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Humic acid fouling in a submerged photocatalytic membrane reactor with binary TiO2–ZrO2 particles
Sovann Khan,김정환,Arcadio Sotto,Bart Van der Bruggen 한국공업화학회 2015 Journal of Industrial and Engineering Chemistry Vol.21 No.1
The binary TiO2–ZrO2 particles were better alternative to TiO2 particles as photocatalyst to reduce humicacid fouling in photocatalytic membrane reactor. The structure of the TiO2–ZrO2 particles was stronglydependent upon the content of zirconium as an additive. A composition of 50% TiO2 with 50% ZrO2 wasoptimal in terms of physicochemical properties. The effect of TiO2–ZrO2 particles on the reduction ofhumic acid fouling was further improved by the presence of divalent cations such as calcium. Nevertheless, the stability of polymeric membranes in longer-term operation using a hybridphotocatalytic membrane reactor for water treatment applications may remain a challenge.
Khan, Sovann,Cho, Haneol,Kim, Donghun,Han, Sang Soo,Lee, Kyu Hwan,Cho, So-Hye,Song, Taeseup,Choi, Heechae Elsevier 2017 Applied Catalysis B Vol.206 No.-
<P><B>Abstract</B></P> <P>Understanding the roles of point defects in optical transitions is a key to the desirable engineering of photochemical materials. In this study, the origins of the significantly varying optical and photochemical properties of Nb-doped anatase TiO<SUB>2</SUB> were systematically investigated, using density functional theory (DFT) calculations and experimental verifications. We found from DFT calculations that the desirable band gap reduction of anatase TiO<SUB>2</SUB> by ∼0.1eV reported in many of experimental reports and the resultant improvements of photocatalytic and photovoltaic efficiencies of Nb<SUP>5+</SUP>-doped anatase TiO<SUB>2</SUB> are due to the formation of complex (Nb<SUB>Ti</SUB>-V<SUB>Ti</SUB>)<SUP>3−</SUP> as the compensator of Nb<SUB>Ti</SUB> <SUP>+</SUP>. Our experiments demonstrated that the O<SUB>2</SUB>-rich annealing, which is expected to increase the concentration of desirable (Nb<SUB>Ti</SUB>-V<SUB>Ti</SUB>)<SUP>3−</SUP> complex, narrows band gap of TiO<SUB>2</SUB> and strongly enhances the photocatalytic activity of Nb-doped TiO<SUB>2</SUB> particle. On the contrary, pure TiO<SUB>2</SUB> showed rather worse photocatalytic performances when annealed in O<SUB>2</SUB>-rich atmosphere, which is due to the formation of deep level by O-interstitial defect (O<SUB>i</SUB>). Theoretically obtained charge effective masses could further explain the different photocatalytic activities of undoped and Nb-doped TiO<SUB>2</SUB>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Using ab initio calculations, we find that narrowed band gap of Nb-doped TiO<SUB>2</SUB> originates from the complex form of defect, (Nb<SUB>Ti</SUB>-V<SUB>Ti</SUB>)<SUP>3−</SUP>. </LI> <LI> To increase the concentration of desirable defect, (Nb<SUB>Ti</SUB>-V<SUB>Ti</SUB>)<SUP>3−</SUP>, we suggest O-rich annealing on Nb-doped TiO<SUB>2</SUB> photocatalyst. </LI> <LI> We experimentally verify that O-rich annealing on Nb-doped TiO<SUB>2</SUB> narrows its band gap and notably improves the photocatalysis. </LI> <LI> From carrier effective mass calculations, we could explain the enhanced photocatalysis of Nb-doped TiO<SUB>2</SUB> crystal. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Khan, Sovann,Kim, Jeonghwan,Sotto, Arcadio,Van der Bruggen, Bart Elsevier 2015 Journal of industrial and engineering chemistry Vol.21 No.-
<P><B>Abstract</B></P> <P>The binary TiO<SUB>2</SUB>–ZrO<SUB>2</SUB> particles were better alternative to TiO<SUB>2</SUB> particles as photocatalyst to reduce humic acid fouling in photocatalytic membrane reactor. The structure of the TiO<SUB>2</SUB>–ZrO<SUB>2</SUB> particles was strongly dependent upon the content of zirconium as an additive. A composition of 50% TiO<SUB>2</SUB> with 50% ZrO<SUB>2</SUB> was optimal in terms of physicochemical properties. The effect of TiO<SUB>2</SUB>–ZrO<SUB>2</SUB> particles on the reduction of humic acid fouling was further improved by the presence of divalent cations such as calcium. Nevertheless, the stability of polymeric membranes in longer-term operation using a hybrid photocatalytic membrane reactor for water treatment applications may remain a challenge.</P>
The Gender Café Project : Cultivating Women’s Activism from the Inside
Rotvatey SOVANN Asian Center for Women's Studies : Ewha Womans Uni 2014 Asian Journal of Women's Studies(AJWS) Vol.20 No.4
Gender-based violence is an important issue in the Cambodian context that has been neglected considerably, but remains a major problem for development and human rights. Gender Café, a project initiated by Gender and Development for Cambodia in 2011, aims at addressing the issue of gender-based violence by empowering women through information and story sharing. In 2013, four specific groups of women―women entertainers, street vendors, factory workers and victims of land eviction―have been identified to become Gender Café members because of their vulnerable status in Cambodian society. With activities, such as gender café events, monitoring and coaching, camping, publication of cases and radio shows, Gender Café intends to support and inspire its members to exercise their rights to become free from gender-based violence. The project has been successful in combating such violence and promoting women’s empowerment.
Good practices for eliminating violence against women in Cambodia
Rotvatey Sovann 이화여자대학교 아시아여성학센터 2019 Asian Journal of Women's Studies(AJWS) Vol.25 No.2
To tackle violence against women in Cambodia, action has been taken by local people, government and Civil Society Organizations (CSOs) in the kingdom. To understand this multi-faceted issue, in this study I highlight four main interventions that address and/or seek to prevent violence against women. By investigating these—“Shaping our future: Developing healthy and happy relationships” project, the “Cambodia Men’s Network,” “Gender and Development Network,” and the “Gender Café”—projects, I identify four themes that correspond with these respectively: education, networking, advocacy and empowerment. The study indicates that these practices have yielded significant results for the prevention of violence against women and girls. While each one has its limitations, it notes the potential of each to address the complex issue of violence against women.
Khan, Sovann,Choi, Heechae,Lee, Seung Yong,Lee, Kwang-Ryeol,Ntwaeaborwa, Odireleng Martin,Kim, Seungchul,Cho, So-Hye American Chemical Society 2017 Inorganic Chemistry Vol.56 No.20
<P>To enhance the photoluminescence of lanthanide oxide, a cleat understanding of its defect chemistry is necessary. In particular, when yttrium oxide, a widely used phosphor,,,. undergoes doping, several of its atomic structures may be coupled with point defects that are difficult to understand through experimental results alone. Here, we report the Strong enhancement of the photoluminescence (PL) of Y2O3:Bi3+ via codoping with Li+ ions and suggest a plausible mechanism for that enhancement using both experimental and computational studies. The codoping of Li+ ions into the Y2O3:Bi3+ phosphor was found to cause significant changes in its structural and optical properties. Interestingly, unlike previous reports on codoping with several other phosphors, we found that Li+ ions preferentially occupy interstitial sites of the Y2O3:Bi3+ phosphor. Computational insights based on density functional theory calculations also indicate that Li+ is energetically more stable in the interstitial sites than in the substitutional sites. In addition, interstitially doped Li+ was found to favor the vicinity of Bi3+ by an energy difference of 0.40 eV in comparison to isolated sites. The calculated DOS showed the formation of a shallow level directly above the unoccupied 6p orbital of Bi3+ as the result of interstitial Li+ doping, which may be responsible for the enhanced PL. Although the crystallinity of the host materials increased with the addition of Li salts, the degree of increase was minimal when the Li+ content was low (<1 ma%) where major PL enhancement was observed. Therefore, we reason that the enhanced PL mainly results from the shallow levels created by the interstitial Li+.</P>