F-对弱吸附间苯二酚光催化降解效率的提升:游离·OH的作用

传统的光催化降解机制认为是光激发产生的氧化活性物质优先对吸附在催化剂表面的污染物分子进行降解,因此,弱吸附性有机物难以接触到光催化剂并发生降解.为探究提升弱吸附有机物光催化降解的机理,本文构建了一个高暴露{001}晶面TiO_2({001}-TiO_2)降解弱吸附间苯二酚(RE)的光催化体系.实验结果表明,所制备的{001}-TiO_2具有强亲水性,并能提供大量的F~-吸附位点.RE在{001}-TiO_2表面的吸附能力很弱,并且光催化降解效果很差.F~-的加入可使RE的光催化降解速率提升近3倍.通过自由基猝灭实验发现,RE的降解主要取决于溶液中游离羟基自由基(·OH)的作用,由于F~-能与{001}-TiO_2亲水表面的羟基及·OH形成强烈的竞争吸附,从而使·OH游离到溶液中氧化降解RE.EPR测试进一步证实了F~-不仅可以促使TiO_2产生更多的游离·OH,同时也能激发产生更多超氧自由基(·O~-_2),推测·O~-_2主要由有效分离的光生电子与O_2或·OH反应生成.综上,本研究明确了游离·OH对弱吸附RE的光催化降解效率起决定作用,F~-促使游离自由基产生的机制可为弱吸附有机污染物的降解提供新思路.

Enhanced photocatalytic degradation of weak absorbed resorcinol by addition of fluoride ions: The role of free hydroxyl radical

According to traditional photocatalytic degradation mechanism, the photocatalytic reactive species can preferentially degrade pollutant molecules which adsorbed on the photocatalysts surface. Therefore, due to the weakly adsorbed organics compounds have less possibility to contact with photocalalysts surface, it is difficult to degrade them in the potocatalytic system. To explore the degradation pathway and identify the degradation limiting step of weakly adsorbed pollutants resorcinol (RE), a photocatalytic system of a TiO₂ photocatalyst with high exposure {001} facets ({001}-TiO₂) was developed. The prepared {001}-TiO₂ was highly hydrophilic and could provide a large number of adsorption sites for fluorine ion (F^-). Experimental results show that the photocatalytic degradation efficiency of RE in {001}-TiO₂ system was poor because of the weak adsorption capacity. However, with the addition of fluorine ion (F^-) in the photocatalytic system, the photo-degradation rate of RE dramatically increased about 3 times. The free radicals quenching experiment shows that the degradation of RE mainly depends on the free hydroxyl radicals (·OH) in solution. The surface·OH continuously dissolved into the solution because F^- can be competitive with the adsorption of hydroxyl groups and·OH on the hydrophilic surface of {001}-TiO₂. The electron paramagnetic resonance (EPR) test further confirms that F^- could not only increase the concentration of free·OH in this photodegradation system, but also promote the production of superoxide radical (·O₂^-), which was produced from the reaction between photo-generated e^- and O₂/·OH. In summary, the free·OH plays a crucial role in the photodegradation of RE. The mechanism that F^- promotes the production of free radicals can provide new insight into the degradation of weak adsorption organics.