The effect of pH on the adsorption of phenol and chlorophenols onto natural zeolite

Enhanced adsorption of phenolic compounds using biomass-derived high surface area activated carbon: Isotherms, kinetics and thermodynamics

The progress of industrial and agricultural pursuits, along with the release of inadequately treated effluents especially phenolic pollutant, has amplified the pollution load on environment. These organic compounds pose considerable challenges in both drinking water and wastewater systems, given their toxicity, demanding high oxygen and limited biodegradability. Thus, developing an eco-friendly, low-cost and highly efficient adsorbent to treat the organic pollutants has become an important task. The present investigation highlights development of a novel adsorbent (CFPAC) by activation of Cassia fistula pod shell for the purpose of removing phenol and 2,4-dichlorophnenol (2,4-DCP). The significant operational factors (dosage, pH, concentration, temperature, speed) were also investigated. The factors such as pH = 2 and T = 20°C were found to be significant at 1.6 g/L and 0.6 g/L dosage for phenol and 2,4-DCP respectively. Batch experiments were further conducted to study isotherms, kinetic and thermodynamics studies for the removal of phenol and 2,4-DCP. The activated carbon was characterised as mesoporous (specific surface area 1146 m2/g, pore volume = 0.8628 cc/g), amorphous and pHPZC = 6.4. At optimum conditions, the maximum sorption capacity for phenol and 2,4-DCP were 183.79 mg/g and 374.4 mg/g respectively. The adsorption isotherm was better conformed to Redlich Peterson isotherm (phenol) and Langmuir isotherm (2,4-DCP). The kinetic study obeyed pseudo-second-order type behaviour for both the pollutants with R2 > 0.999. The thermodynamic studies and the value of isosteric heat of adsorption for both the pollutants suggested that the adsorption reaction was dominated by physical adsorption (ΔHx < 80 kJ/mol). Further, the whole process was feasible, exothermic and spontaneous in nature. The overall studies suggested that the activated carbon synthesised from Cassia fistula pods can be a promising adsorbent for phenolic compounds.

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.

Mango Seed-Derived Hybrid Composites and Sodium Alginate Beads for the Efficient Uptake of 2,4,6-Trichlorophenol from Simulated Wastewater

In this study, mango seed shell (MS)-based hybrid composite and composite beads (FeCl3-NaBH4/MS and Na-Alginate/MS) were designed. Batch and column experimental analyses were performed for the uptake of 2,4,6-trichlorophenol (2,4,6-TCP) from wastewater. The physicochemical characteristics of both composites were also examined. From the batch adsorption experiments, the best adsorption capacities of 28.77 mg/g and 27.42 mg/g were observed in basic media (pH 9–10) at 308 K for FeCl3-NaBH4/MS and 333 K for Na-Alginate/MS with 25 mg/L of 2,4,6-TCP concentration for 120 min. The rate of reaction was satisfactorily followed by the pseudo-second-order kinetics. Equilibrium models revealed that the mechanism of reaction followed the Langmuir isotherm. The thermodynamic study also indicated that the nature of the reaction was exothermic and spontaneous with both adsorbents. Desorption experiments were also carried out to investigate the reliability and reusability of the composites. Furthermore, the efficiency of the adsorbents was checked in the presence of different electrolytes and heavy metals. From the batch experimental study, the FeCl3-NaBH4/MS composite proved to be the best adsorbent for the removal of the 2,4,6-TCP pollutant, hence it is further selected for fixed-bed column experimentation. The column study data were analyzed using the BDST and Thomas models and the as-selected FeCl3-NaBH4/MS hybrid composites showed satisfactory results for the fixed-bed adsorption of the 2,4,6-TPC contaminants.

Intercalation-Induced Ordered Nanostructure in the Interlayer Modified with Methylviologen by Molecular Dynamics Simulation

Intercalation of phenol in montmorillonite, a representative layered material, has historically been investigated, and modification of the interlayer with methylviologen (Mont-MV) results in color change due to formation of a charge-transfer complex. Its detailed nanostructure, however, has yet been revealed owing to its small gallery height and poor crystallinity. In the present study, we performed molecular dynamics simulation to investigate structural changes in Mont-MV by the intercalation of phenol. The value of the basal spacing of Mont-MV was well consistent with that reported experimentally, and the MV cations were distributed horizontally. Successive intercalation of phenol revealed that the interlayer swelled nonlinearly and both the MV cations and phenol molecules were tilted, which were roughly parallel to each other. The obtained ordered nanostructure was similar to that reported in the charge-transfer complex crystal of the MV cation and the naphthol derivative. Thus, the parallel orientation in the interlayer was found to be the key for the color reaction. Combined with the fact that the phenol molecules interacted with the Mont layers, the role of the MV cation was found to be that of a pillar for providing sufficient gallery height, and the formation of the charge-transfer complex is the secondarily derived function.

Preparation of Activated Carbon Derived from Jordanian Olive Cake and Functionalized with Cu/Cu2O/CuO for Adsorption of Phenolic Compounds from Olive Mill Wastewater

Olive oil production generates solid and liquid wastes that cause various environmental problems due to their high phenols and polyphenols load. Although many treatment methods were investigated to manage these wastes, more research is still needed to identify simple and cost-effective approaches. In this study, activated carbon (AC) was prepared from olive cake waste and functionalized with Cu/Cu₂O/CuO for efficient and selective removal of phenolic content from olive mill wastewater (OMW). AC media were characterized by scanning electron/dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrometry, and Brunauer-Emmett-Teller (BET) surface area analysis. The optimum adsorption parameters were investigated, and the adsorption isotherms, thermodynamics, and kinetics were determined. The adsorption of phenols onto copper oxide AC was best described by the Langmuir adsorption with maximum adsorption capacity of 13.9, 12.7, and 9.9 mg/g at 311, 302, and 293 K, respectively. The adsorption reaction was found to be spontaneous and endothermic where ∆H° and ∆G° were found to be 30.104 kJ/mol and -1.765, -2.839, and -3.723 (kJ/mol) at 311, 302, and 293 K, respectively. In addition, the kinetics data were perfectly fit by the pseudo-second-order model. The activated product derived from recyclable olive cake and enriched with inorganic functionality can offer a cost-effective treatment solution for OMW; thus, reducing both the liquid and solid waste generated from the olive mill industry.

Analysis of a Hybrid Suspended-Supported Photocatalytic Reactor for the Treatment of Wastewater Containing Benzothiazole and Aniline

In this work, a study of the main operating variables affecting TiO2/UV photocatalysis was carried out. The treatment of an industrial effluent containing aniline and benzothiazole from the manufacture of accelerants for vulcanization was performed in a TiO2-supported commercial photoreactor. The degradation of both contaminants was monitored by GC-MS analysis. The proposed experiments were able to properly identify the phenomenon of adsorption, as well as to improve the performance of the commercial photoreactor by adding small amounts of TiO2 in suspension. The removal performance, durability of the photocatalytic material, and energy costs were analysed. The results showed that the use of suspensions intensifies the degradation obtaining an improvement of 23.15% with respect to the use of the supported catalyst. For an aniline and benzothiazole solution, the best operating conditions were found at pH = 12.0, introducing 60.0 mg L−1 of suspended TiO2 together with the existing supported catalyst.

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.

Adsorption of Phenol from Aqueous Solution Using Lantana camara, Forest Waste: Kinetics, Isotherm, and Thermodynamic Studies

The present work investigates the potential of Lantana camara, a forest waste, as an adsorbent for the phenol reduction in wastewater. Batch studies were conducted with adsorbent treated with HCl and KOH to determine the influence of various experimental parameters such as pH, contact time, adsorbent dosage, and phenol concentration. The experimental conditions were optimized for the removal of phenol from wastewater. Equilibrium isotherms for the adsorption of phenol were analyzed by Freundlich, Langmuir, Temkin, and Dubinin-Radushkevich isotherm models. Thermodynamic parameters like the Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were also determined and they showed that the adsorption process was feasible, spontaneous, and exothermic in the temperature range of 298–328 K. The kinetic data were fitted with pseudo-second-order model. The equilibrium data that followed Langmuir model with the monolayer adsorption capacity was found to be 112.5 mg/g and 91.07 mg/g for adsorbent treated with HCl and KOH, respectively, for the concentration of phenol ranging from 25 to 250 mg/L. This indicates that the Lantana camara was a promising adsorbent for the removal of phenol from aqueous solutions.

Phenol removal from wastewater by adsorption on zeolitic composite

It is well known that adsorption is an efficient method of removal of various pollutants from wastewater. The present study examines the phenol removal from water by adsorption on a new material, based on zeolitic volcanic tuff. This compound contains zeolitic tuff and cellulose, another known adsorbent, in a mass ratio of 4 to 1. The performances of the new adsorbent composite were compared with those of a widely used adsorbent material, zeolitic volcanic tuff. The adsorbent properties were tested on batch synthetic solutions containing 1-10 mg L(-1) (1-10 ppm) phenol, at room temperature without pH adjustment. The influence of the adsorbent dose, pH and contact time on the removal degree of phenol from water was investigated. The experimental data were modeled using the Langmuir, Freundlich, and Temkin adsorption isotherms. The Langmuir model was found to best represent our data revealing a monolayer adsorption with a maximum adsorption capacity between 0.12 and 0.53 mg g(-1) at 25 °C, for 2.00 g of adsorbent, depending on the initial phenol concentration. The adsorption kinetic study was performed using a pseudo-first- and pseudo-second-order kinetic models illustrating that phenol adsorption on zeolite composite is well described by pseudo-first kinetic equations. Our results indicated that phenol adsorption on the new adsorbent composite is superior to that on the classic zeolite.

Intrinsic Tween 20 improves release and antilisterial properties of co-encapsulated nisin and thymol

Antimicrobial delivery systems have been proposed as potential solutions to improve effectiveness of antimicrobials in food matrixes by shielding antimicrobials from contacting food matrix components and releasing them continuously. In this work, spray-dried capsules were produced from zein solutions with the same concentrations of nisin and thymol but with varying Tween 20 contents for characterization of release kinetics of antimicrobials and antilisterial properties. At intermediate levels of Tween 20, sustained and more complete release of antimicrobials was observed at pH 6.0 and 8.0. Most capsule samples were more effective than free antimicrobials against Listeria monocytogenes in 2% reduced fat milk, and the best capsule treatment reduced the bacterial population by 2 log CFU/mL more than comparable free antimicrobials after 4 h incubation at 25 °C. Our work demonstrated that nonionic surfactant can be conveniently used to modulate characteristics of delivery systems to effectively improve antimicrobial functions in food systems.

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.

Kinetics and thermodynamics of adsorption of ionizable aromatic compounds from aqueous solutions by as-prepared and oxidized multiwalled carbon nanotubes

The adsorption of 1-naphthylamine, 1-naphthol and phenol on as-prepared and oxidized multiwalled carbon nanotubes (MWCNTs) has been investigated. The results illustrated that both as-prepared and oxidized MWCNTs showed high adsorption capacity for the three ionizable aromatic compounds (IACs) studied. Oxidation of MWCNTs increased the surface area and the pore volume, and introduced oxygen-containing functional groups to the surfaces of MWCNTs, which depressed the adsorption of IACs on MWCNTs. Both Langmuir and Freundlich models described the adsorption isotherms very well and the adsorption thermodynamic parameters (DeltaG degrees, DeltaH degrees and DeltaS degrees) were measured. The adsorption for 1-naphthylamine, 1-naphthol and phenol is general spontaneous and thermodynamically favorable. The adsorption of phenol is an exothermic process, whereas the adsorption of 1-naphthylamine and 1-naphthol is an endothermic process. Results of this work are of great significance for the environmental application of MWCNTs for the removal of IACs from large volume of aqueous solutions.

Influence of organic cations sorption on the point of zero charge of natural zeolite

In this paper, the results of the surface modification of natural zeolite with different amounts (2, 5 and 10 mmol M+/100g) of octadecyldimethylbenzyl ammonium ions (ODMBA) are presented. The obtained organozeolites were denoted as OZ-2, OZ-5 and OZ-10. The degree of ion exchange was followed by determination of amounts of inorganic cations released from zeolite. Results confirmed that reaction between ODMBA and starting zeolite has occurred via ion exchange mechanism. The obtained value for point of zero charge, pHpzc, of natural zeolite was 6.8?0.1, while for OZ-2, OZ-5 and OZ-10 pHpzc was 7.0?0.1. Below the pHpzc, the surfaces of materials are positive while at pH values higher than pHpzc their surfaces are negative. Compared to the pHpzc of natural zeolite, no significant differences in pHpzc was observed for all three organozeolites indicating that obtained products have similar functional groups with similar acid and basic characteristics as starting zeolite. The pHpzc was not dependent on the amount of ODMBA ions at the zeolitic surface and the value of pHpzc for all investigated sorbents is the same for all three electrolyte concentrations indicating that the pHpzc of each material is independent of the ionic strength of KNO3.