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Abstrak :
Karbon dioksida (CO2) merupakan gas rumah kaca yang berperan penting dalam peningkatan suhu bumi yang memicu terjadinya pemanasan global. Untuk mengurangi konsentrasi CO2, harus dilakukan konversi CO2 menjadi produk yang memiliki nilai tambah. Pada penelitian ini, metode fotoelektrokimia digunakan untuk mengkonversi CO2 dalam bentuk bikarbonat menggunakan fotokatoda CuBi2O4 yang telah dimodifikasi dengan nanopartikel perak. CuBi2O4 disintesis dengan metode solvotermal dan nanopartikel perak disintesis dengan menggunakan kompleks asam tanat dan natrium sitrat. Fabrikasi fotokatoda dilakukan menggunakan metode doctor blade pada FTO 1x1 cm2. Fotokatoda dimodifikasi menggunakan nanopartikel perak dengan variasi waktu pencelupan yaitu 10s, 30s, dan 50s. Berdasarkan karakterisasi UV-Vis DRS, energi celah pita FTO/CBO (1,77 eV) menurun setelah dimodifikasi dengan nanopartikel perak menjadi 1,71 eV. Hal ini menunjukkan bahwa modifikasi nanopartikel perak dapat memengaruhi sifat elektronik dari semikonduktor CuBi2O4. Pengujian fotoelektrokimia dilakukan dengan sistem tiga elektroda dengan metode linear sweep voltammetry (LSV) dan chronoamperometry (transient chopped light photocurrent) selama 120 detik dengan mati nyala lampu setiap 10 detik. Didapatkan fotokatoda FTO/CBO/Ag 30s memiliki performa yang paling baik, yaitu memiliki onset potensial sebesar -0,008 V, densitas arus sebesar -12,859 mA/cm2 dengan stabilitas foto arus tertinggi yaitu 84,4%. ......Carbon dioxide (CO2) is a greenhouse gases that has an important role in increasing the average temperature of the earth which triggers global warming. In order to reduce the concentration of CO2, it is necessary to convert CO2 into other products that have added value. In this experiment, a photoelectrochemical method was used to convert CO2 in the form of bicarbonate into formic acid using CuBi2O4 photocathode that had been modified with silver nanoparticles. CuBi2O4 was synthesized by solvotermal method and silver nanoparticles were synthesized using a complex of tannic acid and sodium citrate. Fabrication of photocathode was carried out using the doctor blade method with FTO 1x1 cm2. The photocathode was modified using silver nanoparticles with variations in immersion time of 10s, 30s, dan 50s. Based on the UV-Vis DRS characterization, band gap energies of FTO/CBO (1.77 eV) decreased after being modified with silver nanoparticles to 1.71 eV. This data indicates that the modification of silver nanoparticles can affect the electronic properties of the CuBi2O4 semiconductor. Photoelectrochemical testing was carried out with a three-electrode system with linear sweep voltammetry and chronoamperometry (transient chopped light photocurrent) methode for 120 seconds with chopped light every 10 seconds. It was found that the FTO/CBO/Ag 30s photocathode has the best performance, which has an onset potential of -0.008 V, a current density of -12,859 mA/cm2 with the photocurrent stability of 84.4%.

Abstrak :
The main problem with the slurry process is the difficulty in recovering the photocatalyst nanoparticle from water following purification. An alternative solution proposed the photocatalyst be immobilized on magnetic carriers, which would allow them to be recollected from the water suspension following treatment using an external magnetic field. Magnetically photocatalyst composites were prepared using simple heteroagglomeration by applying attractive electrostatic forces between the nanoparticles with an opposite surface charge. The Fe3O4/SiO2/TiO2 photocatalysts were synthesized in an aqueous slurry solution containing Fe3O4/SiO2 and TiO2 nanoparticles under pH 5 conditions. Meanwhile, Fe3O4/SiO2 was prepared by a simple procedure via a coprecipitation of iron(II) and iron(III) ion mixtures in ammonium hydroxide and was leached by sodium silicate. The synthesized samples were investigated to determine the phase structure, the magnetic properties, and the morphology of the composites by X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and transmission electron microscopy (TEM), respectively. The results indicated that the composites contained anatase and rutile phases and exhibited a superparamagnetic behavior. Fe3O4/SiO2 particles, which were of the aggregation spherical form at 20 nm in size, were successfully attached onto the TiO2 surface. The catalytic activity of Fe3O4/SiO2/TiO2 composites was evaluated for the degradation of methylene blue under ultraviolet (UV) irradiation. The presence of SiO2 as a barrier between Fe3O4 and TiO2 is not only improves the photocatalytic properties but also provides the ability to adsorb the properties on the composite. The Fe3O4/SiO2/TiO2 (50% containing TiO2 in composite) were able to eliminate 87.3% of methylene blue in water through the adsorption and photocatalytic processes. This result is slightly below pure TiO2, which is able to degrade 96% of methylene blue. The resulting Fe3O4/SiO2/TiO2 composite exhibited an excellent ability to remove dye from water and it is easily recollected using a magnetic bar from the water. Therefore, they have high potency as an efficient and simple implementation for the dye effluent decolorization of textile waste in slurry reactor processes.