Synthetic dyes from industrial sources, particularly textiles, are major contributors to water pollution due to their non-biodegradable and toxic nature, posing serious environmental and health hazards. Semiconductor metal oxide nanomaterials have emerged as promising photocatalysts for dye degradation, owing to their activity, stability, and tunable structural-electronic properties. This study explores the visible-light-driven photocatalytic degradation of two hazardous dyes-Rose Bengal (RB) and Methylene Blue (MB)-using green-synthesized ZnO nanoparticles (NPs). The NPs were prepared via an eco-friendly route employing Tabernaemontana divaricata flower extract, producing three distinct samples: ZnO0 (17.5 nm), ZnO10 (20.8 nm), and ZnO15 (23.3 nm). Photocatalytic performance was evaluated under varying crystallite sizes, pH, catalyst dosages, and temperatures. Results revealed that activity increased with larger crystallite size, higher catalyst dosage, and elevated temperature, attributable to enhanced surface reactivity and reduced charge carrier recombination. ZnO15 achieved the highest efficiencies-99.14% (RB) and 99.42% (MB) degradation within 90 min-under optimized conditions, with rate constants of 0.07195 min-1 and 0.06922 min-1, respectively. The degradation followed pseudo-first-order kinetics according to the Langmuir-Hinshelwood model. Optimal RB degradation occurred at pH 6, whereas MB degradation peaked at pH 10, reflecting the influence of electrostatic interactions between dye molecules and the ZnO surface. Scavenger experiments indicated that hydroxyl radicals were the dominant reactive species for RB degradation, while photogenerated holes played the key role in MB degradation. ZnO15 maintained significant activity over five successive cycles, suggesting good reusability. This work demonstrates that green-synthesized ZnO is an efficient photocatalyst for dye degradation under visible light and systematically assesses the influence of crystallite size, pH, catalyst loading, and temperature. While promising for wastewater treatment applications, further studies are needed to validate performance in complex effluents and under long-term operational conditions.

Water pollution from synthetic dyes poses a serious environmental threat due to their toxicity and resistance to degradation. This study reports the photocatalytic degradation of Rose Bengal (RB), a hazardous xanthene dye, using green-synthesized cadmium sulfide (CdS) quantum dots (QDs). CdS QDs were prepared with Ocimum sanctum (Tulsi) leaf extract, yielding 3.0-3.6 nm nanocrystals of hexagonal wurtzite structure and a visible-light-responsive bandgap of similar to 2.6 eV. Photocatalytic activity was evaluated under visible light by varying catalyst dosage, solution pH, and temperature. Smaller CdS QDs displayed superior performance, achieving over 91% degradation within 90 min under optimal conditions. Kinetic studies confirmed a first-order degradation process, with higher temperatures and catalyst amounts accelerating the reaction, while alkaline pH reduced efficiency. Maximum removal efficiency of similar to 99.3% was obtained using 60 mg of catalyst at 70 degrees C and pH 6. Thermodynamic analysis yielded an activation energy of 12.48 kJ/mol, with enthalpy and entropy of activation estimated at 9.79 kJ/mol and -242.85 J/mol K, respectively. Scavenger tests identified hydroxyl radicals as the dominant reactive species, followed by superoxide radicals and photogenerated holes. Reusability studies showed similar to 87% efficiency retention after four cycles, confirming catalyst stability and recyclability. This work introduces green-synthesized CdS QDs as highly efficient photocatalysts for RB degradation, achieving near-complete dye removal within 90 min under visible light. Unlike earlier reports with longer degradation times, the study provides systematic optimization of particle size, dosage, pH, and temperature, along with mechanistic insights, highlighting the sustainability and reusability of the catalyst for practical water purification.

The present study systematically investigates the effect of reaction atmosphere on the non-isothermal thermal decomposition of iron(III) acetylacetonate [Fe(C5H7O2)3], a key organometallic precursor for iron oxide nanoparticle synthesis. Thermogravimetric analysis (TGA) was performed at three linear heating rates under nitrogen (N2) and oxygen (O2) atmospheres to elucidate the decomposition behavior and its kinetic–thermodynamic characteristics. Peak deconvolution of the differential thermogravimetric (DTG) profiles revealed a five-step process in N2 and a six-step process in O2. The activation energy (Eα), pre-exponential factor (Aα), and reaction mechanism functions were determined for each step using five integral iso-conversional methods—Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, Tang, Starink, and Vyazovkin—coupled with the master plot method. The estimated kinetic parameters exhibited strong dependence on the degree of conversion, confirming the multistep and complex nature of the decomposition. The activation energy was markedly higher for the later stages in N2, whereas lower values in O2 indicate facilitated decomposition under oxidative conditions. Thermodynamic parameters (ΔH, ΔS, and ΔG) derived from kinetic data suggest endothermic and non-spontaneous decomposition steps in both atmospheres, with larger positive entropy changes in O2 implying increased molecular disorder during oxidation. X-ray diffraction (XRD) analysis of the final residues confirmed the formation of a mixed hematite–magnetite phase under N2 and pure hematite under O2. The comprehensive kinetic and thermodynamic evaluation demonstrates that the reaction atmosphere critically governs both the decomposition pathway and product phase evolution, providing mechanistic insight into the controlled formation of iron oxide nanoparticles from iron(III) acetylacetonate.

Hematite is obtained using different concentrations of P. tuberosa flower extract. XRD and Raman studies confirm the formation of nanometric size (20-30 nm) and the corundum structure. Particle size depends on the extent of flower extract used for synthesis. Frequency and temperature dependent dielectric constant, dielectric loss, ac/dc conductivity and electric modulus have been explored. Large dielectric constant values (6 x 103-40 x 103) at low frequency under room temperature are observed. Dielectric constant (epsilon r ${{\rm{\varepsilon }}}_{r}$) depends on frequency, temperature, particle size and porosity. The nature of the frequency dependence of epsilon r ${{\rm{\varepsilon }}}_{r}$ can be explained with the help of the Maxwell-Wagner-Koop's theory. Correlation between particle size and dielectric constant is attributed to significant lattice distortion resulting from reduced grain size. AC conductivity is analyzed with Jonscher's power law, and correlated-barrier-hopping type of conduction mechanism is proposed in these nanomaterials. Temperature dependence of DC conductivity confirms semiconducting behavior of hematite. Investigation into the electric modulus reveals that both electrical conduction and dielectric polarization are governed by a common mechanism. Present study explores into the process of crystal growth influenced by the plant extract and examines its impact on the dielectric property.

This study investigates the dielectric and electrical properties of zinc ferrite (ZnFe₂O₄) nanoparticles synthesized via a sustainable myco-mediated route using Oyster mushroom extract as a bio-capping agent. Structural analysis confirmed crystallite sizes ranging from 16 to 28 nm, demonstrating that fungal phytochemicals effectively modulate particle size and microstructural parameters. The dielectric constant of the nanoparticles was found to be remarkably high ( 24,854 at low frequencies) with comparatively low dielectric loss, both strongly dependent on frequency, temperature, and particle size. The dielectric dispersion was well-explained by the Cole–Cole model, indicating poly-dispersive relaxation behavior. AC conductivity, interpreted through Jonscher’s power law, revealed distinct conduction pathways: non-overlapping small polaron tunneling (NSPT) for pristine ZnFe₂O₄ and correlated barrier hopping (CBH) for the green-synthesized samples. Electrical modulus analysis further confirmed short-range charge carrier mobility with non-Debye relaxation. Temperature-dependent DC conductivity followed Arrhenius behavior, with activation energies decreasing systematically with increasing particle size, highlighting thermally activated conduction. The synergy of ultra-high dielectric constant, low dielectric loss, and tunable conduction mechanisms underscores the potential of green-synthesized ZnFe₂O₄ nanoparticles for capacitors, memory storage devices, and smart sensors.To the best of our knowledge, this is the first report on dielectric properties of green-synthesized ZnFe₂O₄ nanoparticles, where Oyster mushroom extract not only enables an eco-friendly fabrication route but also provides precise control over dielectric performance through particle size engineering.

In present study, the synthesis of zinc ferrite (ZnFe2O4) nanomaterials using Pleurotus ostreatus (Oyster mushroom) extract using bio-inspired green method is reported. The synthesized ZnFe2O4 nanomaterials are characterized using techniques likes XRD, FTIR, Raman, absorption, photoluminescence, SEM, HR-TEM and magnetic studies. X-ray diffraction analysis confirm the structure, purity and extract control nanoscale size (16.00–28.08 nm) of the ZnFe2O4 nanomaterials. FTIR, Raman, UV–Vis, and photoluminescence studies support the formation of pure ZnFe2O4 nanomaterials. FT-IR analysis identifies different functional groups present in the ZnFe2O4 nanomaterials, while Raman spectra show characteristic peaks corresponding to ZnFe2O4 spinel structures. UV–Vis–NIR absorption spectra, which also show a number of electronic transitions connected to absorption bands and allow estimation of direct (2.19–2.30 eV) and indirect (1.50–1.54 eV) energy band gap values. The absorption data is utilized to calculate Urbach energy (0.37–0.40 eV), which describe the role of defects in these materials. Photoluminescence spectra display two peaks (one in visible region and the others in NIR region) indicating the presence of different defect levels in the nanoparticles. From SEM/TEM images the surface morphology, size, shape, and distribution of the nanoparticles are explored. These ZnFe2O4 nanomaterials show photocatalytic activity under the irradiation of visible light, degrading Methylene Blue and Rose Bengal dyes in water without additional additives. The photodegradation reaction rates are determined, showcasing the potential of these materials in environmental nano remediation. Photodegradation efficiency strongly depends on catalyst’s size, dose and reaction temperature. Controlling the optimizing condition faster photodegradation rate can be achieved. Noted that the catalyst can be recycled. Here, the dye degradation mechanism is discussed. Scavenger test indicates that the OH* radicals majorly lead the photodegradation process. Overall, present study highlights the significant influence of Oyster mushroom extract on the structural, optical and photocatalytic properties of the green synthesized ZnFe2O4 nanomaterials.

In recent years, water pollution has become a pressing global issue because of the continuous release of organic dyes from various industries. Therefore, finding an easy way to remove these harmful dyes from water has drawn the attention of researchers. This study investigates the removal of toxic Rose Bengal (RB) dye using hematite nanoparticles as a visible light photocatalyst without any additive. It is observed that by controlling particle size, quantity of the nanoparticles and reaction temperature, the dye degradation can be improved up to 95.33% with a half-life of 26 min. To understand photodegradation kinetic behavior, the Langmuir-Hinshelwood kinetic equation can be employed. The scavenger test indicated that the OH* radicals majorly led to the photodegradation process. The reaction rate values strongly depended on the size, quantity of the nanoparticles and reaction temperature. Controlling the optimizing condition, faster reaction rate (k = 0.027 min-1) can be achieved as compared to earlier reports. It is also noted that the change in the degradation efficiency of the reused catalyst is negligible when compared to the fresh one. Here, the dye degradation mechanism is discussed. Overall, this study reveals that hematite nanoparticles can be used as efficient photocatalyst for dye degradation applications by optimizing the controlling factors. These observations provide novel perspectives on the development of effective and sustainable photocatalytic technologies for pollution control and water treatment applications.

We report the results obtained on the studies made for temperature and frequency dependence of the dielectric constant, loss and ac conductivity for pristine and green-synthesized ZnO nanoparticles as well as investigations of their electric modulus. Frequency-dependent dielectric studies are carried out with the pelletized samples of ZnO at different temperatures. At lower frequencies (< 1 kHz) and at higher temperatures the ZnO nanoparticles have giant dielectric constant values (~ 4x104), and such a temperature-dependent giant dielectric constant has not been seen earlier, to our knowledge, in any pristine ZnO nanoparticle. In the lower frequency region and below 100○C the nature of temperature dependence of the dielectric constant for pristine ZnO is in contrast with that observed for the green-synthesized ZnO nanoparticles. This anomalous temperature dependence of dielectric constant may be correlated with combined effect of the in-plane and out of plane thermal-expansion coefficients of ZnO. A temperature-dependent poly-dispersive relaxation mechanism in these materials have been observed. The electrical conduction mechanism is found to be significantly modulated by the use of the extract. Electric modulus study reveals that the electrical conduction and dielectric polarization follow the same mechanism in these ZnO nanoparticles. The dependences of the dielectric constant, dielectric loss, conductivity and polarization mechanisms observed in the synthesized ZnO nanoparticles are envisaged as the signatures of the effective control of the flour extract on the crystal growth and formation of grain boundaries. A plausible growth mechanism of the ZnO nanoparticles in presence of the flower extract containing phytochemicals is also provided.

The article describes synthesis of green-mediated hematite nanoparticles (20-30 nm) using Polianthes tuberosa flower extract. Structural, microscopic, and magnetic studies confirm the synthesis of iron oxide nanoparticles of pure hematite phase. Spectroscopic techniques are employed to identify different electronic transitions and defect levels as well as to estimate the energy bandgap and Urbach energy. A correlation among the particle size, bandgap energy, and Urbach energy is noticed. These hematite nanoparticles act as visible light photocatalyst which degrade dye in aqueous medium without the addition of any additives. The catalyst particle size, catalyst quantity, pH of dye solution, and solution temperature have significant impact on the photodegradation process of dye molecules in aq. solution. All observations advocate that green synthesis of hematite nanoparticles with Polianthes tuberosa flower extract can significantly modulate their optical and photocatalytic properties. These materials may find potential uses in water splitting for hydrogen production and purification of water by removing organic pollutants. The study highlights that using commercially cheap starting materials and extract made from naturally available plant parts, materials having huge application potentials can be synthesized at low cost by the simple green synthesis approach.

The present study describes the green synthesis of hematite (α-Fe 2 O 3 ) nanomaterials using the Tabernaemontana divaricata flower extract as a reducing/capping/stabilizing agent and the changes observed in the structural, optical, magnetic and dielectric properties of the product with respect to the pristine counterpart. Powder XRD study showed that use of the extract in green synthesis produces hematite nanomaterials of reduced size, whereas FE-SEM, HRTEM and EDX studies revealed the morphology, particle size distribution, crystallinity as well as the elemental contributions. FT-IR spectroscopy detected the different functional groups and metal-ion bonding present in the synthesized nanomaterials. Raman study observed the seven Raman active (two A 1g and five E g ) modes with different intensities. From the UV–Vis study, different electronic transitions occurred in the hematite nanomaterials were identified, and the direct (1.90–1.97 eV) and indirect (1.21–1.46 eV) energy band gap values were estimated. Two photoluminescence peaks (one in visible and the other in near infrared region) detected in the spectra indicated the presence of various defect levels in the hematite nanoparticles within the energy band gap. Magnetic measurements exhibited the Morin transition to occur in these materials, while Mössbauer spectra successfully showed the magnetic contribution of the iron atoms occupying the core and the surface parts of the nanoparticles. Use of the extract in green synthesis produced hematite nanomaterials with extremely high dielectric constant (~ 10 5 ) and significantly lower dielectric loss at low frequency and at room temperature when compared to the pristine one which signify their huge application potential. The results obtained from the characterization studies made on the pristine and green synthesized hematite nanomaterials revealed that the green synthesis of hematite nanoparticles using Tabernaemontana divaricata flower extract can efficiently modify their optical, magnetic and dielectric properties. Thus, using commercially cheap starting materials and extracts made from naturally available plant parts, materials having huge application potentials (like microwave and energy storage appliances) can be synthesized at low-cost by the simple green synthesis approach.

Background:: Solid state reaction of iron(III)citrate leads to a range of ironbased oxides by varying the reaction conditions, e.g., the presence of co-precursor. The influence of reaction conditions on the kinetics of the solid-state reaction of iron(III)citrate needs to be investigated. Objective:: Kinetic analysis of the solid-state reaction of iron(III)citrate in the presence of a co-precursor has been explored to realize the influences of the co-precursor on the reaction process as well as decomposed material. Method:: Non-isothermal thermogravimetry profiles are deconvoluted to individual reaction steps. The model-free kinetic methodology is utilized to estimate step-wise activation energy and, hence, the reaction mechanism along with the reaction rate. Conversiondependent thermodynamic parameters and nucleation rate are estimated. XRD analysis has been used to characterize the decomposed material. Results:: Thermogravimetry profiles obtained for an iron(III)citrate and malonic acid mixture are deconvoluted into six steps. The decomposed nanomaterial is identified as magnetite (size 10 nm). The observed reaction mechanisms associated with each step are different, where the activation/reaction rate is conversion-dependent. A good fit between the experimental and reverse-constructed conversion profiles is obtained. The nucleation rate at higher temperatures is affected by both the extent of conversion and the heating rate. A possible reaction pathway is proposed. The study elucidates the role of malonic acid as a co-precursor in modifying the thermal reaction of iron(III)citrate and product formation. Conclusion:: This investigation proposes the applicability of suitable co-precursors as a potential controlling factor for preparing iron oxides from iron-based compounds.

In this work, zinc sulfide (ZnS) QDs were synthesized using green technique with the help of Tabernaemontana divaricata flower extract as capping/stabilizing agent, characterized by different physical techniques, like XRD, FESEM, EDX, TEM, FT-IR, XPS, UV–Vis–NIR, and PL, and were compared with their pristine analogue. From XRD analysis, it is observed that the size of the synthesized ZnS QDs lie in 1.79–1.46 nm range and with addition of flower extract particle size decreases. FT-IR analysis indicated the functional groups present in the synthesized QDs. The direct energy band gap (3.21–3.51 eV) values as well as the refractive index values (2.28–2.33) of the QDs were calculated utilizing the absorption data. Due to various defect levels present in the ZnS QDs within the energy band gap, four peaks (three in visible and the other in NIR region) were observed in the PL spectra. Surface morphology and elemental composition of the particles were understood from FESEM and EDX studies. Dielectric constant, loss, and ac and dc conductivity of the materials were studied. At room temperature, all synthesized ZnS materials exhibited high dielectric constant ( ε_r ) values in the low-frequency region. It is found that ε_r values for pristine ZnS QD ( 23,000) are much higher than the green ZnS QDs ( 100–800) where overall dielectric loss is less than 2 which decreases with QD size. Results obtained from the characterization studies conducted on pristine and green-synthesized ZnS QDs elucidate that it is possible to effectively control the size, optical, and dielectric properties of the potentially important ZnS QDs through green synthesis technique.

Recently, we have reported the influence of various reaction atmospheres on the solid-state reaction kinetics of ferrocene, where oxalic acid dihydrate was used as a coprecursor. In this light, present study discusses on the nature of decomposed materials of the solid-state reactions of ferrocene in O-2, air, and N-2 atmospheres. The ambient and oxidative atmospheres caused the decomposition to yield pure hematite nanomaterials, whereas cementite nanomaterials along with alpha-Fe were obtained in N-2 atmosphere. The obtained materials were mostly agglomerated. Elemental composition of each material was estimated. Using the absorbance data, the energy band gap values were estimated and the related electronic transitions from the observed absorption spectra were explored. Urbach energy was calculated for hematite, which described the role of defects in the decomposed materials. The nanostructures exhibited photoluminescence due to self-trapped states linked to their optical characteristics. Raman spectroscopy of hematite detected seven Raman modes, confirming the rhombohedral structure, whereas the D and G bands were visible in the Raman spectra for cementite. Thus, the reaction atmosphere significantly influenced the thermal decomposition of ferrocene and controls the type of nanomaterials obtained. Plausible reactions of the undergoing solid-state decomposition have been proposed.

Thermal decomposition of 1-(ferrocenyl)ethanol was carried out under N 2 and O 2 atmospheres. Peak deconvolution method was used to separate the overlapped peaks and hence to obtain the temperature range of individual reactions. The decomposition followed two steps for N 2 atmosphere while for O 2 atmosphere three steps were observed. The integral iso-conversional methods (FWO, KAS, Tang, Starink, Vyazovkin and Akbi) were used to estimate the activation energy. The activation energies estimated are comparatively higher for FWO method in comparison to other methods while that estimated following other methods are quite close. Step-wise reaction mechanism functions have been determined. Simulated conversion plots were compared with the experimentally observed plots, and their close agreement implied the accuracy of the kinetic method adopted for analysis. Utilising the estimated kinetic parameters, thermodynamic parameters (Δ S , Δ H and Δ G ) were calculated. All estimated kinetic and thermodynamic parameters indicate the strong influence of gaseous medium used for solid state thermal decomposition. Thermally decomposed materials were characterized with powder XRD, SEM and EDX studies. From the characterization results it was concluded that thermal decomposition of 1-(ferrocenyl)ethanol led to the formation of nanocrystalline iron oxides only in oxidative atmosphere. It was proposed that at the initial state of decomposition magnetite might have formed as an intermediate which with increase of temperature first converted to maghemite and then gradually to hematite. The present study, through kinetic analysis and characterization of the decomposed materials, convincingly establishes the significant effect of the reaction atmosphere on the thermal decomposition of an organo-iron compound as well as the nature of the material produced.

Zinc oxide nanoparticles (ZnO NPs) were synthesised using Tabernaemontana divaricata flower extract (TFE) in different weight percentages by facile, eco-friendly and cost-effective green synthesis method. Formation and structure of the ZnO NPs were studied by powder XRD, FT−IR, Raman and TEM studies. The crystals formed are of hexagonal wurtzite structure with biological functional groups attached. Average crystallite size of the ZnO NPs (17.5−23.3 nm) was obtained from the analysis of powder XRD data which increased with increase of TFE amount while the estimated values of dislocation density and micro-strain exhibited an opposite behaviour. The optical (direct and indirect) energy band gap values estimated using UV–vis DRS spectral data decreased with increasing amount of TFE. The photoluminescence spectra for the ZnO NPs exhibited multiple peaks spread over the visible region with one peak in the NIR region indicating the existence of various defect levels of Zn and O. Position of these defect levels within the band gap was assigned which is significantly modulated by TFE. TFE amount-dependent peak shift and/or peak broadening were observed in the Raman spectra of the ZnO NPs which were correlated with the growing disorder in the crystals induced by the extract molecules. FESEM study showed the agglomerated NPs with quasi-spherical morphology. Particle size of the ZnO NPs was estimated from FESEM images. EDX study indicated that increased presence of TFE in ZnO decreased the oxygen content in the synthesised material. HRTEM study revealed the agglomeration of nanoparticles with single crystalline nature. Present study convincingly established that flower extract used for the green synthesis efficiently modified the structure and optical property, defect levels and morphology of the potentially useful ZnO nanoparticles.

Thermal decomposition of a mixture of ferrocene carboxaldehyde and oxalic acid dihydrate in O2 atmosphere produced rod-like hematite nanomaterial. The decomposition reaction was complex as evident from the overlapped multistep reaction steps in the non-isothermal thermogravimetry (TG) profiles obtained in the 300-700 K range. A peak deconvolution method was applied to separate the overlapped reaction steps. The multistep TG profiles were successfully deconvoluted, which showed that the decomposition occurs in six individual steps. However, it was found that only the last three reaction steps were responsible for the production of hematite. To estimate the activation energy values for these thermal reactions, six model-free integral isoconversional methods were used. The activation energy value significantly depends on the extent of conversion in each step; however, the nature of its dependence significantly different for each step. The most probable stepwise reaction mechanism functions for the solid-state reactions were obtained using the master plot method. The reaction mechanism was found to be different for different steps. Utilizing the activation energy and reaction mechanism function, the reaction rates of decomposition for each step were determined. To substantiate the validity of the assumed kinetic models, the experimental conversion curves were compared with the constructed ones, and the agreement was quite reasonable. The conversion-dependent thermodynamic parameters were obtained utilising the estimated kinetic parameters. Role of the co-precursor in the thermal reaction of the precursor was plausibly revealed. The present study describes how the use of a co-precursor significantly enhances the thermal decomposition of the precursor, how hematite nanomaterials can be synthesized from a co-precursor driven solid state reaction at low temperatures, and how the kinetic calculations facilitate the understanding of the solid-state reaction process. This study proposes the use of a suitable combination of precursor and co-precursor for solid-state thermal synthesis of iron-based nanoparticles using organo-iron compounds as precursor and also illustrates the effective application of the thermal analysis technique to understand the decomposition reaction.

We explore the solventless synthesis of iron oxide nanomaterials obtained on thermal conversion of iron(III)citrate in presence of malonic acid and glucose as co-precursors in varying weight ratios and physical characterization of the materials obtained. Pure phase of hematite was found only for a particular combination of precursor and co-precursor and else a mixture of hematite and magnetite. Significant effect of the co-precursors on the nature and size of the synthesized materials was noticed. Gradual conversion of hematite to magnetite with increasing amount of co-precursor was established. Morin transition was observed in the temperature dependent magnetization study for the hematite materials. Absorption spectroscopy exhibited three different electronic transitions that take place within the 3d 5 shell of the octahedrally coordinated Fe 3+ ions for hematite materials. The optical (direct and indirect) band gaps estimated from the Tauc’s plot showed particle size dependence. From photoluminescence study the transitions of trapped electrons in various defect states of oxygen vacancies were observed which led to the appearance of nonradiative peaks. In the Raman spectra the significant bands of hematite (A 1g and E g bands) were noted. From morphology study the hematite nanomaterials appear as clusters of large irregular shaped particles of various sizes. Formation of hematite nanomaterials as observed by XRD studies was supplemented by the SAED patterns obtained in the HRTEM study. Present study established that nano-sized pure hematite materials can be thermally synthesized at comparatively lower temperature on thermal decomposition of iron(III)citrate by varying the weight ratio of suitable co-precursors.

The present article investigates the thermal decomposition of ferrocene in the presence of oxalic acid dihydrate in oxidative and inert atmospheres. A mixture of ferrocene and oxalic acid dihydrate on thermal decomposition in O-2 and N-2 atmospheres produces hematite and cohenite nanomaterials, respectively. These decompositions are complex and reflected through multiple overlapped reaction steps in the thermogravimetry profiles, and peak deconvolution method is adopted to separate the reaction steps involved. It is found that the synthesis of hematite is a two-step process, while that of cohenite is a one-step process. Model-free integral isoconversional methods are adopted to estimate the values of activation energy for these thermal reactions. The most probable reaction mechanism and the reaction rate of thermal decomposition are determined by an intercept-based model fitting method. The reaction mechanism is found to be different for different steps. To verify the suitability of the adopted kinetic models, the experimental conversion curves are compared with the reversely constructed ones and the agreement is quite reasonable. The conversion dependence of thermodynamic parameters is obtained using the estimated kinetic parameters. Comparing the estimated values of the kinetic and thermodynamic parameters, the effect of the reaction atmosphere on the thermal decomposition process of ferrocene is realized. Utilizing the kinetic and thermodynamic parameters conversion-dependent nucleation rates of the reaction steps have been estimated. The present study describes how different nanomaterials of iron can be synthesized starting with the same precursor material, how the reaction (solid and gaseous) atmosphere affects the reaction profile and the residual material, and finally, how kinetic calculations help in understanding the solid state reaction process involved. This study suggests the use suitable combination of precursor, co-precursor, and gaseous reaction atmosphere for the solid-state thermal synthesis of iron-based nanoparticles using organo-iron compounds. The study also highlights the successful application of the peak-deconvolution method.

Hematite nanomaterials were obtained on thermal decomposition of (i) iron (III) citrate, (ii) 3:1 mixture of iron (III) citrate and malonic acid, and (iii) 3:1 mixture of iron (III) citrate and glucose. The average particle size (22–55 nm) of the nanomaterials was significantly affected by the co-precursor. Frequency and temperature dependence of the dielectric constant, dielectric loss and ac conductivity of these hematite nanomaterials were studied. High values of the real part of dielectric constant ( ε^' ) were observed in the low-frequency region which eventually reached a frequency independent constant value above 10 kHz. A decrease in the value of ε^' with increase in temperature and an increase in the ε^' value with increase in the particle size were noticed. For the entire set of nanomaterials, the dielectric loss was found to have a decreasing tendency with increase in frequency with small humps at higher frequencies owing to the existence of relaxing dipoles. These nanomaterials were found to be non-Debye type and poly-dispersive. For all hematite nanomaterials, the ac conductivity followed Jonscher’s power law, and the particle-size-dependent conduction mechanisms (correlated-barrier-hopping for D = 22.5 nm and non-overlapping small polaron tunneling for D > 22.5 nm) in these nanomaterials were established. The dc conductivity values were measured as a function of temperature to confirm the semiconducting nature of these nanomaterials. The activation energy values derived from the dc conductivity studies decreased with increasing size of the nanoparticles. Analysis of the electric modulus study showed that the relaxation peaks shifted towards lower frequency with increasing temperature and found that the electrical conduction and dielectric polarization follow the same mechanism in these nanomaterials. The thermally synthesized hematite nanomaterials exhibited particle-size-dependent high dielectric constant and lower dielectric loss which highlight the synthetic method adopted as well as the synthesized materials’ suitability for applications.