Experimental Study On Sulfite Induced Catalytic Degradation Of Organic Pollutants In Water

The existence of refractory organic matter in wastewater has great harm to human body and environment.It is difficult to degrade wastewater in conventional treatment.Advanced Oxidation Process（SR-AOPs）based on Sulfite has attracted extensive attention because of its high efficiency and high selectivity.Among them,the sulfite for cheap easy be SR-AOPs research focus in the precursor.At present,most sulfites are activated by homogeneous single metal ions to degrade organic pollutants,which is difficult to recover and the catalytic activity is inhibited.Here,we constructed a heterogeneous system containing Co₃O₄nanoparticles and TiO₂ nanotubes to form a p-n heterojunction as a highly active catalyst for sulfite photocatalytic degradation of acetaminophenol（ACE）.In order to improve the photocatalytic activity of TiO₂,Co₃O₄/TiO₂ composites were prepared by co-precipitation method and hydrothermal method.The TiO₂,Co₃O₄/TiO₂ was characterized and analyzed.The existence of TiO₂nanotubes and hexagonal Co₃O₄ nanosheets was observed by SEM,TEM,XRD,EDS mapping,XPS（VB-XPS）and UV-DRS analysis showed that the existence of Co₃O₄ can effectively broaden the light utilization range of Co₃O₄/TiO₂.The formation of p-n heterojunction between Co₃O₄ and TiO₂ promotes the electron transfer from Co₃O₄ to TiO₂,which effectively improves the photocatalytic activity of Co₃O₄/TiO₂.In addition,by comparing the degradation efficiency of different molar ratios of Co and Ti（Co（NO）₂·6H₂O and Ti（SO₄）₂）,it was found that the composite effect was the best when the molar ratio of Co and Ti was 1.5%.Through the analysis of degradation efficiency and kinetics of different process systems,it was found that Light+Co₃O₄/TiO₂+S（Ⅳ）system had excellent wastewater treatment performance.Under the optimal conditions（[Co₃O₄/TiO₂]=1g/L,[S（Ⅳ）]=10 m M,[ACE]=0.01 m M,p H=7）,the degradation rate of ACE could reach 96.78%within 30 min.In the Light+Co₃O₄/TiO₂+S（Ⅳ）system parameter optimization experiment,Na₂SO₃ plays an important role.Low concentration of Na₂SO₃ is conducive to the degradation of ACE,because Co₃O₄/TiO₂ can activate Na₂SO₃ to provide effective SO₄^·-;high concentration of Na₂SO₃ is not conducive to the degradation of ACE,which is mainly due to the occupation of active sites by S（Ⅳ）.At the same time,higher doses of Co₃O₄/TiO₂ can provide more active sites and promote the degradation of ace;However,too much catalyst can reduce the utilization of light in solution and cause material waste.Therefore,we suggest that the concentration of Na₂SO₃ in the solution is controlled at about 10m M,and the amount of Co₃O₄/TiO₂ should be controlled at 1 g/L～2 g/L.In addition,the initial concentration of ACE and k₁ value were fitted,and it was found that k₁ gradually decreased with the increase of ACE concentration.The effects of several inorganic anions on ACE degradation were studied.It was found that they all inhibited ace degradation in varying degrees,with the order of Cl^->CO₃^2->NO₃^->SO₄^2-.The stability and recyclability of Co₃O₄/TiO₂ were studied by cyclic test,and it still has good catalytic activity after five tests.The main active radicals in Light+Co₃O₄/TiO₂+S（Ⅳ）system were determined by radical quenching experiment and ESR capture technique.The results show that h⁺and SO₃^·-play an important role in the system.The TOC of Light+Co₃O₄/TiO₂+S（Ⅳ）system was detected,and it was found that the mineralization degree was not complete,and there might be intermediate products in the system.Fourteen low toxic by-products were detected by HPLC-MC/MC.Four possible degradation pathways were deduced:hydroxylation at C5 site,C-N bond breaking,benzene ring breaking and coupling between free radicals.Moreover,we proposed the mechanism of sulfite photocatalytic activation of Co₃O₄/TiO₂for ACE degradation,which is the generation of free radicals such as^·OH on the surface of the photocatalyst;Na₂SO₃ was activated by the catalyst to produce SO_x^·-complexation with the surface of the catalyst.Finally,the development direction of Light+Co₃O₄/TiO₂+S（Ⅳ）system in wastewater treatment and the problems to be solved are proposed.