In-situ solid phase thermal transformation of self-assembled melamine phosphotungstates produce efficient visible light photocatalysts

Application of polyoxometalates in photocatalytic degradation of organic pollutants

Organic pollutants are highly toxic, accumulative, and difficult to degrade or eliminate. As a low-cost, high-efficiency and energy-saving environmental purification technology, photocatalytic technology has shown great advantages in solving increasingly serious environmental pollution problems. The development of efficient and durable photocatalysts for the degradation of organic pollutants is the key to the extensive application of photocatalysis technology. Polyoxometalates (POMs) are a kind of discrete metal-oxide clusters with unique photo/electric properties which have shown promising applications in photocatalytic degradation. This review summarizes the recent advances in the design and synthesis of POM-based photocatalysts, as well as their application in the degradation of organic dyes, pesticides and other pollutants. In-depth perspective views are also proposed in this review.

Design of core-shell titania-heteropolyacid-metal nanocomposites for photocatalytic reduction of CO2 to CO at ambient temperature

The photocatalytic conversion of CO₂ not only reduces the greenhouse effect, but also provides value-added solar fuels and chemicals. Herein, we report the design of new efficient core-shell nanocomposites for selective photocatalytic CO₂ to CO conversion, which occurs at ambient temperature. A combination of characterization techniques (TEM, STEM-EDX, XPS, XRD, FTIR photoluminescence) indicates that the CO₂ reduction occurs over zinc species highly dispersed on the heteropolyacid/titania core-shell nanocomposites. These core-shell structures create a semiconductor heterojunction, which increases charge separation and the lifetime of charge carriers' and leads to higher electron flux. In situ FTIR investigation of the reaction mechanism revealed that the reaction involved surface zinc bicarbonates as key reaction intermediates. In a series of catalysts containing noble and transition metals, zinc phosphotungstic acid-titania nanocomposites exhibit high activity reaching 50 μmol CO g^-1 h^-1 and selectivity (73%) in the CO₂ photocatalytic reduction to CO at ambient temperature. The competitive water splitting reaction has been significantly suppressed over the Zn sites in the presence of CO₂.

Surface-oxygen vacancy defect-promoted electron-hole separation of defective tungsten trioxide ultrathin nanosheets and their enhanced solar-driven photocatalytic performance

Defective WO₃ ultrathin surface-engineered nanosheets are fabricated by a solvothermal and low-temperature surface hydrogenation reduction strategy. The obtained defective WO₃ ultrathin nanosheets with thicknesses of ∼4 nm possess a relatively large surface area of ∼25 m² g^-1. After surface engineering, the bandgap is narrowed to ∼2.48 eV due to the presence of surface oxygen vacancies, which further enhance the visible light absorption. The defective WO₃ ultrathin nanosheets exhibit excellent solar-driven photocatalytic degradation performance for the complete degradation of the highly-toxic metribuzin herbicide (∼100%). The first-order rate constant (k) of the defective WO₃ ultrathin nanosheets is ∼3 times higher than that of the pristine one. This can be ascribed to the formation of suitable surface-oxygen vacancy defects that promote the separation of photogenerated electron-hole pairs, and the two-dimensional ultrathin structure facilitating the surface engineering as well as furnishing a large number of surface active sites. Moreover, the defective WO₃ ultrathin nanosheets exhibit high stability because the photocatalytic activity remains almost unchanged after 10 cycles, making them favorable for practical applications. This work offers new insights into the fabrication of other high-performance ultrathin nanosheet oxide photocatalysts for environmental applications.