Preparation Of Visible-light-driven Photocatalyst And Its Photocatalytic Performance Under Visible Light

Photocatalytic oxidation technology as one of the pollution control technologies has great application prospect. In view of the currently key scientific issue of low quantum efficiency in photocatalytic technology, in order to improve the activity of visible-light-induced photocatalyst, the visible-light-induced photocatalyst with better photocatalytic property can be obtained by constructing the spheres with hierarchical nanostructures and p-n heterojunction structures which can modify the morphology, structure and photocatalytic ability of photocatalyst. The main works of this research are as follows:(1) The p–n heterojunction with mesoporous BiVO4 framework well-distributed Co3O4 is fabricated. The mesoporous structure is prepared by nanocasting technique using KIT-6 as template, while the incorporation of Co3O4 particles is completed by the impregnation technique using Co(NO3)2 as the raw materials. Transmission electron microscopy(TEM) image shows that Co3O4 particles have been successfully loaded in the framework of the mesoporous BiVO4. Scanning electron microscopy(SEM) and Energy dispersive spectrum(EDS) mapping reveals that Co3O4 particles distribute uniformly in the sample, which is the result of the template effect of the mesoporous structure. Uv-vis absorption spectrum(DRS) indicates that loading the on the surface of mesoporous BiVO4 has increase the light absorption ability of photocatalyst. Compared with BiVO4(2.43 eV), Co3O4/mesoporus BiVO4 has a decreased band gap. Fluorescence spectrum(FL) shows construction of heterojunction with large contact area can effectively promote the separation of photogenerated holes and electrons. Co3O4/mesoporus BiVO4 composite photocatalyst has excellent photocatalytice ability in the removation of RhB under the visible light. The prominent enhancement is induced by the large contact area between Co3O4 and mesoporus BiVO4 which can further restrain the recombination of photogenerated carriers. The influences of the photocatalysts with different supported cobalt content on photocatalytic performance were investigated. When an appropriate amount of Co as 4% is added in the preparation of photocatalyst, the obtained composite photocatalyst has the best photocatalytic performance.(2) Visible-light-driven α-sulfur spheres with hierarchical nanostructures were fabricated by simple solution-phase synthesis with PVP as the template and HCl, Na2SO3·2H2O as raw materials. The effect of the addition quantity of PVP on the physicochemical properties of the photocatalyst was investigated. The obtained α-sulfur spheres with 200 mg PVP has the best photocatalytic performance. The obtained products are systematically studied by TEM, SEM, BET surface area measurement(BET) and FL. When 200 mg PVP is added, TEM, SEM images and BET show α-sulfur hierarchical spheres with hierarchical nanostructures have uniform particle size about 1μm and ultrahigh specific surface area. The research on the adsorption of RhB suggests α-sulfur spheres with hierarchical nanostructures has strong reactant adsorption ability. FL indicates the addition of PVP also can promote the separation of the photogenerated electron and hole. The research of photocatalytic removation of RhB indicates α-sulfur spheres with hierarchical nanostructures has excellent photocatalytic performance. The optimum photocatalytic activity of the α-sulfur spheres photocatalyst for the removation of RhB was almost 3.6 times higher than bulk α-S. The hierarchical nanostructures which can increase the, benefit the adsorption of reactant, accelerate the surface reaction and promote the separation of photogenerated carriers are responsible for this increase.(3) The core–shell heterojunctions of ultra-thin g-C3N4 nanosheet enwrapping spherical a-S composites(a-S@C3N4) were fabricated via a self-assembly process by electrostatic force to realize enhanced photocatalytic ability under visible light. The morphology and photocatalytic ability can be adjusted by tuning the amount of the ultra-thin C3N4 nanosheet. The obtained products are systematically studied by SEM, DRS and FL. Compared with α-sulfur spheres, a-S@C3N4 has larger heterojunctions contact area. DRS reveals the stronger light absorption ability and FL shows highly efficient photogenerated holes and electrons separation which can be attributed to the preferable core–shell heterojunctions structure(showed by SEM images). The a-S@C3N4 composite with 35% composition of C3N4 nanosheet has the highest photocatalytic ability. The degradation rate of Rhodamine B(RhB) with a-S@C3N4(35% C3N4) is 6.7 times faster compared to a-S as photocatalyst. This increase could be attributed to the stronger light absorption ability and the efficient photogenerated holes and electrons separation by the heterojunction with larger contact area, which further promote the separation of photogenerated electrons and hole. In addition, trapping experiments revealed that ·OH-, hole and ·O2- are the mainly active species for α-sulfur spheres in the degradation of RhB. However, after combining the ultra-thin g-C3N4 nanosheet with spherical a-S, the mainly active species for a-S@C3N4 in the degradation of RhB are hole and ·O2-.(4) ultra-thin g-C3N4 nanosheet(g-C3N4 NS)/β-Bi2O3 heterojunctions visible-light-induced photocatalyst was fabricated via electrostatic force using g-C3N4 NS and β-Bi2O3 as the raw materials. The effect of the supported amount of g-C3N4 NS on the physicochemical properties such as morphology, surface area and photocatalytic activity of the photocatalyst was investigated. The obtained products are systematically studied by SEM, TEM, Fourier transform infrared spectroscopy(FT-IR), X-ray photoelectron spectroscopy(XPS), DRS, and FL. SEM and TEM images, FT-IR and XPS shows the the g-C3N4 NS has been wrapped on the spherical β-Bi2O3 particles. DRS and FL indicates the constructing p–n heterojunction with g-C3N4 NS can enhance the separation efficiency of photogenerated carriers and light absorption ability of β-Bi2O3 particles. The research of photocatalytic removation of RhB indicates g-C3N4 NS/β-Bi2O3 has excellent photocatalytic performance. The enhanced photocatalytic performance is firstly attributed to the p–n junction effect of efficient separation of photogenerated charge carriers. The supported amount of g-C3N4 NS also could affect the photocatalytic activity of g-C3N4 NS/β-Bi2O3 heterojunction under visible light. The g-C3N4 NS/β-Bi2O3 composite with 30% composition of g-C3N4 nanosheet has the highest photocatalytic ability.(5) The graphene oxide(GO) is fabricated by chemical oxidation or chemical oxidation combined with ultrasonic irradiation from graphite. Ag3PO4 particles are anchored on the GO by facile ion-exchange method. The as prepared GO and Ag3PO4@GO composites are systematically characterized by XRD, FT-IR, Valence band XPS(VB XPS), Mott–Schottky plots, SEM, BET, DRS and FL. Different oxidation process can affect oxygen-containing functional groups on the surface of GO and the band structure of GO. FT-IR and VB XPS shows that compared with chemical oxidation, the type and quantity of oxygen-containing functional groups in GO have been increased. Besides CH(O)CH and O-H groups, which are formed during chemical oxidation, C=O and COOH groups are also formed in GO by chemical oxidation combined with ultrasonic irradiation. Mott–Schottky plots and VB XPS reveal that the valence band(VB) and conduction band(CB) potentials of GO which are prepared by chemical oxidation are 2.3 eV and-0.75 eV(vs NHE). Howerer through chemical oxidation combined with ultrasonic irradiation The VB and CB potentials of GO are 2.3eV and-0.75eV(vs NHE). SEM images shows the Ag3PO4 particles are decreased to be smaller size by the stabilization effect of GO and are enwrapped by GO. BET and DRS indicates the Ag3PO4@GO has larger surface area and stronger light absorption performance, respectively. The photocatalytic ability of prepared samples is evaluated by the phenol degradation under visible light. The photocatalytic ability of Ag3PO4@GO composite in which the GO is prepared by the addition of ultrasonic irradiation to the chemical oxidation is 4 times to Ag3PO4. This increase can be attributed to abundant oxygen-containing functional groups of GO prepared by the addition of ultrasonic irradiation to the chemical oxidation and energy band matching between GO and Ag3PO4. GO is firstly a stabilizer to prevent the generation of Ag3PO4 particles on the GO surface and a heterojunction structure with larger contact area between Ag3PO4 and GO are formed. Besides the energy band matching between GO and Ag3PO4, the larger contact area could further increased separation efficiency of the photogenerated charge carriers.