The effects of surface modification of nanocrystalline titanium dioxide (TiO 2 ) with specific chelating agents on photocatalytic degradation of nitrobenzene (NB) was investigated in order to design a selective and effective catalyst for removal of nitroaromatic compounds from contaminated waste streams. Mechanisms of NB adsorption and photodecomposition were investigated using infrared absorption and electron paramagnetic resonance spectroscopy. Liquid chromatography and gas chromatography/mass spectrometry were used for byproduct analyses. Arginine, lauryl sulfate, and salicylic acid were found to bind to TiO 2 via their oxygen-containing functional groups. Modification of the TiO 2 surface with arginine resulted in enhanced NB adsorption and photodecomposition, and compared to unmodified TiO 2 . The initial quantum yield for photodegradation of NB in this system was found to be Φ init ) 0.31 as compared to the one obtained for Degussa P25 of Φ init ) 0.18. NB degradation followed a reductive pathway over arginine-modified TiO 2 and was enhanced upon addition of methanol. No degradation of arginine was detected under the experimental conditions. Arginine improved the coupling between NB and TiO 2 and facilitated the transfer of photogenerated electrons from the TiO 2 conduction band to the adsorbed NB. These results indicate that surface modification of nanocrystalline TiO 2 with electron-donating chelating agents is an effective route to enhance photodecomposition of nitroaromatic compounds.

Adsorption and photocatalytic degradation of nitrobenzene (NB) in the presence and absence of phenol (Ph) over UV-illuminated arginine-modified TiO2 colloids have been investigated by infrared absorption, electron paramagnetic resonance spectroscopy, and X-ray absorption spectroscopy. High performance liquid chromatography (HPLC) and gas chromatography/mass spectrometry were used for monitoring degradation conversion rates and byproduct identification. It was found that photodegradation of NB and Ph strongly depends on the nature of the TiO2 surface. Through the use of the HPLC peak area ratio before and after illumination, the photocatalytic decomposition rate of NB and Ph individually using bare TiO2 is nearly identical (1.7 and 1.5, respectively) and occurs via oxidative mechanism. Through the use of arginine-modified TiO2 nanoparticles, a three-fold increase in the NB decomposition rate is observed while no Ph decomposition is observed. Furthermore, the degradation pathway using the arginine-modified photocatalyst is completely altered to a reductive mechanism, providing a more efficient means to degrade nitrocompounds that are already in a highly oxidized state and limiting the number of byproduct. These results indicate that a critical parameter in the photocatalytic decomposition of NB and Ph is their specific adsorption and coupling to the TiO2 surface. Modification of the TiO2 particle surface with chelating agents demonstrates enhanced interaction with the desired target contaminant to impart selectivity to photocatalysis.

Six activated carbon fibers (ACFs) with different chemical and physical properties were prepared by first curing a phenolic resin-coated glass fiber, followed by activation and posttreatment. Their adsorption properties were investigated to evaluate the removal of benzene, toluene, ethylbenzene, and p-xylene (BTEX) and the chemical warfare simulants dissopropylmethyl phosponate (DIMP) and half mustard (HM) from water. The adsorption isotherms showed that ACF SL-2 (activated with CO 2 /H 2 O at 800 °C) has a higher adsorption capacity for BTEX, DIMP, and HM than other ACFs. This suggests that the high adsorption affinity of SL-2 is related to its higher surface area, larger average micropore size of 11.6 Å (especially effective for the adsorption of DIMP), and lower oxygen content of the surface. The adsorption isotherms are well represented by the Freundlich equation. For BTEX, the adsorption parameters based on carbon coating showed that, in all cases, ACFs have a higher K value than the best available data obtained on granulated activated carbon (GAC). The adsorption isotherms of DIMP and HM on ACFs are also presented.

Gas chromatography/mass spectrometry was used to analyze the pyrolytic byproducts from an Army-unique propellant compound (AA2) that is composed of predominantly nitrocellulose and nitroglycerin. Compounds produced by AA2 pyrolysis were compared to compounds detected in the gaseous effluent from AA2 incineration. The light permanent gases and most of the higher molecular weight byproducts produced by AA2 incineration are replicated by laboratory pyrolysis on AA2. The reverse case also holds whereby 18 out of 24 high molecular weight AA2 pyrolytic byproducts are found in the incinerator emissions. Poor matching, however, was obtained between the two processes for the volatile, water-soluble species. None of these low molecular weight compounds produced under pyrolytic conditions were detected in the AA2 incinerator samples, likely indicating inefficient capture of these compounds from the effluent stream. Separate pyrolytic degradation of the individual components of AA2 provides evidence that nearly all of the incomplete combustion products detected during incineration originate not from the prevalent energetic ingredients but rather from the minor and trace additives in AA2. In addition, pyrolysis successfully identified the AA2 components capable of surviving the incineration process intact. This work illustrates the potential of bench-scale pyrolysis for predicting incineration behavior.