Freundlich Isotherm Research Articles

Diclofenac sodium removal by powdered activated carbon of coconut endocarp: process optimization, kinetics, and isotherms

ABSTRACT Emerging contaminants (ECs) have been detected in various environmental compartments, especially in aquatic bodies. Among EC, diclofenac sodium (DS) is one of the most ecotoxic and causes hemodynamic changes, thyroid tumors, and adverse effects under chronic exposure. Therefore, some countries have adopted restrictive legislation, encouraging the development of technology to mitigate this situation. Among the available water treatment processes, adsorption is an effective alternative in technical and economic aspects. In this context, this study aimed to evaluate, on a bench scale, the efficiency of DS removal in powdered activated carbon (PAC) of coconut endocarp. The adsorption of DS was analyzed through central composite design (CCD), using four factors: diclofenac sodium concentration (CDS from 50 to 450 mg · L−1), adsorbent concentration (CPAC from 0.2 to 5 g · L−1), contact time (Ct from 5 to 45 min), and pH (from 5 to 9). The results supported response modeling for adsorption capacity, pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetics, intraparticle diffusion (IPD), and Langmuir and Freundlich isotherms. DS demonstrated an affinity for adsorption on PAC. The maximum adsorption capacity was 169.39 mg · g−1 for PAC (CDS of 331.64 mg · L−1, CPAC of 0.2 g · L−1, Ct of 40.6 min, and pH 5) obtained through duplicate confirmation batches.

Fabrication of CaCO3 Microcubes and Mechanistic Study for Efficient Removal of Pb from Aqueous Solution

Pb(II) contamination in aquatic environments has adverse effects on humans even at a low concentration, so the efficient removal of Pb at a low cost is vital for achieving an environmentally friendly, sustainable, and healthy society. A variety of CaCO3-based functional adsorbents have been synthesized to remove Pb, but the adsorption capacity is still unsatisfactory. Herein, calcite CaCO3 microcubes/parallelepipeds are synthesized via simple precipitation and a hydrothermal approach and found to outperform previously reported nano-adsorbents considerably. The CaCO3 achieves a high removal efficiency for Pb(II) (>99%) at a very low dosage (0.04–0.1 g/L) and an initial Pb(II) concentration of 100 mg/L. The CaCO3 presents an excellent adsorption capacity of 4018 mg/g for Pb(II) removal and depicts good stability over a wide range of pH 6–11. The maximum adsorption kinetics are fitted well by the pseudo-second-order kinetic model, whereas the Freundlich isotherm delineates the adsorption data at equilibrium well, indicating a multilayer adsorption process. The ex situ study confirms that the Pb(II) adsorption mechanism by CaCO3 can be attributed to the rapid metal-ion-exchange reaction between Pb(II) and Ca2+. Furthermore, a red shift in the Fourier Transform Infrared (FTIR) spectroscopy peak from 1386 cm−1 to 1374 cm−1 of CaCO3 after Pb removal indicates the adsorption of Pb onto the surface. This adsorbent provides an opportunity to treat wastewater and can be extended to remove other toxic heavy metals.

Removal of As(V) and Cr(VI) using quinoxaline chitosan schiff base: synthesis, characterization and adsorption mechanism

AbstractElevated Arsenic and Chromium levels in surface and ground waters are a significant health concern in several parts of the world. Chitosan quinoxaline Schiff base (CsQ) and cross-linked chitosan quinoxaline Schiff base (CsQG) were prepared to adsorb both Arsenate [As(V)] and Chromium [Cr(VI)] ions. The thermo-gravimetric analysis (TGA), X-ray diffraction analysis (XRD), and Fourier-transform infrared spectroscopy (FTIR) were used to investigate the prepared Schiff bases (CsQ) and (CsQG). The UV–VIS spectra showed a shift in the wavelength area of the modified polymer, indicating the reaction occurrence, besides the variation of the shape and intensity of the peaks. The XRD patterns showed the incensement of the amorphous characteristic. On the other hand, the thermal stability of the modified polymers is better according to TGA studies; also, the morphology of the modified chitosan was investigated before and after crosslinking (CsQ and CsQG) using a scanning electron microscope (SEM) where the surface was fall of wrinkles and pores, which then were decreased after cross-linking. Contact time, temperature, pH, and initial metal ion concentration were all studied as factors influencing metal ion uptake behavior. The Langmuir, Temkin, Dubinin–Radushkevich, and Freundlich isotherm models were used to describe the equilibrium data using metal concentrations of 10–1000 mg/L at pH = 7 and 1 g of adsorbent. The pseudo-first-order and pseudo-second-order kinetic parameters were evaluated. The experimental data revealed that the adsorption kinetics follow the mechanism of the pseudo-second-order equation with R2 values (0.9969, 0.9061) in case of using CsQ and R2 values (0.9989, 0.9999) in case of using CsQG, demonstrating chemical sorption is the rate-limiting step of the adsorption mechanism. Comparing the adsorption efficiency of the synthesized Schiff base and the cross-linked one, it was found that CsQ is a better adsorbent than CsQG in both cases of As(V) and Cr(VI) removal. This means that cross-linking doesn’t enhance the efficiency as expected, but on the contrary, in some cases, it decreases the removal. In addition, the newly modified chitosan polymers work better in As(V) removal than Cr(VI); the removal is 22.33% for Cr(VI) and 98.36% for As(V) using CsQ polymer, whereas using CsQG, the values are 6.20% and 91.75% respectively. On the other hand, the maximum adsorption capacity (Qm) for As(V) and Cr(VI) are 8.811 and 3.003 mg/g, respectively, using CsQ, while in the case of using CsQG, the Qm value reaches 31.95 mg/g for As(V), and 103.09 mg/g for Cr(VI).

Comprehensive Study on Amino‐Modified Salix Wood Powder Membranes: Preparation, Adsorption Mechanism and Desorption Conditions for Efficient Chlortetracycline Removal

The wastewater of Chlortetracycline (CTC) poses a threat to the balance of aquatic ecosystems, promoting the formation and dissemination of antibiotic‐resistant bacterial strains in the aquatic environment. Moreover, such pollution can directly or indirectly affect human health through water sources, exacerbating the issue of antibiotic resistance. In response to this pollution challenge, Amino‐modified salix wood powder membrane(ASPPM) was prepared by phase transition and wet spinning techniques, aimed at removing CTC from water bodies. Adsorption experiment results show that the ASPPM maximum adsorption capacity for CTC is 458.99 mg/g. In the desorption process, the highest desorption rate of ASPPM for CTC was 79.65%. By fitting pseudo‐first‐order and pseudo‐second‐order kinetic models, it is found that the adsorption process of ASPPM on CTC is predominantly chemical adsorption. By fitting three isotherm models, it is found that the adsorption behavior of ASPPM on CTC is more in accordance with the Freundlich isotherm model, indicating multilayer adsorption on heterogeneous surfaces. The preparation of ASPPM study not only transforms renewable biomass materials into effective tools for environmental purification but also offers a cost‐effective new approach for sustainable environmental management, expanding the application of biomass materials in the field of environmental protection.

Unripe Plantain Peel Biohydrogel for Methylene Blue Removal from Aqueous Solution

Dye contamination is a serious environmental issue, particularly affecting water bodies, driving efforts to synthesize adsorbent materials with high dye-removal capacities. In this context, eco-friendly and cost-effective materials derived from bioresidues are being explored to recycle and valorize waste. This study investigates the synthesis, characterization, and application of a biohydrogel made from unripe plantain peel (PP), modified with carboxymethyl groups and crosslinked using varying concentrations of citric acid (CA), an eco-friendly and economical organic acid. The materials were characterized by ATR-FTIR, TGA, and SEM, confirming the successful synthesis of hydrogels, which exhibited rough, irregular surfaces with micropores. Additionally, the materials were analyzed for their pH point of zero charge, swelling capacity, and methylene blue (MB) dye removal efficiency. The results indicate that the biohydrogel formed with 1% CA exhibited the most favorable characteristics for MB removal. Kinetic studies revealed that the adsorption mechanism is pH-dependent, with equilibrium being reached in 720 min. The Freundlich isotherm model provided the best fit for the adsorption data, suggesting a heterogeneous surface and a multilayer adsorption process, with a maximum retention capacity of 600.8 ± 2.1 mg/g at pH 4. These findings contribute to the development of cost-effective and efficient materials for dye removal, particularly from water bodies.

Mineral Heterostructures for Simultaneous Removal of Lead and Arsenic Ions

This study focuses on Pb2+ and As(V) adsorption on mineral heterostructures based on a mixture of Si, Fe, and Ti oxides (MOHs). Various techniques were performed to analyze the morphological and structural properties of the synthesized metal oxide samples. In addition to the experimental optimization of the parameters determined by the response surface method (RSM), the effects of pH, adsorbent dosage, temperature, and contact duration on the batch and column system adsorption efficiency of single-component and simultaneous lead and arsenate removal were tested. The pseudo-second-order kinetic model and Weber–Morris model were more relevant to the adsorption on the metal(loid)s. The adsorption of Pb2+ was related to the Langmuir isotherm model, while the adsorption of As(V) was fitted to the Freundlich isotherm model. The thermodynamic parameters indicate the spontaneity of the adsorption process with a low endothermic character. The MOHs were more effective in removing Pb2+ and As(V) in the multi-component system (87.7 and 46.1%, respectively) than in the single-component system (56.3 and 23.4%, respectively). This study demonstrates that mineral heterostructures can be effectively used to remove cations and anions from water systems, and due to their fast kinetics, they can be applied to the needs of rapid interventions after pollution.

Enhanced Adsorption and Photocatalytic Activity of Vertically Oriented TiO2 Nanotube Arrays by Li Incorporation

A highly efficient, solid, and easily maneuverable adsorbent and photocatalyst, Li‐incorporated titanate nanotubes that manifest adsorption efficiency of 98.1% and photocatalytic efficiency of 99.6% in 60 min and 97.8% and 98.5%, respectively, in a shorter duration of 20 min, is synthesized by a facile two‐stage electrochemical technique. The modified nanotubes exhibit good cyclic stability of 93.7% photodegradation of malachite green dye after three continuous cycles. The adsorption data show the highest correlation for second‐order pseudo kinetics and Freundlich isotherm, suggesting multilayer chemisorption with an adsorption capacity of kF ≈ 219.51 mg1–1/nL1/ng−1. Fourier transform infrared spectroscopy (FTIR) analysis of the adsorbent before and after the adsorption corroborates the findings. X‐Ray photoelectron spectroscopy reveals the formation of a larger number of oxygen vacancies (Ti3+/Ti2+) that facilitate more carrier release for the production of reactive oxygen species during photocatalysis. X‐Ray diffraction and transmission electron microscopy analysis confirm a secondary rutile phase formation on Li doping that promotes heterogeneous multilayer adsorption. Field‐emission spectroscopic studies reveal a change in the morphology of the doped tubes with porous aggregate formation on the surface. The structural, morphological, and compositional change brought about by Li incorporation facilitates the use of titania nanotubes as an efficient adsorbent cum photocatalyst in the removal of malachite green dye.

Boosting Electrochemical Degradation of Water Pollutants Using Sulfur‐Rich Porous Polyimide‐Derived Laser‐Induced Graphene Catalytic Membrane

Water pollution is an inevitable concern associated with technological advancement. To address this problem, it is necessary to significantly shorten the manufacturing process of porous materials while enabling effective pollutant removal. Herein, a facile, rapid, and scalable approach is reported to obtain sulfur‐doped hierarchically porous laser‐induced graphene (S‐LIG) as a catalytic membrane with three‐dimensional networks by localized laser irradiation, along with possible adsorption and electrochemical degradation mechanisms for pollutant removal. S‐LIG is derived from sulfur‐containing porous polyimide film which is prepared via thermally induced phase separation followed by stepwise thermal imidization. Methylene blue (MB) adsorption behavior on the S‐LIG membrane closely fits the pseudo‐second‐order and Freundlich isotherm models, suggesting a complex sorption mechanism, including both strong chemical interaction and physical adsorption. Furthermore, S‐doping enhances catalytic activity for generating reactive oxygen species (ROS), aiding MB degradation via indirect oxidation, and improves direct oxidation on the anode by accelerating electron transfer at the electrodes. This results in a stable 93% MB degradation at a low 1.5 V after 24 h. Additionally, the impact of solution pH reveals that electrostatic attraction forces under basic conditions and the high generation of ROS under acidic conditions favor adsorption and electrochemical oxidation.

Methylene Blue Adsorption Using Boric Acid Functionalized Activated Carbon: Kinetics, Isothermal, and Thermodynamic Studies

AbstractIn this study, the activated carbon (AC) was prepared from Sesbania sesban plant stem. Boric acid (H3BO3) was used as an activating agent. During calcination, the optimized temperature was kept upto 500 °C for 2 h. The prepared adsorbents were characterized using various techniques such as FT‐IR, scanning electron microscopy, energy dispersive x‐ray spectroscopy, and thermogravimetric analyzer. The prepared adsorbents were used for the removal of methylene blue (MB) dye adsorption. The adsorption experiments were conducted at different pHs such as (2–11), doses (0.0025–0.020 mg), times (30–300 min), MB initial concentrations (100–600 mg L−1), and temperatures (298–318 K), respectively. The maximum MB uptake capacity of the prepared adsorbent was 1380 mg g−1 under optimized adsorption conditions. Furthermore, the kinetic study is well described by pseudo‐second order, whereas the isothermal study showed the Freundlich isotherm was better followed by the equilibrium data. Based on thermodynamic studies, the negative values of ΔG° and ΔH° revealed that the MB adsorption process is spontaneous and exothermic in nature. However, the negative ∆Sxg° value indicates that solid‐solute interaction decreased randomness in the adsorption systems. The overall studies of AC showed that it was better to remove MB from an aqueous solution.

Eco-friendly synthesis and surface modification of ZnO nanoparticles using Pueraria montana root extract: enhanced photocatalytic performance with trisodium pyrophosphate

ABSTRACT The synthesis of zinc oxide (ZnO) nanoparticles using Pueraria montana (kudzu) plant extracts highlights advancements in green nanotechnology. This study explores the use of Pueraria montana roots, rich in phytochemicals such as phenols, terpenoids and flavonoids, which serve as natural reducing and stabilizing agents for nanoparticle synthesis. The eco-friendly production and surface modification of ZnO nanoparticles were achieved using these plant extracts, enhancing their photocatalytic performance with trisodium pyrophosphate (TSPP).Characterization techniques, including XRD, TEM, and FE-SEM, confirmed the nanoparticles’ crystalline structure, with a BET surface area of 14.01 m²/g and a type II adsorption isotherm. The synthesized nanoparticles exhibited exceptional dye degradation capabilities, achieving 99.9% removal of malachite green (MG) and 97.78% for aniline blue (AB). Kinetic analysis revealed a steady-state rate constant (k) of 2 × 10⁻⁴ min⁻¹ for MG where as the response rate constant(k) for the photocatalytic degradation of AB using modified ZnO nanostructures was 3.0 × 10−3 min−1 allowing near-total dye removal within 600 minutes for MG and 350 min for AB . Adsorption studies were well described by Langmuir and Freundlich isotherms, indicating maximum adsorption capacities of 59.7 mg/g for MG and 61.2 mg/g for AB. Surface modification with TSPP improved charge carrier separation and enhanced the generation of reactive oxygen species under UV exposure, further increasing dye degradation efficiency.Statistical analysis indicated high reproducibility, with close mean adsorption values of 99.125 for MG and 97.3125 for AB, supported by small standard deviations. The findings affirm the potential of using Pueraria montana in synthesizing efficient photocatalysts, providing a sustainable and cost-effective approach for water treatment applications. Overall, this research underscores the effectiveness of plant-based materials in advancing eco-friendly nanotechnology solutions.

Machine learning integration with response surface methodology to enhance the removal efficacy of arsenate (V) through sulfur-functionalized mxene coated QPPO/PVA AEM

Arsenic, a poisonous and carcinogenic heavy metal in drinking water, presents severe health risks to humans, including skin lesions, neurological damage, and circulatory disorders. Despite extensive research efforts have been carried out on removing arsenate (As(V)) using membrane technologies, however, there remains a critical need to further enhance membrane removal efficacy to achieve maximum reusability. Thus, to minimize this challenge, herein we explore the impact of S-functionalized Mxene coating over the surface of quaternary ammonium poly (2,6-dimethyl-1,4-phenylene oxide)/polyvinyl alcohol (QPPO/PVA) anion exchange AEM membrane against As(V) removal. To optimize and validate adsorption efficacy, response surface methodology (RSM) study was carried out using a central composite design (CCD) with R2 = 0.995. The significance of these variables was also confirmed by CCD matrix, yielding statistically significant results (p < 0.0001). Adsorption efficacy was further enhanced by employing different machine learning (ML) regression models to finely tune experimental parameters. Among ML models, Random Forest Regression (RFR) has shown highest predictive accuracy (R2 = 0.929, RMSE = 4.57 mg L-1) and identified As(V) concentration as the most influential factor affecting adsorption efficacy. ML-optimization has shown maximum adsorption efficacy at pH (3), contact time (5 min), and As(V) concentration (50 mg L−1). Freundlich isotherm model has shown adsorption capacity of 413 mg/g (R2 = 0.997), while pseudo-second-order kinetic model reflected R2 of 0.989. Thermodynamic assessments (ΔGᵒ, ΔH°, ΔS°) confirmed the process as spontaneous. To the best of our knowledge, this is the first study in which ML is employed to design highly efficient and reliable membranes, providing a novel approach to enhance membrane-based remediation strategies.

Efficient biosorption of Zn(II), Cd(II), and Pb(II) by Aspergillus brasiliensis in industrial wastewater coupled with electrochemical monitoring via sensor enhanced with modified silver nanoparticles.

This work investigates the use of Aspergillus brasiliensis, this particular species of Aspergillus, as a biosorbent for the first time. It is employed to biosorption Zn(II), Cd(II), and Pb(II) and combines the biosorption experiments with electrochemical measurements for in situ analysis. For the experiments, a batch system was employed with the dead biomass. In order to determine the biosorption capacity, the impact of several operational parameters was examined, including pH, temperature, agitation speed, contact time, and initial metal concentration, and the optimum values were 5, 30°C, 150rpm, 2h, and 150ppm, respectively. Using 0.2g biomass in 100mL solution, the maximal uptake of Zn(II), Cd(II), and Pb(II) at ideal conditions was determined to be 33.67, 24.51, and 36.76, respectively. The Langmuir and Freundlich isotherm model was studied for the biosorption process. An electrochemical sensor using nanomaterials is designed and constructed to monitor the concentration of these metals. The silver nanoparticles functionalized with thiosemicarbazide and 6-mercaptohexanoic acid (mercaptohexanoylhydrazinecarbothioamide-coated silver nanoparticles, MHHC-AgNPs) linked to the carboxylated multi-walled carbon nanotubes (MWCNTs) were utilized for glassy carbon electrode modification (MHHC-AgNPs/MWCNTs/GCE). The concentration range of Zn(II) is 0.7-173µg/L, Cd(II) is 1.18-293µg/L, and Pb(II) is 2.17-540µg/L. The detection limits for Zn(II), Cd(II), and Pb(II) are 0.036µg/L, 0.15µg/L, and 0.16µg/L, respectively. Under optimized conditions, these results were obtained using the differential pulse anodic stripping voltammetry method (DPASV). The successful detection of Zn(II), Cd(II), and Pb(II) was achieved by effectively preventing interference from other common ions. It was effectively employed for measuring ions in industrial wastewater, and the results obtained aligned with those acquired from an atomic absorption spectrometer (AAS). Thus, Aspergillus brasiliensis species, along with this electrochemical sensor, can be used to remediate and monitor environmental pollution, Zn(II), Cd(II), and Pb(II), successfully.

Bio-sorption of methylene blue using Datura stramonium leaves as adsorbent

Present study was accomplished to prospect the viability of using the Datura stramonium leaves powder (DS) as an adsorbent to remove the methylene blue from aqueous solution. The physico-chemical characteristics of the studied adsorbent were examined. The optimum parameters such as contact time, particle size, absorbent dose, initial methylene blue concentration, and pH were investigated by performing batch experiments models. The kinetics and the isotherms adsorption were evaluated by varying the initial concentration and using the optimum parameters. The optimum of contact time is 30min, with a removal capacity of 89.60 %. The optimal adsorbent concentration to reach the maximum removal of methylene blue (89.54 %) is 18 g/L. An initial methylene blue concentration of 50 ppm is ideal to reach the maximum capacity of removal (92.72 %). The optimum particle size is 80 mm. The kinetics of the adsorption process are in accordance with the pseudo-second order model. Experimental values of the adsorption capacity are close proximity to the optimum values predicted by the pseudo-second order model. Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Harkin-Jura and Hasley isotherms were applied to represent the data obtained from the adsorption studies. The highest R2 values were related to Freundlich, Dubinin-Radushkevich and Hasley isotherm models.

Development of an eco-friendly geopolymer mortar using slag and fly ash with high bentonite content for thermal and environmental applications

The construction industry is exploring the use of low-cost waste materials to create eco-friendly geopolymer mortar binders. Our study aims to develop various environmentally friendly geopolymer mortar mixes for thermal and adsorption applications using natural materials like bentonite and industrial by-products such as ground-granulated blast furnace slag and fly ash. Ternary geopolymer mortar pastes are prepared using equimolar amounts of slag (GBFS) and fly ash (FA), with 6%, 8%, 10%, and 12% weight of bentonite (BC) from the total geopolymer weight to study the bentonite replacement effect. The prepared mortar are tested for their physico-chemical, mechanical, adsorption, and thermal stability properties (300 °C to 900 °C). The adsorption behavior of eco-friendly geopolymer mortar mixes against crystal violet dye in aqueous solutions is also identified. The study found that adding 6% bentonite to the slag/fly ash-based geopolymer mortar mix yielded the highest mechanical characteristics. Moreover, all the ternary geopolymer mortar mixes exhibited excellent thermal stability up to 900 °C. In adsorption study, the results indicated that the mortar mixes had excellent capacities and adhered well to the Freundlich isotherm model, suggesting potential applications in treating wastewater. Using bentonite in slag/fly ash geopolymer mortar offers a sustainable, cost-effective, and heat-resistant alternative to traditional cement binders.

Versatile silicate-modified hydrochar based on Scutellaria baicalensis-residue for efficiently removing heavy metal-antibiotic co-contamination and relevant bio-contaminants from wastewater

In this study, we utilized typical Chinese medicine herbal residues (CMHRs)－Scutellaria baicalensis (Scutellaria baicalensis Georgi) residue (SR), as the raw material and employed Na2SiO3 and Fe2(SO4)3 as modifying agents to fabricate a novel and multifunctional hydrochar (FeSi-SRHC), which was designed for comprehensive removal of typical contaminants such as Cu2+, Zn2+, tetracycline (TC), and ciprofloxacin (CIP), along with relevant bio-contaminants (resistant bacteria (RBs) and resistance genes (RGs)) present in wastewater. Based on the analysis of adsorption kinetics and Freundlich isotherm, it was found that FeSi-SRHC exhibited physical monolayer adsorption for Cu2+/Zn2+ while mainly chemical multilayer adsorption for TC/CIP in single-contamination system. Furthermore, Langmuir isotherm demonstrated excellent adsorption capacity of FeSi-SRHC towards Cu2+/Zn2+/TC/CIP with maximum capacities of 255.75, 265.26, 425.53, and 404.86 mg/g, respectively. In the co-contamination system, the presence of Cu2+, Zn2+, TC, and CIP exhibited varying degrees of inhibitory or promotive effects on the mutual adsorption by FeSi-SRHC. This divergence stemmed from differences in complexation intensities and concentration ratios among diverse co-existing contaminants. Based on XPS and Density Functional Theory (DFT) analyses, the adsorption process for Cu2+, Zn2+, TC, and CIP by FeSi-SRHC primarily involves pore fill, complexation reactions, ion exchange, hydrogen bonding, π-π stacking interactions, and electrostatic interactions. Bio-contaminant removal experiments revealed that the release of baicalin and wogonoside from FeSi-SRHC disrupts the structure of RBs cells and compromises the integrity of resistance plasmids. The practical application experiment showed that FeSi-SRHC displayed favorable performance for removing heavy metals, antibiotics, and bio-contaminants in actual wastewater. This study presented a “Treating waste with waste” strategy, which provided a method with low carbon, eco-friendly, and inexpensive for CMHRs resources and turning waste into treasure while proposing a idea to address the challenges associated with treating heavy metal, antibiotic, and bio-contaminant contamination in wastewater.

Adsorptive removal of carcinogenic azo dye from aqueous solution using NaCPT@HDTMA

ABSTRACT This study investigated the effectiveness of the clinoptilolite (Na@CPT) surface as an adsorbent for removing anionic dyes. The Na@CPT surface was modified using hexadecyltrimethylammonium bromide (NaCPT@HDTMA) to improve its ability to remove Reactive Blue 171 (RB171) from water. A thorough study was conducted to analyze the adsorption isotherms, kinetics, temperature, and pH effects of RB171 onto Na@CPT and NaCPT@HDTMA. A pH of 1.0 was found to be the optimum value for adsorbents. Kinetic studies revealed that both adsorbents followed the pseudo-second-order kinetic model, with NaCPT@HDTMA exhibiting a faster adsorption process and quickly reaching equilibrium with increasing temperature. The adsorption efficiency of RB171 was found to improve by 83.56% after the modification at 50°C. The equilibrium data showed that the adsorption of RB171 on Na@CPT and NaCPT@HDTMA fit the Freundlich and Langmuir isotherm models, respectively. The thermodynamic parameters showed that the overall adsorption process of both adsorbents was endothermic and spontaneous. NaCPT@HDTMA is a highly effective adsorbent for removing RB171 from aqueous solution due to its low cost and abundant presence in nature.

Efficient separation of cerium from rare earth elements and major impurities using low cost manganese ferrites from highly acidic solutions

Sorption of REEs using spinel-ferrite nanoparticles has received great attention in the last decades, because of combining the advantages of iron and manganese metal oxides. Nano-manganese ferrite (MnFe2O4) was successfully synthesized using the co-precipitation method and modified with the addition of zinc to produce (Mn0.8Zn0.2Fe2O4). The synthesized materials were characterized using FTIR, SEM with EDX-mapping, XRD, chemical stability, and surface area. Several process parameters were studied to optimize the efficiency of Ce(III) separation from La(III), Eu(III), Pb(II), and Fe(III) from highly acidic media. The parameters include contact time, solution pH, and metal ion concentration. The sorption process was well fitted to the pseudo-2nd order model, which confirms the chemical nature of the sorption process where equilibrium was achieved after 30 minutes. The pH study's findings demonstrate that Ce(III) was most effectively separated at a very high, acidic pH of 0.5. Both MnFe2O4 and Mn0.8Zn0.2Fe2O4 have high chemical stability in different media where the weight loss was less than 10 %. The correlation coefficient and residual errors analysis confirm that the non-linear extended sips isotherm model more accurately expresses the behavior of the sorption process than the non-linear Freundlich and Langmuir isotherm models. The modified material Mn0.8 Zn0.2Fe2O4 shows higher sorption capacities for all the studied metal ions than MnFe2O4. The maximum sorption capacities of Ce(III), La(III), Eu(III), Pb(II), and Fe(III) in the mixture were 59.2, 6.5, 6.3, 15.4, and 13.7 mg/g, respectively.

Efficient removal of perfluorooctanoic acid from aqueous matrices using cationic surfactant functionalized graphene oxide nanocomposite: RSM and ANN modeling, and adsorption behaviour

Perfluorooctanoic acid (PFOA), a persistent and recalcitrant emerging organic contaminant, has garnered worldwide attention due to its pervasiveness and strong bioaccumulation, emphasizing the urgent necessity for effective removal strategies. To address PFOA contamination in the global aquatic environment, this study prepared cetyltrimethylammonium bromide (CTAB)-functionalized graphene oxide (GO-C) nanocomposites. The functionality of GO-C is controlled by varying loading ratios of CTAB to achieve satisfactory performance. After preliminary experiments that confirmed the superior performance of GO-C0.5 in PFOA removal, the response surface methodology (RSM) revealed the effects of different process parameters, which followed the sequence: adsorbent dose > pH > time. The optimum PFOA removal of 98.5 % was achieved at adsorbent dose: 200 mg/L, pH: 3.5, and time: 50 min, at an experimental temperature of 298 K. Furthermore, a predictive model using an artificial neural network was developed for PFOA adsorption, which closely aligns with the experimental data (R2: 0.9999). The PFOA adsorption was most accurately represented by Freundlich isotherm (R2: 0.9747) and pseudo-second-order kinetics (R2: 0.9995), with a maximum experimental adsorption capacity of ~709.94 mg/g under RSM optimized conditions. The adsorption mechanism involves electrostatic and hydrophobic interactions and hydrogen bonding, as confirmed by the spectroscopic and zeta potential analyses. Lastly, the competitive adsorption and regeneration experiments underscore the potential of GO-C nanocomposite in removing PFOA. Overall, this study provides insights into the development and application of sustainable and promising adsorbent for the removal of PFOA in wastewater stream.

Removal of phosphate from wastewater using zirconium/iron embedded chitosan/alginate hydrogel beads: An experimental and computational perspective

Adsorptive removal of phosphate plays a crucial role in mitigating eutrophication. Herein, the Zr/Fe embedded chitosan/alginate hydrogel bead (Zr/Fe/CS/Alg) is reported as an effective phosphate adsorbent. This polymer nanocomposite is synthesized by the in-situ reduction of the metals on the polymer matrix. The synthesized adsorbent was characterized by the FTIR, SEM-EDX, TGA, BET, and XPS. The adsorbent showed a maximum phosphate adsorption capacity of 221.72 mg/g at pH 3. The experimental data fit well with the Freundlich isotherm and pseudo-second-order kinetics model, indicating a heterogeneous multilayer surface formation and a chemisorption-dominated adsorption process. Density Functional Theory (DFT) and Monte Carlo (MC) calculations revealed high negative adsorption energy due to the chemisorption of phosphate on the adsorbent. Hence, the major interactions such as electrostatic attraction, hydrogen bonding, and inner-sphere complexation of phosphate adsorption and Zr/Fe/CS/Alg hydrogel beads were investigated from the experimental and computational analysis. The negative values of thermodynamic parameters indicated a spontaneous, exothermic, and less random adsorption process. The synthesized adsorbent exhibited excellent selectivity toward phosphate and maintained 73 % efficiency after six adsorption/desorption cycles. The Zr/Fe/CS/Alg hydrogel beads reduced the phosphate concentration in real wastewater samples from 19.02 mg/L to 0.985 mg/L, suggesting that these nanocomposite hydrogel beads could be a promising adsorbent for real-world applications.

Effect of plant extract additives on the parasitic reaction in alkaline Zn-air batteries

The battery's high energy density, economical price, and ecological sustainability of the Zn-air battery make it a bright future battery technology. However, parasitic reactions, which can diminish the battery's life cycle and efficacy, are the key challenges for potential development of Zn-air batteries. Glycyrrhiza glabra roots extract (GGRE) has been investigated as an alternative hydrogen gas evolution and corrosion inhibitor for Zn-air batteries in order to mitigate the parasitic reaction. The results obtained reveal that the inhibition capacity of the GGRE extract increases with concentration and reaches its highest level (75.6%) around 350 mg L-1 of GGRE extract. GGRE extract is a mixed type inhibitor with a predominately cathodic effect based on the polarization data. The GGRE extract adsorption on the Zn surface complies with Freundlich isotherm. In comparison to the blank Zn-KOH (354 mAh g-1), the battery containing 350 mg L-1 GGRE extract has the highest discharge capacity (533 mAh g-1) and the best cyclability (92.9% retention after 500 cycles). Overall, GGRE extract can significantly optimize the performance of Zn-air batteries.