• Clean Technology
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• v.26 no.4
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• pp.311-320
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• 2020

In this study, the photocatalytic degradation of rhodamine B (RhB), methyl orange (MO) and methylene blue (MB) was carried out under visible light irradiation using CdS and CdZnS/ZnO photocatalysts prepared by a simple precipitation method. This study focused on examining the effect of physicochemical properties of dye and photocatalyst on the reaction pathway of photocatalytic degradation. The prepared photocatalysts were characterized by XRD, UV-vis DRS and XPS. Both the CdS and CdZnS/ZnO photocatalysts exhibit an excellent absorption in the visible light and the UV light regions. It was observed that the photocatalytic degradation of MO proceeds via the same reaction mechanism on both the CdS and CdZnS/ZnO photocatalysts. However, the photocatalytic degradation of RhB and MB was found to proceed through a different reaction pathway on the CdS and CdZnS/ZnO catalysts. It is interesting to note that MB dimer was formed on the CdS catalyst at the beginning of the photocatalytic reaction, while the MB monomer was degraded during the overall photocatalytic reaction on CdZnS/ZnO. The above results may be mainly ascribed to the difference of band edge potential of the conduction band in the CdS and CdZnS/ZnO semiconductors and the adsorption property of dye on the catalysts.

• Applied Chemistry for Engineering
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• v.26 no.3
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• pp.356-361
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• 2015

$Cd_{0.5}Zn_{0.5}S/ZnO$ composite photocatalysts were synthesized using the precipitation method and characterized by XRD, UV-vis DRS, PL and FE-SEM. Photocatalytic activities of the materials were evaluated by measuring the degradation of rhodamine B under visible light irradiation. Contrary to ZnO, $Cd_{0.5}Zn_{0.5}S/ZnO$ materials absorb visible light as well as UV and their absorption intensities in visible region increased with increasing the $Cd_{0.5}Zn_{0.5}S$ amount. The increment in the $Cd_{0.5}Zn_{0.5}S$ content in $Cd_{0.5}Zn_{0.5}S/ZnO$ also leads to reducing the particle size and consequently increasing the specific surface area. $Cd_{0.5}Zn_{0.5}S/ZnO$ materials with the larger $Cd_{0.5}Zn_{0.5}S$ content showed the higher activity in the photocatalytic degradation of rhodamine B under visible light irradiation. Therefore, the heterojunction effect between $Cd_{0.5}Zn_{0.5}S$ and ZnO as well as the adsorption capacity seems to give important contributions to the photocatalytic activity of the $Cd_{0.5}Zn_{0.5}S/ZnO$.

• Analytical Science and Technology
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• v.14 no.3
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• pp.259-265
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• 2001

Photocatalytic degradation of Congo red was performed using various semiconductors as ZnO, CdS, rutile-$TiO_2$ or mixed rutile-$TiO_2$/ZnO. The change of degradation of the dye was investigated by UV-visible spectrophotometric method. The photocatalytic action of CdS was greater than ZnO and rutile-$TiO_2$ in account of low band gap energy of CdS. The rate of photocatalytic degradation reaction increased drastically in according to increasing ratio of ZnO on mixed rutile-$TiO_2$/ZnO. These photocatalytic effect of rutile-$TiO_2$ was suppressed by more stable rutile-$TiO_2$, doping the hydrolysis product with $Zn^{2+}$ prior to calcination onto the rutile-$TiO_2$ surface.

• Current Photovoltaic Research
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• v.1 no.1
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• pp.52-58
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• 2013

Two different window-structured $CuInGaSe_2$(CIGS) solar cells, i.e., CIGS/thin-CdS/ZnO:B(sample A) and CIGS/very thin-CdS/Zn(S/O)/ZnO:B(sample B), were prepared, and the diffusivity of Zn, Cd, S, and B atoms, respectively, in the CIGS, ZnO or Zn(S/O) layer was estimated by a theoretical fit to experimental secondary ion mass spectrometer data. Diffusivities of Zn, Cd, S, and B atoms in CIGS were $2.0{\times}10^{-13}(1.5{\times}10^{-13})$, $4.6{\times}10^{-13}(4.4{\times}10^{-13})$, $1.6{\times}10^{-13}(1.8{\times}10^{-13})$, and $1.2{\times}10^{-12}cm^2/s$ at 423K, respectively, where the values in parentheses were obtained from sample B and the others from sample A. The diffusivity of the B atom in a Zn(S/O) of sample B was $2.1{\times}10^{-14}cm^2/sec$. Moreover, the diffusivities of Cd and S atoms diffusing back into ZnO(sample A) or Zn(S/O)(sample A) layers were extremely low at 423K, and the estimated diffusion coefficients were $2.2{\times}10^{-15}cm^2/s$ for Cd and $3.0{\times}10^{-15}cm^2/s$ for S.

• Bulletin of the Korean Chemical Society
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• v.33 no.1
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• pp.189-193
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• 2012

ZnO nanorods were grown on the $Cd_xZn_{1-x}O$ seed layers with various Cd mole fractions by hydrothermal method. The effects of the Cd mole fraction for $Cd_xZn_{1-x}O$ seed layers on the structural and optical properties of the ZnO nanorods were investigated by scanning electron microscopy, X-ray diffraction, and photoluminescence. The narrowest full-width at half-maximum and largest grain size of the $Cd_xZn_{1-x}O$ seed layers, indicating improvement in crystal quality, were observed at the Cd mole fraction of 0.5. At the Cd mole fraction of 0.5, the largest enhancement in the density, the crystal quality, and the growth rate of the ZnO nanorods was observed while their appearance was not affected significantly by the incorporation of the Cd in the $Cd_xZn_{1-x}O$ seed layers. Consequently, the luminescent properties of the ZnO nanorods were enhanced. The largest improvement in the structural and optical properties of the ZnO nanorods was observed at the Cd mole fraction of 0.5.

• Journal of the Korea Institute of Military Science and Technology
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• v.15 no.4
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• pp.502-506
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• 2012

In order to find the structural characteristics of the thin films of group II-VI semiconductor compounds compared with those of powder materials, films were made of 4 powders of ZnS, CdS, CdSe, and CdTe(Aldrich), each with 99.99 % purity. For the ZnS/CdS multi-layers, the ZnS layer was coated over the CdS layer on an $AlO_x$ membrane, which served as a protective layer within a vacuum at the average speed of 1 ${\AA}$/sec. After studying the structures of the group II-VI semiconductor thin films by using X-ray spectroscopy, we found that the ZnS, ZnS/CdS, CdS, and CdSe films were hexagonal and exhibited some degree of preferred orientation. Also, the particles of the thin films of II-VI semiconductor compounds proved to be more homogeneous in size compared to those of the powder materials. These results were further verified through scanning electron microscopy(SEM), EDX analysis, and powder and thin film X-ray diffraction.

• Clean Technology
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• v.23 no.2
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• pp.196-204
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• 2017

CdZnS/ZnO composite was prepared through low-temperature precipitation and drying method. The property of CdZnS/ZnO as a recyclable photocatalyst for the degradation of rhodamine B (RhB) under visible light irradiation was examined. The sample was characterized by XRD, FE-SEM, XPS, UV-vis DRS and photoluminescence techniques before and after repeated reaction to investigate the change of properties during the photocatalytic reaction. During repeated reaction, the CdZnS/ZnO showed an improved photocatalytic activity and recycle stability. Among two feasible reaction pathways for photocatalytic degradation of RhB, the cleavage of conjugated chromophore was found to predominate over N-dealkylation of chromophore skeleton in the present work. The results indicate that the CdZnS/ZnO, prepared by a simple precipitation method, can be used as a visible-light driven photocatalyst with enhanced cycle stability and activity.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.197.2-197.2
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• 2015

Low-cost, high efficiency solar cells are tremendous interests for the realization of a renewable and clean energy source. ZnTe based solar cells have a possibility of high efficiency with formation of an intermediated energy band structure by impurity doping. In this work, the ZnTe:O/CdS/ZnO structure was fabricated by pulsed laser deposition (PLD) technique. A pulsed (10 Hz) Nd:YAG laser operating at a wavelength of 266 nm was used to produce a plasma plume from an ablated a ZnTe target, whose density of laser energy was 4.5 J/cm2. The base pressure of the chamber was kept at a pressure of approximately $4{\times}10-7Torr$. ZnO thin film with thickness of 100 nm was grown on to ITO/glass, and then CdS and ZnTe:O thin film were grown on ZnO thin film. Thickness of CdS and ZnTe:O were 50 nm and 500 nm, respectively. During deposition of ZnTe:O films, O2 gas was introduced from 1 to 20 mTorr. For fabricating ZnTe:O/CdS/ZnO solar cells, Au metal was deposited on the ITO film and ZnTe:O by thermal evaporation method. From the fabricated ZnTe:O/CdS/ZnO solar cell, current-voltage characteristics was measured by using HP 4156-a semiconductor parameter analyzer. Finally, solar cell performance was measured using an Air Mass 1.5 Global (AM 1.5 G) solar simulator with an irradiation intensity of 100 mW cm-2.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.380-380
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• 2011

ZnO 나노라드 위에 양자점을 증착한 후 그 위에 $TiO_2$를 ALD방법으로 증착하여 그 passivation 효과가 solar cell 효율에 미친 영향에 대한 실험을 진행하였다. Hydrothermal 방법으로 수직한 1차원 형태의 ZnO 나노라드를 성장시킨다. 여기에 SILAR 방법을 거쳐서 CdS 양자점을 증착시키고, 후에 CBD를 이용하여 CdSe 양자점을 증착시킨다. 여기에 마지막으로 amorphous $TiO_2$로 표면을 덮는 과정을 거치는데, $TiO_2$가 ZnO 라드 위에 균일하고 정밀하게 증착되도록 하기 위해서 Atomic Layer Deposition을 이용하였다. 다양한 분석 방법을 통해 $TiO_2$/CdSe/CdS/ZnO 구조를 조사하였으며, ZnO 나노라드 위에 $TiO_2$가 정교하게 올라간 것을 확인한 후에 solar cell에 적용하여 그 효율을 확인하였다.

• Clean Technology
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• v.25 no.1
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• pp.46-55
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• 2019

CdS and CdZnS/ZnO materials were prepared using precipitation method and used as photocatalysts for the photocatalytic degradation of rhodamine B (RhB) under visible light irradiation. The prepared photocatalysts were also characterized by XRD and UV-vis DRS. The results indicated that the photocatalysts with intended crystalline structures were successfully obtained and both the CdS and CdZnS/ZnO can absorb visible light as well as UV. The photocatalytic activities were examined with the addition of scavenger for various active chemical species and the difference of reaction mechanisms over the catalysts were discussed. The $CH_3OH$, KI and p-benzoquinone were used as scavengers for ${\cdot}OH$ radical, photogenerated positive hole and ${\cdot}O_2{^-}$ radical, respectively. The CdS and CdZnS/ZnO showed different photocatalytic degradation mechanisms of RhB. It can be postulated that ${\cdot}O_2{^-}$ radical is the main active species for the reaction over CdS photocatalyst, while the photogenerated positive hole for CdZnS/ZnO photocatalyst. As a result, the predominant reaction pathways over CdS and CdZnS/ZnO photocatalysts were found to be the dealkylation of chromophore skeleton and the cleavage of the conjugated chromophore structure, respectively. The above results may be mainly ascribed to the difference of band edge potential of conduction and valence bands in CdS, CdZnS and ZnO semiconductors and the redox potentials for formation of active chemical species.