2CO3 Microspheres Research Articles

Tempalte-induced interfacial construction of mesoporous CuS hollow spherical caps with tunable height, light receiving region and photocatalytic activities

A new micro/nano-structured material, mesoporous CuS hollow spherical cap (HSC), was fabricated on the surface of a solution by template-induced interfacial reaction. The Cu2(OH)2CO3 microspheres modified with vinyl trimethoxy silane were floated on the mixed aqueous solution of ethanol and thioacetamide, and acted as the template and the copper source. At the solid-liquid interface thioacetamide reacted with Cu2(OH)2CO3 to produce CuS shells around the immersed part of the template, and then the mesoporous CuS HSC was obtain by removal of the template. Controlling the content of ethanol could systemically tune the immersed depth and the HSC height. Such HSCs displayed increased photocatalytic activity in degradation of methyl blue with the decrease of the HSC height. In addition to the conventional specific surface area, the activity regions accessible by light (light receiving region) were analyzed by optical simulation for the first time and considered an important factor in enhancing the photocatalytic activity of HSC structure. The present study not only shows a facile strategy to fabricate activity-tunable CuS HSC photocatalyst, but also establishes a relationship between the geometry of morphology and photocatalytic performance.

Efficiently photocatalytic degradation of monochlorophenol on in-situ fabricated BiPO4/β-Bi2O3 heterojunction microspheres and O2-free hole-induced selective dechloridation conversion with H2 evolution

Herein, hierarchical BiPO4/β-Bi2O3 microspheres have been successfully synthesized via one-step annealing pyrophosphate anchored (BiO)2CO3 microspheres, and utilized as efficient and recyclable photocatalysts for CPs degradation. Notably, the amount-optimized heterojunctional microspheres display high photocatalytic activity for 2-CP degradation, even with 5-time enhancement compared to the classical TiO2 (P25). By means of the surface photovoltage spectra, photocurrent action spectra and CPs adsorption curves, the exceptional photoactivities are mainly attributed to the strong adsorption of 2-CP due to the complexation of Bi on Bi2O3 with empty orbitals and Cl of 2-CP with lone-pair electrons for efficiently modulating holes, and to the prolonged charge lifetime by transferring the photogenerated proper-energy-level electrons of β-Bi2O3 to the in-situ formed nano-BiPO4. It is confirmed that the photogenerated holes are dominant to induce the degradation of 2-CP on BiPO4/β-Bi2O3, and to initiate the selective conversion to the value-added intermediates like 4-acetoxyphenol on O2-free condition, along with H2 evolution.

Nitrogen-doped carbon nanofiber catalyst for ORR in PEM fuel cell stack: Performance, durability and market application aspects

A noble metal-free catalyst based on N-doped carbon nanofibers supported on graphite (N-CNF/Fe) was employed for the oxygen reduction at the cathode of a Nafion PEMFC with a commercial Pt/C anode. Obtained performance in pure H2 and O2 indicated the presence of significant mass-transport limitations when utilizing catalyst loading between 1 and 10 mg cm−2. Strategies to reduce the limitations were explored by optimization of the cathode ionomer content, catalyst loading and application technique. Pore-formers (Li2CO3, (NH4)2CO3 and polystyrene microspheres) were utilized to improve the mass-transport within the layer. A maximum of 72 mW cm−2 and 1400 A g−1 or 300 W g−1 at peak power was demonstrated. The catalyst was then applied to the cathode of a 10-cell fuel cell stack, and a 400-h durability test was conducted. The average cell voltage decay amounted to 162 μV h−1. Finally, a market application analysis was conducted to illustrate the potential and challenges of replacing platinum as cathode catalyst. It was shown that even a near-complete elimination of the cathode catalyst cost by substitution of platinum with a carbon-based catalyst cannot produce a cost competitive product unless both the performance and the durability of the fuel cell with the new catalyst are very close to that of the state-of the art Pt-based system.

Simultaneous Pd2+ doping and Pd metal deposition on (BiO)2CO3 microspheres for enhanced and stable visible light photocatalysis

The band structure and charge separation are two important factors that could largely determine the photocatalysis efficiency. In the present work, novel Pd/Pd2+ co-modified (BiO)2CO3 microspheres (Pd-BOC) were fabricated by a facile in situ one-pot hydrothermal process. The microstructure, interfical structure and electronic structure were investigated with a combined experimental and theoretical approach. The Pd-BOC was applied for photocatalytic removal of NO in air under visible light irradiation. The simultaneously Pd2+ doped and Pd metal deposited (BiO)2CO3 microspheres exhibited highly enhanced visible light photocatalytic activity and stability toward NO removal. DFT calculation indicated that the Pd2+ doping could narrow the band gap by taking part in the formation of valence band. The Pd deposition could improve the charge separation and transfer as revealed with surface photovoltage spectroscopy and transient photocurrent density measurement. These favorable two factors contributed to the enhanced visible light absorption and promoted charge separation, which led to dramatically enhanced visible light activity. The present work could provide new perspectives in co-modification of photocatalysts for high-performance applications.

Mechanism of visible light photocatalytic NO(x) oxidation with plasmonic Bi cocatalyst-enhanced (BiO)2CO3 hierarchical microspheres.

Semimetal bismuth (Bi), as an emerging non-noble metal-based cocatalyst and plasmonic photocatalyst, has attracted significant attention. In this work, a one-pot solvent-controlled synthesis strategy was utilized for the in situ-deposition of plasmonic Bi nanoparticles onto the surfaces of (BiO)2CO3 microspheres (BOC-WE) using bismuth citrate, sodium carbonate, and ethylene glycol as precursors. The introduction of the Bi nanoparticles has a pivotal effect on the morphology, optical and photocatalytic performance of the pristine (BiO)2CO3. The results indicated that the Bi nanoparticles were generated on the surface of (BiO)2CO3 microspheres via the in situ reduction of Bi(3+) by ethylene glycol. The Bi-deposited (BiO)2CO3 microspheres were used for the photocatalytic purification of NOx in air under visible light irradiation. Significantly, the BOC-WE samples exhibited a drastically promoted photocatalytic performance with a NOx removal ratio (η) of 37.2%, superior to pristine (BiO)2CO3 (η = 19.1%), outperforming other well-known visible light photocatalysts, such as C-doped TiO2 (η = 21.8%), BiOBr (η = 21.3%), BiOI (η = 14.9%) and C3N4 (η = 25.5%). The conspicuously enhanced photocatalytic capability can be attributed to the synergistic effects of the surface plasmon resonance (SPR) effect, increased visible light absorption and the efficient separation of electron-hole pairs induced by the Bi nanoparticles. The Bi nanoparticles can act as a non-noble metal-based cocatalyst for strengthening photocatalytic performance, which is similar to the behavior of noble metals (Au, Ag) in enhancing photocatalysis. The mechanism of visible light photocatalytic NOx oxidation was investigated. DMPO-ESR spin-trapping results demonstrated that hydroxyl radicals were confirmed to be the main active species for NOx photo-oxidation. Due to the SPR effect of Bi, the BOC-WE could produce more hydroxyl radicals than BOC, which was responsible for the enhanced NO photo-oxidation ability. Moreover, the BOC-WE photocatalysts showed high photochemical stability under repeated irradiation. This work demonstrates the feasibility of utilizing low cost Bi cocatalysts as a substitute for noble metals to enhance the performance of other photocatalysts. This work could not only provide new insights into the in situ fabrication of Bi/semiconductor nanocomposites, but also pave a new way for the modification of photocatalysts with non-noble metals as cocatalysts to achieve an enhanced performance for environmental and energetic applications.

Synergistic integration of thermocatalysis and photocatalysis on black defective (BiO)2CO3 microspheres

A novel environmental catalyst, black defective (BiO)2CO3 microspheres with efficient performance, was prepared by a vacuum heat treatment method.

In situ synthesis of a C-doped (BiO)2CO3 hierarchical self-assembly effectively promoting visible light photocatalysis

By combination of carbon doping and structural optimization, C-doped (BiO)2CO3 microspheres exhibited highly enhanced and stable visible photocatalytic activity.

Noble Metal-Like Behavior of Plasmonic Bi Particles as a Cocatalyst Deposited on (BiO)2CO3 Microspheres for Efficient Visible Light Photocatalysis

Novel plasmonic Bi nanoparticles deposited in situ in (BiO)2CO3 microspheres (Bi/BOC) were fabricated via a one-pot hydrothermal treatment of bismuth citrate, sodium carbonate, and thiourea. Different characterization techniques, including XRD, SEM, TEM, XPS, UV–vis DRS, PL, time-resolved fluorescence spectra, and photocurrent generation, were performed to investigate the structural and optical properties of the as-prepared samples. The results indicated that the Bi nanoparticles were generated on the surface of (BiO)2CO3 microspheres via the in situ reduction of Bi3+ by thiourea. The Bi nanoparticle deposited (BiO)2CO3 microspheres were employed for the photocatalytic removal of NO in air under visible light irradiation, and the sample exhibited a drastically enhanced photocatalytic activity and oxidation ability. The highly enhanced activity was attributed to the cooperative contribution of the surface plasmon resonance (SPR) effect, the efficient separation of electron–hole pairs, and the prolonged lif...

Effects of Morphology and Crystallinity on the Photocatalytic Activity of (BiO)2CO3 Nano/microstructures

(BiO)2CO3 microspheres and nanoparticles with different crystallinities have been successfully synthesized via a simple hydrothermal route. The as-prepared samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, UV–vis diffuse-reflectance spectroscopy, and nitrogen adsorption–desorption isotherms. The carbonate ions play a key role in controlling the morphology and crystallinity of (BiO)2CO3. The photocatalytic performance of the as-prepared (BiO)2CO3 samples was evaluated toward the removal of NO upon UV-, visible-, and simulated-solar-light irradiation. The results indicated that the photocatalytic activity of (BiO)2CO3 microspheres was higher than that of (BiO)2CO3 nanoparticles, which was mainly attributed to the synergistic effects of hierarchical structure, low crystallinity, and large surface areas.

Synthesis of flower-like, pinon-like and faceted nanoplates (BiO)2CO3 micro/nanostructures with morphology-dependent photocatalytic activity

The flower-like, pinon-like and faceted nanoplates (BiO)2CO3 micro/nanostructures were fabricated by a one-pot template-free method based on hydrothermal treatment of the aqueous mixture of bismuth citrate and sodium carbonate. The morphology of (BiO)2CO3 can be simply controlled by the reaction temperature. X-ray diffraction, scanning electron microscopy, UV–vis diffuse reflection spectra, and photoluminescence spectra were applied to analyze the microstructures and properties of the samples. The flower-like and pinon-like (BiO)2CO3 superstructures were hierarchically self-assembled by nanoplates and showed increased light absorption owing to the multiple light reflection between the nanoplates. The thickness of nanoplates was increased with the increasing reaction temperatures due to the preferred growth along the (110) plane. The (BiO)2CO3 with various micro/nanostructures showed morphology-dependent photocatalytic activity toward removal of aqueous RhB. The as-prepared flower-like (BiO)2CO3 microspheres exhibited highest photocatalytic activity due to the large surface area, increased light absorption, enhanced charge carriers separation, and special architectures of hierarchical nanoplates microspheres, exceeding that of the P25.

Hydrothermal formation of N-doped (BiO)2CO3 honeycomb-like microspheres photocatalysts with bismuth citrate and dicyandiamide as precursors

In order to develop efficient visible light driven photocatalysts for environmental application, novel N-doped (BiO)2CO3 honeycomb-like hierarchical microspheres were fabricated by an one-pot and template-free hydrothermal method, firstly using bismuth citrate and dicyandiamide as precursors. The as-prepared samples were characterized by XRD, SEM, FT-IR, PL, XPS, and UV–vis DRS in detail. The results indicated that the crystal structure and morphology of the samples can be tuned by hydrothermal reaction temperature. The source of nitrogen doping was from dicyandiamide, which also played a key role in hydrolyzing bismuth citrate to produce bismuth ions and citrate ions. The ammonium ions from the decomposition of dicyandiamide reacted with bismuth ions and carbonate ions from decomposition of citrate ions, producing in situ N-doped (BiO)2CO3 microspheres. The doped nitrogen substituted for oxygen in (BiO)2CO3 and was responsible for the band gap reduction of N-doped (BiO)2CO3. The as-prepared N-doped (BiO)2CO3 microspheres were applied for removal of NO in air and exhibited excellent visible light activity, exceeding that of N-doped TiO2 and C-doped TiO2. Time-dependent evolutions of crystal structure, morphology, chemical composition, and optical property were investigated systematically to reveal the growth mechanism of the honeycomb-like (BiO)2CO3 microspheres. The growth process involved multiple steps, including reaction, nucleation, crystallization, aggregation, and recrystallization. The proposed growth mechanism could provide new insights into the design and fabrication of hierarchical materials with advanced properties.

Ammonia induced formation of N-doped (BiO)2CO3 hierarchical microspheres: the effect of hydrothermal temperature on the morphology and photocatalytic activity

Three types of N-doped (BiO)2CO3 hierarchical microspheres composed of 2D nanosheets were fabricated by a one-pot template-free hydrothermal method from bismuth citrate and an ammonia solution under different hydrothermal temperatures. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, nitrogen adsorption–desorption isotherms, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and UV-visible diffuse reflectance spectroscopy. Here, the ammonia worked as a nitrogen resource, doping (BiO)2CO3, and a solvent hydrolyzing the bismuth citrate. The temperature was found to influence the thickness of the nanosheets and the morphology of the N-doped (BiO)2CO3 microspheres. The fascinating morphology of N-doped (BiO)2CO3, including rose-like, hydrangea flower-like and peony flower-like microspheres, can be controllably fabricated by adjusting the hydrothermal temperature. The photocatalytic activities of the as-prepared samples were evaluated towards the removal of NO under visible-light irradiation. Compared to pure (BiO)2CO3, the N-doped (BiO)2CO3 hierarchical microspheres showed enhanced photocatalytic activity. In addition, the hydrangea flower-like and the peony flower-like N-doped (BiO)2CO3 microspheres displayed admirable photocatalytic activity. Finally, a possible formation mechanism of the various morphologies of N-doped (BiO)2CO3 mediated by the reaction temperature was proposed. This work could provide new insights into the controlled synthesis of photocatalytic nano/microstructures for potential environmental applications.

One-pot template-free synthesis, growth mechanism and enhanced photocatalytic activity of monodisperse (BiO)2CO3 hierarchical hollow microspheres self-assembled with single-crystalline nanosheets

This work presents a one-pot template-free synthesis, detailed characterization, growth mechanism and application of well-defined uniform monodisperse (BiO)2CO3 hierarchical hollow microspheres self-assembled with single-crystalline nanosheets. The synthesis was conducted by hydrothermal treatment of bismuth citrate and sodium carbonate in water. Time-dependent evolutions of phase structure, composition, and morphology were investigated systematically and revealed that the growth mechanism of such novel structures involved a unique multistep pathway. First, near amorphous particles were produced through reaction, nucleation, crystallization, and aggregation processes. Then, stacked embryos of intermediate (BiO)4CO3(OH)2 microspheres with attached particles were produced due to dissolution and recrystallization. Subsequently, stacked uniform solid microspheres with small particles attached on edges were generated by the consumption of particles through Ostwald ripening. The stacked microspheres further grew to form monodisperse hierarchical microspheres with a hole in the center, like flower buds. Finally, uniform monodisperse (BiO)2CO3 hierarchical hollow microspheres were produced through layers splitting. The aggregation of the self-assembled nanosheets contributed to the formation of 3D hierarchical architecture containing mesopores, which is favorable for efficient reactants transport and photo-energy harvesting. Furthermore, the band gap structure of (BiO)2CO3 was revealed by the experimental method combined with density functional theoretical calculation. As expected, the novel (BiO)2CO3 hierarchical hollow microspheres exhibited enhanced photocatalytic activity due to the special hierarchical morphology, exceeding that of (BiO)2CO3 particles and commercial P25. The as-prepared uniform (BiO)2CO3 microspheres with well-defined hierarchical hollow structures are also ideal candidates for investigating their architecture-dependent performances in other areas, such as solar energy conversion, catalysis, electronics and so on.

Template-free fabrication and growth mechanism of uniform (BiO)2CO3 hierarchical hollow microspheres with outstanding photocatalytic activities under both UV and visible light irradiation

The morphology-controlled fabrication of nano-/microstructured functional materials has opened up new possibilities to enhance their physical and chemical properties and remains a great challenge. This work represents a one-pot template-free fabrication and growth mechanism of novel rose-like uniform (BiO)2CO3 hierarchical hollow microspheres, which are self-assembled by single-crystal nanosheets. The observation of time-dependent evolution of crystal structure and morphology revealed that the growth mechanism of such a novel structure might involve a unique multistep pathway. First, an amorphous particle was formed during a nucleation and aggregation process. Then, the intermediate (BiO)4CO3(OH)2 of embryonic stacked buds with attached particles were produced due to Ostwald ripening. The driving force for the formation of such embryonic structure is the intrinsic dipole field introduced by the nanosheets as a result of selective adsorption of the citrate ions on some polar surfaces of the nanoparticles. Subsequently, all the particles were consumed and (BiO)4CO3(OH)2 crystals started to transform to (BiO)2CO3 phase by means of repeated reaction-dissolution-recrystallization process in a homocentric layer-by-layer growth style, where carbonate ions substituted OH− groups. Monodisperse buds were then generated and the size of the hollow in the center becomes smaller to reduce surface energy. Finally, all (BiO)4CO3(OH)2 transformed to (BiO)2CO3 phase and uniform monodisperse (BiO)2CO3 roses were produced through layers splitting driven by the OH− group deintercalating from the interlayer spaces of (BiO)4CO3(OH)2. More interestingly, the novel (BiO)2CO3 microspheres exhibited outstanding activities under both UV and visible light irradiation for indoor NO removal, far exceeding that of commercial P25, synthetic C-doped TiO2 and (BiO)2CO3 with particle morphology due to the special hierarchical morphology and band gap structure.