible light absorption, and the efficient charge separation, the hybrid frameworks are capable of all-weather removal of pollutants: they utilize the inter-ribbon pores to gather pollutants in the dark (behaving as collectors) and they rapidly degrade the pollutants in the day (behaving as photocatalysts). In particular, the BiOBr@TiO₂ framework exhibits very impressive sunlight-driven photocatalytic activity, which is much higher than commercially available P25 TiO₂ under the same conditions.

Synthesis of hierarchical Bi2O3/Bi4Ti3O12 p–n junction nanoribbons on carbon fibers from (001) facet dominated TiO2 nanosheets

A novel hierarchical photocatalyst of Bi₂O₃/Bi₄Ti₃O₁₂ p–n junction nanoribbons (NRs) on carbon fibers has been successfully fabricated from the precursor of (001) facet dominated TiO₂ nanosheets (NSs), which provide well-shaped templates.

Stability, durability and regeneration ability of a novel Ag-based photocatalyst, Ag2Nb4O11

A novel Ag-based photocatalyst, Ag₂Nb₄O₁₁, exhibits universal photodegradation activity for dyes as well as high stability, durability and regeneration ability.

A highly efficient visible-light driven photocatalyst: two dimensional square-like bismuth oxyiodine nanosheets

2D square-like BiOI thin nanosheets with exposure of {001} facets present highly efficient visible-light photocatalytic performance.

The stabilities and electronic structures of single-layer bismuth oxyhalides for photocatalytic water splitting

Single-layer BiOX (X = Cl, Br, I) materials are energetically and dynamically stable structures. Single-layer BiOI is a promising photocatalyst for water splitting because of its suitable band gap and appropriate band edge positions.

Layered photocatalyst Bi2O2[BO2(OH)] nanosheets with internal polar field enhanced photocatalytic activity

Layered photocatalyst Bi₂O₂[BO₂(OH)] nanosheets efficiently separated photogenerated carriers due to the internal polar electric field, which enhances the photocatalytic activity.