Optimum Calcination Temperature Research Articles

Optimization of Anatase TiO2 Photocatalyst for Diclofenac Degradation by Using Response Surface Methodology

Titanium oxide semiconductors are considered effective photocatalysts for the degradation of organic pollutants. The photocatalytic activity of titanium dioxide is influenced by several factors, one of which is its phase composition, with anatase being considered the phase with the highest photocatalytic activity. In this work, a simple acid-assisted sol–gel process was used to synthesize a pure anatase phase by varying the synthesis and calcination temperature. The synthesized materials were characterized using various techniques and tested under simulated sunlight irradiation for the photocatalytic degradation of the drug diclofenac sodium (DCF), for which the pseudo-first-order apparent degradation rate constant and mineralization efficiency were determined. A pure anatase phase with high photocatalytic activity (up to 97% TOC removal) was obtained when TiO2 was synthesized at between 70 °C and 100 °C and calcined at between 400 °C and 500 °C. Furthermore, the obtained data were used to predict the optimal anatase synthesis and calcination temperatures for DCF removal using a response surface methodology (RSM) method. The model predicted a synthesis temperature of 71 °C and a calcination temperature of 440 °C, which should result in a pseudo-first-order DCF decay rate constant of 0.055 min−1 and a TOC removal rate of 100%. The experimentally determined values for the degradation rate (0.063 min−1) and TOC removal (97%) were in good agreement with the model’s predicted values.

Optimizing Magnetic, Mechanical, and Electrical Properties of Cobalt-Substituted Zinc Chromite Spinel via Microwave-Hydrothermal Synthesis

Abstract Using the microwave-hydrothermal technique, researchers synthesized a cobalt-substituted zinc chromite spinel structure with the formula Zn1 − xCoxCr2O4 (x = 0.0, 0.25, 0.50, 0.75, 1.0). The resulting powder underwent analysis via X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) to determine the ideal conditions for eliminating organic components from the fired pellet. After establishing the optimal initial calcination temperature, all powder samples were calcined at 600 °C, then compressed and fired at 1300, 1400, 1500, and 1600 °C. The fired pellets were then examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Additionally, researchers evaluated the pellets’ physical, electrical, dielectric, magnetic, and mechanical properties. The findings indicated that 1600 °C was the optimal firing temperature for the pellets. The apparent porosity decreased, and the bulk density increased with increasing Co content and firing temperature. Enhancements in magnetization, mechanical, and electrical conductivity, dielectric properties, and elastic moduli were observed by increasing the cobalt content. Porosity has a significant impact on mechanical properties. The mechanical properties were slightly reduced for zinc-rich pellets. The dielectric constant and the dielectric loss increased with increasing Co content at 1 MHz. In addition, the results show that the dielectric constant and dielectric loss factor decreased with increasing frequency, whereas the A.C. electrical conductivity increased with increasing frequency.

Investigation of the optimum calcination temperature for water treatment plant sludge to develop a sustainable alkali activated concrete

Nowadays, Egypt is treating the Nile River Water to produce drinking water, and this process generates large amounts of waste, around 635 million m3 annually, which is called water treatment plant sludge (WTPS). This WTPS cost the government around 30 million US dollars to return it back to the Nile River in addition to negatively affecting the environment. Therefore, there is an urgent need to find environmentally friendly alternatives that reduce the impact of such an issue. This paper focuses on treating WTPS by drying, grinding and calcining to develop it as an alternative binder for use in alkali-activated concrete. This approach would not only provide green construction material but also reveal an environmental disposal route for the sludge produced in Egypt or in any country has the same issue. The treatment methodology used in this study was based on finding the optimum calcination temperature regime for WTPS after drying and grinding. Fifteen specimens of WTPS powder were used to investigate the optimum calcination temperature and duration by applying different temperatures ranging from 500 °C to 800 °C for various exposure durations of 30, 60 and 90 min. XRD and Chapelle tests were employed to chemically investigate the efficiency of the obtained calcined WTPS specimens, while strength activity index and compressive strength tests were used to mechanically verify the findings of the chemical tests. The results indicated that the calcination regime, which involved applying a maximum temperature of 650 °C for 90 min, achieved the best chemical characteristics and a strength activity index of 145%. Moreover, this regime resulted in a compressive strength of 21 MPa when WTPS powder was used as a precursor in alkali-activated concrete. Additionally, this paper presented a brief comparison of the production cost and energy consumption between cement and WTPS. The comparison demonstrated the efficiency of using WTPS as a replacement for cement, showing that the production of WTPS costs 50% less and consumes 92% less energy than cement.

Production of mortar with calcined alum sludge as partial cement replacement

Alum sludge is a largely generated and disposed waste from water treatment plants. This study aimed to produce mortar using alum sludge calcined at different temperatures (600 – 900 ºC). After the optimal calcination temperature was selected, the calcined alum sludge was used to replace 5, 10, and 15 % of cement by mass in mortar. The performance of the mortars was evaluated based on the workability, compressive strength, flexural strength, porosity, and percentage of water absorption. Mortars with alum sludge calcined at 800 ºC had the highest strength as compared to the other temperatures. The mechanical strength of mortars reduced while the porosity and percentage of water absorbed increased with increasing calcined alum sludge content. Although replacing 5 % of cement with calcined alum sludge would reduce the mechanical strengths by 13 – 15 %, it was still acceptable as it had negligible influence on the porosity and water absorption value of the mortar. In short, the partial substitution of cement with calcined alum sludge should be limited within 5 % to maintain the performance of the mortar.

Transformations of diatomite components and changesin its technical properties caused by calcination at different temperatures – a case study of the Jawornik deposit, Poland

Diatomite rocks from the eastern part of the Polish outer Carpathians come in several varieties with different colour, compactness, amount of clay and sandy substance as well as the degree of silicification. One of them is dark grey blocky diatomite, present in the Jawornik deposit and characterised by average quality. During the tests, it was thermally calcined at temperatures from 300°C to 1,200°C in order to improve its functional properties. The results of observations regarding the changes that the rock and its components underwent under conditions of increasing temperature were presented. The results of thermal analysis, X-ray diffraction and tests of physical properties (i.e. density, water absorption and Vickers microhardness) of the rock were presented. Detailed observations of the rock’s mineral components were made using a scanning microscope. Their physical changes (e.g. cracks or signs of melting) and chemical transformations were described. It has been shown that during calcination, irreversible changes occur in the mineral composition and structure of diatomite. It was proven that for the discussed diatomite the optimal calcination temperature is 900°C, as it ensures the greatest increase in its open porosity by 11% and an almost threefold increase in its hardness. The chemical composition of diatomite also changes due to the combustion of the organic matter present in it and the resulting relative increase in the 1,200 content. Calcination improves the technological features of this variety of diatomite, making it similar to the best quality varieties found in this deposit.

Fabrication of (111) oriented BaTiO3 microplatelets by the topochemical microcrystal conversion

Template crystals with high diameter-to-thickness ratio (DTR) were critical to prepare high-performance texture piezoelectric ceramics. The (111) BaTiO3 templates with high DTR larger than 15 were prepared using the molten salt synthesis. Firstly, the optimized molar ratios of BaCO3/TiO2 and NaCl/KCl for the Ba6Ti17O40 (B6T17) precursor were 6.9:17 and 3:1, respectively. The TG-DSC analysis revealed that the optimal calcination temperature was 1060 °C. Secondly, the highest DTR value for B6T17 could reach at 50:1, which further guaranteed final DTR of (111)-oriented BT templates ranged from 15 to 20 by calcined at 950 °C. The excessively high ratios of NaCl/KCl and high calcination temperature were harmful to the high DTR and the template integrity. Finally, activated (111) BT templates induced matrix powders to form textured diamond-shaped grains successfully.

Optimizing calcination temperature to improve the compressive strength of coal gasification slag-based alkali-activated materials by reducing carbon content and adjusting polymerization degree

The efficient utilization of coal gasification slag (CGS) to prepare alkali-activated materials (AAMs) presents a significant opportunity for addressing the challenges associated with solid waste accumulation and environmental degradation. However, the aluminosilicate glass in CGS is highly polymerized, rendering it challenging to stimulate its potential reactivity. Additionally, the presence of residual carbon impedes the hydration process in AAMs, thereby limiting its applicability. This study focuses on the residual carbon content and polymerization degree of CGS after calcination treatment to overcome these challenges and improve the reactivity of CGS. Results revealed that residual carbon in CGS underwent thermal decomposition, increasing the proportion of aluminosilicate glass components. The degree of polymerization of CGS was reduced by 25 % under calcined conditions at 550°C, whereas at 700°C, CGS recrystallized, and the aluminosilicates were again highly polymerized. The highest reactivity of CGS was observed after calcination at 550°C. The 28 days compressive strength of the prepared AAM paste reached 47.5 MPa, representing an increase of 18.45 % compared to the control. This study innovatively elucidates the physicochemical properties of calcined CGS. It highlights the critical importance of controlling calcination conditions to manage the polymerization degree and phase transformations during carbon removal, thereby enhancing the reactivity and performance of AAMs.

Study of phase transformation of calcium silicate using desert sand as raw materials

AbstractProduction of Portland cement consumes a huge amount of silica mineral. The present work aims to introduce desert sand to replace the natural mineral to achieve green manufacturing of silicate cement clinker, as well as further decreasing the synthesis temperature and increasing the production efficiency. The effects of desert sand, industrial quartz and high‐purity quartz as raw materials, and Al2O3 and Fe2O3 as additives on phase transformation and microstructure of calcium silicate powder were comparably investigated using X‐ray diffractometer, differential scanning calorimeter, and scanning electron microscopy. Results show that the main phases of all samples with different raw materials and additives were 3CaO·SiO2 (C3S) and 2CaO·SiO2 (C2S). In which, the samples prepared using desert sand had the lowest phase transformation temperature for C2S and C3S. When adding Al2O3 and Fe2O3, the phase transformation temperatures of C2S and C3S further decreased, which were 1032.5°C and 1270.9°C, respectively, meanwhile phase content reached the maximum (C2S of 65.6 wt.% and C3S of 61.2 wt.%). In addition, the most uniformly and finely distributed crystalline phases formed at an optimal calcination temperature of 1350°C. This is beneficial for reducing production costs, saving mineral resources, and promoting the sustainable development of the cement industry.

Electrochemical performance enhancement of perovskite-type Li0.3La0.57TiO3 ceramic electrolyte by controlling synthesis parameters

This study investigates the enhancement of the electrochemical performance of perovskite-type Li0.3La0.57TiO3 (LLTO) solid electrolytes through the optimization of synthesis parameters of a sol-gel process. The primary focus lies in examining the impact of calcination temperature on the structural, morphological, and electrochemical properties of LLTO. Our findings reveal that controlling the calcination temperature significantly influences the grain boundary resistance and overall ionic conductivity. The optimal calcination temperature was identified to be 800 °C, yielding a remarkable improvement in ionic conductivity at grain boundaries (0.88 mS/cm), and total ionic conductivity (0.54 mS/cm), at 30 °C. This enhancement is attributed to the refined microstructure, increased density, and reduced porosity, which collectively facilitate lithium-ion diffusion. These advancements in LLTO electrolytes present promising implications for their application in all-solid-state lithium-ion batteries, offering a safer and more efficient alternative to conventional liquid electrolyte systems.

An experimental and theoretical validation of dual role of Fe on improving the photocatalytic performance of doped mixed phase titania

The present work proposes a strategic approach of using Fe doping to form a mixed-phase TiO2 direct Z-scheme catalyst at low onset temperature. The doping-induced modifications are explained from the experimental and theoretical viewpoint. Fe-doped Z-scheme-based mixed-phase TiO2 at optimal calcination temperature (TiFe-400) exhibits maximum photon absorption and reduces charge carrier recombination, enhancing photocatalytic and PEC performance. TiFe-400 has the highest rate constant for the degradation of MB (0.084 min−1 under solar irradiation) and showed exceptional photooxidation current (0.8 mA, 1.3 V vs Ag/AgCl). The Z-scheme formation significantly inhibits the recombination of photocarriers, resulting in a directed migration of charge carriers to the high redox potential mixed-phase TiO2. This migration is validated by identifying the primary reactive species participating in the photocatalytic process. This work, demonstrating both experimental and theoretical approaches, may provide valuable insight into designing stable and inexpensive catalysts for dual applications on an industrial scale.

Optimizing Construction Spoil Reactivity for Cementitious Applications: Effects of Thermal Treatment and Alkaline Activation

Construction spoil (CS), a prevalent type of construction and demolition waste, is characterized by high production volumes and substantial stockpiles. It contaminates water, soil, and air, and it can also trigger natural disasters such as landslides and debris flows. With the advent of alkali activation technology, utilizing CS as a precursor for alkali-activated materials (AAMs) or supplementary cementitious materials (SCMs) presents a novel approach for managing this waste. Currently, the low reactivity of CS remains a significant constraint to its high-value-added resource utilization in the field of construction materials. Researchers have attempted various methods to enhance its reactivity, including grinding, calcination, and the addition of fluxing agents. However, there is no consensus on the optimal calcination temperature and alkali concentration, which significantly limits the large-scale application of CS. This study investigates the effects of the calcination temperature and alkali concentration on the mechanical properties of CS–cement mortar specimens and the ion dissolution performance of CS in alkali solutions. Mortar strength tests and ICP ion dissolution tests are conducted to quantitatively assess the reactivity of CS. The results indicate that, compared to uncalcined CS, the ion dissolution performance of calcined CS is significantly enhanced. The dissolution amounts of active aluminum, silicon, and calcium are increased by up to 420.06%, 195.81%, and 256.00%, respectively. The optimal calcination temperature for CS is determined to be 750 °C, and the most suitable alkali concentration is found to be 6 M. Furthermore, since the Al O bond is weaker and more easily broken than the Si O bond, the dissolution amount and release rate of active aluminum components in calcined CS are substantially higher than those of active silicon components. This finding indicates significant limitations in using CS solely as a precursor, emphasizing that an adequate supply of silicon and calcium sources is essential when preparing CS-dominated AAMs.

OBTAINING COAGULANT FROM AUMINZATAU KAOLIN FOR PPM WASTEWATER PURIFICATION

This article is devoted to the development of methods for obtaining raw materials and coagulants based on Auminzatau kaolin at the Zarkuduk site and the treatment of highly coloured wastewater from the production of paper from rice and wheat straw. The yield of kaolin, treated with a 30 % hydrochloric acid solution at an optimum calcination temperature of 500°C for 90 min, was 97.5 %. The optimum temperature for the interaction of hydrochloric acid is 25 - 30°C for 30 - 45 min. The efficiency of the coagulant application is 97.5 %.

Effect and mechanism of calcination on improving the hydration activity of titanium extraction slag

Titanium extraction slag (TES) is a special waste residue in China’s Panxi region. It exhibits low hydration activity because of its high titanium content and carbon- and chlorine-based impurities introduced during production. Thus, TES wastes can only be stored in large quantities. Oil and gas wells’ high-temperature and high-pressure environments contribute to TES hydration. However, its hydration activity should be improved to transform it into a well cementing material. The optimal calcination temperature was 550 ℃. Using NaOH (6 %) as an activator, the compressive strength values of the calcined TES cured for 1 and 14 days reach 19.23 and 34.40 MPa, respectively, 65.49 % and 39.78 % higher than those of untreated TES. These values meet oil and gas well cementing construction requirements. X-ray diffraction, 29Si nuclear magnetic resonance, scanning electron microscopy, and other characterization methods indicate that calcination can reduce the content of the glassy phase in TES. However, it induces impurity removal and reduces the degree of glassy phase polymerization. Thus, TES’s ion leaching and deposition rates, hydration, and compressive strength after calcination improved. Therefore, the method proposed in this study can be successfully used to convert TES into new cementing materials for large-scale applications.

Lime reactivity and overburning: the case of limestones belonging to Tuscan Nappe sequence (NW Tuscany, Italy)

This study examines limestone properties and calcination process to enhance product quality. Limestone burning produces lime (CaO, calcium oxide) and carbon dioxide (CO2). Lime is a substance highly reactive and turns into slaked lime (Ca(OH)2, calcium hydroxide) when exposed to water. Six limestone samples from Tuscan Nappe sedimentary sequence, outcropping in the Monti d’Oltre Serchio area (NW Tuscany, Italy), were selected and calcined at different temperatures (800, 900, 1000 and 1100 °C). The obtained lime was slaked, and chemical, mineralogical and petrographic analyses were conducted to study its reactivity during slaking process. Key factors influencing lime reactivity were identified: calcination temperature/time and limestone characteristics (chemical and mineralogical composition). The lime reactivity was measured through the rate of lime hydration reaction. Results showed that higher reactivity in lime, lower calcination temperature. The increase in temperature and time leads to an increase of CaO grain size and, consequently, to a decrease in reactivity. Temperature increase has a more significant effect on the increasing of grain size and reactivity than time. The optimal calcination temperature was found to be 900 °C, like that of ancient limekilns. The study emphasized the close link between lime reactivity and chemistry/mineralogy of limestone. Overall, the research provides insights for improving limestone calcination processes and obtaining superior products.

High-Valence Ion Doped Compositionally Partitioned Li[Ni0.78Co0.10Mn0.12]O2 Cathode for Advanced Lithium-Ion Batteries

Numerous approaches have been employed to reduce the intrinsic instability of Ni-rich cathodes. Among them, the introduction of concentration gradient (CG), i.e., a strategy to protect the labile Ni-enriched compartment with a chemically protective Mn-rich shell, has proven successful in commercial applications.1 However, because the segmentation of transition metal (TM) constituents and the formation of unique geometric configurations are characteristics inherited from the CG hydroxide precursor; it is crucial to select the optimal calcination temperature and precisely control it.2 Excessive thermal energy input can result in concentration planarization because the CG of the hydroxide precursor is intrinsically susceptible to the interdiffusion of TM elements during lithiation. Moreover, the immoderate coarsening of the primary particles can eliminate the advantageous features of the CG design by producing equiaxed primary particles.2 In this study, we propose a strategy that can effectively ameliorate the deterioration of Ni-rich CG cathodes resulting from excessive thermal energy input and remarkably improve their electrochemical cycling performance. It was revealed that a trace amount of tungsten incorporation during the cathode calcination can effectively mitigate the high-temperature-induced cathode degeneration and maintain outstanding product quality over a wide range of temperatures. Thus, the proposed strategy opens new avenues for the facile synthesis of long-life Ni-rich CG cathodes. Reference s : [1] Y.-K. Sun, S.-T. Myung, B.-C. Park, J. Prakash, I. Belharouak, K. Amine, Nat. Mater. 8 (2009) 320-324.[2] G.-T. Park, H.-H. Ryu, T.-C. Noh, G.-C. Kang, Y.-K. Sun, Mater. Today 52 (2022) 9-18.

High temperature calcined red mud-cement mortar: Workability, mechanical properties, hydration mechanism, and microstructure

To efficiently utilize red mud (RM) in cement-based materials, this study employed high-temperature calcination to enhance RM's pozzolanic activity. Calcined RM replaced cement in RM-cement mortar, examining the effects of different calcination temperatures and RM addition amounts on the workability and mechanical properties of the mortar. Additionally, XRD, FTIR, SEM-EDS, TAM-Air, and TG were used to explore the hydration mechanism and microstructure of RM-cement mortar. Research showed that as the calcination temperature increased, minerals like Calcite, Hematite, and Cancrinite in RM began to decompose, and the glassy structure increased. At 800 °C, the serrated and amorphous diffraction peaks significantly increased. Calcined RM positively influenced the setting and hardening of cement mortar but negatively affected its fluidity. The optimal calcination temperature for RM was 800 °C, with an optimal addition amount of 10%. The compressive strengths of RM-cement mortar at 3, 7, and 28d, with optimal conditions, are 9.62, 29.94, and 40.12 MPa, respectively, showing increases of 4.25, 1.72, and 1.39 times over untreated RM-cement mortar. When RM was calcined to 800 °C, the diffraction peak intensities of Portlandite, C–S–H, and Ettringite in the RM-cement paste were the highest, and the hydration products interwove to form a dense microstructure. Adding calcined RM extended the induction period of cement, increased the rate of heat release, shortened the acceleration period, and further accelerated the rate of heat release. Nevertheless, the alkaline components in calcined RM pose a certain hindrance to the later stages of cement hydration. In summary, calcining RM to 800 °C enhanced its pozzolanic activity, improved the workability, early hydration, and early strength of cement, and reduced cement consumption and CO2 emissions.

Evaluating rotary and static calcination processes for montmorillonite marl: Pozzolanic properties, compressive strength, and cementitious paste characteristics

Marls, widely available globally, are under research as supplementary cementitious materials. This study investigated metamontmorillonite reactivity and optimal calcination temperatures. The complex composition of marls, including minerals like montmorillonite and dolomite alongside chemical oxides such as CaO and MgO, posed challenges in determining the ideal calcination temperature. Material transformations at varying temperatures were tracked using X-ray diffraction, scanning electron microscopy, and nuclear magnetic resonance techniques. Comparative analysis of static and rotary kilns evaluated mortar compressive strength after 28 days, determining suitable replacement levels and the best calcination temperature. The study determined that calcination at 850 °C maximized pozzolanic reactivity, resulting in the formation of β-C2S. Static furnace calcination showed a slight advantage over rotary kiln. Mortar with 30% calcined marl replacement at water: binder ratio (W/B = 0.45) exhibited the highest compressive strength. Hydration analysis revealed the formation of calcium carboaluminate and hydrotalcite hydrates, with Al/Si = 0.18 composition.

Visible light- and dark-driven degradation of palm oil mill effluent (POME) over g-C3N4 and photo-rechargeable WO3.

The investigations of real industrial wastewater, such as palm oil mill effluent (POME), as a recalcitrant pollutant remain a subject of global water pollution concern. Thus, this work introduced the preparation and modification of g-C3N4 and WO3 at optimum calcination temperature, where they were used as potent visible light-driven photocatalysts in the degradation of POME under visible light irradiation. Herein, g-C3N4-derived melamine and WO3 photocatalyst were obtained at different calcination temperatures in order to tune their light absorption ability and optoelectronics properties. Both photocatalysts were proven to have their distinct phases, crystallinity levels, and elements with increasing temperature, as demonstrated by the ultraviolet-visible spectroscopy (UV-Vis), X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) results. Significantly, g-C3N4 (580°C) and WO3 (450°C) unitary photocatalysts exhibited the highest removal efficiency of POME without dilution due to good crystallinity, extended light absorption, high separation, and less recombination efficiency of electron-hole pairs. Furthermore, surprisingly, the superior energy storage photocatalytic performance with outstanding stability by WO3 achieved an approximately 10% increment during darkness, compared with g-C3N4 under visible light irradiation. Moreover, it has been proven that the WO3 and g-C3N4 photocatalysts are desirable photocatalysts for various pollutant degradations, with excellent visible-light utilization and favorable energy storage application.

Synthesis of strontium hexaferrite (SrFe12O19) by self-propagating high-temperature synthesis (SHS) method and investigation of the effect of milling on morphology and magnetic properties

In this research, strontium hexaferrite (SrFe12O19) was synthesized using the self-propagating high-temperature synthesis (SHS) method, and its structural and magnetic properties were investigated. Raw materials such as strontium peroxide (SrO2), iron (Fe), and iron (III) oxide (Fe2O3) were used to prepare green compact. The current research investigated the effect of milling time and speed on the morphology and magnetic properties of strontium hexaferrite, and the optimum temperature for calcination was obtained. X-ray diffraction (XRD), vibrating magnetometer (VSM), field emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) were used to study the mentioned parameters and choose the optimal conditions for the synthesis of strontium hexaferrite. Milling at speeds of 100, 200, and 300 rpm for 30 and 90 min was investigated. Also, calcination was performed at temperatures of 1000, 1100, 1200, and 1300 °C for 90 min to obtain the optimal temperature. According to the results of VSM analysis, the sample milled at 300 rpm for 90 min and calcined at 1200 °C for 90 min had the highest magnetic properties. Magnetic saturation (MS), magnetic remanence (Mr), and coercivity (HC), with values of 56.43 emu/g, 30.85 emu/g, and 5705.96 Oe, were obtained for this sample. Also, FE-SEM images showing the formation of hexagonal plates with an average particle size of 380 nm after calcination were obtained for the sample with optimal parameters. TEM and HRTEM images also showed the formed particles of strontium hexaferrite with hexagonal morphology.

Deciphering the effect of calcination temperature on crystallinity, morphology, oxygen vacancy and photocatalytic activity of bi-phasic ZnO/ZnCo2O4 heterostructured nanomaterials

This study investigates the synthesis of cobalt incorporated zinc oxide (ZnO) metal oxide via co-precipitation followed by calcination at varying temperatures ranging from 300 °C to 700 °C. X-ray diffraction analysis revealed the presence of two crystallite phases, hexagonal ZnO and wurtzite ZnCo2O4, at temperatures between 500 °C and 700 °C, while only the ZnO phase was observed below 500 °C with ZnCo2O4 remaining amorphous. Morphological evolution revealed the gradual development of a rod-shaped morphology for ZnO phase, reaching peak stability at 500 °C, beyond which the structural rupture occurred. The impact of temperature on oxygen vacancy, surface area, optical band gap energy, and recombination of charge carriers was investigated. Photocatalytic activity against MO dye demonstrated an increase with calcination temperature up to 500 °C, attributed to improved crystallinity. Notably, the sample annealed at 500 °C exhibited the highest photocatalytic activity due to its highly ordered crystallinity, bi-phase composition, and appropriate band gap. However, further increase in calcination temperature led to a rapid decrease in photocatalytic activity due to morphological destruction and loss of crystallinity. These findings highlight the importance of optimizing calcination temperature to tailor the crystallinity, morphology, and photocatalytic activity of mixed metal oxides, offering insights for controlled material synthesis with desired properties.