Photocatalysis oxidative desulfurization of dibenzothiophene in extremely deep liquid fuels on the Z-scheme catalyst ZnO-CuInS2-ZnS intelligently integrated with carbon quantum dots: performance, mechanism, and stability

In this study, we improved the electrochemical and photocatalytic properties of the ZnO-CuInS2-ZnS (ZCZ) material by integrating with carbon quantum dots (CQD) with particle sizes from 2 to 5 nm. The integration of ZnO-CuInS2-ZnS with carbon quantum dots (ZnO-CuInS2-ZnS/CQD:ZCZ-CQD) enhanced the visible light absorption, significantly reduced the electron-hole recombination rate, and facilitated the electron transfer and separation processes as confirmed by UV-visible diffuse reflectance spectroscopy (UV-vis DRS), photoluminescence (PL), and electrochemical impedance spectroscopy (EIS). The successful integration of ZCZ with carbon quantum dots was confirmed using X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM) methods. The ZCZ/CQD photocatalyst removed up to 98.32% of DBT after 120 minutes of reaction, maintained over 90% durability after 10 cycles, and retained its structure without any changes. The ZCZ photocatalyst integrated with CQD enhances faster dibenzothiophene (DBT) removal by 4.46, 3.24, 2.53, and 1.72 times compared to ZnO, CuInS2, ZnS, and ZnO-CuInS2-ZnS, respectively. Factors influencing the oxidation process of DBT including the mass of the photocatalyst, initial DBT concentration, stability, and reaction kinetics were studied. Through active species trapping experiments, this study demonstrated that the formation of ˙O2 - and ˙OH radicals determines the reaction rate. The mechanism of photocatalysis on ZCZ-CQD materials and the intermediate products formed in the process of photocatalytic oxidative desulfurization of dibenzothiophene is proposed based on electrochemical measurements and GC-MS results.

Experimental and Theoretical Study of Stable and Metastable Phases in Sputtered CuInS2

The chalcopyrite Cu(In,Ga)S2 has gained renewed interest in recent years due to the potential application in tandem solar cells. In this contribution, a combined theoretical and experimental approach is applied to investigate stable and metastable phases forming in CuInS2 (CIS) thin films. Ab initio calculations are performed to obtain formation energies, X-ray diffraction (XRD) patterns, and Raman spectra of CIS polytypes and related compounds. Multiple CIS structures with zinc-blende and wurtzite-derived lattices are identified and their XRD/Raman patterns are shown to contain overlapping features, which could lead to misidentification. Thin films with compositions from Cu-rich to Cu-poor are synthesized via a two-step approach based on sputtering from binary targets followed by high-temperature sulfurization. It is discovered that several CIS polymorphs are formed when growing the material with this approach. In the Cu-poor material, wurtzite CIS is observed for the first time in sputtered thin films along with chalcopyrite CIS and CuAu-ordered CIS. Once the wurtzite CIS phase has formed, it is difficult to convert into the stable chalcopyrite polymorph. CuIn5 S8 and NaInS2 accommodating In-excess are found alongside the CIS polymorphs. It is argued that the metastable polymorphs are stabilized by off-stoichiometry of the precursors, hence tight composition control is required.

Phase-Controlled Synthesis and Quasi-Static Dielectric Resonances in Silver Iron Sulfide (AgFeS2 ) Nanocrystals

Ternary metal-chalcogenide semiconductor nanocrystals are an attractive class of materials due to their tunable optoelectronic properties that result from a wide range of compositional flexibility and structural diversity. Here, the phase-controlled synthesis of colloidal silver iron sulfide (AgFeS₂ ) nanocrystals is reported and their resonant light-matter interactions are investigated. The product composition can be shifted selectively from tetragonal to orthorhombic by simply adjusting the coordinating ligand concentration, while keeping the other reaction parameters unchanged. The results show that excess ligands impact precursor reactivity, and consequently the nanocrystal growth rate, thus deterministically dictating the resulting crystal structure. Moreover, it is demonstrated that the strong ultraviolet-visible extinction peak exhibited by AgFeS₂ nanocrystals is a consequence of a quasi-static dielectric resonance (DR), analogous to the optical response observed in CuFeS₂ nanocrystals. Spectroscopic studies and computational calculations confirm that a negative permittivity at ultraviolet/visible frequencies arises due to the electronic structure of these intermediate-band (IB) semiconductor nanocrystals, resulting in a DR consisting of resonant valence-band-to-intermediate-band excitations, as opposed to the well-known localized surface plasmon resonance response typically observed in metallic nanostructures. Overall, these results expand the current library of an underexplored class of IB semiconductors with unique optical properties, and also enrich the understanding of DRs in ternary metal-iron-sulfide nanomaterials.