Changhong Hong

Equilibrium and heat of adsorption of diethyl phthalate on heterogeneous adsorbents

Removal of phthalate esters from water has been of considerable concern recently. In the present study, the adsorptive removal performance of diethyl phthalate (DEP) from water was investigated with the aminated polystyrene resin (NDA-101) and oxidized polystyrene resin (NDA-702). In addition, the commercial homogeneous polystyrene resin (XAD-4) and acrylic ester resin (Amberlite XAD-7) as well as coal-based granular activated carbon (AC-750) were chosen for comparison. The corresponding equilibrium isotherms are well described by the Freundlich equation and the adsorption capacities for DEP followed the order NDA-702 > NDA-101 > AC-750 > XAD-4 > XAD-7. Analysis of adsorption mechanisms suggested that these adsorbents spontaneously adsorb DEP molecules driven mainly by enthalpy change, and the adsorption process was derived by multiple adsorbent-adsorbate interactions such as hydrogen bonding, pi-pi stacking, and micropore filling. The information related to the adsorbent surface heterogeneity and the adsorbate-adsorbate interaction was obtained by Dos model. All the results indicate that heterogeneous resins NDA-702 and NDA-101 have excellent potential as an adsorption material for the removal of DEP from the contaminated water.

Sorption enhancement of 1-naphthol onto a hydrophilic hyper-cross-linked polymer resin

A hydrophilic hyper-cross-linked polymer resin NDA-150 was developed to remove 1-naphthol from the contaminated waters. The sorption performance of 1-naphthol on NDA-150 was explored and compared with that on the commercial hydrophobic resin XAD-4. The sorption rates of 1-naphthol onto both of the two resins obey the pseudo-second-order kinetics, and are limited by the successive steps of film diffusion and intraparticle diffusion. The greater sorption rate on XAD-4 than NDA-150 is probably due to the larger average pore diameter of XAD-4. All the adsorption isotherms can be represented by Langmuir equation. The larger capacity and stronger affinity of NDA-150 than XAD-4 probably result from the abundant microporous structure and polar groups of NDA-150. In aqueous phase hydrophobic XAD-4 adsorbs 1-naphthol driven principally by enthalpy change, while the adsorption onto hydrophilic NDA-150 driven mainly by entropy change. The breakthrough and the total sorption capacity of NDA-150 to 1-naphthol were obtained to be 1.10 and 1.58 mmol mL(-1) resin at 293 K, respectively. Nearly 100% regeneration efficiency for the resin was achieved by ethanol at 313 K.

Removal enhancement of 1-naphthol and 1-naphthylamine in single and binary aqueous phase by acid-basic interactions with polymer adsorbents

In the present study removal performance of 1-naphthol and 1-naphthylamine from wastewater by single and binary adsorption was compared. Synergistic effects were investigated in single-solute, binary-solute, and the preloading adsorption systems at 293 K. Two commercial polystyrene adsorbents Amberlite XAD-4, a macroporous adsorbent, and NDA-100, a hyper-cross-linked adsorbent, were employed here for their frequent use in organic pollutants removal from contaminated waters. All the adsorption isotherms of 1-naphthol and 1-naphthylamine on both adsorbents were found to be well represented by the Langmuir equation. Adsorption capacity of the primary solute was enhanced in the presence of the co-solute, arising presumably from the synergistic effect caused by the laterally acid-base interaction between the adsorbed 1-naphthol and 1-naphthylamine molecules. Due to the stronger adsorption affinity of 1-naphthylamine to nonpolar adsorbents, adsorption enhancement of 1-naphthylamine in the presence of 1-naphthol is greater than that of 1-naphthol in the presence of 1-naphthylamine. The greater synergistic effect of 1-naphthol/1-naphthylamine equimolar mixtures on XAD-4 than that on NDA-100 partly results from the larger average pore size of the former adsorbent. A modified extended Langmuir model is proved to well describe the synergistic adsorption of 1-naphthol/1-naphthylamine equimolar mixtures in the binary-solute system. The synergistic coefficient of one adsorbate is linearly correlated with the amount of the other adsorbed on the adsorbent.

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.