Abstract
Nonylphenol ethoxylates (NPEO) are commercially available non-ionic surfactants that, along with the parent nonylphenol (NP), are considered to be possible endocrine disrupters. NP and NPEO are resistant to conventional aerobic biological water treatment systems. Alternatives to this technology are sought to remove these and other bio-resistant compounds from wastewaters. Composites of the photocatalyst, TiOi, and activated carbon (AC) adsorbents have been prepared, characterised and applied as adsorbents and photocatalysts in removal of phenols and NPEO from aqueous solution. Two methods were utilised to prepare of TiO2/C composites. AC was coated with TiO2 derived from the hydrolysis of Ti(OPr')4, and with Degussa P25 using a polyvinyl alcohol binder that was subsequently carbonised in an inert atmosphere. The TiO2/C composites were characterised by nitrogen adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, UV-visible reflectance spectroscopy and scanning electron microscopy. The AC and TiO2/C adsorption capacity for phenol was observed to be affected by the surface area and surface chemistry of the adsorbent, as well as the pH of solution. The NPEO adsorption capacity and rate of adsorption was found to be dependant on the pore size distribution of the adsorbent. The effect of surface chemistry and solution pH was minimal. The selectivity of the adsorbent in the adsorption of NPEO was studied using HPLC. The rate of photooxidation of phenol was found to be first-order and greatest under basic conditions. This is attributed to changes in the electronic structure of the TiO2 under these conditions that increases the rate of reduction of molecular oxygen, often considered to be the rate limiting step. Photodegradation of NPEO led to the aggregation and sedimentation of TiOz particles. HPLC and GC-MS analysis identified photomineralisation intermediates and the mechanism of photodegradation of NPEO is discussed.