P–N Heterojunction System Eu‐Doped ZnO@GO for Photocatalytic Water Splitting

Abstract

202200106graphene, created by vigorously oxidizing graphite [4][5][6] and is thought of as a single sheet of graphene that is retaining different oxygen-containing groups on both sides of the basal plane as well as on the edges. [7] Due to the creation of sp 3 hybridized C-atoms, which interfere with the π-conjugation in the graphene sheet, GO functions differently from pure graphene and acting as an insulator or shows the p-type semiconducting behavior. [8][9][10] It has been shown that the conduction band (CB) minimum of GO is composed of π* orbitals, which have a higher energy level than that needed for hydrogen generation. Graphene and graphene-based materials are currently being used vigorously for energy conversion applications, including the solar hydrogen generation from water splitting. [11,12] There have been numerous attempts to improve the photocatalytic performance of semiconductor photocatalysts by integrating graphene with them for various applications. [13][14][15][16][17][18] ZnO is an inexpensive, wide-bandgap semiconductor with a bandgap of 3.37 eV, which corresponds to a wavelength of about 375 nm. Its high photoreactivity, good photostability, and low cost favor its use in photocatalytic water splitting (PWS), but its limitations include photocorrosion, backward reaction, poor stability, and inability to absorb visible light. [19] To get around these problems, modifications have been made like coupling with other semiconductors and doping with metal, rare-earth metal, or non-metal ions. [20][21][22][23] Recently, rare-earth metal-doped ZnO has caught the attention of material scientists in this direction because of its superior activity and selectivity to pure ZnO as well as its higher absorption efficiency in the visible region, which can be used to create better optoelectronic devices for harvesting visible light. The dopant causes competitive defects in the ZnO surface, bulk, and lattice. Due to their role in the bandgap contraction and the separation effect of the photocarriers (photoelectron (e − ) and photohole (h + )), these defects are wanted at the surface.The imperfectly filled 4f orbitals of rare-earth metals can trap electrons, reducing charge recombination and enhancing photocatalytic activity. [23] By interacting with 4f orbitals of lanthanoid ions with a variety of functional groups of GO, the light harvesting power of composite will enhanced. In comparison to pure TiO 2 , Khalid et al. studied the La/TiO 2graphene composites revealed higher visible light absorption and improved charge separation capability. Ahmad et al. [25] synthesized europium and terbium -doped ZnO photocatalyst and Here, a feather-like Eu-doped ZnO (particle size ≈ 34.87 µm and E g ≈ 3.13 eV) nanoassembly is synthesized by using the capping agent cetyltrimethylammonium bromide-supported hydrothermal method. The Eu-doped ZnO is loaded onto the graphene oxide (GO) surface as Eu-doped ZnO@GO (particle size ≈ 23.07 µm and E g ≈ 0.79 eV) and applied to measure the photocatalytic water splitting activity in 20% ...

Investigating the synergistic effect of ZnO/GO nanocomposite films for methylene blue removal

“…A heterojunction is a junction between two different semiconductors with different optical energy gaps ( E g). When two semiconductors with different E g, work functions, and electron affinities are brought together, a discontinuity in the energy bands is expected at equilibrium (here ZnO n‐type, GO p‐type electrical conductivity) 61 . This discontinuity creates a built‐in potential barrier at the interface of the two semiconductors, which acts as a barrier for the flow of charge carriers across the junction.…”