Kinetics, thermodynamics and isotherm modeling for removal of nitrate from liquids by facile one-pot electrosynthesized nano zinc hydroxide

Valorization and Upcycling of Acid Mine Drainage and Plastic Waste via the Preparation of Magnetic Sorbents for Adsorption of Emerging Contaminants

Plastic waste poses a serious environmental risk, but it can be recycled to produce a variety of nanomaterials for water treatment. In this study, poly(ethylene terephthalate) (PET) waste and acid mine drainage were used in the preparation of magnetic mesoporous carbon (MMC) nanocomposites for the adsorptive removal of pharmaceuticals and personal care products (PPCPs) from water samples. The latter were then characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), and ζ potential. The results of Brunauer-Emmett-Teller isotherms revealed high specific surface areas of 404, 664, and 936 m2/g with corresponding pore sizes 2.51, 2.28, and 2.26 nm for MMC, MMAC-25%, and MMAC-50% adsorbents, respectively. Under optimized conditions, the equilibrium studies were best described by the Langmuir and Freundlich models and kinetics by the pseudo-second-order model. The maximum adsorption capacity for monolayer adsorption from the Langmuir model was 112, 102, and 106 mg/g for acetaminophen, caffeine, and carbamazepine, respectively. The composites could be reused for up to six cycles without losing their adsorption efficiency. Furthermore, prepared adsorbents were used to remove acetaminophen, caffeine, and carbamazepine from wastewater samples, and up to a 95% removal efficiency was attained.

Modification of natural zeolite clinoptilolite and ITS application in the adsorption of herbicides

The clinoptilolite natural zeolites (NZs) posses low herbicide adsorption capacity demanding acid-, alkali-, or salt chemical modifications that enhance its adsorption. However, this may affect the material structure and charge distribution. Alternatively, zeolites may be synthesized at a high cost and time-consuming process. Consequently, new methods, such as the hydrothermal method, for NZ modification needs to be studied. In this sense, a novel surface-modified zeolite (SMZ), using hexadecyltrimethylammonium bromide (CTAB), in acid media was produced by the hydrothermal method and applied for the adsorption of Atrazine (ATZ), Diuron (DIU) and 2,4-D. Commercial NZ and SMZ were characterized by SEM, XRD, TGA, FT-IR, AA spectroscopy, pHPZC, Zeta potential and N2-physisorption. The SMZ chosen for the adsorption experiments was the one with the highest modification yield and adsorption capacity obtained from a complete design of experiments (CTAB=0.74 ; D=12 Mesh; HCl=0.1 M; t=6 h and T=205 ºC). The adsorption experiments revealed that the SMZ adsorption capacity for the herbicide 2,4-D (qmax=9.02 mg/g) was greater than that obtained for ATZ (qmax=2.11 mg/g) and DIU (qmax=1.85 mg/g), which was explained by the presence of the hydroxyl group and by geometric characteristics of the 2,4-D. Adsorption models' fitting showed that the adsorption of 2,4-D onto SMZ were best described by pseudo-second order kinetic (k2=0.005-0.006 g/mg.min; qe,exp=7.122-8.614 mg/g) and Langmuir isothermal model (KL=0.283-0.499 L/mg; qm=7.167-7.995 mg/g). These results indicate that the hydrothermal method is a viable alternative to enable the use of NZs for the adsorption of emerging contaminants from wastewater.

A novel magnetic adsorbent from activated carbon fiber and iron oxide nanoparticles for 2,4-D removal from aqueous medium

Carbonaceous materials have been widely applied as adsorbents, but there are some factors that affect their efficiency. In this context, advances in nanotechnology provide new and more efficient methodologies for water treatment. This study evaluated the efficiency of a novel carbon-based adsorbent developed from Brazilian polyacrylonitrile textile fiber and functionalized with iron oxide magnetic nanoparticles for the removal of 2,4-dichlorophenoxyacetic acid (2,4-D) from the aqueous medium. The synthesized adsorbent (ACF-Fe3O4) was characterized by FTIR, XRD, VSM, Zeta potential, SEM, EDX, and TEM. The characterization techniques showed that the adsorbent has peaks characteristic of its precursors and superparamagnetic characteristics, confirming the efficiency of the synthesis method. The adsorption tests evaluated the influence of adsorbent dosage, pH of the contaminant solution, contact time and temperature on the removal of 2,4-D. The experimental data were better adjusted by the pseudo-second order kinetic model and by the Langmuir isothermal model. The thermodynamic parameters revealed that the process is exothermic, spontaneous and thermodynamically favorable. Under the best experimental conditions, the maximum adsorption capacity obtained was 51.10 mg g-1 with an adsorbent concentration of 0.33 g L-1, natural pH of the solution, temperature of 288 K at the equilibrium time of six hours. Adsorbent reusage was studied in four desorption cycles. The adsorption mechanism can be explained through π-π bonds, hydrogen bonds and electrostatic interactions. The prepared material presented high-efficiency adsorption capacity of 2,4-D compared to other carbonaceous materials present in the literature, demonstrating its viability for the removal of this contaminant from the aqueous medium.

A comprehensive study on the electronic structure, dielectric and optical properties of alkali-earth metals and transition metal hydroxides M(OH)2

In the present work, the physical properties of alkali-earth metal and transition metal hydroxides are comprehensively investigated using the density functional theory. Here, the alkali-earth metals Ca, Mg, and transition metals Cd, Zn are considered from the II-A and II-B groups in the periodic table of elements. The first principle electronic structure calculations show that these bulk hydroxide materials are direct band gap material. Ca(OH)2 and Mg(OH)2 exhibit an insulating behavior with a very large band gap. However, Cd(OH)2 and Zn(OH)2 are found to be wide band gap semiconductors. The dielectric and optical studies reveal that these materials have a high degree of anisotropy. Hence, the light propagation in these materials behaves differently in the direction perpendicular and parallel to the optical axis, and exhibits birefringence. Therefore, these materials may be useful for optical communication. The calculated electron energy loss suggests that these materials can also be used for unwanted signal noise suppression. The wide band gap makes them useful for high-power applications. Moreover, Ca(OH)2 and Mg(OH)2 are found to be suitable for dielectric medium.

Porous nanocomposites for sorptive elimination of ibuprofen from synthetic wastewater and its molecular docking studies

Pharmaceuticals are a new developing pollutant that is threatening aquatic ecosystems and impacting numerous species in the ecosystem. The aim of this study is the green synthesis of TiO₂-Fe₂O₃-Chitosan nanocomposites in conjunction with Moringa olifera leaves extract and its applicability for ibuprofen removal. Various characterization studies were performed for the synthesized nanocomposites. Box-Behnken design (BBD) is employed to optimize pH, agitation speed, and composite dosage. Equilibrium results show that adsorption process matches with Langmuir isotherm, demonstrating adsorption on the nanocomposite's homogenous surface and follows pseudo-first-order kinetics. Using the BBD, pH, adsorbent dose, and agitation speed were examined as adsorption parameters. Ibuprofen elimination was demonstrated to be most successful at a pH of 7.3, using 0.05 g of nanocomposites at a rotational speed of 200 rpm. Thermodynamic parameters for ibuprofen sorption were carried out and the ΔH and ΔS was found to be 76.23 & 0.233. Molecular Docking was performed to find the interaction between the pollutant and the nanocomposite. UV-vis spectra confirm the 243 nm absorption band corresponding to the nanocomposite's surface plasmon resonances. Fourier transform infrared spectroscopy spectra relate this band to a group of nanocomposites. The findings of this work emphasize the importance of TiO₂-Fe₂O₃-Chitosan nanocomposites for removing ibuprofen from wastewater.

Adsorptive Removal of Rhodamine B Dye Using Carbon Graphite/CNT Composites as Adsorbents: Kinetics, Isotherms and Thermodynamic Study

The study of the adsorption efficiency of new carbon/CNT composites was undertaken to remove a cationic dye, Rhodamine B (RhB), from dye-contaminated wastewater. Indeed, we investigated the effect of different experimental parameters such as time, initial concentration of dye and temperature on the adsorption of RhB by the carbon composites (KS44-0 and KS44-20). The results showed that the adsorption uptake increased with the initial concentration and solution temperature while maintaining a relatively constant pH. The presence of the carbon nanotubes provided more active sites for dye removal and improved the adsorption behavior of Rhodamine B dye. The analysis of the experimental data was conducted using model equations, such as Langmuir, Freundlich and Temkin isotherms. As regards the Freundlich isotherm model, it was the best fit for the equilibrium data obtained from the experiments. The applicability of the pseudo-second-order equation could be explained assuming that the overall adsorption rate is limited by the rate of adsorbate transport that occurs on the pore surfaces of adsorbents. Furthermore, the intraparticle diffusion and Bangham models were used to investigate the diffusion mechanism of RhB absorption onto carbon composites. They showed that multiple adsorption stages occurred simultaneously via pore surface diffusion. Concerning the thermodynamic parameters (∆G°, ∆H°, and ∆S°), they were calculated and explained in the mean of the chemical structure of the adsorbate. Negative standard Gibbs free energy change values (ΔG°_ads) at all temperatures suggested that the adsorption process was spontaneous, and the positive values of the standard enthalpy change of adsorption (∆H°_ads) revealed the reaction to be endothermic. The values of standard enthalpy (ΔH°_ads) and activation energy (E_a) indicated that the adsorption process corresponds to physical sorption. The mechanisms for the removal of Rhodamine B dye from wastewater using carbon composite were predicted. RhB is a planar molecule that is readily adsorbed, in which adsorbed molecules are bound by hydrophobic or other weak interactions due to the π-π interactions between the dyes' aromatic backbones and the hexagonal skeleton of graphite and carbon nanotubes. Thus, the graphite carbon/carbon nanotube composite is believed to play a major role in organic pollutant reduction.

Determination of the Ni(II) Ions Sorption Mechanism on Dowex PSR2 and Dowex PSR3 Ion Exchangers Based on Spectroscopic Studies

This paper estimates the suitability of the strongly basic anion exchangers, Dowex PSR2 and Dowex PSR3, as sorbents of nickel ions in aqueous solutions. These actions are aimed at searching for new solutions due to the growing discharge of nickel into wastewaters, primarily due to its addition to steel. The nickel sorption experiments were conducted under static conditions and resulted in the optimization of pH, phase contact time, initial solution concentration, and temperature. The next step was to calculate the kinetic, isothermal, and thermodynamic parameters. Moreover, the ion exchangers were characterized by means of Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and CHN elemental analysis. It was found that the sorption process was most effective at pH 6 after 240 min and at the temperature of 293 K. The values of the thermodynamic parameters revealed that the adsorption was exothermic and spontaneous. The physicochemical analyses combined with the experimental research enabled determination of the sorption mechanism of Ni(II) ions.

Synthesis of metal-based functional nanocomposite material and its application for the elimination of paracetamol from synthetic wastewater

Non-steroidal anti-inflammatory medicines (NSAIDs) like paracetamol and other substances released into the water system pose serious environmental issues. The current work examines the synthesis of a nanocomposite combined with Moringa olifera aqueous leaf extract as a reducing and stabilizing agent for the green synthesis of nanocomposites. Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Thermogravimetric analysis (TGA), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) were used to investigate metal based functional nanocomposites. The absorption band centered at a wavelength of 243 nm, which corresponds to the surface plasmon resonances of the produced nanocomposite, is confirmed in UV-vis spectra. The distinctive band at this particular wavelength is attributed to a particular group of nanocomposites based on the result from the Fourier transform infrared spectroscopy spectra. The spherical with irregularly shaped aggregates was confirmed by transmission electron microscopy, and the average size of nanoparticles was found to be 1 nm. For the elimination of pharmaceutical contaminants such as paracetamol from aqueous solutions, the adsorptive characteristics of nanocomposites were examined. Temperature, pH, adsorbent dosage, and agitation speed were investigated as adsorption parameters using Box-Behnken Design (BBD). The best removal outcomes were found under the following circumstances: temperature at 303.15 K, pH = 7.5, 0.05 g of nanocomposites at 200 rpm. Based on the adsorption study, the kinetics was found to be pseudo first order (R² > 0.9481) which was validated and fitted by Langmuir isotherm (R² > 0.9973). The adsorption study confirms that it was adsorbed onto the synthesized nanocomposite and found to be present on the homogeneous surface.

Adsorption characteristics of N-rGO for multiple representative trace antibiotics in water

Antibiotics have attracted considerable attention as pollutants; however, they have not been controlled because they cannot be effectively treated via conventional water treatment. In this study, nitrogen-doped reduced graphene oxide (N-rGO) was prepared, and its adsorption performance on multiple trace antibiotics in water was investigated by considering sulfamethoxazole, levofloxacin, clindamycin, tetracycline, penicillin, and chloramphenicol as target pollutants. The results demonstrated that the adsorption process was completed within 60 min at a removal rate exceeding 80%. The adsorption process was in line with the first-order kinetic equation and the Langmuir isothermal adsorption model, with a theoretical maximum adsorption capacity of 1,265.82 mg g^-1 . Meanwhile, the effect of pH value was related to the structure of antibiotics. Simulation studies showed that anions and cations in natural water matrix did not inhibit the adsorption process, whereas humic acid adversely affected the adsorption effect. Characterizations revealed that the N-rGO surface was wrinkled with abundant and diverse oxygen-containing functional groups, which provided suitable conditions for efficient adsorption. The results indicated that N-rGO rapidly and effectively adsorbed trace antibiotics in water, thus providing a basis for constructing an adsorption-catalytic oxidation system. Overall, the proposed method is excellent for treating trace antibiotics in a water environment.

Removal of phosphorus in wastewater by sinusoidal alternating current coagulation: performance and mechanism

The effects of initial total phosphorus (TP) concentration, current density, conductivity and initial pH value on the removal rate of TP and energy consumption, as well as the behaviour and mechanism of phosphorus removal, were investigated by sinusoidal alternating current coagulation (SACC). The flocs produced by SACC were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy FTIR and X-ray photo electron spectroscopy. The thermodynamic and kinetic behaviours of phosphorus removal by iron sol adsorption were also studied in detail. In a self-made SACC reactor equipped with five sets of parallel iron electrodes spacing 10 mm, the removal rate of TP reached 90.9% for a pH 7.0 wastewater with 5 mg dm^-3 TP (κ = 800 μS cm^-1) after being treated for 60 min by applying 2.12 mA cm^-2 sinusoidal alternating current. Compared with direct current coagulation (DCC), SACC exhibits a higher removal efficiency of phosphorus due to the stronger adsorption of the produced flocs. It was found that the adsorption in the SACC process follows pseudo-second-order kinetic with the involvement of the intra-particle model. The adsorption of iron sol to phosphorus was an endothermic and spontaneous process, and its adsorption behaviour can be characterized with Langmuir and Redlich-Peterson isothermal adsorption models. SACC may be employed for the treatment of more complex wastewater combined with biological and/or electrochemical techniques.

Porous Aluminum-Based Metal-Organic Framework-Aminoclay Nanocomposite: Sustainable Synthesis and Ultrahigh Sorption of Cephalosporin Antibiotics

A novel sorbent was synthesized based on MIL-53(Al) MOF grown over an aminoclay (AC) platform, called MIL-53(Al)@AC nanocomposite, via a green and facile hydrothermal method. The nanocomposite was characterized using FT-IR, PXRD, BET, TEM, FESEM, EDS, XPS, TGA, DLS, and zeta potential analyses. BET analysis represented the porous nature and great surface area of MIL-53(Al)@AC. The high crystalline structure for the synthesized nanocomposite was verified using the PXRD pattern. FESEM, EDS, TEM, and XPS analysis proved the successful decoration of MIL-53(Al) over the AC platform. Cephalosporin antibiotics cefixime (CFX) and cephalexin (CPX), which are often present in wastewaters, were utilized to examine the sorption capacity of the nanocomposite. The significant influential factors such as pH, temperature, sorbent amount, ionic strength, and impurity were discussed. At an initial pH of 7.0 ± 0.1, the highest sorption capacities of CFX and CPX on MIL-53(Al)@AC were 784.14 and 747.91 mg g^-1 (T = 298 K, and sorbent amount = 0.1 g L^-1), which were 1.43 and 1.47 times greater compared to that of MIL-53(Al), respectively. The evaluation of experimental results was implemented through the Langmuir and Freundlich isotherm equations. The isothermal data were described nobly by the Freundlich isotherm, which confirmed multilayer adsorption on heterogeneous surfaces (R² > 0.970). A kinetic study indicated that the nanocomposite could adsorb the majority of cephalosporin antibiotics within 30 min. In addition, the experimental data were evaluated via pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. The results indicated that the pseudo-second-order equation agreed more closely with the kinetic data (R² > 0.990). Furthermore, the processes of adsorption were exothermic and spontaneous. The electrostatic attraction, hydrophobic interaction, π-π electron donor-acceptor effect, H-bond, and π-π stacking constituted the main sorption mechanisms. Finally, MIL-53(Al)@AC presented an excellent regeneration performance. Thus, the results revealed the potential application of the MIL-53(Al)@AC nanocomposite for water remediation.

A critical review of various adsorbents for selective removal of nitrate from water: Structure, performance and mechanism

Nitrate is ubiquitous pollutant due to its high water solubility, usually contributing to eutrophication, and posing a threat to aquatic ecosystem and human health. Adsorption approach has been widely used for nitrate removal because of the simplicity, easy operation, and low cost. Adsorbent plays a key role in the adsorptive removal of nitrate. The adsorption performance and adsorption mechanism are determined by the structural feature of adsorbent that is dependent on the preparation method. In this review, various types of adsorbents for nitrate removal were systematically summarized, their preparation, characterization, and adsorption performance were evaluated; the factors influencing the nitrate adsorption performance were discussed; the adsorption isotherm models, kinetic models and thermodynamic parameters were examined; and the possible adsorption mechanisms responsible for nitrate adsorption were categorized; the possible correlation of adsorbent structure to adsorption performance and adsorption mechanism were explained; the potential applications of adsorbents were discussed; finally, the strategies for improving adsorption capacity and selectivity towards nitrate, the challenges and future perspectives for developing novel adsorbent were also proposed. This review will deepen the understanding of nitrate removal by adsorption process and help the development of high-performance adsorbents for selective nitrate removal from water and wastewater.

The use of eggshell membrane for the treatment of dye-containing wastewater: Batch, kinetics and reusability studies

The worldwide consumption of eggs is very high, leading to about 250,000 tons of eggshell membrane (ESM) waste annually. The present research thus investigated the potential use of ESM as an inexpensive and abundant adsorbent for Reactive Red 120 (RR120) in aqueous solutions, a widespread hydrophilic azo dye used in the textile industry. The chemical structure and morphology of ESM were characterized using various spectroscopic methods, including scanning electron microscopy, Fourier transform infrared spectroscopy, and elemental analysis. It was found that natural ESM has a porous structure and surface functional groups that are suitable for the adsorption of the target molecules. The impact of the operating conditions, including the variation in the pH and temperature, on the RR120 sorption capacity and mechanisms of ESM was also analyzed. The maximum monolayer adsorption ability of ESM for RR120 was found to be 191.5 mg/g at 318 K, and the sorption process was spontaneous and endothermic. The adsorption of RR120 onto ESM was significantly influenced by the solution pH and the use of NaOH as eluent, indicating that the driving force for this adsorption was electrostatic attraction. Subsequent desorption experiments using 0.1 M NaOH resulted in satisfactory recovery efficiency. Kinetic, isothermic, and thermodynamic analysis was also conducted to support the experimental findings. The experimental results for the adsorption kinetics of ESM were fitted by a pseudo-second-order model. In conclusion, ESM has the potential to be utilized as an eco-friendly and cost-effective adsorbent for the removal of RR120 from aqueous solutions.

Starch-based magnetic nanocomposite as an efficient absorbent for anticancer drug removal from aqueous solution

In this study, carboxymethyl cassava starch (CMCS)-functionalized magnetic nanoparticles (CMCS@Fe₃O₄) were synthesized via a simple one-pot co-precipitation method using CMCS materials with varying degrees of substitution, and used for the adsorption/removal of doxorubicin hydrochloride (Dox; a clinically available anti-cancer drug) from aqueous solution. The adsorption of Dox was studied using experimental conditions with varied pH, temperature, initial Dox concentration, and CMCS@Fe₃O₄ dosage. The CMCS@Fe₃O₄ adsorbents were characterized by scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and vibrating sample magnetometry. Each CMCS@Fe₃O₄ adsorbent exhibited a cubic inverse spinel iron oxide phase, small particle size, favorable magnetic properties, and good thermal stability. Batch adsorption experiments showed that the Dox adsorption efficiency reached 85.46% at a CMCS@Fe₃O₄ concentration of 20 mg mL^-1 at 303 K in pH 7.0. The adsorption experimental results indicated that the adsorption kinetics followed a pseudo-second-order model and the Langmuir equation. Considering the environmentally nontoxic nature of Fe₃O₄ and starch, the CMCS@Fe₃O₄ material demonstrated significant potential for removing Dox from aqueous solution and in magnetic targeted drug delivery systems for synergistic tumor treatments.

Scalable synthesis of monodisperse and recyclable sulphonated polystyrene microspheres for sustainable elimination of heavy metals in wastewater

Herein, we demonstrate a scalable method for fabricating monodisperse sulphonated polystyrene (SPS) microspheres with abundant sulphonic acid groups and excellent heavy metal removal ability. A comprehensive characterization through SEM, EDS, FT-IR, TG, XRD and XPS confirmed the formation of the SPS microspheres. Take advantage of the abundant sulphonic acid groups on the surface of microspheres, as well as the superior monodisperse properties, adsorption ability of SPS microspheres both in quantity and speed have been enhanced. The adsorption equilibrium obeyed the Langmuir isotherm model with the theoretical maximum capacities of 49.16, 15.38 and 13.89 mg·g-1 for Pb2+, Zn2+ and Cu2+, respectively (30°C, pH = 3.5). Besides, the adsorption equilibriums of Pb2+ onto SPS microspheres can be achieved within only 1 min and the adsorption kinetics can be fitted by a pseudo-second-order kinetics model. More importantly, because of the micron structure of the SPS microspheres, it could overcome the excessive hydrophilia brought by rich sulphonic acid groups and thereby easily separated, which maintain a good recyclable capacity after five regeneration cycles. With the excellent adsorption ability and reusability, SPS microspheres can efficiently handle the polluted water in a convenience and rapid process, which satisfies the sustainable pollution treatment in heavy metals elimination.

Zeolite NaP1 Functionalization for the Sorption of Metal Complexes with Biodegradable N-(1,2-dicarboxyethyl)-D,L-aspartic Acid

The possibility of application of chitosan-modified zeolite as sorbent for Cu(II), Zn(II), Mn(II), and Fe(III) ions and their mixtures in the presence of N-(1,2-dicarboxyethyl)-D,L-aspartic acid, IDHA) under different experimental conditions were investigated. Chitosan-modified zeolite belongs to the group of biodegradable complexing agents used in fertilizer production. NaP1CS as a carrier forms a barrier to the spontaneous release of the fertilizer into soil. The obtained materials were characterized by Fourier transform infrared spectroscopy (FTIR); surface area determination (ASAP); scanning electron microscopy (SEM-EDS); X-ray fluorescence (XRF); X-ray diffraction (XRD); and carbon, hydrogen, and nitrogen (CHN), as well as thermogravimetric (TGA) methods. The concentrations of Cu(II), Zn(II), Mn(II), and Fe(III) complexes with IDHA varied from 5-20 mg/dm³ for Cu(II), 10-40 mg/dm³ for Fe(III), 20-80 mg/dm³ for Mn(II), and 10-40 mg/dm³ for Zn(II), respectively; pH value (3-6), time (1-120 min), and temperature (293-333 K) on the sorption efficiency were tested. The Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin adsorption models were applied to describe experimental data. The pH 5 proved to be appropriate for adsorption. The pseudo-second order and Langmuir models were consistent with the experimental data. The thermodynamic parameters indicate that adsorption is spontaneous and endothermic. The highest desorption percentage was achieved using the HCl solution, therefore, proving that method can be used to design slow-release fertilizers.

Cyclodextrin-based adsorbents for the removal of pollutants from wastewater: a review

Water is a vital substance that constitutes biological structures and sustains life. However, water pollution is currently among the major environmental challenges and has attracted increasing study attention. How to handle contaminated water now mainly focuses on removing or reducing the pollutants from the wastewater. Cyclodextrin derivatives, possessing external hydrophilic and internal hydrophobic properties, have been recognized as new-generation adsorbents to exert positive effects on water pollution treatment. This article outlines recent contributions of cyclodextrin-based adsorbents on wastewater treatment, highlighting different adsorption mechanisms of cyclodextrin-based adsorbents under different influencing factors. The crosslinked and immobilized cyclodextrin-based adsorbents all displayed outstanding adsorption capacities. Particularly, according to specific pollutants including metal ions, organic chemicals, pesticides, and drugs in wastewater, this article has classified and organized various cyclodextrin-based adsorbents into tables, which could pave an intuitive shortcut for designing and developing efficient cyclodextrin-based adsorbents for targeted wastewater pollutants. Besides, this article specially discusses cost-effectiveness and regeneration performance of current cyclodextrin-based adsorbents. Finally, the challenges and future directions of cyclodextrin-based adsorbents are prospected in this article, which may shed substantial light on practical industrial applications of cyclodextrin-based adsorbents.

Treatment of Palm Oil Refinery Effluent Using Tannin as a Polymeric Coagulant: Isotherm, Kinetics, and Thermodynamics Analyses

The refining of the crude palm oil (CPO) generates the palm oil refinery effluent (PORE). The presence of high contents of biochemical oxygen demand (BOD), chemical oxygen demand (COD), turbidity, and suspended solids (SS) in PORE encourages the determination of an effective treatment process to minimize the environmental pollution and preserve aquatic life. In the present study, a biodegradable natural polymer, namely tannin, was utilized as a coagulant to treat PORE. The coagulation experiment was conducted using a jar test apparatus. The tannin coagulation efficiency was evaluated based on the BOD, COD, turbidity, and SS removal from PORE by varying the tannin dose (50-300 mg/L), pH (pH 4-10), treatment time (15-90 min), and sedimentation time (15-90 min). It was found that the maximum removal of BOD, COD, turbidity, and SS was 97.62%, 88.89%, 93.01%, and 90.21%, respectively, at pH 6, a tannin dose of 200 mg/L, 60 min of coagulation time, and 60 min of sedimentation time. Analyses of isotherm models revealed that the Freundlich isotherm model was well fitted with the coagulation study. Kinetics studies show that the pseudo-second-order kinetics model was the well-fitted kinetics model for the BOD, COD, turbidity, and SS removal from PORE using tannin as a polymeric coagulant. The determination of thermodynamics parameters analyses revealed that BOD, COD, turbidity, and SS removal from PORE was spontaneous, exothermic, and chemical in nature. The finding of the present study shows that tannin as a natural polymeric coagulant would be utilized in PORE treatment to avoid toxic sludge generation.

Biodegradable chitosan-ethylene glycol hydrogel effectively adsorbs nitrate in water

Nitrate, existing as inorganic anions in water, possesses high water-solubility and has caused lots of contaminations around the world. It is thus extremely urgent to develop an effective method to effectively remove nitrate from water in a sustainable way. In this study, chitosan-ethylene glycol hydrogel (CEGH) was synthesized using the repeated freezing-thawing procedure. A range of batch sorption experiments were conducted to evaluate CEGH as a nitrate sorbent. The adsorption isotherms of nitrate onto CEGH followed the Langmuir model with coefficient of determination of 0.98 and a maximum Langmuir adsorption capacity of 49.04 mg/g, which is higher than that of other adsorbents. The adsorption of nitrate onto CEGH was affected by pH value and temperature. The results indicate that the main removal mechanism was polarity of CEGH molecules given by functional group O-H and N-H and hydrogen bond interaction between CEGH and nitrate molecules under acidic conditions. Therefore, CEGH, a biodegradable carbon-rich adsorbent, can be widely applied to remove nitrate in wastewater treatment and water body remediation.

High-performance of activated biocarbon based on agricultural biomass waste applied for 2,4-D herbicide removing from water: adsorption, kinetic and thermodynamic assessments

Activated biocarbons were prepared using biomass wastes: sugarcane bagasse, coconut shell and endocarp of babassu coconut; as a renewable source of low-cost raw materials and without prior treatments. These activated biocarbons were characterized by textural analysis, solid-state ¹³C nuclear magnetic resonance spectroscopy, X-ray diffraction and scanning electronic microscopy. Textural analysis results revealed that those activated biocarbons were microporous, with specific surface area values of 547, 991 and 1,068 m² g^-1 from sugarcane bagasse, coconut shell and endocarp of babassu coconut, respectively. The innovation of this work was to evaluate which biomass residue was able to offer the best performance in removing 2,4-dichlorophenoxyacetic acid herbicide (2,4-D) from water by adsorption. Adsorption process of 2,4-D was investigated and the Langmuir and Redlich-Peterson models described best the adsorption process, with R² values within 0.96-0.99. The 2,4-D removal performance were 97% and 99% for the coconut and babassu biocarbons, respectively. q_M parameter values obtained from Langmuir model were 153.9, 233.0 and 235.5 mg g^-1 using sugarcane bagasse, coconut shell and endocarp of babassu, respectively. In addition, the adsorption kinetics were described nicely by the second-order model and the Gibbs free energy parameter values were negative, pointing to a spontaneous adsorption, as well.

Carbon-silica mesoporous composite in situ prepared from coal gasification fine slag by acid leaching method and its application in nitrate removing

Coal gasification fine slag (CGFS) was produced in the coal gasification process which was classified as an industrial solid waste. It was featured with naturally formed amorphous structures and an abundance of silicon, carbon and metal oxides. In this study, on the basis of the composition and structure characteristics of CGFS, a simple hydrochloric acid (HCl) leaching technology was applied to in situ prepare carbon-silica mesoporous composites (CSMCs) from CGFS by fully considering the value of the residual carbon. Special focus was put on the novel mechanism of pore formation in amorphous silica glass microspheres (SGM) during acid leaching. Experimental evidences showed that the metal oxides were uniformly distributed in SGM thus the dissolution of the metal oxides were starting from the surface of SGM, then gradually extending to the interior, and finally leading to form "tree branch" mesoporous channels. In addition, a response surface method was used to predict the optimal reaction conditions and the optimal sample (named as CGFS-O) was successfully prepared. CGFS-O possessed a prominent specific surface area (SSA) (337.51 m²/g) as well as an excellent pore volume (0.341 cm³/g). CGFS-O also exhibited a desirable capacity for NO₃^- removing and the adsorption process was studied detailed by changing different adsorption conditions. Adsorption results proved that CSMCs have the potential to purify wastewater in an economically and environmentally way. Therefore, combined with a proof-of-concept adsorption performance experiment, our study has not only provided a cost-effective strategy to industrially prepare CSMCs, reutilizing CGFS in an environmentally friendly way, but also contributed to the future applications of CSMCs with valuable insights into the pore formation mechanism in SGM during acid leaching process.

Optimization of Mn removal from aqueous solutions through electrocoagulation

Manganese (Mn) was removed from aqueous solutions through electrocoagulation using Al electrodes. Effects of initial Mn concentration (185-405 mg l^-1), the input voltage (1-11 V), inter electrode distance (1-5 cm), and initial pH (2-11) on Mn removal were investigated. Experiments were designed with an orthogonal central composite design on the four variables using the response surface methodology. Analysis of variance was applied and the final Mn concentration was expressed by a mathematical equation. Optimum values of the four factors to get the highest removal were also obtained. As the results showed, electrocoagulation using Al electrodes was able to remove Mn from aqueous solutions efficiently. An equilibrium state was achieved within 195 min. The mathematical model was appropriate to describe experimental data with a high regression coefficient. Kinetics and isotherm data were described appropriately by pseudo-second-order and Langmuir models, respectively. The optimum operating conditions were obtained as pH 9, initial Mn concentration 360 mg l^-1, inter electrode distance 2 cm, and input voltage 10 V. The highest removal efficiency was 92% which is considered a high value.

Zeolites in Phenol Removal in the Presence of Cu(II) Ions-Comparison of Sorption Properties after Chitosan Modification

Nowadays, the contamination of water with phenol is a serious environmental problem. This compound occurs very often with heavy metal ions which makes purification of water even more difficult. This article presents the problem of the removal of phenol from aqueous solutions in the presence of Cu(II) ions on synthetic zeolite NaP1 and zeolite NaP1 modified with chitosan. The adsorbents were determined with the use of Fourier transform infrared spectroscopy (FT-IR), nitrogen adsorption/desorption isotherm, and scanning electron microscopy (SEM). The studies on isotherms and batch kinetics under diversified experimental conditions with respect to initial concentration, contact time, and pH were discussed. Both Cu(II) and phenol adsorption increases with the initial concentration. Different isotherm models correspond well with the data acquired through experiments. The kinetics of adsorption follows the pseudo-second order rate equation. The studies indicate that the obtained sorbents can be employed for efficient removal of phenol from wastewater in the presence of Cu(II) ions.

A novel nanocomposite of aminated silica nanotube (MWCNT/Si/NH2) and its potential on adsorption of nitrite

Several parts of the world have been facing the problem of nitrite and nitrate contamination in ground and surface water. The acute toxicity of nitrite has been shown to be 10-fold higher than that of nitrate. In the present study, aminated silica carbon nanotube (ASCNT) was synthesised and tested for nitrite removal. The synergistic effects rendered by both amine and silica in ASCNT have significantly improved the nitrite removal efficiency. The IEP increased from 2.91 for pristine carbon nanotube (CNT) to 8.15 for ASCNT, and the surface area also increased from 178.86 to 548.21 m² g^-1. These properties have promoted ASCNT a novel adsorbent to remove nitrite. At optimum conditions of 700 ppm of nitrite concentration at pH 7 and 5 h of contact with 15 mg of adsorbent, the ASCNT achieved the maximal loading capacity of 396 mg/g (85% nitrite removal). The removal data of nitrite onto ASCNT fitted the Langmuir isotherm model better than the Freundlich isotherm model with the highest regression value of 0.98415, and also, the nonlinear analysis of kinetics data showed that the removal of nitrite followed pseudo-second-order kinetic. The positive values of both ΔS° and ΔH° suggested an endothermic reaction and an increase in randomness at the solid-liquid interface. The negative ΔG° values indicated a spontaneous adsorption process. The ASCNT was characterised using FESEM-EDX and FTIR, and the results obtained confirmed the removal of nitrite. Based on the findings, ASCNT can be considered as a novel and promising candidate for the removal of nitrite ions from wastewater.

Synthesis of biomass tar-derived foams through spontaneous foaming for ultra-efficient herbicide removal from aqueous solution

Pyrolysis is one of the most important approaches to convert waste biomass into renewable energy and biomaterials, and the tar is the inevitable by-product of this process. In this study, carbon foams were prepared innovatively with biomass tar as the precursor through spontaneous gas foaming approach and used for dicamba removal from aqueous solution. The results showed that prepared carbon foams had unique properties including rich microporous structure and high specific surface area (reaching 1667 m²/g). In addition, the prepared carbons had high thermal stability due to the high graphitic degree. The adsorption results indicated that pH showed a great effect on the adsorption of dicamba onto the prepared carbon foams. The carbon foam exhibited ultra-fast dicamba removal and ultra-high adsorption capacity of 891.74 mg/g at room temperature. The adsorption process was well described by pseudo-second-order kinetics and Langmuir isotherm models. The thermodynamic study indicated dicamba adsorption onto the prepared carbon foams was a spontaneous and exothermic process. In addition, the good reusability from recovery test demonstrated that the prepared carbon foams had promising potential for dicamba removal from aqueous solution.

Zr4+ ions embedded chitosan-soya bean husk activated bio-char composite beads for the recovery of nitrate and phosphate ions from aqueous solution

Removal of nitrate and phosphate ions using Zr4+ ions embedded chitosan-soya bean husk activated bio-char composite beads (Zr-CS-SAC) was carried out by batch mode to overcome the environmental problems due to eutrophication. The adsorbent was well characterized by using Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) analysis with energy dispersive X-ray analyzer (EDX), X-ray diffraction analysis (XRD), Brunauer-Emmett-Teller surface analyzer (BET), thermo-gravimetric analysis (TGA) and differential thermal analysis (DTA) etc. The adsorption equilibrium models of Langmuir, Freundlich and D-R isotherms were evaluated and the results described that the Freundlich model was the best for both the adsorbates of nitrate and phosphates ions with respective capacities of 90.09 and 131.29 mg g-1 at 30 °C. Studies on thermodynamic parameters revealed the endothermic and spontaneous nature of the adsorption. Different kinetic models were studied and found that pseudo-second-order kinetic data were well fitted for adsorption process. These results suggested that Zr-CS-SAC composite beads as a promising adsorbent for the removal of nitrate and phosphate ions from water with good removal efficiency, adsorbability, recyclability and non- toxicity.

Efficient removal of copper ions using a hydrogel bead triggered by the cationic hectorite clay and anionic sodium alginate

Sodium alginate (SA) is a linear biopolymer, which is the nontoxic, biodegradable, and rich in carboxyl and hydroxyl groups. In the paper, the SA-based hydrogel bead was prepared by the cationic hectorite clay and anionic sodium alginate with a simple ionic gelation method under freeze-drying, and the adsorption properties were evaluated by the removal of copper ions from aqueous solutions. The composites were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption isotherm (BET), thermal analysis (TG), and Fourier transform infrared spectroscopy (FT-IR). The pseudo-first-order and pseudo-second-order kinetic models were used to describe the kinetic data and the Langmuir, Freundlich, Dubinin-Radushkevich (D-R), and Temkin models were applied to describe the adsorption isotherms. The results showed that the adsorption process was found to follow the Freundlich isotherm model and the maximum sorption capacity was observed to be 160.28 mg/g under the initial concentration from 10 to 700 mg/L at 45 °C. Adsorption kinetics data fitted well with pseudo-second-order rate model. The porous structure of the composite was responsible for the adsorption of Cu²⁺ ions. But the adsorption ability could be improved by pH. Finally, the adsorption mechanism was suggested. Graphical abstract.

Highly efficient Cd(II) adsorption using mercapto-modified bentonite as a novel adsorbent: an experimental design application based on response surface methodology for optimization

We report the optimization with response surface methodology (RSM) for adsorption conditions required for removal of Cd(II) from an aqueous environment with 3-mercaptopropyl trimethoxysilane-modified bentonite (MMB). Central composite design (CCD) in RSM was used to optimize the most significant adsorption variables of initial pH, temperature (°C), initial Cd(II) concentration (C_o, mg L^-1) and adsorbent dosage (g). With the quadratic model equation obtained from CCD, the optimum values were determined as initial pH 6.40, temperature 20 °C, C_o 49.55 mg L^-1 and adsorbent dosage 0.17 g. Under optimum conditions, the optimum adsorption amount of Cd(II) was 27.55 mg Cd(II)/g adsorbent and adsorption yield was 94.52%. The obtained results showed that the Langmuir and Dubinin Radushkevich (D-R) adsorption isotherms were more suitable for adsorption equilibrium data. The kinetic studies indicated that the pseudo-second-order kinetic model was fitted to the adsorption kinetic data. Additionally, thermodynamic studies indicated that the adsorption process was spontaneous and exothermic. As a result, MMB can be chosen as an effective adsorbent for treating heavy metals such as Cd(II) in wastewater and removing them from aqueous solutions. Furthermore, it is thought that it will positively contribute to the literature since the adsorbent-adsorbate combination (MMB-Cd(II)) is used for the first time.

Selective removal of lead ions from aqueous solutions using 1,8-dihydroxyanthraquinone (DHAQ) functionalized graphene oxide; isotherm, kinetic and thermodynamic studies

An anthraquinone - graphene structure was fabricated and applied for the removal of lead(ii) from aqueous solution. The equilibrium occurred in about 10 min revealing the high adsorption rate at the beginning of the process. The maximum Pb(ii) adsorption capacity of the Fe3O4@DHAQ_GO nanocomposite was about 283.5 mg g-1 that was observed at 323 K and pH 5.5. The Pb(ii) adsorption ability increased with the increasing pH. The isotherm and kinetic studies indicated that the Sips isotherm model and the linear form of the pseudo-second kinetic model had a better fit with the experimental results. The positive value of ΔH 0 indicated endothermic interactions between Pb(ii) and Fe3O4@DHAQ_GO. The negative ΔG 0 indicated that the reactions are spontaneous with a high affinity for Pb(ii). The positive ΔS 0 values indicated increasing randomness at the solid-solute interface during the adsorption process. The selective removal of Pb(ii) by the nanocomposite confirms the presence of higher-affinity binding sites for Pb(ii) than Cd(ii), Co(ii), Zn(ii), and Ni(ii) ions. Furthermore, the Fe3O4@DHAQ_GO nanocomposite revealed an excellent preferential adsorbent for Pb(ii) spiked in drinking water samples containing natural ion matrices. EDTA-2NA 0.01 N was found to be a better elution agent than HCl 0.1 M for the nanocomposite regeneration. After five adsorption/desorption cycles using EDTA-2NA 0.01 N, more than 84% of the adsorbed Pb(ii) was still desorbed in 30 min. Capturing sub-ppm initial concentrations of Pb(ii) and the capability to selectively remove lead from drinking water samples make the Fe3O4@DHAQ_GO nanocomposite practically convenient for water treatment purposes. High adsorption capacity and facile chemical synthesis route are the other advancements.

Adsorption characteristics of metal–organic framework MIL-101(Cr) towards sulfamethoxazole and its persulfate oxidation regeneration

A metal–organic framework, MIL-101(Cr), was used to adsorb sulfamethoxazole (SMZ) in water and activated persulfate (PS) oxidation was investigated to regenerate SMZ-saturated MIL-101(Cr). Adsorption and oxidation were combined in this study. MIL-101(Cr) was characterized by SEM, BET, XPS and FT-IR analyses. Effects of various operating parameters on adsorption efficiency were studied. The dosages of persulfate for SMZ desorption and oxidation were investigated. The results showed that the recommended pH was 6–8 for SMZ adsorption and optimum MIL-101(Cr) dosage was 0.1 g L⁻¹. SMZ adsorption by MIL-101(Cr) was a spontaneous process and nearly exothermic. Saturation adsorption capacity was achieved in 180 s and the adsorption followed the pseudo-second-order model. The maximum adsorption amount of MIL-101(Cr) to SMZ was 181.82 mg g⁻¹ (Langmuir). MIL-101(Cr) also showed good adsorption capacities for sulfachloropyridazine (SCP), sulfamonomethoxine (SMM), and sulfadimethoxine (SDM). Persulfate was helpful for SMZ desorption from the surface of saturated MIL-101(Cr) and sufficient persulfate could simultaneously oxidize the SMZ. XPS analysis showed that the structure of MIL-101(Cr) was stable after the persulfate oxidation process. Regenerated MIL-101(Cr) had the same level of adsorption capacity as fresh MIL-101(Cr). An adsorption–oxidation combined process may be set up based on the results. This study provides basic data for the deep treatment of organic micropollutants in urban water bodies.

A metal–organic framework, MIL-101(Cr), was used to adsorb sulfamethoxazole (SMZ) in water and activated persulfate (PS) oxidation was investigated to regenerate SMZ-saturated MIL-101(Cr).