Thiourea Solution Research Articles

Thiourea leaching of gold in presence of jarosite and role of oxalate

The effect of jarosite generated from bio-oxidation on gold leaching in acidic thiourea solution was studied, and the role of the oxalate additive was also investigated. The biogenetic jarosite was found to markedly raise the thiourea consumption and hinder the gold dissolution. The dominant cause for the detrimental effect of jarosite is likely that iron ions were released from jarosite dissolution in the acidic solution and thus increased the solution potential, resulting in the accelerated decomposition of thiourea and the aggravated passivation of gold surface by the passivating species from thiourea decomposition. However, the addition of oxalate to solution was shown to be effective in weakening the adverse effect of jarosite manifested as much reduced thiourea consumption and enhanced gold dissolution. The possible acting mechanisms of oxalate were revealed by the analyses of solution potential, Zeta potential and XPS. Oxalate could not only weaken the interaction between Fe3+ and thiourea via complexing with Fe3+ but also prevent the passivation species from coating on gold surface through indiscriminate adsorption and electrostatic repulsion.

Effect of spacer length between N atoms of linear alkyl triamines on adsorption of anionic platinum(IV) ions

In this study, the effect of carbon chain length between N atoms in linear alkyl triamines on the adsorption of anionic platinum ions was studied. For this purpose, bis(3-aminopropyl)amine (BAPA-SG) and diethylenetriamine (DETA-SG) groups were covalently bonded to the silica gel surface. The modified silica gels were characterized through C, H, N elemental analyses and FTIR spectroscopy before being utilized for adsorption and preconcentration Pt(IV) ions from aqueous solutions. Various factors influencing the batch adsorption of Pt(IV) ions with BAPA-SG and DETA-SG, such as nitric acid, chloride, initial Pt(IV) concentration, and contact time, were investigated. The adsorption of Pt(IV) ions was most efficient in the solutions containing 0.1 M hydronium and 0.1 M chloride ions. The adsorbed amount of Pt(IV) increased with an increase in the initial concentration of Pt(IV). The adsorption of Pt(IV) ions with BAPA-SG and DETA-SG reached equilibrium in 2 and 4 h, respectively. The kinetics of Pt(IV) adsorption on both modified silica gels were found to be compatible with the Pseudo-second-order kinetic model. Langmuir isotherm accurately described the adsorption Pt(IV) ions with BAPA-SG and DETA-SG, with maximum monolayer adsorption capacities of 158.7 and 227.3 mg/g, respectively. In the column solid phase extraction studies, Pt(IV) ions could be quantitatively recovered from 500 mL sample solutions using both modified silica gels by eluting with acidic thiourea solutions. The recovery of Pt(IV) by DETA-SG from chloride-containing solutions was more effective than with BAPA-SG. As a result, it was concluded that diethylenetriamine-bonded silica gel could adsorb Pt(IV) ions more effectively than bis(3-aminopropyl)amine bonded silica gel.

One-step facile solution synthesis of α-Ag2S nanoparticles and fabrication of multi-layered thin films

The ductility possessed by α-Ag2S renders it a promising candidate for various forthcoming stretchable electronic devices. There is a significant need for a facile approach for producing α-Ag2S thin film with a dense surface. This study has opted for the spin coating technique to prepare α-Ag2S thin films from the colloidal solution. This method starts by mixing AgNO3 and amidino thiourea solution and is easy, straightforward and much less time-consuming compared to self-assembling procedure. The thickness of the film can be well-controlled by coating multiple layers on various substrates. The observed resistive switching behavior in the obtained dense α-Ag2S thin film, along with the integrity of the film in the bending test, suggests its potential utility in electronic applications. It is hoped that our work can offer an innovative mean for crafting flexible α-Ag2S thin film applicable in future devices.

Thiourea Adsorbent for Efficient Removal of Mercury (II)

AbstractThe removal of heavy toxic metals from industrial effluents is extremely important, especially for mercury (Hg), which is classified as a highly toxic even at low concentrations. For this purpose, novel thiourea chelating resins were synthesized as sorbent for Hg (II). Six different polymers of formo‐phenolic types were characterized and evaluated for their chelating properties with respect to Hg (II) extraction. Batch adsorption studies of mercury (II) as a function of pH, initial metal ion concentration, temperature, and time showed that thiourea formo‐phenolic polymers have a good affinity for Hg removal and a high adsorption capacity. Adsorption isotherms (Langmuir and Freundlich) and kinetic models (pseudo‐first and pseudo‐second order) were used to interpret the sorption behavior of the materials. The Langmuir model yielded the best fit with a maximum adsorption capacity of 300 mg/g. Desorption studies were performed with aqueous thiourea solution and showed that the adsorbent is indeed regenerable and can be effectively used for up to three adsorption‐desorption cycles with negligible loss of performance. This study confirmed the potential of thiol‐modified formo‐phenolic resins in sorbent engineering with promising applications in the remediation of mercury‐contaminated water.

DFT, molecular docking and molecular dynamics simulations of 2-imino-4-oxo-1,3-thiazolidine hydrochloride and its activity against Bacillus pasteurii urease

Abstract According to reports, the bioactive thiourea derivative was prepared from the ethanol solutions of thiourea and chloro acetic acid in a 1:1 M ratio. DFT calculations of 2-Imino-4-oxo-1,3-thiazolidine hydrochloride (IOTH) were performed with the use of B3LYP and the 6-311+G(2d,p) basis set. Frontier molecular orbitals, mapped electrostatic potential (MEP) map, and nonlinear optical (NLO) properties of the IOTH were all assessed. The compound was tested for drug-likeness using Swiss ADME. Using B. pasteurii (PDB ID: 4UBP), calculations for molecular docking were then performed on the geometry-optimized structure. In order to determine the complex’s stability and the interactions between ligands and the receptor, the complex was subjected to molecular dynamics (MD) simulations. According to the results, the first hyperpolarizability value (β 0) was 7.459 × 10−24 esu. The large first hyper polarization rate theoretically supported its use in the design of NLO materials. The calculated HOMO–LUMO energy gap value of the IOTH was found to be 2.87 eV. The small HOMO–LUMO energy gap suggested that IOTH is a soft molecule with a high degree of chemical reactivity but poor kinetic stability. The molecular docking study showed that the best ligand pose energy for the IOTH was −101.35 kcal/mol whereas the standard drug (acetohydroxamic acid) was −64.29 kcal/mol. The results demonstrated that the ligand–receptor complex remained stable during the MD simulations due to high binding affinity to Bacillus pasteurii urease. The Lipinski Rule of Five was not violated in any way in the studied compound. This demonstrated that it is bioavailable. During clinical trials, the compound attrition rates would be lower, and the drug would have a better chance of being commercialized.

Solvent extraction separation of Au(III) from Pd(II), Cu(II), Ni(II) in HCl solution using cationic, neutral and basic extractants

AbstractBACKGROUNDEtching solutions of spent printed circuit boards (PCBs) contain precious metal ions like Au(III) and Pd(II) together with Cu(II). Therefore, it is crucial to recover Au(III) and Pd(II) from these solutions. To investigate the possibility of separating Au(III) from the etching solutions, solvent extraction experiments were conducted using synthetic hydrochloric acid solutions containing Au(III), Pd(II), Cu(II), and Ni(II). The solvent extraction behavior of these four metal ions was investigated by using cationic (Cyanex 301, LIX 63), neutral (Cyanex 923 and TBP), and basic (Alamine 336 and Aliquat 336) extractants in the HCl concentration range from 1 to 9 M.RESULTSTBP and Cyanex 923 were successful in separating Au(III) from other metal ions when the HCl concentration was higher than 7 M. When the concentrations of Au(III) and Pd(II) changed from 0.1 to 5 g L−1, TBP was able to selectively extract Au(III) from 7 M HCl solution, while Cyanex 923 was effective in separating Au(III) from 9 M HCl solution. However, Au(III) and Pd(II) were co‐extracted by Alamine 336 and Aliquat 336 from 1 M HCl solution. Thiourea or a mixture of thiourea and HCl solution effectively stripped Au(III) from the loaded organic phases of TBP, Cyanex 923, and amines.CONCLUSIONSAmong the six kinds of the extractants employed in this work, TBP was recommended as an extractant for the selective extraction of Au(III) from the HCl solutions containing Cu(II), Ni(II) and Pd(II) on the basis of high separation degree. © 2023 Society of Chemical Industry (SCI).

Highly selective adsorbents based on silica gel chemically modified with sulfur-containing groups of arched structure for preconcentration and determination of palladium(II) in products of processing of sulfide copper-nickel ore

Adsorbents based on silica gel chemically modified with arch structure 2-aminophenyl disulfide (DSS) and bis[3-(triethoxysilyl)propyl]tetrasulfide (TSS) groups have been synthesized. The proposed adsorbents quantitatively extracted (extraction ∼99 %) only palladium(II) among all platinum metals from solutions of 2 M HCl - pH 4. Quantitative extraction of Pd(II) was not interfered with 106-fold excesses of alkaline, alkaline-earth, 104-fold excesses of non-ferrous metals and iron, 102-103-fold excesses of other platinum metals. Pd(II) was eluted quantitatively (desorption ∼99 %) from the adsorbents surface with 5–10 % thiourea solutions and could be determined in the eluate by inductively coupled plasma optical emission spectrometry (ICP-OES). The adsorption capacity of DSS and TSS adsorbents was not changed after 5 adsorption-elution cycles. The limit of detection of palladium in the analyzed solution, calculated using the 3 s-criterion, was 0.1 μg/L for solid-phase extraction-inductively coupled plasma optical emission spectrometry (SPE-ICP-OES) method with a preconcentration factor of 50. Intensive yellow-orange color of the palladium surface complex was used in the development of express test-methods for its determination. SPE-ICP-OES and test methods were used in the determination of palladium in certified reference materials of sulfide copper-nickel ore and products of its technological processing.

Ultrafast room-temperature activation of nickel foams as highly efficient electrocatalysts

Nickel foams (NF) are widely used electrode substrates that are associated with a wide range of industrial chains and large economic benefits. However, the pristine Ni foams usually possess poor electrochemical activities with dense passivation layers. Herein, an ultra-fast method for activating raw Ni foam was developed by soaking the Ni foam in a formulation solution of thiourea and I2/KI at room temperature for just a few minutes. In the solution, I3− (I2 + I−) acts as an oxidizer to accelerate the formation of Ni2+, while the hydrolysis of thiourea provides a weakly acidic environment and sulfur ions for formation of superficial layer NiS with I doping. The activated Ni foam has a fluffy nanosheet structure and the activity, characterized by the integrated Ni2+/Ni3+ peak area is enhanced by more than 100 times. The activated electrode exhibits high performance towards urea oxidation reaction (UOR) in alkaline electrolytes, delivering a current density of 100 mA cm−2 at only 1.44 V (vs. RHE, reversible hydrogen electrode). The in situ Raman spectroscopy identifies NiOOH as the catalytically active species for urea oxidation and in situ differential electrochemical mass spectrometry (DEMS) isotope tracking experiment reveals an intramolecular N-N bond coupling mechanism during the UOR. The developed activation method is easy to scale up for preparing large-area electrode and the catalytic activity is extended to oxidation of other organic molecules. This work presents a novel ultrafast one-step surface engineering strategy for activating Ni foams into high-performance electrocatalysts.

A hydrazine amidoxime crosslinked polyacrylonitrile resin for efficient extraction of gallium from vanadium-containing waste solution

The conventional Ga(III) adsorption resins suffer from complex synthesis procedure and low raw material utilization rate. In this study, homogeneous porous amidoxime resins were developed using microfluidic and non-solvent-induced phase separation methods, and subsequent modification by crosslinking and grafting. The adsorption results show that the static adsorption capacity of Ga(III) and V(V) under 0.5 mg/mL, 25 °C at 60 min was 25.97 mg/g and 8.09 mg/g, respectively. Ga(III) adsorption followed the pseudo-second-order model, reaching a saturation adsorption capacity of 38.61 mg/g. The Langmuir model effectively described Ga(III) adsorption, with a maximum capacity of 92.1 mg/g. The mechanism showed Ga(III) adsorption was solely influenced by the oxime group. The separation factor for Ga(III) and V(V) was 120, and desorption efficiencies for Ga(III) and V(V) were 89.79% and 6.81% in the 1 M HCl and 0.2 M thiourea solution at 10 min, respectively. Furthermore, the hydrazine amidoxime crosslinked polyacrylonitrile resins maintains a gallium adsorption capacity of 19.40 mg/g after five times, which are promising for separating Ga(III) and V(V) in waste solutions.

Sb2S3 Thin-Film Solar Cells Fabricated from an Antimony Ethyl Xanthate Based Precursor in Air.

The rapidly expanding demand for photovoltaics (PVs) requires stable, quick, and easy to manufacture solar cells based on socioeconomically and ecologically viable earth-abundant resources. Sb2S3 has been a potential candidate for solar PVs and the efficiency of planar Sb2S3 thin-film solar cells has witnessed a reasonable rise from 5.77% in 2014 to 8% in 2022. Herein, the aim is to bring new insight into Sb2S3 solar cell research by investigating how the bulk and surface properties of the Sb2S3 absorber and the current-voltage and deep-level defect characteristics of solar cells based on these films are affected by the ultrasonic spray pyrolysis deposition temperature and the molar ratio of thiourea to SbEX in solution. The properties of the Sb2S3 absorber are characterized by bulk- and surface-sensitive methods. Solar cells are characterized by temperature-dependent current-voltage, external quantum efficiency, and deep-level transient spectroscopy measurements. In this paper, the first thin-film solar cells based on a planar Sb2S3 absorber grown from antimony ethyl xanthate (SbEX) by ultrasonic spray pyrolysis in air are demonstrated. Devices based on the Sb2S3 absorber grown at 200 °C, especially from a solution of thiourea and SbEX in a molar ratio of 4.5, perform the best by virtue of suppressed surface oxidation of Sb2S3, favorable band alignment, Sb-vacancy concentration, a continuous film morphology, and a suitable film thickness of 75 nm, achieving up to 4.1% power conversion efficiency, which is the best efficiency to date for planar Sb2S3 solar cells grown from xanthate-based precursors. Our findings highlight the importance of developing synthesis conditions to achieve the best solar cell device performance for an Sb2S3 absorber layer pertaining to the chosen deposition method, experimental setup, and precursors.

The comparison of gold extraction methods from the rock using thiourea and thiosulfate

AbstractGold extraction from the rock is generally carried out using mercury. However, the high toxicity of mercury has a very dangerous impact on the environment and health. Various efforts have been made to reduce the use of mercury in gold extraction, one of which is the leaching method using thiosulphate and thiourea solution because they have low toxicity and are environmentally friendly. This study aimed to determine the results of gold extraction with thiosulphate and thiourea solution and determined the optimum concentration and time of extraction. The yield of the gold extract with thiosulphate solution was greater than that of thiourea solution. The thiosulphate solution had an optimum concentration of 0.3 M and an optimum time of 2 h. While the thiourea solution had an optimum concentration of 0.2 M and an optimum time of 3 h. The results of the Friedman test on the leaching time and concentration parameters show that leaching time has a significant effect on the Au leaching process, and the concentration parameter does not affect the Au leaching process from solid samples.

New upstream solution for mercury removal from petroleum condensate via HFMC: Thermodynamics, kinetics, DFT and mass transport

This work presents a new solution for the removal of mercury from petroleum condensate via hollow fiber membrane contactor (HFMC), which follows the principles and practices of solvent extraction. Results demonstrate that mercury can be successfully removed from petroleum condensate feed by the synergistic mixture solution of HCl and thiourea as extractant. Under equal circulating flow rates of 1.67 cm3 s−1 of feed and the synergistic extractant (0.5 mol dm−3 HCl and 1.5 mol dm−3 thiourea) at 323.15 K, the percentage of mercury removal reached 98.4%. The values of ∆H° (120 kJ mol−1), ∆S° (0.37 kJ mol−1) and ∆G° (−1.15 kJ mol−1) indicate that the reaction is endothermic, irreversible and spontaneous at 323.15 K, respectively. The results of Fourier-transform infrared spectroscopy (FTIR) confirm that mercury has been removed and is consistent with the obtained reaction mechanism from density functional theory (DFT). To describe the mass transport through HFMC, two mass transport mathematical models corresponding to reaction flux and diffusion flux are considered. The reaction flux model is seen to fit in well with the experimental results. The mass transfer coefficients in the membrane phase (km) and shell side (ks) are 7.45 × 10−6 cm s−1 and 2.09 × 10−5 cm s−1, respectively indicating that the mass transfer in the membrane phase is the controlling step.

Effect of metal ions on gold adsorption onto activated carbon in the acidic thiourea solution: Experiment study and DFT calculation

Thiourea leaching has been regarded as a promising method to substitute cyanidation for gold recovery from ores or concentrates. Activated carbon used in traditional cyanide leaching solution can also be used for gold recovery from thiourea leaching solution. In this paper, the effect of metal ions including Cu2+, Ag+, Pb2+ and Zn2+ on gold adsorption onto activated carbon from acidic thiourea solution was studied for the first time. Results showed that the adsorption process of activated carbon for gold can be well described by the Freundlich isotherm model, and followed the Pseudo-second kinetic model. The adsorption of gold onto activated carbon in thiourea solution may be a ligand exchange reaction. The S of the activated carbon is the electron-accepting atoms, which can form the bond of Au-S with Au in Au[CS(NH2)2]2+. The presence of Pb2+ and Zn2+ did not interfere gold adsorption at gold concentration of 5 mg/L, but hindered gold adsorption at gold concentration of 100 mg/L. When Cu2+ and Ag+ were added in the whole studied concentration range, the gold adsorption could be significantly declined. The adsorption capacity of gold onto activated carbon in the presence of metal ions followed the sequence of Cu2+ < Ag+ < Pb2+ < Zn2+ < no addition of metal ions. Meanwhile, metal ions also adsorbed onto activated carbon, and their adsorption capacity on activated carbon obeyed the descending order of Cu2+ > Ag+ > Pb2+ > Zn2+, consistent with the complexing ability of metal ions with thiourea. The decrease of active site of activated carbon occupied by metal ions was responsible for the decrease of gold adsorption. Based on the DFT analysis, it can be inferred that the ability of metal ions to lose electrons caused the different influence of metal ions on gold adsorption.

Role of foreign ions in the thiourea leaching of gold

Thiourea, as an environmentally friendly gold lixiviant, has the potential to replace highly toxic cyanide. The effect of foreign ions including Cu2+, Ag+, Pb2+, Zn2+, AsO33− and AsO43− on gold leaching in an acidic thiourea solution was investigated in this paper. Leaching results showed that the foreign ions had an adverse effect on thiourea leaching of gold. The gold dissolution (except low Pb2+ concentrations, i.e., < 20 mg/L) and thiourea stability both were in order of no foreign ions ≈ Zn2+ > Pb2+ > AsO33− > AsO43− > Ag+ > Cu2+. The thiourea dissolution of gold could be improved at low concentrations of Pb2+ (<20 mg/L), although the thiourea consumption was also increased. The thermodynamic analysis and the scanning electron microscope (SEM) and X-ray photon spectroscopy (XPS) analyses suggested that the foreign ions resulted in insignificant changes in the corrosion characteristics of leached gold surface and the quantity and chemical state of surface species. The possible mechanism for the effect of foreign ions on thiourea leaching of gold was proposed that the thiourea consumption in the presence of foreign ions was significantly increased, leading to the marked deterioration of thiourea dissolution of gold.

Mass spectrometry of complex compound of bis-thiourea-lead (II) chloride

Complex compounds of lead salts and thiourea are of interest due to the possibility of their practical application as precursors in the deposition of metal sulphide films. It is relevant to establish the relationship between the composition and structure of the initial complex compounds and the structure of the sulphides formed as a result of their thermal destruction. This paper presents the results of studying the complex compounds formed in an aqueous solution of lead chloride and thiourea. The structure of the complex compounds was determined by matrix-assisted laser desorption/ionisation mass spectrometry. The mass spectrometry data confirmed the formation of the [Pb((NH2)2CS)2Cl2] complex in the solution, which is a precursor in the deposition of PbS films. It was demonstrated that mass spectrometry fragmentation of the molecular ion of the [Pb((NH2)2CS)2Cl2] compound leads to the formation of a lead sulphide ion. The obtained data confirm the formation of the lead-sulphur bonds in the inner sphere of the complex compound, which are fragments of the crystal structure of the prospective sulphide formed during the thermolysis of the complex.

Extraction properties of 4-[(hexylsulfanyl)methyl]3,5-dimethyl-1-phenyl-1&lt;i&gt;H&lt;/i&gt;-pyrazole in the palladium(II) recovery from nitric acid solutions

Palladium(II) extraction from nitric acid solutions with a complex-forming reagent, 4-[(hexylsulfanyl)methyl]-3,5-dimethyl-1-phenyl-1 H -pyrazole, was studied using chloroform as a diluent. The reagent extracts Pd(II) with high efficiency from 0.5-5 M. HNO3 solutions. It has been established that palladium(II) is extracted from 2 M. HNO3 solutions by a coordination mechanism with the formation of the extracted compound [Pd(NO3)2μ-L] n ( n &gt; 2). Palladium(II) is quantitatively stripped with a nitric acid solution of thiourea. The reagent is promising for the concentration of Pd(II) from nitric acid solutions and its highly selective separation from Fe(III), lanthanides(III), Al(III), Cu(II), and Ni(II).

New compound N-methyl-N-isopropyl octanthioamide for palladium selective extraction and separation from HCl media

To seek more efficient extractant for Pd recovery from leaching solution of spent automotive catalysts, a new compound N-methyl-N-isopropyl octanthioamide (TA-813) was synthesized and characterized through FT-IR, 1H NMR, ESI-MS and elemental analysis. Its extraction and stripping behaviors for Pd were studied. To evaluate its reusability performance, extraction−stripping cycles were carried out. Finally, TA-813 was applied to separating Pd from simulated leaching solution of spent automotive catalysts. TA-813 shows fast extraction kinetics, high extraction efficiency and specific selectivity for Pd. During extraction two TA-813 molecules coordinate with one Pd. The loaded Pd in the organic phase is efficiently stripped by neutral and acidic thiourea solutions. TA-813 shows no loss in activity after eight extraction−stripping cycles. Even from simulated leaching solution of spent automotive catalysts, in which the concentrations of some purities (La, Ce, Mg, Al) are much higher than that of Pd, Pd is still selectively extracted.

Use of a simple magnetic material for the determination and speciation of very low amounts of silver and gold

Silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) can be separated of their ions by a magnetic dispersive micro-solid phase extraction procedure using non-functionalised ferrite particles. The separation and speciation are based on careful control of the acidity of the medium, without involving oxidation-reduction processes. Thus, using a small amount of ferrite particles (2 mg for a typical 10 mL sample) which is added to the sample as a suspension, Ag(I) as well as both gold species are retained in the sorbent at pH 4, while AgNPs are retained at pH 8. For the selective retention of AuNPs, ammonium diethyl dithiophosphate is added to the medium and the extraction process is repeated at pH 4. In all cases, the analytes are desorbed by treating the solid phase separated by the magnet with 0.1 mL of a thiourea solution at pH 3 and determined by electrothermal atomization atomic absorption spectrometry. For the measurement of silver, a palladium salt is used as a chemical modifier. This is not required for the determination of gold. The enrichment factor is 97 and the detection limits are 12 and 4 ng L−1 for gold and silver, respectively. The reproducibility is close to 5% for the four analytes studied. The reliability of the procedures is checked by standard additions and by the use of four standard reference materials with certified total silver content. Several water samples are analysed, and speciation results are given.

A novel post coordination modulation method to synthesize N/S functionalized ZIF-8 for removal of trace heavy metals from drinking water

The functionalization of metal–organic frameworks (MOFs) has been considered an effective strategy for promoting heavy metals removal from water. Therefore, a novel post coordination modulation method was systematically studied to synthesize ZIF-8 functionalized by 2,5-Dimercapto-1,3,4-thiadiazole (Post-ZIF-8-DMTD) for trace heavy metals removal from drinking water. The effects of addition time and addition amount of DMTD on the structure and adsorption performance of Post-ZIF-8-DMTD were investigated. It was found that addition time of DMTD had minor impact, while addition amount of DMTD had great impact, appropriate DMTD addition amount (375 mg) could not only provide sufficient active sites but also avoid self-polymerization of DMTD. Post-ZIF-8-DMTD exhibited a more regular structure than Before-ZIF-8-DMTD synthesized by direct coordination of mim and DMTD with Zn2+, and had faster adsorption rate and deeper purification capability for trace Pb(II). Post-ZIF-8-DMTD also exhibited good stability, wide suitable pH range, high maximum adsorption capacity (4.34 mg/g) that met WHO effluent Pb(II) concentration standard and excellent capture capacity for many trace heavy metals in tap water, and could be regenerated effectively with thiourea solution. The post coordination modulation method provides a novel and efficient strategy for the functionalization of MOFs, and Post-ZIF-8-DMTD has excellent application prospects in drinking water purification.

Characteristics of 2-chloropyridine and thiourea condensation. Structure of the as-formed products and their effect on coating properties during electrochemical nickel plating

The synthesis and spectral characterisation of 2-pyridylisothiuronium chloride were performed by regulating the rate of feeding 2-chloropyridine into a thiourea solution in ethyl alcohol for ensuring its low concentration in the reaction zone. According to the data of NMR spectroscopy (1H,13С,15N), the obtained compound represents an approximately equimolar mixture of two tautomers: the expected isothiuronium salt and pyridinium chloride with an isothiocarbamide substituting group in the 2nd position. The ability of isothiuronium salt to transit tautomerically to pyridinium salt is determined by the presence of two main centres, including nitrogen atoms of the isothiourea unit and a nitrogen atom of the pyridine ring. A quantum chemical analysis performed using the DFT method showed that the free energy values of the tautomers were similar, with the tautomer protonated on the nitrogen imido-atom being 2.9 (in the gas phase) and 4.7 kcal/mole (taking into account the dimethyl sulphoxide solvent DMSO at the PCM level) more advantageous as compared to the pyridinium salt. A small difference in the tautomer energies determines their formation in an approximately equimolar quantity. A rapid addition (5–10 mL/min) of 2-chloropyridine to the thiourea solution in the reaction zone creates the surplus of the reagent, acting as a base and causing splitting of the isotiuronium salt. This leads to an additional formation of bis(2-pyridyl)sulphide in the reaction medium, representing a valuable ligand for obtaining coordination compounds. The synthesised mixture of tautomers was examined as an additive to the standard nickel-plating electrolyte. In the concentration of 0.3–0.5 g/L, this additive ensured the production of bright low-porous nickel coatings at a sufficiently high current density of 5–10 A/dm2 and a current yield of 98–99 %.