Photocatalytic performance improvement by utilizing GO_MWCNTs hybrid solution on sand/ZnO/TiO2-based photocatalysts to degrade methylene blue dye

In this work, sand/zinc oxide (ZnO)/titanium dioxide (TiO₂)-based photocatalysts were hybridized with graphene oxide (GO) and GO_multi-walled carbon nanotubes (MWCNTs) hybrid solution. The novel hybrid was then used in photocatalysis to degrade dye contamination. The nanocomposite photocatalyst was initially fabricated by growing ZnO nanorods (NRs) via sol-gel immersion followed by synthesizing TiO₂ NRs for different times (5 and 20 h) using a hydrothermal method on sand as a substrate. Prior to the hybridization, the initial GO was synthesized using electrochemical exfoliation and further mixed with 1 wt% MWCNTs to form GO_MWCNTs hybrid solution. The synthesized GO and GO_MWCNTs hybrid solution were then incorporated onto sand/ZnO/TiO₂ nanocomposite-based photocatalysts through immersion. Various sand/ZnO/TiO₂-based photocatalysts were then tested for methylene blue (MB) dye degradation within 3 days. On the basis of UV-Vis measurement, the highest MB degradation was achieved by using sand/ZnO NRs/TiO₂ NRs (5 h)/GO_MWCNTs (92.60%). The high surface area and high electrical conductivity of GO_MWCNTs prolonged the lifetime of electron/hole separation and thus enhanced the photocatalytic performance.

TiO2 modified orthocortical and paracortical cells having enhanced photocatalytic degradation and photoreduction properties

In this study, cortical cells resultant from wool fibers were loaded with TiO₂ nanoparticles in a hydrothermal process and were then engineered as organic-nonorganic hybrid composite photocatalysts for both photodegradation of organic dyes and photoreduction of heavy metal ions. The microstructure and photocatalytic properties of TiO₂ modified cortical cells (i.e. both orthocortical and paracortical cells) were systematically characterized using a series of analytical techniques including FESEM, TEM, element analysis, Mott-Schottky curve, BET specific surface area, Zeta potentials, as well as XRD, FTIR, XPS, DRS, PL, UPS, EDS and ESR spectra. Their photocatalytic performance and trapping experiments of the TiO₂ modified cortical cells were measured in the photodegradation of methylene blue (MB) dye and Congo Red (CR) dye as well as the photoreduction of Cr(VI) ions under visible light irradiation. It was found that anatase TiO₂ nanoparticles were chemically grafted on the surface of the two cortical cells via O-Ti⁴⁺/O-Ti³⁺ bonds, and that TiO₂ nanoparticles were formed inside the orthocortical cells in the hydrothermal process. The TiO₂ modified orthocortical and paracortical cells possessed much higher photocatalytic efficiency than the commercially available TiO₂ nanoparticle powder, Degussa P25, in the photodegradation of cationic MB dye and photoreduction of Cr(VI) ions, while their photocatalytic efficiency in the photodegradation of anionic CR dye is smaller because of their greater negative Zeta potentials and photogenerated holes as the main reactive radical species. In comparison with the TiO₂ modified paracortical cells, the higher photocatalytic efficiency of the TiO₂ modified orthocortical cells was demonstrated in the photodegradation of MB dye solution and this might be due to both the S-doped TiO₂ nanoparticles infiltrated into the naturally hydrophilic orthocortical cells and the primary reactive radical species of photogenerated holes being trapped in the cells.

The preparation and characterization of TiO2/r-GO/Ag nanocomposites and its photocatalytic activity in formaldehyde degradation

A series of TiO₂-rGO-Ag nanocomposites were prepared in this work via a facile one-pot hydrothermal method utilized for formaldehyde (HCHO) photodegradation; using TiO₂, graphene oxide(GO) as well as AgNO₃ as the raw materials, and sodium citrate as a reducing agent. Characterization by X-ray diffraction (XRD), Raman spectra, Transmission electron microscopy (TEM) and Field emission scanning electron microscopy (FESEM) demonstrated that GO and Ag⁺ were reduced during the formation of TiO₂-rGO-Ag nanocomposites. X-ray photoelectron spectroscopy(XPS), UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence spectra(PL) and Photocurrent spectrum measurement were applied to quantitatively characterize the bonding between TiO₂ and rGO, the band gap energy of catalysts as well as electron-hole pairs recombination rate. The results revealed that the introduction of rGO sheets and Ag nanoparticles reduced the band gap energy of catalysts; it also suppressed the recombination of electron-hole pairs. However, C-O-Ti bond, which played a key role in photocatalysis, was reduced to some extent by the existence of Ag. Photodegradation results showed that, when the Ag loading was 9 mol% of TiO₂, the reaction rate constant of formaldehyde (HCHO) removal improved distinctly, by about 22.3 times that of TiO₂. The radical scavenger tests and electron paramagnetic resonance(EPR) analysis revealed that superoxide radical (·O₂ ^-), hole (h⁺), and hydroxylradical (·OH) were reactive species of formaldehyde photodegradation.

Phenol Abatement by Titanium Dioxide Photocatalysts: Effect of The Graphene Oxide Loading

Hetero-photocatalytic graphene-TiO2 materials have, in the literature, been found to possess better photocatalytic activity for environmental applications compared to pure TiO2. These types of materials can be prepared in different ways; however, their photocatalytic performance and quality are not easily controlled and reproduced. Therefore, we synthetized graphene oxide-TiO2 nanoparticles by sol-gel reaction from TiCl4, as precursor, with two different methods of synthesis and with a graphene oxide (GO) loading ranging from 0 to 1.0. This approach led to a good adhesion of GO to TiO2 through the Ti-O-C bonding, which could enhance the photocatalytic performances of the materials. Overall, 0.05 wt % GO loading gave the highest rate in the photodegradation of phenol under visible light, while higher GO loadings had a negative impact on the photocatalytic performances of the composites. The 0.05 wt % GO-TiO2 composite material was confirmed to be a promising photocatalyst for water pollutant abatement. The designed synthetic approach could easily be implemented in large-scale production of the GO-TiO2 coupling materials.