Green valorization of PET waste into functionalized Cu-MOF tailored to catalytic reduction of 4-nitrophenol.

Metal-organic frameworks (MOFs) are attractive functional materials due to their high surface area, high porosity, and flexible compositions. However, the high precursor cost and complex synthetic processes hinder their large-scale applications. Herein, a novel green approach has been developed toward the synthesis of Cu-based MOF by a solvent-free mechano-synthesis method and utilizing consumed polyethylene terephthalate (PET)-derived benzenedicarboxylate (BDC) as the linker. The as-prepared CuBDC and aminated CuBDC (CuBDC-NH2) act as green catalysts for the reduction of deleterious 4-nitrophenol (4-NP) into the value-added 4-aminophenol (4-AP). Compared with CuBDC, CuBDC-NH2 shows increased adsorption capability and reduction efficiency. The mechanism and thermodynamic studies suggest that the adsorption of 4-NP on CuBDC-NH2 is an endothermic, spontaneous, favorable, and physical adsorption process. Furthermore, CuBDC-NH2 can expedite the reduction of 4-NP by participating in an adsorptive catalytic process. With the CuBDC-NH2 catalyst, the catalytic normalized kinetic rate of 4-NP was achieved 11.28 mol/min. mg, outperforming state-of-the-art catalysts, and a complete reduction occur in 5 min for a concentrated effluent (200-ppm 4-NP). The plastic waste-derived MOF-mediated catalytic valorization of organic pollutants demonstrated here opens an avenue for the green recycling/utilization of plastic waste, providing meaningful insights into the sustainable management of organic pollutants in wastewater.

High-performance catalytic reduction of 4-nitrophenol to 4-aminophenol using M-BDC (M = Ag, Co, Cr, Mn, and Zr) metal-organic frameworks.

The catalytic activity of pure metal nanoparticles is always limited by aggregation during the reaction. Therefore, promising candidates such as metal-organic frameworks possess benefits due to their 3D porous structures, high stability, and high specific surface area. In this study, effective and reusable catalysts based on M-BDC metal-organic frameworks were synthesized utilizing five different coordinating metal ions (M = Ag, Co, Cr, Mn, and Zr) as metal nodes and 1-4-benzene dicarboxylic acid (BDC) as an organic linker and used in catalytic reduction of 4-Nitrophenol (4-NP) to 4-Aminophenol (4-AP) for the first time. The as-prepared catalysts were characterized using SEM, EDX, XRD, and FTIR techniques. Based on catalytic performance, Co-BDC showed the best catalytic efficiency compared to the other M-BDC MOF catalysts with a conversion yield of about 99.25 in 2 min. All of the catalysts could catalyze the complete reduction of 4-NP to 4-AP at different reaction times (2-10); however, Mn-BDC could not finish the catalytic reduction reaction even after 20 min. The two more efficient catalysts including Co-BDC and Cr-BDC demonstrated high stability and reusability (more than 85% catalytic efficiency) even after 5 cycles.

Decontamination of Fuchsin dye by carboxymethyl cellulose-graft-poly(acrylic acid-co-itaconic acid)/carbon black nanocomposite hydrogel.

In the present work, carboxymethyl cellulose (CMC) was used to develop hydrogels as adsorbents for wastewater treatment applications due to its surface functionality and modifiable characteristics. Hydrogels (Hyd) were synthesized by grafting copolymers of acrylic acid (AA) and itaconic acid (IA) onto the CMC backbone by free radical polymerization method in order to remediate Fuchsin from aqueous solution. The presence of CMC in copolymer hydrogel of AA and IA (Poly(AA-co-IA)) up to 14.29 wt% enhances equilibrium swelling and removal efficiency. Different novel nanocomposite hydrogel samples were prepared by varying weight percentages of carbon black (CB) nanoparticles in the range of 0 to 12.5 wt%. The addition of CB up to 5 wt% enhanced the swelling and removal efficiency of the Hyd. Brunauer-Emmett-Teller (BET) test gave the surface area of 0.615, and 0.890 m2/g for Hyd and Hyd/CB, respectively, indicating that incorporation of CB led to a significant increase in Hyd surface area. The Maximum removal efficiency of Fuchsin under the optimum conditions was obtained to be 83.33, 93.54, and 98.76 % for Poly(AA-co-IA), Hyd, and Hyd/CB, respectively. The kinetic study showed that the pseudo-second-order is the best-fitted model. Isotherm studies showed that equilibrium data have a good fitness with the Langmuir model with R2 of 0.978, 0.992, and 0.982 for Poly(AA-co-IA), Hyd, and Hyd/CB, respectively. The Langmuir model gave an adsorption capacity of 26.99, 31.6, and 33.75 mg/g for Poly(AA-co-IA), Hyd, and Hyd/CB, respectively. Also, the value of n and RL parameters demonstrated that the adsorption process is physical and favorable for adsorbents. The study of thermodynamic parameters illustrated that the adsorption of Fuchsin using adsorbents is a spontaneous, exothermic, and entropy-decreasing process. Regeneration study showed that CMC-based hydrogels have higher performance in ad(de)sorption cycles than Poly(AA-co-IA) and the addition of CB to the Hyd matrix enhances reusability. Overall, Hyd and Hyd/CB can be used as promising adsorbents for the remediation of Fuchsin due to high swelling and adsorption capability.

Safranin-O cationic dye removal from wastewater using carboxymethyl cellulose-grafted-poly(acrylic acid-co-itaconic acid) nanocomposite hydrogel.

Copolymer of acrylic acid (AA) and itaconic acid (IA) grafted onto sodium carboxymethyl cellulose hydrogel (CMC-g-poly (AA-co-IA)) was successfully synthesized as an adsorbent to remove safranin-O from wastewater. The swelling and removal efficiencies of CMC-g-poly (AA-co-IA) were enhanced by increasing IA/AA molar ratio as well as by incorporation of montmorillonite clay nano-sheets (MMT). The surface area of MMT, CMC-g-poly (AA-co-IA), and CMC-g-poly (AA-co-IA) samples was 15.632, 0.61452, and 0.66584 m2/g, respectively, indicating the effectiveness of MMT nano-sheets in improving hydrogel surface area. The maximum removal efficiency of CMC-g-poly (AA-co-IA)/MMT under optimum conditions i.e., pH of 8, initial concentration of 10 mg/L, adsorbent dose of 2 g/L, and contact time of 40 min was ascertained 99.78% using a response surface methodology-central composite design (RSM-CCD). Pseudo-second-order and Langmuir models giving the maximum monolayer adsorption capacity of 18.5185 mg/g and 19.1205 mg/g for CMC-g-poly (AA-co-IA) and CMC-g-poly (AA-co-IA)/MMT samples, respectively are the best-fitted models for kinetic and equilibrium data. Thermodynamically, safranin-O decontamination was spontaneous, exothermic, and entropy decreasing. Moreover, ad (de)sorption behavior study showed that CMC-g-poly (AA-co-IA)/MMT performance was not changed after multiple recovery steps. Therefore, CMC-g-poly (AA-co-IA)/MMT was considered as a highly potential adsorbent for safranin-O removal from wastewater.

Modification of bio-hydroxyapatite generated from waste poultry bone with MgO for purifying methyl violet-laden liquids.

In the present work, biological hydroxyapatite (Bio-HAp) was generated from waste poultry bone and modified with magnesium oxide (MgO) nanoparticles (Bio-HAp/MgO) and used in the adsorption process of methyl violet (MV). The Bio-HAp and Bio-HAp/MgO mesoporous composites were characterized using physicochemical techniques. Bio-HAp and Bio-HAp/MgO composites had crystalline and mesoporous structures. The specific surface area of Bio-HAp/MgO mesoporous composites (14.7 m2/g) was higher and lower than that of Bio-HAp (4.6 m2/g) and MgO (154.9 m2/g), respectively. The effect of pH (2-10), temperature (25-45 °C), contact time (10-50 min), initial MV concentration (5-25 mg/L), and Bio-HAp/MgO quantity (0.5-2.5 g/L) on the adsorption efficiency was optimized through response surface methodology-central composite design (RSM-CCD). Among four isotherm models, the Freundlich isotherm (R2 > 0.98) was better matched with the equilibrium data. Based on the isotherm parameters (E, n, and RL), the MV adsorption process using Bio-HAp particles and Bio-HAp/MgO mesoporous composites is physical and desirable. The pseudo-second-order (R2 > 0.97) was more potent than the other models for modeling kinetic data. According to the thermodynamic investigation, the MV adsorption was an exothermic and spontaneous process. The mesoporous composite had good reusability to remove MV dye from liquid media up to 5 steps. Bio-HAp particles and Bio-HAp/MgO mesoporous composites were tested for treatment, which significantly reduced the dye content of the real sample.

Heterogeneous Fenton reaction for elimination of Acid Yellow 36 in both fluidized-bed and stirred-tank reactors: Computational fluid dynamics versus experiments.

Heterogeneous Fenton process is a kind of advanced oxidation processes (AOPs) that is significant for wastewater treatment. In the first part of this study, acid yellow 36 (AY36) degradation process has occurred in two kinds of reactors: fluidized-bed and stirred-tank reactors. Performances of these two semi-pilot reactors are compared by evaluating the removal ratio of the dye and pH changes during the process. Pyrite has been used as a heterogeneous catalyst. For obtaining the characteristics of pyrite, XRD, SEM, and FT-IR analysis have been carried out. In the second part of this study, a modified computational fluid dynamics (CFD) method has been utilized to solve the momentum and mass balances for heterogeneous Fenton process in both reactors. In AOPs, free radicals are reactive and have a short lifetime, so that turbulence mixing would be a limiting factor for the reactions that radicals are involved. By introducing a new parameter, named turbulence mixing rate, as a reaction rate for reactive species like hydroxyl radicals, the results of removal ratio and pH changes during the process showed a good agreement between the experiments and the CFD simulations, compared with not including the mixing rate in the CFD simulations (conventional kinetic modeling). In addition, the results revealed the high performance of the fluidized-bed reactor for this process in both experiments and CFD simulation.

Optimization of a textile dye degradation in a recirculating fluidized-bed reactor using magnetite/S2O82- process.

Optimization of Acid Orange 7 (AO7) treatment using heterogeneous Fenton-like method in a recirculating fluidized-bed reactor (FBR) was investigated by using central composite design (CCD). Natural magnetite (NM) as Fenton-like catalyst was characterized using scanning electron microscopy. A nonlinear CCD model was obtained for the prediction of dye degradation as a function of experimental variables such as peroxydisulfate concentration (0.1-0.5 mmol/L), initial AO7 concentration (5-25 mg/L), pH (3-9) and NM dosage (0.25-1.25 g/L) after 105 min of treatment. The calculated results by the model were consistent with the experimental results (R2 = 0.959). Furthermore, the model is suitable to estimate the optimum operational conditions and determine the effects of the parameters for maximum AO7 degradation. Eventually, gas chromatography-mass spectroscopy was used for the recognition of the dye degradation by-products.

Central composite design optimization of pilot plant fluidized-bed heterogeneous Fenton process for degradation of an azo dye.

Optimization of Acid Yellow 36 (AY36) degradation by heterogeneous Fenton process in a recirculated fluidized-bed reactor was studied using central composite design (CCD). Natural pyrite was applied as the catalyst characterized by X-ray diffraction and scanning electron microscopy. The CCD model was developed for the estimation of degradation efficiency as a function of independent operational parameters including hydrogen peroxide concentration (0.5-2.5 mmol/L), initial AY36 concentration (5-25 mg/L), pH (3-9) and catalyst dosage (0.4-1.2 mg/L). The obtained data from the model are in good agreement with the experimental data (R(2 )= 0.964). Moreover, this model is applicable not only to determine the optimized experimental conditions for maximum AY36 degradation, but also to find individual and interactive effects of the mentioned parameters. Finally, gas chromatography-mass spectroscopy (GC-MS) was utilized for the identification of some degradation intermediates and a plausible degradation pathway was proposed.