Advances in Colloid and Interface Science (v.143, #1-2)

Analytical phase diagrams for colloids and non-adsorbing polymer by Gerard J. Fleer; Remco Tuinier (1-47).
We first apply these modifications to the so-called colloid limit, where the size ratio qR  =  R/a between the radius of gyration R of the polymer and the particle radius a is small. In this limit the binodal polymer concentrations are below overlap: the depletion thickness δ is nearly equal to R, and Π can be approximated by the ideal (van 't Hoff) law Π  =  Π 0  =  φ/N, where φ is the polymer volume fraction and N the number of segments per chain. The results are close to those of the original Lekkerkerker theory. However, our analysis enables very simple analytical expressions for the polymer and colloid concentrations in the critical and triple points and along the binodals as a function of qR . Also the position of the cep is found analytically.With these latter two modifications we obtain again a fully analytical model with simple equations for critical and triple points as a function of qR . In the protein limit the binodal polymer concentrations scale as qR 1/γ, and phase diagrams φ qR − 1/γ versus the colloid concentration η become universal (i.e., independent of the size ratio qR ).The predictions of this generalized free-volume theory (GFVT) are in excellent agreement with experiment and with computer simulations, not only for the colloid limit but also for the protein limit (and the crossover between these limits). The qR 1/γ scaling is accurately reproduced by both simulations and other theoretical models.The liquid window is the region between φ c (critical point) and φ t (triple point). In terms of the ratio φ t /φ c the liquid window extends from 1 in the cep (here φ t  −  φ c  = 0) to 2.2 in the protein limit. Hence, the liquid window is narrow: it covers at most a factor 2.2 in (external) polymer concentration.

Adsorption techniques are widely used to remove certain classes of pollutants from wastewater. Phenolic compounds represent one of the problematic groups. Although commercial activated carbon is a preferred adsorbent for phenol removal, its widespread use is restricted due to the high cost. As such, alternative non-conventional adsorbents have been investigated. The natural materials, waste materials from industry and agriculture and bioadsorbents can be employed as inexpensive adsorbents. The review (i) presents a critical analysis of these materials; (ii) describes their characteristics, advantages and limitations; and (iii) discusses the various mechanisms involved. There are several issues and drawbacks concerned on the adsorption of phenolic compounds that have been discussed in this review article. It is evident from the review that low-cost adsorbents have demonstrated high removal capabilities for certain phenolic compounds. In particular, industrial waste might be a promising adsorbent for environmental and purification purposes.
Keywords: Adsorption; Phenol; Substituted phenol; Activated carbon; Low-cost adsorbents;