Synthesis of TiO2 nanoparticles coated on cellulose nanofibers with different morphologies: Effect of the template and sol-gel parameters

Abstract

TiO2 nanoparticles were coated on cellulose nanofibers (CNFs) as template, in three different forms in sol-gel process. CNFs hydrogel template resulted in porous and highly entangled TiO2 nanofibers. A sheet-like TiO2 structure was obtained, when the CNFs aerogel with almost the same structure was used. Finally, the cellulose hydrogel was transformed to alcogel after exchanging the water by isopropanol to minimize the water content in the sol-gel reaction mixture, and it was used as template in a Stöber-modified sol-gel process to produce TiO2 nanowhiskers and nanosheets. The FESEM images showed that increasing the TTIP amount resulted in a three-dimensional nanowhiskers structure and increment of sol-gel reaction time caused the adhesion of nanowhiskers to each other. After sonication during the sol-gel reaction nanorods were obtained. According to XRD patterns and Raman spectroscopy both the bare TiO2 nanoparticles (TNPs) and alcogel-TiO2 consisted of pure anatase phase. UV–Vis DRS results of TNPs and alcogel-TiO2 nanowhiskers showed that the band-gap value decreased significantly from 2.95 eV to 2.72 eV. The FESEM and TEM images confirmed that by increasing the ammonia content from 0.2 to 0.25 vol% to 0.3–0.6 vol%, the shape of the nanowhiskers changed to nanosheets, and the BET specific surface area increased from 52.308 m2/g for TNPs to 86.367 m2/g for nanowhiskers and 76.115 m2/g for nanosheets. The photocatalytic activity of the samples was evaluated by degradation of aqueous methylene blue solution. In UV light all samples showed photodegradation efficiency of more than 98% in less than 120 min. Under visible light the photodegradation efficiency of TiO2 nanowhiskers in 240 min was 45.24% and 47.26% which were higher than that of TNPs (15.07%) and nanosheets (28%–33%).