A new polyoxometalate-TiO2 nanocomposite for efficient visible photodegradation of dye from wastewater, liquorice and yeast extract: Photoelectrochemical, electrochemical, and physical investigations

Photocatalytic removal of toxic dyes, liquorice and tetracycline wastewaters by a mesoporous photocatalyst under irradiation of different lamps and sunlight

Simple recyclable K₅CoW₁₂O₄₀/TiO₂ was synthesized and used to remove methyl orange, rhodamine B, direct red 16 and crystal violet toxic organic dyes, liquorice industrial wastewater and tetracycline (TC) as an antibiotic. Photoactivity of the catalyst was checked out under irradiation of various lamps (such as 18 W fluorescent, 300 W Xenon, LED and IR lamps). The best efficiency was obtained by fluorescent lamp at catalyst loading of 3 g/L, initial pH of 5, initial dye concentration of 5 ppm, complete degradation was achieved after 30 min contact time. Mechanistic investigation showed that·O₂ radicals and h⁺ are majorly responsible for photodegradation in this process. Electrochemical investigation, Nyquist, Bode, Mott-Schottky, Tauc plots and photoluminescence proved that using this photocatalyst delay the electron-hole recombination, increase the lifetime of excited electron, extend light absorption to visible region and improve the light absorption capacity. This photocatalyst work well under winter sunlight. Also 97% and 84% dye removal was obtained for liquorice with 300 and 1000 COD at optimal condition. This catalyst showed similar activity for TC wastewater. Photocatalyst was characterized by FE-SEM, EDX, AFM, FT-IR, XRD, PL, DRS, EIS, BJH and BET.

Heterogeneous UV-Switchable Au nanoparticles decorated tungstophosphoric acid/TiO2 for efficient photocatalytic degradation process

In the present study, gold nanoparticles were locally well-decorated on the surface of TiO₂ using the tungstophosphoric acid (HPW), as UV-switchable reducing intermediate linkers. The prepared Au NPs/HPW/TiO₂ nanostructure was characterized using FTIR, XRD, EDS, SEM and TEM, which confirmed the successful attachment of quasi-spherical Au NPs in the range of 20-30 nm on the surface of HPW modified TiO₂. Also, the FTIR results show that the Au NPs were binded to TiO₂ through the terminal the oxygen atoms HPW. The photocatalytic performance of prepared nanostructures was assessed in degradation of nitrobenzene. The nitrobenzene photodegradation kinetic study revealed that it well followed the Langmuir-Hinshelwood kinetic model with the apparent rate constant of 0.001 min^-1 using anatase TiO₂, 0.0004 min^-1 using HPW, 0.0014 using HPW/TiO₂, while it was obtained 0.0065 min^-1 using Au NPs@HPW/TiO₂ nanostructure. It shows that the photocatalytic rate of the prepared nanocomposites increased by 6.5- and 4.6-fold compared to photoactivity of anatase TiO₂ and HPW/TiO₂ respectively. Also, the photocatalytic mechanism of process was proposed. Moreover, the reusability study confirmed that its photocatalytic activity still remained high after three cycles.

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.

Synthesizing Various Organic Polyacid Compounds for Modifying Forward Osmosis Membranes to Enhance Separation Performance

In order to overcome the challenges of low permeate flux (J_p) and the accompanying reverse solute flux (J_S) during the forward osmosis (FO) membrane separation process, we synthesized four hybrid materials of polyacid-based organic compounds and incorporated them into the selective polyamide (PA) layer to make novel thin-film nanocomposite (TFN) FO membranes. The J_p and J_S of each membrane were evaluated and used along with membrane selectivity (J_p/J_S) as indicators of membrane separation performance. The fabricated and modified membranes were also characterized for ridge and valley surface morphologies with increasing hydrophilicity and finger-shaped parallel channels in the PSf substrate. Moreover, two highly hydrophilic nanoparticles of graphene oxide (GO) and titanium oxide (TiO₂) were introduced with the hybrid materials for PA modification, which can further enhance the J_p of the TFN membranes. The highest J_p of the TFN membranes achieved 12.1 L/m²-h using 0.1% curcumin-acetoguanamine @ cerium polyacid (CATCP) and 0.0175% GO. The characteristic peaks of the hybrid materials were detected on the membrane surface using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, evidencing successful incorporation of the hybrid materials during membrane modification. Here, we present the novel TFN membranes using hybrid materials for separation applications. The reactions for synthesizing the hybrid materials and for incorporating them with PA layer are proposed.

Biotin-Targeted Nanomicellar Formulation of an Anderson-Type Polyoxomolybdate: Synthesis and In Vitro Cytotoxicity Evaluations

This study is aimed at developing a micellar carrier for an Anderson-type manganese polyoxomolybdate (TRIS-MnPOMo) to improve the potency and reduce the general toxicity. The biotin-targeted stearic acid-polyethylene glycol (SPB) polymeric conjugate was selected for the first time as a micelle-forming basis for the delivery of TRIS-MnPOMo to breast cancer cells. The cytotoxicity of TRIS-MnPOMo and its nanomicellar form (TRIS-MnPOMo@SPB) was evaluated against MCF-7, MDA-MB-231 (breast cancer cell lines), and HUVEC (normal cell line) in vitro using the MTT assay. The quantity of cellular uptake and apoptosis level were studied properly using standard methods. The hydrodynamic size, zeta potential, and polydispersity index of the prepared micelles were 140 nm, -15.6 mV, and 0.16, respectively. The critical micelle concentration was about 30 μg/mL, which supports the colloidal stability of the micellar dispersion. The entrapment efficiency was interestingly high (about 82%), and a pH-responsive release of TRIS-MnPOMo was successfully achieved. The micellar form showed better cytotoxicity than the free TRIS-MnPOMo on cancer cells without any significant heme and normal cell toxicity. Biotin-targeted nanomicelles internalized into the MDA-MB-231 cells interestingly better than nontargeted micelles and TRIS-MnPOMo, most probably via the endocytosis pathway. Furthermore, at the same concentration, micelles remarkably increased the level of induced apoptosis in MDA-MB-231 cells. In conclusion, TRIS-MnPOMo@SPB could profoundly improve potency, safety, and cellular uptake; these results are promising for further evaluations in vivo.

Photocatalytic remediation of organic waste over Keggin-based polyoxometalate materials: A review

Photocatalytic remediation of industrial water pollution has courted intense attention lately due to its touted green approach. In this respect, Keggin-based polyoxometalates (POMs) as green solid acids in photocatalytic reaction possess superior qualities, viz. unique photoinduced charge-transfer properties, strong photooxidative-photoreductive ability, high chemical and thermal stability, and so forth. Unfortunately, it suffers from a large bandgap energy, low specific surface area, low recoverability, and scarce utilization in narrow absorption range. Therefore, the pollutant degradation performance is not satisfactory. Consequently, multifarious research to enhance the photocatalytic performance of Keggin-based POMs were reported, viz. via novel modifications and functionalizations through a variety of materials, inclusive of, inter alia, metal oxides, transition metals, noble metals, and others. In order to advocate this emerging technology, current review work provides a systematic overview on recent advancement, initiated from the strategized synthetic methods, followed by hierarchical enhancement and intensification process, at the same time emphasizes on the fundamental working principles of Keggin-based POM nanocomposites. By reviewing and summarizing the efforts adopted global-wide, this review is ended with providing useful outlooks for future studies. It is also anticipated to shed light on producing Keggin-based POM nanocomposites with breakthrough visible- and solar-light-driven photocatalytic performance against recalcitrant organic waste.