Application of polyoxometalates in photocatalytic degradation of organic pollutants

Multi-active photocatalysts of biochar-doped g-C3N4 incorporated with polyoxometalates for the high-efficient degradation of sulfamethoxazole

Sulfamethoxazole (SMX) is one of major antibiotic contaminants in current aqueous environment. In this paper, waste loofah and melamine were co-carbonized to prepare biochar-doped g-C3N4 (CCN) by a one-pot method and then combined with Co2PMo11VO40 (CoPMoV) using a binder to obtain the novel polyoxometalates (POMs) photocatalytic composites (CCN/CoPMoV). The incorporation of CoPMoV dramatically reduced the photogenerated carrier recombination and led to a small band gap. Under visible light, the synergetic activation from biochar, g-C3N4 and POMs can remove 98.5% of SMX (k = 0.215 min-1) in the peroxymonosulfate (PMS) system within 20 min and keep its high stability with the degradation of 88.9% after five cycles. Multi-active sites from CCN/CoPMoV are contributed to develop the most active species of SO4-∙, ·OH, 1O2, and h+. The validity in the degradation of SMX makes CCN/CoPMoV a promising and potential material for the removal of aqueous pollutants in the future.

Self-assembly of hard anions around cationic gold nanorods: potential structures for SERS

The placement of polyoxometalates next to the surface of noble metallic nanoparticles has been found to enhance the surface-enhanced Raman scattering (SERS) effect. The enhancement is believed to stem from either charge (electrostatic attraction) or chemical effects. Anisotropic gold nanorods are recognized as useful nanostructures for SERS, mainly due to the high electric field enhancement at their ends. The presented work examines the use of a polyoxometalate encapsulated gold nanorod for SERS, to assess whether the two enhancement pathways would be synergetic. For this, a gold nanorod-polyoxometalate composite was synthesized by coating cetyltrimethylammonium bromide-stabilized gold nanorods with a silicotungstic Keggin anion through electrostatic attraction. The structure was characterized, confirming that the nanorods have been fully encapsulated by the polyoxometalate. The SERS performance of the composite was assessed in solution using crystal violet as a SERS indicator, finding an analytical enhancement factor of 1.8 × 104 in colloidal solution. The enhancement mechanism was examined first by comparison to gold nanorods stabilized by a cetyltriethylammonium bromide bilayer, cationic thiol bound polyoxometalate, and polyelectrolyte coating. Next, composites made using polyoxometalates of different atomic composition and charge were examined. It was concluded that the polyoxometalate charge had a noticeable effect on the enhancement while the atomic composition did not. Furthermore, high enhancement is observed mainly in cases where the nanorod monolayer allows the sequestration of the dye molecule into the nanoparticle's ligand layer. The proposed mechanism therefore involves the negative charge of the polyoxometalate attracting the positively charged dye, and facilitating the sequestration of the dye within the ligand bilayer, closer to the nanorod's surface.

Recent advances in photocatalytic nanomaterials for environmental remediation: Strategies, mechanisms, and future directions

Innovative and efficient strategies are urgently needed for wastewater treatment and environmental remediation. The photocatalytic degradation properties of photo-responsive nanomaterials (NMs) have become a prime candidate due to their low negative impact and photo-adjustability. Photocatalytic NMs vary in their degradation of different pollutants depending on the type of synthetic material, excitation light source, and physicochemical properties. Essentially, photocatalytic NMs excited by light produce reactive oxygen species (ROS) or metal ions that can degrade complex structure pollutants. Therefore, this review summarises the recent advances of photocatalytic NMs in the environmental application within the last 3 years, focusing on the development schemes, structural analyses, photocatalytic mechanisms, and the degradation effects of dyes, antibiotics, pesticides, phenolic compounds, metals, hormones, and other contaminants. The limitations and future directions are also explained. This review hopes to provide a possible pathway for the subsequent development of novel and efficient photocatalytic NMs to cope with complex and variable polluted environments.

Assessing the Influence of Confinement on the Stability of Polyoxometalate-Functionalized Surfaces: A Soft Sequential Immobilization Approach for Electrochromic Devices

A functionalization process has been developed and the experimental conditions optimized allowing the immobilization of first-row transition metal (Mn+) containing polyoxometalates (POMs) with the formula [M(H2O)P2W17O61](10-n)- on transparent indium-tin oxide (ITO) electrodes for electrochromic applications. Both flat ITO grafted with 4-sulfophenyl moieties and sulfonate-functionalized vertically oriented silica films on ITO have been used as electrode supports to evaluate possible confinement effects provided by the mesoporous matrix on the stability of the modified surfaces and their electrochromic properties. Functionalization involved a two-step sequential process: (i) the immobilization of hexaaqua metallic ions, such as Fe(H2O)63+, onto the sulfonate-functionalized materials achieved through hydrogen bonding interactions between the sulfonate functions and aqua ligands (water molecules) coordinated to the metallic ions facilitating and stabilizing the attachment of the metallic ions to the sulfonated surfaces; (ii) their coordination to [P2W17O61]10- species to generate "in situ" the target [Fe(H2O)P2W17O61]7- moieties. Comparison of the characterized surfaces clearly evidenced a significant improvement in the long-term stability of the nanostructured [Fe(H2O)P2W17O61]7--functionalized silica films compared to the less constrained flat [Fe(H2O)P2W17O61]7--modified ITO electrodes for which a rapid loss of [P2W17O61]10- species was observed. Concordantly, the [Fe(H2O)P2W17O61]7- POM confined in the mesoporous films coated on ITO gave rise to much better and stable electrochromic properties, with a transmittance modulation of 40% at 515 nm.

Multi-stimuli-responsive polymer degradation by polyoxometalate photocatalysis and chloride ions

Photocatalytic polymer degradation based on harnessing the abundant light energy present in the environment is one of the promising approaches to address the issue of plastic waste. In this study, we developed a multi-stimuli-responsive photocatalytic polymer degradation system facilitated by the photocatalysis of a polyoxometalate [γ-PV2W10O40]5- in conjunction with chloride ions (Cl-) as harmless and abundant stimuli. The degradation of various polymers was significantly accelerated in the presence of Cl-, which was attributed to the oxidation of Cl- by the polyoxometalate photocatalysis into a highly reactive chlorine radical that can efficiently generate a carbon-centered radical for subsequent polymer degradation. Although organic and organometallic photocatalysts decomposed under the conditions for photocatalytic polymer degradation in the presence of Cl-, [γ-PV2W10O40]5- retained its structure even under these highly oxidative conditions.

Polyoxometalate nanocluster-infused triple IPN hydrogels for excellent microplastic removal from contaminated water: detection, photodegradation, and upcycling

Microplastic (MP) pollution pervades global ecosystems, originating from improper plastic disposal and fragmentation due to factors like hydrolysis and biodegradation. These minute particles, less than 5 mm in size, have become omnipresent, impacting terrestrial, freshwater, and marine environments worldwide. Their ubiquity poses severe threats to marine life by causing physical harm and potentially transferring toxins through the food chain. Addressing this environmental crisis necessitates a sustainable strategy. Our proposed solution involves a highly efficient copper substitute polyoxometalate (Cu-POM) nanocluster infused triple interpenetrating polymer network (IPN) hydrogel, comprising chitosan (CS), polyvinyl alcohol (PVA), and polyaniline (PANI) (referred to as pGel@IPN) for mitigating MP contamination from water. This 3D IPN architecture, incorporating nanoclusters, also enhances the hydrogel's photodegradation capabilities. Our scalable approach offers a sustainable strategy to combat MPs in water bodies, as demostrated by the adsorption behaviors on the hydrogel matrix under varying conditions, simulating real-world scenarios. Evaluations of physicochemical properties, mechanical strength, and thermal behavior underscore the hydrogel's robustness and stability. Detecting minute MP particles remains challenging, prompting us to label MPs with Nile red for fluorescence microscopic analysis of their concentration and adsorption on the hydrogel. The catalytic properties of POM within the hydrogel facilitate UV-induced MP degradation, highlighting a sustainable solution. Our detailed kinetics and isotherm studies revealed pseudo-first-order and Langmuir models as fitting descriptors for MP adsorption, exhibiting a high maximum adsorption capacity (Qm). Notably, pGel@IPN achieved ∼95% and ∼93% removal efficiencies for polyvinyl chloride (PVC) and polypropylene (PP) MPs at pH ∼ 6.5, respectively, also demonstrating reusability for up to 5 cycles. Post-end-of-life, the spent adsorbent was efficiently upcycled into carbon nanomaterials, effectively removing the heavy metal Cr(VI), exemplifying circular economy principles. Our prepared hydrogel emerges as a potent solution for MP removal from water, promising effective mitigation of the emerging pollutants of MPs while ensuring sustainable environmental practices.

Organoarsonates Enable Single-Site Condensation of Hexalacunary {P2W12} Polyoxotungstates

A systematic study of the condensation reactions of arylarsonic-functionalized [α-P2W12O48]14- units in acidic aqueous media identified that the specific presence of an amino group in the ortho position of the phenyl rings induces a dimerization process that allowed isolation of discrete dimeric polyanions [(o-H2N-C6H4-AsO3)4P4W24O85]14- (1) with an unprecedented polyoxometalate skeleton characterized by two seminal {P2W12} groups joined via a single W-O-W bridge. At the same time, addition of divalent transition metal ions (MnII, CoII, and NiII) in the reaction mixture directed a condensation process on a completely different pathway resulting in one-dimensional (1D) coordination polymers based on V-shaped [{M(H2O)4}P4W24O92(C6H6AsNO)2]14- polyanions (M = MnII (2), CoII (3), and NiII (4)). All polyanions were isolated as hydrated mixed potassium/dimethylammonium salts and thoroughly characterized in the solid state. 31P NMR studies showed that the discrete cluster 1 is comparatively stable in 1 M LiCl aqueous solution and thus represents a potential precursor for subsequent reactions.

Tungsten-based Lindqvist and Keggin type polyoxometalates as efficient photocatalysts for degradation of toxic chemical dyes

Photocatalytic dye degradation employing polyoxometalates (POMs) has been a research focus for several years. We report the facile synthesis of tungsten-based Lindqvist and Keggin-type POMs that degrade toxic chemical dyes, methyl orange (MO) and methylene blue (MB), respectively. The Lindqvist POM, sodium hexatungstate, Na2W6O19, degrades MO under 100 W UV light irradiation within 15 min, whereas the Keggin POM, Ag4PW11VO40, degrades MB under 20 W visible light source within 180 min. The effect of various operating parameters, such as photocatalyst concentration, pH, time, and initial dye concentration, were assessed in the degradation of both dyes. The photoelectrochemical performance of the as-synthesized polyoxometalates shows that the Ag4PW11VO40 shows 2.4 times higher photocurrent density than Na2W6O19 at a potential of 0.9 V vs. Ag/AgCl. Electrochemical impedance analysis reveals that Ag4PW11VO40 exhibits much lower charge transfer resistance as compared to Na2W6O19, which indicates facile charge transfer at the electrode-electrolyte interface. Further Mott-Schottky measurements reveal that both the catalysts possess n-type semiconductivity and the charge carrier concentration of Ag4PW11VO40 (5.89 × 1019 cm-3) is 1.4 times higher as compared to Na2W6O19 (4.25 × 1019 cm-3). This work offers a new paradigm for designing polyoxometalates suitable for efficient photocatalytic degradation of organic dyes.

A review of metal-organic framework (MOF) materials as an effective photocatalyst for degradation of organic pollutants

Water plays a vital role in all aspects of life. Recently, water pollution has increased exponentially due to various organic and inorganic pollutants. Organic pollutants are hard to degrade; therefore, cost-effective and sustainable approaches are needed to degrade these pollutants. Organic dyes are the major source of organic pollutants from coloring industries. The photoactive metal-organic frameworks (MOFs) offer an ultimate strategy for constructing photocatalysts to degrade pollutants present in wastewater. Therefore, tuning the metal ions/clusters and organic ligands for the better photocatalytic activity of MOFs is a tremendous approach for wastewater treatment. This review comprehensively reports various MOFs and their composites, especially POM-based MOF composites, for the enhanced photocatalytic degradation of organic pollutants in the aqueous phase. A brief discussion on various theoretical aspects such as density functional theory (DFT) and machine learning (ML) related to MOF and MOF composite-based photocatalysts has been presented. Thus, this article may eventually pave the way for applying different structural features to modulate novel porous materials for enhanced photodegradation properties toward organic pollutants.

Advances in Polyoxometalates as Electron Mediators for Photocatalytic Dye Degradation

The increasing concerns over the environment and the growing demand for sustainable water treatment technologies have sparked substantial interest in the field of photocatalytic dye removal. Polyoxometalates (POMs), known for their intricate metal-oxygen anion clusters, have received considerable attention due to their versatile structures, compositions, and efficient facilitation of photo-induced electron transfers. This paper provides an overview of the ongoing research progress in the realm of photocatalytic dye degradation utilizing POMs and their derivatives. The details encompass the compositions of catalysts, catalytic efficacy, and light absorption propensities, and the photocatalytic mechanisms inherent to POM-based materials for dye degradation are exhaustively expounded upon. This review not only contributes to a better understanding of the potential of POM-based materials in photocatalytic dye degradation, but also presents the advancements and future prospects in this domain of environmental remediation.

Highly efficient degradation of polyesters and polyethers by decatungstate photocatalysis

Photocatalytic polymer degradation has been recognized as a promising solution to the global disposal of waste plastics. In this work, we revealed that various polyesters and polyethers were efficiently degraded in the presence of a polyoxometalate photocatalyst, specifically, decatungstate ([W10O32]4-, W10). A catalytic amount of W10 initiated the degradation of various polyesters and polyethers under photo-irradiation with a xenon lamp (λ > 350 nm) using O2 (1 atm) as the oxidant in acetonitrile or water. Moreover, this system can promote polymer degradation even under sunlight. The degradation efficiency, assessed from the degradation rate (Mw0 - Mw)/Mw0 (%) (where Mw0 is the Mw before the reaction), of W10 was notably higher than those of previously reported photocatalysts such as titanium oxide, other polyoxometalates, organometallic compounds, and organic dyes.

Adsorption and Photocatalytic Degradation of Methylene Blue on TiO2 Thin Films Impregnated with Anderson-Evans Al-Polyoxometalates: Experimental and DFT Study

In this work, we fabricated a TiO2 thin film, and the same film was modified with an Anderson aluminum polyoxometalate (TiO2-AlPOM). Physical-chemical characterization of the catalysts showed a significant change in morphological and optical properties of the TiO2 thin films after surface modification. We applied the kinetic and isothermal models to the methylene blue (MB) adsorption process on both catalysts. The pseudo-second order model was the best fitting model for the kinetic results; qe (mg/g) was 11.9 for TiO2 thin films and 14.6 for TiO2-AlPOM thin films, and k2 (g mg-1 min-1) was 16.3 × 10-2 for TiO2 thin films and 28.2 × 10-2 for TiO2-AlPOM thin films. Furthermore, the Freundlich model was suitable to describe the isothermal behavior of TiO2, KF (5.42 mg/g), and 1/n (0.312). The kinetics of photocatalytic degradation was fitted using the Langmuir-Hinshelwood model; kap was 7 × 10-4 min-1 for TiO2 and 13 × 10-4 min-1 for TiO2-AlPOM. The comparative study showed that TiO2 thin films reach a 19.6% MB degradation under UV irradiation and 9.1% MB adsorption, while the TiO2-AlPOM thin films reach a 32.6% MB degradation and 12.2% MB adsorption on their surface. The surface modification improves the morphological, optical, and photocatalytic properties of the thin films. Finally, the DFT study supports all the previously shown results.

Two New Compounds Based on Bi-Capped Keggin Polyoxoanions and Cu-Bpy Cations Contain Both CuII and CuI Complexes: Synthesis, Characterization and Properties

Two inorganic-organic hybrid complexes based on bi-capped Keggin-type cluster, {([Cu^II(2,2'-bpy)₂]₂[PMo^VI₈V^V₂V^IV₂O₄₀(V^IVO)₂])[Cu^I(2,2'-bpy)]}∙2H₂O (1) and {[Cu^II(2,2'-bpy)₂]₂[SiMo^VI_8.5Mo^V_2.5V^IVO₄₀(V^IVO)₂]}[Cu^I_0.5(2,2'-bpy)(H₂O)_0.5] (2) (bpy = bipyridine), had been hydrothermally synthesized and structurally characterized by elemental analysis, FT-IR, TGA, PXRD and X-ray single-crystal diffraction analysis. Compound 1 consists of a novel 1-D chain structure constructed from [Cu^I(2,2'-bpy)]⁺ unit linking bi-supported POMs anion {[Cu^II(2,2'-bpy)₂]₂[PMo^VI₈V^V₂V^IV₂O₄₀(V^IVO)₂]}^-. Compound 2 is a bi-capped Keggin cluster bi-supported Cu-bpy complex. The main highlights of the two compounds are that Cu-bpy cations contain both Cu^I and Cu^II complexes. Furthermore, the fluorescence properties, the catalytic properties, and the photocatalytic performance of compounds 1 and 2 have been assessed, and the results show that both compounds are active for styrene epoxidation and degradation and adsorption of Methylene blue (MB), Rhodamine B (RhB) and mixed aqueous solutions.

Novel morphological mono-metallic substituted polyoxometalate immobilized 3-(aminopropyl)-imidazole photocatalysts for visible-light driven degradation: Anti-bacterial activity, membrane bacterial activity applications

A novel keggin-type tetra-metalates substituted polyoxometalate was functionalized by 3-(aminopropyl)-imidazole (3-API) supporting a ligand substitution method. In this paper, polyoxometalate (POMs) (NH₄)₃ [PMo₁₂O₄₀] and transition metal substituted of (NH₄)₃ [{PM^IVMo₁₁O₄₀}.(H₂O)] (M = Mn, V) are used as one of the adsorbents. The 3-API/POMs hybrid have been synthesized and used as adsorbent for the photo-catalysis of azo-dye molecule degradation after visible-light illumination as a simulated organic contaminant in water. The transition metal (M = M^IV, V^IV) substituted keggin-type anions (MPOMs) were synthesized, which reveals the degradation of methyl orange (MO) of about 94.0 % and 88.6 %. Immobilizing high redox ability POMs as an efficient acceptor of photo generated electron, on metal 3-API. In the presence of visible light irradiation result reveals that 3-API/POMs (89.9 %) have incredibly achieved after certain irradiation time and at specific conditions (3)-API/POMs; photo-catalysts dose = 5mg/100 ml, pH = 3 and MO dye concentration = 5 ppm). As the surface of POM catalyst has strong absorption of azo-dye MO molecule engaged as a molecular exploration through photo catalytic reactant. From the SEM images it is clear that the synthesized POMs based materials and POMs conjugated MO have varieties of morphological changes observed such as flakes, rods and spherical like structures. Anti-bacterial study reveals that the process of targeted microorganism occur higher activity against pathogenic bacterium for 180 min of visible-light irradiation is measured in terms of zone of the inhibition. Furthermore, the photo catalytic degradation mechanism of MO using POM, metaled POMs and 3-API/POMs also has been discussed.

Synthesis and comparison of three photocatalysts for degrading tramadol as an analgesic and widely used drug in water samples

Tramadol is an analgesic drug that is mainly excreted in the urine. The entry of Tramadol into water samples causes their biological contamination. Therefore, three catalysts such as bismuth ferrite, cobalt-doped bismuth ferrite, and a magnetized Keggin type of polyoxometalate (α-Fe₂O₃@phosphotungstic acid), were synthesized as photocatalysts to degrade Tramadol in water samples. The morphology and properties of the prepared photocatalysts were evaluated using several techniques. Effects of several factors, including tramadol concentration, pH, hydrogen peroxide concentration, and photocatalyst amount, were studied and optimized by a design experiment procedure based on Box-Behnken design for reducing the number of experiments and cost and investigating the interactions between factors in the photocatalytic degradation process of Tramadol. These factors were optimized for each prepared photocatalyst individually. Under the optimum conditions, the percentages of tramadol degradation and kinetics of the degradation process were evaluated in the presence of each photocatalyst. The tramadol degradation percentages using bismuth ferrite, cobalt-doped bismuth ferrite, and α-Fe₂O₃ @phosphotungstic acid were 81.10% for 120 min, 90.63% for 80 min, and 91.32% for 80 min, respectively. The rate constants of tramadol degradation were 0.0145, 0.0329, and 0.0312 min^-1 for bismuth ferrite, cobalt-doped bismuth ferrite, and α-Fe₂O₃ @phosphotungstic acid, respectively. The results indicated the highest percentage of tramadol degradation and rate of the degradation process were obtained using α-Fe₂O₃ @phosphotungstic acid and cobalt-doped bismuth ferrite, respectively.

A Novel Tri-Functionality pH-Magnetic-Photocatalytic Hybrid Organic-Inorganic Polyoxometalates Augmented Microspheres for Polluted Water Treatment

The severe water pollution from effluent dyes threatens human health. This study created pH-magnetic-photocatalytic polymer microspheres to conveniently separate the photocatalyst nanoparticles from the treated water by applying an external magnetic field. While fabricating magnetic nanoparticles' (MNPs) microspheres, incorporating 0.5 wt.% iron oxide (Fe₃O₄) showed the best magnetophoretic separation ability, as all the MNPs microspheres were attracted toward the external magnet. Subsequently, hybrid organic-inorganic polyoxometalates (HPOM), a self-synthesized photocatalyst, were linked with the functionalized magnetic nanoparticles (f-MNPs) to prepare augmented magnetic-photocatalytic microspheres. The photodegradation dye removal efficiency of the augmented magnetic-photocatalytic microspheres (f-MNPs-HPOM) was then compared with that of the commercial titanium dioxide (TiO₂) photocatalyst (f-MNPs-TiO₂). Results showed that f-MNPs-HPOM microspheres with 74 ± 0.7% photocatalytic removal efficiency better degraded methylene orange (MO) than f-MNPs-TiO₂ (70 ± 0.8%) at an unadjusted pH under UV-light irradiation for 90 min. The excellent performance was mainly attributed to the lower band-gap energy of HPOM (2.65 eV), which required lower energy to be photoactivated under UV light. The f-MNPs-HPOM microspheres demonstrated excellent reusability and stability in the photo-decolorization of MO, as the microspheres retained nearly the same removal percentage throughout the three continuous cycles. The degradation rate was also found to follow the pseudo-first-order kinetics. Furthermore, f-MNPs-HPOM microspheres were pH-responsive in the photodegradation of MO and methylene blue (MB) at pH 3 (acidic) and pH 9 (alkaline). Overall, it was demonstrated that using HPOM photocatalysts in the preparation of magnetic-photocatalytic microspheres resulted in better dye degradation than TiO₂ photocatalysts.

Keggin Cluster Modulated Photocatalytic Activity of Aryl Sulfonium Polyoxometalate Hybrids toward Dichromate Reduction

Dichromate (Cr₂O₇^2-) ion having chromium in its +6 oxidation state is a carcinogen and a potential threat to humans and aquatic life. The photocatalytic reduction of toxic Cr(VI) species into less toxic Cr(III) is an important target in heterogeneous catalysis. In this work, the catalytic activities of a series of Keggin cluster-based aryl sulfonium polyoxometalate hybrids, (FPDS)₃[PMo₁₂O₄₀] (1), (FPDS)₃[PW₁₂O₄₀] (2), (FPDS)₄[SiMo₁₂O₄₀] (3), and (FPDS)₄[SiW₁₂O₄₀] (4), toward the photocatalytic reduction of Cr(VI) have been analyzed and compared. Here, we used the aryl sulfonium counterions to modulate the POM cluster's solubility in water and stabilize the photogenerated e^--h⁺ pair on the cluster. All of the hybrids 1-4 catalyzed the reduction of Cr(VI) to Cr(III) under ultraviolet (UV) irradiation, and their photocatalytic efficiencies followed the order hybrid 1 > hybrid 3 > hybrid 2 > hybrid 4, with the rate-constant values of 0.048, 0.0056, 0.0035, and 0.0028 min^-1, respectively. Hybrid 1 with [PMo₁₂O₄₀]^3- Keggin cluster exhibited the best photocatalytic activity in the series yielding a 99% reduction in 120 min. The reasons behind the best photocatalytic activity of hybrid 1 are identified as its low band gap, less charge recombination, and fast photoresponse. The electron-trapping analyses performed using AgNO₃ revealed electrons as the main reactive species responsible for the photocatalytic reduction of Cr(VI). A plausible photocatalytic mechanism has also been proposed based on electron-trapping experiments. The present study shows that aryl sulfonium Keggin hybrids can function as efficient photocatalysts for Cr(VI) reduction, and their catalytic efficiency varies with the nature of the Keggin cluster.

Multicomponent Composite Membrane with Three-Phase Interface Heterostructure as Photocatalyst for Organic Dye Removal

A multicomponent composite membrane (P-S-T/C) with three-phase interface heterostructure is ingeniously designed. A polydopamine (PDA)-modified conductive carbon fiber cloth (CFC) is used as the substrate. Activated poly(vinylidene fluoride) (PVDF) with titanium dioxide (TiO2) and a silicon dioxide (SiO2) aerogel are electrospun as the top layer. The three-phase interface heterostructure was formed by TiO2, conductive CFC, and the SiO2 aerogel. Its photocatalytic performance is validated by photodegradation of organic dyes in a low-oxygen (O2) water environment. On combining with the capillary condensation of a bilayer structure, P-S-T/C exhibits excellent removal capability for anionic and cationic dyes. Moreover, P-S-T/C exhibits excellent stability and recyclability under simulated sunlight. The mechanism study indicates that the separated photogenerated carriers diffuse to the composite membrane surface rapidly on the three-phase interface of P-S-T/C. The abundant O2 adsorbed on the porous SiO2 aerogel surface acts as an electron (e-)-trapping agent, which can also decrease the work function of the composite materials. Superoxide radicals (•O2 -) play a dominant role in the reaction of photodegradation supported by a free radical-trapping experiment. This work paves a way to design a membrane with photocatalytic performance by constructing the interface heterostructure.

A Polyniobotungstate-Based Hybrid for Visible-Light-Induced Phosphorylation of N-Aryl-Tetrahydroisoquinoline

A new organic-inorganic hybrid based on a Nb/W mixed-addendum polyoxometalate with the formula H₁₄[(Co(H₂O)₃)₂(C₁₀H₈N₂)₄(P₄W₃₀Nb₆O₁₂₃)]·4(C₁₀H₈N₂)·8H₂O (Co-POM) has been synthesized by the solvothermal method and characterized by single-crystal X-ray diffraction (XRD), powder X-ray diffraction (PXRD), elemental analysis, FTIR spectroscopy, UV-vis absorption spectrum, and thermogravimetric analysis (TGA). Importantly, visible-light-absorption peaks around 525 nm for Co-POM indicated that this material should have potential in visible-light-induced organic reactions. Herein, we disclosed visible-light-promoted phosphorylation of N-aryl-tetrahydroisoquinoline using Co-POM as an efficient heterogeneous photocatalyst. In this procedure, diverse phosphorus reagents are compatible at room temperature and in an O₂ atmosphere, giving the corresponding products in good to excellent yields (up to 97%). Simultaneously, this heterogeneous photocatalyst can be recycled up to ten times with a negligible decrease in yield, showing outstanding sustainability and recyclability.

Facile high yield, excellent catalytic performance of polyoxometalate-based lanthanide phosphine oxide complexes: Syntheses, structures, photocatalysis and THz spectra

Water pollution, which continuously threatens human health and the sustainable development of society, has become a major concern. Photocatalytic degradation is an effective strategy to remove organic dyes from wastewater. For this strategy, it is crucial to select the appropriate catalyst. Using triphenylphosphine oxide (OPPh₃) as the ligand, phosphomolybdic acid as the anion template, three new lanthanide complexes [Ln(OPPh₃)₄(H₂O)₃](PMo₁₂O₄₀)∙4C₂H₅OH (1-3) (Ln = Sm, Gd, Tb) were synthesized. The raw materials for the reaction are cheap and readily available. The convenient synthesis method is environmentally friendly, with high yield (70%-80%). Complexes 1-3 are all seven-coordinated mononuclear structures centered on lanthanide ions, [PMo₁₂O₄₀]^3- anions and solvent molecules are not coordinated with metal ions. These mononuclear structures eventually form complicated 3D supramolecular structures through hydrogen bonds, Mo-O ^… π or C-H ^… π weak interactions. Complexes 1-3 photocatalytic degradation of MB have high removal rates, as catalysts have enough stability to be reused, and can be used as excellent catalysts for the degradation of dye molecules in sewage. Among them, the removal rate of MB by photodegradation of complex 2 was highest (99.50%). In addition, the effects of different initial concentrations of MB solution and different types of organic dyes on the photocatalysis experiment were investigated. The photocatalytic reaction mechanism of complexes 1-3 was also studied. Due to the similar structures of complexes 1-3, they have almost the same THz absorption spectra with different absorption intensity, which may be attributed to the difference of the number of weak interactions. Therefore, terahertz spectroscopy can be used as a sensitive method to distinguish and determine small differences between lanthanide-organic complexes. This is the first time that this spectrum has been used to characterize lanthanide phosphine oxide complexes modified by [PMo₁₂O₄₀]^3-.

Modulation of photocatalytic properties through counter-ion substitution: tuning the bandgaps of aromatic sulfonium octamolybdates for efficient photo-degradation of rhodamine B

Modulating the photocatalytic properties of polyoxometalate-organic hybrids through counterion substitution is a less explored concept. In this study, a new series of aromatic sulfonium counterions (ASCs) having the general formula X-C₆H₄-S(Me₂)⁺, where X represents different functional substituents such as -H, -Cl, -Me, and -CHO at the para-position of the sulfonium moiety on a benzene ring, have been used for fine-tuning the optical bandgaps and adsorption properties of octamolybdate [Mo₈O₂₆]^4- hybrids for photocatalytic dye degradation applications. The photodegradation of rhodamine B (RhB) is used as a model reaction, which follows pseudo-first-order kinetics exhibiting counterion-dependent degradation rate constants. The hybrid catalyst bearing a -CHO substituent on the ASC showed the lowest bandgap (2.91 eV) and the highest degradation rate constant (0.0141 min^-1) of the series. A possible mechanism of photocatalytic dye degradation by hybrids involving the generation of reactive oxygen species (ROS) has been proposed, supported by radical scavenging studies. The intermediates formed during the photodegradation of RhB were analyzed and identified using electrospray ionization mass spectrometry (ESI-MS). The present study reveals a new strategy for tuning the photocatalytic properties of hybrids using differently functionalized ASCs and opens up new avenues for novel POM-hybrids as potential photocatalysts for environmental remediation applications.

Solid-state degradation and visual detection of the nerve agent GB by SA@UiO-66-NH2@PAMAM hydrogel

A new sodium alginate (SA) composite hydrogel for rapid solid-state degradation of organophosphorus derivatives and can be used to monitor hydrolysis of nerve agent GB.

Photocatalysis, terahertz time domain spectroscopy and weak interactions of six polyoxometalate-based lanthanide phosphine oxide complexes

Using triphenylphosphine oxide (OPPh3) or tetraethyl ethylenebisphosphonate (L) as ligands, phosphomolybdic acid hydrate as the anion template, six new lanthanide complexes [Nd(OPPh3)4(H2O)3](PMo12O40)∙4CH3CN (1a), [Ln(OPPh3)4(H2O)3](PMo12O40)∙4C2H5OH (2a-4a) (Ln = Dy, Ho, Er),...

Merging the chemistry of metal-organic and polyoxometalate clusters into an enhanced photocatalytic material

The combination of a zirconium metal-organic cluster and a Keggin type polyoxotungstate into a compound of formula [Zr6(µ3-O)4(µ3-OH)4(µ-OOCC6H5)8(H2O)8][SiW12O40] led to a chemically and photochemically stable porous material in which a...

A Keggin-type polyoxomolybdate-based crystalline material formed by hydrothermal transformation: photo/electro-catalytic properties and mechanism study

This study constructs a POM-based crystalline material of [(SiMo12O40)Cu6(2,2′-bipy)6(Mo6O22)] (1). The photocatalytic MB degradation and electrocatalytic nitrite reduction properties of complex 1 are systematically studied for the first time.