Synthesis of mesoporous BiOBr 3D microspheres and their photodecomposition for toluene

Effect of grinding time on bismuth oxyhalides optical and morphological properties influence on photocatalytic removal of organic dye

Herein, we reported the synthesis of BiOX (X = Cl, Br) with different grinding time like 15 min and 30 min to analyze the evolution of physiochemical properties and the morphological evolution. The structural, optical, vibrational properties were examined by standard characterization studies. The formation of bismuth oxyhalides were confirmed by XRD and Raman studies. The crystallite size was decreased as in 30 min grinded sample whereas there is an influence of crystal structure. BiOCl (15 and 30 min) samples expelled the nanoflake like structure with the flakes arranged to form a nanoflower morphology. On comparing BiOCl (15 min), there is high orientation of nanoflakes on BiOCl (30 min) sample. As explored in BiOBr (15 and 30 min) samples, the development of nanoplates were found. The growth of nanoplates was enhanced in the better way in BiOBr (30 min) than BiOBr (15 min). The grinding time has explored a great influence on morphology. The photocatalyst test for prepared photocatalysts was performed to reduce the RhB dye. The photocatalysts showed 74%, 97%, 98% and 99.8% for BiOCl (15 min), BiOCl (30 min), BiOBr (15 min) and BiOBr (30 min). The rate constant value obtained was 0.008, 0.011, 0.021, 0.033 and 0.068 min^-1. BiOBr (30 min) sample achieved higher rate constant value. The hierarchical nanostructures and narrow bandgap has made the samples to be a potential candidate to reduce the toxic pollutants with complete efficiency.

Room-temperature multiple ligands-tailored SnO2 quantum dots endow in situ dual-interface binding for upscaling efficient perovskite photovoltaics with high VOC

The benchmark tin oxide (SnO2) electron transporting layers (ETLs) have enabled remarkable progress in planar perovskite solar cell (PSCs). However, the energy loss is still a challenge due to the lack of "hidden interface" control. We report a novel ligand-tailored ultrafine SnO2 quantum dots (QDs) via a facile rapid room temperature synthesis. Importantly, the ligand-tailored SnO2 QDs ETL with multi-functional terminal groups in situ refines the buried interfaces with both the perovskite and transparent electrode via enhanced interface binding and perovskite passivation. These novel ETLs induce synergistic effects of physical and chemical interfacial modulation and preferred perovskite crystallization-directing, delivering reduced interface defects, suppressed non-radiative recombination and elongated charge carrier lifetime. Power conversion efficiency (PCE) of 23.02% (0.04 cm2) and 21.6% (0.98 cm2, VOC loss: 0.336 V) have been achieved for the blade-coated PSCs (1.54 eV Eg) with our new ETLs, representing a record for SnO2 based blade-coated PSCs. Moreover, a substantially enhanced PCE (VOC) from 20.4% (1.15 V) to 22.8% (1.24 V, 90 mV higher VOC, 0.04 cm2 device) in the blade-coated 1.61 eV PSCs system, via replacing the benchmark commercial colloidal SnO2 with our new ETLs.

Built-in electric field for photocatalytic overall water splitting through a TiO2/BiOBr P-N heterojunction

Photocatalytic overall water splitting to simultaneously obtain abundant hydrogen and oxygen is still the mountain that stands in the way for the practical applications of hydrogen energy, in which composite semiconductor photocatalysts are critical for providing both electrons and holes to promote the following redox reaction. However, the interface between different components forms a deplete layer to hinder the charge transfer to a large extent. In order to enhance the charger transfer from an interface to the surface and promote the spatial separation of electron-hole pairs, a built-in electric field induced by a p-n heterojunction emerges as the best choice. As a touchstone, a p-n heterojunction of TiO2/BiOBr with a strong built-in electric field has been constructed, which presents a wide spectrum response owing to its interleaved band gaps after composition. The built-in electric field greatly enhances the separation and transportation of photogenerated carriers, resulting in fluorescence quenching due to the carrier recombination. The sample also displayed exceptional photoelectron responses: its photocurrent density (43.3 μA cm-2) was over 10 times that of TiO2 (3.5 μA cm-2) or BiOBr (4.2 μA cm-2). In addition, the sample with a molar ratio of 3 : 1 between TiO2 and BiOBr showed the best photocatalytic overall water splitting performance under visible light (λ > 420 nm): the hydrogen and oxygen production rate were 472.7 μmol gcat.-1 h-1 and 95.7 μmol gcat.-1 h-1, respectively, which are the highest values under visible light without other cocatalysts to have been reported in literature for the photocatalyst.

Efficient photodegradation of chlorophenols by BiOBr/NaBiO3 heterojunctioned composites under visible light

Forming heterojunctioned composites is an effective way to develop visible-light-driven photocatalysts. A series of BiOBr/NaBiO₃ composites were synthesized by surface transformation of NaBiO₃ with hydrobromic acid. Commensurate planes of BiOBr and NaBiO₃ enabled the formation of a closely bound interface. Composites with <20wt.% BiOBr exhibited excellent photocatalytic activity towards the degradation of chlorophenols under low intensity visible light (λ>400nm). The best photocatalyst was 9% BiOBr/NaBiO₃ with a quantum yield of 0.365. No photocorrosion was observed after three cycles. Using radical scavengers and inert atmosphere, holes, superoxide and hydroxyl radicals were found to be involved in the photoactivity of the BiOBr/NaBiO₃ composite. Hydroxylated and open-ring diacid molecules were identified as intermediates in the mineralization of 4-chlorophenol.

Multiple halide anion doped layered bismuth terephthalate with excellent photocatalysis for pollutant removal

Doping multiple halide anions into bismuth terephthalate can effectively improve photocatalytic activities. The F^–, Cl^–, Br^– codoped hybrids exhibit excellent photocatalytic activities on RhB and salicylic acid.

Heavy pnictogen chalcohalides: the synthesis, structure and properties of these rediscovered semiconductors

Heavy pnictogen chalcohalides offer various shades from the same palette, like “Paysage” by Nicolas de Staël. Their versatility and tunability lead to a new world of possible applications.

Enhanced visible light photocatalytic activity of BiOBr by in situ reactable ionic liquid modification for pollutant degradation

In this study, hierarchical BiOBr microspheres were synthesized via a one-pot solvothermal method in the presence of imidazole ionic liquids. The resultant samples were characterized by XRD, SEM, HRTEM, PL, EPR, EIS and UV-vis absorption spectroscopy. The photoactivity of BiOBr was evaluated by the photocatalytic degradation of methyl orange (MO) and tetracycline hydrochloride. Oxygen vacancies were detected in the system and proven to be correlated with the activity of the catalyst. It was also revealed that BiOBr microspheres prepared by 1-butyl-3-methylimidazolium bromide at 433 K for 8 hours displayed a superior performance compared to the other samples in the degradation of model organic contaminants. After 4.5 hours of reaction, the highest degradation efficiency of 94.0% was achieved by BiOBr-C₄-Br. Stronger photoluminescence spectral intensities could be obtained as the cationic chain lengths of the ionic liquids reduced gradually. According to our experiments, the better performance of BiOBr-C₄-Br in the degradation of model pollutants can be attributed to the effect of oxygen vacancies. The findings of our work may have important implications for the design of BiOBr.

In this study, hierarchical BiOBr microspheres were synthesized via a one-pot solvothermal method in the presence of imidazole ionic liquids.

F–Bi4TaO8Cl flower-like hierarchical structures: controlled preparation, formation mechanism and visible photocatalytic hydrogen production

Hydrothermal method was employed to prepare the flower-like hierarchical structures of F–Bi₄TaO₈Cl for photocatalytic hydrogen production under visible light irradiation.

Efficient photocatalytic dye degradation over Er-doped BiOBr hollow microspheres wrapped with graphene nanosheets: enhanced solar energy harvesting and charge separation

Er-doped BiOBr hollow microspheres wrapped with graphene nanosheets realizing efficient solar energy harvesting and charge separation for dye degradation.

Enhanced photocatalytic activity of BiOI under visible light irradiation by the modification of MoS2

The suitable modification of MoS₂ with 3D hierarchical BiOI could improve the separation efficiency of photogenerated charge carriers.

Synthesis process and photocatalytic properties of BiOBr nanosheets for gaseous benzene

A series of nano-BiOBr were prepared by an effective hydrothermal method in the presence of cetyltrimethyl ammonium bromide (CTAB) and ethanol at different calcination temperatures. The as-prepared nano-BiOBr samples were characterized by measuring the specific area (S BET), UV-Vis diffuse reflectance spectrum, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results show that the calcination temperature has an important impact on the morphology and microstructure of BiOBr. The nano-BiOBr calcined at 120 °C showed excellent photocatalytic degradation properties for benzene, with photocatalytic degradation rate of 75 % for benzene under UV irradiation for 90 min, and removal efficiency of benzene was significantly enhanced by using nano-BiOBr catalyst compared to UV irradiation alone. BiOBr catalyst possessed good photocatalytic activity even after three consecutive photocatalytic reaction cycles, illustrating its excellent stability. The photocatalytic degradation of benzene followed the first-order kinetics, and the good catalytic capability of nano-BiOBr catalyst can be attributed to its crystalline, hierarchical nanostructure and nanosheet thickness.

Morphology-controlled preparation and plasmon-enhanced photocatalytic activity of Pt-BiOBr heterostructures

Pt-BiOBr nanosheets, microflowers, microspheres and sphere-like microflowers are controllably fabricated via a hydro(solvo)thermal treatment-photodeposition route and adjusting Br sources and solvents in the preparation systems. The simulated sunlight and visible-light photocatalytic properties of various morphological Pt-BiOBr heterostructures are evaluated by the degradation of two aqueous light insensitive organic pollutants, p-nitrophenol (PNP) and tetrabromobisphenol-A (TBBPA), and the relationship between the morphological characteristics and photocatalytic properties of the Pt-BiOBr is revealed accordingly. The sphere-like Pt-BiOBr microflowers and microspheres show considerably higher photocatalytic activity with respect to their microflowers and nanosheets counterparts, and their activity outperforms P25 TiO2. This excellent photoactivity is explained in terms of unique performance of BiOBr and plasmonic metal nanoparticles as well as fascinating morphological characteristics. The Pt-BiOBr heterostructures can be reused four times without obvious activity loss.

Hierarchical photocatalysts

The design, fabrication, performance and applications of hierarchical semiconductor photocatalysts are thoroughly reviewed and apprised.

The solvothermal synthesis and enhanced photocatalytic activity of Zn2+ doped BiOBr hierarchical nanostructures

Zn-doped BiOBr hierarchical nanostructures were fabricated by solvothermal methods. Photocatalytic activity of BiOBr was greatly enhanced by Zn doping.

BiOBr/Bi2MoO6 composite in flower-like microspheres with enhanced photocatalytic activity under visible-light irradiation

BiOBr/Bi₂MoO₆ flower-like microspheres synthesized by a facile solvothermal method, exhibited high photocatalytic activity owing to the enhanced light harvesting via multiple-reflections and the reduced photoelectron–hole recombination.

Monolayered Bi2WO6 nanosheets mimicking heterojunction interface with open surfaces for photocatalysis

Two-dimensional-layered heterojunctions have attracted extensive interest recently due to their exciting behaviours in electronic/optoelectronic devices as well as solar energy conversion systems. However, layered heterojunction materials, especially those made by stacking different monolayers together by strong chemical bonds rather than by weak van der Waal interactions, are still challenging to fabricate. Here the monolayer Bi₂WO₆ with a sandwich substructure of [BiO]⁺–[WO₄]²⁻–[BiO]⁺ is reported. This material may be characterized as a layered heterojunction with different monolayer oxides held together by chemical bonds. Coordinatively unsaturated Bi atoms are present as active sites on the surface. On irradiation, holes are generated directly on the active surface layer and electrons in the middle layer, which leads to the outstanding performances of the monolayer material in solar energy conversion. Our work provides a general bottom-up route for designing and preparing novel monolayer materials with ultrafast charge separation and active surface.

Although they tend to exhibit exciting optoelectronic behaviours, the difficulty in fabricating chemically bonded two-dimensional layered heterojunctions has hindered progress in the area. Here, the authors synthesize sandwich-substructured Bi₂WO₆ monolayers and investigate their photocatalytic activity.

Photocatalytic properties of hierarchical BiOXs obtained via an ethanol-assisted solvothermal process

In this study, bismuth oxyhalide (BiOXs (XCl, Br, I)) semiconductors were prepared by a simple solvothermal method, with ethanol serving as solvent and a series of tetrabutylammonium halide surfactants as halogen sources. Under identical synthetic conditions, BiOBr was more readily constructed into regular flower-like hierarchical architectures. The photocatalytic properties of the materials were studied by monitoring the degradation of rhodamine B (RhB), with visible light absorption, and colorless salicylic acid (SA). It was found that both RhB and SA were rapidly degraded on the surface of BiOBr. BiOCl was rather active for the degradation of RhB, but ineffective toward the degradation of SA. However, neither RhB nor SA could be degraded effectively in the case of BiOI. Further experiments such as UV-visible spectroscopy and detection of OH and O2(-) radicals suggest that the electronic structure of the BiOX photocatalysts is responsible for the difference in their activities.

Construction of amorphous TiO₂/BiOBr heterojunctions via facets coupling for enhanced photocatalytic activity

Facets coupled BiOBr with amorphous TiO2 composite photocatalysts are synthesized via an in situ direct growth approach under microwave irradiation. XRD, SEM and HRTEM characterizations indicate that the heterointerface between BiOBr and amorphous TiO2 occurs mainly on the {001} facets of BiOBr. BET and TEM verify that the heterojunctions possess higher specific surface areas and smaller amorphous TiO2 particle size than bare BiOBr and amorphous TiO2, exhibiting the inhibition function of BiOBr on the growth of TiO2 particles. XPS verifies the interaction between the two components. The degradation of methyl orange (MO) and phenol are used as the objective reaction to evaluate the photocatalytic activity of the as-prepared samples. The reaction rate constant of 15% TiO2/BiOBr composite is 3.4 times greater than that of pure BiOBr, which is attributed to its higher surface area, and efficient separation of photo-generated electron-hole pairs between BiOBr and amorphous TiO2.

Graphitic carbon nitride based nanocomposites: a review

Graphitic carbon nitride (g-C(3)N(4)), as an intriguing earth-abundant visible light photocatalyst, possesses a unique two-dimensional structure, excellent chemical stability and tunable electronic structure. Pure g-C(3)N(4) suffers from rapid recombination of photo-generated electron-hole pairs resulting in low photocatalytic activity. Because of the unique electronic structure, the g-C(3)N(4) could act as an eminent candidate for coupling with various functional materials to enhance the performance. According to the discrepancies in the photocatalytic mechanism and process, six primary systems of g-C(3)N(4)-based nanocomposites can be classified and summarized: namely, the g-C(3)N(4) based metal-free heterojunction, the g-C(3)N(4)/single metal oxide (metal sulfide) heterojunction, g-C(3)N(4)/composite oxide, the g-C(3)N(4)/halide heterojunction, g-C(3)N(4)/noble metal heterostructures, and the g-C(3)N(4) based complex system. Apart from the depiction of the fabrication methods, heterojunction structure and multifunctional application of the g-C(3)N(4)-based nanocomposites, we emphasize and elaborate on the underlying mechanisms in the photocatalytic activity enhancement of g-C(3)N(4)-based nanocomposites. The unique functions of the p-n junction (semiconductor/semiconductor heterostructures), the Schottky junction (metal/semiconductor heterostructures), the surface plasmon resonance (SPR) effect, photosensitization, superconductivity, etc. are utilized in the photocatalytic processes. Furthermore, the enhanced performance of g-C(3)N(4)-based nanocomposites has been widely employed in environmental and energetic applications such as photocatalytic degradation of pollutants, photocatalytic hydrogen generation, carbon dioxide reduction, disinfection, and supercapacitors. This critical review ends with a summary and some perspectives on the challenges and new directions in exploring g-C(3)N(4)-based advanced nanomaterials.

Preparation of novel carbon nanofibers with BiOBr and AgBr decoration for the photocatalytic degradation of rhodamine B

Novel carbon nanofibers with BiOBr and AgBr decoration were prepared and exhibited a high efficiency for the photocatalytic degradation of RhB in aqueous solution and were convenient to separate from water.

Simulated sunlight photocatalytic degradation of aqueous p-nitrophenol and bisphenol A in a Pt/BiOBr film-coated quartz fiber photoreactor

Pt/BiOBr film-coated quartz fiber bundles were prepared by dip-coating combined with photodeposition, and their phase and chemical structures, electronic and optical properties, textural properties as well as morphologies were well-characterized.

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.

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.