Functionalization of polyoxometalates: towards advanced applications in catalysis and materials science

Today, sensing represents one of the key topics in current science and technology. Polyoxometalates (POMs), which are defined as early transition metal clusters, are considered as one of the most growing fields of research and development in sensing. This paper discusses the promising prospects of POMs in sensing. The paper starts with brief definitions about the formation of POMs. The two basic structures of POMs, Keggin and Dawson, as well as some combined structures are discussed. The interesting properties of POMs particularly as acid catalysts, in medicine, in redox chemistry and in magnetism are briefly mentioned. The main methods used for the deposition of POMs on solid supports (substrates) including chemisorption, electrodeposition, encapsulation in polymers and sol–gels, immobilization using the Langmuir–Blodgett process, layer by layer assemblies as well as deposition via formation of hybrid POM–organic moieties are discussed with their advantages and disadvantages. Finally, the potential applications of immobilized POMs on solid substrates as sensors for the detection and determination of analytes both in liquid and in the gas phase are addressed and compared.

Polyoxometalates: formation, structures, principal properties, main deposition methods and application in sensing

A water-insoluble and visible light induced polyoxometalate-based photocatalyst.

Immobilization of photo-Fenton catalysts on porous materials is crucial to the efficiency and stability for water purification. Here we report polydopamine (PDA)-coated porous substrates as a platform for in situ mineralizing β-FeOOH nanorods with enhanced photocatalytic performance under sunlight. The PDA coating plays multiple roles as an adhesive interface, a medium inducing mineral generation, and an electron transfer layer. The mineralized β-FeOOH nanorods perfectly wrap various porous substrates and are stable on the substrates that have a PDA coating. The immobilized β-FeOOH nanorods have been shown to be efficient for degrading dyes in water via a photo-Fenton reaction. The degradation efficiency reaches approximately 100% in 60 min when the reaction was carried out with H2O2 under visible light, and it remains higher than 90% after five cycles. We demonstrate that the PDA coating promotes electron transfer to reduce the electron–hole recombination rate. As a result, the β-FeOOH nanorods wrapped o...

Polydopamine-Coated Porous Substrates as a Platform for Mineralized β-FeOOH Nanorods with Photocatalysis under Sunlight.

The present work gives a critical overview of the recent progresses and new perspectives in the field of photocatalytic membranes (PMs) in photocatalytic membrane reactors (PMRs), thus highlighting the main advantages and the still existing limitations for large scale applications in the perspective of a sustainable growth. The classification of the PMRs is mainly based on the location of the photocatalyst with respect to the membranes and distinguished in: (i) PMRs with photocatalyst solubilized or suspended in solution and (ii) PMRs with photocatalyst immobilized in/on a membrane (i.e., a PM). The main factors affecting the two types of PMRs are deeply discussed. A multidisciplinary approach for the progress of research in PMs and PMRs is presented starting from selected case studies. A special attention is dedicated to PMRs employing dispersed TiO2 confined in the reactor by a membrane for wastewater treatment. Moreover, the design and development of efficient photocatalytic membranes by the heterogenization of polyoxometalates in/on polymeric membranes is discussed for applications in environmental friendly advanced oxidation processes and fine chemical synthesis.

https://www.mdpi.com/2227-9717/6/9/162/pdf

Photocatalytic Membranes in Photocatalytic Membrane Reactors

Novel catalytic membranes have been prepared by linking phosphotungstic acid H3PW12O40 (W12), a polyoxometalate having interesting properties as photocatalyst, on the surface of plasma-modified membranes. Porous flat-sheet membranes made of polyvinylidene fluoride (PVDF) have been prepared by a phase-inversion technique induced by a nonsolvent. These membranes have been modified by plasma treatments on the surface to graft N-containing polar groups that are able to act as binding sites with W12 (PVDF−NH2−W12). A comparison of the surface and bulk properties of the native and modified PVDF membranes has been reported. Catalytic activity of the PVDF−NH2−W12 membranes has been evaluated in the aerobic degradation reaction of phenol in water. Catalytic tests have been carried out in a membrane reactor operating in continuous mode. Better catalytic performances have been observed for the W12 heterogenized on PVDF membrane than for W12 in a homogeneous phase. Moreover, PVDF−NH2−W12 membranes have given proof of...

Linda C. Lopez

Papers

Heterogenization of polyoxometalates on the surface of plasma-modified polymeric membranes