Equilibrium, kinetics and thermodynamics of lead (II) adsorption in bioadsorvent composed by Caryocar coriaceum Wittm barks

Cellulose-based adsorbent using in mercury detection and removal from water via an efficient grafting strategy of fluorometric sensors by click reaction

Mercury pollution in waters attracts lots of attention due to its serious toxicity and high bioenrichment and many efforts have been devoted in the development of adsorbents for mercury detection and removal. Herein, a cellulose-based adsorbent Cell-TriA-HQ is functionalized with quinoline fluorophore by covalent immobilization through "Click reaction" with high yield. In addition to the admirable adsorptive performance, the prepared adsorbent exhibits excellent selectivity and sensitivity towards Hg (II) in water that the detection limit for Hg (II) is determined to be as low as 1.92 × 10-7 M. The sensitive fluorescence enhancement response is considered to be resulted from the inhibition of photo-induced electron transfer between triazole and quinoline groups and the reinforcement of structural rigidity. The easy manipulation along with excellent performance of adsorption capacity, detective ability and reusability for the multifunctional adsorbent makes it potential in mercury monitoring and removal from aqueous solutions in the field of water treatment.

Adsorption of phosphate in aqueous solution by ash from the fruit peel of Caryocar coriaceum Wittm: adsorption characteristics and behavior

High phosphate concentrations in natural waters are associated with eutrophication problems that negatively affect the fauna and flora of ecosystems. As an alternative solution to this problem, we evaluated the adsorptive capacity of the fruit peel ash (PPA) of Caryocar coriaceum Wittm and its efficiency in removing phosphate (PO43-) from aqueous solutions. PPA was produced under an oxidative atmosphere and calcinated at 500 °C. The XRF and EDS analyses of PPA after contact with an aqueous PO43- solution showed an increase in its PO43- content, thus confirming the adsorption of PO43-. The Elovich and Langmuir models are the ones fitting the kinetics and the equilibrium state of the process, respectively. The highest PO43- adsorption capacity was approximately 79.50 mg g-1 at 10 °C. PO43- adsorption by PPA is a spontaneous, favorable, and endothermic process involving structural changes. The highest removal efficiency was 97.08% using a 100 mg.L-1 PO43- solution. In sight of this, PPA has shown potential as an excellent natural bioadsorbent.

A correlation of the adsorption capacity of perovskite/biochar composite with the metal ion characteristics

LaFeO₃/biochar composite is prepared by cellulose-modified microwave-assisted method at 450 °C. The structure is identified by Raman spectrum which, consists of characteristics biochar bands and octahedral perovskite chemical shifts. The morphology is examined by scanning electron microscope (SEM); two phases are observed, rough microporous biochar and orthorhombic perovskite particles. The BET surface area of the composite is 57.63 m²/g. The prepared composite is applied as a sorbent for the removal of Pb²⁺, Cd²⁺, and Cu²⁺ ions from aqueous solutions and wastewater. The adsorption ability reaches a maximum at pH > 6 for Cd²⁺, and Cu²⁺ ions, and is pH-independent for Pb²⁺ ions adsorption. The adsorption follows pseudo 2nd order kinetic model, Langmuir isotherm for Pb²⁺ ions, and Temkin isotherms for Cd²⁺, and Cu²⁺ ions. The maximum adsorption capacities, q_m, are 606, 391, and 112 mg/g for Pb²⁺, Cd²⁺, and Cu²⁺ ions, respectively. The electrostatic interaction is responsible for the adsorption of Cd²⁺, and Cu²⁺ ions on LaFeO₃/biochar composite. In case of Pb²⁺ ions form a complex with the surface functional groups of the adsorbate. LaFeO₃/biochar composite shows high selectivity for the studied metal ions and excellent performance in real samples. The proposed sorbent can be easily regenerated and effectively reused.

Pb(II) Ion Removal Potential in Chemically Modified Ziziphus joazeiro Barks

In this study, five types of modified Ziziphus joazeiro barks were investigated for the removal of Pb(II) ions from aqueous solutions. The samples tested were natural barks, natural powder, washed with water, ethanol at 80% (EE) and 0.5 N NaOH. Batch kinetics experiments were performed under the conditions: 24−25 °C, pH 5.5−5.8, 102 mg·L−1 Pb(NO3)2, 100 rpm and 0.1 g of adsorbent, and analyses of pHpzc and Fourier transform infrared spectroscopy. All adsorbents tested showed potential to remove Pb(II) ions, but the adsorbent washed by 0.5 N NaOH obtained the highest experimental performance (25.5 mg·g−1 at 30 min), while the EE had the least performance (20.4 mg·g−1 at 60 min), and maximum removals of 99.9%. The kinetic models pointed to a probable chemisorption due to the best fit of pseudo-second order and Elovich, and Boyd’s model, suggesting that intraparticle diffusion limits the adsorption until the initial minutes of contact. The Langmuir isotherm fitted better to the experimental data for the NaOH adsorbent, with maximum adsorption capacity equal to 62.5 mg·g−1, although the Temkin model partially fitted, both suggesting the occurrence of chemisorption. The adsorption process is reversible (>81% at 20 min) and hence the adsorbents can be recycled and the Pb(II) ions recovered.

Nano-Silica Modified with Diamine for Capturing Azo Dye from Aqueous Solutions

Nano-silica particles decorated with amine groups (S-DA) were prepared via a simple, one-pot method, and under very mild conditions in an attempt to improve the affinity of the silica nanoparticles toward capturing anionic organic dye, namely, methyl orange (MO). The prepared sample was characterized by different techniques such as XRD for crystallinity, SEM for morphological structure, TGA for thermal stability, BET surface area, and FTIR for surface functional groups. The prepared sample was tested for the removal of MO under different conditions including the mass of adsorbent, pH, initial concentration, and time. Results showed that the adsorption of MO was very fast with equilibrium achieved in less than 30 min and a maximum removal efficiency of 100% for a mass to volume ratio of 10 g/3 L, a pH of 2.5, initial concentration of 10 mgL⁻¹, and under stagnant conditions. These results were compared with a bare nano-silica, which was not able to adsorb more than 3% after 24 h, indicating the important effect of amine groups. Furthermore, recycling the adsorbent was achieved by rinsing the MO-loaded adsorbent with a dilute solution of KOH. The adsorbent maintained 50% of its initial removal efficiency after four adsorption–desorption cycles.

Natural carbohydrate-based thermosensitive chitosan/pectin adsorbent for removal of Pb(II) from aqueous solutions

Biodegradable and eco-friendly adsorbents composed of natural carbohydrates have been used to replace carbon-based materials. This study presents a natural carbohydrate-based chitosan/pectin (CS/Pec) hydrogel adsorbent to remove Pb(II) from aqueous solutions. The physical CS/Pec hydrogel was prepared by blending aqueous CS and Pec solutions at 65 °C, preventing the use of toxic chemistries (crosslinking agents). The thermosensitive CS/Pec hydrogel was quickly created by cooling CS/Pec blend at room temperature. The used strategy created stable CS/Pec hydrogel against disintegration and water dissolution. The as-prepared hydrogel was characterized by infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The adsorbent had 1.688 mmol -COO^- for each gram. These ionized sites bind Pb(II) ions, promoting their adsorption. The adsorption kinetic and equilibrium studies indicated that the Elovich and pseudo-second-order models adjusted well to the experimental data, respectively. The maximum removal capacities (q_m) predicted by the Langmuir and Sips isotherms achieved 108.2 and 97.55 mg/g at 0.83 g/L adsorbent dosage (pH 4.0). The hydrogel/Pb(II) pair was characterized by scanning electron microscopy (SEM), X-ray dispersive energy (EDS), and differential scanning calorimetry (DSC). The chemisorption seems to play an essential role in the Pb(II) adsorption. Therefore, the adsorbent was not recovered, showing low potential for reusability.

Adsorptive removal of Pb(II) ions onto surface modified adsorbents derived from Cassia fistula seeds: Optimization and modelling study

Cassia fistula seeds has been utilized for the abstraction of Pb(II) ions from the aqueous environment. Raw Cassia fistula seeds (RCF) and three different surface modified (physically treated - PMCF and chemically treated - HMCF and SMCF) adsorbent material were taken for investigation. The adsorption properties of these materials and their contact amongst the Pb(II) ion and sorbent materials were characterized by FTIR and SEM analysis. The parameters influencing the adsorption capacity of varied adsorbents were evaluated: maximum solution pH for Pb(II) is 5.0; interactive time is 30 min; dosage is 8.0 g/L for RCF, 4.0 g/L for HMCF, 2.5 g/L for PMCF and 1.0 g/L for SMCF. The modelling study reveals that Freundlich isotherm and Pseudo first order kinetics fits well and the utmost adsorption measurements for the varied adsorbents were found to be 13.22, 28.28, 48.66 and 129.3 mg/g, respectively.

Facile synthesis and characterization of polypyrrole - iron oxide - seaweed (PPy-Fe3O4-SW) nanocomposite and its exploration for adsorptive removal of Pb(II) from heavy metal bearing water

Lead is a widely used heavy metal which is highly toxic to kidney, nervous system and reproductive system. A special featured polypyrrole based adsorbent, with admirable salinity confrontation, environmental stability and reusability, was engaged to remove lead ions from aqueous solution. The advantages of using polypyrrole based adsorbent for heavy metal removal are: ease of synthesis, biocompatibility and high metal selectivity. In this study, polypyrrole - iron oxide - seaweed nanocomposite was proposed to remove lead ions from aqueous solution. A new method was adopted for the synthesis of polypyrrole - iron oxide - seaweed nanocomposite. The nanocomposite was prepared within a short time using ultra-assisted polymerization technique. The synthesized nanocomposite adsorbent was characterized using FTIR, SEM, TEM, EDS, XRD, XPS and zeta potential analysis. The adsorption capability of polypyrrole - iron oxide - seaweed nanocomposite towards lead was explored. The influence of pH, contact time, adsorbent dosage, metal ion concentration and recyclability were investigated. The optimum condition of these parameters was found to be: pH- 5, temperature - 40 °C, initial concentration - 100 mg/L and contact time - 20 min and the results showed that the hybrid composite adsorbed 97.25% Pb (II). Different isotherms such as Langmuir, Freundlich, Temkin and D-R models were also studied for the adsorption of Pb ions. The kinetics of the adsorption process was examined by I order, II order and intra particle diffusion kinetic models. The mechanism of lead adsorption onto the nanocomposite was also explored.

Mechanism and industrial application feasibility analysis on microwave-assisted rapid synthesis of amino-carboxyl functionalized cellulose for enhanced heavy metal removal

The study presented the successful microwave-assisted (MW-assisted) preparation of a novel adsorbent derived from rice straw (RS_MW-AC) and explored its adsorption performance toward heavy metal ions from water. The RS_MW-AC was rapidly synthesized through pretreatment and one step grafting via the MW-assisted approach. The quantitative predictive correlations between target performance of RS_MW-AC and process parameters were obtained through the response surface methodology (RSM). Meanwhile, the optimal preparation process conditions were determined: NaOH solution concentration, 20%; MW irradiation temperature for pretreatment, 100 and 150 °C; MW irradiation time for pretreatment and grafting, 10 and 60 min; EDTAD-RS mass ratio, 3. The RS_MW-AC showed a good adsorption of different heavy metal ions from water (152.39, 55.46, 52.91, 35.60 and 20.11 mg g^-1 for Pb(Ⅱ), Mn(Ⅱ), Cd(Ⅱ), Cu(Ⅱ) and Ni(Ⅱ), respectively). The adsorption behaviors followed the Langmuir model and pseudo second-order kinetics model with a highly significant correlation. Also of note was that amino and carboxyl groups were successfully introduced on the rice straw based on characterization results. Furthermore, preparation mechanism was explored to reveal reasons why microwave irradiation could accelerate the preparation of the adsorbent; its adsorption process was dominated by electrostatic attraction and chelation. Finally, the study made the industrial application feasibility analysis of MW-assisted approach used for pretreatment and graft reaction of agro-waste biomass.