| With the development of global economy,myriads of environmental problems have arisen,especially water pollution,which has a great impact on human health,as well as the continuous development of national economy.The AOP(advanced oxidation property)technology including photocatalytic oxidation of TiO2 nanoparticles has long been considered as a highly effective method to mineralize non-degradable pollutants,and displayed tremendous potential.However,there have been problems in practical applications such as,high agglomeration rate,low recyclability,low visible-light-driven photoactivity and so on.Diatomite,as a natural porous mineral,has been widely applied in many fields like,food production,medicine refinement,air purification,water decontamination,heat insulation and substrate for industrial catalyst.Diatomite shows excellent adsorption capability towards pollutants due to its abundant micro-meso pores.In our work,TiO2 nanoparticles were immobilized onto diatomite,and target pollutant has been enriched on their surface due to the adsorption capability of diatomite,which increased the contact rate between pollutant and TiO2,leading to the "adsorption and degradation" synergy which evetually improved its overall photocatalytic activity.Moreover,the photocatalytic composite was granulated or magnetized to improve its recyclability.Before applied as substrate for TiO2 nanoparticles,crude diatomite was pretreated by calcination or acid-leaching method,in order to eliminate the impurities while preserving its original porous structure.The pretreated diatomite was then loaded with N doped TiO2 particles.The as-prepared photocatalytic composite was characterized,and its photocatalytic activity was evaluated by degradating Rhodamine B(RhB)under visible light irradiation.The TiO2 particles and pretreated diatomite showed strong connection between each other via the formation of Si-O-Ti bond,which prevented the crystal growth of TiO2,and took effect on its the phase-transformation temperature,as well as hindering its agglomeration effect.Among all pretreating methods,acid-leaching showed higher efficiency,and the H2SO4 solution with its concentration as 15 wt%showed best effect on increasing the zeta potential value of diatomite,which resulted in well spread of TiO2 nanoparticles onto its surface,and eventually leaded to high hindering effect,proving that this concentration percentage is the optimal acid-leaching condition,and the corresponding pretreated diatomite is the most suitable carrier for TiO2.N doped TiO2 showed good visible light absorption capability,for N dopant existed in the interstitial position of TiO2 lattice,introducing doping level in the bandgap of TiO2.Besides,N dopant also showed hindering effect towards the TiO2 particles.As N source,urea showed the meso-porous effect on the surface of TiO2 during preparation process.The composite showed excellent micro-meso porous structure due to pretreated diatomite and mesoporous surface of TiO2,this hierarchical surface structure improved the adsorption capability of composite towards RhB.The optimal preparation conditions are as follows:The granulation scheme is the combination of dextrin and HPMC,and their mass ratio is 3:2,while the atomic ratio of N:Ti is 2:1.After 3 hours of photodegradation process towards RhB,its removral rate was 84.8%.After 5 repetitions,this rate dropped to 80.0%.This proved that the composite showed good recyclability.Based on sol-gel method,pretreated diatomite was also loaded with Ce doped or Ce/N co-doped TiO2 particles.The effect of doping on the photoactivity of composite was investigated,as well as the photodegradation mechanism.XPS results indicated that,Ce dopant existed on the surface and interstitial position of TiO2 lattice as Cerium oxides,resulted in the formation of Ce-O-Ti bond.Besides,Ce dopant introduced the Ce 4f impurity level in the bandgap of TiO2,which shortened the bandgap and extend the light absorption of the composite,enabled its visible-light-driven photoactivity.After 3 hours of photodegradation process,Ce-doped pellet eliminated 85.6%of RhB,while co-doped pellet eliminated 87.3%of RhB.After 5 repetitions,this rate dropped to 81.2%and 82.3%,respectively.This proved that the composite pellet showed good recyclability.Based on sol-gel method,the pretreated diatomite was loaded with supermagnetic NiFe2O4 nanoparticle,and the resulted powder was tagged as magnetic diatomite,which was further used as carrier for doped TiO2.The resulted magnetic composite powders showed excellent visible-light-driven photocatalytic activity,thanks to the charge transfer process which took place at the interface between NiFe2O4 and TiO2.N-doped,Ce-doped and co-doped magnetic powders showed good photodegradation results towards RhB,and the corresponding results are 91.5%,94.6%and 96.6%.After 5 repetitions,the removal rate dropped to 89.2%,92.2%and 95.6%.This proved that the magnetic powders all showed good recyclability.Using non-degradable multi-ring compound tetracycline hydrochloride(TC)as the target pollutant,the above co-doped photocatalytic pellet and magnetic powder were applied during the degradation experiment under visible light irradiation.The effect of the following factors was investigated:pH value of TC solution,the amount of photocatalytic sample,impurity components in aquatic environment.Besides,the above photocatalytic pellet and magnetic powder were also applied in the bacteria inactivation experiment under visible light irradiation,and the following three types of bacteria were set as target bacteria:E.coli,S.aureus and K.peneumoniae.The best photoactivity sample among photocatalytic pellet removed 97.0%of TC after 240 min,and the inactivation results towards three bacteria were:86.4%,87.9%and 84.6%.The best photoactivity sample among magnetic powder showed TC removal rate as 98.2%after 180 min,and showed inactivation results towards three bacteria as:93.7%,94.3%and 92.8%.The above two types of photocatalytic composites also showed good photo-stability and recyclability during the degradation of TC,as well as the bacteria inactivation under visible light irradiation,after 5 repetitions. |
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