Green Assembly of Covalently Linked BiOBr/Graphene Composites for Efficient Visible Light Degradation of Dyes

A novel high-performance BiOBr@graphene (BiOBr@G) photocatalyst with a new assembly structure had been demonstrated using a facile hydrothermal method through chemical bonding of reduced graphene oxide and structure-defined BiOBr flakes for improving charge separation and transfer performance, which were first synthesized at room temperature in immiscible solvents without corrosive acids. The prepared samples were characterized, and the BiOBr@G composite realized an efficient assembly portfolio of graphene and BiOBr flakes with defined structures, verified by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman and X-ray photoelectron spectroscopy (XPS), in which BiOBr flakes were covalently linked with the assembled graphene sheets through the Bi-C bond. This composite exhibited remarkable visible light absorbance and efficient photoinduced charge splitting characteristics in comparison with those of pure BiOBr, as established by DRS absorption, photoluminescence radiation, and photocurrent study. Hence, a very small amount (5 mg) of the BiOBr@G composite displayed a complete photodegradation effect on the rhodamine B dye under only 15 min of visible light excitation, which was three times faster than that of pure BiOBr and extremely superior to that of commercial P25. This was probably ascribed to the well-defined BiOBr structure itself, elevated light absorbance, and Bi-C chemical bond inducing quick charge separation and transfer in the BiOBr@G composite. Additionally, investigations on the photocatalytic mechanism displayed that the photogenerated holes in the BiOBr valence band and derivative superoxide radicals played vital roles in the photodegradation of RhB dyes, as reinforced by the electron spin resonance method, where the covalent linking of BiOBr and graphene served as an effective pathway for charge transportation.

Interfacial engineering in 3D/2D and 1D/2D bismuth ferrite (BiFeO3)/Graphene oxide nanocomposites for the enhanced photocatalytic activities under sunlight

3D-particulate and 1D-fiber structures of multiferroic bismuth ferrite (BiFeO₃/BFO) and their composites with 2D-graphene oxide (GO) have been developed to exploit the different scheme of interfacial engineering as 3D/2D and 1D/2D systems. Particulates and fibers of BFO were developed via sol-gel and electrospinning fabrication approaches respectively and their integration with GO was performed via the ultrasonic-assisted chemical reduction process. The crystalline and phase formation of BiFeO₃ and GO was confirmed from the XRD patterns obtained. The electron microscopic images revealed the characteristic integration of 3D particulates (with average size of 100 nm) and 1D fibers (with diameter of ~150 nm and few μm length) onto the 2D GO layers (thickness of ~27 nm). XPS analysis revealed that the BFO nanostructures have been integrated onto the GO through chemisorptions process, where it indicated that the ultrasonic process engineers the interface through the chemical modification of the surface of these 3D/2D and 1D/2D nanostructures. The photophysical studies such as the impedance and photocurrent measurements showed that the charge separation and recombination resistance is significantly enhanced in the system, which can directly be attributed to the effective interfacial engineering in the developed hetero-morphological composites. The degradation studies against a model pollutant Rhodamine B revealed that the developed nanocomposites exhibit superior photocatalytic activity via the effective generation of OH radicals as confirmed by the radical analysis studies (100% degradation in 150 and 90 min for 15% GO/BFO particulate and fiber composites, respectively). The developed system also demonstrated excellent photocatalytic recyclability, indicated their enhanced stability.

A review on bismuth oxyhalide based materials for photocatalysis

Photocatalytic solar energy transformation is the most encouraging solution to alleviate the environmental crisis and energy scarcity. Bismuth oxyhalide (BiOX) is an emerging class of materials that exhibits photocatalytic properties, such as resilient response to light, which causes enhanced energy conversion (solar energy) owing to their exceptional layered structure and attractive band structure. The present review presents a summary of results from the recent developments on the tuning and design of BiOX-based materials to improve the energy conversion. In particular, the preparation and tuning approaches that have the potential to enhance the photocatalytic behavior of BiOX and some other techniques, such as elemental doping, are addressed, which prevent the rapid recombination of charges, and formation of oxygen vacancies, facilitating an improvement in the photocatalytic reaction. Various frameworks are also presented, displaying the significance of BiOX-based nanocomposites. Finally, the main challenges and opportunities associated with the future progress of BiOX-based materials are presented. This review will provide an extended understanding and offer a preferred direction for the innovative design of BiOX-based materials for environmental and especially energy-based applications.

ZnCuInSe/Au/TiO2 sandwich nanowires-based photoelectrochemical biosensor for ultrasensitive detection of kanamycin

A highly selective and sensitive photoelectrochemical (PEC) sensing platform was developed for kanamycin assay based on the aptamer modified sandwich-structured ZnCuInSe/Au/TiO₂ nanowires. Sandwiched between the TiO₂ nanowires and the ZnCuInSe quantum dot (QDs) layer, the Au nanoparticles (Au NPs) serves as a plasmonic photosensitizer and an electron relay, which expand the light absorption range and facilitates the charge transfer. Also, ZnCuInSe QDs, a broad spectrum photosensitizer can capture visible light, which enhance the photocurrent density response. Through the Au-S bond and Cu-S bond, the HS-aptamer were immobilized on the ZnCuInSe/Au/TiO₂ nanowires as a recognition unit for kanamycin. The proposed sensing platform showed excellent assay performance for kanamycin with a linear response range from 0.2 to 250 nM, and high selectivity. By changing the recognizers, the proposed sensing platform could be easily extended to detect other biomolecules, and may have a promising application in bioanalysis.

Self-assembly of carbon nanotube/graphitic-like flake/BiOBr nanocomposite with 1D/2D/3D heterojunctions for enhanced photocatalytic activity

A self-assembled nanocomposite of lamellar BiOBr covalently bonded with conductive network of dispersive one-dimensional carbon nanotubes (1D CNT) and two-dimensional reduced graphitic-like flakes (2D GF) had been in situ constructed using one-pot facile solvothermal technique. Through self-assembly, BiOBr/CNT/GF (BiOBr/CG) displayed three-dimensional architectures in which a strong interfacial contact interaction and covalent banding between BiOBr nanostructures and CNT/GF network appeared. Furthermore, visible-light-driven catalytic activity of BiOBr/CG for RhB dye degradation was superior to that of pure BiOBr or BiOBr/C. Interestingly, the photodegradation activity of the BiOBr/CG nanocomposite could be improved further by subsequent facile annealing treatment, in which the annealed BiOBr/CG-DS had degraded almost 97.9% of RhB dye within only 100 min of visible-light irradiation. Moreover, analysis of the photodegradation mechanism revealed that the repression of electron-hole recombination in the nanocomposites, with sufficient covalent interfacial contact with CNT/GF as effective electron collecting and transferring system, were responsible for the outstanding photocatalytic performance. This effect, in turn, led to the continuous generation of O²- and OH reactive oxygen species for the degradation of RhB dye, which was verified by active species trapping and ESR spectra.

Preparation of BiF3/BiOBr heterojunctions from microwave-assisted method and photocatalytic performances

Novel BiF₃/BiOBr heterojunction photocatalysts were prepared from a fast and stable microwave-assisted method, and characterized by X-ray diffractometry, X-ray photoelectron spectroscopy, scanning electron microscopy, ultraviolet-visible spectroscopy and fluorescence spectroscopy. The photocatalytic activity of BiF₃/BiOBr heterojunctions under light irradiation was significantly higher than pure BiOBr or BiF₃, and was maximized at the Br:F molar ratio of 1:1, as the targeted 20 mg/L Rhodamine B (RhB) solution was completely degraded within 40 min. This was mainly because the unique BiF₃/BiOBr heterojunction formed during photocatalytic degradation accelerated the photoelectron and hole separation, effectively enhanced the quantum efficiency, and thereby strengthened the photocatalytic activity.

Enhanced UV-Vis-NIR activated photocatalytic activity from Fe3+-doped BiOBr:Yb3+/Er3+ upconversion nanoplates: synergistic effect and mechanism insight

A simple strategy for simultaneously enhancing the UC luminescence and UV-Vis-NIR activated photocatalytic activity of BiOBr:Yb³⁺/Er³⁺ nanoplates through Fe³⁺ ion doping.

Recyclable Magnetic Titania Nanocomposite from Ilmenite with Enhanced Photocatalytic Activity

Using ilmenite as a raw material, iron was converted into Fe₃O₄ magnetic fluid, which further was combined with titanium filtrate by a solvothermal method. Finally Fe₃O₄/TiO₂ nanocomposites with the uniform size of 100-200 nm were prepared. This approach uses rich, inexpensive ilmenite as a titanium and iron source, which effectively reduces the production cost. The crystal structure, chemical properties and morphologies of the products were characterized by SEM, TEM, XRD, FTIR, BET, UV-Vis, XPS and VSM. The novel photocatalyst composed of face-centered cubic Fe₃O₄ and body-centered tetragonal anatase-TiO₂ exhibits a spherical shape with porous structures, superparamagnetic behavior and strong absorption in the visible light range. Using the degradation reaction of Rhodamine B (RhB) to evaluate the photocatalytic performance, the results suggest that Fe₃O₄/TiO₂ nanocomposites exhibit excellent photocatalytic activities and stability under visible light and solar light. Moreover, the magnetic titania nanocomposites displayed good magnetic response and were recoverable over several cycles. Based on the trapping experiments, the main active species in the photocatalytic reaction were confirmed and the possible photocatalytic mechanism of RhB with magnetic titania was proposed. The enhanced photocatalytic activity and stability, combined with excellent magnetic recoverability, make the prepared nanocomposite a potential candidate in wastewater purification.

A novel supramolecular preorganization route for improving g-C3N4/g-C3N4 metal-free homojunction photocatalysis

Enhancing the novel g-C₃N₄/g-C₃N₄ metal-free homojunction photocatalysis: efficient solar energy harvesting and charge transfer.

The controllable fabrication of a novel hierarchical nanosheet-assembled Bi2MoO6 hollow micronbox with ultra-high surface area for excellent solar to chemical energy conversion

In this study, we demonstrated that a novel controllable nano-sheet assembled Bi₂MoO₆ micronbox had higher activity for nitrogen fixation and dye degradation.