Adsorption optimization of uranium(VI) onto polydopamine and sodium titanate co-functionalized MWCNTs using response surface methodology and a modeling approach

Highly efficient adsorption of congo red and methyl orange dyes using mesoporous α-Mn2O3 nanoparticles synthesized with Pyracantha angustofolia fruit extract

Due to the many applications of manganese oxides in water treatment, this research aimed to synthesize α-Mn2O3 nanoparticles through a green method and investigate the dye adsorption capacity of them. The α-Mn2O3 nanoparticles were successfully synthesized using KMnO4 and aqueous extract of Pyracantha angustofolia fruits under hydrothermal conditions and calcination. The products were identified using Fourier transform infrared (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), and scanning electron microscopy (SEM) analyses. The adsorption capacity of methyl orange (MO) and Congo red (CR) dyes were evaluated at different concentrations (25, 50, and 75 ppm) using α-Mn2O3 nanoparticles. Results revealed the spherical and porous structure of α-Mn2O3 nanoparticles with a specific surface area of 21.7 m2.g-1. Dye removal significantly increased with pH decrement. The adsorption capacity for MO and CR was 73.07 and 70.70 mg.g-1, respectively. The adsorption data of both dyes followed a pseudo-second-order kinetic model. The best fitted models for MO and CR adsorption were the Langmuir isotherm and the Dubinin-Radushkevich, respectively. In addition, a possible adsorption mechanism was proposed for both dyes. The findings showed that α-Mn2O3 nanoparticles are very efficient adsorbents for removing anionic dyes.

Mono- and Multicomponent Biosorption of Caffeine and Salicylic Acid onto Processed Cape Gooseberry Husk Agri-Food Waste

There is an increasing need to find cost-effective and sustainable solutions for treating wastewater from contaminants of emerging concern (CECs). In this regard, cape gooseberry husk-typically an agri-food waste-is investigated for the first time as a potential biosorbent for the removal of model pharmaceutical contaminants of caffeine (CA) and salicylic acid (SA) from water. Three different preparations of husks were investigated and characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller analysis, zeta potential, and point of zero charge measurements. The activation of the husk led to an increase in the surface area, pore volume, average pore size, and adsorption favorability. The single-component adsorption of SA and CA onto the three husks was investigated at different initial concentrations and pH values to determine the optimal operating conditions. The maximal removal efficiencies of SA and CA reached up to 85 and 63%, respectively, for the optimal husk which also offers a less energy-intensive option in its activation. This husk also exhibited high rates of adsorption that exceeded other husk preparations by up to four times. It was proposed that CA interacts electrostatically with the husk, while SA binds through weak physical interactions (e.g., van der Waals and H-bonding). In binary systems, CA adsorption was highly favored over SA adsorption, owing to its electrostatic interactions. The selectivity coefficients α_SA^CA varied with initial concentration and ranged between 61 and 627. The regeneration of husk was also successful resulting in its re-use for up to four full consecutive cycles, further demonstrating the efficiency of cape gooseberry husk use in wastewater treatment.

Synthesis of mesoporous-structured MIL-68(Al)/MCM-41-NH2 for methyl orange adsorption: Optimization and Selectivity

Here, we report a novel amino-modified mesoporous-structured aluminum-based metal-organic framework adsorbent, MIL-68(Al)/MCM-41-NH₂, for dye sewage treatment. The introduction of molecular sieves overcomes the inherent defects of microporous MOFs in contaminant transfer and provides more active sites to enhance adsorption efficiency. Compared with using organic amino ligands directly, this strategy is ten times cheaper. The composite was well characterized and analyzed in terms of morphology, structure and chemical composition. Batch experiments were carried out to study the influences of essential factors on the process, such as pH and temperature. In addition, their interactions and the optimum conditions were examined using response surface methodology (RSM). The adsorption kinetics, isotherms and thermodynamics were systematically elucidated. In detail, the adsorption process conforms to pseudo-second-order kinetics and follows the Sips and Freundlich isothermal models. Moreover, the maximum adsorption capacity Q_s of methyl orange (MO) was 477 mg g^-1. It could be concluded that the process was spontaneous, exothermic, and entropy-reducing. Several binary dye systems have been designed for selective adsorption research. Our material has an affinity for anionic pigments. The adsorption mechanisms were discussed in depth. The electrostatic interaction might be the dominant effect. Meanwhile, hydrogen bonding, π-π stacking, and pore filling might be important driving forces. The excellent thermal stability and recyclability of the adsorbent are readily noticed. After five reuse cycles, the composite still possesses a removal efficiency of 90% for MO. Overall, the efficient and low-cost composite can be regarded as a promising adsorbent for the selective adsorption of anionic dyes from wastewater.

Highly efficient adsorptive extraction of uranium from wastewater by novel kaolin aerogel

An environment-friendly, low-cost and efficient kaolin aerogel adsorbent (named as KLA) was synthesized via a freeze-drying-calcination method to solve the defect of low uranium removal rate for kaolin (KL). The removal rate of uranium on KLA reached 90.6 %, which was much higher than that of KL (69.2 %) (C₀ = 10 mg L^-1, t = 24 h, pH = 5.0, T = 298 K and m/V = 1.0 g L^-1). The uranium removal behavior on KLA was satisfied with Pseudo-second-order and Langmuir model, which meant that the uranium ions were immobilized on the surface of KLA via chemical reaction. Meanwhile, high temperature was in favor of the removal of uranium on KLA, indicating that the removal process was a spontaneous endothermic reaction. Compared with KL, KLA also presented better cycle ability and its removal rate of uranium was up to 80.5 % after three cycles, which was still higher than that of KL at the first cycle (74.5 %). On basis of the results of SEM, XRD, FT-IR and XPS, it could be concluded that uranium ions were adsorbed by KLA via complexation. Hence, KLA could be regarded as a feasible candidate for the removal of uranium from aqueous solution.

Chromium(III) Removal from Nickel(II)-Containing Waste Solutions as a Pretreatment Step in a Hydrometallurgical Process

This paper presents Cr(III) removal from nickel sulfate waste solutions as a pretreatment step for the modification of hydrogen storage alloys. Adsorption with two cation exchange resins, Dowex G26 (strongly acidic) and MAC-3 (weakly acidic), and precipitation with various solutions were chosen as simple operations for Cr(III) removal from waste solutions. The adsorption of Cr(III) was investigated for both model and real waste nickel solutions. Dowex G26 appeared to be more efficient in Cr(III) removal (R_Cr(III) from 43 to 80%) than MAC-3 (R_Cr(III) from 40 to 53%). However, the adsorption from multi-component solutions (presence of Co(II), Ni(II) and Cr(III)) showed no selectivity in Cr(III) adsorption in comparison to those of Co(II) and Ni(II). Cr(III), Ni(II) and Co(II) were removed at a comparable level (30-36%) from a three-component solution of 10 g/dm³ of each metal ion, and a 56-72% removal of these ions was achieved from the real solution. Therefore, the precipitation of Cr(III) was carried out from a real waste nickel solution to compare its performance with adsorption. The best precipitation solution appeared to be 3 and 30% NaOH due to the quantitative precipitation of Cr(OH)₃ at pH 5 and relatively small co-precipitation of Ni(II) and Co(II) hydroxides (P_Co(II) = 20-52%, P_Ni(II) = 0-54%). Based on the results of the research, it can be concluded that precipitation with a NaOH solution is an efficient pretreatment operation of an electrolyte for further steps of the hydrometallurgical process of nickel electrodeposition and appears to be more selective in the elimination of Cr(III) than adsorption with Dowex G26 resin.