Chao Zeng

Bi2O2(OH)(NO3) as a desirable [Bi2O2]2+ layered photocatalyst: strong intrinsic polarity, rational band structure and {001} active facets co-beneficial for robust photooxidation capability

Developing high-performance photocatalytic materials is of huge significance and highly desirable for fulfilling the pressing need in environmental remediation. In this work, we demonstrate the use of bismuth nitrate Bi2O2(OH)(NO3) as an absorbing photocatalyst, which integrates multiple superiorities, like a [Bi2O2]2+ layered configuration, a non-centrosymmetric (NCS) polar structure and highly reactive {001} facets. Bi2O2(OH)(NO3) nanosheets are obtained by a facile one-pot hydrothermal route using Bi(NO3)3·5H2O as the sole raw material. Photocatalysis assessment revealed that Bi2O2(OH)(NO3) holds an unprecedented photooxidation ability in contaminant decomposition, far out-performing the well-known photocatalysts BiPO4, Bi2O2CO3, BiOCl and P25 (commercial TiO2). Particularly, it displays a universally powerful catalytic activity against various stubborn industrial contaminants and pharmaceuticals, including phenol, bisphenol A, 2,4-dichlorophenol and tetracycline hydrochloride. In-depth experimental and density functional theory (DFT) investigations co-uncovered that the manifold advantages, such as large polarizability and rational band structure, as well as exposed {001} active facets, induced robust generation of strong oxidating superoxide radicals (˙O2−) in the conduction band and hydroxyl radicals (˙OH) in the valence band, thus enabling Bi2O2(OH)(NO3) to have a powerful and durable photooxidation capability. Bi2O2(OH)(NO3) also presents high photochemical stability. This work not only rendered a highly active and stable photocatalyst for practical applications, but also laid a solid foundation for future initiatives aimed at designing new photoelectronic materials by manipulating multiple advantageous factors.

Macroscopic Polarization Enhancement Promoting Photo- and Piezoelectric-Induced Charge Separation and Molecular Oxygen Activation

Efficient photo- and piezoelectric-induced molecular oxygen activation are both achieved by macroscopic polarization enhancement on a noncentrosymmetric piezoelectric semiconductor BiOIO3 . The replacement of V5+ ions for I5+ in IO3 polyhedra gives rise to strengthened macroscopic polarization of BiOIO3 , which facilitates the charge separation in the photocatalytic and piezoelectric catalytic process, and renders largely promoted photo- and piezoelectric induced reactive oxygen species (ROS) evolution, such as superoxide radicals (. O2- ) and hydroxyl radicals (. OH). This work advances piezoelectricity as a new route to efficient ROS generation, and also discloses macroscopic polarization engineering on improvement of multi-responsive catalysis.

A novel apatite-based warm white emitting phosphor Ba3GdK(PO4)3F:Tb3+, Eu3+ with efficient energy transfer for w-LEDs

A Ba3GdK(PO4)3F:Tb3+, Eu3+ phosphor with fluoro-apatite-structure has been fabricated by a conventional high-temperature solid-state reaction. The crystal structure, component element and microstructure of the phosphor have been systematically investigated by X-ray diffraction refinement, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM), respectively. The Ba3GdK(PO4)3F:Tb3+ phosphor shows a blue-greenish emission peak at 547 nm under excitation of 276 nm, while Ba3GdK(PO4)3F:Eu3+ displays a red emission peak near 620 nm with excitation at 396 nm. Efficient energy transfer from Tb3+ to Eu3+ ions takes place in the Ba3GdK(PO4)3F host, and the energy transfer critical distance between Tb3+ and Eu3+ ions along with the resonant energy-transfer mechanism are determined. By tuning the Tb3+/Eu3+ ratio, the emission hue can be modulated from blue-green (0.238, 0.311) to white (0.341, 0.318) and eventually to orange (0.521, 0.335). Moreover, the thermal quenching property of the as-prepared samples was studied in detail, which discloses the high thermal stability.

Coupling of solid-solution and heterojunction in a 2D-1D core-shell-like BiOCl0.5I0.5/Bi5O7I hierarchy for promoting full-spectrum photocatalysis and molecular oxygen activation

We herein describe the coupling of solid-solution and heterojunction in a 2D-1D BiOCl0.5I0.5/Bi5O7I hierarchical architecture for optimizing photoabsorption, energy band levels and charge separation, thereby promoting the photo-oxidation and molecular oxygen activation performance. BiOCl0.5I0.5/Bi5O7I shows a core-shell-like structure with BiOCl0.5I0.5 thin nanoflakes (∼3 to 8 layers) homogeneously vertical coating on the surface of Bi5O7I strips. The photo-responsive range of BiOCl0.5I0.5/Bi5O7I can be orderly tuned from 450nm to 650nm by increasing the BiOCl0.5I0.5 content. Regardless of visible light (λ>420nm) or UV light (365nm) irradiation, BiOCl0.5I0.5/Bi5O7I casts highly promoted photocatalytic activity in decomposing methyl orange (MO) compared to the BiOCl0.5I0.5 and Bi5O7I. This enhancement on full-spectrum photoreactivity is attributable to the facilitated charge separation derived from BiOCl0.5I0.5/Bi5O7I heterojunction with intimate interfacial interaction, which is approved by transient photocurrent response under visible and UV-vis light. To probe the photocatalytic mechanism, active species trapping tests are performed over BiOCl0.5I0.5, Bi5O7I and BiOCl0.5I0.5/Bi5O7I, which reveal superoxide radical (O2-) and hole (h+) take dominant roles in photo-oxidation reaction. BiOCl0.5I0.5/Bi5O7I was also found possessing a stronger ability in molecular oxygen activation with a O2- production rate of 2.22×10-7molL-1h-1, which far outperforms Bi5O7I (1.35×10-7molL-1h-1) and BiOCl0.5I0.5 (1.54×10-7molL-1h-1). It further corroborates the efficient band charge transfer between BiOCl0.5I0.5 and Bi5O7I. This work may furnish a new concept on smart design of high-performance photocatalytic materials via manipulating multiple strategies.

Polypyrrole decorated BiOI nanosheets: Efficient photocatalytic activity for treating diverse contaminants and the critical role of bifunctional polypyrrole

A conducting polymer polypyrrole (Ppy) was first employed to decorate BiOI for fabricating an organic-inorganic hybridized Ppy-BiOI nanocomposite photocatalyst via a facile in situ precipitation strategy at room temperature. The composite and intimate interface was confirmed by FTIR, XPS, SEM, HRTEM and TEM-mapping. In comparison with pristine BiOI, the Ppy-BiOI hybrids present significantly enhanced photocatalytic activity for degradation of Rhodamine B (RhB) under visible light (λ>420nm). Particularly, the Ppy-BiOI composite exhibits an universal photocatalytic performance for removing diverse industrial pollutants and antibiotics, including bisphenol A, 2,4-dichlorophenol, tetracycline hydrochloride and chlortetracycline hydrochloride. The enhanced photocatalytic activity of Ppy-BiOI composite is found attributable to the bifunctional role that Ppy takes. Ppy-BiOI composite has an enhanced specific surface area, which benefits adsorption and generation of more active sites. Notably, high separation and transfer of the photogenerated charge carriers was achieved on the interface between Ppy and BiOI, and the photogenerated hole transfer action of Ppy is demonstrated. Therefore, synergistic effect of adsorption-enrichment and photocatalytic degradation is realized. Our work may offer a guideline to manipulate high-performance Bi-based composite photocatalyst by coupling conducting polymers.

A new green-yellowish emitting fluoro-apatite compound phosphor Ba3TbK(PO4)3F:Sm3+ with high thermal stability

Abstract A novel fluoro-apatite-type compound, Ba 3 TbK(PO 4 ) 3 F was developed via a high-temperature solid-state reaction route for the first time. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and high-resolution TEM (HRTEM) were used to investigate the component element and microstructure of the phosphor was systematically investigated. The luminescence properties of Ba 3 TbK(PO 4 ) 3 F:Sm 3+ were investigated systemically. The results revealed that the Ba 3 TbK(PO 4 ) 3 F:Sm 3+ phosphor could be efficiently excited in a broad wavelength region ranging from 200 to 400 nm, which matched perfectly with the ultraviolet (UV) light-emitting diode (LED) chips. Based on the energy transfer (ET) between Tb 3+ and Sm 3+ , the color hue of Ba 3 Tb 1– n K(PO 4 ) 3 F: n Sm 3+ ( n =0–0.03) was modulated from green (0.305, 0.591) to yellow (0.486, 0.437) area by controlling the Sm 3+ doping concentration. The critical distance between Tb 3+ and Sm 3+ ions in Ba 3 TbK(PO 4 ) 3 F:Sm 3+ was calculated and the corresponding energy quenching mechanism was identified. Fascinatingly, both the Ba 3 TbK(PO 4 ) 3 F and Ba 3 Tb 0.995 K(PO 4 ) 3 F: 0.005Sm 3+ phosphors exhibited very high thermal stability from room temperature (25 °C) to 300 °C, which is extremely important for practical application. In addition, the activation energy for thermal quenching of the Ba 3 Tb 0.995 K(PO 4 ) 3 F:0.005Sm 3+ sample was estimated to be as high as 0.312 eV. These findings demonstrated that as-prepared phosphor may serve as a high-performance candidate for the application in w-LEDs.

Fabrication of Heterogeneous-Phase Solid-Solution Promoting Band Structure and Charge Separation for Enhancing Photocatalytic CO2 Reduction: A Case of ZnXCa1–XIn2S4

Photocatalytic CO2 reduction into solar fuels illustrates huge charm for simultaneously settling energy and environmental issues. The photoreduction ability of a semiconductor is closely correlated to its conduction band (CB) position. A homogeneous-phase solid-solution with the same crystal system always has a monotonously changed CB position, and the high CB level has to be sacrificed to achieve a benign photoabsorption. Herein, we report the fabrication of heterogeneous-phase solid-solution ZnXCa1-XIn2S4 between trigonal ZnIn2S4 and cubic CaIn2S4. The ZnXCa1-XIn2S4 solid solutions with orderly tuned photoresponsive range from 540 to 640 nm present a more negative CB level and highly enhanced charge-separation efficiency. Profiting from these merits, all of these ZnXCa1-XIn2S4 solid solutions exhibit remarkably strengthened photocatalytic CO2 reduction performance under visible light (λ > 420 nm) irradiation. Zn0.4Ca0.6In2S4, bearing the most negative CB position and highest charge-separation efficiency, casts the optimal photocatalytic CH4 and CO evolution rates, which reach 16.7 and 6.8 times higher than that of ZnIn2S4 and 7.2 and 3.9 times higher than that of CaIn2S4, respectively. To verify the crucial role of the heterogeneous-phase solid solution in promoting the band structure and photocatalytic performance, another heterogeneous-phase solid-solution ZnXCd1-XIn2S4 has been synthesized. It also displays an upshifted CB level and promoted charge separation. This work may provide a new perspective into the development of an efficient visible-light driven photocatalyst for CO2 reduction and other photoreduction reactions.

A core–satellite structured Z-scheme catalyst Cd0.5Zn0.5S/BiVO4 for highly efficient and stable photocatalytic water splitting

Fabrication of a Z-scheme photocatalytic system for hydrogen production and overall water splitting has huge potential in confronting the increasing worldwide energy crisis. But it is highly challenging to realize due to the harsh requirement for band edge levels and interfacial contact. Herein, we report the preparation of a high-efficiency and stable Z-scheme catalyst Cd0.5Zn0.5S–BiVO4 with a core–satellite structure through the charge-induced assembly process in a mild water bath. A Cd0.5Zn0.5S–BiVO4 Z-scheme junction shows an enormously enhanced photocatalytic activity for H2 evolution under visible light illumination. The optimal photocatalytic H2 evolution rate reaches 2.35 mmol g−1 h−1, which is 7.13 times higher than that of Cd0.5Zn0.5S, and an appreciable apparent quantum efficiency of 24.1% at λ = 420 nm was achieved. In particular, without any sacrificial donor, the Cd0.5Zn0.5S–BiVO4 Z-scheme junction can overall split water into H2 and O2. The efficient photocatalytic activity of Cd0.5Zn0.5S–BiVO4 is attributed to the formation of an intimate core–satellite structure and a Z-scheme photocatalytic mechanism, which not only greatly benefit the charge separation, but also prompt the photoinduced holes from Cd0.5Zn0.5S to rapidly recombine with the electrons of BiVO4, hence reserving the most favorable reductive and oxidative reaction sites. Meanwhile, it inhibits the photocorrosion of Cd0.5Zn0.5S, guaranteeing the high photochemical stability (no activity decay after half a year). This work provides a new reference for the fabrication of a high-performance Z-schematic photocatalyst for water splitting.