Preparation Of TiO₂/carbonaceous Materials Induced By Sodium Alginate And Its Photocatalytic Properties

The toxic and harmful chemicals in the water have exceeded the standard due to the massive discharge of industrial,domestic,and agricultural sewages,which have caused the destruction of the ecological environment and significantly impacted the domestic water.Obtaining non-toxic water has consequently become ever more critical.Photocatalytic technology has attracted much attention since its invention and is regarded as one of the efficient and environmentally friendly technologies in pollution control.TiO₂is the most promising semiconductor for photocatalytic technology but has some inherent defects,including fast photoelectron recombination and narrow bandgap.Highly conductive carbon modified TiO₂has been considered adequate.Hence,TiO₂carbon matrix composites（TiO₂/C）were prepared by alginate induction.The main research contents are as follows:（1）TiO₂/C nanocomposites were prepared from titanium alginate coordination compound.Their photocatalytic properties for methylene blue（MB）under simulated sunlight were studied.The composites were characterized by SEM-EDS,FT-IR,XRD,XPS,TG-DTG,UV-vis,and N₂adsorption-desorption analysis.The results showed that TiO₂in TiO₂/C composites is a mixture of anatase and rutile.Carbon species existed on the surface of TiO₂/C composites.The bandgap energy of TiO₂/C-20 was as low as 2.23e V,meaning that TiO₂/C-20 had excellent photon absorption performance in both visible and ultraviolet regions.Under simulated sunlight,the degradation rate of MB by sample TiO₂/C-20 reached 97.47%within15 min.The quasi-first-order kinetic rate constant was 0.0855 min^-1,which showed good photocatalytic performance.After 5 cycles of testing,the photodegradation rate of the sample to MB was only reduced by0.72%,which proved the excellent stability of the samples.·O₂^-was the main active species in the photodegradation process.（2）A competitive coordination strategy was employed to regulate the crystal structure and photocatalytic properties of TiO₂/carbon nanocomposites.In preparing the titanium alginate complex,Ca Cl₂,a commonly used coordination agent,was added to obtain the binary complex of titanium alginate and calcium alginate,and the photocatalyst C-TiO₂/Ca CO₃was obtained by calcination.Through the structural characterization of the composite,it was confirmed that the introduction of Ca Cl₂could effectively regulate the crystal shape of TiO₂through coordination competition reaction and realize the transformation from mixed to single anatase phase.Both Ca CO₃and C mainly exist on the surface of the material.The bandgap of C-TiO₂/Ca CO₃was 2.71 e V,which increased the response range of visible light.Under simulated light irradiation,the degradation ratio of MB by C-TiO₂/Ca CO₃could reach 96.46%within 10 min,and the quasi-first-order kinetic rate constant was 1.9028 min^-1,indicating that the material had excellent photocatalytic activity.After 5 cycles,the photodegradation efficiency was almost unchanged,indicating that C-TiO₂/Ca CO₃photocatalyst was recyclable and stable.The photodegradation mechanism showed that h⁺was the main active species in the photodegradation process.（3）Nitrogen-doped TiO₂/carbon nanocomposites were prepared and characterized.Combined with the preparation of TiO₂/C composites,nitrogen-doped TiO₂/carbon nanocomposites(N-TiO_2/C)were obtained at high temperatures with dopamine and sodium alginate as radioligands,Ti⁴⁺as central ions,and dopamine as nitrogen source.The structure characterization showed that N-TiO_2/C was transformed into a single rutile phase at high temperatures.N element was doped into the TiO₂lattice,while C element existed on the surface of the composite material.The bandgap value of N-TiO_2/C is 2.76 e V,which has visible light absorption capacity.The photocatalytic activity test results showed that the degradation rate of N-TiO_2/C for 10 mg/L MB in 15 min was 99.42%,and the degradation ratio of 20 mg/L MB in 90 min was 97.25%,which was higher than TiO₂/C-10 and C-TiO₂/Ca CO₃.The photodegradation efficiency decreased by 8.36%after 5 cycles.The photodegradation mechanism showed that h⁺was the main active species in the photodegradation process.