Graphene Oxide Based Ternary Hybrid Nanocatalyst for Photocatalytic Environmental Remediation

Abstract

The growing global population and modern industrialization are putting the world in danger of an energy crisis and a dramatic rise in environmental pollution. The need for sustainable clean water has increased globally, which has sparked interest in developing alternate methods for achieving this goal. Among the many commonly used techniques for environmental cleanup, visible light-responsive photocatalysis based on semiconductor materials has garnered worldwide interest as an emerging green tool that could efficiently degrade organic and inorganic pollutants into sustainable products. Therefore, in this thesis, an effort has been made to explore the synthesis and photocatalytic application of different graphene oxide (GO) based ternary hybrid nanocatalysts that can be used for visible light induced photocatalytic environmental remediation. The GO based materials were subsequently integrated with metal oxide, mixed metal oxide, etc. nanostructures to prepare Z-scheme ternary hybrid heterostructure with improved optical absorption and enhanced photoelectochemical features which are effectively used for photocatalytic environmental remediation applications. In the first part of the study, sulfur-doped reduced graphene oxide enwrapped magnetic porous nickel ferrite/copper sulfide (SrGO/NiFe2O4/CuS: GNFC) ternary hybrid nanocatalyst was constructed through a facile solvothermal-reflux route. Under exposure to visible light, the optimal GNFC-13 nanocatalyst exhibits outstanding catalytic activity for the photoreduction of 4-Nitrophenol (90.62%) and photodegradation of Tetracycline hydrochloride (94.39%), which is significantly better than that of pristine and doublet nanomaterials, respectively. The explanations for the improved photocatalytic efficiency of GNFC nanocatalysts are due to the porous structures of the magnetic NiFe2O4 and the SrGO surface, which can offer a lot of adsorption sites and, therefore, advantageous for the adsorption enrichment of harmful pollutants. Additionally, in situ photocatalytic degradation and adsorption enrichment working together synergistically may lead to improved pollutant removal efficacy. The Raman and XPS analytical techniques verified the formation of sulfur doped reduced graphene oxide in the GNFC nanocatalyst. The free-radical trapping studies, terephthalic acid test, and nitroblue tetrazolium test disclosed that h+, OH•, e−, and •O2− are cardinal reactive species in the photocatalytic system. The developed Z-scheme charge transfer channelization system of GNFC nanocatalyst has led to the increase of catalytic activity due to the effective photoinduced carrier separation, wider photoabsorption range, high hole oxidation capacity, and high electron reduction power. In the second part, hematite nanoparticles decorated nitrogen-doped reduced graphene oxide/graphitic carbon nitride (NrGO/α-Fe2O3/g-C3N4: NGCF) ternary hybrid nanocatalyst was effectively synthesized using a facile thermal treatment approach followed by calcination. The ternary hybrid nanocatalytic materials exhibited distinct structural, compositional, as well as optoelectrical characteristics, which include high crystallinity, surface exposed reactive site, nanoscale interfacial contact, strong absorption in visible region, fast migration of charge carriers and high resistance to recombination. The nitrogen doping in reduced graphene oxide was confirmed from Raman and XPS analyses. The optimal NGCF-10 nanocatalyst exhibited excellent photocatalytic performance towards Cr(VI) photoreduction (95%) and 2,4-Dinitrophenol photodegradation (88%). Radical trapping experiments suggested the vigorous formation of reactive e−, •O2−, h+ and OH• radicals in aqueous suspension of the NGCF nanocatalyst, which play a pivotal role in the photocatalytic system. The Z-scheme charge transfer channelization mechanism was accepted for the enhanced performance of the NGCF ternary hybrid nanocatalyst system. In the last part of the study, a ZnBi2O4/ZIF-67 derived hollow Co3O4 decorated reduced graphene oxide (rGO/ZnBi2O4/ZIF-Co3O4: ZCG) ternary hybrid nanocatalyst was fabricated through a facile thermal treatment approach. The optimal ZCG-4 heterojunction demonstrated exceptional catalytic effectiveness for the photocatalytic reduction of Cr(VI) (97.4%) and photocatalytic degradation of Rhodamine B (92.5%) when exposed to visible radiation, which is much superior than pristine and doublet nanohybrids. The improved photocatalytic activity may be attributed to the beneficial synergistic interaction between the rGO, ZnBi2O4, and ZIF-Co3O4 nanocomponents in the nanohybrid. The radical trapping studies disclosed that OH•, h+, e−, and •O2− are key reactive species in the photocatalytic system. Based on the data from the various experiments, we infer that the as-prepared ZCG nanocatalyst functions via a Z-scheme charge transfer channelization mechanism, exhibiting a significant suppression of the photogenerated electron-hole pairs charge recombination. In conclusion, the work presented in this thesis unlocks opportunities for energy and material efficient nanocatalysts for photocatalytic environmental remediation applications using GO based nanohybrid materials.