| This paper aimed to develop efficient, non-toxic, stable, low-cost and visible-light responsive photocatalytic materials. First, research progresses of magnetic chitosan and visible-light responsive semiconductor photocatalysts, particularly recent developments of Cu2O-based photocatalysts were reviewed and discussed. Subsequently, magnetic chitosan (MFe3O4/CS NPs) and novel visible-light responsive Cu2O-based nanocomposites (Cu2O/CS NCs, Cu2O/CS-Fe3O4NCs, Cu2O/BiOCl) were obtained by using non-toxic reagents through low-cost, simple but effective, environmentally friendly preparation routes. The structure and adsorption/visible-light photocatalytic decolorization performance of these nanocomposites were investigated. The prepared Cu2O-based nanocomposites could provide large surface areas and more pore structures to improve their adsorption ability of dye and molecular oxygen and promote effective separation of electron-hole pairs, thereby showed enhanced photocatalytic decolorization and stability under visible light irradiation. The research results would provide basic data and theoretical reference for the development of photocatalytic composites and their applications in the fields of wastwater treatment. The main works and conclusions in the present study are as follows:1、In situ preparation of magnetic Fe3O4/chitosan nanoparticles via a novel reduction-precipitation method and their application in adsorption of reactive azo dyeMagnetic Fe3O4/chitosan nanoparticles (MFe3O4/CS NPs) were in situ prepared successfully by a simple reduction-precipitation method through partial reduction of Fe3+with sodium sulfite, precipitation with ammonia at room temperature, and then cross-linking with epoxy chloropropane. The nanoparticles were characterized by HRTEM, BET, XRD, FT-IR, TGA and VSM. MFe3O4/CS NPs were quasi-spherical or ellipsoidal in shape and about7nm in average diameter, exhibiting relatively large surface area, good thermal stability and superparamagnetic property with the saturation magnetization value of17.1emu/g. The adsorption behaviors of MFe3O4/CS NPs towards reactive brilliant red X-3B (X-3B) were investigated, including adsorbent dosage, pH effect, coexisting anions, adsorption equilibrium, adsorption thermodynamics and adsorption kinetics. It was found that the adsorption performances of X-3B on MFe3O4/CS NPs were strongly dependent on both initial pH and the adsorbent dosage. The adsorption equilibrium data fitted well with Langmuir isotherm model and the adsorption process followed the pseudo-second-order kinetic model. Thermodynamic parameters such as free energy (ΔG0), enthalpy (AH0), and entropy (AS0) indicated that the adsorption was spontaneous and endothermic. Besides, the recycling experiments showed good reusability of MFe3O4/CS NPs as adsorbents. 2、Visible-light photocatalytic decolorization of reactive brilliant red X-3B on Cu2O/crosslinked-chitosan nanocomposites prepared via one step processCu2O/crosslinked-chitosan nanocomposites (Cu2O/CS NCs) were in situ prepared via a simple one-step liquid phase precipitation-reduction process and characterized by XRD, FT-IR, SEM, TEM, BET, XPS and UV-vis/DRS. The characterization results showed that Cu2O/CS NCs were almost similar spherical or ellipsoidal and the surface was rough and porous because Cu2O particle was wrapped in chitosan. The chitosan layer was especially favorable for improving the adsorption ability of dye and molecular oxygen and restraining the recombination of electron-hole pairs. The visible-light photocatalytic decolorization behavior of Cu2O/CS NCs was evaluated using reactive brilliant red X-3B (X-3B) as a model pollutant. The influences of various experimental factors including Cu/CS mass ratio, dye initial concentration, photocatalyst amount and initial pH on X-3B decolorization were investigated. It was found that the photocatalytic decolorization process on Cu2O/CS NCs followed apparent pseudo-first-order kinetics model. The optimum mass ratio of Cu/CS is2:1. The dye X-3B could be decolorized more efficiently in acidic media than in alkaline media. Cu2O/CS NCs exhibited enhanced visible-light photocatalytic activity compared with other photocatalysts reported before under similar experimental conditions.3、Magnetically separable Cu2O/chitosan-Fe3O4nanocomposites:Preparation, characterization and visible-light photocatalytic performanceA novel magnetically-separable visible-light-induced photocatalyst, Cu2O/chitosan-Fe3O4nanocomposites (Cu2O/CS-Fe3O4NCs), were in-situ prepared via a facile one-step precipitation-reduction process by using magnetic chitosan chelating copper ions as precursor. The structure and properties of Cu2O/CS-Fe3O4NCs were characterized by XRD, FT-IR, SEM, HRTEM, SAED, EDS, BET, VSM and UV-vis/DRS. The results suggested that Cu2O was wrapped in chitosan matrix embedded with Fe3O4nanoparticles, this structure made the nanocomposites relatively large specific surface area and special dimodal pore structure. Cu2O/CS-Fe3O4NCs showed good superparamagnetism and could be easily separated from solution by an external magnet. The photocatalytic activity of Cu2O/CS-Fe3O4NCs was evaluated by degradation of reactive brilliant red X-3B (X-3B) under visible light irradiation. It was found that X-3B could be decolorized more efficiently in acidic media than in neutral or alkaline media. The efficient decolorization of X-3B was ascribed to synergistic effect of photocatalysis and adsorption, and the long conjugated π system of X-3B was almost completely destroyed in this photocatalytic reaction system. The decolorization rates of X-3B were still above87%after five reaction cycles, indicating that Cu2O/CS-Fe3O4NCs had excellent stability and reusability under visible light irridiation. 4. Synthesis, characterization and properties of novel Cu2O/BiOCl nano-photocatalystNovel Cu2O/BiOCl photocatalyst with unique3D/2D structure and enhanced visible-light photocatalytic activity was constructed using two-step liquid phase method. The microstructure and properties of Cu2O/BiOCl composites were characterized by XRD, FT-IR, FESEM, HRTEM, BET and UV-vis/DRS. Using dye X-3B as a model pollutant, the adsorption and visible-light photocatalytic activities of Cu2O/BiOCI composites were investigated, and the photocatalysis mechanism was explored. The results showed that the staggered spaces and edges of BiOCl nanosheets with about40nm thickness were inlaided with some Cu2O sub-microspheres, and the heterojunction structures were formed at the interface between BiOCl nanosheets and Cu2O sub-microspheres. Compared with pure Cu2O, pure BiOCl and the mechanical mixture of both, Cu2O/BiOCl composites exhibited markedly improved efficiency for photocatalytic decolorization of X-3B. The unique3D/2D and heterojunction structure in composites could increase the pore and BET specific surface area and improve the adsorption properties, on the other hand, it could efficiently enhance the charge separation and migration. The composites with Cu2O/BiOCl molar ratio of1:4showed the highest activity. The effects of various scavengers on photocatalytic efficiency revealed that the removal of X-3B was mainly initiated by reactive radial·O2-and h+. |
PDF Full Text Request