Multifunctional polysaccharide structure as green adsorbent for efficient removal and preconcentration of chlorophenols from the aqueous medium: experimental and modeling approaches

The growing concerns about water pollution have prompted researchers to explore new materials for remediating and purifying it. In recent years, there has been a focus on polysaccharides as eco-friendly polymers that exhibit high efficiency in removing chlorophenols from waste water. This study aims to develop a trifunctional polysaccharide structure using a biodegradable matrix. The chitosan/alginate-polyethyleneimine-phenyl-phosphonamidic acid (CHIT/ALG-PEIPPAA) matrix was employed for removing chlorophenols from water. The study carefully examined the impact of various physicochemical parameters such as pH, reaction time, chlorophenols concentration, temperature, and ionic strength to determine the optimal conditions for the adsorption process. Several techniques were used to confirm the morphology, physicochemical properties, structure, and functionalization of the polymer. Scanning electron microscopy (SEM) images revealed a heterogeneous morphology with agglomerates of different particle sizes, ranging from a few micrometers with irregular shapes. The FTIR spectrum and zeta potential characterization indicated the presence of hydrophilic groups and a highly positive charge (around 31.4 mV) on the surface of the CHIT/ALG-PEIPPAA adsorbent. The optimal pH for chlorophenols removal was found to be approximately 4.4. The kinetic data supported the pseudo-second-order kinetic model, which accurately described the adsorption behavior of both chlorophenol molecules. The fitting of the isotherm analysis revealed that the Langmuir model provided a better representation of the adsorption process. The maximum adsorption capacities for 4-chlorophenol and 2,4-chlorophenol were approximately 118 mg.g-1 and 249 mg.g-1, respectively. The calculated thermodynamic functions confirmed an exothermic and spontaneous adsorption process for chlorophenols, with ∆H values of -6.98 kJ.mol-1 and -2.74 kJ.mol-1 for 4-chlorophenol and 2,4-chlorophenol, respectively. The regeneration process of the CHIT/ALG-PEIPPAA adsorbent showed higher efficacy in the presence of hydrochloric acid (2.0 mol.L-1), resulting in up to 91% desorption of chlorophenols. The CHIT/ALG-PEIPPAA adsorbent demonstrated good reusability after regeneration, with only a slight decrease in extraction efficiency: 34.63% for 4-chlorophenol and 79.03% for 2,4-chlorophenol, under the same optimal conditions as the initial adsorption cycle.

Catalytic Hydrodechlorination of 4-Chlorophenol by Palladium-Based Catalyst Supported on Alumina and Graphene Materials

Hydrodechlorination (HDC) is a reaction that involves the use of hydrogen to cleave the C-Cl bond in chlorinated organic compounds such as chlorophenols and chlorobenzenes, thus reducing their toxicity. In this study, a palladium (Pd) catalyst, which is widely used for HDC due to its advantageous physical and chemical properties, was immobilized on alumina (Pd/Al) and graphene-based materials (graphene oxide and reduced graphene oxide; Pd/GO and Pd/rGO, respectively) to induce the HDC of 4-chlorophenol (4-CP). The effects of the catalyst dosage, initial 4-CP concentration, and pH on 4-CP removal were evaluated. We observed that 4-CP was removed very rapidly when the HDC reaction was induced by Pd/GO and Pd/rGO. The granulation of Pd/rGO using sand was also investigated as a way to facilitate the separation of the catalyst from the treated aqueous solution after use, which is to improve practicality and effectiveness of the use of Pd catalysts with graphene-based support materials in an HDC system. The granulated catalyst (Pd/rGOSC) was employed in a column to induce HDC in a continuous flow reaction, leading to the successful removal of most 4-CP after 48 h. The reaction mechanisms were also determined based on the oxidation state of Pd, which was observed using X-ray photoelectron spectroscopy. Based on the results as a whole, the proposed granulated catalyst has the potential to greatly enhance the practical applicability of HDC for water purification.

Adsorption of chlorophenols on activated pine sawdust-activated carbon from solution in batch mode

In this work, a novel adsorbent, activated carbon (PSAC) developed by the activation of pine sawdust's pyrolytic carbon (PSPC), is applied to adsorb 2,4-dichlorophenol (2,4-DCP) and 4-chlorophenol (4-CP). The optimized preparation conditions of PSAC were presented. The results revealed that equilibrium adsorption capacity (q_e) of PSAC was notably enhanced up to threefold compared with PSPC. The adsorbents were characterized by a variety of techniques such as SEM, XRD, FT-IR, and elemental analysis. The key factors (such as adsorbent dosage, pH, salt concentration, temperature, and contact time) influencing the adsorption process were also studied. The adsorption quantities of PSAC for 2,4-DCP and 4-CP were 135.7 mg·g^-1 and 77.3 mg·g^-1, respectively. The equilibrium adsorption of 4-DCP and 4-CP was suitable to be predicted by the Freundlich and Koble-Corrigan models, while kinetic process was better described by the pseudo-second-order kinetic model and Elovich equation. The process was spontaneous. After repeated regeneration of PSAC with ethanol, the adsorption capacity of PSAC was not significantly reduced, indicating that PSAC can be recycled by regeneration after adsorption of 4-CP. This work provides a viable method to use activated carbon as an effective adsorbent for pollutant removal.

Phenolic Compounds Removal from Olive Mill Wastewater Using the Composite of Activated Carbon and Copper-Based Metal-Organic Framework

As the industry of olive oil continues to grow, the management of olive mill wastewater (OMW) by-products has become an area of great interest. While many strategies for processing OMW have been established, more studies are still required to find an effective adsorbent for total phenolic content uptake. Here, we present a composite of a Cu 1,4-benzene dicarboxylate metal-organic framework (Cu (BDC) MOF) and granular activated carbon (GAC) as an adsorbent for total phenolic content removal from OMW. Experimental results demonstrated that the maximum adsorption capacity was 20 mg/g of total phenolic content (TPC) after 4 h. using 2% wt/wt of GAC/Cu (BDC) MOF composite to OMW at optimum conditions (pH of 4.0 and 25 °C). The adsorption of phenolic content onto the GAC/Cu (BDC) MOF composite was described by the Freundlich adsorption and pseudo-second-order reaction. The adsorption reaction was found to be spontaneous and endothermic at 298 K where ΔS° and ΔH° were found to be 0.105 KJ/mol and 25.7 kJ/mol, respectively. While ΔGº value was -5.74 (kJ/mol). The results of this study provide a potential solution for the local and worldwide olive oil industry.

Efficient capture of radioactive iodine by ZIF-8 derived porous carbon

Due to the rapid diffusion of radioactive iodine, the demand for safe and efficient capture and storage of radioactive iodine is increasing worldwide. The use of porous carbon materials to capture iodine has aroused great interest. This work prepared porous carbon materials derived from polymetallic oxides of the zeolitic imidazolate framework (ZIF) by pyrolysis at 1000 °C. The carbon materials (CZIF-1000) have a high specific surface area of about 1110 m2/g and a total pore volume of 0.92 cm3/g. Adsorption studies have shown that the CZIF-1000 had significant adsorption performance for iodine, and the adsorption capacity can reach 790.8 mg/g at 8h. The potential mechanism of adsorption is that the carbonization causes the charge-transfer interaction and pore size distribution. Compared with the conventional adsorbents, the adsorbents showed faster kinetics and high extraction capacity for iodine. This experiment provides an effective method for designing a highly efficient adsorbent for iodine and broadens the ideas for developing new iodine extraction adsorbents.

Exploring QSPR modeling for adsorption of hazardous synthetic organic chemicals (SOCs) by SWCNTs

In order to understand the physicochemical properties as well as the mechanisms behind adsorption of hazardous synthetic organic chemicals (SOCs) onto single walled carbon nanotubes (SWCNTs), we have developed partial least squares (PLS)-regression based QSPR models using a diverse set of 40 hazardous SOCs having defined adsorption coefficient (logK). The models were extensively validated using different validation parameters in order to assure the robustness and predictivity of the models. We have also checked the consensus predictivity of all the individual models using "Intelligent consensus predictor" tool for possible enhancement of the quality of predictions for test set compounds. The consensus predictivity of the test set compounds were found to be better than the individual models based on not only the MAE based criteria (MAE_(95%) = Good) but also some other validation parameters (Q²_F1 = 0.938, Q²_F2 = 0.937). The contributing descriptors obtained from the QSPR models suggested that the hazardous SOCs may get adsorbed onto the SWCNTs through hydrophobic interaction as well as hydrogen bonding interactions and electrostatic interaction to the functionally modified SWCNTs. Thus, the developed models may provide knowledge to scientists to increase the efficient application of SWCNTs as a special adsorbent, which may be useful for the management of environmental pollution.

Adsorption of chlorophenols from aqueous solutions by pristine and surface functionalized single-walled carbon nanotubes

The adsorption of six kinds of chlorophenols on pristine, hydroxylated and carboxylated single-walled carbon nanotubes (SWCNTs) has been investigated. Pseudo-first order and pseudo-second order models were used to describe the kinetic data. All adsorption isotherms were well fitted with Langmuir, Freundlich and Polanyi-Manes models, due to surface adsorption dominating the adsorption process. The close linear relationship between logKow and logKd suggested that hydrophobicity played an important role in the adsorption. The SWCNTs' adsorption capacity for chlorophenols was weakened by addition of oxygen-containing functional groups on the surface, due to the loss of specific surface area, the increase of hydrophilicity and the reduction of π-π interaction. The best adsorption capacity of pristine SWCNTs, SWCNT-OH and SWCNT-COOH for six chlorophenols varied from 19 to 84mg/g, from 19 to 65mg/g and from 17 to 65mg/g, respectively. The effect of pH on the adsorption of 2,6-dichlorophenol (2,6-DCP), was also studied. When pH is over the pKa of 2,6-dichlorophenol (2,6-DCP), its removal dropped sharply. When ionic strength increased (NaCl or KCl concentration from 0 to 0.02mmol/L), the adsorption capacity of 2,6-DCP on pristine SWCNTs decreased slightly. The comparison of chlorophenols adsorption by SWCNTs, MWCNTs and PAC was made, indicating that the adsorption rate of CNTs was much faster than that of PAC. The results provide useful information about the feasibility of SWCNTs as an adsorbent to remove chlorophenols from aqueous solutions.

Combination of powdered activated carbon and powdered zeolite for enhancing ammonium removal in micro-polluted raw water

Even zeolite is promising in ammonia pollution disposing, its removal efficiency is frequently interfered by organics. As activated carbon has good removal efficiency on organic contaminants, combination of two adsorbents may allow their respective adsorption characteristics into full play. This paper provides a performance assessment of the combination for enhancing ammonium removal in micro-polluted raw water. Gel-filtration chromatography (GFC) was carried out to quantify the molecular weight (MW) range of organic contaminants that powdered activated carbon (PAC) and powdered zeolite (PZ) can remove. The polydispersity difference which also calculated from GFC may indicate the wider organic contaminants removal range of PAC and the relatively centralized removal range of PZ. The jar tests of combination dosing confirm a synergistic effect which promotes ammonium removing. Nevertheless, it also shows an antagonism hindering the due removal performance of the two adsorbents on CODMn, while it is not much evident on UV254. Furthermore, a comparison study with simulated coagulation-sedimentation process was conducted to evaluate the optimum dosing points (spatial and temporal) of PAC and PZ among follows: suction well, pipeline mixer, early and middle phase of flocculation. We suggest to dose both two adsorbents into the early phase of flocculation to maximize the versatile removal efficiency on turbidity, ammonium and organic contaminants.

Synthesis of flower-shaped ZrO2–C composites for adsorptive removal of trichlorophenol from aqueous solution

A novel kind of nanoflake zirconia–carbon (ZrO₂–C) composite exhibited a much improved capacity to adsorb TCP.

Adsorption of trichlorophenol on zeolite and adsorbent regeneration with ozone

A FAU-type zeolite was studied as an adsorbent to remove 2,4,6-trichlorophenol (TCP), a frequently detected recalcitrant pollutant in water bodies. Both adsorption isotherm and kinetics were studied with TCP concentrations from 10 to 100mg/L. It was observed that TCP was effectively adsorbed onto the zeolite with a high adsorption capacity and a high kinetic rate. Freundlich model and pseudo-second-order kinetics were successfully applied to describe the experimental data. The influence of solution pH was also studied. Furthermore, ozone was applied to regenerate the loaded zeolite. It was found that an effective adsorption of TCP was kept for at least 8 cycles of adsorption and regeneration. The ozonation also increased the BET specific surface of zeolite by over 60% and consequently enhanced the adsorption capacity.

Organic xenobiotics removal in constructed wetlands, with emphasis on the importance of the support matrix

Constructed wetlands (CWs) are increasingly popular as an efficient and economical alternative to conventional wastewater treatment processes for removal, among other pollutants, of organic xenobiotics. In CWs, pollutants are removed through the concerted action of their components, whose contribution can be maximized by careful selection of those components. Specifically for non-biodegradable organic pollutants, the materials used as support matrix of CWs can play a major role through sorption phenomena. In this review the role played by such materials in CWs is examined with special focus on the amount of research that has been conducted to date on their sorption properties relatively to organic compounds. Where available, the reports on the utilization of some of those materials on pilot or full-scale CWs are also recognized. Greatest interest has been directed to cheaper and widely available materials. Among these, clays are generally regarded as efficient sorbents, but materials originated from agricultural wastes have also gained recent popularity. Most available studies are lab-scale batch sorption experiments, whereas assays performed in full-scale CWs are still scarce. However, the available lab-scale data points to an interesting potential of many of these materials for experimentation as support matrix of CWs targeted for organic xenobiotics removal.

The investigation of phenol removal from aqueous solutions by zeolites as solid adsorbents

This work reports results on phenol adsorption from aqueous solutions on synthetic BEA (β) and MFI (ZSM-5) zeolites, studied by heat-flow microcalorimetry. For the sake of comparison, the adsorption was performed on activated carbon, a solid customarily used for removal of phenol from water. The obtained values of heats evolved during phenol adsorption indicate the heterogeneity of active sites present on the investigated systems for the adsorption of phenol. In addition, the amounts of adsorbed pollutant were determined and presented in the form of adsorption isotherms, which were interpreted using Langmuir, Freundlich, Dubinin-Astakov and Sips' equations. The latter was found to express high level of agreement with experimental data. The results obtained in this work reveal that the adsorption of phenol on zeolites depends on both Si/Al ratio and on the pore size. Hydrophobic zeolites that possess higher contents of Si show higher affinities for phenol adsorption. Among investigated zeolites, zeolite β possesses the highest capacity for adsorption of phenol. The possibility of regeneration of used adsorbents was investigated by thermal desorption technique. It has been shown that in the case of β zeolite the majority of adsorbed phenol is easily released in the low temperature region.

An adsorption diffusion model for removal of para-chlorophenol by activated carbon derived from bituminous coal

Batch adsorption experiments were carried out to study the adsorptive removal and diffusion mechanism of para-chlorophenol (p-CP) onto Calgon Filtrasorb 400 (F400) activated carbon. The external mass transfer resistance is negligible in the adsorption process carried out under different conditions in batch operation. Intraparticle diffusion model plots were used to correlate the batch p-CP adsorption data; three distinct linear sections were obtained for every batch operation. The textural properties of F400 activated carbon showed that it has a large portion of supermicropores, which is comparable to the size of the p-CP molecules. Due to the stronger interactions between p-CP molecules and F400 micropores, p-CP molecules predominantly diffused and occupied active sites in micropore region by hopping mechanism, and eventually followed by a slow filling of mesopores and micropores. This hypothesis is proven by the excellent agreement of the intraparticle diffusion model plots and the textural properties of F400 activated carbon.

Ammoniacal nitrogen and COD removal from semi-aerobic landfill leachate using a composite adsorbent: fixed bed column adsorption performance

The performance of a carbon-mineral composite adsorbent used in a fixed bed column for the removal of ammoniacal nitrogen and aggregate organic pollutant (COD), which are commonly found in landfill leachate, was evaluated. The breakthrough capacities for ammoniacal nitrogen and COD adsorption were 4.46 and 3.23 mg/g, respectively. Additionally, the optimum empty bed contact time (EBCT) was 75 min. The column efficiency for ammoniacal nitrogen and COD adsorption using fresh adsorbent was 86.4% and 92.6%, respectively, and these values increased to 90.0% and 93.7%, respectively, after the regeneration process.

Adsorptive removal of phenol from contaminated water and wastewater by activated carbon, almond, and walnut shells charcoal

The adsorption process is gaining interest as an effective process for advanced water and wastewater treatment. Phenol, as a toxic material in industrial effluents, should be removed because of its environmental and health effects. The present study involves an investigation of the use of three carbonaceous materials--activated carbon laboratory-grade (ACL), almond shell charcoal (ASC), and walnut shell charcoal (WSC)--as adsorbents for the removal of phenol from aqueous solutions. For the first time, the adsorptive removal of phenol using ASC and WSC was investigated. Findings have been compared with (ACL) results. Batch experiments were carried out to obtain adsorption equilibrium isotherms with phenol-spiked synthetic solutions. The effects of adsorbent amounts, pHo, initial concentration, and contact time on the adsorption of phenol were studied. Maximum removals of phenol from contaminant water with ACL, ASC, and WSC were 99.87, 91.36, and 78.17%, respectively, and from industrial wastewater were 99.71, 85.54, and 65.49%, respectively.

Application of low-cost adsorbents for dye removal--a review

Dyes are an important class of pollutants, and can even be identified by the human eye. Disposal of dyes in precious water resources must be avoided, however, and for that various treatment technologies are in use. Among various methods adsorption occupies a prominent place in dye removal. The growing demand for efficient and low-cost treatment methods and the importance of adsorption has given rise to low-cost alternative adsorbents (LCAs). This review highlights and provides an overview of these LCAs comprising natural, industrial as well as synthetic materials/wastes and their application for dyes removal. In addition, various other methods used for dye removal from water and wastewater are also complied in brief. From a comprehensive literature review, it was found that some LCAs, in addition to having wide availability, have fast kinetics and appreciable adsorption capacities too. Advantages and disadvantages of adsorbents, favourable conditions for particular adsorbate-adsorbent systems, and adsorption capacities of various low-cost adsorbents and commercial activated carbons as available in the literature are presented. Conclusions have been drawn from the literature reviewed, and suggestions for future research are proposed.

In situ orientation-sensitive observation of molecular adsorption on a liquid/zeolite interface by second-harmonic generation

The inherently surface-specific technique of second-harmonic generation was employed to probe the adsorption of an organic molecule, a hemicyanine dye, on b-oriented silicalite-1 films in situ. Measurements were performed in a purpose-built cell for solution experiments. By measuring at two different polarization combinations of the fundamental and second-harmonic light, the orientation of the adsorbed molecules was measured continuously. It has been observed that the adsorbed molecules gradually align themselves with the straight pores of the zeolite crystallites, thus adsorbing into the pores.

Adsorption of phenol and its derivatives from water using synthetic resins and low-cost natural adsorbents: a review

In this article, the technical feasibility of the use of activated carbon, synthetic resins, and various low-cost natural adsorbents for the removal of phenol and its derivatives from contaminated water has been reviewed. Instead of using commercial activated carbon and synthetic resins, researchers have worked on inexpensive materials such as coal fly ash, sludge, biomass, zeolites, and other adsorbents, which have high adsorption capacity and are locally available. The comparison of their removal performance with that of activated carbon and synthetic resins is presented in this study. From our survey of about 100 papers, low-cost adsorbents have demonstrated outstanding removal capabilities for phenol and its derivatives compared to activated carbons. Adsorbents that stand out for high adsorption capacities are coal-reject, residual coal treated with H3PO4, dried activated sludge, red mud, and cetyltrimethylammonium bromide-modified montmorillonite. Of these synthetic resins, HiSiv 1000 and IRA-420 display high adsorption capacity of phenol and XAD-4 has good adsorption capability for 2-nitrophenol. These polymeric adsorbents are suitable for industrial effluents containing phenol and its derivatives as mentioned previously. It should be noted that the adsorption capacities of the adsorbents presented here vary significantly depending on the characteristics of the individual adsorbent, the extent of chemical modifications, and the concentrations of solutes.

Monitoring of monochlorophenols adsorbed on metal (Cu and Zn) supported pumice by infrared spectroscopy

The adsorption of monochlorophenols (o-, m-, p-chlorophenol) on pumice, Zn/pumice and Cu/pumice has been studied through Fourier Transform Infrared (FTIR) Spectroscopy in transmission mode. The data show that after Zn and Cu were supported on pumice, the adsorption of 4-chlorophenol is characterized by the bands at 1591, 1494, 1092 and 824 cm(-1). Adsorption process occurred via metal cations on the surface of pumice. Metal oxides on pumice can mediate binding of p-chlorophenol.

Analysis of adsorption characteristics of 2,4-dichlorophenol from aqueous solutions by activated carbon fiber

In this study experiments were conducted to investigate the adsorption of 2,4-dichlorophenol (2,4-DCP) by activated carbon fiber (ACF) activated by static air. With the results of batch experiments at various temperatures, the adsorption isotherms, kinetics and thermodynamics of this adsorption process were evaluated. Four adsorption isotherm models, Langmuir, Freundlich, Redlich-Peterson and Toth equations, were used to fit the experimental data and the results reveal that the adsorption isotherm models fitted the data in the order of: Langmuir>Redlich-Peterson>Toth>Freundlich isotherms. A pseudo second-order adsorption model was better to describe the adsorption data than the pseudo first-order model and the Bangham model at the temperatures tested. The activation energy was calculated to be 40.90 kJ/mol, while the thermodynamic parameters DeltaH and DeltaS were estimated to be -5.82 kJ/mol and 0.07 kJ/(molK), respectively.

Adsorption of nicotine on different zeolite types, from aqueous solutions

The plant alkaloid, nicotine, is a strongly toxic heterocyclic compound: the lethal dose for an adult human being (40-60 mg) is importantly lower in comparison with the other known poisons such as arsenic or strychni?ne. Cigarettes represent "the most toxic and addictive form of nicotine". Besides the negative effects of nicotine on public health produced by self-administration, recently another potentially very dangerous effect has been recognized: because of its miscibility with water, nicotine can be found in industrial wastewaters, and consequently, in groundwater. Therefore, the problem of nicotine removal from aqueous solutions has became an interesting topic. In this work, the removal of nicotine has been probed by adsorption on solid materials. Adsorption of nicotine on different zeolites (clinoptilolite, ZSM-5 and ? zeolite) and on activated carbon was investigated from aqueous solutions, at 298 K. The obtained results are presented as adsorption isotherms: the amount of adsorbed nicotine as a function of equilibrium concentration. These data were obtained from the residual amount of nicotine in the aqueous phase, by the use of UV spectroscopy. The highest amounts of adsorbed nicotine was found for activated carbon and p zeolite (~ mmol?g-1). The attempt to modify the adsorption properties of ZSM-5 zeolite has been also done: ZSM-5 was modified by ion-exchange with VIII group metal (Cu2+ and Fe3+). In addition, the adsorption of nicotine on ZSM-5 zeolite with different Si/Al ratios has been done. It has been noticed that ion-exchange did not improve the adsorption possibilities, while the adsorption was importantly lower in the case of higher silicon content in ZMS-5 structure. 13C NMR spectra were collected for suspensions formed of solid adsorbent and aqueous solution of nicotine; in this way, the part of nicotine molecule which is most probably connected with the adsorbent was recognized.

Uptake and transformation of phenol and chlorophenols by hairy root cultures of Daucus carota, Ipomoea batatas and Solanum aviculare

Hairy root cultures of Daucus carota L., Ipomoea batatas L. and Solanum aviculare Forst were investigated for their susceptibility to the highly toxic pollutants phenol and chlorophenols and for the involvement of inherent peroxidases in the removal of phenols from liquid media. Roots of D. carota grew normally in medium containing 1000 micromol l(-1) of phenol, whilst normal growth of roots of I. batatas and S. aviculare was only possible at levels up to 500 micromol l(-1). In the presence of chlorophenols, normal root growth was possible only in concentrations not exceeding 50 micromol l(-1), except for I. batatas which was severely affected at all concentrations. Despite the reduction in biomass, the growth of S. aviculare cultures was sustained in medium containing up to 2000 micromol l(-1) of phenol or 2-chlorophenol, and up to 500 micromol l(-1) of 2,6-dichlorophenol. The amounts of phenol removed by the roots within 72 h of treatment were 72.7%, 90.7% and 98.6% of the initial concentration for D. carota, I. batatas and S. aviculare, respectively. For the removal of 2,6-dichlorophenol the values were, respectively, 83.0%, 57.7% and 73.1%. Phenols labelled with 14C were absorbed by the root tissues and condensed with highly polar cellular substances as well as being incorporated into the cell walls or membranes. The results suggest that S. aviculare, an ornamental plant, would be best suited for remediation trials under field conditions.

Decomposition of phenol by hybrid gas/liquid electrical discharge reactors with zeolite catalysts

Application of hybrid gas/liquid electrical discharge reactors and a liquid phase direct electrical discharge reactor for degradation of phenol in the presence and absence of zeolites have been investigated. Hybrid gas/liquid electrical discharges involve simultaneous high voltage electrical discharges in water and in the gas phase above the water surface leading to the additional OH radicals in the liquid phase and ozone formation in the gas phase with subsequent dissolution into the liquid. The role of applied zeolites, namely NH4ZSM5, FeZSM5 and HY, were also studied. Phenol degradation and production of primary phenol by-products, catechol and hydroquinone, during the treatment were monitored by HPLC measurements. The highest phenol removal results, 89.4-93.6%, were achieved by electrical discharge in combination with FeZSM5 in all three configurations of corona reactors. These results indicate that the Fenton reaction has significant influence on overall phenol removal efficiency in the electrical discharge/FeZSM5 system due to the additional OH radical formation from hydrogen peroxide generated by the water phase discharge.

Polymers of Intrinsic Microporosity (PIMs): Bridging the Void between Microporous and Polymeric Materials

Novel types of microporous material are required for chemoselective adsorptions, separations and heterogeneous catalysis. This concept article describes recent research directed towards the synthesis of polymeric materials that possess microporosity that is intrinsic to their molecular structures. These polymers (PIMs) can exhibit analogous behaviour to that of conventional microporous materials, but, in addition, may be processed into convenient forms for use as membranes. The excellent performance of these membranes for gas separation and pervaporation illustrates the unique character of PIMs and suggests immediate technological applications.

Phenol adsorption onto powdered and granular activated carbon, prepared from Eucalyptus wood

Eucalyptus grandis sawdust, a major waste from the growing Uruguayan wood industry, was used in previous work to prepare powdered activated carbon (PAC). In the present work, granular activated carbon (GAC) was prepared by mixing PAC, carboxymethyl cellulose as a binder, and kaolin as reinforcer. Ultimate analysis and surface characterization of GAC and PAC were performed. Phenol adsorption was used as a way to compare the characteristics of different PAC and GAC preparations. Kinetics and isotherms of the different GAC and PAC were performed in a shaking bath at 100 rpm and 298 K. Phenol concentrations were determined by UV spectroscopy. Some kinetics parameters were calculated; from kinetics results, external resistance to mass transfer from the bulk liquid can be neglected as the controlling step. Isotherms were fitted to Langmuir and Freundlich models, and corresponding parameters were determined. Maximum phenol uptakes for all carbons were determined and correlated with carbon characteristics. Thermogravimertic analysis (TGA) determinations were performed in order to study adsorption characteristics and conditions for GAC regeneration after its use. The results showed that phenol is preferentially physisorbed on the carbon of the granules, though some chemisorption was detected. No adsorption was detected in the kaolin-carboxymethyl cellulose mixture.

Sorption of Hydrophobic Molecules by Organic/Inorganic Mesostructures

During the synthesis of micelle-templated silica an intermediate inorganic/organic mesostructure is obtained with an hexagonal arrangement of channels filled by surfactant molecules. The ability of such a mesostructure to solubilize organic molecules from an aqueous solution was investigated. To that end, silica/cationic surfactant mesostructures were prepared under various conditions and their stability toward surfactant release in water was first compared in order to select materials as stable as possible. Swelled mesostructures were also used. The sorption from solution of hydrophobic molecules was then studied. The affinity of the molecules for the mesostructures is directly related to their hydrophobic character as it is derived from their octanol/water partition coefficient. A cooperative effect between hydrophobic molecules and the cationic surfactant that stabilizes the surfactant inside the mesostructure was observed. Interaction energies between the solutes and the mesostructures were determined by microcalorimetry. They varied in accordance with the hydrophobic character of the molecule and, at low sorption amounts, they were of the same order of magnitude as the solubilization enthalpies in bulk micelles. When the sorption increases, the surfactant layer in the mesostructure is not allowed to swell as the free micelle does, and steric limitations in the headgroup area render sorption less favorable.