ABSTRACT
In this study, the biochar obtained from waste cotton fibers was introduced into the Ag-doped g-C3N4/TiO2 hybrid composite through a facile one-step hydrothermal process. The morphology, elemental composition, crystal structure, microstructure, specific surface area, chemical bonding state, energy band structure, and separation efficiency of photoinduced charge carriers of the resultant composite were examined using scanning electron microscope, energy dispersive X-ray spectrometer, X-ray diffractometer, transmission electron microscope, surface area analyzer, X-ray photoelectron spectroscope, Ultraviolet-visible spectrophotometer, ultraviolet photoelectron spectroscope, and photoluminescence spectroscope. The adsorption isotherms, kinetics and thermodynamics of the biochar, Ag-doped g-C3N4/TiO2 and Ag-doped biochar/g-C3N4/TiO2 were evaluated using the model methyl orange dye. The photoacatalytic degradation of the model pollutants including methyl orange, methylene blue, congo red, and tetracycline hydrochloride and the photocatalytic reduction of Cr(VI) ions were also assessed under visible light. Experimental results indicated that the photocatalytic property of the Ag-doped biochar/g-C3N4/TiO2 was significantly enhanced through the adsorption enhancement compared with the Ag-doped g-C3N4/TiO2. This was due to the uniform doping of multi-scale porous biochar with g-C3N4 nanosheet, Ag and TiO2 nanoparticles. The adsorptive enhancement induced by the biochar resulted in the narrowed band gap, suitable electronic energy band structure, and fast separation of photoinduced charge carriers of the Ag-doped biochar/g-C3N4/TiO2, which was probably due to the coexistence of multi-valence Ti+4/+3 and Ag0/+1 species and oxygen-containing groups of biochar. The major reactive species of the Ag-doped biochar/g-C3N4/TiO2 were 1O2 and h+. The MO dye adsorption onto the Ag-doped biochar/g-C3N4/TiO2 followed the Langmuir isotherm model, pseudo-first-order and pseudo-second-order kinetic models, and the adsorption process was an endothermic reaction with entropy reduction effects. As such, the Ag-doped biochar/g-C3N4/TiO2 exhibited a promising application for the treatment of wastewater containing multi-pollutants especially organic dyes and heavy metal ions.
ABSTRACT
In this study, BiFeO3(BFO) nanosheets ground from BFO particles were first incorporated with wool flakes to construct sandwich-like wool-BFO composites using the vibration-assisted ball milling technique in freezing conditions. The wool-BFO composites were then loaded with a thick layer of TiO2nanoparticles to prepare the core-shell-structured wool-BFO-TiO2composites using a hydrothermal synthesis process. The microstructure of the core-shell wool-BFO-TiO2composites and its photocatalytic applications were systematically examined using a series of characterization methods. Trapping experiments and electron spin resonance spectra were also employed to judge the active radical species like superoxide radicals (·O2-), singlet oxygen (1O2), holes (h+), and hydroxyl radicals (·OH) using benzoquinone, furfuryl alcohol, ethylenediamine tetraacetic acid, and tert-butanol as the scavengers, respectively. The photodegradation performance of the wool-BFO-TiO2composites was measured using more resistant methyl orange (MO) dye as the pollutant model. In comparison with the wool-TiO2or wool-BFO composites, the superior photocatalytic properties of the wool-BFO-TiO2composites under visible light irradiation were attributed to the presence of mesopores and macropores, the large specific surface area and intimate interface between wool-BFO composites and TiO2nanoparticles, the coexistence of Fe3+, Fe2+, Bi3+, Bi(3-x)+, Ti4+, and Ti3+species, and the strong visible light harvesting, thus leading to the fast separation of photogenerated electron-hole pairs. The wool-BFO-TiO2composites could be used for the repeated photodegradation of organic pollutants and be recycled easily using a magnet. The active radical species of the wool-BFO-TiO2composites were ·O2-and1O2rather than ·OH and h+, which were involved in the photodegradation of MO dye under visible light irradiation.