Adsorption equilibria and kinetics for phenol and cresol onto polymeric adsorbents: effects of adsorbents/adsorbates structure and interface

Electroanalytical analysis of phenol oxidation using bacteria immobilized by a polycaprolactone coating on the copper electrode surface

The copper electrode modified by bacteria immobilised by a polycaprolactone film was successfully developed by electropolymerisation for the purpose of determining the presence of phenol. Electrochemical techniques such as square-wave voltammetry (SWV), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the electrochemical properties of the Cu-polymer/bacteria electrode. The results show that the intensity of the phenol oxidation peak increases with concentration, allowing us to obtain good analytical results with DL of 2.156 × 10-7 M and QL which is 7.2 × 10-7 M , confirming that the biosensor has excellent electroanalytical activity for phenol oxidation, with good stability and a wide linear range. Our electrode is based on a easily available and inexpensive material, as well as on its simple preparation, which has demonstrated high performance for phenol.

Improving 3-methylphenol (m-cresol) production in yeast via in vivo glycosylation or methylation

Heterologous expression of 6-methylsalicylic acid synthase (MSAS) together with 6-MSA decarboxylase enables de novo production of the platform chemical and antiseptic additive 3-methylphenol (3-MP) in the yeast Saccharomyces cerevisiae. However, toxicity of 3-MP prevents higher production levels. In this study, we evaluated in vivo detoxification strategies to overcome limitations of 3-MP production. An orcinol-O-methyltransferase from Chinese rose hybrids (OOMT2) was expressed in the 3-MP producing yeast strain to convert 3-MP to 3-methylanisole (3-MA). Together with in situ extraction by dodecane of the highly volatile 3-MA this resulted in up to 211 mg/L 3-MA (1.7 mM) accumulation. Expression of a UDP-glycosyltransferase (UGT72B27) from Vitis vinifera led to the synthesis of up to 533 mg/L 3-MP as glucoside (4.9 mM). Conversion of 3-MP to 3-MA and 3-MP glucoside was not complete. Finally, deletion of phosphoglucose isomerase PGI1 together with methylation or glycosylation and feeding a fructose/glucose mixture to redirect carbon fluxes resulted in strongly increased product titers, with up to 897 mg/L 3-MA/3-MP (9 mM) and 873 mg/L 3-MP/3-MP as glucoside (8.1 mM) compared to less than 313 mg/L (2.9 mM) product titers in the wild type controls. The results show that methylation or glycosylation are promising tools to overcome limitations in further enhancing the biotechnological production of 3-MP.

A review on the adsorption of phenols from wastewater onto diverse groups of adsorbents

Phenol and its derivatives are used in numerous industrial processes; these compounds are highly toxic and corrosive, classified as priority pollutants. One of the effective processes for the removal of phenols is adsorption. Numerous and various adsorbents in nature have been researched for this purpose in the past decade. Their adsorption capacities vary from 1 to >1000 mg/g, and are influenced by such factors as the adsorbent’s surface area, pH, temperature, concentration of phenol and surface functional groups, contact time, etc. In this review, adsorbents tested for the removal of phenol and phenol compounds have been classified into four groups: carbonaceous adsorbents, clay and natural mineral adsorbents, polymer-based adsorbents, and novel adsorbents. The highest adsorption capacities were attained by polymer-based adsorbents (>1000 mg/g), whereas natural clays and novel adsorbents showed adsorption capacities of the lower range as compared to the carbonaceous adsorbents. The major advantage of phenol adsorption over other applicable processes is the high potential for phenol recovery and reuse.

Integrated adsorptive technique for efficient recovery of m-cresol and m-toluidine from actual acidic and salty wastewater

An integrated adsorptive technique combining an m-cresol adsorption unit, an acid retardation unit and an m-toluidine adsorption unit in sequence was designed to recover m-cresol and m-toluidine from highly acidic and salty m-cresol manufacturing wastewater. In the first column packed with hypercrosslinked polymeric resin (NDA-99), most m-cresol was captured through π-π and hydrogen-bonding interactions as well as the salting-out effect, while m-toluidine was not absorbed due to protonation. To separate acid from salt, an acid retardation unit was introduced successively to adsorb sulfuric acid by strong base anion exchange resin (201×7). After the acid retardation unit and mild neutralization reaction, the last column filled with NDA-99 was applied to trap neutral m-toluidine from the salty effluent. Moreover, the eluent of the acid retardation unit was utilized as the regenerant to recover m-toluidine, and the recycled high-acidity and low-salinity solution of m-toluidine was directly used to produce m-cresol as the raw material. Therefore, the proposed method not only efficiently recycled m-cresol and m-toluidine, but also reduced the consumption of alkali dramatically (saving 0.1628t/t wastewater). These findings will inspire design of integrated adsorptive techniques for treating complex organic wastewater with high efficiency and low cost.

Highly efficient extraction of phenolic compounds by use of magnetic room temperature ionic liquids for environmental remediation

A hydrophobic magnetic room temperature ionic liquid (MRTIL), trihexyltetradecylphosphonium tetrachloroferrate(III) ([3C(6)PC(14)][FeCl(4)]), was synthesized from trihexyltetradecylphosphonium chloride and FeCl(3) · 6H(2)O. This MRTIL was investigated as a possible separation agent for solvent extraction of phenolic compounds from aqueous solution. Due to its strong paramagnetism, [3C(6)PC(14)][FeCl(4)] responds to an external neodymium magnet, which was employed in the design of a novel magnetic extraction technique. The conditions for extraction, including extraction time, volume ratio between MRTIL and aqueous phase, pH of aqueous solution, and structures of phenolic compounds were investigated and optimized. The magnetic extraction of phenols achieved equilibrium in 20 min and the phenolic compounds were found to have higher distribution ratios under acidic conditions. In addition, it was observed that phenols containing a greater number of chlorine or nitro substituents exhibited higher distribution ratios. For example, the distribution ratio of phenol (D(Ph)) was 107. In contrast, 3,5-dichlorophenol distribution ratio (D(3,5-DCP)) had a much higher value of 6372 under identical extraction conditions. When compared with four selected traditional non-magnetic room temperature ionic liquids, our [3C(6)PC(14)][FeCl(4)] exhibited significantly higher extraction efficiency under the same experimental conditions used in this work. Pentachlorophenol, a major component in the contaminated soil sample obtained from a superfund site, was successfully extracted and removed by use of [3C(6)PC(14)][FeCl(4)] with high extraction efficiency. Pentachlorophenol concentration was dramatically reduced from 7.8 μg mL(-1) to 0.2 μg mL(-1) after the magnetic extraction by use of [3C(6)PC(14)][FeCl(4)].

Adsorption of p-cresol on novel diatomite/carbon composites

Hybrid inorganic/organic adsorbents were synthesized using mixtures of diatomite and carbon charcoal as precursors, and explored for the removal of p-cresol from aqueous solution. The carbon/diatomite composites displayed a bimodal and interconnected porous structure which was partially inherited from both precursors. They display moderate surface areas (between 100 and 400 m(2)g(-1)) due to their large inorganic content (between 70 and 90 wt.%), since the diatomite is a non-porous material. Compared to activated carbons with a more developed porosity, p-cresol adsorption on the prepared carbon/diatomite composites was much faster, showing adsorption capacities similar to those of conventional adsorbents over a wide pH range. These results show a good affinity of p-cresol molecules towards the hybrid inorganic/organic composites, and demonstrate the suitability of these novel materials for the removal of aromatic (polar) molecules, despite their dominant inorganic character.

Adsorption of 5-sodiosulfoisophthalic acids from aqueous solution onto poly(2-vinylpyridine) resin

In the present study, the performance, behavior and mechanism of synthetic poly(2-vinylpyridine) resin (WH-225) adsorbing 5-sodiosulfoisophthalic acids (SIPA) from the aqueous solution were investigated, and two commercial adsorbents, namely, hypercrosslinked adsorbent NDA-100 and macroporous adsorbent XAD-4 were employed as reference. Compared to NDA-100 and XAD-4, WH-225 has the highest capacity for adsorbing SIPA from the aqueous solution, which is verified by the related adsorption experiments. The investigation indicated that electrostatic interaction is an important factor in affecting the adsorption behavior of WH-225. The Freundlich isotherm equation was successfully applied to describe the adsorption isotherms. The negative values of the adsorptive enthalpy changes indicate an exothermic process for WH-225, and the absolute values (<43 kJ mol(-1)) further manifest a physical adsorption process. The column adsorption and desorption tests further proved WH-225 is a promising adsorbent for field applications to remove and recover aromatic acids (e.g. SIPA) from aqueous solution.

Enhanced adsorption of phenol from water by a novel polar post-crosslinked polymeric adsorbent

A novel post-crosslinked polymeric adsorbent PDM-2 was prepared by Friedel-Crafts reaction of pendant vinyl groups without external crosslinking agent. Both the specific surface area and the pore volume of starting copolymer PDM-1 increased significantly after post-crosslinking. Batch adsorption runs of phenol from aqueous solution onto PDM-1 and PDM-2 were investigated. Commercial macroporous resins XAD-4 and AB-8 were chosen as the comparison. Experimental results showed that isotherms of phenol adsorption onto these four polymeric adsorbents could be represented by Freundlich model reasonably. PDM-2 exhibited higher adsorption capacity of phenol than other three adsorbents, which resulted from synergistic effect of larger specific surface area and polar groups on the network. The adsorption process for phenol was proved to be exothermic and spontaneous in nature. Thermodynamic parameters such as Gibb's free energy (DeltaG), change in enthalpy (DeltaH) and change in entropy (DeltaS) were calculated. Kinetics studies indicated that phenol uptake onto PDM-1 and PDM-2 followed the pseudo-second order model and the intraparticle diffusion process was a rate-controlling step. Column adsorption runs demonstrated that nearly 100% regeneration efficiency for PDM-2 by 3BV industrial alcohol and the adsorbate phenol can be easily recovered by further distilling. Continuous column adsorption-regeneration cycles indicated negligible capacity loss of PDM-2 during operation.