Construction Of Bismuth Oxyhalide Composite Catalysts With Enhanced Photocatalytic Activity For The Removal Of Contaminants From Aqueous Solution

As a new kind of advanced oxidation processes?AOPs?,photocatalysis can effectively remove persistent and highly toxic pollutants from water.Bismuth oxyhalides?BiOX,X=Cl,Br,I?have drawn wide concern owing to the unique electronic structure,excellent optical and electrochemical properties.In view of the low adsorption capacity and catalytic efficiency during the degradation of contaminants,it is urgent to broaden the absorption region of visible light,accelerate the separation efficiency of photogenerated carriers,improve the enrichment capacity of pollutants for pristine BiOX,and finally achieve the efficient removal of contaminants from water.In this paper,metal-organic framework?MOF?or carbon quantum dots?CQDs?modified BiOX composite catalysts were prepared via semiconductor recombination.The obtained catalysts were applied to remove persistent organic contaminants and heavy metal ions from water under visible light irradiation.The relationship between the microstructure of composite catalysts and enhanced photocatalytic performance were illustrated in detail.This work can provide a new route for pollutants removal.The main research work are as follows?1?NH₂-MIL-125?Ti?with good charge transport and high photosensitive properties was integrated with BiOCl through solvothermal method,forming NH₂-MIL-125?Ti?/BiOCl composites.The photocatalytic activity was evaluated by using tetracycline?TC?and bisphenol A?BPA?as target water pollutants.As a result,the absorption of visible light increased significantly with the incorporation of NH₂-MIL-125?Ti?.When the doping amount was 10 wt%,the photodegradation rate constants of TC and BPA were around 0.0141 min-1 and 0.0049 min-1,much higher than those of pure BiOCl and NH₂-MIL-125?Ti?.The optical and electrochemical analysis revealed that the photocurrent response value of 10 wt%NH₂-MIL-125?Ti?/BiOCl was about 3.5 and 7 times higher than those of BiOCl and NH₂-MIL-125?Ti?.In addition,the intensity of photoluminescence?PL?was lower than that of BiOCl.Consequently,the introduction of NH₂-MIL-125?Ti?could broaden the absorption region of visible light,enhance the separation and migration efficiency of photogenerated carriers,and the composites displayed enhanced photocatalytic activity for the removal of organic contaminants?2?NH₂-UiO-66 has good stability and charge migration properties.BiOBr nanosheets were grown on the outer surface of NH₂-UiO-66 octahedrons to obtain NH₂-UiO-66/BiOBr composite photocatalyst via a facile solvothermal method.TC and Cr???were employed as the target water pollutants to investigate their photocatalytic oxidation-reduction properties.Scanning electron microscopy?SEM?and transmission electron microscopy?TEM?characterization results showed that NH₂-UiO-66 remained stable before and after solvothermal reaction.Heterostructured NH₂-UiO-66/BiOBr composites were further confirmed based on high-resolution transmission electron microscopy?HRTEM?characterization.And the specific surface area of the composites increased obviously compared to pure BiOBr.The removal rate constants of TC and Cr???over 15 wt%NH₂-UiO-66/BiOBr were about 1.92 and 2.3 times higher than those of pure BiOBr under visible light irradiation.And the presence of inorganic ions(Cl^-?SO₄^2-)inhibited TC degradation significantly.The electrochemical analysis showed that the photocurrent response value of 15 wt%NH₂-UiO-66/BiOBr was 0.4 ?A,about 2 and 40 times higher than those of BiOBr and NH₂-UiO-66,respectively.And the electrochemical impedance value of the composites was lower than those of BiOBr and NH₂-UiO-66.In conclusion,the introduction of NH₂-UiO-66 could increase the specific surface area of composites,improve the separation and migration rate of photogenerated carriers,and finally enhance photocatalytic performance for the removal of TC and reduction of Cr????3?MIL-125?Ti?has large specific surface area and good charge migration properties.A novel MIL-125?Ti?/BiOI microsphere photocatalyst was self-assembly prepared based on MIL-125?Ti?as the substrate material.Rhodamine B?RhB?and TC were employed as the target water contaminants to explore photocatalytic performance of the obtained catalysts.When MIL-125?Ti?content was around 20 wt%,the specific surface area of the composites was 141.17 m² g^-1,much higher than pure BiOI(19.19 m² g^-1).Uner visible light irradiation,the removal efficiency of RhB and TC could reach 99.86%and 73.28%over 20 wt%MIL-125?Ti?/BiOI after irradiation for 120 minutes.The optical and electrochemical analysis displayed that the photocurrent response value of 20 wt%MIL-125?Ti?/BiOI was about 2 and 3.1 times higher than those of BiOI and MIL-125?Ti?.Moreover,the intensity of PL and electrochemical impedance value was lower than those of BiOI and MIL-125?Ti?Besides,the electron spin resonance?ESR?and radicals quenching experiments demonstrated that superoxide radical(O₂^·-)and holes?h⁺?were the major active species during photocatalytic reactions.As a result,the introduction of MIL-125?Ti?could increase the specific surface area of the composites,improve separation efficiency of photoexcited electron-hole pairs and enhance photocatalytic activities?4?Based on the good stability and charge migration properties of NH₂-UiO-66,NH₂-UiO-66/BiOI composites were prepared through a facile reactable ionic liquid assisted method at room temperature.The photocatalytic activities of the as-prepared composite catalysts were evaluated via the removal of TC and Cr???.From the results of SEM and TEM characterizations,it can be found that NH₂-UiO-66 octahedrons were uniformly distributed on the surface of BiOI microspheres.When the doping content of NH₂-UiO-66 was 15.0 wt%,the specific surface area of the composites was about 100.37 m² g^-1,much higher than BiOI(9.37 m² g^-1).Under the irradiation of visible light for 2.5 h and 4 h,the removal efficiency of TC and Cr???could reach 70%and 88.96%over 15 wt%NH₂-UiO-66/BiOI,much higher than pure BiOI and NH₂-UiO-66.The photocurrent response value of the composites was much higher than the two monomers,the PL intensity and electrochemical impedance value was lower.In conclusion,the introduction of NH₂-UiO-66 could increase the specific surface area of the composites,accelerate the migration efficiency of photogenerated carriers from bulk to surface active sites.As such,the composites displayed enhanced photocatalytic performance for the removal of TC and Cr????5?CQDs have up-conversion capacity and excellent electron transfer properties Double regulation of CQDs modified BiOCl/BiOBr composite catalysts were prepared employing ionic liquid as both reactant and high-performance template Several different type of organic contaminants such as RhB,TC,ciprofloxacin?CIP?and BPA were used to evaluate the photocatalytic activity under visible light irradiation.The characterization results demonstrated that the composite cataltsts could be obtained via the tight coupling between CQDs and BiOCl/BiOBr material This could be attributed to the powerful combination between the oxygen-containing functional groups in CQDs and ionic liquid via hydrogen bond.BiOCl/BiOBr material loading with 5 wt%CQDs showed the best photocatalytic performance for the degradation of RhB,about 2.1,3 and 2.8 times higher than those of BiOCl/BiOBr,BiOCl and BiOBr,respectively.And 5 wt%CQDs/BiOCl/BiOBr displayed higher photocatalytic activity for the removal of TC,CIP and BPA.Recycling experiments indicated the reusability and stability of catalyst for contaminants degradation.The introduction of 5 wt%CQDs could significantly improve the absorption of visible light for BiOCl/BiOBr,enhance the photocurrent response value and reduce the arc radius of Nyquist plot.The main reactive species were determined to be superoxide radical(O₂^·-)and holes?h⁺?on account of electron spin resonance?ESR?and radicals quenching experiments.In summary,the introduction of CQDs could enhance the absorption capacity in the visible region,boost the separation and migration efficiency of photogenerated carriers,increase the activation ability of molecular oxygen,and eventually improve the photocatalytic activity for the removal of organic contaminants.