| Along the c-axis,the BiOCl unit cell is alternately stacked by a positively charged[Bi2O2]2+ layer and two layers of negatively charged Cl-ions.The[Cl-Bi-O-Cl]slabs are stacked together by van der Waals interactions through the Cl atoms.The strong intralayer bonding and the weak interlayer van der Waals interaction give rise to highly anisotropic structural,electrical,thermal,optical,and mechanical properties.However,the band gap(Eg)of BiOCl is about 3.4 eV,which means that the photoresponse range of BiOCl is in the ultraviolet region,and that the utilization of sunlight is low.The photocatalytic activity of BiOCl strongly depends on the exposed crystal planes because the photocatalytic reaction occurs at the surface of the catalyst.The different exposed crystal planes have different atomic types,densities,occupied sites,coordination situations,and electronic structures resulting in differences in the physicochemical properties.The rapid recombination of photogenerated electron-hole pairs in BiOCl results in the reduced catalytic activity.In addition,the nano-photocatalyst particles are small.The small particles generally have a large specific surface area,providing more catalytically active sites,which is advantageous for improving photocatalytic efficiency.However,small particles tend to form a suspension in the solution,which are difficult to recycle after the water purification treatment,causing secondary pollution.Therefore,how to extend the photoresponse range,and control the exposed crystal planes,and suppress the recombination of the carrier,and catalyst recycling become the urgent problems to be solved.In order to solve the above problems,researchers have done a lot of researches on the synthesis of BiOCl and their composites with different dimensions,and on the controlling growth of different exposed crystal planes as well as potential applications,and many meaningful results have been achieved.However,there are still many problems to be solved,such as the zero-dimensional synthesis,the control of the ratio of different exposed crystal planes,and the intimate contact between the two phases of the composite.The etherification of alcohols during vapor-thermal reaction provides water for the hydrolysis of Bi+3 precursor,which is advanced for its controllable hydrolysis rate.Our research was carried out using this synthesis method,and the main research contents are as follows:(1)6.3-nm(0D)BiOCI nanoparticles(NPs)and a series of BiOCl samples with different ratios of(001)exposed crystal planes were synthesized through a self-developed vapor—thermal method for the first time.Compared with the other samples,OD BiOCl possesses a higher ratio of(001)exposed planes,more oxygen vacancies and co-existent Bi+3-x and Bi+3+x,and fewer hydroxyl groups adsorbed at the surface of NPs.These surface states bring about the red-shift of the light absorption edge,reduced recombination probability and increased charge transfer rate of photo-generated carriers,consequently enhancing the photocatalytic degradation ability for RhB.In addition,OD BiOCl exhibits hydrophobicity,while the other sample exhibit hydrophily.We have utilized such the method to synthesize a few kinds of photocatalysts and their composites with unique morphology,novel properties and excellent photocatalytic performance;this method paves the way to further improve photocatalytic performances and provides an opportunity to find novel properties.(2)A series of BiOCl samples were synthesized in a mixture of isopropanol and water in different proportions and volumes.With variation of the vapor environment:the nucleation and growth,morphology,specific surface area,valence band state density,the ratio of the exposed(001)planes of BiOCl and the total concentration of defects such as Bi+3-x,Bi+3+x,-OH and Ov can be changed,results in the effects on recombination of photo-generated carriers.Finally,the degradation rate varied from 5.7×10-2 min-1 to 18.2×10-2 min-1.Therefore,the photocatalytic properties of BiOCl can be simply controlled by changing the composition and volume of vapor in the autoclave.(3)The Bi2O2CO3/BiOCl heterojunction was prepared by in-situ growth on BiOCl nanosheets via vapor-thermal method.The ratio between the two phases can be controlled by changing the experimental conditions.The heterojunction have more Bi2O2CO3 with less N-doped,due to the"self-cleaning"ability of the BiOCl lattice and the Bi-O and C-O strong bonds between the layers of Bi2O2CO3 lattice.Compared with other samples,the Bi2O2CO3/BiOCl heterojunction exhibits the red-shifted absorption edge,the lowest luminescence intensity,and the best photocatalytic ability.These results indicate that the in-situ synthesized Bi2O2CO3/BiOCl heterojunction affects the band structure and carrier dynamics of the composite,which affects photocatalytic degradation,light absorption and photo-luminescence.This phenomenon provides a useful experimental basis on the design,preparation,properties and applications of composites.(4)An unprecedented"breaking-to-assembling"methodology to synthesize the?-Fe3N nano-sheets and Fe3O4/?-Fe3N heterogeneous nano-chain bundles is reported.Specifically,the nitrided Fe aggregates with inclusions of s-Fe3N and ?'-Fe4N were electrochemically anodized without and with the assistance of the 0.4 T applied magnetic field.The corrosion of hydrochloric acid electrolyte to ?'-Fe4N breaks the large nitrided Fe aggregates into small particles with the main inclusion of ?-Fe3N nanocrystals,which subsequently assemble to the large hexagonal sheets,due to the consequence of reducing the surface energy,as the anodization potential V is 15 V.Simultaneously,?'-Fe4N was anodized to Fe3O4,especially in the case of high V value of 50 V;subsequently,Fe3O4 and s-Fe3N nanoparticles assemble to the nano-chain bundles driven by the dipole-dipole interaction.In principle,suchlike nano-sheets and nano-chain bundles can be synthesized if the nitrided metals or alloys can be corroded and simultaneously anodized in the conditions of proper eletrolyte and anodization potential.The synthesis of these nano-structures and studies on their properties and applications are in process.(5)Then 2D BiOCl nano-sheets were intimately grown on surfaces of these aboved MNS through the vapor-thermal method with isopropanol and ethylene glycol acting as the solvents,as a result,2D-2D and 1D-2D magnetic photocatalysts were achieved.MNS function as the directing agents of BiOCl growth,controlling the oriented growth of BiOCl;furthermore,they compress the crystal lattice of BiOCl due to the strain at the interface between MNS and BiOCl.BiOCl growing on 2D nano-sheets exhibits the flower-like morphology consisting of square nanosheets,while it exhibits the morphology of epispastic sponge for BiOCl growing on 1D heterogeneous nano-chains,which has not been observed before as far as we know.The synergistic effects of MNS and BiOCl enhance the absorbance in the visible-light region.All the magnetic photocatalysts exhibited the excellent adsorption and degradation abilities to the target pollutants such as rhodamine B,methylene blue and phenol.Herein,using the MNs as the directing agents opens up a new route to realize the oriented assembly and growth of the aggregated nanosheets of BiOCl;this strategy can be popularized to the synthesis of other catalysts. |
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