Preparation Of Indol-based Porous Materials And Their Adsorption Properties Of TNT In Water

Trinitrotoluene(TNT)is one of the most widespread used explosives in both military and industry applications owing to its low sensitivity to exterior stimuli.TNT is also a group C human carcinogen and has toxic effects on environment,human and wildlife health.Thus,the removal of TNT from water system has become a must for the concerns of public security,civilian safety,and environmental protection.Compared to other technologies,adsorption is a promising approach with many advantages such as easy handle,economical with time,and high efficiency over a wide concentration range.Unfortunately,most of the reported adsorbents in the literature are suffering from either low adsorption capacity or long equilibrium time,which limits their practical application.Moreover,the plurality of TNT detection and removal works have been enforced independently,which leads to a complicated process for the simultaneous detection and removal of TNT.In this paper,indole and its derivatives were used as raw materials to prepare indole-based porous materials through Friedel-Crafts alkylation reaction or sol-gel method.The structure and adsorption properties in TNT aqueous solution of these materials were discussed.The main works were as follows:(1)The structures of indole and its derivatives,TNT,etc.were optimized by density functional theory(DFT).The distances and energies interactions between them were calculated,and the adsorption/desorption mechanism of TNT was proposed.The results demonstrated that the strong face-to-point dipole-π interaction existed between indole and TNT with the calculated energy of 42.43 kJ mol-1,and the distance between nitrogen atom of nitro group in TNT and indole ring was 4.04 A.In addition,the indole could adsorb TNT through the hydrogen bonding of indoleamine and TNT.The synergistic effects of hydrogen bonding and electron donor-acceptor interaction between acetone and TNT can realize the desorption of TNT.(2)Using indole,aniline and 4-aminoindole as main raw materials,polymers were prepared by Friedel-Crafts alkylation reaction,their structures were characterized.Due to the strong interaction between aromatic ring(benzene ring and indole ring)and TNT,polybenzazole(PIN),polyaniline(PAB)and polyamindole(PAIN)exhibited excellent adsorption behaviors on TNT.The equilibrium time of PAIN,PIN and PAB was followed the order:PAB(12 h)>PAIN(10 h)>PIN(5 h),and the adsorption process can be described well by pseudo-second-order kinetic model.The maximum adsorption capacities calculated by Langmuir model were followed the order:PAIN(176.7 mg g-1)>PIN(143.7 mg g-1)>PAB(110.1 mg g-1)at 298 K.The rapid and efficient adsorption of TNT by PAIN,PIN and PAB all benefited from the presence of aromatic rings(indole and benzene ring)on the polymer backbone.In addition,primary amine also played a key role in TNT adsorption,so the TNT adsorption capacity of PAIN was greater than PIN.The synergistic effects of dipole-π and electron donor-acceptor interaction was the reason for TNT high adsorption.PAIN can be regenerated in acetone.Using acetone as eluent,the recovery rate of adsorption capacity was kept above 90%in 3 consecutive adsorption-desorption cycles and above 80%after 5 cycles.(3)An indole-based aerogel(4-HIFA)was successfully fabricated for adsorption TNT in aqueous solution by the virtue of synergistic effects of dipole-π and hydrogen bonding of indole and hydroxyl groups with TNT.The influence of diverse factors on TNT adsorption were analyzed.Adsorption kinetic,isotherms and thermodynamic parameters have been estimated from experimental results.The TNT adsorption kinetic was very quickly with the balance time of 2 hours.Additionally,the process can be well accordance with pseudo-second-order model.The maximum adsorption capacity was 117.5 mg g-1 at 293 K.4-HIFA can be effectively recovered in acetone without significant deterioration in its adsorption performance.The adsorption capacity was maintain above 90%over 7 consecutive cycles.(4)An indole-based aerogel,4-AING,was successfully constructed and used in simultaneous visual detection and removal of TNT in aqueous system.The diamino groups in 4-AING endowed it great abilities of recognition and adsorption of TNT through point-to-point electron donor-acceptor interaction.On the other hand,by the help of the adjacent indole groups,the detection and adsorption process could be facilitated and promoted via face-to-point dipole-π interaction.The maximum adsorption capacity was up to 168.6 mg g-1 according to the Langmuir model.Furthermore,the 4-AING could be effectively regenerated without significant deterioration in its adsorption performance over 7 consecutive cycles,demonstrating the good reusability of 4-AING.The prepared 4-AING was exhibited an obvious color change from light brown to dark brown in the presence of TNT,which was visualized through naked-eye.A smartphone was applied for the colorimetric quantify the adsorption capacity of TNT with linearity range of 42.8 to 156.0 mg g-1 with the limit of detection of 2.9 mg g-1.The excellent adsorption and detection performances in real TNT waste waters further confirmed the practical application of 4-AING in real waste water treatment.