Strong Acid Medium Research Articles

Electrochemical Frequency Modulation and Reactivation Investigation of Thioglycolurils in Strong Acid Medium

The Electrochemical frequency modulation and Reactivation investigation results have shown that the anticorrosion inhibitors of 3a,6a- bistolylthioglycoluril, 4,5-dihydroxy-4,5-bistolylimidazolidine-2-thione and 5,5-bistolyl-2-thione-4-imidazolidone maximally reduced H+impacts on metal surface so these inhibitors have decreased the degree of sensitization to intergranular stress corrosion cracking on N80 steel surface.

Polyaniline-coated Ru/Ni(OH)2 nanosheets for hydrogen evolution reaction over a wide pH range

How to improve the performance of ruthenium (Ru)–based catalysts for hydrogen evolution reaction (HER) to replace Pt is an interesting topic. Here, we in situ synthesize a polyaniline (PANI)-coated ultralow Ru-doped Ni(OH)2 nanosheet (RuNi-NSs@PANI) in a 3D integral electrode via a facile dissolution–precipitation strategy and electrodeposition. Results indicate that RuNi-NSs@PANI has a small overpotential of 21.9 mV at a current density of 10 mA cm−2 and a low Tafel slope of 38.54 mV dec−1 in alkaline condition, which is comparable with that of 20% Pt/C. The outstanding performance is attributed to the synergistic effects of the Ru-doped 2D Ni(OH)2 structure, active metallic Ru cluster, PANI coating and 3D integrated Ni electrode. Owing to PANI coating, RuNi-NSs@PANI shows excellent durability with the increase of 36.8% current density retention (from 52.2% for RuNi-NSs increasing to 89% for RuNi-NSs@PANI) compared to the RuNi-NSs sample without PANI coating in strong acidic medium, because the PANI coating could keep H+ from cracking the catalyst structure and therefore enhance the stability. In short, this work indicates that RuNi-NSs@PANI composite is an excellent wide pH range HER catalyst.

Experimental investigations of adipic acid agglomeration behavior under different operating conditions using image analysis technique QICPIC software

The agglomeration behavior in adipic acid crystallization from aqueous solution was experimentally studied under different crystallization conditions. The QICPIC software, which uses image analysis technique, was implemented to evaluate the agglomeration behavior of adipic acid crystals. Primary experimental investigations indicated an important role of cooling rate on the agglomeration and crystal size distribution (CSD) of adipic acid. At slower cooling rates of 17.5 K/h and 6 K/h, larger size particles (80% agglomerates) with bimodal and wide CSD were produced while at a higher cooling rate of 30 K/h a narrower unimodal PSD and smaller size particles with the ratio of agglomerated particles of about 80% were produced. The influence of pH was found to be an important factor when studying the agglomeration behavior of adipic acid. A larger size of the product was measured in the strong acidic medium, indicating enhanced agglomeration. Changing the solvent composition and its effect on the agglomeration of adipic acid were studied. A bimodal and larger size agglomerates are obtained in a pure water solvent while adding ethanol will change the CSD to unimodal shape (no nucleation) with smaller sized agglomerates.

Increasing sustainability on the metallurgical industry by integration of membrane nanofiltration processes: Acid recovery

The metallurgical industry generates large volumes of toxic effluents characterised, generally, by high acidity and a noticeable content of metals (Fe, Cu and Zn) and non-metals (As, Sb, Bi). The toxicity of these streams makes necessary treatment before its discharge to the environment or reuse. Sustainable management of these effluents must be focused on the recovery of low added valuable by-products (e.g. strong acids) to reduce the wastes generated along with the treatment (e.g. sludge). Nanofiltration offers clear advantages for acid recovery instead of the conventional treatments such as neutralisation and precipitation, due to the high membrane transport ratios of single charged ions and high rejection of multi-charged ions. The performance of a semi-aromatic poly(piperazineamide) membrane (NF270) was evaluated for the treatment of effluents from copper metallurgical process streams of off-gases treatment trains. These streams are characterised by a high acidity (pH < 1) due to a mixture of strong (H2SO4, HCl) and weak (H3AsO4) acids and the presence of metallic species (Fe, Cu, Zn). The membrane performance was evaluated in terms of acid recovery and metal ions rejection taking into account their aqueous speciation in strong acid media. The transport of the species across the membrane was characterised according to the Solution-Electro-Diffusion model. The membrane permeances to aqueous species (both charged and non-charged) in strongly acidic solutions were calculated. NF270 showed good results for strong acid recovery, exhibiting high rejections of the metallic impurities. The implications of the presence of large amounts of As present as H3AsO4 should involve a selective removal stage using H2S or Na2S2O3.

Ni nanoparticles on polyaromatic hyperbranched polymer support as a mild, tunable, and sustainable catalyst for catalytic transfer hydrogenation

Hyperbranched polyaromatic polymer (HBP) based on pyridylphenylene dendrimer as a multifunctional monomer was employed as a nanoreactor and a stabilizing matrix for synthesis of catalytic Ni nanoparticles (NPs). The HBP was found to have an effective control over NP size. The Ni NPs synthesized in HBP matrix had diameter between 3 and 4.5 nm with narrow size distribution and were reproducible in several batches. The HBP-encapsulated Ni NPs (Ni-HBP) had a good air stability, high activity, and controlled reactivity in catalytic transfer hydrogenation (CTH) of nitroarenes and alkenes. The catalytic reactions were performed under base-free, heterogeneously-catalyzed conditions without use of high pressure, strong acidic media, or highly flammable hydrogen source. This reduction system showed good tolerance towards hydroxyl, alkyne, or halogen substituents. Moreover, due to mild nature of the catalyst, the reaction may be controlled to selectively reduce only one functional group, leaving another one intact (e.g., nitro-group vs internal alkyne).

Nitrogen-plasma treated hafnium oxyhydroxide as an efficient acid-stable electrocatalyst for hydrogen evolution and oxidation reactions

Development of earth-abundant electrocatalysts for hydrogen evolution and oxidation reactions in strong acids represents a great challenge for developing high efficiency, durable, and cost effective electrolyzers and fuel cells. We report herein that hafnium oxyhydroxide with incorporated nitrogen by treatment using an atmospheric nitrogen plasma demonstrates high catalytic activity and stability for both hydrogen evolution and oxidation reactions in strong acidic media using earth-abundant materials. The observed properties are especially important for unitized regenerative fuel cells using polymer electrolyte membranes. Our results indicate that nitrogen-modified hafnium oxyhydroxide could be a true alternative for platinum as an active and stable electrocatalyst, and furthermore that nitrogen plasma treatment may be useful in activating other non-conductive materials to form new active electrocatalysts.

MOFs-induced encapsulation of ultrafine Ni nanoparticles into 3D N-doped graphene-CNT frameworks as a recyclable catalyst for Cr(VI) reduction with formic acid

Recently, nitrogen-doped carbon encapsulating with transition metal hybrids has attracted extensive interests in catalysis because of its unique microstructure and promising properties. In this work, three dimensional N-doped graphene-CNT frameworks with well encapsulated ultrafine Ni nanoparticles (Ni@N-CNTs/N-G) were developed by a facile two-stage encapsulation strategy by combining Ni-MOFs with melamine as the precursor. In terms of Cr(VI) reduction by using formic acid (HCOOH) as the reductant, N-CNTs/N-G matrix not only protected the encapsulated Ni nanoparticles from poisoning or leaching in strong acid media, but also provided enhanced active sites for Cr(VI) by its rich mesopores and high N content. Among all the products obtained after thermal treatments at different temperatures, Ni@N-CNTs/N-G-800 (pyrolyzed at 800 °C) exhibited superb reduction performance with the efficiency of approximately 99.6%, ascribing to the synergistic effects including the porous 3D framework with large specific surface area, high N-doping level, and large amount of ultrafine Ni nanoparticles. More importantly, its catalytic activity and microstructure rarely changed after 10 times of recycling, suggesting that Ni@N-CNTs/N-G-800 processes excellent stability. This study provides a new strategy of synthesizing transition metal-based catalyst, which can broaden the applicability of MOF materials for heavy metal pollution cleanup.

An efficient headspace gas chromatographic technique for determining humic acid content in fertilizer

A fast, convenient and commercially available approach for analyzing humic acid content in fertilizer using headspace gas chromatography (HS-GC) is presented in this paper. Humic acid is converted into carbon dioxide based on the oxidation of humic acid in strong acidic medium and can be measured via automatic HS-GC. Conditions for the alkaline extraction and the humic acid oxidation process are also optimized. The new technique proved to be precise (RSD ≤ 3.59%) and accurate (relative errors≤9.46% as compared with the spectrophotometric approach). The newly established technique presents a practical tool to routinely analyze humic acid content in fertilizer during the fertilizer production.

Tough, adhesive and conductive polysaccharide hydrogels mediated by ferric solution

In general, chitosan should be dissolved in strong acidic media (such as acetic acid) before it could be applied as hydrogels. However, it was found that chitosan could also be dissolved in the ferric solution to form ferric-chitosan complex via coordination interaction. Subsequently, the ferric-chitosan complex was successfully introduced into the hydrogel system to obtain tough, adhesive and conductive chitosan-polyacrylamide double network (CS-PAAm DN) hydrogels. Surprisingly, CS-PAAm DN hydrogel could repeatedly adhere to various solid materials and biological tissues through physical interactions. The maximum peeling force was 256 N/m on the aluminum surface. Moreover, the hydrogel exhibited adequate mechanical performance (135 kPa, 2332%). And the introduction of ferric chloride could also endow the hydrogel with conductive performance. As a result, the strategy based on tough, adhesive and conductive polysaccharide hydrogels mediated by ferric solution would broaden the path to fabricate a new generation of soft materials for wide applications.

Degradation of emerging contaminants by Co (III) ions in situ generated on anode surface in aqueous solution

Cobalt ion is an environmental contaminant in general. But interestingly, it can also be used to degrade some refractory organic contaminants in water by mediated electrochemical oxidation process (MEOP) based on Co (III). MEOP is a very promising technology, and it can recycling use the mediator ions, Co (III), to degrade refractory organic contaminants in water. However, previous studies for this technology mainly conducted in strong acidic medium, the oxidation ability of this process for emerging contaminants near neutral pH condition was still unclear. Therefore, this study evaluated the emerging contaminants removal and mineralization efficiency of the MEOP-Co (III) around neutral pH, and investigated systematically the influence of series of operating parameters, including initial Co (II) concentration, current density, initial pH, electrolyte, and anions. Results from these studies indicated that the MEOP-Co (III) had a fairly good contaminants removal and mineralization ability for sulfamethoxazole, tetracycline, carbamazepine, diclofenac, and phenol at neutral pH. Besides, no radical was detected in MEOP-Co (III), and the main oxidizing substance was Co (III) ions, which was generated on anode surface. The addition of CO32−/HCO3− could weaken the oxidation ability of MEOP-Co (III), while Cl− and PO43− could enhance the system's oxidation ability. Moreover, a reasonable energy consumption was achieved in MEOP-Co (III), and the highest electric energy per order (EE/O) value was 2.4 kWh·m−3 in this study.

Efficient capture of actinides from strong acidic solution by hafnium phosphonate frameworks with excellent acid resistance and radiolytic stability

A kind of unconventional metal–organic framework (UMOF), hafnium phosphonates (HfP) with different molar fractions P/(P + Hf), were synthesized via a template-free, one-pot method by the reaction between hafnium chloride octahydrate (HfOCl2·8H2O) and amino tris(methylenephosphonic acid) (ATMP); the structure, sorption behaviors for actinides, acid resistance and radiolytic stability of the synthesized materials were then investigated. The results reveal that the materials were amorphous and porous, and HfP with a higher molar fraction P/(P + Hf) exhibited a higher sorption capacity for Th(IV) and U(VI). In 3 mol/L HNO3, Kd values of HfP for Th(IV) and U(VI) were 5.84 × 104 and 5.09 × 103 mL/g, respectively, indicating superiority to other MOF materials in strong acidic solution. The Kd values for tracer amounts of radioactive 239Pu and 237Np were 1.19 × 104 and 6.68 × 103 mL/g in 4 mol/L HNO3, respectively. This is the first case of applying MOF materials to capture transuranic elements from a strong acidic medium. Moreover, the materials were quite stable when dipped into strong acidic solutions, while their sorption performances were unexpectedly enhanced after irradiated by high dosage γ-rays in air. All the results support its anticipated application as actinide sorbents in many practical nuclear processes.

Liquid phase oxidation of cyclohexane over mesoporous cobalt silicates molecular sieves synthesized in strong acidic media by assembly of preformed CoS-1 precursors with triblock copolymer

Cobalt–incorporated mesoporous silica materials [MCoS(n), n = Si/Co = 20; 60] have been successfully prepared in strong acidic media by assembly of preformed CoS-1 precursors with triblock copolymer of the Pluronic type (P123) by a two steps procedure. They were characterized by various techniques including XRD, BET, FT-IR spectroscopy and diffuse reflectance UV–Vis (DRUV–Vis). The results show that the calcined MCoS materials contain Co(II) ions in tetrahedral environments under low and high Co content and the mesoporous walls contain the MFI structure building units. Liquid phase oxidation of cyclohexane using TBHP as oxidant was investigated on MCoS(n). The major products detected are cyclohexanone and cyclohexanol in all cases. The MCoS(n) catalysts are more active when water free TBHP was used and the conversion of cyclohexane increases when cyclohexane to TBHP molar ratio increases from 1:1 to 1:2, while the cyclohexanol selectivity decreases, which is ascribed to a further oxidation of cyclohexanol to cyclohexanone. The catalytic activity of MCoS(n) materials is enhanced as the cobalt content increases. It is worth noting that MCoS(20)is more active than Co-SBA15(20). The most active catalyst MCoS(20) acts as truly heterogeneous catalyst and was very stable after four runs.

Synthesis, characterization and electrochemical evaluation of anticorrosion property of a tetrapolymer for carbon steel in strong acid media

Abstract A novel tetrapolymer (TP) consisting of carboxylate, sulphonate, phosphonate and sulfur dioxide based co-monomers was synthesized using Butler cyclopoymerization technique. The synthesized tetrapolymer was characterized using FTIR, 1H-NMR, 13C NMR and elemental analysis. The performance of the tetrapolymer as a corrosion inhibitor for St37 carbon steel in 15% HCl and 15% H2SO4 acid media was assessed using electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), potentiodynamic polarization (PDP) and electrochemical frequency modulation (EFM) techniques. The influence of addition of a small amount of KI on the corrosion inhibition efficiency of TP was also assessed. Results obtained showed that the tetrapolymer moderately inhibited the corrosion of St37 steel in the acid media with protection efficiency of 79.5% and 61.1% at the optimum concentration of 1000 mg·L− 1 studied in HCl and H2SO4 media respectively. On addition of 5 mmol·L−1 KI to the optimum tetrapolymer concentration, the protection efficiency was upgraded to 90.6% and 93.5% in HCl and H2SO4 environment, respectively. The enhanced performance of the polymer in the presence of KI is due to synergistic action deduced from synergism parameter (S1) which was found to be greater than unity. The tetrapolymer afforded the corrosion inhibition of St37 steel in the acid media by virtue of adsorption of the polymer molecules on the steel surface which was confirmed by ATR-FTIR analysis of the adsorbed film extracted from the steel surface. TP + KI formed complex with St37 steel surface in H2SO4 solution but not in HCl solution.

Acid-free approach towards the growth of vertically aligned TiO2 nanorods as an efficient photoanode for dye-sensitized solar cells

We synthesized the closely packed titanium dioxide nanorods (TiO2 NRs) on fluorine-doped tin oxide (FTO) glass by a facile and cost-effective hydrothermal method. The TiO2 NRs were further utilized as a photoanode for dye-sensitized solar cells (DSSCs). For hydrothermal growth of TiO2 NRs, we utilized an acid-free reaction medium instead of a strong acidic medium, which can reduce the equipment cost as well as the environmental damages. Before employing these TiO2 NRs for DSSCs as a photoanode, the effects of hydrothermal growth parameters on the structural and optical characteristics of TiO2 NRs/FTO glass were investigated. Eventually, the TiO2 NRs with optimized height and diameter were employed to DSSCs and their photovoltaic characteristics were examined.

Radiochemical characterization and decontamination of rare-earth-element concentrate recovered from uranium leach liquors

The paper deals with two rare earth elements (REE) concentrates recovered from uranium leach liquors after sorption separation of uranium. Activity of the REE concentrates was found to be 106 Bq kg−1; Ac-227 and its short-lived daughter products were the main radioactive impurities contributing more than 99% of total activity. Activity of both U-238 + Th-232 in the REE concentrates did not exceed 0.2% of total activity. Extraction by 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester (P-507 extractant) in Shelsol D90 diluent was suggested for REE deactivation. It was shown that thorium may be eliminated by extraction in strong acidic media (pH − 0.5 to − 1), whereas radium extraction was suppressed over the whole studied pH range. Further REE separation to heavy and light groups at pH 1 resulted in selective concentration of actinium in light REE group. The suggested separation flowsheet was tested on the real REE concentrate. It was shown that obtaining non-radioactive fraction of heavy REE is possible.

Targeted Drug Delivery and Treatment of Endoparasites with Biocompatible Particles of pH-Responsive Structure.

Biomaterials conceived for vectorization of bioactives are currently considered for biomedical, biological, and environmental applications. We have produced a pH-sensitive biomaterial composed of natural source alginate and chitosan polysaccharides for application as a drug delivery system via oral administration. The composite particle preparation was in situ monitored by means of isothermal titration calorimetry. The strong interaction established between the macromolecules during particle assembly led to 0.60 alginate/chitosan effective binding sites with an intense exothermic effect and negative enthalpy variation on the order of a thousand kcal/mol. In the presence of model drugs mebendazole and ivermectin, with relatively small and large structures, respectively, mebendazole reduced the amount of chitosan monomers available to interact with alginate by 27%, which was not observed for ivermectin. Nevertheless, a state of intense negative Gibbs energy and large entropic decrease was achieved, providing evidence that formation of particles is thermodynamically driven and favored. Small-angle X-ray scattering provided further evidence of similar surface aspects independent of the presence of drug. The physical responses of the particles to pH variation comprise partial hydration, swelling, and the predominance of positive surface charge in strong acid medium, whereas ionization followed by deprotonation leads to compaction and charge reversal rather than new swelling in mild and slightly acidic mediums, respectively. In vivo performance was evaluated in the treatment of endoparasites in Corydoras fish. Systematically with a daily base oral administration, particles significantly reduced the infections over 15 days of treatment. The experiments provide evidence that utilizing particles granted and boosted the action of the antiparasitic drugs, leading to substantial reduction or elimination of infection. Hence, the pH-responsive particles represent a biomaterial with prominent characteristics that is promising for the development of targeted oral drug delivery.

Mechanical and microstructural properties of cordierite-bonded porous SiC ceramics processed by infiltration technique using various pore formers

Cordierite-bonded porous SiC ceramics were prepared by air sintering of cordierite sol infiltrated porous powder compacts of SiC with graphite and polymer microbeads as pore-forming agents. The effect of sintering temperature, type of pore former and its morphology on microstructure, mechanical strength, phase composition, porosity and pore size distribution pattern of porous SiC ceramics were investigated. Depending on type and size of pore former, the average pore diameter, porosities and flexural strength of the final ceramics sintered at 1400 °C varied in the range of ~ 7.6 to 10.1 µm, 34–49 vol% and 34–15 MPa, respectively. The strength–porosity relationship was explained by the minimum solid area (MSA) model. After mechanical stress was applied to the porous SiC ceramics, microstructures of fracture surface appeared without affecting dense struts of thickness ~ 2 to 10 µm showing restriction in crack propagation through interfacial zone of SiC particles. The effect of corrosion on oxide bond phases was investigated in strong acid and basic salt medium at 90 °C. The residual mechanical strength, SEM micrographs and EDX analyses were conducted on the corroded samples and explained the corrosion mechanisms.

Highly active and stable electrocatalyst of Ni2P nanoparticles supported on 3D ordered macro-/mesoporous Co–N-doped carbon for acidic hydrogen evolution reaction

The novel electrocatalyst with Ni2P nanoparticles supported on 3D ordered macro-/mesoporous Co–N-doped carbon was fabricated, showing excellent performance for hydrogen evolution reaction in strong acidic medium.

Colorimetric and fluorescence sensing of pH with a Schiff-base molecule

2-Hydroxy-5-methyl-3-((quinolin-6-ylimino)methyl)benzaldehyde (HL) has been found to be a ratiometric fluorescent chemosensor for pH. It has been synthesized by Schiff-base condensation reaction between 4-methyl-2,6-diformylphenol and 6-aminoquinoline in 1:1 ratio in methanol and characterized by various standard methods. Fluorescence peak of it appears at 464nm (excitation 360nm) with strong intensity at low pH in Britton Robinson buffer. With the gradual increase in pH value of the medium, intensity at 464nm decreases and a new peak emerges at 529nm with gradual increase in its intensity. Fluorescence intensity of HL remains almost unaffected in the presence of different cations and anions both in acidic and basic media. Fluorescence intensity can be successively altered to its original value with cyclic change of pH between 4.0 and 10.0 indicating stability of the probe in both the media. pKa of HL has been determined to be 6.24. Colorless probe in strong acidic medium turns green in pH of ~ 6 or more under visible light. Under same condition, color changes from blue to green with the illumination of UV irradiation. These changes are handy to detect different pH medium and are in accordance with UV–vis spectral results. Phenolic proton of HL deprotonates in higher pH as is also evident from the theoretical calculations. This probe has been applied to detect pH regions using lemon juice and river (Ganga) water.

Ruthenium ion containing N and S rich triazine based metallopolymer as a low overpotential acid stable electrocatalyst for hydrogen evolution

The rational design of under saturated redox-active metal centers distributed on the organo-polymeric surfaces has gained substantial attention in electrocatalysis. Herein, we report the ruthenium ions containing triazine-trithiolate (M-C3N3S3) metallopolymers chemically coordinated to the copper substrate as a stable, low overpotential electrocatalyst for H2 evolution in strong acidic media. The XPS analyses confirm the presence of Ru4+/Ru3+ and Cu2+/Cu1+ in the metallopolymers. XPS and FTIR spectral analysis suggest the presence of disulphide linkages. A significant overpotential reduction for hydrogen evolution is observed with CuRu-C3N3S3 metallopolymer of just ∼−145 to −155 mV vs RHE to attain −10 mA cm−2 in 0.5 M H2SO4. The high exchange current densities and double layer capacitance could be attributed to the protonation capacity of redox-active centers and the uncoordinated ligand centers (N and S). The concerted proton-electron transfer mechanism improves the H2 evolution. These metallopolymers show a low onset hydrogen evolution potential of just −45 mV vs RHE (i = −1 mA cm−2). Tafel slope values suggest the Volmer-Heyrovsky mechanism is involved in HER. The potentiostatic impedance spectral analyses indicate, CuRuTCA show the reduction in charge transfer resistance of nearly 10 and 700 times with respect to CuNiTCA and bare Cu electrodes respectively. These electrodes display an excellent long-term stability for hydrogen evolution.