Search Results (28)

Progressive research on reducing engine emissions is highly valued due to the emissions’ significant environmental and health impacts. This comprehensive comparative study examines the catalytic efficiency of manganese (Mn) and cerium silica (Ce-Si) synthesis catalyst-based molds in a diesel engine using a selective catalytic reduction (SCR) technique with diesel and diesel–plastic oil blend (DPB) (B50). In addition to Fourier transform infrared spectroscopy (FTIR) studies, X-ray diffraction (XRD), scanning electron microscopy (SEM), and the Brunauer–Emmett–Teller (BET) method are utilized to characterize the produced molds before and after exhaust gas passes. The Ce-Si-based mold demonstrates superior redox capacity, better adsorption capacity, and better thermal stability, attributed to enhanced oxygen storage and structural integrity compared to the Mn-based mold. Under minimum load conditions, nitrogen oxide (NO) reduction efficiency peaks at 80.70% for the Ce-Si-based mold in the SCR treatment with DPB fuel. Additionally, significant reductions of 86.84%, 65.75%, and 88.88% in hydrocarbon (HC), carbon monoxide (CO), and smoke emissions, respectively, are achieved in the SCR treatment under optimized conditions. Despite a wide temperature range, Ce-Si-based mold promotes high surface area and superior gas diffusion properties. Overall, the Ce-Si-based mold provides efficient emission control in diesel engines, which paves a path for developing better environmental sustainability. The outcomes contribute to advancing environmental sustainability by supporting the achievement of SDGs 7, 11, and 13. Full article

Non-hygroscopic borosilicate glasses containing Ce³⁺ and Mn²⁺ ions were prepared using the conventional melt-quenching method. The electrochemical equilibrium of the Ce and Mn oxidation states has a significant effect on the energy levels and luminescence of both elements. Consequently, the oxidation states in the glasses were analyzed using a combination of XPS, EPR, and absorption spectroscopy. The oxidation–reduction equilibrium was altered by systematically changing three factors: the Mn concentration, the presence or absence of SnO as a reducing agent, and the optical basicity of the glass. Upon excitation with light with a wavelength of 320 nm, the prepared glasses exhibited a blue luminescence band in the region of 350–450 nm, corresponding to the Ce³⁺ ion, and a broad, weak red luminescence emission in the region of 540–640 nm, corresponding to Mn²⁺ ions. To obtain a high luminescence intensity for both bands, it was necessary to reduce the MnO content below 1 mol.%. Furthermore, doping the glasses with Sn²⁺ ions helped to maintain both cerium and manganese in low oxidation states, resulting in measurable luminescence in both observed bands. These low oxidation states of Ce and Mn can also be achieved by reducing the optical basicity of the glass through the addition of MgO. The general relationships obtained could potentially be applied in the production of light-emitting diodes or field-emission displays that utilize energy transfer. Full article

Mono- and di-substituted cerium oxide catalysts, viz. Ce_0.95Cu_0.05O_2-δ, Ce_0.90Cu_0.10O_2-δ, Ce_0.90 Cu_0.05Mn_0.05O_2-δ, Ce_0.85Cu_0.10Mn_0.05O_2-δ, and Ce_0.80Cu_0.10Mn_0.10O_2-δ, were synthesized via a one-step urea-assisted solution combustion method. The elemental composition and textural and structural properties of the catalysts were determined by various physical, electronic, and chemical characterization techniques. Hydrogen temperature-programmed reduction showed that co-doping of copper and manganese ions into the CeO_2-δ lattice improved the reducibility of copper. Powder XRD, XPS, HR-TEM, and Raman spectroscopy showed that the catalysts were a singled-phased, solid-solution metal oxide with a cerium oxide cubic fluorite (cerianite) structure, and evidence of oxygen vacancies was observed. Catalytic results in the preferential oxidation of CO in a hydrogen-rich stream showed that complete CO conversion occurred between 150 and 180 °C. Furthermore, at 150 °C, Ce_0.90Cu_0.05Mn_0.05O_2-δ, Ce_0.90 Cu_0.10O_2-δ, and Ce_0.85Cu_0.10Mn_0.05O_2-δ catalysts were the most active, achieving complete CO conversion and CO₂ selectivity of 81, 79, and 71%, respectively. The catalysts performed moderately in the presence of CO₂ and water, with the Ce_0.90Cu_0.05Mn_0.05O_2-δ catalyst giving a CO conversion of 80% in CO₂, which decreased to about 60% when water was added. Full article

Amoxicillin (AMX) is utilized in the treatment of several infectious diseases, and its concentration in wastewater has increased quite significantly over the years, posing high health hazards for humans and other living organisms. Investigations are in progress globally to eliminate AMX and other related pollutants using several methods that include adsorption, photolysis, photocatalytic degradation, photoelectrocatalytic degradation, and electrochemical conversion. AMX can be eliminated efficiently from the environment using photodegradation, either by photolysis or a photocatalytic process. Several types of semiconductor NMs have been used to eliminate AMX and other related drugs present in wastewater. This review spans the photodegradation studies conducted during the years 2018–2024 to degrade and eliminate AMX in aquatic systems. Several studies have been reported to eliminate AMX from different water streams. These studies are categorized into TiO₂-containing and non-TiO₂-based catalysts for better comparison. A section on photolysis is also included, showing the use of UV alone or with H₂O₂ or PS without using any nanomaterial. A tabulated summary of both types of catalysts showing the catalysts, reaction conditions, and degradation efficiency is presented. Researchers have used a variety of reaction conditions that include radiation types (UV, solar, and visible), pH of the solution, concentration of AMX, number of nanomaterials, presence of other additives and activators such as H₂O₂ as oxidant, and the influence of different salts like NaCl and CaCl₂ on the photodegradation efficiency. TiO₂ was the best nanomaterial found that achieved the highest degradation of AMX in ultraviolet irradiation. TiO₂ doped with other nanomaterials showed very good performance under visible light. WO₃ was also used by several investigators and found quite effective for AMX degradation. Other metal oxides used for AMX elimination were derived from molybdenum, zinc, manganese, copper, cerium, silver, etc. Some researchers have used UV and/or visible irradiation or sunlight, without using solid catalysts, in the presence of oxidants such as H₂O₂. A summarized description of earlier published reviews is also presented. Full article

Manganese oxide-cerium oxide supported on titanate nanotubes (i.e., MnCe/TiNTs) were prepared and their catalytic activities towards NH₃-SCR of NO were tested. The results indicated that the MnCe/TiNT catalyst can achieve a high NO removal efficiency above 95% within the temperature range of 150–350 °C. Even after exposure to a HCl-containing atmosphere for 2 h, the NO removal efficiency of the MnCe/TiNT catalyst maintains at approximately 90% at 150 °C. This is attributed to the large specific surface area as well as the unique hollow tubular structure of TiNTs that exposes more Ce atoms, which preferentially react with HCl and thus protect the active Mn atoms. Moreover, the abundant OH groups on TiNTs serve as Brønsted acid sites and provide H protons to expel Cl atom from the catalyst surface. The irreversible deactivation caused by HCl can be alleviated by H₂O. That is because the dissociated adsorption of H₂O on TiNTs forms additional OH groups and relieves HCl poisoning. Full article

Metal oxide nanoparticles (MONP/s) induce DNA damage, which is influenced by their physicochemical properties. In this study, the high-throughput CometChip and micronucleus (MicroFlow) assays were used to investigate DNA and chromosomal damage in mouse lung epithelial cells induced by nano and bulk sizes of zinc oxide, copper oxide, manganese oxide, nickel oxide, aluminum oxide, cerium oxide, titanium dioxide, and iron oxide. Ionic forms of MONPs were also included. The study evaluated the impact of solubility, surface coating, and particle size on response. Correlation analysis showed that solubility in the cell culture medium was positively associated with response in both assays, with the nano form showing the same or higher response than larger particles. A subtle reduction in DNA damage response was observed post-exposure to some surface-coated MONPs. The observed difference in genotoxicity highlighted the mechanistic differences in the MONP-induced response, possibly influenced by both particle stability and chemical composition. The results highlight that combinations of properties influence response to MONPs and that solubility alone, while playing an important role, is not enough to explain the observed toxicity. The results have implications on the potential application of read-across strategies in support of human health risk assessment of MONPs. Full article

Arsenic (As) frequently emerges in paddy soils, necessitating measures to combat soil pollution and protect rice crops from As contamination. In this study, a novel functional biochar (MBC) by loading cerium manganese oxide was prepared, and its effects on soil As immobilization and As uptake by rice in two different As-contaminated paddy soils of 68.99 and 158.52 mgAs·kg⁻¹ (marked as soil-L and soil-H, respectively) were detected. The pot experiment manifested that MBC performed better in stabilizing soil As than original biochar. The incorporation of MBC facilitated the conversion of soil active As to the stable state, promoted the growth of rice plants, and reduced As uptake by rice. Specifically, the total plant biomasses for MBC treatment were increased by 16.13–70.07% and 12.36–92.58% in soil-L and soil-H compared with CK (without material input), respectively. MBC treatments resulted in a reduction of As contents by 34.67–60.13% in roots, 43.68–66.90% in stems, and 54.72–64.65% in leaves for soil-L. Furthermore, in soil-H, the As content in rice roots, stems, and leaves showed a decrease by 49.26–79.03%, 87.10–94.63%, and 75.79–85.71% respectively. This study provides important insights for the remediation of As-contaminated paddy soil using MBC. Full article

Novel yttrium-doped CeO₂, MnO_x, and CeMnO_x composites are investigated as catalysts for low-temperature NH₃-SCR. The study involves the preparation of unmodified oxide supports using a citrate method followed by modification with Y (2 wt.%) using two approaches, including the one-pot citrate method and incipient wetness impregnation of undoped oxides. The NH₃-SCR reaction is studied in a fixed-bed quartz reactor to test the ability of the prepared catalysts in NO reduction. The gas reaction mixture consists of 800 ppm NO, 800 ppm NH₃, 10 vol.% O₂, and He as a balance gas at a WHSV of 25,000 mL g⁻¹ h⁻¹. The results indicate that undoped CeMnO_x mixed oxide exhibits significantly higher deNO_x performance compared with undoped and Y-doped MnO_x and CeO₂ catalysts. Indeed, yttrium presence in CeMnO_x promotes the competitive NH₃-SCO reaction, reducing the amount of NH₃ available for NO reduction and lowering the catalyst activity. Furthermore, the physical-chemical properties of the prepared catalysts are studied using nitrogen adsorption/desorption, XRD, Raman spectroscopy, temperature-programmed reduction with hydrogen, and temperature-programmed desorption of ammonia. This study presents a promising approach to enhancing the performance of NH₃-SCR catalysts at low temperatures that can have significant implications for reducing NO emissions. Full article

To reveal the regularity of variation in the rare earth occurrence states of weathered crust elution-deposited rare earth ores, ore samples from different weathering crust layers were obtained by performing the sequential extraction procedure. The order of rare earth contents firmly obeyed the following sequence: the weathered layer > humic layer > partly weathered layer. The occurrence states of rare earth elements were mainly the ion exchange state, carbonate bound state, iron–manganese oxide state, organic binding state and residual state. The proportions of rare earth elements found in the rare earth ion exchange state of the weathered layer, humic layer and partly weathered layer were 78.55%, 73.53% and 53.88%, respectively. The light rare earth elements (LREEs) found in the rare earth ion exchange state were enriched in the upper part of the weathering crust, while the heavy rare earth elements (HREEs) were enriched in the lower part. There were also obvious negative anomalies in the content of cerium in the ion exchange state. The content of rare earth elements found in the carbonate bound state was small, and the rare earth partition pattern was basically consistent with that of the ion exchange state, which had little effect on the differentiation of the rare earth elements. The iron–manganese oxide state was mainly enriched with cerium, and the content of cerium increased with the depth of the weathering crust. The iron–manganese oxide state was the main factor causing the phenomenon of the anomaly in the cerium content. Meanwhile, the iron oxides in the iron–manganese oxide state were mainly hematite and goethite. The organic binding state mainly beneficiated yttrium and cerium by complexation and certain adsorption. The content of elements found in the rare earth residual state was related to the degree of weathering and reflected the release sequence of rare earth elements in the mineralization process. Clarifying the rare earth occurrence states is conducive to better revealing the metallogenic regularity of weathered crust elution-deposited rare earth ores. In addition, the results can provide a valuable reference for expanding the available rare earth resources and the efficient comprehensive utilization of rare earth ore. Full article

Porous cerium oxide (ceria) nanoparticles were prepared with and without manganese (Mn) by using the flash combustion technique. Samples with different loadings (Ce/Mn ratio ranged from 100 to 10) were prepared by using a one-step process and water only as a solvent. Moreover, citric acid was utilized as a fuel in an aqueous medium, and the overall synthesis mixture was dried at 100 °C overnight and then calcinated at 550 °C for 3 h. The obtained final solid product was characterized by inductively coupled plasma (ICP), X-ray powder diffraction (XRD), diffuse reflectance ultraviolet-visible spectroscopy (DR-UV-Vis), and scanning electron microscopy (SEM), which was coupled with Energy Dispersive X-Ray Analysis (EDX), high resolution transmission electron microscopy (HR-TEM), and photoluminescence (PL) analysis. The characterization data showed that Mn ions were totally incorporated into the framework of ceria up to the applied loading. Under visible light illumination, the photocatalytic activity of the prepared samples was tested in the decolorization reaction of methyl green (MG) dye (wavelength greater than 425 nm). The results showed that increasing Mn content improved the photocatalytic activity of ceria. The sample with a Ce/Mn ratio of 10 performed 1.8 times better than bare porous ceria. Finally, the reusability of the best-performing sample was investigated in four consecutive runs without treatment, and slight deactivation was monitored after the fourth run. Full article

A set of ceria-manganese mixed metal oxide catalysts with varying Ce:Mn ratios were prepared by coprecipitation using sodium carbonate and were evaluated for the total oxidation of propane and naphthalene. Manganese-rich samples were the most active, with Ce_0.25Mn_0.75O_x having the highest activity. Catalysts were characterised using X-ray diffraction, Brunauer–Emmett–Teller (BET) surface area, Raman spectroscopy, temperature programmed reduction (TPR), electron microscopy, and X-ray photoelectron spectroscopy (XPS), establishing that the high activity of Ce_0.25Mn_0.75O_x was due to the formation of phase-separated Mn-substituted ceria and Mn₂O₃ phases that were not simultaneously present in the other catalysts. The catalyst preparation technique for the most active ratio was investigated using co-precipitation by urea, oxalic acid and citric acid, and mechanochemical grinding. For propane, the mechanochemical and urea catalysts were more active than the carbonate coprecipitated catalyst, due to greater surface area and increased phase separation. This work demonstrates that ceria-manganese mixed metal oxides are more active than the parent oxide, but that preparation technique is also important for controlling activity. Full article

Toxicological effects of metal-oxide-engineered nanomaterials (ENMs) are closely related to their distinct physical–chemical properties, especially solubility and surface reactivity. The present study used five metal-oxide ENMs (ZnO, MnO₂, CeO₂, Al₂O₃, and Fe₂O₃) to investigate how various biologically relevant media influenced dissolution behaviour. In both water and cell culture medium (DMEM), the metal-oxide ENMs were more soluble than their bulk analogues, with the exception that bulk-MnO₂ was slightly more soluble in water than nano-MnO₂ and Fe₂O₃ displayed negligible solubility across all tested media (regardless of particle size). Lowering the initial concentration (10 mg/L vs. 100 mg/L) significantly increased the relative solubility (% of total concentration) of nano-ZnO and nano-MnO₂ in both water and DMEM. Nano-Al₂O₃ and nano-CeO₂ were impacted differently by the two media (significantly higher % solubility at 10 mg/L in DMEM vs. water). Further evaluation of simulated interstitial lung fluid (Gamble’s solution) and phagolysosomal simulant fluid (PSF) showed that the selection of aqueous media significantly affected agglomeration and dissolution behaviour. The solubility of all investigated ENMs was significantly higher in DMEM (pH = 7.4) compared to Gamble’s (pH 7.4), attributable to the presence of amino acids and proteins in DMEM. All ENMs showed low solubility in Gamble’s (pH = 7.4) compared with PSF (pH = 4.5), attributable to the difference in pH. These observations are relevant to nanotoxicology as increased nanomaterial solubility also affects toxicity. The results demonstrated that, for the purpose of grouping and read-across efforts, the dissolution behaviour of metal-oxide ENMs should be evaluated using aqueous media representative of the exposure pathway being considered. Full article

Based on the porous carbon material from citric acid residue, catalysts of different Ce-Mn ratios were prepared with incipient-wetness impregnation (IWI) to delve into their acetone-degrading performance and relevant mechanisms. When the Ce-Mn molar ratio is 0.8, the prepared catalyst Ce_0.8-Mn/AC shows abundant and uniformly dispersed Mn and Ce particles on the surface. The content of Mn and Ce on the Ce_0.8-Mn/AC surface reaches 5.64% and 0.75%, respectively. At the acetone concentration of 238 mg/m³ (100 ppm), the laws of acetone degradation in different catalysts at different catalyzing temperatures and with various oxygen concentrations were studied, and we found that the rate of acetone degradation by Ce_0.8-Mn/AC can exceed 90% at 250 °C. Cerium oxide and manganese oxide are synergistic in the catalytic degradation of acetone. Adding cerium to manganese-based catalysts can increase the oxygen migration rate in the catalysts and thus raise the reduction rate of lattice oxygen in manganese oxide. The results offer new ideas and approaches for the efficient and comprehensive utilization of bio-fermentation by-products, and for the development of cheap and high degradation performance catalysts for acetone. Full article

Perovskite-type catalysts were widely used in the field of automobile exhaust purification due to their inherent physicochemical properties and excellent doping characteristics. A series of La_1−xM_xCo_1−yN_yO₃ (M = Ce, Ca; N = Fe, Mn) perovskite-type catalyst samples were prepared by sol-gel method for the four-way purification of PM, NO_x, CO, and HC emitted by diesel exhaust. The activity of catalyst samples was tested by simulation experiments and hydrogen temperature-programmed reduction (H₂-TPR). Catalyst samples were characterized by means of XRD, FT-IR, SEM, BET, and XPS analysis. The results demonstrated that the perovskite-type catalyst samples with a particle pore size of 3–5 μm can be prepared by sol-gel method. When A-site of LaCoO₃ perovskite-type oxide was doped by cerium ions, the catalyst samples produced small distortion. The doping of cerium ions to A-site was more conducive to the four-way purification of diesel exhaust than calcium ions. La_0.8Ce_0.2CoO₃ perovskite-type samples showed the best purification efficiency, and the purification efficiencies of PM, NO_x, CO, and HC were 90%, 85%, 94%, and 100%, respectively. When the B-site of La_0.8Ce_0.2CoO₃ perovskite was doped with iron ions, the purification efficiency of catalyst samples for PM and NO_x can be further enhanced. When the B-site of La_0.8Ce_0.2CoO₃ perovskite was doped with manganese ions, the purification efficiency of the catalyst samples for PM can be further enhanced. It can be seen from the simulation experiments that La_0.8Ce_0.2Co_0.7Fe_0.3O₃ perovskite was the best doping amount, and the purification efficiencies of PM, NO_x, CO, and HC were 95%, 92%, 94%, and 100%, respectively. Full article

A propane combustion catalyst based on Mn and Ce and supported by SBA-15 was prepared by the “two-solvents” method aiming at the possible application in catalytic converters for abatement of alkanes in waste (exhaust) gases. The catalyst characterization was carried out by SAXS, N₂-physisorption, XRD, TEM, XPS, EPR and H₂-TPR methods. The catalysts’ performance was evaluated by tests on the combustion of methane, propane and butane. The reaction kinetics investigation showed that the reaction orders towards propane and oxygen were 0.7 and 0.1, respectively. The negative reaction order towards the water (−0.3) shows an inhibiting effect on the water molecules. Based on the data from the instrumental methods, catalytic experiments and mathematic modeling of the reaction kinetics, one may conclude that the Mars–van Krevelen type of mechanism is the most probable for the reaction of complete propane oxidation over single Mn and bi-component Mn-Ce catalysts. The fine dispersion of manganese and cerium oxide and their strong interaction inside the channels of the SBA-15 molecular sieve leads to the formation of difficult to reduce oxide phases and consequently, to lower catalytic activity compared to the mono-component manganese oxide catalyst. It was confirmed that the meso-structure was not modified during the catalytic reaction, thus it can prevent the agglomeration of the oxide particles. Full article