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Novel clays: Solid-state synthesis, characterization and cation exchange selectivity
Sridhar Komarneni,Ramesh Ravella 한국물리학회 2008 Current Applied Physics Vol.8 No.1
Several novel swelling mica-type clays have been synthesized by solid-state processes. Synthetic clays of ideal compositions such asNa2Si6Al2Mg 6O20F4 ÆxH2O (Na-2-mica), Na3Si5Al3Mg 6O20F4 ÆxH2O (Na-3-mica) and Na4Si4Al4Mg 6O20F4 ÆxH2O (Na-4-mica) havebeen prepared and characterized by powder X-ray diraction (XRD), scanning electron microscopy (SEM) and27Al and29Si solid-statemagic angle spinning nuclear magnetic resonance (MASNMR) spectroscopy. Powder XRD showed that all syntheses yielded water swol-len micas withc-axis spacing of. 1.2 nm except in the case of Na-2-mica which also showed a small peak of anhydrous mica phase with ac-axis spacing of 0.96 nm. Solid-state27Al MASNMR spectroscopy revealed that almost all the Al is present in the tetrahedral environ-29Si MASNMR spectroscopy revealed dierent Si (Al) nearest neighbor environments dependingupon the composition of the various micas. Selective cation exchange studies were performed on the various micas using 0.5 N NaClsolution containing 12.9 ppm Sr2+ or 8.12 ppm of La3+. The results showed, for the rst time, that Na-3-mica has a high selectivityfor the trivalent cation tested. The previously reported high selectivity of these synthetic micas for the divalent cations has been con-rmed. These selective cation exchange studies are of relevance in cation separations from drinking and waste waters.
Mineral-Based Slow Release Fertilizers: A Review
Noh, Young Dong,Komarneni, Sridhar,Park, Man Korean Society of Soil Science and Fertilizer 2015 한국토양비료학회지 Vol.48 No.1
Global population is expected to reach nine billion in 2050 and the total demand for food is expected to increase approximately by 60 percent by 2050 as compared to 2005. Therefore, it is important to increase crop production in order to meet the global demand for food. Slow release fertilizers have been developed and designed in order to improve the efficiency of fertilizers. Mineral-based slow release fertilizers are useful because the minerals have a crystalline structure and are environmentally friendly in a soil. This review focuses on slow release fertilizers based on montmorillonite, zeolite, and layered double hydroxide phases as a host for nutrients, especially N. Urea was successfully stabilized in the interlayer space of montmorillonite by the formation of urea-Mg or Ca complex, $[(Urea)_6Mg\;or\;Ca]^{2+}$ protecting its rapid degradation in soils. Naturally occurring zeolites occluded with ammonium nitrate and potassium nitrate by molten salt treatment could be used as slow release fertilizer because the occlusion process increased the capacity of zeolites to store nutrients in addition to exchangeable cations. Additionally, surface-modified zeolites could also be used as slow release fertilizer because the modified surface showed high affinity for anionic nutrients such as nitrate and phosphate. Moreover, there were attempts to develop and use synthetic layered double hydroxide as a carrier of nitrate because it has positively charged layers which electrostatically bond nitrate anions. Kaolin was also tested by combining with a polymer or through the mechanical-chemical process for slow release of nutrients.
Mineral-Based Slow Release Fertilizers
Young Dong Noh,Sridhar Komarneni,Man Park 한국토양비료학회 2015 한국토양비료학회지 Vol.48 No.1
Global population is expected to reach nine billion in 2050 and the total demand for food is expected to increase approximately by 60 percent by 2050 as compared to 2005. Therefore, it is important to increase crop production in order to meet the global demand for food. Slow release fertilizers have been developed and designed in order to improve the efficiency of fertilizers. Mineral-based slow release fertilizers are useful because the minerals have a crystalline structure and are environmentally friendly in a soil. This review focuses on slow release fertilizers based on montmorillonite, zeolite, and layered double hydroxide phases as a host for nutrients, especially N. Urea was successfully stabilized in the interlayer space of montmorillonite by the formation of urea-Mg or Ca complex, [(Urea)6Mg or Ca]<SUP>2+</SUP> protecting its rapid degradation in soils. Naturally occurring zeolites occluded with ammonium nitrate and potassium nitrate by molten salt treatment could be used as slow release fertilizer because the occlusion process increased the capacity of zeolites to store nutrients in addition to exchangeable cations. Additionally, surface-modified zeolites could also be used as slow release fertilizer because the modified surface showed high affinity for anionic nutrients such as nitrate and phosphate. Moreover, there were attempts to develop and use synthetic layered double hydroxide as a carrier of nitrate because it has positively charged layers which electrostatically bond nitrate anions. Kaolin was also tested by combining with a polymer or through the mechanical-chemical process for slow release of nutrients.
Solvothermal Synthesis of CZTS Nanoparticles in Ethanol: Preparation and Characterization
Xinlong Yan,Xiaoyan Hu,Sridhar Komarneni 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.10
In this work, a low-cost, non-toxic and convenient one-pot solvothermal route to synthesize Cu2ZnSnS4 (CZTS) nanoparticles is reported. The effects of solvothermal temperature and reaction time on the structure, morphology and optical properties of the as-synthesized product were investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) measurements and X-ray photoelectron spectroscopy (XPS). The results showed that the crystallinity of the CZTS powders was influenced by the solvothermal temperature and reaction time. The band gap of selected CZTS samples was near the optimum value for photovoltaic solar conversion in a single-band-gap device.
Katsuki, Hiroaki,Choi, Eun-Kyoung,Lee, Won-Jun,Cho, Woo-Seok,Hwang, Kwang-Taek,Huang, Wenyan,Komarneni, Sridhar Elsevier 2017 CERAMICS INTERNATIONAL Vol.43 No.16
<P><B>Abstract</B></P> <P>The effect of mixing process of FeCl<SUB>3</SUB> and NaOH solution on the formation of platy (hexagonal) α-Fe<SUB>2</SUB>O<SUB>3</SUB> was investigated at 160 and 180°C by the hydrothermal process. The crystal growth of platy α-Fe<SUB>2</SUB>O<SUB>3</SUB> was promoted at higher hydrothermal temperature, higher concentration of NaOH solution and by the addition of FeCl<SUB>3</SUB> solution to NaOH solution instead of the reverse addition. Platy crystals of α-Fe<SUB>2</SUB>O<SUB>3</SUB> showed dark red wine color while nanophase equiaxed crystals showed yellowish red color. The platy crystals of 3–6µm in average diameter kept their platy structure after heating at 900 and 1100°C in air due to their higher thermal stability towards sintering.</P>