Study On Adsorption And Photocatalytic Degradation Of Chlorobenzenes With TiO₂Coated On Multi-Walled Carbon Nanotubes

In this research, using methyl orange as a model pollutant, the composite photocatalysts (MWNTs/TiO2) were optimized prepared by the Sol-Gel method. The results show that, photocatalytic activity of the composite photocatalysts was highest, which was calcinated at temperature of500℃for3h, when pH=3, pss dosage=5g/L and the amount of multi-walled carbon nanotubes was1.5%of nano-TiO2mass. The SEM images shows that nano-TiO2was evenly coated on the surface of the multi-walled carbon nanotubes after it was attached on mutil-walled carbon nanotubes. Its outer diameter was thickened from20-40nm to about60-80nm. It could be seen that MWNTS/TiO2contained Ti, C, O, Na and S elements, mainly to Ti, O and C elements based, via EDX. Determined by the surface analyzer, specific surface area of the purified MWNTs and the optimized MWNTs/TiO2were80.103m2/g and39.610m2/g respectively; MWNTs surface is mainly micro pore diameter range, and MWNTs/TiO2is mainly medium pore diameter range. Qualitative analysis by FTIR, it shows that the oxygen-containing functional groups of the purified MWNTs and optimized MWNTs/TiO2mainly existed on the surface are hydroxyl (-OH), carbonyl (-C=O), carboxyl (-COOH), etc. MWNTs has a strong absorption peak, while the absorption peak of MWNTS/TiO2has been reduced and weakened relatively.Using the optimized prepared MWNTs/TiO2and nano-TiO2, the results of the comparative experiment revealed that both the photocatalytic degradation of1,2,4-trichlorobenzene can be used to describe by the first order reaction. The photocatalytic reaction rate constant of MWNTs/TiO2on1,2,4-trichlorobenzene was0.0196h-1, which was increased by about63.3%compared to that with nano-TiO2-The comparative experiments of photocatalytic degradation were studied, by the optimized MWNTs/TiO2on methyl orange and1,2,4-trichlorobenzene. The results were found that photocatalytic degradation reaction rate constants of MWNTs/TiO2on methyl orange and1,2,4-trichlorobenzene were0.0367h-1and0.0196h-1, which was increased by14.6%and63.3%compared to that with nano-TiO2respectively. Under optimal conditions the prepation of the composite photocatalyst had good photocatalytic degradation effects on chlorobenzenes.The comparative experiments of the adsorption of trichlorobenzene by MWNTs and MWNTs/TiO2were studied, and the results showed that, under the same conditions, the maximum adsorption capacities of1,2,3-trichlorobenzene were71.8mg/g by MWNTs and3.0mg/g by MWNTs/TiO2. the adsorption kinetics curve of the adsorption of1,2,3-trichlorobenzene by MWNTs and MWNTs/TiO2was agreement, the two adsorption reaction can be used to describe by the pseudo second order kinetic equation, the rate constants were0.0836g-mg-1·min-1and0.4159g·mg-1·min-1, shows a stronger adsorption driving force of MWNTS/TiO2. This two kinds of equations are both following the Freundlich adsorption thermodynamics, and both be the spontaneous endothermic reaction. The strong adsorption of MWNTs and MWNTs/TiO2on trichlorobenzene base on the hydrophobic force, hydrogen bonding and the Ï€ electron conjugation between surface of MWNTs or MWNTs/TiO2and trichlorobenzene benzene. But it may be mainly through the effect of Ï€ electron conjugation achieved.Using typical chlorobenzenes as the target removal, the experiments were studied for photocatalytic degradation and the synergistic reaction of MWNTs/TiO2, it was found that, the photocatalytic degradation rate constants of HCB and PeCB by MWNTs/TiO2were0.0664h-1and0.0670h-1, and this data significantly higher than other chlorobenzenes. However, the data of1,4-DCB was only0.0430h-1, which was the lowest in typical chlorobenzenes. Its typical chlorobenzenes1,2,4-TCB,1,2,4,5-TeCB, PeCB and HCB photocatalytic degradation of the main path are:1,2,4-TCBâ†'1,4-DCB;1,2,4,5-TeCBâ†'1,2,4-TCBâ†'1,4-DCB;PeCBâ†'1,2,4,5-TeCBâ†'1,2,4-TCBâ†'1,4-DCB;HCBâ†'PeCBâ†'1,2,4,5-TeCBâ†'1,2,4-TCBâ†'1,4-DCB. After composite the MWNTs and nano-Ti02, the result of removaling1,2,3-TCB has been markedly improved, which fully reflects that MWNTs/TiO2has the adsorption and photodegradation synergistic reaction. The solution temperature or pH values decreasing, will help MWNTs/TiO2to removal1,2,3-TCB; increasing the dosage of MWNTs/TiO2or the intensity of UV light will help MWNTs/TiO2to removal1,2,3TCB.Therefore, using the adsorption and photodegradation synergistic reaction of the MWNTs/TiO2to removal chlorobenzene compounds speedy and completely will have a broad market prospect.