Sol–gel synthesis,crystal structure,surface morphology,and optical properties of Eu2O3-doped La2Mo3O12 ceramic

In this paper, we report the synthesis of the La–Mo–O tartrate gel precursors with the initial composition for La₂Mo₃O₁₂ ceramic prepared from different starting materials by an aqueous sol–gel synthesis route using tartaric acid as a complexing agent. Moreover, the La–Mo–O carbonate–tartrate and nitrate–tartrate gel precursors doped with x % of Eu₂O₃ (x = 0.5, 1.0, 2.0, 4.0, and 8.0) by aqueous sol–gel synthesis method were also prepared. The thermal decomposition of both the La–Mo–O carbonate–tartrate and nitrate–tartrate gels, which is the critical stage of this preparation technique, is investigated in detail. X-ray diffraction, scanning electron microscopy, and ultraviolet–visible spectroscopy were used for the determination of crystal structure, surface morphology, and optical properties of the La–Mo–O:xEu₂O₃ samples annealed at 400, 500, 600, 700, 800, 900, and 1,000 °C temperatures, respectively. The obtained results show that the thermal decomposition of the La–Mo–O tartrate gel precursors has occurred in a separate manner. The differences that came up during the thermal treatment of La–Mo–O tartrate gels have related only with the initial composition that determined the different crystallization ways of final compounds. Besides, the dopant concentration mainly influences the size of obtained particles and agglomeration of synthesized final materials. The initial composition of the La–Mo–O gel precursors has significant influence on the formation of final crystal phases at relatively lower temperatures than was expected according to the TG–DTA measurements. Finally, the optical properties of La–Mo–O tartrate gel precursors annealed at 500 °C depend on the nature of the initial compounds, which were used during the aqueous sol–gel process.     

Structural,mechanical and electronic properties of transition metal hydrides MH2 (M = Ti,Zr, Hf,Sc, Y,La, V and Cr)

First-principles calculations have been carried out to investigate the structural, mechanic and electronic of transition metal hydrides MH₂ (M = Ti, Zr, Hf, Sc, Y, La, V and Cr). It is found that TiH₂ is mechanically unstable because of a negative C₄₄ = −21.31 GPa and C₁₁–C₁₂ < 0, the same behavior can be found in MH₂ (M = Zr, Hf, and Y) compounds. Also there is a strong interaction between M (Ti, Zr, Hf, Sc, Y, La, V and Cr) and H. On the other hand, the H–H bond orders are always negative or nil reason of brittleness.     

Straightforward synthesis of Ti-doped YSZ gels by chemical modification of the precursors alkoxides

Translucent, homogeneous, and monolithic gels of the [(ZrO₂)_0.92(Y₂O₃)_0.08]_1?x(TiO₂)_x system, where x = 0, 0.05, 0.08, and x = 0.10 (mol), have been reliably obtained, for the first time, by a sol–gel route from zirconium (IV) n-propoxide (Zr(OPrⁿ)₄), yttrium acetate hydrate and titanium (IV) isopropoxide (Ti(OPrⁱ)₄). Chemical modification of both alkoxides, zirconium (IV) n-propoxide and titanium (IV) isopropoxide, by acetic acid allows us to change the hydrolysis and condensation behavior of them. Their modification implies the formation of chelating and bridging acetates avoiding the formation of precipitates. The line width and some shoulders in the FT-IR spectra of the solution, resulting of the mixture of the precursors and the catalysts, during the hydrolysis reaction suggest that both coordinations, chelating and bridging, should occur. Furthermore, the separation of the steps of hydrolysis and condensation allows to achieve conditions under which hydrolysis of the molecular precursor is slowed, whereas condensation is promoted under chemical reversibility to ensure a crystalline product at low calcination temperatures. In addition, the formation of metalloxane bondings (M–O–M’, M and M’ = Zr, Y, and Ti) has been confirmed by FT-IR throughout the sol–gel process. At about 630 °C, the crystallization of yttria stabilized zirconia (YSZ) for x = 0 or a titania-doped yttria stabilized zirconia solid solution (Ti-doped YSZ) for x = 0.05, 0.08, and 0.10 is detected by DTA-TG. By SEM-EDX and TEM-EDX the presence of Zr, Y, and Ti elements, in the adequate proportions according to the nominal compositions, has been proven in both dried and calcined gels.     

Electrical conductivity and Hf4+ ion substitution range in NaSICON system

In this paper, we present the synthesis and characterizations of NaSICON-type ionic conducting ceramics of the general formula Na_1+xM_1.775Si_x−0.9P_3.9−xO₁₂ with 1.8 ≤ x ≤ 2.2 and M = Zr or Hf. The effect of the total substitution of zirconium by hafnium on electric properties has been studied. The various compositions were prepared by using the sol–gel method and the synthesized precursors were characterized by coupled DTA–TG. The oxides obtained after pyrolysis of the precursors were identified by X-ray diffraction. A sintering study by thermodilatometry permits to select the best thermal cycle adapted to our ceramics. Furthermore, the electric conductivity of the sintered ceramic samples was characterized by complex impedance spectroscopy. These results show that ceramics containing Zr synthesized by soft method, present a higher total conductivity than those obtained in literature (to be around 10⁻⁴ S cm⁻¹). The total substitution of Zr by Hf still improves this conductivity for some compositions.     

Investigation of the molybdate(II)-3-hydroxyflavone complex

Summary Investigations on the composition of the molybdate(II)-3-hydroxyflavone complex and its stability constant have been carried out in 70% ethanolic solutions at room temperature (20°C), in the presence of a buffer atpH 6.30±0.05 and ionic strength 0.015. It has been found that a complex [MoO₃(C₁₅H₉O₃) ₂ ^2– ] whose stability constant ranges from 15.13 atpH 6.25 to 13.02 atpH 7.00 is formed. Conditions are given for the determination of 3-hydroxyflavone by means of the reaction of complex formation in 50% ethanol atpH 6.60±0.05 and an ionic strength of 0.0225.

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Untersuchung des Molybdat(II)-3-hydroxyflavon-Komplexes

Zusammenfassung Die Untersuchungen der Zusammensetzung des Komplexes und seiner Stabilitätskonstante wurden in 70% Ethanol, bei Raumtemperatur (20°C), in Anwesenheit von Puffer beipH=6.30±0.05 und der Ionenstärke 0.015 ausgeführt. Es wird der Komplex [MoO₃(C₁₅H₉O₃) ₂ ^2– ] gebildet, die Stabilitätskonstanten reichen von 15.13 beipH 6.25 bis zu 13.02 beipH 7.00. Es wurden die Bedingungen zur quantitativen Bestimmung von 3-Hydroxyflavon mittels des Molybdenkomplexes in 50% Ethanol, beipH=6.60±0.05 und der Ionenstärke 0.0225 ermittelt.

     

New Ternary Compounds MxTa11−xGe8 (M=Ti, Zr, Hf): Structure and Stabilization

The title compounds M_xTa_11−xGe₈ (M=Ti, Zr, Hf) were prepared from the pure elements by arc-melting and subsequent induction heating at temperatures between 1200°C and 1400°C. X-ray powder diffraction studies of the samples were performed using the Guinier technique and the respective powder patterns were refined with a structure model based on the orthorhombic Cr₁₁Ge₈-structure type (oP76, Pnma). The homogeneity ranges of the compounds were determined to be 0.9<x<1.3 (M=Ti), 0.7<x<1.3 (M=Zr) and 0.7<x<2.4> (M=Hf) by means of electron probe microanalysis. Chemical bonding, electronic structure and site preferences are discussed based on extended Hückel calculations performed on hypothetical binary Ta₁₁Ge₈.     

Investigation of the uranil(II)—3-Hydroxyflavone complex

Summary By the application of suitable spectrophotometric methods andpH-metric measurements it has been established that uranyl ion and 3-hydroxyflavone form a [UO₂(C₁₅H₉O₃)]⁺ complex. The concentration stability constant of the complex was determined by Bent-French's (₁=8.59 atpH=3.5) and Bjerrum's (from 8.68 atpH=4 to 6.14 atpH=7) methods. Conditions are given for the spectrophotometric determination of 3-hydroxyflavone by means of the complex. The regression equation is calculated and the accuracy of the method is determined. All investigations were carried out with 80% ethanolic solutions at room temperature (20°), the spectrophotometric measurements being performed at a constantpH (3.5) and a constant ionic strength (0.01M).

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Untersuchung des Uranil(II)—3-Hydroxyflavon-Komplexes

Zusammenfassung Unter der Anwendung von geeigneten spektrophotometrischen Methoden sowiepH-metrischen Messungen wurde gefunden, daß das UO ₂ ²⁺ -Ion und 3-Hydroxyflavon den Komplex [UO₂(C₁₅H₉O₃)]⁺ bilden. Die Stabilitätskonstante des Komplexes wurde nach Bent und French (₁=8.59 beipH=3.5) und nach Bjerrum (von 8.68 beipH=4 bis 6.14 beipH=7) bestimmt. Es werden die Bedingungen für die spektrophotometrische Bestimmung des 3-Hydroxyflavons mit Hilfe des Komplexes angegeben, die Regreßgleichung berechnet und die Genauigkeit der Methode ermittelt. Alle Untersuchungen wurden in 80proz. Ethanol bei Raumtemperatur (20°), die spektrophotometrischen Untersuchungen bei konstantempH-Wert und Ionenstärke (0.01M) durchgeführt.

     

Approaching compositional limits of perovskite – type oxides and oxynitrides by synthesis of Mg0.25Ca0.65Y0.1Ti(O,N)3, Ca1–xYxZr(O,N)3 (0.1 ≤ x ≤ 0.4), and Sr1–xLaxZr(O,N)3 (0.1 ≤ x ≤ 0.4)

Partial substitution of cations and anions in perovskite-type materials is a powerful way to tune the desired properties. The systematic variation of the cations size, the partial exchange of O²⁻ for N³⁻ and their effect on the size of the optical band gap and the thermal stability was investigated here. The anionic substitution resulted in the formation of the orthorhombic perovskite-type oxynitrides Mg_0.25Ca_0.65Y_0.1Ti(O,N)₃, Ca_1-xY_xZr(O,N)₃, and Sr_1–xLa_xZr(O,N)₃. A two-step synthesis protocol was applied: i) (nano-crystalline) oxide precursors were synthesized by a Pechini method followed by ii) ammonolysis in flowing NH₃ at T = 773 K (Ti) and T = 1273 K (Zr), respectively. High-temperature synthesis of such oxide precursors by solid–state reaction generally resulted in phase separation of the different A-site cations. Changes of the crystal structures were investigated by Rietveld refinements of the powder XRD data, thermal stability by DSC/TG measurements in oxygen atmosphere, oxygen and nitrogen contents by O/N analysis using hot gas extraction technique, and optical band gaps by photoluminescence spectroscopy. By moving from Mg_0.25Ca_0.65Y_0.1Ti(O,N)₃ via Ca_1–xY_xZr(O,N)₃ to Sr_1–xLa_xZr(O,N)₃, the degree of tilting of the octahedral network is reduced, as observed by an increase in the B–X–B angles caused by the simultaneously increasing effective ionic radius of the A-site cation(s). In general, increasing substitution levels on the A-site (Y³⁺ and La³⁺) are accompanied by an enhanced replacement of O²⁻ by N³⁻. In all three systems, this anionic substitution resulted in a reduction of the optical band gap by approximately 1 eV (Ti) and up to 2.1 eV (Zr) compared to the respective oxides. For Mg_0.25Ca_0.65Y_0.1Ti(O,N)₃ an optical band gap of 2.2 eV was observed, appropriate for a solar water splitting photocatalyst. The Zr-based oxynitrides required a by a factor of 2 higher nitrogen contents to significantly reduce the optical band gap and the measured values of 2.9 eV–3.2 eV are larger compared to the Ti-based oxynitride. Bulk thermal stability was revealed up to T = 881 K. In general, the thermal stability decreased with increasing substitution levels due to an increasing deviation from the ideal anionic composition as demonstrated by O/N analysis.     

A chemiluminescence sensor for the determination of hydrogen peroxide

A chemiluminescence one-shot sensor for hydrogen peroxide is described. It is prepared by immobilization of cobalt chloride and sodium lauryl sulphate in hydroxyethyl cellulose matrix cast on a microscope cover glass. Luminol, sodium phosphate and the sample are mixed before use and applied on the membrane by a micropipette. The calibration graph is linear in the range 20-1600 μg/L, and the detection limit of the method (3σ) is 9 μg/L. A relative standard deviation of 4.5% was obtained for 100 μg/L H₂O₂ (n = 11). The sensor has been applied successfully to the determination of hydrogen peroxide in rainwater.     

Catalysts for enantioselective Biginelli reaction based on the composite silica-zirconia xerogels prepared using different zirconium sources

The composite silica-zirconia xerogels have been prepared via sol–gel method using zirconium oxychloride, oxynitrate, acetate and sodium silicate as the precursors. The prepared materials have been characterized using FTIR, TG/DTA, EDX and surface area analyses. It has been established that surface area of silica-zirconia xerogels significantly depends on the zirconium source, but phase transitions and structural features of the xerogels seem to be unaffected by the choice of the zirconia precursor. Prepared xerogels increase the activity of chiral inductor in the asymmetric Biginelli reaction. The anion of the zirconium salt adsorbed on the surface of the synthesized material and the presence of Si–O–Zr heterolinkages determines the reaction yield. The highest chemo- and enantioselectivity towards formation of ee isomer have been provided by the catalyst prepared from zirconium oxychloride.     

Preparation of TiO2 nanocrystallites by hydrolyzing with gaseous water and their photocatalytic activity

TiO₂ nanocrystallites were prepared from precursors tetra-n-butyl titanate (Ti(OC₄H₉)₄) and titanium tetrachloride (TiCl₄). The precursors were hydrolyzed by gaseous water in autoclave, and then calcined at predetermined testing temperatures. The samples were characterized by X-ray diffraction (XRD), thermogravimetry–differential thermal analysis (TG–DTA), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectra (FT-IR), and UV–vis diffuse reflectance spectra (DRS). The photocatalytic activities of the samples were evaluated by the photobleaching of methylene blue (MB) in aqueous solution and the photocatalytic oxidation of propylene in gas phase at ambient temperature. The results showed that the anatase phase nanocrystalline TiO₂ could be obtained at relatively low temperatures (for precursor Ti(OC₄H₉)₄ at 110 °C and for TiCl₄ at 140 °C, respectively), and that the as prepared samples exhibited high photocatalytic activities to photobleach MB in aqueous solution. As the calcination temperatures increasing, the decolor ratio of MB increased and reached the maximum value of nearly 100% at 600 °C, and then decreased. The photobleaching of MB by all samples followed the pseudo-first-order kinetics with respect to MB concentration. The photodecomposition amount of propylene by TiO₂ nanocrystallites calcined at 600 °C from precursor of Ti(OC₄H₉)₄ is 21.6%, which is approaching to that by Degussa P25 TiO₂ (24.9%).     

FT-EPR Spectroscopic Study of Silicophosphate Glasses Derived from Gels

(100-x) mole% SiO₂-x mole% P₂O₅-glasses withx=1–9 have been prepared by the sol-gel process using tetraethylorthosilicate and triethylphosphate as precursors. The gels were fired at various temperatures up to 950°C and then exposed to γ-ray irradiation to induce paramagnetic centers. CW-EPR and FT-EPR Spectroscopies were employed at temperatures between 4 and 300 K in order to determine the resulting structures. The dried gels exhibited four types of O ₂ ⁻ -ions trapped in pores of different sizes. The gels fired atT=670°C exhibited theE’ ₁-center and non-bridging oxygen as a results of the fracture of the Si-O-Si bonds. At higher temperatures, the spectra of the POHC, POHC ^b ,E’, and CH ₃ ⁻ -centers have been detected that are a function ofx andT.     

Structural thermal and textural studies on cobalt oxide/alumina supported catalysts

CoO/Al₂O₃ catalysts containing amounts of cobalt ranging form 2 to 20% were prepared atpH 11 from neutral mesoporous alumina composed of γ-Al₂O₃ and poorly crystalline boehmite, and were then dried at 80?C. X-ray diffraction, DTA and TG techniques were used to study the structural changes produced upon thermal treatment up to 700?C. Soaking of the alumina in cobalt ammine complex solutions for a period of 10 days (the time required for equilibrium) resulted in a series of catalyst samples (I–V). Another sample (III-a) was soaked for a period of 5 days only in order to study the effect of the soaking time upon the equilibrium conditions. Cobalt aluminate (CoAl₂O₄) bands were characterized in all catalyst samples except III-a. They increased in intensity with increasing cobalt content. Surface species appeared in samples heated to 80?C, and others persisted at 150?C. Heating to temperatures above 200?C resulted in the formation of cobalt oxides, due to decomposition of the surface compounds. DTA and TG studies showed that this was more pronounced at higher concentrations of cobalt. Samples heated at 500?C and above did not undergo any further structural changes, except that the boehmite in the support was converted to γ-Al₂O₃. The variations in the surface parameters followed the same pattern as found previously [1], demonstrating that the catalyst samples are mesoporous, with retention of two ranges of pore size in most cases.     

EXAFS Study of Amorphous Precursors for Pb(Zr,Ti)O3 Ceramics

In as-hydrolyzed amorphous precursors of Pb(Zr,Ti)O₃ (PZT) ceramics with various Zr/Ti ratios prepared from lead acetate and transition metal n-butoxides in parent alcohol medium the local environment of constituent metal atoms has been determined by EXAFS. The local zirconium atom environment in high-Zr precursors consists of distorted octahedra of oxygen atoms with all the bonds made up of Zr–O–Zr links. For low-Zr precursors a smaller distortion of the oxygen octahedra is observed, and two Ti atoms are found in the second shell. The titanium local environment is almost independent of the Zr/Ti ratio, with five oxygen atoms in the first and two titanium atoms in the second shell of neighbors. Lead atoms contain two oxygen atoms in the first coordination shell. Pb–O–M (M = Zr, Ti) links are identified in all precursors: the former at Zr/Ti 75/25 and the latter at lower Zr/Ti ratios. Although a pronounced tendency for the homocondensation of zirconium species is found down to a Zr/Ti 50/50 ratio, heterometallic links (Pb–O–M) are determined in PZT precursors.     

ZrxTixAl1-2xO2的制备及其在三效催化剂上的应用

Zr_0.5Ti_0.5O₂(ZT) and Zr_0.25Ti_0.25Al_0.5O₂(ZTA) mixed oxides were prepared by co-precipitation method and characterized by low temperature adsorption-desorption， XRD and NH₃-TPD. The activity of Pt/Zr_0.5Ti_0.5O₂ and Pt/ Zr_0.5Ti_0.5Al_0.5O₂ catalysts was evaluated using the simulated gases. The results show that ZTA samples exhibit higher specific surface area， larger pore volume and proper surface acidic amount and acidity in comparison with ZT. The results of the catalytic test indicate that Pt/ZT and Pt/ZTA catalysts exhibit excellent low-temperature catalytic activity and lower light-off temperatures of hydrocarbon， carbon monoxide and nitrogen oxides， especially better conversion for nitrogen oxides (NO_x). The addition of Al₂O₃ into ZT enhanced the anti-aging property of Pt/ ZTA catalysts due to the excellent textural， structural， surface acidity and thermal stability.     

Thermal behavior of silicophosphate gels obtained from different precursors

Phosphosilicate glasses are of great interest in important fields, such as optical active systems, energy generating systems, humidity sensors, and as materials for biomedical applications. Many studies were accomplished to establish the influence of different reaction parameters on the evolution and final structure of sol–gel prepared phosphosilicate gels. In the present work, we studied the thermal behavior of the silicophosphate gels obtained starting with different phosphorous precursors, the influence of these precursors on the composition and structure of the resultant gels, and their evolution with thermal treatment. By Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and thermodifferential analysis (DTA/TG), and Differential Scanning calorimetry coupled with Mass Spectrometry (DSC-MS), it was established that the type of the precursors essentially influences the composition and structure and consequently the thermal behavior of the obtained gels. In the case of triethylphosphate precursor, all used methods of investigation have shown that the ester is trapped in the silica matrix and it is eliminated during the thermal treatment. Triethylphosphite partially hydrolizes and reacts with the silica network during post-preparation thermal treatment. Only in the case of H₃PO₄, an interaction with TEOS takes place and leads to Si–O–P bond formation. By thermal treatment, the gels with different composition and structure lead to materials with different properties.     

LaCoO3 formation from precursors obtained by water-based sol–gel method with citric acid

In the present work the LaCoO₃ formation from gel precursors obtained by water-based sol–gel method with citric acid was studied. As precursors La and Co nitrates were used. The obtained gels were analyzed by TG/DTA and TG/AGE. The decomposition of the gels takes place in two main steps with the evolution of the same volatile compounds (H₂O, CO₂ si NO₂) leading to the conclusion that two types of bonding of the components in the gels occurred. The decomposition of the gels takes place up to 400 °C. The gels thermally treated at 600 °C lead to single pure perovskite rhombohedral phase of lanthanum cobalt oxide (LaCoO₃).     

Structure and optical properties of [Ba1–xY2x/3](Zr0.25Ti0.75)O3 powders

[Ba_1–xY_2x/3](Zr_0.25Ti_0.75)O₃ powders with different yttrium concentrations (x = 0, 0.025 and 0.05) were prepared by solid state reaction. These powders were analyzed by X-ray diffraction (XRD), Fourier transform Raman scattering (FT-RS), Fourier transform infrared (FT-IR) and X-ray absorption near-edge (XANES) spectroscopies. The optical properties were investigated by means of ultraviolet–visible (UV–vis) absorption spectroscopy and photoluminescence (PL) measurements. Even with the addition of yttrium, the XRD patterns revealed that all powders crystallize in a perovskite-type cubic structure. FT-RS and FT-IR spectra indicated that the presence of [YO₆] clusters is able to change the interaction forces between the O–Ti–O and O–Zr–O bonds. XANES spectra were used to obtain information on the off-center Ti displacements or distortion effects on the [TiO₆] clusters. The different optical band gap values estimated from UV–vis spectra suggested the existence of intermediary energy levels (shallow or deep holes) within the band gap. The PL measurements carried out with a 350 nm wavelength at room temperature showed that all powders present typical broad band emissions in the blue region.     

Effects of Ti and Zr Substituted on the Electrochemical Characteristics of MgNi-Based Alloy Electrodes

Mg-based hydrogen storage alloys MgNi, Mg0.9Ti0.1Ni, and Mg0.9Ti0.06Zr0.04Ni were successfully prepared by means of mechanical alloying （MA）. The structure and the electrochemical characteristics of these Mg-based materials were studied. The X-ray diffraction （XRD） result shows that the main phases of the alloys exhibit amorphous structure. The scanning electron microscopy （SEM） photograph shows that the particle size of Ti and Zr substituted alloys was about 2-4 μm in diameter. The cycle lives of the alloys were prolonged by adding Ti and Zr. After 50 charge-discharge cycles, the discharge capacity of Mg0.9Ti0.06Zr0.04Ni was 91.74% higher than that of MgNi alloy and 37.96% higher than that of Mg0.9Ti0.1Ni alloy. The main reason for the electrode capacity decay is the formation of Mg（OH）2 （product of Mg corrosion） at the surface of alloy. The potentiodynamic polarization result indicates that Ti and Zr doping improves the anticorrosion in an alkaline solution. The electrochemical impedance spectroscopy （EIS） results suggest that proper amount of Ti and Zr doping improves the electrochemical catalytic activity significantly.     

Characterization, conductivity and photocatalytic studies of AHfM(PO4)3 (A = Na and Ag; M = Ti and Zr) powders synthesized by sol–gel method

Materials belonging to NASICON family of compositions NaHfM(PO₄)₃ and AgHfM(PO₄)₃ (M = Ti and Zr) are prepared by sol–gel and ion exchange methods, respectively. Ethylene glycol is used as a gelating agent. All the compositions are characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, ³¹P MAS NMR, UV–Vis DRS, XPS and energy dispersive spectral methods. All these phosphates are crystallized in rhombohedral lattice with space group $R\overline{3} c$ R 3 ¯ c . These compounds exhibit characteristic PO₄ vibrational modes in their FT-IR spectra. The ³¹P MAS NMR gave broad signals indicating distribution of chemical environments around P ion. The dc and ac conductivity of AgHfM(PO₄)₃ (M = Ti and Zr) are higher compared to their sodium containing compounds. The Cole–Cole plots of impedance show semicircles between 373 and 623 K. The variation of dc conductivity with temperature follows the Arrhenius equation. The photocatalytic activity of all the samples was studied against methylene blue decomposition using sun light. AgHfM(PO₄)₃ (M = Ti and Zr) have shown higher photoactivity than the sodium containing Nasicons.