A nanocomposite (namely rGOTi) was prepared by loading 0.33 weight percent of reduced graphene oxide (rGO) on commercial TiO 2 nanoparticles using a hydrothermal method. The as-prepared nanocomposite was characterized using surface and bulk analytical techniques such as X-ray photoelectron spectroscopy, X-ray diffraction, and Fourier transform infrared and Raman spectroscopies. Also, the surface area was measured using the Brunauer-EmmettTeller technique. In addition, the UV-Vis diffuse reflectance spectroscopy measurements have shown that the band gap energy for TiO 2 was lowered from 3.11 to 2.96 eV when it was composited with rGO to form the rGOTi. The kinetics of the degradation of phenol, p-chlorophenol, and p-nitrophenol (separate or mixed) and their intermediates using the as-prepared nanocomposite photocatalyst compared to the bare TiO 2 nanoparticles was tested using UV and Xenon lamps (mainly a visible light source) as photoexcitation sources in the presence and absence of H 2 O 2 . In general, it was revealed that the photocatalytic activity of the rGOTi using a visible light source, in the presence of H 2 O 2 , is significantly higher than that when (1) a UV lamp and/or (2) TiO 2 nanoparticles were used. Also, the presence of H 2 O 2 led to higher degradation rates of all the phenolic compounds regardless the type of photoexcitation source.

Graphical AbstractLinear Sweep Voltammograms (LSVs) at a scan rate of 50 mV s -1 shows the enhanced electrocatalytic properties of the hydrogen-reduced graphene oxide/TiO 2 composite compared to the GC electrode in (i & ii) oxygen and (iii & iv) argon-saturated 0.5 M H 2 Graphene oxide (GO) was synthesized from commercial graphite using a modified Hummers' method. Three different methods were used to prepare GO/TiO2 composites. GO was (i) initially impregnated over TiO2 (GOTi) and then reduced using a stream of hydrogen gas at 450 °C (H2RGOTi), (ii) reduced using hydrazine hydrate solution (HH) in a 1000-W microwave oven (HHRGO) and then loaded on the TiO2 (HHRGOTi) or (iii) hydrothermally reduced (RGO) then loaded on TiO2 (RGOTi). Different characterization techniques were used e.g. X-ray photoelectron spectroscopy (XPS), X-ray diffraction patterns (XRD) and UV-Vis, Fourier transform infrared (FT-IR) and Raman Spectroscopy. The effect of the GO reduction method on the photocatalytic activity of the aforementioned composites towards the degradation of phenol in the presence and absence of (i) UV and (ii) H2O2 was examined. High phenol degradation rates were achieved using the RGOTi photocatalyst, compared to the TiO2 nanoparticles, under UV illumination. On the other hand, the H2RGOTi composite has shown the highest electrocatalytic activity towards oxygen reduction reaction in presence of UV illumination.

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Nanocomposites (CNTi) with different mass ratios of carbon nitride (C3N4) and TiO2 nanoparticles were prepared hydrothermally. Different characterization techniques were used including X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), transmission electron spectroscopy (TEM) and Brunauer-Emmett-Teller (BET). UV-Vis DRS demonstrated that the CNTi nanocomposites exhibited absorption in the visible light range. A sun light - simulated photoexcitation source was used to study the kinetics of phenol degradation and its intermediates in presence of the as-prepared nanocomposite photocatalysts. These results were compared with studies when TiO2 nanoparticles were used in the presence and absence of H2O2 and/or O3. The photodegradation of phenol was evaluated spectrophotometrically and using the total organic carbon (TOC) measurements. It was observed that the photocatalytic activity of the CNTi nanocomposites was significantly higher than that of TiO2 nanoparticles. Additionally, spectrophotometry and TOC analyses confirmed that degraded phenol was completely mineralized to CO2 and H2O with the use of CNTi nanocomposites, which was not the case for TiO2 where several intermediates were formed. Furthermore, when H2O2 and O3 were simultaneously present, the 0.1% g-C3N4/TiO2 nanocomposite showed the highest phenol degradation rate and the degradation percentage was greater than 91.4% within 30 min.