Study On Cobaltate/Carbon-based Composites For Photocatalytic Degradation Of Organic Pollutants

Recently,the issue of water contaminated by organic dyes and antibiotic emissions is increasingly prominent,which badly affects eco-systerm and harms human’s health.Photodegradation of pollutants in water has many merits,such as energy conservation,low-cost,strong oxidation and so forth.Therefore,in this article we designed bimetal oxide MCo₂O₄（M=Ni,Fe）/carbon-based composite,2D hexagonal sheet NiCo₂O₄/carbon nanofibers（2D HS-Ni Co₂O₄/CNFs）and 3D hollow porous sphere FeCo₂O₄/cotton carbon fibers（3D HPS-FeCo₂O₄/CCFs）,for studying the degradation of organic dyes（methylene blue,malachite green）and antibiotics（tetracycline）under visible light.the main research of this report is following:2D HS-NiCo₂O₄/CNFs was synthesized by hydrothermal-calcination method.its feature of structure,composition,microstructure and specific surface area were characterized by X-ray diffraction（XRD）,X-ray photoelectron spectrometer（XPS）,scanning electron microscopy（SEM）and N2 adsorption-desorption.The influential factor of this catalytic reaction was investigated.the degradation efficiency of MB catalysised by NiCo₂O₄/CNFs was 91.3 % under optimal conditions after visible light（λ≥420nm）irradiation for 2 hours.The experiment of degradation reaction kinetics showed the degradation of MB with NiCo₂O₄/CNFs obeyed pseudo-first-order kinetic model and the observed rate constant(0.01298 min^-1)was 1.6 times that of pure NiCo₂O₄(0.00809 min^-1).the effect of anions existed in the degradation process was studied,the results showed co-existing anions discussed could inhibit the degradation of MB to some extent and the inhibition of anions could be ranked as follow: NO3-≈SO₄^2->CO32-≈PO43-.Radical capture experiments showed the active species participating in the degradation reaction of MB under visible light were hydroxyl radical（· OH）and superoxide radical(·O^2-).Combining Mott-Schottky experiments and band gap analysis as well as the final products to the degradation of MB were analyzed by HPLC and IC,a possible degradation mechanism was proposed.3D HPS-FeCo₂O₄/CCFs was prepared by hydrothermal-calcination method using cotton as carbon source and its properties were characterized by experiments that including XRD,XPS,SEM,PC and so forth.the specific surface area of FeCo₂O₄/CCFs was 11.6 times that of FeCo₂O₄.The effects of reaction temperature,amount of catalyst,amount of carbon source,pH of solution and other conditions were investigated.The performance of FeCo₂O₄/CCFs in photo-degradation MG/TC under optimal conditions were evaluated.The results showed the degradation efficiency of MG using FeCo₂O₄/CCFs as photocatalyst after visible light irradiation for 2 hours was 97.2 % and that was still 81.5 % after four regeneration-catalysis cycles;the degradation efficiency of TC was 72.7 % after visible light irradiation for 6 hours.Degradation kinetics experiment showed the kinetic studies of the degradation of MB/TC under visible light obeyed pseudo-first-order kinetic model and the observed rate constant were 0.0144 min^-1 and 0.0028 min^-1,respectively.the mineral products and degradation process were analyzed by HPLC-MS.Radical capture experiments and photoluminescence spectral analysis disclosed that the active species involved in the process of degradation reaction of FeCo₂O₄/CCFs under visible light were · OH and ·O^2-.Combining the analysis of band gap and photo-electrochemical measurements,the reaction mechanism of FeCo₂O₄ / CCFs to catalyze the degradation of organic pollutants was revealed.