| Membrane filtration is an efficient technology for water treatment, while the single rejected function and membrane fouling restrict its application. Integrating photocatalysis with membrane filtration thus forming the photocatalytic membrane, the organic contaminants in water can be mineralized by reactive oxygen species (ROS) produced from photocatalysis. The integrated process can not only improve the effluent water quality by degradation pollutants via photocatalysis but also solve the issues of membrane fouling. However, currently photocatalytic materials involved building up functional layer are mainly focused on the TiO2based photocatalysts, which suffer from the obstacle of fast charge recombination and poor visible light response. Therefore, in this study the photocatalytic membranes based on heteroj unction structure and with visible light response were developed, respectively. The detail work as blow:The CNTs-TiO2/Al2O3composite membrane based on heterojunction between CNTs and TiO2was fabricated by sol-gel method. The effects of CNTs content on charge separation was investigated. The result showed that the composite exhibited the highest photocurrent density with1%CNTs which was6times as much as pure TiO2. The pore sizes of the photocatalytic membrane can be controlled by tuning the dip-coating time. Humic acid (HA) with the concentration of10mg·L-1was chosen as the target to investigate the water treatment performance of the photocatalytic membrane. The results showed that, for coupling process, the HA removal rate of CNTs-TiO2/Al2O3membrane was10%higher than that of TiO2/Al2O3which indicated the efficient charge separation resulting in the superior performance on water treatment. Besides that, for the coupling process, the removal rate of HA was4times and2times as much as that of photocatalytic process and membrane filtration, respectively which displayed synergistic effect. The permeate flux for the coupling process was3times as much as membrane filtration alone, exhibiting dramatic anti-fouling capacityA water treatment device based on CNTs-TiO2/Al2O3tublar membrane with the pilot-scale (10t·d-1) was constructed and its performance on water treatment was investigated. The performance of water treatment for the device was evaluated by using the feed water from giving water plant of Dalian city after flocculation and precipitation. The results showed that the bacteria with the concentration of105cfu-L-1could be removed completely.67%of CODMnn with the initial concentration of2.4mg·L-1and38%of TOC with the initial concentration of2.4mg·L-1could be degraded respectiv, which exhibited good performance.An atomic single layer graphite carbon nitride (SL g-C3N4) with visible light response was fabricated. The characterization of morphology confirmed its thickness of0.5nm. The ultra2D structure not only benefits for charge diffusion but also shortens the charges transport distance. Therefore, the SL g-C3N4exhibited high conductivity and low charge transfer resistance. Results of photo-electronically chemical measurements showed that the charge density on the surface of SL g-C3N4was4.8times as much as that of bulk g-C3N4. The life time of photogenerated charges for SL g-C3N4was3.6times as long as that of bulk g-C3N4. Taking these advantages, the SL g-C3N4displayed excellent photogenerated charge separation. The photocurrent density was16times as much as that of bulk g-C3N4. For the photocatalytic degradation of RhB, the kinetic constants of SL g-C3N4was nearly3.0,8.8,10.2,16.4,37.1and93.8times as much as that of g-C3N4nanosheet (g-C3N4NS thickness of2-3nm), CdS, bulk g-C3N4, N-TiO2, P25and BiVO4, respectively.E. coli was chosen as the target to investigate the photocatalytic disinfection efficiency of SL g-C3N4. The results showed that E. coli with the concentration of2×107cfu·mL-1could be killed completely over the SL g-C3N4within4h, which is comparable with other visible light driven photocatalysts contained heavy metal ions such as Ag. As well as the photocatalytic efficiency was2log and3log units higher than that of g-C3N4NS and bulk g-C3N4, respectively. The scavenger experiments indicated that h+was the most important ROS. Observed by TEM, with the reaction time increased, the cell wall was degraded gradually and a leakage of the interior component occurred, which indicating the E. coli was killed compoletely by destructing there cell wall.Taking g-C3N4NS/reduced graphene oxide (g-C3N4NS/RGO) and cellulose acetate (CA) as the photocatalyst of functional layer and separated layer, respectively, a g-C3N4NS/RGO/CA composite membrane with visible light response was developed. The content of RGO in composite was optimized by investigating the photocatalytic efficiency on RhB degradation. RhB and E. coli were taken as the targets to investigate the water treatment performance of the composite membrane. Resulting from the efficient photocatalytic degradation, the g-C3N4NS/RGO/CA membrane exhibited high removal rate on RhB (60%) which was4times as much as that of membrane filtration alone. On the other hand, the coupling process for E. coli removal was3log units higher than membrane separation alone. During the running process, the permeate flux for the coupling process was1.5times as much as that of membrane separation alone, which indicated the membrane fouling was decreased. |
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