Intraparticle Diffusion Model Research Articles

Taguchi method for optimization of Cr(VI) removal, isotherm, kinetic and thermodynamic studies

In this study, Taguchi optimization method was applied to determine the optimum operating conditions for batch adsorption of Cr(VI) from aqueous solution. Initial pH of solution, adsorbent dose, initial hexavalent chromium concentration, contact time and adsorbent type were selected as the variables, and the removal efficiency of Cr(VI) was chosen for the designated response. L18(35) orthogonal array, signal-to-noise (S/N) ratio and analysis of variance statistical procedures were applied to identify the effect of each operating parameter on the removal of Cr(VI) from aqueous solution. The signal-to-noise (S/N) ratio results showed that the optimal combination for Cr(VI) removal was at pH 1.0, adsorbent dose of 3.6 g.L−1, Cr(VI) concentration of 30 mg.L−1, contact time of 95 min and olive leaves as adsorbent type. A removal of 95.09% was obtained at these optimum conditions. The analysis of variance of the data revealed that initial pH of solution was the most dominant parameter affecting Cr(VI) removal efficiency, followed by adsorbent type, adsorbent dose, contact time and initial metal concentration. Under optimal conditions, adsorption kinetic of Cr(VI) was studied and modeled using the pseudo first-order, pseudo-second-order and intraparticle diffusion models. It was found that the pseudo-second-order model fitted the adsorption data most with the highest determination coefficient (R2 = 0.996). Freundlich isotherm model, with regression coefficient R2 of 0.953, fit well with the equilibrium isotherm data. The Langmuir maximum adsorption capacity was found to be 62.5 mg.g−1. The experimental values of ΔH°, ΔG° and ΔS° revealed that the adsorption process was spontaneous and endothermic.

Synthesis of Tubular Hydroxyapatite and Its Application in Polycaprolactone Scaffold Materials.

Nano-hydroxyapatite (HAp) is an ideal material in the field of biomedicine due to its good biocompatibility and bioactivity. However, a significant drawback of pure HAp materials is their inferior mechanical properties. Therefore, in this rigorous investigation, the optimal calcium-to-phosphorus ratio for the synthesis of HAp was meticulously delineated, followed by its nuanced modification using KH550 (γ-aminopropyltriethoxysilane). This was further amalgamated with polycaprolactone (PCL) with the aim of providing a superior material alternative within the domain of bone scaffold materials. The post-modified HAp demonstrated enhanced interfacial compatibility with PCL, bestowing the composite with superior mechanical characteristics, notably a peak bending strength of 6.38 ± 0.037 MPa and a tensile strength of 3.71 ± 0.040 MPa. Scanning electron microscope (SEM) imagery revealed an intriguing characteristic of the composite: an initial ascension in porosity upon HAp integration, subsequently followed by a decline. Beyond this, the composite not only exhibited stellar auto-degradation prowess but also realized a sustained release cycle of 24 h, markedly optimizing drug utility efficiency. A kinetic model for drug dispensation was developed, positing an adherence to a pseudo-second-order kinetic principle. In tandem, through the formulation of an intra-particle diffusion model, the diffusion mechanisms pre- and post-modification were deeply probed. Cytotoxicity assays underscored the composite's exemplary biocompatibility. Such findings accentuate the vast potential of the modified HAp-PCL composite in bone tissue engineering, heralding a novel and efficacious avenue for impending bone defect amelioration.

Thiol-modified olive-stone biochar preparation for Hg(II) removal from aqueous solutions

Mercury (Hg) is a heavy metal whose toxicity poses significant environmental and health risks. Utilising biochar prepared from biomass waste is a straightforward and effective method for removing mercury from water. This research centred on producing a thiol-functionalised biochar derived from olive-stone waste for the removal of mercury (II) from aqueous solutions. Characterisation analyses confirmed successful functionalisation. The biochar, despite having a limited specific surface area (4.14 m2/g) due to raw material nature and pyrolysis conditions, exhibited a notable ability for mercury (II) adsorption, primarily attributed to the thiol-modified surface. Adsorption was assessed using a 23 factorial design, with the variables being adsorption time, biochar dose and initial mercury (II) concentration in the solution. Biochar dose emerged as the most influential factor, followed by adsorption time and, lastly, initial mercury (II) concentration. The peak removal efficiency of the model stood at 98.19%. The kinetics aligned with the pseudo-first-order and intraparticle diffusion models, suggesting a surface adsorption mechanism coupled with pore diffusion. This work accentuates the potential of olive-derived biochar, when thiol enhanced, in treating aqueous systems contaminated with mercury (II).

Co-Transport of Aniline and TNT with Loess Colloid Particles in Saturated Loess Columns: Mechanism and Processes

The transport of mobile colloidal particles with organic pollutants in porous media has attracted considerable attention. Aniline and 2,4,6-trinitrotoluene (TNT), as aromatic compounds and key components of energetic materials, are continuously released into the environment. This study compared the co-transport of loess colloidal particles with aniline and TNT, aiming to investigate the influence of structural and physicochemical properties of the pollutants. The colloids were prepared and characterized, and static adsorption and dynamic column experiments were conducted. The results indicate that the adsorption processes of aniline and TNT both conformed to the quasi-second-order kinetic and the intra-particle diffusion models, with aniline exhibiting higher rate constants than TNT. The main adsorption mechanism involved van der Waals force, hydrogen bonding, and electrostatic interaction. Response surface experiments indicated that the adsorption capacity increased with higher initial concentration of organic compound but decreased with larger particle size and higher Na+ concentration. In column experiments, the adsorption of loess colloid particles on aniline and TNT was strongly correlated with the concentration of loess colloid particles. Loess colloid particles could be used as carriers to enhance the co-transport, with aniline exhibiting a faster transport rate due to the differences in polarity and molecular structure compared to TNT. In summary, loess colloidal particles enhanced the transport behavior of aniline and TNT in saturated loess columns. The differences in polarity and molecular structure of aniline and TNT further affect their co-transport mechanism in loess.

High organic sulfur coal derived carbon-based sorbent for Hg0 capture from coal-fired flue gas

To develop the high value utilization of high organic sulfur coal instead of combustion as well as save the cost of mercury pollution control, we attempted to transmute the inherent sulfur of high organic sulfur coal, in the case of LF coal (which is from Linfen city, China), to active sulfur species for mercury capture by doping metal oxides, and CuO performed best among various metal oxides. The sorbent (or activated sample) prepared from LF coal with doping CuO is labelled LF+Cu-A, around which a series of experiments were conducted. Firstly, the effects of operational conditions, including GHSV (gas hourly space velocity), temperature and flue components, on the mercury capture performance of LF+Cu-A were thoroughly investigated, and results showed that LF+Cu-A had an excellent mercury capture performance. The average mercury capture efficiency is 97.8 % during a two-hour test under N2+O2+H2O+SO2+NO atmosphere with GHSV of 240000 h−1 and temperature of 120 °C. Secondly, the experimental data were fitted by four kinetic models, and it is found that the mercury adsorption process under low temperatures (60, 90, 120 °C) and high temperature (150 °C) are in the best agreement with the pseudo-first-order model and the intra-particle diffusion model respectively. Last, the mercury capture mechanisms of LF+Cu-A were revealed by Hg-TPD (Hg-temperature programed desorption) experiment, Raman analysis and XPS (X-ray photoelectron spectrometer) spectra, and it is indicated that the multiple sulfur species and Cu2+ play roles in the mercury capture process, during which elemental mercury are oxidized to HgS and fixed on the surface of LF+Cu-A.

Effect of calcination temperature on hydroxyapatite in fluoride removal from groundwater: Process optimization and kinetic study

The present study investigates the defluoridation capacity of calcium hydroxyapatite as an efficient and environmentally safe adsorbent material. Calcium hydroxyapatite was synthesized by co-precipitation route using Ca/P = 1.76 ratio followed by calcination at various temperature ranges (30–900 °C) and termed as CaHAP-T. The physical and chemical properties of CaHAP-T samples were analyzed by TGA, SEM, BET, XRD, TEM, UV-DRS, FTIR, and NMR techniques. The CaHAP-900 sample exhibited exceptionally excellent thermal stability, crystallinity and ion-exchange capacity. Furthermore, the parametric studies revealed 98.12 ± 1.03 % fluoride removal efficiency at 30 °C temperature and 30 min contact time at neutral pH using 1 g/50 mL of adsorbent dose. The well-fitted pseudo-second-order and intraparticle diffusion model indicates the chemisorption combined with diffusion control of fluoride ions sorption on CaHAP-900 adsorbent. This work offers a deep understanding of the removal of fluoride ions from contaminated groundwater in prevalent areas and the calcium hydroxyapatite (CaHAP-900) can be utilized as an efficient cost-effective adsorbent material.

The performance of an eco-friendly adsorbent for methylene blue removal from aqueous solution: Kinetic, isotherm, and thermodynamic approaches

The current study aims to determine how well pomegranate peel can remove Methylene Blue (MB) from an aqueous solution. For this purpose, kinetic, isotherm, and thermodynamic adsorption studies were performed in a batch system. The rate of MB adsorption was rapid and reached equilibrium at about 60 minutes. The adsorption capacity reached approximately 42.71 mg g-1 at the initial dye concentration of 100 mg L-1. The kinetic modeling of MB adsorption was conducted using pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion models. The pseudo-second-order model was found to be the most adequate for fitting the kinetic data based on R2, RMSE, ARE, and ?2 values. It was also discovered that MB adsorption onto pomegranate peel is not simply rate-limited by intraparticle diffusion. The isotherm approach showed a maximum adsorption capacity of 67.78 mg g-1 at 298 K using 2 g L-1 of pomegranate peel. Equilibrium modeling was also conducted. The four statistical values highlighted the better fit of the Langmuir model than the Freundlich model. Additionally, the exothermic and spontaneous nature of the adsorption process was revealed by thermodynamic research. These findings demonstrate the effectiveness of pomegranate peel as an eco-friendly absorbent for MB removal.

Zn-Al layered double hydroxide nanoparticles for efficient removal of food dyes from wastewater

The ability of layered double hydroxides clay (LDH) produced from ZnAl-NO3 to remove Sunset Yellow FCF (E110), Azorubine (E122), Tartrazine (E102), and Brilliant Blue FCF (E133) from an aqueous solution was studied. The effects of various variables on adsorption were studied. The obtained results show that the adsorption of various food dyes depends on the initial concentration, dose, pH, contact time, and temperature. The adsorption capacities at an equilibrium time of 40 min for E133, E122, E110, and E102 were 18.21, 21.46, 13.19, and 20.58 mg/g, respectively. The adsorption equilibrium data for aqueous solutions were analyzed using Langmuir and Freundlich isotherms and a thermodynamic study. Adsorption kinetics data for aqueous solutions was studied using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. The morphology for Zn-Al LDH was investigated by scanning electron microscopy (SEM) and BET (pore size = 0.004 cc/g). Equilibrium data were studied by Freundlich, Langmuir, and Temkin isotherms. As for thermodynamics, the value of ∆H° is negative, which means that the adsorption method is exothermic at a temperature range of 288–338 K. ∆S ° is a negative value indicating that the randomness is low, ∆G° is also negative means that the reaction is spontaneous. The FTIR spectroscopic analysis of LDH before and after the adsorption also confirms that the adsorption of food dyes was smooth and spontaneous on Zn-Al LDH providing an excellent and easy-to-use adsorption method for industrial application of wastewater treatment.

A facile method for synthesis of bismuth oxide nanoparticles on anion exchange resin and its salt removal ability for saline water

In this work, a method was applied to produce bismuth oxide nanoparticles on anion exchange resin (AR@Bi2O3), which was then applied effectively for removing salts in aqueous solution of NaCl and real-world saline water. The results from SEM, EDX, XRD, and FTIR confirm the preparation of AR@Bi2O3 with a crystalline structure and high purity as well as the effective adsorption of salt on the surface of the material. The salt removal was investigated under various conditions of contact time, solution pH, adsorbent mass, initial salt concentration, and solution temperature. The salt adsorption of AR@Bi2O3 reached an equilibrium capacity of 280 mg/g after 45 min, which is best described by the intraparticle diffusion model. Moreover, pH 5 was found to be the optimal value for salt adsorption and Freundlich is the best model for describing the adsorption process, which was a spontaneous process (∆G < 0). The adsorption capacity of the AR@Bi2O3 material likely remained stable at over 260 mg/g even after 10 cycles of adsorption-regeneration, indicating a great potential for practical application of AR@Bi2O3 in saline water treatment.

Adsorption properties of M-UiO-66 (M = Zr(IV); Hf(IV) or Ce(IV)) with BDC or PDC linker.

The increasing CO2 emissions and their direct impact on climate change due to the greenhouse effect are environmental issues that must be solved as soon as possible. Metal-organic frameworks (MOFs) are one class of crystalline adsorbent materials that are thought to have enormous potential in CO2 capture applications. In this research, the effect of changing the metal center between Zr(IV), Ce(IV), and Hf(IV), and the linker between BDC and PDC has been fully studied. Thus, the six UiO-66 isoreticular derivatives have been synthesized and characterized by FTIR, PXRD, TGA, and N2 adsorption. We also report the BET surface area, CO2 adsorption capacities, kinetics, and the adsorption isosteric heat (Qst) of the UiO-66 derivatives mentioned family. The CO2 adsorption kinetics were evaluated using pseudo-first order, pseudo-second order, Avrami's kinetic models, and the rate-limiting step with Boyd's film diffusion, interparticle diffusion, and intraparticle diffusion models. The isosteric heats of CO2 adsorption using various MOFs are in the range 20-65 kJ mol-1 observing differences in adsorption capacities between 1.15 and 4.72 mmol g-1 at different temperatures due to the electrostatic interactions between CO2 and extra-framework metal ions. The isosteric heat of adsorption calculation in this report, which accounts for the unexpectedly high heat released from Zr-UiO-66-PDC, is finally represented as an increase in the interaction of CO2 with the PDC linker and an increase in Qst with defects.

Comprehensive analysis of cationic dye removal from synthetic and industrial wastewater using a semi-natural curcumin grafted biochar/poly acrylic acid composite hydrogel.

Polymer composites offer a tailored framework as an exceptional candidate for water treatment due to their tunable chemical structure, porous 3D architecture, physiochemical stability, accessibility, pH-sensitivity and ease of use. In this study, curcumin-engineered biochar is embedded into a cross-linked polyacrylic acid hydrogel matrix using in situ polymerization for developing a semi-natural adsorbent for the removal of cationic dye from an aqueous solution. The physicochemical features of the generated composite hydrogel are significantly influenced by the implementation of curcumin-grafted biochar into the polyacrylic acid substrate. Comprehensive characteristic approaches were employed to explore all aspects of the adsorbent's properties, especially its removal efficacy. The methodical adsorption study was accomplished by monitoring dynamic factors such as pH, adsorbent content, time frame, and initial dye concentration. The presence of the porous aromatized structure of biochar, active oxygen-enrich functional groups (carboxyl, hydroxyl, keto, enol, ether) coupled with the conjugated curcumin structure facilitate the effective establishment of hydrogen bonds, electrostatic interactions, π-π interactions, electron donor-acceptor and charge-assisted H-bonding with the malachite green (MG) and rhodamine B (Rho) molecules. The highest adsorption capacities of MG and Rho reached 521 mg g-1 and 741 mg g-1 respectively, in the range of neutral pH, considering their molecular nature, functionalities, and unique adsorption mechanisms. The isothermal modeling was carried out with Henry, Langmuir, Jovanovic, Freundlich, Temkin, and Koble-Corrigan models to determine the adsorption system. Additionally, the kinetic data were assessed with Bangham, pseudo-first-order, pseudo-second-order, intra-particle, and liquid film diffusion models to ascertain the rate-limiting phase. The Koble-Corrigan and Langmuir isotherm models (R2 > 0.997) as well as pseudo-second-order (R2 > 0.998) and Elovich (R2 = 0.983 and 0.995) kinetics models provide a substantial level of concordance with empirical findings. The analysis of non-linear diffusion models revealed that the Bangham (R2 > 0.995) pore and liquid film diffusion (R2 > 0.960) models has major influence on the rate of the adsorption procedure. The binary adsorption test demonstrated higher efficacy of the synthesized adsorbent in the removal of malachite as compared to rhodamine. This study sheds light on the design of a cost-effective semi-natural polymeric composite for treating dye-polluted wastewaters, a major milestone toward environmental and ecological sustainability.

Removal and adsorption kinetics of methylene blue dye by pristine cotton husk bracts (Gossypium hirsutum L.) from agroindustrial waste

In the present study, pristine cotton husk bracts (CHk), an agricultural waste, were successfully employed as an adsorbent for the removal of methylene blue (MB). Batch adsorption experiments were performed as a function of contact time, pH, adsorbent dosage, and initial dye concentration (1–100 mg/L). The experimental results indicate that 20 mg of CHk removed 94% of 20 mg/L dye. Adsorption dye kinetic was analyzed using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. Furthermore, adsorption data were modeled using the Langmuir, Freundlich, and Temkin isotherms. The kinetic study reveals that the present adsorption process followed a pseudo-second-order, with a qe= 96.56 mg/g and, k2 = 0.109 min−1 at pH 7. Adsorption followed the Langmuir isotherm; the adsorption equilibrium results show a qm = 458.72 mg/g and kL= 0.1622 L/mg, using 20 mg of CHk. The equilibrium parameter value (RL) was observed to be in the interval of 0.0580 to 0.8604. Thermodynamic results indicate that the adsorption mechanism between CHk and MB is spontaneous, exothermic, and with a decrease in the disorder of the adsorbate molecules on the adsorbent surface; at all the temperatures studied (293, 313, 333 K). The use of CHk agroindustrial waste is an ideal option for the treatment of industrial textile effluent in environmental cleansing.

Simultaneous removal of triadimefon and dinotefuran by a new biochar-based magnesium oxide composite in water: Performances and mechanism

In recent years, the ecological security has been seriously threatened by the residues of pesticides in the environment. In this study, a new biochar-based magnesium oxide composite (MTBC) was successfully prepared using Traditional Chinese Medicine residues and MgCl2 solution, and then applied for the removal of triadimefon (TDF) and/or dinotefuran (DIN) in water. Batch experiments results indicated that 86.42 and 87.86 % of TDF and DIN removals could be obtained by MTBC within 120 min, respectively. The TDF adsorption process was proved to be well fitted with the pseudo-second-order kinetic, Elovich, liquid film diffusion, Intra-particle diffusion and Langmuir isothermal models. The TDF adsorption by MTBC was a spontaneous endothermic reaction, and chemical adsorption process was dominant. The inhibitory of the coexisting anions on TDF removal followed the order of SO42−＜Cl−＜HPO43−＜HCO3–. Both TDF and DIN could be simultaneously removed by MTBC at the certain concentrations levels. The possible removal mechanism for the adsorption of TDF and DIN by MTBC was proposed, both TDF and DIN were rapidly distributed and adsorbed on MTBC surface, then diffused into the interior pores structure and were finally adsorbed on MTBC through various reaction processes. The TDF removal process might be involved with hydrogen bonding, π-π interaction, pore filling and electrostatic interaction, while DIN removal might be involved with hydrogen bonding, pore filling and electrostatic interaction. These findings suggested that biochar-based magnesium oxide composite was an effective adsorbent for the remediation of agricultural effluents containing TDF and DIN.

EDTA functionalized Mg/Al hydroxides modified biochar for Pb(II) and Cd(II) removal: Adsorption performance and mechanism

This study has successfully synthesized layered double hydroxide (LDH) biochar (E-Mg/Al-LDH BC) with ethylenediaminetetraacetic acid (EDTA) and examined its adsorption capabilities towards Pb(II) and Cd(II). The results demonstrate that the kinetics of heavy metal removal can be well described by the pseudo-second-order model. The intraparticle diffusion model indicates that the controlling steps for Pb(II) and Cd(II) are not uniform. The adsorption isotherm for Cd(II) conforms to the Langmuir model, while for Pb(II), it adheres to the Freundlich model. The distribution coefficient (Kd) shows that Pb has a significantly higher competitive adsorption capacity than Cd(II). Therefore, in comparison to single adsorption, the maximum adsorption capacity of Cd(II) in competitive adsorption decreased by 58.86%, while Pb(II) only decreased by 13.54%. Surface complexation, cation exchange, chemical precipitation, electrostatic interaction, and cation-π bonding are the inherent mechanisms by which E-Mg/Al-LDH BC removes heavy metal ions. E-Mg/Al-LDH BC has the potential to remediate heavy metal-contaminated water, and it also provides insights for the application of modified biochar in the treatment of multi-metal water pollution.

Triazole and methylthio modified covalent organic frameworks for enhancing Hg(II) adsorption from water

The presence of mercury (Hg(II)), a highly toxic pollutant in the aquatic environment, motivates researchers to use an effective method to remove it from water. Herein, we synthesized COF-TAZ and COF-TOE via post-modification with 3-mercapto-1,2,4-triazole and 4-(methylsulfanyl)thiophenol to form triazole group and methylthio group, respectively, and followed by characterization with SEM, FTIR, and XRD, etc. The adsorption behaviors of Hg(II) on two modified COFs were evaluated by adsorption kinetic models using the pseudo-first order, pseudo-second order and intra-particle diffusion models, as well as isotherm models, i.e., Langmuir and Freundlich models. COF-TAZ and COF-TOE manifested maximum experimental uptake capacity of 108.09 mg g−1 and 104.85 mg g−1, respectively. Notably, COF-TAZ exhibited commendable binding selectivity towards Hg(II) and displayed a good recycling ability, with a removal percentage still above 90% after five cycles. Especially, the adsorption mechanisms of COF-TAZ and COF-TOE were clarified by FTIR, XPS and DFT calculations, suggesting that electrostatic interaction and chelation were involved in the adsorption process. This study shows that functionalized COFs have good application prospects in effective removal of heavy metals in water.

Photothermal self-floating aerogels based on chitosan functionalized with polydopamine and carbon nanotubes for removal of arsenic from wastewater

Although wastewater disposal in evaporation ponds may be a cost-effective strategy for wastewater management, it overlooks water recycling and can possibly pose significant threats to the surrounding environment. The development of photothermal materials with functional groups capable of adsorbing toxic contaminants offers a promising opportunity for detoxification and potentially solar-driven recycling of wastewater disposed in evaporation ponds. In this study, ultralight aerogels based on chitosan (Ch), a natural biodegradable polymer, functionalized with mussel-inspired polydopamine (PDA) and carbon nanotubes (CNT) were fabricated through a facile approach and examined for the removal of arsenic from water. Three aerogels, namely chitosan, CNT/Ch, and PDA@CNT/Ch were fabricated and characterized using SEM, FTIR, TGA, XPS, and BET surface area analysis. Adsorption isotherms, thermodynamics, and kinetics were systematically investigated, revealing the feasibility of the fabricated aerogels for arsenic removal from aqueous solutions. The UV–Vis and photothermal analysis indicated excellent light-absorption and light-to-heat conversion performance of the functionalized aerogels. Arsenic adsorption by aerogels occurred rapidly and reached equilibrium within 30 to 60 min and was well-fitted by pseudo second-order kinetics model. The Langmuir model well described the adsorption isotherm, and the maximum adsorption capacities were found to be 31.5, 36.6, and 38.7 mg/g at neutral pH for chitosan, CNT/Ch, and PDA@CNT/Ch, respectively. The adsorption mechanism was studied by FTIR and XPS analysis and the adsorption pathway was evaluated using intraparticle diffusion model. This study broadens the scope of utilizing aerogels for the detoxification and potential recycling of wastewater from diverse sources and effluents disposed in evaporation ponds.

Ultra-high specific surface area activated carbon from Taihu cyanobacteria via KOH activation for enhanced methylene blue adsorption

Biomass-based activated carbon (CBACs) was successfully prepared by pyrolysis-activation of Taihu cyanobacteria. When the impregnation ratio and activated temperature were 2 and 800 oC, respectively, the optimal CBACs possessed an ultra-high specific surface (2178.90 m2·g−1) and plenty of micro-and meso-pores, as well as a high pore volume (1.01 cm3·g−1). Ascribed to ultra-high surface area, π-π interaction, electrostatic interaction, as well as hydrogen bonding interactions, the CBACs displayed huge superiority in efficient dye removal. The saturated methylene blue (MB) adsorption capacity by CBACs could be as high as 1143.4 mg·g−1, superior to other reported biomass-activated carbons. The adsorption was endothermic and modelled well by the pseudo-second-order kinetic, intra-particle diffusion, and Langmuir models. This work presented the effectiveness of Taihu cyanobacteria adsorbent ascribed to its super large specific surface area and high adsorption ability.

CTAB-modified peanut husk pre-treated with KMnO4 as an eco-friendly adsorbent for the uptake of Congo red in solution: adsorption and mechanism study.

A cationic surfactant (cetyltrimethylammonium bromide, CTAB)-modified peanut husk pretreated with potassium permanganate (KMnO4) was developed and applied as an adsorbent for the removal of Congo red (CR) in aqueous solution. The surface morphology and physicochemical characteristics of the adsorbent labelled as PNK-CTAB were assessed using well-established analytical techniques. The efficiency of PNK-CTAB was assessed via the batch adsorption method using distilled water, tap water and river water as aqueous medium. Results of the batch study showed that the adsorption capacity of PNK-CTAB could reach 70.5mgg-1 at 313K due to its improved surface properties and functionalities. Furthermore, the uptake of CR onto PNK-CTAB was found to be best described by the Elovich model thus suggesting adsorption on a heterogeneous surface, whereas fitting of intraparticle diffusion model indicated the significant role of mass transfer mechanism in the process. The equilibrium data was found to be well described by Langmuir, Temkin and Freundlich models albeit the latter was the best fit. Further analysis of the associated thermodynamics indicated the adsorption process to be endothermic, spontaneous in nature and likely mediated by physisorption processes. The excellent adsorption efficiency of PNK-CTAB toward CR within a wide pH range, negligible influence of some commonly occurring salts, good reusability efficiency, low cost (as confirmed by its cost analysis) and its ability to reduce the cytotoxicity of CR towards human embryonic kidney (HEK) 293 cells suggest the good prospects of this adsorbent for practical applications.

Bio-adsorption of heavy metals from aqueous solution using the ZnO-modified date pits

The bio-adsorption of heavy metals (including Cu2+, Ni2+, and Zn2+) in aqueous solution and also in an industry wastewater using the ZnO-modified date pits (MDP) as the bio-adsorbent are investigated. The fresh and used bio-adsorbents were characterized by FT-IR, SEM, BET, and XRD. The bio-adsorption parameters (including the pH of solution, the particle size of MDP, the shaking speed, the initial concentration of heavy metals, the dosing of MDP, the adsorption time, and the adsorption temperature) were screened and the data were used to optimize the bio-adsorption process and to study the bio-adsorption isotherms, kinetics, and thermodynamics. Two adsorption models (Langmuir isotherm model and Freundlich isotherm model) and three kinetic models (pseudo-first-order model, pseudo-second-order model, and intra-particle diffusion model) were applied to model the experimental data. Results show that the maximum adsorption amount of Cu2+, Ni2+, and Zn2+ on a complete monolayer of MDP are 82.4, 71.9, and 66.3 mg g−1, which are over 4 times of those of date pits-based bio-adsorbents reported in literature. The bio-adsorption of heavy metals on MDP is spontaneous and exothermic, and is regulated by chemical adsorption on the homogeneous and heterogeneous adsorption sites of MDP surface. This work demonstrates an effective modification protocol for improved bio-adsorption performance of the date pits-based bio-adsorbent, which is cheap and originally from a waste.

Aluminum Montmorillonite/Polyaniline Hybrid Composite-Based Organogels for the Expurgation of Carcinogenic Chlorophenols and Congo Red Dye from Defiled Water Sources.

Chlorophenol and Congo Red dye being highly toxic are well known for their carcinogenic activity. This work focuses on preparing an organogel for the removal of both chlorophenol and Congo Red. PAni molecules were grafted in situ between the layers of montmorillonite (MMT) to form a PAni/MMT composite, which was further modified to form a gel structure. The composite was thoroughly characterized by high-resolution X-ray diffraction (HR-XRD), Fourier transform infrared (FT-IR) analysis, Brunauer-Emmett-Teller (BET) analysis, and thermogravimetric analysis (TGA). The gel was further analyzed by scanning electron microscopy (SEM) and by studying the rheological properties. The resulting gel exhibited an impressive solvent uptake, with a maximum of 2084% (20 times) for chlorophenol, while the dye adsorption capacity was 349.72 mg/g with 99.44% removal efficiency. The adsorption proceeded with the pseudo-second-order model followed by the Langmuir monolayer adsorption model and Weber's intraparticle diffusion model. The sorbent was found to be selective among cationic dyes while retaining 83% of dye even in the fifth cycle. The hybrid sorbent shows great promise for sustainable purposes, and the results of this study are certainly encouraging.