Synthesis and thermal decomposition of neodymium(III) peroxotitanate to Nd<Subscript>2</Subscript>TiO<Subscript>5</Subscript>

Neodymium(III) peroxotitanate is used as a precursor for obtaining Nd₂TiO₅. The last one possesses numerous valuable electrophysical properties. TiCl₄, Nd(NO₃)₃·6H₂O and H₂O₂ in mol ratio 1:2:10 were used as starting materials. The reaction ambience was alkalized to pH = 9 with a solution of NH₃. The obtained neodymium(III) peroxotitanate and intermediate compounds of the isothermal heating were proved by the help of quantitative analysis and infrared spectroscopy (IRS). It has Nd₄[Ti₂(O₂)₄(OH)₁₂]·7H₂O composition. The absorption band observed in IRS at 831 cm^?1 relates to a triangular bonding of the peroxo group of Ti, at 1062 cm^?1—terminal groups Ti–OH and at 1491 and 1384 cm^?1—the bridging OH^?-groups Ti–O(H)–Ti. Nd₂TiO₅ was obtained by thermal decomposition of neodymium(III) peroxotitanate. The isothermal conditions for decomposition were determined on the base of differential thermal analysis, thermogravimetric and differential scanning calorimetry results in the temperature range of 20–1000 °C. The mechanism of thermal decomposition of Nd₄[Ti₂(O₂)₄(OH)₁₂]·7H₂O to Nd₂TiO₅ was studied. In the temperature range of 20–208 °C, a simultaneous decomposition of the peroxo groups by the separation of oxygen and hydrate water is conducted and Nd₄[Ti₂O₄(OH)₁₂] is obtained. From 208 to 390 °C, the terminal OH^?-groups are separated and Nd₄[Ti₂O₇(OH)₆] is formed. In the range of 390–824 °C, the bridging OH^?-groups are completely decomposed to Nd₂TiO₅. The optimal conditions for obtaining nanocrystalline Nd₂TiO₅ are 900 °C for 6 h and 20–80 nm.     

Sonication-polished anodic TiO<Subscript>2</Subscript> nanotube array-based photoanode for efficient solar energy conversion

In this work, the capping layer atop anodic TiO₂ nanotube arrays (NTAs), which hinders filling of other guest materials and transport of charge carriers, is discerned to be TiO₂ nanotapes. Then, it is completely removed by a novel sonication-polishing (SP) treatment, after which Sb₂S₃ is subsequently introduced to fill the nanotubes by chemical bath deposition. The morphological, structural, and optical properties of the SP-treated TiO₂ NTAs and TiO₂ NTAs/Sb₂S₃ heterogeneous structures are characterized systematically. The results indicate that SP treatment opens the tops of nanotubes with diameters of ～120 nm, which endure a phase conversion from amorphous to anatase after calcination at 450 °C; besides, stibnite Sb₂S₃ with a band gap of ～1.75 eV inside the TiO₂ networks is formed upon heat treatment at 330 °C in Ar, which enhances the absorption in visible light range. The photoelectrochemical (PEC) and photovoltaic properties for the SP-treated TiO₂ NTAs are investigated. Results shows that the photoresponse of TiO₂ NTAs is improved by the SP treatment, and the photocurrent for the TiO₂ NTAs/Sb₂S₃ electrode is substantially enhanced as compared to the bare TiO₂ one. A high efficiency of 6.28 % is achieved in a TiO₂ NTAs/Sb₂S₃ PEC cell. In addition, charge recombination in the photoanode of dye-sensitized solar cells (DSSCs) is observed to be greatly retarded by using the SP-treated TiO₂ NTAs as compared to TiO₂ nanoparticles (NPs). Thus, the SP anodic TiO₂ NTAs are promising in applications in various PEC areas such as photocatalysis and sensitized solar cells.     

Photoelectrochemical starch-O<Subscript>2</Subscript> biofuel cell consisting of chlorophyll derivative-sensitized TiO<Subscript>2</Subscript> anode and enzyme-based cathode

A new photoelectrochemical starch-O₂ biofuel cell has been developed, consisting of chlorin-e₆ (Chl-e₆) adsorbed on a TiO₂ layer onto an optical transparent conductive glass electrode as a photoanode, bilirubin oxidase (BOD)-modified electrode as a cathode, and a solution containing starch, glucoamylase, glucose dehydrogenase and NAD⁺ as fuel. The short-circuit photocurrent and the open-circuit photovoltage of this cell are 9.0 μA cm^?2 and 530 mV, respectively. The maximum power, FF and \(\eta\) values are estimated to be 1.7 μW cm^?2, 0.36 and 0.0017 %, respectively. Thus, this new type of the photochemical starch-O₂ biofuel cell has been developed by using the visible light photosensitization of Chl-e₆ on a TiO₂ film photoanode.     

Degradation of ofloxacin by UVA-LED/TiO<Subscript>2</Subscript> nanotube arrays photocatalytic fuel cells

The degradation of ofloxacin (OFX) at low concentration in aqueous solution by UVA-LED/TiO₂ nanotube arrays photocatalytic fuel cells (UVA-LED/TiO₂ NTs PFCs) was investigated. TiO₂ nanotube arrays (TiO₂ NTs) photoanode prepared by anodization-constituted anatase–rutile bicrystalline framework. The results indicated that the degradation efficiency of OFX by UVA-LED/TiO₂ NTs PFC was significantly enhanced by 14.3% compared with UVA-LED/TiO₂ NTs photocatalysis. The pH affected the degradation efficiency markedly; the highest degradation efficiency (95.0%) and the pseudo-first-order reaction rate constant k value (0.049 min^?1) were achieved in neutral condition (pH 7.0). The degradation efficiency increased with the increasing concentration of dissolved oxygen (DO) in the UVA-LED/TiO₂ NTs PFC. The main reactive species of OFX degradation are positive holes (h⁺) and superoxide ion radicals (O ₂ ^·? ) in a DO sufficient condition. Furthermore, the possible pathways of OFX degradation were proposed.     

Heterostructured CoO/3D-TiO<Subscript>2</Subscript> nanorod arrays for photoelectrochemical water splitting hydrogen production

Homogeneous p-type cobalt (II) oxide (CoO) nanoparticles were successfully deposited on n-type three-dimensional branched TiO₂ nanorod arrays (3D-TiO₂) through photochemical deposition and thermal decomposition to form a novel CoO/3D-TiO₂ p-n heterojunction nanocomposite. Due to the narrow band gap of CoO nanoparticles (~2.4 eV), the as-synthesized CoO/3D-TiO₂ exhibited an excellent visible light absorption. The amounts of deposited CoO nanoparticles obviously influence the hydrogen production rate in the photoelectrochemical (PEC) water splitting. The as-synthesized CoO/3D-TiO₂-5 obtains the highest PEC hydrogen production rate of 0.54 mL h^?1 cm^?2 after five-time CoO deposition cycles (at a potential of 0.0 V vs Ag/AgCl). The photocurrent density of CoO/3D-TiO₂-5 is 1.68 mA cm^?1, which is ca. 2.5 times greater than that of pure 3D-TiO₂. The results showed that the formation of internal electrical-field between the CoO/3D-TiO₂ heterojunction, which has a direction from n-type TiO₂ to p-type CoO, facilitated the charge separation and transfer and resulted in a high efficiency and stable PEC activity.     

Synthesis,structure and thermal decomposition of [Ni(NH<Subscript>3</Subscript>)<Subscript>6</Subscript>][VO(O<Subscript>2</Subscript>)<Subscript>2</Subscript>(NH<Subscript>3</Subscript>)]<Subscript>2</Subscript>

The compound [Ni(NH₃)₆][VO(O₂)₂(NH₃)]₂ was prepared and characterized by elemental analysis and vibrational spectra. The single crystal X-ray study revealed that the structure consists of [Ni(NH₃)₆]²⁺ and [VO(O₂)₂(NH₃)]⁻ ions. As a result of weak interionic interactions V′···O_p (O_p-peroxo oxygen), ([VO(O₂)₂(NH₃)]⁻)₂ dimers are formed in the solid-state. The thermal decomposition of [Ni(NH₃)₆][VO(O₂)₂(NH₃)]₂ is a multi-step process with overlapped individual steps; no defined intermediates were obtained. The final solid products of thermal decomposition up to 600°C were Ni₂V₂O₇ and V₂O₅.     

Sensitization of Mn with CdS nanoparticles via electrochemical deposition technique for photocurrent enhancement of nanomaterial’s-sensitized photoelectrochemical cells

A photoconversion efficiency of 2.12% was obtained under visible light illumination by nanostructure-sensitized photoelectrochemical cells using Mn/CdS as sensitizer loaded on TiO₂ nanotube arrays (NTAs) (Mn/CdS/TiO₂). Sensitization of Mn on CdS nanoparticles pre-loaded on TiO₂ NTAs was carried out by a two-step electrodeposition method. Compared with unsensitized TiO₂ NTAs, the photocurrent had increased from 0.03 to 4.12 for Mn/CdS/TiO₂ prepared at 1 min. The effects of deposited Mn on the physical, chemical, and photoelectrochemical properties of the CdS/TiO₂ NTAs nanostructure were investigated by using UV–visible diffuse reflectance spectroscopy, X-ray diffractometry, and field-emission scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. The photoelectrochemical analysis was examined in a three-electrode system under a halogen illumination by using the prepared film as the photo-anode.     

Photoelectrochemical sensing of hydrogen peroxide at zero working potential using a fluorine-doped tin oxide electrode modified with BiVO<Subscript>4</Subscript> microrods

The authors describe a highly efficient photoelectrochemical (PEC) scheme for the determination of hydrogen peroxide (H₂O₂). BiVO₄ microrods were hydrothermally synthesized and deposited on fluorine - doped tin oxide (FTO) glass which acts as the working electrode. Scanning electron microscopy, X-ray powder diffraction and Raman spectroscopy were utilized for the characterization of the microrods. On irradiation with visible light, the holes generated in the microrods are capturing electrons from H₂O₂ to produce a photocurrent at an operating potential of 0 V vs. Ag/AgCl. Under optimal conditions, the photocurrent increases with the concentration of H₂O₂ in the range from 50 μmol·L^?1 to 1.5 mmol·L^?1, and the limit of detection is 8.5 μmol·L^?1 (at 3σ). A repeatability and intermediate precision of ≤6.6% was accomplished at H₂O₂ levels of 0.1, 0.5 and 1.0 mmol·L^?1. The method was applied to the determination of H₂O₂ in spiked sterilized milk samples and gave satisfactory results. As the method works at zero potential, the photocurrent can be measured with simple instrumentation such as digital multimeters, and this will enable expensive electrochemical workstations to be replaced in future.

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Graphical abstract An enzyme-free photoelectrochemical sensing strategy is described for sensitive determination of hydrogen peroxide in foodstuff using fluorine-doped tin oxide electrode modified with BiVO4 microrods.

     

Glucose biosensors based on Ag nanoparticles modified TiO2 nanotube arrays

A GOx/Ag/TiO₂ glucose biosensor was achieved by photoreducing Ag nanoparticles on TiO₂ nanotube arrays (NTAs) following with adsorption of GOx. The morphology, structure, and element component of Ag/TiO₂ NTAs were characterized by scanning electron microscope, transmission electron microscope, and X-ray diffraction. Ag nanoparticles were uniformly deposited on surface of TiO₂ NTAs with average size of 15 nm and the size and distribution changed with the immersing time of TiO₂ NTAs in AgNO₃ aqueous solution. Electrochemical properties of Ag/TiO₂ NTAs were characterized by cyclic voltammetry and amperometric detection of H₂O₂, revealing that TiO₂ NTAs with immersing time of 30 min achieve the best electrochemical activity. The GOx/Ag/TiO₂ NTAs biosensor with optimum conditions achieves a sensitivity of 0.39μA mM^?1 cm^?2 with liner range from 0.1 to 4 mM.     

Electrospun Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> composite nanofibers for enhanced high-rate lithium ion batteries

Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers with the mean diameter of ca. 60 nm have been synthesized via facile electrospinning. When the molar ratio of Li to Ti is 4.8:5, the Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers exhibit initial discharge capacity of 216.07 mAh g^?1 at 0.1 C, rate capability of 151 mAh g^?1 after being cycled at 20 C, and cycling stability of 122.93 mAh g^?1 after 1000 cycles at 20 C. Compared with pure Li₄Ti₅O₁₂ nanofibers and Li₂TiO₃ nanofibers, Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers show better performance when used as anode materials for lithium ion batteries. The enhanced electrochemical performances are explained by the incorporation of appropriate Li₂TiO₃ which could strengthen the structure stability of the hosted materials and has fast Li⁺-conductor characteristics, and the nanostructure of nanofibers which could offer high specific area between the active materials and electrolyte and shorten diffusion paths for ionic transport and electronic conduction. Our new findings provide an effective synthetic way to produce high-performance Li₄Ti₅O₁₂ anodes for lithium rechargeable batteries.     

Room temperature synthesis of CdS nanoparticle-decorated TiO2 nanotube arrays by electrodeposition with improved visible-light photoelectrochemical properties

Controllable CdS nanoparticles (NPs) decorated on TiO₂ nanotube arrays (NTAs) were prepared via electrodeposition in DMSO solution at room temperature, aiming to improve the photoelectrochemical properties of TiO₂ NTA electrode in visible-light region. By tuning the concentrations of sulfur and Cd^2 + as well as the deposition time, CdS NPs with different sizes can be controllably synthesized at room temperature. Excellent photocurrent response and incident photo to current conversion efficiency were achieved with smaller CdS NPs with optimal reactant concentrations and deposition time, which can be attributed to highly efficient charge separation and high dispersion of CdS NPs on both inner and outer surfaces of TiO₂ nanotubes.     

Kinetics and mechanism of the reduction of monochloramine by hydroxylamine and hydroxylammonium ion

The kinetics and mechanism by which monochloramine is reduced by hydroxylamine in aqueous solution over the pH range of 5–8 are reported. The reaction proceeds via two different mechanisms depending upon whether the hydroxylamine is protonated or unprotonated. When the hydroxylamine is protonated, the reaction stoichiometry is 1:1. The reaction stoichiometry becomes 3:1 (hydroxylamine:monochloramine) when the hydroxylamine is unprotonated. The principle products under both conditions are Cl^–, NH⁺₄, and N₂O. The rate law is given by ?[d[NH₂Cl]/dt] = k₊[NH₃OH⁺][NH₂Cl] + k₀[NH₂OH][NH₂Cl]. At an ionic strength of 1.2 M, at 25°C, and under pseudo‐first‐order conditions, k₊= (1.03 ± 0.06) ×10³ L · mol^?1 · s^?1 and k₀=91 ± 15 L · mol^?1 · s^?1. Isotopic studies demonstrate that both nitrogen atoms in the N₂O come from the NH₂OH/NH₃OH⁺. Activation parameters for the reaction determined at pH 5.1 and 8.0 at an ionic strength of 1.2 M were found to be ΔH? = 36 ± 3 kJ · mol^–1 and Δ S? = ?66 ± 9 J · K^?1 · mol^?1, and Δ H? = 12 ± 2 kJ · mol^?1 and Δ S? = ?168 ± 6 J · K^?1 · mol^?1, respectively, and confirm that the transition states are significantly different for the two reaction pathways. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 124–135, 2006     

Preparation of CuCr<Subscript>2</Subscript>O<Subscript>4</Subscript> nanopowders using two different chromium sources

CuCr₂O₄ spinel powders were synthesized starting from different chromium sources, namely (i) chromium oxide (α-Cr₂O₃) and (ii) ammonium dichromate ((NH₄)₂Cr₂O₇). The copper source was a Cu(II) carboxylate-type complex. The Cu(II) carboxylate complex was obtained by the redox reaction between Cu(NO₃)₂·3H₂O and 1,3-propanediol (1,3PG) at 130 °C. In the first case (i), we have started from a mixture of α-Cr₂O₃, Cu(NO₃)₂·3H₂O and 1,3PG that upon heating formed the copper malonate complex, which decomposed around 220 °C forming an oxide mixture (CuO + α-Cr₂O₃). In the second case (ii), (NH₄)₂Cr₂O₇, Cu(NO₃)₂·3H₂O and 1,3PG were homogenously mixed. Heating this mixture at 130 °C resulted, in situ, in the Cu(II) complex. On controlled temperature increase, the violent decomposition of (NH₄)₂Cr₂O₇ took place at 180 °C along with the decomposition of the Cu(II) complex, leading to an amorphous oxide mixture of Cr₂O_3+x and CuO. By annealing the samples in the temperature range 400–1000 °C, the spinel phase (CuCr₂O₄) was obtained in both cases: (i) at 800 °C and (ii) at 600 °C as a result of the interactions between the precursors used, when the oxide system was amorphous and highly reactive. The presence of CuCr₂O₄ was highlighted by XRD and FTIR analyses.     

Temperature programmed desorption of F-doped SnO<Subscript>2</Subscript> films deposited by inverted pyrosol technique

Fluorine-doped tin dioxide (FTO) films were deposited on silicon wafers by inverted pyrosol technique using solutions with different doping concentration (F/Sn=0.00, 0.12, 0.75 and 2.50). The physical and electrical properties of the deposited films were analyzed by SEM, XRF, resistivity measurement by four-point-probe method and Hall coefficient measurement by van der Pauw method. The electrical properties showed that the FTO film deposited using the solution with F/Sn=0.75 gave a lowest resistivity of 3.2·10^–4 ohm cm. The FTO films were analyzed by temperature programmed desorption (TPD). Evolved gases from the heated specimens were detected using a quadruple mass analyzer for mass fragments m/z, 1(H⁺), 2(H₂ ⁺), 12(C⁺), 14(N⁺), 15(CH₃ ⁺), 16(O⁺), 17(OH⁺ or NH₃ ⁺), 18(H₂O⁺ or NH₄ ⁺), 19(F⁺), 20(HF⁺), 28(CO⁺ or N₂ ⁺), 32(O₂ ⁺), 37(NH₄F⁺), 44(CO₂ ⁺), 120(Sn⁺), 136(SnO⁺) and 152(SnO₂ ⁺). The majority of evolved gases from all FTO films were water vapor, carbon monoxide and carbon dioxide. Fluorine (m/z 19) was detected only in doped films and its intensity was very strong for highly-doped films at temperature above 400°C.     

Photoelectrochemical Detection of Glucose by Using an Enzyme‐Modified Photoelectrode

A new photoelectrochemical method for the determination of glucose based on the photoelectrochemical effect of poly(thionine) photoelectrode to hydrogen peroxide (H₂O₂) was reported. The H₂O₂‐sensitive photoelectrode was fabricated by electropolymerizing thionine on the surface of ITO electrode. And then glucose oxidase was immobilized on the photoelectrode via the aid of chitosan enwrapping, forming an enzyme‐modified photoelectrode. The photoelectrode was employed as an electron acceptor; H₂O₂ from the catalytic reaction of enzyme was employed as an electron donor, developing an analytical method of glucose without hydrogen peroxidase. In the paper, the photoelectrochemical effects of photoelectrode to H₂O₂ and glucose were studied. The effects of the bias voltage and the electrolyte pH on the photocurrent were investigated. The linear response of glucose concentrations ranged from 0.05 to 2.00 mmol/L was obtained with a detection limit of 22.0 µmol/L and sensitivity of 73.2 nA/(mmol·L^?1). The applied feasibility of method was acknowledged through monitoring the glucose in practical samples.     

Polyethyleneoxide (PEO)-based, anion conducting solid polymer electrolyte for PEC solar cells

Solid polymer electrolyte membranes were prepared by complexing tetrapropylammoniumiodide (Pr₄N⁺I^?) salt with polyethylene oxide (PEO) plasticized with ethylene carbonate (EC), and these were used in photoelectrochemical (PEC) solar cells fabricated with the configuration glass/FTO/TiO₂/dye/electrolyte/Pt/FTO/glass. The PEO/Pr₄N⁺I^?+I₂?=?9:1 ratio gave the best room temperature conductivity for the electrolyte. For this composition, the plasticizer EC was added to increase the conductivity, and a further conductivity enhancement of four orders of magnitude was observed. An abrupt increase in conductivity occurs around 60–70 wt% EC; the room temperature conductivity was 5.4?×?10^?7 S cm^?1 for 60 wt% EC and 4.9?×?10^?5 S cm^?1 for the 70 wt% EC. For solar cells with electrolytes containing PEO/Pr₄N⁺I^?+I₂?=?9:1 and EC, IV curves and photocurrent action spectra were obtained. The photocurrent also increased with increasing amounts of EC, up to three orders of magnitude. However, the energy conversion efficiency of this cell was rather low.     

Photocatalytic degradation kinetics of methyl orange in TiO2–SiO2–NiFe2O4 aqueous suspensions

Photocatalytic degradation of methyl orange by TiO₂–SiO₂–NiFe₂O₄ suspensions was investigated. Adsorption studies revealed photocatalytic degradation occurred mainly on the surface of the TiO₂–SiO₂–NiFe₂O₄. The disappearance of the compound followed the zero-order kinetics according to the Langmuir–Hinshelwood model and the rate constant was 0.0035 mg L^?1 min^?1. The rate constant depended on the amount of photocatalyst, initial pH, and the presence of additional scavengers. ^?OH radicals and h⁺ had important roles in the photocatalytic degradation of methyl orange by TiO₂–SiO₂–NiFe₂O₄.     

One-dimensional porous Ag/AgBr/TiO<Subscript>2</Subscript> nanofibres with enhanced visible light photocatalytic activity

One-dimensional (1D) Ag/AgBr/TiO₂ nanofibres (NFs) have been successfully fabricated by the one-pot electrospinning method. In comparison with bare TiO₂ NFs and Ag/AgBr/PVP (polyvinylpyrrolidone) NFs, the 1D Ag/AgBr/TiO₂ NFs photocatalyst exhibits much higher photocatalytic activity in the degradation of a commonly used dye, methylene blue (MB), under visible light. The photocatalytic removal efficiency of MB over Ag/AgBr/TiO₂ NFs achieves almost 100 % in 20 min. The photocatalytic reaction follows the first-order kinetics and the rate constant (k) for the degradation of MB by Ag/AgBr/TiO₂ NFs is 5.2 times and 6.6 times that of Ag/AgBr/PVP NFs and TiO₂ NFs, respectively. The enhanced photocatalytic activity is ascribed to the stronger visible light absorption, more effective separation of photogenerated electron-hole pairs, and faster charge transfer in the long nanofibrous structure. The Ag/AgBr/TiO₂ NFs maintain a highly stable photocatalytic activity due to its good structural stability and the self-stability system of Ag/AgBr. The mechanisms for photocatalysis associated with Ag/AgBr/TiO₂ NFs are proposed. The degradation of MB in the presence of scavengers reveals that h⁺ and ^?O ₂ ^? significantly contribute to the degradation of MB.     

Thermal properties,phase transitions,vibrational and reorientational dynamics of [Mn(NH<Subscript>3</Subscript>)<Subscript>6</Subscript>](NO<Subscript>3</Subscript>)<Subscript>2</Subscript>

[Mn(NH₃)₆](NO₃)₂ crystallizes in the cubic, fluorite (C1) type crystal lattice structure (Fm \( \overline{3} \) m) with a = 11.0056 Å and Z = 4. Two phase transitions of the first-order type were detected. The first registered on DSC curves as a large anomaly at T _C1 ^h  = 207.8 K and T _C1 ^c  = 207.2 K, and the second registered as a smaller anomaly at T _C2 ^h  = 184.4 K and T _C2 ^c  = 160.8 K (where the upper indexes h and c denote heating and cooling of the sample, respectively). The temperature dependence of the full width at half maximum of the band associated with the δ_s(HNH)F_1u mode suggests that the NH₃ ligands in the high temperature and intermediate phase reorientate quickly with correlation times in the order of several picoseconds and with activation energy of 9.9 kJ mol^?1. In the phase transition at T _C2 ^c probably only a some of the NH₃ ligands stop their reorientation, while the remainders continue to reorientate quickly with activation energy of 7.7 kJ mol^?1. Thermal decomposition of the investigated compound starts at 305 K and continues up to 525 K in four main stages (I–IV). In stage I, ²/₆ of all NH₃ ligands were seceded. Stages II and III are connected with an abruption of the next ²/₆ and ¹/₆ of total NH₃, respectively, and [Mn(NH₃)](NO₃)₂ is formed. The last molecule of NH₃ per formula unit is freed at stage IV together with the simultaneous thermal decomposition of the resulting Mn(NO₃)₂ leading to the formation of gaseous products (O₂, H₂O, N₂ and nitrogen oxides) and solid MnO₂.