Hexagonal CdS Research Articles

Synthesis of Zn2TiO4@CdS Core‐shell Heteronanostructures by Novel Thermal Decomposition Approach for Photocatalytic Application

AbstractZn2TiO4@CdS core‐shell heteronanostructures with Zn2TiO4 as core and CdS nanoparticles as shell have been synthesized for the first time by a novel thermal decomposition approach. The size of CdS nanoparticles in the shell can be easily tuned by varying the amount of single molecular precursor (bis(thiourea)cadmium acetate, [Cd(CS(NH2)2)2]⋅(CH3COO)2). Various state‐of‐art analytical techniques prove the formation of Zn2TiO4@CdS core‐shell heteronanostructures. Powder XRD results confirm the presence of cubic Zn2TiO4 and hexagonal CdS in the core‐shell heteronanostructures. SEM and TEM studies indicate spherical morphology for pure Zn2TiO4 and formation of core‐shell structure in Zn2TiO4@CdS with Zn2TiO4 as core and CdS nanoparticles as shell. XPS measurements prove the presence of Zn2+, Ti4+, Cd2+ and S2− in the Zn2TiO4@CdS core‐shell heteronanostructures. The synthesized Zn2TiO4@CdS core‐shell heteronanostructures were explored for photocatalytic degradation of crystal violet in an aqueous solution. The core‐shell heteronanostructures exhibit better photocatalytic activity as compared to their parent materials.

Hexagonal CdS photoanode modified with Pt and cobalt phosphate cocatalyst for efficient photoelectrochemical performance

The recombination of electron-hole pairs and the slow surface catalytic reactions have been deemed as the core problem affecting the efficiency of photoelectrochemical (PEC) performance. Here we synthesized hexagonal CdS photoanode on FTO substrate by hydrothermal method. Cobalt-phosphate (Co-Pi) and Pt cocatalysts were simultaneously decorated on the inner and outer surfaces of CdS (denoted as Pt/CdS/Co-Pi), which showed efficient charge separation/transfer performance on account of trapping the electrons with Pt and transferring holes with Co-Pi. As a result, the Pt/CdS/7.5Co-Pi photoanode showed a maximum photo-current of 5.05 mA/cm−2 at 0.28 V vs RHE under solar simulated illumination, which was 8.3 times higher than that of pure CdS photoanode. This work presents a promising guideline to design and fabricate an eco-friendly and sunlight-driven photoanode for the PEC water-splitting system.

Cu-MOF assisted synthesis of CuS/CdS(H)/CdS(C): Enhanced photocatalytic hydrogen production under visible light

CuS/CdS(H)/CdS(C) photocatalysts were synthesized via the hydrothermal method by employing thiourea, Cd(CH3COO)2·3H2O and copper 1,4-benzenedicarboxylate MOF (CuBDC). The photocatalysts were characterized by XRD, XPS, BET, TEM and UV–vis diffuse reflectance spectra. Interestingly, hexagonal CdS (CdS(H)) and cubic CdS (CdS(C)) were formed with phase junctions in one step when CuBDC was introduced in the synthesis process, in addition, CuS nanoparticles were deposited on CdS. However, only hexagonal CdS was obtained without CuBDC. It demonstrated that CuBDC was not only the precursor of CuS but also the structural modifier for CdS. With the reduction of re-combination of photo-induced electrons and holes caused by phase junctions and the enhancement of visible-light absorptions due to the loading of CuS, all CuS/CdS(H)/CdS(C) photocatalysts had higher photocurrent densities under visible-light irradiation, and consequently the higher rates of H2 production than pure CdS(H). Typically, the catalyst with 2.89 wt% of Cu showed a highest rate of H2 evolution at 2042 μmol/g/h.

Effect of TiO2 doping on structural and optical properties of CdSZn3(PO4)2 nanocomposites

Pure and (0.3, 0.6 and 0.9 mol%) TiO2-doped CdSZn3(PO4)2semiconducting nanocomposites were successfully synthesized by hydrothermal route. The structural compositions, surface morphology, diffuse reflectance spectroscopy and luminescence properties of all the nanocomposites were systematically investigated. X-ray diffraction pattern exhibits the co-existence of both hexagonal phase of CdS and a mixer of γ and β monoclinic Zn3(PO4)2 phases with high crystalline order. Upon increasing of TiO2 content from 0.3 to 0.9 mol%, γ-Zn3(PO4)2 phase is decreasing while β-Zn3(PO4)2 phase is found to increase. Further, it has been found that the TiO2 additive atoms did not segregate to form secondary phases but led to variation in grain size, local disorder and local strain in the nanocomposites. The average crystallite size of nanocomposites is in the range 22–25 nm. The surface morphology of the samples was clearly shown as flakes surrounded by hexagonal CdS spheres like heterostructure type morphology. EDAX results confirm the stoichiometry of all the samples with slight variation of CdS content with increasing TiO2 dopant content. Optical band gap values are found to decrease from 2.52 to 2.44 eV with increasing TiO2 content. Further, photoluminescence studies revealed that all the samples exhibited strong fluorescence in the visible wavelength region and the chromaticity characteristics from CIE diagram were also explored in search of their applicability for commercial LED applications.

Visible light response and heterostructure of composite CdS@ZnS–ZnO to enhance its photocatalytic activity

In this work, CdS@ZnS–ZnO composites were prepared by the temperature-programmed hydrothermal method combined with the microwave-assisted hydrothermal method. The composite consisted mainly of cubic phase ZnS, hexagonal phase CdS and hexagonal phase ZnO, and presented a spherical structure with relatively uniform size and shape. There were heterostructures between CdS, ZnS and ZnO in the spherical structure. At the same time, the grain size, specific surface area, average pore diameter and pore volume of the composited material changed significantly, and its light absorption performance in the visible light region was obviously enhanced, and the photocatalytic activity was also greatly improved. Under ultraviolet light, CdS@ZnS–ZnO can degrade simulated pollutants by more than 90% within 20 min. In addition, the results of hydrogen evolution from photolysis of water showed that the ternary composite CdS@ZnS–ZnO had excellent hydrogen evolution capacity compared with pure CdS, ZnS and ZnO, whose hydrogen evolution amount can reach 3647 μmol g−1 in 8 h, was 298 times than that of P25. Moreover, it still maintained a high hydrogen evolution capacity after 4 cycles.

Nitrogen-doped graphene quantum dots decorated ZnxCd1-xS semiconductor with tunable photoelectric properties

In this study, ZnxCd1-xS/N-GQDs composites with different Zn/Cd ratios were synthesized via a facile solvothermal process. A series of techniques were introduced to investigate the effect of Zn/Cd ratios and N-GQDs on the performances of ZnxCd1-xS/N-GQDs. The results show that the crystal structure and photoelectric performance of the composites can be tuned via adjusting the Zn/Cd ratios. ZnxCd1-xS/N-GQDs composites transform from a hexagonal structure to a cubic structure with the increase of Zn content, and the diffraction peaks are located between hexagonal phase CdS and cubic phase ZnS. Meanwhile, the photocurrent responses and electrochemical impedance present good tunability via adjusting the Zn/Cd ratios. Zn0.9Cd0.1S/N-GQDs composites with the higher photocurrent value of 3.79 μA cm−2 and lower interfacial impedance are superior to ZnxCd1-xS/N-GQDs composites with other Zn/Cd ratios. Moreover, the introduction of N-GQDs obviously enhances the photoelectric properties of the semiconductor.

Deep subwavelength confinement and threshold engineering in a coupled nanorods based spaser.

In recent years, extensive efforts have been made for design and fabrication of low threshold spasers or plasmonic nanolasers at a deep subwavelength scale. Plasmonic nanolasers with coupled-nanorods structure can realize this purpose due to energy concentration in nano size volumes and effective amplification mechanisms. In this study, a group of structures based on metallic and CdS coupled nanorods are designed and analyzed using the finite element method (FEM). By changing the lateral adjacent surfaces of the metal and semiconductor nanorods through utilizing regular polygons as the cross sections of the nanorods, different characteristics of the plasmonic nanolaser are investigated. Simulation results show that the mode area normalized by the diffraction limit area is as low as 0.0062 in the structures based on hexagonal metallic core with circular semiconductor nanorods while structures based on circular Ag core with hexagonal CdS nanorods can provide a low threshold gain as 1.310 μm-1. Also, it is shown that if ZnO be used as the semiconductor gain material instead of CdS, a normalized mode area of almost one tenth can be attained in a structure with dodecagonal metallic core and circular ZnO nanorods.

High-Quality Hexagonal Nonlayered CdS Nanoplatelets for Low-Threshold Whispering-Gallery-Mode Lasing.

Low threshold micro/nanolasers have attracted extensive attention for wide applications in high-density storage and optical communication. However, constrained by quantum efficiency and crystalline quality, conventional semiconductor small-sized lasers are still subjected to a high lasing threshold. In this work, a low-threshold planar laser based on high-quality single-crystalline hexagonal CdS nanoplatelets (NPLs) using a self-limited epitaxial growth method is demonstrated. The as-grown CdS NPLs show multiple whispering-gallery-mode lasing at room temperature with a threshold of ≈0.6 µJ cm-2 , which is the lowest value among reported CdS-based lasers. Through power-dependent lasing studies at 77 K, the lasing action is demonstrated to originate from a exciton-exciton scattering process. Furthermore, the edge length- and thickness-dependent lasing threshold studies reveal that the threshold is inversely proportional to the second power of lateral edge length while partially affected by vertical thickness, and the lasing modes can be sustained in NPLs as thin as 60 nm. The lowest threshold emerges with the thickness of ≈110 nm due to stronger energy confinement in the vertical Fabry-Pérot cavity. The results not only open up a new avenue to fabricate nonlayered material-based coherent light sources, but also advocate the promise of nonlayered semiconductor materials for the development of novel optoelectronic devices.

Synthesis and photocatalytic property of cubic phase CdS

In order to understand the nanostructure-based architectures and phase structures of CdS on the photocatalytic property, we have synthesized 3 D flower-like CdS with cubic phase and hexagonal phase CdS nanoparticles by hydrothermal method. The as-prepared samples have been characterized by XRD, FESEM, and UV–Vis. The photocatalytic activity has been evaluated by the photocatalytic degradation of methylene blue (MB) under simulated visible-light irradiation. FESEM results reveal that the morphologies of cubic phase CdS are flower-like structures, and the morphologies of hexagonal phase CdS are nanoparticles. The optical energy band gap of flower-like CdS is 2.25 eV from UV–Vis result. Moreover, the flower-like CdS exhibits better photocatalytic activity and its highest degradation rate to MB can reach 90.4% than that of CdS nanoparticles.

Synthesis and magnetic properties of Fe‐doped CdS nanorods

Hexagonal CdS and Fe-doped CdS nanorods were synthesised by a facile hydrothermal method and characterised by X-ray diffraction, energy dispersive X-ray spectroscopy, UV-vis absorption, photoluminescence, and X-ray photoelectron spectroscopy. The magnetic properties of undoped and Fe-doped CdS nanorods were investigated at room temperature. The experimental results demonstrate that the ferromagnetism of the Fe-doped CdS nanorods differs from that of the undoped CdS nanorods. The remanence magnetisation ( M r ) and the coercive field ( H c ) of the Fe-doped CdS nanorods were 4.9 × 10 -3 emu/g and 270.6 Oe, respectively, while photoluminescence properties were not influenced by doping. First-principle calculations show that the ferromagnetism in Fe-doped CdS nanocrystal arose not only from the Fe dopants but also from the Cd vacancies, although the main contribution was due to the Fe dopants.

Photocatalytic Performance of Cubic and Hexagonal Phase CdS Synthesized via Different Cd Sources

CdS has been widely used in photocatalysis, by virtue of its sensitivity to visible-light irradiation. But CdS has two crystalline phases, which are not equally well understood. Hence, we synthesized cubic phase and hexagonal phase hierarchical CdS with different Cd sources by the hydrothermal method. These as-prepared CdS samples were characterized by powder x-ray diffraction (PXRD), field emission scanning electron microscopy (FESEM), ultraviolet–visible spectrophotometer (UV–Vis), and room temperature photoluminescence (PL). Photocatalytic degradation of methylene blue was evaluated under simulated visible-light irradiation. PXRD results revealed that the CdS samples manifested a cubic phase when the Cd source was CdCl2, but the CdS assumed a mixed hexagonal and cubic phase when the Cd source was Cd(NO3)2. FESEM results indicate that the morphologies of CdS are both flower-like structures. The optical energy band gap of cubic phase CdS is 2.26 eV, but mixed hexagonal and cubic phase CdS is 2.24 eV according to UV–Vis results. PL results show that CdS samples of both phases have a similar emission peak near 560 nm, which is consistent with UV–Vis absorption spectrums. In addition, mixed hexagonal and cubic phase CdS exhibits better photocatalytic activity than cubic phase CdS.

Effect of Gd doping on structural, optical properties, photoluminescence and electrical characteristics of CdS nanoparticles for optoelectronics

Synthesis of pure and 0.1 to 5 wt.% Gd-doped CdS nanoparticles (NPs) was achieved through a modified domestic microwave-assisted route in a short timespan at 700 W power. The formation of hexagonal CdS NPs was verified via X-ray diffraction analysis, and no structural variation was observed except for lattice variation. The size of the crystallites (D), dislocation concentration, and lattice strain were calculated, and the D was in the range of 3–6 nm. Fourier transform-Raman analysis confirmed the presence of 1LO, 2LO, and 3LO modes at 294.76, 590, and 890 cm−1, respectively, in all the synthesized nanostructures, with minute variations in their positions due to doping; however, no new mode was observed. The position of the vibration modes was red shifted compared to that of the bulk material, indicating a confinement effect. Scanning electron microscopy (SEM) mapping/energy-dispersive X-ray spectroscopy revealed homogeneous doping of Gd and the presence of all the constituents in the final products. The morphology of the synthesized materials was tested via field-emission SEM, which revealed spherical NPs with small dimensions. Additionally, high-resolution transmission electron microscopy was performed to visualize the shape and size of the prepared 0.1% Gd:CdS NPs. The energy gap was calculated using the Kubelka–Munk theory and found to be in the range of 2.31–2.41 eV. The photoluminescence emission spectra exhibited two green emission peaks at 516 ± 2 nm and 555 ± 2 nm and showed the reduction of defects with Gd doping in terms of intensity quenching. The dielectric constant (ε'), loss, and alternating-current electrical properties were studied in the high-frequency range. The values of ε' were in the range of 17–27. An enhancement of these values was observed for CdS when it was doped with Gd. The electrical conductivity exhibited frequency power law behavior.

Comparative study on photocatalytic degradation of Congo red using different clay mineral/CdS nanocomposites

Clay mineral/CdS nanocomposites were successfully prepared via hydrothermal technique in the presence of different clay minerals for photocatalytic degradation of Congo red. The relevant structures and properties were systematically characterized and studied, including phase composition, crystal size, color, optical property and morphology of the obtained nanocomposites. The generated hexagonal CdS nanoparticles with a diameter of 30–60 nm were well anchored on the surface of clay minerals. Interestingly, the types of clay minerals affected the UV–Vis absorbance and band-gap energy of clay mineral/CdS nanocomposites, and the clay mineral/CdS nanocomposites derived from one-dimensional halloysite, sepiolite, and palygorskite exhibited higher photocatalytic activity for Congo red degradation than that of two-dimensional lamellar kaolin and montmorillonite. In addition, incorporating of clay minerals not only effectively decreased the size of CdS nanoparticles without the obvious aggregation, but also guard against electrochemical corrosion of CdS during photocatalytic degradation.

Acid Leaching-Based Synthesis of CdS Yellow Ceramic Pigment with Discarded Ni-Cd Batteries

There is increasing interest in the ceramic industry in the development of pigments with intense tonalities that can be produced from low-cost alternative raw materials and also can fulfill technological and environmental requirements. This work reports on the preparation and characterization of CdS yellow ceramic pigment derived from Ni-Cd batteries through an acid leaching process. Cadmium was chemically extracted with HCl and tributylphosphate (TBP) and reacted with H2S to form CdS. The obtained yellow powder is composed of agglomerated particles with nanometer sizes and hexagonal and rod-shaped crystals. Rietveld refinement indicated that these particles consist of cubic and hexagonal CdS. CIELab colorimetric parameters revealed a bright yellow color (L*=77.8, a*=13.7 and b*=76.2), similar to that of commercial Cd Yellow pigment. The extraction of Cd from Ni-Cd batteries could be a low-cost and environmentally friendly solution for the production of CdS-based ceramic pigments.

In situ preparation of CdS decorated ZnWO4 nanorods as a photocatalyst for direct conversion of sunlight into fuel and RhB degradation

In situ synthesis of monoclinic ZnWO4 nanorods decorated with hexagonal CdS nanoparticles by a facile solvothermal method used as photocatalysts for hydrogen production under solar light.

Doping effect investigation of Li-doped CdS thin films

ABSTRACTLi-doped CdS (CdS:Li) thin films with 0, 1, 2 and 3 wt-% Li concentrations were prepared by the spray technique using a perfume atomiser. The effect of Li doping concentration on the structural, optical, electrical and magnetic properties was systematically investigated and the results are reported in this paper. Analysis of the microstructure indicates that all the films consist of a hexagonal CdS phase with a strong (0 0 2) preferential growth texture. Nanoneedles were evinced from the SEM images of the doped films. Optical studies reveal that the transparency and band gap were dependent on Li-doping content. Hall effect measurements reveal that all the doped films exhibit p-type conductivity and the resistivity values strongly depend on the occupancy of Li atoms on the substitutional and interstitial sites of the CdS lattice. Room temperature ferromagnetism was observed for the doped films.

Self-constructed facet junctions on hexagonal CdS single crystals with high photoactivity and photostability for water splitting

Crystal facets engineering of semiconductor catalysts with different exposed facets has been proven as a versatile approach to enhance their photocatalytic performance. Herein, for the first time, a facet-junction engineered hexagonal CdS single crystal with exposing {0001} and {101¯0} facets was synthesized by hydrothermal reaction via adjusting the molar ratio of S2−/Cd2+ precursor. The co-exposed {0001} and {101¯0} facets on hexagonal CdS single crystals with continuous band bending and well-defined epitaxial interfaces showed highly efficient visible-light-induced H2 evolution. The maximum photocatalytic H2 production rate of 24.33 mmol h−1 g−1 is obtained over the facet-junction engineered hexagonal CdS-5 single crystals with an apparent quantum efficiency of 11.18% at 470 nm, which is about 5.27 times greater than CdS-1 nanoparticles. Also, superior photostability is also achieved, even after 25 consecutive cycles during 100 h light irradiation keeping impregnated in strong alkaline sacrificial agent beyond 20 days, the initial photoactivity is still remained. The enhanced photocatalytic H2 evolution activity and photostability can be ascribed to the type-II band alignment between the co-exposed {0001} and {101¯0} facets that significantly promoted the separation rate of photo-generated electrons and holes. And the small amount of sulfur vacancies are also benefit for the photocatalytic hydrogen evolution activity of CdS-5. The time-resolved fluorescence (TRPL) decay and photoelectrochemical test further proved the effective spatial charge separation. This work provides a feasible and simple strategy for designing of facet-junction engineered CdS single crystals with highly efficient photocatalytic activity and unprecedented photostability.

Negative Capacitance Effect in Ag/α-In2Se3/CdS/CdSe/C Dual Band Stop Filters

In the current study, a 1.5 μm thick three channel microwave band filter is designed and characterized. The thin film device which was constructed from the indium selenide, cadmium sulfide and cadmium selenide stacked dielectric materials sandwiched between silver and carbon films is studied by means of x-ray diffraction, energy dispersive x-ray analysis and impedance spectroscopy techniques. It was observed that the Ag thin film substrate induced the formation of the hexagonal α-In2Se3 phase of indium selenide. The x-ray analysis has also shown that the deposition of hexagonal CdS over Ag/α-In2Se3 and that of hexagonal CdSe over α-In2Se3/CdS under vacuum pressure of 10−8 bar is of a highly strained and mismatched physical nature. The impedance spectroscopy analysis in the frequency domain of 0.10–1.80 GHz has shown that; while the Ag/α-In2Se3/C channel exhibit negative capacitance (NC) effects in the frequency domain of 0.10–1.40 GHz, the Ag/α-In2Se3/CdS/C and the Ag/α-In2Se3/CdS/CdSe/C channels displayed a NC feature in the domains of 1.24–1.40 GHz and 1.10–1.56 GHz, respectively. The fitting of the capacitance spectra in accordance with the modified Ershov model allowed determining the NC and band filtering parameters. It was also observed that, although the Ag/α-In2Se3/C channel behaves as a high frequency low pass filter, the second and third channels displayed band stop filter features with notch frequencies of 1.38 GHz and 1.49 GHz, respectively. The features of the device nominate it for use as a parasitic capacitance canceller and as a three channels microwave filter.

Surface polarons and optical micro-cavity modulated broad range multi-mode emission of Te-doped CdS nanowires

The optical confinement and strong carrier coupling within a semiconductor nanostructure cavity are crucial for the modulation of emission properties. Fundamental understanding of the light–matter interaction in a low dimensional system is important. In this paper, we synthesized high-quality hexagonal Te-doped CdS nanowires by two-step chemical vapor deposition and investigated systematically the doping concentration, temperature, excitation power, excitation wavelength dependent Raman, photoluminescence and carrier lifetime decay. Scanning electron microscopy, energy dispersive x-ray spectrometry and x-ray diffraction confirmed Te-doping in the as-prepared samples. The strong surface optical (SO) phonon mode is observed in the micro-Raman spectra of an individual Te–CdS nanowire, which is unsuitable in large-sized structures. In situ micro-photoluminescence (μ-PL) characterization shows dominant confined defect state emission with whispering gallery mode (WGM) characteristics. The emission peak position shifts under increased excitation power, demonstrating the inelastic scattering by bound carriers. In addition, the short wavelength emission modes are dominant at a low temperature (80 K) while the long wavelength emission modes are dominant at a high temperature (300 K) due to different recombination processes contributing to the WGM resonant bands, which was also confirmed by the time-resolved PL measurement. All these results reflect strong coupling between the surface evanescent-wave in the WGM cavity and the SO phonon/polaron, which will facilitate the rational tailoring of surface/interface relevant properties for nanophotonic device applications.

First principles study of the optical emission of cadmium yellow: Role of cadmium vacancies

We study the role of structural defects in the CdS-based cadmium yellow paint to explain the origin of its deep trap states optical emission. To this end, we combine a first principles study of Cd- and S- vacancies in the wurtzite (101¯0) CdS surface with experimental photoluminescence spectroscopy of the commercial hexagonal CdS pigment. Computational results clearly state that the presence of cadmium vacancies in the pigment surface alters the electronic structure of cadmium sulfide by forming acceptor levels in the gap of the semiconductor. Such levels are consistent with the optical emission from trap state levels detected in the CdS pigment. This finding provides a first step towards the understanding of the photo-physical mechanisms behind the degradation of this modern pigment, widely used in impressionist and modernist paintings.