Potential of Capparis decidua plant and eggshell composite adsorbent for effective removal of anionic dyes from aqueous medium

The presence of hazardous dyes in wastewater poses significant threats to both ecosystems and the natural environment. Conventional methods for treating dye-contaminated water have several limitations, including high costs and complex operational processes. This study investigated a sustainable bio-sorbent composite derived from the Capparis decidua plant and eggshells, and evaluated its effectiveness in removing anionic dyes namely tartrazine (E-102), methyl orange (MO), and their mixed system. The research examines the influence of initial concentration, contact time, pH, adsorbent dosage, and temperature on the adsorption properties of anionic dyes. Optimal removal of tartrazine (E-102), methyl orange (MO), and their mixed system was achieved at a pH of 3. The equilibrium was achieved at 80 min for MO and mixed systems, and 100 min for E-102. The adsorption process showed an exothermic nature, indicating reduced capacity with increasing temperature, consistent with heat release during adsorption. Positive entropy values indicated increased disorder at the solid-liquid interface, attributed to molecular rearrangements and interactions between dye molecules and the adsorbent. Isotherm analysis using Langmuir, Freundlich, Temkin, and Redlich-Peterson models revealed that the Langmuir model best fit the experimental data. The maximum adsorption capacities of 50.97 mg/g, 52.24 mg/g, and 56.23 mg/g were achieved for E-102, MO, and the mixed system under optimized conditions, respectively. The pseudo-second-order kinetic model demonstrated the best fit, indicating that adsorption occurs through physical and chemical interactions such as electrostatic attraction, pore filling, and hydrogen bonding. Hence, the developed bio-sorbent could be a sustainable and cost-effective solution for the treatment of anionic dyes from industrial effluents.

Removal of fluorouracil from aqueous environment using magnetite graphene oxide modified with γ-cyclodextrin

Fluorouracil (FU) is a widely utilized antineoplastic medication in the pharmaceutical industry for combating gastrointestinal cancers. However, its presence in wastewater originating from pharmaceutical facilities and hospital effluents has a potential effect on DNA, and cannot be efficiently eliminated through conventional treatment methods. Consequently, the adoption of advanced technologies becomes crucial for effectively treating such wastewater. Accordingly, this study investigated the efficiency of magnetite graphene oxide nanocomposite functionalized with γ-cyclodextrin for removing fluorouracil from aqueous solutions. The magnetite graphene oxide nanocomposite functionalized with γ-cyclodextrin was synthesized via the hydrothermal method. Next, the effect of pH, temperature, adsorbent content, and contact time on the fluorouracil removal efficiency was explored. Ultimately, the experimental data were matched against Langmuir, Freundlich, and Temkin isotherms and Kinetic models. Accordingly, the efficiency of the absorbent used was dependent on the pH, contact time, temperature, and initial concentration of the adsorbent. The results indicated that the maximum removal efficiency for fluorouracil was achieved within the contact time of 45 min and adsorbent content of 0.020 g. In addition, the optimal pH for removing the medicine was 7. The conditions of the adsorption process followed Langmuir isotherm with correlation coefficients of 0.992 and a quasi-second kinetic model with a correlation coefficient of 0.999, with the maximum adsorption capacity of the adsorbent synthesized for the evaluated medicine estimated as 190.9 mg/g. The results showed that the magnetite graphene oxide nanocomposite functionalized with γ-cyclodextrin could be used as an effective and available adsorbent for removing fluorouracil from pharmaceutical wastewater.

Correlation between cocoa shell modifications by CTAB and its dye adsorption properties

Cocoa shell was modified whit sodium hydroxide (NaOH) and cationic surfactant cetyltrimethylammonium bromide (CTAB) to increase surface functionality, surface area, and positive charge density. The prepared adsorbent CC-OH-CTAB was used to remove indigo carmine (IC) and bromocresol green (BCG) dyes from water. The optimal pH for IC and BCG adsorption were 2 and 4, respectively. The equilibrium was attained after a contact time of 30 min for IC and 120 min for BCG. The maximum adsorption capacity (Qmax) of IC and BCG obtained was 85.1 mg g-1 and 192.7 mg g-1, respectively. The Liu isotherm model best described the equilibrium results. The adsorption kinetics model showed that IC and BCG adsorption onto CC-OH-CTAB followed the pseudo-first-order and pseudo-second-order model, respectively. The regeneration and reusability experiments indicated that CC-OH-CTAB had much stability and excellent performance meanwhile repeatedly used. Finally, the insertion of CTAB on the CC-OH surface proved to be an excellent way to improve the adsorption performance of this material concerning dyes.

Copper and zinc adsorption from bacterial biomass - possibility of low-cost industrial wastewater treatment

The increasing interest of all stakeholders to achieve environmental protection with socioeconomic development puts pressure on industrial processes for less negative impact on the environment. The use of biomass for wastewater treatment has increased due to its low costs and technical feasibility. The present study aimed the use of biomass from a waste of known polluted area for the adsorption of Zn and Cu in a fixed-bed reactor. Samples were collected in Cubatão (Brazil) and cultivated in LB medium. Resulting cultivable bacterial communities were identified as Enterococcus faecalis and Pseudomonas aeruginosa. Adsorption experiments were performed varying the metallic ion concentration and the amount of biomass. Adsorption experiments showed efficiency rates up to 90%. As the concentration of metallic ions increased, the adsorption efficiency decreased, indicating that the active sites were saturated. Activated charcoal demonstrated lower adsorption rates than biomass. Elution process showed that HNO₃ had better efficiency than HCl. Zn adsorption fitted better for Lineweaver-Burk model (Q_max= 200 mg/g of biomass), while Cu adsorption fitted better for Langmuir model (Q_max= 164 mg/g of biomass). Results here demonstrated that the adsorption of Zn and Cu simulating an industrial wastewater by the biomass from a contaminated area is technically feasible.

Optimization Study of the Capacity of Chlorella vulgaris as a Potential Bio-Remediator for the Bio-Adsorption of Arsenic (III) from Aquatic Environments

This study examined the ability of the green microalgae Chlorella vulgaris to remove arsenic from aqueous solutions. A series of studies was conducted to determine the optimal conditions for biological arsenic elimination, including biomass amount, incubation time, initial arsenic level, and pH values. At 76 min, pH 6, 50 mgL^-1 metal concentration, and 1 gL^-1 bio-adsorbent dosage, the maximum removal of arsenic from an aqueous solution was 93%. The uptake of As (III) ions by C. vulgaris reached an equilibrium at 76 min of bio-adsorption. The maximum adsorptive rate of arsenic (III) by C. vulgaris was 55 mg/gm. The Langmuir, Freundlich, and Dubinin-Radushkevich equations were used to fit the experimental data. The best theoretical isotherm of Langmuir, Freundlich, or/and Dubinin-Radushkevich for arsenic bio-adsorption by Chlorella vulgaris was determined. To choose the best theoretical isotherm, the coefficient of correlation was used. The data on absorption appeared to be linearly consistent with the Langmuir (q_max = 45 mgg^-1; R² = 0.9894), Freundlich (k_f = 1.44; R² = 0.7227), and Dubinin-Radushkevich (q_D-R = 8.7 mg/g; R² = 0.951) isotherms. The Langmuir and Dubinin-Radushkevich isotherms were both good two-parameter isotherms. In general, Langmuir was demonstrated to be the most accurate model for As (III) bio-adsorption on the bio-adsorbent. Maximum bio-adsorption values and a good correlation coefficient were observed for the first-order kinetic model, indicating that it was the best fitting model and significant in describing the arsenic (III) adsorption process. SEM micrographs of treated and untreated algal cells revealed that ions adsorbed on the algal cell's surface. A Fourier-transform infrared spectrophotometer (FTIR) was used to analyze the functional groups in algal cells, such as the carboxyl group, hydroxyl, amines, and amides, which aided in the bio-adsorption process. Thus, C. vulgaris has great potential and can be found in eco-friendly biomaterials capable of adsorbing arsenic contaminants from water sources.

Incorporation of acridine orange and methylene blue in Langmuir monolayers mimicking releasing nanostructures

The efficiency of methylene blue (MB) and acridine orange (AO) for photodynamic therapy (PDT) is increased if encapsulated in liposomes. In this paper we determine the molecular-level interactions between MB or AO and mixed monolayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG) and cholesterol (CHOL) using surface pressure isotherms and polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). To increase liposome stability, the effects from adding the surfactants Span® 80 and sodium cholate were also studied. Both MB and AO induce an expansion in the mixed monolayer, but this expansion is less significant in the presence of either Span® 80 or sodium cholate. The action of AO and MB occurred via coupling with phosphate groups of DPPC or DPPG. However, the levels of chain ordering and hydration of carbonyl and phosphate in headgroups depended on the photosensitizer and on the presence of Span® 80 or sodium cholate. From the PM-IRRAS spectra, we inferred that incorporation of MB and AO increased hydration of the monolayer headgroup, except for the case of the monolayer containing sodium cholate. This variability in behaviour offers an opportunity to tune the incorporation of AO and MB into liposomes which could be exploited in the release necessary for PDT.

Supramolecular Control of Photonic Response and Sensing of Nitricoxide using Iron(III) Corrole Monolayers and Their Stacks

In this work, we assemble amphiphilic iron(III) corroles at air-water interfaces into well-defined quasi-two-dimensional molecular monolayers and theirs stacks for sensing of nitric oxide (NO). For this purpose, we use the Langmuir-Blodgett (LB) technique, which allows varying the packing density of iron(III) corroles anchored to the aqueous subphase via one molecular side. The stacks of ten down to three molecular monolayers on the front and back sides of the substrates are sufficiently optically dense to detect NO binding to the layers photometrically. This sensing with few layers demonstrates the potential for electronic detection, where very thin surface functionalizations enable efficient electronic communication between the layer and the (semi)conductor. Despite increasing optical densities, the spectral responses to NO exposure become smaller with increasing packing density until the collapse point of the monolayers is reached. This demonstrates that the highest molecular efficiency for binding and detection of NO is achieved at the smallest packing densities. This finding is relevant to all molecular sensor films with axial binding of analytes to the sensor molecules and demonstrates the advantage of sensor molecule assembly into monolayers on water-air interfaces using the LB technique.

Synthesis of Xanthan Gum Anchored α-Fe(2)O(3) Bionanocomposite Material for Remediation of Pb (II) Contaminated Aquatic System

Increases in community and industrial activities have led to disturbances of the environmental balance and the contamination of water systems through the introduction of organic and inorganic pollutants. Among the various inorganic pollutants, Pb (II) is one of the heavy metals possessing non-biodegradable and the most toxic characteristics towards human health and the environment. The present study is focussed on the synthesis of efficient and eco-friendly adsorbent material that can remove Pb (II) from wastewater. A green functional nanocomposite material based on the immobilization of α-Fe₂O₃ nanoparticles with xanthan gum (XG) biopolymer has been synthesized in this study to be applied as an adsorbent (XGFO) for sequestration of Pb (II). Spectroscopic techniques such as scanning electron microscopy with energy dispersive X-ray (SEM-EDX), Fourier transform infrared (FTIR), transmission electron microscopy (TEM), X-ray diffraction (XRD), ultraviolet visible (UV-Vis) and X-ray photoelectron spectroscopy (XPS) were adopted for characterizing the solid powder material. The synthesized material was found to be rich in key functional groups such as -COOH and -OH playing important roles in binding the adsorbate particles through ligand-to-metal charge transfer (LMCT). Based on the preliminary results, adsorption experiments were conducted, and the data obtained were applied to four different adsorption isotherm models, viz the Langmuir, Temkin, Freundlich and D-R models. Based on the high values of R² and low values of χ², the Langmuir isotherm model was found to be the best model for simulation of data for Pb (II) adsorption by XGFO. The value of maximum monolayer adsorption capacity (Q_m) was found to be 117.45 mg g^-1 at 303 K, 126.23 mg g^-1 at 313 K, 145.12 mg g^-1 at 323 K and 191.27 mg g^-1 at 323 K. The kinetics of the adsorption process of Pb (II) by XGFO was best defined by the pseudo-second-order model. The thermodynamic aspect of the reaction suggested that the reaction is endothermic and spontaneous. The outcomes proved that XGFO can be utilized as an efficient adsorbent material for the treatment of contaminated wastewater.

Evaluation of ciprofloxacin (CIP) and clarithromycin (CLA) adsorption with weathered PVC microplastics

The sorption kinetics of two of the most frequently used antibiotics onto recycled (weathered) polyvinyl chloride (PVC) was investigated, using Freundlich and Langmuir isotherm models. Various experimental conditions were set, including pH, contact time, rotational speed, temperature, and initial concentration. The batch experimental results indicated that Freundlich model was better fitted than Langmuir (R²: 98.7 and 84.7, for CIP and CLA respectively). Maximum adsorption capacity is 45.9 mg/g and 22.0 mg/g for CIP and CLA, respectively. Enthalpy (ΔH), and entropy (ΔS) values were negative for CIP, indicating that the reaction was exothermic and spontaneous, respectively. It was vice versa for CLA. Field emission scanning electron microscope (FESEM) and Fourier transform infrared spectrometer (FT-IR) analysis confirmed the physical adsorption mechanism. The results demonstrated that the recycled PVC microplastic has a good capacity for adsorption for both antibiotics.

Persistent organic pollutants in model fungal membranes. Effects on the activity of phospholipases

Soils are the final sink for multiple organic pollutants emitted to the environment. Some of these chemicals which are toxic, recalcitrant and can bioaccumulate in living organism and biomagnify in trophic chains are classified persistent organic pollutants (POP). Vast areas of arable land have been polluted by POPs and the only economically possible means of decontamination is bioremediation, that is the utilization of POP-degrading microbes. Especially useful can be non-ligninolytic fungi, as their fast-growing mycelia can reach POP molecules strongly bond to soil minerals or humus fraction inaccessible to bacteria. The mobilized POP molecules are incorporated into the fungal plasma membrane where their degradation begins. The presence of POP molecules in the membranes can change their physical properties and trigger toxic effects to the cell. To avoid these phenomena fungi can quickly remodel the phospholipid composition of their membrane with employing different phospholipases and acyltransferases. However, if the presence of POP downregulates the phospholipases, toxic effects and the final death of microbial cells are highly probable. In our studies we applied multicomponent Langmuir monolayers with their composition mimicking fungal plasma membranes and studied their interactions with two different microbial phospholipases: phospholipase C (α-toxin) and phospholipase A1 (Lecitase ultra). The model membranes were doped with selected POPs that are frequently found in contaminated soils. It turned out that most of the employed POPs do not downregulate considerably the activity of phospholipases, which is a good prognostics for the application of non-ligninolytic fungi in bioremediation.

Comparison of three different structures of zeolites prepared by template-free hydrothermal method and its CO2 adsorption properties

In this study, zeolite sodalite SOD (50NaO₂:Al₂O₃:5SiO₂), zeolite LTA (2NaO₂:Al₂O₃:1.926SiO₂) and zeolite FAU (16NaO₂:Al₂O₃:4SiO₂) of different structures were synthesized successfully through simple conventional hydrothermal crystallization technique without using any template agent. Morphological analysis of three different types of zeolites revealed that the samples exhibit three different shapes such as the "Raspberry-like", "Dice" cube like and "Octahedral" shaped morphology respectively. The thermal stability was found to be about 4.8%, 14.6% and 20.5% for the synthesized zeolites SOD, LTA and FAU respectively. From the N₂ adsorption-desorption studies, it was observed that adsorption types IV and I correspond to the synthesized samples. CO₂ adsorption by the synthesized zeolite SOD, LTA and FAU were examined in the pressure range from 0 to 101.325 kPa at a constant temperature of 297.15 K. The highest adsorption capacity of 3.7 mmol/g was obtained for zeolite FAU. The synthesized zeolite was studied using a nonlinear regression curve fit to determine the adsorption isotherm model using Langmuir and Freundlich isotherm model. It has been found that the synthesized zeolites have a large electric field gradient due to which they can strongly adsorb quadrupole of CO₂ molecules.

Synthesis of novel epichlorohydrin cross-linked β-cyclodextrin functionalized with reduced graphene oxide composite adsorbent for treatment of phenolic wastewater

A novel composite consisting reduced graphene oxide-functionalized beta-cyclodextrin epichlorohydrin polymer (RGO-βCD-ECH) was synthesized for the treatment of phenolic wastewater. Batch study of phenolic pollutants (2,4-dichlorophenol, 2-chlorophenol, and phenol) was analyzed using the synthesized composite as an adsorbent from an aqueous solution. The optimized parameters were temperature 25 °C, adsorption time 60 min, solution pH 7, and dosage 0.25 g/L. The isotherm data were more suitably fitted by the Langmuir isotherm model. The maximum uptake for 2,4-dichlorophenol, phenol, and 2-chlorophenol was 702.853, 659.475, and 674.155 mg/g, respectively, at 25 ± 1 °C. The kinetic data for all the phenolic pollutants follow the pseudo-second-order model, and the rate was controlled by film diffusion. Thermodynamic data revealed that the process of removing phenolic pollutants is spontaneous and endothermic. The composite can be used up to five cycles with a small reduction in the removal. Adsorption performance of the synthesized composite for synthetic industrial effluents shows that up to 78% removal occurred in 60 min adsorption time. Based on the remarkably rapid adsorption and high adsorption capacity, the synthesized composite can be considered an efficient adsorbent for treating phenolic pollutants from wastewater.

Effect of deuteration on a phosphatidylcholine lipid monolayer structure: New insights from vibrational sum-frequency generation spectroscopy

We used vibrational sum-frequency generation (VSFG) spectroscopy to elucidate the possible effect of various levels of isotopic substitution (H/D) on the properties of the DPPC monolayer by probing DPPC/D₂O interface. We found that deuteration of the choline group has a great impact on monolayer properties, while monolayers with deuterated alkyl chains do not exhibit any differences under our experimental conditions. In addition, deuteration of the choline group strongly affected the hydration of the phosphate group. We showed by probing symmetric stretching vibration of phosphate group that denser packing only slightly reduced the hydration of DPPC-d13 and DPPC-d75 monolayers. Moreover, addition of calcium ions, which generally cause a marked dehydration of the lipid monolayer, had no effect on lipid monolayers with deuterated choline group. We proposed that one way to explain this experimental finding could be deuteration induced changes in the structure of lipid's choline group, resulting in a well-hydrated but Ca²⁺ ion blocking structure. These results have important implications for various spectroscopic techniques, which commonly use deuteration of phospholipids to circumvent overlapping between vibrational bands.

A re-analysis of NH4+ sorption on biochar: Have expectations been too high?

Sorption of nutrients such as NH₄⁺ is often quoted as a critical property of biochar, explaining its value as a soil amendment and a filter material. However, published values for NH₄⁺ sorption to biochar vary by more than 3 orders of magnitude, without consensus as to the source of this variability. This lack of understanding greatly limits our ability to use quantitative sorption measurements towards product design. Here, our objective was to conduct a quantitative analysis of the sources of variability, and infer which biochar traits are more favourable to high sorption capacity. To do so, we conducted a standardized remodelling exercise of published batch sorption studies using Langmuir sorption isotherm. We excluded studies presenting datasets that either could not be reconciled with the standard Langmuir sorption isotherm or generated clear outliers. Our analysis indicates that the magnitude of sorption capacity of unmodified biochar for NH₄⁺ is lower than previously reported, with a median of 4.2 mg NH₄⁺ g^-1 and a maximum reported sorption capacity of 22.8 mg NH₄⁺ g^-1. Activation resulted in a significant relative improvement in sorption capacity, but absolute improvements remain modest, with a maximum reported sorption of 27.56 mg NH₄⁺ g^-1 for an activated biochar. Methodology appeared to substantially impact sorption estimates, especially practices such as pH control of batch sorption solution and ash removal. Our results highlight some significant challenges in the quantification of NH₄⁺ sorption by biochar and our curated data set provides a potentially valuable scale against which future estimates can be assessed.

Fabrication of alginate@silver nanoparticles (Alg@AgNPs) bionanocomposite for the sequestration of crystal violet dye from aqueous solution

In the present study, alginate@silver nanoparticles (Alg@AgNPs) bionanocomposite has been fabricated successfully and further explored for the removal of crystal violet (CV) dye from the aqueous solution. The surface morphology of the (Alg@AgNPs) bionanocomposite was characterized by various modern analytical techniques such as SEM-EDX, TEM, FTIR and XRD. The maximum adsorption was observed at optimum condition of (pH 7, adsorbent dose 0.01 g, equilibrium time 240 min and initial concentration 20 mg L^-1). The maximum monolayer adsorption capacity was found to be 186.93 mg g^-1 at 30 °C. The experimental data were further validated by various isotherm models and on the basis of highest correlation coefficient (R², 0.99), Langmuir model was found to be best fitted model. Pseudo-second order kinetic model obeyed best for the experimental data with a highest correlation coefficient (R², 0.99) at all studied temperature. In thermodynamic studies, the positive value of enthalpy change (∆H⁰) and entropy change (∆S⁰) confirmed the process to be endothermic and spontaneous in nature. Desorption studies shows that 83 % of the adsorbed CV can be desorbed in first cycle and can be regenerated up to 4th cycle effectively with 0.1 M HCl. Therefore, (Alg@AgNPs) bionanocomposite could be harnessed as a potential adsorbent for the removal of hazardous CV dye from the waste water.

Quantitative evaluation of mercury adsorption and removal efficacy of Spirulina (Arthrospira platensis) powder in mice

Spirulina is a blue-green alga, grown in alkaline water and used for detoxification of several toxic metal ions. Apart from its nutritional value, it is also used for the decontamination of toxic metal ions. Therefore, present study was envisaged to evaluate the adsorption and removal efficiency of Spirulina powder for mercury. The adsorption efficiency of Spirulina was evaluated in terms of weight of adsorbent, contact time, simulated gastric (SGF) and intestinal (SIF) fluid, and mercury concentration. In vivo removal efficacy of Spirulina for mercury was evaluated in mice. The mercury content in major tissues, urine and feces was estimated. The whole tissue retention and excretion of mercury after treatment with Spirulina were taken as a measure of its metal ions removal efficacy. Activated charcoal was taken as a standard adsorbent for comparative study. The maximum adsorption capacity of Spirulina and charcoal for mercury was found to be 66.667 and 158.730 mg g^-1 in water, 83.33 and 94.340 mg g^-1 in SGF and 125.0 and 133.33 mg g^-1 in SIF, respectively. In mice, Spirulina and activated charcoal were significantly reduced the mercury deposition in tissues and facilitated their excretion through feces. Spirulina has shown good adsorption and removal efficacy like activated charcoal. Therefore, Spirulina can be used as a potential adsorbent to remove mercury from the body.

Fabrication and Characterization of Xanthan Gum-cl-poly(acrylamide-co-alginic acid) Hydrogel for Adsorption of Cadmium Ions from Aqueous Medium

The present research demonstrates the facile fabrication of xanthan gum-cl-poly(acrylamide-co-alginic acid) (XG-cl-poly(AAm-co-AA)) hydrogel by employing microwave-assisted copolymerization. Simultaneous copolymerization of acrylamide (AAm) and alginic acid (AA) onto xanthan gum (XG) was carried out. Different samples were fabricated by changing the concentrations of AAm and AA. A sample with maximum swelling percentage was chosen for adsorption experiments. The structural and functional characteristics of synthesized hydrogel were elucidated using diverse characterization tools. Adsorption performance of XG-cl-poly(AAm-co-AA) hydrogel was investigated for the removal of noxious cadmium (Cd(II)) ions using batch adsorption from the aqueous system, various reaction parameters optimized include pH, contact time, temperature, and concentration of Cd(II) ions and temperature. The maximum adsorption was achieved at optimal pH 7, contact time 180 min, temperature 35 °C and cadmium ion centration of 10 mg·L-1. The XG-cl-poly(AAm-co-AA) hydrogel unveiled a very high adsorption potential, and its adsorption capacities considered based on the Langmuir isotherm for Cd(II) ions was 125 mg·g-1 at 35 °C. The Cd(II) ions adsorption data fitted nicely to the Freundlich isotherm and pseudo-first-order model. The reusability investigation demonstrated that hydrogel retained its adsorption capacity even after several uses without significant loss.

Adsorption and desorption of nutrients from abattoir wastewater: modelling and comparison of rice, coconut and coffee husk biochar

Enrichment of water bodies with nutrients from wastewater is one of the causes of eutrophication to aquatic ecosystems. This study investigated the use of biochar derived from rice husk, coconut husk, and coffee husk in adsorbing nitrates (NO3-N) and nitrites (NO2-N) from slaughterhouse wastewater. It also explored the desorption efficiencies of the adsorbed nutrients to ascertain the applicability of the enriched biochars as slow-release fertilizers. To characterize the physicochemical properties of the biochars, scanning electron microscopy (SEM) was used. Fourier transforms infrared spectroscopy (FTIR), elemental analysis (CHNO) Langmuir and Freundlich, and the isotherm models were employed to fit the experimental equilibrium adsorption data. It was observed that the Langmuir isotherm model has the best fit of NO3- N and NO2- N on all the biochars. And this was based on the coefficient of correlation values. Also, the coconut husk biochar has the highest adsorption capacities of NO3-N and NO2-N at 12.97 mg/g, and 0.244 mg/g, respectively, attributing to its high porosity as revealed by the SEM images. The adsorption capacities for the rice husk char were 12.315 and 0.233 mg/g, while that for coffee husk char were12.08 mg/g and 0.218 mg/g for NO3-N and NO2-N, respectively. The relatively higher amount of NO3-N adsorbed to that of NO2-N could be attributed to its higher initial concentration in the solution than nitrite concentration. The desorption efficiencies of nitrates were 22.4, 24.39, and 16.79 %, for rice husk char, coconut husk char and coffee husk char, respectively. For the rice husk char, coconut husk char and coffee husk char, the nitrites desorption efficiencies were 80.73, 91.39, and 83.62 %, respectively. These values are good indicators that the studied biochar can be enriched with NO3- N and NO2- N and used as slow-release fertilizers.

Terahertz-Based Method for Accurate Characterization of Early Water Absorption Properties of Epoxy Resins and Rapid Detection of Water Absorption

Moisture is detrimental to the performance of epoxy resin material for electrical equipment in long-term operation and insulation. Therefore, moisture absorption is one of the critical indicators for insulation of the material. However, some relevant test methods, e.g., the direct weighing method, are time-consuming, and it usually takes months to complete a test. For this, it is necessary to have some modification to save the test time. Firstly, the study analyzes the present prediction method (according to ISO 62:2008). Under the same accuracy, the time required is reduced from 104 days to 71 days. Subsequently, the Langmuir curve-fitting method for water absorption of epoxy resin is analyzed, and the initial values of diffusion coefficient, bonding coefficient, and de-bonding coefficient are determined based on the results of molecular simulation, relevant experiment, and literature review. With the optimized prediction model, it takes only 1.5 days (reduced by 98% as compared with the standard prediction method) to determine the moisture absorbability. Then, the factors influencing the prediction accuracy are discussed. The results have shown that the fluctuation of balance at the initial stage will affect the test precision significantly. Accordingly, this study proposes a quantitative characterization method for initial trace moisture based on the terahertz method, by which the trace moisture in epoxy resin is represented precisely through the established terahertz time-domain spectroscopy system. When this method is used to predict the moisture absorbability, the experimental time may be further shortened by 33% to 1 day. For the whole water absorption cycle curve, the error is less than 5%.

A management framework for phosphorus use on agricultural soils using sorption criteria and soil test P

The variation in sorption and desorption of phosphorus (P) among soil types is not captured in current agronomic advice for agri-environmentally sustainable use of P. Phosphorus use is typically based on soil test P (STP) and soils are assumed to have the same rate of response to added P, regardless of sorption properties. The development of P sorption categories, coupled with STP information could improve fertiliser decision making, by making it more site specific and soil type specific. A framework for P sorption specific advice is proposed here integrating soil P sorption dynamics with STP for agronomic and environmental management, at farm and catchment scale. Using a national population of agricultural soils, laboratory measurement of Langmuir sorption maximum (Smax₅₀, mg kg^-1) and binding energy (k₅₀, l mg^-1), were coupled with STP (Morgan P) to derive novel categories for P management advice, specifically addressing the build-up and draw-down phases of P in soils. In addition to measured values, Smax₅₀ and k₅₀ were predicted from MIR spectroscopy and pedotransfer functions and used to allocate soils into these new sorption categories. The allocation of soils into a P management category using predicted values indicated that pedotransfer functions offered greater reliability (90% allocation accuracy using an independent test set), however MIR spectroscopy is faster and less resource intensive (67% allocation accuracy using an independent test set). Phosphorus sorption dynamics should be interpreted alongside soil test P and P Index information so that water quality policy can consider the difference between high and very high STP soils based on sorption information. In the absence of laboratory data on P sorption, soils can be classified into P management classes using predicted values from spectroscopy (rapid and cheap) or pedotransfer functions (greater reliability). Further development of the MIR methodology is recommended along with field validation.

Biosorption of Zn(II) from Seawater Solution by the Microalgal Biomass of Tetraselmis marina AC16-MESO

Biosorption refers to a physicochemical process where substances are removed from the solution by a biological material (live or dead) via adsorption processes governed by mechanisms such as surface complexation, ion exchange, and precipitation. This study aimed to evaluate the adsorption of Zn²⁺ in seawater using the microalgal biomass of Tetraselmis marina AC16-MESO “in vivo” and “not alive” at different concentrations of Zn²⁺ (0, 5, 10, and 20 mg L⁻¹) at 72 h. Analysis was carried out by using the Langmuir isotherms and by evaluating the autofluorescence from microalgae. The maximum adsorption of Zn²⁺ by the Langmuir model using the Q_max parameter in the living microalgal biomass (Q_max = 0.03051 mg g⁻¹) was more significant than the non-living microalgal biomass of T. marine AC16-MESO (Q_max = 0.02297 mg g⁻¹). Furthermore, a decrease in fluorescence was detected in cells from T. marina AC16-MESO, in the following order: Zn²⁺ (0 < 20 < 5 < 10) mg L⁻¹. Zn²⁺ was adsorbed quickly by living cells from T. marine AC16-MESO compared to the non-living microalgal biomass, with a decrease in photosystem II activities from 0 to 20 mg L⁻¹ Zn²⁺ in living cells.

Sustainable removal of Ni(II) from waste water by freshly isolated fungal strains

The release of untreated wastewater containing biotoxic substances in the form of heavy metals is one of the most crucial environmental and health challenges faced by our community. The recent advances in microbes derived removal has propelled bioremediation as a better and effective alternative to conventional techniques. Present study investigates the detoxification mechanisms evolved by the nickel (Ni(II)) resistant fungal strains, isolated from the industrial drain sites. The molecular detailing of the isolated fungal isolates confirms their identity as Neurospora crassa and Aspergillus flavus. Laboratory-scale experiments have established influence of different ranges of dose, pH, time, and metal concentration on the removal and uptake trends. Further, the variations in the carbon and nitrogen sources and agitation conditions has revealed the best substratum for achieving optimum results for the industrial exploitation of these microbes. SEM micrographs and FTIR spectra elucidates the superficial alterations on the mycelium of the fungal isolates and the involvement of active functional groups in the bioremediation of Ni(II) respectively. Biosorption of Ni(II) on living biomass has followed the Langmuir adsorption model. The findings of the study have provided a promising insight in the simultaneous action of different mechanistic removal approaches to explore a large scale removal of Ni(II) from the waste generating industries.

Malachite green adsorption from aqueous solutions onto biochar derived from sheep manure: adsorption kinetics, isotherm, thermodynamic, and mechanism

The adsorption of Malachite Green (MG) from aqueous solution was achieved using biochar derived from sheep manure pyrolyzed at 450 °C. Sheep manure biochar was characterized before and after adsorption of MG by SEM and FTIR. In addition, surface area measurement was performed by BET surface area and pore analyzer. The influence of contact time, pH, dose, temperature, and initial MG concentrations on the adsorption of MG onto sheep manure biochar (SMB) was investigated in experiments. Langmuir, Freundlich, Temkin, and Dubinin-Raduskevich isotherm models were used to analyze the data. Results assumed best fitting model is Langmuir isotherm model (R² value 0.99). Mean free adsorption energy (E) was obtained 94.71 kJ mol^-1, R_L value was between 0.013 and 0.14. That indicates monolayer, favorable, and physisorption adsorption, as well as an endothermic adsorption process. Maximum uptake value from Langmuir model obtained 208.33 mg g^-1. Surface area of SM biochar was 11.731 m² g^-1.NOVELTY STATEMENTThis study is the first study on the adsorption of malachite green dye substance on sheep manure derived biochar.A natural and cheap adsorbent with high dye removal, such as 208,33 mg g^-1.A guiding study for the conversion of agricultural waste into products with highly added value.

Adsorption of Hexavalent Chromium and Divalent Lead Ions on the Nitrogen-Enriched Chitosan-Based Activated Carbon

Optimizing the physicochemical properties of the chitosan-based activated carbon (Ch-ACs) can greatly enhance its performance toward heavy metal removal from contaminated water. Herein, Ch was converted into a high surface area (1556 m2/g) and porous (0.69 cm3/g) ACs with large content of nitrogen (~16 wt%) using K2CO3 activator and urea as nitrogen-enrichment agents. The prepared Ch-ACs were tested for the removal of Cr(VI) and Pb(II) at different pH, initial metal ions concentration, time, activated carbon dosage, and temperature. For Cr(VI), the best removal was at pH = 2, while for Pb(II) the best pH for its removal was in the range of 4-6. At 25 °C, the Temkin model gives the best fit for the adsorption of Cr(VI), while the Langmuir model was found to be better for Pb(II) ions. The kinetics of adsorption of both heavy metal ions were found to be well-fitted by a pseudo-second-order model. The findings show that the efficiency and the green properties (availability, recyclability, and cost effectiveness) of the developed adsorbent made it a good candidate for wastewaters treatment. As preliminary work, the prepared sorbent was also tested regarding the removal of heavy metals and other contaminations from real wastewater and the obtained results were found to be promising.

Utilization of Ag2O-Al2O3-ZrO2 decorated onto rGO as adsorbent for the removal of Congo red from aqueous solution

The water resources contamination in an alarming concern for sustainable environment. This has led to development of new technologies and materials for waste water detoxification. In the present study, we have fabricated novel trimetallic based mixed oxides decorated reduced graphene oxide (rGO) composite using facile microwave method and utilized it as an adsorbent for the removal of congo red dye from aqueous solution. The final composite showed highly agglomerated metal oxides present on the rGO surface. The high surface area and activity of the synthesized adsorbent resulted in its high adsorption capacity of 333.32 mg/g for congo red. The Langmuir model better explained the isotherm data indicating the monolayer adsorption of congo red molecules onto Ag₂O-Al₂O₃-ZrO₂/rGO surface. The grander adsorption ability of Ag₂O-Al₂O₃-ZrO₂/rGO towards organic dye indicate its probable utilization in the removal of other dyes also from wastewater.

Immunochemical method for penthiopyrad detection through thermodynamic and kinetic characterization of monoclonal antibodies

Immunoassays are nowadays being employed for rapid contaminant analysis in clinical, environmental, and agrochemical samples. A thorough characterization of the antibody‒antigen interaction can bring light to the immunoreagent selection process in order to develop sensitive and robust tests. Thus, determination of equilibrium and reaction rate constants is usually recommendable. However, this can be quite tricky for low molecular weight compounds, and competitive strategies are commonly followed to estimate apparent affinity values. In the present study, a collection of monoclonal antibodies to penthiopyrad was raised for the first time, and apparent equilibrium constants were assessed by the Langmuir model using three different competitive enzyme-linked immunosorbent assay formats. The obtained K_D values from antibody-coated assays were quite close to the corresponding K_D values calculated from surface plasmon resonance (SPR) evaluation. These studies were employed to select a pair of immunoreagents for immunoassay development. The K_D value for penthiopyrad of the selected antibody obtained by SPR was 0.28 nM. The optimized direct assay showed an IC₅₀ value for penthiopyrad of 0.42 nM (0.15 ng mL^-1) in buffer. The limit of quantification for grape, must, and wine samples was 10 ng mL^-1. An excellent correlation was found when immunochemical results were compared with those from LC-MS/MS. As an application case, it was determined that 58% of penthiopyrad was still found in wine after fermentation.

Key roles of the crystal structures of MgO-biochar nanocomposites for enhancing phosphate adsorption

The affinity of biochar (BC) adsorbing phosphate was weak, while generation of magnesium oxide (MgO)-BC nanocomposites that transformed the crystal structures of BC would change the adsorption processes in improving the phosphate adsorption. Hereon, four different crystal structure of absorbents were selected to illustrate why the crystal structures and surface properties of absorbents were of great importance for the phosphate adsorption. The results showed that MgO/KBC with higher combination degree between MgO and KBC could change the normal crystal structure (MgO/KBC1, MgO phase (dominant)) to C-Mg-O phase (dominant). Therefore, MgO/KBC could achieve highest adsorption rate (k₂, 8.059 g mg^-1 min^-1) and q_m (maximal adsorption capacity, 121.950 mg g^-1) for phosphate adsorption among absorbents, and even it had high anti-interference capacity for anions and natural organic matter (NOM). The mechanisms of MgO/KBC for phosphate adsorption were hydrogen-bond interaction, inner-sphere complexation and surface chemical adsorption; adsorption of phosphate on MgO/KBC1 was mainly controlled by inner-sphere complexation (Mg-O-PO₃H^2-, Mg-O-PO₃H₂^- species). In addition, the adsorbability of MgO/KBC for phosphate could be restored after recalcination, which further proved that an efficient nanocomposite, calcinated from waste biomass (fallen leaves), was proposed to control eutrophication.

Efficacy of agricultural waste derived biochar for arsenic removal: Tackling water quality in the Indo-Gangetic plain

Arsenic (As), a geogenic and extremely toxic metalloid can jeopardize terrestrial and aquatic ecosystems through environmental partitioning in natural soil-water compartment, geothermal and marine environments. Although, many researchers have investigated the decontamination potential of different mesoporous engineered bio sorbents for a suite of contaminants, still the removal efficiency of various pyrolyzed agricultural residues needs special attention. In the present study, rice straw derived biochar (RSBC) produced from slow pyrolysis process at 600 °C was used to remove As (V) from aqueous medium. Batch experiments were conducted at room temperature (25 ± 2 °C) under different initial concentrations (10, 30, 50, 100 μg L^-1), adsorbent dosages (0.5-5 μg L^-1), pH (4.0-10.0) and contact times (0-180 min). The adsorption equilibrium was established in 120 min. Adsorption process mainly followed pseudo-second order kinetics (R² ≥ 0.96) and Langmuir isotherm models (R² ≥ 0.99), and the monolayer sorption capacity of 25.6 μg g^-1 for As (V) on RSBC was achieved. Among the different adsorbent dosages and initial concentrations used in the present study, 0.2 g L^-1 (14.8 μg g^-1) and 100 μg L^-1 (13.1 μg g^-1) were selected as an optimum parameters. A comparative analysis of RSBC with other pyrolyzed waste materials revealed that RSBC had comparable adsorption ability (per unit area). These acidic groups are responsible for the electron exchange (electrostatic attraction, ion-exchange, π-π/n-πinteractions) with the anionic arsenate, which facilitates optimum removal (>60%) at 7 < pH < pH_PZC. The future areas of research will focus on decontamination of real wastewater samples containing mixtures of different emerging contaminants and installation of biofilter beds that contains different spent adsorbents/organic substrates (including biochar) for biopurification study in real case scenario.

Biosorption of cyanate by two strains of Chlamydomonas reinhardtii: evaluation of the removal efficiency and antioxidants activity

Two strains of the chlorophyte Chlamydomonas reinhardtii, a wild type (WT) and a transgenic strain (C.CYN) contained an exogenous cyanase gene (CYN), were used to investigate the growth and cyanate biosorption capability through the analysis of the adsorption equilibrium isotherm. The potential antioxidants activity of the algal strains was also investigated under cyanate concentration. The antioxidants activity of both C.CYN and WT were enhanced by the application of cyanate.Two adsorption isotherm models and the sorption kinetics were used to check the efficiency of the cyanate removal process. The results showed the biosorbent efficiency of Chlamydomonas in the removal of KCNO from aqueous solution. The C.CYN strain has great efficiency to remove cyanate as compared to the WT. The maximum percentage of cyanate removal was 83.75% for the C.CYN and 50% for the WT as treated with 0.8 mg.ml^-1 KCNO. The data were adapted to the nonlinear Langmuir model on the basis of the coefficient of determination. The calculated q_max was 0.54 and 0.42 µg.mg^-1 for C.CYN and WT which correlated to the experimental one (0.67 and 0.4 µg.mg^-1, respectively). Our data highlight the application of the transgenic algal strain toward the removal of highly toxic materials as cyanate.Novelty statement The main objective of this work is to find out an efficient genetically-modified Chlamydomonas strain to remove the highly toxic cyanate compound from contaminated area. Moreover, to evaluate the biosorption ability of this transgenic strain with its wild one via two adsorption isotherm (the Langmuir and Freundlich) models. Also, to estimate the antioxidants activity of these strains under the cyanate toxicity through four different assays.

Application of Natural Clinoptilolite for Ammonium Removal from Sludge Water

Sludge water (SW) arising from the dewatering of anaerobic digested sludge causes high back loads of ammonium, leading to high stress (inhibition of the activity of microorganisms by an oversupply of nitrogen compounds (substrate inhibition)) for wastewater treatment plants (WWTP). On the other hand, ammonium is a valuable resource to substitute ammonia from the energy intensive Haber-Bosch process for fertilizer production. Within this work, it was investigated to what extent and under which conditions Carpathian clinoptilolite powder (CCP 20) can be used to remove ammonium from SW and to recover it. Two different SW, originating from municipal WWTPs were investigated (SW1: c₀ = 967 mg/L NH₄-N, municipal wastewater; SW2: c₀ = 718–927 mg/L NH₄-N, large industrial wastewater share). The highest loading was achieved at 307 K with 16.1 mg/g (SW1) and 15.3 mg/g (SW2) at 295 K. Kinetic studies with different specific dosages (0.05 g_CLI/mg_NH4-N), temperatures (283–307 K) and pre-loaded CCP 20 (0–11.4 mg/g) were conducted. At a higher temperature a higher load was achieved. Already after 30 min contact time, regardless of the sludge water, a high load up to 7.15 mg/g at 307 K was reached, achieving equilibrium after 120 min. Pre-loaded sorbent could be further loaded with ammonium when it was recontacted with the SW.

Reduced Graphene Oxide-Based Foam as an Endocrine Disruptor Adsorbent in Aqueous Solutions

A stable and magnetic graphene oxide (GO) foam-polyethyleneimine-iron nanoparticle (GO-PEI-FeNPs) composite has been fabricated for removal of endocrine disruptors-bisphenol A, progesterone and norethisterone-from aqueous solution. The foam with porous and hierarchical structures was synthesized by reduction of graphene oxide layers coupled with co-precipitation of iron under a hydrothermal system using polyethyleneimine as a cross linker. The presence of magnetic iron nanoparticles facilitates the separation process after decontamination. The foam was fully characterized by surface and structural scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The foam exhibits a high adsorption capacity, and the maximum adsorption percentages are 68%, 49% and 80% for bisphenol A, progesterone and norethisterone, respectively. The adsorption process of bisphenol A is explained according to the Langmuir model, whereas the Freundlich model was used for progesterone and norethisterone adsorption.

Study of High-Density Polyethylene (HDPE) Kinetics Modification Treated by Dielectric Barrier Discharge (DBD) Plasma

In this work, the plasma was used in the dielectric barrier discharge (DBD) technique for modifying the high-density polyethylene (HDPE) surface. The treatments were performed via argon or oxygen, for 10 min, at a frequency of 820 Hz, voltage of 20 kV, 2 mm distance between electrodes, and atmospheric pressure. The efficiency of the plasma was determined through the triple Langmuir probe to check if it had enough energy to promote chemical changes on the material surface. Physicochemical changes were diagnosed through surface characterization techniques such as contact angle, attenuated total reflection to Fourier transform infrared spectroscopy (ATR-FTIR), X-ray excited photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Plasma electronics temperature showed that it has enough energy to break or form chemical bonds on the material surface, impacting its wettability directly. The wettability test was performed before and after treatment through the sessile drop, using distilled water, glycerin, and dimethylformamide, to the profile of surface tensions by the Fowkes method, analyzing the contact angle variation. ATR-FTIR and XPS analyses showed that groups and bonds were altered or generated on the surface when compared with the untreated sample. The AFM showed a change in roughness, and this directly affected the increase of wettability.

Differentiation Between Metronidazole Residues Disposal by Using Adsorption and Photodegradation Processes Onto MgO Nanoparticles

Background

Metronidazole (MNZ) is an antibiotic form that is considered as a dangerous environmental pollutant due to its widespread use as growth promoters in livestock and aquaculture operations along with its therapeutic application for humans.

Purpose

The objective of this work was to conduct a comparative study between the efficiency of the adsorption and photocatalytic degradation of MNZ in an aqueous solution by using magnesium oxide nanoparticles (MgO NP) under different effects, as well as evaluate the performance, reusability and cost study.

Materials and Methods

Several instruments such as XRD, EDX, SEM, and TEM were used to characterize the chemical composition and morphological properties of the synthesized MgO NP, while the GC-MS analysis was used to monitor the degradation pathway of MNZ particles within 180 min. The simple photo-batch reactor was used to investigate the degradation of MNZ under the effect of UV radiation, initial concentration of MNZ, pH, catalyst loading, inorganic salts addition, time, and temperature.

Results

The degradation efficiency is mainly divided into two steps: 35.7% for maximum adsorption and 57.5% for photodegradation. Adsorption isotherm models confirmed that the process nature is chemisorption and appropriate Langmuir model, as well as to be a nonspontaneous and endothermic reaction according to the thermodynamic study. Adsorption constant during dark condition is smaller than typical adsorption equilibrium constant derived from the Langmuir-Hinshelwood kinetic model through photodegradation of MNZ that follows pseudo-first-order kinetics. Toxicity rates were reduced considerably after the photodegradation process to 88.21%, 79.84%, and 67.32% and 57.45%, 51.98%, and 43.87% by heamolytic and brine shrimp assays, respectively, for initial MNZ concentrations (20, 60, and 100 mg/L).

Conclusion

We significantly recommend using MgO NP as a promising catalyst in the photodegradation applications for other organic pollutants in visible light.

Concentration and adsorption of Pb and Cu in microplastics: Case study in aquatic environment

Microplastics are proven as heavy metals vector, but the adsorption mechanism still unclear. This study investigated the adsorption of Pb and Cu in microplastics in the Musi River and the environment effect. This study was conducted in 10 stations along the Musi River to the estuary. The polymers of microplastics were dominated by PP and followed by PE, PES, PVC, and nylon. The average concentration of Pb (0.0347 mg L^-1 for water and 0.470 mg kg^-1 for microplastics) was higher than Cu (0.0138 mg L^-1 for water and 0.091 mg kg^-1 for microplastics). The highest concentration of both metals in water and microplastics were found in the estuary. Environment parameters have different effects on the adsorption. The present study found that the adsorption processes were following the Freundlich model. The interaction metal-microplastic was physisorption. Pb and Cu will attach through weak bonds and easy to release into the aquatic ecosystem.

Freeze-dried synthesized bifunctional biopolymer nanocomposite for efficient fluoride removal and antibacterial activity

Local fluoride contamination and bacterial infections in potable water have dangerous effects on the human body and are today a global concern. In this study, we have synthesized a pH-responsive bifunctional biopolymer nanocomposite (HAZ) of humic acid with incorporating aluminum zirconium bimetallic oxide by deep freeze-drying method. Fast nucleation and interconnection of nanoparticles form a highly porous network because of sublimation of frozen HAZ. This duo nanocomposite has efficiently worked for fluoride removal and showed potent antibacterial activity against the Escherichia coli Gram-negative and Staphylococcus aureus Gram-positive bacteria. The X-ray photoelectron spectroscopy (XPS) analysis demonstrates that the hydroxyl groups act as a pivot in the ion exchange process of adsorption, each element of bimetallic oxide primarily takes part in the adsorption mechanism. The maximum adsorption capacity of the adsorbent was 180.62 mg/g at pH seven. Thermodynamic parameters like Gibbs free energy change (ΔG⁰), entropy (ΔS⁰), and enthalpy (ΔH⁰) indicate that the process was endothermic, feasible, and taken place by a chemisorption mechanism. This is the first novel freeze-dried bifunctional biopolymer nanocomposite composed of humic acid natural polymer incorporated with Al-Zr metal oxide, and it exhibited three times higher adsorption efficacy with excellent antibacterial action at a concentration of 5 µg/mL of the nanocomposite.

Adsorption of natural annatto dye by kaolin: kinetic and equilibrium

The adsorption of annatto dye was analysed using kaolin clay as the adsorbent. In this work, the influence of the adsorbent particle size, agitation (0 and 100 rpm), temperature (25, 40, and 60°C), and salt presence (sodium chloride and sodium sulphate at 1, 2 and 3 wt%) on the adsorption process was studied. The adsorption increased 14.21% for particles smaller than 45 µm and the agitation (100 rpm) led to an increase of 22.41% compared to the system without agitation. The ΔG° (237.711 kJmol^-1) indicated that the adsorption process was spontaneous. The negative value of ΔS° (-408.999 Jmol^-1K^-1) and ΔH° (-115.829 kJmol^-1) showed an exothermic physisorption process. The adsorption kinetics follows the pseudo-second-order model. In the adsorption equilibrium, the tested models provided good correlation coefficients ranging from 0.744 to 0.999 with the best fit observed for the Langmuir model. The maximum adsorption capacity of the kaolin clay for the annatto dye was obtained at 25°C with 1% of sodium sulphate (q _max = 59.88 mgg^-1).

Modeling of adsorption flux in nickel-contaminated synthetic simulated wastewater in the batch reactor

In the present investigation, physico-chemical characterization of composite material revealed the presence of fluffy surface structure with crystalline look and negatively charged surface functional groups. The study of adsorption flux by using dimensionless numbers φ (2.62), N_k (62.68) and λ (1.17 × 10^-5) proved that adsorption of nickel ions on the surface of composite material was mostly film diffusion-limited with maximum surface area coverage coupled with weakened surface tension. The results of intraparticle diffusivity and Boyd plot model showed that at the onset of process, film diffusion was the primary mechanism involved and at the later stage intraparticle diffusion played a critical role as rate governing step. The values of film (0.65 × 10^-8 cm² sec^-1) and pore diffusivity (1.8 × 10^-12 cm² sec^-1) coefficients showed that the adsorption process is dependent upon two different types of diffusion namely film and pore diffusion. Overall, transport and reshuffling mechanism had no substantial role in adsorption dynamics of nickel ions on the surface of composite material. Sorption isotherm and kinetics modeling showed higher values of regression coefficients for Langmuir isotherm (R² = 0.99) and pseudo-second-order kinetic model (R² = 0.99) compared to other models. This showed that sorption of nickel followed monolayer coverage with chemisorption at optimized process parameters like pH 6, biosorbent dose 0.1 g/L, temperature 50 °C, agitation rate180 rpm, adsorbate concentration100 mg/L and contact time 60 minutes. The positive value of enthalpy of adsorption (ΔH = + 10.41 kJ/mole) and entropy (ΔS = +58.19 J/mol K) showed that binding of nickel ions on the surface of the composite material was endothermic with improved randomness at solid-liquid interface. The negative value of (ΔG = -6.4 to -8.67 kJ/mol) showed spontaneous nature of nickel adsorption on composite material in the liquid phase.

Sequestration of toxic congo red dye from aqueous solution using ecofriendly guar gum/ activated carbon nanocomposite

In the present study, a potential Guar gum/activated carbon nanocomposite as an adsorbent was synthesized and utilized for the sequestration of toxic congo red dye from synthetic wastewater. The nanocomposite was characterized using different techniques such as SEM, EDX, TEM, FTIR and XRD. Various physico-chemical parameters such as influence of contact time, pH, adsorbent dose, temperature and initial dye concentration were investigated to optimize conditions for maximum adsorption of congo red. Equilibrium data fitted well with Langmuir isotherm model having maximum adsorption capacity of 831.82 mgg-1 at 313 K. The kinetic studies demonstrated that the adsorption followed a pseudo-second order kinetic model. The thermodynamic study showed that the adsorption of congo red onto nanocomposite was spontaneous, exothermic with decreased in randomness at solid/liquid interface. The regeneration study indicated that the nanocomposite could be reused successfully upto five consecutive cycles. Therefore, the present material can be effectively and efficiently urilized for the removal of congo red dye from aqueous solution as well as industrial wastewater.

Binding Capacity and Selectivity of Functionalized and Un-functionalized Carbon Nanotubes for Development of Copper-Detecting Printable Sensor

Carbon nanotubes (CNTs) have unique properties which can be modified through surface functionalization. The ability of several functionalized and un-functionalized CNTs to bind copper was investigated as a first step toward developing a printable CNT-based sensor to detect copper in aqueous systems. Binding capacity and specificity were shown to vary by functionalization and vendor. CNTs from two vendors were tested, and the equilibrium binding data was fitted using two isotherm models. Calculated q_max (mg/g) values indicated one vendor's carboxyl-functionalized CNTs had the greatest binding capacity (94-115 mg/g), while other carboxyl-functionalized CNTs and amine-functionalized CNTs had similar capacities to un-functionalized CNTs (15-30 mg/g). Hydroxyl-functionalized CNTs had the lowest copper binding capacity (7-8 mg/g) of the CNTs tested. Freundlich isotherms showed no obvious trends in binding affinity, but suggested that binding was primarily due to chemisorption. Variations in CNT size, functionalization percentage, and purity could explain, partially, the observed adsorption differences.

Acid Red 66 Dye Removal from Aqueous Solution by Fe/C-based Composites: Adsorption, Kinetics and Thermodynamic Studies

The presence of synthetic dyes in water causes serious environmental issues owing to the low water quality, toxicity to environment and human carcinogenic effects. Adsorption has emerged as simple and environmental benign processes for wastewater treatment. This work reports the use of porous Fe-based composites as adsorbents for Acid Red 66 dye removal in an aqueous solution. The porous FeC and Fe/FeC solids were prepared by hydrothermal methods using iron sulfates and sucrose as precursors. The physicochemical properties of the solids were evaluated through X-ray diffraction (XRD), Scanning electron microscopy coupled with Energy dispersive spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared s (FTIR), Raman and Mössbauer spectroscopies, nitrogen adsorption–desorption isotherms, Electron Paramagnetic Resonance (EPR) and magnetic saturation techniques. Results indicated that the Fe species holds magnetic properties and formed well dispersed Fe₃O₄ nanoparticles on a carbon layer in FeC nanocomposite. Adding iron to the previous solid resulted in the formation of γ-Fe₂O₃ coating on the FeC type structure as in Fe/FeC composite. The highest dye adsorption capacity was 15.5 mg·g⁻¹ for FeC nanocomposite at 25 °C with the isotherms fitting well with the Langmuir model. The removal efficiency of 98.4% was obtained with a pristine Fe sample under similar experimental conditions.

Hydrothermal synthesis of LaFeO3 nanoparticles adsorbent: Characterization and application of error functions for adsorption of fluoride

The adsorption of fluoride from aqueous solution by lanthanum ferrite nanoparticles (LaFeO₃ NPs) synthesized by the hydrothermal method has been investigated. This experimental study was conducted on a laboratory scale. The effects of various operating parameters such as pH (3-11), LaFeO₃ NPs dosage (0.1-1.0 g/L), contact time (15-120 min), temperature (303-318 K), and initial concentration of fluoride (15-40 mg/L) on fluoride adsorption were studied. The results showed that under optimal conditions of fluoride concentration of 20 mg/L, pH of 5, LaFeO₃ NPs dosage of 0.9 g/L, temperature of 308 K, and contact time of 60 min, maximum percentage removal of 94.75 % was obtained. The process of fluoride adsorption on LaFeO₃ NPs was found to depend on the Freundlich adsorption and Koble-Corrigan isotherm models. The monolayer adsorption capacity of LaFeO₃ NPs was 2.575 mg/g. The kinetic data fitted best into the pseudo-second-order model considering the values of the regression coefficients (r²) and error functions used. The thermodynamics study indicated that the adsorption process was exothermic (ΔH°< 0) and spontaneous (ΔG°< 0) in nature. It could be concluded that the synthesized LaFeO₃NPs can be used as an effective adsorbent for fluoride ions removal from aqueous solutions.

In Situ Copolymerized Polyacrylamide Cellulose Supported Fe3O4 Magnetic Nanocomposites for Adsorptive Removal of Pb(II): Artificial Neural Network Modeling and Experimental Studies

The inimical effects associated with heavy metals are serious concerns, particularly with respect to global health-related issues, because of their non-ecological characteristics and high toxicity. Current research in this area is focused on the synthesis of poly(acrylamide) grafted Cell@Fe3O4 nanocomposites via oxidative free radical copolymerization of the acrylamide monomer and its application for the removal of Pb(II). The hybrid material was analyzed using different analytical techniques, including thermogravimetric analysis (TGA), Fourier transform-infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) analysis. The efficacious impact of variable parameters, including contact time, pH, material dose, initial Pb(II) concentration, and the temperature, was investigated and optimized using both batch and artificial neural networks (ANN). Surface digestion of metal ions is exceedingly pH-dependent, and higher adsorption efficiencies and adsorption capacities of Pb(II) were acquired at a pH value of 5. The acquired equilibrium data were analyzed using different isotherm models, including Langmuir, Freundlich, Temkin, and Redlich-Peterson models. In this investigation, the best performance was obtained using the Langmuir model. The maximum adsorption capacity of the material investigated via monolayer formation was determined to be 314.47 mg g-1 at 323 K, 239.74 mg g-1 at 313 K, and 100.79 mg g-1 at 303 K.

Comparative study for adsorption of methylene blue dye on biochar derived from orange peel and banana biomass in aqueous solutions

Biochar pyrolyzed at 800 °C from banana (B_b) and orange peels (OP_b) was applied for sorption of methylene blue (MB) dye in a batch system. OP_b showed better affinity for MB dye than B_b with rapid increase in sorption capacity and percent removal for both biochars attaining equilibrium at 30 min. Chemisorption was suggested as the rate limiting step based on the best fitting of the pseudo-second-order reaction kinetics to the batch adsorption data. Linear increase in sorption capacity was seen as the initial MB dye concentration increased from 50 to 300 mg g^-1 with a 40 % decrease in removal efficiency. An increase of 90 mg g^-1 in sorption capacity for both biochars with a 15 and 30 % increase in removal efficiency for OP_b and B_b, respectively, was observed after increasing the solution pH from 2 to 6 or 8. An increase in sorption capacity of about 150 mg g^-1 was seen by increasing the biochar dose from 0.1 to 0.5 g. Langmuir isotherm model represented the adsorption data well as reflected by the high values of R² (0.99) when using both biochar, while least representation of adsorption data was seen in H-J isotherm as estimated from very low R² (0.6-0.66) for both types of biochar. An endothermic nature of MB dye sorption was suggested based on the linear increase in sorption capacity with an increase in solution temperature from 30 to 60 °C. This was further confirmed by the observed positive changes in standard entropy and standard enthalpy while negative values of Gibbs-free energies proposed the non-spontaneous natures of MB dye sorption on to both biochars. The effective sorption of MB dye demonstrated the potential of plant-based biochar as economically viable adsorbents for MB dye.

Chitosan cross-linked with κ-carrageenan to remove cadmium from water and soil systems

In this study, magnetic bio-adsorbent based on chitosan with high molecular weight was prepared. To stabilize under acidic condition, the synthesized magnetic chitosan was cross-linked with κ-carrageenan (mChitoCar). The magnetic bio-adsorbent was characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The results indicated that mChitoCar had desirable magnetic-sorption properties, and magnetic/bio-adsorbent was successfully synthesized and cross-linked. The present nanocomposite was applied to remove and immobilize Cd2+ from water and soil systems. Adsorption and desorption of cadmium by the chitosan bio-adsorbent were investigated using batch experiments. Isotherm data were described by using Freundlich, Langmuir, Dubinin-Radushkevich, and Temkin models, and better fitting was introduced by Freundlich model in both water and soil systems. The maximum adsorption capacity (b) of cadmium onto mChitoCar appeared to increase from the water system to the soil system, from 750.2 to 992.7 μmol/g, respectively. The adsorption mechanism with the help of potential theory indicates the adsorption of cadmium onto the mChitoCar surface is following chemical adsorption type. To evaluate the efficiency of the modified chitosan as a good bio-adsorbent in water and soil system, the difference between adsorption and desorption amounts, Δq, was calculated. By comparing the amounts of Δq, the bio-adsorbent is not economically feasible at high initial concentrations in the water system. But, the bio-adsorbent used can be relatively economic as a soil modifier.

Adsorption of glyphosate on Brazilian subtropical soils rich in iron and aluminum oxides

We investigated the adsorption of glyphosate onto five subtropical soils of Paraná and São Paulo states, Brazil, a region of intense agricultural activities, aiming at the determination of kinetic and isotherm adsorption parameters which enable the evaluation of the potential leaching of the herbicide. The adsorption was fast, being described by the pseudo-second order and intraparticle diffusion models, thus suggesting that mixed mechanisms are involved. The Oxisol containing the highest concentrations of metal oxides (209.5 g kg-1 Fe2O3 and 160.2 g kg-1 Al2O3) was the sample with the highest rate constant, indicating the adsorption sites are readily available. All the soils are rich in aluminum and iron oxides, explaining the Freundlich coefficients (KF) between 642 and 1360 mg1-1/n kg-1 L1/n, which are higher than most of the coefficients described for other soils around the world. The maximum desorption (15% of the adsorbed amount) was observed for the Oxisol. For the other soils, desorption ranged from 2 to 7%. These results suggest that the leaching of free glyphosate to nearby surface and groundwaters is unlikely unless excessive doses are used. The adsorption parameters are useful for managing the right doses applied to the crops, thus avoiding contamination of adjacent areas.

The unique features of non-competitive vs. competitive sorption: Tests against single volatile aromatic hydrocarbons and their quaternary mixtures

The adsorption characteristics of four aromatic hydrocarbons (i.e., benzene, toluene, xylene, and styrene) onto ground-activated carbon were investigated both independently and as a mixture of the four at <10 Pa partial pressures (e.g., 0-100 ppm concentration range). The maximum sorption capacities for benzene, toluene, styrene, and xylene were measured both as a sole component and as a mixture (at 10 Pa). In the former, the values were approximately 123, 184, 272, and 238 mg g^-1, respectively. In contrast, the latter values were 5, 52, 222, and 248 mg g^-1 respectively, showing dramatic reduction in lighter compounds (below C7) relative to heavier ones (above C8). The mechanistic detail of sorption has been explained in terms of Henry's law and Langmuir, Freundlich, Dubinin-Radushkevich, and Elovich isotherm models. The linearized Langmuir adsorption isotherm analysis showed three sorption pressure regions: low (<1 Pa, retrograde), intermediate (1-4 Pa), and high (4-10 Pa). As such, the outcome of this study offers a unique opportunity to acquire detailed information on the dramatic and dynamic effects of the sorptive interaction between competing sorbates, along with a common sorption process between sorbent and sorbate at 298 K.

Basic Blue Dye Adsorption from Water using Polyaniline/Magnetite(Fe3O4) Composites: Kinetic and Thermodynamic Aspects

Owing to its exciting physicochemical properties and doping-dedoping chemistry, polyaniline (PANI) has emerged as a potential adsorbent for removal of dyes and heavy metals from aqueous solution. Herein, we report on the synthesis of PANI composites with magnetic oxide (Fe3O4) for efficient removal of Basic Blue 3 (BB3) dye from aqueous solution. PANI, Fe3O4, and their composites were characterized with several techniques and subsequently applied for adsorption of BB3. Effect of contact time, initial concentration of dye, pH, and ionic strength on adsorption behavior were systematically investigated. The data obtained were fitted into Langmuir, Frundlich, Dubbanin-Rudiskavich (D-R), and Tempkin adsorption isotherm models for evaluation of adsorption parameters. Langmuir isotherm fits closely to the adsorption data with R2 values of 0.9788, 0.9849, and 0.9985 for Fe3O4, PANI, and PANI/Fe3O4 composites, respectively. The maximum amount of dye adsorbed was 7.474, 47.977, and 78.13 mg/g for Fe3O4, PANI, and PANI/Fe3O4 composites, respectively. The enhanced adsorption capability of the composites is attributed to increase in surface area and pore volume of the hybrid materials. The adsorption followed pseudo second order kinetics with R2 values of 0.873, 0.979, and 0.999 for Fe3O4, PANI, and PANI/Fe3O4 composites, respectively. The activation energy, enthalpy, Gibbs free energy changes, and entropy changes were found to be 11.14, -32.84, -04.05, and -0.095 kJ/mol for Fe3O4, 11.97, -62.93, -07.78, and -0.18 kJ/mol for PANI and 09.94, -74.26, -10.63, and -0.210 kJ/mol for PANI/Fe3O4 respectively, which indicate the spontaneous and exothermic nature of the adsorption process.

Adsorption of molybdenum by melanin

Background

Melanin is detectable in various sense organs including the skin in animals. It has been reported that melanin adsorbs toxic elements such as mercury, cadmium, and lead. In this study, we investigated the adsorption of molybdenum, which is widely recognized as a toxic element, by melanin.

Methods

Molybdenum level of the mouse skin was measured by inductively coupled plasma mass spectrometry. The pigmentation level of murine skin was digitalized as the L* value by using a reflectance spectrophotometer. An in vitro adsorption assay was performed to confirm the interaction between molybdenum and melanin.

Results

Our analysis of hairless mice with different levels of skin pigmentation showed that the level of molybdenum increased with an increase in the level of skin pigmentation (L* value). Moreover, our analysis by Spearman’s correlation coefficient test showed a strong correlation (r = − 0.9441, p < 0.0001) between L* value and molybdenum level. Our cell-free experiment using the Langmuir isotherm provided evidence for the adsorption of molybdenum by melanin. The maximum adsorption capacity of 1 mg of synthetic melanin for molybdenum was 131 μg in theory.

Conclusion

Our in vivo and in vitro results showed a new aspect of melanin as an adsorbent of molybdenum.

Electronic supplementary material

The online version of this article (10.1186/s12199-019-0791-y) contains supplementary material, which is available to authorized users.

The effect of diverse metal oxides in graphene composites on the adsorption isotherm of gaseous benzene

The effective removal technique is necessary for the real world treatment of a hazardous pollutant (e.g., gaseous benzene). In an effort to develop such technique, the adsorption efficiency of benzene in a nitrogen stream (5 Pa (50 ppm) at 50 mL atm min^-1 flow rate and 298 K) was assessed against 10 different metal oxide/GO composite materials (i.e., 1: graphene oxide Co (GO-Co (OH)₂), 2: graphene oxide Cu (GO-Cu(OH)₂), 3: graphene oxide Mn (GO-MnO), 4: graphene oxide Ni (GO-Ni(OH)₂), 5: graphene oxide Sn (GO-SnO₂), 6: reduced graphene oxide Co (rGO-Co(OH)₂), 7: reduced graphene oxide Cu (rGO-Cu(OH)₂), 8: reduced graphene oxide Mn (rGO-MnO), 9: reduced graphene oxide Ni (rGO-Ni(OH)₂), and 10: reduced graphene oxide Sn (rGO-SnO₂)) in reference to their pristine forms of graphene oxide (GO) and reduced graphene oxide (rGO). The highest adsorption capacities (at 100% breakthrough) were observed as ~23 mg g^-1 for both GO-Ni(OH)₂ and rGO-SnO₂, followed by GO (~19.1 mg g^-1) and GO-Co(OH)₂ (~18.8 mg g^-1). Therefore, the GO-Ni(OH)₂ and rGO-SnO₂ composites exhibited considerably high capacities to treat streams containing >5 Pa of benzene. However, the lowest adsorption capacity was found for GO-MnO (0.05 mg g^-1). Alternately, if expressed in terms of the 10% breakthrough volume (BTV), the five aforementioned materials showed values of 0.50, 0.46, 0.40, 0.44, and 0.39 L g^-1, respectively. The experimental data of target sorbents were fitted to linearized Langmuir, Freundlich, Elovich, and Dubinin-Radushkevich isotherm models. Accordingly, the non-linear Langmuir isotherm model revealed the presence of two or more distinct sorption profiles for several of the tested sorbents. Most of the sorbents showed type-III isotherm profiles where the sorption capacity proportional to the loaded volume.

Polymer Coating and Lipid Phases Regulate Semiconductor Nanorods' Interaction with Neuronal Membranes: A Modeling Approach

The interplay between nanoparticles (NPs) and cell membranes is extremely important with regard to using NPs in biology applications. With the aim of unraveling the dominating factors on the molecular scale, we have studied the interaction between polymer-coated semiconductor nanorods (NRs) made of cadmium selenium/cadmium sulfur and model lipid membranes. The zeta potential (ζ) of the NRs was tuned from having a negative value (-24 mV) to having a positive one (+11 mV) by changing the amine content in the polymer coating. Supported lipid bilayers (SLBs) and lipid monolayers (LMs) were used as model membranes. Lipid mixtures containing anionic or cationic lipids were employed in order to change the membrane ζ from -77 to +49 mV; lipids with saturated hydrophobic chains were used to create phase-separated gel domains. NR adsorption to the SLBs was monitored by quartz crystal microbalance with dissipation monitoring; interactions with LMs with the same lipid composition were measured by surface pressure-area isotherms. The results showed that the NRs only interact with the model membrane if the mutual Δζ is higher than 70 mV; at the air-water interface, positively charged NRs remove lipids from the anionic lipid mixtures, and the negative ones penetrate the space between the polar heads in the cationic mixtures. However, the presence of gel domains in the membrane inhibits this interaction. The results of the Derjaguin-Landau-Verwey-Overbeek model frame indicate that the interaction occurs not only due to electrostatic and van der Waals forces, but also due to steric and/or hydration forces.