| Photocatalytic technology is a new environmental protection technology gradually developed in the 1970 s.Titanium dioxide photocatalyst is one of the most studied by scholars at home and abroad beacuase of it has a lot of advantages such as non-toxic, harmless, no secondary pollution,having good photocatalytic activity,difficult to corrosion and so on. In recent years, the application of TiO2 is more and more widely, not only can be used in cosmetics, functional fiber, plastic, paint, fine ceramics but also rapid development in the field of water treatment.Research and application form of TiO2 photocatalyst divided into two kinds,including suspension system and the load system. In suspension system TiO2 nanoparticles having a large surface area and high photocatalytic efficiency but there are easy to reunite, difficulties in separation and recycling.Load system solves the problem of recovery difficulting, but the photocatalytic efficiency is greatly reduced. Magnetic carrier photocatalytic system although solved the problem of lower efficiency but unable to industrial application.Flocculation is one of the most important unit in the process of water treatment, it has a wide application range and lower cost,the main role of the object is water repellent sol and suspended particles. The TiO2 particles in the suspension system distribute in the range of 2251151nm,it is a typical colloidal dispersion system.Use flocculant flocculation precipitation of TiO2 idea in theory is feasible. In the study of Ki-Chang Lee,after P25 TiO2 photocatalytic degradation, using flocculant to settlement.When the concentration of flocculant for 8 to 12 mg/L, the turbidity can achieve 0.5 NTU.The early stage of the laboratory experiments exploring the optimal dosing quantity of flocculating agent and pH value, experimental results show that organic synthesis high polymer flocculant has better flocculating settling effects for TiO2 and NPAM works best.On the basis of existing, in this paper selected nonionic polyacrylamide（NPAM）,cationic polyacrylamide（CPAM） and anionic polyacrylamide（APAM） three kinds of polyacrylamide type flocculant separately for flocculation recycle TiO2 in the suspension system. After reading the relevant literatures,preliminary selected mixing condition of flocculation experiment, making suspension residual turbidity as evaluation indexesto get the best dosing quantity. Under the condition of the optimal dosing quantity are optimized mixing conditions by the orthogonal experiment, exploring different ultrasonic power and ultrasonic time on TiO2 light catalyst effect after flocculation sedimentation. Use of nonionic polyacrylamide（NPAM） flocculation recovery of TiO2 under the condition of some of the best,such as dosage,mixing conditions, ultrasonic power and time. Then to repeat 10 times experiments of “flocculation-redispersion-photocatalysis”to explore the influence of phenoldegradation rate.The following conclusions by the experiments:（1） Flocculant NPAM, CPAM and PAM on suspension system of P25 TiO2 has good flocculation sedimentation effect, but in P25 TiO2 suspension it exist optimal concentration,too high or too low can’t make the flocculation sedimentation effect best.NPAM, CPAM and APAM optimal concentration in suspension system of P25 TiO2 are 8mg/L,9mg/L,4mg/L respectively,and the corresponding residual turbidity of suspension are 2.78 NTU, 4.43 NTU,4.61 NTU.（2） Selecting L9（34） orthogonal test table to optimize the flocculation mixing conditions and then design single factor experiment for settling time.ultimately get best flocculation mixing combination condition of NPAM CPAM APAM. After validate the optimized conditions, getting the corresponding suspending liquid turbidity are 1.28 NTU,3.11 NTU,3.19 NTU.Compared with turbidity that have not been optimized conditions,these turbidity are decreasing.This conclusion show that flocculation mixing condition was optimized and P25TiO2（3）Under the best condition of the optimum flocculation kinetics, flocculant NPAM,CPAM, APAM P25 of suspension system of TiO2 flocculation recovery rate were 99.6%,99.4% and 99.4% respectively.（4） In Suspension system P25 TiO2 need 24 h to separating from the water by natural sedimentation and residual turbidity of suspension is 10.2NTU.（5） Suspension system of P25 TiO2 has centralized particle size distribution after ultrasonic oscillation and particle size in the range of 225 1151 nm cumulative distribution rate is 100%.After adding the flocculant, P25 TiO2 particle size increases significantly,but after ultrasonic oscillation can recovered.（6） P25 TiO2 flocs formed by NPAM CPAM APAM to the experiment of photocatalytic degradation phenol,photocatalytic efficiency has fallen by 6.5%, 7.7% and 6.5%respectively.After ultrasonic P25 TiO2 can restore the phenol degradation rate.（7）Flocculant PAM and P25 TiO2 photocatalyst concentration of 25 mg /L of phenol only extremely weak adsorption,the degradation of phenol is TiO2 photocatalysis.（8） After using NPAM flocculation and recycle P25TiO2 for ten times experiment of“flocculation recycle-redispersion-photocatalysis”. After 10 times experiment foud tant photocatalytic degradation of P25 TiO2 rate fell by only 5%.This proved that P25 TiO2 could be repeatedly recycled.（9） By ten times “flocculation-redispersion-photocatalysis”experiment,the experimental results can be seen that Photocatalyst flocculation recycle by NPAM could make TiO2 high photocatalytic efficiency. After the calculation found that compared with not recycling, cansave cost 89.9%. |
