Synthesis and characterization of novel Co-PWB bronze using TGA/DTA, XRPD, FTIR and SEM-EDS methods

Phosphate tungsten bronzes (PWBs) constantly attract a lot of attention due to their interesting chemical, electrical, optical, and mechanical features [1]. Heteropoly acid hydrate H3PW12O40×29H2O (PWA) was obtained by dissolving Na2WO4×2H2O in a H3PO4-HCl mixture and by extracting the precipitate with ether at room temperature. The dehydration process of H3PW12O40×29H2O (PWA) to H3PW12O40×6H2O (6- PWA) is done by heating of PWA in a kiln at 80 °C. An aqueous solution of H3PW12O40×6H2O is then mixed with an aqueous solution of CoCl2×6H2O, gently heated to initiate the crystallization process, and left overnight to complete crystallization. The obtained with (CoHPW12O40×nH2O, CoPWA) is then heated in a furnace, from room temperature to 600 °C, during which cobalt phosphate tungsten bronze crystals are formed. Obtained CoPWB was further characterized by FTIR, XRPD and SEM-EDS methods which confirmed the formation of the desired structure. In this work, cobalt phosphate tungsten bronze was synthesized and characterized for the first time in order to obtain more information about its structure, chemical characteristics and potential practical application. A potential practical application of Co-PWB is in its incorporation into aqueous lithium-ion batteries and catalysts in the Briggs Rauscher reaction

Electrochemical testing of iron phosphor tungsten bronzes as potential electrode material

In this work, synthesized 12-tungstenphosphoric acid (H3PW12O40 ∙ nH2O, PWA) was further ionically exchanged with Fe3+ ions, which led to the formation of the FePWA salt (FePW12O40 x nH2O). FePWA was then subjected to thermal analysis (TGA/DTA), which determined the phase transition temperature ( i.e., when the Keggin anion collapses). The temperature of collapsing the Keggin anion is about 600 °C, at which phosphate tungsten bronzes doped with iron (FePWB) are obtained. Obtained FePWB was further characterized by XRPD and FTIR, which confirmed the formation of the desired structure. FePWA and FePWB were examined as an electrode material for aqueous rechargeable batteries due to the channels and cavities present in their structure. Experiments were done in aqueous solutions of 6 M LiNO3 by cyclic voltammetry. The differences in the redox processes of heteropoly acid salts and iron-doped bronze were discussed thoroughly and correlated with the XRPD and FTIR results. The catalytic activity is also investigated by Briggs-Rauscher method followed potentiometricaly

Crystallographic investigation of the iron phosphate tungsten bronze (Fe-PWB)

In this paper, 12-tungstenphosphoric acid (PWA) was synthesized in combination with FeCl3 at room temperature (25 °C). At such manner, Fe3+ ion exchange gave new 12-tungstenphosphoric salt of the transition metal iron (FePW12O40×nH2O; Fe-PWA). Thermal analysis determined the temperature of about 596 °C of the phase transition, i.e., the temperature at which the structure of the Kegin anion is disturbed. Therefore, it was chosen temperature above the breakdown of the Kegin anion of 650 °C, and which is required to obtain phosphate tungsten bronzes (PWB) doped with iron (Fe-PWB). The sample was kept in the oven for 10 min. Such obtained new Fe-PWB doped bronze was further investigated by the X-ray powder diffraction (XRPD) and Rietveld methods. The XRPD patterns of Fe-PWA and Fe-PWB were taken in the 3–90° 2θ angle range, and clearly reveal crystallographic and structural differences between these two phases. Determined unit-cell parameters of Fe-PWB obtained by the Rietveld method in the monoclinic crystallographic system are as following: a0 = 7.53(2) Å; b0 = 7.51(1) Å; c0 = 7.64(1) Å; β0 = 89.7(2)° and V0 = 431(2) Å3. These unit-cell parameters were compared with PWB, as well as other previously characterized doped bronzes (LiPWB and Ca-PWB). It can be concluded that inserting of the Fe3+ ion into the PWB’s structure was undoubtedly proven, and have the most influence to the axis a0 (i.e. it significantly increased), angle β0 (i.e., it significantly decreased), and volume V0 (i.e., it significantly increased). On the other hand, influence to the axis c0 is quite smaller (i.e. it slightly decreased), whereas influence to the axis b0 is minor. Such behavior is also very different in comparison to the Li-PWB and Ca-PWB

Detection of Cu2+ ions in aqueous solution via emission quenching of colloidal EuPO4 ultrasmall nanoparticles

EuPO4 and Eu3+-activated REPO4 (RE = La, Dy, Er) ultrasmall fluorescent nanoparticles (NPs) with an average diameter of 2.1 nm were prepared via colloidal synthesis and tested for sensing Cu2+ and other heavy-metal ions. The pure monoclinic monazite crystal structure (space group P121/n1) of the synthesized particles was confirmed using X-ray diffraction measurements, and transmission electron microscopy images showed round particles with a narrow particle-size distribution. The NPs exhibited intense red emission, which is characteristic of the f-f electronic transition of Eu3+, and the quenching of their emission in the presence of heavy-metal ions was revealed by dispersing colloidal particles in a TRIS buffer and then performing photoluminescence measurements. Strong quenching of the emission (at a rate of 0.195 μM−1) was observed upon the addition of Cu2+ ions over the concentration range of 0–10 μM with a limit of detection of 60 nM for Cu2+. The recovery of nearly 90% of the original emission intensity of the probe was achieved via the addition of ethylendiaminetetraacetic acid and was possible in five quenching/recovery cycles. © 201

Synthesis and characterization of heteropoly acid salts doped with Zn2+ ions

Heteropoli kiseline i soli heteropoli kiselina su interesantne za izučavanje jer se mogu strukturno modifikovati u fosfat volframovu bronzu termičkim tretmanom na oko 600 °C. U ovom radu sintetisali smo 12-volfram fosfornu kiselinu, H3PW12O40 × nH2O - (PWA). Sinteza soli je obavljena jonskom izmenom dodavanjem ekvimolarnih količina ZnCl2 u rastvor heteropoli kiseline. Karakterizacija je izvršena korišćenjem infracrvene spektroskopije Furijeove transformacije (FTIR), difrakcije rendgenskih zraka na prahu (XRPD), skenirajuće elektronske mikroskopije (SEM) i ciklične voltametrije. Dobijeni rezultati otvaraju nove pravce istraživanja Zn-PWA kao potencijalni elektrodni materijal

Phosphate tungsten bronze doped with Zn2+ ions: synthesis and characterization

The tungsten bronzes exhibit interesting chemical, electrical and optical properties. Phosphatetungsten bronzes (PWBs) were obtained by thermal treatment of heteropoly compound 12- tungstenphosphoric acid (H3PW12O40 × nH2O) and their salts (PWA × nH2O; n = 29, 21, 14 and 6). In this work, the metal element zinc was used to dope 12-tungstenphosphoric acid (H3PW12O40 × nH2O), whereby a salt of heteropoly acid (Zn2+HPW12O40×nH2O, Zn-PWA). Zn- PWA was then subjected to thermal analysis TGA/DTA to determine the phase transition of the heteropoly acid salt in the novel phosphate tungsten bronzes doped with zinc (ZnPWB). The temperature phase transition occurs at a temperature of about 600 oC. Characterization of newly obtained material was performed using Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRPD), scanning electron microscopy (SEM) and cyclic voltammetry, which confirmed thermal transformation and the formation of Zn doped bronze. The obtained results open new directions of Zn-PWB research as a potential electrode material, as a catalyst for the reduction of oxygen in acidic electrolytes, due to the specific color and its thermal stability, Zn- PWB could also be used as a pigment

Synthesis, characterization and electrochemical properties of iron doped phosphate tungsten heteropoly acid (Fe-PWA) and it’s bronze (Fe-PWB): Comparative study

In this work, synthesized 12-tungstenphosphoric acid (H3PW12O40 × nH2O; PWA) was further ionically exchanged with Fe3+ ions, which led to the formation of the 12-tungstophosporic acid iron salt, (FePW12O40 × nH2O; Fe-PWA). Fe-PWA was then subjected to thermal analysis (TGA/DTA), determining the phase transition temperature of 576 °C from Fe-PWA to its corresponding phosphate tungsten bronze doped with iron, Fe-PWB. Using the X-ray powder diffraction (XRPD), Fourier-transform infrared spectroscopy (FTIR), and Scanning electron microscopy with an energy dispersive X-ray spectroscopy (SEM-EDS) method, the obtained Fe-PWA and Fe-PWB were additionally characterized, and compared. Due to channels and cavities in their structures, Fe-PWA and Fe-PWB were next examined as electrode materials for aqueous rechargeable batteries. Electrochemical measurements were done in aqueous solutions of 6 M LiNO3 by cyclic voltammetry. Fe-PWA and Fe-PWB exhibit different redox processes, which are discussed thoroughly in this work. Electrochemical results are showing that within the Fe-PWA structure, more Li+ ions can be intercalated in the first discharge cycle, but consecutive cycling leads to a fast capacity fade. While the Fe-PWB redox process was stable during cycling, its specific capacity is limited by the material's poor electrical conductivity. Improvements in Fe-PWB conductivity must be addressed in future studies in order to boost material’s electrochemical performance.У овом раду синтетисана је 12-волфрам фосфорна киселина (H3PW12О40 × nH2О; PWA), која је даље јонски допирана са Fe3+ јонима, што је довело до формирања соли гвожђа 12-волфрам фосфорне киселине Fe-PWA соли (FePW12О40×nH2О). Fe-PWA је затим испитан помоћу термијске анализе (TGA/DTА), фазни прелаз Fe-PWA одиграва се на температури од 576 oC, формирајући фосфат волфрамову бронзу допирану гвожђем Fe-PWB. Применом метода дифракције рендгенских зрака на праху, инфрацрвене спектроскопије са Фуријеовом трансформацијом и скенирајуће електронске микроскопије уз енергетску дисперзивну рендгенску спектроскопију, добијени Fe-PWB је додатно карактерисан, чиме је потврђена жељена структура. Због канала и шупљина у њиховим структурама, Fe-PWA и Fe-PWB су затим испитани као електродни материјали за пуњиве батерије. Електрохемијска мерења вршена су у воденим растворима 6М LiNО3 цикличном волтаметријом. Електрохемијски резултати показују да унутар структуре Fe-PWA, више Li+ јона може бити интеркалирано у првом циклусу пражњења, али даље циклирање доводи до брзог смањења капацитета. Док је редокс процес Fe-PWB био стабилан током циклирања, његов специфични капацитет је ограничен слабом електричном проводљивошћу материјала. Специфични капацитет Fe-PWB је скоро незнатан, па је неопходно оптимизовати његове физичко-хемијске особине како би се вредност његовог специфичног капацитета повећала. Побољшање проводљивости Fe-PWB биће истраживана у будућим студијама, како би се побољшале електрохемијске перформансе материјала

Crystallographic investigation of the iron phosphate tungsten bronze (Fe-PWB)

In this paper, 12-tungstenphosphoric acid (PWA) was synthesized in combination with FeCl3 at room temperature (25 oC). At such manner, Fe3+ ion exchange gave new 12-tungstenphosphoric salt of the transition metal iron (FePW12O40×nH2O; Fe-PWA). Thermal analysis determined the temperature of about 596 oC of the phase transition, i.e., the temperature at which the structure of the Kegin anion is disturbed. Therefore, it was chosen temperature above the breakdown of the Kegin anion of 650 oC, and which is required to obtain phosphate tungsten bronzes (PWB) doped with iron (Fe-PWB). The sample was kept in the oven for 10 minutes. Such obtained new Fe-PWB doped bronze was further investigated by the X-ray powder diffraction (XRPD) and Rietveld methods. The XRPD patterns of Fe-PWA and Fe-PWB were taken in the 3-90o 2θ angle range, and clearly reveal crystallographic and structural differences between these two phases. Determined unit-cell parameters of Fe-PWB obtained by the Rietveld method in the monoclinic crystallographic system are as following: a0 = 7.53(2) Å; b0 = 7.51(1) Å; c0 = 7.64(1) Å; β0 = 89.7(2)o; and V0 = 431(2) Å3. These unit-cell parameters were compared with PWB, as well as other previously doped bronzes (Li-PWB and Ca-PWB). It can be concluded that inserting of the Fe3+ ion into the PWB’s structure was undoubtedly proven, and have the most influence to the axis a0 (i.e., it significantly increased), angle β0 (i.e., it significantly decreased), and volume V0 (i.e., it significantly increased). On the other hand, influence to the axis c0 is quite smaller (i.e., it slightly decreased), whereas influence to the axis b0 is minor. Such behavior is also very different in comparison to the Li-PWB and Ca-PWB