Naik Amarja P, Salkar Akshay V, Majik Mahesh S, Morajkar Pranay P
Department of Chemistry, Goa University, Taleigao Plateau 403206, Goa, India.
Photochem Photobiol Sci. 2017 Jul 1;16(7):1126-1138. doi: 10.1039/c7pp00090a. Epub 2017 May 26.
The photocatalytic degradation mechanism of Amaranth, a recalcitrant carcinogenic azo dye, was investigated using mesoporous anatase TiO under sunlight. Mesoporous anatase TiO of a high photocatalytic activity has been synthesized using a sol-gel method and its photocatalytic activity for the degradation of Amaranth dye has been evaluated with respect to Degussa P25. The effect of bi-dentate complexing agents like oxalic acid, ethylene glycol and urea on the surface properties of TiO catalyst has been investigated using TG-DTA, FTIR, HR-TEM, SAED, PXRD, EDS, UV-DRS, PL, BET N adsorption-desorption isotherm studies and BJH analysis. The influence of catalyst properties such as the mesoporous network, pore volume and surface area on the kinetics of degradation of Amaranth as a function of irradiation time under natural sunlight has been monitored using UV-Vis spectroscopy. The highest rate constant value of 0.069 min was obtained for the photocatalytic degradation of Amaranth using TiO synthesized via a urea assisted sol-gel synthesis method. The effect of the reaction conditions such as pH, TiO concentration and Amaranth concentration on the photodegradation rate has been investigated. The enhanced photocatalytic activity of synthesized TiO in comparison with P25 is attributed to the mesoporous nature of the catalyst leading to increased pore diameter, pore volume, surface area and enhanced charge carrier separation efficiency. New intermediates of photocatalytic degradation of Amaranth, namely, sodium-3-hydroxynaphthalene-2,7-disulphonate, 3-hydroxynaphthalene, sodium-4-aminonaphthalenesulphonate and sodium-4-aminobenzenesulphonate have been identified using LC-ESI-MS for the very first time, providing direct evidence for simultaneous bond cleavage pathways (-C-N-) and (-N[double bond, length as m-dash]N-). A new plausible mechanism of TiO catalysed photodegradation of Amaranth along with the comparison of its toxicity to that of its degradation intermediates and products is proposed.
采用介孔锐钛矿型二氧化钛在阳光下研究了顽固性致癌偶氮染料苋菜红的光催化降解机理。通过溶胶-凝胶法合成了具有高光催化活性的介孔锐钛矿型二氧化钛，并相对于德固赛P25评估了其对苋菜红染料的光催化降解活性。使用热重-差示热分析（TG-DTA）、傅里叶变换红外光谱（FTIR）、高分辨透射电子显微镜（HR-TEM）、选区电子衍射（SAED）、粉末X射线衍射（PXRD）、能谱分析（EDS）、紫外-可见漫反射光谱（UV-DRS）、光致发光（PL）、BET氮气吸附-脱附等温线研究和BJH分析等方法研究了草酸、乙二醇和尿素等双齿络合剂对二氧化钛催化剂表面性质的影响。利用紫外-可见光谱监测了介孔网络、孔体积和表面积等催化剂性质对自然光照射下苋菜红降解动力学的影响。通过尿素辅助溶胶-凝胶合成法合成的二氧化钛对苋菜红进行光催化降解，获得了最高速率常数0.069 min⁻¹。研究了pH值、二氧化钛浓度和苋菜红浓度等反应条件对光降解速率的影响。合成的二氧化钛与P25相比光催化活性增强归因于催化剂的介孔性质导致孔径、孔体积、表面积增加以及电荷载流子分离效率提高。首次使用液相色谱-电喷雾电离质谱（LC-ESI-MS）鉴定了苋菜红光催化降解的新中间体，即3-羟基萘-2,7-二磺酸钠、3-羟基萘、4-氨基萘磺酸钠和4-氨基苯磺酸钠，为同时发生的键断裂途径（-C-N-）和（-N=N-）提供了直接证据。提出了二氧化钛催化苋菜红光降解的新的合理机理，并比较了其与降解中间体和产物的毒性。
