They justified their outcome by weakening forces between sorbent and phenols resulting in decrease of the uptake. They also defined this phenomenon as the shielding effect [ 22 ]. The change in pH affects chemistry of both the adsorbate and the adsorbent by shifting the equilibrium dissociation process of solutes and surface functional groups of the sorbent towards ionized or unionized form.
Thus, adsorption of phenols is limited by the acid-base characteristic of the adsorbent and its microporosity, which subsequently influences kinetics and effectiveness of the overall process.
Higher values of uptake are observed for the compounds in undissociated form [ 30 , 61 ]. Therefore, most of phenols such as weak acids are better adsorbed from neutral or acidic solutions. At lower pH values, oxonium ions are present in solution and they prevent dissociation of surface acidic groups. Accordingly, adsorption capacity is the highest [ 19 ]. The same applies to phenols, their transition point between acidic and basic form is associated with their pKa value.
Below this value dominates acidic form and above it the conjugated base-phenoxide ion takes advantage. The uptake of phenols decreases at higher pH, when the molecules turn into phenolate ions and the surface of the adsorbent is negatively charged.
The presence of electrostatic repulsive forces impedes adsorption [ 16 , 57 ]. Thus, the more acidic the surface of sorbent, the lower the adsorbability of phenols. However, some researchers report the in certain pH range, adsorption for most phenols initially increases with the rise in pH to reach a certain value and then decreases with further increase in pH [ 16 , 56 ]. This phenomenon can be explained by the fact that, in the presence of oxonium ions the surface functional groups of adsorbent gain a positive charge.
As a result, adsorption of water increases and cluster formation takes place. Consequently, some of more active sites are not available. Second, already adsorbed molecules of phenols can block the entrances to fine pores and cause decrease in uptake. This effect is stronger at the lowest pH values [ 33 ]. Moreover, the rise in temperature increases the rate of the sorption process and leads to the disappearance of the effects associated with surface chemical composition [ 33 ].
In contrast, chemisorption is an endothermic process. Therefore, Shaarani and Hameed observed the increase of temperature slightly increases the uptake of 2,4-dichlorophenol at a higher concentration.
They also found that the change of temperature alters the equilibrium capacity of the adsorbent for particular adsorbates [ 30 ]. Influence of oxygen for process of phenols sorption was at first perceived for carbon adsorbents; hence, the facts presented here have been developed only based on the results obtained for these materials.
When phenols are adsorbed under oxic and anoxic conditions, differences in the uptake can be observed. The sorption capacities of some sorbents are higher under oxic conditions that imply promoting action of molecular oxygen in this process [ 3 , 49 ]. The increase in adsorption is attributed to the oxidative coupling reaction leading to formation of timers or more substituted derivatives of phenols multimers that are attached to the surface of adsorbent [ 33 , 55 ].
The course of the process can be explained as follows: the molecules of phenols and those of oxygen diffuse to the surface of carbon, where they are preadsorbed.
The adsorbed oxygen molecules form superoxo ions that yield rearrangements and further reactions with surface functional groups and adsorbed phenols leading to creation of various surface compounds. Thus, described reaction occurs only on the surface of carbon and is catalyzed by it [ 33 ].
The oligomerization of 2-chlorophenol depends on the overall competitive effect of 2-nitrophenol and 2-methylphenol [ 1 ];. Irreversible adsorption of phenols is closely related to process of chemical adsorption involving chemical reaction between adsorbates and surface functional groups of adsorbent [ 55 ].
As it was described above, the hydrogen bonding arising in the system adsorbate-active centers of adsorbent strengthens interactions and sorptive capacity, but also can cause difficulties related to irreversible sorption [ 18 ].
It can be also considered that phenol molecules or phenoxide radicals can react with active sites on a carbon surface, which leads to creation of covalent bond between them [ 33 ]. Tessmer et al. Other studies demonstrate that lactone surface groups are responsible for both irreversibility of phenol adsorption due to chemical reaction and decrease in the difference between adsorption in oxic and anoxic conditions [ 33 ].
And another one proves that irreversible adsorption to carbon surfaces does not depend on oxidative coupling reaction, but oxidative coupling may enhance irreversible adsorption when experimental conditions are conductive pH of solution high enough, microporosity of adsorbent [ 63 ]. The discrepancies in this matter indicate that it is a topic still open for discussion and further research. A lot of scientific research was performed in order to study and understand the process of sorption of phenolic compounds.
This chapter presents the complexity of this process and shows how many different factors have influence on it. The starting point is chemical structure and overview of physical and chemical properties of phenol and its ring-substituted derivatives. This characteristic is the basis to explain the behavior of the molecules in solution and during sorption. Next, the way phenols interact with the most popular sorbents are shortly described.
Finally, factors influencing the sorption process were characterized. Sorption characteristic depends on electronic states of both an adsorbent surface and an adsorbate. Their presence in larger pores can limit access to micropores pore blocking effect and lead to competition between the process of micropore filling and adsorption on active sites;. Although so many works were devoted to studies on phenols sorption, the general mechanism of the process is still not fully understood and explained.
There are some issues and unsolved problems requiring further investigations:. There is still no consensus in the matter, what kind of the adsorbent functional groups has favorable and which undesirable influence on adsorption of phenols.
Process of irreversible adsorption due to oxidative coupling requires additional studies confirming the proposed in literature mechanisms. Most of the studies concern the process of sorption of single compounds. Only a few research studies relate to multicomponent system, in which competitive adsorption take place. This aspect is particularly important from environment protection point of view. Interferents, such as ions from salts or organic contaminants of natural or anthropogenic origin, impede quantitative analysis of phenols in waste water.
Relatively little studied are processes of cyclic adsorption—desorption, reproducibility of the adsorption properties and regeneration of adsorbent, which are extremely important for utility reasons. Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3. Help us write another book on this subject and reach those readers. Login to your personal dashboard for more detailed statistics on your publications. We are IntechOpen, the world's leading publisher of Open Access books.
Built by scientists, for scientists. Our readership spans scientists, professors, researchers, librarians, and students, as well as business professionals. Downloaded: Abstract Sorption of phenolic compounds is a very complex process and many factors influence it.
Introduction There is a huge variety of phenolic compounds in our natural environment. Table 1. Table 2. Adsorbent properties 4. Physical properties of an adsorbent Many studies were carried out to find the correlation between specific surface area of sorbent and uptake of phenolic compounds. In general, an adsorption process consists of three following steps: transport of the adsorbates from the bulk solution to the adsorbent exterior surface, diffusion of molecules to the pore of adsorbent, although a small amount of adsorbate is retained on the external surface and proper adsorption of the solutes on the interior surface of the micropores and in capillary spaces of the adsorbent.
Chemical properties of an adsorbent Chemical composition of the adsorbent surface determines the mechanism of phenols adsorption. This phenomenon can be explained by strong interactions of phenols with the surface groups that lead to the creation of polymorphic forms of phenol [ 33 ], hydration process of polar groups e. Adsorbate properties Adsorption of small organic molecules, especially containing functional groups, is affected by surface chemistry.
Hence polar substances like salts are more soluble in it. Phenoxide ion is more polar than phenol itself. Hence is more soluble in water. In general, when we are adding alkalies means we are adding their aqueous solutions and not the pure compounds. Phenol is also soluble in water to some extent. It is also used in phenolization, a surgical procedure used to treat an ingrown nail , in which it is applied to the toe to prevent regrowth of nails.
Injections of phenol have occasionally been used as a means of rapid execution. In particular, phenol was used as a means of extermination by the Nazis during the Second World War. Phenol injections were given to thousands of people in concentration camps, especially at Auschwitz-Birkenau.
Injections were administered either by medical doctors or by their assistants; such injections were originally given intravenously , more commonly in the arm , but injection directly into the heart , so as to induce nearly instant death, was later preferred [ citation needed ]. One of the most famous inmates at Auschwitz to be executed by carbolic acid injection was St. Maximilian Kolbe, a Catholic priest who volunteered to undergo three weeks of starvation and dehydration in the place of another inmate and who was finally injected with carbolic acid so that the Nazis could make more room in their holding cells.
This discovery made in may be relevant to the origin of life question as phenol is a fragment of the biomolecule tyrosine. However, as tyrosine is known to result directly from hydroxylation of phenylalanine in modern biological systems, [7] the implications of prebiotic phenol are questionable at best. Read what you need to know about our industry portal bionity. My watch list my. My watch list My saved searches My saved topics My newsletter Register free of charge.
Keep logged in. Cookies deactivated. Water is polar in nature while Ether is non-polar. Ethers are very slightly soluble in water at around 6. This is due to the presence of oxygen in ethers which interact with hydrogen in water to produce H-bonding to make it slightly soluble.
Are amines soluble in water? Solubility in water The small amines of all types are very soluble in water. Although the tertiary amines don't have a hydrogen atom attached to the nitrogen and so can't form hydrogen bonds with themselves, they can form hydrogen bonds with water molecules just using the lone pair on the nitrogen.
Does phenol react with plastic? As far as I know there are no real rules, as different substances react differently with different containers, for instance HF hydrofluoric acid will react with glass, but not with plastics, whereas phenol will melt some plastics but won't affect glass. These should be stored in plastic. Is sodium phenoxide soluble in water? Decomposes in air. Soluble in water. In both cases, a corrosive alkaline solution forms that is a strong irritant to skin and eyes.
Does aniline dissolve in water? Moderately soluble in water.
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