DEVELOPMENT OF TIO2/CNCS NANOCATALYST FOR CO2 PHOTOCATALYTIC CONVERSION TO SOLAR FUELS USING NANOBUBBLE REACTOR

• Main Author: Madani, Haroki
• Format: Dissertations
• Language: Indonesia
• Subjects: Teknik kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/81069
• Institution: Institut Teknologi Bandung

Photocatalytic CO2 conversion is a strategic solution to reduce CO2 emissions and simultaneously produce various solar fuels (methane, methanol, formic acid, and formaldehyde). However, this method has the drawback of very low conversion, which is below 0.15%. These drawback can be overcome by improving the photocatalyst material and photocatalysis process. This research generally aims to improve the performance of multiphase CO2 photocatalysis using TiO2 nanocatalyst, CNCs nanocrystals, and nanobubbles reactor. This research initiates the novelty of combining the use of Cellulose Nanocrystals (CNCs) from the material aspect and CO2 nanobubble from the process aspect to improve the performance of multiphase CO2 photocatalysis. This series of research is divided into four stages consisting of synthesis of CNCs nanocrystals from TKKS, modification of TiO2 photocatalyst, photocatalyst activity test, and kinetics and reactor modeling. The synthesis of CNCs nanocrystals was carried out by ammonium persulfate (APS) oxidation method either directly or indirectly. The direct method was carried out by reacting the TKKS raw material with APS solution directly with varying APS concentration, reaction temperature, and reaction time. Meanwhile, the indirect method was carried out by applying alkaline pretreatment and bleaching to the TKKS raw material before reacting with the solution. The best conditions for the synthesis of CNCs nanocrystals were at 2 M APS concentration, 60 °C temperature, and 15 hours reaction time. The direct method synthesis produced rod-shaped CNCs particles with a length of 95.8±14.5 nm, a diameter of 7.4±0.9 nm, and a degree of crystallinity of 74.8%. Meanwhile, the indirect method synthesis produced spherical CNCs particles with a diameter of 32.96±10.05 nm and a degree of crystallinity of 76.2%. Modification of TiO2 photocatalyst was carried out by the addition of CNCs nanocrystals and nitrogen doping. CNCs nanocrystals are used both as a support for dispersing TiO2 nanocatalysts and a template for making mesoporous TiO2. Modification with nitrogen doping aims to lower the band gap so that the photocatalyst can have activity under visible light irradiation. Based on experimental results, TiO2 with support CNCs successfully formed even without calcination process. Mesoporous TiO2 photocatalysts that use CNCs as templates have anatase and brookite phases, with the majority of the phases being anatase, which is above 80%. The mesoporous structure successfully increases the surface area of TiO2 photocatalyst from 5.08 m2/g to 142.7 m2/g in the variation of 1 g CNCs for 1 mL TTIP. Nitrogen doping can reduce the band gap of TiO2 on TiO2/CNCs photocatalyst from 3.2 eV to 3.1 eV as evidenced by the results of band gap calculations with Kubelka-Munk plots and the presence of photocatalytic activity in visible light irradiation. Photocatalyst activity tests were conducted with batch and continuous reactors. Nanobubble generation was carried out by hydrodynamic cavitation method for batch reactors and porous ceramic method for continuous reactors. The generation of nanobubbles both with hydrodynamic cavitation and porous ceramic produced bubbles with two size clusters, namely nanobubbles with sizes below 400 nm and microbubble bubbles with sizes between 2 to 10 microns. The results of the activity test on the batch reactor showed the presence of methanol products with a retention time of 2 minutes on the GC characterization results curve. Meanwhile, the activity test in the continuous reactor produced CO, CH4, and CH3OH products. The use of nanobubble in the CO2 photocatalysis reaction for 6 hours successfully increased the concentration of CH4 products by 6 times, from 3.71 mmol/gcatalyst/hour to 20,00 mmol/gcatalyst/hour and CH3OH products by 1.5 times, from 3,60 mmol/gcatalyst/hour to 5,78 mmol/gcatalyst/hour. Kinetics modeling was performed based on the first-order model and the Sips model. The first-order kinetic model can be used in the multiphase CO2 photocatalysis reaction with a fairly good fit. The addition of the assumption of methanol conversion to methane in the first-order model can improve the fit between the model and experiment with correlation coefficients for CO, CH3OH, and CH4 products of 0.996, 0.901, and 0.915, respectively. Based on the Sips model, the multiphase CO2 photocatalysis reaction has a heterogeneity factor value of 1.33 which indicates that there is a deviation from the ideal homogeneous catalyst surface.