Photocatalyst Properties And Primary Applications In Paper Industry Of TiO₂/zeoiite Composite

TiO₂photocatalytic technology was found in1972, it has wide applicationprospects in environmental sanitation because of its excellent mineralization abilityof organic pollutants and sterilizing effect through damaging cell wall or cellmembrane of bacteria, thus it has become one of the hottest topics both at home andabroad. TiO₂can be used as wastewater treatment agent, filler and antimicrobialagent in paper industry. However, there are some difficulties in separation andrecycling, and it was prone to agglomeration, inactivation, and cause secondarypollution when TiO₂was used directly. The above problems can be relieved bysupported TiO₂photocatalyst, the most popular loaded materials are active carbon,SiO2, clay and synthetic zeolite. China is a country abundant in zeolite resources,with a storage of40billion tons, the researches on the applications of TiO₂/zeolitecomposite in paper making industry are valuable subjects, for they are expected tonot only explore new ways of wastewater treatment in papermaking, develop theenvironmentally friendly inorganic antibacterial agents, but also promote to practicalapplications of natural zeolites and of TiO₂photocatalytic technology.In the study, the primary applications of TiO₂/zeolite composite in treatment ofcolorful wastewater and as antimicrobial agent in papermaking were introduced.Firstly, we studied the effects of three modified methods in respect to acid, alkali andsalt on zeolite structure and photocatalytic activitiees of TiO₂/zeolite composites,prepared with natural zeolite. Meanwhile, the bactericidal activities on S. aureus andE. coli of TiO₂/zeolite composites respectively doped with Fe³⁺, Zn²⁺, Cu²⁺and Ag+were analyzed.The natural zeolite obtained from Lingchuan, Guilin, Guangxi, whcih wasanalyzed by XRD,FTIR,Raman,SEM,EDS,BET, etc. The characteristic diffractionpeaks of anatase TiO₂were observed form XRD spectrum of TiO₂/zeolite composite,prepared by sol-gel method, which was subject to the temperature of200°C for4hours. The photocatalytic activities of composites in degradation of colourfulwastewater were influenced by pH value, the load amount of TiO₂, the dosage ofcomposite, the original consistency of colorful wastewater, air mass flow, the amountof H2O2, recycled times, ect. The results showed that the optimal load amount of TiO₂was28%and the optimal amount of TiO₂/zeolite composite was2g/L when the pHvalue was6.86and the original consistency of methyl orange was fixed on15mg/L. The photocatalytic activities of TiO₂/zeolite composite, with zeolite modified byacid, alkali and salt, were investigated. Both acid modification and salt modificationenhanced photocatalytic performances of TiO₂/Zeolite composites, and the formermethod got better effect, the optimal modification consistency were0.4mol/L and1.0mol/L respectively. On the contrary, alkali modification induced the lost ofphotocatalytic ability of composite.The influences of Fe³⁺,Zn²⁺,Cu²⁺and Ag+doping on photocatalytic abilities ofcomposites, based on natural zeolited modified by0.4mol/L hydrochloric acid, wereinvestigated. Both Fe³⁺and Zn²⁺doping enhanced the photocatalytic abilities ofcomposites, and the influences of Cu²⁺doping were slightly. A small quantity of Ag+doping can improved the photocatalytic abilities of composites, but then decreasedwhen the doping level was too high. The influences of metal ions doping on thephotocatalytic ability of composite were dependant on ionic radius, charges, energylevels and doping levels etc. The optimal doping levels of Fe³⁺, Zn²⁺, Cu²⁺and Ag+were1.0%,2.0%,1.5%and0.5%respectively.The influences of Fe³⁺,Zn²⁺,Cu²⁺and Ag+doping on antibacterial properties ofcomposites, based on natural zeolite modified by0.4mol/L hydrochloric acid, wereindagated when the doping levels were1.0%,2.0%,1.5%and0.5%relatively. It wasfound that the composite doped with Ag+showed the best antibacterial effect.Antibacterial papers were made from natural zeolite and TiO₂/zeolite composites.The filler retention was not so desirable in terms of the traditional added method ofcationic starch and filler, which can be improved by adding the filler modified withcationic starch. With natural zeolite and TiO₂/zeolite composites added in the paper,the density, air permeability, opacity and evenness of which were improved, however,the paper strength involving tear, burst and tensile indecies were dereased, while thebrightness was a little negativly affected.The results of antibacteria experiment of papers showed that, with no UVirradiated, the antibacterial effects of TiO₂/zeolite composite without metal ionswere very weak, those of TiO₂/zeolite composite with Fe²⁺and Zn²⁺were medium,while TiO₂/zeolite composite with Cu²⁺and Ag+give the best antibacterial effects. Itshowed that TiO₂had no obvious antibacterial effects without UV irradiation, butmetal ions brought sterilizing effect to TiO₂, and the order of decreasing sterilizingeffect of composite was arranged as Ag+, Cu²⁺, Zn²⁺and Fe³⁺. The application ranges of TiO₂/zeolite composite may be widely expanded by Ag+and Cu²⁺doping. UV,metal ion and TiO₂all gave a certain sterilizing effects under UV irradiation.