Effect of synthesis duration and HCl acid concentration on the formation of hydrothermally synthesised TiO2 nanoparticles
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It is known when synthesising nanomaterial on laboratory scale, a variation in a single synthesis parameter may alter the product. Numerous synthesis techniques have been employed in the synthesis of titanium dioxide with varying phase, size and shape. It was found that changes in the phase directly affect their properties and application, such as treating of textile wastewater by photodegradation. However, when synthesising nanoparticles, changes to any reaction parameters and/or kinetics can have a desirable or undesirable effect on titanium dioxide nanoparticles. There is therefore a need to understand how HCl acid concentration (homogeneous catalyst) and shortened gel formation duration affect synthesis of TiO2 nanoparticles and photocatalytic properties. A sol-gel followed by hydrothermal treatment was employed to synthesise 2.8 grams of titanium dioxide nanorods for the duration of 96 hours, initially. A systematic study was conducted to exploit reaction kinetics by varying HCl acid concentration (3, 4, 5 molar), water feed for TiO2 gel formation (72, 24, 12 hours), and hydrothermal treatment time for the transformation of gel to crystalline TiO2 (1–20 hours). The photocatalytic activity of synthesised TiO2 nanoparticle was evaluated, when irradiated with a UV-C bulb to degrade an industrial textile dye, methylene blue. Systematic studies were successful in identifying the effects HCl acid concentration, gel formation time and lengthened hydrothermal treatment time have on TiO2 nanoparticles’ phase, size and shape. Increased HCl concentrations for shortened gel formation times resulted in mixed phases of TiO2, decreases in particle size and particle shape deformed from nanorods. Increased photocatalytic activity was found for a decrease in the rutile and increase in the brookite phase percentage, but this plateaued after 42% brookite phase. Furthermore, lengthened hydrothermal treatment assisted in phase transformation of particles synthesised at shortened gel formation times for high HCl acid concentrations. Pure rutile TiO2 was synthesised at a sixth of the initial synthesis time. Furthermore, the effects of changes in nanoparticles on the photocatalytic activity was discussed. Moreover, exploiting reaction kinetics resulted in the synthesis of a more efficient photocatalytically active TiO2 nanoparticle sample at shortened synthesis time.