Search Results (11)

Methyl ethyl ketone (MEK) is among the most extensively utilized solvents in various industrial applications. In this study, we present a highly efficient synthesis route for MEK via the decarboxylation of biomass-derived levulinic acid, using potassium persulfate (K₂S₂O₈) and silver nitrate (AgNO₃) as key reagents. The specific roles of AgNO₃ and K₂S₂O₈ were thoroughly investigated. Additional silver species, such as Ag₂O and AgO, were also detected during the reaction. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analyses provided evidence of the evolution of solid phases throughout the reaction. Based on these findings, we propose a radical decarboxylation mechanism initiated by the generation of sulfate radicals (SO₄•⁻) through the catalytic breakdown of K₂S₂O₈ by AgNO₃. This mechanistic understanding, combined with a parametric study, enabled us to achieve an unprecedented level of levulinic acid conversion (97.9%) and MEK yield (86.6%) with this system, surpassing all previously reported results in the literature. Full article

A water-soluble ternary copolymer bearing carboxyl, sulfonic, and amide functional groups was synthesized using ammonium persulfate-catalyzed free radical polymerization in water, resulting in high monomer conversion. This copolymer was then complexed with aluminum sulfate, forming an admixture containing Al(SO₄)(OH)·5H₂O, which was subsequently combined with silica gel. Characterization revealed that the synthesized copolymer formed a large, thin membrane that covered both the aluminum compounds and the silica gel blocks. The introduction of this complex admixture, combining the copolymer and aluminum sulfate, not only reduced the setting times of the cement paste but also enhanced the mechanical strengths of the mortar compared to using aluminum sulfate alone. The complex admixture led to the formation of katoite, metajennite, and C₃A (tricalcium aluminate) in the mortar, demonstrating significant linking effects, whereas pure aluminum sulfate could not completely transform C₃S within 24 h. Further addition of silica gel to the complex admixture further shortened the setting times of the paste, slightly reduced compressive strength, but improved flexural strength compared to the initial complex admixture. The silicon components appeared to fill the micropores and mesopores of the mortar, accelerating cement setting and enhancing flexural strength, while slightly decreasing compressive strength. This study contributed to the development of new cementing accelerators with improved hardening properties. Full article

Recent research on atmospheric particle formation has shown substantial discrepancies between observed and modeled atmospheric sulfate levels. This is because models mostly consider sulfate originating from $\mathrm{S}{\mathrm{O}}_2$ oxidation by •OH radicals in mechanisms catalyzed by solar radiation while ignoring other pathways of non-radical $\mathrm{S}{\mathrm{O}}_2$ oxidation that would substantially alter atmospheric sulfate levels. Herein, we use high-level quantum chemical calculations based on density functional theory and coupled cluster theory to show that monoethanolamine (MEA), a typical alkanolamine pollutant released from $\mathrm{C}{\mathrm{O}}_2$ capture technology, can facilitate the conversion of atmospheric $\mathrm{S}{\mathrm{O}}_2$ to sulfate in a non$–$•OH$–$radical oxidation mechanism. The initial process is the MEA-induced $\mathrm{S}{\mathrm{O}}_2$ hydrolysis leading to the formation of ${\mathrm{H}\mathrm{O}\mathrm{S}\mathrm{O}}_2^{-}$•${\mathrm{M}\mathrm{E}\mathrm{A}\mathrm{H}}^{+}$. The latter entity is thereafter oxidized by ozone (${\mathrm{O}}_3$) and nitrogen dioxide ($\mathrm{N}{\mathrm{O}}_2$) to form ${\mathrm{H}\mathrm{S}\mathrm{O}}_4^{-}$•${\mathrm{M}\mathrm{E}\mathrm{A}\mathrm{H}}^{+}$, which is an identified stabilizing entity in sulfate-based aerosol formation. Results show that the ${\mathrm{H}\mathrm{O}\mathrm{S}\mathrm{O}}_2^{-}$•${\mathrm{M}\mathrm{E}\mathrm{A}\mathrm{H}}^{+}$ reaction with ${\mathrm{O}}_3$ is kinetically and thermodynamically more feasible than the reaction with ${\mathrm{N}\mathrm{O}}_2$. The presence of an additional water molecule further promotes the ${\mathrm{H}\mathrm{O}\mathrm{S}\mathrm{O}}_2^{-}$•${\mathrm{M}\mathrm{E}\mathrm{A}\mathrm{H}}^{+}$ reaction with ${\mathrm{O}}_3$, which occurs in a barrierless process, while it instead favors HONO formation in the reaction with ${\mathrm{N}\mathrm{O}}_2$. The investigated pathway highlights the potential role alkanolamines may play in $\mathrm{S}{\mathrm{O}}_2$ oxidation to sulfate, especially under conditions that are not favorable for •OH production, thereby providing an alternative sulfate source for aerosol modeling. The studied mechanism is not only relevant to sulfate formation and may effectively compete with reactions with sulfur dioxide and hydroxyl radicals under heavily polluted and highly humid conditions such as haze events, but also an important pathway in MEA removal processes. Full article

The particle size distribution (PSD) in emulsion polymerization (EP) has been modeled in the past using either the pseudo bulk (PB) or the 0-1/0-1-2 approaches. There is some controversy on the proper type of model to be used to simulate the experimental PSDs, which are apparently broader than the theoretical ones. Additionally, the numerical technique employed to solve the model equations, involving hyperbolic partial differential equations (PDEs) with moving and possibly steep fronts, has to be precise and robust, which is not a trivial matter. A deterministic kinetic model for the PSD evolution of ab initio EP of vinyl monomers was developed to investigate these issues. The model considers three phases, micellar nucleation, and particles that can contain $n\ge 0$ radicals. Finite volume (FV) and weighted-residual methods are used to solve the system of PDEs and compared; their limitations are also identified. The model was validated by comparing predictions with data of monomer conversion and PSD for the batch emulsion homopolymerization of styrene (Sty) and methyl methacrylate (MMA) using sodium dodecyl sulfate (SDS)/potassium persulfate (KPS) at 60 °C, as well as the copolymerization of Sty-MMA (50/50; mol/mol) at 50 and 60 °C. It is concluded that the PB model has a structural problem when attempting to adequately represent PSDs with steep fronts, so its use is discouraged. On the other hand, there is no generalized evidence of the need to add a stochastic term to enhance the PSD prediction of EP deterministic models. Full article

In archaea and sulfate-reducing bacteria, heme is synthesized via the siroheme-dependent pathway. The last step of this route is catalyzed by the Radical SAM enzyme AhbD and consists of the conversion of iron-coproporphyrin III into heme. AhbD belongs to the subfamily of Radical SAM enzymes containing a SPASM/Twitch domain carrying either one or two auxiliary iron–sulfur clusters in addition to the characteristic Radical SAM cluster. In previous studies, AhbD was reported to contain one auxiliary [4Fe-4S] cluster. In this study, the amino acid sequence motifs containing conserved cysteine residues in AhbD proteins from different archaea and sulfate-reducing bacteria were reanalyzed. Amino acid sequence alignments and computational structural models of AhbD suggested that a subset of AhbD proteins possesses the full SPASM motif and might contain two auxiliary iron–sulfur clusters (AuxI and AuxII). Therefore, the cluster content of AhbD from Methanosarcina barkeri was studied using enzyme variants lacking individual clusters. The purified enzymes were analyzed using UV/Visible absorption and EPR spectroscopy as well as iron/sulfide determinations showing that AhbD from M. barkeri contains two auxiliary [4Fe-4S] clusters. Heme synthase activity assays suggested that the AuxI cluster might be involved in binding the reaction intermediate and both clusters potentially participate in electron transfer. Full article

The persulfate-based advanced oxidation processes employing heterogeneous photocatalysts to generate sulfate radicals (SO₄^•−) from peroxydisulfate ion (PDS, S₂O₈²⁻) have been extensively investigated to remove organic pollutants. In this work, BiOX (X = Cl, Br, and I) photocatalysts were investigated to activate PDS and enhance the transformation rate of various organic substances under UV (398 nm) and Vis (400–700 nm) radiation. For BiOCl and BiOBr, in addition to excitability, the light-induced oxygen vacancies are decisive in the activity. Although without organic substances, the BiOI efficiency highly exceeds that of BiOBr and BiOCl for PDS activation (for BiOI, 15–20%, while for BiOBr and BiOCl, only 3–4% of the PDS transformed); each BiOX catalyst showed enhanced activity for 1,4-hydroquinone (HQ) transformation due to the semiquinone radical-initiated PDS activation. For sulfamethoxypyridazine (SMP), the transformation is driven by direct charge transfer, and the effect of PDS was less manifested. BiOI proved efficient for transforming various organic substances even under Vis radiation. The efficiency was enhanced by PDS addition (HQ is wholly transformed within 20 min, and SMP conversion increased from 40% to 90%) without damaging the catalyst; its activity did change over three consecutive cycles. Results related to the well-adsorbed trimethoprim (TRIM) and application of biologically treated domestic wastewater as a matrix highlighted the limiting factors of the method and visible light active photocatalyst, BiOI. Full article

A visible-light-Fenton-like reaction system was constructed for the selective conversion of peroxymonosulfate to sulfate radical. Au@CoS, when doped on monoclinic BiVO₄ {010} facets, promoted spatial charge separation due to the different energy band between the m-BiVO₄ {010} and {110} facets. The visible-light response of m-BiVO₄ was enhanced, which was attributed to the SPR effect of Au. And the photogenerated electrons were transferred from the m-BiVO₄ {010} facet to Au via a Schottky junction. Owing to higher work function, CoS was able to capture these photoelectrons with acceleration of the Co(Ⅱ)/Co(Ⅲ) redox, enhancing peroxymonosulfate conversion to sulfate radical (Co²⁺ + HSO₅⁻→ Co³⁺ + •SO₄⁻ + OH⁻). On the other hand, holes accumulated on m-BiVO₄ {110} facets also contributed to organics oxidation. Thus, more than 95% of RhB was degraded within 40 min, and, even after five cycles, over 80% of RhB could be removed. The radical trapping experiments and EPR confirmed that both the sulfate radical and photogenerated hole were the main species for organics degradation. UV-vis DRS, photoluminescence (PL) and photoelectrochemical analyses also confirmed the enhancement of the visible-light response and charge separation. In a pilot scale experiment (PMS = 3 mM, initial TOC = 151 mg/L, reaction time = 4 h), CoS-Au-BiVO₄ loaded on glass fiber showed a high mineralization rate (>60%) of practical wastewater. Full article

In recent years, high fine particulate (PM_2.5) pollution episodes with high ozone (O₃) levels have been observed in Shanghai from time to time. However, their occurrence and characteristics remain poorly understood. Meanwhile, as a major precursor of tropospheric hydroxyl radical (OH) that initiates the formation of hydroperoxyl and organic peroxy radicals, HONO would inevitably affect the formation of O₃, but its role in the formation of O₃ during the double high-level PM_2.5 and O₃ pollution episodes remains unclear. In this study, the characteristics of the double high pollution episodes and the role of HONO in O₃ formation in these episodes were investigated based on field observation in urban Shanghai from 2014 to 2016. Results showed that high PM_2.5 pollution and high O₃ pollution could occur simultaneously. The cases with data of double high O₃ and PM_2.5 concentrations accounted for about 1.0% of the whole sampling period. During the double high pollution episodes, there still existed active photochemical processes, while the active photochemical processes at high PM_2.5 concentration were conductive to the production and accumulation of O₃ under a VOC-limited regime and a calm atmospheric condition including high temperature, moderately high relative humidity, and low wind speed, which in turn enhanced the conversions of SO₂ and NO₂ and the formation and accumulation of secondary sulfate and nitrate aerosols and further promoted the increase of PM_2.5 concentration and the deterioration of air pollution. Further analysis indicated that the daytime HONO concentration could be strongly negatively correlated with O₃ concentration in most of the double high pollution episodes, revealing the dominant role of HONO in O₃ formation during these pollution episodes. This study provides important field measurement-based evidence for understanding the significant contribution of daytime HONO to O₃ formation, and helps to clarify the formation and coexistence mechanisms of the double high-level O₃ and PM_2.5 pollution episodes. Full article

Novel flower-shaped C-dots/Co₃O₄{111} with dual-reaction centers were constructed to improve the Fenton-like reaction activity and peroxymonosulfate (PMS) conversion to sulfate radicals. Due to the exposure of a high surface area and Co₃O₄{111} facets, flower-shaped C-dots/Co₃O₄{111} could provide more Co(II) for PMS activation than traditional spherical Co₃O₄{110}. Meanwhile, PMS was preferred for adsorption on Co₃O₄{111} facets because of a high adsorption energy and thereby facilitated the electron transfer from Co(II) to PMS. More importantly, the Co–O–C linkage between C-dots and Co₃O₄{111} induced the formation of the dual-reaction center, which promoted the production of reactive organic radicals (R•). PMS could be directly reduced to SO₄⁻• by R• over C-dots. On the other hand, electron transferred from R• to Co via Co–O–C linkage could accelerate the redox of Co(II)/(III), avoiding the invalid decomposition of PMS. Thus, C-dots doped on Co₃O₄{111} improved the PMS conversion rate to SO₄⁻• over the single active site, resulting in high turnover numbers (TONs). In addition, TPR analysis indicated that the optimal content of C-dots doped on Co₃O₄{111} is 2.5%. More than 99% of antibiotics and dyes were degraded over C-dots/Co₃O₄{111} within 10 min. Even after six cycles, C-dots/Co₃O₄{111} still remained a high catalytic activity. Full article

This study was focused on the generation of sulfate radicals and their applicability as powerful oxidants for degrading complex organic compounds with the final objective of operating in flow systems. To this end, the removal of two compounds from the pharmaceutical industry was assessed, lissamine green and prednisolone. Initially, sulfate radicals were generated by the activation of persulfate with iron as homogenous catalyst, and the key parameters involved in the process, as catalyst concentration and oxidant dosage, were evaluated. Furthermore, with the aim of preventing the secondary contamination due to metal leaching and to be operate in a continuous mode, a heterogeneous catalyst was developed. For it, the iron was fixed on a cationic resin as Amberlite IR120 Na⁺ form. It was demonstrated that the removal of both pollutants increases with greater catalyst dosages, achieving a decay of 85% within 25 min with 30 g·L⁻¹ of catalyst. Moreover, the reuse capability of the catalyst was tested, illustrating that it is rough enough for its reuse. Conversely, in order to develop a continuous treatment in flow system, a fixed bed reactor was constructed and its feasibility was proven. Different experiments with residence times from 10 min to 60 min were performed, obtaining a removal level of ≈95% and 90% for prednisolone and lissamine green, respectively, at residence time of 60 min. In conclusion, the potential of sulfate radicals-based technology for degrading organic contaminants has been demonstrated. Full article

The effect of the irreversible addition-fragment chain transfer agent, butyl(2-phenylallyl)sulfane (BPAS), on the course of the emulsion polymerization of styrene and on the product molecular weight was investigated. The emulsion polymerizations were performed using various amounts of sodium dodecyl sulfate (SDS) as the surfactant and potassium peroxodisulfate (KPS) as the initiator. The relationships between the rates of polymerization (\(R_{p} \)) and the number of particles per volume (\(N_{c} \)) with respect to the concentrations of KPS, SDS, and BPAS were found to be \(R_{p} \propto \left\lbrack KPS \right\rbrack^{0.29} \), \(N_{c} \propto \left\lbrack KPS \right\rbrack^{0.26} \),\(R_{p} \propto \left\lbrack SDS \right\rbrack^{0.68} \), \(N_{c} \propto \left\lbrack SDS \right\rbrack^{0.72} \), and \(R_{p} \propto \left\lbrack BPAS \right\rbrack^{- 0.73} \) . The obtained relationships can be attributed to the exit of the leaving group radicals on BPAS from the polymer particles. The experimental values of the average number of radicals per particle (\(\overset{\_}{n} \)) were strongly dependent on the BPAS concentration and were in good agreement with the theoretical values (\({\overset{\_}{n}}_{theo} \)) from model calculations. The number-average molecular weight (\(\overset{\_}{M_{n}} \)) can be controlled by BPAS over nearly the entire conversion range, which is also in agreement with the mathematical model. In addition, the transfer rate coefficient (\(k_{tr} \)) of BPAS can be estimated as 326 L/mol/s at 70 \(^\circ\)C. Moreover, similar good results were found for the tested redox reactions at 30 \(^\circ\)C. Full article