Leaching Of Metal Ions Research Articles

Peroxymonosulfate activation by carbon-encapsulated metal nanoparticles: Switching the primary reaction route and increasing chemical stability

This study explores the technical merits of carbon encapsulation via an electrical wire explosion method to enhance the peroxymonosulfate activation performance of metals. Reflecting the nature of core-shell structures, the outer carbon layers hampered the reductive conversion of peroxymonosulfate to sulfate radicals by the inner metal cores, whereas the metal cores increased the overall electrical conductivity as a pivotal factor in non-radical activation. Hence, the impact of carbon wrapping hinged on the peroxymonosulfate reduction capability of the metals, i.e., kinetic retardation in organic degradation with reactive Cu, Fe, and Ni-Fe, but acceleration with unreactive Ni. Further, composite fabrication switched the major degradative pathway from radical-induced oxidation to mediated electron transfer, as determined from the effects of methanol and chloride, formaldehyde and bromate formation yields, reactivity toward multiple organics, and electron paramagnetic resonance spectral features. The protective carbon shells enabled pH-insensitive peroxymonosulfate activation, prevented metal ion leaching, and alleviated catalyst deactivation.

Activation of peroxymonosulfate by CuCo2O4-GO for efficient degradation of bisphenol A from aqueous environment

A new catalyst, CuCo2O4 supported on graphene oxide (CuCo2O4-GO), was synthesized as a heterogeneous catalyst to activate peroxymonosulfate (PMS) for the degradation of bisphenol A (BPA). In this study, highly efficient degradation of BPA by PMS (0.2 mM) activated with CuCo2O4-GO (100 mg/L) was achieved and the degradation efficiency was 100% within 5 min at initial pH 7.0. The reaction rate constant (2.662 min−1) of BPA by CuCo2O4-GO/PMS was 35.49 times greater than that of CuCo2O4/PMS (0.075 min−1), and the optimal percentage of GO was 20%. The catalytic activity of CuCo2O4-GO as synthesized in this work was much higher than that of CoFe2O4-GO which has been reported previously. In addition, the degradation efficiency increased with the rise of catalyst dose and PMS dosage, it exhibited the best performance at pH 7.0. The detection of radicals by electron paramagnetic resonance (EPR) and quenching experiments indicated that SO4− was the main free radical that responsible for the degradation of BPA while OH also was produced in the CuCo2O4-GO/PMS system. The CuCo2O4-GO maintained its catalytic activity during the repeated batch experiments and the leaching of metal ion was limited. Finally, the toxicity of BPA decreased synchronously during the reaction process and higher content of TOC removal was achieved by CuCo2O4-GO/PMS than that of CuCo2O4/PMS. The performance of CuCo2O4-GO/PMS in actual water indicated that CuCo2O4-GO/PMS system had great potential in practical application in the degradation of refractory organic pollutants in water.

A novel perspective process for alumina extraction from coal fly ash via potassium pyrosulfate calcination activation method

Alumina extraction is considered as one of the promising trends for the value-added use of coal fly ash (CFA). In this study, a moderate potassium pyrosulfate (K2S2O7) calcination activation method was used to extract alumina from CFA. The calcined conditions including X1: K2S2O7/Al2O3 molar ratio (2–4), X2: calcining temperature (180–220 °C), X3: calcining time (2–4 h) was optimized by using response surface method based on 3-factor 3-degree Box-Behnken design. The effects of confirmed factors were fitted in a quadratic regression polynomial equation. The main and interacting influences between variables were studied by using the analysis of variance and 3D plots, respectively. The results show the alumina extraction rate was more influenced by K2S2O7/Al2O3 molar ratio. The optimized conditions were identified as K2S2O7/Al2O3 as molar ratio 3.55:1, calcining temperature up to 212 °C and calcining time of 3.1 h, in which the alumina extraction rate was recorded as 93.28%. The characteristics of CFA and leaching residues were studied by using XRD, SEM and 27Al and 29Si MAS-NMR. Results show that K2S2O7 removes the aluminum and effectively breaks the high polymerization units of Si–O–Al and Al–O. The mineral transformation during calcined reaction follows as K2S2O7 + CFA (mullite, corundum, and amorphous phase) → aluminum tri-potassium sulfate → leached residues rich in silicate + leached metal ions. The surface chemical reactions controlled the calcining process. The apparent rate constant was found to be 3.12 to 4.18 × 10−3 min−1 at the temperature range of 180–220 °C, respectively. The apparent activation energy was refereed to be 13.579 kJ/mol. These findings indicate that the potassium pyrosulfate calcination activation method gets a high level of the extracting rate, and is industrially applicable to extract alumina.

Enhanced catalytic oxidation of benzotriazole via peroxymonosulfate activated by CoFe2O4 supported onto nitrogen-doped three-dimensional graphene aerogels

The system of peroxymonosulfate (PMS) activated by CoFe2O4 has been widely investigated to degrade organic pollutants. However, low catalytic activity for extremely recalcitrant organic pollutants (e.g. benzotriazole (BTA)) and potential leaching of metal ions limit its further application. As such, CoFe2O4 supported on N-doped 3D graphene aerogels (CoFe2O4/N-3DG) was developed for highly efficient BTA degradation with improved stability and recyclability. It turns out that the degradation rate constant of BTA in CoFe2O4/N-3DG/PMS (0.0254 ± 0.0012 min−1) system was 19.5 times higher than that in CoFe2O4/PMS (0.0013 ± 0.0024 min−1) system. Three N species (pyridine, pyrrole and graphite N) enhanced the redox activity, electron transfer efficiency and active site density of CoFe2O4/N-3DG, thereby positively enhancing the catalytic performance. Furthermore, it is attributed to the synergistic effect of N-3DG-mediated non-radical pathway and CoFe2O4-dominated radical pathway. Particularly, multiple reactive oxygen species (ROS, •OH, SO4−•, O2–• and 1O2) and direct electron transfer achieve effective degradation of BTA. Ultimately, BTA was broke down to smaller intermediates or mineralized to CO2 in three main pathways, involving three ring-opening reaction of benzene and triazole. In addition, the leaching of total Co and Fe ions are reduced by 88% and 57% than counterparts from CoFe2O4 after four reaction cycles, respectively, demonstrating improved stability and reusability. Overall, this study will expand the good application of graphene aerogels and provide new insights of enhancing the degradation of extremely recalcitrant organic pollutants by catalyzed PMS system.

Recovery of Gold from the Refractory Gold Concentrate Using Microwave Assisted Leaching

Microwave technology has been confirmed to be suitable for use in a wide range of mineral leaching processes. Compared to conventional leaching, microwave-assisted leaching has significant advantages. It is a proven process, because of its short processing time and reduced energy. The purpose of this study was to enhance the gold content in a refractory gold concentrate using microwave-assisted leaching. The leaching efficiencies of metal ions (As, Cu, Zn, Fe, and Pb) and recovery of gold from refractory gold concentrate were investigated via nitric acid leaching followed by microwave treatment. As the acid concentration increased, metal ion leaching increased. In the refractory gold concentrate leaching experiments, nitric acid leaching at high temperatures could limit the decomposition of sulfide minerals, because of the passive layer in the refractory gold concentrate. Microwave-assisted leaching experiments for gold recovery were conducted for the refractory gold concentrate. More extreme reaction conditions (nitric acid concentration > 1.0 M) facilitated the decomposition of passivation species derived from metal ion dissolution and the liberation of gangue minerals on the sulfide surface. The recovery rate of gold in the leach residue was improved with microwave-assisted leaching, with a gold recovery of ~132.55 g/t after 20 min of the leaching experiment (2.0 M nitric acid), according to fire assays.

Synthesis, characterization, and applications of novel Co(II)‐pyridoxalphosphate‐Schiffbase/SBA‐15 as a nanocatalyst for the green synthesis of benzothiazole heterocycles

AbstractMesoporous heterogeneous santa barbara amorphous (SBA)‐15‐supported cobalt complex, as a novel nanocatalyst containing N–O chelating Schiff‐base ligand was successfully synthesized by the reaction of SBA‐15 and Cobalt(II)‐Schiff‐base complex. The Co(II)‐Schiff base complex also was prepared for the first time, by the reaction of pyridoxal 5′‐phosphate or PLP (biological active form of vitamin B6), 3‐(aminopropyl)‐triethoxysilane in methanol that complexation with CoCl2. The subsequent grafting of entitled complex to SBA‐15 afforded Co(II)‐PLP‐Schiff base/SBA‐15 mesoporous catalyst. Characterization of the product was carried out with powder X‐ray diffraction, Brunauer–Emmett–Teller nitrogen adsorption–desorption, transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, atomic absorption spectroscopy, and inductively coupled plasma, Fourier‐transform infrared spectroscopy. The results revealed the retention of the textural properties and hexagonally uniform structures of SBA‐15 during the grafting procedure. This nanocatalyst was applied successfully for one‐pot synthesis of various benzothiazole heterocycles under green conditions. This catalyst is an active, reusable, and stable nanomaterial with no leaching of metal ions to the reaction medium. It was used for the synthesis of desired benzothiazole heterocycles by the cyclo‐condensation of aryl‐aldehydes with 2‐aminothiophenol with good to excellent yields and under green conditions.

Optimization of Sintering Parameters of 316L Stainless Steel for In-Situ Nitrogen Absorption and Surface Nitriding Using Response Surface Methodology

This research investigates the simultaneous sintering and surface nitriding of 316L stainless steel alloy using powder metallurgy method. The influence of sintering temperature and dwell time are investigated for maximum nitrogen absorption, densification and increased microhardness using response surface methodology (RSM). In this study, 316L stainless steel powder was compacted at 800 MPa and sintered at two different temperatures of 1150 and 1200 °C with varying dwell times of 1, 3, 5 and 8 h in nitrogen atmosphere. The sintered compacts were then characterized for their microstructure, densification, microhardness and nitrogen absorption. The results revealed that increased dwell time assisted nitrogen to diffuse into stainless steel matrix along with the creation of nitride layer onto the sample surface. The microhardness and density also increased with increasing dwell time. A densification of 7.575 g/cm3 and microhardness of 235 HV were obtained for the samples sintered at 1200 °C temperature with 8 h dwell time. The simultaneous sintering and surface nitriding technique developed in this research work can help in improving corrosion resistance of this material and controlling leaching of metal ions for its potential use in biomedical applications.

Synthesis of FeCo alloy encapsulated nitrogen-doped graphitized carbon: High catalytic activation and low metal ion leaching in microwave assisted Fenton reaction

Abstract As an efficient non-precious metal catalyst, FeCo alloy was widely used in various catalytic reactions. Owing to the organic pollution in ecosystem, it has attracted much attention in heterogeneous Fenton reaction. Unfortunately, their application was restricted by slow process and high leaching. To overcome these shortcomings simultaneously, herein, FeCo@nitrogen-doped graphitized carbon (NGC) core/shell composite was synthesized via one-step annealing Prussian blue analogue. In microwave assisted Fenton reaction (MAFR), malachite green (MG) degradation time was only 2.5 min, and the rate constant was 2.0 min−1, about 20 times higher than heterogeneous Fenton reaction. Synergistic index was 3.88, meaning extra 288% of removal efficiency was yield in peroxymonosulfate (PMS)+MW+FeCo@NGC system. The effect of microwave-activation was divided into thermal effect and non-thermal effect. SO4·− produced through thermal effect occupied 73% ± 8% of total number. The contribution of thermal effect was estimated to be 65% ± 7% for MG removal. Non-thermal effect was clarified by hotspots effect theory. Due to protection of NGC shell, Co3+/2+ leaching in composite was only one-tenth of pure FeCo. FeCo@NGC composite could be rapidly recycled due to ferromagnetic behavior with saturation magnetization of 98.7 emu/g. 89.3% of degradation efficiency was maintained after the 5th cycle.

In vitro behavior of silk fibroin-based composite resorbable bone fixation devices

There are between 12 and 15 million bone fractures in the United States annually, and many of them require the implantation of an internal fixation device, which helps anchor severely fractured bones to ensure they heal properly. The current standard for such a device relies on the use of metals like stainless steel or titanium due to their superior mechanical properties and propensity to be bioinert. However, these materials are known to cause stress shielding and metal ion leaching, which often lead to the need for a second surgery to remove the implant. For these reasons, there has been considerable interest in creating a fixation device that would provide mechanical stability during healing, but then safely degrade over time, eventually leaving only the patient's own bone. While there are degradable fixation devices on the market, they are made of polymeric materials and have poor mechanical properties, limiting their use to none- and low-load-bearing applications, such as maxillofacial fracture fixation. The present study investigates the use of silk fibroin, hydroxyapatite, and polylactic acid to make resorbable composites to be used as bone fixation devices for load-bearing applications. Using silk fibroin fibers, hydroxyapatite nanowhiskers, and a polylactic acid matrix, three-phase composites were fabricated that has a flexural modulus and strength up to 21.1 GPa and 536 MPa, respectively. Additionally, in vitro analyses showed that the composites degrade slowly via surface erosion and show good initial biocompatibility. These results show great promise for the use of these composites as load-bearing fracture fixation devices. Statement of SignificanceSilk fibroin fibers and hydroxyapatite nanowhiskers were used to fabricate a three-phase composite material for the purpose of load-bearing bone fracture fixation devices. Currently, the bone fixation market is dominated by metals, which cause stress shielding and metal ion leaching, often requiring a second surgery to remove the implant. There are bioresorbable options, made from polymers like poly(lactic-co-glycolic acid), which safely degrade in vivo, leaving only the patient's natural bone and eliminating the need for a second surgery. This study seeks to bridge the gap, creating a device that supports load-bearing fractures while remaining fully resorbable in vivo. The material in this study exhibits the highest bending modulus and strength of any bioresorbable composite found in literature.

The removal of phosphate by thermally treated red mud from water: The effect of surface chemistry on phosphate immobilization

This study investigated thermal treatment of red mud (RM) and its effect on phase composition, surface property, and sorption capacity exemplified by phosphate. Dehydration (∼600 °C), decomposition of carbonate minerals (700 °C–800 °C), and silicate/aluminate formation (900 °C–1000 °C) occurred upon thermal treatment of RM. Grain growth and vitrification that rendered initial morphology changes and decreased the specific surface area of RM from 26.5 to 4.1 m2/g when treated from 600 to 1000 °C, respectively. Surface acidity, i.e., intrinsic acidity constant and surface acidity density, decreased as well after thermal treatment at 600 °C due to burnouts of organics then increased upon further elevated-temperature treatment because of phase transformation. Thermal activation enhanced phosphate adsorption density (μmol/m2). Multilayer sorption aided by leached metal ions was responsible for phosphate immobilization.

Plasma deposition of antimicrobial coatings based on silver and copper on polypropylene

This paper addresses the issue of plasma treatment of the surface of polypropylene (PP) using sputtering of silver (Ag) and copper (Cu) and their oxides with MS-PVD in order to impart antimicrobial activity. It was found that plasma treatment of PP with Cu and Ag based layers allows to provide excellent antimicrobial properties due to a constant release of metal ions. The samples of PP treated with Cu and CuO were characterized by highest antimicrobial properties and stability of the coatings. The most stable and least effective coating against bacteria was Ag-PP sample. In turn, AgO-PP was characterized by the lowest stability in aqueous conditions and strong antimicrobial activity. It was found that leaching of metal ions from the surface of treated PP even in exceptional levels plays a crucial role in bactericidal activity.

Biomaterial functionalized cerium nanocomposite for removal of fluoride using central composite design optimization study

Excess fluoride concentration in drinking water is a global issue, as this has an adverse effect on human health. Several adsorbents have been synthesized from natural raw material to remove fluoride from water. Reported adsorbents have some problems with the leaching of metal ions, fewer adsorption sites, and low adsorption capacity. Therefore, to address this, an effective biomaterial derived from the Luffa cylindrica (LC), containing many active sites, was integrated with a nano form of cerium oxide to form a robust, biocompatible, highly porous, and reusable LC–Ce adsorbent. This synthesized biosorbent offers better interaction between the active sites of LC–Ce and fluoride, resulting in higher adsorption capacity. Several factors, influence the adsorption process, were studied by a central composite design (CCD) model of statistical analysis. Langmuir’s and Freundlich’s models well describe the adsorption and kinetics governed by the pseudo–second–order model. The maximum monolayer adsorption capacity was found to be 212 and 52.63 mg/g for LC–Ce and LC, respectively determined by the Langmuir model. Detailed XPS and FTIR analyses revealed the underlying mechanism of fluoride adsorption via ion-exchange, electrostatic interaction, H–bonding, and ion-pair formation. All the results indicate that LC–Ce could serve as a suitable adsorbent for efficient fluoride removal (80–85%).

Polyphenol-metal network derived nanocomposite to catalyze peroxymonosulfate decomposition for dye degradation.

Persulfate based advanced oxidation process is a promising technology for refractory contaminants removal. Cobalt is considered as the most efficient metal in catalyzing peroxymonosulfate decomposition. Although different cobalt based nanomaterials have been developed, easy aggregation and metal ion leaching during catalytic reaction would result in its deficiency. To address the above issue, in this work, carbon supported Co/CoO core-shell nanocomposite was in-situ fabricated by using polyphenol-metal coordinate as precursor. Results indicated that cobalt nanoparticle with size of 10nm was successfully prepared and well dispersed within the carbon matrix. By using as-prepared material as catalyst, 50mg/L orange II was completely removed under the condition of 0.2g/L peroxymonosulfate, 0.05g/L catalyst, pH=4.0-10.0. Both sulfate and hydroxyl radicals were formed during peroxymonosulfate decomposition, while sulfate radical dominated the pollutant removal. Mechanism study revealed that the cobalt was the key site for catalyzing peroxymonosulfate decomposition. This work might provide valuable information in designing and fabricating metal anchored carbon composite catalyst for efficiently and cost-effectively activate peroxymonosulfate.

Kinetic analysis on the mesoporous formation of coal gasification slag by acid leaching and its thermal stability

Coal gasification slag is abundant of unburned carbon and inorganic matters such as silica, alumina and calcium oxide. The mesoporous structure of coal gasification slag can be produced by acid leaching of metal ions. Therefore, it is very important to study the acid leaching process of coal gasification slag. At the same time, in order to broaden the application fields of coal gasification slag, the thermal stability of the as-prepared pore structure should meet the requirements of various occasions. Using coal gasification coarse slag (CS) and coal gasification fine slag (FS) as raw materials, this study investigated the kinetic characteristics of mesoporous formation and optimized the acid leaching conditions. The results of BET, BJH, SEM, XPS and chemical tests showed that under the condition of acid-ash ratio (molar ratio) of 1.0, liquid-solid ratio (volume/mass) of 4:1 and acid leaching temperature of 90 °C, the formation of mesoporous structure by acid leaching was a process of first-order kinetic reaction. According to the analysis of XRD, it was found that the thermal stability of both CS and FS had been greatly improved after acid leaching because of the siliceous enrichment.

Effect of DLC Films with and without Silver Nanoparticles Deposited On Titanium Alloy.

Diamond-like carbon (DLC) film is a biocompatible hard coating material that can prevent the leaching of metal ions. This study evaluates the structural characteristics of DLC, with and without silver nanoparticles, deposited by plasma (PECVD) on titanium alloy (Ti-6Al-4V) and bone formation in contact with DLC films. Sixty Ti-6Al-4V samples were used divided in: uncoated, coated with DLC and coated with DLC-Ag. After structural characterization, samples were fixed bilaterally at the rabbit's mandible. After 15 and 90 days, samples were characterized again and bone formation in the area was analyzed by histomorphometry. Statistical analysis was performed by two-way ANOVA. Both the DLC and DLC-Ag films were firmly adhered and showed a high electrical resistance without significant changes in the Raman spectrum after in vivo integration. After 15 days, there were immature bone trabeculae in the interface and partially covering the surface. After 90 days, mature bone filled the interface and coved the surface. There was no statistically significant difference among the three groups in both periods. In conclusion, osseointegration with DLC, DLC-Ag and uncoated Ti-6Al-4V is similar. However, DLC and DLC-Ag coverings have the advantage of electrical insulation and can presumably control bacterial activity and ion leaching.

Catalytic Degradation of Humic Acid by Mn-Cu/Al-MCM-41 Catalyst in Electro-Fenton/Chlorine Processes: Influencing Factors, Mechanisms, and Kinetics

Degradation of humic acid (HA) in heterogeneous electro-Fenton/chlorine processes was investigated using a catalyst of Mn-Cu bimetallic oxides supported on Al-containing MCM-41. The catalyst was synthesized by co-precipitation method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption–desorption, and X-ray photoelectron spectroscopy (XPS) techniques. The bimetallic oxide catalyst exhibited a higher activity compared to monometallic one. Adding Al in the bimetallic oxide catalyst enhanced the stability of the catalyst, reduced metal ion leaching, increased the initial ratio of Mn3+/Mn4+ and Cu+/Cu2+, and slightly enhanced the degradation efficiency of HA and corresponding chemical oxygen demand (COD). The effect of Mn and Cu content in MCM-41, catalyst dosage, pH value, and initial concentration of HA and salinity on degradation efficiency were investigated. A high COD reduction about 91.5% and general current efficiency (GCE) about 41.7% have been achieved under the optimal conditions of pH 6, salinity 1000 mg/L, catalyst dosage 0.5 g/L, HA sodium salt concentration 200 mg/L, and reaction time 60 min. A possible mechanism for the reaction was suggested. Kinetic analysis showed that HA degradation in the electro-Fenton/chlorine processes was fit with first-order kinetics.

Photocatalytic treatment of tannery wastewater using reduced graphene oxide and CdS/ZnO to produce hydrogen with simultaneous sulfide abatement

This paper addresses the photocatalytic treatment of sulfide-rich liming bath wastewater from tanneries in an oxygen-free atmosphere. The photoactivity assessment of composites obtained from cadmium sulfide (CdS) and zinc oxide (ZnO) hybridization as well the influence of reduced graphene oxide (RGO) on the photocatalytic activity to generate hydrogen and mitigate sulfide was performed under visible-light irradiation. The results of the X-ray diffraction analysis allowed us to identify the crystalline phases in each synthesized sample. The photocatalysts RGO/(CdS)1.0/(ZnO)0.4 and RGO/(CdS)1.0/(ZnO)0.73/(ZnS)0.57 showed the best performances for hydrogen production of 1.6 mmol g −1cat h−1 and 1.4 mmol g −1cat h−1, respectively, with mitigation of 80–90% of the sulfide content in the tannery wastewater. Long-term reaction tests indicated that the photocatalysts are active for a period of 24 h, and they retain the photoactivity after three photocatalytic cycles. The materials have demonstrated great potential for application in energy recovery from tannery wastewater with simultaneous sulfide abatement, especially the photocatalyst RGO/(CdS)1.0/(ZnO)0.73/(ZnS)0.57, which is more eco-friendly because of its lower cadmium content and minimal leaching of this toxic metal ion during photocatalytic treatment.

Gold Biomineralization on Bacterial Biofilms for Leaching of Au3+ Damages Eukaryotic Cells.

Heavy metals not only pollute the environment but also are health and environmental hazard. Bacteria constitute inexpensive and eco-friendly material to eliminate and recycle heavy metals via biomineralization and biosorption. However, the effect of metal biomineralization in bacterial biofilms on the ecological balance of bacteria and infectious diseases is unclear. This study aimed to explore the interaction between a eukaryotic cell line HEK293T and mineralized Escherichia coli, using a model of gold biomineralization on E. coli biofilms (E. coli-Au). In our present model, bacterial activity was not disrupted and bacterial adhesion and invasion were enhanced. E. coli-Au invaded the cytoplasm and nuclei of HEK293T cells and damaged them via intracellular growth and multiplication. The present findings indicate that metal biomineralization in bacterial biofilms for leaching of heavy metal ions is hazardous to eukaryotic cells and even human health.

Calcined CoAl-layered double hydroxide as a heterogeneous catalyst for the degradation of acetaminophen and rhodamine B: activity, stability, and mechanism.

Peroxymonosulfate (PMS) activated by nanomaterials presents one of the most promising strategies to generate reactive species for remediation of organic pollutant-contaminated water. In this study, CoAl-layered double hydroxide (CoAl-LDH) and calcined CoAl-LDH (CoAl-CLDH) were employed as catalysts for PMS activation towards aqueous organic pollutants degradation. Our experiments showed that the leaching of metal ions from catalyst can be significantly mediated by calcination treatment, which can avoid the secondary contamination. The stable CoAl-CLDH exhibited a high catalytic activity, which is comparable to that of the unstable CoAl-LDH. Importantly, reactive species quenching and electron paramagnetic resonance (EPR) results revealed that singlet oxygen (1O2) is the dominant reactive species and plays a crucial role in the catalytic oxidation process in CoAl-CLDH/PMS system. A possible mechanism was proposed for the activation of PMS on the CoAl-CLDH. We demonstrate that CoAl-CLDH is a highly active and stable heterogeneous catalyst for efficient catalytic oxidation of organic pollutants (such as acetaminophen and rhodamine B (RhB)) via activation of PMS.

Monitoring metal ion leaching in oil-ZnO paint systems with a paramagnetic probe

Zinc oxide (ZnO), used as a pigment since the 19th C., is highly reactive when mixed with drying oils. Indeed, the combination of metal-based pigments and drying oils may react to form metal complexes in paint, which may lead to the aggregation of metal carboxylates or soaps. Whereas the mechanism and chemistry behind metal soap formation has been studied in depth, little research has focused on the changes that affect the inorganic pigment particles. In this work, we concentrate on the first phase of these reactions and monitor the evolution of an oil-ZnO paint system through Electron Paramagnetic Resonance (EPR) spectroscopy. By employing CuII as a paramagnetic probe, the progression of metal ion leaching from ZnO is followed through the switching of CuII from a silent tetrahedral coordination in ZnO bulk to an EPR active pseudo-octahedral coordination. Complementarily, the effective concentration of dissolved or extracted Zn and Cu is quantified through Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). The experiment probes the spontaneous metal ion release in oil-based paint films and demonstrates that the kinetics of this phenomenon proceeds with a very steep increase in the first hours after mixing. This is followed by the saturation of the grow rate after a few days that we ascribe to the passivation of the ZnO pigment surface by carboxylate groups, which hinders the further leaching of metal ions, leading to a steady-state before the complete hardening or oxidation of the paint film.