Photodecomposition of Different Organic Dyes Using Fe-CNT/TiO₂ Composites under UV and Visible Light

Zhang, Kan,Meng, Ze-Da,Oh, Won-Chun The Korean Ceramic Society 2010 한국세라믹학회지 Vol.47 No.2

The Fe-treated CNT/$TiO_2$ photocatalysts mixed with anatase and rutile phase have been developed for the decomposition of non-biodegradable different organic dyes like methylene blue (MB), rhodamine B (Rh.B), and methyl orange (MO) in two conditions as ultraviolet and visible light respectively. The results indicate that all the Fe-CNT/$TiO_2$ composites proved to be more efficient photocatalysts since degradation of MB at higher reaction rates, tthe decomposition rate of different dyes increases with an increase of $Fe^{3+}$ concentration in composites the highest rate of decomposition of different dyes was noted under UV irradiation. These results can indicate that the large CNT network is facilitate the electron transfer and strongly adsorb dye molecules on the texted photocatalysts, iron is reactive in the photo-Fenton process resulting in high production of OH radicals and also high activity of the photocatalyst. And Fe particles can generate more photoinduced electrons to conduction band of $TiO_2$ under visible light irradiation. The composites of Fe-CNT/$TiO_2$ photocatalysts synthesized by a sol-gel method were characterized by BET, TEM, SEM, XRD and EDX.

Photocatalytic Degradation of Methylene Blue by ACF/TiO₂ and ACF/ZnO Composites under UV Light

Zhang, Kan,Oh, Won-Chun Materials Research Society of Korea 2010 한국재료학회지 Vol.20 No.1

Methylene blue (MB) was degraded by $TiO_2$ and ZnO deposited on an activated carbon fiber (ACF) surface under UV light. The ACF/$TiO_2$ and ACF/ZnO composites were characterized by BET, SEM, XRD, and EDX. The BET surface area was related to the adsorption capacity for composites. The SEM results showed that titanium dioxide and zinc oxide are distributed on the ACF surface. The XRD results showed that the ACF/$TiO_2$ and ACF/ZnO composites contained a unique anatase structure for $TiO_2$ and a typical hexagonal phase for ZnO respectively. These EDX spectra showed the presence of peaks of Ti element on ACF/$TiO_2$ composite and peaks of Zn element on the ACF/ZnO composite. The blank experiments for either illuminating the MB solution or the suspension containing ACF/$TiO_2$ or ACF/ZnO in the dark showed that both illumination and the catalyst were necessary for the mineralization of organic dye. Additionally, the ACF/$TiO_2$ composites proved to be efficient photocatalysts due to degradation of MB at higher reaction rates. The addition of an oxidant $([NH_4]_2S_2O_8)$ led to an increase of the degradation rate of MB for ACF/$TiO_2$ and ACF/ZnO composites.

A Novel Synthesis and Photonic Effect of Fe-CNT/TiO₂ Composites by Controlling of Carbon Nanotube Amounts

Zhang, Kan,Meng, Ze-Da,Oh, Won-Chun Materials Research Society of Korea 2010 한국재료학회지 Vol.20 No.3

Titanium dioxide ($TiO_2$) particles deposited on different quantitative Fe-treated carbon nanotube (CNT) composites with high photocatalytic activity of visible light were prepared by a modified sol-gel method using TNB as a titanium source. The composites were characterized by BET, XRD, SEM, TEM and EDX, which showed that the BET surface area was related to the adsorption capacity for each composite. From TEM images, surface and structural characterization of for the CNT surface had been carried out. The XRD results showed that the Fe-ACF/$TiO_2$ composite mostly contained an anatase structure with a Fe-mediated compound. EDX results showed the presence of C, O, and Ti with Fe peaks in the Fe-CNT/$TiO_2$ composites. The photocatalytic activity of the composites was examined by degradation of methylene blue (MB) in aqueous solution under visible light, which was found to depend on the amount of CNT. The highest photocatalytic activity among the different composites was related to the optimal content of CNT in the Fe-CNT/$TiO_2$ composites. In particular, the photocatalytic activity of the Fe-CNT/$TiO_2$ composites under visible light was better than that of the CNT/$TiO_2$ composites due to the introduction of Fe particles.

Conformal Coating Strategy Comprising N-doped Carbon and Conventional Graphene for Achieving Ultrahigh Power and Cyclability of LiFePO₄

Zhang, Kan,Lee, Jeong-Taik,Li, Ping,Kang, Byoungwoo,Kim, Jung Hyun,Yi, Gi-Ra,Park, Jong Hyeok American Chemical Society 2015 NANO LETTERS Vol.15 No.10

<P>Surface carbon coating to improve the inherent poor electrical conductivity of lithium iron phosphate (LiFePO4, LFP) has been considered as most efficient strategy. Here, we also report one of the conventional methods for LFP but exhibiting a specific capacity beyond the theoretical value, ultrahigh rate performance, and excellent long-term cydability: the specific capacity is 171.9 mAh/g (70 mu m-thick electrode with similar to 10 mg/cm(2) loading mass) at 0.1 C (17 mA/g) and retains 143.7 mAh/g at 10 C (1.7 A/g) and 95.8% of initial capacity at 10 C after 1000 cycles. It was found that the interior conformal N-C coating enhances the intrinsic conductivity of LFP nanorods (LFP NR) and the exterior reduced graphene oxide coating acts as an electrically conducting secondary network to electrically connect the entire electrode. The great electron transport mutually promoted with shorten Li diffusion length on (010) facet exposed LFP NR represents the highest specific capacity value recorded to date at 10 C and ultralong-term cyclability. This conformal carbon coating approach can be a promising strategy for the commercialization of LFP cathode in lithium ion batteries.</P>

Double 2-dimensional H₂-evoluting catalyst tipped photocatalyst nanowires: A new avenue for high-efficiency solar to H₂ generation

Zhang, Kan,Qian, Shifeng,Kim, Wanjung,Kim, Jung Kyu,Sheng, Xiaowei,Lee, Jun Young,Park, Jong Hyeok Elsevier 2017 Nano energy Vol.34 No.-

<P><B>Abstract</B></P> <P>Asymmetric or symmetric metal-tipped one-dimensional (1D) semiconductors are promising systems for efficient photocatalytic reactions such as solar-to-fuel conversion because of ultrafast exciton dynamics that arise at the specific heterostructure interface. However, synthesizing such unique nanostructures experiencing colloid growth on noble metal that has faced a formidable challenge in practical application because these synthesis conditions are not suitable to deploy in mass production. Here, we report the gram-scale mass production of symmetric MoS<SUB>2</SUB>-tipped CdS nanowires (S-MtC NWs) via edge-terminated attachment in a binary solvent. The factors influencing the formation of symmetric heterostructures are investigated by varying the types of precursors, initial concentration, and solvent composition. Under visible-light irradiation (λ≥420nm), the S-MtC NWs exhibit superior photocatalytic H<SUB>2</SUB> evolution activity (12.6mmol/g/h) compared to common Pt/CdS NWs (2.6mmol/g/h), corresponding to an apparent quantum yield of 37.6% at 420nm. This impressive photocatalytic ability is ascribed to spatially separated redox-active sites in the S-MtC NWs, in which the reduction and oxidation sites are at the MoS<SUB>2</SUB> tip and the CdS stem, respectively. Additionally, it is found that the length of CdS NWs as higher aspect ratio as possible could get better photocatalyst H<SUB>2</SUB> performance. The symmetry of 2D MoS<SUB>2</SUB> tips and 1D CdS NWs may provide advanced avenues for specific co-catalyst decoration, enabling co-catalysts to be selectively located at reduction or oxidation sites for other targeted solar artificial syntheses.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Symmetric 2D tipped 1D heterostructured nanowires were synthesized. </LI> <LI> The tipped structure exhibited the spatially separated redox-active sites. </LI> <LI> Theoretical simulation demonstrated one order of magnitude decrease in energy barrier. </LI> <LI> The photocatalytic performance of symmetric heterostructure was superior to asymmetric counterpart. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Symmetric 2D tipped 1D heterostructured nanowires synthesized by edge-terminated attachment exhibit efficient spatial charge separation effect and the longer the better photocatalytic activity, resulting in photocatalytic H<SUB>2</SUB> activity of 12.6mmol/h·g with excellent long-term durability (>10h) without additional passivation under visible light (λ≥420nm).</P> <P>[DISPLAY OMISSION]</P>

The Photocatalytic Decomposition of Different Organic Dyes under UV Irradiation with and without H₂O₂ on Fe-ACF/TiO₂ Photocatalysts

Zhang, Kan,Oh, Won-Chun The Korean Ceramic Society 2009 한국세라믹학회지 Vol.46 No.6

The Fe-ACF/$TiO_2$ composites were prepared by a sol-gel method and were characterized by nitrogen adsorption, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Energy Dispersive X-ray (EDX). The Fe-ACF/$TiO_2$ composites were developed for the decomposition of organic dyes by using a UV lamp. The decomposition effect was investigated under various conditions, such as three selected non-biodegradable organic dyes like Methylene Blue (MB), Methyl Orange (MO), Rhodamine B (Rh.B), and in the presence of Fe and hydrogen peroxide ($H_2O_2$). The photocatalytic activity was derived from possible combination effects, such as (1) adsorption of ACF, (2) generation of electron/hole by $TiO_2$, (3) photo-Fenton reaction of Fe, and (4) oxidation of $Fe^{2+}\;to\;Fe^{3+}\;by\;H_2O_2$.

Photonic Aspects of MB Degradation on Fe-carbon/TiO2 Composites under UV Light Irradiation

Kan Zhang,Ze-Da Meng,오원춘 한국세라믹학회 2010 한국세라믹학회지 Vol.47 No.5

Fe-carbon/TiO2 composites were prepared by a sol-gel method using AC, ACF, CNT and C60 as carbon precursors and were characterized by means of BET surface area, X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). The activity of the prepared photocatalysts was investigated by degradation reaction of methylene blue (MB) irradiated with UV lamp. Effects of different carbon sources and irradiation time on photocatalytic activity were also investigated. The results showed that the photocatalytic activity of the Fe-carbon/TiO2 composites was much higher than that of pristine TiO2 and Fe/TiO2 composites. The prominent photocatalytic activity of Fecarbon/TiO2 composites could be attributed to both the effects of photo-adsorption and electron transfer by carbon substrate. In addition, the higher photocatalytic activity of Fe-carbon/TiO2 composites can be compared with that of carbon/TiO2 and Fe /TiO2 composites due to cooperative effects between Fe and carbon.

Effect of Heat-Treated Temperature on Surface Crystal Structure and Catalytic Activity of ACF/ZnO Composite under Ultraviolet Irradiation and Ultrasonication

Zhang, Kan,Oh, Won-Chun The Korean Ceramic Society 2010 한국세라믹학회지 Vol.47 No.2

ACF/ZnO photocatalyst was synthesized by a sol-gel method using activated carbon fiber (ACF) and Zn $(NO_3)_2$ as precursors. Samples were characterized by Brunauer-Emmett-Teller measurements (BET), scanning electron microscope (SEM), X-ray diffraction (XRD), and energy dispersive X-ray (EDX). The XRD results showed that ACF/ZnO composites only included a hexagonal phase by heat-treated temperature at $400^{\circ}C$, $500^{\circ}C$, $600^{\circ}C$, and $700^{\circ}C$. The SEM analysis revealed that the ACF/ZnO composites did not exhibit any morphological changes of the catalyst surface according to the different heat-treated temperatures. The photocatalytic activity of the samples was tested for degradation of methylene blue (MB) solutions under ultraviolet (UV) light and ultrasonication respectively. The results showed that the photocatalytic activity of ACF/ZnO composites heat-treated at $500^{\circ}C$ was higher than other samples, which is ascribed to the fine distribution of ZnO particles on the surface of the ACF. In addition, an ultrasound of low power (50 W) was used as an irradiation source to successfully induce ACF/ZnO composites to perform sonocatalytic degradation of MB. Results indicated that the sonocatalytic method in the presence of ACF/ZnO composites is an advisable choice for the treatments of organic dyes.

Photodegradation of MB on Fe/CNT-TiO₂ Composite Photocatalysts Under Visible Light

Zhang, Kan,Meng, Ze-Da,Choi, Jong-Geun,Oh, Won-Chun Materials Research Society of Korea 2010 한국재료학회지 Vol.20 No.5

The composite photocatalysts of a Fe-modified carbon nanotube (CNT)-$TiO_2$ were synthesized by a two-step sol-gel method at high temperature. Its chemical composition and surface properties were investigated by BET surface area, scanning electron microscope (SEM), Transmission Electron Microscope (TEM), X-ray diffraction (XRD) and ultraviolet-visible (UV-Vis) spectroscopy. The results showed that the BET surface area was improved by modification of Fe, which was related to the adsorption capacity for each composite. Interesting thin layer aggregates of nanosized $TiO_2$ were observed from TEM images, probably stabilized by the presence of CNT, and the surface and structural characterization of the samples was carried out. The XRD results showed that the Fe/CNT-$TiO_2$ composites contained a mix of anatase and rutile forms of $TiO_2$ particles when the precursor is $TiOSO_4{\cdot}xH_2O$ (TOS). An excellent photocatalytic activity of Fe/CNT-$TiO_2$ was obtained for the degradation of methylene blue (MB) under visible light irradiation. It was considered that Fe cation could be doped into the matrix of $TiO_2$, which could hinder the recombination rate of the excited electrons/holes. The photocatalytic activity of the composites was also found to depend on the presence of CNT. The synergistic effects among the Fe, CNT and $TiO_2$ components were responsible for improving the visible light photocatalytic activity.

Effect of Heat-Treated Temperature on Surface Crystal Structure and Catalytic Activity of ACF/ZnO Composite under Ultraviolet Irradiation and Ultrasonication

Kan Zhang,오원춘 한국세라믹학회 2010 한국세라믹학회지 Vol.47 No.2

ACF/ZnO photocatalyst was synthesized by a sol-gel method using activated carbon fiber (ACF) and Zn (NO3)2 as precursors. Samples were characterized by Brunauer-Emmett-Teller measurements (BET), scanning electron microscope (SEM), X-ray diffraction (XRD), and energy dispersive X-ray (EDX). The XRD results showed that ACF/ZnO composites only included a hexagonal phase by heat-treated temperature at 400oC, 500oC, 600oC, and 700oC. The SEM analysis revealed that the ACF/ZnO composites did not exhibit any morphological changes of the catalyst surface according to the different heat-treated temperatures. The photocatalytic activity of the samples was tested for degradation of methylene blue (MB) solutions under ultraviolet (UV) light and ultrasonication respectively. The results showed that the photocatalytic activity of ACF/ZnO composites heat-treated at 500oC was higher than other samples, which is ascribed to the fine distribution of ZnO particles on the surface of the ACF. In addition, an ultrasound of low power (50 W) was used as an irradiation source to successfully induce ACF/ZnO composites to perform sonocatalytic degradation of MB. Results indicated that the sonocatalytic method in the presence of ACF/ZnO composites is an advisable choice for the treatments of organic dyes.