Integrated adsorption and photocatalytic removal of methylene blue dye from aqueous solution by hierarchical Nb_(2)O_(5)@PAN/PVDF/ANO composite nanofibers

This work presents the development of hierarchical niobium pentoxide(Nb_(2)O_(5))-based composite nanofiber membranes for integrated adsorption and photocatalytic degradation of methylene blue(MB)pollutants from aqueous solutions.The Nb_(2)O_(5) nanorods were vertically grown using a hydrothermal process on a base electrospun nanofibrous membrane made of polyacrylonitrile/polyvinylidene fluoride/ammonium niobate(V)oxalate hydrate(Nb_(2)O_(5)@PAN/PVDF/ANO).They were characterized using field-emission scanning electron microscopy(FE-SEM),X-ray diffraction(XRD)analysis,and Fourier transform infrared(FTIR)spectroscopy.These composite nanofibers possessed a narrow optical bandgap energy of 3.31 eV and demonstrated an MB degradation efficiency of 96%after 480 min contact time.The pseudo-first-order kinetic study was also conducted,in which Nb_(2)O_(5)@PAN/PVDF/ANO nanofibers have kinetic constant values of 1.29×10^(-2) min^(-1) and 0.30×10^(-2) min^(-1) for adsorption and photocatalytic degradation of MB aqueous solutions,respectively.These values are 17.7 and 7.8 times greater than those of PAN/PVDF/ANO nanofibers without Nb_(2)O_(5) nanostructures.Besides their outstanding photocatalytic performance,the developed membrane materials exhibit advantageous characteristics in recycling,which subsequently widen their practical use in environmental remediation applications.

Optimized photocatalytic regeneration of adsorption-photocatalysis bifunctional composite saturated with Methyl Orange

Photo-responsive adsorption-photocatalysis nanocomposites are generally used in water and wastewater decontamination;however,the prolonged adsorption capacity of composites and the role of adsorption in concomitant photocatalysis are typically neglected.These composites can be regenerated under light irradiation as their adsorption capacity decreases.Herein,a novel adsorption-photocatalysis bifunctional nanocomposite,Bi-doped TiO2 supported on powdered activated carbon(Bi2O3/TiO2/PAC),was prepared using the solimpregnation-hydrothermal procedure.Bi2O3/TiO2/PAC with a secondary calcination temperature of 700℃under a nitrogen atmosphere was selected for maximum adsorption capacity on Methyl Orange(MO).The composite displayed an excellent adsorption capacity and was easily separated and recycled.The results demonstrate that 71.2%photocatalytic regeneration efficiency could be attained under visible light irradiation for 1 hr at an intensity of 750 W/m^2 and pH 7.Characterization of the as-prepared Bi2O3/TiO2/PAC nanocomposite(700℃)indicates that it possesses a highly specific surface area and great optical properties,showing bifunctional adsorption-photocatalysis characteristics.The p-n heterojunction of the composite played a dominant role in the photocatalytic regeneration process,and effective degradation of MO could be achieved along with composite regeneration.

Fly ash-based geopolymer as a novel photocatalyst for degradation of dye from wastewater

The geopolymer synthesized by alkali-activated fly ash was firstly used as a novel photocatalyst for degradation of methylene blue （MB） dye from wastewater. The geopolymer is composed of nanoparticulates with an average particle size of about 50 nm, More than 90% of pore volume in the fly ash-based geopolymet predominately centralized on the pore size in the range of 17-700 nm. The degradation efficiency of MB dye by fly ash-based geopolymer catalyst was up to 92.79% under UV irradiation due to the synergistic effect of adsorption and semiconductor photocatalysis. The pseudo-first-order and pseudo-second-order rate equations as well as intra-particle diffusion rate equation were employed to correlate analysis for the adsorption kinetics of MB dye, The experimental data agreed well with pseudo-second-order rate equation in both cases of with UV and without UV irradiations. The intra-particle diffusion process is not the rate determining step. The photocatalytic degradation of MB dye in solution obeys third-order reaction kinetics.

Enhancement of photocatalytic efficiency by in situ fabrication of BiOBr/BiVO_4 surface junctions

Surface junctions between Bi OBr and BiVO4 were synthesized. The BiOBr/BiVO4 with 1 wt.%of Bi OBr exhibited the highest photocatalytic activity in the degradation of Rh B under visible-light irradiation. It was found that the highly efficient adsorption of Rh B molecules via the electrostatic attraction between Br-and cationic ／N（Et）2 group played a key role for the high photocatalytic activities of BiOBr/BiVO4. This efficient adsorption promoted the N-deethylation of Rh B and thus accelerated the photocatalytic degradation of Rh B.Moreover, the metal-to-metal charge transfer（MMCT） mechanism was proposed, which revealed the concrete path paved with Bi–O–Bi chains for the carrier migration in BiOBr/BiVO4. The interaction between photoexcited Rh B＊ and the Bi^（3＋） in BiVO4 provided the driving force for the migration of photo-generated carriers along the Bi–O–Bi chains. This work has not only demonstrated the important role of efficient adsorption in the photocatalytic degradation of organic contaminants, but also developed a facile strategy to improve the efficiency of photocatalysts.

Synthesis and characterisation of potassium polytitanate for photocatalytic degradation of crystal violet

Potassium titanate nanostructures were synthesised by hydrothermal treatment of TiO2 （P25） in KOH and H2O2. As-produced powders were characterised by scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, and nitrogen adsorption-desorption methods. Longitudinally-oriented-wire-like structures with a length up to several micrometres and diameters ranging from 10 to 30 nm were obtained. Larger size fibrous nanowires resulting from the hydrotherrnal treatment showed high affinity in adsorbing crystal violet （CV）, which was mainly due to their high surface area. The photocatalytic bleaching of CV solution revealed that the wires are photoactive under ultraviolet light irradiation. Macroporous nanowires are considered as effective adsorbents of CV, capable of photocatalvtic degradation, and they can be easily separated from the solution by settling.