Wide pH Range Research Articles

Development of Biological Coating from Novel Halophilic Exopolysaccharide Exerting Shelf-Life-Prolonging and Biocontrol Actions for Post-Harvest Applications.

The literature presents the preserving effect of biological coatings developed from various microbial sources. However, the presented work exhibits its uniqueness in the utilization of halophilic exopolysaccharides as food coating material. Moreover, such extremophilic exopolysaccharides are more stable and economical production is possible. Consequently, the aim of the presented research was to develop a coating material from marine exopolysaccharide (EPS). The significant EPS producers having antagonistic attributes against selected phytopathogens were screened from different marine water and soil samples. TSIS01 isolate revealed the maximum antagonism well and EPS production was selected further and characterized as Bacillus tequilensis MS01 by 16S rRNA analysis. EPS production was optimized and deproteinized EPS was assessed for biophysical properties. High performance thin layer chromatography (HPTLC) analysis revealed that EPS was a heteropolymer of glucose, galactose, mannose, and glucuronic acid. Fourier transform infrared spectroscopy, X-ray diffraction, and UV-visible spectra validated the presence of determined sugars. It showed high stability at a wide range of temperatures, pH and incubation time, ≈1.63 × 106 Da molecular weight, intermediate solubility index (48.2 ± 3.12%), low water holding capacity (12.4 ± 1.93%), and pseudoplastic rheologic shear-thinning comparable to xanthan gum. It revealed antimicrobial potential against human pathogens and antioxidants as well as anti-inflammatory potential. The biocontrol assay of EPS against phytopathogens revealed the highest activity against Alternaria solani. The EPS-coated and control tomato fruits were treated with A. solani suspension to check the % disease incidence, which revealed a significant (p < 0.001) decline compared to uncoated controls. Moreover, it revealed shelf-life prolonging action on tomatoes comparable to xanthan gum and higher than chitosan. Consequently, the presented marine EPS was elucidated as a potent coating material to mitigate post-harvest losses.

Multi-dimensional MoS2/S-doped-CoP heterostructure nanoarrays as an efficient electrocatalyst for hydrogen evolution reaction

Developing efficient and economical electrocatalysts for hydrogen evolution reaction (HER) over a broad pH range has received considerable attention. In this work, we prepared multi-dimensional MoS2/S-CoP heterojunction catalysts by utilizing the carbon clothes supported ZIF-67 array as templates combining with Mo-ion exchange and high-temperature phosphorization-sulfidation strategy. The introduction of MoS2 into S-CoP results in electron redistribution and the formation of a distinctive space charge region at the two-phase contact interface, thereby effectively tuning surface properties, enhancing electron conductivity, and improving electrocatalytic activity. According to Density Functional Theory (DFT) calculations, the introduction of MoS2 is advantageous for the adsorption and desorption of H*, resulting in the value of ΔGH* very close to zero. Furthermore, the adsorbed water molecules are more readily activated, rendering the ΔGH2O-dis decrease, thus significantly promoting HER activity. These features contribute to robust HER electrocatalytic performance in a wide pH range and even in seawater, which is also beneficial for industrial applications. In particular, MoS2/S-CoP exhibits superior HER performance in alkaline seawater, requiring only 197 and 228 mV to reach the current densities of 100 and 200 mA cm-2, respectively. This study offers novel perspectives on high-performance heterostructures for HER electrocatalysts in alkaline seawater environments.

Production and characterization of protease enzyme from Acinetobacter pittii using peanut meal as substrate

ABSTRACT A significantly high protease enzyme yield of 617 U/ml was achieved with Acinetobacter pittii as the microorganism and peanut oil meal as the substrate. Peanut oil meal, which consists of proteins (40-60%) and carbohydrates (22-30%), serves as a sufficient source of nitrogen and carbon necessary for microbial growth and production of enzymes. Moreover, peanut meal offers the advantages of being affordable and available in large quantities, making the meal suitable for cost-effective enzyme production. In the present study, two bacterial strains and one fungal strain were selected to produce proteases utilizing peanut oil meal as the substrate. The experimental conditions during the enzyme production, including pH and temperature, were optimized. In addition, the substrate was enriched with various carbon and nitrogen sources. The microbial strains were streaked on nutritional agar (for bacteria) and potato dextrose agar (for fungus). Following an incubation period, the plates were stored at 4°C for further studies. The molecular weight of partially purified proteases of Acinetobacter pittii was found to be ≅ 95.5 kDa. Potassium nitrate was the most ideal nitrogen source (up to 411% increase in activity) and fructose was the best carbon source (425% increase). These enzymes exhibited excellent temperature tolerance and were capable of functioning over a wide pH range. Furthermore, the obtained proteases demonstrated ability to coagulate milk effectively, indicating their potential for various food-related applications.

USE OF BSC AFTER ACID SOLUTION TO DEVELOP THE EXPANSION PROPERTIES OF CEMENT

Formation of hydroxyl complexes in the Fe(0)-Fe(II)-glycine-water system from pH at I=0.5 mol/l, temperature 298.15 K, СFe(II)=1×10-4 and СGly=3×10-3 mol/l were studied by the Clark–Nikolsky oxidative potential method. Experimental curves of the dependence of the EMF of the system on the concentrations of hydrogen, iron(II) and glycine ions: рН, рСох, pCL, respectively, are obtained. They allowed us to establish that the processes of complexation in the studied system proceed stepwise in a wide pH range from 1.0 to 8.2. The type and number of coordinated ligands and the total composition of the complex compounds formed were determined. Chemical models of complex formation reactions and model parameters of coordination compounds have been compiled. The values of the angular coefficients, the domain of dominance and the constants of the formation of complexes are determined. The formation of the following coordination compounds is shown: [Fe(OH)(H2O)5]+; [FeHL(H2O)5]2+; [Fe(HL)(OH)(H2O)4]+; [Fe(OH)2(H2O)4]0 and [Fe2(HL)2(OH)2(H2O)8]2+.

Microporous Ag/AgCl on a Titanium Scaffold for Use in Capillary Reference Electrodes.

AgCl-coated silver fabricated with the thermal-electrolytic method can be used to prepare more reproducible reference electrodes than Ag/AgCl prepared with alternative methods such as electrolytic and chemical AgCl deposition or thermal fabrication. However, thermal-electrolytic fabrication requires a scaffold material upon which to build the layers upon. Platinum and rhodium have been used for this purpose as they are mechanically strong and chemically inert, but their cost is prohibitive for wider application. Herein, we report the stability of Ag/AgCl reference electrodes built atop a titanium scaffold using the thermal-electrolytic method and the use of these Ti/Ag/AgCl constructs in capillary-based reference electrodes. Electrochemical characterization shows that the probable presence of small amounts of oxygen at the Ti/Ag interface does not affect the reference electrode performance; in particular, over a wide pH range, the half-cell potential is pH independent. The electrical resistance of the Ti/Ag/AgCl/KCl system is dominated by the charge transfer resistance at the interface of the AgCl to KCl solution but is kept very small by the large AgCl surface area and a high solution concentration of chloride. The resulting high exchange current minimizes the effect of system impurities on the reference half-cell potential. Capillary-based reference electrodes comprising Ti/Ag/AgCl show exceptionally low potential drifts (as low as 0.03 ± 2.01 μV/h) and standard deviations of the potential at or below ±0.5 mV over a 60 h period. These capillary-based reference electrodes are suitable for very small sample volumes while still providing a free-flowing liquid junction that prevents reference electrode contamination.

Tuning the carboxyl content of carbon quantum dots by an electrochemical exfoliation method to enhance Fenton-like reactions for contaminants removal in a wide pH range

The complexation of CQDs with Fe(III) through -COO-Fe bond in the CQDs-Fe(III)/H2O2 system can accelerate the Fe(III)/Fe(II) cycle and broaden the pH range for application. However, the yield and carboxyl content of CQDs prepared by conventional electrochemical exfoliation were limited, which hampered the application of CQDs and the enhancement of CQDs Fenton-like process. Hence, in this study, carboxyl-rich and high-yield CQDs were successfully prepared by electrochemical exfoliation of graphite rods in hydrogen peroxide (H2O2) solution. The results suggested that the yield and carboxyl content of the optimal CQDs (CQD@5) were 1.49 and 2.01 times those of CQDs prepared by the conventional electrochemical exfoliation method (CQD@0), respectively. Subsequently, the CQDs were applied in CQDs-Fe(III)/H2O2 systems for phenol degradation. Due to 1.73 times the carboxyl of CQD@ 5 complexing with Fe(III) than that of CQD@ 0, the kinetic constant and removal of the CQD@ 5-Fe(III)/H2O2 system for phenol degradation were 2.36 and 1.44 times those of the CQD@ 0-Fe(III)/H2O2 system at pH= 6, respectively. Under the same condition, Fe(III)/H2O2 and Fe(II)/H2O2 showed negligible degradation performance. Furthermore, the removals of phenol in the CQD@ 5-Fe(III)/H2O2 system were 1.08–7.77 times those of the CQD@ 0-Fe(III)/H2O2 system at pH= 4–8, respectively. Finally, the effect of Fe(III), CQDs, and H2O2 dosages on the phenol degradation, reusability, and universality of CQD@ 5-Fe(III)/H2O2 were investigated individually. In summary, this work provides a new method for tuning the CQDs yield and carboxyl content, which enhances pollutant degradation in CQDs-Fe(III)/H2O2 systems at a wide pH range.

Lytic phages isolated from Egypt for biocontrol of potato soft rot caused by Pectobacterium carotovorum

Pectobacterium carotovorum is an economically important phytopathogen causing destructive bacterial soft rot disease in many ornamental plants and fruit and vegetable crops worldwide, including potato. Phage therapy is a promising and environmentally safe alternative to combat bacterial diseases either in the field or during storage. In this study, we characterized two novel P. carotovorum-specific phages, designated PcaP1EGY and PcaP2EGY, isolated from soil in Egypt. We also sequenced the genomes of the two phages, which are the first two complete genome sequences determined for P. carotovorum-infecting podoviruses from Egypt. Phages PcaP1EGY and PcaP2EGY have a high phage titer of 1012 PFU/mL and growth characteristics of an exclusively lytic life cycle. Both phages displayed specificity to and visible lysis activity against all four tested strains of P. carotovorum. They both had a latent period of 30 min and a high burst size of approximately 599 PFU/infected cell for PcaP1EGY and 570 for PcaP2EGY. Additionally, they exhibited remarkable survivability under a wide range of pH, temperature, salt concentration and UV exposure conditions. Both phages, when used alone or in combination, significantly reduced in vitro growth of P. carotovorum after 4 h at all tested multiplicity of infection. Phages PcaP1EGY and PcaP2EGY offered significant protection for both potato tubers and potato plants against soft rot disease caused by P. carotovorum in both our tuber maceration test and greenhouse pot experiment as compared to tubers/plants inoculated with P. carotovorum without receiving any phage treatment. Our results suggest that phages PcaP1EGY and PcaP2EGY have great biocontrol potential against potato soft rot disease caused by P. carotovorum either in the field or during storage after harvest.

Precise Engineering of the Electrocatalytic Activity of FeN4-Embedded Graphene on Oxygen Electrode Reactions by Attaching Electrides.

Using first-principles calculations combined with a constant-potential implicit solvent model, we comprehensively studied the activity of oxygen electrode reactions catalyzed by electride-supported FeN4-embedded graphene (FeN4Cx). The physical quantities in FeN4Cx/electrides, i.e., work function of electrides, interlayer spacing, stability of heterostructures, charge transferred to Fe, d-band center of Fe, and adsorption free energy of O, are highly intercorrelated, resulting in activity being fully expressed by the nature of the electrides themselves, thereby achieving a precise modulation in activity by selecting different electrides. Strikingly, the FeN4PDCx/Ca2N and FeN4PDCx/Y2C systems maintain a high oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) activity with the overpotential less than 0.46 and 0.62 V in a wide pH range. This work provides an effective strategy for the rational design of efficient bifunctional catalysts as well as a model system with a simple activity-descriptor, helping to realize significant advances in energy devices.

Synthesis and performance of guanidinium-based cationic organic polymer for the efficient removal of TcO4-/ReO4-

Cationic organic polymers have found relatively extensive utility for TcO4-/ReO4- removal, but the harsh preparation conditions constrain their practical application. The bifunctional guanidinium-based cationic organic polymer (GBCOP) was successfully and facilely synthesized in benign conditions within 1 h. Batch experiments showed that GBCOP exhibited rapid removal kinetics (1 min, >98.0%) and a substantial removal capacity of 536.8 mg/g for ReO4-. Even in 1000-fold co-existing NO3- anions, the removal efficiency of GBCOP for ReO4- was 74.0%, indicating its good selectivity. Moreover, GBCOP had high removal efficiencies for ReO4- across a wide pH (3.0–10.0) range and presented remarkable stability under the conditions of strong acid and base. GBCOP could be reused four times while removing 80.8% ReO4- from simulated Hanford wastewater. SEM and XPS results revealed that the mechanism of ReO4- removal involved Cl- ion exchange within the channels of GBCOP. Theoretical calculation results supported that existing the strong electrostatic interaction between guanidinium and ReO4-. This dual-function GBCOP material is cost-effective and holds significant potential for large-scale preparation, making it a promising solution for TcO4- removal from nuclear wastewater.

Facet-dependent peroxymonosulfate activity and mechanism of CuO for degradation of organic pollutants

CuO is currently used as an effective activator for peroxymonosulfate (PMS), which exhibits complex radical, nonradical, or both activation pathways. However, there exists a knowledge gap concerning the relationship between CuO exposed facets and the PMS activation pathway, which should require further investigation. This study employed a simple and facile hydrothermal method to controllably prepare CuO samples with exposed {010} and {001} facets (referred to as CuO-010 and CuO-001, respectively). The main aim was to further study the facet-dependent PMS activation mechanism. The experimental results showed that the CuO-001 exhibited significantly higher activation efficiency than the CuO-010 due to the different surface atomic arrangement. Furthermore, scavenging experiments and EPR analyses revealed that CuO-010 exhibited both radical (SO4•− and •OH) and non-radical (1O2) pathways, synergistically degraded tetracycline (TC) and 4-nitrophenol (4-NP). Conversely, the CuO-001 displayed non-radical (1O2) and Cu(Ⅲ) intermediates, collaborating to oxidize the degradation of TC and 4-NP. More importantly, the generated 1O2 species and Cu(Ⅲ) intermediates exhibited a preference for reacting with amino or phenolic compounds containing electron-rich functional groups. Moreover, the CuO-001 also showed excellent resistance to anion interference, stability, and compatibility of a wide pH range. The outcomes of this study provide new insights into the comprehensiveness facet-dependent activation of PMS and the design of efficient metal oxide catalysts using the facet strategy for effective degradation of amino/phenolic pollutants in wastewater.

Manganese doped hollow cobalt oxide catalysts for highly efficient oxygen evolution in wide pH range

Heteroatomic substitution of spinel oxides can theoretically optimize oxygen evolution reaction (OER) via redistribution of charges and modification of d-band center. However, the wide pH range of electrocatalysis and catalytic mechanism are still great challenges. Herein, we successfully construct heteroatom Mn-substituted spinel Co3O4 (Mn-Co3O4) with porous hollow sphere structure for highly efficient and wide pH range OER. Benefiting from the atomic Mn-substitution and charge transfer, the Co site in Mn-Co3O4 displays an increased ratio of Co3+/Co2+. Electrochemical measurements demonstrate that Mn-Co3O4 exhibited superior OER activities with small overpotentials of only 305, 520 and 460 mV to afford a current density of 10 mA cm−2 in alkaline, neutral and acidic media, respectively. Meanwhile, Mn-Co3O4 also possesses favorable long-term stability in wide-pH electrolyte. The improved reaction kinetics of Mn-Co3O4 are mainly attributed to the unique hollow sphere structure with high specific surface area, and the increased high valency of Co, which can introduce the d-band center modification of Mn-Co3O4, and reduce the adsorption energy of oxygen intermediates in rate-determining step (RDS).

Easy-regeneration Mn-doped ZIF-67 derivate adsorbent with ultra-high adsorption capacity for tetracycline hydrochloride in wastewater

Adsorption capacity and reusability are critical to the practical applications of metal–organic framework (MOF)-based adsorbents. In this work, an easy-regeneration ZIF-67 derivate adsorbent (Mn-ZIF-400) was synthesized by calcining the manganese-modified MOF ZIF-67 (Mn-ZIF-67) precursor at 400 °C in air for the first time. Mn-ZIF-400 reveals an ultra-high adsorption capacity for tetracycline hydrochloride (TCH) (qmax = 1191.5 mg⋅g−1 at 308 K at pH = 4) in a wide pH range (pH = 3–10) owing to its great surface area (816.2 m2⋅g−1), surface polyvalent metal ions (Co2+/Co3+, Mn2+/ Mn 3+/ Mn4+), abundant surface oxygen species (including –COOH, –OH etc.) and π-electrons from benzene-ring. The adsorption mechanism of TCH on Mn-ZIF-400 belongs to the monolayer chemisorption mainly by π-π conjugation/π-cation interactions, hydrogen/coordination bonding, and pore filling. It also can maintain high adsorption performance in an actual aqueous environment. More importantly, Mn-ZIF-400 showed enhanced water stability and reusability after modification and no obvious loss in adsorption capacity in four recycles via simple water washing, being a promising adsorbent for antibiotic elimination.

Immobilization of ionic liquids onto chloromethylated polystyrene as a strategy for highly efficient and selective recovery of Au(III) from gold slag and PCBs

The recovery of Au(III) has become a focal point of interest due to its significance in resource utilization and addressing environmental contamination. In this study, [C3NH2Mim]Cl-CMPS and PPh3-CMPS were successfully developed by immobilizing [C3NH2Mim]Cl and triphenylphosphine (PPh3) onto chloromethylated polystyrene beads (CMPS). The adsorbents demonstrated consistently high adsorption efficiency (>95 %) at a wide pH range. The [C3NH2Mim]Cl-CMPS and PPh3-CMPS exhibited exceptional selective adsorption ability for Au(III), and the adsorption process adhered to the PSO and Langmuir model. The adsorption efficiency of Au(III) remained constant after five consecutive cycles, highlighting outstanding reusability performance. Furthermore, as the existence of multiple coexisting metal ions, [C3NH2Mim]Cl-CMPS and PPh3-CMPS could efficiently and selectively capture Au(III) from the gold slag and PCBs lixivium, which is promising for Au recovery in practice.

13 C NMR as an analytical tool for the detection of carbonic acid and pKa determination.

NMR spectroscopy has become a standard technique in studies both on carbon capture and storage. 13 C NMR allows the detection of two peaks for carbonated aqueous samples: one for CO2(aq) and another one for the species H2 CO3 , HCO3 - , and CO3 2- -herein collectively named Hx CO3 x-2 . The chemical shift of this second peak depends on the molar fraction of the three species in equilibrium and has been used to assess the equilibrium between HCO3 - and CO3 2- . The detection of H2 CO3 at low pH solutions is hindered, because of the concurrent liberation of CO2 when the medium is acidified. Herein, a valved NMR tube facilitates the detection of the Hx CO3 x-2 peak across a wide pH range, even at pH1.8 where the dominant species is H2 CO3 . The method employed the formation of frozen layers of NaH13 CO3 and acid solutions within the tube, which are mixed as the tube reaches room temperature. At this point, the tube is already securely sealed, preventing any loss of CO2 to the atmosphere. A spectrophotometry approach allowed the measurement of the actual pH inside the pressurized NMR tube. The chemical shift for H2 CO3 was determined as 160.33 ± 0.03 ppm, which is in good agreement with value obtained by DFT calculations combined with Car-Parrinello molecular dynamics. The H2 CO3 pKa value determined by the present method was 3.41 ± 0.03, for 15% D2 O aqueous medium and 0.8mol/L ionic strength. The proposed method can be extended to studies about analogs such as alkyl carbonic and carbamic acids.

Efficient reduction of hexavalent chromium by Fe-Mn bimetallic nanoparticles: Performance and role of manganese

Modification of zero-valent iron by manganese doping is a potential way to improve the properties of zero-valent iron, but the role of manganese in Fe/Mn bimetallic nanoparticles during the reduction process of hexavalent chromium is not yet fully recognised. Nano-Fe/Mn bimetals (NFMB) was synthesized through one-step chemical reduction method and characterized by Transmission Electron Microscope (TEM), Scanning Electron Microscope-Energy Dispersive Spectrometer (SEM-EDS) and X-ray Photoelectron Spectroscopy (XPS). The results showed that dispersed particles owned a rough surface and six functional groups, namely, C-O, C=O, O-H, and -COOH, Fe-O, Mn-O. XPS analysis results showed that four elements in NFMB: Fe, Mn, C, and O, along with Fe0, Mn0, Fe2O3, and FeOOH were confirmed. The composition analysis indicated an approximate content of Fe (16.74 %) and Mn (12.59 %), with the detection of Cr (1.51 %) after the reaction. The batch experiments revealed a significant enhancement of reduction efficiency of Cr (VI) at a lower pH level and higher temperature, with a consistent removal rate of around 99.9 % within the pH range of 3-9, showcasing the adaptability of NFMB across a wide pH range. The maximum removal capacity of Cr (VI) by NFMB was determined to be 35.54 mg·g−1. The removal process involved the adsorption of Cr (VI) to the surface of NFMB, followed by a series of chemical reduction and precipitation processes, and the final removal from the aqueous solution. Therefore, the Fe/Mn bimetallic nanocomposites was proved to be promising for the removal of Cr (VI) from aqueous environments.

Isolation and characterization of lactic acid bacteria producing a potent anti-listerial bacteriocin-like inhibitory substance (BLIS) from chhurpi, a fermented milk product.

Nowadays, the bacteriocin industries have seen significant growth, supplanting chemical preservatives in its ability to improve the shelf-life and safety of food. The increasing customer desire to use natural preservatives has fueled advancing bacteriocin research. The objective of this study was to identify lactic acid bacteria (LAB) that produce bacteriocin-like inhibitory substance (BLIS) and have strong anti-listerial activity. We have identified and analyzed a LAB obtained from chhurpi samples, a popular milk-derived product in the Himalayan regions of India and Nepal. The strain was studied and identified based on its morphological, biochemical, and physiological characteristics. Furthermore, the molecular 16s-rDNA analysis suggests that the strain was Lactococcus sp. RGUAM1 (98.2% similar to Lactococcus lactis subsp. hordniae NBRC 100931T). The isolated strain can produce a potent BLIS, which has shown efficacy against three gram-positive bacteria responsible for food spoilage, such as Listeria monocytogenes (MTCC 657), Staphylococcus aureus subsp. aureus (MTCC 87), Lactobacillus plantarum (MTCC 1407), Lactobacillus paraplantarum (MTCC 12904). The scanning electron microscope (SEM) image illustrates that the crude cell-free supernatant (CFS) disrupts the cell envelope, leading to the release of cellular contents and the clustering of cells. In addition, this BLIS can easily withstand a wide range of pH (2-12), temperature (up to 100°C for 15min), bile salt (0.3% W/V), salinity (4% W/V), and enzyme activity of 1600AU/ml against Listeria monocytogenes. Our research offers a robust framework and valuable insights into bio-preservation and its potential applications in diverse food products.

Fabrication of pollution-free coal gangue-based catalytic material utilizing ferrous chloride as activator for efficient peroxymonosulfate activation

Novel coal gangue-based persulfate catalyst (CG-FeCl2) was successfully synthesized by the means of calcinating under nitrogen atmosphere with the addition of ferrous chloride tetrahydrate (FeCl2·4H2O). The phase transformation of the prepared materials and gas products during the heating process are thoroughly investigated. It is suggested that ferrous chloride participated in the phase transformation and formed Si-O-Fe bonds. And the main gaseous products are H2O, H2, and HCl during the heating process. Besides, the ability of CG-FeCl2 to activate peroxymonosulfate (PMS) for catalytic degradation of polycyclic aromatic hydrocarbons (PAHs) and phenol was deeply studied. More than 95% of naphthyl, phenanthrene and phenol were removed under optimizied conditions. In addition, 1O2, ·OH, and SO4·− were involved in the CG-FeCl2/PMS system from the free radical scavenging experiment, where 1O2 played a major role during the oxidation process. Furthermore, CG-FeCl2/PMS system exhibited superior stability in a relatively wide pH range and the presence of common anion from related degradation experiments. Overall, the novel CG-FeCl2 is an efficient and environmentally friendly catalyst, displaying potential application prospect in the field of PAHs and phenol-contaminated wastewater treatment.

The combination of inorganic phosphate and pyrophosphate 31 P-NMR for the electrodeless pH determination in the 5-12 range.

Potentiometry is the primary pH measurement method, but alternatives are sought beyond glass electrodes operative limitations. In nuclear magnetic resonance (NMR) experiments, electrodeless pH sensing is important to track changes along titrations, during chemical reactions or inside compartmentalized environments inaccessible to electrodes, for instance. Although several interesting NMR pH indicators have been already presented, the potential of inorganic phosphate is overlooked, despite its common presence in NMR samples as the buffer main component. Its use for electrodeless pH determination can be expanded by exploiting all its three proton dissociations. This study was aimed at verifying the use of inorganic phosphate 31 P chemical shift to sense pH variations, and at exploring the complementary use of pyrophosphate ions to cover a wide pH range. A simple set of equations is presented to utilize both phosphate and pyrophosphate 31 P chemical shift in combination for accurate pH determination without a glass electrode over the 5-12 pH range, and without affecting the spectrum of other nuclei. The present study demonstrated an average deviation of 0.09 (maximum <0.2) pH unit from glass electrode measurements. The trimethylphosphate can be used as a suitable chemical shift reference for both 31 P and 1 H (also 13 C), with its hydrolysis being significant only at pH > 12. The method was also demonstrated by determining the pKa of three distinct molecules in a mixture and by comparing the results to those obtained when the glass electrode was used to measure the pH. The approach shown here can be easily tuned to different experimental conditions.

Iron containing sludge-derived carbon towards efficient peroxymonosulfate activation: Active site synergy, performance and alternation mechanism

Converting industrial sludge into catalytic materials for water purification is a promising approach to simultaneously realize effective disposal of sludge and resource of water. However, manipulating the high efficiency remains a huge challenge due to the difficulty in the active sites control of the sludge. Herein, we proposed a constitutive modulation strategy by the combination of hydrothermal and pyrolysis (HTP) for the fabrication of defects-assistant Fe containing sludge-derived carbon catalysts on upgrading performance in peroxymonosulfate (PMS) activation for pollutant degradation. Adjustable defects on dyeing sludge-derived carbon catalysts (DSCC) were achieved by introducing oxygen or nitrogen functional precursors (hydroquinone or p-phenylenediamine) during hydrothermal processes and by further pyrolysis, where O was detrimental while N was beneficial to defect generation. Compared to the DSCC with less defects (DHSC-O), the defect-rich sample (DHSC-2N) exhibited superior catalytic performance of PMS activation for bisphenol A (BPA) elimination (k = 0.45 min−1, 2.52 times of DHSC-O), as well as 81.4% total organic carbon (TOC) removal. Meanwhile, the degradation capacity was verified in wide pH range (2.1–8.1) and various aqueous matrices, reflecting the excellent adaptability and anti-interference performance. Furthermore, the continuous-flow experiments on industrial wastewater showed synchronous BPA and chemical oxygen demand (COD) removal, implying great potential for practical application. Solid electron paramagnetic resonance (EPR) and 57Fe Mösssbauer spectra analysis indicated that the defects acted as secondary active sites for Fe sites, which were beneficial to accelerating the electron transfer process. The only Fe active sites preferred the radical pathway. The controllable reaction tendency provides possibilities for the on-demand design of sludge-based catalysts to meet the requirements of practical wastewater treatment under Fenton-like reaction.

Magnetic CoFe alloy@N-CNTs as fenton-like activator for the efficient abatement of imidacloprid: Kinetics, transformation mechanisms, and toxicity assessment

A magnetic bimetal-carbon nanohybrid, CoFe alloy@N-CNTs was designed to activate peroxydisulfate (PDS) for the degradation of imidacloprid (IMI). Under optimal conditions, 5 mg/L of IMI were completely removed within 6 h with a mineralization degree of 42.9 %. Moreover, a high rate of IMI removal was observed over a wide pH range and in the presence of different anions and humic acids. Stability tests conducted over five cycles and material characterizations confirmed the stability of CoFe alloy@N-CNTs. Furthermore, radical and non-radical oxidation contributed to the degradation process based on the results of quenching experiments, electron paramagnetic resonance (EPR), radical quantification and X-ray photoelectron spectroscopy (XPS). Hydroxylation was identified as the main degradation pathway through mass spectrometry observation, frontier electron densities (FEDs) theory calculations, fluorescence intensities and mineralization degree. Additionally, the predicted ecotoxicity of IMI and its intermediates towards three aquatic organisms using ECOSAR software was not harmful or low toxic, verifying the potential application of this technique from an ecological risk perspective. This study provides valuable insights for designing metal–carbon nanohybrids as efficient Fenton-like catalyst in water treatment.