Metal-free adsorption and photodegradation methods for methylene blue dye removal using different reduction grades of graphene oxide

Abstract

The release of organic pollutants and dyes into the environment by industries has had profound and harmful effects on both humans and ecosystems. Graphene oxide (GO) and its reduced form have been investigated for their effectiveness in removing pollutant dyes. GO nano-powder was synthesized using an improved version of Hummer’s method and subsequently thermally reduced at various temperatures, including 125, 150, 175, and 200°C, under vacuum conditions. In the X-ray diffraction spectra, an intense (002) diffraction peak was initially observed at 9.136° (2θ) for pristine GO. This peak gradually shifted towards higher angles as the reduction process took place and eventually disappeared when the GO was reduced at 200°C. The intensity ratio of the D and G bands (ID/IG ratio) for GO nano-powder in the Raman spectra decreased from 0.94 to 0.76 due to the reduction process. The FTIR spectra of GO and reduced graphene oxide (rGO) also illustrated the reduction process. The bandgap of pristine GO significantly decreased from 2.31 to 0.73 eV, as determined by ultraviolet-visible (UV−Vis) diffuse reflectance spectrophotometry during the reduction process. The surface area and pore volume of both pristine GO and rGO-150 were determined using the BET (Brunauer-Emmett-Teller) and BJH (Barrett-Joyner-Halenda) methods. The results indicated an increase in the BET surface area from 6.61 to 7.86 m2/g and a corresponding enhancement in pore volume from 0.118 to 0.128 cc/g after reduction. The adsorption and photocatalytic degradation behavior of pristine GO and reduced graphene oxides (rGOs) were examined using methylene blue dye. The pristine GO demonstrated impressive adsorption capability, effectively removing the dye by 85.78% within just 15 minutes and achieving nearly 97% removal after 4 hours. In contrast, the highest photocatalytic degradation of methylene blue, at 47.58%, was attained for the rGO sample reduced at 150 °C under the illumination of visible light.