Strong Acid Medium Research Articles

Eutectogel adhesives with underwater-enhanced adhesion to hydrophilic surfaces and strong adhesion in harsh environments

It has been a challenge to achieve strong adhesion strength for gel adhesives in water. In this study, a novel eutectogel adhesive is synthesized via one-step photoinitiated polymerization of N-vinylpyrrolidone (NVP) in deep eutectic solvent (DES). The abundant hydrogen bonding interactions and the hydrophilic polyvinylpyrrolidone network structure endow the eutectogel with excellent adhesion to both hydrophilic and hydrophobic surfaces in air and underwater. Moreover, for hydrophilic substrates, the underwater adhesion strength of the eutectogel adhesives is 1.3 times larger than that in air, demonstrating an underwater-enhanced adhesion effect. In contrast, for hydrophobic substrates, the underwater adhesion strength is lower than in air. Furthermore, strong adhesion performance is maintained even in boiling water, strong acidic medium, strong basic medium, and organic solvents. The experimental and simulation results have unveiled the underwater adhesion enhancement mechanism of the eutectogel. It is believed that the designed eutectogel will show great promise in the development of the next-generation of gel adhesives with underwater adhesion capabilities and high environmental adaptability.

Sodium humate as green corrosion inhibition for enhanced corrosion resistance of EH40 ship plate steel

A new green corrosion inhibitor was extracted and prepared from available and inexpensive natural humic plant humus for the corrosion inhibition of EH40 steel in a 15 % HCl medium. The corrosion inhibition properties of SH were evaluated using weight loss, cyclic voltammetry, potentiodynamic polarization and electrochemical impedance spectroscopy. The morphology of EH40 steel was characterized using scanning electron microscopy, atomic force spectroscopy and x-ray photoelectron spectroscopy. It was found that, the optimum concentration of sodium humate was 1.0 gL−1 with an inhibition efficiency of above 95 %. The corresponding corrosion inhibition mechanism was proposed, in which the corrosion inhibitor formed a film on the surface of EH40 steel as a result of the synergistic adsorption effect of chemistry and physics, improving its corrosion retention in the strong acid medium.

Silica-Reinforced AMP-Calcium Alginate Beads for Efficient and Selective Removal of Cesium from a Strong Acidic Medium.

Due to the significant selectivity for Cs+, ammonium molybdophosphate (AMP) possesses potential to uptake radiocesium from high-level liquid waste (HLLW), whereas its micro-crystalline structure and fine powder morphology limit its industrial application. Although the granulation method with alginate is prospective for the preparation of an AMP exchanger, the mechanical strength of obtained beads may be insufficient for application. In this context, we prepared silica-reinforced AMP-calcium alginate (ACS) beads and evaluated their performance for Cs+ removal from strong acidic solutions. It was found that the addition of silica in the fabrication significantly improved the mechanical strength of the beads in comparison to those without silica. Notably, the beads with an AMP/silica mass ratio of 1.0 exhibited an exceptional mechanical strength, surpassing that of ACS beads composed of other components. The batch experiment results indicated that the Cs+ adsorption follows a non-linear pseudo-second-order rate equation. The distribution coefficient of Cs+ was high even in extreme acidic conditions (∼1.6 × 102 mL/g in 8.0 mol/L HNO3 solution). The Cs+ adsorption can be well fitted with the Langmuir model, and the estimated maximum exchange capacity in 3.0 mol/L HNO3 could reach 23.9 mg/g. More importantly, ACS beads showed excellent selectivity toward Cs+ uptake over eight co-existing metal ions in simulated HLLW, with separation factor values all above 145. The column experiment exhibited that the beads can serve as the stationary phase in columns to effectively remove Cs+. The findings of this study are significant as they provide insights into the development of efficient materials for radiocesium removal from high-level liquid waste. The results demonstrate the potential of silica-reinforced ACS beads for Cs+ adsorption, with promising applications in industrial settings.

Synthesis of Dibenzo[b,h][1,5]naphthyridin-7(12H)-ones: The Pictet–Spengler Reaction versus a Rearrangement of 4-Phenyl[1,3]oxazolo[4,5-c]quinolines

AbstractTwo approaches were proposed for the synthesis of dibenzo[b,h][1,5]naphthyridin-7(12H)-ones. The one-step method based on the Pictet–Spengler reaction of 3-amino-2-phenylquinolin-4(1H)-one with aromatic aldehydes requires heating in a strong acidic media, which leads to significant limitations on the possible products. The second approach is based on the conversion of 3-amino-2-phenylquinolin-4(1H)-one to 4-phenyl[1,3]oxazolo[4,5-c]quinolines followed by rearrangement under the action of AlCl3. A significant advantage of the two-step synthesis is the possibility of obtaining a wider range of dibenzo[b,h][1,5]naphthyridin-7(12H)-ones, including those not available using the Pictet–Spengler reaction.

Enhancing simultaneous determination of some angiotensin II receptor antagonists and amlodipine in plasma using HPTLC with fluorescence densitometry: Independent fluorescence detection of the co-administrative drugs in the mixture across various pH conditions

A novel and highly sensitive high-performance thin-layer chromatographic (HPTLC) method was developed and validated to quantify a combination of five pharmaceutical mixtures spiked to human plasma. The compounds comprised Amlodipine (AML) along with five angiotensin II receptor antagonist drugs (AIIRAs), namely Olmesartan (OLM), Telmisartan (TLM), Candesartan (CAN), Losartan (LOS), and Irbesartan (IRB). HPTLC was performed on silica gel 60 F254 plates using a mobile phase of Toluene: ethyl acetate: methanol: acetone: acetic acid (6:1.5:1:0.5:1, v/v/v/v/v). In a pioneering move, a reflectance/fluorescence detection mode was employed to identify two concurrently administered drugs at different pH levels for the first time. This method utilized the same chromatographic system, incorporating a specific measurement for AML at a neutral medium to achieve its maximum fluorescence at a 360 nm excitation wavelength, and measuring emission using a 540 nm optical filter. The process involved obtaining a very low fluorescence response from AIIRA. Subsequently, to enhance AIIRA’s fluorescence, the plate was sprayed with perchloric acid to transition to a strong acidic medium, ultimately attaining the maximum fluorescence of AIIRA using various excitation wavelengths and a 400 nm emission filter. Through this strategic process, we could optimize the fluorescence signals of both drugs, thereby elevating the sensitivity of detection for this drug combination. AML demonstrated a linear range of 18–300 ng/band, while AIIRAs drugs exhibited a linear range of 6–150 ng/band. The method satisfied the International Conference on Harmonization (ICH) criteria for recovery, precision, repeatability, and robustness, showcasing exceptional sensitivity. The approach was successfully applied to quantify AML and AIIRAs drugs in both bulk drug and plasma samples, achieving high recovery percentages and minimal standard deviations.

Efficient acidic CO2 electroreduction to formic acid by modulating electrode structure at industrial-level current

Acidic CO2 electroreduction has the potential to synthesize low carbon footprint chemicals using renewable electricity. However, proton-rich environments can lead to strong hydrogen evolution reaction (HER) and severe degradation of electrochemical CO2 reduction reaction (CO2RR) performance. Modulating electrode structure plays a critical role in improving the local microenvironment of CO2RR electrolytes. Here, by covering the catalyst layer with a hydrophobic silica aerosol layer, the surface of the catalyst is protected from corrosion, thereby increasing the efficiency and stability of the system. In the flow cell, the Sn-C/SiO2-3 catalyst has high formic acid (HCOOH) selectivity at high current density (∼90 % at −400 mA cm−2). Importantly, the Sn-C/SiO2-3 catalyst can operate stably for 45 h at −400 mA cm−2. Combined in situ infrared analysis reveals that hydrophobic SiO2 aerosol layer can engineer the local microenvironment over the Sn-C catalyst surface by increasing the coverage of *OCHO to improve the CO2RR, which ultimately promotes high-efficiency CO2 conversion to HCOOH in strong acidic media. This surface coating strategy for adjusting the interface microenvironment can also be used for other electrocatalytic reactions.

ZnO@ activated carbon derived from wood sawdust as adsorbent for removal of methyl red and methyl orange from aqueous solutions

Activated carbon (AC) and ZnO@AC composite derived from wood sawdust were prepared to be utilized as adsorbents for methyl red (MR) and methyl orange (MO) anionic dyes from the aqueous solutions. The maximum adsorption capacity of the AC and ZnO@AC composite toward both dyes was achieved in the strong acidic medium (pH = 3), and under stirring for 60 min. The kinetic studies revealed that the adsorption of MR and MO dyes onto the AC and ZnO@AC composite fitted well with the pseudo-second-order model. Furthermore, the intraparticle diffusion and Elovich kinetic models confirmed the adsorption is controlled by external surfaces, and the adsorption is chemisorption process. The isotherm results indicated that the MR and MO dye adsorption occurred via monolayer adsorption, and the estimated maximum adsorption capacities of both dyes onto the ZnO@AC composite were higher than those achieved by AC. Thermodynamic analysis suggested that the adsorption is endothermic and spontaneous. The mechanism for MR, and MO dyes adsorption onto the AC and ZnO@AC composite is proposed to be controlled by electrostatic bonding, π–π interactions, and ion exchange, while H-bonding and n–π interactions were minor contributors. This study reveals the potential use of carbon-based adsorbents derived from wood sawdust for the removal of anionic dyes from wastewater.

An overview on acylation methods of α-chitin

This article overviews the acylation methods of α-chitin developed over the last four decades. The acylation of polysaccharides has been identified as a useful approach for conferring properties such as thermoplasticity. Owing to the poor solubility of α-chitin, its acylation using acid anhydrides and acyl chlorides has been traditionally investigated under heterogeneous conditions in strong acidic media. Although chitin chains depolymerize under acidic conditions, the resultant derivatives exhibit certain properties and functions. Solvents, such as LiCl/N,N-dimethyladcetamide, ionic liquids, and deep eutectic solvents, are suitable for α-chitin dissolution; therefore, acylation methods for α-chitin under homogeneous conditions have been developed using these solvents as reaction media. The functional materialization of the resultant derivatives was achieved by introducing appropriate substituents and controlling their ratios.

Theoretical design of active Ga2O3 monolayer-based catalysts for electrocatalytic HER.

Electrocatalytic hydrogen evolution reaction (HER) offers a sustainable and clean route for hydrogen production. Developing a high-efficiency HER catalyst is extremely essential toward meeting future energy needs. Herein, the Sn-doped Ga2O3 monolayer, O-defected Ga2O3 monolayer, and Ru-adsorbed Ga2O3 monolayer with high electrocatalytic performances toward HER are reported (their H adsorption free energies are 0.169, 0.126 and 0.065 eV, respectively). The Sn-doped Ga2O3 monolayer follows the Volmer-Heyrovsky mechanism, and the O-defected Ga2O3 monolayer and Ru-adsorbed Ga2O3 monolayer are suitable for Volmer-Tafel mechanisms. The strain from -4% to 4% in the X- or Y-direction could linearly modulate the HER activities of the Sn-doped Ga2O3 monolayer and O-defected Ga2O3 monolayer. The Sn-doped Ga2O3 monolayer, O-defected Ga2O3 monolayer, and Ru-adsorbed Ga2O3 monolayer only manifest high HER catalytic activities in the strong acidic media. These phenomena can provide a rational approach to enhance the HER activity for Ga2O3 monolayer-based materials.

Versatile Surface Chemistry of Carbon-Based Nanoplatforms by Covalent Bonding, Non-Covalent Linking, Crosslinking, and Self-Assembling

This mini-review discussed the best-known chemical and synthetic methodologies used in the last years to modify carbon allotropes, with an interest in nanotechnology. In this perspective, chemistry with optoelectronics applications and recent trends within bio-applications focusing mainly on graphene and its derivatives were considered. So, the mini-review intended to focus on methodologies to add functional groups with varied reactivities, polymer chemistry, and nanoscale control. These methodologies provide insight for further developments. In this manner, traditional methods using strong acid media to convert simple carbon bonds into carboxylic acid and aldehydes organic functional groups were shown and discussed. Hence, chemical modifications in a variety of solvents could be developed. Notably, many organic chemical reactions, such as bimolecular nucleophilic substitution (SN2), click chemistry, and photochemical reactions, showed essential insights in designing the carbon-based material modifications and the bottom-up method. Moreover, incorporating atomic entities within graphene material defects led to interesting spectroscopic and quantum properties. The atomic change added blemishes to this homogeneous structure, which was tuned to modify optical properties. In addition, the review was also oriented towards the discussion on incorporating polymeric films, such as boron- and silicon-based monomers, to form polymeric-modified carbon-based slides. In this way, organoboranes and organosilanes permitted chemical functionalization because their chemical modification was more accessible on nanosurfaces. Moreover, emphasis was placed on exploiting non-covalent bonding with ions and polarized molecules with the highly electronic densities of graphene and its derivatives. In this manner, the manuscript intends to summarize the main types of reactions and synthetic pathways reported until today. Therefore, particular focus was given to chemical composition, 2D and 3D chemical structures, and their properties related to non-covalent interactions. Thus, based on the properties and reactivity of carbon allotropes, the review was intended to open the analysis and discussion, considering the design of new carbon-based materials, hybrid nanocomposites, and metamaterials.

Visible-light-assisted base-catalyzed, one-pot synthesis of highly functionalized cinnolines

Abstract The synthesis of cinnolines has found great interest due to their diverse biological and industrial potency. Yet, the reported synthetic protocols for their synthesis showed limitations that involve harsh reaction conditions such as strong acidic or basic medium, low reaction yields, and using expensive and high loading catalysts. The C–H functionalization has been recognized as intriguing synthetic approach for the synthesis of aromatic/heteroaromatic scaffolds over the past two decades. Here, we reported a novel metal-catalyzed free photocatalytic synthesis of polyfunctionally substituted cinnolines. When ethyl 1-aryl-5-cyano-4-methyl-6-oxo-1,6-dihydropyridazine-3-carboxylates and nitrostyrene derivatives are irradiated with white light (LED 30 W) in ethanol in the presence of piperidine (30 mol%) in open air for 8 h at room temperature, the corresponding polyfunctionally substituted cinnolines are obtained in excellent yields (90–95%) via C–H activation of pyridazine methyl group and nitrostyrene (–N═O) function. Several merits were achieved, which are as follows: (1) the reaction is metal-free; (2) the reaction proceeds with increasing energy efficiency; (3) diversity of functionally substituted cinnolines; (4) high EcoScale value, which reflects the greens of the reaction; and (5) ease handling either in conducting the reaction or in the isolation of products.

Enhanced synergistic removal of Cu(II) and Cr(VI) with multifunctional biomass hydrogel from strong-acid media

Simultaneous recovery of heavy metal ions (HMIs) such as Cu(II) and Cr(VI) from strong-acid media was a great challenge due to the inhibition of protons. Herein, a novel biomass hydrogel (CMC/PEI-PD) containing various groups (bis-picolylamine, amino, and hydroxyl groups) was newly prepared by a facile two-step process. The static experiments relating pH, kinetics and isothermal co-adsorption confirmed the synergistic effect towards Cu(II) and Cr(VI) consistently. Specifically, the adsorption capacities of Cu(II) and Cr(VI) at pH 2.0 increased by 23.73% and 40.18% in comparison with the single systems. Moreover, coexistence of inorganic anions and cations could further increase the adsorption of Cu(II) and Cr(VI) by 59.90% and 43.39%, respectively. At the same time, the adsorption and desorption ratios for both HMIs remained stable. The superior performance came from the two dominant mechanisms of co-removal. On the one hand, Cu(II) chelated by bis-picolylamine group attracted Cr(VI) in the form of cation bridge, thus promoting Cr(VI) adsorption. On the other hand, the protonated amine group attracted Cr(VI) by electrostatic interaction and weakened the inter-cationic repulsion by electrostatic shielding, thus promoting Cu(II) adsorption. In addition, the dynamic column experiment towards simulated acidic electroplating wastewater involving Cu(II)–Cr(VI)–Ni(II) certified the high efficiency and feasibility of the co-removal. Therefore, CMC/PEI-PD owned great potential in the separation of typical HMIs even directly from strong-acid media.

A specific purple–blue color reaction between tryptophan and tyrosine in concentrated acidic medium

Electron transfer between tryptophan (Trp) and tyrosine (Tyr) is often accompanied with transient emission of visible blue-purple light, which is very common in numerous laser-induced photolysis experiments. However, recent experiments have shown that in the absence of pulse radiolysis, by mixing Trp and Tyr in concentrated aqueous hydrochloric acid can also produce a blue–purple color as it was observed in photolysis experiments. Unexpectedly, this color is quite stable in strong acid media (it can be kept at room temperature for at least a week). It is proposed that after initial formation of Trp radical products (TrpH▪+/Trp▪) by the solvent radical oxidation, charge-transfer complexes were generated via electron transfer reactions between Trp radical products and phenol of Tyr or their directly hole-trapping mechanism, which exhibit a blue-purple color. In this work, HPLC analysis and density functional calculations show that there are loosely reversible associations in the charge-transfer complexes which can be stabilized by strong hydrogen bonding. A Trp radicals signal was observed but the intensity was not so strong as expected. This color reaction exhibits high selectivity towards Trp and Tyr, and thus it can be a convenient method for naked-eye identifying the coexistence of these two amino acids or protein modifications of related to them.

(Invited) Synthesis and Characterization of New Catalyst Materials for Electrocatalysis

In this talk I will discuss some of our recent explorations of new catalyst materials for electrocatalysis for renewable fuels and energy, including the synthesis and characterization of these materials. First, I will briefly describe our report of an efficient acid-stable N2-plasma treated hafnium oxyhydroxide electrocatalyst for hydrogen evolution and oxidation reactions (HER and HOR). Lack of a highly active, stable, earth-abundant electrocatalyst for carrying out HER and HOR in strongly acidic conditions is a major technical challenge for developing economical polymer electrolyte membrane (PEM)-based electrolyzers and fuel cells. We found that processing Hf oxide with an atmospheric N2 plasma forms an acid-insoluble hafnium oxynitride material, and we propose that under electrochemical environments this material is transformed into an active oxynitride hydroxide that demonstrates unprecedented high catalytic activity and stability for both HER and HOR in strong acidic media for earth-abundant materials. The zero onset potentials and high current densities demonstrate that this material is a promising alternative to Pt group metal (PGM) catalysts, opening new opportunities to develop technologically and economically viable unitized regenerative fuel cell (URFC) systems and cost-effective PEM electrolyzers. Furthermore, these results have broad implications for using nitrogen incorporation (e.g. by N2 plasma treatment) to activate other non-conductive compounds and films to form new active electrocatalysts.I will discuss our recent observations on the reaction-driven restructuring of defective PtSe2 into an ultrastable electrocatalyst for the oxygen reduction reaction (ORR), which is of interest for accelerating the commercialization of PEM fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs). We have found that the restructured defective PtSe2 electrocatalyst had 1.3 times the specific activity and 2.6 times the mass activity of a commercial Pt/C catalyst, and maintained this superior ORR activity even after 126,000 cycles in accelerated durability tests.I will describe our report of a highly active hafnium-modified iridium oxide (IrHfxOy) electrocatalyst for the oxygen evolution reaction (OER), a reaction that limits development of energy efficient and economically viable a wide range of energy conversion devices. Iridium oxide (IrOx) is the current benchmark electrocatalyst for OER due to its superior performance and excellent stability, but large scale applications using IrOx are impractical due to its low abundance and high cost. We have found an IrHfxOy electrocatalyst that demonstrated ten times higher activity in alkaline conditions (pH = 11) and four times higher activity in acid conditions (pH = 1) than an IrOx electrocatalyst. The highest intrinsic mass activity of the IrHfxOy catalyst in acid conditions was calculated as 6950 A gIrOx -1 at an overpotential (η) of 0.3 V. I will also discuss our research on phosphorus-doped Hf-Ru oxide (denoted here as HfxRuyPO) electrocatalysts for OER in which we demonstrated a strategy for efficiently promoting the durability of RuO2. This research was motivated by the need to address the rapid corrosion and precipitation of highly efficient precious metal (Ir, Ru, and Rh) nanoparticle catalysts in the harsh environment of OER in PEM electrolyzers for hydrogen fuel generation. We found that when the HfxRuyPO catalysts possessed a Hf:Ru atomic ratio of 1:2, they exhibited a highly efficient and stable OER activity over 40 hours. By XPS and Raman analyses, the HfPO component was found to play a significant role in improving the durability of RuO2 through the formation of a HfOOH phase, which also possessed a higher OER activity and lower impedance.Most recently we are investigating metal-organic frameworks (MOFs) and MOF-derived (MOF-d) materials as electrocatalysts for renewable fuels and energy applications.

Exclusive separation of Cu(II) with aminophosphonic acid-functionalized hydrogel from strong acidic media

Strong acidic heavy metal ions (HMIs) wastewater (pH < 3.0) is characterized by widespread source, mixed composition and high toxicity, which is extremely difficult to control and meet the requirements of HMIs separation and resource recovery. Herein, a novel aminophosphonic acid-functionalized hydrogel (CMC/PEI-P) was prepared successfully and applied to highly-selective separate Cu(II) from strong acidic media (SAM) (pH = 2.0). Thanks to the abundant and outward amino phosphonic acid groups, the maximum adsorption capacity and the initial adsorption rate constant were 119.41% and 116.64% higher than those of the precursor CMC/PEI. Most importantly, the exclusive separation with the super-high selectivity coefficients (+∞) could unexpectedly achieve with CMC/PEI-P even from the mixed polymetallic SAM. Furthermore, the purity of Co(II) in strong acidic cobalt-rich solution could be increased to more than 99.50%, with the benefit of about 200 times higher than the cost. The predominant mechanisms existed in the coordination with various active groups such as phosphonate, amine and hydroxyl. According to Density Functional Theory (DFT) calculations, the tetradentate coordination configuration with the best stability could be formed involving CMC/PEI-P and Cu(II). Therefore, this work explored a new pathway for the cost-effective separation and purification toward Cu(II) directly especially from SAM.

Pre-electrolysis of LiClO4 in Acetonitrile: Electrochemically Induced Protolytic Carbon-Carbon Bond Formation of Benzylic Ethers and Acetals with Allyl Trimethylsilane and Other Carbon Nucleophiles.

The pre-electrolysis of LiClO4 in acetonitrile in an undivided cell applying only "catalytic" amounts of current (e.g., 0.05 F) led to the formation of a strong acidic medium for the activation of benzylic ethers and acetals. The activated primary and secondary benzylic ethers and acetals could be converted with a range of carbon nucleophiles, such as allyl trimethylsilane, silyl enol ethers, and enol acetates, for the formation of new carbon-carbon bonds. A chemoselective reaction was observed when electron-deficient benzylic acetals were converted with allyl trimethylsilane to the monoallylated products, whereas an electron-rich benzylic acetal led to the double allylated product under activation of both ether groups.

Synthesis of g-C3N4@WO3 nanocomposites for dye adsorptive removal in water medium: Equilibrium and kinetics studies

In this research, WO3, g-C3N4, and g-C3N4@WO3 nanocomposites were synthesized from Na2WO4.2H2O and urea precusors via the hydrothermal method in a strong acid medium. Physico-chemical characteristics of WO3, g-C3N4, and g-C3N4@WO3 nanocomposites were examined by means of XRD, Raman, FTIR, FE-SEM, BET, and UV-Vis spectroscopy. The produced materials were then applied for studying adsorptive removal of methylene blue (MB) as a model pollutant from aqueous solutions. The results showed that g-C3N4@WO3 nanocomposites were successfully synthesized, with a hexagonal shape and an average crystal size of in the range of 15.4–20.7 nm. The surface area (68.3 m2/g) of g-C3N4@WO3 nanocomposites was 2.37 times higher compared to sole WO3, and g-C3N4@WO3 composites were mesoporous materials with a typical average pore diameter of 4.5 nm. It was revealed that the MB adsorption process occurred extremely quickly, reaching equilibrium after only about 20 min, with a maximum uptake of MB of 190 mg/g which was significantly higher than other adsorbents. The adsorption process was followed the first-order-kinetics model and the adsorbent showed high durability in adsorbing MB, with a slight decline in adsorption efficiency after 4 cycles (from 98.7% to 95.9%). This research provides an easy method for producing high adsorption capacity nanocomposite which can be applied for efficient removal of MB from water.

Synthesis of acidic modified UiO‐66 by concentrated sulphation form and its application in the production of fatty acids ethyl esters

AbstractIn this article, UiO‐66 metal–organic frameworks containing structural modifications were synthesized and characterized to increase acidic surface behaviour for application in heterogeneous acid catalysis to produce fatty acid ethyl esters (FAEE) from degummed soybean oil. The solvothermal route synthesized UiO‐66, and the post‐synthesis acid modifications were done by sulphation reaction in strong acidic medium. The synthesized materials were characterized by physicochemical techniques such as X‐ray diffraction (XRD), C‐ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectrometer (FTIR), and N2 physisorption, observing a strong structural modification of the original UiO‐66, but no signal of sulphated ZrO2 was presented. However, the acidic characteristics on the material's surface were increased. A central compound centred on face 23 experiments design was carried out to evaluate three essential reaction variables: temperature, time, and alcohol/oil ratio, obtaining an optimized fit for the UiO‐66‐S35 of temperature at 140°C, time of 3 h, and molar ratio of 16. The optimized statistical adjustment was applied in the reuse cycles assays in three catalyst cycles, reaching the maximum yield of 95% in FAEE, keeping the catalyst active at the end of 3 cycles.

Synthesis of core–shell magnetic nanocomposite bearing phosphonic acid ligand for uranium extraction from strong HNO3 solution

Recovery of uranium from strong acid media using magnetic nanomaterials as sorbents is vital for sustainable nuclear energy, due to their superparamagnetism and large specific surface energy. However, it remains a huge challenge to develop magnetic nanomaterials for extracting uranium from strong acid media, since magnetic nanomaterials often suffer from poor structural stability and low uranium adsorption performance in strong acid media. Herein, a novel core–shell magnetic nanocomposite Fe3O4@SiO2/P (MBA-VPA) bearing phosphonic acid was fabricated by distillation-precipitation polymerization of N, N'-methylene diacrylamide (MBA) with vinylphosphonic acid (VPA) around the surface of Fe3O4 decorated by SiO2 (Fe3O4@SiO2). By optimizing the polymerization system, high concentration of phosphonic acid with high free movement degree was led into the surface of the sorbent. Under applied conditions (c(H+) = 4 mol L−1, T = 298 K and t = 3 h), the sorbent showed a record-breaking maximum adsorption capacity (qmax) of 262.5 mg g−1 with an excellent selectivity for uranium in the presence of multi-ions. The adsorption capacity of the sorbent in strong HNO3 increased remarkably with increase of the concentration and free movement degree of phosphonic acid. By coating Fe3O4 with an inert SiO2, the sorbent exhibited excellent acidic resistance in strong HNO3. The sorbent could also be magnetically recovered within 15 s, and repeated at least six times without obvious reduction in adsorption capacity. The excellent adsorption performance in strong HNO3 media was primarily assigned to the abundant accessible PO groups, evidenced by X-ray photoelectron spectroscopy (XPS), control experiments and density functional theory (DFT). Most importantly, this work provides a new perspective for developing highly active, excellent acidic resistance, and recyclable magnetic nanomaterials for extracting uranium from strong acid media.

On the mechanism of the Folin test for uric aci

The mechanism of the interaction of uric acid with sodium tungstate in phosphoric acid (Folin test) is described. This insight involves the following steps: addition of tungstic acid to the carbon-carbon double bond in uric acid. Protolysis of the organometallic ester gives rise to dihydroxyoxotungsten and an epoxide, via a concerted mechanism. Acid catalyzed ring opening of the oxirane produces a vicinal diol via reaction of the intermediate carbocation with water. Isomerization of the resulting carbinolamide groups is enhanced by the resonance of the ureido group. Breaking of the second carbinolamide gives urea and alloxan, 5-ketobarbituric acid hydrate. Uric acid oxidation in strong acidic medium like phosphoric acid produces alloxan, whereas oxidation in alkaline, neutral, or slightly acidic medium, gives allantoin.