Thiourea Solution Research Articles

Determination of cobalt in food by magnetic solid-phase extraction (MSPE) preconcentration by polyaniline (PANI) and polythiophene (PTH) coated magnetic nanoparticles (MNPs) and microsample injection system – flame atomic absorption spectrometry (MIS-FAAS)

Magnetic nanoparticles (MNPs) named Fe3O4@coPANI-PTH were synthesized by coating Fe3O4 nanoparticles (NPs) with a polyaniline (PANI)/polythiophene (PTH) co-polymer. The feasibility of Fe3O4@coPANI-PTH as the nanosorbent for magnetic solid-phase extraction (MSPE) was evaluated for the determination of Co(II) in real samples using microsample injection system – flame atomic absorption spectrometry (MIS-FAAS). Parameters (sample pH, adsorbent mass, eluent volume, sample volume, and co-existing ion effects) influencing the preconcentration of cobalt were optimized. Under the optimum conditions at pH 10, cobalt was completely adsorbed by 100 mg Fe3O4@coPANI-PTH from 60 mL sample and eluted quantitatively (≥ 95%) using 1.0 mL of 0.2% thiourea solution in a mixture of 2 mol L−1 HCl and 1 mol L−1 HNO3. The adsorption capacity and characteristics of Fe3O4@coPANI-PTH for cobalt were evaluated with isotherm studies. The accuracy of the optimized method was evaluated by measuring certified reference materials (CRMs) and spiked real samples. The relative error and standard deviation were below 6.0% for the CRM and real sample analyses. The limit of detection was 1.6 μg L−1. The determination of ultra-trace cobalt amounts in various soft drinks, spice, vegetable, and water samples was achieved satisfactorily with this method.

Bio-Oxidation of a Double Refractory Gold Ore and Investigation of Preg-Robbing of Gold from Thiourea Solution

Carbonaceous sulfidic gold ores are commonly double refractory and thus require pretreatment before gold extraction. In this paper, the capacity of pre-bio-oxidation can simultaneously decompose sulfides or deactivate carbonaceous matters (CM) from a double refractory gold ore (DRGO) using pure cultures of A. ferrooxidans or L. ferrooxidans, and a mixed culture containing A. ferrooxidans and L. ferrooxidans was investigated. The results showed that direct thiourea leaching of the as-received DRGO yielded only 28.7% gold extraction, which was due to the encapsulation of sulfides on gold and the gold adsorption of CM. After bio-oxidation, thiourea leaching of the DRGO resulted in gold extraction of over 75–80%. Moreover, bio-oxidation can effectively reduce the adsorption of carbon to gold. XRD, SEM-EDS and FTIR analysis showed that many oxygen-containing groups were introduced on the surface of DRGO during bio-oxidation, while the C=C bond was cleaved and the O–C–O and C–N bonds were degraded, causing a decrease in active sites for gold adsorption. Moreover, passivation materials such as jarosite were formed on the surface of DRGO, which might reduce the affinity of CM for gold in solutions. In addition, the cleavage of the S–S band indicated that sulfides were oxidized by bacteria. This work allows us to explain the applicability of pre-bio-oxidation for degrading both sulfides and CM and increasing gold recovery from DRGO in the thiourea system.

Light-activated polydopamine coatings for efficient metal recovery from electronic waste

Metal ion adsorption from industrial wastewater has received increasing attention for the elimination of heavy metals and selective recovery of precious metals. Among the precious metals found in E-waste, gold has attracted considerable attention because of its wide range of practical applications and high economic value. However, the adsorbents used at present for the recovery of precious metals have very low adsorption capacity and poor metal selectivity for commercial uses. Herein, we introduce a new photochemical route for the selective and efficient adsorption of gold ions using bio-inspired metal-philic coatings. Internal surfaces of the mesoporous polymer microspheres were coated with polydopamine via the oxidative polymerization of catecholamines. The polydopamine layer served as a selective photo-active reductant for gold ions. Under 1-sun simulated illumination, the polydopamine layer selectively reduced gold ions to generate metallic gold nuclei. Moreover, once the metallic gold nanostructures were formed, localized surface plasmon further enhanced the reduction of gold ions. The combined effects increased the maximum amount of gold ions adsorbed per unit mass of the adsorbent up to 26 times compared to that in the dark. The adsorbed metallic gold was re-dissolvable in a thiourea solution for the complete recovery of gold ions. The selectivity toward gold ions among various metal ions was demonstrated using a solution mixture containing eight different metal ions that are commonly found in industrial wastewater. Density functional theory calculations revealed that reduction of gold on the polydopamine layer was energetically favorable, while the reduction of other metal ions was not. The dramatic increase in the maximum adsorption capacity and selectivity owing to the combined effect of the photochemical activation and polyphenol chemistry renders this process a promising approach toward urban mining of novel metal ions from electronic wastes.

Effects of Thickness on Optical and Structural Properties of Lead Sulphide (PbS) Thin Film Prepared by Chemical Bath Deposition (CBD)

Nanocrystalline PbS thin films were deposited on glass substrates with various deposition times using chemical bath deposition technique. PbS thin films were prepared by using a solution of Lead nitrate and thiourea by using NaOH salt as a complexing agent and ammonia solution as a pH adjuster at 65 0 C. The study was carried out for thickness in the range of (0.16-1.03m). The structural properties were carried out by X-ray diffraction (XRD). The X-ray diffraction patterns reveal that the films exhibit the cubic face centered structure. The crystalline sizes of the films increased with increasing film thickness. The morphological properties were studied by SEM and showed that films were well adherent to the substrate, uniform, small crystal size and covered the entire substrate surface completely. The optical properties of these films have been studied and show that PbS thin films have the values of energy gap varied between (0.88-1.34 eV) with increasing film thickness. Keywords: CBD, XRD, band gap, PbS thin film DOI: 10.7176/CMR/12-7-01 Publication date: September 30 th 2020

MoS2/graphene/carbonized melamine foam composite catalysts for the hydrogen evolution reaction

A melamine-based carbon foam was obtained from a melamine foam (2×2×2 cm3), which was then coated with graphene by immersing it in 400 mL of a suspension of reduced graphene oxide in water with concentrations of 25 to 100 mg/L. MoS2/graphene/carbonized melamine foam composites for use as catalysts for the hydrogen evolution reaction were synthesized by the hydrothermal growth of MoS2 nanosheets on the graphene-coated carbon foams in a mixed solution of molybdic acid disodium salt and thiourea. Results indicate that MoS2 nanosheets with a thickness of 15–20 nm were uniformly distributed on the three-dimensional carbon foam substrates coated with different amounts of graphene. The amount of graphene coating has a great influence on the hydrogen evolution performance. The composite prepared with a graphene concentration of 25 mg/L has the best electrochemical performance, its initial overpotential at a 10 mA cm–2 current density is 163 mV, and the corresponding Tafel slope is 76 mV dec–1. It has also the lowest impedance, which shows that coating the carbon foam with an appropriate amount of reduced graphene oxide accelerates electron migration and improves the hydrogen evolution performance.

Pit-Induced Electrochemical Layer Dissolution and Wave Propagation on an Au(111) Surface in an Acidic Thiourea Solution

The mesoscopic evolution of the electrochemical dissolution of a Au(111) facet in acidic thiourea solutions was studied with an in situ electrochemical atomic force microscopy (EC-AFM). At the open...

2-Mercaptobenzimidazole derivative of chitosan for silver sorption – Contribution of magnetite incorporation and sonication effects on enhanced metal recovery

The recycling of precious and strategic metals from secondary resources (including E-wastes) is of critical importance for the recovery of scarce metals widely used in High-Tech devices. Therefore, the development of efficient and selective sorbents is of great importance. The grafting of 2-mercaptobenzimidazole onto chitosan microparticles allows developing highly selective sorbents. The incorporation of magnetite particles is also a strategic aspect for facilitating the use and recovery of microparticles. Sonication (at two different frequencies: 37 kHz and 80 kHz) shows high potential for improving both kinetic and thermodynamic aspects associated with silver uptake on 2-MBI-chitosan materials. Sorption capacities as high as 3 mmol Ag g−1 can be obtained with contact times as low as 20–30 min. The sorption isotherms are successfully fitted by the Langmuir and the Sips equations, while the kinetic profiles are modeled using the pseudo-second order rate equation and the resistance to intraparticle diffusion. The sorption process is exothermic: the sonication (and the frequency of sonic generator) strongly changes the thermodynamic parameters. The sonication also speeds up metal desorption, which is highly efficient using acidic thiourea solutions: the sonication allows also reducing the concentration of thiourea in the eluent required for complete silver elution. The sorbent shows remarkable stability is terms or sorption and desorption for five successive recycling runs. The acid leachates of printed circuit board are efficiently treated with the 2-MBI-chitosan sorbent for the recovery, enrichment and separation of precious metals (Ag, Au and Pd) from base metals (major elements: iron copper, aluminum, tin).

Formation of CZTSSe absorber layer using thiourea treatment of CZTSe

In the present work, CZTSe (Cu 2 ZnSnSe 4 ) films were deposited by Thermal evaporation technique. The as deposited films were annealed at 450 °C for 10 min. To incorporate Sulfur in the CZTSe film and to replace some of the Se by S, the films (as deposited and annealed) were treated with Thiourea solution (1 Molar). Further the films were annealed at 450 °C for 10 min after the thiourea treatment. Finally the films were characterized for phase analysis using XRD and Raman. The composition analysis was done using EDXRF. The band gap of the film varies according to the S/Se ratio. Compositional analysis as obtained from ED-XRF, shows the required ratio of Cu/(Zn + Sn) < 1 and Zn/Sn > 1 for all the films. The conductivity and mobility of the films changes with variation in sulfur and selenium ratio. The obtained electrical and optical properties of CZTSe absorber layer after thiourea treatment are suitable for device application .

Fast and effective recovery of Au(III) from aqueous solution by a N-containing polymer

In this work, a N-containing polymer was successfully synthesized by one-step treatment with 3-amine-1,2,4-triazole ligands and Zn(II) using the thermal solvent method, and employed to recover Au(III) from water. The adsorption kinetics was comprehensively studied through kinetics models including pseudo-first-order model, pseudo-second-order model, moving boundary model and Weber-Morris model. It is found that the overall adsorption rate was determined by chemical adsorption, and the rate-limiting step of diffusion steps is film diffusion. Rising temperature can improve the adsorption rate significantly, making the adsorption equilibrium time be reduced from 6 h at 298 K to 2 h at 318 K. The adsorption isotherm can be described well by Sips model, indicating it is a heterogeneous adsorption. The material shows high adsorption capacity towards Au(III) up to 1073 mg/g. It shows strong affinity towards Au(III) in the mixture solutions containing Au(III), Cu(II), Zn(II), Co(II), Cd(II), Pb(II) and Ni(II) ions. The material can be easily and completely desorbed by thiourea solution and still maintains its adsorption performance only with a slight decrease after three cycles. Combined with studies on pH influence, adsorption kinetics, adsorption isotherm and XPS analysis, it can be concluded that the adsorption mechanism could be attributed to electrostatic interaction, the coordination of the Zn–OH and -C-N/-CN- with Au(III), and partial reduction of Au(III) to Au(I) by –NH group on the polymer. The N-containing polymer is an excellent candidate for Au(III) recovery efficiently and selectively from aqueous solution.

Enhanced adsorption properties of zirconium modified chitosan-zeolite nanocomposites for vanadium ion removal

The novel hybrid adsorbents, which were composed of nanozeolite and nanochitosan (NZ@NCT) and nanozeolite-multi walled carbon nanotube and nanochitosan (CNZ@NCT) were produced by simple method. The adsorption capacity of synthesized nanocomposites towards vanadium (V) was compared with that of a clinoptilolite-nanochitosan nanocomposite (CPL@NCT) obtained from natural zeolite. Zirconium (Zr) was employed to modify prepared nanocomposites because Zr (IV) has a strong affinity towards oxyanions such as V. Zr-modified nanocomposites and their pristine nanocomposites were comparatively characterized by different techniques. Batch experiments were conducted to find out the influence of different experimental factors. The adsorption capacities of all prepared materials towards V ions decreased with temperature increasing from 298 to 348 K. The calculated values of the thermodynamic parameters ΔH and ΔG demonstrated that the adsorption was exothermic and spontaneous. The adsorption process was described by the Freundlich isotherm and pseudo-second order model. The V species loaded nanocomposites could be regenerated by 0.5 M HCl–1.0 M thiourea solution. The adsorption performance was not considerably influenced by the coexistence of the nickel ( Ni2+) but nitrate (NO3−) and sulfate (SO42−) revealed slightly greater negative effects. The as-prepared nanocomposites can be used in three adsorption cycles without specific changing its adsorption efficiency.

Design, synthesis, and study of Pd(II) ion-imprinted functionalized polymer.

Selective metal ions' extraction and recovery has various applications in the analytical field. Metal ions need to be extracted, detected, and quantified. For that purpose, ion-imprinted polymers have earned a great deal of attention during the past two decades. Pd2+ ion-imprinted hollow silica particles including an isatin Schiff base were prepared by Schiff base condensation of (3-aminopropyl)triethoxysilane and isatin. The prepared Schiff base ligand was coordinated to the target Pd2+ cations, the polymerizable Pd-complex was set aside to form gel in the company of tetraethoxysilane and the target Pd2+ cations were subsequently removed from the cross-linked silica network by means of acidified thiourea solution. All materials throughout this synthesis process were investigated utilizing mass spectrometry, elemental analysis, FTIR, and 1H-NMR. The morphological structure of both Pd2+ ion-imprinted and non-ion-imprinted silica polymer were pictured by scanning electron microscopy. Several batches were studied exploiting both Pd2+ ion-imprinted and non-ion-imprinted silica polymer to test their functionality for selective extraction of Pd2+ cations in multi-ionic solution of Ni2+, Co2+, Cu2+, Mn2+, and Pd2+.

Highly selective extraction of palladium from spent automotive catalyst acid leachate using novel alkylated dioxa-dithiacrown ether derivatives

Novel macrocyclic extractants were synthesized and employed in liquid–liquid extraction (LLE) for palladium/platinum (Pd/Pt) separation in aqueous feed source. Dioxadithia-benzo-crown ether diols (BCES2O2) 2g–2i were prepared through bis-epoxide cyclization with aqueous 1,2-benzenedithiol under mild basic conditions. For improved miscibility and stability in the organic diluent (i.e. toluene), 2g–2i were alkylated to afford dimethoxy-BCES2O23g–3i. LLE experiments reveal their high stability, extraction efficiency, and separation performance (βPd2+/Pt2+=104−105) in highly acidic feed solutions (∼6M HCl). The most suitable extractant 3i followed a 1:1 3i-Pd2+ complex with stability constant Kex∼105. Density functional theory calculations reveal that the rigid cavity size (1.58–1.65Å) of 3i is ideal for Pd2+ (1.56Å) in forming S4 coordination geometry. The Pd2+ can be repeatedly extracted by 3i [in toluene] and stripped by 1M HCl+0.15M thiourea solution without performance deterioration. Each cycle can be accomplished <1h based on the derived extraction (kex=0.038min−1) and stripping (kstrip=0.063min−1) rate constants. The high extraction efficiency (99.5%) and purity (98.5%) of recovered Pd2+ from simulated acidic spent automobile catalyst liquor demonstrate the potential of 3i [in toluene] LLE system for selective Pd2+ recovery from automotive wastes.

Electrochemical adsorption and passivation on gold surface in alkaline thiourea solutions

An electrochemical method was used to examine Au surface absorption and passivation under the most commonly employed pH conditions in an alkaline Au leaching system. The polarization at different pH values was obtained through the current step curve. At pH 10, no absorption layer was formed. When the pH was increased to 11, an absorption layer was formed through the Au electrode reaction. At pH 12, the entire system could not be stabilized, even after long durations because of the thiourea oxidation and decomposition. The samples were analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM). AFM observations of the Au plating surface and SEM–EDS analyses for the Au-coated graphite surface indicated that a passivation membrane was formed on the Au surface after its use in the alkaline thiourea Au leaching system. Two-step leaching was used to confirm the conclusions drawn from the experimental results. The two-stage experimental results further confirmed the existence of a passivation membrane.

Investigation of absorber and heterojunction in the pure sulphide kesterite

This paper aims to study the properties of the absorber layer and the heterojunction in kesterite solar cells. The Cu2ZnSnS4 (CZTS) thin films were layered on a glass substrate from a colloidal solution of metal salts and thiourea dissolved in a mixture of water and ethanol and deposited by spin coating technique. The samples were then heat treated in a furnace, in the presence of sulphur powder and under a nitrogen gas flow. The results revealed the formation of homogeneous layers of a pure kesterite phase of CZTS crystallites after heat treatment with correct stoichiometry and oxidation states. The optical transmission measurements indicate an energy band-gap of 1.4eV and an absorption coefficient of 104cm−1. These CZTS thin films, elaborated by spin coating process, were integrated for electronic properties evaluation in a heterojunction in the following configuration: SnO2:F (FTO) and Molybdenum as back contact, CdS as tampon and the CZTS film as absorber layer. The band alignment at the CdS–CZTS heterojunction indicates a cliff-like conduction band offset (CBO) even close to be a flat band.

Mechanism of a catalytic silver(I)-complex: assisted electroless deposition of inductance coil on poly(ethylene terephthalate) film

In this work, silver nitrate, thiourea, bisphenol A diglycidyl ether (BADGE), and propylene glycol methyl ether (PM) were selected for designing a silver(I)-complex to trigger the deposition of inductance coil on PET film through electroless copper plating. The most stable silver(I)-complex structure is formed when the ratio of thiourea molecules and silver ions is 3 to 1 by quantum chemical calculations based on density functional theory (DFT). Meanwhile, XRD test demonstrates that the white precipitate crystallized from PM solution of thiourea and silver nitrate is [Ag(SC(NH2)2)3]NO3, which is consistent with theoretical calculations. The cross section of PET film with copper patterns and interconnection holes characterized by metallurgical microscope proves that the silver(I)-complex is able to initiate copper deposition on the surface and through hole wall of PET film. The measured inductance values at operating frequency from 1 to 50 MHz indicate that the fabricated flexible inductor is capable of being integrated into flexible electronics when the bending angles are within 45°. Additionally, the inductor can also be utilized as an angel sensor when the bending angles are in the range of 60° to 180° at 10 MHz.

Selective adsorption of Pd (II) by ion-imprinted porous alginate beads: Experimental and density functional theory study

In this study, a novel thiourea grafted porous sodium alginate-based adsorbent was synthesized by combining ion-imprinting and direct templating method. Due to ion-imprinting, the prepared adsorbent has demonstrated outstanding selectivity towards Pd (II) from bi-metallic solution at different pH values. Langmuir and both pseudo-first and pseudo-second kinetic equations were used to describe the adsorption isotherm and kinetics, respectively. FT-IR, XPS, and SEM-EDX analyses suggested that selective adsorption of Pd (II) was dominated by electrostatic interactions at pH 1.0 and chelation on imprinted sorption sites at pH 3.0. Density functional theory (DFT) calculation further explained the effect of ion-imprinting and provided two binding configurations, which is consistent with characterization analyses. The pregnant adsorbent can be regenerated and reused by thiourea solution in dilute hydrochloric acid. Therefore, the synthesized adsorbent would be useful as a selective adsorbent for the enrichment of Pd (II) from effluents.

Method development for determination of trace amounts of palladium in environmental water samples by ICP-MS/MS after pre-concentration on thiol-functionalized MCM-41 materials

The anthropogenic cycle of Pd in the environment, its fate and impact is still unknown due to limitations of measurement techniques. For separation and pre-concentration of Pd(II) ions, mesoporous silica materials MCM-41 were synthesized and functionalized with different amounts of 3-mercaptopropyltrimethoxysilane (MPTMS) by co-condensation and grafting methods. The structural and textural properties of materials were characterized using XRD, TEM, SEM and BET techniques. The results proved that functionalization with thiol groups did not significantly affect structural and textural parameters of synthesized sorbents. The Pd(II) ions were quantitatively retained on sorbents functionalized by grafting in acidic solutions (pH 2), efficiently eluted with 0.1 mol L−1 thiourea solution in 1 mol L−1 HCl and determined by electrothermal atomic absorption spectrometry (ETAAS). The limit of detection (LOD) of the developed SPE ETAAS method was 0.06 ng mL−1, and the pre-concentration factor was 30. For analysis of Pd in environmental water samples inductively coupled plasma mass spectrometry (ICP-MS) in MS/MS mode was used. Spectral interferences on 105Pd caused by the presence of Sr in water samples were eliminated using helium (5 mL min−1) or ammonia (7 mL min−1) gas in collision/reaction cell. The developed SPE ICP-MS method is characterized by good selectivity in the presence of interfering elements and chloride ions and detection limit of 0.0002 ng mL−1. Its accuracy was confirmed by analysis of spiked water samples. The application of ICP-MS together with efficient separation/pre-concentration of analyte on thiol-functionalized MCM-41 sorbents allows to determine Pd in environmental water samples at pg mL−1 level.

A simple method for determination of mercury (II) ions by PNBS-doped carbon dots as a fluorescent probe

A simple and efficient fluorometric method is described for detecting mercury (II) ions. Carbon quantum dots doped with nitrogen, sulfur, phosphorus, and boron were prepared by a one-step hydrothermal method for first time that involves heating of a solution of glucose, thiourea, boric acid, and phosphoric acid in an autoclave simultaneously for 5 h at 200° C. The carbon quantum dots with phosphorus, sulfur, boron, and nitrogen atom (PNBS-CQDs) are a viable probe for fluorometric detection of Hg2+. Unlike CQD-based probes reported so far, the addition of Hg2+ causes a decrease in fluorescence signal (with excitation/emission maxima at 450/530 nm). The probe has a linear response in the 25.0 μM to 1500.0 mM of Hg2+ concentration range with 5.0 µM (S/N = 3) and 16.5 µM for LOD and LOQ, respectively. The developed method was successfully applied for determining the mercury (II) ions in real samples.

Study of Ho doped Ag2S thin films prepared by CBD method

Abstract Ho doped Ag2S thin films were grown on the glass substrate by chemical bath deposition (CBD) method at room temperature. The bath contained aqueous solution of silver nitrate, thiourea, EDTA, ammonia and holmium nitrate. Silver nitrate was used as a silver (Ag+) ion source; thiourea as sulfur (S−) ion source, EDTA was a complexing agent while ammonia was used to maintain pH, Ho(NO3)3 was taken as a source of Ho ions. The optical absorption edge of undoped (pure) and Ho doped silver sulfide films was determined between 324 nm and 298 nm showing blue shift as compared to bulk Ag2S. Band gaps calculated from Tauc plot also showed an increase in values for doped samples. The increase in band gap indicates reduced particle size in the prepared Ho doped films. The photoluminescence emission peaks were observed at around 578 nm to 601 nm wavelength and excitation peaks were found at 351 nm to 294 nm for undoped and doped films. The SEM micrograph consists of globular ball type and flower type structures observed in the prepared films of Ho doped Ag2S.

Thermo-sensitive Hydrogel Incorporating Maleic Anhydride Modified Microcrystalline Cellulose

The thermo-sensitive hydrogel incorporating maleic anhydride modified mcirocrystalline cellulose was prepared by two steps. At first, the mixture of maleated and fumarated celluloses were produced by a solvent-free procedure, in which the biopolymer was added to molten maleic anhydride. Secondly, the photo-polymerization of n-isopropyl acrylamide (NIPAM) with the modified biopolymer was carried out in water/NaOH/urea/thiourea solution by using 1173 as the photo-initiator. The derivatives were characterized by FTIR and SEM. It was a clear temperature dependence on the volume of the grafted hydrogel in deionized water that generated by the coil-to-globule transition of poly (NIPAM) in aqueous media from the lower critical solution temperature (LCST) of PNIPAM to the upper critical solution temperature (UCST). From the absorbance of the gel to methylene blue, it was shown that the quasi-second-order kinetics could fit the experimental data well.