Development of photocatalytic nanocomposite based on titanium dioxide and reduced graphene oxide

Abstract

U ovom radu pripravljen je grafenov oksid (GO) oksidacijom prirodnog grafita (≤50 μm) koristeći Hummersovu metodu. Hidrotermalnom/solvotermalnom metodom te naknadnom toplinskom obradom pri 300 °C pripravljene su nanočestice nanokompozita na bazi titanijeva dioksida i reduciranoga grafenova oksida (TiO2@rGO) s masenim udjelom rGO od 4, 8 i 16 mas.%. Sintetizirani fotokatalizatori karakterizirani su različitim strukturnim, morfološkim i optičkim metodama karakterizacije nanomaterijala. Adsorpcija i fotokatalitička aktivnost pripremljenih nanočestica TiO2 i TiO2@rGO nanokompozita ispitana je na procesu djelotvornosti razgradnje vodene otopine bojila metilenskog modrila. Praćen je utjecaj početne koncentracije i pH vrijednosti otopine bojila, koncentracije katalizatora, vodene matrice i izvora zračenja. Ispitana je mogućnosti ponovne upotrebe TiO2@rGO fotokatalizatora u tri ciklusa. Dobiveni rezultati karakterizacije pripravljenih materijala ukazuju na postojanje interakcija između TiO2 i rGO odnosno Ti–O–C veze što potvrđuje uspješnu pripravu TiO2@rGO nanokompozita. Nadalje, dodatkom rGO povećana je specifična površina, smanjen je energetski procjep i povećana je djelotvornost fotokatalitičke razgradnje metilenskog modrila u odnosu na nanočestice TiO2. Određena je optimalna količina (8 mas.%) reduciranoga grafenova oksida u nanokompozitu na bazi titanijeva dioksida i reduciranoga grafenova oksida za učinkovitu fotokatalitičku razgradnju metilenskog modrila. Utvrđeno je da je optimalna fotokatalitička djelotvornost razgradnje metilenskog bojila postignuta 99,20 % za početnu koncentraciju bojila od 10 mg·L–1 i početnu koncentraciju katalizatora od 0,5 g·L–1 pri 22 ± 0.5 °C. Ustanovljeno je da je model pseudo prvog reda prihvatljiv za opis kinetike fotokatalitičke razgradnje metilenskog modrila primjenom pripravljenih fotokatalizatora. Rezultati su pokazali da se pripravljeni TiO2@rGO_8 mas.% nanokompozit može koristiti u tri uzastopna ciklusa uz zadržavanje fotokatalitičke aktivnost preko 90 %.In this study, graphene oxide was prepared by the oxidation of natural graphite flakes (≤50 μm) using Hummer's method. Nanoparticles of nanocomposites based on titanium dioxide and reduced graphene oxide (TiO2@rGO) with percentage weights of rGO of 4, 8, and 16 wt.%, were prepared by the hydrothermal/solvothermal synthesis method and thermally treated at 300 °C. The synthesised photocatalysts were characterised by various structural, morphological, and optical characterisation methods for nanomaterials. The adsorption and photocatalytic activity of the prepared TiO2@rGO nanocomposite were tested on their efficacy in the removal of methylene blue dye from water. Furthermore, the photocatalytic efficiency of the prepared photocatalysts was tested by changing various parameters such as the irradiation source, the concentration of the catalyst, the initial concentration of the dye model solution, the pH of the dye solution and the water matrix. The possibility of reusing TiO2@rGO photocatalyst for three cycles was tested. The results obtained for the characterisation of the prepared materials indicate the existence of interactions between TiO2 and rGO, i.e., the Ti–O–C bond, which confirms the successful preparation of TiO2@rGO nanocomposites. The addition of rGO increased the specific surface area, decreased the band gap energy, and increased the photocatalytic efficiency of methylene blue removal from water compared to TiO2 nanoparticles. The results of photocatalytic activity indicate that the amount of rGO in the prepared TiO2@rGO nanocomposites plays a significant role in the application of different photocatalytic parameters. The optimal amount (8 wt.%) of reduced graphene oxide in the nanocomposite for the efficient photocatalytic decomposition of methylene blue was determined. It was determined that the optimal photocatalytic efficiency of methyl dye degradation was achieved 99.20 % for an initial dye concentration of 10 mg·L– 1 and an initial catalyst concentration of 0.5 g·L– 1 at 22 ± 0.5 °C. It was found that the pseudo first-order model is acceptable for describing the kinetics of the photocatalytic decomposition of methylene blue using the prepared photocatalysts. The results showed that the TiO2@rGO_8 wt.% nanocomposite can be used for three consecutive cycles while maintaining photocatalytic activity over 90 %