Shape-dependent Photocatalytic Activity Research Articles

Size- and shape-dependent photocatalysis of porphyrin nanocrystals

Abstract

Facile synthesis of cubic Ag/Ag2O composites and its shape-dependent photo-catalytic activity examination

Ag/Ag2O polyhedrons, cubes and octahedron-like crystals have been fabricated via a simple chemical precipitation at room temperature. Based on experimental results, a reasonable formation mechanism was proposed, the concentration of NaOH may play a crucial role in the growth of Ag/Ag2O composites with different morphology. Subsequently, the as-synthesized samples were used in the photo-catalytic degradation of methyl orange to explore its photo-catalytic performance. It was found that the cubic Ag/Ag2O exhibited the highest photo-catalytic activity with almost 100% degradation efficiency in 50 min, which may due to the cubic Ag/Ag2O has strong visible light absorption properties, tremendous amount of free radicals and high separation rate of electron–hole pairs. Furthermore, the photo-induced free radicals were measured by electron paramagnetic resonance (EPR) measurement. Research demonstrates that the ⋅O2− and ⋅OH radicals are the predominant active species. And the feasible mechanism of photo-catalytic degradation is further discussed in detail.

Constructing TiO2 nanoparticles patched nanorods heterostructure for efficient photodegradation of multiple organics and H2 production

Morphology and exposed facets controlled synthesis of TiO2 has attracted numerous interests due to their fascinating shape-dependent photocatalytic activity, while it still remains in a great challenge to construct TiO2 nanocrystals with surface heterojunction. Here we innovatively constructed a heterostructure of TiO2 nanoparticles patched nanorods (i.e., NP/NR), where the NP and NR were predominately enclosed with the {101} and {100} facets, respectively. Since the highly dispersed nanoparticles (smaller than 10nm) were closely contacted with nanorods and their electronic band structures are mismatched, it is very likely to form a NP-{101}/NR-{100} surface heterojunction, which significantly facilitates the charge separation and transfer. The ratio of NP to NR is an important factor to govern the NP dispersion, the contact with NR, and the charge separation efficiency, thus determining their photocatalytic activity. Compared with the NP and NR alone, NP0.5/NR0.5 has the optimum ratio and shows an excellent cycling capability for methyl orange degradation (99% retention over 6 cycles) and superior activity for both the photodegradation of multiple organics (2 times faster) and water splitting to H2 (over 10 times enhancement). A possible charge transfer mechanism on NP-{101}/NR-{100} surface heterojunction has also been proposed to understand the relationship between materials structure and performance. Together with the mechanism study, the nanostructure innovation will advance the development of functional materials for renewable energy and sustainable environment.

3D Flowerlike α-Fe2O3@TiO2 Core–Shell Nanostructures: General Synthesis and Enhanced Photocatalytic Performance

The 3D flowerlike α-Fe2O3@TiO2 core–shell nanocrystals with thorhombic, cubic, and discal morphologies are synthesized for photocatalytic application. α-Fe2O3 nanocrystals were prepared via a Cu2+, Zn2+, and Al3+ ion-mediated hydrothermal route. The α-Fe2O3@TiO2 core–shell nanocrystals are obtained via a hydrothermal and annealing process. The shape-dependent photocatalytic activities of these as-obtained α-Fe2O3@TiO2 core–shell nanocrystals are measured. The results reveal that the discal α-Fe2O3@TiO2 nanocrystals exhibit the best photocatalytic activity relative to the other two core–shell nanocrystals because the discal α-Fe2O3 nanocrystals possess more rough surface and surface defects. The fast interfacial charge-transfer process and the wide spectral response could be the driving force for the enhanced photocatalytic performance. These core–shell architectures provide a positive example for synthesis of novel composite nanomaterial.

Synthesis of cuprous oxide with morphological evolution from truncated octahedral to spherical structures and their size and shape-dependent photocatalytic activities

In this study, a facile room-temperature solution-chemical route has been developed to synthesize Cu2O crystals with various sizes and morphologies. Adjustment of feeding speed of the aqueous mixture of polyvinyl pyrrolidone (PVP) and ascorbic acid (AA) enables the Cu2O crystal morphology and size evolution. It is also interesting to find that, simple alteration of the feeding speed of AA aqueous solution enables the size of Cu2O crystals evolved, while the morphology of Cu2O crystals keep unchanged. These Cu2O crystals samples were used as photocatalysts for the decomposition of methyl orange (MO) under visible light irradiation. The results show that Cu2O spiny spheres with hierarchical structure exhibited superior photocatalytic activity compared with truncated octahedrons and spheres. In addition, the photocatalytic activity of truncated octahedral Cu2O can be greatly improved by decreasing the size of Cu2O particles. The work demonstrated a novel strategy for the shape and size-controlled synthesis of Cu2O crystals with superior photocatalytic activities.

Toward Facet Engineering of CdS Nanocrystals and Their Shape-Dependent Photocatalytic Activities

Controlling the shape or morphology of semiconductor nanocrystals is central to their enhanced physical and chemical properties. Herein, using CdS as a model photocatalyst, we demonstrate that the crystal habit of a visible-light-active semiconductor can be quantitatively controlled through synthesis kinetics. Growth rate control of {0001} facets (r1) and {1011} facets (r1′) of CdS nanocrystals was achieved by simply employing a syringe pump, which enables us to finely tune the crystal shape from nanocones, to nanofrustums, and further to nanoplates. These shape-controlled samples, showing altered proportions of {0001} to {1011} facets, were used to investigate the crystal-facet dependence of solar hydrogen production. The results indicate that CdS nanoplates with the largest {0001} facets showed the highest photocatalytic activity. This work not only advances our knowledge on the growth mechanism of semiconductor crystals but also illustrates a robust method to targeted crystal design of semiconductors...

Morphology-controlled self-assembly and synthesis of photocatalytic nanocrystals.

Abilities to control the size and shape of nanocrystals in order to tune functional properties are an important grand challenge. Here we report a surfactant self-assembly induced micelle encapsulation method to fabricate porphyrin nanocrystals using the optically active precursor zinc porphyrin (ZnTPP). Through confined noncovalent interactions of ZnTPP within surfactant micelles, nanocrystals with a series of morphologies including nanodisk, tetragonal rod, and hexagonal rod, as well as amorphous spherical particle are synthesized with controlled size and dimension. A phase diagram that describes morphology control is achieved via kinetically controlled nucleation and growth. Because of the spatial ordering of ZnTPP, the hierarchical nanocrystals exhibit both collective optical properties resulted from coupling of molecular ZnTPP and shape dependent photocatalytic activities in photo degradation of methyl orange pollutants. This simple ability to exert rational control over dimension and morphology provides new opportunities for practical applications in photocatalysis, sensing, and nanoelectronics.

Enhanced photocatalytic CO₂-reduction activity of anatase TiO₂ by coexposed {001} and {101} facets.

Control of TiO2 crystal facets has attracted enormous interest due to the fascinating shape-dependent photocatalytic activity of this material. In this work, the effect of the ratio of {001} and {101} facets on the photocatalytic CO2-reduction performance of anatase TiO2 is reported. A new "surface heterojunction" concept is proposed on the basis of the density functional theory (DFT) calculations to explain the difference in the photocatalytic activity of TiO2 with coexposed {001} and {101} facets.

Determination of reactive oxygen species from ZnO micro-nano structures with shape-dependent photocatalytic activity

ZnO micro/nano structures with different morphologies have been prepared by the changing solvents used during their synthesis by solvothermal reaction. Three typical shapes of ZnO structures including hexagonal, bell bottom like and multi-pod formed and were characterized by scanning electron microscopy and X-ray diffraction. Multi pod like ZnO structures exhibited the highest photocatalytic activity toward degradation of methyl orange. Using electron spin resonance spectroscopy coupled with spin trapping techniques, we demonstrate an effective way to identify precisely the generation of hydroxyl radicals, superoxide and singlet oxygen from the irradiated ZnO multi pod structures. The type of reactive oxygen species formed was predictable from the band gap structure of ZnO. These results indicate that the shape of micro-nano structures significantly affects the photocatalytic activity of ZnO, and demonstrate the value of electron spin resonance spectroscopy for characterizing the type of reactive oxygen species formed during photoexcitation of semiconductors.

Shape-dependent photocatalytic activity of Bi5O7I caused by facets synergetic and internal electric field effects

The shape-dependent photocatalytic activity of Bi5O7I is caused by facets synergetic and internal electric field effects.

Controllable microwave and ultrasonic wave combined synthesis of ZnO micro-/nanostructures in HEPES solution and their shape-dependent photocatalytic activities

Size- and morphology-controlled zinc oxide (ZnO) micro-/nanostructures have been successfully synthesized via a facile and rapid microwave and ultrasonic wave combined method in HEPES solution (HEPES=2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid). The as-prepared ZnO products are characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and UV–vis diffuse reflection spectroscopy (DRS). Various morphologies of ZnO products, including grenade-like, column-like, spindle-like, rod-like, shuttle-like and flower-like micro-/nanostructures are obtained, which are strongly dependent on Zn/HEPES moral ratio, pH value and Zn precursor. It is found that HEPES plays a crucial role in the formation of ZnO micro-/nanostructures with controllable size and morphology. The photocatalytic activities of the prepared ZnO micro-/nanostructures are evaluated by degradation of methylene blue (MB) under UV light irradiation, among which spindle-like ZnO microstructures exhibit superior photocatalytic activity compared with other ZnO products.

Controllable synthesis and shape-dependent photocatalytic activity of ZnO nanorods with a cone and different aspect ratios and of short-and-fat ZnO microrods by varying the reaction temperature and time

ZnO nanorods with a cone and different aspect ratios and short-and-fat ZnO microrods were synthesized via a hydrothermal reaction of Zn with Zn(CH3COO)2 and H2O. The control over these ZnO nanocrystals with a wurtzite structure and different shapes was achieved by adjusting only the reaction temperature and time. A possible kinetic mechanism was proposed to account for the growth of these ZnO nanocrystals with different shapes. Photocatalytic activities of ZnO nanocrystals with distinctive shapes in the degradation of methyl orange were investigated. The results indicate that the photocatalytic ability of the ZnO nanorods with a cone and different aspect ratios is stronger than that of the short-and-fat microrods.