Langmuir Isotherm Model Research Articles

Optimization, Kinetic and Thermodynamic Study of Rhodamine B Removal by Zinc Chloride-activated Arachis hypogaea (Groundnut Husk) biochar

Adsorption of dye from industrial effluent before discharge into the environment has become a major challenge to the food, pharmaceutical, textile, photographic and cosmetic industries. This has led scientists to the search for suitable green solutions. Carbonized and zinc chloride activated Arachis hypogaea (groundnut husk) in a 1:1 ratio was used as an adsorbent for the removal of Rhodamine B from aqueous solution. The adsorbent was characterized by ash content, bulk density, moisture content, pH, Iodine number, surface area and functional group analyses. Key parameters such as initial pH, initial concentration of Rhodamine B dye, temperature and contact time were investigated. The equilibrium data obtained were correlated with Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms. It was found that both the Freundlich and Langmuir isotherms fit well to the data. The Langmuir isotherm model best describes the uptake of Rhodamine B onto zinc chloride activated groundnut husk biochar with R2 > 0.997. Maximum Rhodamine B. dye removal was observed at a pH of 11.0, with an adsorbent dosage of 1.0 g, a contact time of 125 min, an initial dye concentration of 20 mg/L and a temperature at 315 K. The efficiency of zinc chloride activated groundnut husk biochar for Rhodamine B removal was 99.55% for dilute solutions at 50 g/L. The Fourier Transform Infrared (FTIR) spectra recorded before and after activation showed the numbers of functional groups available for Rhodamine B. molecules to bind onto in the studied adsorbent. The kinetic data were best described by the pseudo-first-order and pseudo second-order models, while the thermodynamic studies indicated a spontaneous and endothermic nature in the adsorption of Rhodamine B by the zinc chloride modified groundnut husk. This research clearly details an innovative approach to utilizing carbonized and zinc chloride-activated Arachis hypogaea (groundnut husk) as an eco-friendly adsorbent for the removal of Rhodamine B from industrial effluents.

A Facile Two-Step Utilization of Sorghum Waste Derived Activated Carbon

Sorghum (Sorghum bicolor (L.) Moench) is an agricultural commodity that produces waste, including stems, during its cultivation. Sorghum stems can be used as an alternative precursor for forming activated carbon (AC) with a high surface area by utilizing ZnCl2 as an activator and followed by a pyrolysis process at 750 °C under N2 gas. In this study, AC from sorghum stems was sequentially used as an adsorbent for heavy metals in wastewater, as well as applied as an anode material for lithium-ion batteries. From the characterization analysis, the synthesized AC has an amorphous structure, a high carbon content of > 90%, and a surface area of 1189 m2/g. AC was applied to adsorb 10, 50, and 100 ppm of metal cobalt (Co) at 30 °C. The adsorption isotherm and kinetics of metal Co showed an adsorption capacity of around 28.2 mg/g. The Langmuir isotherm model also describes Co adsorption and follows the pseudo-first-order equation. As for the Li-ion anode material, the ACs material is fabricated on a cylindrical battery with LiNi0.8Co0.1Mn0.1O2 as the counter cathode material. The specific discharge capacity results are 104 mAh/g at the voltage window of 2.7-4.3 V. The sequential utilization of sorghum stem-derived activated carbon can improve the product’s sustainability, and such an approach is promising to be applied in other biomass-based waste treatments.Keywords: Activated carbon, adsorption, battery, biomass, sorghum

Eco-Friendly Green Approach to the Biosorption of Hazardous Dyes from Aqueous Solution on Ragweed (Ambrosia artemisiifolia) Biomass

The presented research includes the preparation, characterization, and implementation of magnetic biosorbent (Fe3O4/RWB), obtained from ragweed (Ambrosia artemisiifolia) biomass. Fe3O4/RWB was examined for the removal of a hazardous dye, malachite green (MG), from an aqueous solution in a batch system. The effects of the experimental parameters—initial dye concentration (10–300 mg/L), contact time (0–120 min), biosorbent dose (1–5 g/L), initial pH (2–10), ionic strength (0–1 mol/L), and temperature (298–318 K) on dye biosorption—were studied. The results showed that increases in biosorbent dose, contact time, and initial pH led to an increase in biosorption efficiency, while the increase in initial dye concentration, the ionic strength, and temperature had the opposite effect. The biosorption kinetics for MG on Fe3O4/RWB were analyzed with pseudo-first-order, pseudo-second-order, and Elovich kinetic models, while the Langmuir, Freundlich and Temkin isotherm models were used for equilibrium data analysis. It was observed that the MG biosorption followed the pseudo-second-order kinetic model, whereas the Langmuir model was the best fit for the equilibrium biosorption data of MG, with a Qmax of 34.1 mg/g. the desorption of MG from Fe3O4/RWB indicated reusability in five adsorption/desorption cycles, good performance, and potential in practical applications.

Enhancing Adsorption Performance of Ce(III) by Amine-Thiourea and Aniline-Modified Magnetic Chitosan Nanocomposites.

To enhance the adsorption performance of chitosan for rare earth ions, two novel magnetic chitosan-based adsorbents were prepared by using chitosan-coated magnetic silica nanoparticles modified with amine-thiourea and aniline. The structure of copolymers was analyzed using characterization methods such as X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis, confirming the successful synthesis of modified magnetic chitosan nanocomposites. The investigation explored the influence of pH, contact time, dosage, initial concentration, and temperature on the adsorption performance. Comparative studies revealed a significantly enhanced adsorption performance after modification. The chitosan-coated magnetic silica nanoparticles modified with aniline (PAN-CS/Fe3O4@SiO2) reached adsorption saturation in about 120 min with a capacity of 136 mg/g, while the chitosan-coated magnetic silica nanoparticles modified with amine-thiourea (TSC-CS/Fe3O4@SiO2) exhibited a higher adsorption capacity of 156 mg/g for Ce(III). Both materials demonstrated strong agreement with the Langmuir isotherm model and pseudo-second-order kinetics. Thermodynamic analysis indicated that Ce(III) adsorption is both spontaneous and endothermic. Examination of the adsorption mechanisms suggested that the effective adsorption of Ce(III) is due to the strong synergistic effects of chelation and electrostatic interactions involving amino, carboxyl, and hydroxyl groups. This study demonstrates that chitosan modified with amine-thiourea and aniline is an effective approach to significantly enhance the rare earth ion adsorption by chitosan.

Adsorptive Removal of Dyes: A Comparison of Graphene Oxide to Granular Activated Carbon and Zeolite NaY

Synthetic carbon-based compounds are a prevalent wastewater contaminant that can adversely impact water resources due to their potential carcinogenic and toxic effects on aquatic biota and human health. This research investigates the versatility of graphene oxide (GO) as an alternative to commonly used adsorbents (zeolite NaY (NaY) and granular activated carbon (GAC)) for removal of synthetic cationic dyes. Rhodamine B (RhB) and methylene blue (MB), were selected as the target contaminants to represent cationic synthetic dyes with differing molecular sizes and structural compositions. Batch experiments using GO, NaY, and GAC as adsorbents were used to assess both physicochemical interactions between adsorbent surfaces and contaminants, and removal efficiency. GO demonstrated the highest removal efficiency for both target contaminants—at 99% and 86%, respectively—while the lowest removal efficiency was observed for NaY. Langmuir, Freundlich, Temkin, and BET isotherm models were used to describe the adsorption isotherms. Overall, GO demonstrated a more robust and higher removal efficiency of cationic dyes compared with GAC and NaY, indicating the potential of graphene oxide for the removal of complex structured organic contaminants in wastewater treatment.

Sustainable Activated Carbon from Agricultural Waste: A Study on Adsorption Efficiency for Humic Acid and Methyl Orange Dyes

In this study, porous activated carbon was produced from coffee waste and used as an effective adsorbent for the removal of humic acid (HA) from seawater and methyl orange (MO) dye from aqueous solutions. Phosphoric acid H3PO4 was used as an activating agent for the chemical activation of these agricultural wastes. The characterization of the activated carbon obtained using a scanning electron microscope (SEM), Fourier-transform infrared (FTIR) spectroscopy analysis, X-ray diffraction (XRD) and the Brunauer–Emmett–Teller (BET) method revealed that the activated carbon products exhibited high porosity and the formation of various functional groups. The effects of different parameters were examined using batch adsorption experiments, such as the adsorbent masses, pH, initial pollutant concentration and contact time. The results show that the performance increased with an increased adsorbent mass (up to 0.25 g/L) and decreased initial concentration of the adsorbent tested. On the other hand, this study clearly showed that the adsorption efficiency of the MO on the raw spent coffee grounds (SCGs) waste was around 43%, while no removal was observed for the humic acid. The experiments demonstrated that the activated carbon synthesized from the used coffee grounds (the efficiency was compared with commercial activated carbon (CAC) with a difference of 13%) was a promising alternative to commercially available adsorbents for the removal of humic acid from seawater. To understand and elucidate the adsorption mechanism, various isothermal and kinetic models were studied. The adsorption capacity was analyzed by fitting experimental data to these models. The experimental data for methyl orange dyes were analyzed using Langmuir and Freundlich isothermal models. The Freundlich isotherm model provided a superior fit to the equilibrium data, as indicated by a higher correlation coefficient (R2) than that of the Langmuir model. The maximum adsorption was observed at pH 3. The Freundlich adsorption capacity was found to be 333 mg/g adsorbent. The PAC showed a high adsorption capacity for the MO and HA. The PAC showed the highest adsorption capacities for the HA and MO compared with the other adsorbents used (SCGs and CAC) and would be a good material to increase the adsorption efficiency for humic acid removal in the seawater pretreatment process. In addition, the prepared AC BET surface area was 520.40 m2/g, suggesting a high adsorption capacity. This makes the material potentially suitable for various applications that require a high surface area. These results indicate that high-quality sustainable activated carbon can be efficiently produced from coffee waste, making it suitable for a wide range of adsorbent applications targeting various pollutants.

Adsorption of Phosphate from Aqueous Solution Using Hydrochar Produced from Agricultural Wastes

Excess phosphorus (P) in agricultural runoff can cause eutrophication in nearby waterbodies. Therefore, it is crucial to remove P from agricultural runoff before it reaches aquatic environments. This study evaluated the P adsorption potential of adsorbents prepared via co-hydrothermal carbonization of multiple agricultural wastes, including dairy manure (DM), corn stover (CS), and eggshell (ES), followed by thermal activation. The performance of the prepared adsorbents was investigated by both batch and column experiments. The activated hydrochar (AHC) with a DM/CS/ES ratio of 1:0:1 showed the highest P adsorption capacity of 209 ± 0.6 and 65.97 ± 9.04 mg/g in batch and column experiments, respectively. The P adsorption mechanism was well described by the Langmuir isotherm model (R2 > 0.8802) and the pseudo-second-order kinetics model (R2 > 0.8989). The adsorbent indicated the longest breakthrough and exhaust time of 210 and 540 min, respectively, with an adsorbent dose of 1 g and an initial concentration of 25 mg P/L. The breakthrough curve was well described by the Thomas model (R2 > 0.971). Thus, this study indicates that AHC with eggshell has high potential for use as an adsorbent for P removal from agricultural runoff.

Adsorption Studies of Ternary Metal Ions (Cs+, Sr2+, and Co2+) from Water Using Zeolite@Magnetic Nanoparticles (Z@Fe3O4 NPs)

The mixture of three metal ions (Cs+, Sr2+, and Co2+) is commonly found in radioactive waste, which induces several negative health effects. The removal of multiple metal ions is a true challenge for researchers due to the competitive adsorption of ions onto adsorbents. In this study, three metal ions, namely Cs+, Sr2+, and Co2+, have been successfully removed simultaneously from water using zeolite@magnetic nanoparticles (Z@Fe3O4 NPs). The optimized condition for the adsorption of ternary metal ions was obtained at an adsorbent weight of 0.2, pH of 6.0~7.0, and contact time of 60 min. The adsorption mechanism of ternary metal ions onto the surface of Z@Fe3O4 NPs was studied using the Pseudo-first-order, Pseudo-second-order, Elovich, and Intra-particle diffusion models. The Dubinin–Radushkevich Temkin, Freundlich, and Langmuir isotherm models were used to study the isotherm adsorption. The ternary metal ion adsorption (Cs+, Sr2+, and Co2+) on Z@Fe3O4 NPs was followed by the Pseudo-second-order model (PSO) with correlation coefficient (R2) range of 0.9826–0.9997. Meanwhile, the adsorption isotherms of ternary metal ions on Z@Fe3O4 NPs were in line with the Langmuir model with R2 values higher than 0.9206, suggesting monolayer chemisorption with maximum adsorption capacities of 48.31, 15.02, and 10.41 mg/g for Cs+, Sr2+, and Co2+, respectively. Thus, the selectivity trend in the ternary metal ions system towards the Z@Fe3O4 NPs is observed to be Cs+ > Sr2+ > Co2+, which indicates that the competitive effect of Cs+ is the strongest compared to Sr2+ and Co2+ions.

Electrochemical sensor for vascular endothelial growth factor based on self-assembling DNA aptamer structure

Developing vascular endothelial growth factor (VEGF) protein is essential for early cancer diagnosis and cancer treatment monitoring. This study presents the design and characterisation of an electrochemical sensor utilising a self-assembling DNA aptamer structure for the sensitive and selective detection of VEGF. The aptamer structure comprises three different parts of single-stranded DNA that are assembled prior to integration into the sensor. Polypyrrole (Ppy)-based layers were deposited onto screen-printed carbon electrodes (SPCEs) using an electrochemical deposition technique, followed by the entrapment of a self-assembled DNA aptamer structure within electrochemically formed Ppy matrix ((DNA aptamer)/Ppy). The response to the sensor toward VEGF was measured by the pulsed amperometric detection (PAD), highlighting the enhanced performance of DNA aptamer/Ppy configuration compared to bare Ppy. The sensor exhibited high sensitivity, achieving a limit of detection (LOD) of 0.21 nM for VEGF. The interaction behaviour between VEGF in the solution and the immobilise DNA aptamer/Ppy-based structure was analysed using Langmuir isotherm model. The developed electrochemical biosensor in promising for in vitro applications in early cancer diagnostics and treatment monitoring, enabling rapid screening of patient samples.

Removal of metaldehyde and acetamiprid by extracted cellulose from biomass incorporated with copper after acetylation

The presence of pesticides in water have reached to an alarming level in some parts of the world and have caused deteriorating effects on human health. Reclamation of portable water from such contaminants have become mandatory. Scientists around the world are trying to devise new methods of water purification. The target can be achieved either by limiting the use of pesticides for agriculture purposes or by devising unique methods for their recoveries from contaminated water. In this context, herein cellulose has been extracted from Populus nigra, subjected to acetylation using acetic acid in the acidic medium (sulfuric acid). The modified acetylated cellulose was treated with Cu-based salt to enable the metallic combination. The prepared sorbent was characterized by UV, SEM, EDX, XRD, and FTIR techniques. Two insecticides; metaldehyde and acetamiprid in synthetic waste-water solution were subjected for adsorption on the modified sorbent in a series of experiments to evaluate the impact of contact time, sorbent dosage, pH, and temperature. Optimum conditions established in a series of experiments such as 80 and 60 min of contact time for acetamiprid and metaldehyde respectively, pH of 8 and 9 (slightly basic) correspondingly for the mentioned pesticides, and a 0.08 g adsorbent dosage were used in the estimation of kinetics and isothermal parameters. The kinetic data successfully followed the pseudo-second-order kinetic model whereas, the isothermal data was found to be best fitted by Langmuir isotherm model in the case of acetamiprid and by Freundlich in the case of metaldehyde. The regeneration study was performed for both the pesticides showing more than 70 % removal capabilities of fabricated adsorbent after three consecutive cycles. The prepared adsorbent could be a better alternative of commercial activated carbon however, further experiments are encouraged to investigate the full environmental application spectrum of the fabricated sorbent.

The adsorption performance of high crystallinity Na-p zeolites prepared from oil shale ash for the waste water treatment

ABSTRACTS The Na-p type zeolite has been prepared by the alkali fusion hydrothermal synthesis method using the pure oil shale ash (OSA) and mixture of OSA and coal fly ash (CFA) as raw materials, which was used for adsorption of methylene blue (MB). The XRD spectra of zeolite synthesized from pure oil shale residue under different conditions indicated that the optimal experimental conditions were determined as follows: acid leaching concentration of 10%, sodium hydroxide dosage of 7 g, crystallization temperature of 130°C, and crystallization time of 12 h. Under the same conditions, zeolite was synthesized using the mixture of OSA and CFA, and its properties were characterized using XRD, SEM, and BET techniques. The results showed that the specific surface area and crystallinity of the zeolite prepared from the mixture were 59.6 m2/g and 86.32%, respectively, which were higher than that of pure OSA (20.6 m2/g and 64.07%). When 0.05 g of zeolite was added to the 35 mg/L MB solution and adsorbed for 180 min, the removal rates of MB by pure OSA, single-source zeolite and zeolite prepared from the mixture were 27.6%, 83.4%, and 99.2%, respectively. The adjusted R square verified that the pseudo-second-order kinetics and Langmuir isotherm model were the best fitting models. The maximum adsorption capacity (Qmax) of zeolite prepared from the mixture for MB was 55.5 mg/g. The above results proved that the novel material prepared in this study could be a potential effective wastewater treatment material.

Efficient removal of paracetamol, diclofenac sodium, and tetracycline using green synthesized Fe-zn co-doped sunflower seed shells

ABSTRACT In this study, carbon material obtained from sunflower seed shells and doped with Fe and Zn using mint extract (Fe-Zn-SSSC) was prepared, and the usability of this adsorbent in the removal of paracetamol, diclofenac sodium, and tetracycline was investigated. Fe-Zn-SSSC was characterized by SEM-EDX and FTIR. Additionally, the effects of pH and adsorbent dosage on the removal of paracetamol, diclofenac sodium, and tetracycline were investigated. The removal rates of paracetamol, diclofenac sodium, and tetracycline were obtained as 88.7%, 65.4%, and 76.0% at a pH of 4, after 1 hour of adsorption with 5 g/L Fe-Zn-SSSC, respectively. The best removal of paracetamol, diclofenac sodium, and tetracycline was obtained at pH 4, with qmax values calculated as 14.51 mg/g, 6.33 mg/g, and 8.99 mg/g, respectively. It was determined that the adsorption of paracetamol, diclofenac sodium, and tetracycline with Fe-Zn-SSSC was more compatible with the Langmuir isotherm model and pseudo-second-order kinetic model. As a result, this study demonstrates that carbon materials synthesized from sunflower seed shells can serve as an effective and low-cost adsorbent for drug from water.

Styrene divinyl benzene beads (SM-2) functionalized with triisobutylphosphine sulfide for selective uptake of palladium(II) from nitric acid medium

Resins impregnated with organic extractants regarded as effective adsorbent materials due to their ability for selective sorption. These resins consist of a polymeric material that is infused with accessible organic extractants. Furthermore, these resins merge the unique properties and the distinctive characteristics of both liquid-liquid extraction and solid-liquid sorption processes. In this work, the impregnation of Styrene divinyl benzene beads (SM-2 beads) with triisobutylphosphine sulfide (TIBPS = CYANEX 471X) was prepared. A SM-2 bead functionalized with CYANEX 471X (SM-2-TIBPS beads) was characterized using scanning electron microscope (SEM) and Fourier-transform infrared spectroscopy (FT-IR) techniques and investigated for recovery and separation of palladium ions from a 3 M nitric acid solution. Various parameters were studied, as shaking time effect, nitric acid concentration, SM-2-TIBPS beads weight, Pd(II) concentration and temperature. The Pd(II)/SM-2-TIBPS sorption system has an endothermic nature and was fitted with a Langmuir isotherm model with a 0.9860 regression factor. The kinetics modeling was fitted with PSO and IPD models with regression factors of 0.9889 and 0.9959, respectively. The maximum monolayer sorption capacity of SM-2-TIBPS was found to be 17.47 ± 0.9 mg/g. The sorption of Pd(II) from different media at 3 M takes the following sequence: HNO3 > HCl > H2SO4. Desorption of about 76.38 ± 2.4% was achieved with (1 M + 1 M) of thiourea + HCl after one desorption stage. Effect of other interfering ions, as Pt(II), Pb(II), Eu(III), Cu(II), Mo(VI), Co(III), Zr(IV), Fe(III), Cd(II), and Ce(III), indicates high separation factors between Pd(II) and other investigated metal ions, which ranged from 9.4 to 35.

Sulfonate-Bonded Conjugated Microporous Polymer Hollowed-Out Spheres to Capture Fluoroquinolone Antibiotics and Cationic Dyes from Wastewater.

Developing adsorbent materials for the efficient removal of multiple organic pollutants in water is of importance technological significance. In the present work, a kind of conjugated microporous polymer (CMP) with a hollow sphere structure was constructed by applying SiO2 nanoparticles as a template and 1,3,5-triethynylbenzene (TEB) and 2,7-dibromocarbazole (27-DBCZ) as building blocks via the Sonogashira-Hagihara cross-coupling reaction. In order to further improve the dispersibility of the as-resulting CMPs in water, hydrophilic CMPs (H-S-CMPs) were obtained by a sulfonation modification. The adsorption performance of H-S-CMPs on dyes and antibiotics was investigated, which was based on different experimental parameters such as the initial concentration, contact time, temperature, pH, and adsorbent dose. The adsorption isotherm, kinetics, and thermodynamics were also studied, and the possible adsorption mechanism of H-S-CMPs was discussed. The experimental results illustrated that the adsorption process of H-S-CMPs on dyes and antibiotics is more consistent with the Langmuir isotherm model and the pseudo-second-order kinetic model. The maximum adsorption capacities of H-S-CMPs for rhodamine B (RhB), methylene blue (MB), ciprofloxacin, and norfloxacin were 206.2, 324.7, 222.2, and 216.9 mg/g, respectively, which were determined according to the Langmuir isothern model. In addition, the adsorption mechanism of H-S-CMPs may be attributed to the synergistic effects of hydrogen bonding, electrostatic attraction, π-π stacking, and pore filling. After 5 cycles, H-S-CMPs still maintained good stability, and their removal rate of dyes could reach more than 70%. Notably, this polymeric hollow microsphere has been less extensively investigated as an adsorbent for the removal of dyes and antibiotics. As a result, based on the designable flexibility of CMPs and the unique structure of hollow microspheres, the material holds great promise for wastewater treatment in the presence of multiple pollutants.

Innovative eco-friendly methyl orange removal: Mechanism, kinetic, and thermodynamic study using starch cryogel-integrated mesoporous silica nanoparticles

This study introduces a novel, eco−friendly composite, uncalcined mesoporous silica nanoparticles incorporated into a starch cryogel (MSNs-Cry), designed for the effective removal of methyl orange (MO) from water. MSNs−Cry integrates uncalcined mesoporous silica nanoparticles (MSNs) within a starch cryogel network, leveraging the high adsorption capacity of MSNs. The composite achieved a maximum adsorption capacity of 18.98 mg g⁻1 and demonstrated high removal efficiencies of 99.00 % ± 0.21 % in synthetic water (10 mg L−1 MO) and 92.77 % ± 1.76 % in real wastewater containing 0.43 mg L−1 MO. The Langmuir isotherm model provided a superior fit (R2 = 0.9930) compared to the Freundlich model (R2 = 0.9180), and the adsorption kinetics followed a pseudo−second−order model (R2 = 0.9917). The primary adsorption mechanisms included electrostatic attraction, hydrophobic interactions, and hydrogen bonding. The process was endothermic (ΔH° = 31.3 kJ mol−1), spontaneous, and more favorable at higher temperatures (ΔG° = −34.2 to −38.6 kJ mol−1 at 298–318 K). In the presence of sodium silicate at 13.1 times the MO concentration, removal efficiency drops by 35.77 %, and with sodium sulfate and urea at 100 times the MO concentration, it decreases by 8.65 %. Despite these challenges, MSNs−Cry effectively removes MO in the presence of the anionic dye Congo Red and metal ions, demonstrating its selective adsorption capabilities. The tablet form of MSNs−Cry prevents the loss of uncalcined MSNs, mitigating potential environmental and operational impacts. Additionally, the composite's effectiveness at a natural pH of 6.65 eliminates the need for pH adjustment, offering a cost−effective solution for real−world applications. This study establishes MSNs−Cry as a promising material for sustainable water purification.

Sugarcane Bagasse Based Adsorbents and their Adsorption Efficacy on Removal of Heavy Metals from Nakuru Industrial Wastewater: Optimization, Kinetic and Thermodynamic Aspects

Currently, researchers are seeking to reduce heavy metal contamination from the environment, using agricultural waste materials like rice husk, groundnuts shells among others. The study focused on the removal of Cu(II), Pb(II), Cd(II), Ni(II), and Cr(III) ions from aqueous solutions and Nakuru industrial wastewater using sugarcane bagasse (NSCB) and valorised bagasse ash (VSCB), as alternative low-cost agricultural waste bio-sorbents. To achieve this goal, sugarcane bagasse was collected from Nzoia sugar industry in western Kenya, while the valorised bagasse was obtained by heating sugarcane bagasse sample in a muffle furnace at 300°C for three hours. Furthermore, batch adsorption studies were performed, and the effects of several factors, i.e. adsorbent particle size, pH, contact time, initial heavy metal ions concentration and temperature were investigated to optimise the removal efficiency of Pb, Cu, Cd, Ni, and Cr. The optimal adsorption conditions were pH of 5.0, adsorbent dosage of 0.1 g and ≤ 150µm particle size, equilibrium time of 60 minutes and at 25 degrees Celcius. The removal kinetics of the metal ions onto both adsorbents fitted well with the pseudo-second-order model. The removal kinetics of the metal ions onto both adsorbents fitted well with the pseudo-second-order model. The adsorption of Pb2+ and Ni2+ onto NSCB fitted better with the Freundlich isotherm model, while Cd2+, Cu2+ and Cr3+ showed better fit for the Langmuir isotherm model. As for VSCB adsorbent, Cr3+ has a better fit with the Langmuir isotherm model whereas Pb2+, Ni2+, Cd2+, and Cu2+ fitted well on the Freundlich isotherm model. Freundlich constant’s (1/n) values and the separation factor (RL) from the Langmuir isotherm model indicate that the metal ions were favourably adsorbed onto the adsorbents. Langmuir isotherm model was used to estimate the maximum adsorption capacities (qmax) for Cu(II), Pb(II), Ni(II), Cd(II), and Cr(III). The negative free energy change (∆G) values revealed that adsorption process of the metal ions onto NSCB and VSCB was spontaneous. Fourier Transform Infrared Spectroscopy (FTIR) was used for characterization studies. Interactions with metal ions caused the frequencies of the active functional groups, –OH, C=O and C=C, on the bio-sorbent surfaces to shift to higher values. Therefore, sugarcane bagasse and valorised bagasse have demonstrated higher potential to remove relatively all selected heavy metals in the industrial wastewater at controlled pH.

The facile preparation of polydopamine-modified sepiolite and its adsorption properties and microscopic mechanism for cadmium ion

Natural sepiolite (SEP) has the characteristics of cation exchange, abundant reserves, low cost, and environmental friendliness, but its adsorption capacity for heavy metal pollutants is limited. Because polydopamine (PDA) molecules contain rich functional groups such as phenolic and amino groups, in the present work, dopamine and natural sepiolite were utilized as raw materials to prepare polydopamine-modified sepiolite composite (SEP/PDA) by simple co-precipitation method. According to Langmuir isotherm model, the maximum adsorption capacity of SEP/PDA for Cd2+ can reach 203.21 mg/g at 298 K. At the initial concentration of 100 mg/L, the adsorption capacity was 2.9 times that of natural sepiolite. The composite material has good reusability and anti-cationic interference performance and has 100 % removal ability of low concentration Cd2+ in actual electroplating wastewater. Density Functional Theory (DFT) calculations were performed to obtain the electronic structure information. To elucidate the microscopic mechanism, molecular surface analyses, Interaction Region Indicator (IRI), Atom In Molecules (AIM) theory, Bond Order Density (BOD), and Electron Localization Function (ELF) were conducted. These analyses revealed that the amino nitrogen and phenolic oxygen atoms in the dopamine molecules donate lone pair electrons to coordinate with cadmium ions. Polydopamine, which possesses multiple oxidation states, contains catechol, quinone, and indole or a lesser extend pyrrole groups that can complex with cadmium ions, resulting in the formation of a surface complex. This coordination significantly enhances the adsorption properties of the SEP/PDA composite.

Saraca asoca-assisted green synthesise of ZnO nanoplatelets for photocatalytic activity and adsorption kinetics

ABSTRACT ZnO nanoplatelets (ZnO NPLs) have been successfully synthesised using microwave-assisted technique (400 W, 180 sec) with the plant extract Saraca-asoca. The surface morphology analysis confirms ZnO’s plate-like nanostructure, leading to the creation of ZnO NPLs. The results show excellent photocatalytic performance (at 125 W for both UV and visible light) and effectiveness against malachite green (MG), methyl orange (MO) and rhodamine B (RhB). Notably, ZnO NPLs break down malachite green (MG) exceptionally well, reaching a maximum degradation efficiency of 92% in under 30 min (UV light). Moreover, ZnO NPLs have been evaluated for MG adsorption characterised by the pseudo-first-order kinetic model, alongside the Freundlich and Langmuir isotherm models. In the Freundlich model, the maximal adsorption capacity is determined to be 331 mg/g. These new faceted ZnO NPLs have a great potential for use in photocatalytic and adsorption processes that aim to reduce aqueous pollutants.

Green room-temperature fabrication of phosphotungstic acid functionalized MOF-808 for efficient removal of cationic antibiotics

ZrⅣ-based metal–organic frameworks (MOFs)–featuring exceptional water stability, large surface area, and structural tunability–hold promise for efficient antibiotics adsorption from water. However, their inherent positive charge in neutral environments and the harsh conditions required for their synthesis hinder their effective removal of cationic antibiotics. To address this challenge, a green one-pot synthesis approach was proposed to fabricate phosphotungstic acid-functionalized MOF-808 (termed as PTA@MOF-808) at room temperature for elevated antibiotic adsorption. This approach not only leverages the strong electronegativity of PTA to improve electrostatic interactions and π-π stacking but also finely tailors the pore size of MOF-808, resulting in enhanced adsorption capacity of PTA@MOF-808. The influence of PTA loading, solution pH, and absorbent dosage on the performance of PTA@MOF-808 were studied in detail. Adsorption experiments demonstrated that PTA@MOF-808 outperformed unmodified MOF-808 in removing various positively charged antibiotics, with 5 % PTA@MOF-808 exhibiting maximum adsorption capacities of 548.1 mg g−1 and 482.9 mg g−1, for DOX and TCHC, respectively. The adsorption process followed the Langmuir isothermal model and the pseudo-second-order kinetic equation. Furthermore, the composite PTA@MOF-808 displayed excellent reusability after multiple adsorption–desorption cycles. These findings highlight the potential of PTA@MOF-808 as a promising absorbent for removing specific antibiotics from water, with significant implications for wastewater treatment.

PH-Responsive Alginate/Chitosan Gel Films: An Alternative for Removing Cadmium and Lead from Water.

Biosorption, a non-expensive and easy method for removing potentially toxic metal ions from water, has been the subject of extensive research. In this context, this study introduces a novel approach using sodium alginate and chitosan, versatile biopolymers that have shown excellent results as biosorbents. The challenge of maintaining high efficiencies and reuse is addressed by developing alginate/chitosan-based films. These films, prepared using solvent casting and crosslinking methods, form a hydrogel network. The alginate/chitosan-based films, obtained using the eco-friendly polyelectrolyte complex method, were characterized by FTIR, SEM, TGA, and DSC. The study of their swelling pH response, adsorption, and desorption behavior revealed promising results. The adsorption of Pb was significantly enhanced by the presence of both biopolymers (98%) in a shorter time (15 min) at pH = 6.5. The adsorption of both ions followed a pseudo-second-order kinetic and the Langmuir isotherm model. The desorption efficiencies for Cd and Pb were 98.8% and 77.6% after five adsorption/desorption cycles, respectively. In conclusion, the alginate/chitosan-based films present a highly effective and novel approach for removing Cd and Pb from water, with a promising potential for reuse, demonstrating their strong potential in potentially toxic metal removal.