| A wide variety of toxic inorganic and organic chemicals are discharged into theenvironment as industrial wastes, causing serious water, air, and soil pollution. Waterpollution caused by organic dye and toxic heavy metal ions has become a seriousenvironmental problem. These synthetic dyes and toxic metal ions, even at lowconcentrations, have deteriorated water resources and drinking water and easilyaccumulated in the human body throughout the food chain, causing a variety ofdiseases and disorders. So, it is necessary to remove these metal ions and dyes fromindustrial effluents for their subsequent safe disposal and preventing from secondpollution.The properties of hybrided nanocomposites were various because of thedifferent interaction between POMs and inorganic or organic compounds in term withdifferent POMs doped into polymers.POMs have great capabilities to accept anddonate various numbers of electrons, and they play as electron pools for transportingelectrons from semiconductors to other substrates nearby. Therefore, the surfaceelectrons of materials were able to be effectively photointroduced by POMs, and theintensity of visible light was increasing. Electrospinning is the most suitable techniquefor production of one-dimension nanocomposite materails. The advantages include itsrelative ease, low cost, high speed, vast materials selection, and versatility.Additionally, the technique allows control over fiber diameter, microstructure, andarrangement.In view of above these reasons, the heteropoly acid was regarded as a substraete,and the one-dimension composites were prepared with the electrospinning technology.The adsorptions of composite materials were discuused through the dye and heavymetal ions. The Ag/HPA/PVA tri-nanocomposite materials were fibracated onphotoreduction after the fibrous materails absorbed the silver cation. A certainmaterail has the better photocatalytic activity. The aim was realizaed that the metalions in aqueous solution was recycled and reused.The immobilization PW12/PVA composite fibers were fabricated by electrospinning technology and thermal treatment, and their morphologies, diameterof fibers, FT-IR, UV-DRS, XRD and XPS were characterized. The stability ofH3PW12O40was compared with PW12/PVA nanofibrous membranes in the differentpH dyes solution. The adsorption effect of adsorbent was discussed between anionicdyes (Methyl orange) and Cationic dyes (Rhodamine B), therefore, the reason andmechanism of PW12/PVA nanofibers adsorbed dyes that were speculated. Theadsorption studies were carried out at different temperature and the effects of pH, inthe meanwhile, the effect of contact time and initial dye concentrations of adsorbate,etc., on the adsorption were also investigated. On the basis of adsorption data theLangmuir and Freundlich adsorption isotherm models were also discussed. Thekinetics models of the pseudo-second-order and pseudo-first-order were exploited totest the experimental data. The Langmuir adsorption isotherm model and thepseudo-second-order model showed good fit to the experimental data. The rateconstant increased with increase in temperature indicating endothermic nature ofadsorption. The adsorption isotherm constants thus obtained were employed tocalculate thermodynamic parameters like Gibb’s free energy, change in enthalpy andentropy. The ΔG are negative, indicating the spontaneity and feasibility of theseprocesses, The positive value ofΔH further confirms that the adsorption processes areendothermic in nature. The positive value of ΔS infers increase of randomness atsolid-solution interface during the adsorption of Rh B dye on the active sites ofPW12/PVA nanofibers. Moreover, positive value of ΔS reflects affinity of theadsorbent for Rh B, and there is a strong affinity between the adsorbent and adsorbate.Regarding poly (vinyl alcohol)/Phosphotungstic acid (PW12/PVA) gel asprecursor, it was immobilized by thermal and chemical cross-linked treatment. Theprecursor was reduced to heteropoly blue（PW124-）by irradiation the compositesmaterials with ultraviolet light.Then, the blue colors PW124/PVA thin films wereimmersed into AgNO3solution, and the precipitating silver NPs onto the surface ofnanofibrous mats took place within a few minutes. Finally, tri-compositesnanomaterials were obtained. The mechanism of formation the Ag/PW12/PVAnanocomposites was investigated. The morphologies and internal structure oftri-composites materials were firmed by FTIR, XRD, UV-DSR, SEM, TEM and XPScharacterizations. An attempt has been made to study the effect of process parameters viz., solution pH, initial dye concentration and different light on photocatalyticdegradation of Rh B. The results show that the photocatalytic decolorization of thedyes in four nanocomposites materials can be described by the first-orde-kineticmodel. Furthermore, we show that the AgNP-deposited on the nanofibers display anexcellent catalytic activity and reusability for the photocatalytic Rh B.Poly (vinyl alcohol)/silicotungstic acid (PVA/H4SiW12O40) gel as precursor, thesilver nanoparticles (NPs) were selectively deposited on the surface of thePVA/H4SiW12O40nanofibers by using electrospinning and photoreduction methods.X-ray photoelectron spectroscopy, Fourier transformation infrared spectroscopy, andUV–vis diffuse reflectance spectroscopy were used to affirm the structure andformation of tri-component nanohybrids. Field environmental scanning electronmicroscope and transmission electron microscopy indicate that the average diameterof silver NPs was changed from25nm to50nm, with decreasing the relativeconcentration of SiW12in the as-electrospun nanofibers. The nanocomposites exhibitexcellent photocatalytic activity in degradation of Rhodamine B. This result arisesfrom the synergistic effects and the large specific surface areas ofAg/PVA/H4SiW12O40tri-component nanohybrids. This is from the presence silverNPs that make the photoexcited electrons efficiently transfer to oxygen viaPVA/SiW12nanofibers and hinder electron–hole pair recombining and enhance thetransport capacity of the electrons. The reaction mechanism of photocatalytic dyecomposites was studied and discussed through providing with illustrations anddetailed reaction scheme and the reaction equation.HPA is a special inorganic substance due to its special structure, which canprovide different atoms and tungsten atom can be substituted by one or more metalions. A wide variety of inorganic oxide can be obtained through different process.Regarding heteroploly acid or poly (vinyl alcohol)/H3PW12O40gel as precursors, theparticles and ultra-fine fibers tungsten oxide (WO3) was prepared by usingelectrospinning and calcinating techniques. The morphologies and structure of WO3were measured using FT-IR、Raman、UV-DRS、XRD and SEM. Scanning electronmicroscope (SEM) shows that the average diameter of fibrous WO3were changedfrom200nm to600nm after calcined PVA/H3PW12O40fibers at600and800C,respectively. X-ray diffraction (XRD) and Raman spectroscope revealed that the fibrous WO3was monoclinic phase, however, the particles WO3was orthorhombicand monoclinic phase. The band-gap energies were observed by UV–vis diffusereflectance spectra. The small size WO3exhibits excellent photocatalytcic activity indegradation of Rhodamine B at365nm wavelength. This is contributed to the effectof size and porosity. The reaction mechanism of photocatalytic dye was discussedthrough providing with illustrations and detailed reaction scheme and the reactionequation. |
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