Polyacrylamide Flocculation Recovery Of Nano-TIO₂ Photocatalyst In Suspension System And Its Effect On The Photocatalytic Degradation Of Phenol

Semiconductor photocatalytic technology is considered to be the most ideal environmental purification technology.Photocatalysts such as TiO₂ have been widely used in the field of photocatalysis due to their safety and stable performance.Because of its large specific surface area and good dispersion,TiO₂ has high catalytic efficiency,but the recycling method is not mature.In this paper,three kinds of polyacrylamide flocculants are used for flocculation recovery and reuse of nano-TiO₂ in suspension state.It is proposed to improve the recovery method of suspended TiO₂ so that it can be applied in the actual pollution treatment process.Three different types of polyacrylamide flocculants?anionic polyacrylamide APAM,cationic polyacrylamide CPAM,nonionic polyacrylamide NPAM?were selected for flocculating and recovery of nanometer titanium dioxide in suspension system.The optimum dosage,optimum kinetic conditions and optimum system pH were obtained for different flocculants.Taking phenol as the target pollutant,100W mercury lamp as the light source,taking phenol concentration,free radical quencher and pH as the influencing factors,the photocatalytic degradation of phenol in suspension system was carried out in order to discuss the degradation ability of TiO₂ for phenol and its intermediate products and mineralization degreeAnionic polyacrylamide APAM,non-ionic polyacrylamide NPAM flocculant flocculant was used to flocculate and recover nano-TiO₂ in suspension system.The flocculating recovered nanometer titanium dioxide was redispersed to degrade phenol.The suspension nanometer TiO₂ was flocculated and recovered by PAM for many times,and then dispersed to degrade phenol.Discussing the influence of PAM on phenol degradation and the change law of phenol intermediate product in the degradation process.According to the experiment,the following conclusions are drawn:?1?When the concentration of anionic polyacrylamide APAM is 1mg/L,the flocculation recovery effect of nano-TiO₂ in suspension system is the best.When the concentration of ion polyacrylamide NPAM is 2.6mg/L,the flocculation recovery effect of nano-TiO₂ in suspension system is the best.?2?Optimal flocculation and mixing conditions of anionic polyacrylamide APAM:mi xing speed:290r/min;Duration:120s;Slow mixing stage:mixing speed:120r/min;Duration:5min.At this time,the turbidity of the solution is 4.84 NTU.Non-ionic polyacrylamide NPAM flocculation mixing conditions:mixing speed:290 r/min;Duration:130s;Slow mixi ng stage:mixing speed:110r/min;Duration:6min.At this time,the turbidity of the solutio n is 5.53 NTU.?3?When the pH value is 4 and 5,the non-ionic polyacrylamide NPAM has the best flocculation recovery effect on the nanometer titanium dioxide in the suspension system,the turbidity of the solution is maintained between 7¹0NTU,and the concentration of the remaining titanium dioxide in the solution is between 0.5mg/L⁵mg/L.Under acidic conditions,anionic polyacrylamide APAM has good flocculation recovery effect on nano-TiO₂ in suspension system.It indicates that APAM flocculation recovery suspension system has a wide range of pH application.?4?Nano-TiO₂ has no obvious physical adsorption effect on phenol.In the photocatalytic process,the TOC value decreased to 37.23 NTU,although the phenol concentration gradually decreased to complete degradation.The results show that phenol is not fully mineralized,and the intermediate product that cannot be degraded is generated during the degradation process.After addition of TiO₂ catalyst,phenol was completely degraded,TOC value was reduced to 0NTU,and phenol was fully mineralized.?5?When the pH of nano-TiO₂ solution in suspension system approaches neutral,the degradation rate of phenol is higher.When the pH of the nano-titanium dioxide solution decreases or increases,the degradation rate for phenol starts to decrease slowly.According to the size of phenol degradation rate,the order of pH of phenol degradation by nano-TiO₂solution in suspension system is:pH=7>pH=8>pH=5>pH=6>pH=4>pH=9.According to the decrease rate of TOC,the pH of the degradation rate of phenol by nano-TiO₂ in suspension system is as follows:pH=7>pH=6>pH=5>pH=8>pH=9>pH=4.?6?Hydroxyl radical quencher isopropanol has a certain effect on the photocatalytic degradation of phenol,which can accelerate the degradation rate of phenol.But it is not the main factor,i.e.the hydroxyl radical is not the main active species.Optical hole quencher EDTA has a great influence on the photocatalytic degradation of phenol,which can greatly improve the degradation rate of phenol by nano-TiO₂.Photogenic holes are the main active species in the photocatalytic process.?7?The intermediate products of phenol degradation include phthalene,resorcinol,terephthal and benzoquinone.When the photocatalytic reaction was carried out to 30 min,the concentration of the intermediate products reached the maximum.?8?When 10 mg/L APAM was not added,the four intermediate products of phenol,resorcinol,bisphenol and benzoquinone reached the maximum concentration at 20 min.After the addition of 10mLAPAM,the degradation path of phenol was changed.In the process of photocatalytic degradation,no catechol is produced.and resorcinol,paraquinone and benzoquinone reach the maximum value after 15 min.Polyacrylamide promotes phenol degradation and alters the degradation path of phenol.