(248ad) Enhancing Selectivity of 4-Nitrophenol Degradation By Using Molecular Imprinted Codoped-TiO2 Under Simulated Solar Light

In many polluted waters, the presence of highly hazardous and non-biodegradable pollutants at low levels is accompanied by the coexistence of other lowly toxic biodegradable pollutants at high levels. A preferable approach to treat such waste waters is to degrade the highly hazardous pollutants first with photocatalytic treatment and then handle it biologically. The codoped-TiO₂ photocatalysts have been widely applied for the wastewater treatment because of high photocatalytic activity and chemical stability under visible light. However, it is still difficult to realize selective removal of harmful low-level pollutants from complicated waste waters in the presence of other high-level less-harmful pollutants via photocatalytic treatment, because the photocatalytic degradation of organic contaminants on codoped-TiO₂ is basically non-selective. Thus, it is necessary to promote the selectivity of codoped-TiO₂ photocatalysts. A new strategy of increasing this selectivity is the surface modification of codoped-TiO₂ via coating a thin layer of molecular imprinted polymers (MIPs), which provides molecular recognition ability toward the target pollutants. The 4-nitrophenol was selected as simulated highly hazardous pollutant and o-phenylenediamine as the functional monomer to generate the novel MIPs coated photocatalysts in this work. First, we prepared a codoped-TiO₂ sample which has high photocatalytic activity under simulated solar light. Then, the novel MIPs coated codoped-TiO₂ (MIP-codoped-TiO₂) were designed and prepared by using o-phenylenediamine as the functional monomer and 4-nitrophenol as the target molecular. The polymerization was initiated by UV light illumination on codoped- TiO₂ without using any other chemical initiator, causing in situ coating a thin MIPs layer of a target pollutant on codoped TiO₂ nanoparticles. Last, an aqueous solution of 4-nitrophenol (2mg/L, target pollutant at low level) and phenol (50mg/L, nontarget pollutant at high level) was chosen as the simulated wastewater system, because the target and nontarget pollutants in the chemical nature and molecular size/shape is similar, which can greatly indicate selectivity of photocatalysts. MIP-codoped-TiO₂was adopted as the photocatalyst of selective adsorption and degradation of 4-nitrophenol. The results indicated that MIP-codoped-TiO₂ nanocomposites showed higher adsorption capacity for 4-nitrophenol than for codoped-TiO₂ nanoparticles. Moreover, the degradation rate of 4-nitrophenol could be increased 80% by using the MIP-codoped-TiO₂, comparing with the codoped-TiO_2, under simulated solar light, while the degradation rate of phenol was decreased 90%. The increased selectivity of MIP-codoped-TiO₂ was mainly attributed to the special interaction between the target molecules and the footprints polymer via the functional groups (-OH and -NO₂).