Photocatalytic reductive destruction of azo dyes by polyoxometallates: Naphthol blue black

Photocatalytic degradation of naphthol blue from Batik waste using functionalized TiO2-based composites

This work provides a first-time comparative study examining the photocatalytic activity of functionalized TiO₂-based composites to eliminate naphthol blue in Batik wastewater. Reduced graphene oxide (RGO) was synthesized by oxidizing solid graphite using the Hummers' method followed by sonication and reduction. N-doped TiO₂ (N-TiO₂) was synthesized from titanium tetrachloride (TiCl₄) and urea (CH₄N₂O) precursors by the sol-gel method. N-TiO₂ modified RGO (RGO/NT) was synthesized using a hydrothermal method from N-TiO₂ and RGO. Prepared TiO₂-based composites and commercial TiO₂, for comparison were characterized using Fourier transform infrared spectrometer (FTIR), X-Ray diffractometer (XRD), scanning electron microscope-energy dispersive X-ray (SEM-EDX), and UV-Vis diffuse reflectance spectrometer (UV-Vis DRS). FTIR characterization indicated Ti-N bonding in N-TiO₂ and RGO/NT. XRD patterns showed that commercial TiO₂ had a rutile phase, while N-TiO₂ and RGO/NT had an anatase phase with crystal sizes of 30.09, 16.28, and 12.02 nm, respectively. SEM results displayed the presence of small and glossy white N-TiO₂ dispersed on the surface of RGO. Characterization using UV-Vis DRS showed that the band gap energy values for TiO₂, N-TiO₂, and RGO/NT were 3.25, 3.12, and 3.08 eV with absorption regions at the wavelengths of 382, 398, and 403 nm, respectively. The highest photocatalytic activity for RGO/NT for degrading naphthol blue was obtained at pH 5, with a photocatalyst mass of 60 mg, and an irradation of 15 min. Photocatalytic degradation by RGO/NT on Batik wastewater under visible light showed higher effectivity than under UV light.

Investigation of applicability of Electro-Fenton method for the mineralization of naphthol blue black in water

In this study, mineralization and color removal performance of electro-Fenton method were examined in water containing naphthol blue black (NBB), a diazo dye. NBB was totally converted to intermediate species in a 15-min electrolysis at 60 mA, but complete de-colorization took 180 min. A very high oxidation rate constant ((3.35 ± 0.21) x 10¹⁰ M^-1s^-1) was obtained for NBB, showing its high reactivity towards hydroxyl radicals. A very high total organic carbon (TOC) removal value (45.23 mg L^-1) was obtained in the first 60 min of the electro-Fenton treatment of an aqueous solution of NBB (0.25 mM) at 300 mA, indicating the mineralization efficiency of the electro-Fenton method. Mineralization current efficiency values obtained at 300 mA gradually decreased from 24.18% to 4.47% with the electrolysis time, indicating the presence of highly parasitic reactions. Gas chromatography-mass spectrometry analyses revealed that the cleavage of azo bonds of NBB led to formation of different aromatic and aliphatic oxidation intermediates. Ion chromatography analysis showed that ammonium, nitrate and sulfate were the mineralization end-products. The concentration of sulfate ion reached to its quantitative value at the 4th h of electrolysis. On the other hand, the total concentration of ammonium and nitrate ions reached to only 61% of the stoichiometric amount of initial nitrogen after a 7 h electrolysis. Finally, it can be said that the electro-Fenton method is a suitable and efficient method for the removal of NBB and its intermediates from water.

Electrospun H4SiW12O40/cellulose acetate composite nanofibrous membrane for photocatalytic degradation of tetracycline and methyl orange with different mechanism

H₄SiW₁₂O₄₀ (SiW₁₂)/cellulose acetate (CA) composite nanofibrous membrane was prepared by electrospinning in which CA was employed as the support of SiW₁₂. Characterization with Fourier transformation infrared spectroscopy (FT-IR), Energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) indicated that SiW₁₂ has been successfully loaded into the CA membrane and its Keggin structure remained intact. The as-prepared composite membrane exhibited enhanced photocatalytic activity in the decomposition of tetracycline (TC) and methyl orange (MO) compared with pure SiW₁₂ under ultraviolet irradiation. The optimal mass ratio of SiW₁₂ to CA was 1:4, and the corresponding degradation efficiency for TC and MO was 63.8% and 94.6%, respectively. It is noteworthy that the degradation rate of MO increased more evidently than that of TC under the same conditions, which may be attributed to the different role that CA nanofibrous membrane played in the TC and MO photodegradation process. Besides providing more contact area between SiW₁₂ and the pollutant in TC photodegradation, CA membrane played an additional role that donated electron to SiW₁₂ in the MO degradation process, leading to a different photocatalytic mechanism with greatly enhanced degradation rate. Moreover, the composite membrane presented an excellent reusability, which was mainly ascribed to the water-insolubility of CA and the hydrogen bonds between CA and SiW₁₂. This work will be useful for the design of biopolymer-based membrane photocatalysts applied to antibiotics and dyes wastewater treatment.

The basket-type dimer layers based on tetra-electron reduced heteropoly blue directed by copper/nickel and strontium linkers

Two basket-type dimer layers have been prepared, which exhibit highly efficient catalytic ability for the degradation of typical dyes and bifunctional electrocatalytic behaviors.

Electrospinning preparation of a H4SiW12O40/polycaprolactam composite nanofibrous membrane and its greatly enhanced photocatalytic activity and mechanism

H₄SiW₁₂O₄₀/polycaprolactam (PA6) composite nanofibrous membranes with a minimum average diameter of ∼70 nm were prepared by an electrospinning technique.

Anchoring H3PW12O40 on 3-aminopropyltriethoxysilane modified graphene oxide: enhanced adsorption capacity and photocatalytic activity toward methyl orange

A novel PW₁₂/GO–NH₂ hybrid was obtained via an impregnation method, which exhibited enhanced adsorption capacity and photocatalytic activity.

High-efficiency photo- and electro-catalytic material based on a basket-like {Sr⊂P6Mo18O73} cage

The first 8-connected 2D layer based on basket-liked {Sr⊂P₆Mo₁₈O₇₃} cage was prepared, which exhibits high-efficient photodegradation ability for MB, RhB, and AP under visible and UV light, as well as bifunctional electrocatalytic behavior.

Synthesis and photoelectric properties of new Dawson-type polyoxometalate-based dimeric and oligomeric Pt(ii)-acetylide inorganic–organic hybrids

New polyoxometalate-based Pt(ii)-acetylide hybrids were prepared and their photoelectric properties as hybrid LB films were studied.

Functionalization and post-functionalization: a step towards polyoxometalate-based materials

Polyoxometalates (POMs) have remarkable properties and a great deal of potential to meet contemporary societal demands regarding health, environment, energy and information technologies. However, implementation of POMs in various functional architectures, devices or materials requires a processing step. Most developments have considered the exchange of POM counterions in an electrostatically driven approach: immobilization of POMs on electrodes and other surfaces including oxides, embedding in polymers, incorporation into Layer-by-Layer assemblies or Langmuir-Blodgett films and hierarchical self-assembly of surfactant-encapsulated POMs have thus been thoroughly investigated. Meanwhile, the field of organic-inorganic POM hybrids has expanded and offers the opportunity to explore the covalent approach for the organization or immobilization of POMs. In this critical review, we focus on the use of POM hybrids in selected fields of applications such as catalysis, energy conversion and molecular nanosciences and we endeavor to discuss the impact of the covalent approach compared to the electrostatic one. The synthesis of organic-inorganic POM hybrids starting from bare POMs, that is the direct functionalization of POMs, is well documented and reliable and efficient synthetic procedures are available. However, as the complexity of the targeted functional system increases a multi-step strategy relying on the post-functionalization of preformed hybrid POM platforms could prove more appealing. In the second part of this review, we thus survey the synthetic methodologies of post-functionalization of POMs and critically discuss the opportunities it offers compared to direct functionalization.

Straightforward synthesis of new polyoxometalate-based hybrids exemplified by the covalent bonding of a polypyridyl ligand

A new polyoxometalate-based organic-inorganic platform has been designed for further facile derivatization and covalent attachment of organic linkers; this is exemplified by the grafting of a polypyridyl ligand.