Adsorption and desorption hysteresis of 4-nitrophenol on a hyper-cross-linked polymer resin NDA-701.

Removal and recovery of aromatic pollutants from water by solid adsorbents have been of considerable concern recently. Relatively limited information is available on desorption kinetics and isotherms aspects. In the present study, batch desorption experiments of loaded 4-nitrophenol on a hyper-cross-linked polymer resin NDA-701, a polymeric adsorbent Amberlite XAD-4 and a granular activated carbon GAC-1 were carried out to study the effects of reaction temperature and pore-size distribution of adsorbents. 4-Nitrophenol desorbed rapidly in the early stages, followed by a much slower release, which was described well by a first-order two-component four-parameter model. The adsorption and desorption equilibrium isotherms were well described by Freundlich equation and the apparent adsorption-desorption hysteresis (hysteresis index) for 4-nitrophenol followed an order as: NDA-701 approximately XAD-4<<GAC-1. Analysis of adsorption-desorption process suggested that higher reaction temperature and larger proportion of macropore of adsorbents favoured desorption kinetic and reduced adsorption-desorption hysteresis. All the results indicated that NDA-701, with a specific bimodal property in macro- and micropore region, had excellent potential as an adsorption material for achieving high removal and recovery of 4-nitrophenol from the contaminated water. These results will also advance the understanding of the adsorption and desorption behavior of hyper-cross-linked polymer resin in the wastewater treatment systems.