Chu-Ya Wang

Novel Bi12O15Cl6 Photocatalyst for the Degradation of Bisphenol A under Visible-Light Irradiation

Bisphenol A (BPA), a typical endocrine-disrupting chemical, is widely present in water environments, and its efficient and cost-effective removal is greatly needed. Among various physicochemical methods for BPA degradation, visible-light-driven catalytic degradation of BPA is a promising approach because of its utilization of solar energy. Bismuth oxychloride (BiOCl) is recognized as an efficient photocatalyst, but its band gap, >3.0 eV, makes it inefficient for solar energy utilization, especially for degrading nondye pollutants like BPA. Thus, preparation and application of bismuth oxychloride photocatalysts with an increased visible-light activity are essential. In this work, inspired by density functional theory calculations, a novel bismuth oxychloride photocatalyst, Bi12O15Cl6, was designed. The nanosheets were successfully synthesized using a facile solvothermal method followed by a thermal treatment route. The prepared Bi12O15Cl6 nanosheets had a favorable energy band structure and thus exhibited a superior visible-light photocatalytic activity for degrading BPA. The BPA degradation rate by the Bi12O15Cl6 was determined to be 13.6 and 8.7 times faster than those for BiOCl and TiO2 (P25), respectively. The photogenerated reactive species and degradation intermediates were identified, and the photocatalytic mechanism was elucidated. Furthermore, the as-synthesized Bi12O15Cl6 nanosheets remained stable in the photocatalytic process and could be used repeatedly, demonstrating their promising application in the degradation of diverse pollutants in water and wastewater.

Synthesis of BiOClxBr1−x Nanoplate Solid Solutions as a Robust Photocatalyst with Tunable Band Structure

The use of bismuth oxyhalides as photocatalysts has received extensive interest because of their high photocatalytic activity and stability. However, available methods for the synthesis of bismuth oxyhalides with tailored morphologies, well-defined facets, and tunable band gaps are still lacking. In this work, two-dimensional BiOClx Br1-x solid solution with exposed {001} facets and tunable band gaps were synthesized by using solvothermal methods. The BiOClx Br1-x solid solution nanoplates crystallized in a homogeneous crystal structure but possessed continuously tuned band gaps from 3.39 to 2.78 eV by decreasing the ratio of Cl/Br. Among the synthesized nanoplates, the BiOCl0.5 Br0.5 sample exhibited the highest photocatalytic activity for degrading Rhodamine B (RhB), a typical organic pollutant, under visible light. The highest photoactivity of the BiOCl0.5 Br0.5 sample was attributed to a synergetic effect of higher surface area, facets exposed, and optimized band structure. The results are of profound significance for the design of novel photocatalyst materials.

Fabrication of BiOBrxI1−x photocatalysts with tunable visible light catalytic activity by modulating band structures

A series of BiOBrxI1−x solid solutions were explored as novel visible light-sensitive photocatalysts. These BiOBrxI1−x solid-solution photocatalysts grew into two-dimensional nanoplates with exposed (001) facets and possessed continuously modulated band gaps from 2.87 to 1.89 eV by decreasing the Br/I ratio. The photocatalytic activities of these samples were measured, and the samples exhibited visible light-driven activities for the degradation of Rhodamine B (RhB). In particular, BiOBr0.8I0.2 exhibited the highest activity for the degradation of RhB. This result could be attributed to the balance between the effective light absorption and adequate redox potential. Additionally, investigations into the photocatalytic mechanism showed that the photodegradation of RhB over BiOBr0.8I0.2 solid-solution photocatalysts involved direct holes oxidation, in which the reaction that dominated during photocatalysis was determined by the potential of the valence band. Furthermore, a high stability in the photocatalytic activity of BiOBr0.8I0.2 was demonstrated by the cycling photocatalytic experiment and long-term irradiation, which might offer opportunities for its practical application as a catalyst.

Ni–Pd core–shell nanoparticles with Pt-like oxygen reduction electrocatalytic performance in both acidic and alkaline electrolytes

Fabrication of non-Pt high-performance oxygen reduction reaction (ORR) catalysts is essential for the application of fuel cells. In this work, monodisperse bimetallic Ni–Pd core–shell nanoparticles (NPs) with tunable shell compositions and contents were synthesized by using a modified one-pot colloidal approach and characterized. Also, the core shell structure dependence of their ORR performance without the interruption of an intermetallic phase was explored. The core–shell structured catalysts (Ni@Pd3/C NPs) exhibited a robust ORR activity and stability with a high onset potential of 0.99 V, a half-wave potential of 0.87 V and an average electron transfer number of 3.91 in 0.1 M HClO4. Furthermore, a high onset potential of 0.98 V, a half-wave potential of 0.86 V and an average electron transfer number of 3.98 were achieved in 0.1 M KOH. These results are comparable to those of the commercially available Pt/C catalysts. Moreover, the catalysts also maintained a good long-term cycling stability in both acidic and alkaline electrolytes. Thus, this work demonstrates that the ORR performance of the Ni–Pd alloy could be boosted through constructing the core–shell structure with a Pd-enriched surface and the Ni–Pd model alloy could be further applied to assess the role of the Pd-based core–shell structure in other electrochemical catalytic reactions.

Ammonia sensing by closely packed WO3 microspheres with oxygen vacancies

Ammonia (NH3), is a precursor for the formation of atmospheric fine particulate matter (PM2.5), and thus establishing efficient and cost-effective methods to detect ammonia emission is highly desired. Transition metal oxide semiconductors-based sensors for electrochemical gas sensing have been extensively explored. Among various types of semiconductors, tungsten oxide (WO3) possesses an anisotropic layered crystalline structure and is recognized as a promising material for gas sensing. However, the performance of commercial WO3 is unsatisfactory because of its high impedance and low charge transportation efficiency. Thus, the modification of commercial WO3 is needed to make it an efficient ammonia sensor material. In this work, closely packed WO3 microspheres with oxygen vacancies were synthesized successfully through a novel two-step hydrothermal route. Our WO3 showed a good selectivity to ammonia sensing, and its response intensity was 2.6 times higher than that of commercial WO3 because of its optimized conductivity. Moreover, the mechanism behind its robust ammonia sensing performance was elucidated. The effectiveness of the as-prepared WO3 microspheres for ammonia sensing also suggests a new strategy for modifying transition metal oxide materials.