Brønsted-Lewis acidic ionic liquid-derived ZnS quantum dots: synthesis, characterization, and multifunctional applications in pollutant degradation and iodine sorption

A pair of Brønsted-Lewis acidic chlorozincate ionic liquids based on 2-alkyl-1,3-disulfoimidazolium cations (1a & 1b) was developed with complex anionic speciation [Zn2Cl6]2-/[ZnCl4]2-. These ionic liquids were further used as templates for fabricating ZnS quantum dots (QDs) via a grinding method. The ZnS QDs were characterized using various techniques. The use of ionic liquids (ILs) containing complex metal chloride anions resulted in small size and porous nature of the QDs. The presence of various types of defects was verified through XPS, EPR and photoluminescence spectroscopic analyses. These two QDs were used as reusable and recyclable catalysts for the degradation of a broad spectrum of pollutants such as crystal violet (CV), methylene blue (MB), malachite green (MG), morin hydrate, and oxytetracycline (OTC) under UV light irradiation. Free radical scavenging experiments showed that ˙OH and ˙O2- acted as primary reactive species during the degradation process. These QDs were further employed for iodine sorption experiments in water and hexane solutions. The XPS analysis revealed that the adsorption process occurred in molecular (I2) and polyiodide (I3-) forms. The recyclability study of the iodine sorption revealed that the QDs could retain 90.6% and 89.4% of their initial efficiency after the 5th cycle in water and hexane solution, respectively. No such reports regarding the use of Brønsted-Lewis acidic chlorozincate ionic liquids for the synthesis of mesoporous defective ZnS QDs has been published. Moreover, the utilization of the pristine ZnS QDs for iodine capture experiments is reported for the first time.

Controllable synthesize of ZnS/PbS nanostructure and their structural and morphological properties

ZnS is an appealing material with wide potential applications in optoelectronics, sensors, and photocatalysis due to its fascinating properties, low cost, and eco-friendly. In this paper, we report the synthesis of ZnS nanowires and nanorods via a simple thermal-evaporation method using different concentrations of PbS as a dopant. The prepared nanostrutures were investigated in detalis using a scanning electron microscopy (SEM), X-ray diffraction (XRD), and high resolution transmission electron microscopy (HRTEM). The results show that the fabricated ZnS nanowire/nanorod has a wurtzite (hcp) structure. In addition, based on the experimental results, the growth mechanism of the prepared nanostructures is reported. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray (EDX) mapping analyses confirmed that the ZnS nanorods were stoichiometric without impurities or defects, whereas PbS quantum dots were formed inside the high-quality nanowires. The formation mechanism of ZnS nanowires is discussed based on the vapor-liquid-solid (VLS) growth model. Results demonstrated that thermal evaporation is a simple and effective techniques for producing high-quality heterostructured ZnS nanowires with potential applications in different fields.

In-situ growth of zinc sulfide on the surface of alginate-based biomass carbon: A new material for removing methylene blue/basic fuchsin and copper ions

This work aims to prepare a composite adsorbent with a fixed shape to improve the performance of carbon materials and to solve the problem of adsorbent in powder form which is difficult to recycle after use. The BC-ZnS composite system was successfully prepared by hydrothermal method based on the preparation of biomass carbon (BC) using alginate (Alg), while the ZnS component was grown in-situ on the surface of BC. The effects of Alg, Zn source, hydrothermal temperature and time on the synthesis of BC-ZnS were explored, the results indicated that ZnS was successfully grown in-situ on the BC surface, while the BC maintained its original morphology. BC-ZnS showed excellent adsorption capacity for methylene blue (MB), basic fuchsin (BF), and copper ions (Cu2+), reaching 301.50 mg/g for MB and exhibiting good cyclic stability. The adsorption of MB/BF/Cu2+ by BC-ZnS was characterized by the presence of multiple forces, where the BC component mainly depended on the electrostatic force of Alg residue, while the ZnS involves electrostatic forces, ion exchange and Lewis acid/base soft-soft interactions. The adsorption process conforms to pseudo-first-kinetics and is a spontaneous entropy-increasing process. BC-ZnS can be a candidate for reusable wastewater treatment and has excellent potential for application.

Adsorption Study of Congo Red Dye from Synthetic Wastewater at Different Concentrations Using Zinc Sulfide Nanoparticles

Zinc sulfide (ZnS) nanoparticles were fabricated using the chemical precipitation method. The X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM) techniques were used to investigate the structural parameters of the formed ZnS. The hexagonal crystal structure of the Zn and ZnS phases was formed. The average crystallite size of the ZnS phase is 10.3 nm, which is much smaller than that of the Zn phase (54.5 nm). Several frequencies and phonon modes were detected in the Raman scattering spectrum belonging to the ZnS nanoparticles. The synthesized ZnS nanoparticles were used as catalysts to eliminate the Congo red (CR) dye, with different concentrations, from synthetic wastewater. The impact of the CR dye concentration and shaking period on the adsorption of CR was thoroughly investigated, and various adsorption kinetic models were tested. After 3 h of shaking, the adsorption efficiency reached 26.01% for 40 mg/L CR dye and 27.84% for 20 mg/L CR dye. The adsorption capacities of the CR dye in the presence of ZnS are 16% and 9% for 40 and 20 mg/L, respectively. Based on the correlation factor, the intraparticle diffusion kinetic model was considered the best of the tested models.

Photocatalytic Degradation of Single and Binary Mixture of Brilliant Green and Rhodamine B Dyes by Zinc Sulfide Quantum Dots

We present the preparation of octadecylamine-capped ZnS quantum dots from bis(morpholinyldithiocarbamato)Zn(II) complex. The complex was thermolyzed at 130 °C in octadecylamine at different times, to study the effect of reaction time on the morphological and photocatalytic properties of the ZnS quantum dots. Powder X-ray diffraction patterns confirmed a hexagonal wurtzite crystalline phase of ZnS, while HRTEM images showed particle sizes of about 1–3 nm, and energy band gaps of 3.68 eV (ZnS–1), 3.87 eV (ZnS–2), and 4.16 eV (ZnS–3) were obtained from the Tauc plot for the ZnS nanoparticles. The as-prepared ZnS were used as photocatalysts for the degradation of brilliant green, rhodamine B, and binary dye consisting of a mixture of brilliant green-rhodamine B. The highest photocatalytic degradation efficiency of 94% was obtained from ZnS–3 with low photoluminescence intensity. The effect of catalytic dosage and pH of the dyes solution on the photocatalytic process shows that pH 8 is optimal for the degradation of brilliant green, while pH 6.5 is the best for photocatalytic degradation of rhodamine B. The degradation of the binary dyes followed the same trends. The effect of catalytic dosage shows that 1 mg mL⁻¹ of the ZnS nano-photocatalyst is the optimum dosage for the degradation of organic dyes. Reusability studies show that the ZnS quantum dots can be reused five times without a significant reduction in degradation efficiency.

Ethylenediamine-assisted growth of multi-dimensional ZnS nanostructures and study of its charge transfer mechanism on supercapacitor electrode and photocatalytic performance

In recent years, much interest has been raised by materials with multi-purpose characteristics as the performance of electrochemical energy devices such as supercapacitors and photocatalytic activities depend strongly on the properties of materials. This study delineates various parameters like morphology, energy band gap, charge transfer resistance, different defect states, diffusion coefficient and functional groups adsorbed on the surface of material to assess the performance of supercapacitor electrodes and photocatalytic degradation efficiency of synthesised multi-dimensional ZnS nanostructures. Ethylenediamine (EN)-mediated multi-dimensional ZnS nanostructures were grown by the solvothermal route. One-dimensional (1D), 2D and 3D morphologies were obtained by varying the ratio of de-ionised water and EN, taken as 1:3, 1:2 and 1:1, respectively. The EN molecules effectively capped most of the surfaces of the ZnS nanoparticles formed, preventing agglomeration of nanoparticles due to the decrement in surface energy. The oriented attachment of these clusters resulted in the formation of 1D, 2D and 3D morphologies. The plausible chemistry in the formation of 1D, 2D and 3D nanostructures has been elaborated. Charge transfer properties of prepared electrodes have been examined using the electrochemical impedance spectroscopy (EIS) technique because better charge transfer causes diminishing electron/hole recombination and hence better photodegradation efficiency. Among the synthesised materials, the 2D nanostructure degraded the eosin Y dye to maximum 90.71% efficiency with rate constant 34 × 10^-3 min^-1. 2D nanostructures possess better charge transfer and hence better photodegradation efficiency. Various studies using methods of UV-vis, Fourier-transform infrared, Brunauer-Emmett-Teller, x-ray photoelectron spectroscopy and photoluminescence spectra are in good agreement with the obtained photodegradation results. After analysing cyclic voltammetry curves and EIS, a higher diffusion coefficient is obtained for 1D nanostructure material, hence a higher specific capacitance and higher energy density of 159.12 F g^-1 and 22.75 KWh kg^-1 are found in this case. Only 9% loss of specific capacitance is found after 1000 cycles, showing a relatively high cycling stability in 3D nanostructures. The excellent supercapacitive property can be attributed to the porous structure and high specific surface area. Thus, the synthesised multi-dimensional ZnS nanostructures are proved to be a potential candidate for both photocatalytic and supercapacitor electrode performance.

Selective removal of anionic dyes with exceptionally high adsorption capacity and removal of dichromate (Cr2O72-) anion using Ni-Co-S/CTAB nanocomposites and its adsorption mechanism

An adsorbent Ni-Co-S/CTAB nanocomposites have been synthesized at low temperature in aqueous medium using nickel acetate, cobalt acetate, thioacetamide and hexadecyltrimethyl ammonium bromide (CTAB) as reagents. The nanocomposites exhibited exceptionally high adsorption capacity towards anionic adsorbates with high selectivity. The maximum adsorption capacity of nanocomposites were 1995.02 mg g^-1 for Congo red (CR), 2223.15 mg g^-1 for Methyl orange (MO) anionic dyes and 790.69 mg g^-1 for Cr₂O₇^2- metal anion. They exhibit negligible adsorption ability towards cationic dyes 2.33 mg g^-1 for MB and 42.05 mg g^-1 for RhB. The nanocomposite is able to adsorb anionic dyes from a binary mixture of cationic and anionic dyes with high separation factor. It also shows good results with synthetic effluents. The removal of adsorbates followed modified Zhu and Gu isotherm model. FTIR and Zeta-potential measurement confirmed that electrostatic interactions are predominating factor for the adsorption of anionic adsorbates followed by hydrophobic interactions between adsorbates. Moreover, ethanol is used to regenerate the adsorbent and reused up to five times with good adsorption capacities. Thus, the nanocomposite can be used as an efficient adsorbent for the removal and seperation of anionic adsorbates from binary mixtures as well as synthetic effluents.

Controlled Fabrication of K2Ti8O17 Nanowires for Highly Efficient and Ultrafast Adsorption toward Methylene Blue

Advanced adsorbents need high adsorption rate and superior adsorption capability to clean up organic methylene blue (MB) from wastewater. We prepared K₂Ti₈O₁₇ nanowires grown along the [0 1 0] direction with a one-step hydrothermal method. The K₂Ti₈O₁₇ nanowires with tens of nanometers in diameter and tens of micrometers in length were achieved with smooth surfaces and twisted wire-like morphology. The K₂Ti₈O₁₇ nanowires exhibit high uptake capacity of ∼208.8 mg·g^-1 in the MB removal under equilibrium pH = 7. The adsorption equilibrium of MB onto the K₂Ti₈O₁₇ adsorbent is achieved with a 97% removal rate of MB within only ∼21 min, which is the shortest adsorption time among the recently reported inorganic adsorbents toward MB. The adsorption process has a good agreement with the well-known pseudo-second-order kinetic model (k₂ = 0.2) and the Langmuir isotherm model. Fourier transform infrared measurements suggest that the adsorption can be assigned to the hydrogen bonding and electrostatic attraction between MB and K₂Ti₈O₁₇. This ultrafast removal ability is due to the larger (0 2 0) interplanar spacing and zigzag surface structure of the nanowires, which provide abundant active adsorption sites. Thermodynamic parameters reflect the spontaneous, exothermic, and feasible uptake of MB. Besides, K₂Ti₈O₁₇ nanowires enjoy high adsorptive ability for chromium(VI) ions and photocatalytic removal toward NO. This work highlights the great significance of K₂Ti₈O₁₇ nanowires as a low-cost promising material used for the adsorptive elimination of organic contaminations in fast water purification on a large scale.

Defect-Enriched Nitrogen Doped-Graphene Quantum Dots Engineered NiCo2 S4 Nanoarray as High-Efficiency Bifunctional Catalyst for Flexible Zn-Air Battery

Flexible Zn-air batteries have recently emerged as one of the key energy storage systems of wearable/portable electronic devices, drawing enormous attention due to the high theoretical energy density, flat working voltage, low cost, and excellent safety. However, the majority of the previously reported flexible Zn-air batteries encounter problems such as sluggish oxygen reaction kinetics, inferior long-term durability, and poor flexibility induced by the rigid nature of the air cathode, all of which severely hinder their practical applications. Herein, a defect-enriched nitrogen doped-graphene quantum dots (N-GQDs) engineered 3D NiCo₂ S₄ nanoarray is developed by a facile chemical sulfuration and subsequent electrophoretic deposition process. The as-fabricated N-GQDs/NiCo₂ S₄ nanoarray grown on carbon cloth as a flexible air cathode exhibits superior electrocatalytic activities toward both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), outstanding cycle stability (200 h at 20 mA cm^-2 ), and excellent mechanical flexibility (without observable decay under various bending angles). These impressive enhancements in electrocatalytic performance are mainly attributed to bifunctional active sites within the N-GQDs/NiCo₂ S₄ catalyst and synergistic coupling effects between N-GQDs and NiCo₂ S₄ . Density functional theory analysis further reveals that stronger OOH* dissociation adsorption at the interface between N-GQDs and NiCo₂ S₄ lowers the overpotential of both ORR and OER.

A green and general strategy for the synthesis of hollow Ag/CdS nanocomposites for superior SERS performance

In this study, we developed a convenient, environmentally friendly approach for the fabrication of hollow Ag/CdS composites, which presented superior SERS performance.

An in situ solid-state heredity-restriction strategy to introduce oxygen defects into TiO2 with enhanced photocatalytic performance

A green, solid-state heredity-restriction strategy was constructed to create in situ oxygen vacancies in TiO₂ without the aid of reductant.