Humic acid fouling in a submerged photocatalytic membrane reactor with binary TiO₂–ZrO₂ particles

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>

Flame synthesized Y2O3:Tb3+-Yb3+ phosphors as spectral convertors for solar cells

Khan, Sovann,Park, Bo-In,Han, Joon Soo,Lee, Seung Yong,Cho, So-Hye Springer-Verlag 2018 Research on chemical intermediates Vol.44 No.8

Flame-synthesized Y2O3:Tb3+ nanocrystals as spectral converting materials

Khan, Sovann,Han, Joon Soo,Lee, Seung Yong,Cho, So-Hye Springer-Verlag 2018 JOURNAL OF NANOPARTICLE RESEARCH Vol.20 No.9

Unexpected Roles of Interstitially Doped Lithium in Blue and Green Light Emitting Y₂O₃:Bi³⁺: A Combined Experimental and Computational Study

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>

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.

Defect engineering toward strong photocatalysis of Nb-doped anatase TiO₂: Computational predictions and experimental verifications

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>

ZnS nanoparticles as new additive for polyethersulfone membrane in humic acid filtration

Jing Guo,Sovann Khan,조소혜,김정환 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.79 No.-

In this report, well-dispersed ZnS nanoparticles were applied as inorganic additives for polyethersulfone(PES) membrane to improve anti-fouling performance. ZnS nanoparticles were synthesized by lowtemperature precipitation and phase inversion method was used to embed them into PES membrane forhumic acid (HA)filtration. Intrinsic properties of the PES-ZnS composite membrane developed wereinvestigated at different ZnS loadings. Compared to the control PES membrane, the PES-ZnS membraneimproved hydrophilicity, porosity and thermal stability. Effect of ZnS on theflux recovery of the PESmembrane fouled with HA was more pronounced than that as TiO2 was used as embedding materials.

Synergetic control of band gap and structural transformation for optimizing TiO₂ photocatalysts

Choi, Heechae,Khan, Sovann,Choi, Junghyun,Dinh, Duong T.T.,Lee, Seung Yong,Paik, Ungyu,Cho, So-Hye,Kim, Seungchul Elsevier 2017 Applied Catalysis B Vol.210 No.-

<P><B>Abstract</B></P> <P>Impurity doping and synthesizing polymorphic particles are the common strategies to improve activity of TiO<SUB>2</SUB> photocatalyst by lowering the band gap and enhancing electron-hole separation rate. However, these two approaches have side effects. Doping of impurities make space charge region (SCR) thinner near the surface, which requires smaller sized particles than undoped TiO<SUB>2</SUB> for the optimal performance. Polymorphic TiO<SUB>2</SUB> particles, in which rutile and anatase phases coexist in a particle, are usually large due to energetic unstability of the rutile phase in a fine particle. For this contradiction that one needs small size while the other needs large size, two effects are not easy to be combined. In this study, we suggest a <I>dual-doping</I> strategy to solve the contradictory problem of SCR reduction by donor doping and inevitable size growth in polymorphic particles. We successfully dope W, a band gap narrower, into fine size of polymorphic particles by Sn-codoping, a promoter of the anatase-to-rutile transformation (ART), and demonstrate greatly improved photocatalytic activity. The accelerated ART by Sn-doping could keep the size of polymorph junctioned TiO<SUB>2</SUB> small (∼10nm) as lower temperature annealing become able to induce the ART. The concept of dual doping with a band gap narrower and an ART promoter provides a way to synthesize highly active photocatalysts by overcoming the drawback from shortened SCR length.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Band gap narrowing by W-doping into TiO<SUB>2</SUB>. </LI> <LI> Electron-hole separation at rutile-anatase boundary of Sn-doped TiO<SUB>2</SUB>. </LI> <LI> Separately controllable band gap and phase boundary in TiO<SUB>2</SUB> nano-particles by co-doping. </LI> <LI> W-doping in ∼10nm polymorphic TiO<SUB>2</SUB> nano-particles at lowered temperature. </LI> <LI> Simultaneously enhanced photo-absorption rate and electron-hole separation rate. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Preparation and immobilization of zinc sulfide (ZnS) nanoparticles on polyvinylidene fluoride pellets for photocatalytic degradation of methylene blue in wastewater

Guo, Jing,Khan, Sovann,Cho, So-Hye,Kim, Jeonghwan Elsevier 2019 APPLIED SURFACE SCIENCE - Vol.473 No.-

<P><B>Abstract</B></P> <P>ZnS nanoparticles with 90 nm diameter were synthesized by low-temperature method and immobilized onto the surface of polyvinylidene fluoride (PVDF) pellets prepared by phase inversion method. Results by FTIR and X-ray photoelectron spectroscopy revealed that the ZnS nanoparticles were immobilized tightly on the PVDF surface without their release and losing photocatalytic activity. The UV-absorption spectra showed that the PVDF matrix had no adverse effect on the optical properties of ZnS nanoparticles. Due to large size (5 mm) and excellent mechanical stability, the PVDF-ZnS pellets could be easily dispersed in the photocatalytic reactor treating methylene blue solution. The removal efficiency of the methylene blue with the PVDF-ZnS pellets was higher (more than 95%) than that observed by the control PVDF pellets or ZnS nanoparticles tested. No change in the removal efficiency was observed as the PVDF-ZnS pellets were reused by performing photocatalytic tests at the same experimental conditions repeatedly.</P> <P><B>Highlights</B></P> <P> <UL> <LI> ZnS nanoparticles were synthesized by low-temperature precipitation method. </LI> <LI> ZnS nanoparticles were deposited on PVDF pellets by phase inversion method. </LI> <LI> PVDF-ZnS pellets showed high photocatalytic activity for removal of organic dye. </LI> <LI> PVDF-ZnS pellets were dispersed easily in photocatalytic reactor treating organic dye. </LI> <LI> PVDF-ZnS pellets had a mechanical strength without losing ZnS nanoparticles. </LI> </UL> </P>

Near-IR Quantum Cutting Phosphors: A Step Towards Enhancing Solar Cell Efficiency

Abhijit P. Jadhav,조소혜,Sovann Khan,김선진 한국진공학회 2014 Applied Science and Convergence Technology Vol.23 No.5

The global demand for energy has been increasing since past decades. Various technologieshave been working to find a suitable alternative for the generation of sustainable energy. Photovoltaic technologies for solar energy conversion represent one of the significant routesfor the green and renewable energy production. Despite of remarkable improvement in solarcell technologies, the generation of power is still suffering with lower energy conversionefficiency, high production cost, etc. The major problem in improving the PV efficiency isspectral mismatch between the incident solar spectrum and bandgap of a semiconductormaterial used in solar cell. Luminescent materials such as rare-earth doped phosphor materialshaving the quantum efficiency higher than unity can be helpful for photovoltaic applications. Quantum cutting phosphors are the most suitable candidates for the generation of two ormore low-energy photons for the absorption of every incident high-energy photons. Thephosphors which are capable of converting UV photon to visible and near-IR (NIR) photonare studied primarily for photovoltaic applications. In this review, we will survey variousnear IR quantum cutting phosphors with respective to their synthesis method, energy transfermechanism, nature of activator, sensitizer and dopant materials incorporation and energyconversion efficiency considering their applications in photovoltaics.