Oxide Calcination Research Articles

Enhancing the Acidity Window of Zeolites by Low-Temperature Template Oxidation with Ozone.

Revisiting the impact of the first and often deemed trivial postsynthetic step, i.e., a high-temperature oxidative calcination to remove organic templates, increases our understanding of thermal acid site evolution and Al distributions. An unprecedented degree of control over the acidity of high-silica zeolites (SSZ-13) was achieved by using a low-temperature ozonation approach. Fourier transform infrared spectroscopy of adsorbed probe molecules and solid-state NMR spectroscopy reveal the complexity of the thermal evolution of acid sites. Low-temperature activated (ozonated) zeolites maintain the original Brønsted acidity content and high defect content and have virtually no Lewis acidity. They also preserve the "as-made" Al distribution after crystallization and show a clear link between synthesis conditions and divalent cation capacity, as measured with aqueous cobalt ion uptake. The synthesis protocol is found to be the main contributor to Al proximity, yielding record high exchange capacity when ozonated. After conventional calcination at 500-600 °C, however, the presence of water leads to the gradual depletion of Brønsted acid sites, in particular, in small crystals. This work indicates that low-temperature ozonation followed by thermal activation at different temperatures can be used as a novel tool for tuning the amount and nature of acid sites, providing insights into the activity of zeolites in acid-catalyzed reactions, such as CO2 hydrogenation to dimethyl ether, and thereby expanding the possibilities of rational acidity tuning.

Green strategy for recovering cathode materials from end-of-life lithium-ion batteries using grape pomace

The extraction of critical metals from End-of-life lithium-ion batteries (EOL LIBs) have garnered particular attention for efficient resource recycling. This study provides a method for recycling EOL LIBs using grape pomace (GP) as a reducing agent. The efficacy of this method is demonstrated using LiNixCoyMnzO2 (NCM) cathode material. Kinetic studies suggest that the leaching process of the cathode material in H2SO4 + GP is governed by internal diffusion. The leachate efficiencies of lithium, cobalt, manganese and nickel, surpassed 98 % through manipulation of the thermodynamic conditions. The NCM523 cathode materials are successfully regenerated from the leachate by removing impurities, evaporating and crystallizing, dry ball milling at room temperature and oxidative calcination. Electrochemical data of the regenerated layered oxide phase also showed that the leachate could be upgraded to next-generation materials. This study presents a sustainable with industrial applicability for the large-scale recycling of EOL LIBs.

Investigation of the Waelz oxide calcination process in tubular rotary kilns

Investigation of the Waelz oxide calcination process in tubular rotary kilns

Enhanced photocatalytic performance of coaxially electrospun titania nanofibers comprising yolk-shell particles

The present paper reports the fabrication of novel types of hybrid fibrous photocatalysts by combining block copolymer (BCP) templating, sol–gel processing, and coaxial electrospinning techniques. Coaxial electrospinning produces core–shell nanofibers (NFs), which are converted into hollow porous TiO2 NFs using an oxidative calcination step. Hybrid BCP micelles comprising a single plasmonic nanoparticle (NP) in their core and thereof derived silica-coated core–shell particles are utilized as precursors to generate yolk-shell type particulate inclusions in photocatalytically active NFs. The catalytic and photocatalytic activity of calcined NFs comprising different types of yolk-shell particles is systematically investigated and compared. Interestingly, calcined NFs comprising silica-coated yolk-shells demonstrate enhanced catalytic and photocatalytic performance despite the presence of silica shell separating plasmonic NP from the TiO2 matrix. Electromagnetic simulations indicate that this enhancement is caused by a localized surface plasmon resonance and a confinement effect in silica-coated yolk-shells embedded in porous TiO2 NFs. Utilization of the coaxially electrospun TiO2 NFs in combination with yolk-shells comprising plasmonic NPs reveals to be a potent method for the photocatalytic decomposition of numerous pollutants. It is worth noting that this study stands as the first occurrence of combining yolk-shells (Au@void@SiO2) with porous electrospun NFs (TiO2) for photocatalytic purposes and gaining an understanding of plasmon and confinement effects for photocatalytic performance. This approach represents a promising route for fabricating highly active and up-scalable fibrous photocatalytic systems.

Highly selective ion precipitation flotation for ternary Co–Zn–Mn separation: Stepwise chelation capture of Co and Zn from simulated zinc hydrometallurgy wastewater

Ion precipitation flotation technology was demonstrated to be an efficient method for the separation of valuable metals from low-concentration solution. However, the selective separation of three metals from mixing solution is a great challenge, and highly selective reagents are the key to polymetallic separation. In this work, stepwise separation of Co and Zn from the simulated zinc hydrometallurgy wastewater containing ternary Co–Zn–Mn metals by ion precipitation flotation process was proposed. It's demonstrated that organic reagents of 1-nitroso-2-naphthol (NN) and sodium dimethyldithiocarbamate (SDDC) had excellent selectivity for the capture of Co and Zn to form respective precipitate from wastewaters via the chelation reactions. After precipitation, dodecylpyridinium chloride (DPC) and tetradecyltrimethylammonium bromide (TTAB) were chosen as surfactants for the separation of Co and Zn sediments from the solution via the flotation process. The effects of solution pH, molar ratio, reaction temperature, and reaction time on the selective precipitation efficiencies of Co and Zn as well as the effects of surfactant dosage and flotation gas velocity on the flotation separation efficiencies were systematically investigated. It's demonstrated that the comprehensive recovery rates of Co, Mn, and Zn reach 98%, 90%, and 99%, respectively. After separation, oxidation calcination of the foam products was conducted to prepare high-purity Co3O4 and ZnO nanoparticles in which the organic matters were burnt out with gas emissions. The stepwise chelation capture mechanisms of Co and Zn by highly selective precipitation reagents were minutely discussed. It's demonstrated that the proposed selective stepwise precipitation and flotation method is suitable for recovery of critical metal ions from low-concentration polymetallic wastewaters.

Oxygen-rich and moderate/low temperature calcination treatment of chromium containing sludge for high efficient Cr recovery and toxicity reduction

The chromium (Cr) pollution of soil has recently gained a lot of attention for the demand of environmental protection. One of its main resources is from the landfill of the chromium containing sludge (CCS) that produces from reduction–precipitation treatment of the Cr(VI) wastewater. In this work we provide an improved alkaline oxidation calcination (AOC) treatment for CCS, which achieves high Cr recovery efficiency at relatively low calcination temperature and oxygen-rich conditions. The leaching risk of the final residue is much reduced compared to the conventional calcination. It reveals that by using air flow the oxidation efficiency is effectively improved to a value of near to ∼ 90 % at 450 ℃. The thermal analyses of the reaction suggest that Cr (III) in CCS transforms to chromite at the temperature range of 340–450 ℃, which ensure the subsequent oxidation. On the other hand, it reveals that at higher temperature ( 500 ℃) it will produce CaFe oxides which are confirmed to be dissolved in the leachate of the toxicity test. The concentration of Cr (III) increases obviously, which could be associated with the release of Cr(III) that doped into CaFe oxides as solid solution. The transformations of the CCS components during the AOC process are depicted in detail. The method proposed here enables high oxidation efficiency of CCS and meanwhile avoids the environmental risk of final residue.

Quench-induced surface engineering of NiO/NiSex hybrid for highly enhanced electrochemical oxygen evolution reaction

To achieve sustainable production of hydrogen fuel through electrochemical water splitting, efficient and low-cost electrocatalysts for the kinetically sluggish oxygen evolution reaction (OER) are urgently desirable. Herein, a calcination-quenching strategy to synthesize core-shell NiO@NiSex nanorods (NiSex is the core and NiO is the shell) with tailored surface compositions and structures is reported. In the calcination step, a NiO@NiSex nanostructure supported on nickel foam (NF) (denoted as NiO@NiSex/NF) was formed via oxidative calcination of highly conductive NiSe in situ grown on NF (denoted as NiSe/NF). Subsequently, the as-obtained NiO@NiSex/NF electrode at the high temperature state was rapidly placed in a cold iron salt solution to achieve the quenching process. The results conclusively demonstrated that the quenching process resulted in iron doping and vacancies generation on the surface of NiO, effectively reconfiguring the desired surface of the catalyst, thus giving rise to notably enhanced electrocatalytic performance for OER in alkaline media. As a result, the quenched-engineered NiO@NiSex/NF electrode requires ultralow overpotentials of 231 and 265 mV to yield current densities of 10 and 100 mA cm−2, respectively, and presents a very low Tafel slope of 28.9 mV dec−1 as well as excellent durability, with the performance superior to most of metal oxide catalysts reported to date. This work extends the use of quenching chemistry in fabrication of high-performance metal oxide catalysts for energy related applications.

Bifunctional catalyst consisting of In-modified GaZrOx ternary solid solution oxide and SAPO-34 for efficiently converting CO2 into light olefins

Converting CO2 into light olefins (C2=–C4=) using oxide–zeolite bifunctional catalyst is a new strategy for producing light olefins. Herein, a series of bifunctional catalysts comprising In-doped GaZrOx oxides and SAPO-34 molecular sieves for CO2 hydrogenation to light olefins are reported, and their catalytic mechanisms are investigated using in situ spectroscopy. After optimizing the In doping amount, oxide calcination temperature, oxide coupling mode with SAPO-34, and reaction conditions, the bifunctional catalysts achieved 82.8% C2=–C4= selectivity, 24% CO2 conversion, and up to 10.1% C2=–C4= yield. Furthermore, no considerable deactivation was observed after 100 h of the reaction. Various characterization and experimental results indicate that adding In to GaZrOx promotes oxygen-vacancy generation and enhances the adsorption activation of CO2 and H2, thereby promoting the formation of formate (HCOO*) and methoxy (CH3O*) intermediates and improving the catalytic performance of the C2=–C4= synthesis from CO2.

Fabrication of cobalt-zinc bimetallic oxides@polypyrrole composites for high-performance electromagnetic wave absorption

Composite materials that combine magnetic and dielectric losses offer a potential solution to enhance impedance match and significantly improve microwave absorption. In this study, Co3O4/ZnCo2O4 and ZnCo2O4/ZnO with varying metal oxide compositions are successfully synthesized, which are achieved by modifying the ratios of Co2+ and Zn2+ ions in the CoZn bimetallic metal–organic framework (MOF) precursor, followed by a high-temperature oxidative calcination process. Subsequently, a layer of polypyrrole (PPy) is coated onto the composite surfaces, resulting in the formation of core–shell structures known as Co3O4/ZnCo2O4@PPy (CZCP) and ZnCo2O4/ZnO@PPy (ZCZP) composites. The proposed method allows for rapid adjustments to the metal oxide composition within the inner shell, enabling the creation of composites with varying degrees of magnetic losses. The inclusion of PPy in the outer shell serves to enhance the bonding strength of the entire composite structure while contributing to conductive and dielectric losses. In specific experimental conditions, when the loading is set at 50 wt%, the CZCP composite exhibits an effective absorption bandwidth (EAB) of 5.58 GHz (12.42 GHz-18 GHz) at a thickness of 1.53 mm. Meanwhile, the ZCZP composite demonstrates an impressive minimum reflection loss (RLmin) of −71.2 dB at 13.04 GHz, with a thickness of 1.84 mm. This study offers a synthesis strategy for designing absorbent composites that possess light weight and excellent absorptive properties, thereby contributing to the advancement of electromagnetic wave absorbing materials.

Enhanced Activity and Stability of Heteroatom-Doped Carbon/Bimetal Oxide for Efficient Water-Splitting Reaction.

The research community is actively exploring ways to create cost-efficient and high-performing electrocatalysts for the oxygen evolution reaction. In this investigation, an innovative technique was employed to produce heteroatom-doped carbon containing NiCo oxides, i.e., HC/NiCo oxide@800, in the form of a three-dimensional hierarchical flower. This method involved the reduction of a bimetallic (Ni, Co) metal-organic framework, followed by carefully controlled oxidative calcination. The resulting porous flower-like structure possess numerous advantages, such as expansive specific surface areas, excellent conductivity, and multiple electrocatalytic active sites for both hydrogen and oxygen evolution reactions. Moreover, the presence of oxygen vacancies within HC/NiCo oxide@800 significantly enhances the conductivity of the NiCo substance, thus expediting the kinetics of both the processes. These benefits work together synergistically to enhance the electrocatalytic performance of HC/NiCo oxide@800. Empirical findings reveal that HC/NiCo oxide@800 electrocatalysts demonstrate exceptional catalytic activity, minimal overpotential, and remarkable stability when deployed for both hydrogen evolution and oxygen evolution reactions in alkaline environments. This investigation introduces a fresh avenue for creating porous composite electrocatalysts by transforming metal-organic frameworks with controllable structures. This approach holds promise for advancing electrochemical energy conversion devices by facilitating the development of efficient and customizable electrocatalytic materials.

Flexible core–shell structured Al-Cu alloy phase change materials for heat management

The development of core–shell structured phase change materials (PCMs) with tunable melting points has been attracted much attention for thermal storage of solar energy, and a flexible shell is crucial for their practical applications. Herein, we prepared microencapsulated Al-Cu alloy PCMs (MEPCMs) with a flexible shell by a deposition-oxidizing calcination method. The Cu nanoparticles are chemically deposited on the surface of Al powders by a rapid replacement reaction, which further promotes the formation of Al-Cu alloy microspheres and the oxidation of Al to form Al2O3 shell during oxidation calcination. The prepared MEPCMs show excellent thermal cyclic performance and tunable melting point (549–592 °C). The presence of a thin film between the Al2O3 shell and Al-Cu alloy core may act as a buffer to accommodate volume change during melting-freezing process, obtaining a flexible core–shell structure. The heat storage density of Al-Cu alloy MEPCMs decreases by only 0.09% after 100 melting-freezing cycles, indicating high thermal cycling stability. In addition, the microencapsulated Al-Cu alloys present high latent heat (208.6–222.3 J·g−1) and relatively high thermal conductivity (∼1.8 W·(m·K)−1), which makes it attractive for application in high-temperature thermal storage systems.

Electrochemical energy storage from spent coffee grounds-derived carbon by KOH activation

Carbon obtained from spent coffee grounds (SCG) was activated using various molarities of KOH. Before the chemical activation step, the SCG was carbonized using either an oxidative calcination process at 300 °C in room condition or thermal annealing at 600 °C in an argon atmosphere. We observe that the use of oxidative calcination has a significant effect on the specific surface area of the activated carbon, on the texture, the morphology, and the electrochemical properties. The samples that received oxidative calcination before the chemical activation step showed specific capacitances of around 205 F g−1 at 5 mV s−1, while those carbonized in an argon atmosphere showed specific capacitances of around 82 F g−1 to 5 mV s−1. These differences in electrochemical properties are related to the increase of carboxyl groups on the sample's surface due to the oxidative calcination process. These carboxyl groups interact with K+ ions coming from the KOH solution. The improved impregnation of K+ ions on the SCG that was calcinated in room conditions allows for generating a higher specific surface area (1789 m2 g−1) in these samples compared to those that were thermally annealed in argon (658 m2 g−1).

Metal-support interaction induced atomic dispersion and redispersion of Pd on CeO2 for passive NOx adsorption

Atomically dispersed metal catalysts have attracted extensive attention in the fields of heterogeneous catalysis due to the enhanced intrinsic activity and selectivity in many energy and environment related reactions, while they suffer from sintering under harsh reaction conditions. Herein, atomically dispersed Pd/CeO2 was synthesized and investigated as a passive NOx adsorber (PNA) material. The strong interaction between CeO2 and Pd creates Pd-O-Ce linkages with 100% utilization of Pd for NOx trapping, being one of the most active oxide-based PNAs up to date. Although a sulfation treatment can substantially reduce NOx storage capacity (NSC) on the Pd/CeO2, a two-step desulfation process, including a cold plasma treatment and an oxidative calcination, can recover near 90% of its original NSC. Desulfation caused Pd aggregating into nanoparticles (NPs), while reconstruction of Pd-O-Ce moieties was achieved by prolonged oxidation at 500 °C, driving by the strong metal-support interaction between Pd and CeO2. The Pd/CeO2 system exemplifies the advantages of the metal and oxide support interaction for the atomic dispersion of Pd and redispersion of sintered Pd NPs. Monitoring this dynamic interaction enables the atomically dispersed metal structure to be modulated in controlled reaction environments, being such an example, the enhanced performance of Pd/CeO2 in PNA applications was shown in the present manuscript.

A sustainable process for selective recovery of metals from gallium-bearing waste generated from LED industry

With the rapid development of the LED industry, gallium (Ga)-bearing waste generated is regarded as one of the most hazardous as it typically contains heavy metals and combustible organics. Traditional technologies are characterized by long processing routes, complex metal separation processes and significant secondary pollution emission. In this study, we proposed an innovative and green strategy to selectively recovery Ga from Ga-bearing waste by using a quantitative phase-controlling transition process. In the phase-controlling transition process, the gallium nitride (GaN) and indium (In) are converted to alkali-soluble gallium (III) oxide (Ga2O3) and alkali-insoluble indium oxides (In2O3) by oxidation calcination, while nitrogen is converted into diatomic nitrogen gas instead of ammonia/ammonium (NH3/NH4+). By selective leaching with NaOH solution, nearly 92.65% of Ga can be recycled with a leaching selectivity of 99.3%, while little emissions of NH3/NH4+. Ga2O3 with a purity of 99.97% was obtained from the leachate which is also economy promising by economic assessment. Therefore, the proposed methodology compared to the conventional acid and alkali leaching methods is potentially greener and more efficient process for extracting valuable metals from nitrogen-bearing solid waste.

In Situ Construction of Manganese Oxide Photothermocatalysts for the Deep Removal of Toluene by Highly Utilizing Sunlight Energy.

The alternative use of electric energy by renewable energy to supply power for catalytic oxidation of pollutants is a sustainable technology, requiring a competent catalyst to realize efficient utilization of light and drive the catalytic reaction. Herein, in situ-synthesized manganese oxide heterostructure composites are developed through solvothermal reduction and subsequent calcination of amorphous manganese oxide (AMO). 95% of toluene conversion and 80% of CO2 mineralization were achieved over amorphous manganese oxide calcined at 250 °C (AMO-250) under light irradiation, and catalyst stability was maintained for at least 40 h. Highly utilization of light energy, uniformly dispersed nanoparticles, large specific surface area, improved metal reducibility, and oxygen desorption and migration ability at low temperature contribute to the good catalytic oxidation activity of AMO-250. Light activated more lattice oxygen to participate in the reaction via the Mars-van Krevelen (MvK) mechanism, and traditional e--h+ photocatalytic behavior exists over the AMO-250 heterostructure composite as an auxiliary degradation path. The reaction pathways of photothermocatalysis and thermocatalysis are close, except for the emergence of different copolymers, where light enhances the deep conversion of intermediates. A proof-of-concept study under natural sunlight has confirmed the feasibility of practical application in the photothermocatalytic degradation of pollutants.

Facile Synthesis of ZnO/ CuO Composite Nanofiber with Outstanding Photocatalytic Degradation Properties for Humic Acid

The zinc oxide (ZnO)/ copper oxide (CuO) composite nanofiber materials are synthesized by a combination of electrospinning and oxidation methods. The results show that products obtained by oxidative calcination maintain the proportion of elements in the precursor and reproduce the original fiber and pore structure. According to different phase analyses, the composite process changes the energy band structure of the system and improve the separation of photogenerated electron hole pairs. In addition, oxidation temperature affects the morphology and properties of products. After illumination for 2.5 h, the degradation rate of humic acid of ZnO/ CuO composite nanofibers synthesized by oxidation at 550∘C reaches 70%, which is higher than that of the materials and single component pure materials obtained at different oxidation temperatures.

Titanium oxide improves boron nitride photocatalytic degradation of perfluorooctanoic acid

Boron nitride (BN) has the newly-found property of degrading recalcitrant polyfluoroalkyl substances (PFAS) under ultraviolet C (UV-C, 254 nm) irradiation. It is ineffective at longer wavelengths, though. In this study, we report the simple calcination of BN and UV-A active titanium oxide (TiO2) creates a BN/TiO2 composite that is more photocatalytically active than BN or TiO2 under UV-A for perfluorooctanoic acid (PFOA). Under UV-A, BN/TiO2 degraded PFOA ∼ 15 × faster than TiO2, while BN was inactive. Band diagram analysis and photocurrent response measurements indicated that BN/TiO2 is a type-II heterojunction semiconductor, facilitating charge carrier separation. Additional experiments confirmed the importance of photogenerated holes for degrading PFOA. Outdoor experimentation under natural sunlight found BN/TiO2 to degrade PFOA in deionized water and salt-containing water with a half-life of 1.7 h and 4.5 h, respectively. These identified photocatalytic properties of BN/TiO2 highlight the potential for the light-driven destruction of other PFAS.

Protons in Catalytic Architectures: Near (NMR) and Far (Impedance)

High performance in the realm of electrochemical energy/catalysis/sensing requires WIRING! —the timely arrival and departure of the electrons, ions, and molecules necessary for reactivity. Architectural design of mesoscale porous nanostructures integrates such multifunctionality to ensure that timely electronic, ionic, and mass transport occurs to electrified reactive interfaces. We probe the nature of proton transport in TiO2 aerogels modified with Au nanoparticles (NPs) as a function of relative humidity using impedance spectroscopy for a long-range assessment and 1H NMR for an environmental assessment of shorter-range proton diffusion and spin–spin relaxation. We synthetically site the Au NPs either between the covalently bonded TiO2 NPs that comprise the oxide aerogel network or by supporting them on the preformed, calcined oxide aerogel; we prepare two Au weight loadings (1 and 4 wt%) using both geometric arrangements of Au∣∣TiO2. A high degree of intimacy between Au nanoparticles and the networked TiO₂ nanoparticles affects the nature of proton transport of the aerogel as a function of equilibration with gas-phase water, decreasing the resistance to proton transport along the oxide network. The presence of even a modest weight loading of Au NPs increases the ionicity of the catalytic platform over that of native, Au-free TiO₂ aerogel.

Green Synthesis of Cadmium Oxide Nanoparticles with Various Plant Extracts and their Use as an Anticancer Agent

The co-precipitation method was used to produce cadmium oxide nanoparticles (CdO NPs) with different plant extracts such as Tinospora Cardifolia (stems), Rhododendron arboretum (flower), Pichrorhiza Kurroa (roots), Nardostachys jatamansi (roots), Acorus Calamus (roots), Corylus Jacquemontii (seeds), and Emblica Officinalis (fruit). To extract organic matter from the as-prepared sample, it was calcined at a temperature ranging from 500-600⁰ C. X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FTIR), and Transmission electron microscopy (TEM) were used to investigate the structure and morphology of the calcined oxide nanoparticles. The CdO NPs were well amorphous particle form and had an average particle size of 20-55 nm. The cytotoxicity of the Pichrorhiza Kurroa shows strong antiproliferative activity against rat skeletal myoblast cell lines (L-6).

Design and synthesis of TiO2/C nanosheets with a directional cascade carrier transfer.

Directed transfer of carriers, akin to excited charges in photosynthesis, in semiconductors by structural design is challenging. Here, TiO2 nanosheets with interlayered sp2 carbon and titanium vacancies are obtained by low-temperature controlled oxidation calcination. The directed transfer of carriers from the excited position to Ti-vacancies to interlayered carbon is investigated and proven to greatly increase the charge transport efficiency. The TiO2/C obtained demonstrates excellent photocatalytic and photoelectrochemical activity and significant lithium/sodium ion storage performance. Further theoretical calculations reveal that the directional excited position/Ti-vacancies/interlayered carbon facilitate the spatial inside-out cascade electron transfer, resulting in high charge transfer kinetics.