Search Results (75)

Catalytic oxidation has become a crucial technology for removing CO from industrial flue gas. However, the complex composition of flue gas (including NH₃, NO, SO₂, H₂O, etc.) poses significant challenges to the catalytic activity and stability of catalysts. In this work, we propose a new strategy for constructing highly efficient catalysts by loading a Pd component onto TiO₂ nanosheets (NSs) with predominantly exposed {001} facets. It has been revealed that the well-connected channels, abundant oxygen vacancies and Ti³⁺ species on the TiO₂(NS) support facilitate the formation of highly dispersed and electron-rich Pd nanoparticles. The weak adsorption of impurities such as NH₃, SO₂, NO and H₂O on these active sites promotes the adsorption and activation of the target reactants (CO and O₂), thereby enhancing catalytic activity. Furthermore, such reduced adsorption inhibits the aggregation of Pd nanoparticles and synergizes with the intrinsically weak NH₃ adsorption of TiO₂(NS) to suppress ammonium sulfate species deposition, thereby enhancing long-term catalytic stability. This work advances TiO₂ facet engineering in catalysis and offers new design concepts for efficient CO oxidation catalysts in complex atmospheres. Full article

The valorization of agro-industrial residues represents a strategic approach to advancing sustainability and circular bioeconomy principles in the food sector. Although bacterial cellulose (BC) production from waste substrates has been widely explored, limited attention has been given to the role of nitrogen source modulation in complex fermentation systems. This study evaluated passion fruit peel hydrolysate (PFPH), a cellulose- and hemicellulose-rich by-product, as an alternative carbon source for BC production using a symbiotic culture of bacteria and yeast (SCOBY) under static conditions. Acid hydrolysis and detoxification were performed to obtain fermentable sugars while minimizing inhibitory compounds. Different nitrogen sources and purification strategies were comparatively assessed. The highest purified BC yield (81 g L⁻¹ of culture medium) was obtained using ammonium sulfate, whereas sodium nitrate promoted greater impurity removal (77.51% mass reduction). Structural and chemical analyses (FTIR, XPS, and XRD) confirmed effective delignification, enhanced surface purity, and increased crystallinity. SEM revealed a homogeneous nanofibrillar network, and thermogravimetric analysis indicated thermal stability up to approximately 300 °C. Soil burial assays showed 26% mass loss after 42 days, demonstrating controlled biodegradation consistent with food packaging requirements. Overall, PFPH proved to be an efficient and sustainable substrate for BC biosynthesis. The modulation of nitrogen source significantly influenced both production yield and structural properties, highlighting the potential of this system for developing environmentally responsible biopolymer materials for food packaging applications. Full article

The main goal of this study was to develop methods for quality control of naftifine hydrochloride in solution and cream forms, focusing on “Quantitative Determination” and “Related Impurities.” New, precise, accurate, and environmentally friendly high performance liquid chromatography (HPLC) methods were developed for the determination of naftifine hydrochloride and its impurities. “Quantitative determination” was performed using a diode array detector at 254 nm with an isocratic mobile phase (1.154 g of ammonium acetate R dissolved in 300 mL of water R, followed by the addition of 0.2 mL of glacial acetic acid R, mixed well) and methanol (30:70). The chromatographic columns Gemini C18 and Luna C18 were used. “Related impurities” were separated at 270 nm using a gradient mobile phase consisting of 10 M sodium octanesulfonate, 0.4 g/L disodium hydrogen phosphate anhydrous solution (pH 6.5), acetonitrile, and the Synergi Hydro-RP chromatographic column. The developed method, validated according to ICH guidelines, showed run times of 55 min for impurity analysis and 6 min for active ingredient determination. The methods were successfully applied to the quality control of the solution and cream. Full article

A robust and stability-indicating Reverse Phase-High Performance Liquid Chromatography (RP-HPLC) method was developed and validated for the quantitative determination of bexagliflozin and its related impurities in accordance with the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH Q2(R1)) guidelines. Chromatographic separation was achieved on a C18 column using a mobile phase of methanol and ammonium acetate buffer (pH 4.2) in a 60:40 (v/v) ratio, with a flow rate of 1.0 mL·min⁻¹ and UV detection at 220 nm. The method was validated for linearity, sensitivity (LOD and LOQ), precision, robustness, and system suitability, all within acceptable limits for low-concentration analysis. Excellent linearity (r² > 0.999) and precision (%RSD 0.3–4.4%) confirmed its reliability for stability assessment. The assay was performed at 100 µg·mL⁻¹, where all validation parameters showed %RSD values ≤ 2%, demonstrating high precision and robustness. Forced degradation studies under acidic, basic, oxidative, photolytic, and thermal conditions revealed a major degradation product formed under acidic stress. This product was isolated and structurally characterized using LC–MS, ¹H NMR, and ¹³C NMR, and is reported here for the first time. The proposed RP-HPLC method proved to be specific, precise, and reliable for the determination of bexagliflozin and its related impurities, making it suitable for routine stability testing, quality control, and pharmaceutical development applications. Full article

The presence of impurities such as Ca, Mg, and Al during the precipitation of rare earths (REs) using ammonium bicarbonate directly affects product purity. It is necessary to optimize precipitation methods and conditions to improve the separation efficiency between REs and impurities. In this study, RE (La and Ce) ions were precipitated using ammonium bicarbonate solution, and the separation efficiency of REs from Al, Fe, Ca, and Mg ions was investigated with or without the addition of triammonium citrate (TAC). The results showed that as long as the precipitation yield of REs was controlled below 94%, Ca and Mg ions would not enter the precipitation in the absence of other impurities, and the purity of the obtained rare earth oxides (RE₂O₃) was close to 100%. The presence of Al and Fe impurities would reduce the separation efficiency of REs from Ca and Mg. Therefore, Al and Fe must be separated before the precipitation of REs. First, Fe was completely precipitated by controlling the pH value to 4.12. Then, by filtering out the isolation and adjusting the pH value to 4.6, approximately 84% of Al³⁺ was precipitated, with a loss of REs of about 6%. Finally, the pH value was increased to 6.43, and REs were completely precipitated, yielding rare earth carbonate. The RE₂O₃ purity of its calcination product was 97.8% with Al and Mg contents of 1.05% and 0.21%, respectively, and no Ca or Fe was detected. This indicated that Mg can enter the product by co-precipitation with Al. To address this, a small amount of TAC was added during the pre-removal of Fe and Al to facilitate the complete removal of Al. By controlling the precipitation yield of REs at 94%, the purity of the final RE₂O₃ reached 99.6% with an Al content of 0.09%. Furthermore, using a continuous precipitation crystallization method, RE₂O₃ purity can be achieved at 99.8% with an Al content of 0.06%. Full article

Micron-sized near-spherical α-Al₂O₃ powders are widely used as thermal fillers due to their high thermal conductivity, high packing density, good flowability, and low cost. During the high-temperature calcination, the resulting α-Al₂O₃ powders often exhibit an aggregated worm-like morphology owing to limitations in solid-state mass transfer. Researchers have employed various mineralizers to regulate the morphology of α-Al₂O₃ powders; however, the preparation of micron-sized highly spherical α-Al₂O₃ powders via solid-state calcination is still a great challenge. In this work, micron-sized near-spherical α-Al₂O₃ powders were synthesized through high-temperature calcination using hydratable alumina (ρ-Al₂O₃) as precursor with water-soluble mineralizer ammonium fluoroborate (NH₄BF₄). ρ-Al₂O₃ can undergo a hydration reaction with water to form AlO(OH) and Al(OH)₃ intermediates, serving as an excellent precursor. With the addition of 0.1 wt% NH₄BF₄, the product exhibits an optimal near-spherical morphology. Excessive addition (>0.2 wt%), however, significantly promotes the transformation of α-Al₂O₃ from a near-spherical to a plate-like structure. Further studies reveal that the introduction of NH₄BF₄ not only modulates the crystal morphology but also effectively reduces the content of sodium impurities in the powder through a high-temperature volatilization mechanism, thereby enhancing the thermal conductivity of the powder. It is shown that the thermal conductivity of the micron-sized α-Al₂O₃/ epoxy resin composites reaches 1.329 ± 0.009 W/(m·K), which is 7.4 times that of pure epoxy resin. Full article

Addressing the technological bottlenecks in the efficient utilization of clay-type Li deposits in China, this study systematically investigates Li occurrence states and develops clean extraction processes using the Jinyinshan clay-type Li deposit in southern Hubei as a case study. The research aims to provide technical guidance for subsequent geological exploration and development of such deposits. Analytical techniques, including AMICS, EPMA, and LA-ICP-MS, reveal that Li primarily occurs in structurally bound forms within cookeite (82.55% of total Li), illite (6.65%), and rectorite (5.20%), with mineral particle sizes concentrated in fine-grained fractions (<45 μm). Leveraging process mineralogical insights, two industrially adaptable blank roasting–acid leaching processes were innovatively developed. Process I employs a full flow of blank roasting–hydrochloric acid leaching–Li-Al separation–Ca/Mg removal–concentration for Li precipitation–three-stage counter-current washing. Optimizing roasting temperature (600 °C), hydrochloric acid concentration (18 wt%), and leaching parameters achieved a 92.37% Li leaching rate. Multi-step purification yielded lithium carbonate with >99% Li₂CO₃ purity and an overall Li recovery of 73.89%. Process II follows blank roasting–sulfuric acid leaching–Al removal via alum precipitation–Al/Fe removal–freeze crystallization for sodium sulfate removal–Ca/Mg removal–concentration for Li precipitation–three-stage counter-current washing. Parameter optimization and freezing impurity removal achieved an 89.11% Li leaching rate, producing lithium carbonate with >98.85% Li₂CO₃ content alongside by-products like crude sodium chloride and ammonium alum. Both processes enable resource utilization of Al-rich residues, with the hydrochloric acid-based method excelling in stability and the sulfuric acid-based approach offering superior by-product valorization potential. This low-energy, high-yield clean extraction system provides critical theoretical and technical foundations for scaling clay-type Li deposit utilization, advancing green Li extraction and industrial chain development. Full article

Rhenium metal is extensively utilized in the aerospace industry for the manufacturing of various superalloys due to its unique properties, and plays an indispensable role in the field of high technology. Rhenium resources are primarily associated with copper, molybdenum, and other metal ores. Ammonium perrhenate is predominantly derived from copper and molybdenum ore roasting flue gas scrubbers containing various impurities in the rhenium-containing contaminated acid. The complex composition of the contaminated acid renders the enrichment and purification of ammonium perrhenate more challenging, necessitating further research and development of the technology. This paper reviews the research progress in ammonium perrhenate enrichment and purification technology, encompassing chemical precipitation, adsorption, extraction, ion exchange, extraction chromatography, and recrystallization. It analyses the advantages and limitations of various methods, with the aim of providing a reference for future developments in ammonium perrhenate enrichment and purification technology. Furthermore, the paper presents a prospective view on the development of ammonium perrhenate enrichment and purification technology, focusing on the objective of obtaining more selective purification materials and more efficient purification techniques for ammonium perrhenate. Full article

Substantial amounts of nitrogenous (N) compounds, as well as bisphenol A (BPA) and bisphenol S (BPS), contribute to the impurities of pharmaceutical contamination (PC) in wastewater, which have detrimental effects on the environment, humans, and aquaculture. The anammox processes is primarily used to treat wastewater contamination, in which certain microbial communities play a crucial role. In this regard, the present study focuses on microbial communities and the functional genes involved in the anammox process. Further, the current study highlights the secondary (biological) and tertiary (advanced) methods; these techniques are more effective solutions for PC treatment. Anammox bacteria are the primary drivers of the wastewater’s ammonium and nitrite removal process. However, overall, 25 anammox species have been recognized between five important genera, including Anammoxoglobus, Anammoximicrobium, Brocadia, Kuenenia, and Jettenia, which are mainly found in activated sludge and marine environments. The group of bacteria called anammox has genes that encode enzymes such as hydrazine synthase (HZS), hydrazine dehydrogenase (HDH), nitrite oxidoreductase reductase (NIR), hydroxylamine oxidoreductase (HAO), and ammonium monooxygenase (AMO). The anammox process is responsible for developing about 30% to 70% N gases worldwide, making it a critical component of the nitrogen cycle as well. Therefore, this review paper also investigates the pathways of hydrazine, an intermediate in the anammox process, and discusses the potential way to significantly decrease the N-compound contamination from wastewater systems and the environmental effects of determined organic contaminants of BPA and BPS. Full article

This research examines the influence of ammonium (NH₄⁺) impurities on the kinetic behavior, activation energy, crystal structure, morphology, and purity of cobalt sulfate hexahydrate using the cooling crystallization method. Characterization results indicate that ammonium at all concentrations affects the crystallization process, with a minimum concentration required to alter crystal characteristics. At ammonium concentrations up to 3.75 g/L, the crystal growth rate decreases, while activation energy increases. Furthermore, the crystal structure does not change, and crystal purity decreases by approximately 0.2%. This decline is insignificant and tends to stagnate, suggesting a maximum adsorption limit of impurities onto the crystal. At ammonium concentrations of 5 g/L, the crystal growth rate increases, and activation energy decreases. This shift in behavior is caused by the formation of Tutton’s salt, (NH₄)₂Co(SO₄)₂·6H₂O, which significantly reduces crystal purity by 1%. Additionally, the presence of ammonium does not alter the crystal shape. Full article

This study explores the use of alkaline earth metal carboxylates as sustainable alternatives to conventional ammonium-based lixiviants for the eco-friendly extraction of weathered crust elution-deposited rare earth ores. We investigated the impact of lixiviant concentration, pH, and leaching temperature on the extraction efficiency of rare earths and aluminum, utilizing magnesium acetate and calcium acetate alongside traditional ammonium salts. The results showed that a leaching rate exceeding 91% for rare earths was achieved, while aluminum leaching remained under 30% at 298 K, pH 6.5–7.0, and 0.20 mol/L concentration of carboxylates. Notably, magnesium acetate was particularly effective in extracting medium and heavy rare earths at lower concentrations. A double electric layer model was used to clarify the leaching mechanism, indicating that zeta potential and double electric layer thickness were significantly affected by the concentration and pH of the leaching agents. Overall, this method presents an efficient approach for low-impurity extraction, offering valuable insights for sustainable mineral resource development. Full article

This study investigates the ethanol gas-sensing mechanisms of ZnO nanocrystals with distinct morphologies, synthesized via a hydrothermal method using various alkali sources. Significant differences in the gas-sensing performance and morphology of ZnO samples synthesized with ammonium carbonate (Na₂CO₃), hexamethylenetetramine (HMTA), ammonia solution (NH₃·H₂O), and sodium hydroxide (NaOH) were observed. ZnO were confirmed to be impurity-free through XRD analysis, and their morphological features were characterized by SEM. TEM, XPS, and FTIR were employed to further analyze the crystal structure and binding energy of ZnO. To elucidate the underlying mechanisms, density functional theory (DFT) calculations combined with electron depletion layer theory were applied to assess charge transfer processes and identify the most sensitive ZnO crystal planes for ethanol detection. Experimental gas-sensing tests, conducted across 5–1000 ppm ethanol concentrations within a 150–350 °C range, showed that ZnO prepared with Na₂CO₃, HMTA, and NaOH was responsive at high ethanol concentrations as low as 100 °C, while ZnO synthesized with ammonia required 250 °C to exhibit sensitivity. All ZnO samples demonstrated excellent recovery at low concentrations at 250 °C. By integrating experimental findings with theoretical insights, this study provides a comprehensive understanding of ethanol gas-sensing mechanisms in ZnO, highlighting the role of crystal plane engineering and charge transfer dynamics as critical factors influencing gas response. Full article

This paper presents a method for obtaining cobalt(II) perrhenate from waste derived from two types of materials, i.e., Li-ion battery scrap, or more precisely, battery mass, and superalloy scrap. Both of the above-mentioned materials are a source of Co. However, a source of rhenium is perrhenic acid produced from ammonium perrhenate (recycled) by the ion exchange method using resins. Co(OH)₂ can be precipitated from solutions resulting from the leaching of Li-ion battery mass, sludge from the Zn-Pb industry and superalloy scrap. The compound, after proper purification, can be used in a reaction with perrhenic acid to form Co(ReO₄)₂. The reaction should be conducted under the following conditions: time 1 h, room temperature, 30% excess of cobalt(II) hydroxide, and rhenium concentration in HReO₄ from about 20 g/dm³ to 300 g/dm³. This work shows that with the use of Co(OH)_2, obtained from waste, an anhydrous form of cobalt(II) perrhenate can be obtained, containing < 1000 ppm of the cumulative metal impurities. Full article

Solifenacin (SFC) is a potent muscarinic antagonist that effectively reduces bladder muscle contraction, thereby alleviating symptoms such as frequency of micturition and urgency. Oxidation of SFC leads to the formation of impurities like Impurity K. Effective analysis and control of this impurity is crucial for ensuring compliance with regulatory standards and safeguarding patient health. To address these challenges, we propose a novel one-step synthesis of Impurity K from SFC. Impurity K was synthesized using cerium(IV) ammonium nitrate (CAN) in water/acetonitrile as the solvent. Additionally, we describe a new HPLC-MS method for the detection of Impurity K in solifenacin succinate tablets. Full article

The chlorination mechanism of neodymium oxide for the production of anhydrous neodymium chloride was analyzed based on the reaction temperature and reaction ratio of ammonium chloride, considering the suppression of the generation of NdOCl, an intermediate product of the reaction process. The results were obtained by distinguishing the shape of the produced NdCl₃ (powder and bulk) and the setup of the chlorination equipment, reflecting its sensitivity to moisture and oxygen. The powdered form of NdCl₃ produced at 400 °C and under argon gas flow was identified as NdCl₃·6(H₂O), while the bulk form of NdCl₃ produced by melting at 760 °C after a chlorination process consisted of anhydrous NdCl₃ and NdCl₃∙n(H₂O). The powdered NdCl₃ produced in an argon gas environment with a controlled level of oxygen (below 16.05 ppm) and moisture (below 0.01 ppm) content was identified as single-phase anhydrous NdCl₃ and showed the highest chlorination conversion rate of 98.65%. The addition of overstoichiometric ratios of NH₄Cl in the chlorination process decreased the total amount of impurities (N, H, and O) in the NdCl₃ product and increased the conversion rate of NdCl₃. Full article