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Photocatalytic improvement of Mn-adsorbed <i>g</i>-C<sub>3</sub>N<sub>4</sub>
Zhang, Weibin,Zhang, Zhijun,Kwon, Sangwoo,Zhang, Fuchun,Stephen, Boandoh,Kim, Ki Kang,Jung, Ranju,Kwon, Sera,Chung, Kwun-Bum,Yang, Woochul Elsevier BV 2017 Applied Catalysis B Vol.206 No.-
<P><B>Abstract</B></P> <P>This study employed experimental results and theoretical calculations to investigate Mn-adsorbed <I>g</I>-C<SUB>3</SUB>N<SUB>4</SUB> as a potential photocatalyst with high efficiency. Mn was chosen as the incorporating element, because among the 3<I>d</I> transition metals it exhibits the highest binding energy and most suitable band edge positions. The photocatalytic efficiency of Mn-adsorbed <I>g</I>-C<SUB>3</SUB>N<SUB>4</SUB> is 3 times higher that of pristine <I>g</I>-C<SUB>3</SUB>N<SUB>4</SUB>. Although small variations in the phase and surface morphology were observed, which were confirmed to not be the determining factors to improve efficiency. The factors that affect the high photocatalytic efficiency are therefore the electronic structure, optical absorption, and band edge variations after Mn-adsorption. The Mn atoms stably are bonded with N atoms, due to the strong absorption energy and ionic bond. Moreover, reduction of the <I>g</I>-C<SUB>3</SUB>N<SUB>4</SUB> band gap after Mn-adsorption results in a red shift of the absorption band edge. The half-filled Mn 3<I>d</I> state introduces impurity states into the forbidden band gap, which will increase the life time of charge carriers. In addition, the up-shifting of band edges of Mn-adsorbed <I>g</I>-C<SUB>3</SUB>N<SUB>4</SUB> leads to inhibition of the electron-hole recombination. As a consequence, the photocatalytic efficiency of Mn-adsorbed <I>g</I>-C<SUB>3</SUB>N<SUB>4</SUB> is enhanced due to the combination of the aforementioned effects.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The photocatalytic efficiency of Mn-adsorbed <I>g</I>-C<SUB>3</SUB>N<SUB>4</SUB> is three times higher that of pristine <I>g</I>-C<SUB>3</SUB>N<SUB>4</SUB>. </LI> <LI> The Mn atoms adsorbed on <I>g</I>-C<SUB>3</SUB>N<SUB>4</SUB> stably form ionic bond with N atoms, as confirmed by DFT calculation and experiment. </LI> <LI> The photocatalytic efficiency enhancement of Mn-adsorbed <I>g</I>-C<SUB>3</SUB>N<SUB>4</SUB> is attributed to the decrease of band gap, the half-filled Mn 3d states in the forbidden gap, and the up-shifting of band edges. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Zhang, Weibin,Zhang, Zhijun,Yang, Woochul American Scientific Publishers 2015 Journal of nanoscience and nanotechnology Vol.15 No.10
<P>First-principles total energy studies are used to investigate the stability of hydrogenated MoS2 monolayer (MoS2-H-x) (x = 1-8), which is a compound with different numbers of H atoms adsorbed on the MoS2 surface. Energetically, the S-top side of the MoS2 is found to be the most favorable for H-adsorption. H2S and graphene are well-known to be stable, and MoS2-H-x is predicted to be even more stable because its binding energy is lower than that of H2S and its formation energy and adsorption energy are lower than those of graphene. The analysis of the electronic density distribution and the orbital hybrid also shows that MoS2-H-x forms stable structures. In addition, the influence of the number of the adsorbed H-atoms in the MoS2-H-x on the electronic structure of the compound is also investigated. The MoS2-H-x band structure exhibits a dispersion and the MoS2-H-x band gap gradually decreases from 1.72 eV to 0 eV as the number of adsorbed H atoms increases. The corresponding work function increases as a result of the strengthening of the dipole moment formed between the H atoms that are adsorbed and the hydrogenated MoS2.</P>
Energy spread minimization in a cascaded laser wakefield accelerator via velocity bunching
Zhang, Zhijun,Li, Wentao,Liu, Jiansheng,Wang, Wentao,Yu, Changhai,Tian, Ye,Nakajima, Kazuhisa,Deng, Aihua,Qi, Rong,Wang, Cheng,Qin, Zhiyong,Fang, Ming,Liu, Jiaqi,Xia, Changquan,Li, Ruxin,Xu, Zhizhan American Institute of Physics 2016 Physics of plasmas Vol.23 No.5
The Design of an Efficient Proxy-Based Framework for Mobile Cloud Computing
Zhang, Zhijun,Lim, HyoTaek,Lee, Hoon Jae The Korea Institute of Information and Commucation 2015 Journal of information and communication convergen Vol.13 No.1
The limited battery power in the mobile environment, lack of sufficient wireless bandwidth, limited resources of mobile terminals, and frequent breakdowns of the wireless network have become major hurdles in the development of mobile cloud computing (MCC). In order to solve the abovementioned problems, This paper propose a proxy-based MCC framework by adding a proxy server between mobile devices and cloud services to optimize the access to cloud services by mobile devices on the network transmission, application support, and service mode levels. Finally, we verify the effectiveness of the developed framework through an experimental analysis. This framework can ensure that mobile users have efficient access to cloud services.
An Efficient Framework for Computation Offloading In Mobile Cloud Computing
Zhijun Zhang,HyoTaek Lim,Hoon Jae Lee 한국정보통신학회 2014 2016 INTERNATIONAL CONFERENCE Vol.6 No.1
With the emergence of mobile cloud computing (MCC), Mobile applications are becoming increasingly, there is a significant increase of mobile subscriptions, the drives need a strong demand for mobile cloud applications and services for mobile device users. However, mobile terminals are resource-constrained and therefore, running these applications directly on it is not satisfactory given a user’s expectations. This paper proposes a novel offloading service that can seamlessly offload some of the tasks of a mobile application from mobile terminals to cloud. Offloading computation to the cloud effectively expands the usability of mobile terminals beyond their physical limits, and also greatly extends their battery charging intervals through potential energy savings. The system architecture and key components of the proposed offloading service are presented, prototyped, and evaluated. The results of experiments and simulations have demonstrated the effectiveness and efficiency of this offloading service for mobile applications.
Facile enhancement of photocatalytic efficiency of g-C<sub>3</sub>N<sub>4</sub> by Li-intercalation
Zhang, Weibin,Zhang, Zhijun,Choi, Soo Ho,Yang, Woochul Elsevier 2019 CATALYSIS TODAY - Vol.321 No.-
<P><B>Abstract</B></P> <P>We report significant enhancement of photocatalytic properties of g-C<SUB>3</SUB>N<SUB>4</SUB> by a facile Lithium (Li)-intercalation method. The Li atoms are successfully and stably intercalated into the interlayer of g-C<SUB>3</SUB>N<SUB>4</SUB> by <I>n</I>-butyl lithium (<I>n</I>-BuLi). The photocatalytic activity of the Li-intercalated g-C<SUB>3</SUB>N<SUB>4</SUB> was observed to be significantly improved by 2.8 times in degradation of a dye (RhB), compared to that of pristine g-C<SUB>3</SUB>N<SUB>4</SUB>. The synergetic effects of the narrowed band gap, enhanced surface area, establishment of an interlayer pathway, and positive shift in the valence band position improve the photocatalytic activity of the Li-intercalated g-C<SUB>3</SUB>N<SUB>4</SUB>. Our discovery provides a promising route to manipulate the photocatalytic activity simply by increasing the Li concentration after the growth process of the g-C<SUB>3</SUB>N<SUB>4</SUB>, gaining a deeper understanding of the improvement in the photocatalytic efficiency.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The Li atoms are stably intercalated into the interlayer of g-C<SUB>3</SUB>N<SUB>4</SUB>. </LI> <LI> The photocatalytic efficiency of Li-intercalated g-C<SUB>3</SUB>N<SUB>4</SUB> improves 2.8 times. </LI> <LI> The enhanced efficiency is due to synergetic effects induced by Li-intercalation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Zhang, Cheng,Xie, Minmin,Zhang, Yi,Zhang, Xiaopeng,Feng, Chong,Wu, Zhijun,Feng, Ying,Yang, Yahui,Xu, Hui,Ma, Tai The Korean Gastric Cancer Association 2022 Journal of gastric cancer Vol.22 No.2
Purpose: This study aimed to identify prognostic factors for patients with distant lymph node-involved gastric cancer (GC) using a machine learning algorithm, a method that offers considerable advantages and new prospects for high-dimensional biomedical data exploration. Materials and Methods: This study employed 79 features of clinical pathology, laboratory tests, and therapeutic details from 289 GC patients whose distant lymphadenopathy was presented as the first episode of recurrence or metastasis. Outcomes were measured as any-cause death events and survival months after distant lymph node metastasis. A prediction model was built based on possible outcome predictors using a random survival forest algorithm and confirmed by 5×5 nested cross-validation. The effects of single variables were interpreted using partial dependence plots. A contour plot was used to visually represent survival prediction based on 2 predictive features. Results: The median survival time of patients with GC with distant nodal metastasis was 9.2 months. The optimal model incorporated the prealbumin level and the prothrombin time (PT), and yielded a prediction error of 0.353. The inclusion of other variables resulted in poorer model performance. Patients with higher serum prealbumin levels or shorter PTs had a significantly better prognosis. The predicted one-year survival rate was stratified and illustrated as a contour plot based on the combined effect the prealbumin level and the PT. Conclusions: Machine learning is useful for identifying the important determinants of cancer survival using high-dimensional datasets. The prealbumin level and the PT on distant lymph node metastasis are the 2 most crucial factors in predicting the subsequent survival time of advanced GC.
Weibin Zhang,Hoon Young Cho,Zhijun Zhang,Woochul Yang,Ki Kang Kim,Fuchun Zhang 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.9
The electronic structure and the optical properties of Mn-decorated graphitic carbon nitride (g- C3N4) were investigated using the density functional method. The large absorption energy of the Mn atoms on the g-C3N4 surface was found to suppress the clustering of the Mn atoms, which led to a conservation of the photocatalytic activity. The electronic structures of the Mn-decorated g-C3N4 showed that impurity energy levels emerged in the forbidden band of g-C3N4 and that the band edge of g-C3N4 shifted upward to 0.40 eV. In addition, the calculated optical constants showed that the novel photon absorption in the range of visible light originated from electronic transitions from the N 2p states in the upper valence band to impurity Mn 3d states. Moreover, the photon absorption reached a maximum when all sites of triangular N holes were decorated with Mn atoms. Our results provide evidence that the Mn-decorated C3N4 system could be a highly-efficient photocatalyst for solar light due to the extension of the range of photon absorption to include almost all visible light.
Mengmeng Zhang,Yamin Cheng,Zhiwei Li,Xiaohong Li,Laigui Yu,Zhijun Zhang 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2019 NANO Vol.15 No.01
An inorganic–organic nanohybrid flame retardant, HNT@CS@Fe3O4, is prepared by Halloysite nanotubes (HNT) as nanotemplate, chitosan (CS) as char-forming agent and ferroferric oxide (Fe3O4) playing in a catalytic role, aiming to endow enhanced flame-retardant performance of its nanohybrid. Results show that HNT@CS@Fe3O4 nanohybrids have a corn-like structure and can significantly improve the flame retardancy and thermal stability of epoxy resin (EP). Especially, the initial thermal degradation temperature of EP/HNT@CS@Fe3O4 is significantly improved by 24 ℃ relative to pure EP, and the residual carbon yield under air atmosphere is 8.8 wt.%, which is significantly higher than other EP composites, indicating a higher thermal stability is offered by the as-prepared nanohybrid. The limiting oxygen index of EP/10HNT@CS@Fe3O4 is 31.3%, which is 10.2% higher than that of pure EP. Meanwhile, the HNT@CS@Fe3O4 nanofiller reduces the peak heat release rate, CO production and peak smoke production release of EP nanocomposite by 32.0%, 44.0% and 33.0% in a cone calorimeter test, respectively. This is because the HNT-based composite can form a three-dimensional network structure into the EP matrix to inhibit heat release and diffusion of flammable moieties upon burning of EP. In the meantime, the incorporated Fe3O4 nanoparticle can in situ catalyze the charring of CS and EP matrix on the surface of HNT during the combustion process, which also contributes to the significantly increased fire safety of EP.