Microwave-assisted synthesis of ZnS@CuInxSy for photocatalytic degradation of coloured and non-coloured pollutants

Copper indium sulfide (CuInS2) exhibits strong visible light absorption and thus has the potential for good photocatalytic activity; however, rapid charge recombination limits its practical usage. An intriguing strategy to overcome this issue is to couple CuInS2 with another semiconductor to form a heterojunction, which can improve the charge carrier separation and, hence, enhance the photocatalytic activity. In this study, photocatalysts comprising CuInS2 with a secondary CuS phase (termed CuInxSy) and CuInxSy loaded with ZnS (termed ZnS@CuInxSy) were synthesized via a microwave-assisted method. Structural and morphological characterization revealed that the ZnS@CuInxSy photocatalyst comprised tetragonal CuInS2 containing a secondary phase of hexagonal CuS, coupled with hexagonal ZnS. The effective band gap energy of CuInxSy was widened from 2.23 to 2.71 as the ZnS loading increased from 0 to 30%. The coupling of CuInxSy with ZnS leads to long-lived charge carriers and efficient visible-light harvesting properties, which in turn lead to a remarkably high activity for the photocatalytic degradation of brilliant green (95.6% in 5 h) and conversion of 4-nitrophenol to 4-nitrophenolate ions (95.4% in 5 h). The active species involved in these photocatalytic processes were evaluated using suitable trapping agents. Based on the obtained results, photocatalytic mechanisms are proposed that emphasize the importance of h+, O2•-, and OH- in photocatalytic processes using ZnS@CuInxSy.

Combinational Intercalation-Conversion-Intercalation reaction of CuInS2@PPy anode for Sodium-Ion batteries

Polypyrrole-coated CuInS2 (CuInS2@PPy) composite was prepared through the chemical vapor transport method and subsequent in situ polymerized coating strategy. In this unique nanoarchitecture, the PPy coating layer plays a crucial role in improving the conductivity of the composite, suppressing the volume change of CuInS2, and maintaining the structural integrity of electrode material upon cycling. In addition, the electrochemical reaction mechanism and kinetics of CuInS2@PPy were investigated in-depth. Benefitting from the synergism of its combinational intercalation-conversion-intercalation reaction mechanism and the high conductivity of the PPy coating layer, CuInS2@PPy electrode exhibits superior rate capability and cycling stability for sodium-ion batteries, with a capacity of 404.8 mA h g-1 at 4 A g-1 over 2500 cycles.

An insight of light-enhanced electrochemical kinetic behaviors and interfacial charge transfer of CuInS2/MoS2-based sensing nanoplatform for ultra-sensitive detection of chloramphenicol

Owing to the effective combination between MoS₂ sheets with CuInS₂ nanoparticles (NPs), a direct Z-scheme heterojunction was successfully constructed and proved as a promising structure to modify the working electrode surface with the aim of enhancing overall sensing performance towards CAP detection. Herein, MoS₂ was employed as a high mobility carrier transport channel with a strong photo-response, large specific surface area, and high in-plane electron mobility, while CuInS₂ acted as an efficient light absorber. This not only offered a stable nanocomposite structure but also created impressive synergistic effects of high electron conductivity, large surface area, highlight exposure interface, as well as favorable electron transfer process. Moreover, the possible mechanism and hypothesis of the transfer pathway of photo-induced electron-hole pairs on the CuInS₂-MoS₂/SPE as well as their impacts on the redox reaction of K₃/K₄ probes and CAP were proposed and investigated in detail via a series of calculated kinetic parameters, demonstrating the high practical applicability of light-assisted electrodes. Indeed, the detection concentration range of the proposed electrode was widened from 0.1 to 50 μM, compared with that of 1-50 μM without irradiation. Also, the LOD and sensitivity values were calculated to be approximately 0.06 μM and 0.4623 μA μM^-1, which is better than that of 0.3 μM and 0.095 μA μM^-1 without irradiation.

Ferrihydrite synthesis in the presence of amino acids and artificial seawater

Ferrihydrite is widespread in clays, soils, and living organisms and was found on Mars. This iron-mineral could be found on the prebiotic Earth, which also contained simple monomeric amino acids. For prebiotic chemistry, it is important to understand how amino acids have an effect on the process of iron oxide formations. There are three important results in this work: (a) preconcentration of cysteine and aspartic acid, (b) formation of cystine and probably the cysteine peptide occurred during ferrihydrite syntheses, and (c) amino acids have an effect on iron oxide synthesis. For samples containing aspartic acid and cysteine, their presence on the surface or mineral structure can be confirmed by FT-IR spectra. Surface charge analysis showed a relatively high decrease for samples synthesized with cysteine. Scanning electron microscopy did not show marked morphological differences among the samples, except for the seawater sample containing cysteine, which had a lamina-shaped morphology surrounded by circular iron particles, indicating the possible formation of a cysteine structure involving iron oxide particles. The thermogravimetric analysis of the samples indicates that the presence of salts and amino acids in the synthesis of ferrihydrite has an effect on the thermal behavior of the iron oxide/amino acids and modifying the water-loss temperature. The heating of the cysteine samples, synthesized in distilled water and artificial seawater, showed several peaks of degradation of cysteine. In addition, heating of the aspartic acid samples produced the polymerization of this amino acid and peaks of degradation of it. FTIR spectra and XRD patterns did not indicate the precipitation of methionine, 2-aminoisobutyric acid, lysine, or glycine with the iron oxide formations. However, the heating of the glycine, methionine and lysine samples, synthesized in artificial seawater, showed peaks that could be attributed to the degradation of them. Then this could be an indication that these amino acids precipitate with the minerals during the syntheses. Also, the dissolution of these amino acids in artificial seawater prevents the formation of ferrihydrite.

Synergistic Cr(VI) Reduction and Chloramphenicol Degradation by the Visible-Light-Induced Photocatalysis of CuInS2: Performance and Reaction Mechanism

Despite significant scientific efforts in the field of water treatment, pollution of drinking water by toxic metal ions and synthetic organic compounds is becoming an increasing problem. The photocatalytic capabilities of CuInS₂ nanoparticles were examined in this study for both the degradation of chloramphenicol (CAP) and the reduction of Cr(VI). CuInS₂ nanoparticles were produced using a straightforward solvothermal approach and subsequently characterized by many analysis techniques. Simultaneous photocatalytic Cr(VI) reduction and CAP oxidation by the CuInS₂ nanoparticles under visible-light demonstrated that lower pH and sufficient dissolved oxygen favored both Cr(VI) reduction and CAP oxidation. On the basis of active species quenching experiments, the possible photocatalytic mechanisms for Cr(VI) conversion with synchronous CAP degradation were proposed. Additionally, the CuInS₂ retains a high rate of mixed pollutant removal after five runs. This work shows that organic contaminants and heavy metal ions can be treated concurrently by the visible-light-induced photocatalysis of CuInS₂.

Confinement Matters: Stabilization of CdS Nanoparticles inside a Postmodified MOF toward Photocatalytic Hydrogen Evolution

Insights into developing innovative routes for the stabilization of photogenerated charge-separated states by suppressing charge recombination in photocatalysts is a topic of immense importance. Herein, we report the synthesis of a metal-organic framework (MOF)-based composite where CdS nanoparticles (NPs) are confined inside the nanosized pores of Zr⁴⁺-based MOF-808, namely, CdS@MOF-808. Anchoring l-cysteine into the nanospace of MOF-808 via postsynthetic ligand exchange allows the capture of Cd²⁺ ions from their aqueous solution, which are further utilized for in situ growth of CdS NPs inside the nanosized MOF pores. The formation of CdS@MOF-808 opens up a possibility for visible-light photocatalysis as CdS NPs (1-2 nm) are a well-studied semiconductor system with a band gap of ∼2.6 eV. The confinement of the CdS NPs inside the MOF pores, close to the Zr⁴⁺ cluster, opens up a shorter electron transfer route from CdS to the catalytic Zr⁴⁺ cluster and shows a high rate of H₂ evolution (10.41 mmol g^-1 h^-1) from water with a loading of 3.56 wt % CdS. In contrast, a similar composite in which CdS NPs are stabilized on the external surface of MOF-808 reveals poor activity (0.15 mmol g^-1 h^-1). CdS NPs stabilized on the MOF-808 surface show slower and inefficient electron transfer kinetics compared to CdS stabilized inside the nanospace of the MOF, as realized by the transient absorption measurements. Therefore, this work unveils the critical role of stabilizing the photosensitizer NPs in close proximity of the catalytic sites in MOF systems towards developing highly efficient H₂ evolution photocatalysts.

Synthesis of hydroxide-enriched cerium-doped oxy-sulfide catalyst for visible light-assisted reduction of Cr(vi)

Semiconductor catalysts are significantly attractive materials for different cutting-edge applications, including the detoxification of toxic pollutants.

Tuning of the morphological and electronic properties of In2S3 nanosheets by cerium ion intercalation for optimizing photocatalytic activity

The influence of cerium on the evolution of the morphological and optoelectronic properties of In₂S₃ nanostructures has been experimentally and theoretically investigated.

Designing novel morphologies of l-cysteine surface capped 2D covellite (CuS) nanoplates to study the effect of CuS morphologies on dye degradation rate under visible light

Novel CuS@l-Cys NPs are designed by a hydrothermal route. The effects of synthetic parameters on the morphologies of CuS@l-Cys NPs were investigated. CuS@l-Cys NPs exhibit an enhanced dye degradation rate under visible light.

Sb2S3 Thickness-Related Photocurrent and Optoelectronic Processes in TiO2/Sb2S3/P3HT Planar Hybrid Solar Cells

In this work, a comprehensive understanding of the relationship of photon absorption, internal electrical field, transport path, and relative kinetics on Sb₂S₃ photovoltaic performance has been investigated. The n-i-p planar structure for TiO₂/Sb₂S₃/P3HT heterojunction hybrid solar cells was conducted, and the photon-to-electron processes including illumination depth, internal electric field, drift velocity and kinetic energy of charges, photo-generated electrons and hole concentration-related surface potential in Sb₂S₃, charge transport time, and interfacial charge recombination lifetime were studied to reveal the key factors that governed the device photocurrent. Dark J-V curves, Kelvin probe force microscope, and intensity-modulated photocurrent/photovoltage dynamics indicate that internal electric field is the main factors that affect the photocurrent when the Sb₂S₃ thickness is less than the hole diffusion length. However, when the Sb₂S₃ thickness is larger than the hole diffusion length, the inferior area in Sb₂S₃ for holes that cannot be diffused to P3HT would become a dominant factor affecting the photocurrent. The inferior area in Sb₂S₃ layer for hole collection could also affect the V_oc of the device. The reduced collection of holes in P3HT, when the Sb₂S₃ thickness is larger than the hole diffusion length, would increase the difference between the quasi-Fermi levels of electrons and holes for a lower V_oc.

Solar light harvesting with multinary metal chalcogenide nanocrystals

The paper reviews the state of the art in the synthesis of multinary (ternary, quaternary and more complex) metal chalcogenide nanocrystals (NCs) and their applications as a light absorbing or an auxiliary component of light-harvesting systems. This includes solid-state and liquid-junction solar cells and photocatalytic/photoelectrochemical systems designed for the conversion of solar light into the electric current or the accumulation of solar energy in the form of products of various chemical reactions. The review discusses general aspects of the light absorption and photophysical properties of multinary metal chalcogenide NCs, the modern state of the synthetic strategies applied to produce the multinary metal chalcogenide NCs and related nanoheterostructures, and recent achievements in the metal chalcogenide NC-based solar cells and the photocatalytic/photoelectrochemical systems. The review is concluded by an outlook with a critical discussion of the most promising ways and challenging aspects of further progress in the metal chalcogenide NC-based solar photovoltaics and photochemistry.

Facile and Robust Solvothermal Synthesis of Nanocrystalline CuInS₂ Thin Films

This work demonstrates that the solvothermal synthesis of nanocrystalline CuInS₂ thin films using the amino acid l-cysteine as sulfur source is facile and robust against variation of reaction time and temperature. Synthesis was carried out in a reaction time range of 3–48 h (at 150 °C) and a reaction temperature range of 100–190 °C (for 18 h). It was found that at least a time of 6 h and a temperature of 140 °C is needed to produce pure nanocrystalline CuInS₂ thin films as proven by X-ray and electron diffraction, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy. Using UV-vis spectroscopy, a good absorption behavior as well as direct band gaps between 1.46 and 1.55 eV have been determined for all grown films. Only for a reaction time of 3 h and temperatures below 140 °C CuInS₂ is not formed. This is attributed to the formation of metal ion complexes with l-cysteine and the overall slow assembly of CuInS₂. This study reveals that the reaction parameters can be chosen relatively free; the reaction is completely nontoxic and precursors and solvents are rather cheap, which makes this synthesis route interesting for industrial up scaling.