Sol-gel and solid-state fluorination of lithium cobalt oxide for Li-ion secondary batteries

A series of fluorinated LiCoO2 compounds, LiCoO2−xFx with x = 0.05 − 0.65, were synthesised by both a sol-gel and a solid-state method. The sol-gel method utilises LiNO3 and Co(NO3)2.6H2O as Li and Co sources respectively, water and 1-butanol as solvent for the fluoride precursor LiF, and citric acid as the chelating agent. The prepared materials were compared using pXRD, SEM, Raman, TG and DTA analyses. pXRD revealed a secondary phase appearing at x= 0.25 in materials prepared by the sol-gel method and as early as x= 0.08 in materials prepared by the thermal solid-state method. Materials prepared by the thermal solid-state method required higher temperatures and longer times than materials prepared by the sol-gel method. The results showed that more fluorine can be incorporated in the LiCoO2 structure by the sol-gel than the solid-state method. The secondary phase was identified as lithium oxydifluoride, LiCoOF2. Relatively pure material with stoichiometry could be prepared by both methods. The space was determined as either 2 or 1 and the unit cell dimensions for the two alternatives are reported. This secondary phase has been reported in the literature, but had not been positively identified at the time of submission of this dissertation. Keywords: fluorinated LiCoO2; LiCoO2−xFx; sol-gel fluorination; solid-state fluorination; lithium oxydifluoride.Dissertation (MEng)--University of Pretoria, 2017.Chemical EngineeringMEngUnrestricte

Self-assembled micro and nano rod-shaped porphyrin@Bi12O17Cl2 composite as an efficient photocatalyst for degradation of organic contaminants

DATA AVAILABILITY : The datasets generated during and or analyzed during the current study are available from the corresponding author on reasonable request.Please read abstract in the article.The National Research Foundation of South Africa and Rand Water Company (South Africa).https://link.springer.com/journal/11671am2024Chemical EngineeringNon

Self-assembled micro and nano rod-shaped porphyrin@Bi12O17Cl2 composite as an efficient photocatalyst for degradation of organic contaminants

Abstract Bi12O17Cl2 is a potential photocatalyst in practical applications due to its excellent photostability, visible light activity, and competitive bandgap energy. However, the fast recombination of photogenerated charge carriers makes it impractical for pollution mitigation. Recently, aggregated porphyrins have emerged as photosensitizers in light-dependent applications such as photocatalysis. Although Bi12O17Cl2 and porphyrin can function as separate photocatalysts, their photocatalytic properties in terms of visible light adsorption, charge separation and transport, can be improved when they are combined to form heterostructure. In this study, rod-shaped aggregated 5,10,15, 20-Tetrakis (4-carboxyphenyl) porphyrin was synthesized by CTAB-assisted, self-assembly strategy and Bi12O17Cl2 by a facile microwave method. The porphyrin and Bi12O17Cl2 were combined to generate a series of x %Porphyrin@Bi12O17Cl2 having 0.02% wt., 0.1% wt., 0.4% wt., 1% wt. and 10% wt. as compositions of porphyrin. The materials’ photocatalytic degradation efficiency was tested on Rhodamine B dye as a representative pollutant. The best and worst performances were reported for 1%Porphyrin@Bi12O17Cl2 and 10%Porphyrin@Bi12O17Cl2, respectively, which are 3.1 and 0.5 times increases in efficiency compared to pure Bi12O17Cl2. From the radical trapping experiment, electrons and superoxide were the dominant reactive species in the degradation process. The enhanced photocatalytic capability of the materials was attributed to the photosensitizing property of porphyrin and the heterojunction formation, which promotes the separation of photogenerated charge carriers. A plausible step-scheme (S-scheme) was proposed for the photocatalytic degradation mechanism. The S-scheme provided the high redox potential of the photogenerated charge carriers. The findings herein offer a new option for improving the photocatalytic performance of Bi12O17Cl2 for environmental applications through the photosensitization strategy. Graphical abstrac