Mild Alkaline Conditions Research Articles

Control by atomic layer deposition over the chemical composition of nickel cobalt oxide for the oxygen evolution reaction

Anion exchange membrane water electrolysis (AEMWE) is a promising technology for renewable electricity-driven water splitting toward hydrogen production. However, application of AEMWE at industrial scale requires the development of oxygen evolution reaction (OER) electrocatalysts showing long-term stability under mild alkaline conditions. Among these, nickel cobalt oxide thin films are considered promising candidates. The ideal chemical composition of these oxides remains debatable, with recent literature indicating that rock-salt NiCoO2 may exhibit similar OER activity as the traditional spinel NiCo2O4. In this work, we present the development of a plasma-enhanced atomic layer deposition (ALD) process of nickel cobalt oxide thin films (∼20 nm) with focus on the role of their chemical composition and crystal structure on the OER activity. The film composition is tuned using a supercycle approach built upon CoOx cycles with CoCp2 as a precursor and O2 plasma as a co-reactant and NiOx cycles with Ni(MeCp)2 as a precursor and O2 plasma as a co-reactant. The films exhibit a change in the crystallographic phase from the rock-salt to spinel structure for increasing cobalt at. %. This change is accompanied by an increase in the Ni3+-to-Ni2+ ratio. Interestingly, an increase in electrical conductivity is observed for mixed oxides, with an optimum of (2.4 ± 0.2) × 102 S/cm at 64 at. % Co, outperforming both NiO and Co3O4 by several orders of magnitude. An optimal electrocatalytic performance is observed for 80 at. % Co films. Cyclic voltammetry measurements simultaneously show a strong dependence of the OER-catalytic performance on the electrical conductivity. The present study highlights the merit of ALD in controlling the nickel cobalt oxide chemical composition and crystal structure to gain insight into its electrocatalytic performance. Moreover, these results suggest that it is important to disentangle conductivity effects from the electrocatalytic activity in future work.

Oxidation of Pharmaceuticals by Ferrate(VI)-Amino Acid Systems: Enhancement by Proline.

The occurrence of micropollutants in water threatens public health and ecology. Removal of micropollutants such as pharmaceuticals by a green oxidant, ferrate(VI) (FeVIO42-, Fe(VI)) can be accomplished. However, electron-deficient pharmaceuticals, such as carbamazepine (CBZ) showed a low removal rate by Fe(VI). This work investigates the activation of Fe(VI) by adding nine amino acids (AA) of different functionalities to accelerate the removal of CBZ in water under mild alkaline conditions. Among the studied amino acids, proline, a cyclic AA, had the highest removal of CBZ. The accelerated effect of proline was ascribed by demonstrating the involvement of highly reactive intermediate Fe(V) species, generated by one-electron transfer by the reaction of Fe(VI) with proline (i.e., Fe(VI) + proline → Fe(V) + proline•). The degradation kinetics of CBZ by a Fe(VI)-proline system was interpreted by kinetic modeling of the reactions involved that estimated the rate of the reaction of Fe(V) with CBZ as (1.03 ± 0.21) × 106 M-1 s-1, which was several orders of magnitude greater than that of Fe(VI) of 2.25 M-1 s-1. Overall, natural compounds such as amino acids may be applied to increase the removal efficiency of recalcitrant micropollutants by Fe(VI).

Effects of alkali treatment on structural and functional properties of chickpea protein isolate and its interaction with gallic acid: To improve the physicochemical stability of water–in–oil emulsions

To expand the application of chickpea protein isolate (CPI) in water–in–oil (W/O) emulsion systems and to address its limitations in inhibiting lipid oxidation in W/O emulsions, alkali treatment was used to enhance the functional properties of CPI and to promote its combination with gallic acid (GA). The results showed a slight increase in the antioxidant activity of CPI upon pH 11 treatment, which was attributed to the exposure of sulfhydryl groups (3.39 μmol/g). The interfacial activity of CPI treated with pH 11 was enhanced (e.g., interfacial tension of 1.72 mN/m and interfacial adsorption of 93.20%). In addition, the alkali treatment promoted the covalent binding of CPI and GA, especially under mild alkaline conditions (pH 9, the binding equivalent was 13.12 mg/g protein). The results of amino acid and intrinsic fluorescence spectrum indicated that the binding sites for CPI and GA might include Met, Glu, His, Lys, Arg and Trp residues. The combination of CPI and GA further changed the structural and functional properties of CPI. When alkali–treated CPI and CPI–GA combinations were added to emulsions, the increase in physical stability was attributed to a reduction in droplet size and an increase in ζ–potential. In terms of chemical stability, the higher interfacial activity and the higher GA binding equivalent of CPI contributed to the higher accumulation of GA at the droplet interface. This ultimately improved the chemical stability of the W/O emulsion (57.03% and 61.34% reduction in primary and secondary oxidation products respectively). This work provides guidance on the application of interfacial engineering to modify proteins with high interfacial and low antioxidant activity and to improve the physicochemical stability of W/O emulsions.

Enhanced adsorption of PFOA with nano MgAl2O4@CNTs: influence of pH and dosage, and environmental conditions

Perfluorooctanoic acid (PFOA) has received extensive attention due to its widespread distribution in the environment and concerns of its exposure to human health. Nano-MgAl2O4 modified carbon nanotubes (CNTs) were synthesized, characterized, and used as nanoadsorbents to remove ppb (μg/L)-levels of PFOA from drinking water and brackish groundwater. Nano-MgAl2O4@CNTs composite materials were characterized by UV-Vis, FT-IR, DLS, p-XRD, BET, and SEM with EDX. The adsorption isotherms and kinetic studies were fitted to a Freundlich and to a pseudo-second-order models, respectively. Composite nano-MgAl2O4@CNTs remove over 99% of PFOA (100 ppb) from water in 3 hours, and completely (100%) in 3.5 hours. The optimal pH range is under mild alkaline conditions (pH = 7.5-9.0). Electrostatic and hydrophobic interactions drive the PFOA adsorption onto MgAl2O4@CNTs. The adsorption data of ground and drinking water samples indicated that nano-MgAl2O4@CNTs is an efficient nanoadsorbent for PFOA removal.

Ultrasound enhanced solubilization of forest biorefinery hydrolysis lignin in mild alkaline conditions.

In the forest biorefinery, hydrolysis lignin (HL) is often dissolved with high concentration NaOH solution, followed by acid precipitation to obtain purified HL. For the first time, this study evaluates the effect of ultrasound (US) on the dissolution of industrially produced HL in aqueous NaOH solutions and the acid precipitation yield of HL. The solubility of HL in mild aqueous NaOH solutions was studied with and without US treatment at 20kHz concerning the solid-to-liquid ratio, molecular weight of dissolved fractions and structural changes in dissolved HL. Results showed that the solubility of HL at 25°C was strongly dependent on NaOH concentration. However, the US treatment significantly improved the solubility of HL, reaching a solubility plateau at 0.1 NaOH/HL ratio. US treatment enhanced the solubilization of HL molecules with higher MW compared to conventional mixing. The increase of HL solubility was up to 30% and the recovery yield of purified lignin with acid precipitation was 37% higher in dilute NaOH solution. A significant result was that the Mw of dissolved HL in homogeneous alkali solutions decreased with US treatment. SEC, HSQC and 31P NMR analyses of dissolved HL characteristics showed that both, the mechanoacoustic and sonochemical solubilization pathways contribute to the dissolution process. However, US does not cause major changes in the HL structure compared to the native lignin. Indeed, US technology has the potential to advance the dissolution and purification of HL in biorefineries by reducing the amount of chemicals required; thus, more controlled and environmentally friendly conditions can be used in HL valorization.

Vanillin-derived α,ω-diene monomer for thermosets preparation via thiol–ene click polymerization

Novel vanillin-derived α,ω-diene monomer was synthesized via Williamson and Tishchenko reaction, which was readily polymerized with thiols to obtain thiol-ene networks with tunable material properties and satisfactroy degradability under mild alkaline conditions.

Efficient synthesis of Co2+–Co3+ hydrotalcite-like compounds via NaOH precipitation in methanol–water under mild alkaline conditions

Divalent/trivalent cobalt hydrotalcite-like compounds (Co2+–Co3+ HTlc) were synthesized via precipitation under mild alkaline conditions by using NaOH as precipitant and methanol–water as solvent. The influences of synthetic parameters including CH3OH:H2O volume ratio, precipitation pH, and hydrothermal treatment on the HTlc formation were investigated. The crystalline phase, morphology, and chemical composition of the synthesized samples were characterized by XRD, FTIR, SEM, TG–MS, and iodometric titration. The formation of Co2+–Co3+ HTlc was strongly affected by the methanol content and a single Co2+–Co3+ HTlc phase was obtained by raising the CH3OH:H2O ratio to 4:1–8:1. It was suggested that the presence of methanol increased the concentration of dissolved oxygen and promoted the oxidation of Co2+ into Co3+, leading to complete transformation of α-Co(OH)2 into Co2+–Co3+ HTlc. Moreover, single-phased Co2+–Co3+ HTlc was available at pH between 10 and 12, and they were hydrothermally stable by treatment at 60 °C for 24 h. Under the synthetic conditions, complete precipitation of cobalt ions was achieved. This highlights that the developed synthesis process is an efficiency way for quantitative synthesis of cobalt HTlc.

Hydrogen-polarized vacuum ultraviolet photolysis system for enhanced destruction of perfluoroalkyl substances

Reductive water treatment using hydrated electrons (eaq−) is a promising technology to destruct perfluoroalkyl substances; however, it faces challenges of slow reaction kinetics, undesirable chemical addition, and high energy consumption. Herein, we developed a hydrogen (H2)-polarized water photolysis system using vacuum UV (VUV) light at 185 nm for reductive destruction of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). The 185-nm photons directly photolyzed H2O and OH- into HO·, H·, and eaq−. H2 elevated the quasi steady-state concentration of eaq− 18 times in untuned VUV systems through eliminating the scavenging effect of dissolved oxygen and converting hydroxyl radicals (HO·/O·-) into eaq−. The polarization effect of H2 increased the degradation of PFOA from 10 % to 95 % and the defluorination from 17 % to 94 % and led to 87 % of defluorination for PFOS. The pH impacted VUV photon adsorption between H2O and OH- and shifted the equilibrium between H· and eaq−, which led to an optimal pH of 10.3 for PFOA destruction. The presence of chloride and sulfate enhanced the production of eaq− and promoted PFOA destruction. H2-polarized VUV water photolysis systems produced high levels of eaq− from clean water constituents and significantly reduced energy consumption for PFAS treatment under mild alkaline conditions.

Oxidation of micropollutants by visible light active graphitic carbon nitride and ferrate(VI): Delineating the role of surface delocalized electrons

The treatment of recalcitrant micropollutants in water remains challenging. Ferrate(VI) (FeVIO42−, Fe(VI)) has emerged as a green oxidant to oxidize organic molecules, however, its reactivity with recalcitrant micropollutants are sluggish. Our results demonstrate enhanced oxidation of carbamazepine (CBZ) by three types of visible light-responsive graphitic carbon nitride (g-C3N4) photocatalyst in absence and presence of ferrate(VI) (FeVIO42−, Fe(VI)) under mild alkaline conditions. The g-C3N4 photocatalysts were prepared by thermal process using urea, thiourea, and melamine and were named as CN-U, CN-T, and CN-M, respectively. The degradation efficiency of CBZ, in both visible light-g-C3N4 and visible light-g–C3N4–FeVIO42- systems followed the order of CN-U > CN-T > CN-M. The mechanisms for this trend was elucidated by measuring physiochemical properties of the microstructures with various surface and analytical techniques. Results suggest the dominating role of specific surface area and surface delocalized electrons of microstructures in degrading CBZ. Crystallinity, morphology, and surface functional groups may not directly associate with CBZ degradation. The CN-U has higher specific surface area and surface delocalized electrons than CN-T and CN-M and therefore the highest degradation efficiency of CBZ. The surface electrons likely generated O2●- and 1O2 in the visible light-g-C3N4 system. The additional oxidants, FeV and FeIV in the visible light-g–C3N4– FeVIO42− system led to higher degradation efficiency than the visible light-g-C3N4 system. Results suggest that the surfaces of g-C3N4 may be prepared preferentially with high levels of delocalized electrons at the surface of microstructures to enhance degradation of micropollutants.

Tunning the Activity of Silver Alloy Electrocatalysts for the Oxygen Reduction Reaction in Alkaline Media

A bottleneck to achieve efficient and stable electrocatalysts for Anion Exchange Membrane Fuel Cells (AEMFCs) is the relatively slow kinetics of the oxygen reduction reaction (ORR) taking place at the cathode. The rather mild alkaline conditions in the AEMFC enable the utilization of various PGM-free catalysts, which brings up new possibilities of finding abundant and inexpensive electrocatalysts without compromising the power density. From theory and previous experiments, it is known that Au and Ag bind oxygen weakly, whereas other transition metals (e.g., Pd, Cu, Fe, Ni) bind strongly to oxygenated species1. Therefore, a suitable geometric arrangement between Ag, an abundant metal with relatively high specific activity, and other metals may give rise to optimum binding of oxygen and thus a high activity. A good strategy to improve the activity of Ag-based catalysts could be a rational design of alloys that can enhance the intrinsic activity of Ag by both ensemble and electronic effects2–4. The former is based on the combination of active sites that facilitate the initial oxygen binding together with Ag active sites that help desorb hydroxide anions, whereas the latter is induced by the alloying metal (which binds oxygenated species strongly) on the electronic structure of the overlaying Ag that tunes its binding to oxygen5. Herein, we report the fabrication and characterization of Ag thin-films alloyed with Pd, Ni, Cu and Mo as a tool to investigate the ORR reaction in terms of ensemble and electronic effects and thus relate alloy composition and geometric arrangement with ORR activity. Ag thin-film model catalysts are fabricated by means of physical vapor deposition methods (PVD) with high control over the amount of material deposited. By varying alloy composition and evaluating electrochemical activity and stability, together with detailed physical characterization, the degree and extent of electronic effects are elucidated. In the same way, sputtering of the same amount of Ag on thin-films of different metals evidences the role of the alloying metal on tuning the activity of Ag through an adjustment of its d-band that changes the binding of oxygenated species, as well as through an ensemble effect that provides active sites for the first elementary steps of the reaction. These results provide insights for more tailored design of electrocatalysts in alkaline media by shedding new light on the mechanisms through which the ORR kinetics are improved in alkaline media. Nørskov, J. K. et al. Origin of the overpotential for oxygen reduction at a fuel-cell cathode. J. Phys. Chem. B 108, 17886–17892 (2004).Betancourt, L. E. et al. Enhancing ORR Performance of Bimetallic PdAg Electrocatalysts by Designing Interactions between Pd and Ag. ACS Appl. Energy Mater. 3, 2342–2349 (2020).Slanac, D. A., Hardin, W. G., Johnston, K. P. & Stevenson, K. J. Atomic ensemble and electronic effects in Ag-rich AgPd nanoalloy catalysts for oxygen reduction in alkaline media. J. Am. Chem. Soc. 134, 9812–9819 (2012).Zamora Zeledón, J. A. et al. Tuning the electronic structure of Ag-Pd alloys to enhance performance for alkaline oxygen reduction. Nat. Commun. 12, 1–9 (2021).Stamenkovic, V. et al. Changing the Activity of Electrocatalysts for Oxygen Reduction by Tuning the Surface Electronic Structure. Angew. Chemie 118, 2963–2967 (2006).

Alkaline hydrolysis and discrimination of propolis at different pH values using high throughput 2D IR spectroscopy and LC-MS/MS

Propolis has become a valuable byproduct of meliponiculture industry in recent years, due to its remarkable pharmacological importance. The propolis of Heterotrigina itama was extracted at pH 8–10 using ultrasonication. The results found that alkaline hydrolysis improved propolis quality, particularly at the mild alkaline condition. This was because higher amount of phenolics and flavonoids with higher antioxidant capacity for propolis at pH 8. The quality of propolis extracted at different pH values could be differentiated using 2D IR correlation spectroscopic analysis via the vibrational interaction of chemical functional groups under thermal perturbation. The variance could be detected by off-diagonal peaks in the region of 800–1500 cm−1, belonging to CC bending and CO stretching bands. The small variance was further confirmed by using high throughput mass screening technique of LC-MS/MS coupled with principal component analysis to reveal the signature compounds such as (xanthone C-glycosides, anthraquinone, procyanidin, procyanidin and resveratrol) in propolis.

Supramolecular Assembly and Reversible Transition and of Chitosan Fluorescent Micelles by Noncovalent Modulation

Chitosan-based intelligent artificial systems have been of increasing interest for their biocompatibility, multifunctionality, biological activity, and low cost. Herein, we report the fabrication of supramolecular nanoparticles based on water-soluble chitosan (WCS) and 1,1 ′ ,1 ″ ,1 ″ ′ -(ethene-1,1,2,2-tetrayl)tetrakis(benzene-4,1-diyl) tetrakis(azanediyl)tetraacetic acid (TPE-(N-COOH)4), which is capable of reversible transition between polyion complexes (PICs) and hydrogen bonding complexes (HBCs) with tunable aggregation-induced emission driven by pH value. The PIC micelles could be formed via electrostatic interaction between ammonium cations and carboxylate anions under mild alkaline conditions. The formation of the micelles dramatically blocks the nonradiative pathway and enhances the fluorescence of TPE moieties, and the maximum fluorescence intensity was achieved near the isoelectric point due to the restriction of intramolecular motion. In addition, the fluorescence intensity and size of the PIC micelles exhibited a temperature response in the range from 20 to 80°C. Upon adjusting the solution pH to 2, the PIC micelles were reconstructed into hydrogen-bonding complexes while the hydrogen bonding interaction between the protonated carboxyl groups of TPE-(N-COOH)4 and chitosan. Moreover, the size of the micelles underwent a remarkable decrease, whereas the fluorescence emission was further enhanced by ~6.25-fold. The pH actuated micellar transition from PIC to HBC with tunable fluorescence performance is fully reversible. This study provides novel multifunctional materials that are of great importance for their potential application in the fields of optoelectronic devices and chemical and biomedical sensors.

New Mobilization Pathway of Antimonite: Thiolation and Oxidation by Dissimilatory Metal-Reducing Bacteria via Elemental Sulfur Respiration.

Antimony (Sb) mobilization is widely explored with dissimilatory metal-reducing bacteria (DMRB) via microbial iron(III)-reduction. Here, our study found a previously unknown pathway whereby DMRB release adsorbed antimonite (SbIII-O) from goethite via elemental sulfur (S0) respiratory reduction under mild alkaline conditions. We incubated SbIII-O-loaded goethite with Shewanella oneidensis MR-1 in the presence of S0 at pH 8.5. The incubation results showed that MR-1 reduced S0 instead of goethite, and biogenic sulfide induced the formation of thioantimonite (SbIII-S). SbIII-S was then oxidized by S0 to mobile thioantimonate (SbV-S), resulting in over fourfold greater Sb release to water compared with the abiotic control. SbIV-S was identified as the intermediate during the oxidation process by Fourier transform ion cyclotron resonance mass spectrometry and electron spin resonance analysis. The existence of SbIV-S reveals that the oxidation of SbIII-S to SbV-S follows a two-step consecutive one-electron transfer from Sb to S atoms. SbV-S then links with SbIII-S by sharing S atoms and inhibits SbIII-S polymerization and SbIII2S3 precipitation like a "capping agent". This study clarifies the thiolation and oxidation pathway of SbIII-O to SbV-S by S0 respiration and expands the role of DMRB in the fate of Sb.

Iron(V)/Iron(IV) species in graphitic carbon nitride-ferrate(VI)-visible light system: Enhanced oxidation of micropollutants

This paper investigated for the first time the visible light-induced oxidation of micropollutants using graphitic carbon nitride (g-C3N4) photocatalyst in the presence of ferrate(VI) (FeVIO42−) under mild alkaline conditions. The studied micropollutants have different molecular structures (i.e., carbamazepine (CBZ), sulfamethoxazole (SMX), sulfadimethoxine (SDM), trimethoprim (TMP), diclofenac (DCF), flumequine (FLU), atenolol (ATL), and caffeine (CAF)). Enhanced oxidation of all investigated micropollutants by the combined g-C3N4-FeVIO42− system was observed compared to g-C3N4 or FeVIO42− alone under visible light irradiation. For example, 5.0 µM CBZ could be almost completely degraded in 5.0 min by the g-C3N4-FeVIO42− system. Comparatively, only ∼ 40% degradation of CBZ occurred by g-C3N4 or FeVIO42− alone in 5.0 min under the same condition. Similar observations were found with other micropollutants, and the magnitude of enhancement varied with the structure of the micropollutants. The degradation experiments with and without oxygen in solution suggested the generation of O2●- and 1O2 in g-C3N4-visible light system. However, with the presence of FeVIO42− in solution, the g-C3N4-visible light system generated high-valent iron-oxo intermediates (FeV/FeIV) as the oxidizing species, evidenced by the selective conversion of methyl phenol oxide (PMSO) to PMSO2, to cause increased oxidation of micropollutants. A plausible mechanism involving reactive species to oxidize micropollutants by the g-C3N4-FeVIO42− system under visible light irradiation was discussed. Oxidized products of CBZ were identified to reveal possible reaction pathways. The results of the g-C3N4-FeVIO42−-visible light system provided a new advanced oxidation process to synergistically degrade micropollutants in water efficiently.

Ferrate(VI)-peracetic acid oxidation process: Rapid degradation of pharmaceuticals in water

This paper presents, for the first time, an oxidation process of ferrate(VI) (Fe(VI), FeO42-)-peracetic acid (CH3C(O)OOH, PAA) to rapidly degrade micropollutants in water. The effect of concentrations of Fe(VI) and PAA showed that complete removal (degradation below detection limit) of a pharmaceutical, carbamazepine (CBZ, 10.0 µM), could be achieved in 60 s at a molar ratio of Fe(VI) to CBZ of 20.0 and 100.0 µM PAA under mild alkaline condition (pH 9.0). The results of the experiments performed in the presence of quenching agents, i.e., tert-butyl alcohol and 2,4-hexadiene, suggested that the iron-based reactive species (Fe(V)/Fe(IV)) and/or acetylperoxyl radicals (CH3C(O)OO●/CH3C(O)O●) were most likely responsible for the rapid oxidation of CBZ, rather than the hydroxyl radical (●OH). The major role of Fe(V)/Fe(IV) was supported by the high mass balance between loss of PMSO and formation of PMSO2 (>90%) during the oxidation of PMSO by Fe(VI)-PAA, which was not observed in the absence of iron species, i.e., PAA-Co(II)-PMSO system having acetylperoxyl radicals as reactive species. Significantly, the Fe(VI)-PAA oxidation process could degrade several other pharmaceuticals (i.e., sulfamethoxazole, sulfadimethoxine, trimethoprim, atenolol, propranolol, and caffeine) within 60 s, indicating its great potential in eliminating pollutants of emerging concern from water.

Bioactive films based on barley β-glucans and ZnO for wound healing applications

In this study, mixtures based on β-glucans and proteins are extracted from barley, in mild (MA) and high (HA) alkaline conditions, and employed with zinc oxide (ZnO) to prepare bioactive films for wound healing. Composition of extracts and properties of resulting films depend on pH extraction conditions. MA based samples show weak physical interactions among mixture components, whereas in HA films the extent of these interactions is larger. Consequently, their chemico-physical properties are significantly different, as demonstrated by FT-IR, thermal, mechanical and morphological analyses. ZnO with its bound water molecules acts as a slight plasticizer in MA, as shown by the lower Tg and the decrease of elastic modulus. In HA, this effect is evidenced up to ZnO 1%, and above this concentration an increase of strength at break is observed. Finally, MA and HA films show intrinsic antimicrobial properties, enhanced by ZnO, which make them exploitable as wound dressings.

Some critical observations about the degradation of glass: The formation of lamellae explained

This study demonstrates that the mechanism responsible for the transformation of glass into a degradation layer is pH-dependent. In acid conditions, the transformed glass is homogeneous and brittle. In mild alkaline conditions, transformed glass is heterogeneous due to the presence of lamellae composed of silica nanoparticles and the occurrence of Ca-rich inclusions. The fundamental difference between acid and alkaline conditions cannot be explained by the currently accepted degradation mechanism based on ion exchange. To explain this critical observation, we propose a refined degradation mechanism based on existing knowledge that involves several inwardly moving reaction fronts. The fronts responsible for the transformation of the silicate network into amorphous silica are also responsible for the morphology of the transformed glass. We have identified the feedback mechanism that explains the formation of lamellae in alkaline conditions.

Single-Step Green Synthesis of Highly Concentrated and Stable Colloidal Dispersion of Core-Shell Silver Nanoparticles and Their Antimicrobial and Ultra-High Catalytic Properties.

The versatile one-pot green synthesis of a highly concentrated and stable colloidal dispersion of silver nanoparticles (Ag NPs) was carried out using the self-assembled tannic acid without using any other hazardous chemicals. Tannic acid (Plant-based polyphenol) was used as a reducing and stabilizing agent for silver nitrate in a mild alkaline condition. The synthesized Ag NPs were characterized for their concentration, capping, size distribution, and shape. The experimental results confirmed the successful synthesis of nearly spherical and highly concentrated (2281 ppm) Ag NPs, capped with poly-tannic acid (Ag NPs-PTA). The average particle size of Ag NPs-PTA was found to be 9.90 ± 1.60 nm. The colloidal dispersion of synthesized nanoparticles was observed to be stable for more than 15 months in the ambient environment (25 °C, 65% relative humidity). The synthesized AgNPs-PTA showed an effective antimicrobial activity against Staphylococcus Aureus (ZOI 3.0 mM) and Escherichia coli (ZOI 3.5 mM). Ag NPs-PTA also exhibited enhanced catalytic properties. It reduces 4-nitrophenol into 4-aminophenol in the presence of NaBH4 with a normalized rate constant (Knor = K/m) of 615.04 mL·s−1·mg−1. For comparison, bare Ag NPs show catalytic activity with a normalized rate constant of 139.78 mL·s−1·mg−1. Furthermore, AgNPs-PTA were stable for more than 15 months under ambient conditions. The ultra-high catalytic and good antimicrobial properties can be attributed to the fine size and good aqueous stability of Ag NPs-PTA. The unique core-shell structure and ease of synthesis render the synthesized nanoparticles superior to others, with potential for large-scale applications, especially in the field of catalysis and medical.

Randomly heterogeneous oleophobic/pH-responsive polymer coatings with reversible wettability transition for multifunctional fabrics and controllable oil–water separation

Stimuli-responsive surfaces with wettability change between superhydrophilic and superhydrophobic are susceptible to oil contamination which often ruins the surface. Herein, a coating with pH-switchable wettability transition between superamphiphobic and superhydrophilic-superoleophobic is achieved by rationally designing oleophobic/pH-responsive polymer heterogeneous chemistry. Fabrics modified with this coating show repellency to both water and oils, while upon exposure to acidic water (pH = 1) the fabrics change to be superhydrophilic-superoleophobic within a short response time of <5 s. More importantly, the superamphiphobicity of the fabric can be restored under mild alkaline condition (pH = 10), and the transition is reversible for many cycles. The effective in situ or ex situ wettability change under acidic/alkaline water treatment makes the coated fabric capable of separating oil–water mixture or even some mixtures of immiscible organic solvents. In addition, the coated fabric is also demonstrated to be promising as a new class of functional fabrics that provide protection against water and many oils in one condition, and can change to be hygroscopic, anti-static, oil-repellent and anti-oil-fouling in the other condition for improved wear comfort and self-cleaning.

Fast and mild alkaline solvothermal synthesis of nanostructured flower-like Na2Ti3O7 and its methylene blue adsorption capacity

This work reports a facile solvothermal synthesis of hierarchical flower-like Na2Ti3O7 structures with fast and high methylene blue adsorption capacity. A mesoporous architecture of Na2Ti3O7 with a surface area of 159.63 m2-g-1 was produced under mild alkaline conditions (2 M NaOH) and a short reaction time (8 h). Interestingly, methylene blue adsorption equilibrium on the Na2Ti3O7 powders was achieved in a short time of 10 min. The pseudo-second-order kinetic model and the Langmuir isotherm model described the adsorption mechanism. The synthesized Na2Ti3O7 powders have interesting features that highlight their suitability for environmental applications.